ABAQUS tutorial
Contents
1. Once you are done plotting all the graphs you want type set hard copy off return Any further plots you make will not be output to the mpl file For example if you now type contour v mises return the contour plot will not be printed 4 Now we will exit ABAQUS Post end return 5 To print our graphs we now need to turn the tutorial mpl file into a postscript file that can be sent to the printer To do this go the the ABAQUS command window and type abaqus plot device cps job tutorial http www engin brown edu courses En175 Abaqustut abaqustut htm 24 of 37 4 13 2007 11 12 12 AM ABAQUS tutorial If this doesn t work you should try p abaqus abaqus plot device cps job tutorial The program will ask you a number of questions concerning the format you wish to adopt for the printed file The appropriate responses should be obvious in most cases you should accept the default Finally when you have answered all the questions ABAQUS Plot will produce a postscript file named tutorial ps If you asked ABAQUS Plot to print each page to a separate file it will produce three files named tutorial page _1 ps tutorial page 2 ps and tutorial_page_3 ps You can view the file using Ghostview or convert it into a pdf file using Adobe Distiller and then view the file with Adobe Acrobat Reader or Adobe Acrobat Exchange There is also some software that will read in postscript files and allow you to edit them and print th2. 2 4 on page 1 1 2 17 of Example Problems Vol 1 is job 1010204 Unfortunately the numbering scheme used for the input files is not always consistent so you usually have to try putting zeros in random places to find the correct name for example if 1010204 didn t work the next guess would be 101024 110204 etc You can type abaqus findkeyword and then supply a keyword name to see a list of example problems that use the keyword Unfortunately most of the list scrolls off the top of the window and there doesn t seem to be much you can do about it but if you can read really fast you will find this feature helpful Consult TAs the prof other students Or call your Mom http www engin brown edu courses En175 Abaqustut abaqustut htm 37 of 37 4 13 2007 11 12 12 AM
3. Online help with ABAQUS Post In the ABAQUS Post window type help return http www engin brown edu courses En175 Abaqustut abaqustut htm 10 of 37 4 13 2007 11 12 12 AM ABAQUS tutorial A black window will open with a list of ABAQUS Post commands To get help with any command just type the command name 9 ABAQUS Post Mesh and Boundary Condition Display 1 The first step is to read the results of an analysis into ABAQUS Post Our example simulation created two files that can be read into ABAQUS Post tutorial res tutorial fil The file named tutorial 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 The file named tutorial 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 The results file is most useful when you want to create x y plots of stress v time stress v strain or similar To read the restart file type restart file tutorial return A black window will pop up with lots of interesting information in it Ignore the useful information and type return anywhere in the window When you read the restart file with this syntax all quantities displayed will represent the state of the solid at the very end of the analy
4. input file by typing in appropriate keywords with a text editor The easiest thing to do will be to copy an existing file and modify it for other problems 5 Running ABAQUS 1 Double click the ABAQUS icon on your desktop A window with a black background should appear 2 In the Abaqus Command window change directories to ABAQUS tutorial http www engin brown edu courses En175 Abaqustut abaqustut htm 5 of 37 4 13 2007 11 12 12 AM ABAQUS tutorial 3 In the Abagus Command window type Your Prompt gt abaqus return I dentifier tutorial return User routine file return The identifier should always be the name of the inp file without the inp extension The user routine file will always be blank in anything we run in this course It is needed only when you start to write your own subroutines to run within ABAQUS This starts the ABAQUS program running Note that the program runs in the background so although the prompt comes right back in the ABAQUS window this does not mean the program has finished Note also that some special computations e g using the SYMMETRIC MODEL GENERATION key will cause ABAQUS to ask you some more questions during execution 4 Using explorer or by opening a directory window examine the files in the directory tutorial Click here if you don t know how to do this You should see the following files tutorial inp tutorial dat tutorial log tutorial res tutorial bat tutor
5. return display curve return gt strsstrn return gt return The y axis of the first curve strain becomes the x axis of the new curve strsstrn while the y axis of the second curve stress becomes the y axis of the new curve Check the initial the stress strain curve to make sure that it is correct The material point at node 1919 is subjected to uniaxial stress so the stress strain curve should if the numerical analysis is accurate match the uniaxial stress strain curve for the material 13 Printing output from ABAQUS Post It takes three steps to print out results from ABAQUS Post http www engin brown edu courses En175 Abaqustut abaqustut htm 23 of 37 4 13 2007 11 12 12 AM ABAQUS tutorial If you have not already done so start ABAQUS Post and read in tutorial res 1 First type set hard copy on in the ABAQUS Post window With this option set every time you enter a command such as draw contour display curve that changes the ABAQUS Post display the new display is also output to a device neutral file called tutorial mpl This file will later be converted to a form that can be printed 2 As an example we will draw the mesh the displaced mesh and an x y plot of stress draw return draw displaced return path node list generate variable s22 name splot distance absolute return gt 119 131 1 return gt return display curve return gt splot return gt return 3
