Shear wave dispersion and mechanical relaxation spectra

It is shown that a mechanical stress relaxation spectrum may be obtained directly from measurements of the dispersion of shear waves in viscoelastic media. The effectiveness of this spectrum, in terms of its sensitivity and accuracy in parametrizing distributions of stress relaxation in the frequency domain, is demonstrated with reference to several published spectra. Of the three different forms of stress relaxation spectrum which may be obtained directly from oscillatory shear measurements, only that based on the group and phase velocities of shear waves is found adequate in terms of sensitivity to the presence of adjacent relaxation mechanisms in the systems considered herein.