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Durability and Fatigue Life Analysis Using MSC.Fatigue PAT318 Course Notes
March 2002
PAT318, Section 0, March 2002 P/N P3*V2002*Z*Z*Z*SM-PAT318-NT1
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DISCLAIMER
MSC.Software Corporation reserves the right to make changes in specifications and other information contained in this document without prior notice. The concepts, methods, and examples presented in this text are for illustrative and educational purposes only, and are not intended to be exhaustive or to apply to any particular engineering problem or design. MSC.Software Corporation assumes no liability or responsibility to any person or company for direct or indirect damages resulting from the use of any information contained herein. User Documentation: Copyrightã ã 2001 MSC.Software Corporation. Printed in U.S.A. All Rights Reserved. This notice shall be marked on any reproduction of this documentation, in whole or in part. Any reproduction or distribution of this document, in whole or in part, without the prior written consent of MSC.Software Corporation is prohibited. MSC and MSC. are registered trademarks and service marks of MSC.Software Corporation. NASTRAN is a registered trademark of the National Aeronautics and Space Administration. MSC.Nastran is an enhanced proprietary version developed and maintained by MSC.Software Corporation. MSC.Marc, MSC.Marc Mentat, MSC.Dytran, MSC.Patran, MSC.Fatigue, MSC.Laminate Modeler, and MSC.MVision are all trademarks of MSC.Software Corporation. All other trademarks are the property of their respective owners.
PAT318 Course Director:
[email protected] PAT318, Section 0, March 2002
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TABLE OF CONTENTS Section 1.0
Page Overview of Durability and Fatigue Life Company Overview ……………………………………………………………………………………………….. 1-3 Course Schedule …….…………………………………………………………………………… … … … … … 1-9 MSC.Fatigue Features …………………………………………………………………………………… … … . 1-10 MSC.Fatigue User Interface …………………………………………………………………………… … … … 1-11 Computer Aided Engineering Solutions … … … … … … … … … … … … … … … … … … … … … … 1-12 Durability Management … … … … … … … … … … … … … … … … … … … … …… … … … … … .. 1-13 What is Durability … … … … … … … … … … … … … … … … … … … … …… … … … … … … … .. 1-15 What Drives Durability Management … … … … … … … … … … … … … … … … … … … … …… … . 1-18 Traditional Approach without CAE: Build it, Test it, Fix it … … … … … … … … … … … … … … … …. 1-21 Add CAE: Analyze and Optimize … … … … … … … … … … … … … … … … … … … … … … … … . 1-22 Predicting Product Life 1 –Build and Use … … … … … … … … … … … … … … … … … … … … … . 1-23 Predicting Product Life 2 – Add Sign-off Testing … … … … … … … … … … … … … … … … … … … 1-24 Predicting Product Life 3 – Add Simulation Testing … … … … … … … … … … … … … … … … … … 1-25 Predicting Product Life 4 – Add CAE … … … … … … … … … … … … … … … … … … … … … … … 1-26 Integrated Durability Management Activities … … … … … … … … … … … … … … … … … … … … . 1-27 Integration … … … … … … … … … … … … … … … … … … … … … … … … … … … … … … … … 1-28 Design Approaches … … … … … … … … … … … … … … … … … … … … … … … … … … … … .. 1-29 History of Fatigue – Early Days … … … … … … … … … … … … … …… … … … … … … … … … … 1-30 A Short History of Fatigue -1 … … … … … … … … … … … … … … … … … … … … … … … … … .. 1-31 A Short History of Fatigue -2 … … … … … … … … … … … … … … … … … … … … … … … … … … 1-34 A Short History of Fatigue -3 … … … … … … … … … … … … … … … … … … … … … … … … … .. 1-37 A Short History of Fatigue -4 … … … … … … … … … … … … … … … … … … … … … … … … … .. 1-39 Fatigue Life Calculation Methods ………………………………………………………………………………. 1-40 S-N Method Similitude … … … … … … … … … … … … … … … … … … … … … … … … … … …… 1-42 Crack Initiation (Strain –Life) Method Similitude … … … … … … … … … … … … … … … … … … … . 1-43 Crack Propagation Method Similitude … … … … … … … … … … … … … … … … … … … … … … .. 1-44 Fatigue Failure and Training … … … … … … … … … … … … … … … … … … … … … … … … … ... 1-45
PAT318, Section 0, March 2002
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TABLE OF CONTENTS Section 1.0
Page Overview of Durability and Fatigue Life The Physical Basis for Fatigue … … … … … … … … … … … … … … … … … … … … … … … … … 1-46 Slip and Stage I Growth … … … … … … … … … … … … … … … … … … … … … … … … … … … 1-47 Initiation and Propagation … … … … … … … … … … … … … … … … … … … … … … … … … … .. 1-48 Use of Fatigue Technology … … … … … … … … … … … … … … … … … … … … … … … … … … . 1-50 Fatigue Calculations in … … … … … … … … … … … … … … … … … … … … … … … … … … … .. 1-51 Who does what Fatigue Calculations … … … … … … … … … … … … … … … … … … … … … … … 1-52 Design against Fatigue … … … … … … … … … … … … … … … … … … … … … … … … … … … .. 1-53 Exploiting Fatigue Analysis – the 5 box trick … … … … … … … … … … … … … … … … … … … … .. 1-55 Durability Tools for Analysis and Test … … … … … … … … … … … … … … … … … … … … … … …1-57 Integrated Approach to Durability … … … … … … … … … … … … … … … … … … … … … … … …. 1-58 How Testing supports Analysis … … … … … … … … … … … … … … … … … … … … … … … … … 1-59 How Analysis supports Testing … … … … … … … … … … … … … … … … … … … … … … … … … 1-60
2.0
Overview of MSC.Fatigue What’s in MSC.Fatigue ………………………………………………………..………………………………….. 2.3 Life Prediction Process …………………………………………………………………………………………… 2-5 Elastic Stress or Strain Prediction Methods ……………………………………………………………………. 2-7 Transient Dynamic Case …………………………………………………………………………… … …………2.16 Frequency Domain ………………………………………………………………………………………………. 2.17 Vibration Fatigue Methods ……………………………………………………………………………………….. 2.18 FE Mesh Considerations …………………………………………………………………………………………. 2.19 MSC.Fatigue Analysis Process ………………………………………………………………………………….. 2.20 MSC.Fatigue Main Form ………………………………………………………………………………………….. 2.21 Geometry/Stress –Strain Results …………………………………………………………………………………2.24 Materials Database Manager …………………………………………………………………………………….. 2.26 Loading Time History Database Manager ……………………………………………………………………….2.29 Stress Life Analysis (S-N) ……………………………………………………………………………………….. 2.32 Crack Initiation Analysis (E-N) …………………………………………………………………………………… 2.33
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TABLE OF CONTENTS (cont.)
Section 2.0
Page Overview of MSC.Fatigue Crack Growth Analysis (LEFM) ………………………………………………………………………………….. 2.34 Post-Processing: Results …………………………………………………………………………………………. 2.36 Post-Processing: design Optimization ………………………………………………………………………….. 2.39 Advanced Features: MSC.Fatigue Spot weld ………………………………………………………………….. 2.41 MSC.Fatigue Software Strain Gauge …………………………………………………………………………… 2.47 MSC.Fatigue Utilities ……………………………………………………………………………………………… 2.52 MSC.Fatigue Vibration ……………………………………………………………………………………………. 2.54 Multiaxial Fatigue ………………………………………………………………………………………………….. 2.59
3.0
MSC.Fatigue User Interface The Five Box Fatigue Analysis Trick ………………………………… ………………………………………… 3.3 Overview of MSC.Fatigue Analysis Process …………………………………………………………………… 3.4 Running an FEA using MSC.Patran …………………………………………………………………………….. 3.5 Or Import the model and results …………………………………………………………………………………. 3.6 MSC.Fatigue Main Form ………………………………………………………………………………………….. 3.7 Loading Information Form ………………………………………………………………………………………… 3.8 Material Information Form …………………………………………………………………………………….. … 3.9 Solution Parameters Form ……………………………………………………………………………………….. 3.10 MSC.Fatigue Files ………………………………………………………………………………………………… 3.11 Job Control Form ………………………………………………………………………………………………….. 3.13 Results Form ………………………………………………………………………………………………………..3.14 Graphical Display of Fatigue Results …………………………………………………………………………….3.15
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TABLE OF CONTENTS (cont.)
Section 4.0
Page Overview of Patran Building a model using Patran ………………………………………………………………………………….. 4.3 Step 1 - Analysis Preferences …………………………………………………………………………………… 4.4 Step 2 - Import/Build Geometry ………………………………………………………………………………….. 4.6 Step 3 – Creating an Analysis Model ……………………………………………………………………………. 4.7 Step 4 – Perform the Analysis …………………………………………………………………………………….4.12 Step 5 – Evaluate Results …………………………………………………………………………………………4.13 Customization ……………………………………………………………………………………………………… 4.15 Starting MSC.Patran ……………………………………………………………………………………………… 4.16 MSC.PATRAN File Option ………………………………………………………………………………………. 4.17 MSC.Patran Files …………………………………………………………………………………………………. 4.18 The Main Form ……………………………………………………………………………………………………. 4.19 Typical Widgets used in MSC.Patran …………………………………………………………………………… 4.21 System Icons ………………………………………………………………………………………………………. 4.22 Entity Picking ………………………………………………………………………………………………………. 4.24 Viewing/Model Manipulation ………………………………………………………………………………………4.29 List Processor ……………………………………………………………………………………………………… 4.30 Entity ID Syntax …………………………………………………………………………………………………… 4.31 MSC.Patran Standards …………………………………………………………………………………………… 4.32 Online Help ………………………………………………………………………………………………………… 4.33
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TABLE OF CONTENTS (cont.)
Section
5.0
Page
Geometry Modeling Topological Structures ………………………………… ………………………………………………………… 5.3 Geometry Building Blocks …………………………………………………………………………………………5.4 Importing, Exporting Geometry and FEM ………………………………………………………………………. 5.12 MSC.Patran Database Access ………………………………………………………………………………….. 5.17 File Export Options ……………………………………………………………………………………………….. 5.21 Geometry Construction …………………………………………………………………………………………… 5.24 Geometry Form Anatomy ………………………………………………………………………………………… 5.25 Select Menu ……………………………………………………………………………………………………….. 5.26 Geometry Entities – Point ………………………………………………………………………………………… 5.27 Geometry Entities – Curve ………………………………………………………………………………………. 5.33 Geometry Entities – Surface …………………………………………………………………………………….. 5.44 Geometry Entities – Solid ………………………………………………………………………………………… 5.59 Solid Geometry Boolean …………………………………………………………………………………………. 5.66 Geometric Entities – Coordinate frame …………………………………………………………………………. 5.67
6.0
Meshing Finite Element ………………………………… …………………………………………………………………. 6.3 Introduction to Finite Element Meshing ………………………………………………………………………… 6.5 MSC.Patran Meshing Algorithms ………………………………………………………………………………. 6.6 Iso (Mapped) Mesher) …………………………………………………………………………………………… 6.7 Paver (Free) Mesher for Surfaces ……………………………………………………………………………… 6.10 Iso (Mapped) Mesh Vs. Paver (Free) Mesh …………………………………………………………………… 6.12 Meshing Control using Mesh Seeds …………………………………………………………………………… 6.16 Tetrahedral Mesher TET Mesh …………………………………………………………………………………. 6.17 Sweep Mesher ……………………………………………………………………………………………………. 6.19 Association of Finite Elements to Geometry …………………………………………………………………… 6.21 Finite Element Form ……………………………………………………………………………………………… 6.22
PAT318, Section 0, March 2002
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TABLE OF CONTENTS (cont.)
Section
6.0
Page
Meshing Where to Start with Meshing .……………………………………………………………………………………. 6.23 Mesh Seeding …………………………………………………………………………………………………….. 6.24 Meshing Parametric Solids ………………………………………………………………………………………. 6.28 Tetmeshing Solids ………………………………………………………………………………………………… 6.29 Tetmeshing from 2D Elements surrounding Volume ………………………………………………………….. 6.31 FEM Creation Tool Transform …………………………………………………………………………………… 6.32 Sweep Meshing …………………………………………………………………………………………………… 6.33 FEM Creation Tool Element/Edit ……………………………………………………………………………….. 6.35 Equivalence – Tie Elements Together ………………………………………………………………………….. 6.37 Irregularity Checks ………………………………………………………………………………………………… 6.40 FEM Editing – Node/Move ……………………………………………………………………………………….. 6.41 FEM Editing – Node/Offset ………………………………………………………………………………………. 6.42 FEM Editing – Node/Project ……………………………………………………………………………………… 6.43 Node Editing Example ……………………………………………………………………………………………. 6.44
7.0
Viewing Viewing …………………………………………………………………………………………………………….. 7.3 Transformations of View …………………………………………………………………………………………. 7.4 Fit Model to Screen and Select New Center …………………………………………………………………… 7.5 Select Corners (Local Zoom) and Zoom by Factor ……………………………………………………………. 7.6 Specify View using Angles ………………………………………………………………………………………. 7.7 User Defined Views .………………………………………………………………………………………………. 7.8 General Clipping Planes …………………………………………………………………………………………. 7.9
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TABLE OF CONTENTS (cont.)
Section
8.0
Page
Groups Introduction to Groups ……………………………………………………………………………………………. 8.3 Example of Groups ……………………………………………………………………………………………….. 8.4 Groups Terminology ………………………………………………………………………………………………. 8.5 Group Manipulation ……………………………………………………………………………………………….. 8.6 Creating a Group ………………………………………………………………………………………………….. 8.7 Method of Creating a Group ……………………………………………………………………………………… 8.8 Display a Group …………………………………………………………………………………………………… 8.9 Modifying Groups …………………………………………………………………………………………………. 8.10 Moving or Copying between Groups ……………………………………………………………………………. 8.11 Setting Current Group ……………………………………………………………………………………………. 8.12 Transforming Groups …………………………………………………………………………………………….. 8.13 Deleting Groups …………………………………………………………………………………………………… 8.14 Notes on Groups ………………………………………………………………………………………………….. 8.15
9.0
Display Display ……………………………………………………………………………………………………………… 9.3 Entity Type Display ……………………………………………………………………………………………….. 9.4 Group Display ……………………………………………………………………………………………………… 9.5 Plot/Erase ………………………………………………………………………………………………………….. 9.6 Highlighting ………………………………………………………………………………………………………… 9.8 Geometric Attributes ……………………………………………………………………………………………… 9.9 Finite Element and LBC/Element Property Display Attributes ……………………………………………….. 9.11 Titles Example …………………………………………………………………………………………………….. 9.12 Spectrums …………………………………………………………………………………………………………. 9.13
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TABLE OF CONTENTS (cont.)
Section
10.0
Page
Analysis Setup Analysis Setup ……………………………………………………………………………………………. …….. Setting up the Analysis …………………………………………………………………………………………… Results Translation Back into MSC.Patran ……………………………………………………………………. Reading a MSC.Nastran Bulk Data File ………………………………………………………………………..
11.0
Lists Lists Overview …………………………………………………………………………………………………….. How to Create a List ……………………………………………………………………………………………… Boolean Operations ………………………………………………………………………………………………. Boolean Example ………………………………………………………………………………………………….
12.0
11.3 11.4 11.5 11.6
Viewports Viewports ………………………………………………………………………………………………………….. Why use Viewports ……………………………………………………………………………………………….. Creating Viewports ……………………………………………………………………………………………….. Current Viewport ………………………………………………………………………………………………….. Viewports and Groups …………………………………………………………………………………………….
13.0
10.3 10.4 10.5 10.6
12.3 12.4 12.5 12.6 12.7
Results Results Introduction ………………………………………………………………………………………………. 13.3 The Results Main Form …………………………………………………………………………………………… 13.6 Results Plot Types ………………………………………………………………………………………………… 13.7
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TABLE OF CONTENTS (cont.) 13.0
Results Quick Plot Form …………………………………………………………………………………………………… 13.11 Quick Plot Animation Form ………………………………………………………………………………………. 13.12 Results Post-processing Procedure ……………………………………………………………………………...13.13 Select Results Form ………………………………………………………………………………………………. 13.14 Target Entities Form ………………………………………………………………………………………………. 13.16 Display Attributes Form …………………………………………………………………………………………… 13.18 Plot Options Form …………………………………………………………………………………………………. 13.19 Fringe Plot Options ……………………………………………………………………………………………….. 13.22 Deformed Shape Plots …………………………………………………………………………………………… 13.32 Vector Marker Plot ……………………………………………………………………………………………….. 13.33 Marker Display Attributes ………………………………………………………………………………………… 13.34 Create Results Form ……………………………………………………………………………………………… 13.35 X-Y Graph Plotting ……………………………………………………………………………………………….. 13.37 Text Report Writer ………………………………………………………………………………………………… 13.38 Freebody Results …………………………………………………………………………………………………. 13.41 Creating a Range ………………………………………………………………………………………………….. 13.43 Results with Multiple Viewports ………………………………………………………………………………….. 13.46 Results Animation …………………………………………………………………………………………………. 13.47 Quick Plot Animation ……………………………………………………………………………………………… 13.49 Animation Control Setup …………………………………………………………………………………………. 13.50 Animation Options Form …………………………………………………………………………………………. 13.51 Animation Control ………………………………………………………………………………………………… 13.52 Setting up Non-Quick Plot Animation ………………………………………………………………………….. 13.53
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TABLE OF CONTENTS (cont.) 14.0
X-Y Plotting X-Y Plot ……………………………………………………………………………………………………………. XY Plot Terminolgy ……………………………………………………………………………………………….. Curve Data from File ……………………………………………………………………………………………… Scale and Range …………………………………………………………………………………………………. Titles ……………………………………………………………………………………………………………….. Modify Display Parameters ……………………………………………………………………………………… Modify XY Window ……………………………………………………………………………………………….. Modify Curve ……………………………………………………………………………………………………….
15.0
14.3 14.4 14.5 14.6 14.7 14.8 14.9 14.10
MSC.Patran Files MSC.Patran Files ………………………………………………………………………………………………… Reverting your Database ………………………………………………………………………………………… Rebuilding a Database …………………………………………………………………………………………… MSC.Patran Files - Generating Hardcopy Plots ………………………………………………………………. MSC.Patran Files – Customization Files ……………………………………………………………………….
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15.3 15.4 15.5 15.6 15.7
TABLE OF CONTENTS (cont.) 16.0
Stress-Life (S-N) Theory Stress-Life (S-N) Theory ………………………………………………………………………………………… 16.3 Some Definitions …………………………………………………………………………………………………. 16.4 S-N Analysis ………………………………………………………………………………………………………. 16.5 S-N Curve …………………………………………………………………………………………………………. 16.6 S-N Approach ……………………………………………………………………………………………………… 16.9 S-N Curves ………………………………………………………………………………………………………… 16.11 Component S-N Curves ………………………………………………………………………………………….. 16.15 S-N Method Similitude ……………………………………………………………………………………………. 16.18 Variable Amplitude Loads –Miner’s Rule and Rainflow Counting …………………………………………… 16.20 Miner’s Rule – Block Loading ……………………………………………………………………………………. 16.21 Nonlinear Damage Theory ……………………………………………………………………………………….. 16.26 Rainflow Cycle Counting …………………………………………………………………………………………. 16.29 Analysis Route – An Overview ………………………………………………………………………………….. 16.35 Influence on Fatigue Life .………………………………………………………………………………………… 16.36 Mean Stresses Corrections ……………………………………………………………………………………… 16.40 Component Size …………………………………………………………………………………………………… 16.46 Type of Loading ……………………………………………………………………………………………………. 16.49 Notches …………………………………………………………………………………………………………….. 16.51 Surface Treatment & Finish ……………………………………………………………………………………… 16.63 How do we get pre-compression? ………………………………………………………………………………. 16.69 Stress Life in MSC.Fatigue ………………………………………………………………………………………. 16.70 Goodman based Factor of Safety (f) ……………………………………………………………………………. 16.71 Summary of Total Life Method …………………………………………………………………………………… 16.73 Example Problem …………………………………………………………………………………………………. 16.75 Exercise …………………………………………………………………………………………………………….. 16.82
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TABLE OF CONTENTS (cont.) 17.0
Strain-Life (E-N) Theory Strain-Life (E-N) Theory ………………………………………………………………………………………… 17.3 Strain Life Testing …………………………………………………………………………………………………. 17.8 The S-N and E-N Life Curves ……………………………………………………………………………………. 17.11 Materials Characterization ……………………………………………………………………………………….. 17.12 The Bauschinger Effect …………………………………………………………………………………………… 17.16 Masing’s Hypothesis (Stabilized) Hysteresis Loop) …………………………………………………………… 17.18 Strain Control Vs. Stress Control ……………………………………………………………………………….. 17.20 Cyclic Softening …………………………………………………………………………………………………… 17.21 Cyclic Hardening …………………………………………………………………………………………………. 17.22 Cyclic Stress-Strain Curve Determination ……………………………………………………………………… 17.23 Strain Life Results from a series of LCF Tests ………………………………………………………………… 17.27 Coffin-Manson-Basquin Equation ………………………………………………………………………………. 17.29 Transition Fatigue Life Calculation ……………………………………………………………………………… 17.31 Variability in Material Behaviour and the effects on Fatigue Life Prediction ……………………………….. 17.33 Variable Amlitude Loads – Counting Cycles …………………………………………………………………… 17.34 Rainflow Counting and Stress/Strain Space …………………………………………………………………… 17.38 Mean Stress Corrections …………………………………………………………………………………………. 17.40 Exercise ……………………………………………………………………………………………………………. 17.44 Elastic-Plastic Correction and Local Geometry ……………………………………………………………….. 17.45 Use of Kf in Strain Life Modeling ………………………………………………………………………………… 17.48 E-P Correction including Kf………………………………………………………………………………………. 17.50 Refinement to the Neuber Method ………………………………………………………………………………. 17.51 Seeger-Beste Method and Mertens-Dittman Method …………………………………………………………. 17.54 Surface factors ……………………………………………………………………………………………………. 17.58 Stress Strain Tracking, Neuber Analysis, Material memory and Damage Calculation ……………………. 17.60 Example Problem: E-N Analysis of a “Spider” ………………………………………………………………… 17.73 Exercise …………………………………………………………………………………………………………….. 17.77
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TABLE OF CONTENTS (cont.) 18.0
Multiaxial Fatigue Why do Multiaxial Fatigue Fatigue Calculations? ……………………………………………………………… 18.3 The Life Prediction Process E-N Approach ……………………………………………………………………. 18.4 Tensor Representation of Stress State ………………………………………………………………………… 18.7 Stress Tensor Rotation ………………………………………………………………………………………….. 18.10 Principal Stresses (and Strains) …………………………………………………………………………………. 18.11 Free Surface Stresses ……………………………………………………………………………………………. 18.16 Multiaxial Assessment ……………………………………………………………………………………………. 18.17 Example: Near Proportional Loading …………………………………………………………………………… 18.18 Example: Non-Proportional Loading ……………………………………………………………………………. 18.21 Effect of Multiaxiality on Plasticity, Notch Modeling and damage Modeling ………………………………… 18.23 Exercise ……………………………………………………………………………………………………………. 18.24 Deviatoric Stresses ……………………………………………………………………………………………….. 18.25 Yield Criteria ……………………………………………………………………………………………………….. 18.26 Equivalent Stress and Strain Methods ………………………………………………………………………….. 18.30 Some Equivalent Stress/Strain Criteria …………………………………………………………………………. 18.32 S-N with Equivalent Stress ………………………………………………………………………………………. 18.33 E-N with Equivalent Strain ………………………………………………………………………………………... 18.34 Comments on Equivalent Strain Methods ………………………………………………………………………. 18.38 ASME Pressure Vessel Code ……………………………………………………………………………………. 18.40 Notch Rules for Proportional Loading …………………………………………………………………………… 18.43 Extending Neuber to Non-Proportional Loadings ……………………………………………………………… 18.49 Multiaxial Fatigue Theory ………………………………………………………………………………………… 18.55 MSC.Fatigue Multiaxial Analysis ………………………………………………………………………………… 18.58 Normal Strain Method ……………………………………………………………………………………………. 18.61 Shear Strain Method ……………………………………………………………………………………………… 18.62
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TABLE OF CONTENTS (cont.) 18.0
Multiaxial Fatigue Smith-Topper-Watson-Bannantine Method …………………………………………………………………… Fatemi-Socie Method …………………………………………………………………………………………….. Wang-Brown Method …………………………………………………………………………………………….. Dang-Van Method ………………………………………………………………………………………………… Summary of Approach …………………………………………………………………………………………… A Multiaxial Assessment ………………………………………………………………………………………… Exercise ……………………………………………………………………………………………………………
19.0
18.63 18.64 18.66 18.72 18.80 18.81 18.85
Fatigue Crack Propagation Fatigue Crack Propagation (LEFM) Method …………………………………………………………………… 19.3 Crack Stress Concentration …………………………………………………………………………………….. 19.6 Modes of Crack Opening ………………………………………………………………………………………… 19.7 Mechanics of Cracks …………………………………………………………………………………………….. 19.8 K Controlled fracture …………………………………………………………………………………………….. 19.12 Stages of fatigue Crack Growth ………………………………………………………………………………… 19.14 Factors Affecting Crack Growth Rate ………………………………………………………………………….. 19.19 Crack Tip Plasticity ………………………………………………………………………………………………. 19.20 Mean Stress (R-Ratio) Effects ………………………………………………………………………………….. 19.22 Variable Amplitude Loads ………………………………………………………………………………………. 19.24 Environment ………………………………………………………………………………………………………. 19.25 Calculating Lifetimes ……………………………………………………………………………………………… 19.26 Crack Growth Laws ………………………………………………………………………………………………. 19.27 MSC.Fatigue Crack Growth Analysis Steps …………………………………………………………………… 19.29 Summary of Approach ……………………………………………………………………………………………. 19.32 MSC.Fatigue Crack Growth Analysis - Applications ……………………………………………………………19.33 Example Problem: Crack Propagation Analysis ………………………………………………………………. 19.34 Exercise ……………………………………………………………………………………………………………. 19.40
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TABLE OF CONTENTS (cont.) 20.0
Spotweld Fatigue Motivation ………………………………………………………………………………………………………….. Structural Stress Based Method ………………………………………………………………………………… How do we model Spotwelds …………………………………………………………………………………… Structural Stress Calculations ………………………………………………………………………………….. Fatigue Properties – Typical Test Specimen …………………………………………………………………. Damage Calculation Procedure ………………………………………………………………………………… Results Postprocessing Options ……………………………………………………………………………….. Polar Plot of Damage ……………………………………………………………………………………………. Example Problem: A Spotweld Analysis ………………………………………………………………………. Exercise ……………………………………………………………………………………………………………
21.0
20.3 20.5 20.7 20.9 20.11 20.13 20.14 20.16 20.17 20.22
MSC.Fatigue Software Strain Gauge Software Strain Gauge …………………………………………………………………………………………… 21.4 Correlation Applications …………………………………………………………………………………………. 21.6 Welded Structure Analysis ………………………………………………………………………………………. 21.8 Gauge Definition ………………………………………………………………………………………………….. 21.10 Implementation ……………………………………………………………………………………………………. 21.11 Example Problem: A Software Strain gauge …………………………………………………………………… 21.12 Correlation Techniques ………………………………………………………………………………………….. 21.16 Exercise ……………………………………………………………………………………………………………. 21.17
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TABLE OF CONTENTS (cont.) 22.0
Vibration Fatigue Analysis Overview ………………………………………………………………………………………………………….. 22.3 Benefits of Vibration Fatigue ……………………………………………………………………………………. 22.5 How do we Calculate Damage ………………………………………………………………………………….. 22.6 What is a PSD …………………………………………………………………………………………………….. 22.10 Expected Zeroes, Peaks and Irregularity Factor from a PSD ………………………………………………... 22.12 Probability Density Functions (PDF’S) …………………………………………………………………………. 22.14 Dirlik Solution ……………………………………………………………………………………………………… 22.15 Other Solution Methods ………………………………………………………………………………………….. 22.16 Summary of Features …………………………………………………………………………………………….. 22.18 Example Problem: Vibration Fatigue ……………………………………………………………………………. 22.20 Exercise …………………………………………………………………………………………………………… 22.26
23.0
MSC.Fatigue Utilities Utilities Overview …………………………………………………………………………………………………. 23.3 PTIME (Time History Manager) …………………………………………………………………………………. 23.5 Time History Manipulation Tools ………………………………………………………………………………… 23.6 Graphical Editing of Data – “GED” ……………………………………………………………………………… 23.13 Time History Analysis/Statistics ………………………………………………………………………………… 23.14 Filtering ……………………………………………………………………………………………………………. 23.17 Frequency Analysis ………………………………………………………………………………………………. 23.19 Peak Valley regeneration – “REGEN” ………………………………………………………………………….. 23.12 Fatigue Analysis (local or test based) Tools …………………………………………………………………… 23.23 Other Fatigue Related Tools …………………………………………………………………………………….. 23.24 Time Correlated Damage – “TCD” ……………………………………………………………………………… 23.26 Stress Concentration Library “KTAN” …………………………………………………………………………… 23.27 Rosette Analysis – “SSA” ……………………………………………………………………………………….. 23.28 Data Conversion and other Utilities ……………………………………………………………………………. 23.29 Exercise …………………………………………………………………………………………………………… 23.30
PAT318, Section 0, March 2002
S0-18
SECTION 1 OVERVIEW OF DURABILITY AND FATIGUE LIFE ANALYSIS
PAT318, Section 1, March 2002
S1-1
PAT318, Section 1, March 2002
S1-2
COMPANY OVERVIEW n
The MSC.Software corporation (formerly MacNeal-Schwendler Corporation) has been supplying sophisticated computer-aided engineering (CAE) tools since 1963
n
MSC.Software is the developer, distributor, and supporter of the most complete and widely-used structural analysis program in the world, MSC.Nastran as well as the first commercial nonlinear analysis program in the world, MSC.Marc. u u u u
u
MSC.Nastran MSC.Marc MSC.Patran MSC.Dytran
u u u u
PAT318, Section 1, March 2002
S1-3
MSC.MVision MSC.Fatigue MSC.Laminate Modeler MSC.Autoforge and more
COMPANY OVERVIEW (CONT.) n
MSC.Software Milestones u
1963
Company founded by Dr. Richard MacNeal and Mr. Robert Schwendler. Developed first program called SADSAM for Structural Analysis by Digital Simulation of Analog Methods. This was the forerunner of MSC’s flagship program, MSC.Nastran.
u
1965
MSC participates in NASA-sponsored project to develop a unified approach to computerized structural analysis. The program became known as NASTRAN (NASA Structural Analysis Program)
PAT318, Section 1, March 2002
S1-4
COMPANY OVERVIEW (CONT.) u
1965
A team of researchers at Brown University initiated the development of the technology leading to the MARC program.
u
1971
The MARC Analysis Research Corporation was founded.
u
1972
MSC releases proprietary version of NASTRAN, called MSC.Nastran.
u
1972
MAR Corporation releases the first proprietary version of MARC, the first commercial Nonlinear finite element analysis program.
PAT318, Section 1, March 2002
S1-5
COMPANY OVERVIEW (CONT.)
u
1994
MSC merged with PDA Engineering (Developer of PATRAN) to become the largest single provider of finite element analysis (FEA) software to the CAE market.
u
1999
MSC.Software merged with MARC Analysis Research to lead both the linear and the nonlinear analysis worldwide CAE market.
PAT318, Section 1, March 2002
S1-6
COMPANY OVERVIEW (CONT.)
u
1994
MSC merged with PDA Engineering (Developer of PATRAN) to become the largest single provider of finite element analysis (FEA) software to the CAE market.
u
1999
MSC.Software merged with MARC Analysis Research to lead both the linear and the nonlinear analysis worldwide CAE market.
PAT318, Section 1, March 2002
S1-7
MSC CLIENT SUPPORT n
With corporate headquarters in Santa Ana, California, MSC.Software maintains regional sales and support offices worldwide. u
MSC Technical Support Hotline 1-800-732-7284 (USA/Canada). Staffed Monday through Friday 7:00 a.m. to 3:00 p.m. Pacific Standard Time.
u
E-mail support (USA/Canada) at
[email protected] [email protected]
u
Support (USA/Canada) Fax 714-979-2900 Internet support http://www.mscsoftware.com
u
PAT318, Section 1, March 2002
S1-8
COURSE SCHEDULE Day 1:
Day 3 (Continued):
Intro to Fatigue Analysis MSC.Fatigue Software Overview MSC.Fatigue User Interface User Interface Exercises
Intro to Multi-axiality Hands-On Exercises
Day 4: Crack Propagation LEFM Exercises Spot weld Software Strain Gauge Vibration Fatigue Hands-On Exercises Advanced Features MSC.Fatigue Utilities
Day 2: User Interface (Continued) Stress-Life (S-N) Theory Influences on Fatigue Life S-N Exercises
Day 3: Strain-Life (E-N) Theory Mean Stress Correction E-N Exercises
PAT318, Section 1, March 2002
S1-9
MSC.FATIGUE FEATURES n
MSC.Fatigue is an advanced Fatigue life estimation program for use with finite element analysis. It provides state-of-the-art Fatigue analysis tools which can be used to optimize the life of a product early in the design process. Key capabilities include: u u u u u u u u
Total Life Analysis (S-N) based on nominal stress-life Crack Initiation Analysis (E-N) or the local strain method Crack Growth Analysis - linear elastic fracture mechanics Spot and Seam Weld Analysis Vibration Fatigue analysis Materials and Time History Databases Biaxiality Analysis leading to Multiaxial Fatigue Life Calculations Software Strain Gauge and other Utilities
PAT318, Section 1, March 2002
S1-10
MSC.FATIGUE USER INTERFACE n
MSC.Fatigue has a graphical user interface which consists of the following major components: u u u u u
Windows-Style User Interface Finite Element Model and Results Import Analysis Preferences Engineering Functionality Results Visualization
PAT318, Section 1, March 2002
S1-11
COMPUTER AIDED ENGINEERING SOLUTIONS... MSC Finite Element Analysis Software
Materials & Loading Information MVI - Flightloads
Engineering Services
MSC
MSC Institute Training Services
PAT318, Section 1, March 2002
S1-12
Tailored Software Solutions
DURABILITY MANAGEMENT
MEASUREMENT
TEST
nCode MSC ANALYSIS
PAT318, Section 1, March 2002
S1-13
A partnership for excellence in durability technology
PAT318, Section 1, March 2002
S1-14
WHAT IS DURABILITY?
PAT318, Section 1, March 2002
S1-15
n
Durability is… do ben u u
n
the ability to do what its supposed to for as long as its supposed to do it!
Reliability is… u
having half a chance of doing what its supposed to for as long as its supposed to do it!
PAT318, Section 1, March 2002
S1-16
n
Fatigue is ... u
n
the process where repeated variations in loading cause failure even when the nominal stresses are below the material yield strength;
and is… u
made up of crack initiation and subsequent crack growth as a result of cyclic, plastic deformation.
PAT318, Section 1, March 2002
S1-17
WHAT DRIVES DURABILITY MANAGEMENT?
PAT318, Section 1, March 2002
S1-18
GOALS, DRIVERS AND REALITIES n
Competition requires FASTER concept-to-customer.
n
Costs/profits require CHEAPER products, materials and manufacturing processes.
n
Functionality requires BETTER products with hi-tech features and performance.
n
Legislation requires products with LONGER, more durability and inspection periods.
n
The customer requires the last mile/flight/hour to be the same as the first.
PAT318, Section 1, March 2002
S1-19
reliable
PRODUCT DEVELOPMENT LIFECYCLE COSTS
Cumulative Cost
Production Pilot
Production
Engineering Prototype
Engineering Prototype Mechanical Prototype
DESIGN FIX
TEST
CAE for Durability
Concept Concept
Mechanical Prototype
Development Time Traditional Design Development CAE Design Objectives
PAT318, Section 1, March 2002
S1-20
TRADITIONAL APPROACH WITHOUT CAE: BUILD IT, TEST IT, FIX IT Generate idea
Build it
Fix it
Test it
OK?
