On the fatigue response of aluminium specimens reinforced with carbon–epoxy patches

Fatigue tests were carried out on various types of aluminium specimens to characterize the beneficial effect of composite patches on undamaged and damaged aluminium substrates. The influence of both the machining process and the specimen geometry on the fatigue properties is first discussed. Undamaged and damaged specimens are patched and their fatigue strength is compared to their expected counterpart obtained with the S–N curve of plain aluminium. It is shown that the shear strength of the adhesive strongly influences the fatigue response of the patched specimens, especially for the highest loading levels. The shear strength of the adhesive is obtained by coupling some quasi-static tests and a suitable numerical model. When the maximum shear stress in adhesive is nearly equal to the shear strength, early failure of the specimens subjected to fatigue loading is observed. This clearly underlines the influence of this latter parameter on the fatigue response of patched structures.