Metallographic analysis of fretting fatigue damage in Ti-6Al-4V MA and 7075-T6 aluminum

Fretting fatigue tests were conducted utilizing axial fatigue load application at various maximum fatigue stress levels and normal pressures. Materials investigated were titanium Ti-6A1-4V mill annealed (MA) and aluminum 7075-T6. Subsequent to testing, the specimens were sectioned and metallographically examined to investigate the relationship between fretting damage, fretting induced cracking and reduction of specimen fatigue life.At all maximum fatigue stress levels investigated a given amount of fretting damage was required before any fatigue life reduction occurred. Presumably, the damage leads to the development of cracks in the fretted areas. Metallographie studies of the fretted areas have revealed that multiple cracks form and are propagated by fatigue. Some evidence was found to indicate that fretting debris is forced into the microcracks as they develop, thus explaining, in part, the significant reduction in life caused by the fretting.