Study of fretting fatigue crack nucleation in 7075-T6 aluminum alloy

This paper addresses many issues related to fretting fatigue crack nucleation. It discusses the mechanism(s) as well as the life to fretting fatigue crack nucleation in aluminum alloy 7075-T6 in contact with the same material. Fretting causes different types of damage on the fretted surfaces of specimens. It will eventually lead to crack nucleation if loading conditions are appropriate. A hypothesis that explains this observation states that fretting damage grows under the influence of the stress field induced by fretting fatigue until the damage threshold is reached. At this point the stress concentration at the root of these damage areas causes cracks to nucleate. This hypothesis is supported by scanning electron micrographs of the fracture specimens and also by the results obtained from the interrupted fretting fatigue tests. Metallographic examination and the scanning electron microscopy analysis of some of the specimens also showed that subsurface crack nucleation is possible under certain conditions. This evidence and related discussions are included in this paper.