A Study of Interaction and Coalescence of Micro Surface Fatigue Cracks in Aluminium 7050

Abstract

Multi-site cracks may occur in structural components in shallow notches, in corroded areas, or as a result of multiple notches such as in fuselage lap joints, and they are inherently a stochastic phenomenon. The interaction and coalescence of multiple cracks pose a challenge to the accurate prediction of fatigue crack growth rates and the residual strength of these components. It is, therefore, important to quantify the interaction and coalescence of multiple surface cracks. In this paper we study the interaction and coalescence of multiple surface cracks in 7050-T7451 aluminium plates. Experiments have been carried out under constant amplitude and spectrum loading, using coupons containing artificial micro-cracks with a surface length of ~50 μm. Within the framework of linear elastic fracture mechanics, three-dimensional finite element analyses were conducted to determine the interaction between cracks. The interaction factors were subsequently used for crack growth analysis of coplanar cracks. It was found that the numerical results correlated well with the experimental data for both constant amplitude and spectrum loading. It is envisaged that the outcome of this study will form a part of a stochastic model, leading to improved fatigue life assessment in the short crack regime for the material considered.