Cavitation erosion as a kind of dynamic damage

摘要

The purpose of this work is to show that the spherical shock waves arising in a liquid during cavitation bubble collapse can lead to formation of deep needle-like pits on the solid surface. The nature of dynamic damage during cavitation erosiqn is the spallation caused by interference of rarefaction waves. Rarefaction at spherical wave impact arises when the velocity of contact surface boundary becomes less than the speed of sound in a target. If the tension caused by the focused rarefaction wave exceeds the spall strength of material, channel spall cracks can arise. At low pulsed loading, spall cracks are formed in a dynamic fatigue mode. Needle-like damage arises upon focusing rarefaction waves. In terms of our model, a system of cylindrical spall cracks is consecutively formed around a deeper axial spall needle-like crack. Upon subsequent loading, each crack acts as a source of new rarefaction wave. Newly formed cylindrical spall cracks suppress the growth of the cracks of previous generation and give birth to the cracks of next generation. A distinctive fea?ture is that the cracks are first formed at the periphery of damageability zone, subsequent cracks having a lower depth.