Numerical simulation of the deformation behavior of metallic materials under cavitation induced load in the incubation period

Abstract

Numerical simulations are performed to improve the understanding of the pit formation in metallic materials due to cavitation-induced impacts. Under the influence of cavitation, metallic materials show plastically deformed surface regions, called pits, which are created due to the high impact pressure induced by a cavitation bubble collapse. Both the observation of the collapse and the measurement of the wall-load development require complex experiments. In this study, isolated wall-near bubble collapses are calculated with the help of CFD-simulations to evaluate the radial pressure distribution regarding the temporal maximum of pressure, further referred to as “wall-load profile”. The resulting wall-load profiles show a different number of local maxima, depending on the dominant hydrodynamic mechanism, i.e. liquid jet- or shock wave impact. With regard to the corresponding standoff-distance L0/R0, different cases of possible wall-load profiles are classified. These wall-loads are implemented into a Finite-Element (FE) software to visualize the elastic and plastic material response for three different model materials. The resulting pit geometries and the corresponding plastic strain distributions vary in accordance to the applied wall-load profile, which is directly affected by the dominant hydrodynamic mechanism. In certain cases, the resulting pits in the material show plateau-like displacements with crescent-shaped plastic strain distributions, which are related to the collapse of a toroidal bubble fragment. In addition to this, cavitation pits are generated in a copper specimen by short-term cavitation experiments. Selected pits are exemplarily measured by atomic force microscopy and then qualitatively compared to the numerically calculated pit geometries.