Institute of Fundamental Technological Research

The article presents a constitutive model aimed at simulation of martensitic transformation induced by stress and plastic strain coupled with the hardening process in austenitic steels. The yield and transformation conditions are assumed to depend on back stresses evolving during plastic deformation and transformation processes. Their interaction affects essentially the hardening rate of a material. The thermodynamic background is reviewed and applied with both free energy and dissipation functions used in derivation of the rules of flow, hardening and transformation kinetics. The constitutive model parameters are specified and next the simulation of strain hardening for monotonic and cyclic loading is presented for the cases of uniaxial tension-compression and for combined tension-torsion deformation programs. The effect of strain ratcheting is analyzed for the cases of uniaxial and combined loading. It is shown that the transformation process is shown to essentially reduce the ratcheting strain.

Martensitic transformation, Plastic deformation, Back stresses, Yield and transformation conditions, Hardening rates

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 X t, 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 X t. 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.

plastic deformation, martensitic transformation, kinematic hardening, back stresses, cyclic deformation, increased hardening rates, decreased ratcheting strains

The work presents an elasto-plastic material model with mixed hardening taking into account martensitic transformation. Modification of the kinematic hardening rule is proposed by relating back stress to the generalized thermodynamic force by a nonlinear function dependent on the fraction of martensite. The martensitic evolution is expressed in terms of isotropic hardening parameter by introducing proper free energy related force. The proposed model has been applied to predict hysteretic response for cyclic tension and compression tests for austenitic steel.