ABSTRACT
So far, our discussion on the mechanical behavior has considered only timeindependent deformation. However, the mechanical behavior of materials may also be time dependent. This can give rise to time-dependent strains or crack growth that can result, ultimately, in component failure or damage. For several materials deformed at temperatures above about 0.3-0.5 of their melting temperatures, Tm (in K), time-dependent deformation can occur by creep or stress relaxation. This may result ultimately in a range of failure mechanisms that are illustrated schematically in Fig. 15.1. In crystalline metals and their alloys, creep damage can occur by stress-assisted diffusion and/or dislocation motion. Microvoids may also form and coalesce by the same mechanisms during the final stages of creep deformation. Furthermore, creep damage mechanisms may occur at crack tips, giving rise ultimately to creep crack growth phenomena.
