Use of cavitating jet for introducing compressive residual stress

In an attempt to strengthen the surface of materials, the potential of usin g: a cavitating jet to form compressive residual stress has been investigat ed. Introducing compressive residual stress to a material surface provides improvement of the fatigue strength and resistance to stress corrosion crac king. in general. cavitation causes damage to hydraulic machinery. However, cavitation impact can be used reform compressive residual stress in the sa me way as shot peening, In the initial stage, when cavitation erosion progr esses, only plastic deformation, without mass lass, takes place on the mate rial surface, Thus, it is possible to form compressive residual stress with out any damage by considering the intensity and exposure time of the cavita tion attack. Cavitation is also induced by ultrasonic, I;igh-speed water tu nnel and high-speed submerged water jet, i.e., a cavitating jet. The great advantage of a cavitating jet is that the jet causes the cavitation whereve r the cavitation impact is required To obtain the optimum condition for the formation of compressive residual stress bl using a cavitating jet, the re sidual stresses on stainless steel (JIS SUS304 and SUS316) and also copper (JIS C1100) have been examined by changing the exposure time of the cavitat ing jet. The in-plane normal stresses were measured in three different dire ctions on the surface plane using the X-my diffraction method, allowing for the principal stresses to be calculated. Both of the principal stresses ar e found changing from tension to compression within a 10 s exposure to the cavitating jet. The compressive residual stress as a result of the cavitati ng jet was found to be saturated after a certain time, but it starts decrea sing, and finally, it approaches zero asymptotically. It could be verified in the present study that it,was possible to form compressive residual stre ss by using a cavitating jet, and the optimum processing rime could also be realized The great difference between the water jet in water and air has a lso been shown in this regard [S1087-1357(00)00501-3].