The High Strain‐rate Fracture Characteristics of Ductile Metals at Elevated and Sub‐ambient Temperatures

Abstract

High strain-rate tensile tests have been carried out on pre-notched specimens of OFHC copper and Remko iron at both elevated and cryogenic temperatures. When properly expressed as a function of stress triaxiality at the centre of the notch (as predicted by numerical simulations of the experiment), the ductility of copper was found ta be independent of temperature over a range from -190°C to 300°C. The specially-processed Remko iron was found to undergo a ductile-to-brittle transition at a temperature dependent on the stress triaxiality and the particular batch of the material. Otherwise the fully ductile strains-to-failure (when expressed as a function of stress triaxiality) for iron were found to decrease with increasing temperature up to 400°C; this being the maximum temperature tested. NOMENCLATURE do =initial minimum diameter df = post-fracture minimum diameter T, = melting temperature To = test start temperature T, = reference temperature (20°C) Ef = effective plastic strain at failure = 2 In(d,/d,) u, = Von Mises effective stress urn = mean stress T** =homologous temperature = (T, -T,)/(Tm -T,)

Determination of the high strain rate fracture properties of ductile materials using a combined experimental/numerical approach

“…5 where the dynamic local failure strains are significantly greater than the corresponding quasi-static values. This trend is as reported for other metals when the effect of the adiabatic temperature rise on the local stress and strain parameters is taken into account [18]. Note that the failure mechanism remained one of ductile void growth and intergranular fracture throughout and no evidence of twinning deformation has been reported for this alloy [16].…”