Add finite strain invariant material model

[anne-glerum]

At the moment, the visco_plastic material model allows for strain weakening based on the first compositional field tracking the strain rate invariant. However, there is no plugin that actually tracks the second strain rate invariant on a field (there is a particle propery integrated_strain_invariant) in the source directory. @naliboff is working on creating a comprehensive visco-elasto-plastic material model including the strain tracking, but for now I've copied the plugin from benchmarks/buiter_et_al_2008_jgr.

[jdannberg]

If you want to have this as a real material model instead of a plugin in the benchmarks folder, you should also remove it from the benchmarks/buiter_et_al_2008_jgr folder, and use this new material model in the benchmark instead (so that we don't duplicate the code).

Otherwise, if this is only a temporary solution anyway, and all you worry about is using the plugin in your models, you can always include it via set Additional shared libraries in the input file.

[anne-glerum]

Alright, the finite strain tracking has been moved to the viscoplastic material model and the benchmark now only uses the viscoplastic material model.

Note that the test visco_plastic_yield_strain_weakening needs to be updated, because it uses three fields to track the independent components of the strain tensor and no time stepping is done, so there is no strain weakening.

[naliboff]

👍 Thanks for putting this in. After this is merged I'll fix the visco_plastic_yield_strain_weakening test and add in option to use the full finite strain tensor.

[bangerth]

/run-tests

[bangerth]

Can you rebase to force the tester to run again?