6. t 2 to t 3 ABAQUS will always print out the state of the solid at the end of each step When you type restart step 2 in ABAQUS Post and then plot something you will see the state of the solid at the end of step 2 in this case at time t 2 Let s check this out We will compare the plastic zone size in the solid at times t 1 t 2 and t 3 1 If you have not already done so start up ABAQUS Post and read in tutorial res 2 Now we will open up three windows to display all three times on the same picture Type window name first maximum 0 4 1 0 minimum 0 0 0 6 return window name second maximum 0 7 0 7 minimum 0 3 0 3 return window name third maximum 1 0 1 0 minimum 0 6 0 6 return Here the maximume specifies the coordinates of the upper right hand corner of the window while the minimum specifies the lower left hand corner You can also use window name Cursor and then click on the screen with the mouse to define the corners of the window but don t try that now or else you will have an extra window open that you don t want 3 Now we will plot contours of plastic strain at t 1 t 2 and t 3 in the three windows Type window name first return set fill on return restart step 1 return contour v pemag return window name second return restart step 2 return contour v pemag return window name third return restart step 3 return http www engin brown ed
7. to the next The final number is the increment in node numbers from one row to the next All the elements have been assigned to a set named PLATE SOLID SECTION MATERIAL STEEL ELSET PLATE Finally we need to tell ABAQUS what each element is made of To do this we assign a material named STEEL to the elements named PLATE using the SOLID SECTION key The properties of STEEL are defined below Material Property Definition We need to specify the behavior of the material we called STEEL Here we define an isotropic elastic plastic material with Young s modulus 210 GPA and Poisson s ratio 0 31 and a plastic strain v stress curve approximated by a set of piecewise linear segments MATERIAL NAME STEEL Specify the Young s modulus and Poisson s ratio with the ELASTIC keyword ELASTIC 210 E09 0 31 Specify yield stress v plastic strain with the PLASTIC keyword The data pairs are true stress true strain for a uniaxial tension test PLASTIC 200 2E06 0 0 246 0E06 0 0235 294 0E06 0 0474 http www engin brown edu courses En175 Abaqustut abaqustut htm 32 of 37 4 13 2007 11 12 12 AM ABAQUS tutorial 374 0E06 0 0935 437 0E06 0 1377 480 0E06 0 18 Time independent boundary conditions Next we need to specify how the plate is loaded This is done in two stages Any boundary conditions which do not vary with time are defined before we start the analysis In this case the left hand boundary and the bottom
8. will be provided for you You will run ABAQUS and then use ABAQUS Post to look at the results of your analysis Next you will take a detailed look at the ABAQUS input file and start setting up input files of your own After completing this tutorial you should be in a position to do quite complex two and three dimensional finite element computations with ABAQUS and will know how to view the results We will continue using ABAQUS to solve various problems throughout the rest of this course 3 Steps in running ABAQUS Create an input file ABAQUS works by reading and responding to a set of commands called KEYWORDS in an input file The keywords contain the information to define the mesh the properties of the material the boundary conditions and to control output from the program To see the ABAQUS input file for the plate problem click here Run the program On Windows NT ABAQUS is controlled by typing commands into a DOS type window Post processing There are two ways to look at the results of an ABAQUS simulation You can ask the program to print results to a file which you can look at with a text editor This is painful Alternatively you can use a program called ABAQUS Post which can be used to plot various quantities that may be of interest We will begin this tutorial by running through all these stages with a pre existing input file then look in more detail at how to set up an input file http www engin brown edu co
9. ABAQUS tutorial D n EN175 Advanced Mechanics of A n J A A CO SPEY Solids Division of Engineering Brown University ABAQUS tutorial 1 What is ABAQUS ABAQUS is a highly sophisticated general purpose finite element program designed primarily to model the behavior of solids and structures under externally applied loading ABAQUS includes the following features Capabilities for both static and dynamic problems The ability to model very large shape changes in solids in both two and three dimensions Avery extensive element library including a full set of continuum elements beam elements shell and plate elements among others A sophisticated capability to model contact between solids An advanced material library including the usual elastic and elastic plastic solids models for foams concrete soils piezoelectric materials and many others Capabilities to model a number of phenomena of interest including vibrations coupled fluid structure interactions acoustics buckling problems and so on The main strength of ABAQUS however is that it is based on a very sound theoretical framework As an practicing engineer you may be called upon to make crucial decisions based on the results of computer simulations While no computer program can ever be guaranteed free of bugs ABAQUS is among the more trustworthy codes Furthermore as you will see if you consult the ABAQUS theory manual HKS develope
10. analysis use the STATIC key word The first number on the following line suggests an initial value for the time increment that ABAQUS should take while calculating the deformation in this step Since we expect the plate to deform elastically in this step it makes sense to take a time increment equal to the step size ABAQUS should be able to go straight to the solution at the end of the step without taking little steps to get there The second number specifies the time interval for this load step The step starts at time t 0 and ends at time t so the time interval is 1 Two additional optional parameters are also available the third number specifies a minimum value for the time increment and the last number specifies a maximum value We have not used these parameters here DLOAD AMPLITUDE HIST EDGE P2 82 E06 Now we specify the loading applied to the plate We select distributed loads pressure acting on face 2 P2 of all the elements in set EDGE We take the load magnitude to be 82 MPA so that when it is scaled by HIST the stress reaches 82MPA at time t Note that by definition DLOAD defines pressure i e compressive normal stress to be positive so we apply tensile loading by making the pressure negative EL FILE POSITION AVERAGED AT NODES S E Next we specify what variables we d like printed to the history file for post processing We are going to print all stress components S and strain components E These v
