During hot working, deformation of metals such as copper or austenitic steels involves
features of both diffusional flow and dislocation motion. As such, the true stress-true strain
relationship depends on the strain rate. At low strain rates (or high temperatures), the stress-strain
curve displays an oscillatory behavior with multiple peaks. As the strain rate increases (or as the
temperature is reduced), the number of peaks on the stress-strain curve decreases, and at high strain
rates, the stress rises to a single peak before settling at a steady-state value. It is understood that
dynamic recovery is responsible for the stress-strain behavior with zero or a single peak, whereas
dynamic recrystallization causes the oscillatory nature. In the past, most predictive models are based
on either modified Johnson-Mehl-Avrami kinetic equations or probabilistic approaches. In this work,
a delay differential equation is utilized for modeling such a stress-strain behavior. The approach takes
into account for a delay time due to diffusion, which is expressed as the critical strain for nucleation
for recrystallization. The solution shows that the oscillatory nature depends on the ratio of the critical
strain for nucleation to the critical strain for completion for recrystallization. As the strain ratio
increases, the stress-strain curve changes from a monotonic rise to a single peak, then to a multiple
peak behavior. The model also predicts transient flow curves resulting from strain rate changes.
Modification of Charpy machine for the acquisition of stress-strain curve in thermoplastics
