Fatigue life of an aerospace aluminium alloy subjected to cold expansion and a cyclic temperature regime

This paper describes experimental work that was carried out to study the influence of cyclic temperature variation on the fatigue life of fastener holes in an aerospace aluminium alloy after they had been subjected to cold expansion. Three different batches of specimen were produced for fatigue testing. The first samples had the fastener hole left in the ‘as drilled’ state, the second and third batches had their drilled holes cold expanded by directly force fitting an oversized pin through the hole. In addition, the third batch with cold expanded holes was then subjected to a representative range flight cycle temperature variations. The results reveal that the cyclic temperature variation, rather than relaxing the residual stress and thus the cold expansion effect, as was feared, has actually extended the fatigue life of the cold expanded holed specimens tested. It is believed that this is because the temperature changes have tended to neutralise the local peak residual stresses which can occur at the surface faces.