Influence of Shot Peening Process on Contact Fatigue Behavior of Gears

Shot peening is a cold working process used to increase mechanical strength of metal parts under fatigue load. It introduces compressive residual stresses and surface hardening in the surface layers of metallic materials by the impact of a shot flow against the metallic surface under controlled conditions. Shot peening can be made by using different kinds of machines, the most common of which are the pneumatic and the centrifugal ones. This article shows how the kind of process used can influence the results of the treatment. Four groups of gears were peened using different peening machines (pneumatic and centrifugal). The measurement of residual stresses and hardness allowed to evidence the different effect of the shot peening process. Contact fatigue tests showed that contact fatigue life is influenced by the process selected and that the choice of the Almen Intensity should consider also the kind of machine used.