Sign-up for free online course on ANSYS simulations!Step 8: Postprocess the Results
Plot Deformed Shape
Main Menu > General Postproc > Plot Results > Deformed Shape
Select Def + undef edge and click OK.
This plots the deformed and undeformed shapes in the Graphics window. The maximum deformation DMX is 0.026148 inches as reported in the Graphics window. We should check that our results make sense. It appears that the boundary conditions have been satisfied as the tip of the shaft moves downward and the hole at the other end of the crank is held in place.
Animate the deformation
Utility Menu > PlotCtrls > Animate > Deformed Shape...
Select Def + undeformed and click OK. Select Forward Only in the Animation Controller. This is also a good way to check the boundary conditions have been applied correctly. Close the Animation Controller.
Plot Nodal Solution of von Mises Stress
Main Menu > General Postproc > Plot results > Contour Plot > Nodal Solu
For a quick refresher on von Mises stress, click Help. Search for von mises and click on the result 2.4 Combined Stresses and Strains.
Select Nodal Solution > Stress > von Mises stress and click OK. To change the range of stresses displayed, go to
Utility Menu > PlotCtrls > Style > Contours > Uniform Contours ...
and select User specified. Specify a range of minimum 0 and maximum 25000. We can now see more color variation in the model, and easily pick out the red areas.
When you plot the "Nodal Solution", ANSYS obtains a continuous distribution as follows:
1. It determines the average at each node of the values of all elements connected to the node.
2. Within each element, it linearly interpolates the average nodal values obtained in the previous step.
This procedure is in effect a smoothing operation.
The stress concentration located at the tip of the shaft can be ignored as the force is applied as a point load. Let's look at the results just for the crank by deselecting the elements within the pedal shaft volume. Go to
Utility menu > Select > Entities ...
Select Volumes, By Num/Pick, From Full and click Apply. Pick the crank volume and click OK. After we've selected a volume, we must next select all the elements in this volume. In the Select Entities window, select Elements, Attached to, Volumes and click Apply. Click Replot to display the new selection. Notice the deformation is exaggerated, revealing that deformation is primarily caused by torsion.
To select the whole model again, go to Utility Menu > Select > Everything.
Comparing the σxx Stress with von Mises Stress
To verify that the bending stress in the crank is relatively insignificant, we can compare the element σxx solution with the elemental von Mises solution.
General Postproc > Plot Results > Contour Plot > Element Solu
Click on Stress, then X-Component of stress , then Apply. Notice that the top-left and bottom-right corners of the cutout area are now blue, and that the scale has been readjusted to show that blue is now a large negative stress value. If this were a case of pure bending, we would expect the top of the crank to be in tension, not compression!
If grey areas are appearing in your contour plots, you should go to Utility Menu > PlotCtrls > Style > Contours > Uniform Contours ..., select Auto calculated, and click OK.
To find out information about specific points on the model, go to
General Postproc > Query Results > Subgrid Solu
Select Stress, X-direction SX, and click OK. The picking window will appear, and you can click on any point in the model. Click OK when finished.
Compare the stress values with the von Mises stress. (Click on von Mises stress, then OK)
Investigate the Stress Concentration
Let's zoom in on the red area. Use the mouse wheel to zoom in and out in the view area. Some other viewing functions: Holding down the Ctrl key and the left mouse button allows you to pan the view, while holding the Ctrl key and the right mouse button allows you to rotate the view. Hold down the right mouse button and draw a rectangle to zoom in on a specific region.
Recall that the nodal solution shows smoothed stress values. Let's compare the nodal solution with the element, i.e. non-smoothed, solution.
General Postproc > Plot Results > Contour Plot > Element Solu
Click on Stress, then von Mises Stress, then the OK button. In the vicinity of the cut-out corners, there are fairly significant discontinuities in the von Mises stress across adjacent elements. This suggests that we need to refine the mesh at least in this region. This is done in the next step.
Go to Step 9: Validate the results