Sustainable surface modification using cavitation impact for enhancing fatigue strength demonstrated by a power circulating-type gear tester

In order to enable the manufacture of lightweight materials for transportation equipment, such as cars and aircraft, an improvement in the fatigue strength of materials is required, as these forms of transport are designed taking fatigue fracture into consideration. Surface treatment procedures, such as shot peening, are generally employed to improve fatigue strength. Shot peening deforms metallic materials to produce work hardening and introduce compressive residual stress, leading to improved fatigue strength. Although shot peening is an effective and reliable method against fatigue fracture, the shot eventually becomes dust and industrial waste. Recently, a peening method without the use of shot using cavitation impact has been developed. This is called 'cavitation peening'. In the present paper, gears, which are typical machine components, were examined in order to demonstrate the improvement in fatigue strength by cavitation peening. Gears made of carburised chromium molybdenum steel were treated by cavitation peening and shot peening. The fatigue strength was evaluated using a power circulating-type gear test machine. Under the conditions employed, the gear lifetime was limited by fracture at the root of the tooth. The improvement in the fatigue strength of gears treated by cavitation peening was 24% and in those treated by shot peening it was 12% compared with non-peened gears. It was demonstrated that cavitation peening can improve the fatigue strength of gears without the use of shot.