Methodology of fatigue life assessment on components with porosity clusters

This paper focuses on the fatigue life estimation of metallic components containing a group of porosities as manufacturing defects. In order to represent these defects, six groups of fatigue tests with different Through Drilled Holes (TDH) clusters have been carried out on 7075-T6 aluminium alloy samples. Main characteristics of such defects (of every single hole, spatial density or gradient of elementary sizes) have been studied to determine their influences on the fatigue life. Experimental tensile fatigue tests have been performed on all TDH samples with load ratio R = 0.1. For the finite element simulations of the fatigue crack growth, a semi-elliptical initial crack with size similar to a typical particle of 7075-T6 aluminium alloy has been chosen. Indeed, such a particle is often responsible for crack initiation in this kind of material. For crack growth, the Paris' type propagation law and Forman's law have been used in the modelling. Local stress redistribution due to the presence of the TDH implies mix-mode behavior which has been examined by using the G-Theta method. Simulations results allow realistic lifetime estimations according to the experimental results. Moreover, a strong dependence of the crack paths and fatigue lifetime on the defect characteristics has been proved and quantified.