Equivalent Plastic Strain (PEEQ)

Hi there,

 Can you refer me to any literature concering measuring Equivalent Plastic Strain in general (with interest in anisotropic plasticity (Hill, Hoffman)). I've found in literature two different measures. Mises PEEQ and "Power" PEEQ, both defined as in attachment. Abaqus uses "Mises PEEQ" in Clasic Metal Plasticity, whereas for Hill Plasticity (Which is set up with plastic potentials) "Power PEEQ" measure is used. I'm currently writing UMAT for Hoffman's plasticity and I've found that "Mises PEEQ" doesn't work with Hill model (Nevertheless it is mentioned in "Computational Methods for plasticity. Theory and Aplication" that it can be used in that model). I've found also that "Power PEEQ" works well with both Hill and Mises plasticity and I'm looking for clues for PEEQ measure which can be used in Hoffman's model.

PS. "Power PEEQ" is term I found on the Internet so not sure if it's real term. It was also refered as to "Energy PEEQ"