Physics and mechanism of ultrasonic impact

More and more experts and researchers in industry express their interest in the application of deformation effects of various peening techniques on the metal surface. This is primarily due to a relatively simple directional change in condition at the surface and in sub-surface layers of the material as a result of plastic deformation due to impulses of force caused, among other things, by converting ultrasonic oscillations of various impacting elements (indenters) at the treated surface. These effects are of a stochastic nature and their duration (or the time of impact) is generally measured in units of microseconds. To obtain relatively uniform coverage, an operator may use several treatment passes. However, a stochastic nature of single impacts makes it difficult to obtain a uniform distribution of deformations and hence surface characteristics as specified, in particular, by the engineering standards. We have developed the methods and means of implementing the ultrasonic impact and controlling its parameters. A fundamental distinction of the ultrasonic impact is that its duration is measured in the range from hundreds of microseconds to units of milliseconds, while the parameters responsible for the effects upon the surface may be adjusted according to the task. It is important to note that in the frequency range of processing ultrasound of up to 80 kHz this feature of the ultrasonic impact allows utilizing the plastic deformation region as a matched membrane to transmit ultrasonic oscillations and excite ultrasonic stress waves in the material being treated. These phenomena, in turn, initiate highly effective relaxation processes, plastic deformation and, as a result thereof, effects upon the structure and properties of the material, which are adequate to the task. This paper describes the theory and the results of the experimental investigations into the physics of the ultrasonic impact. Also, the mechanism of the ultrasonic impact implementation based on high-power ultrasonic transducers is addressed. The paper is aimed at engineers and researchers in the area of industrial application of high-power ultrasonics.