Enhancing the Aggressive Strength of a Cavitating Jet and Its Practical Application

Abstract

A cavitating jet is a useful tool for the practical application of cavitation. Cavitation impact arises when bubbles collapse and can be utilized to modify the surfaces of materials as an alternative to shot peening. Peening methods using cavitation impact are called "cavitation peening" or "cavitation shotless peening", as shot is not required. In cavitation peening, cavitation is generated by injecting a high-speed water jet into water, i.e., a cavitating jet. In practical applications, it is very important to maximize the aggressive strength of the jet. In the present paper, in order to do this, the outlet geometry of the nozzle of a cavitating jet was optimized. High-speed observations were carried out to investigate any instability in the jet. The introduction of compressive residual stress into stainless steel was demonstrated to show the effect of cavitation peening. Scaling-and velocity-effects, i.e., the effect of the injection pressure, at the nozzle throat was also examined. It was shown that a large cavitating jet at low injection pressure was more aggressive than a small jet at high injection pressure, for the same power.

Optimum Injection Pressure of a Cavitating Jet for Introducing Compressive Residual Stress into Stainless Steel

“…The peening method is called "cavitation shotless peening", as shot are not required, or simply called "cavitation peening". The introduction of compressive residual stress into various steels using a cavitating jet has been reported (1)(2) (7)(8)(9)(10)(11)(12)(13)(14) . The improvement in the fatigue strength of metallic materials treated by a cavitating jet has also been reported (15)(16)(17)(18)(19)(20) .…”

Cavitation Peening: A Review

“…Then, a classification map for cavitation peening and water jet peening was proposed considering cavitation number σ and s opt , which was normalized by the nozzle throat diameter d, as shown in Figure 18 [95]. More than 150 points [17,[39][40][41]96,100,102,106,[121][122][123][124][125][126][127] are plotted in Figure 18, and the line described by Equation 7divides two regions, i.e., the first and second peak regions. The upper right hand region is cavitation peening and the lower left hand side region is the water jet peening region.…”

“…Schematic diagram of aggressive intensity of the cavitating jet using several types of nozzles.The other important parameter related to the nozzle is nozzle size, i.e., diameter of the nozzle throat. To demonstrate the peening effect of nozzle size,Figure 15shows residual stress as a function of the depth from the surface with changing nozzle diameter from 0.35 to 2 mm at p1 = 30 MPa and p2 = 0.1 MPa[100]. The tested material was stainless steel SUS316L.…”

“…Effect of nozzle diameter on introduction of compressive residual stress compared with non-peened (NP) (stainless steel)[100].…”

Fatigue Strength of Steel Rollers and Gears Treated by Cavitation Peening with Short Processing Time (A Case of Processing Time of 1 min and 5 min)

“…Our previous study revealed that the fatigue life of cavitation-peened steel rollers increased with increasing processing time of the CP within a processing time of 30 min. After that, CP condition has been optimized to obtain the larger surface hardness and larger surface compressive residual stress (6) . Shorter processing time of surface treatment method for machine elements is important to promote greater efficiency and productivity.…”