Micromechanical Studies of Cyclic Creep Fracture Under Stress-Controlled Loading

Abstract

Abstract. This paper deals with a study of intergranular failure by creep cavitation under stress-controlled cyclic loading conditions. Loading is assumed to be slow enough that diffusion and creep mechanisms (including grain boundary sliding) dominate, leading to intergranular creep fracture. This study is based on numerical unit cell analyses for a planar polycrystal model with the grains and grain boundaries modeled individually, in order to investigate the interactions between the mechanisms involved and t o account for the build-up of residual stress fields during cycling. The behaviour of a limiting case with a facet-size microcrack yields important insight for damage accumulation under balanced loading. Under unbalanced loading, the time-average accumulation of creep cavitation gives rise to macroscopic ratchetting, while its rate is demonstrated to depend subtly on material and loading conditions.

Creep-Fatigue Crack Initiation Simulation of a Modified 12% Cr Steel Based on Grain Boundary Cavitation and Plastic Slip Accumulation

“…According to the observation in the experiment of van der Giessen and Tvergaard [ 42 ], the typical value of during the growth of the cavity is 75°, which is adopted in this model.…”

“…The cavities nucleate and grow under the action of external force. When the condition of cavities coalescence ( a/b = 0.8) is satisfied [ 42 ], the cavities at the grain boundary stop growing, which means that the grain boundary is completely destroyed by the creep cavity, so we define the accumulated creep damage as: …”