[CIG-SHORT] Elastoplastic material question

[Eric Lindsey]

The spatial database info got cut off, sorry about that. Here are the
relevant values of the various parameters I'm imposing; these are all
simpleDBs.

spatialdb/x_tract.spatialdb:
// X-coord, Y-coord, shear-traction, normal-traction
0.0  0.0  0.0e+06  -0.2e+06

spatialdb/initial_stress.spatialdb:
// (1) x coordinate (km)
// (2) y coordinate (km)
// (3) stress-xx (Pa)
// (4) stress-yy (Pa)
// (5) stress-xy (Pa)
0.0  0.0 -0.2e+06 -0.2e+06 0.0e+06

spatialdb/mat_druckerprager.spatialdb:
// (1) x coordinate (m)
// (2) y coordinate (m)
// (3) density (kg/m^3)
// (4) vs (m/s)
// (5) vp (m/s)
// (6) friction-angle (degree)
// (7) cohesion (kPa)
// (8) dilatation-angle (degree)
0.0  0.0   2500.0  3000.0  5291.502622129181 30.0 5.0 30.0

On Mon, Nov 18, 2013 at 5:01 PM, Eric Lindsey <elindsey at ucsd.edu> 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:
>