STRESS RUPTURE IN METALS AND CERAMICS.

Mechanisms of nucleation and growth of cavities in grain boundaries in metals and ceramics are reviewed. A stress and time condition for nucleation is derived and it is suggested that the junctions of three interfaces such as those formed between inclusions and grain boundaries are the most probable sites for nucleation. In metals, cavities can also grow by power law creep for which a strain and strain rate condition for fracture is obtained. In those ceramic materials, which contain a glass phase in the grain boundaries, the fracture process is dominated by the viscous flow of the glass and the formation of cavities in the glass phase. There is opportunity for new micro-mechanical-modelling and experimental work in ceramic materials which could lead to the design of new ceramics with unusual properties such as superplasticity. In metals, the influence of environment, multiaxial stresses, and notches on cavitation are recommended as topics for further research.