Discussion Forum

Hello,

I am looking at stresses near the boundaries of a multistep model. Step 1 is stationary in which I apply a prescribed displacement ranging between 5-30% elongation in the Z direction. In step 2 I apply boundary loads directed in the transverse plane (x and y direction). This requires me to fix the model in the x and y direction in the second step. What is the best way to fix the face in the x and y directions on either end of the model? I have tried it a few different ways and have been unsuccessful, as the x and y constraints in step 2 cause poor behavior in my boundary elements.

First, if I simply have a fixed constraint on one end (fixed in xyz) and a prescribed displacement on the opposite Z end (elongation 5-30% in z direction, 0 displacement in x or y), the solution to the stationary step has extremely high shear stresses at the boundary since edge constraints do not allow for compression at the faces on the z ends of the model as it is fixed in x and y.

I have tried to have different boundary conditions for step 1 and 2, but these solutions are not properly solved and I end up with an essentially exploded model out to infinity. For example, in step one I fixed the model in the Z direction on one Z face, then elongated it in the Z direction on the opposite Z face. No x and y constraints are used in the first step. In the second step, I then use the "modify physics" tool to disable the prescribed displacements and add fixed constraints to the z faces. However, this does not appear to behave as I would like it to. The geometry does not apply fixed constraints on the boundaries of the solution from step 1, and the results are unintelligible. I believe it is applying a fixed constraint on the material coordinates, not at the new deformed spatial coordinates.