Now there are actual analytical J2 plast. b.marks

I've made 4 J2 plasticity benchmarks for the implementation
that I have made of the vonmises model. All benchmarks run
from t=0 to t=2, at t=1 yield initiates. All benchmarks are
uniaxial strain. It's run for parameters that are believable
for copper (except the hardening parameter). The four benchmarks
are:

no hardening
isotropic hardening
kinematic hardening
isotropic/kinematic mixed hardening.