Durability and Fatigue Life Analysis Using MSC.fatigue

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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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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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Section

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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


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Section

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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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Section

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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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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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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


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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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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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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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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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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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


S0-18

SECTION 1 OVERVIEW OF DURABILITY AND FATIGUE LIFE ANALYSIS


S1-1


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


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)


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.


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.


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.


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


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


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


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


S1-11

COMPUTER AIDED ENGINEERING SOLUTIONS... MSC Finite Element Analysis Software

Materials & Loading Information MVI - Flightloads

Engineering Services

MSC

MSC Institute Training Services


S1-12

Tailored Software Solutions

DURABILITY MANAGEMENT

MEASUREMENT

TEST

nCode MSC ANALYSIS


S1-13

A partnership for excellence in durability technology


S1-14

WHAT IS DURABILITY?


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!


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.


S1-17

WHAT DRIVES DURABILITY MANAGEMENT?


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.


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


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


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


S1-23

PREDICTING PRODUCT LIFE 2 - ADD SIGN-OFF TESTING

Customer Usage

Accelerated Sign-off Test

Re-Design


S1-24

Product Life

PREDICTING PRODUCT LIFE 3 - ADD SIMULATION TESTING

Customer Usage

Simulated Component Test


Measured Service Loading Re-Design


S1-25

Product Life

PREDICTING PRODUCT LIFE 4 - ADD CAE Customer Usage


Simulated Component Test

Measured Service Loading Stress Analysis Material Properties

Product Life

Correlation Computer-based Fatigue Life Simulation

Product Life

Re-Design Optimize


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


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.


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.


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


S1-31

Wohler’s Railway Component Test Rig


S1-32

Stress Amplitude

Unnotched Shaft

Notched Shaft

Log (Fatigue life) Some of Wohler’s data for rotating bending tests


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


S1-34

CRACK INITIATION AND GROWTH - STAGE I AND II

~1mm

Persistent Slip band formation


Stage I Crack Growth

S1-35

Stage II Crack Growth

MICROSTRUCTURAL CRACK GROWTH da/dN

a


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


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)


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


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


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


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


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


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.


S1-47

INITIATION AND PROPAGATION


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


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.


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


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.


S1-52

DESIGNING AGAINST FATIGUE n

Requirements: u u u u u


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’


S1-54

EXPLOITING FATIGUE ANALYSIS - THE 5 BOX TRICK LOADS

GEOMETRY

BLACK BOX

Wrong answer

ANALYSIS

LIFE (42) Garbage OUT

MATERIALS Garbage IN


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


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.


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.


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


S1-59

HOW ANALYSIS SUPPORTS TESTING n n n n

Eliminating unnecessary tests Test acceleration Gauge type selection and positioning Test design


S1-60

“Engineering is the art of being approximately right rather than exactly wrong”

-Quote by Prof. Rod Smith University of Sheffield,1990


S1-61


S1-62

SECTION 2 OVERVIEW OF MSC.FATIGUE


S2-1


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


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


Stress or Strain

S2-5

LIFE

LIFE PREDICTION PROCESS: APPROACH measured strains

constitutive model

stress and strain components elastic strains from FEA


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)


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.


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


S2-9

EXAMPLE - STEERING KNUCKLE


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


500

1000

1500 point

Screen 1


S2-11

QUASI-STATIC STRAIN CALIBRATION & SUPERPOSITION Time Histories

FE Loadcase Results

FE Loadcase Loads

This process is repeated for each node/element


S2-12

Local Strain Histories

STEERING KNUCKLE


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)


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


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


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


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


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


Fatigue Crack Analyzer

CRG

S2-20

DYH

XYD

Results Listing

MSC.FATIGUE MAIN FORM Geometry

Materials

Postprocessing

Analysis

Loading Optimization


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


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



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


S2-24


Materials

Analysis

Post-processing



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.


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


1E1

1E2

1E3

1E4 1E5 Life (Cycles)

S2-27

1E6

1E7

1E8

1E9

METHODOLOGY

Geometry

Materials

Analysis

Post-processing



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


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


S2-30

12


Materials

Analysis

Post-processing



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


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


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


S2-34

METHODOLOGY

Geometry

Materials

Analysis

Post-processing



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


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


S2-37

POST-PROCESSING: HISTOGRAM PLOTS Cycles vs. Damage


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


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


S2-40

ADVANCED FEATURES: MSC.FATIGUE SPOT WELD


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


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


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


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


S2-45

Mx

FATIGUE RESULTS FOR SHOCK TOWER


S2-46

MSC.FATIGUE SOFTWARE STRAIN GAUGE A virtual test facility in the MSC.Fatigue environment


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.


