Fretting Fatigue in Aircraft Components Made of Ti-Al-V Alloys

This paper presents typical examples of premature fatigue failures originating from fretting damage in aircraft components manufactured from (α+β) titanium alloys, namely, Ti-6Al-4 V and Ti-2.5Al-2 V. The signatures of fretting damage in the Ti-alloy components with different contacting materials, namely, pure-Ti and a high strength Cr-Mosteel, and the manifestation of the fretting damage in fatigue crack initiation have been discussed. Two examples, one on failure of bolt of main rotor blade fork of a helicopter, and the other on failure of a hydraulic pipeline of an aircraft, have been presented. In the first case, an incident of premature fatigue failure occurred in the blade fork bolt during service, involving fatigue cracking at the flange region of the collar close to the bolt-head. The fretting damage at the flange of the collar was associated with pitting, spalling and sub-surface crack generation at the flange-bush interface. In the case of hydraulic pipeline failure, fretting damage was observed between two titanium alloy tubes in contact. Study showed that the reason for setting-in fretting damage at the joint was due to inadequate closeness of the fit that was formed by swaging.