NO NO
Begin Production PAT318, Section 1, March 2002
Out of time? YES
S1-21
ADD CAE: ANALYSE AND OPTIMIZE Generate idea Analyse Optimize NO
Previous experience
OK? Build it
Correlate test & analysis
Test it NO
PAT318, Section 1, March 2002
OK? S1-22
Measure YES
Begin Production
PREDICTING PRODUCT LIFE 1 - BUILD AND USE
Customer Usage
Product Life
Check Life Based on Customer Usage
Build it and Use It
PAT318, Section 1, March 2002
S1-23
PREDICTING PRODUCT LIFE 2 - ADD SIGN-OFF TESTING
Customer Usage
Accelerated Sign-off Test
Re-Design
PAT318, Section 1, March 2002
S1-24
Product Life
PREDICTING PRODUCT LIFE 3 - ADD SIMULATION TESTING
Customer Usage
Simulated Component Test
Accelerated Sign-off Test
Measured Service Loading Re-Design
PAT318, Section 1, March 2002
S1-25
Product Life
PREDICTING PRODUCT LIFE 4 - ADD CAE Customer Usage
Accelerated Sign-off Test
Simulated Component Test
Measured Service Loading Stress Analysis Material Properties
Product Life
Correlation Computer-based Fatigue Life Simulation
Product Life
Re-Design Optimize
PAT318, Section 1, March 2002
S1-26
INTEGRATED DURABILITY MANAGEMENT ACTIVITIES Modern Integrated Approach
DESIGN ANALYSIS
Analytical Loads Kinematic Modelling
Structural Integrity Optimization
DATA & CORRELATION
CORRELATION
DATA
DEVELOPMENT ANALYSIS DATA
MEASURED STRAINS & LOADS
Characterisation Correlation with FEA Assess Modifications
Measurement Validation Correction
SIMULATION TEST Verification Monitoring Correlation
DATA
PAT318, Section 1, March 2002
DATA
S1-27
INTEGRATION n
Achieving Faster, Cheaper, Better Integrated Durability Management requires: u u u u
Integrated multi-disciplinary teams. Integrated software tools common to all departments. Integrated data exchange within company structure. Integrated data exchange between the company and its suppliers and service providers.
PAT318, Section 1, March 2002
S1-28
DESIGN APPROACHES n
SAFE LIFE u
n
FAIL SAFE u
n
Evaluate expected life, use a margin of safety, design to survive expected service life, then retire.
Provides redundant load paths, design to fail into a safe condition and survive until repair.
DEFECT TOLERANCE u
Assumes flaws do exist, design to live with some crack growth below critical size, requires regular inspections.
PAT318, Section 1, March 2002
S1-29
HISTORY OF FATIGUE – EARLY DAYS Over design 42 Under design 7
Product life used to be a hit and miss affair PAT318, Section 1, March 2002
S1-30
A SHORT HISTORY OF FATIGUE - 1 1828 1839 1849 1850
ALBERT tests mine hoist chains under cyclic loading PONCELET designs mill wheels with cast iron axles. First uses the term ‘Fatigue’ in a book on mechanics IMechE debate the "CRYSTALLIZATION" theory on WÖHLER conducts first systematic Fatigue investigations on axles. Develops the ROTATING-BENDING Fatigue test, S-N curves and the concept of Fatigue LIMIT Starts the development of design strategies for Fatigue. Identifies importance of cyclic and mean stresses
PAT318, Section 1, March 2002
S1-31
Wohler’s Railway Component Test Rig
PAT318, Section 1, March 2002
S1-32
Stress Amplitude
Unnotched Shaft
Notched Shaft
Log (Fatigue life) Some of Wohler’s data for rotating bending tests
PAT318, Section 1, March 2002
S1-33
A SHORT HISTORY OF FATIGUE - 2 1864 1886 1903 1910 1920
FAIRBAIRN experiments with repeated loads BAUSCHINGER first documents Stress-Strain HYSTERESIS EWING & HUMPHREY disprove the Crystallisation theory and show that Fatigue is due to SLIP BAIRSTOW investigates stress-strain response during cycling - develops concepts of cyclic HARDENING and SOFTENING GRIFFITH investigates cracks in glass - the birth of FRACTURE MECHANICS
PAT318, Section 1, March 2002
S1-34
CRACK INITIATION AND GROWTH - STAGE I AND II
~1mm
Persistent Slip band formation
PAT318, Section 1, March 2002
Stage I Crack Growth
S1-35
Stage II Crack Growth
MICROSTRUCTURAL CRACK GROWTH da/dN
a
PAT318, Section 1, March 2002
S1-36
A SHORT HISTORY OF FATIGUE - 3 1955
MANSON and COFFIN investigate Fatigue under STRAIN conditions - thermal cycling - low cycle & plastic strain considerations 1959 PARIS and ERDOGAN present first systematic method for handling CRACK PROPAGATION using fracture mechanics 1961 FORSYTH identified stage I and stage II crack propagation 1961 - NEUBER proposed a method for estimating elastic-plastic stresses and strains at stress concentrations 1968 - MATSUISHI and ENDO present the rainflow method for cycle counting
PAT318, Section 1, March 2002
S1-37
STRAIN LIFE RESULTS FROM A SERIES OF LCF TESTS Life Curve Display Total strain curve fit
Total strain data
Elastic strain curve fit
Elastic strain data
Plastic strain curve fit
Plastic strain data
1E0
Sf': 670 MPa b : -0.0582
L o g S tr a in
1 E -1
(X/Y) Ef': 0.374 1 E -2
c : -0.54 E : 2.05E5 MPa (X/Y)
1 E -3
: Run-out pts
1 E -4 1E0
1E1
1E2
1E3
1E4
1E5
Log Life (Reversals)
PAT318, Section 1, March 2002
S1-38
1E6
1E7
1E8
A SHORT HISTORY OF FATIGUE - 4 1982 - Battelle Labs in the US estimated annual cost of Fatigue and fracture to the US was 4.4% of GDP (Billions of $) and that cost could be reduced by 29% by application of current technology 1982 - nCode International established to market Fatigue life estimation software & consultancy services 1990 - MSC.Fatigue launched by PDA Engineering
PAT318, Section 1, March 2002
S1-39
FATIGUE LIFE CALCULATION METHODS n
S-N (Total Life Method) u
n
e-N (Crack Initiation Method) u
n
Relates local strain to crack initiation life
LEFM (Crack Propagation Method) u
n
Relates nominal or local elastic stress to total life
Relates stress intensity to crack propagation rate
All methods rely on SIMILITUDE
PAT318, Section 1, March 2002
S1-40
f Total Life
S-N PAT318, Section 1, March 2002
=
i
Crack Initiation
Local Strain S1-41
p +
Crack Growth
LEFM
S-N METHOD - SIMILITUDE
σ nom
σ nom The life of this . . . . . . . . . . . . . . . . is the same as the life of this . . . . . if both are subject to the same nominal stress PAT318, Section 1, March 2002
S1-42
CRACK INITIATION (STRAIN - LIFE) METHOD SIMILITUDE
e
e
The crack initiation life here . . . . . is the same as it is here . . . . . if both experience the same local strains PAT318, Section 1, March 2002
S1-43
CRACK PROPAGATION METHOD - SIMILITUDE
This crack . . . . . . . grows at the same rate as this one if both experience the same stress intensity factors
PAT318, Section 1, March 2002
S1-44
FATIGUE FAILURE AND TRAINING
"Despite 150 years of Fatigue research, unintended Fatigue failures still occur. More research will NOT reduce the incidence of Fatigue failure - more education will!"
-Quote by Prof. D. Socie University of IIIinois,1990
PAT318, Section 1, March 2002
S1-45
THE PHYSICAL BASIS OF FATIGUE n
n
n
Fatigue failures typically start at the surface of a specimen or component Fatigue failures start at small microscopic cracks and accordingly are very sensitive to even minute stress raisers It has been demonstrated that the Fatigue failure process is related to reversed plastic flow
PAT318, Section 1, March 2002
S1-46
SLIP AND STAGE I GROWTH n
n
n
Under cyclic loading the slip bands tend to group into packets or striations, forming both ridges and crevices There is good evidence that the crevices are closely associated with the initiation of cracks. Small localised deformations (called extrusions and intrusions) may occur in the slip bands. These surface disturbances are approximately 1 to 10 microns. They constitute initial microcracks.
PAT318, Section 1, March 2002
S1-47
INITIATION AND PROPAGATION
PAT318, Section 1, March 2002
S1-48
INITIATION AND PROPAGATION n
n
The process of Fatigue encompasses the entire range from the formation of a microcrack in a persistent slip band to the propagation of a long crack in an elastic-plastic continuum. There are many ways of starting a small crack: u u u u u u
cracking or debonding of second phase particles, natural scratches and machining marks on the surface corrosion pits or intergranular attack porosity from casting laps from forging and forming brittle surface layers
PAT318, Section 1, March 2002
S1-49
USE OF FATIGUE TECHNOLOGY n
Fatigue Technology is not new (50-170 years old);
n
A collection of empirical rules to fit observed behaviour;
n
Does not require the engineer exploiting it to understand all the finer points;
n
Can be used (with training and experience) to achieve IDM goals.
PAT318, Section 1, March 2002
S1-50
FATIGUE CALCULATIONS IN…? n
Concept design phase: u u
n
Verification phase: u u
n
Analytical loads, previous design loads, estimated properties, early design optimization
Measured loads, real properties, design refinement and optimization
Production phase: u
Continued development, new markets, firefighting
PAT318, Section 1, March 2002
S1-51
WHO DOES WHAT FATIGUE CALCULATIONS? n
Design analyst: u u
n
Development engineer u u
n
Measures data on the “real component”, tells the design analyst where its wrong and how to fix it.
Test rig engineer u u
n
Design optimization for durability on the “virtual component”
Pre-predicts rig tests and edits out non damaging parts to speed them up.
Production engineer u u
Investigates service failures, monitors production, feeds back improvement ideas.
PAT318, Section 1, March 2002
S1-52
DESIGNING AGAINST FATIGUE n
Requirements: u u u u u
PAT318, Section 1, March 2002
higher performance lower weight longer life reasonable cost as soon as possible
S1-53
DESIGNING AGAINST FATIGUE n
Constraints: u u u
u u
u
life calculations are much less precise than strength calculations Fatigue properties can not be inferred from static mechanical properties laboratory tests often exhibit scatter and are difficult to translate to full size components full scale prototype testing is often required to confirm an acceptable life designs should be ‘defect tolerant’ - stressing and materials selection to ensure slow crack growth and detectability before failure where possible designs should be ‘fail safe’
PAT318, Section 1, March 2002
S1-54
EXPLOITING FATIGUE ANALYSIS - THE 5 BOX TRICK LOADS
GEOMETRY
BLACK BOX
Wrong answer
ANALYSIS
LIFE (42) Garbage OUT
MATERIALS Garbage IN
PAT318, Section 1, March 2002
Lots more wrong answers very quickly RE-DESIGN RE-ANALYSE
S1-55
EXPLOITING FATIGUE ANALYSIS n
The information required for rapid and effective Fatigue analysis can be broken down into: u u u
a description of the loading environment a description of the geometry of the component material specific information on the deformation behaviour and Fatigue properties
PAT318, Section 1, March 2002
S1-56
DURABILITY TOOLS FOR ANALYSIS AND TEST n
The Fatigue modelling tools used in design analysis and in test analysis use: u u u
n
the same time history files the same materials databank information the same Fatigue algorithms (and similitude)
The only difference is that the analyst uses an FE model while the tester uses a strain gauge.
PAT318, Section 1, March 2002
S1-57
INTEGRATED APPROACH TO DURABILITY n
Facts: u
u
u
u
Testing is not a good way to optimize designs, but is always required for sign-off. Useful Fatigue analysis requires verification and good test-based information. Neither Testing nor Analysis have exclusively the “right” Fatigue answer; therefore its not an argument between rivals. Best results are obtained when an integrated approach is adopted incorporating analysis and testing.
PAT318, Section 1, March 2002
S1-58
HOW TESTING SUPPORTS ANALYSIS n n n n n
Provision of load data Provision of material Fatigue properties Verification of stress/strain analysis results Correlation of life predictions Final sign-off
PAT318, Section 1, March 2002
S1-59
HOW ANALYSIS SUPPORTS TESTING n n n n
Eliminating unnecessary tests Test acceleration Gauge type selection and positioning Test design
PAT318, Section 1, March 2002
S1-60
“Engineering is the art of being approximately right rather than exactly wrong”
-Quote by Prof. Rod Smith University of Sheffield,1990
PAT318, Section 1, March 2002
S1-61
PAT318, Section 1, March 2002
S1-62
SECTION 2 OVERVIEW OF MSC.FATIGUE
PAT318, Section 2, March 2002
S2-1
PAT318, Section 2, March 2002
S2-2
WHAT’S IN MSC.FATIGUE? n
Analysis methods: u u u u u u u u
n
n
Stress Life (S-N) Crack Initiation (E-N) Fracture Mechanics Weld Fatigue Vibration Fatigue Multiaxial Fatigue Spotweld Fatigue Software strain gauge
u
u
u u
u
Available in 2 options u u
Integrated in MSC.Patran Standalone MSC.Fatigue Pre&Post
PAT318, Section 2, March 2002
Features:
S2-3
Time-domain (Quasi-static or Transient analysis) Frequency-domain (forced or random vibration) Fast preview analysis Design optimization & sensitivity analysis Import from: MSC.NASTRAN, ABAQUS, ANSYS, MSC.MARC, SDRC Ideas
MSC.FATIGUE CAPABILITIES Analysis Options
Geometry & FEA Results
•Stress (total) Life •Strain (initiation) Life
Fatigue Life Contours Cross Plot of Data : S61STRAIN1KT
DISPLAY OF SIGNAL: TEST101.DAC
•Crack Propagation
1500
7 6 5 4
Kt( )
Strain (uE)
•Vibration Fatigue •Multi-axial Fatigue
-1500 Time (seconds)
0
2
•Spot/SeamWeldAnalyzer
12
1
1E3
1E4
1E5
1E6
Life(Miles)
•Software Strain Gauge
Test (Lab) Results
3
Sensitivity Analysis and Optimization
•Utilities Strain Life Plot 605M30 Sf': 857 b: -0.067 Ef': 0.636 c: -0.579
Strain Amplitude (M/M)
DAMAGE HISTOGRAM DISTRIBUTION FOR : TRACK05.DHH Maximum height : 4.8548 Z Units : %
1E-1
4.8548 1E-2
Damage Z-Axis 0 0
1E-3
1E0
1E1
1E2
1E3
1E4
1E5
1E6
1E7
Life (Reversals)
1574.7
Materials and Loading Information PAT318, Section 2, March 2002
808.7 Mean uE Y-Axis
Range uE X-Axis
1E8
-750.4
Damage Distributions S2-4
LIFE PREDICTION PROCESS
Loads
PAT318, Section 2, March 2002
Stress or Strain
S2-5
LIFE
LIFE PREDICTION PROCESS: APPROACH measured strains
constitutive model
stress and strain components elastic strains from FEA
PAT318, Section 2, March 2002
ε-N
LIFE
damage model
constitutive model and notch rule
S2-6
ELASTIC STRESS OR STRAIN PREDICTION METHODS n
Time-domain: u u
n
Quasi-Static method (with or without “inertia relief”) Transient method (direct or modal)
Frequency-domain: u u
Forced Vibration Response (transfer function method) Random Vibration (PSD input to / output from NASTRAN)
PAT318, Section 2, March 2002
S2-7
QUASI-STATIC ANALYSIS n
n n
Identify set of static FE loadcases and constraints to simulate service environment Measure or predict loading histories Pk( t ) Elastic stress histories calculated from linear superposition: σ
ij , e
(t) =
å k
æ σ ij , e , k P k ( t ) çç è P k , fea
where k = loadcase i.d.
PAT318, Section 2, March 2002
S2-8
ö ÷ ÷ ø
STRAIN COMBINATION, CYCLE COUNTING, ELASTO-PLASTIC CORRECTION, AND DAMAGE CALCULATION [εij](t)
Combination
εq(t) εq = Max. Absolute Principal Signed von Mises Signed Tresca Component
Cycle Counting
Range-Mean Histogram
Material Properties
Elastic Plastic Conversion & Damage Calculation
LIFE
PAT318, Section 2, March 2002
S2-9
EXAMPLE - STEERING KNUCKLE
PAT318, Section 2, March 2002
S2-10
LOADING HISTORIES Force(Newtons)
LOAD03.PVX
84.71
Sample = 1 Npts = 1610 Max Y = 84.71 Min Y = -50.05 -50.05 0
500
1000
1500 point
Force(Newtons)
LOAD02.PVX
7720
Sample = 1 Npts = 1610 Max Y = 7720 Min Y = -7998 -7998 0
500
1000
1500 point
Force(Newtons)
LOAD01.PVX
3769
Sample = 1 Npts = 1610 Max Y = 3769 Min Y = -2654 -2654 0
500
1000
1500 point
Screen 1
PAT318, Section 2, March 2002
S2-11
QUASI-STATIC STRAIN CALIBRATION & SUPERPOSITION Time Histories
FE Loadcase Results
FE Loadcase Loads
This process is repeated for each node/element
PAT318, Section 2, March 2002
S2-12
Local Strain Histories
STEERING KNUCKLE
PAT318, Section 2, March 2002
S2-13
FE ANALYSIS FOR STATICALLY BALANCED CASE n
n n n n
Ideally determine all Free Body Diagram (FBD) loads (and check for static balance) At least 6 DOF constraints (can be arbitrary if all FBD loads are used) Redundant constraints must be realistic Location of constraint may be chosen arbitrarily or for convenience (e.g. where loads are not easily measured)
PAT318, Section 2, March 2002
S2-14
FE ANALYSIS FOR STATICALLY UNBALANCED CASE n
n
n n
Must determine all FBD loads (unless there is partial support, e.g. a hinge) Constrain 1 node for 6 DOF (unless there is a hinge for instance) Use “Inertia Relief” Inertia Relief calculates the reaction forces and mass matrix at the constrained node and redistributes inertia loads according to the calculated accelerations
PAT318, Section 2, March 2002
S2-15
TRANSIENT DYNAMIC CASE n
Time histories of stress or strain calculated directly using FE transient analysis.
n
Analysis driven by measured vertical forces, accelerations. FE analysis time consuming for large models.
n
PAT318, Section 2, March 2002
S2-16
FREQUENCY DOMAIN Frequency domain analysis can account for dynamic (resonant) effects
Response variation
Time Domain Fast Fourier Transform (FFT) (throw away phases) 5
10
15
Response2 Hertz
20
Power Spectrum
Time in seconds
Frequency (Hz)
Inverse Fourier Transform (IFT) (create random phases) PAT318, Section 2, March 2002
S2-17
Frequency Domain
VIBRATION FATIGUE METHODS The PSD can be used to estimate the statistics of the stress history and to estimate a PDF of Stress Range Total plot of file NOISE.CYH
DISPLAY OF NOISE.PSD
50
Cycles
RMS Power (MPa^2. Hz^-1)
753.5
0
0
0
Frequency (Hz.)
1494.141
0
Original Title : Stress
PAT318, Section 2, March 2002
S2-18
Range
796
FE MESH CONSIDERATIONS n
n
n
n
FE Stress Analysis is a pre-processing activity for durability analysis Global stiffness convergence is a necessary but not a sufficient condition for a good FE model The essential requirement is for good local stress information in the critical areas For crack initiation calculations this normally means good stresses at free surfaces
PAT318, Section 2, March 2002
S2-19
MSC.FATIGUE ANALYSIS PROCESS MSC/PATRAN - Applications MSC.Fatigue
FIN
NOR
LST
FNF
Fatigue Results Filter
Global Fatigue Analyzer
FEF
FPP
Factor of Safety Analyzer
FOS
DAC
Design Optimization Analyzer
FAL DCL KFC
DAC FES TDB Fatigue Pre-Processor
P3/PATRAN - Applications Results
PAT3FAT
MDB DHH
TCY KSN
PAT318, Section 2, March 2002
Fatigue Crack Analyzer
CRG
S2-20
DYH
XYD
Results Listing
MSC.FATIGUE MAIN FORM Geometry
Materials
Postprocessing
Analysis
Loading Optimization
PAT318, Section 2, March 2002
S2-21
ANALYSIS PROCESS Quasi-Static, Strain-Life Example Results from Linear FE give LoadStrain relationship Strain-Life relationship used to calculate damage per cycle and summed to give Life
Geometry
Materials
Strain time histories calculated for each node by linear superposition
Rainflow cycle count & elasticplastic correction
Analysis
Postprocessing
Loading Optimization
Up to 100 simultaneous ‘load’ (Force, disp etc.) time histories
Critical nodes can be identified and reanalyzed PAT318, Section 2, March 2002
S2-22
METHODOLOGY Geometry
Materials
Analysis
Post-processing
Loading Optimization
PAT318, Section 2, March 2002
S2-23
GEOMETRY / STRESS-STRAIN RESULTS: n
n
Linear FE Results (stress or strain) u Linear Static (up to 100 load cases) u Transient Dynamic u Stress Frequency Response u PSD of Stress Components FE Codes u MSC.NASTRAN u ABAQUS u ANSYS u MSC.MARC u LS-DYNA3D u SDRC u Others
PAT318, Section 2, March 2002
S2-24
METHODOLOGY Geometry
Materials
Analysis
Post-processing
Loading Optimization
PAT318, Section 2, March 2002
S2-25
MATERIALS DATABASE MANAGER
n
Facilities for u u u u u
Data Entry, Deletion, & Editing Searching on Descriptive Data Database Entry Listing Graphical Display Multiple Material Designation DIN, SAE, ASTM, etc.
PAT318, Section 2, March 2002
S2-26
Steel Aluminum Titanium
Copper
MATERIALS DATABASE MANAGER: A typical S-N curve S-N Data Plot MANTEN_SN SRI1: 3162 b1: -0.2 b2: 0
E: 2.034E5 UTS: 600
Stress Range (MPa)
1E4
1E3
1E2
1E1 1E0
PAT318, Section 2, March 2002
1E1
1E2
1E3
1E4 1E5 Life (Cycles)
S2-27
1E6
1E7
1E8
1E9
METHODOLOGY
Geometry
Materials
Analysis
Post-processing
Loading Optimization
PAT318, Section 2, March 2002
S2-28
LOADING TIME HISTORY DATABASE MANAGER: n
Facilities for: u
u u u u u u
Creation (waves, point by point, graphical, etc.) Graphical Display and Editing Arithmetic & Graphical Manipulation Graphical Cutting and Pasting Automatic Units Conversion Searching ASCII File Import
PAT318, Section 2, March 2002
S2-29
Wind Transmission Waves Suspension
LOADING TIME HISTORY DATABASE MANAGER: DISPLAY OF SIGNAL:
TEST102.DAC
1500
Strain (uE)
A typical load history showing random loading sequences
-1500 Time (seconds)
0
PAT318, Section 2, March 2002
S2-30
12
METHODOLOGY Geometry
Materials
Analysis
Post-processing
Loading Optimization
PAT318, Section 2, March 2002
S2-31
STRESS LIFE ANALYSIS (S-N): S-N Data Plot
Features u u u u
u
u u
u u u
Rainflow Cycle Counting Mean Stress Correction Welded Structures Statistical Confidence Parameters Palmgren-Miner Linear Damage User Defined Life Material and Component S-N Surface Conditions Factor of Safety Analysis Biaxiality Indicators
PAT318, Section 2, March 2002
MANTEN_SN SRI1: 3162 b1: -0.2 b2: 0
E: 2.034E5 UTS: 600
1E4
Stress Range (MPa)
n
1E3
1E2
1E1 1E0
S2-32
1E1
1E2
1E3
1E4 1E5 Life (Cycles)
1E6
1E7
1E8
1E9
CRACK INITIATION ANALYSIS (E-N): n
e Strain
Features u u u u u u u u u u
Based on Local Strain Concepts Mean Stress Correction Elastic-Plastic Conversion Statistical Confidence Parameters Palmgren-Miner Linear Damage User Defined Life Cyclic Stress-Strain Modeling Surface Conditions Factor of Safety Analysis Biaxiality Indicators
PAT318, Section 2, March 2002
S2-33
Time
1/2cycle 1cycle
1/2cycle 1cycle 1cycle 1/2cycle
s
e
CRACK GROWTH ANALYSIS (LEFM) n
Features u u
u
u u u u u
u u
Cycle-by-Cycle Modeling Time-sequenced Rainflow Cycle Counting Multi-environment Material Properties Kitagawa Minimum Crack Sizing Threshold Modeling Crack Closure and Retardation User Defined Life Fracture Toughness Failure Criterion Surface or Embedded Cracks Modified Paris Law
PAT318, Section 2, March 2002
S2-34
METHODOLOGY
Geometry
Materials
Analysis
Post-processing
Loading Optimization
PAT318, Section 2, March 2002
S2-35
POST-PROCESSING: RESULTS
n
Contour Plotting of: u u u u
u u
n
Life Estimates Log of Life Damage Component Specific Life Units (Flights, Miles, etc.) Factor-or-Safety Multiaxiality Indicators
X-Y Plots of Sensitivity Studies
PAT318, Section 2, March 2002
S2-36
POST-PROCESSING: RESULTS n
Tabular Results of: u u u u u u
Individual Nodes/Elements Most Damaged Nodes/Elements Statistical Summary of Damage Distribution Interactive Results Interrogation of All Life and Damage Estimates Factor-or-Safety Multiaxiality Indicators
PAT318, Section 2, March 2002
S2-37
POST-PROCESSING: HISTOGRAM PLOTS Cycles vs. Damage
PAT318, Section 2, March 2002
S2-38
POST-PROCESSING: DESIGN OPTIMIZATION n
Localized Analysis for Evaluation of Alternative: u u
u u u u
u u
Surface Conditions Material Types / Parameters Statistical Confidence Design Geometry Loading Conditions Residual Stresses and Stress Concentrations Mean Stress Design Life
PAT318, Section 2, March 2002
S2-39
POST-PROCESSING: DESIGN OPTIMIZATION
n
n
n
n n n n
Search for Better/Worse Material Allowables Based on Design Life Calibration to Test Results Sensitivity Calculations X-Y Plotting Histogram Plotting User Preferences
PAT318, Section 2, March 2002
S2-40
ADVANCED FEATURES: MSC.FATIGUE SPOT WELD
PAT318, Section 2, March 2002
S2-41
STRUCTURAL STRESS BASED METHOD ( Rupp - Storzel – Grubisic)
n
n
n
n n
Coarse mesh only required, with spot welds modeled as stiff beam elements Beams are used as " force transducers " to obtain forces and moments transmitted through the spot welds Forces and moments are used to calculate " structural stresses " Life is calculated using Miner's rule Method is generally applicable and handles multiaxial loading
PAT318, Section 2, March 2002
S2-42
Spotweld “Nugget”
Beam Element d
HOW DO WE MODEL SPOTWELDS? The 5 Box Trick Geometry (Beam Elements)
Loading
Fatigue Analysis
(Time History)
(Spot Weld Analyser)
Material (Weld S-N Data)
Optimization & Testing
PAT318, Section 2, March 2002
S2-43
Post Processing
STRUCTURAL STRESS CALCULATIONS The structural stresses are calculated from the forces and moments on each beam element : My My Fy
My
Fy Fz
Fy
Fx Fz
Fz
Mx
Fx Mx
Fx Mx
Nugget
Sheet 2
PAT318, Section 2, March 2002
S2-44
Sheet 1
STRUCTURAL STRESS CALCULATIONS E.G. stresses in sheet : Fz
σ r ,max = σr
Fx , y
My
πds
Fy
Fz = 1.744 2 s
. σ r ,max = 1872
Fx s
M x,y
d
ds 2
Similar equations for stresses in nugget Corrections made for size effect
PAT318, Section 2, March 2002
S2-45
Mx
FATIGUE RESULTS FOR SHOCK TOWER
PAT318, Section 2, March 2002
S2-46
MSC.FATIGUE SOFTWARE STRAIN GAUGE A virtual test facility in the MSC.Fatigue environment
PAT318, Section 2, March 2002
S2-47
SOFTWARE STRAIN GAUGE n
n
A Finite Element tool allowing the creation of Stress and Strain time histories at arbitrary locations on a Finite Element Model Surface Uses: u u
n
Finite Element Model Results Verification Comparison of Strain Values with Test Time Histories
Previous FEA techniques have only permitted comparison of single Stress or Strain values.
PAT318, Section 2, March 2002
S2-48
CORRELATION APPLICATIONS
Software Strain Gauges
FEA Model Surface
Hub Strain
Hub Strain
Real World Structure
time
time
PAT318, Section 2, March 2002
S2-49
GAUGE DEFINITION n
The gauges are defined as FEA groups, each containing between 1 to 3 elements.
n
Standard gauge definitions: u u u u u
n
Uni-axial Gauges T Gauges Delta Gauges Rectangular Gauges Planar and stacked formulations.
User defined gauges may also be created u
definitions stored in a gauge definition file (gauges.def)
PAT318, Section 2, March 2002
S2-50
IMPLEMENTATION n
Gauge position: u u u
n
Gauge results: u u u
n
Anywhere on the FEA model surface Any orientation Covering multiple finite elements. Averaged results from the underlying finite elements Replicates the geometric averaging with actual instrumentation. Transformed to the coordinate system and alignment of the software strain gauge.
Up to 200 simultaneous Software Strain Gauges
PAT318, Section 2, March 2002
S2-51
MSC.FATIGUE UTILITIES Time History Reporting Tools: u
u u u
n
Contour Plots of time history data Surface Plotting Polar Display Facilities Automated Report Quality Plotting
D IS P L AY OF S IGN AL : NOIS E .D AC 0.5
Accel (g)
n
Time History Manipulation Tools u u
u u u
u
Arithmetic Manipulation Linear Smoothing Algorithms Fourier Filtering Butterworth Filtering Multiple File Manipulation (Cut & Paste, etc.) Graphical Editing of Time Histories
PAT318, Section 2, March 2002
-0.6 0
S2-52
Time (s ecs)
15
MSC.FATIGUE UTILITIES (Contd.) n
Time Series Analysis Tools:
DISPLAY OF SIGNAL:
TEST101.DAC
8191 points.
u
u
u
u
Running Statistical Analysis Frequency & Waterfall Analysis Probability Density & Joint Probability Density Analysis Rainflow Cycle Counting & Level Crossing Analysis Strain Gauge Signal Analysis
741 pts/secon
Displayed:
8191 points.
from pt 1
Full file data:
Strain (uE)
u
1500
Max
= 1499
at 7.105 seconds
Min
= -1445
at 9.672 seconds
Mean = 39.89
S.D. = 444.5
-1500
RMS
Time (seconds)
0
= 446.2
12
CYCLE HISTOGRAM DISTRIBUTION FOR : S61STRAINS.CYO
n
Test-based Fatigue Analysis: u
u
u
Maximum height : 205
Fatigue analysis based on strain gauge signals Total Life (S/N) and Time to Initiation (ε-N) analysis Uses a data base of Stress Concentration Factors KT for critical location stress determination
PAT318, Section 2, March 2002
Z Units :
205
Cycles Z-Axis
0
912.57 0 Mean uE
Range uE
Y-Axis
X-Axis 1414
S2-53
-487.42
MSC.FATIGUE VIBRATION n
Features: u
u u
u
u
u
Resolution of stresses onto Principal planes Multi input loads Correlation effects using Cross PSD’s Stress tensor stationarity checks Calculate Fatigue life from PSDs Uses 7 solution methods including;Dirlik, Steinberg and Narrow Band solutions
PAT318, Section 2, March 2002
Input Loads Construct FE model and designate input and output nodes
-5
x 10
éG xx Gxy ê êGxy G yy êG xz G yz ë
Gxz ù ú Gyz ú Gzz úû
Calculate 6 component stresses at each output node and compute the principal stresses
p( 2.5 Ra ng 2 e, 1.5 Me 1 an) 0.5 0 200
200
400 600 Range [MPa]
Check stationarity of the principal axes
400
0 800
-200
Mean [MPa]
Choose stress parameter and compute PSD of stress at each output node
Fatigue Life
S2-54
WHY USE FREQUENCY DOMAIN?
Wind speed
Hub Stress
Time Domain
time time
Output
PSD
Frequency Domain
Transfer function frequency
PAT318, Section 2, March 2002
S2-55
PSD Stress
Input
frequency
BENEFITS OF VIBRATION FATIGUE n
n n
n
Analyse structures with dynamic responses to random loading without requiring full transient analysis Fatigue analysis is relatively rapid Analysis can be included much earlier in the design cycle Ability to analyse ‘what if’ scenarios interactively
PAT318, Section 2, March 2002
S2-56
HOW DO WE CALCULATE DAMAGE? Loading (PSD)
Material (S-N analysis)
Fatigue Analysis (Vibration Fatigue)
Geometry (FE Analysis)
Optimization & Testing
PAT318, Section 2, March 2002
S2-57
Post Processing
HOW DO WE CALCULATE DAMAGE? TIME DOMAIN Steady state or
TIME HISTORY
RAINFLOW COUNT
STRESS RANGE HISTOGRAM
Transient Analysis
FREQUENCY DOMAIN PSD
Fatigue MODELLER
Transfer M0 M1 M2
Function
M 4
PAT318, Section 2, March 2002
S2-58
BLACK BOX
PDF
Fatigue LIFE
MULTIAXIAL FATIGUE n n
n
n
n
Handles proportional and non-proportional loadings Incorporates Mroz-Garud model and energy based notch correction procedure 6 critical plane damage models including WangBrown method and SocieBannantine “shear” and “normal” models High cycle (Fatigue limit) calculations using the Dang-Van and MacDiarmid methods. Post-processing including polar damage plots
PAT318, Section 2, March 2002
Polar Plot of Data : DEMO Theta=90
Theta=45
90 120
60
150
30
180
1E-9
1E-8
1E-7
1E-6
210
330
240
300 270
Polar Plot of Type A and Type B damage for Wang-Brown Method
S2-59
0
PAT318, Section 2, March 2002
S2-60
SECTION 3 MSC.FATIGUE USER INTERFACE
PAT318, Section 3, March 2002
S3-1
PAT318, Section 3, March 2002
S3-2
THE FIVE BOX FATIGUE LIFE ANALYSIS “TRICK” Loading Data
Geometry
Computer-Based Analysis
Life
Materials Data
The Three Inputs PAT318, Section 3, March 2002
The Analysis S3-3
The Answer!