11. ariables are normally only computed at element integration points so we use the EL FILE keyword to ask ABAQUS to print them to a file However we are really interested in values of stress and strain at the nodes in this case so we set the POSITION AVERAGED AT NODES flag to have ABAQUS calculate the varibles at nodes END STEP This keyword ends the step definition http www engin brown edu courses En175 Abaqustut abaqustut htm 35 of 37 4 13 2007 11 12 12 AM ABAQUS tutorial Second Load Step STEP AMPLITUDE RAMP STATIC 1 0 1 0 The second step lasts from time t to f 2 so the step time is 1 sec again We ask ABAQUS to try to get to the end of the step in 1 increment using an increment time of 1 sec This is a bit optimistic There is a lot of plasticity in this step so ABAQUS will actually end up taking several load increments DLOAD AMPLITUDE HIST EDGE P2 82 E06 The distributed load magnitude is 82MPa again since it gets scaled by the load factor in HIST to bring it to the correct magnitude HIST 2 at time 2 sec so HIST 82 166MPa EL FILE POSITION AVERAGED AT NODES S E END STEP Third load step You should get the idea by now STEP AMPLITUDE RAMP STATIC 1 0 1 0 DLOAD AMPLITUDE HIST EDGE P2 82 E06 EL FILE POSITION AVERAGED AT NODES S E END STEP http www engin brown edu courses En175 Abaqustut abaqustut htm 36 of 37 4 13 2007 11 12 12 AM ABAQUS tutorial 15 Sett
12. boundary are symmetry boundaries NSET NSET BOTTOM GENERATE 119 131 1 NSET NSET LEFT GENERATE 1919 1931 1 First we define a node set which contains all the nodes on the top and bottom boundary using the NSET GENERATE key The syntax for the line following is first node number in the set last node number in the set increment between node numbers in the set BOUNDARY BOTTOM YSYMM LEFT XSYMM Now we define the boundary conditions The node set BOTTOM is has symmetry about the Y 0 axis imposed and the node set LEFT has symmetry about the X 0 plane imposed Information defining time varying loads Next we define some information about the loading To load the plate we will apply a distributed load right hand boundary We need to define the elements on this boundary We generate and element set named EDGE using the ELSET GENERATE key This works just like the NSET GENERATE key ELSET ELSET EDGE GENERATE http www engin brown edu courses En175 Abaqustut abaqustut htm 33 of 37 4 13 2007 11 12 12 AM ABAQUS tutorial 30 830 100 We proceed to define some information about the time variation of the loads Here we will ramp the loads steadily from zero at time t 0 to a maximum at time t 3 0 We define this time variation in an object known as an AMPLITUDE Here we have named the AMPLITUDE HIST and have told ABAQUS that the x coordinates of the data pairs following represent total time Then we enter pa
13. ctivity We begin by defining the first element To do this we use the ELEMENT key The option TYPE CPS4 tells ABAQUS that we want the element to be a plane stress 4 noded element For a list of available element types consult Sect 14 1 3 of the ABAQUS user manual On the next line we define the element connectivity The first number is the element number The next four numbers are the node numbers entered in order going counterclockwise around the element You can enter connectivity for as many elements as you wish one line at a time following the ELEMENT keyword If you wanted to you could enter connectivities for each element by hand ELGEN ELSET PLATE http www engin brown edu courses En175 Abaqustut abaqustut htm 31 of 37 4 13 2007 11 12 12 AM ABAQUS tutorial 19 12 1 1 18 100 100 Now we generate element connectivity for all the remaining elements The ELGEN key generates a block of elements one row at a time The first number specifies the first element in the first row This element must already have its connectivity defined The second number is the number of elements in each row The third number is the increment between neighboring element numbers in the row The fourth number is the change in node numbers of corresponding nodes between neighboring elements The fifth number is the number of rows to be defined including the first one The third number is the increment in element numbers from one row
14. e end of the step and still give an accurate convergent solution You don t know a priori how many increments ABAQUS will take You can find out however by looking at some of the output files You can look at tutorial sta for example which shows the following information SUMMARY OF JOB INFORMATION STEP INC ATT SEVERE EQUIL TOTAL TOTAL STEP INC OF DOF IF DISCON ITERS ITERS TIME TIME TIME MONITOR RIKS 1 1 1 0 4 4 1 00 2 1 2 0 4 4 1 25 2 2 1 0 3 3 1 50 2 3 1 0 4 4 1 88 2 4 1 0 4 4 2 00 3 1 3 0 5 5 2 06 3 2 1 0 3 3 2 13 3 3 1 0 3 3 2 19 http www engin brown edu courses En175 Abaqustut abaqustut htm 17 of 37 4 13 2007 11 12 12 AM 1 00 1 000 0 250 0 2500 0 500 0 2500 0 875 0 3750 1 00 0 1250 0 0625 0 06250 0 125 0 06250 0 188 0 06250 ABAQUS tutorial 2 28 0 281 0 09375 2 42 0 422 0 1406 2 63 0 633 0 2109 2 95 0 949 0 3164 3 00 1 00 0 05078 Ww WW Ww w COND Uf PrPrPrPPH oO OOO O e BBW WwW PB BW WwW This file is continually updated and can be monitored during and ABAQUS computation The first column shows which step ABAQUS is currently analyzing The second column shows which time increment ABAQUS has reached The seventh column shows the current time From this information we learn that the first step was completed in one increment this is because the plate did not reach yield until the end of the increment so very large time steps could be taken The second step was completed in four increment
