# Nonlinear modeling of plastics in SW

Question asked by Dermott McHugh on Jan 15, 2014
Latest reply on Oct 21, 2014 by Jared Conway

I am trying to simulate a press fit plastic retaining ring in Solidworks Simulation using a Nonlinear study. I am using the 2d axisymmetric simplification.

For boundary conditions, all edges of items 1 2 and 3 are constrained such that the parts are essentially rigid. Body #2 is completely fixed. Body #3 is fixed in the horizontal direction and a downward displacement is applied from time = 0 to time = .5 so that it contacts Body #2. Body #1 is fixed in the horizontal direction and an upward displacement is applied from time = .5 to time = 1 so the that it also contacts Body #3. Body #4 is the press fit ring of interest. I am using no penetration contact sets with no friction.

The press fit ring is made of UHMWPE. A representative true stress/strain curve is shown here:

To try and simplify the material model, I have been using a bilinear plasticity simplification. Ex = 850 MPa and Etan = 104 MPa. Poisson's ratio is 0.46.

For a first run, I ran with a linear elastic model to test out the contact and boundary conditions. Shown is the stress plot at time = 1. Maximum stress is 122 MPa.

When I run the plastic model, I get failure at Step > 1 with the classic error message referencing a load limit or buckling:

Here is the stress state when the solver kicks the bucket: Hard to see I know, but it has basically just come into contact.

Does anyone have any ideas about what might be going wrong here? It seems like the contact is failing for some reason with the plastic material condition. One thing I have noticed helps the solution get further is to increase my ETan, making the material stiffer after yield, but obviously this doesn't represent the material I will be using.