Fretting fatigue behavior of Ti–6Al–4V with dissimilar mating materials

Abstract

The effects of dissimilar mating materials on fretting fatigue behavior of titanium alloy, Ti–6Al–4V were investigated. Fretting fatigue configuration involved cylindrical pads on the flat specimen. Specimens were made of Ti–6Al–4V and cylindrical pads were made of Ti–6Al–4V, aluminum alloy 2024 and Inconel 718 alloy. All fretting fatigue tests were conducted at 200 Hz with the maximum axial stress ranging from 400 to 700 MPa, and stress ratio, R ranging from nominal value of 0.0–0.7. Applied normal loads for each material of pads were set to provide a constant Hertzian peak pressure of 292 MPa. Finite element analysis of fretting fatigue specimens was also conducted. Results showed that there was no significant effect of different pad materials on fretting fatigue life of Ti–6Al–4V at the same applied effective stress. W- or V-shaped surface profiles of the fretting scar were observed with three pad materials, but the specimen tested with aluminum 2024 pad material showed the narrowest scar due to the lowest hardness of aluminum 2024 pad material and the smallest slip region, which was verified from finite element analysis. Microscopic analysis showed that cracks originated at the contact surface and crack orientations were approximately ±45° from a perpendicular to the loading direction. Four critical plane based parameters: Findley, Smith–Watson–Topper, shear stress range (SSR), and modified shear stress range (MSSR) parameters, were evaluated in terms of ability to correlate/predict number of cycles for crack initiation (nucleation and growth to a certain size), crack location and crack angle. All parameters were effective to correlate with number of cycles to crack initiation regardless of pad materials, but only SSR and MSSR parameters could predict both location and orientation of the crack correctly.