Q1: Mechanism/phenomenon involved in the improvement of fatigue strength of a material by shot peening is the

ANS:A - induction of residual compressive stress on the surface.

The mechanism/phenomenon involved in the improvement of fatigue strength of a material by shot peening is: Induction of residual compressive stress on the surface. Shot peening is a surface treatment process used to improve the fatigue strength and durability of materials, particularly metals. During shot peening, small spherical particles (shots) are propelled at high velocity onto the surface of the material. Upon impact, these shots create localized plastic deformation, resulting in the formation of residual compressive stresses on the surface. The induced compressive stresses help to counteract the tensile stresses that develop during cyclic loading, such as those experienced during fatigue loading conditions. By introducing compressive stresses, shot peening inhibits the initiation and propagation of cracks, thereby increasing the fatigue strength and fatigue life of the material. While shot peening may also result in some level of stress concentration removal and grain refinement, the primary mechanism responsible for the improvement in fatigue strength is the induction of residual compressive stress on the surface of the material.