I am modeling cyclic plasticity with a plane strain condition, a strained controlled test. I am using the von Mises yield criterion and linear isotropic hardening. Using a two-step return mapping algorithm I calculated the consistency parameter (d_gamma). I followed the steps mentioned (reference: Computational Inelasticity, J.C Sumo, T.J.R Hughes).
My questions are
1. How do I calculate the accumulated plastic strain? Do I need to calculate it for all the directions? I took the initial value of accumulated plastic strain equal to zero.
2. The graph is not quasi-linear after plotting stress-strain data for cyclic cases. I do not know what is adding up or my implementation is wrong.
Thank you
If you use the von mises yield criterion, you compute the accumulated plastic strain in the same manner as you compute the equivalent yield stress (Von Mises) but using plastic components. Just take care, because the accumulated plastic strain is always increasing, so you have to compute the equivalent plastic strain increment first, based on the plastic tensor increment, and then add the increment to the previous value.
Either you will never accumulate the plastic strain on a cyclic test.
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