OVERVIEW OF MSC/FATIGUE ANALYSIS PROCESS n n n n
Define Loading History Define Fatigue Material Properties Set Up and Run the Fatigue Analysis Select Solution Parameters u u u u
n
Select Solution Parameters Submit the Job Monitor the Job Progress Read in the Results
Evaluate Resulting Life Predictions
PAT318, Section 3, March 2002
S3-4
RUNNING AN FEA USING MSC.PATRAN
2 - Import Geometry
2 - Build Geometry
1 - Select Analysis Code
4 - Perform the Analysis
3 - Create Analysis Model
PAT318, Section 3, March 2002
S3-5
5 - Evaluate Analysis Results
OR IMPORT THE MODEL AND RESULTS n
Use Results from a Previous Stress Analysis
n
Import Nodes and Elements and Stress/Strains from the Results File (.op2 for MSC/NASTRAN)
n
Use Model and Results Filtering to reduce Model size and Fatigue Analysis Run Times
PAT318, Section 3, March 2002
S3-6
MSC.FATIGUE MAIN FORM n
n
n
n
n
General setup parameters are used to define generic parameters for the Fatigue job Jobnames and Titles are used to identify Fatigue Jobs in MSC.Patran Specific setup forms are used to specify parameters unique to fatigue analysis such as fatigue material properties, load time histories, etc. Job control is used to submit and monitor fatigue jobs Results is used to post-process fatigue results
PAT318, Section 3, March 2002
S3-7
LOADING INFORMATION FORM Loading Time Histories may be imported, created, modified, and displayed by clicking on the Database Manager button Result Parameters define the stress analyzer’s result details A Loading Time History is selected by clicking on the appropriate name in the list box
PAT318, Section 3, March 2002
S3-8
MATERIAL INFORMATION FORM n
n
n
Fatigue Material Properties are created / reviewed by clicking on the Database Manager button The fatigue material properties may be selected by clicking on its name in the material list box Clicking on the “O.K.” button will save the specified properties and hide the form
PAT318, Section 3, March 2002
S3-9
SOLUTION PARAMETERS FORM n
n
n
The Solution Parameter form is used to define fatigue analysis specific parameters Clicking on “O.K.” will save the supplied information for future retrieval Clicking on “Cancel” will close the form without saving the altered data values
PAT318, Section 3, March 2002
S3-10
MSC.FATIGUE FILES MS C/PATR AN - Applications MSC/FATIGUE
LST FIN
NOR
FNF
Fatigue R esults Filter
Global Fatigue Analyzer
FEF
FPP
Factor of Safety Analyzer
FOS
DAC
Design Optimization Analyzer
FAL DCL KFC
DAC FES TDB Fatigue Pre-P rocessor
P3/PATRAN - Applications Results
PAT3FAT
MDB DHH
TCY KSN
PAT318, Section 3, March 2002
Fatigue Crack Analyzer
CRG
S3-11
DYH
XYD
Results Listing
Files Created in MSC/FATIGUE Filename
Description
jobnameFIN jobnameFNF
Job parameter file (ASCII) Neutral file for P3/FATIGUE
jobnameFES jobnameASC *DAC
P3/FATIGUE input file ASCII version of the JOBNAMESFES file Loading time history file
jobnameFPP PFATIGUE.PRT jobnameMSG jobnameSTA jobnameABO jobnameFEF jobnameRMN jobnameFPR jobnameTCY *KSN jobnameCRG
P3/FATIGUE intermediate results file P3/FATIGUE session file P3/FATIGUE message file P3/FATIGUE status file P3/FATIGUE alert file Global multi-node analysis results file Results menu file File to indicate job running in current directory Time ordered stress cycles file K solution file Crack growth results file
jobnameKFL jobnameDCL jobnameFAL jobnameCYH jobnameDHH jobnameFOS
Stress concentration-Life XY data Design criterion-Life XY data Scale factor-Life XY data Rainflow cycle distribution at node n Damage distribution at node n Factor of safety results file
PAT318, Section 3, March 2002
S3-12
JOB CONTROL FORM n
n
n
Fatigue Analysis Jobs are submitted to the local “host” using the job control form The Job may be monitored on a regular basis Jobs may also be aborted from this form
PAT318, Section 3, March 2002
S3-13
RESULTS FORM n
The Fatigue results for completed jobs may be read into MSC.Patran
n
The results may be displayed using standard MSC.Patran post-processing functions u
Results
u
Insight
PAT318, Section 3, March 2002
S3-14
GRAPHICAL DISPLAY OF FATIGUE RESULTS n
n
Fatigue results may be displayed by selecting the “Results” switch from the top menu bar Fatigue results include u u u u u u
Damage Log of Damage Life (repeats) Log Life (repeats) Life (User Defined Units) e.g. Laps, Flights, etc. Log of Life (User Defined Units)
PAT318, Section 3, March 2002
S3-15
PAT318, Section 3, March 2002
S3-16
SECTION 4 OVERVIEW OF PATRAN
PAT318, Section 4, March 2002
S4-1
PAT318, Section 4, March 2002
S4-2
BUILDING A MODEL USING MSC.PATRAN The Main Form 2 - Import Geometry
1 - Select Analysis Code
4 - Perform the Analysis 5 - Evaluate 3 - Create Analysis Results Analysis Model
2 - Build Geometry
PAT318, Section 4, March 2002
S4-3
STEP 1 - ANALYSIS PREFERENCES New Model Preferences n n
n
Appears when creating a new database Used for specifying global model tolerance. An entity within the tolerance of another is considered to be a duplicate. Also, two entities within the tolerance of each other are considered to be coincident. Alternative method for specifying global model tolerance is Preferences/Global
PAT318, Section 4, March 2002
S4-4
STEP 1 - ANALYSIS PREFERENCES (CONTINUED)
n
n
PAT318, Section 4, March 2002
Select/Revise Analysis Code Preference before defining Materials, Element Properties, or Load/Boundary Conditions Analysis Preferences eliminates the confusion
S4-5
STEP 2 – IMPORT/BUILD GEOMETRY n
Geometric Modeling: u
Import a CAD Model from l l l l l
u
u
CATIA Pro/ENGINEER CADDS 5 EUCLID-3 Unigraphics
Import a CAD model via an IGES, ACIS, Parasolid-XMT, or STEP file Build the geometry model entirely in MSC.Patran
Y Z
X
Imported CAD model
PAT318, Section 4, March 2002
S4-6
STEP 3 – CREATING AN ANALYSIS MODEL Finite Element Mesh n
Nodes and Elements (connectivity) can be created by u
Mapping Mesher (IsoMesher) l l
u
l
l
n
X
N-sided (edged) trimmed surfaces Y (displayed as Magenta) Mapped Mesher Quad Elements 3 or 4 sided surfaces (displayed as Green)
Auto TetMesher l
u
Z
Paver Mesher l
u
3 or 4 sided surfaces (displayed as Green) 5 or 6 faced solids (displayed as Blue)
N-faced solids, B-rep Solids (displayed as White) 6 faced solids (displayed as Blue)
Sweeping Base Elements Mesher
Mesh Seeds are used to define the node density and spacing
X
Z Y
Quads swept to Hex Elements PAT318, Section 4, March 2002
S4-7
STEP 3 – CREATING AN ANALYSIS MODEL (CONTINUED) Verification n
Check the quality of the finite element model u u u
n
Element Boundary Checks (“crack” detection) Element Nodal Connectivity (Normals, Negative Volume) Element Distortion Checks (Aspect Ratio, Face Taper, etc.)
Elements are color-coded based on user-defined criteria .2372 .2214 .2056 .1898 .1740 .1582 .1423 .1265 .1107 .09490 .07908
Y
.06326 .04745
X
Z
.03163 .01582 .0000007040
PAT318, Section 4, March 2002
S4-8
STEP 3 – CREATING AN ANALYSIS MODEL (CONTINUED) Material Properties n
The material properties can be manually input, accessed from the MSC.Patran Materials Selector, input externally Materials Selector Select Database...
Query...
Column Headers...
Query Command Apply
Auto Execute
Current Database: mil5f_cn2.des CNAME Row 1 of 95 Row 2 of 95 Row 3 of 95 Row 4 of 95 Row 5 of 95 Row 6 of 95 Row 7 of 95 Row 8 of 95
15-5PH Stainless 15-5PH Stainless 17-4PH Stainless 17-4PH Stainless 17-4PH Stainless 17-4PH Stainless 17-7PH Stainless 17-7PH Stainless
DENS lb/in^3 0.283 -00.282 0.283 0.284 -00.276 -0-
E11C psi 2.92e+07 -03e+07 3e+07 3e+07 -03e+07 -0-
Selected Cell Data CNAME (Common Name): 15-5PH Stainless Steel
Display Material’s Properties...
Materials Selector
Manual Input PAT318, Section 4, March 2002
S4-9
Clear
STEP 3 – CREATING AN ANALYSIS MODEL (CONTINUED) Element Properties n
Element type and physical properties defined with the Properties application n
n
PAT318, Section 4, March 2002
S4-10
Once the analysis code preference is chosen only permitted physical properties are available If detailed information is needed, the interface manuals are on-line
STEP 3 – CREATING AN ANALYSIS MODEL (CONTINUED) n n n
Applied directly to the geometry or FE model Variations defined by fields XY Plots used to verify the field
LEGEND Force Variation 360. 300. 240. 180.
Y
120.
Z
X
60. 0. 0. 1.00 2.00 3.00 4.00 5.00 6.00
PAT318, Section 4, March 2002
S4-11
STEP 4 – PERFORM THE ANALYSIS
n
n
Select code-specific solution procedures and parameters Submit directly from MSC.Patran
PAT318, Section 4, March 2002
S4-12
STEP 5 – EVALUATE RESULTS n n
n
Displayed with Results or Insight applications Filtered based on model attributes, numerical values or user-defined criteria Different results displayed concurrently using multiple viewports §Time: 10:58:26 §Date: 11/30/94
Isosurface Val= 0.5000E+03 Node Scalar1 Color Index B 0.129E+04 A 0.121E+04 0 0.113E+04 9 0.105E+04 8 0.968E+03 7 0.887E+03 6 0.806E+03 5 0.725E+03 4 0.643E+03 3 0.562E+03 2 0.481E+03 1 0.400E+03 Min = 2.442558E-01 Max = 2.380629E+03 Min ID = 1730 Max ID = 950 Isos_1: STRESS COMPONENTS Von Mises (NON-LAYERED) Default Max DEFLECTION = 1.82E-03
PAT318, Section 4, March 2002
S4-13
WHERE TO GO FOR HELP MSC.Patran Product Coordinator at your company MSC.Patran SUPPORT “Hot Line” (1-800-732-7284) Technical Support for all MSC.Patran products Email support at “
[email protected]” Fax (714-979-2990) Monday through Friday 7 am to 3 pm Pacific Standard Time
MSC.Software Website (http://www.mscsoftware.com) MSC.Software Institute (1-800-732-7211) Training Classes offered for all MSC.Patran products E-mail support at “
[email protected]” Classes held regularly at domestic and international MSC.Software offices
PAT318, Section 4, March 2002
S4-14
CUSTOMIZATION Customer Options Site Specific Item...
n n
n
n
PCL – MSC.Patran Command Language PCL can be used to create custom-made menus and forms Use PCL to automate repetitive tasks and apply complicated Load/BCs MSC Institute’s PAT304 course shows how to do all of the above
PAT318, Section 4, March 2002
S4-15
Site Specific Form
Site Specific Application Site Specific Geometry Access...
Experimental modal Import...
Acoustic Analysis...
Cancel
STARTING MSC.PATRAN In the terminal window click the desk top icon to invoke MSC.Patran or type Patran MSC Patran
Welcome to MSC.Patran Version 9.0 22600 03:36:58 PM Setting up Windows Environment
PAT318, Section 4, March 2002
S4-16
MSC.PATRAN FILE OPTION
q New Database q Open Database q Revert to Original Database
q Session... q Close q Quit q Save q Save a Copy
PAT318, Section 4, March 2002
S4-17
Create a new empty database Open a previously created database Allows the deletion of all the changes made in the current modeling session (Revert must be enabled for this to be available) Execute PATRAN commands from a file Close the current database but keep PATRAN active Close the current database and stop PATRAN Saves the database up to and including the last command Save a copy of the database under a different name
MSC.PATRAN FILES Name
File Type
Comments
Model_name.db
Database
One per model, relatively large.
Model_name.db.bkup
Database
Backup database is created if revert is enabled.
patran.ses.number
Session File
A Session File is opened at P3 start-up and it is closed when you quit MSC.Patran.
model_name.db.jou
Journal File
One per model, record of all PCL commands from database creation to present, concatenated session files. EXTREMELY useful for rebuilding a database.
model_name.out
Neutral File
Created using Export. Can be used as a backup for analysis model.
PAT318, Section 4, March 2002
S4-18
Menu Bar
THE MAIN FORM
Applications
History Box Command Line
n
n
n
n
Tool Bar
Menu Bar selection affects global environment (e.g. Viewing, Imaging, and Preferences) Application selections only apply to a certain portion of the model (i.e. Geometry, Loads/BCs, etc.) Application selections are mutually exclusive -- only one can be selected at a time Unavailable selections are shown in a lighter typeface (“Ghosted”)
PAT318, Section 4, March 2002
S4-19
THE MAIN FORM (CONCLUDED)
n n
n
Tool bar provides quick access to frequently used procedures Actions taken within MSC.Patran session can be traced in the history box Command line allows the input of PCL commands and MSC.Patran2 NOODL Rule commands
PAT318, Section 4, March 2002
S4-20
TYPICAL WIDGETS USED IN MSC.PATRAN q Toggle button is an on/off switch
q Data selection is done by highlighting item
q Select databox is used to enter data
q Radio buttons allow exclusive selection among options
q Data insertion can be made by placing the mouse at the desired location, clicking the left mouse button, and typing in the desired data
q “...” Suffix denotes that a subordinate form will open up upon clicking the button
q Existing text can be edited q Slide bar assigns a value to associated variable; i.e. threshold for aspect ratio test q Apply causes action to execute q Hyphens indicate action can be undone only immediately after its execution
PAT318, Section 4, March 2002
q Control icon allows the switching between different actions; i.e. icon can be set to highlight or split in this example
q Causes the content of a form to reset back to default values; the default values may be constant or can change
S4-21
SYSTEM ICONS Refresh Button - refresh screen
Display Cleanup Button - resets graphics to defaults
Undo Button -
PAT318, Section 4, March 2002
will undo just last command. When an action is performed, the created data is saved in the computer’s memory. When the next action is performed the data previously written to memory will be saved in the Patran data base.
S4-22
SYSTEM ICONS (CONCLUDED) Interrupt Button - stops operation in progress
Heartbeat -
Green indicates MSC.Patran is waiting for user input - Blue indicates MSC.Patran is performing an operation that can be stopped with the interrupt button - Red indicates that MSC.Patran is performing a process that cannot be interrupted
PAT318, Section 4, March 2002
S4-23
ENTITY PICKING n
Picking is performed in two ways: u
u
n
Keyboard entry into a databox, e.g. Curve List Graphical picking with the mouse
“List processor” is the program responsible for the interpretation of the user input, e.g. Curve 1:3
PAT318, Section 4, March 2002
S4-24
ENTITY GRAPHICAL PICKING n
n
n
n
n
Individual and collective entity picking is controlled by the Picking option under Preferences For Single Entity Picking, a portion of the selected entity must be within the physical limits of the cursor For Centroid Single Picking, the closest entity to the location of the cursor will be picked Additional tools are available to aid the process of picking, such as Cycle picking The Preselection Settings highlight the Entity and Label (ID #) of the entity before you select it
PAT318, Section 4, March 2002
S4-25
CURSOR PICKING Entity
Multiple Picking
Move the cursor to the entity label/centroid and press the left mouse button
Hold the shift key down and select the entities with the left mouse button`
Shift
PAT318, Section 4, March 2002
S4-26
CURSOR PICKING (CONTINUED) Select Rectangle (Click & Drag)
Select Polygon
Ctrl You may also select this icon from the toolbar PAT318, Section 4, March 2002
Note: To complete your selection double click the left mouse button S4-27
CURSOR PICKING (CONCLUDED) Deselect
Move the cursor to the entity’s label/centroid and click on the right mouse button
Cycle Picking
Picking an entity underneath another, or that is Selection close to other entities. Surface 3 Surface 7
Shift
Previous
Next
If you hit the space bar while an entity is selected it will temporarily erase the entity so you can select the one underneath PAT318, Section 4, March 2002
S4-28
VIEWING/MODEL MANIPULATION -x
+y
-y +x
Mouse Rotate XY
PAT318, Section 4, March 2002
Mouse Rotate Z
Mouse Translate XY
S4-29
Mouse Zoom
LIST PROCESSOR n
n n n
The list processor verifies the syntax, checks for existence and performs rudimentary geometry operations such as calculating the intersection of two curves The list processor parses the contents for the select databox The application only recognizes specific types of data The list processor is generic and is used by all applications for consistency
PAT318, Section 4, March 2002
S4-30
ENTITY ID SYNTAX Syntax
Description
Point 1 2 3
Refers to points 1, 2 and 3
Point 1:9:2
Points 1 through 9 by 2
Curve 1 2, 3/ 4
Different forms for delimiters: space, “,” and “/”
Surface 3.1
References an entity associated with a higher order one (i.e. edge 1 of surface 3, that is similar to a curve)
Solid 1:10.2
Combinations of entity ID syntax is possible (face 2 of solids 1 through 10)
[x y z]
Square brackets signifies coordinate specification
[xn28, 1, 2]
Individual coordinates can reference existing entities, such as x = the x coordinate of node 28
[1, zp5, 3] [1, z5, 3]
y = the z coordinate of point 5 When a point is referenced the letter “p” can be dropped
[1, 2, ‘-64.0/20.0‘]
Mathematical operations like division are possible to determine the individual components
< > signifies a vector definition
{[ ][ ]}
Signifies an axis with first point representing the base and the second determining the direction
PAT318, Section 4, March 2002
S4-31
MSC.PATRAN STANDARDS If your cursor becomes a pointing hand:
This means there is an error window somewhere on your screen that must be acknowledged before you can continue
Sample Error Window PAT318, Section 4, March 2002
S4-32
ON-LINE HELP Activation
To start, click on Help by system icons
PAT318, Section 4, March 2002
S4-33
ON-LINE HELP (CONTINUED) System n
There are two ways to use the help system: u
Topical help allows the user to access the complete MSC.Patran Help System l l l
u
General MSC.Patran Philosophy Tutorials on the use of MSC.Patran Features and Functions
Context sensitive help is used to describe the contents of a form in question - F1
PAT318, Section 4, March 2002
S4-34
ON-LINE HELP (CONTINUED) Top Menu The following navigation menu appears at the top of each help page Part 3: Geometry Modeling Accessing/Importing/Exporting Page 2-2
■ Done
Options
- Select an OptionLibrary Contents Index Getting Started Examples Sales & Support Help on Help
Page Locator Options
Done
Brief title of the current help page Allows the user to access other documents in the system Trace back to previously displayed pages Page backward & forward Exit help document
PAT318, Section 4, March 2002
S4-35
PAT318, Section 4, March 2002
S4-36
SECTION 5 GEOMETRIC MODELING
PAT318, Section 5, March 2002
S5-1
PAT318, Section 5, March 2002
S5-2
TOPOLOGICAL STRUCTURES n n
MSC.PATRAN combines topological structures to define geometry The topological entities within MSC.PATRAN are: 7
6
Face Vertex
8
5
Body 3
Edge 1 n n
4
Vertices hold positions for an edge, face, and body All topological entities can be cursor selected to perform MSC.PATRAN functions (e.g. Surface 10.2)
PAT318, Section 5, March 2002
S5-3
GEOMETRY BUILDING BLOCKS Point (Cyan)
n
n
A point is a 0 dimensional CAD entity; it represents a location in space; 3-space in MSC.PATRAN MSC.PATRAN creates points automatically when constructing curves, surfaces, and solids u
u
Y
Z
Points are created at vertices, e.g. surface vertices (“corners”) It is not always necessary to construct entities starting with their points, e.g. surface going from point to point
9 X
X Z
PAT318, Section 5, March 2002
S5-4
Y
GEOMETRY BUILDING BLOCKS (CONTINUED) Curve (Yellow) P2 n
n
A curve is a general vector function of the single parametric variable ξ1; it can have many types of mathematical forms: A curve has:
(X,Y,Z) = function ( ξ1)
u u
n
Two points, with one at each end A parametric coordinate (ξ1) whose domain is from 0.0 at P1 (its origin) to 1.0 at P2
ξ1
P(ξ1)
5 P1
ξ1
Z Z
Y X Y X
Meshed with bar elements
5 Bar Element PAT318, Section 5, March 2002
S5-5
GEOMETRY BUILDING BLOCKS (CONTINUED) Surface (Simple or complex)
n
n
n
Surface types can be simple (Green) or complex/general (Magenta) A simple surface is a general vector function of the two parametric variables ξ1,ξ2: A simple surface has:
P2 P1 ξ
ξ
2
ξ
1
ξ
2
12
1
P( ξ1,ξ2)
(X,Y,Z) = function (ξ ,ξ )
u u
n
1 2 3 or 4 bounding edges A parametric origin and parametric coordinates whose domains are from 0 to 1
A simple surface with 3 visible edges has a fourth edge that is degenerate
P3
P4 Z
Z Y X Y X
PAT318, Section 5, March 2002
S5-6
GEOMETRY BUILDING BLOCKS (CONTINUED) Surface (continued) A simple surface can be meshed with either the IsoMesh (mapped) or Paver (free) meshers Curve of constant
n
parametric value
2 4
Display Line for visualizing surface
2 4
2/3 1
ξ
1
ξ
1/3
1 2
1
3
1
1/3
3
2/3
Surface 1
IsoMesh Mesh of Surface 1 Nodes follow curves of constant parametric value
PAT318, Section 5, March 2002
S5-7
GEOMETRY BUILDING BLOCKS (CONTINUED) Surface (concluded)
n
A complex or general trimmed surface (magenta) has more than 4 edges (N-sided) and can have inner boundaries u u u u
Not defined parametrically, e.g. ξ1,ξ2 not used It is a “trimmed” parametric surface Must be meshed with the Paver mesher Meshes perimeter of surface first General Trimmed Surface
Paver Mesh
21
24
23
25 22 20 19
PAT318, Section 5, March 2002
18
S5-8
Perimeter of surface
GEOMETRY BUILDING BLOCKS (CONTINUED) Solid (Simple or Complex) n
u
n
u
n
Vector function of three parametric variables ξ1,ξ2,ξ3
Z
X
A simple solid has: u
n
Y
Simple or parametric solid (blue)
4 to 6 bounding faces Parametric origin and coordinates whose domains are from 0 to 1
A simple solid with 4 to 5 visible faces has some degenerate faces Parametric solids are meshed with the IsoMesh (mapped) mesher (hex, wedge, or tet elements)
P(ξ1,ξ2,ξ3 ) P
6
P
S5-9
7
P
8
ξ
3
ξ
P2 P3
2
P
1
PAT318, Section 5, March 2002
P
5
ξ
1
P
4
GEOMETRY BUILDING BLOCKS (CONTINUED) Solid (concluded) n
Complex or non-parametric solids (N-faced) (white) u
u
u
Non-parametric solids can be either Patran native B-Rep (boundary representation) or parasolid B-Rep CAD solids can be accessed as B-Rep or parasolid solids and can be meshed using the automatic TetMesh algorithm Meshes faces with tri-s, then perimeter of solid with tet-s first
B-Rep Solid
PAT318, Section 5, March 2002
Tetrahedral Mesh
S5-10
GEOMETRY BUILDING BLOCKS (CONCLUDED) Planes, Vectors
n
n
n
Infinite planes and vectors are used for certain geometric operations, such as solid break by a plane A plane is uniquely defined by vector representing its normal and a point on the plane A MSC.PATRAN vector quantity is defined by a magnitude, a direction and a point of origin
Vector
Plane PAT318, Section 5, March 2002
S5-11
IMPORTING, EXPORTING GEOMETRY AND FEM
PAT318, Section 5, March 2002
S5-12
FILE IMPORT OPTIONS
PAT318, Section 5, March 2002
S5-13
FILE IMPORT OPTIONS (CONCLUDED)
Geometry kernal type
CAD part
Standard format
PAT318, Section 5, March 2002
S5-14
EXAMPLE – UNIGRAPHICS CAD MODEL IMPORT n n n n
PAT318, Section 5, March 2002
Select “Import...” from the File menu Set Unigraphics as the Source Select desired UG part file Optional filtering of entities is available based on entity type (e.g. Sheet Body), CAD layer and if sewing is to be done
S5-15
EXAMPLE – UNIGRAPHICS CAD MODEL IMPORT (CONCLUDED) Unigraphics options Unigraphics Options...
n
is used to filter the Unigraphics entities being imported
Filter Options include: u u u u
Entity Type Entity Layers Trimmed Surface Type Sew Sheet Bodies
PAT318, Section 5, March 2002
S5-16
MSC.PATRAN DATABASE ACCESS n
n
n
n
MSC.PATRAN database content can be transferred between different databases Import option allows the specification of entity type, ID offset, name prefix, and conflict resolution tools “Equivalence Option” allows common entities in the databases to be equivalenced Preview option provides access to summary information
PAT318, Section 5, March 2002
S5-17
MSC.PATRAN DATABASE ACCESS (CONTINUED) n
MSC.Patran databases can be accessed by selecting “MSC.PATRAN DB” as the source
PAT318, Section 5, March 2002
S5-18
MSC.PATRAN DATABASE ACCESS (CONTINUED) n
Importing options controls u u u
Which entities to import How to import entities Resolve conflict
PAT318, Section 5, March 2002
S5-19
MSC.PATRAN DATABASE ACCESS (CONTINUED) n
n
Merged finite element models may be equivalenced Options on how MSC.PATRAN will deal with Discrete deal with Discrete FEM Fields on import
PAT318, Section 5, March 2002
S5-20
FILE EXPORT OPTIONS
PAT318, Section 5, March 2002
S5-21
FILES EXPORTED n
IGES file u
u u u
n
Points and all curve and surface types, e.g. trimmed parametric surface No geometric solids FEM nodes and elements No results
Patran neutral file u u
u
Parametric cubic geometry FEM consisting of nodes, elements, material properties, element properties, coordinate frames, etc. No results
PAT318, Section 5, March 2002
S5-22
FILES EXPORTED (CONCLUDED) n
Parasolid xmt file u u
n
Specific types of parasolid geometry Can specify the parasolid version
Step file u u
AP203 – geometry only AP209 – geometry, mesh, analysis, and/or results
PAT318, Section 5, March 2002
S5-23
GEOMETRY CONSTRUCTION n
Geometry can be constructed in MSC.PATRAN by: u u
Editing imported CAD geometry (Edit/Surface/Sew) Building with respect to existing geometry (Create/Solid/Extrude) Gliding a Solid from a Surface
Extracting a Curve 1
u
Creating copies of existing geometry (Transform) Mirroring
Rotating
PAT318, Section 5, March 2002
S5-24
GEOMETRY FORM ANATOMY n
The strategy behind working with the geometry form: u u
Create Point
Set an objective, such as creating a point Provide the details associated with creating the entity using the specified method
Delete Curve
“Action”
Surface
Solid
XYZ
Point
Curve
Surface
Extract
Chain
Trimmed
Face
Interpolate
Manifold
XYZ
XYZ
Project
Revolve
Revolve
Revolve
PAT318, Section 5, March 2002
S5-25
“Object” “Method”
SELECT MENU Pick only geometry point or finite element node Pick only geometry point Pick only finite element node n n
n
n
n
PAT318, Section 5, March 2002
Provides an entity selection filter Cursor placed in list box displays select menu Select menu icons filter entity selection, e.g. only entities selected are of type of chosen filter icon Selections available depend on what is being done, e.g. create a point using XYZ option allows screen picking of only the entities on front of model S5-26
GEOMETRIC ENTITIES - POINT
PAT318, Section 5, March 2002
S5-27
CREATE/POINT/XYZ n n
Create points at X, Y, Z location Locations where points are to be created may be specified by either: u
(X,Y,Z) coordinates (list of coordinates), e.g.
[0 50 50] [0 0 70] u
Picking a choice from the select menu and following the menu prompts, e.g. Node
1
PAT318, Section 5, March 2002
2
S5-28
3
POINT CREATE 1
1 1
Create a point at the center of an arc
x
x3
a
ξ1
3 2
1
Create a point at a ξ parametric location 1
2
1
x4 x 1
2
5
x
1
x
3
6
1 2
Create points nonuniformly on a curve PAT318, Section 5, March 2002
1
Create a point at the intersection of a curve and surface S5-29
SHOW/POINT/DISTANCE n
PAT318, Section 5, March 2002
Provide user with information for the distance between two points and other related information
S5-30
GEOMETRY TRANSFORM* Method
Comment
Translate
Translate entity through a specified vector
Rotate
Rotate entity about a defined axis through a given angle
Scale
Use a multiplicative factor applied to individual coordinate
Mirror
Create a mirror image of entity across a defined plane
Mcoord
Transform entity in one coordinate frame into another with same relative position
Pivot
Transform entity within a plane defined by a pivot and two and points
Position
Entity transformed to a set of destination-position-points will maintain its relative position to a set of original-position-points
Vsum
Vector sum of the coordinate locations of two sets of existing entities to create a new entity
Mscale
Existing entity is simultaneously moved, scaled, rotated and/or warped to a new position
* Transform operations for geometry types point, curve, surface and solid
PAT318, Section 5, March 2002
S5-31
POINT ASSOCIATE/DISASSOCIATE n n n n
Associated points are used to guide the meshers Points can be associated with curve and surface type geometry It is only possible to associate points to curves or surfaces which are within the global model tolerance of the points Associated geometry is a restriction to the meshers After Association: 2
5
After Paver Meshing:
3
5
2
3
6
9
1
10
6
7
10
8
Y ZX
n n
PAT318, Section 5, March 2002
7
9
1
4
8
Y ZX
1
4
Only the Paver uses associated points interior to surfaces Associated points can be disassociated S5-32
GEOMETRIC ENTITIES - CURVE
PAT318, Section 5, March 2002
S5-33
CREATE/CURVE/POINT/3 POINT n
n
Create a curve using a cubic parametric polynomial Middle point, Point 3, is at parametric location ξ1=0.75 2 ( ξ 1 =1)
3 ( ξ 1 =0.75)
( ξ 1 =0) 1
PAT318, Section 5, March 2002
1
S5-34
GEOMETRY TYPES n
Patran has the capability of creating various types of geometry, for example u u
n
Implicit form, i.e. conic, elliptical Explicit form, i.e. parametric cubic, Beizier, NURBS
Patran uses Neutral File convention to indicate that cubic parametric geometry will be created, e.g.
2 3 X = a 0 + a 1 ξ1 + a2 ξ 1 + a 3 ξ 1
n n
with a similar equation for Y and Z Neutral File convention can be selected under Geometry Representation in Preferences/Geometry Some geometry is created using only Neutral File convention, e.g. Create/Curve/Point
PAT318, Section 5, March 2002
S5-35
CREATE/CURVE/CHAIN Create a composite curve from two or more existing curves or edges It retains exactly all the information of the constituent curves
n
n
Individual Curves
Chain (Composite) Curve
1
3 2
Chain Curve use for Trimmed Surface
Individual Curves 9 6
8 10
11
5
7 4
3 Y
Y
Z X
PAT318, Section 5, March 2002
Z X
S5-36
AUTO CHAINING FEATURE n
n n
n
Provide user with interactive, more controllable way to chain curves Chaining starts by selecting a starting curve Decisions on how to proceed with the chaining process are made through the toggles and buttons on the form, i.e. Next (find another possible “path” for chain), or OK (proceed along the current path) Accessible from Create/Curve/Chain Create/Surface/Trimmed forms
PAT318, Section 5, March 2002
S5-37
CREATE/CURVE/MANIFOLD n
n
Manifold refers to creating new geometry on (coincident with) existing geometry PATRAN 2 convention approximates manifold within specified tolerance 2
Before
Surface 7 1
2 6
After 1
PAT318, Section 5, March 2002
S5-38
CURVE CONSTRUCT 1
2
2 1 1
3 Must use the select menu for picking the curve and point 6
3
2
2
6
7 1
5
3
2
1 3
1
4
1
PAT318, Section 5, March 2002
4
8
5
7 4
8
S5-39
5
EDIT/CURVE/BREAK n
Creates two curves by “breaking” an original curve or edge at a parametric position along the curve between 0.0 and 1.0
Trimmed Surface 3 Edge 7
Point 21 is created at parametric 0.4 position along u (or c1) direction
2
1 21 0.4
3
PAT318, Section 5, March 2002
S5-40
3
CURVE EDIT 2
1
3 2
1
3 2
1
Must use select menu for picking the curve and point
3
1
PATRAN extracts points from all curves and creates one spline curve from them
Complex mathematical representation of single curve
6 1
1
Mathematical representation of original curve using set of simple curves (cubic parametric)
The parametric coordinate for each curve is represented by a line with a 1
S5-41
7 8 1
1
6
1
PAT318, Section 5, March 2002
2
1 1
7
1
18
CURVE SHOW 1
2 1
1
1 2 Curve ID 1
Start Point
End Point
Length
Type
1
2
1.414235
ParametricCubic
Curve ID
Start Point
End Point
Length
Center
Radius
Type
1
2
3.141593
[ 0. 1.75 0. ]
1.
Arc
1
4
3
5 1
1
2
2
1
1
3 First Curve ID Secon Curve ID 1
2
Angle 45.
Minimum Distance Minimum Location1 Minimum Location2 0.
PAT318, Section 5, March 2002
[ 0.5 0 0 ]
1on>. [ 0.5 0 0 ]
1on>.
S5-42
2
6 3
2
4
Curve ID
Start Point
End Point
Length
Type
1
1
2
1.4
ParametricCubic
2
3
4
0.4
ParametricCubic
3
5
6
0.9
ParametricCubic
CURVE ASSOCIATE/DISASSOCIATE n n n n n n
Associated curves are used to guide the meshing of surface. Can only associate curves which are within the global model tolerance Associated geometry is restriction to meshers The curves can be mesh seeded Only the Paver uses associated curves interior to surfaces Associated geometry can be disassociated After Association 1
After Paver Meshing
2
1 2
Y Z
PAT318, Section 5, March 2002
Y
3
4
X
Z
S5-43
X
GEOMETRIC ENTITIES - SURFACE
PAT318, Section 5, March 2002
S5-44
PARAMETRIC SURFACE CREATE 5
3
3 1
6
2 1
1
5
2
3 3
1
1
4
9
2
4
8
Curves must be non-intersecting
Curves must be end-to-end 1
1
2 3
1
1 8
2 3 Y
Must use the select menu for picking both surface and point Z
PAT318, Section 5, March 2002
S5-45
4 X
TRIMMED SURFACE CONSTRUCTION Three options for creating a trimmed surface in MSC.PATRAN
PAT318, Section 5, March 2002
S5-46
TRIMMED SURFACE CONSTRUCTION (CONCLUDED) n
In creating a trimmed surface must define it’s edges u
Chain together curves to form closed loops l l
n
Define curvature of surface u u
n
One outer loop to define the outer boundary As many inner loops as necessary (if any) to define holes/cutouts
Planar trimmed for a flat surface Surface trimmed requires a parent parametric surface to define the curvature of the new surface; only one surface permitted
For composite trimmed creation must specify all surfaces to be combined
PAT318, Section 5, March 2002
S5-47
CREATE TRIMMED SURFACE EXAMPLE n
n
n
The outer loop list must have only one continuous closed loop curve ID, e.g. Curve 14 The inner loop list can have as many continuous closed loop curve ids as needed, e.g. Curve 13, 15, 16 Without the parent parametric surface, an infinite number of trimmed surfaces could be visualized Trimmed Surface
Curves 1 14 13 15
2
16
Y
Y Z
PAT318, Section 5, March 2002
X
Z
S5-48
X
CREATE SURFACES n n
One surface created from all of the selected surfaces Meshing will ignore the original interior vertices and edges
Original Surfaces
Composite Surface
Composite Surface with Mesh
PAT318, Section 5, March 2002
S5-49
CREATE COMPOSITE SURFACE n
A composite surface is created from multiple surfaces u
u
n
n
User defines boundary features such as vertices, inner loops, and curves at perimeter gaps (Preview Boundary) Vertices u
u
n
PAT318, Section 5, March 2002
Useful for coarse meshing a region of numerous surfaces Can use parametric composite surfaces to create parametric solids, which can be hex meshed
Use All Edge Vertices – all vertices at outer perimeter of surfaces in Surface List Vertex List – if only use some vertices, e.g. create parametric surface
Inner Loop Option – All, None, Select (some)
S5-50
CREATE COMPOSITE SURFACE (CONTINUED) n
Preview Boundary u
u
Curve or Edge
PAT318, Section 5, March 2002
S5-51
Can use Preview Boundary to add (create) or remove curves or edges on the “fly” to define desired outer perimeter Select menu can only be used to pick curves or surface edges
CREATE COMPOSITE SURFACE (CONCLUDED) n
Options can be used to automate surface creation u
u
PAT318, Section 5, March 2002
S5-52
Perimeter (boundary) gaps less than Cleanup Tol. will be closed Gap Distance is similar to Cleanup Tol., except it refers to gaps between internal edges of surfaces
CREATE MIDSURFACE FROM SOLID n
n n
Manual
Create surface midway through thickness of portions of a parasolid solid Use for “shell meshing” a solid Two modes for creation u
Automatic l
u
Specify the thickness of the regions for which surfaces are to be created
Manual
Automatic
l
Two faces of a given solid between which a mid-surface is to be created must be specified n n
PAT318, Section 5, March 2002
S5-53
Solid Face List – a face Offset Solid Face List – opposing face
SURFACE EDIT 1
1
1
2 3
4
5
3
6
2
Complex mathematical representation
Set of cubic parametric surfaces PAT318, Section 5, March 2002
1
2
1
2
Can use simultaneously with all surfaces S5-54
SURFACE EDIT (CONCLUDED) Point 35
Parametric Surface 6
Trimmed surface 8 with hole
Trimmed surface with hole Parametric Surface 2
Parametric surface without hole
Trimmed surface 4 Remove Vertex
Point 44
New Vertex Trimmed surface
PAT318, Section 5, March 2002
Parametric surface S5-55
EDGE MATCH SURFACE 2
n
n
n
n
PAT318, Section 5, March 2002
Mesh continuity requires adjacent surfaces be congruent Two non-congruent surfaces may be “matched” along adjacent edges Congruency can also be enforced using Edit/Surface/Break Edit/Surface/Sew includes Edge Match and Edit/Point/Equivalence
S5-56
3
8
3 1 6
5
2 1
4
All surfaces have four edges Add vertex to surface 1 at point 5
7
SURFACE TRANSFORM Mirror Option First, select the appropriate select menu icon – coordinate direction 1 Second, click on local Coordinate System 1 from the viewport to establish the mirror plane to be coincident with the local YZ-Plane Third, select the geometry to be mirrored
n
n
n
Before
Z
After
1
Z 1
X
X
Y
PAT318, Section 5, March 2002
Y
S5-57
VERIFY SURFACE BOUNDARY n
Plots free and non-manifold surface edges in model u
u
Free edge: no congruent adjacent surface edge (magenta circle) Non-manifold edge: shared by more than two surface edges (blue dot)
Free edge X
Y z
PAT318, Section 5, March 2002
Non-manifold edge S5-58
GEOMETRIC ENTITIES - SOLID
PAT318, Section 5, March 2002
S5-59
SOLID CONSTRUCTION
16 4
18 17
1
15
Use set of any type of surfaces to create a B-rep solid
Use nonintersecting parametric surfaces to create parametric solid
1
5
3 2 4
2
1
1
1 Use 5 parametric surfaces to create 6 faced parametric solids PAT318, Section 5, March 2002
Glide a parametric surface along a curve to create a parametric solid S5-60
CREATE B-REP OR PARAMETRIC SOLID BY EXTRUDING SURFACE n
n
IsoMeshable n
TetMeshable
n
n
PAT318, Section 5, March 2002
Extrude a surface (or solid face) to create a solid Select to create either a TetMeshable (B-rep) or IsoMeshable (parametric) solid If select TetMeshable the surface can be parametric or trimmed If select IsoMeshable the surface must be parametric Parasolid tool
S5-61
CREATE B-REP OR PARAMETRIC SOLID BY REVOLVING SURFACES n
n
IsoMeshable
n
n
Revolve a surface (or solid face) to create a solid Similar to extrude – select either TetMeshable or IsoMeshable Same restrictions on surface types as for extrude Parasolid tool
TetMeshable
PAT318, Section 5, March 2002
S5-62
CREATE PRIMITIVE SOLIDS n n
n
n
n
PAT318, Section 5, March 2002
Create B-rep solids of various basic shapes Shapes are Block, Cylinder, Cone, Sphere, and Torus Solid can be created quickly using the dialogue or it can be created manually using Geometry/Create/Solid/B-rep and supplying a list of surfaces Primitive solid can only be meshed with the TetMesher Parasolid tool
S5-63
SOLID EDIT Method
Comment
Break
Break a solid into multiple solids using a selected option such as a surface, parametric location etc.