15. e element closest to our point of interest has number 19 This is a 4 noded element and so has 4 integration points We will plot the stress at integration point number 1 which is closest to the point of interest read curve name stress element 19 integration point 1 http www engin brown edu courses En175 Abaqustut abaqustut htm 21 of 37 4 13 2007 11 12 12 AM ABAQUS tutorial variable s22 return display curve return gt stress return gt return This displays the variation of stress with time Note that the time scale starts at t instead of zero If you plot results from a restart file the state at t 0 is not available 9 History plots are best done using data in a results file that s the one with extension fil rather than a restart res file because you can access stresses and other element variables at the nodes and you can include data at t 0 To read the variation of 722 at node 119 this node has coordinates x 0 01 y 0 from the results file type results file file tutorial return read curve name newstres node 119 variable s22 return display curve return gt newstres return gt return Now the stress at t 0 is included 10 Variables are available in the results file only if they were specifically requested in the input file For example if you try read curve name newmises node 119 variable mises return display curve return gt newmises return gt retu
16. e to see if the computation was successful If the program ran successfully you should see a message saying ANALYSIS COMPLETE WITH 7 WARNING MESSAGES ON THE MSG FILE JOB TIME SUMMARY USER TIME SEC 20 000 SYSTEM TIME SEC 3 0000 TOTAL CPU TIME SEC 23 000 WALLCLOCK TIME SEC 36 The times listed above may differ on your computer depending on the speed of the processor and the memory available The warning message is a bit scary but is actually nothing to worry about We ll see why it appears later You can explore the rest of this file to see what else is there MAKE SURE YOU CLOSE THE FILE BY EXITING THE TEXT EDITOR BEFORE PROCEEDING http www engin brown edu courses En175 Abaqustut abaqustut htm 7 of 37 4 13 2007 11 12 12 AM ABAQUS tutorial 6 ABAQUS ERRORS 1 Next we will deliberately introduce an error into the ABAQUS input file tutorial inp to see what an unsuccessful run looks like Open the file tutorial inp with a text editor and change the line near the top that says RESTART WRITE FREQ 1 to RESTART WONK FREQ 1 Save the file in Text Only format Now repeat step 3 in Running ABAQUS to run ABAQUS again You will get an additional prompt as follows Old job files exist Overwrite y n y return 2 Check the files in the directory ABAQUS tutorial again This time not all the files will be there because the run was unsuccessful 3 Open the file called tutorial log with a tex
17. em out in another format The ABAQUS plots on this web site were read into Micrografx Designer edited and then printed out as gif files Finally you can print the postscript file on any postscript printer On the NT workstations in Prince Lab you can print a ps file by dragging it onto the icon labelled PSPrint on your desktop 14 A detailed look at an ABAQUS input file We are ready to start learning how to use ABAQUS itself First we will look at the input file for the hole in a plate problem and then start doing some simple exercises to learn how to set up new problems Before looking at the input file you may find it helpful to review the problem being solved You can either click here to see the full input file with detailed comments or read below to see an explanation of each command in the file You can find detailed documentation about each keyword in volume III of the ABAQUS Standard user manual or in the online documentation The input file is divided into the following general sections General ABAQUS commands controlling printing and naming the analysis Mesh generation commands Material property definition Time independent Boundary condition specifications Commands specifying time varying loads and controlling ABAQUS time steps and increments hl aed ale eel http www engin brown edu courses En175 Abaqustut abaqustut htm 25 of 37 4 13 2007 11 12 12 AM ABAQUS tutorial You will see that many lines i
18. ge the line http www engin brown edu courses En175 Abaqustut abaqustut htm 9 of 37 4 13 2007 11 12 12 AM ABAQUS tutorial LOUSDy 5E0255 E 002 1031 5 E 02 5 E 02 Re run ABAQUS don t forget to save the inp file first then check the file tutorial dat again ABAQUS really freaks out with this problem You should see 96 fatal errors If you have no life you might like to try and see if you can produce more errors than this by inserting a single character in the input file 6 Before proceeding correct the input file and re run ABAQUS Check the dat file and log file to make sure that the job ran properly 7 Running ABAQUS Post 1 If you have not already done so run ABAQUS with a correct input file tutorial inp You can download an error free copy of the tutorial file by clicking here if you need to 2 To run ABAQUS Post you will need to start a program called Exceed first Find Exceed on the Start menu of your desktop and select it to start it running A window will be displayed briefly and an icon should appear on your toolbar if the program started properly 3 Make sure you have an ABAQUS command window open set to the appropriate directory In the ABAQUS command window type abaqus post 4 A window should appear which will be used to display results of the ABAQUS run To do so you type commands in the bottom left hand corner of the window We will try a few useful commands in the next section 8
19. ial sta tutorial msg tutorial fil Fortunately you can happily ignore most of these files The only ones you need to look at are tutorial log tutorial sta tutorial msg and tutorial dat We will also use tutorial res and tutorial fil later 5 Open the file called tutorial log with a text editor 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 J OB tutorial COMPLETED This means that ABAQUS is done and you can safely look at the results 6 Open the file called tutorial sta with a text editor You will see columns of numbers headed by http www engin brown edu courses En175 Abaqustut abaqustut htm 6 of 37 4 13 2007 11 12 12 AM ABAQUS tutorial SUMMARY OF J OB INFORMATION STEP INC ATT SEVERE EQUI L TOTAL TOTAL STEP I NC OF DOF IF DISCON I TERS I TERS TI ME TI ME LPF TI ME LPF MONITOR RI KS I TERS FREQ This file is continuously updated by ABAQUS as it runs and tells you how much of the computation has been completed You can monitor this file while ABAQUS is running We will discuss the meaning of data in this file in more detail later 7 Open the file called tutorial 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 You should first check the end of the fil
