Acoustoelastic Coefficients of High Polymer by Spectral Analysis. Acoustoelastic Coefficients of Longitudinal Waves in Acryl.

Abstract

Acoustoelasticity is expected to be a powerful method for nondestructive evaluation of the internal stress of materials. The technique is based on the speed shift of ultrasonic waves due to nonlinearity of the elastic coefficients. If the viscocity of the material is high, such as in high polymers, the speed of an ultrasonic wave depends on the frequency of the wave. In general, the nonlinearity of elastic coefficients of such materials is also significant, so that the relation between the speed shift and the stress becomes nonlinear. A theoretical foundation is given for the acoustoelastic laws of viscoelastic material with higher-order nonlinearity. This paper also presents a technique for determination of the speed and the nonlinear acoustoelastic coefficients by spectral analysis of the waveforms. For longitudinal waves propagating in acryl under uniaxial stress, the dependence of the speed and the acoustoelastic coefficients on the frequency and the uniaxial stress is discussed.