FAILURE INSTABILITY OF A DEBONDED INTERFACE IN THE PRESENCE OF A MAINCRACK

The problem of fracture initiating from an edge crack in a nonhomogene ous beam made of two dissimilar linear elastic materials that are part ially bonded along a common interface is studied by the strain energy density theory. The beam is subjected to three-point bending and the u nbonded part of the interface is symmetrically located with regard to the applied loading. The applied load acts on the stiffer material, wh ile the edge crack lies in the softer material. Fracture initiation fr om the tip of the edge crack and global instability of the composite b eam are studied by considering both the local and global stationary va lues of the strain energy density function, dW/dV. A length parameter I defined by the relative distance between the maximum of the local an d global minima of dW/dV is determined for evaluating the stability of failure initiation by fracture. Predictions on critical loads for fra cture initiation from the tip of the edge crack, crack trajectories an d fracture instability are made. In the analysis the load, the length of the edge crack and the length and position of the interfacial crack remained unchanged. The influence of the ratio of the moduli of elast icity of the two materials, the position of the edge crack and the wid th of the stiffer material on the local and global instability of the beam was examined. A general trend is that the critical load for crack initiation and fracture instability is enhanced as the width and the modulus of elasticity of the stiffer material increase. Thus, the stif fer material acts as a barrier in load transfer.