Characterisation of equivalent initial flaw sizes in 7050 aluminium alloy

This paper summarises a collation of crack growth related data from a significant number of fatigue tests on commercial quality 7050-series aluminium alloy tested under various F/A-18 aircraft spectra. The data presented consist of quantitative fractography measurements of the fracture surfaces including effective initiating defect size and type (mechanical, environmental or chemical). Three different surface conditions were considered: chemically etched, glass bead peened and machined. The purpose of providing these data was to facilitate analyses on the parameters governing the propagation of fatigue cracks in the 7050-series aluminium alloy. Here an investigation to determine whether surface finish or applied stress and spectra have any bearing on the initial defect size or the damage type is summarised. Based on this investigation, it appears that the applied stress and spectra have no correlation to the size of the equivalent initiating flaw; however, the surface finish appears to influence the various crack-initiating mechanisms and to govern the formation of the damage type.