MECHANICAL MODEL ON BRITTLE CRACK INITIATION AND PROPAGATION

A mechanical model is presented in this paper to describe the initiati ng and propagating of brittle cracks. Two criteria have been deduced f rom the model to determine the effects of such factors as local stress state, surface and grain boundary energies as well as local grain bou ndary orientation on the initiating and propagating of both intergranu lar and transgranular brittle cracks. By which the role of adding B in Ni3Al base alloys to improve their ductility temper and hydrogen embr ittlements in steels and other alloys as well as the random feature of brittle crack initiation could be explained.