Experimental and numerical investigation of damage on an aluminum surface by single-bubble cavitation

For a better understanding and modeling of cavitation, investigations of isolated single-bubble events are useful. They allow for describing and quantifying the physics of the bubble collapse and its interaction with surrounding material. The generation of such single bubbles in a liquid using an electric spark or focused laser beam is well described in the literature, and sophisticated analyses of bubble dynamics near surfaces exist. However, only a few studies addressed the material damage induced by single-bubble collapse. This article presents experiments in water, generating single bubbles with 3-mm diameters at various defined distances to the polished surface of a commercially pure aluminum specimen. The collapse of each laser-induced bubble was captured by high-speed imaging. A detailed quantitative analysis of the surface damage was performed using 3-D profilometry. A single bubble created a shallow pit with a typical depth of 1 to 2 μm. The overall statistics of the damage parameters, such as pit depth and volume, are consistent with previous investigations. Outliers with unusually small or multiple pits can be explained by the high-speed images of the corresponding bubble collapse. The image sequences also help identify effects of the edge of the specimen surface. In addition, a complementary numerical investigation of single bubbles based on the Navier-Stokes equations was used to obtain flow characteristics near the surface, such as microjet impact and pressure. For the commercially pure aluminum used in this study, simulation and measured surface damage correlate well. The methods developed here provide a basis for studies on more complex engineering materials.