Acoustic Properties of Metals and Magnetostrictive Materials

Abstract

The process of inducing plastic flow in metals under the combined action of static and large vibratory stresses using a high-powered horn driver is discussed. In particular, where the metal is ferromagnetic, one has the situation that many properties of the material, including magnetic properties, change under the combined stress action. This necessarily affects the end uses of the material as, for example, in magnetostrictive transducers. Experiments are described in which the properties of nickel are investigated, for example, and the plastic flow threshold curve under combined stress action is determined. It is found that vibratory stress is much more effective in producing flow than static stress. In addition, it is found that, subsequent to the occurrence of plastic flow, the mechanical Q of a sample is altered but partially recovers over a period of hours at room temperature, and the material is hardened against further flow. The separation of the total energy loss into macroeddy, elastic, and microeddy loss is discussed. The alteration of the magnetic properties of plastically flowed samples is quite marked at points near the flow maxima in the samples containing standing intense acoustic waves, and the change in internal friction provides a possible means for predicting impending fatigue in metals without destruction of the materials. [This work was supported by the Office of Naval Research.]