1. Stress Relaxation Workshop Six REFERENCE: Training Manual Implicit Creep (4-32)

2. Workshop Supplement September 30, 2001 Inventory #001492 W6-2 Workshop Six: Stress Relaxation (Implicit Creep) Plate with Fillet Purpose Run a stress relaxation problem of a model with implicit creep. Goal Solve a model with implicit creep which experiences an imposed displacement. The subsequent run will be the stress relaxation of the part Become familiar with turning rate effects on/off. Model Description 3D PLANE182 solid with linear elastic properties and implicit creep.

3. Workshop Supplement September 30, 2001 Inventory #001492 W6-3 Workshop Six: Stress Relaxation (Implicit Creep)... Plate with Fillet 1.Read in the input file named “ANL_W06_StressRelax.inp” Use the GUI menu method: –Utility Menu > File > Read Input From… Select the file “ANL_W06_StressRelax.inp” Click on [OK] or Command Input method: –/INPUT,ANL_W06_StressRelax,inp Notes: This will read in an input file which will generate the geometry, loads, and boundary conditions for the current exercise. We will have a 3D part comprised of SOLID185 elements. The current database will be erased, and the jobname will be changed to “Exercise_6”. The graphics and other settings will also be set to be consistent with these slides.

4. Workshop Supplement September 30, 2001 Inventory #001492 W6-4 Workshop Six: Stress Relaxation (Implicit Creep)... Plate with Fillet Before continuing with the exercise, you can also examine the mesh and the boundary conditions on the plate to become more familiar with the model. There are symmetry boundary conditions imposed on X=0, Y=0, and Z=0. The edge of the ‘arm’ has an imposed displacement of 0.5 units. This analysis will be carried out in two load steps: –The first load step will have creep effects off (default). The displacement on the arm will be imposed. –The second load step will have creep effects turned on. The displacement on the arm will remain constant. We will run the analysis for a long duration to see the stress relaxation in the arm.

5. Workshop Supplement September 30, 2001 Inventory #001492 W6-5 Workshop Six: Stress Relaxation (Implicit Creep)... Plate with Fillet 2.Verify the element options for SOLID185 (8-node quad) Use the GUI menu method: –Main Menu > Preprocessor > Element Type > Add/Edit/Delete … Select “Type 1 SOLID185” Click on [Options] Verify element options, then click on [OK] Select [Close] or Command Input method: –/PREP7 –ETLIST Notes: Element type 1 will use the “Full integration” formulation (a.k.a. B-Bar method). Although it is also known as “Selective Reduced Integration”, the wording here refers to deviatoric terms. Hence, SOLID185 has “full” (B-Bar) and “reduced” (URI) integration options for deviatoric terms.

6. Workshop Supplement September 30, 2001 Inventory #001492 W6-6 Workshop Six: Stress Relaxation (Implicit Creep)... Plate with Fillet 3.Add creep properties Use the GUI menu method: –Main Menu > Preprocessor > Material Props > Material Models … Select “Structural > Nonlinear > Inelastic > Rate Dependent > Creep > Creep only > Mises Potential > Implicit > 6: Modified Time Hardening (Primary) ” You will be prompted to input linear elastic materials first. Click on [OK] Enter “200e3” for “EX” and “0.3” for “PRXY” Click on [OK] Enter “2e-10” for “C1”, “1” for “C2”, “1.5” for “C3”, and “0” for “C4” as shown on right. Click on [OK] Select “Material > Exit” or Command Input method: –MP,EX,1,200e3 –MP,PRXY,1,0.3 –TB,CREEP,1,1,,6 –TBDATA,1,2e-10,1,1.5,0.0

7. Workshop Supplement September 30, 2001 Inventory #001492 W6-7 Workshop Six: Stress Relaxation (Implicit Creep)... Plate with Fillet 4.Specify Solution Options for first load step. Use the GUI menu method: –Main Menu > Solution > -Analysis Type- Sol’n Control … Select “Large Displacement Static” under “Analysis Options” Enter “1e-8” for “Time at end of loadstep” Enter “1” for “Number of substeps” Enter “1” for “Max no. of substeps” Enter “1” for “Min no. of substeps” Select “Write every substep” for “Frequency” Click on [OK] or Command Input method: –/SOLU –NLGEOM,ON –TIME,1e-8 –NSUBST,1,1,1 –OUTRES,ALL,ALL Notes: We will impose the displacement initially. There will be no creep effects for the first loadstep. Since we use TIME=1e-8 (i.e., a very small value), when we start the creep analysis, it will start near TIME=0.0. We also limited the number of substeps to 1 since the initial displacement should converge quickly, as the creep effects will be off.

8. Workshop Supplement September 30, 2001 Inventory #001492 W6-8 Workshop Six: Stress Relaxation (Implicit Creep)... Plate with Fillet 5.Solve the first load step Use the GUI menu method: –Main Menu > Solution > -Solve- Current LS After reviewing the status window, close it by selecting “File > Close” To start the analysis, click on [OK] or Command Input method: –SOLVE Notes: The first load step only has an imposed displacement with creep effects off. This loadstep should run quickly. Do NOT leave the Solution processor. We will run a second loadstep next.

9. Workshop Supplement September 30, 2001 Inventory #001492 W6-9 Workshop Six: Stress Relaxation (Implicit Creep)... Plate with Fillet 6.Specify Solution Options for second load step which includes creep effects. Use the GUI menu method: –Main Menu > Solution > -Analysis Type- Sol’n Control … Enter “150” for “Time at end of loadstep” Enter “100” for “Number of substeps” Enter “1e5” for “Max no. of substeps” Enter “10” for “Min no. of substeps” Do not click on [OK] yet. Go to next slide. or Command Input method: –TIME,150 –NSUBST,100,1e5,10 Notes: We will run the second load step with creep effects. Because “time” has significance in a creep analysis, the value and units of time are important. Also, a large enough number of substeps must be specified to capture the creep response accurately.

