Nondestructive Characterization of Fretting Fatigue Damage

Fretting fatigue has been the cause of many premature failures in aerospace components. There is a growing need of nondestructive evaluation techniques to characterize damage and detect cracks due to fretting fatigue. This paper presents a methodology to characterize the fretting fatigue damage by analyzing the surface topography and to detect cracks under fretting fatigued surface by imaging heat generation due to high amplitude acoustic excitation. The White Light Interference Microscopy (WLIM) was used to obtain three-dimensional surface profilometry data of fretted and non-fretted regions of titanium alloy (Ti-6A1-4V) specimens subjected to different number of fretting fatigue cycles. Surface topography measurements were analyzed in terms of the Power Spectral Density (PSD) and Fretting Fatigue Damage Parameter (FFDP). The FFDP showed an increasing trend in magnitude with increasing numbers of fretting fatigue cycles, when the fretting fatigue damage occurred through stick-slip condition. When the fretting fatigue damage occurred due to gross sliding, the FFDP did not show enough change. Thus, it appears that FFDP may be used as an indicator of the degradation of fretted surface under stick-slip condition. Cracks in presence of fretting fatigue damage were imaged using Sonic infrared technique. This technique appears to have a capability to detect cracks with a resolution of at least 200 μm. The benefits and limitations of thes two NDE techniques for fretting fatigue damage evaluation and crack detection are discussed.