Blend
Create a set of cubic parametric solids from a set of parametric solids such that the first derivative of shape is continuous across interfaces
Disassemble
Disassemble a B-rep solid into a set of surfaces (may be parametric or trimmed)
Refit
Replace an existing complex shaped parametric solid with a set of simple cubic parametric solids. The extent to which the new solids match the original solid depends on how many solids are created. Also, can create a parasolid solid.
Reverse
Reverse the parametric directions associated with the solid
Boolean
Add, subtract, or intersect parasolid solids. Parasolid tool
Edge Blend
Create fillets or chamfers. Parasolid tool
Imprint
Break parasolid faces at edges of other solids. Parasolid tool
Shell
Remove space from parasolid solid to create walls. Parasolid tool
PAT318, Section 5, March 2002
S5-64
EDIT SOLID BY REFIT n
Edit parametric solid three ways u
Option Tri Cube Net causes a set of cubic parametric solids to be created to represent the original solid l
u
u
u
Refit parameters u Density, v Density, w Density*
Option Tri Parametric is similar to Tri Cubic Net except a tolerance is used instead of u Density, etc. Option To Parasolid causes a parasolid solid to be created from the original solid Parasolid tool
* Density is the number of solids that will be created in the u, v, w direction, respectively PAT318, Section 5, March 2002
S5-65
Solid Geometry Boolean Solids to be combined can be B-rep, parasolid solid, and/or parametric Solids could have been created in Patran or imported Boolean operations are Add, Subtract, and Intersect Any combination of solid types results in creating a B-rep solid Parasolid tool
n
n
n
n
n
1
B-rep
PAT318, Section 5, March 2002
Add
2
Parametric
S5-66
3
B-rep from Add
GEOMETRIC ENTITIES – COORDINATE FRAME
PAT318, Section 5, March 2002
S5-67
CREATING ALTERNATIVE COORDINATE FRAMES Z
B
P=(X,Y,Z)
C
Z
φ
B
B P=(R,θ ,φ)
C Z A
X
Y
X
Rectangular X Y Z n
A
Y R
θ
P=(R,θ ,Z) Z
R
Cylindrical R θ Z
θ
C
R
θ A R
φ Spherical R θ φ
These 3 axes are generically referred to as the 1, 2, and 3 axes with the above definitions, respectively
PAT318, Section 5, March 2002
S5-68
θ
COORDINATE CREATE Method
Comment
3Point
Create a coordinate frame by defining an origin, a point along the axis 3 and a point in the 1-3 plane
Axis
A point on axis i and another on axis j
Euler
Three consecutive rotations about user defined axes
Normal
Specify an origin and a surface
PAT318, Section 5, March 2002
S5-69
CREATE COORDINATE ALIGNED WITH SURFACE NORMAL n
n
n
n
Creates a rectangular coordinate system Origin at a point on a surface or solid face Coordinate frame axis 3 aligned normal to the surface or face Coordinate frame axis 1 aligned with ξ1
Coordinate Frame 7
7 5
2
Z X
S5-70
Z X
Surface 1
Y
PAT318, Section 5, March 2002
Point 5
Y
1
SECTION 6 MESHING
PAT318, Section 6, March 2002
S6-1
PAT318, Section 6, March 2002
S6-2
FINITE ELEMENTS n
A finite element model is a hypothetical discretization of a component or a system into small regularly shaped regions where the analysis is actually performed
Component (Geometric Model)
PAT318, Section 6, March 2002
S6-3
Finite Element Model
FINITE ELEMENTS n
Finite elements come in different shapes and forms
Bar
Tet n
Tri
Wedge
Linear and parabolic elements PAT318, Section 6, March 2002
S6-4
Quad
Hex
INTRODUCTION TO FINITE ELEMENT MESHING n
Meshing a model consists of several tasks: u
Create appropriate geometry l l
u u u
n
Parametric or non-parametric Remove unneeded features, e.g. small corners
Specify the element topology (e.g. parabolic) and size Specify a mesher, e.g. Paver Identify the mesher for each region, and how the meshers will be controlled
MSC.Patran has several meshing algorithms: u u u u
IsoMesh (mapped mesher) Paver (free mesher) TetMesh Sweep mesh
PAT318, Section 6, March 2002
S6-5
MSC.PATRAN MESHING ALGORITHMS
IsoMesh Mesh
Sweep Mesh
Paver Mesh PAT318, Section 6, March 2002
Tet Mesh Tetrahedral Mesh S6-6
ISO (MAPPED) MESHER Steps in IsoMesh Creation
n
All IsoMesh mesh paths are identified by the IsoMesher u
An IsoMesh mesh path is a set of topologically parallel geometric edges (i.e. surface or solid edges)
5
b
b a
1 a
4
2
b a
a
3
Gap is larger than Global Model Tolerance
In the example above, Surface 1:3 are congruent and Surface 4:5 are congruent, but Surfaces 3 and 4 are not congruent. Two of the individual mesh paths are labeled “a” and “b”. PAT318, Section 6, March 2002
S6-7
ISO (MAPPED) MESHER (CONTINUED) n
The IsoMesher determines the number of elements across the width (edges) of each mesh path, based on the following priority: u u u
Adjoining meshed regions that are topologically congruent Mesh Seeds on an edge (controls creation of nodes on curve or edge) Global Edge Length (GEL) Note: Number of elements is independent between mesh paths c
ξ2
c
b
ξ2
b
( ξ1 , ξ2 )
Node
a
ξ2
ξ2
a
ξ1
n
ξ1
d
b
ξ1
c
ξ1
ξ1
The IsoMesher determines the physical location of each node to be created from the vector function defining the shape of the geometry, e.g. (X,Y,Z) = function (ξ1,ξ2)
n
The IsoMesher creates the nodes and “element” connectivity Note: The IsoMesher can be used only with geometry that is defined parametrically PAT318, Section 6, March 2002
S6-8
ISO (MAPPED) MESHER (CONCLUDED) Adjacent meshes on surfaces 1 and 2
Adjacent mesh controlled
Mesh seed controlled
Edge Mesh Seeded
GEL Controlled 5
1
3
2
4
5
6*
1
3
2
4
6*
*Surfaces 1:6 n
When no mesh seeds or adjoining mesh occur in a mesh path, the Global Edge Length and the longest edge in the mesh path determine the number of elements per edge as follows:
Number of Elements =
PAT318, Section 6, March 2002
Longest Geometric Edge Length Global Edge Length S6-9
PAVER (FREE) MESHER FOR SURFACES Used with all surface types The Paver meshes at the surface boundary (perimeter) first, then, moves spiraling into the interior; the Paver does not follow parametric directions, e.g. ξ1,ξ2 Only the Paver recognizes associated (hard) points and curves inside surfaces
n n
n
2
3
12
16 13
17
15 12
30
14 11
29
10 28
27
19
32
25
20
1 Z
4
Z
21 1
Y Y
X 1
22 2
3
23 3
4
X
PAT318, Section 6, March 2002
9
S6-10
4 5
5 6
20
2
Z
21
X 1
3
25
23
9 6
24 4
5
10 7
19
3 4
26
34
22
11 8
20
18
2
27
35
33
7 9
21
25
17
1
Y
28
36
32
13 10
22
24
16 8
24
29
31
19
14 11
23
15
6
16
30
18
7
15 12
14 10
26
15
1
17
11 8
31
16 13
9
14 18
12
7
13
8 5
6
2
PAVER MESHER FOR SURFACES (CONCLUDED) 2
3 1 3 56
5 5 54
5 3 52 51
5 0 49
45
14
15
44
15
16
43
16
14
10
1
18
8
19
7
12
3
n
1
4
17
41
18
2
40
19
39
20
38
21
22
37
6 5
Y Z X
42 1
21
20
Y Z X
11
9
17
5
1 3 56
48 47 46
23 2 4 25
2 6 27
2 8 29
4 22
36
Y
30 31 32 33 34 35
Z
X
5 5 54
53
52
5 1 50
49
48
47
2 3 81
8 2 83
8 4 85
86
9 5 114 115 116 36
2 4 25
2 6 27
28
30
31
29
32
33
34
The number of elements per edge are based on the following priority: u u u
Adjoining meshed regions that are topologically congruent Mesh Seeds Global edge length
PAT318, Section 6, March 2002
S6-11
46
1 10 72 101 100 99 102 1 03 11 1 1 13 1 09 4 5 10 4 127 1 05 112 1 08 4 4 64 7 3 12 8 106 65 13 4 107 133 43 7 4 12 9 66 1 0 11 98 88 89 9 12 42 75 130 97 67 9 0 41 8 1 76 13 1 96 7 68 91 2 40 77 132 12 0 63 3 1 21 39 69 92 6 78 62 5 4 57 61 38 70 79 93 60 59 12 2 119 58 125 80 123 126 71 94 117 118 37 124 8 7
35
ISO (MAPPED) MESH VS PAVER (FREE) MESH MESH SURFACES IsoMesh n
n n
n
n
Paver
Surface must be parametric – 3 or 4 sided Parameterization followed Interior elements are controlled by edge constraints (e.g. mesh seed) Interior associated geometry not recognized User control u u
n n n
n
n
u
Different smoothing algorithms Can select different element patterns, e.g. triangular elements on surface
PAT318, Section 6, March 2002
Any surface including N-sided Parameterization not used Interior elements are not controlled by edge constraints Interior associated geometry is recognized User control
u
S6-12
Curvature check for curved surfaces Min./Max. element edge lengths
ISO (MAPPED) MESH VS PAVER (FREE) MESH (CONTINUED) Simple Surfaces
Iso Mesh
Surface 36
Paver Mesh
PAT318, Section 6, March 2002
S6-13
ISO (MAPPED) MESH VS PAVER (FREE) MESH (CONTINUED) IsoMesh and Paver Meshes
1
2
GEL = 1/4
GEL = 1/2
1. First, this surface meshed using Paver
All surfaces are 1 X 1 PAT318, Section 6, March 2002
3
GEL = 1/3
2. Second, this surface 3. Last, this surface meshed using Paver (matched existing meshes) S6-14
meshed using IsoMesh (Notice the mesh seeds are identical, but meshes are quite different)
ISO (MAPPED) MESH VS PAVER (FREE) MESH (CONTINUED) Mesh Parameters n
IsoMesh Parameters u
Define mesh smoothing parameters and mesh patterns
n
Paver Parameters u
u
u
PAT318, Section 6, March 2002
Allows for a tri element if element count on the boundary is odd numbered Curvature check allows for refinement of elements on highly curved boundaries Control for internal element size. Default range is set to largest and smallest element on the boundary. S6-15
MESHING CONTROL USING MESH SEEDS n
n
Mesh seeds are used to guide the mesher by specifying the number or lengths of elements to be created Mesh seeds are useful in mesh transition Abrupt transition
Transition control of IsoMesh with mesh seeds
(1)
(2)
Note: (1) seeded for 2 elements
Two Surfaces
(2) seeded for 6 elements (3) seeded for 4 elements PAT318, Section 6, March 2002
(1)
S6-16
Less abrupt transition
(3)
(2)
TETRAHEDRAL MESHER TET MESH n
Solid mesher generates tetrahedral elements for solids defined with an arbitrary number of faces (B-Rep or parasolid solids) u
Uses Delauney algorithm l
Uses tria mesh on faces to generate tetrahedral elements in the interior of the solid. MSC.Patran performs the following: Meshes Vertices Meshes Edges Meshes Faces Meshes Solids
n n n n
Tet meshes into the interior of solid using tri mesh as “seed”
Tri element meshes all faces first
Y
Y
Z
Z
X
PAT318, Section 6, March 2002
S6-17
X
TETRAHEDRAL MESHER TETMESH (CONCLUDED) n
Robust and fast u
n
Global parameters for meshing u u
u
n
Meshes B-Rep solids with silver faces Global edge length Create P-element mesh (allows elements with greater distortion) Curvature check – more elements at curved geometry, e.g. more elements on fillets
Allows excellent mesh control: u
u
Creates meshes congruent to adjoining meshed regions (2D or 3D) that are topologically congruent Creates meshes that follow mesh seeds and hard points on solid edges
PAT318, Section 6, March 2002
S6-18
SWEEP MESHER n
n
Sweep a lower order element (or node) through space to create higher order element, i.e. a quad is swept into a hex Several sweeping techniques are available (Extrude, Glide, etc.) to handle complex configurations Glide 1D to 2D Glide curve 1D bar elements
n
Mesh from a sweeping has no association with geometric entities, hence, properties and LBC’s must be applied directly on the finite elements PAT318, Section 6, March 2002
S6-19
ASSOCIATED POINTS/CURVES n n n
Associated points/curves are used for controlling meshing of regions (including interior) of the model Associated points/curves are regular geometric entities that have been associated with parent geometry Associated Geometry is also referred to as Hard Geometry Surface quad meshed Surface created by extruding Curve 1 up
Face quad meshed 1
Hex mesh created by sweeping quad elements down Edge of surface associated to face of solid Mesh seeds applied on curve 1
n
What meshers could be used? PAT318, Section 6, March 2002
S6-20
ASSOCIATION OF FINITE ELEMENTS TO GEOMETRY n
n
n
When geometry (i.e. curve, surface, solid) is meshed (i.e. Isomesh, Paver) the mesh (finite elements) is associated automatically to the geometry If a mesh is “imported” onto geometry (i.e. File/Import, Finite Elements/Transform) it is not automatically associated to the geometry; it must be associated manually, Finite Elements/Associate Why is it important to have a mesh associated to geometry? Application region in Loads/BCs and/or Properties
PAT318, Section 6, March 2002
S6-21
FINITE ELEMENT FORM n n
Create Mesh Seed
Set an objective, such as creating a mesh Provide the details to complete the task, i.e. element type
Transform Mesh
Uniform
Curve
One-Way Bias
2 Curves
Two Way Bias
Surface
Curve Based
Solid
PAT318, Section 6, March 2002
“Action”
Node
Element
Edit
“Object”
Edit
“Type”
S6-22
WHERE TO START WITH MESHING n
Things to consider before meshing a model u
u
u
u u
Check if the model has special features that may simplify its representation as a F.E. model, i.e. symmetry Determine if there are regions of the model that can be ignored for meshing (i.e. ignore some small features that otherwise might force the overall mesh to be much finer) Determine the size of the elements by inspecting the dimensions of the model and any critical features as fillets Are there any critical areas where the mesh should be finer Choose the type of element (i.e. shell versus solid) that is best suited for the nature of the model and the loading on it
PAT318, Section 6, March 2002
S6-23
MESH SEEDING n
n n
Mesh seeding on curves or edges is used to control the number and size of elements generated for the model Also, it is used for transitioning a mesh between different densities MSC.Patran has different methods to generate the seeding u u u u u
Uniform seed bias (equally spaced nodes) Non-uniform seed bias (variable spacing) Curve based seeding (automatic in highly curved regions) Tabular, including using existing nodes PCL function
PAT318, Section 6, March 2002
S6-24
NON-UNIFORM MESH SEED BIAS
Surface 1
Mesh Ratio = 4
Surface 1
Mesh Ratio = 0.25 (or -4)
Cyan arrows indicate positive edge direction PAT318, Section 6, March 2002
S6-25
CURVE BASED MESH SEEDING n
Variable or Uniform distance along a curve u
n
Order of element to be created u
n
PAT318, Section 6, March 2002
Linear causes more mesh seeds to be created
Refine mesh based on chordal tolerance u
n
Length Ratio dictates the ratio of the length of adjacent elements
Max h, or Max h/L
Specify minimum and maximum element length, or minimum and maximum number of elements S6-26
TABULAR MESH SEEDING n
n n n n
Arbitrary distribution of mesh seed along a curve/edge Location can be defined in real or parametric space Sort seed location in ascending order Reverse seed locations Create mesh seeds at existing nodes or points and if desired assign them to edge of adjacent surface
PAT318, Section 6, March 2002
S6-27
MESHING PARAMETRIC SOLIDS n n n
n
IsoMesher is used with any parameterized solid Same IsoMesh Parameters … as for surfaces Solids should be congruent for congruent mesh creation Material will be assigned in the Properties application
Congruent Simple Solids PAT318, Section 6, March 2002
S6-28
TETMESHING SOLIDS TetMeshing B-Rep Solids
n
n n
TetMesh Parameters allow control over the mesh generation Specify element topology Input List is used to specify geometric solids (e.g. Solid 1) or 2D elements (e.g. tri elements) PAT318, Section 6, March 2002
S6-29
TETMESHING SOLIDS (CONCLUDED) n
n
n
The P-Element option generates a coarse mesh (good for P-element analysis) The number of elements in curved geometry is specified by the value of Max h/L The smallest element edge length is specified using the Global Edge Length * (times) the list entry, e.g. Global Edge Length * 0.2
PAT318, Section 6, March 2002
S6-30
TETMESHING FROM 2D ELEMENTS SURROUNDING VOLUME
Tri element
n
Tet meshing volume with just 2D triangular elements (no quadrilateral elements permitted): u
u
Create 2D mesh with IsoMesh and/or Paver on all surfaces that bound the entire volume Equivalence nodes to sew all elements together l
u
u
Verify that there are no elements with free edges
Orient all element normals so they are pointing outward Select bounding 2D mesh for Input List
PAT318, Section 6, March 2002
S6-31
FEM CREATION TOOL TRANSFORM n
Transform, constructs new elements by performing a rigid-body or curvilinear translation u u u
Translate: rigid-body or curvilinear translation Rotate: rigid-body rotation Mirror: Reflect Elements and Nodes about a mirror plane
Mirror Plane
PAT318, Section 6, March 2002
S6-32
SWEEP MESHING n
Sweeping creates higher dimension elements by sweeping lower dimension elements through a prescribed path u
n
n n n
n n
PAT318, Section 6, March 2002
Nodes to Bars, Bars to Quads, Quads to Hexes
Several sweep methods are available, i.e. Arc, Extrude, Glide, Vector field, etc. Sweeping is applied to base mesh Used for constant cross-section Number of elements through thickness is determined by the Mesh Control form Can generate non-uniform mesh through thickness Mesh is not associated with geometry
S6-33
SWEEP MESHING (CONTINUED) Extrusion direction (Vector)
n n
n
PAT318, Section 6, March 2002
Direction Vector is the direction of extrusion Extrude Distance is the total distance to extrude (“thickness”) Base mesh is the set of elements representing a cross section
S6-34
FEM CREATION TOOL ELEMENT/EDIT n
The Finite Element application has many tools to create finite elements without using a mesher u
Create allows the user to create elements by selecting existing nodes, points, or vertices
PAT318, Section 6, March 2002
S6-35
FEM CREATION TOOL ELEMENT/EDIT (CONCLUDED) n
Create u
u
Element Shape and Topology are selected from the form Pattern allows for creation of elements on the face or edge of higher dimensioned element l l
Quad and Tri from element face Bars from element edge or piecewise linear
Quad elements skinned over hex faces
PAT318, Section 6, March 2002
Bar elements generated on element edges S6-36
EQUIVALENCE – TIE ELEMENTS TOGETHER Before 13
14 7
9
8
4
2 1 29
11
1
1
25
7 2
2 30
21
14 23 11 18
16
13
14
15
16
12
9
10
11
12
9
10
11
12
6
7
8
2
3
4
26
27
28
1 5
6
1 7
8
2 4 32
1 29
28
25
5
2 1
2 30
3 31
4 32
1
26
27
28
25
15
2
10
15
1
18 27
22
14
3
17
13
13
8
3 31
26
16
6
1
6
After
9
5
16
17
15
10
5
During
2
2
24
21
22
23
24
21
22
23
24
20
17
18
19
20
17
18
19
20
12 19
Use cube or sphere to establish closeness PAT318, Section 6, March 2002
S6-37
EQUIVALENCING n n n n
Replaces nodes to tie elements together Higher numbered node ID deleted, lower numbered node is saved Changes propagate through all selected FEM data Equivalence algorithm is controlled by a tolerance parameter
PAT318, Section 6, March 2002
S6-38
EQUIVALENCE FORM n
Equivalencing can be applied to: u u u
n
n
n
n
PAT318, Section 6, March 2002
All - the whole model in database Group – selected groups List – a specific list of nodes
The equivalencing tolerance is specified by the user, with it defaulted to the global model tolerance MSC.Patran will not collapse an element edge, e.g. quad shape to tria shape Selected nodes can be excluded from Equivalencing Tolerance Cube is the recommended method (speed)
S6-39
IRREGULARITY CHECKS n
General mesh/element checks u u u u u
n
Element specific distortion checks u
n n
Boundary or “Crack” detection Elements Duplication Normals Nodal connectivity Jacobian Deviation form basic shaped elements, i.e. taper
Curvature and singularity tests for quadratic elements Color-coding based on node or element ID numbers
PAT318, Section 6, March 2002
S6-40
FEM EDITING – NODE / MOVE n
Node modification tools u u
Move a node from one position to another This tool can be used to fix non-congruent meshes
PAT318, Section 6, March 2002
S6-41
FEM EDITING – NODE / OFFSET n
n
Node Offset - moves a node along a defined vector by a given magnitude Example u u u
u u
Move a node to produce a less skewed element Create vector by Tip and Base points Magnitude is calculated upon selection of two nodes, 1.2205, reset to .12205 for 10% increments. Select node to move Linear movement
Vector Dir
PAT318, Section 6, March 2002
S6-42
FEM EDITING – NODE / PROJECT n
Node Project u
u
u
u
Closest to Surface – projection along normal to surface that passes through node Define Vector – allows the user to define a vector to project along onto a surface View Vector – project along an arbitrary screen Z vector Closest To Curve – project using the closest approach to a curve or edge
PAT318, Section 6, March 2002
S6-43
NODE EDITING EXAMPLE Problem:
Use Node Editing to realign the nodes on edge 3 of Surface 1 with the nodes on edge 1 of Surface 2
1
2
Y Z
X
PAT318, Section 6, March 2002
S6-44
NODE EDITING EXAMPLE (CONTINUED) n
n
To change the location of a node, first identify its new location by specifying coordinate values or by using the Select Menu options in Node Locations Using Node List, identify the node to be relocated
Before
After
1st click 2nd click
15,4
15 4
PAT318, Section 6, March 2002
S6-45
PAT318, Section 6, March 2002
S6-46
SECTION 7 VIEWING
PAT318, Section 7, March 2002
S7-1
PAT318, Section 7, March 2002
S7-2
VIEWING
n
Orients view of model in the viewport u u u u u
n
PAT318, Section 7, March 2002
Translation, rotation, zoom Fitting model in screen Local zoom Along vector Clipping (cutting) model
Changing the view does not alter the model in any way
S7-3
TRANSFORMATIONS OF VIEW Translation and Zoom actions
Rotations about axes
Fit View
These parameters also affect mouse settings PAT318, Section 7, March 2002
S7-4
Transformation Control Parameters
FIT MODEL TO SCREEN AND SELECT NEW CENTER n n
Fit View fits model into viewport Move viewport’s focal point to mouse-defined location u
Choose “Select Center” from pull down menu, move cursor to selected point and click left mouse button
Current Window Original Center
New Window
New Center
PAT318, Section 7, March 2002
S7-5
SELECT CORNERS(LOCAL ZOOM) AND ZOOM BY FACTOR Use tool to zoom in on selected display regions Select corners for a new window
Before
After
PAT318, Section 7, March 2002
S7-6
SPECIFY VIEW USING ANGLES n
Change the view of model by changing the view angle of rotation about the axes of either the global or screen coordinate system
“View” Terminology: Model
- Global model axes stay fixed to the model - Screen axes are fixed to the graphics screen - Rotations relative to the zero rotation position - Rotations relative to the current position
Screen Absolute Relative
n
n
PAT318, Section 7, March 2002
S7-7
Screen axes are fixed to graphics device and never move Model axes are “body-fixed” and move with the model
USER DEFINED VIEWS Y
Z
X
Default view
Y
X
Top view Z Y Z
X
Side view
Typical icon n n
Standard model views can be selected for display Custom views can be created and stored for future reference PAT318, Section 7, March 2002
S7-8
GENERAL CLIPPING PLANES 14
23 20
22
7 17 19 24
9
25 28 26 27 18 29
4
16 12 15
21
n
n
n
PAT318, Section 7, March 2002
Arbitrary clipping planes can be created, deleted, displayed, and modified using the Clipping Planes form Clipping planes can be defined in model space, so they move with the model Multiple clipping planes may be active concurrently (maximum of 6 at one time)
S7-9
PAT318, Section 7, March 2002
S7-10
SECTION 8 GROUPS
PAT318, Section 8, March 2002
S8-1
PAT318, Section 8, March 2002
S8-2
INTRODUCTION TO GROUPS n
n
n
n
n n
Allows geometric and FE entities to be divided into separate groups for various modeling and post-processing tasks A group named “default_group” is created automatically when a new database is created Newly created items automatically become members of the current group Any number of groups can be created, and entities may belong to more than one group Groups become permanent members of the database Name of current group is displayed as part of Viewport banner
PAT318, Section 8, March 2002
S8-3
EXAMPLE OF GROUPS n
What is a Group? u u u
Any subset of model A collection of entities Separate groups for geometry & finite elements
Elements
Geometry
n
Create subsets when working with large models
Total PAT318, Section 8, March 2002
Middle S8-4
Ends
GROUPS TERMINOLOGY n
Current u u
n
Target u u u
n
Group into which newly created entities are placed Only one group may be current at a time Group that will be acted upon Translate entities from the Target Group to the Current Group Modify the appearance of the Target Group
Posted u u u
Group is displayed in a viewport A group may be posted to more than one viewport More than one group may be posted to a viewport
PAT318, Section 8, March 2002
S8-5
GROUP MANIPULATION n
Getting beyond “default_group”
n
Manipulate groups by clicking a Group in the main menu bar Group options can be selected from the Group pull down menu, or the Action choice on the Group form
n
PAT318, Section 8, March 2002
S8-6
CREATING A GROUP n
n n
n
n
PAT318, Section 8, March 2002
Choose Group/Create, or change the Action to create in the Group menu Assign new group name The default is to make the new group the Current Group (new entities assigned to) Use the Group Contents options to select group member categories, i.e. Add Entity Selection, Add All Geometry, Add All FEM, Add All Orphans, Add All Entities Loads, boundary conditions, coordinate frames, fields, load cases and results are not group members
S8-7
METHOD OF CREATING A GROUP
PAT318, Section 8, March 2002
Select Entity
Select the desired entities from the screen
Property Set
Select element property set names (user specified), i.e. prop_1, prop_2
Property Type
Select element property type, i.e. 2D shell, 3D solid
Loads/BCs Set
Select load and boundary condition set names, i.e. lbc_1, lbc_2
Loads/BCs Type
Select load and boundary condition types, i.e. displacement, force
Material
Select material set names, i.e. matl_1, matl_2
Element Topology
Select element topology, i.e. hex8, quad4
Element Shape
Select element shape, i.e. 2D, 3D, bar
Element ID
Specify element number range, e.g. start ID = 1, End ID = 327
MPC Type
Select MPC type, i.e. RBAR, RBE2
Boolean
Perform set operations on contents of groups, e.g. operation of union on groups group_A and group_B
S8-8
DISPLAY A GROUP n
n
Choose Group/Post, or change the action to Post in the Group menu Choose which groups are to be posted in the current viewport u u u
u
PAT318, Section 8, March 2002
A single mouse click will highlight one group Drag for continuous selection Hold down to select a set of continuous groups in series Hold down to select non-contiguous groups
S8-9
MODIFYING GROUPS n n n
n
PAT318, Section 8, March 2002
Select a Target Group for modification Use “Rename…” to rename the target group Member List to Add/Remove buttons and Global Add/Remove buttons actually modify the target group’s members Selectable Members switch will allow the group to be visible and selectable. Turning this switch off will allow the group to be visible, but not selectable.
S8-10
MOVING OR COPYING BETWEEN GROUPS n n
n
n
Used to transfer entities between groups rapidly Select “Move” if you want the entities to be moved to the “To Group” Select “Copy” to duplicate entities in both “From Group” and “To Group” Indicate the entities you wish to transfer with the “Selected Entities…” button
PAT318, Section 8, March 2002
S8-11
SETTING CURRENT GROUP n
Set Current u u
u
Make a group current by highlighting its name Making a group current will post it to the current viewport Entities created will be assigned to current group
PAT318, Section 8, March 2002
S8-12
TRANSFORMING GROUPS n
Transform (copy) members (entities) of groups u u
u
u
Select transformation Method, i.e. Translate, Rotate Transform entities in Target Group to the Current Group Can delete original entities and use their IDs for new entities Element Properties and LBCs can optionally be copied, transformed or ignored
PAT318, Section 8, March 2002
S8-13
DELETING GROUPS n n
n
n
PAT318, Section 8, March 2002
Can delete any group except the current group Option given to delete name of group only (keep entities) Deleting entities in a group will remove them from database regardless of possible membership in other groups Entities which are exclusive to a deleted group will become orphaned entities
S8-14
NOTES ON GROUPS n n
A Group can be current without being posted If you are creating entities that are not being displayed, you can: u
n
n
Use Group/Post to check whether the current group is posted to the current viewport
The only way to have more than one render style displayed simultaneously is to be in “Group Display Mode” Group Display is a useful tool when postprocessing. Different results can be plotted using different render styles (deformed shape = wireframe, Von Mises Stress = Fringe, etc.)
PAT318, Section 8, March 2002
S8-15
PAT318, Section 8, March 2002
S8-16
SECTION 9 DISPLAY
PAT318, Section 9, March 2002
S9-1
PAT318, Section 9, March 2002
S9-2
DISPLAY
n
n
Display tools are used to organize and enhance the appearance of the model in viewports Two types of display modes: u u
n n
Entity mode targets entities by type (i.e. all curves are yellow, all quads are white) Group mode targets by group (i.e. default group is wireframe, bracket group is shaded yellow)
Display type is global (affects all open viewports) Only one type of display mode may be used at a time PAT318, Section 9, March 2002
S9-3
ENTITY TYPE DISPLAY n
Modify entity display properties u
u
u
u
u
PAT318, Section 9, March 2002
S9-4
Model Render Style applies to all entities Shade Color applies to all entities Colors of each Entity Type are unique for each entity Show or hide Entity Labels Label Font Size applies to all entities
GROUP DISPLAY n
Modify display properties by group u u u u u u
n
PAT318, Section 9, March 2002
S9-5
Select a set of groups Render style Shade Color Labels on or off Label size Toolbar, Quickpicks
Unique for a given group
PLOT/ERASE n
n
n
n
Toolbar, Quickpick button for plot/erase
PAT318, Section 9, March 2002
S9-6
Unclutter graphics display by temporarily removing entities from the display Actions affect only the display Settings will not be saved when the database is closed Erase is different from Delete
PLOT/ERASE EXAMPLE
Hidden line plot with the FEM displayed and the geometry erased (No conflict)
Hidden line plot when geometry and FEM overlap (Numerical conflict) n n n
PAT318, Section 9, March 2002
Select Display – Plot/Erase Click on Repaint the screen S9-7
HIGHLIGHTING n
n n n
Find any posted entity by entering its name and ID number (i.e. Element 32) … Find entities associated to other entities using Tools/List/Create Highlight color is modified under Preferences/Graphics Dynamic highlighting can be turned on under Preference/Picking
32
PAT318, Section 9, March 2002
S9-8
GEOMETRIC ATTRIBUTES n
n
Geometric properties may be altered to enhance display (i.e. display lines, chordal tolerance, parametric directions, entity colors and labels) Toolbar, Quickpick buttons
Display Lines
PAT318, Section 9, March 2002
S9-9
Point Size
Labels
GEOMETRIC SHRINK AND DISPLAY LINES 22 12
1 2 1 1
1 2
21 2 1
21
Before 2 1 21 21 21 2 1
12 2 1
2 1
21
1 1 12
12 2
1 2 21
2 1
1 2 21
PAT318, Section 9, March 2002
21
22 1
S9-10
FINITE ELEMENT AND LBC/ELEMENT PROPERTY DISPLAY ATTRIBUTES n
FEM u u u u u
n
Element shrink Free edges and faces Node size Colors and labels Coordinate frames
LBC/Element Props. u u u u u u u u
PAT318, Section 9, March 2002
S9-11
LBC display toggles Colors Show on FEM only Vector attributes Beam Display Pin DOF’s Spring DOF’s Coordinate frames
TITLES EXAMPLE 162.5
162.5
158.1
158.1
153.6
153.6
Transient - Thermal Analysis of a Simple Plate Model
149.1 144.7 140.2
135.7 131.3 100 < T(t) T(t) < 162.5 126.8
131.3 100 F (Constant)
126.8
122.3
122.3
Linear Variation
117.9
Y
108.9
X
Before n n n n
108.9 Adiabatic BottomEdge
Z
104.5
104.5
X
After
100.0
Type Title in Target Title listbox Select Title Color and Font Size Select Create Move Title to desired position using cursor while form is open
PAT318, Section 9, March 2002
117.9 113.4
113.4
Z
144.7 140.2
Adiabatic Top Edge
135.7
Y
149.1
S9-12
100.0
SPECTRUMS n
n
n
PAT318, Section 9, March 2002
S9-13
Color spectrum can be modified to improve understanding of results and other distributed quantities Continuous tone fringe plots can be rendered and the interpolation between any two colors controlled (e.g. 2 = quadratic) Modified color spectra can be created, named and saved for current and future use
PAT318, Section 9, March 2002
S9-14
SECTION 10 ANALYSIS SETUP
PAT318, Section 10, March 2002
S10-1
PAT318, Section 10, March 2002
S10-2
ANALYSIS SETUP
n
n n
n
Analysis form automatically customized to userselected analysis code Analysis Parameters are selectable from this form Optionally can submit and monitor status of the analysis jobs across the network For MSC.Nastran, this form can also be used to read an existing bulk data file into the MSC.Patran database (MSC.Nastran files can also be read using File/Import)
PAT318, Section 10, March 2002
S10-3
SETTING UP THE ANALYSIS n
n
n
n
The analysis model may be prepared for the entire model or the current group Select Translation Parameters to specify the output format, solver version, etc. Select the Solution Type to specify the type of solver run, e.g. linear static Select Subcases u u
n
n
PAT318, Section 10, March 2002
Select Patran Load Case Select entities to be output to the print and results files, i.e. displacements, stresses
Select the subcases already defined using Subcase Select The run-ready file can be submitted directly to the target analysis code
S10-4
RESULTS TRANSLATION BACK INTO MSC.PATRAN n
n
Completed analysis results can be read back into MSC.Patran for post-processing Under the Object option menu, one may choose to “Translate” Results Entities
Stresses, deformation
Model Data
Nodes, elements
Both
Both model and results
Be sure to click
PAT318, Section 10, March 2002
S10-5
READING A MSC.NASTRAN BULK DATA FILE n
n
n
n
n
PAT318, Section 10, March 2002
Existing MSC.Nastran bulk data files can be read into MSC.Patran to verify and update models that were not created inside MSC.Patran The MSC.Nastran bulk data file reader is used to translate the model into MSC.Patran Any statement not recognized will be optionally displayed in a window by area: file management, executive deck, case control deck, or bulk data deck Numbering offsets can be set to none, automatic, or manually input for each entity type The Output 2 file reader will only import nodes, elements and coordinate systems. The bulk data reader will also read MPC’s, material and element properties, load sets and subcases S10-6
SECTION 11 LISTS
PAT318, Section 11, March 2002
S11-1
PAT318, Section 11, March 2002
S11-2
LISTS OVERVIEW
n n
n
Create list of entities based on given criterion Lists can be used as input for various applications, such as Application Regions for element properties Criteria for list creation are: u u
n
Attributes, such as location, results value, assigned properties Association with other entities, such as Points, Edges, Elements, Groups, etc.
