Using the Finite Element Method to Calibrate Bimaterial Specimens for Interface Fracture

An investigation into the behavior of a crack along the interface between two dissimilar materials (a coating and a substrate) was conducted by using a finite element analysis in conjunction with state-of-art interfacial fracture mechanics. A comprehensive parametric study involving non-dimensional ratios of material properties, crack depths and coating thicknesses was performed. Appropriate test specimen geometries were selected and analyzed according to guidelines suggested in the literature. The results obtained in this study provide a powerful tool for both calibration of bimaterial test specimens, and studies pertaining to physical fracture processes, such as delamination and spallation of coating layers from substrates. Finally, a case involving a thermal spray of aluminum oxide coating (METCO 130) on a 0.25 in thick low carbon steel substrate was analyzed. Test data on the elastic modulus of the coating, which is the main material property factor in the energy release rate, were reported for a range of spraying distances (distance from the gun to the surface of the substrate). The results are discussed in terms of the best choice of spraying distance.