Impact simulation and different hardening rules

[evenjl]

Hi guys!

I am currently working on a project with stiffened aluminium plates subjected to impact loading with a hemispherical indenter. The simulations worked just fine until I tried a different hardening rule.
I use power law in my base model, but some problems seem to arise when I try to use voce law (2-terms).

The model is shown below. I have different material properties for the plate, the stiffeners and for the welds. The Cockroft-Latham criterion is used to describe fracture.

The analysis stops halfway through because of some warnings/errors:

"Master surface ASSEMBLY_M_SURF-63 of contact pair # 12 contains
facets with out-of-plane warping of at least 20.000 degrees in
increment 108420. Large warping that develops during an analysis
often corresponds to severe distortion of the underlying elements.
It may be appropriate to rerun the analysis with a refined mesh."

***ERROR: Excessive distortion of element number 6045 of instance PLATE1


***ERROR: Excessive distortion of element number 6046 of instance PLATE1


***ERROR: Excessive distortion of element number 6047 of instance PLATE1


***ERROR: Excessive distortion of element number 6112 of instance PLATE1


***ERROR: Excessive distortion of element number 6113 of instance PLATE1


***ERROR: Excessive distortion of element number 6114 of instance PLATE1


I have tried to redefine the mesh - but with no results.
To be clear, the error messages above is not a problem as long as I use the power law.

As the curves show, voce gives much lower stresses than the power law - but it has never been a problem in other projects I have been working on.


Any thoughts?


Thanks
Even