10. Workshop Supplement September 30, 2001 Inventory #001492 W6-10 Workshop Six: Stress Relaxation (Implicit Creep)... Plate with Fillet 7.Specify Solution Options for second load step which includes creep effects. Use the GUI menu method: Select the “Nonlinear” tab Turn on “Include strain rate effect” under “Creep Option” Click on [OK] or Command Input method: –RATE,ON Notes: We have turned on creep effects for the second load step. We have not specified a value for “Implicit Creep ratio” above. The default of “0” means that no creep limit will be imposed. Usually, a value of 1-10 should suffice. Later in this exercise, we will see the significance of the creep limit ratio.

11. Workshop Supplement September 30, 2001 Inventory #001492 W6-11 Workshop Six: Stress Relaxation (Implicit Creep)... Plate with Fillet 8.Solve the second load step Use the GUI menu method: –Main Menu > Solution > -Solve- Current LS After reviewing the status window, close it by selecting “File > Close” To start the analysis, click on [OK] or Command Input method: –SOLVE Notes: Note the settings in the /STATUS window. This will be load step number 2, which will run until end time of 150. There is no creep criterion specified.

12. Workshop Supplement September 30, 2001 Inventory #001492 W6-12 Workshop Six: Stress Relaxation (Implicit Creep)... Plate with Fillet After the solution is complete, note the information in the output window/file. A sample is shown below. The CREEP RATIO is printed at the end of each substep (analogous to plastic strain increment when plasticity is active). In this problem, the creep ratio is near 1.0 towards the end of the solution. Since we have not specified any creep ratio control limit, the output echoes this fact. Because the solution converges without difficulty and no creep limit is set, the substeps keep increasing (recall that our min substep was 10 or, to put another way, our max time increment was 150/10=15). The max substep has been reached, as shown in the output below (time increment is circled). FORCE CONVERGENCE VALUE = 885.9 CRITERION= 4.123 DISP CONVERGENCE VALUE = 0.2474E-02 CRITERION= 0.2500E-01 <<< CONVERGED EQUIL ITER 1 COMPLETED. NEW TRIANG MATRIX. MAX DOF INC= 0.2598E-03 FORCE CONVERGENCE VALUE = 0.2466E-01 CRITERION= 3.706 <<< CONVERGED >>> SOLUTION CONVERGED AFTER EQUILIBRIUM ITERATION 1 *** LOAD STEP 2 SUBSTEP 14 COMPLETED. CUM ITER = 16 *** TIME = 137.672 TIME INC = 15.0000 *** CREEP RATIO = 1.029 CRITERION FOR CREEP RATIO CONTROL = none *** AUTO TIME STEP: NEXT TIME INC = 12.328 DECREASED (FACTOR = 0.8219) FORCE CONVERGENCE VALUE = 476.8 CRITERION= 2.236 DISP CONVERGENCE VALUE = 0.1333E-02 CRITERION= 0.2500E-01 <<< CONVERGED EQUIL ITER 1 COMPLETED. NEW TRIANG MATRIX. MAX DOF INC= 0.1412E-03 FORCE CONVERGENCE VALUE = 0.7321E-02 CRITERION= 2.017 <<< CONVERGED >>> SOLUTION CONVERGED AFTER EQUILIBRIUM ITERATION 1 *** LOAD STEP 2 SUBSTEP 15 COMPLETED. CUM ITER = 17 *** TIME = 150.000 TIME INC = 12.3281 *** CREEP RATIO = 0.9818 CRITERION FOR CREEP RATIO CONTROL = none

13. Workshop Supplement September 30, 2001 Inventory #001492 W6-13 Workshop Six: Stress Relaxation (Implicit Creep)... Plate with Fillet 9.Review equivalent creep strains Use the GUI menu method: –Main Menu > TimeHist Postpro > Variable Viewer Select the “Exercise_6.rst” results file. The Time-History variable viewer will appear, as shown on the right. Click on the “+” (Add Data) icon. Select “Nodal Solution > Creep Strain > von Mises creep strain”. Click on [OK] Select a node near the fillet, as shown on the right. In this case, node #250 was chosen. Select [OK] when done. In the Time-History variable viewer window, click on the “Graph” icon (Graph Data). A plot of equivalent creep strain vs. time will be shown (see next slide). or Command Input method: –/POST26 –ANSOL,2,250,EPCR,EQV,eqvcreep –PLVAR,2

14. Workshop Supplement September 30, 2001 Inventory #001492 W6-14 Workshop Six: Stress Relaxation (Implicit Creep)... Plate with Fillet A plot of equivalent creep strain vs. time is shown below. The results can also be listed by clicking on the “Text” icon (list data) or using PRVAR,2 command. You can obtain other results such as stress to see the relaxation as a function of time. TIME 250 EPCREQV EPCREQV_ 2 0.10000E-07 0.00000 1.5000 0.284803E-06 3.0000 0.161082E-05 5.2500 0.652206E-05 8.6250 0.225200E-04 13.688 0.710450E-04 21.281 0.210696E-03 32.672 0.588118E-03 47.672 0.137173E-02 62.672 0.238485E-02 77.672 0.346323E-02 92.672 0.444944E-02 107.67 0.524221E-02 122.67 0.581050E-02 137.67 0.617755E-02 150.00 0.637037E-02

15. Workshop Supplement September 30, 2001 Inventory #001492 W6-15 Workshop Six: Stress Relaxation (Implicit Creep)... Plate with Fillet Also, you can go in the General Postprocessor to review stresses and strains. Below is an animation of von Mises stress contours, along with a graph of equivalent creep strain.