I am currently trying to write a UMAT in Abaqus for plane-stress combined hardening. I have been following the algorithm set out in box 3.3 in Chapter 3 of the book Computational Inelasticity by Simo and Hughes.
I am having trouble with the calculation of the plastic multiplier. I am confused by the equation for R[SUP]2[/SUP]. Is the variable K a constant value for the isotropic hardening modulus? (as on pg 9 and 96) Or is it a function of equivalent plastic strain? (as on pg 91 and 129)
Thanks for your help,