S2-48

CORRELATION APPLICATIONS

Software Strain Gauges

FEA Model Surface

Hub Strain

Hub Strain

Real World Structure

time

time


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)


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


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


-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


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


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


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


S2-56

HOW DO WE CALCULATE DAMAGE? Loading (PSD)

Material (S-N analysis)

Fatigue Analysis (Vibration Fatigue)

Geometry (FE Analysis)



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


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


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


S2-60

SECTION 3 MSC.FATIGUE USER INTERFACE


S3-1


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


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


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


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


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


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


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


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


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


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


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


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)


S3-15


S3-16

SECTION 4 OVERVIEW OF PATRAN


S4-1


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


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


S4-4

STEP 1 - ANALYSIS PREFERENCES (CONTINUED)

n

n


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


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


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


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


S4-11

STEP 4 – PERFORM THE ANALYSIS

n

n

Select code-specific solution procedures and parameters Submit directly from MSC.Patran


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


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


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


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


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


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.


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”)


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


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


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 -


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


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


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


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


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


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


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


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


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


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


S4-35


S4-36

SECTION 5 GEOMETRIC MODELING


S5-1


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)


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


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


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


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


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


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


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


S5-12

FILE IMPORT OPTIONS


S5-13

FILE IMPORT OPTIONS (CONCLUDED)

Geometry kernal type

CAD part

Standard format


S5-14

EXAMPLE – UNIGRAPHICS CAD MODEL IMPORT n n n n


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


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


S5-17

MSC.PATRAN DATABASE ACCESS (CONTINUED) n

MSC.Patran databases can be accessed by selecting “MSC.PATRAN DB” as the source


S5-18


Importing options controls u u u

Which entities to import How to import entities Resolve conflict


S5-19


n

Merged finite element models may be equivalenced Options on how MSC.PATRAN will deal with Discrete deal with Discrete FEM Fields on import


S5-20

FILE EXPORT OPTIONS


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


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


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


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


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


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


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


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


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


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


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


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


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


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


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


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


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


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


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


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.


[ 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


Y

3

4

X

Z

S5-43

X

GEOMETRIC ENTITIES - SURFACE


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


S5-45

4 X

TRIMMED SURFACE CONSTRUCTION Three options for creating a trimmed surface in MSC.PATRAN


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


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


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


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


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


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


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


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


Parametric surface S5-55

EDGE MATCH SURFACE 2

n

n

n

n


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


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


Non-manifold edge S5-58

GEOMETRIC ENTITIES - SOLID


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


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


S5-62

CREATE PRIMITIVE SOLIDS n n

n

n

n


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


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


Add

2

Parametric

S5-66

3

B-rep from Add

GEOMETRIC ENTITIES – COORDINATE FRAME


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


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


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


Point 5

Y

1

SECTION 6 MESHING


S6-1


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)


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


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 =


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


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


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


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


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


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


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


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


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


“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


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


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


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


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


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


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


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


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


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


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


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


S6-38

EQUIVALENCE FORM n

Equivalencing can be applied to: u u u

n

n

n

n


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


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


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


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


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


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


S6-45


S6-46

SECTION 7 VIEWING


S7-1


S7-2

VIEWING

n

Orients view of model in the viewport u u u u u

n


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


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


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


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


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


S7-10

SECTION 8 GROUPS


S8-1


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


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


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


S8-6

CREATING A GROUP n

n n

n

n


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


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


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


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


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


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


S8-13

DELETING GROUPS n n

n

n


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.)


S8-15


S8-16

SECTION 9 DISPLAY


S9-1


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


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


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


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


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


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


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


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


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


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


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


S9-14

SECTION 10 ANALYSIS SETUP


S10-1


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)


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


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


S10-5

READING A MSC.NASTRAN BULK DATA FILE n

n

n

n

n


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


S11-1


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


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


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


S11-5

BOOLEAN EXAMPLE

n n n


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


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


S11-8

SECTION 12 VIEWPORTS


S12-1


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


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


S12-4

CREATING VIEWPORTS No limit on how many viewports one can create


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


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


S12-7


S12-8

SECTION 13 RESULTS


S13-1


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


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


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


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


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


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


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


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


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


S13-12

RESULTS POST-PROCESSING PROCEDURE n n n n n n n


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”


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


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


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


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


S13-19

Plot Options Button

PLOT OPTIONS FORM (CONTINUED) n

Coordinate transformation options u u u

u u u

u

n

n


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


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


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:


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.


