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

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.