Mixed Mode Loading of an Interface Crack Subjected to Creep Conditions

Interface cracks are seldom subjected to pure Mode I or pure Mode II conditions. Station~y interface cracks between two distinct, bonded elastic-creep materials subjected to remotely applied mixed mode loading are simulated. The finite element method (FEM) is used to examine crack tip fields and candidate driving force parameters for crack growth. Plane strain conditions are assumed. In most cases a functionally graded transition layer is included between the two materials. Examples of such systems include weld metal (WM) and base metal (BM) interfaces in welded or repaired boiler components subjected to elevated temperatures. Numerical solutions based on the asymptotic fields of the homogeneous and heterogeneous Arcan-type specimens are presented. Creep ductifity-based damage models are used to predict the initial crack propagation trajectory. The incorporation of functionally graded transition layer regions affects the evolution of timedependent stress components in the vicinity of the crack tip. The magnitude and direction of crack tip propagation can then be optimized with respect to interface properties.