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


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


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.


S13-29

FRINGE PLOT OPTIONS (CONCLUDED) n

Define PCL Expression u

u

u

u


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


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


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


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


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


S13-35

Specify set of results

CREATE RESULTS FORM (CONCLUDED) n

PCL Function for user defined expression u

u

u

u


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


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


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


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


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)


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


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


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


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


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


S13-47

TYPICAL RESULTS ANIMATION

Frame 1

Frame 7

Frame 13

Frame 20


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


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


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


S13-51

ANIMATION CONTROL n

n

n

n


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


S13-53

7


S13-54

SECTION 14 X-Y PLOTTING


S14-1


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


S14-3

XY PLOT TERMINOLOGY


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.


S14-5

SCALE AND RANGE n

Scale u u u

n

Range u


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.


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


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


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


.800

1.20

S14-10

SECTION 15 MSC.PATRAN FILES


S15-1


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.


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


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


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


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


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.


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


Allows you to select a different template database

S15-9


S15-10

SECTION 16 STRESS-LIFE (S-N) THEORY

PAT318, Chapter 16, March 2002

S16-1


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


S16-3

Some Definitions


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


S16-5

S-N Curve


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


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


S16-10

S-N Curves


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


S16-12

Material S-N Curves Log(Stress)

Steel or Ti

Al alloy or steel in seawater


S16-13

Log(Life)

Scatter in S-N curves


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


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


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.


S16-19

Variable Amplitude Loads - Miner’s Rule and Rainflow Counting


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


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


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)


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.


S16-26

Variable Amplitude Loads - Estimating Lifetime -


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



S16-29


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


S16-30

Cycle Count Matrix


S16-31

Rainflow Counting and Stress/Strain Space


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


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


S16-35

N

Damage Counting

Influences on Fatigue Life


S16-36

Factors Influencing Fatigue Life •Mean stress


S16-37

Mean Stresses


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.


S16-39

Mean Stress Corrections


S16-40

Mean Stress Corrections Unsafe

Un-Safe Safe

Un-Safe

Haigh Diagram PAT318, Chapter 16, March 2002

S16-41


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).


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


Haigh Diagram PAT318, Chapter 16, March 2002

S16-44

Factors Influencing Fatigue Life • Mean stress • Component size


S16-45

Component Size Small laboratory specimens and large engineering structures Influence of Specimen Size on Endurance Limit:


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


S16-47

Factors Influencing Fatigue Life • Mean stress • Component size • Type of loading


S16-48

Type of Loading Problem: • Data from rotating bend tests • Structure sees tension or torsion


S16-49

Factors Influencing Fatigue Life • Mean stress • Component size • Type of loading • Notches and discontinuities


S16-50

Notches


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.


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


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


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 .


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.


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 )


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)


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.


S16-59

Effect of Notch Factor Transition Life

1000 cycles

Kf’ Stress

unn

otc hed

no tch ed

Kf

Life


S16-60

Curve for Estimation of Kf’ (From Juvinall)


S16-61

Factors Influencing Fatigue Life • Mean stress • Component size • Type of loading • Notches and discontinuities • Surface treatment & finish


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.


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


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.


S16-66

Correction for Surface Finish Transition Life

1000 cycles

pol ish

Stress

ed

ro ug h

Life


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.


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)


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.


S16-71

Goodman Based Factor of Safety (f) Calculation Goodman Based: Factor of Safety =

Gerber Based: Factor of Safety =


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

•


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.


S16-74

Example Problem: S-N Analysis of a Keyhole Specimen Perform simple S-N analysis. Single load input (fully reversed loading).


S16-75

Loading Info Setup


S16-76


S16-77

Plot Simple Loading


S16-78

Select the Created Loading


S16-79

Material Info Setup


S16-80

Submit Job Read Results Display Life Contours


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


S16-82

SECTION 17 STRAIN-LIFE (EN) THEORY


S17-1


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.


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.


