FINITE ELEMENT ANALYSIS IN ABAQUS
Siddhartha Ghosh* and Swapnil B. Kharmale** * Assistant Professor, ** Research Scholar (PhD Student )
Department of Civil Engineering Indian Institute of Technology, Bombay
ABAQUS : General ABAQUS is a highly sophisticated, general purpose finite element program, designed primarily to model the behavior of solids and structures under externally applied loading. Salient features of ABAQUS
Capabilities for both static and dynamic problems
The ability to account all types of nonlinearities viz. material non-linearity
and geometric non-linearity
A very extensive element library, including a full set of continuum elements,
beam elements, shell and plate elements
A sophisticated capability to model contact between solids
Capabilities to model a number of phenomena of interest, including
vibrations, coupled fluid/structure interactions, acoustics, buckling problems, and so on. (From:www.abaqus.comand and www.engin.brown.edu/courses/en175/abaqustut/abaqustut) www.engin.brown.edu/courses/en
ABAQUS : General The ABAQUS suite consists of three core products: • ABAQUS/Standard, For traditional implicit finite element analyses such as static, dynamics, thermal, all powered with the widest range of contact and nonlinear material options • ABAQUS/Explicit For transient dynamics and quasi-static static analyses using an explicit approach appropriate in many applications such as drop test, crushing and many manufacturing processes. and nvironment) • ABAQUS/CAE (Complete Abaqus Environment) It provides a complete modelling and visualization environment for ABAQUS analysis products. It has direct access to CAD models, advanced meshing and visualization
ABAQUS : General Here we focus on ABAQUS/Standard
Solver Structure Command Line
ABAQUS CAE
ABAQUS STANDARD
Now we will model and analysis a single story Steel Plate Shear Wall (SPSW1) through ABAQUS/CAE (Note that it could be possible to create the model through command line which will be discussed later)
ABAQUS/CAE Layout You can start ABAQUS CAE from the START menu or with a command line by typing abaqus cae in a Command window. Following figure shows how an ABAQUS/CAE looks Title bar Menu bar
Tool bar Context bar
View port
Toolbox Area
Canvas & Drawing area
Prompt area Message area
ABAQUS CAE modules I)PREPROCESSING • Part – Create individual parts • Property – Create and assign material properties • Assembly – Create and place all parts instances • Step – Define all analysis steps and the results you want • Interaction – Define any contact information • Load- Define and place all loads and boundary conditions • Mesh – Define your nodes and elements II)ANALYSIS • Job – Submit your job for analysis III)POSTPROCESSING • Visualization- View your results
3-Dimensional Dimensional FEM Problem (Pushover Analysis of SPSW) To
start learning ABAQUS CAE we will work through modelling a single story Steel Plate Shear Wall (SPSW1) specimen which includes geometric nonlinearity (initial out-of-plane deformations during fabrication). The specimen is subjected to monotonic lateral load (Non-linear static pushover analysis)
Problem
Statement
To find the ultimate load carrying capacity (Lateral load) of single story steel plate shear wall (SPSW1) (SPSW by non-linear static push over analysis.
