A damage-based cohesive zone model of intergranular crack growth in a nickel-based superalloy

A cohesive zone model is utilized to simulate grain boundary interface decohesion under load reversals with hold time being imposed at the maximum load level. This study considers the role of creep–fatigue and environment, which have been introduced as scalar damage parameters. These parameters are coupled with the traction–displacement laws governing the grain boundary cohesion and surrounding time-dependent deformation field. The accumulation of reversible fatigue damage is described using a damage rate law as a function of the elastic potential energy of the interface while creep damage is introduced using a modified Kachanov–Rabotnov type law. The role of environment is modeled by considering the grain boundary dynamic embrittlement occurring as a consequence of oxygen diffusion and accumulation in the grain boundary fracture path. The separation of damage laws into creep, fatigue, and environment, allows the examination of the influence of the different mechanisms on the intergranular crack growth rate. Theoretical aspects of the model are discussed and finite element simulations of intergranular crack growth are performed on a nickel-based superalloy, IN100, at 700℃ to illustrate the main features of the model and its comparison with the experimental data.