Elastic constants of isotropic media

Abstract

Using ultrasonic waves of continuously varying frequency, it was recently observed1 in this laboratory that characteristic thickness shear modes could be transmitted through crystal plates and communicated to liquids in the form of consequential longitudinal strains. Further work on these lines has revealed that such modes can be similarly transmitted through isotropic media. This offers a new method of obtaining the entire frequency spectrum of a given plate, and therefore its elastic constants, even when it is available only as a small fragment. Using a tourmaline wedge with a frequency range of 3-12 megacycles per second, plates of glass, steel and brass have been studied. Values of Young's modulus Y and the rigidity modulus n obtained are compared with the usual static results in the accompanying table.