Mixed-mode crack propagation of stiffened curved panels repaired by composite patch under combined tension and shear cyclic loading

In this study, finite element method is used to investigate the fracture analyses, crack growth trajectory and fatigue life of curved stiffened panels repaired with composite patches subjected to combined tension and shear cyclic loadings. For this purpose, finite element modeling is performed for consideration of real 3-D crack-front in general mixed-mode conditions. Contact elements are used between the crack surfaces on two crack sides to prevent interferences of crack surfaces and a complementary program was developed to handle the automatic fatigue crack growth modeling. The effects of various patch layups and shear–tension loading ratios on fracture parameters of repaired aluminum panels are investigated. It is shown that as the shear to tension ratio increases, the patch layups with orientations of almost perpendicular to the crack trajectory become more efficient in term of fatigue crack growth life when compared with the patch layups parallel to the tension orientation like [90]4[90]4. It will be shown that as the effect of shear loading is decreased around the crack-front due to the increasing of stiffener spacing ratio the values of KIIKII are decreased and consequently shear loading effects on tilting the crack trajectories are decreased.