On the hardening rule for austenitic steels accounting for the strain induced martensitic transformation
The elasto-plastic hardening model for austenitic steels undergoing plastic strain induced martensitic transformation is presented with application to both monotonic and cyclic loading processes. The kinematic hardening rule is assumed and expressed in terms of the back stress Z composed of two portions X and Xt , the first related to plastic strain, the other to phase transformation and volume fraction of martensite. The transformation process is assumed to be driven by the back stress difference X – Y, where Y is the transformation back stress related to growth of the martensitic phase. The non-linear coupling of hardening and phase transformation processes occurs due to interaction of back stresses X and Xt. The thermodynamic framework is applied by introducing state variables and conjugate forces used in specifying the plastic flow and evolution rules. The model is applied to simulate cyclic hardening response for uniaxial tension-compression tests and for combined tension-torsion tests. The cyclic stress-strain curves for specified strain amplitudes are used in material parameter calibration.