Lists are not stored in the database, but can be added to a Group
PAT318, Section 11, March 2002
S11-3
HOW TO CREATE A LIST Create Two Lists:
List A: All Nodes at x=18 (+ 1.0 Tolerance) List B: All Elements associated with those nodes
n n n
PAT318, Section 11, March 2002
Create List A Nodes at X = 18 + 1
n n
S11-4
Create List B Elements Associated with Nodes in List A When using a List as input, enclose the List name in back quotes (e.g. `lista`)
BOOLEAN OPERATIONS n
Boolean operations are used to manipulate lists u u u
n
Intersection operation finds common items in both lists Union combines items in both lists Results of subtracting one list from another
Example: u
Elements with a Von Mises stress result value > 20,000 and a temperature result value > 300
PAT318, Section 11, March 2002
S11-5
BOOLEAN EXAMPLE
n n n
PAT318, Section 11, March 2002
Plot Von Mises stress Create List A Elements with a Von Mises stress result value greater than 20K
S11-6
n n n
Plot temperatures Create List B Elements associated with a temperature result value greater than 300
BOOLEAN EXAMPLE (CONCLUDED)
n n
PAT318, Section 11, March 2002
Use Boolean Operation to create List C Contents of List C are all elements at a temperature greater than 300 and Von Mises stress greater than 20,000 psi
S11-7
PAT318, Section 11, March 2002
S11-8
SECTION 12 VIEWPORTS
PAT318, Section 12, March 2002
S12-1
PAT318, Section 12, March 2002
S12-2
VIEWPORTS
n
What is a Viewport? u
Separate graphics window Has a unique name (shown in the banner)
u
Has an associated view
u
n n
Any number of viewports may be created and posted Each viewport can be moved, resized, iconified, posted and unposted
PAT318, Section 12, March 2002
S12-3
WHY USE VIEWPORTS Different groups in separate viewports
Different views of same groups Isometric
Front Geometry
FEM
Different pieces of your model in separate viewports
Different results in different viewports – each with its own range
Part
Whole
PAT318, Section 12, March 2002
S12-4
CREATING VIEWPORTS No limit on how many viewports one can create
PAT318, Section 12, March 2002
S12-5
CURRENT VIEWPORT n
The Current Viewport is the u u u
n n
Viewport in which view commands will be applied Viewport in which titles will be posted Viewport in which post-processing will be done
Only one viewport can be current at a time To change Current Viewport n
n
Click in area just inside the outer border to make a posted viewport current Or Viewport/Modify/Change Target Viewport/Make Current
Posted Viewport Current Viewport
PAT318, Section 12, March 2002
S12-6
VIEWPORTS AND GROUPS n n
Any number of groups may be assigned to a viewport Only one group is current per viewport. Each viewport may have a different current group box_beam.db - viewport_1 - fem_temp- group
box_beam.db - viewport_3 - fem- group
box_beam.db - viewport_2 - View_2_fem2- group
PAT318, Section 12, March 2002
S12-7
PAT318, Section 12, March 2002
S12-8
SECTION 13 RESULTS
PAT318, Section 13, March 2002
S13-1
PAT318, Section 13, March 2002
S13-2
RESULTS INTRODUCTION n
n
The Results post processing module can be used to process scalar, vector, and tensor results into a variety of graphical display types Results can come form many analysis types: u
u
n
Structural, thermal, cfd, electromagnetic Static or dynamic
The results can be read through u
u
u
Standard translators, e.g. analysis menu for MSC.Nastran PATRAN 2.5 .dis, .els, or .nod formats in File/Import/Results Read into database via PCL
PAT318, Section 13, March 2002
S13-3
RESULTS INTRODUCTION (CONTINUED) n
Results from various analysis runs can be stored in the same database under different result cases u u u
n n
Static Transient – each time step = 1 Result Case Non-linear – each load increment = 1 Result Case
More than one load case can be operated on simultaneously Results can be filtered based on attributes or numerical values
PAT318, Section 13, March 2002
S13-4
RESULTS INTRODUCTION (CONCLUDED) n
Results can be displayed in any coordinate system u
n
n
Vector components in local coordinate system 1
New results may be derived by linearly combining existing results, using a user-defined PCL expression or PCL function, etc. Any plot can be saved in a file and retrieved for future use
PAT318, Section 13, March 2002
S13-5
THE RESULTS MAIN FORM n
Procedure u
u
u
n
Set Action to Create and select type of plot (the Object) Select the Result Case(s) and the result type Apply to add the plot to the display
Plots can be animated by clicking the Animate button when the plot is created
PAT318, Section 13, March 2002
S13-6
RESULT PLOT TYPES n
n
Quick Plot – quick and “easy” access for fringe, deformed, or combined plot or animation Deformation plot – more options, e.g. Target Entities
Quick Plot
PAT318, Section 13, March 2002
Deformation Plot
S13-7
RESULT PLOT TYPES (CONTINUED) n n
Fringe plot – on the deformed or undeformed model Element Fill plot – one color per element on the deformed or undeformed model
Fringe Plot PAT318, Section 13, March 2002
Element Fill Plot S13-8
RESULT PLOT TYPES (CONTINUED) n n
Vector (Marker) plots – at nodes or element centroids Tensor (Marker) plots – displayed in elemental or principal coordinate system
Vector Plot n
Animation
Animation – deformed and/or fringe plots can be animated
PAT318, Section 13, March 2002
S13-9
RESULT PLOT TYPES (CONCLUDED) n
XY Plot (Graph) – u u u u
u u u
n
Text report writer - create formatted text for analysis reports
PAT318, Section 13, March 2002
S13-10
Results vs. Global Variable Results vs. Another Result Result vs. Distance Result along any user-specified Geometric Entity Global Variable vs. Global Variable Result with respect to a Local System Result along a Arbitrary Path
QUICK PLOT FORM n
Quick Plot result display form has been designed to accommodate easy access to basic postprocessing feature such as: u u u u
n
Fringe plots Deformed plots Combined fringe and deformation plots Quick animation
Simple Deformed, Fringe, or combination plots can be created and animated with very few menu selections: u u u u u
Select Result Case Select Fringe Result Select Deformation Result Click on Animation (if desired) Apply
PAT318, Section 13, March 2002
S13-11
QUICK PLOT ANIMATION FORM n n
n
Deformed Shape (static or “modal”) and/or fringe animation can be performed The defaults are to animate both fringes and deformation with the modal method in 2D, 15 frames You can change any of these options through the Animation Options form u
u
u
Modal animation creates frames by multiplying the results from –1.0 to +1.0; Ramped goes from 0 to +1.0 2D uses in plane animation, 3D lets you rotate the model with the middle mouse button while the model is still animating The more frames you select, the smoother the animation, but more computer resources are used
PAT318, Section 13, March 2002
S13-12
RESULTS POST-PROCESSING PROCEDURE n n n n n n n
PAT318, Section 13, March 2002
Set Action to Create Select the plot type (Object), i.e. deformation, fringe, etc. Select the Result Case(s), i.e. static, modal, transient, etc. Select the result type, i.e. deformation, stress, strain, etc. Select the position, e.g. layer in shell Select the Quantity, i.e. Min. Principal, Component, etc. Modify Target Entities, Display Attributes, Plot and Animation Options as desired using icons at top of form
S13-13
SELECT RESULTS FORM n
When multiple result cases are in the database you can cursor select one or more from the unabbreviated Select Result Case(s) list u u
u
n n n
Click on one to select it Select a continuously listed set using click and drag Select a discontinuous set by Ctrl-clicking
If desired filter using Select Subcases Position selection for beam or shell layered results The particular result value component or derived quantity plotted can be selected from Quantity pull-down menu or from “Show As”
PAT318, Section 13, March 2002
S13-14
Select Subcases
SELECT RESULTS FORM (CONCLUDED) n
Select Subcases
To filter Results Case(s): u u
Click on Select Subcases Setup one or more filters using Filter Method: l l l l
u
u
Global Variable Character String Subcase IDs A combination of the above
Select Filter to see the resulting list of Selected Result Case(s) Click Apply if the list is what you wanted
PAT318, Section 13, March 2002
S13-15
TARGET ENTITIES FORM Target Entities button n
Results in the Select Result Case(s) can be plotted on targeted entities based on: u u u u
Current Viewport (default) A set of Elements or Nodes Groups Materials, Properties, or Element types
PAT318, Section 13, March 2002
S13-16
TARGET ENTITIES FORM (CONCLUDED) n
Depending on the plot type, additional Display Controls Include: u u u u u u u u
n
Nodes Elements Faces/Free Faces Edges/Free Edges Corners Element Centroids Element Nodes Element All Data
Remember that lists can also be created and used with groups to act as user-defined filters (i.e. elements with 10,000
S13-17
DISPLAY ATTRIBUTES FORM n
n
The Display Attributes form will change to match the plot type and results entity selected Parameters are filtered such that only those appropriate for the currently selected plot type are displayed
PAT318, Section 13, March 2002
S13-18
Display Attributes Button
PLOT OPTIONS FORM n
The Plot Options Form is used to control the following: u
u u
u
u
u u u
Coordinate Transformation, e.g. transform vector components Scale Factor – multiply results by factor Filter Values – filter results displayed using result values Averaging Domain and Method – how element results are combined Extrapolation method – how results are combined in an element Use a PCL Expression Re-loading of an existing Plot Saving current plot for Future Use
PAT318, Section 13, March 2002
S13-19
Plot Options Button
PLOT OPTIONS FORM (CONTINUED) n
Coordinate transformation options u u u
u u u
u
n
n
PAT318, Section 13, March 2002
None – Patran global coordinate system used, Coord 0 CID – Patran local coordinate system, e.g. Coord 3 Projected CID – coordinate system projected onto element, e.g. Coord 2.1 Global – Patran global coordinate system, Coord 0 Default – results are kept in the solver coordinate system(s) Material – element coordinate systems based on a material definition and angle. Only for quad and tri topology. Element IJK – Patran defined element coordinate systems. These can be different from solver element coordinate systems.
Patran user manual provides detailed information on these transformations MSC.Nastran default for CQUAD elements is Projected Global, in which the xx – comp stress is in the direction of the Global X axis projected onto the shell element
S13-20
COORDINATE TRANSFORMATION TENSOR EXAMPLES σxx
σyy
Local Coord 1
Projected CID, Select CF Axis Coord 1.2, changing axis changes σxx direction by 908
CID, Select Coordinate Frame Coord 1
3
4
Coord 0
2
σxx 1
Global – uses Patran Coord 0 PAT318, Section 13, March 2002
Element IJK – uses first two element nodes for σxx direction S13-21
FRINGE PLOT OPTIONS n
Averaging Definition provides different options to determine the result values at nodes shared by adjacent elements
n
1
2
4
3
Domain All Entities: all result values at a node are averaged producing a single value u None: no averaging at node result values at a node are Material averaged if the contributing Property elements are of the same Type, Material or Element Property, or Target Entities are part of the defined Target Entity set Element Type u
PAT318, Section 13, March 2002
S13-22
AVERAGING DEFINITION/DOMAIN FOR COARSE AND FINE MESHED MODEL
Coarse mesh, average all elements
Coarse mesh, no averaging
Fine mesh, average all element Fine mesh, no averaging Note: Derive/Average and Shape Fn. was used PAT318, Section 13, March 2002
S13-23
FRINGE PLOT OPTIONS (CONTINUED) n
Averaging Definition options – (continued) u
Method l
When both averaging and derivation of a new result invariant (such as determining von Mises stress from the stress tensor) are to be performed the user has the following options: n
n
PAT318, Section 13, March 2002
Derive/Average: calculates the derived result invariant at the integration points, extrapolates that to the nodes, then plots the average Average/Derive: extrapolates the component values to the nodes, averages them, then calculates the derived result using the average nodal component values
S13-24
Fringe Plot Options (continued) n
Averaging Definition options – (concluded) u
Method l
Difference:
l
Sum:
PAT318, Section 13, March 2002
plots the magnitude of the absolute difference between the largest and smallest of the values at a node plots the sum of all values at a node
S13-25
AVERAGING DEFINITION/METHOD FOR COARSE AND FINE MESHED MODEL
Coarse mesh, Difference
Fine mesh, Difference
Note: All Entities and Shape Fn. Used.
PAT318, Section 13, March 2002
S13-26
FRINGE PLOT OPTIONS (CONTINUED) n
Extrapolation of element results to the element’s nodes can be done as follows: u
Average: result is averaged within the element, then the averaged value is assigned to the element’s nodes
1 Node Result = N
PAT318, Section 13, March 2002
S13-27
N
Σ i=1
(Element Result)
Fringe Plot Options (continued) Extrapolating surface n
Extrapolation options – (concluded) u
u
u
u
Shape Fn.:
result value at the element’s nodes is determined from fitting an extrapolating surface through the known element result values Centroid: the centroid value of the extrapolation surface is used at the element’s nodes Min: the smallest of the integration point values is used Max: the largest of the integration point values is used
PAT318, Section 13, March 2002
S13-28
Element Integration point, + Element result value,
EXTRAPOLATION/AVERAGE FOR COARSE AND FINE MESHED MODEL
Coarse mesh
Fine mesh
Note: All Entities and Derive/Average used.
PAT318, Section 13, March 2002
S13-29
FRINGE PLOT OPTIONS (CONCLUDED) n
Define PCL Expression u
u
u
u
PAT318, Section 13, March 2002
S13-30
There is only one Independent Variable. It is named SCALAR. It is the scalar variable that is being used to create the fringe plot, e.g. Von Mises stress under Select Results/Quantity Can use standard arithmetic operations (e.g. +) and Intrinsic Functions (e.g SIND) Input the desired PCL Expression, e.g. $SCALAR + 273.15 Only one result case is allowed. If multiple result cases are needed use Utilities/Results/Result Toolbox.
DISPLAY FRINGE PLOT FOR INSIDE OF 3D MODEL n
Show color results fringe for interior of 3D model u u
u
PAT318, Section 13, March 2002
S13-31
Create a clipping plane Create a fringe plot using Results, including Target Entities/Additional Display Control/Faces Also, can use Insight by creating a fringe plot on planes of constant coordinate value
DEFORMED SHAPE PLOTS Scale Factor = 0.1
Scale Factor = 0.2
n
n
n
PAT318, Section 13, March 2002
Deformed and Undeformed features (e.g. color, Render Style, Line Style are changed in this form) The scale is set based on either model size or actual deformation (True Scale) Undeformed shape can be toggled off S13-32
VECTOR MARKER PLOT n n
n
Vector components or resultants can be rendered Vector plot Display Attributes and Plot Options forms control the display of any nodal vector quantity Vector Results can be plotted with respect to any Coordinate System
PAT318, Section 13, March 2002
S13-33
MARKER DISPLAY ATTRIBUTES n
The Vector length and style can be changed in the Display Attributes form Vectors anchored at the Tip
Vectors anchored at the Base
PAT318, Section 13, March 2002
S13-34
CREATE RESULTS FORM n n
The Create/Results form is used to select, manipulate, and combine results Create derived results based on using the following operations for the specified set of results: u
u
u u u u
Combine – linear combination of set members Maximum – new result case with maximum from set of results Minimum – minimum from set of results Sum – sum results in result set Average – average results in result set Demo – create dummy result case for existing mesh
PAT318, Section 13, March 2002
S13-35
Specify set of results
CREATE RESULTS FORM (CONCLUDED) n
PCL Function for user defined expression u
u
u
u
PAT318, Section 13, March 2002
S13-36
Independent Variables that are available are dependent on type of results being used, i.e. Nodal Scalar has $SCALAR, Nodal Tensor has $XX, $YY, etc. Can use standard arithmetic operators (e.g. +) and Intrinsic Functions (e.g. SIND) Input desired PCL Expression, e.g. SQRT($XX**2 + $YY**2) This represents (σxx2 + σyy2)1/2 for tensor results Only one result case allowed. Use PCL expression for multiple result cases by using Utilities/Results/Result Toolbox.
X-Y GRAPH PLOTTING n n
n
n
Select Results Cases Select the Y – axis result and Quantity, and X – axis entity Click on Target Entities icon and select entities for which the XYPlot is to be generated Click on “Apply” to generate the XY Plot
PAT318, Section 13, March 2002
S13-37
TEXT REPORT WRITER n
n
Writes out requested results information to the MSC.Patran parent window (Preview option) or to a file Report Type options: u u u
n
Full – results and all related information Summary – max/min and associated Nodes or Elements Data only
Results, Target Entities and Plot Options are very similar to those of other Plot Types
PAT318, Section 13, March 2002
S13-38
TEXT REPORT WRITER (CONTINUED)
Scalar Value Loadcase ID Subcase ID Layer ID X Location Y Location Z Location Magnitude CID Material ID X Component YComponent ZComponent Material Name Property ID Property Name ACID
n
Report Type Options:
n
Available Data Includes: u u
u u u u u u
u u
PAT318, Section 13, March 2002
S13-39
Loadcase, Subcase, Layer ID X, Y, Z Location of Integration Point or Node Stress Components Stress Invariants Magnitude of Deformation Result CID Material Name and ID X, Y, Z Components of Deformation Property Name and ID Analysis CID of Node
TEXT REPORT WRITER (CONCLUDED) n
Display Attributes form u
Format l
l
l
PAT318, Section 13, March 2002
S13-40
Report format and column ordering can be adjusted to the users needs Page Title, Header and Footer can be specified Real and Integer Number format can be specified
FREEBODY RESULTS n
n n
n
Graphical display of freebody diagrams from results values Option to create new load sets Currently supported results are from MSC.Nastran Data must be available from Grid Point Force Balance Table (GPFORCE=ALL)
PAT318, Section 13, March 2002
S13-41
EXAMPLE FREEBODY RESULTS REVIEW 235.00
126.25
447.52
981.00
1089.75
1447.52
External Loads
Reaction Forces
151.30
513.59 405.13 648.83
170.13
513.59
648.83
386.30
Internal Section Loads PAT318, Section 13, March 2002
S13-42
CREATING A RANGE n
To create a new range, you can go to Display Attributes – Range – Define Range, or Pull down Display/Ranges… Step 6: Assign the range to the current viewport (OR use Viewport/Modify/ Change Range)
Step 1: Create a range (one for each viewport) Step 2: select Data Method Step 3: select Thresholding
Step 5: Apply
Step 4: Calculate range
PAT318, Section 13, March 2002
S13-43
CREATING A RANGE (CONTINUED) DATA METHOD n
Semi-Auto u
n
Semi-Auto (Delta) u
n
Discrete sub-range starting from a value extending to a value (can leave holes)
Middle: u
PAT318, Section 13, March 2002
Discrete sub-range starting from a value
From/To: u
n
Contiguous sub-ranges starting from a value then incrementing (or decrementing) by a delta value
From: u
n
Contiguous subranges starting from and ending at user-supplied values (or use Fit Results)
Contiguous sub-ranges defined by their mean value
S13-44
CREATING A RANGE (CONCLUDED) Thresholding n n
For either of the semi-auto data methods All results between Start and/or End of results and start of threshold will be colored uniformly u
n
PAT318, Section 13, March 2002
End < threshold value < Start
Press Calculate, and if satisfactory press Apply
S13-45
RESULTS WITH MULTIPLE VIEWPORTS
Fringe Plot of Von Mises Stress Values n
Wireframe Deformed Shape
Same model in both viewports, but displays created using different groups
PAT318, Section 13, March 2002
S13-46
RESULTS ANIMATION n
n
n
n
Modal and transient animation can be performed in Results Transient animation can be performed with respect to any global variable, such as time, load case, or frequency All posted tools will be displayed during an animation, but only the tools with animation enabled will change from frame to frame Animation controls appear automatically when a plot is animated
PAT318, Section 13, March 2002
S13-47
TYPICAL RESULTS ANIMATION
Frame 1
Frame 7
Frame 13
Frame 20
PAT318, Section 13, March 2002
S13-48
QUICK PLOT ANIMATION n
n
n
To perform a simple modal animation, select Action: Create, Object: Quick Plot Select the desired fringe and/or vector result Click on and hit Apply to create the animation frames
PAT318, Section 13, March 2002
S13-49
ANIMATION CONTROL SETUP n
n
So far we have discussed setting up and controlling Quick Plot animation of a single Results Case Animation sequences pertaining to global variables (e.g. transient animation) and modal analysis can be performed in greater detail by clicking the Animation Options button when the plot is created
PAT318, Section 13, March 2002
S13-50
Animation Options button
ANIMATION OPTIONS FORM n
n
When creating a plot clicking the Animate button sets the Animate Method pull-down menu on the Animation Options form to a value, e.g., Global Variable Animate Method: u
u
u
Global Variable – allows the animation of a tool with respect to any global variable (only available when more than one Results Cases have been selected) Modal – applies a sine function (-1 < sine < 1) to the tool’s response Ramp – allows animation of a tool’s response by multiplying the response by a range of scale factors from 0 to 1
PAT318, Section 13, March 2002
S13-51
ANIMATION CONTROL n
n
n
n
PAT318, Section 13, March 2002
Once the animation has stared, you can pause and change the animation attributes Animation Sequence: u
Cycle:
u
Bounce:
animation cycles in a circular manner (frame1,2,…,max,1,2,…,max, etc.) animation cycles from max to min (frame 1,2,…,max,max-1, etc.)
Once the animation is paused, it can be advanced forward one frame at a time and the start/end frames may be changed To terminate the animation tool select the Stop Animation button
S13-52
SETTING UP NON-QUICK PLOT ANIMATION n
Procedure for setting up the animation as you create the plot
On the Select Results form
1
4
On the Animation Options form
Set Action to Create and Object to the desired plot type
Select Animation Options button
Set Animate Method to Global 5 Variable
Select a set of 2 Result Cases and a result type Select the Number of Frames
3
6
Click on Animate Hit Apply
PAT318, Section 13, March 2002
S13-53
7
PAT318, Section 13, March 2002
S13-54
SECTION 14 X-Y PLOTTING
PAT314, Section 14, March 2002
S14-1
PAT314, Section 14, March 2002
S14-2
X-Y PLOT
n n n
Manages appearance of XY windows Manages display of curves in XY windows Fully integrated with results, loads, properties, and material data
PAT314, Section 14, March 2002
S14-3
XY PLOT TERMINOLOGY
PAT314, Section 14, March 2002
S14-4
CURVE DATA FROM FILE Contents of File “file_1.xyd” File
Format
XY DATA If XY pairs
XYDATA, beautiful_curve -3. -2.8
Curve name
-2.3 -2. -2.099999 -1.3 -1.7 -0.30000001 -1.6 0.660000003 -1.3 1.3
Data set 1
-0.899998 2.2 -2.330001 2.7 0. 1.7 0.3300001 0.4000001 YDATA
YDATA, new_curve
If Y only
100.
(X initial
100.
And Xdelta
300.
Will be
300.
Specified
500.
Under curve
500.
Data
400.
Attributes)
300.
Data set 2
200. 0.
PAT314, Section 14, March 2002
S14-5
SCALE AND RANGE n
Scale u u u
n
Range u
PAT314, Section 14, March 2002
Linear Semi-Log Log-Log Controls method used to determine start and end points for the X and Y axes
S14-6
TITLES XY Plot: database_name: XYWindow1 LEGEND quadratic_load
20.0
Load Case 4
0.
% distance from left of window
-20.0
% distance from top of window
-60.0
-40.0
-80.0 -100. -1.05-.700-.350 0.
PAT314, Section 14, March 2002
S14-7
.350 .700 1.05
MODIFY DISPLAY PARAMETERS n
Virtually anything you see on the screen can be modified XY Plot: database_name: XYWindow1
n
XY Window:
n
Curve:
n
Legend:
n
Axis:
n
Plot Titles:
Analysis versus Test Test Data temp_vs_time
Load Case 4 0.
1.50
3.00
4.50
6.00
7.50
9.00
27.0
Temperature (C) Versus Time (sec)
22.5
18.0
13.5
9.00
4.50
Node 6 0. 0.
1.50
3.00
4.50
PAT314, Section 14, March 2002
6.00
7.50
9.00
S14-8
Location, Border, Background, Color Post/Unpost, Line Style, Name, Data, Symbols, Color,Thickness, Curve Fit Method On/Off, Location, Border, Text, Background, Color Line Style, Scale, Label Formats, Titles, Tick Marks, Grid Lines Location, Size, Color, Post/Unpost
MODIFY XY WINDOW Border Background
PAT314, Section 14, March 2002
S14-9
MODIFY CURVE n
Available symbol types q
Dot
q
Square
q
Fill Diamond
q
Circle
q
Fill Square
q
Arrowhead
q
Fill Circle
q
Triangle
q
Fill Arrowhead
q
X
q
Fill Triangle
q
Hexagon
q
Plus
q
Diamond
q
Fill Hexagon
LEGEND Variable_load 20.0 0. -20.0 -40.0 -60.0 -80.0 -100. -1.20
-.800
-.400
0.
.400
PAT314, Section 14, March 2002
.800
1.20
S14-10
SECTION 15 MSC.PATRAN FILES
PAT318, Section 15, March 2002
S15-1
PAT318, Section 15, March 2002
S15-2
MSC.PATRAN FILES Name
File Type
Comments
model_name.db
Database
One per model, relatively large.
model_name.db.bkup
Database
Backup database is created if revert is enabled
patran.ses.number
Session file
A Session File is opened at P3 start-up and it is closed when you quit MSC.Patran.
model_name.db.jou
Journal file
One per model, record of all PCL commands from database creation to present-concatenated session files. EXTREMELY useful for rebuilding a database
model_name.out
Neutral file
Created using Export. Can be used as a backup for analysis model
model_name.db_m
Marker file
Created when NFS access method is invoked. Contains absolute pathname
CAD_partfile_name.exp.bxp
Express Neutral file
Intermediate file created during CAD model access. The .exp(text) file can be accessed on any platform.
PAT318, Section 15, March 2002
S15-3
REVERTING YOUR DATABASE
n
n
Reverting to original database allows you to eliminate the changes you have made in the current modeling session Reverting to original database occurs if “revert_enabled” is set to “TRUE” in the setting.pcl file u u
Edit file manually Or set Enable Revert Operation to on, then, close the database
PAT318, Section 15, March 2002
S15-4
REBUILDING A DATABASE Using a Journal File
n n n n
Run MSC.Patran, but, do not open a database Select “Rebuild” from File/Utilities Select a journal file of choice Apply
PAT318, Section 15, March 2002
S15-5
MSC.PATRAN FILES Generating Hardcopy Plots
n
Choice of printing single or multiple viewports or XY windows on a single page Supported drivers are:
q
CGM
q
HPGL
q
HPGL/2
q
Patran Hard
q
PS
q
EPS
n
PAT318, Section 15, March 2002
S15-6
MSC.PATRAN FILES (CONTINUED) Customization Files n
Add printers by editing the p3_printers.def file u u
u
n
p3_printers.def file is located in the $P3_HOME directory Customize printer options by copying the p3_printers.def file to your local or home directory The p3 search path is .,~, $P3_HOME
Quickpick.def and toolbar.def files are available to customize
PAT318, Section 15, March 2002
S15-7
MSC.PATRAN FILES (CONTINUED) Advanced Start-up Files Name
Edit
Location
Comments
settings.pcl
ASCII edit with System Editor
Working directories, home, or P3_HOME
Settings for MSC.Patran variables (hardware or software Imaging, automatic refresh of viewports, plotter parameters, options for warning messages, etc.)
p3epilog.pcl p3prolog.pcl
ASCII edit with system Editor
Working directories, home, or P3_HOME
PCL files read at MSC.Patran start-up are used to pre-define PCL variables, precompile PCL functions, and create user-defined or customized widgets
template.db
Binary edit within MSC.Patran
P3_HOME (default)
A “pristine” database that is copied when a new database is created. Can be preloaded with desired settings, selections, data, etc.
PAT318, Section 15, March 2002
S15-8
MSC.PATRAN FILES (CONCLUDED) n n
Can change which template is copied to be new database By default, MSC.Patran looks in the P3_HOME directory, e.g. /MSC/patran3
Select Change Template bottom
PAT318, Section 15, March 2002
Allows you to select a different template database
S15-9
PAT318, Section 15, March 2002
S15-10
SECTION 16 STRESS-LIFE (S-N) THEORY
PAT318, Chapter 16, March 2002
S16-1
PAT318, Chapter 16, March 2002
S16-2
Stress-Life (S-N) Theory
n
The S-N approach estimates total life without distinguishing crack initiation from crack propagation
n
It usually requires that the test data relate to the geometry of the structure under assessment (structure S-N curves)
n
Material S-N curves can also be generated from smooth specimen test data; they are subsequently modified to reflect the effects of notches, surface conditions, etc. of the real structure
PAT318, Chapter 16, March 2002
S16-3
Some Definitions
PAT318, Chapter 16, March 2002
S16-4
S-N Analysis
n n
n
n
Input is cycles of STRESS Also known as “High Cycle Fatigue” or “Nominal Stress Approach” Nominal stress cycles must be elastic (hence high cycle) though local stresses at the critical location will be plastic In MSC.Fatigue SN analysis, elastic FE results are used directly (no plasticity correction)
Actual Stress at Critical location Measured nominal stresses
PAT318, Chapter 16, March 2002
S16-5
S-N Curve
PAT318, Chapter 16, March 2002
S16-6
Wohler’s Railway Component Test Rig (1852 to 1870) PAT318, Chapter 16, March 2002
S16-7
S tres s Amplitude
Unnotched S haft
Notched S haft
Log (fatigue life)
Some of Wohler’s data for rotating bending tests PAT318, Chapter 16, March 2002
S16-8
S-N Approach
n
The S-N approach uses the (assumed elastic) nominal stress range (S) as a measure of the severity of fatigue loading
n
Life to failure (two pieces) is recorded in experiments
n
Tests at several levels of stress range characterise the S-N curve
n
Such a curve can be derived for smooth specimens, for individual components, for sub-assemblies, or for complete structures
PAT318, Chapter 16, March 2002
S16-9
S-N Approach
• The uses of the S-N approach include: • establishing a well defined fatigue curve for the • • • •
purposes of design determination of a fatigue strength at a specified life demonstration of improved fatigue resistance from a material or surface treatment acceptance of material for manufacturing purposes answering questions posed by a service failure
PAT318, Chapter 16, March 2002
S16-10
S-N Curves
PAT318, Chapter 16, March 2002
S16-11
S-N Curves
n
Steels tested with constant amplitude loading normally exhibit a fatigue limit - a stress below which no fatigue damage appears to occur.
n
The fatigue limit is associated with the difficulty a crack has in getting past the first grain boundary, or dominant microstructural barrier. It can be reduced or eliminated after e.g. a few large loads, or in corrosive environment, etc.
n
Aluminum alloys do not seem to exhibit no such limit
PAT318, Chapter 16, March 2002
S16-12
Material S-N Curves Log(Stress)
Steel or Ti
Al alloy or steel in seawater
PAT318, Chapter 16, March 2002
S16-13
Log(Life)
Scatter in S-N curves
PAT318, Chapter 16, March 2002
S16-14
Component S-N curves
n
For some components or features, especially structural joints such as welds, there are so many things modifying the behaviour of the base material that there is little point in applying corrections to a material S-N curve
n
In cases like this it is best to use a nominal stress-life curve which applies particularly to that component or feature
PAT318, Chapter 16, March 2002
S16-15
Component S-N Curves may use remote or nominal stress
_ Nominal Stress P A
A
P
P
CLASS F WELD DETAIL (BS7608) PAT318, Chapter 16, March 2002
S16-16
Stress ran ge ( σ 0 ) log scale
BS7608 Weld S-N Curves Static Limitations
1
constant amplitude loading in clean air Effective curve obtained under variable amplitude
m
loading, equivalent to changing slope of sr - N curve above N = 10
( σ0 )
1 m+2
1 1
7
10 Endurance N (cycles) - log scale
PAT318, Chapter 16, March 2002
S16-17
S-N Method - Similitude
σ nom
σ nom The life of this . . . . . . . . . . . . . . . . is the same as the life of this . . . . . if both are subject to the same nominal stress PAT318, Chapter 16, March 2002
S16-18
S-N Method - Similitude
n
n
The S-N method assumes that the life of a component or structure is the same as that of a laboratory test specimen if both are subject to the same nominal stresses. If the conditions in the test are different to those in the structure, similitude breaks down, and we need to make corrections for factors such as mean stress, environment, surface finish, etc.
PAT318, Chapter 16, March 2002
S16-19
Variable Amplitude Loads - Miner’s Rule and Rainflow Counting
PAT318, Chapter 16, March 2002
S16-20
Miner’s Rule - Block Loading Miner’s rule assigns a “damage” of 1/Nf to each cycle where Nf is the number of cycles to failure at that load level (determined from an S-N curve) Failure is predicted to occur when the total damage reaches a value of 1. If total damage D < 1 life is predicted to be 1/D repeats
PAT318, Chapter 16, March 2002
S16-21
Damage Counting with Miner 300 Cycles
Material Life Curve
S
M ea n
60000
Range
Damage = å
10
0M Pa
100 MPa
i
Ni Nf
∴ Accumulate d damage = PAT318, Chapter 16, March 2002
S16-22
300 = 0 .5 % Life 60000
N
Palmgren–Miner Damage Summation Law
PAT318, Chapter 16, March 2002
S16-23
Stress Amplitude (log scale)
Effect of Miner’s rule on S-N curve Original S-N Curve S-N Curve after Application of Stress for n 1 Cycles
S1
n1
N1
N1
Cycles to Failure (log scale)
PAT318, Chapter 16, March 2002
S16-24
S1
Advantages & Disadvantages of the Linear (Miner) Damage Theory Advantages: 1. Simple 2. Generally falls within the ball park of tests e.g.
Σ( ni ⁄ Nfi ) varies between 0.61 to 1.45 - Mean is 1.0
Disadvantage: Assumes that the level of stress has no effect on the damage ratio, for example: tests do indicate that high stress cycles followed by low stress cycles cause more damage than the other way around. PAT318, Chapter 16, March 2002
S16-25
Non-Linear Damage Theory p
Advantages: - D = (nf/Nfi) takes into account both sequence & load level effects. -if p is known well experiments evidence suggests we get somewhat better results. Disadvantages: - p has to be determined experimentally from a family of stress curves of a given material and so is very difficult to obtain. -for most situations load histories are pseudorandom, i.e. we don’t know load history. -finding p is difficult-need many tests at different stress levels.
Conclusion: Nonlinear theory does not buy us much and is difficult to use. Consequently it is not used in practice, and therefore is not in MSC.Fatigue.
PAT318, Chapter 16, March 2002
S16-26
Variable Amplitude Loads - Estimating Lifetime -
PAT318, Chapter 16, March 2002
S16-27
What Drives the Fatigue Crack?
Stress or Strain
Stress or Strain
• Stress or Strain Cycles:
Time
Time
Time History
Peak Valley Extraction
• Require Cycle Range & Mean PAT318, Chapter 16, March 2002
S16-28
Rainflow Cycle Counting
Rainflow Cycle Counting
PAT318, Chapter 16, March 2002
S16-29
Rainflow Cycle Counting
n
n
The story goes Matsuishi and Endo got the idea for the method while watching rain water cascading down a pagoda roof. Basic rules: rain flows down from each turning point and continues until either: u u
n
it is interrupted by flow from above, or it reaches a turning point which is larger that the one it started from and in the same sense
Good way of representing cycles is Rainflow Cycle Count Matrix
PAT318, Chapter 16, March 2002
S16-30
Cycle Count Matrix
PAT318, Chapter 16, March 2002
S16-31
Rainflow Counting and Stress/Strain Space
PAT318, Chapter 16, March 2002
S16-32
Rainflow Counting and Stress/Strain Space n
n
n
Materials under cyclic loading exhibit “material memory” effect (they “remember” the largest previously reached stress-strain state) What is stress-strain curve in monotonic loading is hysteresis loop in cyclic loading Rainflow counting identifies closed hysteresis loops as cycles u
Some cycles stand within the largest hysteresis loop and some hang; this depends on cycle sequence
PAT318, Chapter 16, March 2002
S16-33
Damage Counting with Miner 300 Cycles
Material Life Curve
S
M ea n
60000
Range
Damage = å
10
0M Pa
100 MPa
i
Ni Nf
∴ Accumulate d damage = PAT318, Chapter 16, March 2002
S16-34
300 = 0 .5 % Life 60000
N
Analysis Route - An Overview Time History
Information
Stress or Strain
Stress or Strain
Loose Frequency Information
Peak Valley Rainflow Cycle Extraction Loose Sequence Counting
Time
Time
S
LIFE
100 MPa
60000
Life
Damage Histogram
PAT318, Chapter 16, March 2002
S16-35
N
Damage Counting
Influences on Fatigue Life
PAT318, Chapter 16, March 2002
S16-36
Factors Influencing Fatigue Life •Mean stress
PAT318, Chapter 16, March 2002
S16-37
Mean Stresses
PAT318, Chapter 16, March 2002
S16-38
Mean Stresses
n n n
n
Stress ratio: R = σmin/σ σmax Most fatigue tests are conducted at R = -1 (fully reversed loading). If we have cycles with other R values we should make corrections to the stress range in order to be able to compare the cycles to the S-N curve determined at R=-1. Note: compressive mean stresses do not influence fatigue life.
PAT318, Chapter 16, March 2002
S16-39
Mean Stress Corrections
PAT318, Chapter 16, March 2002
S16-40
Mean Stress Corrections Unsafe
Un-Safe Safe
Un-Safe
Haigh Diagram PAT318, Chapter 16, March 2002
S16-41
Mean Stress Corrections
n
Most popular mean stress corrections are Goodman and Gerber methods.
n
Real test data tend to lie between the two, with the Goodman method being more conservative (i.e. safer).
