Evaluation of the fracture toughness of structural steels under high-speed deformation

We investigated the dynamic crack resistance (fracture toughness) of low-alloy structural steels within a broad range of change of temperature (173–323°K) and loading rate (10^–5–120 m/sec) on standard specimens tested under conditions of three-point bending by a drop weight. As velocity parameters determining the conditions of high-speed deformation of metal in the zone of prefailure we considered the speed of opening of the crack tip and the rate of local plastic deformation on the contour of its blunted tip. To calculate in dependence on the loading conditions, the corresponding expression is presented. We evaluated experimentally the mechanical properties of the investigated steels at different temperatures T and strain rates, and we also considered the possibility of determining theoretically the dynamic yield strength that is used in establishing the value of. We present the correlation between the transition temperature of the metal to ductile failure T_v and the velocity parameters.Translated from Problemy Prochnosti, No. 5, pp. 51–59, May, 1993.