Mechanism of transformation plasticity and the unified constitutive equation for transformation-thermo-mechanical plasticity with some applications

Abstract

Transformation plasticity is known to occur in weaker mother phase due to the progress of new phase with higher strength. A phenomenological mechanism is discussed, in the first part of the paper, why the transformation plastic deformation takes place under a stress level even lower than the characteristic yield stress of mother phase: This is principally based on the difference in thermal expansion coefficient in both phases. Bearing in mind that it is also a kind of plastic strain, a unified plastic flow theory is derived by introducing the effect of progressing new phase into the yield function of stress, temperature and plasticity related parameters. Thus obtained strain rate reveals to include the transformation plastic part in addition to mechanical and thermal plastic components. As examples of the application of the theory, temperature-elongation diagrams depending on applied stress are shown. Inelastic response for a fire resistant steel under varying temperature and stress as a model of a fire followed by the extinguishment is simulated being compared with experimental data.