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


S17-5

STRAIN - LIFE METHOD


S17-6

STRAIN LIFE CURVE Note: area enclosed represents the amount of plastic strain


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.


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


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


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


S17-12

Stress

STRESS-STRAIN RESPONSE

Strain


S17-13

Stress

REVERSING THE LOADING DIRECTION

Strain


S17-14

Stress

REVERSING THE LOADING DIRECTION AGAIN

Strain Material Memory


S17-15

THE BAUSCHINGER EFFECT

Masing: stress strain curve = twice the cyclic stress strain curve


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.


S17-17

MASING’S HYPOTHESIS (STABILIZED HYSTERESIS LOOP)


S17-18

MASING’S HYPOTHESIS (STABILISED HYSTERESIS LOOP)


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.


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


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


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


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)


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)


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.


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 =


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.


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

=


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


S17-32

VARIABILITY IN MATERIAL BEHAVIOUR AND THE EFFECTS ON FATIGUE LIFE PREDICTION n n n n n


Chemical composition Heat treatment Cast vs. wrought Surface treatments Degree of deformation

S17-33

VARIABLE AMPLITUDE LOADS - COUNTING CYCLES


S17-34

RAINFLOW CYCLE COUNTING


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


S17-36

RAINFLOW CYCLE COUNT MATRIX


S17-37

RAINFLOW COUNTING AND STRESS/STRAIN SPACE


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


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


S17-40

MORROW CORRECTION


S17-41

SMITH WATSON TOPPER CORRECTION


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)


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



S17-44

ELASTIC-PLASTIC CORRECTION AND LOCAL GEOMETRY


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.


S17-46

ELASTIC-PLASTIC CORRECTION Elastic FE Strain

1

Cyclic StressStrain Curve

2

σ

Neuber Equation Solution point

ε

∆εe


∆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


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.


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


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)


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


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.).


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


1E1

1E2

1E3

1E4 1E5 1E6 Life (Reversals)

S17-59

1E7

1E8

1E9

STRESS STRAIN TRACKING, NEUBER ANALYSIS, MATERIAL MEMORY AND DAMAGE CALCULATION


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)


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’


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!


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


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)


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


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


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


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


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.


S17-73

REVIEW STRESS CONTOURS


S17-74

FATIGUE ANALYSIS n n n

Reference single load (sine01) Create new group for analysis Submit Job


S17-75

PLOT LIFE CONTOURS


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



S17-77


S17-78

SECTION 18 MULTIAXIAL FATIGUE

PAT318, Section 18,March 2002

S18-1


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


S18-3

THE LIFE PREDICTION PROCESS E - N APPROACH measured strains

plasticity modelling

stress and strain components elastic strains from FEA


constitutive model and notch rule

S18-4

LIFE damage model

2-D STRESS STATE σyy τyx

σxx

y

τxy τyx

x


τxy

σyy

S18-5

σxx

3-D STRESS STATE σyy σzz τyz

τyx τzx

σxx

y

σzz x

z


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


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


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‘


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


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


S18-11

MOHR’S CIRCLE FOR STRESS (2D)

τxy σ2

−τxy τmax

σy

2θ

σx

τ


S18-12

σ1 σ

MOHR’S CIRCLES FOR TRIAXIAL STRESS

σ3

τmax

σ2

τ


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


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


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:


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


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)


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


S18-21

EXAMPLE: NON-PROPORTIONAL LOADING GAGE1.ABS Stress MPa

GAGE1.ABS Stress MPa

Time range : 0 secs to 183.6 secs


200

200

100

100

0

0

-100

-100

-200 -1

-200 -0.5

0

0.5


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


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



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


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


S18-26

2

THE VON MISES YIELD CRITERION σ3

von Mises yield surface

hydrostatic stress

σ2 σ1


S18-27

VON MISES AND TRESCA IN DEVIATORIC STRESS SPACE S1 von Mises Tresca 2 σy 3

S2

S3


S18-28

VON MISES AND TRESCA IN PRINCIPALS σ2 von Mises Tresca

σ1


S18-29

EQUIVALENT STRESS AND STRAIN METHODS

Extension of the use of yield criteria to fatigue under combined stresses


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


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


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


(

)

(

)

∆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...


' ∆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


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)


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


(

∆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



strain criterion


Any

Tresca


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


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


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


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


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


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


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


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


S18-52

DIRECTION OF CRACK GROWTH


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.


