Material parameters are essential for calibrating constitutive models and hence the simulation of material behaviour. At high strain rates, adiabatic heating becomes significant. A testing methodology is sought to decouple the heating effects from the strain rate effects to parameterise and understand each contributing factor. Whilst similar efforts have been undertaken, it is unclear if only the adiabatic heating effects have been removed and if any other effect is introduced. Furthermore, the existence of a heat generation distribution is not known and assumed to be uniform.
Interrupted uniaxial tensile tests have been devised to isolate out adiabatic heating effects from strain rate and can be retrofitted onto existing test systems. The work hardening rate between the monotonic and interrupted tensile tests showed a significant difference which also varied dependent on strain rate. Post-mortem microstructural analysis on both monotonic and interrupted tensile tests revealed a complex interplay between the dislocation densities, twinning and dynamic recrystallisation that affected the work hardening rate of 316L stainless steel. The interrupted loading path promoted increase in dislocation densities, whilst increasing strain rate induced more twinning and adiabatic heating provided thermal assistance for dynamic recrystallisation.
Adiabatic heat generation distribution was approximated by considering geometrically necessary dislocations, twin boundaries, and non-indexed areas of electron backscatter scans in the necked region of 316L stainless steel. No distribution was found to favour the tensile axis or specimen edge and supports the assumption that heat is generated evenly through the specimen thickness. Thermal imaging cameras and digital image correlation were used simultaneously and the Taylor-Quinney coefficient was found to depart from the commonly assumed value of 0.9.
This study is the first to study the microstructural differences between monotonic and interrupted uniaxial tensile tests and highlight its importance when directly comparing between the two tests...