Fracture and determination of a lifetime of in-service mechanical components with porosity cluster in an aluminium alloy

Abstract

This paper focuses on the fatigue lifetime estimation of metallic components containing group of porosities as manufacturing defects. In order to represent these defects, six test specimens with different Side Drilled Holes (SDH) clusters, have been made of 7075-T6 aluminium alloy. Main characteristics of such defect (elementary size of porosities, spatial density or gradient of elementary sizes) have been studied by taking it into account in a FEM modelling in fatigue to determine their influence on the lifetime. Experimental tensile fatigue tests have been performed on all SDH samples with load ratio R=0.1. Semi-elliptical surfaces with a size of a typical Mg2Si particle of the studied alloy have been chosen as initial cracks for multiple crack propagation. Indeed, such a particle is often responsible for the initiation of a crack in this type of material. For crack growth, Paris’ type propagation law has been used. Local stress redistribution due to presence of the SDH implies mix-mode behaviour which has been considered by using G-theta method. Simulations results allowed realistic lifetime estimation according to the experimental ones. Moreover, a strong dependency of the crack paths and fatigue lifetime on the defect characteristics has been proved and quantified.