Mechanism of Destruction of Solid Surface Films by Acoustically Induced Cavitation

Abstract

The cavitational destruction of a thin layer of varnish put on a glass plate was studied by means of high speed photography at the rate of 2000 frames per second. Experiments were carried on in an inactive liquid (water) at the frequency 8000 cps. It was found that the destruction of the film is caused at least by two different factors. Primarily, it is observed as the result of big cavitation bubble collapes in the immediate vicinity of the surface. The obseravation of such bubbles indicates large amplitudes and complex forms of vibration. It is important to note that the process itself of bubble formation and its oscillations at the very surface of the film are without influence on the film; but the bubble collapse leads in the first 1/2000 sec to destruction of the film extending on a circle with the center coinciding with the position of the bubble at the moment of collapse. Another type of destruction is caused by small bubbles with smooth surfaces which quickly penetrate between the film and the glass at a destroyed spot, causing small irregular bits of film to detach from the surface.