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Cavitation impact induced by a cavitating jet can be utilized to improve fatigue strength in the same way as shot peening. The peening method using cavitation impact is known as "cavitation shotless peening", as shot are not required. For practical purposes, enhancement of the cavitation impact is required in order to get a better peening effect and to shorten the processing time. In the present paper, intensification of the cavitation impact was successfully realized by injecting a low-speed water jet around a cavitating jet in water, and an improvement in the fatigue strength of stainless steel was demonstrated by subjecting treated materials to a fatigue test. The fatigue strength of stainless steel was improved by about 28 % by cavitation shotless peening compared with a non-peened specimen. In order to clarify the mechanism for surface enhancement by cavitation shotless peening, the residual stress on the surface was measured using an X-ray diffraction method. It was shown that cavitation shotless peening using a cavitating jet with an associated low-speed water jet in water introduced compressive residual stress on the surface of the steel. Interestingly, it was also found that the full width at half maximum of the X-ray diffraction profile from the surface decreased, even though compressive residual stress of about 500 MPa had been introduced by the cavitation shotless peening.

Equibiaxial compressive residual stress is introduced into steel after peening in order to improve both its resistance to stress corrosion cracking and its fatigue strength. Thus, a nondestructive and relatively quick method to evaluate the equibiaxial compressive residual stress in a surface layer modified by peening is required in order to evaluate the peening intensity needed to enhance the integrity of structural components. The purpose of the work reported here is to establish an eddy current method to evaluate equibiaxial compressive stress which can be applied to the residual stress introduced into various non-ferromagnetic materials after peening. To this end, hydraulic jacks were used to elastically deform specimens of the austenitic stainless steel, Japanese Industrial Standard (JIS) SUS316L, thereby introducing an equibiaxial compressive stress. In the case of SUS316L steel, stress-induced martensitic transformation is rare. The electromagnetic properties of these specimens were then measured. In addition, the eddy current signals from peened specimens were compared with these. The results demonstrate that it is possible to establish a method for evaluating the equibiaxial stress utilizing eddy current signals.

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