Study on Residual Stress Relaxation Behaviour and Modelling of Shot-Peened TC4 Titanium Alloy

Residual stress induced by shot peening (SP) is inherently unstable. Stress relaxation has attracted widespread attention, and related research has been carried out. This study aims to study the residual stress relaxation phenomenon in a shot-peened TC4 titanium alloy due to cyclic load. Numerical simulations and experiments were performed to investigate the effects of the applied load amplitude, the number of cycles, the depth and the load ratios. The study may make contributions to the literature on understanding the residual stress relaxation induced by shot peening. The numerical and experimental results showed that the relaxation rate of the residual stress is correlated to the applied stress amplitude. Most of the relaxation of the residual stress was observed in the first cycle, which is up to 47.2% and 62.3% after 1000 cycles for the two different shot peening intensities. After the high relaxation at the first cycle, the residual stresses gradually decreased at a lower rate, remaining almost stable for up to 1000 cycles. The experimental residual stress in the specimens at a load of 550 MPa decreased more than that for a load of 450 Mpa; the decrease was more than 29.6% for the 550 MPa load with 1000 cycles, and the relaxation was stable after 10,000 cycles. Also, the relaxations in the surface and depth were studied. The maximum residual stress was more prone to relaxation. The presented model of residual stress relaxation, validated with experimental data, showed good agreement for the residual stress relaxation.