Details of SPSW1 SPSW
Lateral Force- Deformation Behavior of SPSW
Selection of Element for Modelling SPSW1 SPSW Infill Panel Element Boundary Element
By using 3-Dimensional Shell By using 3-Dimensional Beam Element
PART MODULE −
Create a new part as Infill_Panel
3-D planar
Type : Deformable
Basic feature: shell
Approximate
size:
6x6
(Note :- ABAQUS follows consistent unit so be specific to keep same unit. Here we kept SI units i.e. m for length N for force etc)
Part:- Infill_Panel The following picture shows how a Part Infill_Panel look
−
Create another new part as Boundary_Element
3-D planar
Type : Deformable
Basic feature: wire
Approximate size: 6 x6
Part:Boundary_Element Boundary_Element
Infill_Panel and Boundary_Element Parts in ABAQUS/CAE
Property Module
We will add the material Steel and give it values E= 2.0E+11N/m2 Poisson's ratio ν= 0.3, Yield Stress = 2.0E+08N/m2,Plastic strain=0 (Note that elastically-perfectly plastic relationship is used for steel) We will create section called Shellsection and give it category of Shell ,Continuous Shell/Homogenous and assign a thickness of 0.0025 0025m with thickness integration point 5 Assign material to this section
Property Module (Continued)
Also create section called Boundarysection_col and Boundarysection_bea and give it category of Beam Create profile namely Columns and Beams using Ishaped cross section Assign same material to this section also
Boundarysection_col
I-Section profile for Columns
I-Section Section profile for Beams
Property Module (Continued)
Assign Shellsection to part named Infill_Panel
Assign Boundarysection_col and Boundarysection_bea with Columns and Beams profile to part named Bounary_Element
Assembly Module
Now we will create two independent instances using parts Infill_Panel and Boundary_Element Its easy to mesh the assembly as a whole using
independent instances
Step Module By default there is a Initial Step in Abaqus (i.e.. System made step) which is used to define the Boundary Conditions We will add a step after system made initial step called Transverse load
The procedure type is General and type is Static. The nlgeom=Yes means geometric
nonlinearity is on to account for large deformations Keep the Output Request as preselected (By Default)
Step Module (Continued) After step called Transverse Load create a next analysis step Lateral Load The procedure type is General and type is Static Riks . Again nlgeom=Yes means geometric nonlineaarity is on to account for large deformations
Interaction Module In this module we will define the contact between two independent part namely Infill_Panel and Boundary_Element
Create surface Infill_Panel_Master in part Infill_Panel
Similarly create surface Boundary_Element_Slave in part Boundary_Element
Once these surfaces are created we can provide contact between them through Interaction module
Selection of Master surface
Selection of Slave surface
Interaction between two parts namely Infill_Panel and Boundary_Element
Creating Boundary Conditions in Initial Step Create boundary conditions in Initial step (System made step)
There are two type of Boundary conditions for this problem namely
Bottom extreme nodes are fixed (U1=U2=U3 3=UR1=UR2=UR3=0)
Edges are restrained in z-direction (U3=0)
Bottom extreme nodes are fixed (U1=U =U2=U3=UR1=UR2=UR3=0 i.e. Encastre)
Edges are restrained in z-direction z (U3=0)
Mesh Module Now we will mesh the assembly
Before that we will assign the shell element to Infill_Panel part. The shell element is S4R
Also assign the beam element to Boundary_Element part. The beam element is B31
Assigning S4R R Element to Infill_Panel part
Assigning B31 Element to Boundary_Element part
Mesh Module (Continued) After assigning proper element to each of part next step is seeding. Here we are using mesh of 20x20 for Infill_Panel part and we will discritize each boundary element into 20 parts. So for whole assembly mesh density will be 20x20.
Meshing of whole Assembly of SPSW1 SPSW
Load Module STEP:- Transverse Load :- Apply a concentrated load (named as CFORCE-1)of 2N at middle node in negative z-direction (i.e. Along 3-axis)
Load Module (Continue) STEP:- Lateral Load :- Apply a concentrated load (named as CFORCE-2)of 1000N at the TOPNODES in positive x-direction (i.e. Along 1-axis). axis). Remember here we kept the displacement contro trol thus load magnitude mentioned above is used as load control during initial part of analysis
Job Module We will create a job called SPSW1 Once this has been created just submit the job.
The analysis should only take a couple of minutes.
Here you have an option to select analysis viz Full analysis or Explicit analysis or Restart Submitting job after elapsed time
Visualization Module (Post processing) −
Once your analysis is complete we want to see the results.
−
First we will see the deformed shape of SPSW1 in Step Transverse Load. (Remember this step is created to have initial out-of out plane deformation (due to fabrications). So the deformed shape is somewhat similar to buckling of plate )
Visualization Module (Continued) −
Now we will see the deformed shape of SPSW1 in Step Lateral Load. (This step is static push over . Here out of plane deformations start increasing with increase in lateral load, and the buckling along the compression diagonal can be very clearly seen from the deformed shape of SPSW1 at the end of analysis)
Visualization Module (Continued) −
If we look at Von Mises stress distribution we see
Visualization Module (Continued) Here we will create X-Y plot First plot is of Horizontal component of Total Force developed at bottom extreme node vs increment
Creating X-Y X data
Visualization Module (Continued)
Selection of bottom extreme nodes to create X-Y X data
Visualization Module (Continued)
Visualization Module (Continued) Similarly create plot of Horizontal displacement (U1) of top node vs increment
Visualization Module (Continued) −
Now we will create a plot of Base shear (which is sum of horizontal component of total force developed at extreme bottom nodes (which are fixed support)) and lateral displacement of Top node
About ABAQUS Command line use (Input file creation ) Note:All models are called input files.
