Cavitation Shotless Peening for Improvement of Fatigue Strength

Abstract

1 Abstract This paper gives an overview of the art, crafl and science of Shotless as a new method of turning the traditional negative effects of cavitation in hydrodynamic machinery to more positive industrial applications. Impact at cavitation bubble collapse can be used to improve the fatigue strength just as the same way as shot peening. Cavitation impacts can peen the surface without the use of shot. Hence, it is a kind of shotless peening, and herein termed as Cavitation Shotless Peening (CSP). The peened surface by CSP is less rough compared with shot peening, since there is no solid body collision involved. In the present study, cavitation impacts were produced by a submerged high speed water jet with cavitation, ie., a cavitating jet. The cavitating jet differs completely fiom a normal waterjet in air. To explore the potentials of CSP as a means of inducing surface compressive residual stress and subsequently increasing fatigue strength of materials, silicon-manganese alloy (XS SUP7) and an aluminum alloy (JIS AC4CI-I) specimens were peened by a cavitating jet. The residual stress was measured by an X-ray diffraction method. Experimenkd results confirmed that the rotating beam (R = -1) fatigue strength of silicon-manganese alloy increased by 41% while that of aluminum alloy increased by 56% in comparison with non-peened specimens.