Analysis of Residual Stresses Following Overloading of Cold Expanded Holes Using the X-ray Diffraction Technique and Finite Element Method

Abstract

Cold working of holes is an effective method used to enhance the fatigue life of aerospace structures. The method introduces a zone of compressive residual stresses around the hole, which attenuates fatigue crack growth rates by reducing the effective stress intensity factor range. Therefore, the method reduces the tendency for fatigue cracks to initiate and grow under cyclic loading. Aircraft components are subjected to a complicated sequence of variable fatigue loading during service. Residual stresses around cold expanded holes can be relaxed because of the plastic deformation produced by in-service loading. We have studied the changes of residual stress distribution around a 4% cold expanded hole in 2024-T351 aluminium alloy, when the plate was subjected to different values of compressive overloading. Results from an FE model and X-ray diffraction measurements are presented and compared.