Damage modeling of the single crystal superalloy SRR99 under monotonous creep

Abstract

The evolution of material damage of single crystal superalloys depends not only on the load conditions, but also strongly on the lattice orientation. Using the theory of continuum damage mechanics, a phenomenological creep damage model for cubic single crystal superalloys is derived. In this model, a symmetric second-order damage tensor is used to describe the anisotropic nature of damage. The damage deactivation and reactivation is represented by an active damage tensor. As the effects of the current state of damage on the deformation process and on the damage development are different in nature, separate effective stresses for creep and damage are defined. Furthermore, a mapped damage active stress is introduced to reflect the influence of material symmetry on the damage growth rate by using an orientation function. Based on microscopic observations, it is assumed that only the principle tensile damage active stresses are responsible for the damage development, and that the anisotropy of the damage evolution mainly depends on the principle directions of the damage active stress and the material symmetry. Within the framework of thermodynamics, the damage evolution law is constructed by considering both the initial material anisotropy and the anisotropic influence of the current state of damage. Based on the effective stress concept, this damage model has been implemented into a three-dimensional anisotropic viscoplastic model and applied to the simulation of the creep damage behavior of the single crystal superalloy SRR99 at 760°C.