•An input file has two sections; Model and History •The Model section contains all the information about the model and comes before the history section. •The History section is what you do to the model. You work on the model in Steps. •Input files have a .inp extension and can be created in any ASCII (text) editor.
Now we will discuss how to create the model SPSW1 through an input file and then we will run it through windows command prompt or through ABAQUS CAE
Simple Input File (Model Section) **The lines starting with ** (2 asterisks) commented and are ignored ** by the **ABAQUS solver. Other lines beginning with a single * denotes an ABAQUS keyword.
****************************************************************************** *Heading
SPSW1 *Preprint, echo=YES, model=YES, history=YES, contact=YES ****************************************************************************** **The *PREPRINT key controls what information is printed to the file named **SPSWl.dat. Here, we have asked ABAQUS to print out absolutely everything. The consequence Once the input file is correct, **SPSWl.dat file is rather large as a consequence. **you can set all the options to NO to reduce the size of the file.)
****************************************************************************** ** (Creating geometry of model)
****************************************************************************** ** PARTS *Part, name=PART-1-1 ****************************************************************************** ** (Defining the control node coordinate)
****************************************************************************** *NODE 1, 0., 0., 0. 21, 3, 0. 0. *NGEN, nset=bottom 1, 21, 1 ****************************************************************************** **(nset=bottom is a node set which contains node started from 1 to 21 with an **interval of 1)
****************************************************************************** *NCOPY, CHANGE NUMBER=420, OLD SET=bottom, SHIFT, new set=top 0, 3, 0
*NFILL bottom, top, 20, 21 *Element, type=S4R 1, 1, 2, 23, 22 21, 22, 23, 44, 43 ****************************************************************************** **(Generating the intermediate shell elements in increment through *ELGEN command)
****************************************************************************** *ELGEN, elset=bottom 1, 20, 1, 1 *ELGEN 21, 20, 1, 1, 19, 21, 20 ****************************************************************************** ** (Creating master elements by using *Element command.)
****************************************************************************** *Element, type=B31 500, 1, 2 1000, 421, 422 1500, 1, 22 2000, 21, 42 *ELGEN, elset=beam 500, 20, 1 1000, 20, 1 1500, 20, 21 2000, 20, 21 ****************************************************************************** **(By using *Elset command one can made different set or group of element which **will be helpful while assigning material properties,boundary conditions,loading **etc.)
******************************************************************************
*Elset, elset=BEAM 500, 501, 502, 503, 504, 505, 506, , 513, 514, 515 516, 517, 518, 519, 1000, 1001, 1002, 1002 1009, 1010, 1011 1012, 1013, 1014, 1015, 1016, 1017, 1018, 1018 1505, 1506, 1507 1508, 1509, 1510, 1511, 1512, 1513, 1514, 1514 2001, 2002, 2003 2004, 2005, 2006, 2007, 2008, 2009, 2010, 2010 2017, 2018, 2019 *Nset, nset=_PICKEDSET2, internal, generate 1, 441, 1 *Elset, elset=_I1, internal, generate 1, 400, 1 *Elset, elset=_I5, internal, generate 500, 519, 1 *Elset, elset=_I2, internal, generate 1000, 1019, 1 *Elset, elset=_I3, internal, generate 1500, 1519, 1 *Elset, elset=_I4, internal, generate 2000, 2019, 1 ** Region: (Section-1-_I1:Picked) *Elset, elset=_I1, internal, generate 1, 400, 1 ** Section: Section-1-_I1 *Shell Section, elset=_I1, material=Steel 0.0025, 5
507,
508,
509,
510,
511,
512,
1003, 1004, 1005, 1006, 1007, 1008, 1019, 1500, 1501, 1502, 1503, 1504, 1515, 1516, 1517, 1518, 1519, 2000, 2011, 2012, 2013, 2014, 2015, 2016,
