Abstract
Repair of aeronautical structures by composite patch bonding has shown its effectiveness in several studies during the last few decades. This repair technique leads to a retardation in the propagation of repaired cracks via load bridging across the patch throughout the adhesive layer, interfacing it with the repaired structure. The purpose of this study is to analyze the behavior of patch-repaired cracks present in thin plates made of aluminum alloy 7075-T6 and subjected to a single tensile overload. The sequence of application of overload on the fatigue behavior was also studied. Fatigue tests were conducted on Al 7075-T6 notched specimens where crack growth and number of cycles to failure were monitored for different patching/overload scenarios. A detailed fractographic study was performed on failed specimens to analyze the micromechanical behavior of the crack growth related to each scenario. The obtained results showed that the application of the overload before bonding the patch leads to an almost infinite fatigue life of the repaired plates.
Highlights
Operational aeronautical structures are, most often, subjected to fatigue loadings with variable amplitude
Especially plane stress, higher plasticity around the crack front leads to a blunting of the crack tip, reported by several authors who studied overloaded specimens made of aeronautical aluminum alloys, such as 2024-T3 or 7075-T6 [8,9,10]
Bichler and Rippan [11] showed that the crack blunting increases the effective stress intensity factor (SIF), which causes an initial acceleration in the crack propagation, but the closure level increases rapidly as the crack grows because of the wedging action of the overload
Summary
Operational aeronautical structures are, most often, subjected to fatigue loadings with variable amplitude. This transfer makes it possible to reduce the stresses intensity around the crack front leading to the reduction of the crack propagation rate and the improvement of the fatigue life of the damaged structure [12,13,14,15,16] It has been shown in the literature that the effectiveness of composite patch repairs depends on a large number of parameters that can be classified as follows: (i) mechanical properties of repaired material, composite material, and adhesive type [17,18,19]; (ii) geometrical properties of the composite [20,21,22] (iii); and nature of the fatigue loading [23,24,25]. The aim of the study is to explain by the fractographic approach the interaction between the retardation effects due to the overload and the presence of a composite patch
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