Experimental and numerical analysis of fatigue properties improvement of a Titanium alloy by shot peening

Shot peening (SP) is a mechanical surface treatment commonly performed to improve the fatigue behavior through creation of compressive residual stresses close to surface and work hardening of the same layer of material. Notwithstanding wide application of shot peening in the industrial environment, the determination of optimal peening condition for Ti alloys is still more an art than a science, taking into account that there is not a well established method to choose the process parameters in order to enhance the fatigue behavior. In this paper a comprehensive numerical and experimental study is presented aimed at finding the optimized peening conditions based on characterization of surface layer of material after multiple impacts. The numerical simulations provide a quantitative description of shot peening effects in terms of residual stress field and thickness of work-hardened surface layer. Comparison with numerical results, obtained by means of X-ray diffraction (XRD) shows a very good correspondence. Finally the results of experimental bending fatigue tests, performed on shot peened specimens by means of Rumul Cracktronics machine, confirm that shot peening significantly increases the fatigue strength of the considered Titanium alloy