****************************************************************************** **(*Shell section command will create shell section having thickness =0.0025m with 5 no. of integration point) ******************************************************************************
** Region: (Section-2-_I5:Picked), (Beam Orientation:Picked) *Elset, elset=_I5, internal, generate 500, 519, 1 ** Section: Section-2-_I5 Profile: Profile-1 Profile ****************************************************************************** ** (*Beam section command will create beam of I-cross section) ****************************************************************************** *Beam Section, elset=_I5, material=Steel, temperature=GRADIENTS, section=I 0.0381, 0.0762, 0.059182, 0.059182, 0.006604 006604, 0.006604, 0.004318 0.,0.,1. ** Region: (Section-3-_I2:Picked), (Beam Orientation:Picked) *Elset, elset=_I2, internal, generate 1000, 1019, 1 ** Section: Section-3-_I2 Profile: Profile-2 Profile *Beam Section, elset=_I2, material=Steel, temperature=GRADIENTS, section=I 0.0381, 0.0762, 0.059182, 0.059182, 0.006604 006604, 0.006604, 0.004318 0.,0.,1. ** Region: (Section-4-_I3:Picked), (Beam Orientation:Picked) *Elset, elset=_I3, internal, generate 1500, 1519, 1 ** Section: Section-4-_I3 Profile: Profile-3 Profile *Beam Section, elset=_I3, material=Steel, temperature=GRADIENTS, section=I 0.0381, 0.0762, 0.059182, 0.059182, 0.006604 006604, 0.006604, 0.004318 0.,0.,-1. ** Region: (Section-5-_I4:Picked), (Beam Orientation:Picked) *Elset, elset=_I4, internal, generate 2000, 2019, 1
** Section: Section-5-_I4 Profile: Profile-4 Profile *Beam Section, elset=_I4, material=Steel, temperature=GRADIENTS, section=I 0.0381, 0.0762, 0.059182, 0.059182, 0.006604 006604, 0.006604, 0.004318 0.,0.,-1. *End Part ****************************************************************************** ** (Used to assemble the different individual parts here in current problem only one part is used.)
****************************************************************************** ** ASSEMBLY *Assembly, name=Assembly *Instance, name=PART-1-1, part=PART-1-1 *End Instance ** *Nset, nset=topnode, instance=PART-1-1 431 *Nset, nset=_PICKEDSET11, internal, instance=PART-1-1 instance=PART 421, 422, 423, 424, 425, 426, 427, 428, 428 434, 435, 436, 437, 438, 439, 440, 441 *Nset, nset=_PICKEDSET13, internal, instance=PART-1-1 instance=PART 221, instance=PART *Nset, nset=_PickedSet8, internal, instance=PART-1-1 1, 21 *Nset, nset=_PickedSet9, internal, instance=PART-1-1 instance=PART 2, 3, 4, 5, 6, 7, 8, 9, 10, 10 11, 12, 13, 14, 15, 16, 17 18, 19, 20, 22, 42, 43, 63, 64, 84, 85, 105, 106, 126, 127, 147, 148 168, 169, 189, 190, 210, 211, 231, 232, 252, 253, 273, 274, 294, 295, 315, 316 336, 337, 357, 358, 378, 379, 399, 400, 420, 421, 422, 423, 424, 425, 426, 427 428, 429, 430, 431, 432, 433, 434, 435, 436, 437, 438, 439, 440, 441
*Nset, nset=_PickedSet10, internal, instance=PART-1-1 instance=PART 2, 3, 4, 5, 6, 7, 8, 9, 10, 10 11, 12, 13, 14, 15, 16, 17 18, 19, 20, 421, 422, 423, 424, 425, 426, 426 427, 428, 429, 430, 431, 432, 433 434, 435, 436, 437, 438, 439, 440, 441 *End Assembly ****************************************************************************** ** (With this Geometry of model ends)
****************************************************************************** ** MATERIALS ****************************************************************************** ** (*Material command is used to define material which has been used to **different component of model It include all engineering properties of **material) ****************************************************************************** *Material, name=Steel *Elastic 2.0e+11, 0.3 *Plastic 2.50+08, 0. ****************************************************************************** ** BOUNDARY CONDITIONS ****************************************************************************** ** (*Boundary command is used to create appropriate boundary **conditions)
****************************************************************************** ** Name: Disp-BC-1 Type: Symmetry/Antisymmetry/Encastre Antisymmetry/Encastre *Boundary _PickedSet8, ENCASTRE ** Name: Disp-BC-2 Type: Displacement/Rotation *Boundary _PickedSet9, 3, 3 *Boundary _PickedSet10, 2, 2
Simple Input File (History Section) ** STEP: Transverse load ****************************************************************************** ** (*Step command is used to create different analysis step like Static **General, Static Riks, Dynamic, Dynamic Explicit etc. In each analysis **step one can define corresponding loading on model) ****************************************************************************** *Step, name="Transverse load ", nlgeom=YES ****************************************************************************** **(nlgeom=YES means geometric nonlinearity is on to account for large **deformations) ****************************************************************************** *Static 1., 1., 1e-05, 1. ** LOADS ** Name: CFORCE-1 Type: Concentrated force ****************************************************************************** **(*Cload command is used for concentrated load. A load of 2N is applied at middle node i.e._PICKEDSET13 in negative z-direction direction to initiate initial imperfection in plate )
