THE DYNAMICS OF DISLOCATION GENERATION AT CRACK TIPS AND THE DUCTILE-BRITTLE TRANSITION

During the last few years there has been interest in the phenomena which control whether crystalline solids containing cracks deform in a brittle or ductile manner. One of the main conclusions is that the role of dislocations generated from external sources, as compared with that of dislocations nucleated at and emitted from the crack tip, in controlling T//c is not understood. The purpose of the present paper is to report on some recent experiments on Si and theoretical computations which address this and other problems covering the ductile-brittle transition of intrinsically brittle materials. Fracture experiments were carried out using 4-point bend tests on rectangular bars of float zone Si.