Taylor–Quinney Coefficient Derived from Dynamic In-Plane Torsion: Stress-State-Dependent Isothermal-to-Adiabatic Transition Functions for Thermo-Mechanical Modeling

The accurate estimation on the conversion of plastic work into heat is essential for the successful thermomechanical simulation of metallic structures that are deformed plastically. In the present work, the results from dynamic in-plane torsion experiments are exploited for the first time to determine the Taylor-Quinney coefficient for very large strains. Uniaxial tension (UT), notched tension, and shear (SH) specimens are also performed to broaden the range of stress states and strain rates (0.001/s to 900/s). In all experiments, an optical high-speed camera provided access to the surface strain fields through digital image correlation (DIC), while an infrared high-speed camera measured the corresponding temperature fields. Terminal temperatures of up to 368 degrees C are observed in the high strain rate torsion experiments (900/s). Coupled thermo-mechanical simulations are performed using a non-associated Hill'48 plasticity model with a modified Johnson-Cook type of temperature and rate-dependent hardening law. A novel isothermal-to-adiabatic regime transition function depending on strain rate, plastic strain and stress triaxiality is proposed to treat the temperature as an internal variable in purely mechanical simulations. This reduces computational cost by up to an order of magnitude as compared to coupled thermo-mechanical analyses, while offering comparable accuracy.