Mixed-mode fracture analysis of aluminium repaired panels using composite patches

Three-dimensional analyses are conducted to study the fatigue crack growth of panels containing mixed-mode cracks, reinforced with composite patches. A procedure is developed to obtain the crack trajectories using dynamic mesh generation for repaired panels in both mode-I and mixed-mode conditions. It is shown that the fatigue crack growth life obtained using mid-plane fracture parameters of the repaired panels in mode-I condition are almost compatible with the experimental results, however, they are non-conservative in some cases. The calculated fatigue crack growth life using un-patched surface fracture parameters are too conservative. It is shown that in both mode-I and mixed-mode crack loading conditions the J-integral values at mid-plane of the cracked plates are reduced with increasing the patch thickness; however, they depend on the patch thickness at un-patched surface at the crack-tip. The crack propagation path may be changed by the amount of about 10% due to the various fibers orientations of the patch. It is also shown that the patch thickness has not a considerable effect on the crack propagation path. Furthermore, there are considerable differences between the life obtained using un-patched surface and mid-plane fracture parameters for various patches thicknesses and layers angles of the repaired panels. The optimum patch layer angle considering maximum fatigue crack growth life of the repaired panels with an inclined crack angel of 45° is also obtained. Finally, a simple formulation is presented to justify the trend of finite element results obtained for single-sided repaired panels with various patch thicknesses.