PAT318, Chapter 16, March 2002
S16-42
Correcting for the Effect of Mean Stress σa σm + =1 Se Su n
Goodman method
n
Gerber method
2
σa æ σm ö +ç ÷ =1 Se è Su ø
σ a = stress amplitude σ m = mean stress S u = ultimate tensile stress S e = equivalent stress for σ m = 0 PAT318, Chapter 16, March 2002
S16-43
Mean Stress Corrections
Haigh Diagram PAT318, Chapter 16, March 2002
S16-44
Factors Influencing Fatigue Life • Mean stress • Component size
PAT318, Chapter 16, March 2002
S16-45
Component Size Small laboratory specimens and large engineering structures Influence of Specimen Size on Endurance Limit:
PAT318, Chapter 16, March 2002
S16-46
Component Size The endurance limit used for design (Se) can be calculated from the experimental endurance limit (S’e) from any size specimen: Se=S’e Csize
PAT318, Chapter 16, March 2002
S16-47
Factors Influencing Fatigue Life • Mean stress • Component size • Type of loading
PAT318, Chapter 16, March 2002
S16-48
Type of Loading Problem: • Data from rotating bend tests • Structure sees tension or torsion
PAT318, Chapter 16, March 2002
S16-49
Factors Influencing Fatigue Life • Mean stress • Component size • Type of loading • Notches and discontinuities
PAT318, Chapter 16, March 2002
S16-50
Notches
PAT318, Chapter 16, March 2002
S16-51
Notches
n
n
n
Another factor that will reduce the life of a component is a notch or stress concentration. Usually, unless the metal is of very high strength, the fatigue limit of the component is not reduced by as much as you might expect from the Kt factor. The difference between Kt and Kf is due to the notch sensitivity of the material, which is greatest for high strength metals.
PAT318, Chapter 16, March 2002
S16-52
Dealing with Stress Concentrations
n
n
It is seldom possible to stick the strain gauges at the critical location. In practice put the strain gauges close to the critical location and use a stress correction factor ‘ Kt’ to scale them up to the critical value.
Actual Stress at Critical location σ = S . Kt Measured nominal stress = S
PAT318, Chapter 16, March 2002
S16-53
Two Ways of Using Kt (SN Analysis) Modify the time history
n
n
Modify the Fatigue Life Curve
Calculate new time history by multiplying the original by Kt. This appears the easiest but could take a long time to compute with large time history files.
n
n
n
n
PAT318, Chapter 16, March 2002
S16-54
Reduce the fatigue life curve. This uses a value called the fatigue reduction factor Kf. Kf is a function of Kt and a material’s susceptibility to notches. Conservatively take Kf = Kt
Effect of Stress Concentration in Fatigue In fatigue, the effect of a stress concentrating notch is to reduce the fatigue stress at a given life. This is defined as the “Fatigue Strength Reduction Factor” and is given the symbol Kf . Strictly, Kf can only be obtained from long life fatigue tests and is a ratio: Kf
Un-notched fatigue strength = ------------------------------------------Fatigue strength for the notch
It is dependant on material as well as local geometry and is generally less than Kt .
PAT318, Chapter 16, March 2002
S16-55
Relationship between Kf and Kt Kt depends on geometry only and is relatively easy to obtain but Kf depends on material as well, and in theory, should be measured for all possible combinations of both. Can we derive Kf from Kt ? First, we define the parameter, q, the notch sensitivity factor as:
q
= (Kf - 1) / (Kt - 1)
For notch insensitive materials, Kf =1 and q=0. For perfectly notch sensitive materials Kf = Kt and q=1.
PAT318, Chapter 16, March 2002
S16-56
Relationship between Kf and Kt EMPIRICALLY, it has been found that: q=1/(1+a/r) where r is notch root radius and “a” is a function of material UTS: a = 0.0254 ( 2079 / UTS ) 1.8 MPa & mm units Combining gives an EMPIRICAL rule for Kf from Kt: Kf = 1 + ( Kt - 1 ) / ( 1 + a / r )
PAT318, Chapter 16, March 2002
S16-57
The Effect of Kt and Kf on Fatigue Life Cross Plot of Data : KFEFFECT NOTCHED
UNNOTCHED
1000 800 600
SMOOTH
Amplitude(MPa)
400
200
Kt=3, Kf=2.67
1E3
1E4
1E5
1E6 Life(Cycles)
PAT318, Chapter 16, March 2002
S16-58
1E7
1E8
The Effect of Kt and Kf on Fatigue Life
n
n
The notch does not have such a large effect at short lives as it does at long. This is often dealt with by having a separate Kf’ factor at 1000 cycles.
PAT318, Chapter 16, March 2002
S16-59
Effect of Notch Factor Transition Life
1000 cycles
Kf’ Stress
unn
otc hed
no tch ed
Kf
Life
PAT318, Chapter 16, March 2002
S16-60
Curve for Estimation of Kf’ (From Juvinall)
PAT318, Chapter 16, March 2002
S16-61
Factors Influencing Fatigue Life • Mean stress • Component size • Type of loading • Notches and discontinuities • Surface treatment & finish
PAT318, Chapter 16, March 2002
S16-62
Surface Treatment & Finish
n
Fatigue cracks usually start at the surface, therefore the condition of the surface can have a large impact on the life of a component.
n
The smoother the surface, the longer it takes to initiate a fatigue crack.
n
Residual stresses in the surface can also affect the rate of initiation. Residual compression will delay the crack initiation in high cycle load cases. Surface treatments are used to induce residual surface stresses.
PAT318, Chapter 16, March 2002
S16-63
Dealing with Surface Effects ε /S
Increasing residual pre-compression at the surface rises and tilts the Fatigue life curve as shown. The greatest benefits are realised in the high cycle, low stress ranges. Reducing surface quality causes the life curve to pitch downwards in a similar manner.
107 Cycles
1000 Cycles
PAT318, Chapter 16, March 2002
S16-64
N
Surface Finish
Note: the curves are for steels only. PAT318, Chapter 16, March 2002
S16-65
Surface Finish
n
The effect of surface finish is typically obtained from curves such as on the previous slide. •
•
n
The strength reduction factor is related to the surface finish factor and the strength of the steel. Sometimes the curves are for qualitative finishes such as “good machined”.
The effect of surface roughness is typically accounted for by applying a reduction factor to the stress at the endurance or fatigue limit. •
On a log-log plot, the slope of the stress life curve is adjusted, with the stress at 1000 cycles being unaffected.
PAT318, Chapter 16, March 2002
S16-66
Correction for Surface Finish Transition Life
1000 cycles
pol ish
Stress
ed
ro ug h
Life
PAT318, Chapter 16, March 2002
S16-67
The Effect of Residual Compression
Compression
Tension
Compression
Tension
+ Surface Compression Stress
Compression
= Oscillating bending Stress
This effect only works for high cycle cases where the applied surface stress is insufficient to overcome the residual pre-compression. PAT318, Chapter 16, March 2002
Tension
S16-68
Resulting surface stress never goes into tension therefore surface crack doesn’t initiate
How Can We Get Pre-Compression?
n
Shot Peening u
n
Cold Rolling u
n
Fire ball bearings at the surface to induce precompression Roll the component surface to induce precompression in the surface
Nitriding u
Heat up component in an ammonia environment. The component expands and Nitrates from the gas react with the metal. The component contracts on cooling and is compressed.
PAT318, Chapter 16, March 2002
S16-69
Stress-Life in MSC.Fatigue n
Features u u u
S-N Data Plot MANTEN_SN SRI1: 3162
b1: -0.2
b2: 0
E: 2.034E5
u
UTS: 600
u
Stress Range (MPa)
1E4
u 1E3
u u
1E2
u u 1E1 1E0
1E1
1E2
1E3
1E4
1E5
Life (Cycles)
PAT318, Chapter 16, March 2002
1E6
1E7
1E8
1E9
u
Elastic Stresses Rainflow Cycle Counting Mean Stress Correction Welded Structures Statistical Confidence Parameters Palmgren-Miner Linear Damage User Defined Life Material and Component S-N Surface Conditions Factor of Safety Analysis Biaxiality Indicators
S16-70
Goodman Based Factor of Safety (f) σa × f σm -------------- + -------- = 1 S σ e u
× σa = Se ( 1 – σm ⁄ σ u ) ∴
Se f = --- ( 1 – σ a
= Endurance Limit ;
e
σ m ⁄ σu )
σ=u Ultimate stress
The factor by which we can increase our alternating stress (for a given mean stress), without causing any fatigue failure.
PAT318, Chapter 16, March 2002
S16-71
Goodman Based Factor of Safety (f) Calculation Goodman Based: Factor of Safety =
Gerber Based: Factor of Safety =
PAT318, Chapter 16, March 2002
e ( 1 – σm ⁄ σ u ) CSurf × C Size -------------------------------------- × ------------------------------------k σ f a
1⁄2 æ1 – ( σ ⁄ σ ) 2 ö CSurf × C Size m u ø eè --------------------------------------------------------- × ------------------------------------kf σa
S16-72
Summary Total Life Method •
Estimates the total fatigue life to catastrophic failure. Makes no distinction between crack initiation and crack growth.
•
Uses local or nominal stress as the control parameter
•
Fatigue life computed from the log stress vs. log cycles (S-N) curve.
•
Fatigue life estimates are associated with a probability of failure due to the large amount of scatter in the S-N curve.
•
Reduces complex random waveforms to a list of cycles with a given range and mean using Rainflow cycle counting
•
PAT318, Chapter 16, March 2002
S16-73
Summary Total Life Method (Contd) S-N method is appropriate for assessing damage in: • Long life fatigue problems where there is little plasticity since the S-N method is based on nominal elastic stress • Components where the crack initiation and growth models are not appropriate, e.g. composites and welds. • Situations where a large amount of preexistent S-N data is available • Components which are required by a control body to be designed for fatigue using standard data such as the MIL handbook data • Mean stress effects are taken into account by Goodman or Gerber algorithms.
PAT318, Chapter 16, March 2002
S16-74
Example Problem: S-N Analysis of a Keyhole Specimen Perform simple S-N analysis. Single load input (fully reversed loading).
PAT318, Chapter 16, March 2002
S16-75
Loading Info Setup
PAT318, Chapter 16, March 2002
S16-76
PAT318, Chapter 16, March 2002
S16-77
Plot Simple Loading
PAT318, Chapter 16, March 2002
S16-78
Select the Created Loading
PAT318, Chapter 16, March 2002
S16-79
Material Info Setup
PAT318, Chapter 16, March 2002
S16-80
Submit Job Read Results Display Life Contours
PAT318, Chapter 16, March 2002
S16-81
Exercise •
Perform Quick Start Guide Chapter 3 Exercise, “A Simple S-N Analysis.”
•
Perform Quickstart Guide Chapter 12 Exercise, “Miscellaneous Features.”
•
Be sure to ask for help if there’s anything you don’t understand
PAT318, Chapter 16, March 2002
S16-82
SECTION 17 STRAIN-LIFE (EN) THEORY
PAT318, Section 17, March 2002
S17-1
PAT318, Section 17, March 2002
S17-2
STRAIN-LIFE (EN) THEORY n
n
Strain-life method is one of the most common life prediction methods used in the automotive industry. It is also called the local strain approach, the crack initiation method, and the strain-life approach.
PAT318, Section 17, March 2002
S17-3
STRAIN-LIFE (EN) THEORY n
n
n
Practically, crack initiation means that a crack of around 1-2 mm has developed. This is often a high proportion of the component life. Many automotive components are designed to survive some significant plastic strains in use (especially on the test track!). The E-N method will handle these better than the S-N method which basically ignores plasticity. The E-N method is not very suitable for structural joints such as welds, spot welds etc.
PAT318, Section 17, March 2002
S17-4
CRACK INITIATION (STRAIN - LIFE) METHOD SIMILITUDE
e
e
The crack initiation life here . . . . . is the same as it is here . . . . . if both experience the same local strains
PAT318, Section 17, March 2002
S17-5
STRAIN - LIFE METHOD
PAT318, Section 17, March 2002
S17-6
STRAIN LIFE CURVE Note: area enclosed represents the amount of plastic strain
PAT318, Section 17, March 2002
S17-7
STRAIN LIFE TESTING n
n
Normally, polished cylindrical specimens of around 6-8 mm diameter are tested according to the appropriate standards, though flat coupons may also be used. The tests are carried out in strain control; the test machine uses the output from the strain gauge (clip gauge) to provide feedback to the servo-controlled test machine.
PAT318, Section 17, March 2002
S17-8
STRAIN CONTROLLED TESTING n
n n n
n
n
Test carried out to ASTM E606 or equivalent High quality test specimen Polished surface Precision machined for minimum surface residual stress Strain monitoring using high quality clip gauge Alignment very important
PAT318, Section 17, March 2002
S17-9
E-N ANALYSIS Input is time history of STRAIN Also known as “Low Cycle Fatigue” or “Local Strain Approach” Local strains can be elastic or plastic hence its suitability for Low Cycle fatigue
ε
Plastic (Low Cycle Fatigue Line)
Elastic (High Cycle Fatigue Line)
N PAT318, Section 17, March 2002
S17-10
THE S-N AND E-N LIFE CURVES Low Cycle Region (EN Method)
High Cycle Region (SN or EN Method)
E-N Life Curve 'Infinite Life'
S-N Life Curve
ε/S S-N & E-N curves coincide in high cycle region because nominal stresses will be linear elastic
1000 Cycles
PAT318, Section 17, March 2002
10 7 Cycles
S17-11
N
E-N can also be used in low cycle region. S-N cannot, because linear stress-strain relationship is invalid
MATERIALS CHARACTERIZATION
PAT318, Section 17, March 2002
S17-12
Stress
STRESS-STRAIN RESPONSE
Strain
PAT318, Section 17, March 2002
S17-13
Stress
REVERSING THE LOADING DIRECTION
Strain
PAT318, Section 17, March 2002
S17-14
Stress
REVERSING THE LOADING DIRECTION AGAIN
Strain Material Memory
PAT318, Section 17, March 2002
S17-15
THE BAUSCHINGER EFFECT
Masing: stress strain curve = twice the cyclic stress strain curve
PAT318, Section 17, March 2002
S17-16
CYCLIC STRESS STRAIN BEHAVIOUR n
n
The Bauschinger effect: the yield stress in reversed loading is not as large as the initial stress in absolute value. Masing’s hypothesis: the hysteresis curve is the same shape as the cyclic stressstrain curve, but doubled up in both directions.
PAT318, Section 17, March 2002
S17-17
MASING’S HYPOTHESIS (STABILIZED HYSTERESIS LOOP)
PAT318, Section 17, March 2002
S17-18
MASING’S HYPOTHESIS (STABILISED HYSTERESIS LOOP)
PAT318, Section 17, March 2002
S17-19
STRAIN CONTROL VS. STRESS CONTROL n n
n
n
n
Strain Control actually uses an extensometer in the servo loop. Stress Control is actually load control. Strain Control controls plastic strain, the parameter which directly controls fatigue damage. Stress Control controls the wrong parameter. Local Stress and Strain are only “equivalent”, i.e. linearly related, under purely elastic conditions i.e. when there shouldn’t be any fatigue damage.
PAT318, Section 17, March 2002
S17-20
CYCLIC SOFTENING strain(mm/mm)
STRAIN.DAC
SOFT.DAC stress MPa
5E-3
0
Time range : 0 secs to 435 secs
800 -5E-3
1
600 0
100
200
300
3
400
Se c s .
stress(MPa)
5 7 9
400
CONTROL PARAMETER SOFT.DAC
200
600 400
0 200 0
-200
-200
-400
-400 0
100
200
300
8 6 4 2
400
Se c s .
-600 -0.01
RESPONSE PARAMETER Screen 1
-5E-3
0
5E-3
strain (mm/mm)
Note: Hysteresis loops normally stabilize after some number of cycles
PAT318, Section 17, March 2002
S17-21
0.01 Screen 1
CYCLIC HARDENING strain(mm/mm)
STRAIN.DAC
HARD.DAC stress MPa
5E-3
0
Time range : 0 secs to 435 secs
800 -5E-3
0
100
200
300
7,9 5 3
400
1
400
Se c s .
CONTROL PARAMETER stress(MPa)
600
HARD.DAC 200
600 1
400
5
3
9
7
0
200 0
-200
-200 4
-400
6
-400
8
0
2 4
2
100
200
300
400
Se c s .
-600
RESPONSE PARAMETER
6,8
-5E-3 Screen 1
0
5E-3
strain (mm/mm)
Note: Hysteresis loops normally stabilize after some number of cycles
PAT318, Section 17, March 2002
S17-22
0.01 Screen 1
CYCLIC STRESS-STRAIN CURVE DETERMINATION Companion samples are tested at various strain levels and cycled until the hysteresis loops become stabilized. Stable hysteresis loops are superimposed and the tips connected to form the cyclic stress-strain curve. This method is time consuming and requires many samples.
Companion Samples Method PAT318, Section 17, March 2002
S17-23
CYCLIC STRESS-STRAIN CURVE DETERMINATION This method has become widely accepted. It is very quick, and produces good results. One specimen is subjected to a series of blocks of gradually increasing and decreasing strain amplitude. After a few blocks (3 or 4) the material stabilizes and eventually, at around 20 blocks, it fails. The cyclic stress-strain curve is determined by connecting the tips of the hysteresis loops.
Incremental Step Test Method PAT318, Section 17, March 2002
S17-24
STRESS-STRAIN RELATIONSHIPS Monotonic
σ éσ ù ε = +ê ú E ëKû
Cyclic Stress-Strain Plot
1
n
σ a éσ a ù ε= +ê ú E ë K' û Ramberg-Osgood Relationships
PAT318, Section 17, March 2002
1
n'
Stress (MPa)
Cyclic
Strain (M/M)
nCode nSoft
S17-25
SEPARATION OF ELASTIC & PLASTIC STRAIN FROM THE STABLE HYSTERESIS LOOP Cross Plot of Data : 10
Total strain range
Stress(MPa)
200
Plastic strain range 0
-200
-4000
-2000
0 Strain(uE)
PAT318, Section 17, March 2002
S17-26
2000
4000
STRAIN LIFE RESULTS FROM A SERIES OF LCF TESTS Life Curve Display Total strain curve fit
Total strain data
Elastic strain curve fit
Elastic strain data
Plastic strain curve fit
Plastic strain data
1E0
Sf': 670 MPa b : -0.0582
L o g
S tr a in
1 E -1
(X/Y) Ef': 0.374 1 E -2
c : -0.54 E : 2.05E5 MPa (X/Y)
1 E -3
: Run-out pts
1 E -4 1E0
1E1
1E2
1E3
1E4
1E5
1E6
Log Life (Reversals)
PAT318, Section 17, March 2002
S17-27
1E7
1E8
STRAIN LIFE RESULTS FROM A SERIES OF LCF TESTS n
n
n
Basquin showed that for high cycle fatigue, fatigue life has a power law relationship with elastic strain. Coffin and Manson did the same for low cycle fatigue and plastic strain. Add the two together and you have a relationship between total strain and fatigue life covering low and high cycle fatigue.
PAT318, Section 17, March 2002
S17-28
COFFIN-MANSON-BASQUIN EQUATION ε tot = ε el + ε pl Coffin Manson
Basquin
ε el =
σ 'f E
ε pl = ε f (2Nf )
b
'
(2Nf )
εa =
PAT318, Section 17, March 2002
σ 'f E
b
c
(2Nf ) + εf (2Nf )
S17-29
'
c
STRAIN LIFE CURVE
The Transition Life, 2N , represents f the life at which the elastic and plastic curves intersect.
PAT318, Section 17, March 2002
S17-30
TRANSITION FATIGUE LIFE CALCULATION ∆εe 2
∆εp
=
The Transition Fatigue Life value is determined by equating the elastic and plastic components.
2
σ’f b c ' (2Nf ) = ε f (2Nf ) at Nf = Nt E 1
2Nt
=
PAT318, Section 17, March 2002
é ε fE ù êë K úû '
(b-c)
S17-31
STRAIN LIFE CURVE At shorter lives more plastic strain is present and the loop is wider. At longer lives the loop is narrower, representing less plastic strain
PAT318, Section 17, March 2002
S17-32
VARIABILITY IN MATERIAL BEHAVIOUR AND THE EFFECTS ON FATIGUE LIFE PREDICTION n n n n n
PAT318, Section 17, March 2002
Chemical composition Heat treatment Cast vs. wrought Surface treatments Degree of deformation
S17-33
VARIABLE AMPLITUDE LOADS - COUNTING CYCLES
PAT318, Section 17, March 2002
S17-34
RAINFLOW CYCLE COUNTING
PAT318, Section 17, March 2002
S17-35
RAINFLOW CYCLE COUNTING n
n
The story goes Matsuishi and Endo got the idea for the method while watching rain water cascading down a pagoda roof. Basic rules: rain flows down from each turning point and continues until either: u u
n
it is interrupted by flow from above, or it reaches a turning point which is larger that the one it started from and in the same sense
Good way of representing cycles is Rainflow Cycle Count Matrix
PAT318, Section 17, March 2002
S17-36
RAINFLOW CYCLE COUNT MATRIX
PAT318, Section 17, March 2002
S17-37
RAINFLOW COUNTING AND STRESS/STRAIN SPACE
PAT318, Section 17, March 2002
S17-38
RAINFLOW COUNTING AND STRESS/STRAIN SPACE n
n
n
Materials under cyclic loading exhibit “material memory” effect (they “remember” the largest previously reached stress-strain state) What is stress-strain curve in monotonic loading is hysteresis loop in cyclic loading Rainflow counting identifies closed hysteresis loops as cycles u
Some cycles stand within the largest hysteresis loop and some hang; this depends on cycle sequence
PAT318, Section 17, March 2002
S17-39
MEAN STRESS CORRECTIONS n
There are two main methods for correcting for mean stress in the local strain approach: u
u
Morrow it moves the elastic life line up and down according to the mean stress of each cycle Smith-WatsonTopper uses a damage parameter which includes the maximum stress of each cycle
PAT318, Section 17, March 2002
S17-40
MORROW CORRECTION
PAT318, Section 17, March 2002
S17-41
SMITH WATSON TOPPER CORRECTION
PAT318, Section 17, March 2002
S17-42
SWT VS MORROW n n n
SWT makes bigger corrections than Morrow SWT tends to be conservative (tension). SWT tends to be non-conservative (compression)
PAT318, Section 17, March 2002
S17-43
EXERCISE n
Perform Quick Start Guide Chapter 4 Exercise, “Rainflow Cycle Counting”
n
Perform Quick Start Guide Chapter 5 Exercise, “Component S-N Analysis”
n
Be sure to ask for help if there’s anything you don’t understand
PAT318, Section 17, March 2002
S17-44
ELASTIC-PLASTIC CORRECTION AND LOCAL GEOMETRY
PAT318, Section 17, March 2002
S17-45
STRAIN LIFE MODELLING The Local Strain Method requires the notch root local stresses and strains to model the plasticity that leads to fatigue damage. These can be derived by:
n
n n
Measurement from a strain gauge precisely located at the critical location. Elastic-plastic finite element analysis with a very refined mesh. Using an empirical rule, usually NEUBER’S RULE (but not always) to estimate elastic-plastic strain from nominal strain or Linear FE results.
Neuber worked in statics, not fatigue, but noticed that the ratios of plastic strain and plastic stress were different.
PAT318, Section 17, March 2002
S17-46
ELASTIC-PLASTIC CORRECTION Elastic FE Strain
1
Cyclic StressStrain Curve
2
σ
Neuber Equation Solution point
ε
∆εe
PAT318, Section 17, March 2002
∆σ∆ε=Ε∆εe2
S17-47
USE OF Kf IN STRAIN LIFE MODELLING The strain concentration factor, Kε = ε / e is > Kt and the stress concentration factor, Kσ = σ / s is < Kt after plastic yielding. Neither are known but Neuber found that their geometric average was equal to Kt . Hence Neuber’s Rule is simply: Kε . Kσ = ( Kt ) 2 Re-arrangement of this Rule gives a useful equation: ( Kt ) 2 s .e = σ . ε
PAT318, Section 17, March 2002
S17-48
USE OF Kf IN STRAIN LIFE MODELLING (Contd.) Another re-arrangement gives: ( Kt e ) 2 E = σ . ε in which the LHS is known. This can be solved with the cyclic stress strain curve equation simultaneously to derive σ and ε .
Topper simply replaced Kt by Kf to make Neuber’s Rule applicable in fatigue analysis for local stress strain tracking.
PAT318, Section 17, March 2002
S17-49
E-P CORRECTION INCLUDING Kf
CSSC
2 3
σ
Kf Neuber Equation Solution point s
1
e
ε PAT318, Section 17, March 2002
S17-50
REFINEMENTS TO THE NEUBER METHOD n
n
n
The Neuber Method is an approximation, suitable for stress and strain estimation where plasticity is limited, e.g. at notches. At locations where there is no well defined notch, it may underestimate the strains. The Seeger-Beste and Mertens-Dittmann methods use a shape factor or plastic strain concentration factor to modify the amount of the estimated stress redistribution
PAT318, Section 17, March 2002
S17-51
SHARP AND MILD NOTCHES Plastic Zone
σ
Neuber hyperbola
ε PAT318, Section 17, March 2002
S17-52
NEUBER METHOD - FORMULATION USED IN SOFTWARE Ramberg - Osgood Equation:
σe Cyclic Stress - strain
σ
σa æ σa ö εa = +ç ÷ Ε è Κ' ø
1
∆ ε ∆σ æ ∆ σ ö = +ç ÷ 2 2Ε è 2Κ ' ø
1
n'
Hysteresis curve
εe ε Neuber Formulation (assumes uniaxial stess-strain behaviour)
PAT318, Section 17, March 2002
S17-53
σ ε = εe2Ε
n'
SEEGER-BESTE METHOD AND MERTENSDITTMAN METHOD These methods take into account plasticity which is more extensive by moving the origin of the Neuber hyperbola to a point calculated using plastic strain concentration factors :
ε = ε
S17-54
e
/α
p
<
and
Lp αp = Ly PAT318, Section 17, March 2002
<
<
− σ )εe = (σ − σ )ε <
σ =σ e /α p
e
<
where :
<
(σ
e
<
Seeger-Beste Equation :
− σ )(ε e − ε )= (σ − σ )(ε − ε ) <
(σ
Mertens-Dittmann Equation :
MERTENS-DITTMAN METHOD Graphical representation of Mertens-Dittmann Method
σ =σ
e
/α
p
ε = ε
e
/α
p
<
σe
<
σ
new origin at (
<
ε
PAT318, Section 17, March 2002
εe
ε S17-55
<
ε ,σ <
<
σ
)
SEEGER-BESTE METHOD Graphical representation of Seeger-Beste Method
<
σe
σ = σ
e
/α
p
σ <
new origin at ( 0 , σ )
<
σ
εe PAT318, Section 17, March 2002
ε S17-56
SHAPE FACTORS (PLASTIC STRAIN CONCENTRATION FACTORS) Assuming elastic-perfectly plastic loading, the yield moment for a rectangular cross section bar in bending is: σy A
BA 2 My = σy 6
B
The plastic limit moment is :
σy BA 2 Mp = σy 4
So the shape factor αp = Mp/My = 1.5 PAT318, Section 17, March 2002
S17-57
SURFACE FACTORS As in the S-N method, surface factors can be used to modify the strain life curves to account for surface finish etc. These factors are applied to the elastic strain-life curve at the endurance limit. Polished, untreated, stress free, is considered as the starting point with Surface Factor = 1 (as in LCF test specimens).
n
Extra factors are required for: u u u u
surface finish (ground, machined, hot rolled, cast, forged, corroded); surface treatment (nitrided, shot peened, cold rolled): loading mode (axial, bending, torsion) anything else (environment etc.).
PAT318, Section 17, March 2002
S17-58
USE OF Kf FOR SURFACE FINISH Strain Life Plot EN24V Sf': 1282 b: -0.075 Ef': 1.424 c: -0.732 en24mod Sf': 1282 b: -0.1325 Ef': 1.424 c: -0.732
S t r a in
A m p lit u d e ( M /M )
1E0
1E-1
1E-2
Polished 1E-3
Forged 1E-4 1E0
PAT318, Section 17, March 2002
1E1
1E2
1E3
1E4 1E5 1E6 Life (Reversals)
S17-59
1E7
1E8
1E9
STRESS STRAIN TRACKING, NEUBER ANALYSIS, MATERIAL MEMORY AND DAMAGE CALCULATION
PAT318, Section 17, March 2002
S17-60
STRESS-STRAIN TRACKING & DAMAGE CALCULATION e(t)
P Nominal stress, strain - s,e
CSSC
SWT-Life
Cyclic Stress-Strain Plot
STW Life Plot
Mild_Steel n': 0.159 K': 816 E: 2E5
Mild_Steel Sf': 757 b: -0.089 Ef': 0.541 c: -0.547
0 0
0.01
0.03 Strain (M/M)
PAT318, Section 17, March 2002
P a ra m e te r
1E2
1E1
S T W
S tr e s s
( M P a )
(M P a )
564
1E-1
1E0
1E-2 1E0
P 1E1
1E2
1E3
1E4
1E5
1E6
1E7
1E8
Life (Reversals)
S17-61
1E9
Local stress, strain - s,e
STRESS-STRAIN TRACKING e(t) B
A
B = e1 , B
C
D = De3 , D
C = De2 E = De4
D
known Kf A
C E PAT318, Section 17, March 2002
S17-62
STRESS-STRAIN TRACKING - 1ST EXCURSION e(t) e1
s
B
Kf.e1 . Kf.s1 = NP1 B
A s 1 = E . e1 Kf.s1
CSSC ε = σ / E + (σ / k’)1/n’
PAT318, Section 17, March 2002
s1 A e1 Kf.e1 S17-63
ε1 . σ1 = NP1 plotting position is ε1, σ1
ε
STRESS-STRAIN TRACKING
Basic Rule: Reset the origin and set off in the right direction!
PAT318, Section 17, March 2002
S17-64
∆e2 B (ε1 , σ1 )
2nd Excursion e(t) B
σ
∆s2
C 2 x CSSC ∆ε = ∆σ / E + 2(∆σ / 2k’) 2 1/n’ ∆ε2 . ∆σ2 = NP2 plotting position is ε2 =(εε1- ∆ε2), σ1- ∆σ2) σ2=(σ PAT318, Section 17, March 2002
A
ε Kf. ∆e2 . Kf. ∆s2 = NP2
C (εε2 , σ2 )
S17-65
B (εε1 , σ1 )
3rd Excursion e(t)
D
σ
D (ε3 , σ3 )
C ∆ε3 . ∆σ3 = NP3 plotting position is ε3 =(εε2+ ∆ε3), σ2+ ∆σ3) σ3=(σ
PAT318, Section 17, March 2002
A (0,0)
C (εε2 , σ2 )
S17-66
ε
B
4th Excursion - Material Memory e(t) B
σ
D
C
E
plotting position is NOT ε4 =(εε3- ∆ε4), σ4=(σ σ3- ∆σ4) BUT ε4 =(εε2- ∆ε5), σ4=(σ σ2- ∆σ5)
PAT318, Section 17, March 2002
D
ε
A E C Not E
S17-67
Extracted Cycle
σ
σmax SWT = σmax . ∆ε/2
ε
∆ε PAT318, Section 17, March 2002
S17-68
Partial Damage for the Extracted Cycle STW Life Plot
(M P a )
Mild_Steel Sf': 757 b: -0.089 Ef': 0.541 c: -0.547
1E2
P a ra m e te r
SWT = σmax . ∆ε/2
1E1
S T W
SWT
1E-1
1E0
1E-2 1E0
d=1/ Nf
PAT318, Section 17, March 2002
S17-69
1E1
1E2
1E3
2Nf
1E4
1E5
Life (Reversals)
1E6
1E7
1E8
1E9
Damage Summation for All the Extracted Cycles n Damage for each cycle:
d i = 1 / N fi
n Damage sum for the “repeat”:
D = Σ di
n Life to crack initiation in “repeats”:
Ni = 1 /D
PAT318, Section 17, March 2002
S17-70
IMPLEMENTATION IN MSC.FATIGUE n
For each node or element: u u u u
u
u
True stress-strain tracking too time-consuming Rainflow cycle count elastic strain time history Correct each cycle for plasticity using Neuber (or similar) Calculate mean stress for each cycle for both ‘hanging’ and ‘standing’ within largest cycle Calculate damage for ‘hanging’ and ‘standing’ and record mean damage for each cycle Sum damage for all cycles to give total life
PAT318, Section 17, March 2002
S17-71
CRACK INITIATION IN MSC.FATIGUE n
e Strain
Features: u u u u u u u u u u
Based on Local Strain Concepts Mean Stress Correction Elastic-Plastic Conversion Statistical Confidence Parameters Palmgren-Miner Linear Damage User Defined Life Cyclic Stress-Strain Modeling Surface Conditions Factor of Safety Analysis Biaxiality Indicators
PAT318, Section 17, March 2002
S17-72
Time
1/2cycle 1/2cycle
1cycle
1cycle 1cycle 1/2cycle
s
e
EXAMPLE PROBLEM: E-N ANALYSIS OF A “SPIDER” Perform simple crack initiation analysis of a “spider”. Single input load. Create new database and read in the results.
PAT318, Section 17, March 2002
S17-73
REVIEW STRESS CONTOURS
PAT318, Section 17, March 2002
S17-74
FATIGUE ANALYSIS n n n
Reference single load (sine01) Create new group for analysis Submit Job
PAT318, Section 17, March 2002
S17-75
PLOT LIFE CONTOURS
PAT318, Section 17, March 2002
S17-76
EXERCISE n
Perform Quick Start Guide Chapter 6 Exercise, “A Simple E-N Analysis”
n
Perform Quick Start Guide Chapter 7 Exercise, “Residual Stress”
n
Be sure to ask for help if there’s anything you don’t understand
PAT318, Section 17, March 2002
S17-77
PAT318, Section 17, March 2002
S17-78
SECTION 18 MULTIAXIAL FATIGUE
PAT318, Section 18,March 2002
S18-1
PAT318, Section 18,March 2002
S18-2
WHY DO MULTIAXIAL FATIGUE CALCULATIONS? n
Fatigue analysis is an increasingly important part of the design and development process
n
Many components have multiaxial loads, and some of those have multiaxial loading in critical locations
n
Uniaxial methods may give poor answers needing bigger safety factors
PAT318, Section 18,March 2002
S18-3
THE LIFE PREDICTION PROCESS E - N APPROACH measured strains
plasticity modelling
stress and strain components elastic strains from FEA
PAT318, Section 18,March 2002
constitutive model and notch rule
S18-4
LIFE damage model
2-D STRESS STATE σyy τyx
σxx
y
τxy τyx
x
PAT318, Section 18,March 2002
τxy
σyy
S18-5
σxx
3-D STRESS STATE σyy σzz τyz
τyx τzx
σxx
y
σzz x
z
PAT318, Section 18,March 2002
τzy τxy
σyy
S18-6
τxz
σxx
TENSOR REPRESENTATION OF STRESS STATE n
n
n n
n
n
Stresses can be represented as tensor Diagonal terms are direct stresses Other terms are shear stresses For equilibrium purposes it must be symmetric On free surface (z is surface normal) all terms with “z” disappear. Can be written σij
PAT318, Section 18,March 2002
éσxx τ xy τ xz ù ê ú êτ yx σ yy τ yz ú êτzx τzy σzz ú ë û
S18-7
STRAIN TENSOR n
n
n
n
n
Strains can also be represented by tensors Diagonal terms are the direct strains and the other terms are shear strains For equilibrium the matrix is symmetric Shear strains, e.g. εxy are half the engineering shear strain γxy Can be written εij
PAT318, Section 18,March 2002
éεxx εxy εxz ù ê ú êε yx ε yy ε yz ú êεzx εzy εzz ú ë û
S18-8
TRANSFORMATION OF CO-ORDINATES Z Z’
Y’ Y
X X‘
PAT318, Section 18,March 2002
S18-9
STRESS TENSOR ROTATION n
n
n
~ S' = TST
Stress or strain tensors can be rotated to a different coordinate system by a transformation matrix. The matrix contains the direction cosines of the new co-ordinate axes in the old system The tensor is pre-multiplied by the matrix and post-multiplied by its transpose
PAT318, Section 18,March 2002
él11 ê T = êl21 êël31
l12 l22 l32
l13 ù ú l23 ú l33 úû
l11, l12, l13 are the direction cosines of the X’ axis in the original system and so on.
