Thermodynamic Investigation of Glassy Polycarbonate Under Slow Torsion by Experimentally Characterizing Adiabatic Temperature Rise

Background: Amorphous polymers are widely employed in engineering applications where their constitutive models need to be verified using characterization data such as synchronous stress–strain and plastic dissipation. It is convenient to conduct slow strain rate experiments, but measuring the adiabatic temperature rise remains challenging because the estimation of the heat transfer still has a lack of accuracy. Objective: A suitable method was developed for simultaneously measuring stress–strain and adiabatic temperature for polycarbonate subjected to slow torsion (< 1 s⁻¹). Methods: The thermal and mechanical responses were measured through synchronizing the digital image correlation, IR thermography and the sensors of torsion machine. The related adiabatic temperature can be calculated by prescribing the equivalent heat transfer using a simple convection model, whose coefficient was determined using a parametric fitting based on the measurement of temperature drop after the mechanical loading. To obtain the precise heat calculation, an ideal convection coefficient was established by using the earlier stage of the temperature drop because the primary form of heat transmission at this stage was convection. At last, a plastic work-to-heat conversion model with a Taylor-Quinney coefficient was used to validate the characterized results. Results: It shows that three and a quarter cycles of reversed cyclic shear strains from -0.51 to 0.43 will result in an increase in the adiabatic temperature of roughly 45˚C. This value agrees well with the theoretical value of about 47 ˚C calculated using the Taylor-Quinney coefficient. Conclusions: An experimental method for glassy polycarbonate’s thermodynamic investigation under slow torsion is established based on the accurate estimation of adiabatic temperature rise in the presence of heat transfer.