Comparison between cavitation peening and shot peening for extending the fatigue life of a duralumin plate with a hole

In order to demonstrate the advantages of cavitation peening, in which the impact due to cavitation bubbles collapsing is used to mechanically treat a surface, compared with shot peening, the fatigue lives of peened specimens comprising duralumin plates with open holes were evaluated. In the present experiment, cavitation bubbles were generated by injecting a high speed water jet into a water filled chamber, producing what is known as a cavitating jet. The specimens, which had either a chamfered or rounded edge hole, were treated by cavitation peening and shot peening, then tested using a tensile fatigue test. The fatigue life of the shot peened specimen was equal to or less than that of the as machined specimen, whereas cavitation peening extended the fatigue life. When the cavitating jet was injected in such a way that the cavitation bubbles collapsed at the wall surrounding the hole, the fatigue life at a maximum tensile stress, σ_max, of 150 MPa was extended by more than a factor of ten. It was also demonstrated that cavitation peening introduced compressive residual stress of about 300 MPa into the wall surrounding the hole.