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

Abstract

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 δ and the rate of local plastic deformation έ on the contour of its blunted tip. To calculate έ 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 $$\sigma _{0.2} ^d $$ that is used in establishing the value of $$\dot \varepsilon $$ . We present the correlation between the transition temperature of the metal to ductile failure Tv and the velocity parameters $$\dot \delta , \dot \varepsilon $$ .