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.


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


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.


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


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


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:


S18-61

SHEAR STRAIN METHOD

n


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:


S18-62

SMITH-TOPPER-WATSON-BANNANTINE METHOD

n


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


S18-63

FATEMI-SOCIE METHOD n


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


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


)

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


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’


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


(

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


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


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


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


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


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


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


S18-75

DANG-VAN PLOT τ(t)

Damage occurs here !!!

τ + a ⋅ ph − b = 0

ph(t)

τ − a ⋅ ph +b = 0


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


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


S18-78

DANG VAN FACTOR OF SAFETY PLOT


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.


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


500

1000

1500 point

Force(Newtons)

LOAD01.PVX

3769


500

1000

1500 point

Screen 1


S18-82

LOG-LIFE CONTOUR PLOT (IN REPEATS)


S18-83

EXAMPLE MULTIAXIALITY INDICATORS

Angle Spread

Mean Biaxiality


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


S18-85


S18-86

SECTION 19 FATIGUE CRACK PROPAGATION


S19-1


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


S19-3

FRACTURE MECHANICS TRIANGLE

Stress Intensity (K)

Crack Size (a)


Stress (s)

S19-4

FRACTURE MECHANICS RECTANGLE Cycles to Failure (Nf)

Final Crack Size (af)

Initial Crack Size (ai)


Stress Range (DS)

S19-5

CRACK STRESS CONCENTRATION A crack is an extreme stress/strain concentrator

Elastic Stress Concentration σmax = Ktσ


Kt=(1+2a/b)

Kt=3

S19-6

b = 0 --> Kt = ∞

MODES OF CRACK OPENING


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, ... )


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


S19-9

LINEAR ELASTIC FRACTURE MECHANICS


S19-10

LINEAR ELASTIC FRACTURE MECHANICS


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)


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


S19-13

STAGES OF FATIGUE CRACK GROWTH


S19-14

FATIGUE CRACK GROWTH MECHANISMS n n

Reversed plasticity Corrosion


S19-15

CRACK PROPAGATION METHOD SIMILITUDE

This crack . . . . . . . grows at the same rate as this one if both experience the same stress intensity factors


S19-16

CRACK GROWTH RATES ARE CONTROLLED BY ∆K Fast Fracture Effects

da --dN

Paris Law Region da --- = C∆Km dN ∆K Threshold Effects


∆K = Y ∆σ √ πa S19-17

PROPAGATION RATES


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


S19-19

CRACK TIP PLASTICITY


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


S19-21

MEAN STRESSES (R-RATIO EFFECTS)

Kmin R= Kmax


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.


S19-23

VARIABLE AMPLITUDE LOADS High - low sequences change the crack closure


S19-24

ENVIRONMENT Crack growth rates are higher in corrosive environments (e.g. salt water) than in air. They are the lowest in vacuum.


S19-25

CALCULATING LIFETIMES n

Need: u u u u u

Initial crack size Final crack size Stress range K calibration Material growth law


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)


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)


S19-29

IMPLEMENTATION IN MSC.FATIGUE

Time Cycle Counter

Geometry function Library

KSN

TCY

MDB

CRACK GROWTH ANALYSER

CRG


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)


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


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


S19-33

EXAMPLE PROBLEM: CRACK PROPAGATION ANALYSIS n n

Lug problem Single load


S19-34

LINEAR ELASTIC FRACTURE MECHANICS ANALYSIS (LEFM)


S19-35

DEFINE A CRACK AND PLOT COMPLIANCE FUNCTION


S19-36

LOADING INFO SETUP


S19-37

MATERIAL INFO SETUP

n

Create a group “far_field” with node 223 in it only.


S19-38

PERFORM LEFM ANALYSIS


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



S19-40

SECTION 20 SPOT WELD FATIGUE


S20-1


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


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


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


S20-5

Spotweld “Nugget”

Beam Element

AN AUTOMOTIVE PART WITH SPOT WELDS


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


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


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


S20-10

Mx

FATIGUE PROPERTIES - TYPICAL TEST SPECIMEN


S20-11

FATIGUE PROPERTIES - GENERIC S-N CURVES


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)


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 ...


S20-14

FATIGUE RESULTS FOR SHOCK TOWER


S20-15

POLAR PLOT OF DAMAGE


S20-16

EXAMPLE PROBLEM:A SPOT WELD ANALYSIS Perform spot weld analysis.

