Effects of grain boundary heterogeneities on creep fracture studied by rate-dependent cohesive model

To simulate creep fracture of ceramics at high temperatures, we have developed a user-defined element (UEL) subroutine and a user-defined material properties (UMAT) subroutine to analyze the rate-dependent cohesive behavior of the grain boundary and the creep deformation of the grain, respectively, and implemented them in ABAQUS. The model presented here accounts for grain boundary sliding, nucleation of grain boundary cavities, their growth by diffusion and creep, and link up of microcracks to form macrocracks. Numerical examples demonstrate that the rate-dependent cohesive element has a better numerical stability than the existing work and the entire cavity growth process can be simulated. Also, in the presence of grain boundary heterogeneities, stress distribution becomes localized which, in turn, induces localized grain boundary cavitation and promotes creep fracture.