Effect of bead quantity in ultrasonic shot peening: Surface analysis and numerical simulations

Ultrasonic shot peening is a cold surface treatment used to extend the fatigue life of metallic components. This process is performed in a closed chamber where spherical beads are moved by sonotrode vibration. Thousands of impacts on treated material induce compressive residual stresses, which are responsible for the lifetime improvement by holding back micro-crack propagation. The present study shows the effect of the number of beads used in the process on the treated surface. Two INCONEL 690 samples were peened with different bead quantities during a short time to obtain coverage lower than 100%. The surface analysis of the peened sample showed that the number of beads strongly affected the number of impacts and their depth distribution. Then, numerical analysis combining bead dynamic simulations by discrete elements with single impact simulations by finite elements was performed. The numerical results were in good agreement with the experimental data, which validates the present method. Thus, the effects of bead quantities on compressive residual stress were quantified. As a key result, the study showed that in the present peening configuration, an increasing number of beads concentrated the compressive residual stress onto the treated surface.