Finite element analysis of cracks in aging aircraft structures with bonded composite-patch repairs

Bonded composite-patch repair has been used to transfer load from cracked structures to the reinforcement such that subsequent crack propagation is reduced. In this study, the mechanical behavior of a single edge v-notch Al7075-T6 plate repaired with 1-ply and 4-ply composite patches was investigated through the finite element method. Contour integral method was used to define and evaluate the stress intensity factors at the crack tip. The effect of the adhesive epoxy film, patch material, thickness and ply orientations on the evolution of the stress intensity factor (SIF) of the repaired structure was examined. The results indicated that the SIF of the notched plate is reduced by 1/6-1/20 as a result of the bonded composite-patch repair. The crack mouth opening displacement (CMOD) is reduced even further by 80-83%. Shear strength and thickness of the adhesive bond were the largest factors in the effectiveness of patch repair.