The effect of rapidly varying contact stress fields on fretting fatigue

An experimental and analytical study of the effect of varying contact stress fields on the initiation life of fretted specimens is conducted for two high strength alloys commonly used in the aerospace industry, namely Al4%Cu and Ti-6Al-4V. The experiments reveal there is a contact size effect in fretting fatigue life. Two critical plane models are used to predict the observed experimental lives. The results show that these models may provide over-conservative life estimates for fretting tests subjected to more rapidly varying contact stress fields. The existence of a critical stressed layer, or volume, is used to explain these results qualitatively, and averaging methods are then developed to allow the extension of the critical plane approach to cases of rapidly varying contact stress fields. It is shown that a critical averaging dimension of the order of the grain size of the material appears to give realistic estimates of fatigue life and predicts the observed size effect reported in the experimental work.