I am trying to use COSMOS 2008 Adv Pro to model a flat
indentor pushing into a semi-infinite plane of a relatively soft
material. The load on the indentor is high enough to yield the soft
material in the plane, which leaves behind a permanent impression
in the soft material when the indentor is withdrawn. As an output
of the analysis, I would like to produce a load-displacement curve
for the indenting operation.

The indentor material is a linear elastic material with a high elastic modulus. The soft plane material is a non-linear with a defined stress-strain curve that looks like a classic plastically deforming metal. The yield strength of the plane material is significantly below the indentor's yield strength.

My non-linear static model behaves well thoughout the elastic range, but when the plastic deformation becomes significant, the simulation diverges and the solver chokes.

Is this typical behavior for COSMOS Non-linear when dealing with these sorts of problems? It's my interpretation that the simulation runs smoothly until the deformation of mesh in the soft material is big enough that the deformation of the mesh elements reaches some critical value. I've seen some papers describing using FEA to simulate this type of phenomenon, but non using any of the COSMOS products.

Please let me know if you have any experience with running this type of simuation. Your input will be much appreciated.

Thanks,

Eric

The indentor material is a linear elastic material with a high elastic modulus. The soft plane material is a non-linear with a defined stress-strain curve that looks like a classic plastically deforming metal. The yield strength of the plane material is significantly below the indentor's yield strength.

My non-linear static model behaves well thoughout the elastic range, but when the plastic deformation becomes significant, the simulation diverges and the solver chokes.

Is this typical behavior for COSMOS Non-linear when dealing with these sorts of problems? It's my interpretation that the simulation runs smoothly until the deformation of mesh in the soft material is big enough that the deformation of the mesh elements reaches some critical value. I've seen some papers describing using FEA to simulate this type of phenomenon, but non using any of the COSMOS products.

Please let me know if you have any experience with running this type of simuation. Your input will be much appreciated.

Thanks,

Eric

Cosmos can only handle a max strain in the order of 10%. The other thing you should check is that you need a "true stress strain" relationship. It is easy to convert from and nominal or engineering stress strain relationship. Just put trues stress strain into google and it comes up pretty quick. The other thing I try to do is go with a bilinear model first, which in reality is a pretty decent approximation of a yielding metal for a lot of applications. You never want to have a true negative stiffness. If that works then I woudl say you have a problematic stress strain curve. If it doesn't well things get tougher as large element distrotions can cause problems. Cosmos does not support in solution remeshing so on that one I have no help that I know works. You could try mesh tuning - trial and error - and see if anything gets the solution to advance.