Residual stress modelling and analysis of a 7075-T6 hourglass specimen after foreign object damage

Foreign Object Damage (FOD) is a major cause of fatigue failure in aircraft engine components. The impact of objects is responsible for the introduction of defects and residual stresses which influence the fatigue life. 7075-T6 aluminum alloy is commonly used for manufacturing of aerospace components due to its high strength-to-density ratio. In this paper the effect of FOD on the integrity of 7075-T6 alloy was investigated experimentally and by Finite Element (FE) analysis. In the experiment a steel ball was fired at a 7075-T6 hourglass specimen at its middle cross section by using a compressed-air gun device, which caused plastic deformation in the shape of a crater. After the impact, the specimen was subjected to rotating bending fatigue test until it failed. In order to simulate the ball impact on the hourglass specimen, a FE analysis in Abaqus Explicit was conducted, by means of which the plastic deformation and residual stress state were assessed. The maximum tensile residual stress in the middle cross section appeared at the locations where the crack initiation was observed in the experiment.