Inducing very high cycle fretting-fatigue in the ultrasonic regime

• Very high cycle fretting–fatigue was induced at ultrasonic frequency.
• Conventional fatigue strength of the steel in study decreased until 109 cycles.
• Fatigue strength was divided by 1.5 when submitted to fretting at 106–109 cycles.
• Fretting brought crack initiation site to surface, rare in very high cycle fatigue.
• A linear pattern between diameter of worn surfaces and stress amplitude was observed.

Early crack initiation due to fretting may have an important role in fatigue strength of steel components, mainly in the very high-cycle regime, i.e., beyond a million cycles.This work aimed to induce very high-cycle fretting–fatigue on a medium strength steel alloy in the ultrasonic regime. Specimens were subjected to push–pull fatigue and 10 μm-amplitude fretting with crossed cylinders configuration. The normal load was held constant at 30 N.Results showed a knockdown factor of 1.5 for the fatigue strength in the fretting condition under study. The average diameter of the fretted surfaces was found to linearly increase with decreasing axial bulk stress amplitude.