Cavitation impacts induced by a submerged water jet with cavitation, i. e. a cavitatiog jet, can introduce the compressive residual stress into metals as same way as shot peening. In case of peening by using cavitation impacts, shots are not required, then it is called cavitation shotless peening CSP. The blade/disk dovetail joint in turbine engine commonly fails due to fretting fatigue. The introduction of the compressive residual stress is the most significant factor in improvement of fretting fatigue behavior of metals. In order to investigate the possibility of CSP on reduction of fretting fatigue of titanium alloy, Ti6Al4V, the residual stress of the titanium alloy peened by CSP was measured by using an X-ray diffraction method. It was concluded that CSP can introduce the compressive residual stress into the titanium alloy. The compressive residual stress at the surface peened by CSP is larger than that of shot peening and the roughness of CSP is smoother than that of shot peening.
Cavitation Shotless Peening (CSP) is a new method of surface modification. Cavitation impacts induced by the collapse of cavitation bubbles produce compressive residual stress and work hardens the material surface. In the case of CSP, shots are not required and therefore we call it Cavitation Shotless Peening. In CSP, cavitation is induced by a submerged high-speed water jet, i. e., a cavitating jet, for which the intensity and region of cavitation impact can be controlled by parameters such as the upstream pressure and nozzle size. The authors have already shown that the lifetime of forging die treated by CSP can be extended by about 50% compared with non-peened forging die. In this paper, in order to make clear the mechanism by which the lifetime of forging die is increased, an alloy tool steel (JIS SKD61) was tested both in peened and non-peened conditions. Compressive residual stress was measured by an X-ray diffraction method. It was evident from a comparison between the non-peened specimen and the cavitation shotless peened specimen that CSP improved the mechanical properties of the forging die thus giving it a longer lifetime.
Cavitation Shotless Peening (CSP) is a new method of surface modification. Cavitation impacts induced by collapses of cavitation bubbles produce compressive residual stress and work hardening on the material surface. In the case of CSP, shots were not required and that is why we call it Cavitation Shotless Peening. At CSP, cavitation was induced by high-speed submerged water jet with cavitation, i.e., a cavitating jet, whose intensity and occurring region of cavitation impacts could be controlled by parameters such as upstream pressure and nozzle size. The authors have already revealed that lifetime of forging die treated by CSP was extended by about 50% compared with the non-peened forging die. In this paper, in order to make clear the mechanism of increase of lifetime of forging die, alloy tool steel (JIS SKD61) was tested both in non-peened and peened conditions. Compressive residual stress was measured by an X-ray diffraction method. Comparison between the non-peened specimen and cavitation shotless peened specimen revealed that improved mechanical properties leading to longer life-time of the forging die were favourable in CSP.
This paper gives an overview of the art, craft and science of "Cavitation Shotless Peening" 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 Cavitation Shottless 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 sturdy, cavitation impacts were produced by a submerged high speed water jet with cavitation, i.e., a cavitating jet. The cavitating jet differs completely from a normal water jet 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 (JISSUP7) and an aluminum alloy (JIS AC4CH) specimens were peened by a cavitating jet. The residual stress was measured by an X-ray diffraction method. Experimental 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.
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