steinberg-lund
rho0 reference density g0 ya initial shear modulus, athermal flow stress a b pressure and temperature dependence of shear modulus beta n ystarmax work hardening (initial plastic work is set in initial state) t0 reference temperature (usually 300 K) c1 c2 Tact yp rate-dependence ytmin minimum yt, e.g. 1.0e-8