Effect of machined surface texture on fretting crack nucleation under radial loading in conformal contact

This paper presented the influence of machined surface texture on fretting cracks behaviors of Titanium alloy Ti–6Al–4V under radial loading in conformal contact. The contacted holes of specimen were machined with combined helical and flank milling before fretting fatigue tests, and a special fretting fatigue test apparatus was proposed to focus on conformal contact fretting fatigue (CCFF) test under radial loading. The test results showed that all the specimens failed at the contact area where characterizes an inner obtuse angle between the material flow direction (or cutting direction) and the direction of the tangential component of the contact force. The area with higher surface skewness and kurtosis values was also prone to nucleate fretting fatigue crack. These results suggested that the corresponding machining conditions in hole-making and surface strengthen processes should be adjusted to guide the production of surface texture properties, in terms of obtaining desirable lower skewness and kurtosis features to relieve nucleation of fretting cracks. Additionally, the debris in conformal contact tended to aggregate towards the partial slip zone (PSZ) due to the conformal geometry and form a compacted layer in the gross slip zone (GSZ) subjected to radial loading. These characteristics exacerbated and alleviated fretting damage in the PSZ and GSZ, respectively. In this research, a set of suitable milling parameters for the hole flank milling process in terms of prolonging fretting fatigue life were also defined.