Acoustic Determination of the Physical Constants of Rubber-Like Materials

Abstract

The elastic and viscous constants of rubber-like materials may be determined, under conditions of very small strain, through measurements of acoustic phase velocity and acoustic attenuation. The attenuation in such materials is usually high, with the result that the elastic and viscous constants must be computed by means of rigorous relations involving attenuation and velocity, rather than the approximate relations which are usually employed. The necessary relations are presented for the case of longitudinal waves in thin strips. An experimental method is described which has been used to measure acoustic phase velocity and attenuation in thin narrow strips in the frequency range from one to 26 kilocycles. One end of the sample strip is driven by a vibration generator. The phase and amplitude of the signal received by a moving detector are plotted automatically as a function of distance along the strip. On a particular sample the r.m.s. error in a series of measurements of velocity and attenuation ranged from 2 to 9 percent and 6 to 12 percent, respectively, over the frequency range. Sample acoustic data and the computed elastic and viscous coefficients are given for a carbon-black buna-N cement.