Multiple loading inputs at shock tower.


S20-17

SOLUTION PARAMETERS SETUP


S20-18

MATERIAL INFO SETUP


S20-19

LOADING INFO SETUP


S20-20


S20-21

EXERCISE

■

Perform Quickstart Guide Chapter 13 Exercise, “A Spot Weld Analysis”

■



S20-22

SECTION 21 MSC.FATIGUE SOFTWARE STRAIN GAUGE


S21-1


S21-2

A virtual test facility in the MSC.Fatigue environment


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.


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.


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


S21-6

-495

CORRELATION APPLICATIONS (Contd.)

Software Strain Gauges FEA Model Surface Hub Strain

Hub Strain


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


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


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.


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


S21-11

EXAMPLE PROBLEM: A SOFTWARE STRAIN GAGE Introduce software strain gage as a correlation tool on a mounting lug.

Multiple loading inputs.


S21-12

SOFTWARE STRAIN GAGE SETUP

and elements that define surface

Define node to initially put gage on ...


S21-13

LOADING INFO SETUP


S21-14

PERFORM ANALYSIS

■ ■ ■

Define material and loading Extract time histories from rosette Perform rosette analysis and correlation


S21-15

CORRELATION TECHNIQUES ■ ■ ■ ■

Overlays and cross plots Rosette analysis Single location uniaxial life analyzer Single location multiaxial life analyzer


S21-16

EXERCISE

■

Perform Quickstart Guide Chapter 15 Exercise, “A Software Strain Gauge”

■



S21-17


S21-18

SECTION 22 VIBRATION FATIGUE ANALYSIS


S22-1


S22-2

OVERVIEW

n n n n

Why use frequency domain? Benefits of vibration fatigue Review of theory Summary of features


S22-3

WHY USE FREQUENCY DOMAIN?

time

time

Output

Transfer Function frequency


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


S22-5

HOW DO WE CALCULATE DAMAGE? Loading (PSD)

Material

Fatigue Analysis

(S-N analysis)

(Vibration Fatigue)

Geometry (S-N Analysis)



S22-6

Post Processing


TIME HISTORY

RAINFLOW COUNT


FATIGUE LIFE STRESS RANGE HISTOGRAM

Transient Analysis


FATIGUE MODELLER

PDF

FATIGUE LIFE

Transfer M0 M1 M2

Function

M 4


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


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.


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


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


TIME HISTORY

RAINFLOW COUNT


FATIGUE LIFE

Transient Analysis



FATIGUE MODELLER

PDF

FATIGUE LIFE

Transfer M0 M1

Function

M2 M 4


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


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.


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


S22-20

SINGLE LOAD Time-domain Analysis (static FE result)

Frequency-domain Analysis (At Frequency = 0 Hz) Frequency-domain Analysis (one of several frequencies)


S22-21

TIME-DOMAIN LOADING INFO SETUP


S22-22

FREQUENCY-DOMAIN LOADING INFO SETUP


S22-23

FREQUENCY-DOMAIN LOADING INFO - MULTIPLE PSDS -


S22-24

RESULTS: Static case: Combined loads

Vibration: uncorrelated loads

Vibration: correlated loads


S22-25

EXERCISE

n

Perform Quick Start Guide Chapter 16 Exercise, “Vibration Fatigue”

n



S22-26

SECTION 23 MSC.FATIGUE UTILITIES


S23-1


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


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.


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


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)


S23-6

MATHEMATICAL MANIPULATION OF DATA - “ART”


S23-7

SPREADSHEET MULTICHANNEL EDITOR “COE”


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


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


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


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)


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


C o u n ts

0.08


0

0 -1442.3682

Strain (uE)

1496.079

-1442.3682


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


S23-16

FILTERING

n n

Butterworth Filtering (BFL) Fast Fourier Filtering (FFF)


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


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)


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


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


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


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


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


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)


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)


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


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


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 .


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


20

40

60

80


100 S E C S .

S13101.ABS Strain UE

0.4018

Biaxiality Ratio (No un its)

PRS.BAX


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)



S23-28

5 0

1 0 0


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)


S23-29

EXERCISE n

Perform Quickstart Guide Chapter 17 Exercise, “Fatigue Utilities”

n



S23-30

Durability and Fatigue Life Analysis Using MSC.fatigue

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