1. Springback Analysis Workshop 10

2. Workshop Supplement March 15, 2001 Inventory #001458 WS10-2 Utility Menu > File > Read Input from … > stamp.inp > OK Exercise - Springback Analysis 1. Read in the input file “stamp.inp” The input stamp.inp creates the model for a sheet metal stamping operation. A rigid punch is displaced downward to form a blank against a rigid die. The material properties (bilinear isotropic plasticity for the blank), loading scenario, and boundary conditions have already been defined. Automatic single surface contact is used. After solving the explicit dynamic portion of the analysis (i.e., the stamping), the thickness and stress results for the SHELL163 elements (i.e., the blank) along with the nodal displacements will be read into ANSYS and an implicit springback analysis will be conducted. Linear elastic unloading is assumed from the formed state (stamped configuration).

3. Workshop Supplement March 15, 2001 Inventory #001458 WS10-3 2. Save the database and solve the analysis. ANSYS Toolbar > SAVE_DB Solution: SOLVE > OK 3. Animate the von Mises stress results for the blank only. Utility Menu > Select > Entities > Elements > By Attributes > Material num > 1 > OK Utility Menu > Select > Entities > Nodes > Attached to > Elements > From Full > OK General Postproc: - Read Results - Last Set Utility Menu > Plot Ctrls > Style > Displacement Scaling > 1.0 (true scale) Utility Menu > Plot Ctrls > Animate > Over Results > Current Load Step > Range/Increment: 1 to 51 by 5 > Auto Contour Scaling: Off > Animation time delay: 0.5 > Display Type: Stress > Von Mises > OK

4. Workshop Supplement March 15, 2001 Inventory #001458 WS10-4 4. Enter POST26 and plot the motion of a node on the blank. TimeHist Postpro: Settings > File > stamp.his > OK TimeHist Postpro: Defines Variables > Add > Nodal DOF result > OK Pick the node at the vertex of the blank (node 1) and then pick OK Next, define “node1uy” to be the Y Translation (UY) of node 1 and pick OK Close the variable menu box and then Store the variable data. TimeHist Postpro: Store Data > Merge w/ existing > OK

5. Workshop Supplement March 15, 2001 Inventory #001458 WS10-5 Finally, plot the displacement of this node (NVAR1) versus time. TimeHist Postpro: Graph Variables > 2 > OK The plot indicates that the motion of the blank has tapered off enough to perform the implicit springback solution. If there was a great deal of oscillatory motion at the end of this solution, the explicit analysis should probably be repeated with some form of damping (EDDAMP command). Also, the loading scenario might not have been very realistic, causing infinite accelerations, etc.

6. Workshop Supplement March 15, 2001 Inventory #001458 WS10-6 5. Re-select everything in the model and save the database. Utility Menu > Select > Everything ANSYS Toolbar > SAVE_DB 6. Change the Jobname to “spring” for the implicit springback analysis. Utility Menu > File > Change Jobname … > spring > OK By renaming the Jobname, the explicit dynamic results stored in “stamp.rst” will not be overwritten. Instead, the implicit springback results will be saved to the file “spring.rst”. The corresponding database should be used when reviewing the results, since explicit elements are not valid in an implicit analysis and implicit elements are not valid in an explicit analysis.

7. Workshop Supplement March 15, 2001 Inventory #001458 WS10-7 7. Enter PREP7 and convert the explicit element types to implicit. Preprocessor: Element Type > Switch Elem Type > Explic to Implic > OK SHELL163 element formulation #10 (Belytschko-Wong-Chiang) was used in the stamping analysis. This formulation is recommended for explicit-to-implicit sequential solutions. When the element types are converted, the keyopts and real constants are set to their default values. Although the SHELL181 elements do not have the original thickness information after the conversion process, the final stamping thicknesses will be automatically imported into the model (along with the element force and moment data) before the implicit springback solution is conducted. The ETCHG command is used to convert the explicit elements to their companion implicit ones.

