Effect of Strain Rate Upon Plastic Flow of Steel

TLDR

Increasing strain rate shifts metal deformation from isothermal to adiabatic, altering the stress‑strain response. The study tests whether changes in strain rate and temperature produce equivalent effects on the stress‑strain relation of metals. For typical steels, the strain‑rate/temperature equivalence holds, allowing high‑rate behavior to be predicted from moderate‑rate, low‑temperature tests, though at low temperatures the adiabatic plastic range shows a negative initial slope that destabilizes homogeneous deformation.

Abstract

An experiment has been designed to check a previously proposed equivalence of the effects of changes in strain rate and in temperature upon the stress-strain relation in metals. It is found that this equivalence is valid for the typical steels investigated. The behavior of these steels at very high rates of deformation may, therefore, be obtained by tests at moderate rates of deformation performed at low temperatures. The results of such tests are described. Aside from changing the isothermal stress-strain relation, an increase of strain rate tends to change the conditions from isothermal to adiabatic. It is found that at low temperatures, the adiabatic stress-strain relation in the plastic range is radically different from the isothermal, having an initial negative rather than a positive slope. This initial negative slope renders unstable homogeneous plastic deformation.