Fretting fatigue behaviour of shot-peened Ti-6Al-4V at room and elevated temperatures

Fretting fatigue behaviour of shot-peered titanium alloy, Ti-6A1-4V was investigated at room and elevated temperatures. Constant amplitude fretting fatigue tests were conducted over a wide range of maximum stresses, sigma(max) = 333 to 666 MPa with a stress ratio of R = 0.1. Two infrared heaters, placed at the front and back of specimen, were used to heat and maintain temperature of the gage section of specimen at 260degreesC. Residual stress measurements by x-ray diffraction method before and after fretting test showed that residual compressive stress was relaxed during fretting fatigue. elevated temperature induced more residual stress relaxation, which, in turn, decreased fretting fatigue life significantly at 260degreesC. Finite element analysis (MA) showed that the longitudinal tensile stress, or,, varied with the depth inside the specimen from contact surface during fretting fatigue and the largest orgy could exist away from the contact surface in a certain situation. A critical plane based fatigue crack initiation model, modified shear stress range parameter (MSSR), was computed from MA results to characterize fretting fatigue crack initiation behaviour. It showed that stress relaxation during test affected fretting fatigue life and location of crack initiation significantly. MSSR parameter also predicted crack initiation location, which matched with experimental observations and the number of cycles for crack initiation, which showed the appropriate trend with the experimental observations at both temperatures.