Elastic-plastic response of cracked crystals

The elastic-plastic response of cracked perfect crystals is closely associated with the crack stability at near-zero temperatures and the intrinsic ductile and brittle behaviour of crystals. This response is studied predominately in theoretical way because of extremely complicated experimental verification. The crack remains stable (ductility) when a dislocation emission from the crack tip takes place before fracture while an unstable crack (brittleness) corresponds to the cleavage fracture caused by the interatomic-bond breaking at the crack tip. New results of application of the improved Kelly, Tyson and Cottrell approach (KTC-criterion) concerning a wide group of crystals is presented. The problem of elastic-plastic response is solved for both plane stress and plane strain conditions at the crack tip. A comparison with the Rice and Thomson criterion and available experimental data is made. (orig.)