Study on the kinetics of thermomechanical response accompanying plastic instability in mild steel

• Heat power and strain rate evolutions reveal the strain localizations accompanying Lüders instability precisely without the influence of the signatures of prior plastic localization.
• The occurrence of delayed localized yielding during the initial stages of uniform strain hardening is successfully mapped using heat power and strain rate evolutions.
• The fraction of heat power dissipated is found to be relatively more in the load plateau involving strain localizations accompanying Lüders bands than the strain hardening region.

This paper deals with the analysis of heat power and strain rate evolutions accompanying Lüders instability in mild steel to quantitatively probe the kinematics of the associated localization during tensile testing. Thermomechanical parameters such as dissipative heat power, stored power and energy conversion rate ratios are estimated to provide an insight into the deformation behavior and the associated rate of energy conversions involved in each region of the load–time curve. It is shown that compared to temperature and strain evolutions, heat power and strain rate evolutions provide more quantitative information on the plastic strain localization during nucleation and growth of Lüders bands without the effects of the signatures of prior plastic localization. The occurrence of delayed localized yielding during the initial stages of uniform strain hardening is successively studied using heat power and strain rate evolutions. The difference in magnitude of yielding experienced by the specimen during the propagation of two different Lüders bands is clearly demonstrated by the estimated dissipative heat and stored powers. Estimated energy conversion rate ratios convey that fraction of heat power dissipated is relatively more in the load plateau involving strain localizations than the strain hardening region.