rpalinka

rpalinka

I'm running an analysis of contact between two parts with very dissimilar materials. I can specify a displacement on the higher modulus part and the analysis converges in less than a half hour. I can then sum forces in the direction of the displacement. This yields a force value. But if instead of defining a displacement, I specify this force on the same part for exactly the same model, it either doesn't converge or it takes over 24 hours to converge. How is this? Am I doing something wrong? The analysis type is 3D nonlinear static. I've tried quasi-static with the force case with the same result.

Victor

Hello rpalinka

Are both parts still fully constrained after removing the displacement? If not, there may rigid body motion preventing it from finding a path to a solution. Some ways to solve it:

Add a constraint though an artificial low-stiffness support to prevent rigid body motion. The easiest way is by adding an elastic support anywhere on the free part.

If it's having trouble converging at the beginning, it can help to start with a smaller force, such as with a quadratic function instead of the default linear. Do that with quasi-static and automatic time stepping turned on in Analysis settings then specify the force with a formula like 123 * t^2.

Make the contact surfaces flat with no initial gap. Sometimes it works OK like that.

Or you might avoid the problem using nonlinear dynamic response so it doesn't need to be in static equilibrium all the time.