****************************************************************************** *Cload _PICKEDSET13, 3, -2. ** ** OUTPUT REQUESTS *Restart, write, frequency=0 ****************************************************************************** **(*Restart command in ABAQUS allows multi step analysis. Here one can use **frequency=n that means saving the output after n interval,frequency =overlay means **directly give output at end of step without saving intermediate increment result, **frequency=0 means to save output for each interval)
******************************************************************************
** FIELD OUTPUT: F-Output-1 *Output, field *Node Output CF, RF, TF, U ** FIELD OUTPUT: F-Output-2 *Element Output, directions=YES E, ESF1, MISESMAX, NFORC, PE, PEEQ, S, SE, SEE, SF ** HISTORY OUTPUT: H-Output-1 *Output, history, variable=PRESELECT *End Step ****************************************************************************** ** STEP: Lateral load *Step, name="Lateral load", nlgeom=YES, inc=10000 ****************************************************************************** **(In “Static Riks” step 0.1 indicate initial time increment 100 indicate time **period of step 1e-10 indicate minimum time increment allowed 1 indicate **maximum time increment allowed 20 indicates load proportionality factor, **topnode, 1, 0.05 indicates the displacement control means stop analysis when **x- directional displacement reached up to 0.05m) ****************************************************************************** *Static, riks 0.1, 100., 1e-10, 1., 20., topnode, 1, 0.05 0 ** LOADS ** Name: CFORCE-2 Type: Concentrated force ****************************************************************************** **(A load of 10000N is applied at top edge nodes i.e._PICKEDSET11 in **positive x-direction for static pushover analysis.) ****************************************************************************** *Cload _PICKEDSET11, 1, 10000.
** OUTPUT REQUESTS *Restart, write, frequency=0 ** FIELD OUTPUT: F-Output-3 *Output, field *Node Output CF, RF, TF, U ** FIELD OUTPUT: F-Output-4 ************************************************************************** ** (Field output will give the selected output) ************************************************************************** *Element Output, directions=YES E, EE, ESF1, IE, MISESMAX, NFORC, PE, PEEQ, S, SF ** HISTORY OUTPUT: H-Output-2 *Output, history, variable=PRESELECT *End Step
To run ABAQUS Input File on Command Prompt
•
At the command line abaqus job=filename int (say SPSW)
Output Files created during running an Analysis Following files were created during running C:\Temp\Tutorial\SPSW1)
an analysis in a directory of job file (say
SPSW1.odb:-Out put database file which contains all requested field output and history output database for given job. SPSW1.dat:-This file contains all kinds of information about the computations that ABAQUS has done. In particular, if ABAQUS encounters any problems during the computation, error and warning messages will be written to this file.
SPSW1.log:- You will see some information about the time it took to for ABAQUS to complete execution. You should also see that the file ends with
ABAQUS JOB SPSW1 COMPLETED SPSW1.res:-The file named SPSW1.res is called a `restart file’ (the file always has .res extension). This file contains full information about the analysis. The restart file is most useful if you want to plot the finite element mesh, or contours of stress, displacement, etc
SPSW1.sta:-This file is continuously updated by ABAQUS as it runs, and tells you how much of the computation has been completed.
SPSW1.msg:-The file named SPSW1.msg contains much more information concerning the increments used, the iterative process, and the tolerances that ABAQUS has applied to determine whether a solution has converged.
SPSW1.fil:-The file named SPSW4.fil is called a `results file’ (the file always has a .fil extension). This file contains data that were specifically requested in the ABAQUS input file.
THANK YOU!