20. ing up your own ABAQUS input file To help you set up your own input files a template file has been provided for you Click here to see it and use your browser download it following the same procedure that you used to download tutorial inp The template file reminds you of the general layout for the input file and contains a list of useful keywords in each section You can type ABAQUS commands directly into the template file if you wish or use it as a quick reference list of keywords To learn how to use each keyword you will need to refer to the ABAQUS documentation The following sources of information are available 1 Online documentation select Start on the toolbar select Programs on the popup menu select ABAQUS and then ABAQUS documentation The documentation includes instructions for using the documentation One word of warning make sure you only refer to the ABAQUS Standard manual We will not be using ABAQUS Expicit There are several hard copies of the ABAQUS manuals in the Prince Lab Computer Balcony Do not remove the manuals from the balcony ABAQUS comes with an extensive set of example problems The examples are described in the ABAQUS Example Problems Manuals two vols You can download copies of the examples by typing abaqus fetch in ABAQUS command window and then typing the example job name on the next line The name of the job corresponds to the number of the listing of each example file for example listing 1 1
21. irs of numbers time load magnitude with four pairs to each line you can have fewer than four pairs on the last line AMPLITUDE NAME HIST TIME TOTAL TIME 0 0 0 0 1 0 1 0 2 0 2 0 3 0 3 0 Load Step Definition In doing the analysis we will apply the load in a series of STEPS The first load step lasts from time f 0 to time t ABAQUS will always print out the state of the plate at the end of a load step so we will have some results that show the plate just starting to yield at the edge of the hole at time t The second load step lasts from time t to t 2 The plastic zone should grow significantly during this step The last load step lasts from time t 2 to t 3 The whole plate should begin to yield towards the end of this load step First Load Step STEP AMPLITUDE RAMP To start the analysis we use the STEP key The AMPLITUDE RAMP key is rather confusing here in the STEP key the AMPLITUDE does not refer to a predefined history of load as described above but tells ABAQUS how to apply the load during this time step If you specify AMPLITUDE RAMP the load is applied smoothly while if you say AMPLITUDESSTEP the load is applied at once STATIC 1 0 1 0 We tell ABAQUS that this is a quasi static analysis The stress fields are in static http www engin brown edu courses En175 Abaqustut abaqustut htm 34 of 37 4 13 2007 11 12 12 AM ABAQUS tutorial equilibrium throughout the history of load To choose a static
22. is set fill on return draw return http www engin brown edu courses En175 Abaqustut abaqustut htm 12 of 37 4 13 2007 11 12 12 AM ABAQUS tutorial report elements return Now click on any element in the mesh and information concerning the element will be displayed at the bottom of the window To exit this option click on the little X at the bottom left hand corner of the black window The key report nodes return tells you about nodes 12 You can also display the boundary conditions applied to the mesh by typing set bc display on draw If you have superb eyesight you will see some little dots on the left and bottom edges of the mesh Zoom in and you will see arrows representing the constraints applied to the bottom of the mesh 13 Before proceeding to the next section type reset all return 10 ABAQUS Post Field Plots If you have not already done so start up ABAQUS Post and read in tutorial res 1 To view the deformed shape of the solid after loading type draw displaced return You can use the mouse to drag the mesh away from the text message that appears on the window Note that the deformation is grossly exaggerated to show it clearly the scale factor is displayed on the text message 2 Recall that by default ABAQUS Post will display the state of the solid at the very end of whatever load history was specified in the input file To see the results at other times you can type restart s
23. jacent nodes and the node number at the center of the circular arc this must already be defined here we defined it using the NODE command http www engin brown edu courses En175 Abaqustut abaqustut htm 28 of 37 4 13 2007 11 12 12 AM ABAQUS tutorial D o gt a Lao pumas V om om C2 eo _ V3 NGEN NSET OUTER 131 1031 100 Now we generate nodes on the right hand boundary Again we specify the first node the last node and the increment between neighboring nodes on this boundary The nodes on this boundary are assigned to a set named OUTER 1931 1831 lt _ Dag NGEN NSET OUTER 1031 1931 100 http www engin brown edu courses En175 Abaqustut abaqustut htm 29 of 37 4 13 2007 11 12 12 AM ABAQUS tutorial The next key defines nodes on the top boundary These nodes are also added to the set named OUTER we LLL NFILL NSET PLATE BIAS 0 8 HOLE OUTER 12 1 Finally we fill in the remaining nodes by connecting the nodes on the boundary HOLE and the boundary OUTER in a set of radial lines To learn about how this keyword works consult the ABAQUS Standard manual All the nodes within the solid are assigned to a set named PLATE http www engin brown edu courses En175 Abaqustut abaqustut htm 30 of 37 4 13 2007 11 12 12 AM ABAQUS tutorial ELEMENT TYPE CPS4 19 119 120 220 219 Next we define the element conne
24. n the inp file begin with a This is a comment marker like in C and everything following a is ignored by ABAQUS Other lines begin with a single This denotes an ABAQUS keyword Some lines begin with numbers or text These are data lines as required by ABAQUS keywords General ABAQUS instructions The file starts with a set of general instructions to ABAQUS HEADING STRESS ANALYSIS FOR A PLATE WITH A HOLE The HEADING key allows you to define a title for your analysis This will be printed in output files to allow you to identify them later PREPRI NT ECHO YES HISTORY YES MODEL YES The PREPRINT key controls what information is printed to the file named tutorial dat Here we have asked ABAQUS to print out absolutely everything The tutorial dat file is rather large as a consequence Once the input file is correct you can set all the options to NO to reduce thesize of the file RESTART WRITE FREQ 1 The RESTART key tells ABAQUS Standard to print out a tutorial res file which will be used by ABAQUS Post during post processing The key FREQ 1 tells ABAQUS to print out information about every increment in Load FILE FORMAT ZERO INCREMENT The FILE FORMAT key tells ABAQUS Standard to print certain information to the tutorial fil file This file is also used later by ABAQUS Post Here we have asked ABAQUS to print values at the start of the analysis i e before the loads are applied http www engin b
