An Engineering Approximation on the Transformation of Plastic Work into Heat at Various Strain Rates and Stress States

¹ Swiss Federal Institute of Technology (ETH), Zurich, Switzerland
² Inspire AG, Zurich, Switzerland
³ Univ. Bretagne Sud, UMR CNRS 6027, IRDL, F-56100 Lorient, France

^* Corresponding author: xueyang.li@inspire.ch

Abstract

Accurate estimation of plastic work conversion into heat is crucial for analyzing metals under dynamic deformation. This study investigates DP800 sheet metal specimens across nine strain rates (0.001/s to 150/s) using notched tension (NT) and shear (SH) specimens to explore stress-state effects. Surface strain fields are monitored via digital image correlation (DIC) using a high-speed optical camera, while temperature rise due to plastic dissipation is measured using a high-speed infrared camera. A temperature rise of 170K is observed at 150/s, with minimal rise at 0.001/s. A Hill′48 yield surface combined with a modified Johnson-Cook hardening law accurately predicts force-displacement and strain histories. We compare two methods of treating the conversion of the plastic work into heat: (1) coupled thermo-mechanical simulations, which are accurate but computationally expensive, and (2) treating temperature as an internal state variable, neglecting heat transfer. We then propose a transition function incorporating both strain rate and stress state dependencies, enabling the internal variable method to achieve comparable accuracy to coupled thermo-mechanical simulations with a marginal increase in computational cost over pure mechanical analysis.