MICROMECHANICAL STUDIES OF CYCLIC CREEP FRACTURE UNDER STRESS-CONTROLLED LOADING

This paper deals with a study of intergranular failure by creep cavita tion under stress-controlled cyclic loading conditions. Loading is ass umed to be slow enough that diffusion and creep mechanisms (including grain boundary sliding) dominate, leading to intergranular creep fract ure. This study is based on numerical unit cell analyses for a planar polycrystal model with the grains and grain boundaries modeled individ ually, in order to investigate the interactions between the mechanisms involved and to account for the build-up of residual stress fields du ring cycling. The behaviour of a limiting case with a facet-site micro crack yields important insight for damage accumulation under balanced loading. Under unbalanced loading, the time-average accumulation of cr eep cavitation gives rise to macroscopic ratchetting, while its rate i s demonstrated to depend subtly on material and loading conditions.