25. rn you will get an error message because Mises stresses weren t stored 11 Note that now that you typed results file file all curves will be read from the results file until you specify otherwise To go back to reading from the restart file and then read the Mises stress from an integration point type set history restart file return read curve name nm element 19 integration point 1 variable mises return display curve return gt nm return http www engin brown edu courses En175 Abaqustut abaqustut htm 22 of 37 4 13 2007 11 12 12 AM ABAQUS tutorial gt return 12 Let s go back to reading curves from the results file Type set history results file return 13 We can also plot the variation of stress with strain at a node we ll try 1919 this time since there is a nice big plastic strain there instead of plotting stress as a function of time To do this we first read stress v time and strain v time as two separate curves and then combine them to create stress v strain First read the stress v time curve at node 1919 we ll replace the old curve named newstres read curve name newstres node 1919 variable s11 return gt Overwrite return Now read the strain v time curve read curve name strain variable e11 node 1919 return Now we will create a stress v strain graph Define curve name strsstrn operation combine return gt strain return gt stress return gt
26. rown edu courses En175 Abaqustut abaqustut htm 26 of 37 4 13 2007 11 12 12 AM ABAQUS tutorial Mesh Generation Next there follow a set of lines defining the mesh Nodes are generated first then the element type and element connectivity are specified ABAQUS 1931 NODE 101 0 0 0 0 119 1 0E 02 0 0 1919 0 0 1 E 02 131 5 E 02 0 0 1031 5 E 02 5 E 02 1931 0 0 5 E 02 First we define five key nodes which will be used to generate further nodes later The positions of these nodes are shown in the picture above The NODE keyword starts node definition On the lines below enter the node number and x y and z for 3D coordinates http www engin brown edu courses En175 Abaqustut abaqustut htm 27 of 37 4 13 2007 11 12 12 AM ABAQUS tutorial Note that the first node number 101 is not actually in the solid at all It is used when generating the mesh but is not used in the finite element computation 101 NGEN LINE C NSET HOLE 119 1919 100 101 Now we use the NGEN command to generate further nodes First we generate a line of nodes around the perimeter of the hole The LINE C option of NGEN tells ABAQUS that the nodes you generate should be on a circular arc The NSET HOLE option of NGEN gives a name HOLE to all the nodes on this boundary We will use this name later The following line specifies the first node on the arc the last node on the arc the increment in node numbers between ad
27. rs really understand continuum mechanics since many of them are Brown Ph Ds this goes without saying For this reason ABAQUS is used by a wide range of industries including aircraft manufacturers automobile http www engin brown edu courses En175 Abaqustut abaqustut htm 1 of 37 4 13 2007 11 12 12 AM ABAQUS tutorial companies oil companies and microelectronics industries as well as national laboratories and research universities ABAQUS is written and maintained by Hibbitt Karlsson and Sorensen Inc HKS which has headquarers in Pawtucket RI The company was founded in 1978 by graduates of Brown s Ph D program in solid mechanics and today has several hundred employees with offices around the world 2 Tutorial Overview In this tutorial you will learn how to run ABAQUS Standard and also how to use ABAQUS Post to plot the results of a finite element computation First you will use ABAQUS to solve the following problem A thin plate dimensions 10cm x 10 cm contains a hole of radius 1cm at its center The plate is made from steel which is idealized as an elastic strain hardening plastic solid with Young s modulus E 210 GPa and Poisson s ratio V 9 3 The uniaxial stress strain curve for steel is idealized as a series of straight line segments as shown below ABAQUS 400 300 100 0 05 0 10 0 15 Strain The plate is loaded in the horizontal direction by applying tractions to its bo
28. s and the third step was completed in 8 increments The file named tutorial 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 You need a Ph D to be able to figure most of that stuff out We can see the meaning of the warning messages that were referred to in the dat file however every time ABAQUS has to reduce the time increment due to convergence problems a warning message is printed to the msg file This is nothing to worry about everything is working perfectly ABAQUS prints information concerning the state of the solid to the res and fil files at the end of each increment 4 To go back to a single window type window remove all return 4 To look at the plastic zone at time t 2 42 step 3 increment 5 type restart step 3 increment 5 return contour v pemag return 12 ABAQUS Post X Y Plots http www engin brown edu courses En175 Abaqustut abaqustut htm 18 of 37 4 13 2007 11 12 12 AM ABAQUS tutorial ABAQUS Post can also be persuaded to plot variations of stress displacement etc with position within the solid or can display stresses strains etc as a function of time at a point in the solid or can even plot stress as a function of strain or anything else for that matter The procedure to do this is rather weird We will begin by plotting x y graphs of field quanti
29. sis We will see how to display data at other times lower down 2 Now we can start plotting things Type draw return in the ABAQUS Post window This will plot the undeformed finite element mesh 3 To display node numbers with the mesh type set n numbers on return http www engin brown edu courses En175 Abaqustut abaqustut htm 11 of 37 4 13 2007 11 12 12 AM ABAQUS tutorial draw return 4 To display element numbers with the mesh type set el numbers on return draw return 5 To zoom in and out of the mesh right click on the mesh and drag the mouse left or right while continuing to hold the mouse button down 6 To move the mesh around on the window center click on the mesh and drag the mouse 7 To rotate the FEM mesh left click and drag the mouse and or left click with the shift key held down while dragging the mouse This is not too helpful with a 2D mesh but is very useful in 3D 8 Another useful way to zoom in on a small region is zoom cursor return Now click on the mesh at two points The two points define opposite corners of a box When you type draw return the region within the box will be scaled to fit the full window 9 To turn off element numbers and node numbers again type set el numbers off n numbers off return draw return 10 To get back to the original view of the mesh type reset all return draw return 11 Another useful option for checking a mesh
