Effects of shot-peening on fretting-fatigue behavior of Ti-6Al-4V

The effects of shot-peening on the fretting fatigue behavior of titanium alloy, Ti-6Al-4V v ere investigated. Specimens were shot-peened as per AMS 2432 standard. X-ray diffraction analysis measured a maximum compressive stress of 800 MPa at the spect. men surface, which reduced to zero at a depth of 188 mum. The compensatory residual tensile stress in the specimen was estimated using a curve fitting technique, the maximum value of which was found to be 260 MPa at a depth of 255 mum. Fretting fatigue tests were conducted at room temperature at a cyclic frequency of 200 Hz. Scanning electron microscopy of the shot-peened fretting fatigue specimens showed that the crack initiated at a point below the contact surface, the depth of which was in the range of 200-300 mum. Finite element analysis of the fretting fatigue specimens was also conducted. Fatigue life diagrams were established for the fretting fatigue specimens with and without shot-peening, and were compared to those under the plain fatigue condition, i.e. without fretting. Shot-peening improved the fretting fatigue life of Ti-6Al-4V; furthermore, it moved the crack initiation site from the fretting contact region to a region inside the specimen. Moreover, stress analysis showed that the fatigue failure of shot-peened specimens was caused by the compensatory tensile residual stress.