Stress relaxation behavior of shot-peened Ti–6Al–4V under fretting fatigue at elevated temperature

Relaxation behavior of residual stress in a shot-peened titanium alloy, Ti–6Al–4V subjected to fretting fatigue was investigated at room and elevated temperatures. Constant amplitude fretting fatigue tests were conducted at several maximum stress levels, σmax ranging from 333 to 666 MPa with a stress ratio of 0.1. Two heaters, placed at the front and back of specimen, were used to heat and maintain the temperature in the gage section of specimen at 100 and 260 °C. Residual stress was measured using the X-ray diffraction method. There was relaxation of residual compressive stress during fretting fatigue at room and elevated temperatures, which in turn manifested in the reduction of fretting fatigue life. Greater stress relaxation occurred when higher temperature, stress range and contact load were applied, however, contact load had a considerably smaller effect. Stress relaxations due to elevated temperature and mechanical load (i.e. fretting fatigue) were found to be independent processes within the test conditions of this study, such that they can be linearly superimposed to predict the total stress relaxation from fretting fatigue at elevated temperature.