S18-10
PRINCIPAL STRESSES (AND STRAINS) n
n n
The principal stress axes are the set in which the diagonal terms disappear. In these directions the direct stresses reach their extreme values The maximum shear strains occur at 45 degrees to the principal axes. The principal stresses can be calculated from:
σ3 − I1σ 2 + I 2 σ − I3C = 0 where I1 = σ x + σ y + σ z I 2 = σ x σ y + σ y σ z + σ y σ z − τ2xy − τ2xz − τ2yz I3 = σ x σ y σ z + 2τ xy τ xz τ yz − σ x τ2yz − σ y τ2xz − σ z τ2xy
PAT318, Section 18,March 2002
S18-11
MOHR’S CIRCLE FOR STRESS (2D)
τxy σ2
−τxy τmax
σy
2θ
σx
τ
PAT318, Section 18,March 2002
S18-12
σ1 σ
MOHR’S CIRCLES FOR TRIAXIAL STRESS
σ3
τmax
σ2
τ
PAT318, Section 18,March 2002
S18-13
σ1 σ
GENERALIZED HOOKE’S LAW FOR 3-D σx v εx = − (σ y + σ z ) E E σy v εy = − (σ z + σ x ) E E σz v εz = − (σ x + σ y ) E E τ xy τ yz τ zx , γ yz = , γ zx = γ xy = G G G E where G = 2(1 + v ) PAT318, Section 18,March 2002
S18-14
GENERALIZED HOOKE’S LAW FOR 3-D vE E {ε xx + ε yy + ε zz } + σ xx = ε xx (1 + v )(1 − 2v ) 1+ v vE E {ε xx + ε yy + ε zz } + σ yy = ε yy (1 + v )(1 − 2v ) 1+ v vE E {ε xx + ε yy + ε zz } + σ zz = ε zz (1 + v )(1 − 2v ) 1+ v
PAT318, Section 18,March 2002
S18-15
FREE SURFACE STRESSES z
y x
Stress state on free surface is biaxial - principal stresses σ1 and σ2 (where | σ1 |>| σ2 |) lie in the x-y plane
PAT318, Section 18,March 2002
S18-16
MULTIAXIAL ASSESSMENT n
Ratio of Principals or Biaxiality Ratio: u
u u u
σ2 ae = σ1
Stress state can be characterised by ratio of principal stresses and their orientation (angle) If orientation and ratio are fixed, loading is proportional. Otherwise loading is non-proportional Biaxiality analysis: l l l
ae = -1: ae = +1: ae = 0:
PAT318, Section 18,March 2002
Pure Shear Equi-Biaxial Uni-axial
S18-17
EXAMPLE: NEAR PROPORTIONAL LOADING 1301
Strain(UE)
S131A.DAC
Sample = 409.6 Npts = 9446 Max Y = 1301 Min Y = -392.3 -392.3 0
2
4
6
8
10
12 Seconds
121.1
Strain(UE)
S131B.DAC
Sample = 409.6 Npts = 9446 Max Y = 121.1 Min Y = -284.3 -284.3 0
2
4
6
8
10
12 Seconds
2663
Strain(UE)
S131C.DAC
Sample = 409.6 Npts = 9446 Max Y = 2663 Min Y = -298.7 -298.7 0
2
4
6
8
10
12 Seconds
Screen 1
PAT318, Section 18,March 2002
S18-18
EXAMPLE: NEAR PROPORTIONAL LOADING S131.ABS Strain UE
S131.ABS Strain UE
Tim e range : 0 secs to 23.06 secs
Tim e range : 0 secs to 23.06 secs
5000
5000
4000
4000
3000
3000
2000
2000
1000
1000
0
0
-1000 -1
-0.5
0
0.5
Biaxiality Ratio (No units)
1
-1000 -50
Screen 1
Biaxiality ratio vs. σ1 PAT318, Section 18,March 2002
0
50
Angle (Degrees)
Orientation of σ1 vs. σ1 S18-19
Screen 1
EXAMPLE: NEAR PROPORTIONAL LOADING n
The left plot indicates that the ratio of the principal stresses is nearly fixed at around 0.4, especially if the smaller stresses are ignored.
n
The right hand plot shows that the orientation of the principal stresses is more or less fixed.
n
This is effectively a proportional loading (these calculation assume elasticity)
PAT318, Section 18,March 2002
S18-20
EXAMPLE: NON-PROPORTIONAL LOADING 161.4
GAGE 1X( uS)
GAGE103.DAC
Sample = 200 Npts = 3.672E4 Max Y = 161.4 Min Y = -81.32 -81.32 0
559.5
50
100
150
GAGE 1Z( uS)
GAGE102.DAC
Sample = 200 Npts = 3.672E4 Max Y = 559.5 Min Y = -274.6 -274.6 0
716.2
50
100
150
GAGE 1Y( uS)
GAGE101.DAC
Sample = 200 Npts = 3.672E4 Max Y = 716.2 Min Y = -651 -651 0
50
100
150
S creen 1
PAT318, Section 18,March 2002
S18-21
EXAMPLE: NON-PROPORTIONAL LOADING GAGE1.ABS Stress MPa
GAGE1.ABS Stress MPa
Time range : 0 secs to 183.6 secs
Time range : 0 secs to 183.6 secs
200
200
100
100
0
0
-100
-100
-200 -1
-200 -0.5
0
0.5
Biaxiality Ratio (No units)
1
-50
Screen 1
0 Angle (Degrees)
50 Screen 1
Both the ratio and orientation of σ1 and σ2 vary considerably: non-proportional loading. PAT318, Section 18,March 2002
S18-22
EFFECT OF MULTIAXIALITY ON PLASTICITY, NOTCH MODELLING AND DAMAGE MODELLING φp Uniaxial
φp constant
Proportional Multiaxial
φp constant
Non-Proportional Multiaxial
φp may vary
a a= 0 -1 < a < +1 a may vary
Increasing Difficulty (and Rarity) OK Need a Tricky Decreasing Confidence
PAT318, Section 18,March 2002
S18-23
EXERCISE n
Perform Quick Start Guide Chapter 11 Lesson,“ A Multiaxial Assessment” Sections 11.1 through 11.4 where you will assess whether or not the stress state is multiaxial.
n
Be sure to ask for help if there’s anything you don’t understand
PAT318, Section 18,March 2002
S18-24
DEVIATORIC STRESSES The deviatoric stresses Sx,y,z are given by:
A useful concept in multiaxial fatigue and especially in plasticity is that of deviatoric stresses. The deviatoric stresses are the components of stress that deviate from the hydrostatic stress.
S x = σ x − Ph S y = σ y − Ph S z = σ z − Ph
The hydrostatic stress Ph is an invariant:
The shear stresses are unchanged
1 Ph = (σ x + σ y + σ z ) 3
PAT318, Section 18,March 2002
S18-25
YIELD CRITERIA When the stress state is not uniaxial, a yield point is not sufficient. A multiaxial yield criterion is required. The most popular criterion is the von Mises yield criterion. All common yield theories assume that the hydrostatic stress has no effect, i.e. the yield criterion is a function of the deviatoric stresses. The von Mises criterion - based on distortion energy - can be expressed in terms of principal stresses:
(
S12
+
S 22
+
S 32
)=
3σ y2 2
or
1 2
(σ 1 − σ 2 ) + ( σ 2 − σ 3 ) + ( σ 3 − σ 1 ) = σ y 2
2
The Tresca Criterion can be expressed:
τ max
éσ1 − σ 2 σ 2 − σ 3 σ 3 − σ1 ù σ y = max ê , , ú= 2 2 2 2 êë úû
PAT318, Section 18,March 2002
S18-26
2
THE VON MISES YIELD CRITERION σ3
von Mises yield surface
hydrostatic stress
σ2 σ1
PAT318, Section 18,March 2002
S18-27
VON MISES AND TRESCA IN DEVIATORIC STRESS SPACE S1 von Mises Tresca 2 σy 3
S2
S3
PAT318, Section 18,March 2002
S18-28
VON MISES AND TRESCA IN PRINCIPALS σ2 von Mises Tresca
σ1
PAT318, Section 18,March 2002
S18-29
EQUIVALENT STRESS AND STRAIN METHODS
Extension of the use of yield criteria to fatigue under combined stresses
PAT318, Section 18,March 2002
S18-30
EQUIVALENT STRESS AND STRAIN METHODS n
They don’t account for the known fact that fatigue failure occurs in specifically oriented planes. Rather these approaches “average” the stresses/strains to obtain a failure criterion with no regard to the direction of crack initiation.
n
Tresca and von Mises are not sensitive to the hydrostatic stress or strain
n
They don’t account for mean stresses
n
They don’t really handle out-of-phase stresses or strains
PAT318, Section 18,March 2002
S18-31
SOME EQUIVALENT STRESS/STRAIN CRITERIA n
Maximum Principal Stress
σ 1 = σ eq
n
Maximum Principal Strain
ε 1 = ε eq
n
Maximum Shear Stress (Tresca Criterion)
σ eq σ1 − σ 3 = τ eq = 2 2
n
Shear Strain (Tresca)
n
von Mises stress
ε 1 − ε 3 γ max (1 + ν ) ε eq = = 2 2 2 1 2
n
n
von Mises strain
( σ 1 − σ 2 ) 2 + (σ 2 − σ 3 ) 2 + ( σ 3 − σ 1 ) 2
1 (1 + ν ) 2
(ε1 − ε 2 ) 2 + (ε 2 − ε 3 ) 2 + (ε 3 − ε1 ) 2 ν=
Note that n can be found from PAT318, Section 18,March 2002
S18-32
ν eε e + ν pε p εe + ε p
= σ eq
= ε eq
S-N WITH EQUIVALENT STRESS ∆σ = σ ′f (2 N 2
)
b
n
Basquin equation for uniaxial
n
Using (Abs) Max Principal
∆σ 1 = σ ′f (2 N f 2
n
Using Max Shear
σ ′f ∆ τ max (2 N = 2 2
n
Using von Mises
∆ σ VM = σ ′f (2 N 2
PAT318, Section 18,March 2002
S18-33
f
)
b
)
b
f
)
b
f
E-N WITH EQUIVALENT STRAIN n
n
n
n
σ 'f ∆ε = 2 E
Coffin-Manson-Basquin equation for uniaxial
τ 'f
PAT318, Section 18,March 2002
(
)
(
)
∆γ = 2N f 2 G
Adapted for Torsion
γ σ 1 = τ and ε 1 = , so 2
f
' ∆ε 1 σ f = 2N f 2 E
Using (Abs) Max Principal
But if we assume the principal stress/strain criterion
(2 N )
σ 'f ∆γ = 2N f 2 G
(
S18-34
)
b
+
b
2ε 'f
b
b
+ε
' f
(2 N ) f
+ ε 'f
(2 N )
+γ
(2 N )
(2 N ) f
' f
c
c
c
f
f
c
E-N WITH EQUIVALENT STRAIN (CONT.) n
Similarly, based on the Tresca criterion……
n
…and based on the von Mises Criterion
n
which is the same as...
PAT318, Section 18,March 2002
' ∆γ σ f (2 N f )b + (1 + ν p )ε 'f (2 N f )c = 2 2G
∆ γ (1 + ν e )σ 'f (2N f )b + (1 + ν p )ε 'f (2N f )c = 2 E
2 (1 + ν e )σ 'f ∆γ = 2N 2 3E
(
S18-35
f
)
b
+
3
ε 'f
(2 N ) f
c
THE NEED FOR A SIGN 250
Cylindrical notched specimen with axial sine loading
-250
maximum principal
Stress(MPa)
0
1
2
3 Seconds
250
-250
minimum principal
Stress(MPa)
0
1
2
3 Seconds
250
absolute maximum principal
Stress(MPa)
Tension
σ
-250
0
1
2
3 Seconds
250
von Mises stress
Stress(MPa)
τ -250
Compression
1
2
3 Seconds
250
σ
0
-250
maximum shear stress
Stress(MPa)
0
1
2
3 Seconds
Screen 1
τ PAT318, Section 18,March 2002
S18-36
TORSION STRAIN-LIFE COEFFICIENTS PREDICTED BY 3 EQUIVALENT STRAIN THEORIES (IN TERMS OF UNIAXIAL FATIGUE CONSTANTS) Torsional Strain-Life curve Coefficient
VonMises Stress/Strain
Max. Principal Stress/Strain
Max Shear Stress Strain
τ ′f
γ ′f
σ ′f 3
3 ⋅ ε ′f
σ ′f
2 ⋅ ε ′f
σ ′f 2
1 .5 ⋅ ε ′f
If you compare the results of these methods for axial and torsion there can be differences of up to a factor of 2 on stress and strain PAT318, Section 18,March 2002
S18-37
COMMENTS ON EQUIVALENT STRAIN METHODS n
They don’t account for the known fact that fatigue failure occurs in specifically oriented planes. Rather these approaches “average” the stresses/strains to obtain a failure criterion with no regard to the direction of crack initiation.
n
Tresca and von Mises are not sensitive to the hydrostatic stress or strain
n
They don’t account for mean stresses
n
They don’t really handle out-of-phase stresses or strains
PAT318, Section 18,March 2002
S18-38
FAILURE OF EQUIVALENT STRESS METHOD FOR OUT-OF-PHASE LOADING - AN EXAMPLE: n
Axial Stress:
n
Shear Stress:
n
Von Mises Stress:
σ x = σ sin ω t σ τ xy = cos ω t 3 1 = σ x 2 + σ x 2 + 6τ xy 2 2 = σ (No Alternating Stress)
(
)
= No Fatigue Damage? n
Signed Von Mises will predict damage, but it will underestimate the damage (non-conservative)
PAT318, Section 18,March 2002
S18-39
ASME PRESSURE VESSEL CODE n n
n n n n
This method is based on the concept of relative von Mises Strain equivalent to signed von Mises strain for proportional loadings The ASME pressure vessel code uses the equivalent strain parameter:
No path dependence Non-conservative for non-proportional loading No directionality Not sensitive to hydrostatic stress ìï 2 ∆ε eq = MAX ( wrt . time) í ïî 3
PAT318, Section 18,March 2002
(
∆ε11 − ∆ε 22
) ( 2
+ ∆ε 22 − ∆ε 33
S18-40
) ( 2
+ ∆ε 33 − ∆ε11
)
2
ü 2 2 2 ï + 6 ∆ε12 + ∆ε 23 + ∆ε 31 ý ïþ
(
)
SIMPLE METHODS FOR PROPORTIONAL LOADINGS -1
a~0
0
stress criterion
Absolute Maximum Principal
Absolute Maximum Principal
Absolute Maximum Principal
strain criterion
Absolute Maximum Principal
Any
Tresca
PAT318, Section 18,March 2002
S18-41
EFFECT OF MULTIAXIALITY ON PLASTICITY, NOTCH MODELLING AND DAMAGE MODELLING φp Uniaxial
OK
φp constant
Proportional Multiaxial Non-Proportional Multiaxial
a
φp constant
Increasing Difficulty (and Rarity)
a= 0 Need a -1 < a < +1 Tricky
φp may vary
a may vary Decreasing Confidence
PAT318, Section 18,March 2002
S18-42
NOTCH RULES FOR PROPORTIONAL LOADING n
When the loading is no longer uniaxial, the uniaxial stress strain curve is no longer enough on its own
n
Two methods which address this problem are the parameter modification method due to Klann, Tipton and Cordes, and the Hoffmann-Seeger method.
n
Both these methods extend the use of the von Mises criterion to post yield behaviour
n
Both methods assume fixed principal axes and fixed ratio of stresses or strains
PAT318, Section 18,March 2002
S18-43
PARAMETER MODIFICATION METHOD (KLANN-TIPTON-CORDES) The ratio ε2/ε1 of the principal strains is assumed to be constant in this case
First define cyclic stress-strain curve using the RambergOsgood formula :
σq æ σq ö εq = +ç ÷ Ε è Κ' ø
1
n'
Digitise the cyclic stress-strain curve and for each point calculate Poisson’s ratio from the equation :
Calculate the biaxiality ratio from :
ε2 + v' ε1 a= ε2 1 + v' ε1 PAT318, Section 18,March 2002
ö σq 1 æ1 v' = − ç − ve ÷ ø Eε q 2 è2 S18-44
PARAMETER MODIFICATION METHOD (KLANN-TIPTON-CORDES) CONT. It can be shown that the values of the principal strains and stresses can be calculated from:
ε1=εq σ 1 =σ q
Fit the following equation to the calculated modified parameters:
σ1 æσ1ö ε1 = * +ç *÷ èΚ ø Ε
1 − v' a 1− a + a 2
PAT318, Section 18,March 2002
n*
The modified modulus is calculated explicitly from:
1 1− a + a
1
E Ε = 1- ve a e *
2
S18-45
MODIFIED STRESS-STRAIN CURVE PARAMETERS ae = 1
σ1
ae = 0 ae = -1
ε1 PAT318, Section 18,March 2002
S18-46
HOFFMAN AND SEEGER METHOD Calculate Von Mises equivalent strain from combined strain parameter e.g. from: The Neuber correction is then carried out on this formulation :
σ q ε q = ε q,e
The effective Poisson’s ratio is calculated as for the Parameter Modification Method, as are: a, σ, ε1 and ε2/ ε1 PAT318, Section 18,March 2002
ε q,e = ε 1,e
1 − a e +a e 2 1 − a e ve
S18-47
2
HOFFMAN AND SEEGER METHOD CONT. The other required stresses and strains are calculated from:
ε2
æε2ö = ε 1ç ÷ èε1ø
ε3 = εq
v' (1 + a) 1- a + a 2
These can then be used to calculate any other combined parameter e.g. signed Tresca
PAT318, Section 18,March 2002
S18-48
σ2 = a σ1
EXTENDING NEUBER TO NON-PROPORTIONAL LOADINGS n
This topic is important because it permits non-proportional multiaxial fatigue life predictions to be made based on elastic FE
n
The aim is to predict an average sort of elastic-plastic stress-strain response from a pseudo-elastic stress or strain history
n
It is necessary to combine a multiaxial plasticity model with an incremental formulation of a notch correction procedure and to make some other assumptions
PAT318, Section 18,March 2002
S18-49
BUCZYNSKI-GLINKA NOTCH METHOD n
The Neuber method is only suitable for uniaxial or proportional loadings
n
Where the loading is non-proportional and the stress-strain response is path dependent it must be replaced by an incremental version
σε = σ eε e σ ije ∆ ε ije + ε ije ∆ σ ije = σ ijN ∆ ε ijN + ε ijN ∆ σ ijN
PAT318, Section 18,March 2002
S18-50
BUCZYNSKI-GLINKA METHOD n
This rule has to be combined with a multiaxial plasticity model such as the Mroz-Garud model
n
Additionally some assumptions are required, e.g. that the ratios of the increments of strains, stresses or total strain energy in certain directions are the same for the elastic as the elastic-plastic case. Glinka-Buczynski use total strain energy
n
One of these assumptions is necessary to be able to reach a solution of the equations
PAT318, Section 18,March 2002
S18-51
WHAT HAPPENS WHEN THE LOADING IS NOT UNIAXIAL? n
For proportional loadings a different cyclic stress - strain curve is required
n
For non-proportional loadings, a 1 dimensional cyclic plasticity model is no longer sufficient
n
Neuber’s rule does not work for non-proportional loadings
n
Uniaxial rainflow counting doesn’t work for non-proportional loadings
n
Simple combined stress-strain parameters do not predict damage well
PAT318, Section 18,March 2002
S18-52
DIRECTION OF CRACK GROWTH
PAT318, Section 18,March 2002
S18-53
DIRECTION OF CRACK GROWTH n
When the biaxiality ratio is negative (type A), the maximum shear plane where cracks tend to initiate is oriented as shown in the diagram. u
n
When the biaxiality is positive (type B), however, the cracks tend to be driven more through the thickness. u
n
In the early stages of initiation the type A cracks grow mainly along the surface in mode 2 (shear), before transitioning to Mode 1 normal to the maximum principal stress.
These are therefore more damaging for the same levels of shear strain.
Uniaxial loading is a special case.
PAT318, Section 18,March 2002
S18-54
MULTI-AXIAL FATIGUE THEORY n
Crack Initiation demonstrated to be due to: u
Slip occuring along planes of Maximum Shear, starting in grains most favorably oriented w.r.t. the Maximum Applied Shear stress
u
Stage I (Nucleation & Early growth) is confined to Shear Planes. Here both Shear and Normal Stress/ Strain control the crack growth rate.
u
Stage II crack growth occurs on planes oriented normal to the Max. Principal Stress. Here the magnitude of the Max. Principal stress and strain dominates crack growth.
PAT318, Section 18,March 2002
S18-55
MULTI-AXIAL FATIGUE THEORY (CONT.) n
Proportion of Life spent in Stage I, and II depend on: u u
Loading Mode and Amplitude Material Type (Ductile Vs. Brittle)
n
Crack Initiation Life Refers to the time taken to develop Engineering Size Crack, and Includes Stage I and Stage II.
n
Stage I or Stage II may dominate Life. In uniaxial, the Controlling Parameters in both Stages are directly related to the uniaxial stress or strain. But NOT so in Multi-axial case.
n n n
PAT318, Section 18,March 2002
S18-56
MULTI-AXIAL FATIGUE THEORY (CONT.) n
For non-proportional loading, the “Critical Planes” vary vary with time.
n
Cracks growing on a particular Plane may impede the progress of cracks growing on a different plane.
n
Multi-axial Fatigue Theory for Non-proportional Loading, MUST attempt, to a greater or lesser extent, to incorporate some of the above observations, to have any chance of success in real situations.
PAT318, Section 18,March 2002
S18-57
MSC.FATIGUE MULTI AXIAL ANALYSIS (b) Tension
(a) Torsion
σ1ε
γ
γ
γ n
σ1ε Shear Strain on the plane of maximum shear will extend the fatigue crack u
n
Amongst other things, progress will be opposed by the friction between the crack faces
The separation of the cracked faces due to the presence of the normal strains in case b, will eliminate friction. Consequently the crack tip experiences all the applied shear load. Hence this case is more damaging. PAT318, Section 18,March 2002
S18-58
MSC.FATIGUE MULTI AXIAL ANALYSIS n
Critical Plane Approach: u
(Recognizing that fatigue damage (crack) is directional) considers accumulation of damage on particular planes
u
Typically damage is considered at all possible planes say @ 15 deg. interval, and the worst (critical) plane selected.
u
Employs variations on the Brown-Miller Approach:
∆γ + ∆Σ n = C 2 u
Equivalent fatigue life results for equivalent values of the material constant, C
PAT318, Section 18,March 2002
S18-59
MSC.FATIGUE MULTI AXIAL ANALYSIS n
Four Planar Approaches: u u u u
n
Two complex Rainflow Counting Methods: u u
n
Normal Strain Smith-Watson-Topper-Bannantine Shear Strain Fatemi-Socie
Wang-Brown Wang-Brown with Mean Stress Correction
Dang-Van Total Life Factor of Safety Method
PAT318, Section 18,March 2002
S18-60
NORMAL STRAIN METHOD
n
A Critical Plane Approach u
u u
n
Calculates the Normal Strain Time History and Damage on 18 multiple planes, Fatigue Results reported on the worst plane Fatigue Damage Based on Normal Strain Range No mean Stress Correction
Used with Type ‘A’ Cracks:
PAT318, Section 18,March 2002
S18-61
SHEAR STRAIN METHOD
n
A Critical Plane Approach u
u u
n
Calculates the Shear Strain Time History and Damage on 36 multiple planes, Fatigue Results reported on the worst plane Fatigue Damage Based on Shear Strain Range No mean Stress Correction
Used with Type ‘B’ Cracks:
PAT318, Section 18,March 2002
S18-62
SMITH-TOPPER-WATSON-BANNANTINE METHOD
n
A Critical Plane Approach u
u u
n
Calculates the Normal Strain Time History and Damage on 18 multiple planes, Fatigue Results reported on the worst plane Fatigue Damage Based on Normal Strain Range Uses a Mean Stress Correction based on Maximum Normal Stress
Used with Type ‘A’ Cracks
PAT318, Section 18,March 2002
S18-63
FATEMI-SOCIE METHOD n
A Critical Plane Approach u
u u u
n
Calculates the Shear Strain Time History and Damage on 36 multiple planes, Fatigue Results reported on the worst plane Fatigue Damage Based on Shear Strain Range Uses a Mean Stress Correction based on Maximum Normal Stress Uses Material Constant ‘n’
Used with Type ‘B’ Cracks
PAT318, Section 18,March 2002
S18-64
CRITICAL PLANE DAMAGE MODELS n
n
n
n
∆ε n σ ′f = 2N f 2 E
(
Normal Strain
SWT - Bannantine
σ ′f 2 ∆ε n 2N f ⋅ σ n ,max = 2 E
Shear Strain
∆γ (1 + ν e )σ ′f = 2N f 2 E
Fatemi-Socie
(
(
∆γ 2
æ ö (1 + ν e ) σ ç1 + n n ,max ÷ = σ ′f 2 N f ç ÷ E σ è y ø
(
(
) (
)
S18-65
)
(
2b
+ ε ′f 2 N f
)
(
c
+ σ ′f ⋅ ε ′f 2 N f
)
b+ c
) + (1 + ν )ε ′ ( 2 N ) b
p
b
+ 1 + ν p ε ′f 2 N f
PAT318, Section 18,March 2002
)
b
+
)
f
n(1 + ν e )σ ′f 2 2 Eσ y c
+
(
)
f
(
2N f
n 1 + ν p ε ′f σ ′f 2σ y
c
(
)
2b
2N f
)
b+ c
WANG-BROWN METHOD n
A complex recursive multi-axial Rainflow Counting Method
n
A Mean Stress Correction Method is available
n
May be quite slow especially for long loading histories
n
Recommended for a variety of proportional and non-proportional loadings
PAT318, Section 18,March 2002
S18-66
WANG-BROWN METHOD n
Calculates a different Critical Plane for each rainflow reversal
n
For each reversal the damage is calculated on the critical i.e. maximum shear plane, whether case A or B
n
Uses Normal Strain Range, Maximum Shear Strain
n
Material Parameter ‘S’
PAT318, Section 18,March 2002
S18-67
WANG-BROWN METHOD
Mean Stress Correction using Mean, Normal Stress
ε ≡
σ ′f − 2. σ n , m ean γ m ax + S . δε n = 2N 1 + ν ′ + S (1 − ν ′ ) E
PAT318, Section 18,March 2002
(
S18-68
f
)
b
(
+ ε ′f 2 N
f
)
c
TYPICAL POLAR DAMAGE PLOT Polar Plot of Data : DEMO Theta=90
Theta=45
90 120
60
150
30
180
1E-9 1E-8 1E-7 1E-6
210
0
330 240
300 270
Polar Plot of Type A and Type B damage for W ang-Brown Method
PAT318, Section 18,March 2002
S18-69
MULTI-AXIAL LIFE CALCULATION METHODS: NONPROPORTIONAL LOADING I. Multiaxial Method
Example: Knuckle, Chapter 11 (QSG)
Life (Repeats)
Normal Strain
106,000
SWT-Brannantine
316,000
Mean Biaxiality Ratio: -0.6
Shear Strain
18,500
Biaxiality S.D. = 0.18
Fatemi-Socie
27,000
Most Popular Angle = -64 deg
Wang-Brown
30,500
Angle Spread = 90 deg
Wang-Brown + Mean
26,000
At Node 1045: Max Stress Range = 508 Mpa
II. Equivalent Strain Method Abs. Max. Principal Strain
PAT318, Section 18,March 2002
S18-70
97,300
MULTI-AXIAL LIFE CALCULATION METHODS: 90 DEG OUT OF PHASE LOADING I. Multiaxial Method
Life (Cycles)
Material: Manten
Normal Strain
4.12E+07
Axial Stress, Sx = 25,000 psi
SWT-Brannantine
2.80E+04
Shear Stress, Sxy = 14,434 psi
Shear Strain
1.41E+05
Fatemi-Socie
1.70E+05
Wang-Brown
6.63E+06
Wang-Brown + Mean
8.55E+05
II. Eqivalent Strain Method
PAT318, Section 18,March 2002
Abs. Max. Principal Strain
2.88E+07
Signed Von Mises Strain
2.88E+07
Signed Tresca Strain
8.41E+06
S18-71
DANG-VAN METHOD n
High-Cycle Fatigue applications designed for infinite life
n
Calculates Factor-of-Safety of the design
n
Uses S-N total life method
n
Ideal applications: Bearing Design, Vibration induced fatigue
PAT318, Section 18,March 2002
S18-72
THE DANG VAN CRITERION n
The Dang Van criterion is a fatigue limit criterion
n
It is based on the premise that there is plasticity on a microscopic level, leading to shakedown
n
After shakedown, the important factors for fatigue are the amplitude of the microscopic shear stresses and the magnitude of the hydrostatic stress
n
The method has a complicated way of estimating the microscopic residual stress
PAT318, Section 18,March 2002
S18-73
THE DANG VAN CRITERION Fatigue damage occurs if:
τ (t ) + a ⋅ ph(t ) − b ≥ 0 where τ(t) and ph(t) are the maximum microscopic shear stress and the hydrostatic stress at time t in the stabilized state. They can be calculated from:
{
1 τ ( t ) = Tresca Sij ( t ) + devρij* 2
}
“a” and “b” are material properties
PAT318, Section 18,March 2002
S18-74
(
)
1 ph(t ) = σ xx + σ yy + σ zz (t ) 3
THE DANG VAN CRITERION n
The parameter “b” is the shear stress amplitude at the fatigue limit
n
The parameter “a” is in effect the mean stress sensitivity, with the mean stress being represented by the hydrostatic stress
n
dev ρij* is the deviatoric part of the stabilised residual stress
PAT318, Section 18,March 2002
S18-75
DANG-VAN PLOT τ(t)
Damage occurs here !!!
τ + a ⋅ ph − b = 0
ph(t)
τ − a ⋅ ph +b = 0
PAT318, Section 18,March 2002
S18-76
STABILIZED RESIDUAL STRESSES:
(
ρ * devρ * ij
)
n
The stabilized local residual stresses are calculated by means of an iteration in which convergence assumes a stabilized state, a state of elastic shakedown.
n
As the loading sequence is repeated the “yield surface” grows and moves with a combination of kinematic and isotropic hardening until it stabilises
n
The stabilised yield surface is a 9 dimensional hypersphere that encompasses the loading history
PAT318, Section 18,March 2002
S18-77
DANG-VAN CRITERION SUMMARY n
Is a High-Cycle fatigue criterion (infinite fatigue life)
n
Can deal with three-dimensional loading
n
Can deal with general multiaxial loading
n
Is constructed on the basis of microscopic level: the scale of one or a few grains
n
Can identify the direction of crack initiation
PAT318, Section 18,March 2002
S18-78
DANG VAN FACTOR OF SAFETY PLOT
PAT318, Section 18,March 2002
S18-79
SUMMARY OF APPROACH n
Assume uniaxial and find critical locations
n
Assess multiaxiality at critical locations by checking biaxiality ratio and angle of principal
n
If angle constant and constant αe < 0, use Hoffman-Seeger (or Parameter Modification) biaxiality correction and abs max principal
n
If angle constant and constant αe > 0, use Hoffman-Seeger biaxiality correction and signed Tresca
n
If angle varies greatly with time, needs multiaxial
n
If αe varies greatly with time, needs multiaxial PAT318, Section 18,March 2002
S18-80
A MULTIAXIAL ASSESSMENT Perform crack initiation analysis of a knuckle. Multiple (12) loading inputs. Assess multiaxiality.
PAT318, Section 18,March 2002
S18-81
LOADING INFO SETUP
12 loads associated with 12 FE results
Force(Newtons)
LOAD03.PVX
84.71
Sample = 1 Npts = 1610 Max Y = 84.71 Min Y = -50.05 -50.05 0
500
1000
1500 point
Force(Newtons)
LOAD02.PVX
7720
Sample = 1 Npts = 1610 Max Y = 7720 Min Y = -7998 -7998 0
500
1000
1500 point
Force(Newtons)
LOAD01.PVX
3769
Sample = 1 Npts = 1610 Max Y = 3769 Min Y = -2654 -2654 0
500
1000
1500 point
Screen 1
PAT318, Section 18,March 2002
S18-82
LOG-LIFE CONTOUR PLOT (IN REPEATS)
PAT318, Section 18,March 2002
S18-83
EXAMPLE MULTIAXIALITY INDICATORS
Angle Spread
Mean Biaxiality
PAT318, Section 18,March 2002
S18-84
EXERCISE n
Perform Quick Start Guide Section 11.5 of the Chapter 11 Lesson “A Multiaxial Assessment” where you run a multiaxial analysis. u
u
Perform Quick Start Guide Chapter 9 Exercise, “Design Philosophies” which reviews S-N and E-N analysis methods, and introduces LEFM. Be sure to ask for help if there’s anything you don’t understand
PAT318, Section 18,March 2002
S18-85
PAT318, Section 18,March 2002
S18-86
SECTION 19 FATIGUE CRACK PROPAGATION
PAT318, Section 19, March 2002
S19-1
PAT318, Section 19, March 2002
S19-2
FATIGUE CRACK PROPAGATION (LEFM) METHOD n n
n
n n n
What remnant life is there after initiation? What is the safe life or inspection schedule for a component that is or may be cracked? The crack growth method is based on the principles of Linear Elastic Fracture Mechanics (LEFM) It relates stress intensity factors to crack growth rates It uses cycle-by-cycle calculations to predict lifetimes It is frequently used in Aerospace, Offshore, and Power Generation industries
PAT318, Section 19, March 2002
S19-3
FRACTURE MECHANICS TRIANGLE
Stress Intensity (K)
Crack Size (a)
PAT318, Section 19, March 2002
Stress (s)
S19-4
FRACTURE MECHANICS RECTANGLE Cycles to Failure (Nf)
Final Crack Size (af)
Initial Crack Size (ai)
PAT318, Section 19, March 2002
Stress Range (DS)
S19-5
CRACK STRESS CONCENTRATION A crack is an extreme stress/strain concentrator
Elastic Stress Concentration σmax = Ktσ
PAT318, Section 19, March 2002
Kt=(1+2a/b)
Kt=3
S19-6
b = 0 --> Kt = ∞
MODES OF CRACK OPENING
PAT318, Section 19, March 2002
S19-7
MECHANICS OF CRACKS
n
Stress Intensity Factor KI
n
General form of K K = Yσ πa where the geometry function Y = Y (a/w, B, ... )
PAT318, Section 19, March 2002
S19-8
TYPICAL GEOMETRY FUNCTIONS
n
n
n
Through Crack in Infinite Plate u Y = 1 Edge Crack in Semi-Infinite Plate u Y = 1.12 Edge Crack in Finite Plate u Y = 1.12 - 0.231(a/w) + 10.55(a/w)2 21.72(a/w)3 + 30.30(a/w)4
PAT318, Section 19, March 2002
S19-9
LINEAR ELASTIC FRACTURE MECHANICS
PAT318, Section 19, March 2002
S19-10
LINEAR ELASTIC FRACTURE MECHANICS
PAT318, Section 19, March 2002
S19-11
K CONTROLLED FRACTURE K Controls the stress around the tip
Fracture Zone
Plastic Zone
n
n
In small scale yielding K controls everything near the tip - plasticity - void growth - cracking Fracture occurs when K = KIC (The Fracture Toughness)
PAT318, Section 19, March 2002
S19-12
ASSUMPTIONS OF SMALL SCALE YIELDING
n
Plastic zone size:
1 rp = 6π
n
æK ö ç ÷ çσ ÷ è yø
2
For LEFM to be valid, the plastic zone size must be small compared to crack length a and component geometry:
1 rp ≤ (a, t , b, w,...) 25
PAT318, Section 19, March 2002
S19-13
STAGES OF FATIGUE CRACK GROWTH
PAT318, Section 19, March 2002
S19-14
FATIGUE CRACK GROWTH MECHANISMS n n
Reversed plasticity Corrosion
PAT318, Section 19, March 2002
S19-15
CRACK PROPAGATION METHOD SIMILITUDE
This crack . . . . . . . grows at the same rate as this one if both experience the same stress intensity factors
PAT318, Section 19, March 2002
S19-16
CRACK GROWTH RATES ARE CONTROLLED BY ∆K Fast Fracture Effects
da --dN
Paris Law Region da --- = C∆Km dN ∆K Threshold Effects
PAT318, Section 19, March 2002
∆K = Y ∆σ √ πa S19-17
PROPAGATION RATES
PAT318, Section 19, March 2002
S19-18
FACTORS AFFECTING CRACK GROWTH RATE
n n n
n n
Crack tip plasticity (crack closure) Mean stresses Threshold region (for low loads or short cracks) Variable amplitude loading (overloads) Environment
PAT318, Section 19, March 2002
S19-19
CRACK TIP PLASTICITY
PAT318, Section 19, March 2002
S19-20
PLASTIC ZONE AND CRACK CLOSURE n n
n
n
As crack grows, small region of plasticity develops around crack tip Plastically deformed regions are surrounded by material that remains elastic As material is unloaded, plastic region causes crack surfaces to be pulled toward each other causing CRACK CLOSURE Crack closure can be induced by: u u u
overloads corrosion effects surface roughness
PAT318, Section 19, March 2002
S19-21
MEAN STRESSES (R-RATIO EFFECTS)
Kmin R= Kmax
PAT318, Section 19, March 2002
S19-22
SHORT CRACKS n
n
SHORT CRACKS: u
they tend to be free of closure effects.
u
LEFM is not applicable to them, in general.
u
They typically have higher growth rates than long cracks.
NOTE: long cracks do not grow if ∆K is smaller than a threshold value ∆Kth.
PAT318, Section 19, March 2002
S19-23
VARIABLE AMPLITUDE LOADS High - low sequences change the crack closure
PAT318, Section 19, March 2002
S19-24
ENVIRONMENT Crack growth rates are higher in corrosive environments (e.g. salt water) than in air. They are the lowest in vacuum.
