Effects of curing thermal residual stresses on fatigue crack propagation of aluminum plates repaired by FML patches

One of the main disadvantages of using composite patches in repair of metallic panels is development of thermal residual stresses due to the curing cycles of the bonded repairs. Fiber Metal Laminates (FMLs) have the overall larger thermal expansion coefficients when compared with the fully composite patches. In this study, the thermal residual stresses that occur due to the thermal expansion coefficient mismatch between the FML patch and underlying cracked aluminum panel are investigated using both numerical and experimental studies. The fatigue crack growth behaviors of centrally cracked aluminum panels in mode-І condition with single-side repairs of FML patches that are made by alternating layers of aluminum and glass fiber-epoxy are carried out. Sensitivity of the curing temperature on fatigue crack-growth life extension and crack-front shape of the repaired panels is also investigated. It is shown that implementing of various curing temperatures do not significantly affect the thermal residual stresses, crack-growth lives and crack-front shapes of the repaired panels by FML patches.