GET_F_PLANESTRESSHARDMIXVAF - evaluates the yield function

Comments

Assumptions: plane stress, isotropic hardening (Voce), kinematic hardening (Armstrong-Frederick).

Input Arguments

theta (double) - material parameters

H_isotropic (double) - isotropic hardening parameters

sigmaV (double) - Cauchy stress under plane stress conditions in Voigt notation (sigma_11, sigma_22, sigma_22)

gamma (double) - plastic multiplier

sigmaV_back (double) - back stress

Output Arguments

f (double) - value of the yield function