Mixed mode fracture in an inclined center crack repaired by composite patching

The use of bonded composite patches is among favorite reinforcement methods for repairing cracked structures. Although extensive research studies deal with the safety evaluation and life prediction of repaired components, most of these investigations are concentrated on pure mode I loading (or opening mode of crack deformation). Meanwhile in many engineering structures, cracked components are subjected to mixed mode I/II. In this paper the effects of composite patching are investigated on fracture behavior of an inclined center crack, under different combination of modes I and mode II loading conditions. A three-dimensional finite element model of the single-sided repaired specimen is used to study the effect of composite patching on the crack tip parameters (KI, KII and T-stress). Then the fracture initiation angle and the fracture strength of repaired crack are predicted by using the generalized maximum tangential stress criterion. The effects of composite laminate configuration and adhesive properties on the performance of bonded composite patch are also investigated herein. It is shown that parameters like mode mixing, patch thickness and properties of film adhesive can influence significantly the crack tip parameters and hence the fracture strength of the repaired specimens under mixed mode loading conditions.