Strain Rate History Effects in Body-Centered-Cubic Metals

This paper presents a discussion of the strain rate history effects that occur during the deformation of body-centered-cubic (BCC) metals. It is divided into two parts: a brief review of previous work, which also includes some new data, followed by an analysis of material behavior based on previous and new results. The review discusses early experiments on steels and other BCC metals in which interrupted tests were performed. These tests consist of loading initially at one strain rate, unloading, and reloading at a second strain rate, either higher or lower than the first. Early experiments of this type had revealed a substantial difference in response between BCC and face-centered-cubic (FCC) metals. The review also includes results of incremental strain rate tests with large jumps in strain rate, augmented by a series of experiments designed to study strain rate history effects in steel. The latter consist of incremental tests performed on specimens of an AISI 1020 hot-rolled steel over the temperature range 83 K ≤ T ≤ 494 K. Results indicate that at temperatures near the ambient and for relatively small shear strains (up to γ ≈ 0.20) strain rate history effects play a minor role compared with strain rate effects per se. However, for low temperatures and for dynamic aging temperatures, strain rate history effects are shown to be of considerable importance. The second part of the paper concentrates on an analytical discussion of adiabatic coupling during deformation and on constitutive modeling of deformation in BCC metals.