30. splay curve return gt syy return gt sxx return gt return Do you see anything wrong with the value of sxx at x 0 Why What could cause this error 4 For a 3D analysis you can ask for curves to be generated along a straight line instead of entering a list of node numbers To produce the results we want here we would enter path start 0 01 0 0 end 0 05 0 0 variable s22 name syy distance absolute return Unfortunately this does not work in 2D so you are stuck entering node lists 5 There are various commands you can use to change the appearance of the x y plot For example graph axes x title x y title normal stress x grid solid y grid solid return display curve return gt syy return gt return Unfortunately no matter how hard you try x y plots output from ABAQUS Post look pretty shitty If you want publication quality output your best bet is to print the data and plot it with something else or print out a postscript file and then edit it with another graphics package 6 The path defined by the node list need not be a straight line For example to plot the variation of Mises stress around the perimeter of the hole use path node list generate variable mises name sm distance absolute return gt 119 1919 100 return gt return http www engin brown edu courses En175 Abaqustut abaqustut htm 20 of 37 4 13 2007 11 12 12 AM ABAQUS tutorial graph axes x ti
31. t editor Note the error message there 4 Open the file called tutorial dat with a text editor You will see that the end of the file contains the following statements THE PROGRAM HAS DISCOVERED 3 FATAL ERRORS EXECUTION IS TERMINATED END OF USER INPUT PROCESSING JOB TIME SUMMARY http www engin brown edu courses En175 Abaqustut abaqustut htm 8 of 37 4 13 2007 11 12 12 AM ABAQUS tutorial USER TIME SEC 0 0000 SYSTEM TIME SEC 0 0000 TOTAL CPU TIME SEC 0 0000 WALLCLOCK TIME SEC 2 This again shows that ABAQUS ran into trouble during execution Search the file backwards for the occurrence of ERROR to find the lines XBRROR UNKNOWN PARAMETER WONK CARD IMAGE RESTART WONK FREQ 1 NOTE DUE TO AN INPUT ERROR THE ANALYSIS PRE PROCESSOR HAS BEEN UNABLE TO INTERPRET SOME DATA SUBSEQUENT ERRORS MAY BE CAUSED BY THIS OMISSION ERROR EITHER THE PARAMETER READ OR WRITE MUST BE SPECIFIED CARD IMAGE RESTART WONK FREQ 1 ERROR PARAMETER FREQUENCY IS ONLY MEANINGFUL IF THE WRITE PARAMETER IS ALSO SPECIFIED CARD IMAGE RESTART WONK FREQ 1 This will tell you what part of the input file is causing problems and if you are lucky you will understand the error message Notice that ABAQUS programmers still seem to be using punch cards ABAQUS is coded in FORTRAN too for real 5 Try another error Change the line RESTART WONK FREQ 1 back to RESTART WRITE FREQ 1 This time chan
32. tep 1 return draw displaced return http www engin brown edu courses En175 Abaqustut abaqustut htm 13 of 37 4 13 2007 11 12 12 AM ABAQUS tutorial This will display the deformed mesh at the end of the first load step In this case the deformed mesh doesn t look very different at the end of the first step but you should see a message in the bottom left hand corner of the screen telling you that the current step is 1 3 To remove the undeformed mesh type set undeformed off return draw displaced return 4 To see the actual displacements without magnification type set d magnification 1 0 return draw displaced return 5 To plot a contour of the horizontal component of stress g 1 type contour v s11 return 6 To show the contours as solid colors instead of lines type set fill on return contour v s11 return 7 To remove the mesh to see the contours more clearly type set outline perimeter return or set outline off return contour v s11 return 8 To turn the mesh back on again type set outline element return 9 You can plot all field quantities the same way Examples include v s22 v s12 v s33 etc plot various stress components v mises plots von Mises stress 10 You can do vector plots too For example vector plot v u return shows arrows whose length and orientation correspond to the vector displacement at each node Obviously you can only do a vector plot of a vec
33. ties with position in the solid If you have not already done so start up ABAQUS Post and read in tutorial res 1 First we will plot the variation of a5 with distance along the base First we define a set of data known as a curve by using the path keyword path node list variable s22 name syy distance absolute return gt 119 return gt 120 return gt 121 return Continue typing in numbers in increasing order until you get to gt 131 return gt return This procedure defines a set of x y data pairs at each node entered in the list The x coordinate is zero at the first node and is incremented by the distance between nodes for each subsequent node in the list The y coordinate is s22 The group of all the data pairs generated by this command has been given the name syy To find the list of nodes you need for the path of interest it is simplest to plot the mesh with node numbers 2 Now we can plot these x y data points display curve return gt syy return gt return 3 We can define and plot other data on the same graph Instead of typing in a list of nodes this time we will use the generate key to generate the list automatically http www engin brown edu courses En175 Abaqustut abaqustut htm 19 of 37 4 13 2007 11 12 12 AM ABAQUS tutorial path node list generate variable s11 name sxx distance absolute return gt 119 131 1 return gt return di