PAT318, Section 19, March 2002
S19-25
CALCULATING LIFETIMES n
Need: u u u u u
Initial crack size Final crack size Stress range K calibration Material growth law
PAT318, Section 19, March 2002
S19-26
CRACK GROWTH LAWS n
There are many crack growth “laws” in the literature: u u u u u u u
Paris (the most known) Forman (MSC/Fatigue uses similar method for fast fracture correction) Lucas-Klesnil Elber Walker Wheeler Willenborg (MSC/Fatigue uses extension of this model)
PAT318, Section 19, March 2002
S19-27
EFFECTIVE ∆K APPROACH n
n
The key to MSC/Fatigue crack growth analysis is the correction of the apparent ∆K (based on applied load) to an effective ∆K (i.e. the crack driving force actually seen at the crack front) Usual Method
da = f (∆K , R, ∆K TH , K IC , history , environment ) dN n
MSC.Fatigue Method
∆K eff = f (∆K , R, ∆KTH , K IC , history , environment ) da = C ∆K effm dN PAT318, Section 19, March 2002
S19-28
MSC/FATIGUE CRACK GROWTH ANALYSIS STEPS
n n n
Input next cycle Calculate apparent ∆K from lookup table Correct to effective ∆K for u u u u u
n n
closure/short crack notch field influence static fracture mode contribution history effects environmental effects
da = C ∆Keffm a = a+da (if no fast fracture, go to next cycle)
PAT318, Section 19, March 2002
S19-29
IMPLEMENTATION IN MSC.FATIGUE
Time Cycle Counter
Geometry function Library
KSN
TCY
MDB
CRACK GROWTH ANALYSER
CRG
PAT318, Section 19, March 2002
S19-30
Materials Database Manager
CYCLE-BY-CYCLE CRACK GROWTH Features:
n u u
u u u u u u u u
Cycle-by-Cycle Modelling Time-sequenced Rainflow Cycle Counting Multi-environment Material Properties Kitagawa Minimum Crack Sizing Threshold Modelling Crack Closure and Retardation User Defined Life Fracture Toughness Failure Criterion Surface or Embedded Cracks Modified Paris Law (modified Willenborg model)
PAT318, Section 19, March 2002
S19-31
SUMMARY OF APPROACH n
Identify critical region and select node/element for nominal stress
n
Identify geometry from library of compliance functions
n
Identify initial crack size
n
MSC.Fatigue calculates change in crack length on a cycle-by-cycle basis until fast fracture occurs
n
Life estimates are normally within a factor of 2 if all the control parameters are modeled correctly
PAT318, Section 19, March 2002
S19-32
MSC/FATIGUE CRACK GROWTH ANALYSIS - APPLICATIONS n n n n n
Design analysis Pre-prediction of test programs Inspection strategy Failure investigation Decision support
PAT318, Section 19, March 2002
S19-33
EXAMPLE PROBLEM: CRACK PROPAGATION ANALYSIS n n
Lug problem Single load
PAT318, Section 19, March 2002
S19-34
LINEAR ELASTIC FRACTURE MECHANICS ANALYSIS (LEFM)
PAT318, Section 19, March 2002
S19-35
DEFINE A CRACK AND PLOT COMPLIANCE FUNCTION
PAT318, Section 19, March 2002
S19-36
LOADING INFO SETUP
PAT318, Section 19, March 2002
S19-37
MATERIAL INFO SETUP
n
Create a group “far_field” with node 223 in it only.
PAT318, Section 19, March 2002
S19-38
PERFORM LEFM ANALYSIS
PAT318, Section 19, March 2002
S19-39
EXERCISE n
Perform Quick Start Guide Chapter 8 Exercise, “Introduction to Crack Growth”
n
Perform Quick Start Guide Chapter 10 Exercise, “Multiple Loads”
n
Be sure to ask for help if there’s anything you don’t understand
PAT318, Section 19, March 2002
S19-40
SECTION 20 SPOT WELD FATIGUE
PAT318, Section 20, March 2002
S20-1
PAT318, Section 20, March 2002
S20-2
MOTIVATION ■
■
■
■ ■
About 50% of automotive structural durability problems are associated with spot-welds About 80% of automotive body durability problems are associated with spot-welds The tooling cost for 1 spot weld on an automated production line is about $30,000 Late additions may cost twice this amount Besides any structural importance, the durability of spot welds can have an important effect on perceived quality
PAT318, Section 20, March 2002
S20-3
CURRENT PRACTICE ■
■
■
There is increasing pressure in the automotive industry to reduce development times. Less prototypes means more CAE. There are no commonly available tools for life prediction of spotwelds Spot-weld numbers, positions and sizes are typically decided by: ◆
◆
The component engineer, based on panel stresses (spot-welds are often not modelled at all) and experience The production engineer, based on what is possible / economical
PAT318, Section 20, March 2002
S20-4
STRUCTURAL STRESS BASED METHOD ( Rupp - Storzel - Grubisic ) ■
■
■
■ ■
Coarse mesh only required, with spot welds modeled as stiff beam elements Beams are used as " force transducers " to obtain forces and moments transmitted through the spot welds Forces and moments are used to calculate " structural stresses " Life is calculated using Miner's rule Method is generally applicable and handles multiaxial loadings
PAT318, Section 20, March 2002
S20-5
Spotweld “Nugget”
Beam Element
AN AUTOMOTIVE PART WITH SPOT WELDS
PAT318, Section 20, March 2002
S20-6
HOW DO WE MODEL SPOTWELDS? The 5 Box Trick Geometry (Beam Elements)
Loading (Time History)
Fatigue Analysis (Spot Weld Analyzer)
Material (Weld S-N Data) Optimization & Testing PAT318, Section 20, March 2002
S20-7
Post Processing
LOADING HISTORY ON DAMPER
PAT318, Section 20, March 2002
S20-8
STRUCTURAL STRESS CALCULATIONS The structural stresses are calculated from the forces and moments on each beam element : My My Fy
My Fy Fz
Fy
Fx Fz
Fz
Mx
Fx Mx
Fx Mx
Nugget
Sheet 2
PAT318, Section 20, March 2002
S20-9
Sheet 1
STRUCTURAL STRESS CALCULATIONS E.G. stresses in sheet : Fz
σ r ,max = σr
Fx, y
π ds
■
Fy
Fz . = 1744 s2
. σ r ,max = 1872 ■
My
Fx s
M x, y
d
ds 2
Similar equations for stresses in nugget Corrections made for size effect
PAT318, Section 20, March 2002
S20-10
Mx
FATIGUE PROPERTIES - TYPICAL TEST SPECIMEN
PAT318, Section 20, March 2002
S20-11
FATIGUE PROPERTIES - GENERIC S-N CURVES
PAT318, Section 20, March 2002
S20-12
DAMAGE CALCULATION PROCEDURE ■
■
Stresses and fatigue damage are calculated at 10 intervals around the spot weld for the 2 sheets and the nugget Stress histories are calculated from :
σk Pk( t ) σ (t ) = å Pk ■
where k = static loadcase i.d., or from transient F.E. Life is calculated using Linear Damage Summation (Miner's Rule)
PAT318, Section 20, March 2002
S20-13
RESULTS POSTPROCESSING OPTIONS ■ ■ ■ ■
Listing the results files, life, damage, crack location etc... Plotting in MSC.Fatigue (Insight) Polar plotting of damage " What if ? " games ...
PAT318, Section 20, March 2002
S20-14
FATIGUE RESULTS FOR SHOCK TOWER
PAT318, Section 20, March 2002
S20-15
POLAR PLOT OF DAMAGE
PAT318, Section 20, March 2002
S20-16
EXAMPLE PROBLEM:A SPOT WELD ANALYSIS Perform spot weld analysis.
Multiple loading inputs at shock tower.
PAT318, Section 20, March 2002
S20-17
SOLUTION PARAMETERS SETUP
PAT318, Section 20, March 2002
S20-18
MATERIAL INFO SETUP
PAT318, Section 20, March 2002
S20-19
LOADING INFO SETUP
PAT318, Section 20, March 2002
S20-20
PAT318, Section 20, March 2002
S20-21
EXERCISE
■
Perform Quickstart Guide Chapter 13 Exercise, “A Spot Weld Analysis”
■
Be sure to ask for help if there’s anything you don’t understand
PAT318, Section 20, March 2002
S20-22
SECTION 21 MSC.FATIGUE SOFTWARE STRAIN GAUGE
PAT318, Section 21, March 2002
S21-1
PAT318, Section 21, March 2002
S21-2
A virtual test facility in the MSC.Fatigue environment
PAT318, Section 21, March 2002
S21-3
SOFTWARE STRAIN GAUGE ■
■
A Finite Element tool allowing the creation of Stress and Strain time histories at arbitrary locations on a Finite Element Model Surface Uses: ◆ ◆
■
Finite Element Model Results Verification Comparison of Strain Values with Test Time Histories
Previous FEA techniques have only permitted comparison of single Stress or Strain values.
PAT318, Section 21, March 2002
S21-4
DESCRIPTION ■
A virtual strain gauge on a finite element model. This gauge can produce theoretical result time histories from multiple time varying applied loads
■
Time histories may be extracted at any point on the mesh surface
■
Results based on either standard or user defined strain gauge definitions.
■
The results from static, transient or quasi static finite element loading.
PAT318, Section 21, March 2002
S21-5
CORRELATION APPLICATIONS ■
Allows correlation between theoretical calculations with experimentally determined results.
DISPLAY OF SIGNAL: SAETRN.DAC 17081 points.
1000
9 pts/Secs
Displayed: 4501 points. from pt 1
Strain (uE)
Full file data:
■
Max = 999 at 0 Min = -495
Permits greater confidence in the finite element model of the real world structure.
at 1743
Mean = 385.3 S.D. = 235
-600
RMS = 451.3 Time (Secs)
0
■
Stress / Strain results may be subsequently analysed as:
500
CYCLE HISTOGRAM DISTRIBUTION FOR : SAETRN.CYO Maximum height : 16
◆ ◆ ◆
Cycle Counts PSD results Damage / Life Values
Z Units :
16 Cycles Z-Axis 0
999
0 Mean uE Y-Axis
Range uE X-Axis 1508.9
PAT318, Section 21, March 2002
S21-6
-495
CORRELATION APPLICATIONS (Contd.)
Software Strain Gauges FEA Model Surface Hub Strain
Hub Strain
Real World Structure
time PAT318, Section 21, March 2002
time S21-7
WELDED STRUCTURE ANALYSIS ■
The Software Strain Gauge is also of benefit to the analyst performing MSC.Fatigue weld durability calculations in accordance with British Standard 7608.
■
When calculating fatigue life for welded structures the loading direction is of importance
■
The strain gauge allows extraction of time histories prior to Rainflow cycle counting in specific directions on an FEA structure
PAT318, Section 21, March 2002
S21-8
WELDED STRUCTURE ANALYSIS (Contd.) The Gauge tool allows access to strain time histories at the weld toe, providing important information for weld durability calculations.
Software Strain Gauges
Real World Structure
FEA Model
CLASS F WELD DETAIL (BS7608) PAT318, Section 21, March 2002
S21-9
GAUGE DEFINITION ■
The gauges are defined as FEA groups, each containing between 1 to 3 elements.
■
Standard gauge definitions: ◆ ◆ ◆ ◆ ◆
■
Uni-axial Gauges T Gauges Delta Gauges Rectangular Gauges Planar and stacked formulations.
User defined gauges may also be created ◆
definitions stored in a gauge definition file.
PAT318, Section 21, March 2002
S21-10
IMPLEMENTATION ■
Gauge position: ◆ ◆ ◆
■
Gauge results: ◆ ◆ ◆
■
Anywhere on the FEA model surface Any orientation Covering multiple finite elements. Averaged results from the underlying finite elements Replicates the geometric averaging with actual instrumentation. Transformed to the coordinate system and alignment of the software strain gauge.
Up to 200 simultaneous Software Strain Gauges
PAT318, Section 21, March 2002
S21-11
EXAMPLE PROBLEM: A SOFTWARE STRAIN GAGE Introduce software strain gage as a correlation tool on a mounting lug.
Multiple loading inputs.
PAT318, Section 21, March 2002
S21-12
SOFTWARE STRAIN GAGE SETUP
and elements that define surface
Define node to initially put gage on ...
PAT318, Section 21, March 2002
S21-13
LOADING INFO SETUP
PAT318, Section 21, March 2002
S21-14
PERFORM ANALYSIS
■ ■ ■
Define material and loading Extract time histories from rosette Perform rosette analysis and correlation
PAT318, Section 21, March 2002
S21-15
CORRELATION TECHNIQUES ■ ■ ■ ■
Overlays and cross plots Rosette analysis Single location uniaxial life analyzer Single location multiaxial life analyzer
PAT318, Section 21, March 2002
S21-16
EXERCISE
■
Perform Quickstart Guide Chapter 15 Exercise, “A Software Strain Gauge”
■
Be sure to ask for help if there’s anything you don’t understand
PAT318, Section 21, March 2002
S21-17
PAT318, Section 21, March 2002
S21-18
SECTION 22 VIBRATION FATIGUE ANALYSIS
PAT318, Section 22, March 2002
S22-1
PAT318, Section 22, March 2002
S22-2
OVERVIEW
n n n n
Why use frequency domain? Benefits of vibration fatigue Review of theory Summary of features
PAT318, Section 22, March 2002
S22-3
WHY USE FREQUENCY DOMAIN?
time
time
Output
Transfer Function frequency
PAT318, Section 22, March 2002
PSD Stress
Input
PSD
Frequency Domain
Hub Stress
Wind speed
Time Domain
frequency S22-4
BENEFITS OF VIBRATION FATIGUE n
n n
n
Analyse structures with dynamic responses to random loading without requiring full transient analysis Fatigue analysis is relatively rapid Analysis can be included much earlier in the design cycle Ability to analyse ‘what if’ scenarios interactively
PAT318, Section 22, March 2002
S22-5
HOW DO WE CALCULATE DAMAGE? Loading (PSD)
Material
Fatigue Analysis
(S-N analysis)
(Vibration Fatigue)
Geometry (S-N Analysis)
Optimization & Testing
PAT318, Section 22, March 2002
S22-6
Post Processing
HOW DO WE CALCULATE DAMAGE? TIME DOMAIN Steady state or
TIME HISTORY
RAINFLOW COUNT
STRESS RANGE HISTOGRAM
FATIGUE LIFE STRESS RANGE HISTOGRAM
Transient Analysis
FREQUENCY DOMAIN PSD
FATIGUE MODELLER
PDF
FATIGUE LIFE
Transfer M0 M1 M2
Function
M 4
PAT318, Section 22, March 2002
S22-7
BLACK BOX
FATIGUE LIFE
WHAT DOES AN FFT TELL US? Magnitude of FFT Area of spike = amplitude of sin wave
|FFT|
Time history A
FFT
ω
time
frequency
ϕ
Argument of FFT The argument of the FFT gives the phase angle ϕ of the sinusoidal wave
Single sinusoidal eddy of frequency ω, amplitude A and initial phase angle ϕ
PAT318, Section 22, March 2002
S22-8
WHAT DOES AN FFT TELL US? n n
The FFT is a complex number given with respect to frequency. A sine wave of frequency ω, amplitude A and initial phase angle ϕ is represented in the frequency domain by a spike occurring at ω along the frequency axis. u
If the magnitude of the complex FFT is plotted, then the area under the spike is found to be the amplitude A of the sine wave. When the argument of the complex FFT is plotted then the area is found to be initial phase angle ϕ of the sine wave.
PAT318, Section 22, March 2002
S22-9
WHAT IS A PSD? In a PSD we are only interested in the amplitude of each sine wave and are not concerned with the phase relationships between the waves. def
Definition
PSD
1 = 2T
FFT 2
PSD
The area under each spike represents the Mean Square of the sine wave at that frequency
frequency PSD PAT318, Section 22, March 2002
S22-10
We cannot determine what the phase relationships between the waves are any more
MOMENTS FROM A PSD mn =
∞
ò
f
n
⋅G
( f )d f
=
0
(Stress)2
å
n
⋅G
( f )⋅δ f
In practice, m0, m1, m2 and m4 are sufficient to compute all of the information required for the subsequent fatigue analysis
fk
Hz
Gk(f) Frequency, Hz
PAT318, Section 22, March 2002
f
S22-11
EXPECTED ZEROS, PEAKS AND IRREGULARITY FACTOR FROM A PSD mn =
∞
ò
f
n
⋅ G ( f )d f =
0
(Stress)2
å
n
⋅G( f
)⋅δf
m2 E0 = m0
fk
m4 EP = m2
Hz
Gk(f) Frequency, Hz These statistical parameters are needed for subsequent fatigue analyses. PAT318, Section 22, March 2002
f
S22-12
E0 m22 = γ= EP m0⋅ m4
EXPECTED ZEROS, PEAKS AND IRREGULARITY FACTOR FROM THE TIME SIGNAL Number of upward zero crossings,
Stress (MPa)
Time History
x
E[0] = 3
x
x
x x
Number of peaks,
E[P] = 6
x time
Irregularity factor,
1 second
= upward zero crossing x = peak PAT318, Section 22, March 2002
S22-13
γ=
E[0] E[P]
= 3 6
PROBABILITY DENSITY FUNCTIONS (PDF’S) To get pdf from rainflow histogram divide each bin height by
p(S)
S t × dS
P(S i)
dS Stress Range (S)
S t = total number of cycles dS = bin width
The probability of the stress range occurring between dS dS Si − and S i + = P ( Si ). ds 2 2 PAT318, Section 22, March 2002
S22-14
DIRLIK SOLUTION p( S ) D = f ( m0 , m1 , m2 , m4 ) D1 ⋅e Q
p (S ) D = where;
D2 =
z=
S 2 ⋅ m0
1 − γ − D1 + D 1− R
2 1
−Z Q
−Z
+
2
D2 ⋅Z 2⋅R 2 ⋅ + D3 ⋅Z ⋅e e 2 R 2 ⋅ m0
m2 γ= m0 ⋅ m4
m1 m2 xm = ⋅ m0 m4
D1 =
−Z 2
2
2⋅ ( xm − γ 2 ) 1+ γ 2
2 − x − D γ m 1 125 . ⋅ (γ − D 3 − D 2 ⋅ R) R = D3 = 1 − D1 − D2 Q = 1 − γ − D 1 + D 12 D1
A widely applicable solution developed after extensive Monte Carlo simulation of a wide range of likely stress response conditions PAT318, Section 22, March 2002
S22-15
OTHER SOLUTION METHODS The best method in all cases
Dirlik
Chaudhury & Dover
Wirsching
Hancock
Steinberg
Electronic components (USA) PAT318, Section 22, March 2002
Tunna
Narrow Band
S22-16
Developed for offshore use
Railway engineering (UK) The original solution
HOW DO WE CALCULATE DAMAGE? TIME DOMAIN Steady state or
TIME HISTORY
RAINFLOW COUNT
STRESS RANGE HISTOGRAM
FATIGUE LIFE
Transient Analysis
STRESS RANGE HISTOGRAM
FREQUENCY DOMAIN PSD
FATIGUE MODELLER
PDF
FATIGUE LIFE
Transfer M0 M1
Function
M2 M 4
PAT318, Section 22, March 2002
S22-17
BLACK BOX
FATIGUE LIFE
SUMMARY OF FEATURES n
n
n n n n n n
Calculate fatigue life from PSDs Uses 7 solution methods including; Dirlik, Steinberg and Narrow Band solutions Ability to handle multiple, partial and fully correlated loads Mean Stress Correction Palmgren-Miner Linear Damage Material and Component S-N Model Surface Conditions Factor of Safety Analysis Biaxiality Indicators
PAT318, Section 22, March 2002
S22-18
DISPLAY OF NOISE.PSD 8E-5
RMS Power (Volts^2. Hz^)
n
0 0
nCode nSoft
Frequency (Hz.)
1500
PROCESS ALTERNATIVES n
Use NASTRAN to calculate PSD’s of Stress directly and use directly in MSC.Fatigue u
n
Disadvantage : Only basic stress components available as output (no principals etc.)
Use NASTRAN to calculate complex transfer function between inputs and stress results. MSC.Fatigue combines transfer function with input PSD’s and Cross spectra to calculate principal stresses vs freq. u
Disadvantage: More data for MSC.Fatigue to process.
PAT318, Section 22, March 2002
S22-19
EXAMPLE PROBLEM: VIBRATION FATIGUE Example of vibration fatigue analysis of a bracket. Three load inputs. Critical area: around circular hole. Using transfer function method of vibration fatigue
PAT318, Section 22, March 2002
S22-20
SINGLE LOAD Time-domain Analysis (static FE result)
Frequency-domain Analysis (At Frequency = 0 Hz) Frequency-domain Analysis (one of several frequencies)
PAT318, Section 22, March 2002
S22-21
TIME-DOMAIN LOADING INFO SETUP
PAT318, Section 22, March 2002
S22-22
FREQUENCY-DOMAIN LOADING INFO SETUP
PAT318, Section 22, March 2002
S22-23
FREQUENCY-DOMAIN LOADING INFO - MULTIPLE PSDS -
PAT318, Section 22, March 2002
S22-24
RESULTS: Static case: Combined loads
Vibration: uncorrelated loads
Vibration: correlated loads
PAT318, Section 22, March 2002
S22-25
EXERCISE
n
Perform Quick Start Guide Chapter 16 Exercise, “Vibration Fatigue”
n
Be sure to ask for help if there’s anything you don’t understand
PAT318, Section 22, March 2002
S22-26
SECTION 23 MSC.FATIGUE UTILITIES
PAT318, Section 23, March 2002
S23-1
PAT318, Section 23, March 2002
S23-2
UTILITIES OVERVIEW n
n n
Derived from nCode International’s nSoft engineering analysis software Builds upon functionality in Time History Manager (PTIME) Provides tools for : u u u u u
data manipulation data translation data filtering statistical & frequency analysis local and test based fatigue analysis
PAT318, Section 23, March 2002
S23-3
UTILITIES OVERVIEW (Contd.) n
Note: u
u u
u
Program names from nSoft have been prefixed with an additional ‘m’ in MSC.Fatigue thus ‘QLD’ becomes ‘mQLD’ etc. this prevents any conflict between different installations of MSC.Fatigue and nSoft on the same machine. The Quickstart guide reflects this name change however this summary and the MSC.Fatigue pull-down menus do not.
PAT318, Section 23, March 2002
S23-4
PTIME (TIME HISTORY MANAGER) n
MSC.Fatigue includes data processing functions within Time History Manager (PTIME): u u u u u u
ASCII File Input Waveform creation Block Cycle Definition Rainflow Cycle Counting Polynomial Data Transformation Data Display Tools
PAT318, Section 23, March 2002
S23-5
Time History Manipulation Tools
n n n n n n n
Arithmetic Manipulation (ART) Spreadsheet Multichannel Editor (COE) Edit, Extract & Join Data (LEN) Combine Multiple Channels (MFM) User defined formulae (FRM) Multiple File Peak Valley Extraction (PVXMUL) Graphical Data Editor (GED)
PAT318, Section 23, March 2002
S23-6
MATHEMATICAL MANIPULATION OF DATA - “ART”
PAT318, Section 23, March 2002
S23-7
SPREADSHEET MULTICHANNEL EDITOR “COE”
PAT318, Section 23, March 2002
S23-8
EDIT, EXTRACT & JOIN DATA - “LEN”
rear g2(g)
A0 4 .DAC
10 5 0 -5 -10 0
20
40
60
80
100
rear g2(g)
120
s ecs
3A0 4 .DAC
10 5 0 -5 -10 0
20
40
60
80
100
120
s ecs
S creen 1
PAT318, Section 23, March 2002
S23-9
COMBINE MULTIPLE CHANNELS - “MFM”
rear g2(g)
10
A04.DAC
5 0 -5 -10
0
10
20
30
rear g2(g)
secs
3A04.DAC
10 5 0 -5 -10
0
10
20
30
secs
Screen 1
PAT318, Section 23, March 2002
S23-10
MULTIPLE FILE PEAK VALLEY EXTRACTION“PVXMUL”
Shortens loading time histories by retaining only the maxima & minima (turning points). Gating can be used to ignore small cycles by absolute or percentage values. Maintains ‘phase’ across channels by considering all channels simultaneously. If a turning point is found in any input channel, the corresponding point is written to all the output .pvx files. PAT318, Section 23, March 2002
S23-11
MULTIPLE FILE PEAK VALLEY EXTRACTION“PVXMUL” Gauge 1(uE)
S61.DAC
1 0 00
Spike on all 3
-2 0 0 0
10
20
S am ple = 409.6 N pt s = 1.354E 4 Max Y = 928.8 Min Y = -0.344 30
seco n d s
Gauge 2(uE)
S62.DAC
20
S am ple = 409.6 N pt s = 1.354E 4 Max Y = 15.83 Min Y = -119.8 -1 2 0 0
10
20
30 seco n d s
Gauge 3(uE)
S63.DAC
800
S am ple = 409.6 N pt s = 1.354E 4 Max Y = 722.4 Min Y = -485.6 -6 0 0 0
10
20
30 seco n d s
Screen 1
Input .DAC files Gauge 1(uE)
S61.PVX
1 0 00
Spike still in synch
-2 0 0
20 0 0
4000
6 0 00
8 0 00
S am ple = 1 N pt s = 1.022E 4 Max Y = 928.8 Min Y = -0.344
1E4 p o in t
20
Gauge 2(uE)
S62.PVX
S am ple = 1 N pt s = 1.022E 4 Max Y = 15.83 Min Y = -119.8 -1 2 0
20 0 0
4000
6 0 00
8 0 00
1E4 p o in t
Gauge 3(uE)
S63.PVX
800
S am ple = 1 N pt s = 1.022E 4 Max Y = 722.4 Min Y = -485.6 -6 0 0
20 0 0
4000
6 0 00
8 0 00
1E4 p o in t
Screen 1
Output .PVX files - reduced number of points PAT318, Section 23, March 2002
S23-12
GRAPHICAL EDITING OF DATA - “GED”
A04.DAC
rear g2 (g)
3
2
1
0
- 1
- 2
1
3
1
3
. 2
time
1
3
. 4
1
3
. 6
( s ec s )
3 A 0 4 .D A C
rear
g2
(g)
3
2
1
0
-1
-2
13
1 3 .2
ti m e
PAT318, Section 23, March 2002
1 3 .4
(s e c s )
S23-13
1 3 .6
TIME HISTORY ANALYSIS/ STATISTICS n n
Amplitude Distribution Analysis (ADA) Running Statistics (RSTATS)
PAT318, Section 23, March 2002
S23-14
AMPLITUDE DISTRIBUTION ANALYSIS - “ADA” the probability of a certain amplitude in the time domain
DISPLAY OF SPIKES.ADA
DISPLAY OFSPIKES.ADA
100
P r o b . . C u m
(
T im
e
2000
P o in t C o u n t
D e n
a t le v e l ( s e c o n d s )
1.2
DISPLAY OF SPIKES.ADA
C o u n ts
0.08
DISPLAY OF SPIKES.ADA
0
0 -1442.3682
Strain (uE)
1496.079
-1442.3682
PAT318, Section 23, March 2002
0 Strain (uE)
1496.079
-1442.3682
S23-15
0.2 Strain (uE)
1496.079
2.9443359
Rise (uE)
2941.3915
RUNNING STATISTICS - “RSTATS” - calculating statistics for user-defined windows of data
1500
S tra i n (u E )
-1500 0
SP I K ES.DAC
2
4
6
8
10 seconds
1500
R un ning
M a x (u E )
SP I K ES.MAX
-1500 2
4
6
8
10 s
1500
R un ning
M i n (u E )
R un ning
M e a n (u E )
R un ning
Abs
SP I K ES.MI N
-1500 2
4
6
8
10 s
1500
-1500
2
SP I K ES.MEA
4
6
8
10 s
1500
M a x (u E )
SP I K ES.ABS
-1500 2
4
6
8
10 s
896.1
R un ning
R M S (u E )
SP I K ES.R MS
114.7 2
4
6
8
10 s
861.9
R un ning
S D (u E )
R un ning
A re a (u E )
38.68
2
SP I K ES.R SD
4
6
8
10 s
59.91
-52.8
2
SP I K ES.AR E
4
6
8
10 s
Screen 1
PAT318, Section 23, March 2002
S23-16
FILTERING
n n
Butterworth Filtering (BFL) Fast Fourier Filtering (FFF)
PAT318, Section 23, March 2002
S23-17
DATA FILTERING - “FFF” & “BFL” Frequency Domain n
Fast Fourier Filter (FFF) u u u u
n
Low Pass High Pass Band Pass Band Reject
Uses FFT and Inverse-FFT to remove frequency content
PAT318, Section 23, March 2002
Time Domain n
Butterworth Filter (BFL) u u u u
n n n
S23-18
Low Pass High Pass Band Pass Band Reject
Simulates hardware filter Forwards and ForwardsBackwards Methods Up to 8th order cut off
FREQUENCY ANALYSIS n n
Auto Spectral Density (ASD) Frequency Response Analysis (FRA)
PAT318, Section 23, March 2002
S23-19
AUTO SPECTRAL ANALYSIS - “ASD” - Calculating frequency content of data using FFT
n
n
n n n
PSD u Area under PSD = Mean square amplitude ASD u Area under ASD = amplitude ESD u ESD = PSD x Time Real & Imaginary Magnitude & Phase of FFT
PAT318, Section 23, March 2002
S23-20
FREQUENCY RESPONSE ANALYSIS - “FRA” - transfer function analysis of single input - single output linear system 2.924E-3
n
n
n
PSDs of input & output Cross-Power Spectra between input & output Gain, phase & coherence relationships
RMS Power(g^2. Hz^-1)
0 0
20
G01.SXX
40
60
80
Sample = 10 Npts = 1024 Max Y = 2.924E-3 Min Y = 0
100 Hz.
1.611E-3
RMS Power(g^2. Hz^-1)
0
20
G01.SYY
40
60
80
Sample = 10 Npts = 1024 Max Y = 1.611E-3 Min Y = 6.655E-7
100 Hz.
1.352E-3
RMS Power(g^2. Hz^-1)
0 0
20
G01.SXY
40
60
80
Sample = 10 Npts = 1024 Max Y = 1.352E-3 Min Y = 0
100 Hz.
2.632
Gain(No units)
0.1248 0
20
G01.GAI
40
60
80
Sample = 10 Npts = 1024 Max Y = 2.632 Min Y = 0.1248
100 Hz.
180
Phase(Degrees)
-179.9 0
20
G01.PHA
40
60
80
Sample = 10 Npts = 1024 Max Y = 180 Min Y = -179.9
100 Hz.
0.9959
Coherence(No units)
0 0
20
G01.COH
40
60
80
Sample = 10 Npts = 1024 Max Y = 0.9959 Min Y = 0
100 Hz.
Screen 1
PAT318, Section 23, March 2002
S23-21
PEAK VALLEY REGENERATION - “REGEN” - generating a time history from a cycle matrix Original peak valley history for comparison
434
A Pillar(uE)
STRAIN.PVX Sa mple = 1 N pts = 3 98 5 M a x Y = 43 4 M in Y = -7 15 .9
-715.9 0
1000
2000
3000 Point
418.2
Magnitude(uE)
STRRM.DAC Sa mple = 1 N pts = 3 98 4 M a x Y = 41 8 .2 M in Y = -7 06 .9
-706.9 0
1000
2000
3000 Seconds
425.4
Magnitude(uE)
STRMM.DAC Sa mple = 1 N pts = 3 98 4 M a x Y = 42 5 .4 M in Y = -7 07 .7
-707.7 0
1000
2000
3000 Seconds
392.9
Magnitude(uE)
STRMKV.DAC Sa mple = 1 N pts = 3 98 5 M a x Y = 39 2 .9 M in Y = -7 14
-714 0
1000
2000
3000 Seconds
434
Strain(uE)
-706.9 0
STRIRF.DAC Sa mple = 1 N pts = 3 98 5 M a x Y = 43 4 M in Y = -7 06 .9 1000
2000
3000 Seconds
Screen 1
PAT318, Section 23, March 2002
S23-22
Fatigue Analysis (local or test based) Tools n n n n n
Stress-Life Analysis (SLF) Strain-Life Crack Initiation (CLF) Multiaxial Strain-Life (MLF) Frequency Domain Fatigue (FLF) Crack Growth LEFM (FCG)
PAT318, Section 23, March 2002
S23-23
Other Fatigue Related Tools
n n n n n
Cycles Damage Analysis (CDA) Time Correlated Damage (TCD) Stress Concentration Library (KTAN) Cycles / Matrix Listing (CYL) Rosette Analysis (SSA)
PAT318, Section 23, March 2002
S23-24
CYCLES AND DAMAGE ANALYSIS - “CDA” - comparing 2D plots of 3D histogram data Total plot of file STRAIN
10.67
Cycles
Damage %
224.2
0
0 0
4174
Range Cycle
Damage
Compares number of cycles with the damage contribution of that stress or strain range PAT318, Section 23, March 2002
S23-25
TIME CORRELATED DAMAGE - “TCD” - identifying the damaging portions of data STRAIN-LIFE FATIGUE ANALYSIS RESULTS SUMMARY Time Correlated Fatigue damage Analysis S t r a in U E
1273
Load History OS_LSW.DAC
-1 2 6 .3
-1 5 2 6 D a m a ge
Time Correlated
C um . D a m a ge
Damage
Cumulative Fatigue Damage
0
20
PAT318, Section 23, March 2002
40
60 TIM E S E C S .
S23-26
80
100
STRESS CONCENTRATION LIBRARY “KTAN” - calculating Kt for standard geometries stress
A d
o
B
o o o
d/4
d
A
s
r
h
r
d/8
r M
t Kt = 0.22 + 1 ------------------0.2 0.4 (r/t) . (h/t)
M
M
Kt is at point B (15 deg from vertical) N.B. Kt at point A is constant = 1.6
M t
3 Nominal stress = M / ( 3.142 d / 32 ) In this case r / d = 0.1
Choose from graphical library of geometries and stress concentrations
PAT318, Section 23, March 2002
S23-27
ROSETTE ANALYSIS - “SSA” - analyzing the stress state of rosette data Stress-Strain Analysis & Multiaxial Assessment n n
n
n
n
Mohr’s Circle Calculates strain components from rosette Biaxiality ratio vs Principal plots Angle vs Principal plots Elastic- plastic conversion
Mohrs Circle for Strain
Gauge : Rectangular
E1 =
1000
uE
E2 =
500
uE
E3 =
500
uE
530.7
SPRING SEAT(UE)
-78.67 0
20
PRS.MAX
40
60
80
100 S E C S .
Principals : Max =
1104
uE
Min =
396
uE
Shear =
707
uE
Angle =
-23
degs.
from Grid 1
-135.9
SPRING SEAT(UE)
-687.6 0
20
PRS.MIN
40
60
80
Sample = 74 Npts = 8294 Max Y = -135.9 Min Y = -687.6
100 S E C S .
343.4
SPRING SEAT(UE)
PRS.ABS
S13101.ABS Strain UE
-687.6 0
20
40
60
80
Sample = 74 Npts = 8294 Max Y = 343.4 Min Y = -687.6
100 S E C S .
Time range : 0 secs to 23.06 secs
5 0 0 0
668.6
SPRING SEAT(UE)
PRS.SHR
4 0 0 0 Dominant Biaxiality Ratio -->
3 0 0 0
-1151 0
2 0 0 0
20
40
60
80
Sample = 74 Npts = 8294 Max Y = 668.6 Min Y = -1151
100 S E C S .
1 0 0 0
89.78
Angle(Deg rees)
PRS.ANG
0
-1 0 0 0 -1
-0 .5
0
0 .5
1
-89.98 0
Biaxiality Ratio (No units)
20
40
60
80
Sample = 74 Npts = 8294 Max Y = 89.78 Min Y = -89.98
100 S E C S .
S13101.ABS Strain UE
0.4018
Biaxiality Ratio (No un its)
PRS.BAX
Time range : 0 secs to 23.06 secs
5 0 0 0
-0.9427 0
4 0 0 0
20
40
60
80
100 S E C S .
3 0 0 0
<-- Dominat Angle to the Zero Gauge
2 0 0 0
1 0 0 0 0
-1 0 0 0 -1 0 0
-5 0
0 Angle (Degrees)
PAT318, Section 23, March 2002
Sample = 74 Npts = 8294 Max Y = 530.7 Min Y = -78.67
S23-28
5 0
1 0 0
Sample = 74 Npts = 8294 Max Y = 0.4018 Min Y = -0.9427
DATA CONVERSION & OTHER UTILITIES n
Data Conversion u u u
n
Binary to ASCII (DTA) MTS RPCTM File translators (DACREM/REMDAC) Cycles Matrix to Time History (REGEN)
Other Functions u u u u u
Convert data across platforms (CONFIL) View / Edit Data Header (FILMNP) Plotting setup on UNIX (PLTSYS) Viewing Plots on UNIX (QPLOT) Windows Plot Manager on NT (WNPLOT)
PAT318, Section 23, March 2002
S23-29
EXERCISE n
Perform Quickstart Guide Chapter 17 Exercise, “Fatigue Utilities”
n
Be sure to ask for help if there’s anything you don’t understand
PAT318, Section 23, March 2002
S23-30