[CIG-SHORT] Elastoplastic material question

[Brad Aagaard]

Eric,

Have you verified convergence of the linear and nonlinear solvers up to 
the point you get an error? If the solver doesn't converge, you will get 
garbage that could show up as weird behavior.

Brad


On 11/18/2013 05:01 PM, Eric Lindsey wrote:
> I'm having trouble understanding the DruckerPragerPlaneStrain material. I'm
> using a simple homogeneous domain with no faults, and a simple Dirichlet BC
> imposing shear on the top/bottom. I've imposed an initial isotropic
> compression, then I add the shear displacement gradually until it should
> exceed the yield stress. On the sides I have a Neumann condition to
> maintain the normal stress; for the moment I just set the shear tractions
> to zero, but this value doesn't affect the results I'm getting. I expected
> to see uniform plastic shear throughout the domain, but instead get the
> message:
>
> RuntimeError: Infeasible stress state - cannot project back to yield
> surface.
>
> If I include "allow_tensile_yield = True", the model runs, but instead of
> homogeneous strain I'm getting the attached result. This is strange because
> at no point should the material be under absolute tension; the maximum
> shear stress in the elastic case is never larger than the magnitude of
> compressive stress. I think I am misunderstanding the setup of this
> material somehow; hopefully it's a simple error? Input files are attached,
> the elastic case works just fine. Any suggestions would be much appreciated.
>
> Thanks,
> Eric
>
> Relevant lines from the spatial databases:
>
>
>
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