34. tle s y title mises stress return display curve return gt sm return gt return 7 You can also manipulate the data in an X Y curve For example we could compute the resultant vertical force acting on a section of the bottom boundary by integrating the normal stress distribution F x Onds 0 To do this with ABAQUS Post use define curve name result operation integrate return gt syy return This generates a new curve named result which is the integral of syy To plot it type display curve return gt result return gt return The curve should theoretically cross zero at x 0 04 but as you see there is a slight error in the finite element computation This error could be reduced by using a finer finite element mesh It is always worth doing checks like this to test the accuracy of your numerical solutions 8 ABAQUS Post will also do another kind of x y plot Instead of plotting variables as a function of position you can plot variables as a function of time as the load is applied to the solid For example we will plot the time variation of an at the point near 0 01 0 0 this is on the edge of the hole We are plotting results from a restart file remember that we read in the restart file right at the beginning of this section so the stresses are defined only at the integration points within each element and are not available at the nodes By drawing the mesh with element numbers we see that th
35. tor valued http www engin brown edu courses En175 Abaqustut abaqustut htm 14 of 37 4 13 2007 11 12 12 AM ABAQUS tutorial function 11 You can also display numerical values of variables stress displacements etc at nodes or integration points whichever applies by typing report values v s11 return Then click with the mouse on any element Values of stress at each element integration point will be printed at the bottom of the screen To exit this option click on the little cross at the bottom left hand corner of the black window To see displacements type Report values v ul return Then click on any node to see the horizontal component of displacement there 11 ABAQUS STEPS AND INCREMENTS You may have noticed when reading the restart file that ABAQUS was telling you which step was being read and which increment This is somewhat mysterious so we will explore how ABAQUS controls time during an analysis next stress MPa 200 OG EE EE 1234 5 6 pee rar ERRES TOENAM AA increm ents OQ LA time sec Deep When you set up an ABAQUS Standard input file you tell ABAQUS to apply load to http www engin brown edu courses En175 Abaqustut abaqustut htm 15 of 37 4 13 2007 11 12 12 AM ABAQUS tutorial a solid in a series of steps For the hole in a plate problem we applied load to the solid in three steps from t 0 to t 1 step 1 from t 1 to t 2 step 2 and finally from
36. u courses En175 Abaqustut abaqustut htm 16 of 37 4 13 2007 11 12 12 AM ABAQUS tutorial contour v pemag return You should see three contour plots at the end showing plastic strain contours The deep blue color is the contour level for zero plastic strain showing areas that have not yet yielded The red color has the highest plastic strains In the first window there will only be a small plastic zone at the edge of the hole This plastic zone grows as the load is increased You can see this in the other two windows On the third window most but not quite all of the plate has started to deform plastically So what s the deal with the increments Well because the plate is deforming plastically this is a nonlinear problem the stress is a nonlinear function of the nodal displacements This means that ABAQUS needs to iterate to find the correct solution a Newton Raphson iteration is used to solve the nonlinear equilibrium equations and also means that ABAQUS cannot accurately compute the plastic strain that results from a large change in loads Indeed if ABAQUS tries to take a very large time step it may not be able to find a solution at all To get around this problem ABAQUS automatically subdivides a large time step into several smaller increments if it finds that the solution is nonlinear This process is completely automatic and ABAQUS will always take the largest possible time increments that will reach th
37. undary http www engin brown edu courses En175 Abaqustut abaqustut htm 2 of 37 4 13 2007 11 12 12 AM ABAQUS tutorial stress MPa 200 Ocm 166 sgunuddspensiatustunsas DQ 3 Jabiri L 2 3 time sec 10cm The magnitude of the loading increases linearly with time as shown You may recall that a circular hole in a plate has a stress concentration factor of about 3 At time t 1 therefore the stress at point A should just reach yield the initial yield stress of the plate is 200MPa At time t 3 the load should be enough to cause a significant portion of the plate to yield We will specifically request ABAQUS to print the state of the solid at time t 1 t 2 and t 3 to see the development of plasticity in the plate Observe that the plate and the loading is symmetrical about horizontal and vertical axes through the center of the plate We only need to model of the plate therefore and can apply symmetry boundary conditions on the the bottom and side boundaries The finite element mesh you will use for your computations is shown below The elements are plane stress 4 noded quadrilaterials Symmetry boundary conditions are applied as shown and distributed tractions are applied to the rightmost boundary http www engin brown edu courses En175 Abaqustut abaqustut htm 3 of 37 4 13 2007 11 12 12 AM ABAQUS tutorial r mmett Ld The ABAQUS input file that sets up this problem
38. urses En175 Abaqustut abaqustut htm 4 of 37 4 13 2007 11 12 12 AM ABAQUS tutorial BEFORE RUNNING ABAQUS FOR THE FIRST TI ME 1 Open an MS DOS window on your workstation the command to open the window is located in the Start menu on your toolbar 2 Type mk_ABAQUS in the MS DOS window If the command executes correctly icons to start ABAQUS and to open the ABAQUS documentation should appear on your desktop In addition a directory called ABAQUS should be created in your home directory 4 Downloading the sample ABAQUS input file 1 If you completed the preceding step correctly a directory called ABAQUS should have been created in your home directory Within your ABAQUS directory create a subdirectory called tutorial to store your input files and results ABAQUS will generate a vast number of output files and to keep track of them it is convenient to keep all the files associated with a particular problem in one directory 2 Download the example ABAQUS file To do so click here You will see the input file appear in the frame Click anywhere on the frame then select Save Frame As from the File menu on the top left hand corner of your browser In the popup window find the directory called ABAQUS tutorial and save the file as tutorial inp 3 Open tutorial inp with a text editor Take a quick look at the file and make sure that it downloaded correctly 4 Exit the text editor In future you will create your own ABAQUS
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