ANS:B - Shot peening

The process used for setting up compressive stresses in the surface of a metal to improve its fatigue strength is shot peening. Shot peening is a surface treatment process where small spherical media, typically steel shot or glass beads, are propelled against the surface of a metal component using compressed air or centrifugal force. As these media particles impact the surface, they create numerous small indentations or dimples. These indentations induce compressive residual stresses in the surface layer of the metal, which counteract the tensile stresses experienced during cyclic loading, such as in fatigue conditions. By introducing compressive residual stresses, shot peening helps to inhibit crack initiation and propagation, thereby improving the fatigue strength and fatigue life of the metal component. This process is widely used in industries such as aerospace, automotive, and manufacturing to enhance the durability and performance of critical components subjected to cyclic loading.