Abstract
Three-dimensional and nonlinear finite element method is used to estimate the performance of the bonded composite repair of metallic cracked aircraft structures by analyzing the J integral and the plastic zone size around the crack tips for single and double symmetric patches. Several calculations have been realized to extract the plasticized elements around the crack tip. The obtained results show that, the double symmetric patch has a considerable beneficial effect on the repair performance compared to the single patch. A correction factor was introduced to the calculated values of the SIF for single patch in order to compensate for the effect of the plastic zone in the un-patched face of the repaired structure.