8. Workshop Supplement March 15, 2001 Inventory #001458 WS10-8 8. Remove any nonlinear material properties from the stamping analysis. In the command input line type TBDEL,PLAW,1 9. Turn off element shape checking. Preprocessor: Checking Ctrls > Shape Checking > Off > OK Nonlinear material properties are not valid, since linear elastic unloading is assumed for the springback phase. Although not necessary for this model, it is a good idea to turn off element shape checking, since the elements could have undergone considerable deformation in the LS- DYNA analysis.

9. Workshop Supplement March 15, 2001 Inventory #001458 WS10-9 10. Update the geometry to the final stamped configuration. Preprocessor: - Modeling - Update Geom > 1 > 1 > 51 > stamp.rst > OK Utility Menu > Plot > Elements The final configuration from the explicit solution is now the initial configuration for the springback solution. All displacements will be referenced from this new starting point. The actual motion of the blank will be based on the restraints that are applied. ( UPGEOM command )

10. Workshop Supplement March 15, 2001 Inventory #001458 WS10-10 11. Select only the blank elements (unselect the rigid tooling). Since the punch and die are rigid bodies, they are irrelevant in a springback analysis. Utility Menu > Select > Entities > Elements > By Attributes > Material num > 1 > OK Utility Menu > Select > Entities > Nodes > Attached to > Elements > From Full > OK Utility Menu > Plot > Elements

11. Workshop Supplement March 15, 2001 Inventory #001458 WS10-11 12. Enter Solution and apply additional boundary conditions. Springback analyses require sufficient restraints to prevent rigid body motion. First Select the nodes along the top of the blank being held by the holder: Utility Menu: Select > Entities > Nodes > By location -Y Coordinates > -.1,.1 > Reselect Then Apply the constraint in the Y-Direction Solution: - Loads - Apply > - Structural - Displacement > On Nodes > Pick All > OK > UY > 0.0 > OK

12. Workshop Supplement March 15, 2001 Inventory #001458 WS10-12 12. Apply additional boundary conditions. (Cont.) Reselect Back all of the nodes in the blank Utlility Menu: Select Entities > Nodes > Attached To > Elements Unlike in an explicit analyses, an implicit analysis will not converge if there is rigid body motion. UY - Constraints

13. Workshop Supplement March 15, 2001 Inventory #001458 WS10-13 13. Import the shell thicknesses and stresses from the explicit analysis. Use the RIMPORT command to bring in the shell thicknesses and element force and moment data from the final stamped configuration of the explicit dynamic analysis. As previously mentioned, the data from the very last substep can be in error if the loading curves were not extended slightly past the termination time… Currently, the RIMPORT command only supports LS- DYNA, but other codes will be supported in the future. Solution: - Loads - Apply > - Structural - Other > Import Stress … > DYNA run > 1 > 51 > stamp.rst > OK

14. Workshop Supplement March 15, 2001 Inventory #001458 WS10-14 14. Specify the analysis options for the implicit solution. Although the springback analysis assumes linear elastic unloading, large deformations are allowed, so the NLGEOM,ON command should be used. The sparse solver will be selected for this model, but the other ANSYS implicit solvers are available, too.. Solution: Analysis Type … > Sol’n Control..: Analysis Options> Large Displacement Static 15. Save the model and solve the springback analysis. ANSYS Toolbar > SAVE_DB Solution: - Solve - Current LS > OK > Yes > Yes (to warning prompts)

15. Workshop Supplement March 15, 2001 Inventory #001458 WS10-15 16. Examine the springback results. General Postproc: - Read Results - Last Set Utility Menu > Plot Ctrls > Style > Displacement Scaling > User specified > 10.0 > OK Utility Menu > Plot Ctrls > Pan, Zoom, Rotate > Obliq > OK General Postproc: Plot Results > - Contour Plot - Nodal Solu … DOF solution > Translation - USUM > Def + undef edge > OK

16. Workshop Supplement March 15, 2001 Inventory #001458 WS10-16 A displacement magnification factor of ten was used for the following plot.