Analytical expression for the stress-strain curve of a dual phase material comprising two different strength level phases. Discussion of the results of the multiple X-ray peak method.

Abstract

Equations expressing a tensile stress-strain relation of a dual phase material composed of a strong, brittle martensite and a weak, ductile austenite are proposed. This dual phase contains a constant volume of each phase and we call this the equation for a constant volume model (abbr. CVM). The experimental stress-strain data of the dual phase having various ratios of martensite to austenite are obtained and are analyzed by the equation using a computer with a multiregression program, and their best-fit flow curves are obtained. The above analysis of the co-operative deformation mechanism of two phases, which is balanced in stress and strain, shows that deformation starts with a bonding mechanism close to an equal strain chain and then gradually changes to one close to an equal stress chain as the plastic strain increases. The analysis of the plastic stress and strain concentrations in each phase is given in detail. These results are shown to agree excellently with the experimental data obtained from the X-ray residual stress measurements. The strain hardening exponent and the ultimate tensile strain of the dual phase decrease from the value of austenite to that of martensite as the volume of the latter increases.