Debye relaxation equations for a standard linear solid with high relaxation strength

Abstract

In internal friction measurements, relaxational effects are very often analysed in terms of the classical Debye equations, which are derived for processes with low relaxation strength. In a theoretical study it is shown that, in the case of high relaxation strength processes, deviations from the features of the Debye plots for damping and modulus defect occur. Calculations have been performed as well for the experimental situation of constant frequency as for resonance measurements. Whereas for the former only a shift of the modulus defect with respect to the peak maximum occurs, for the latter an even larger shift of the peak maximum and a narrowing of the peak plotted as a function of relaxation time is observed. Moreover, the influence of a temperature-dependent relaxation strength is studied and seen to yield an asymmetric damping peak when plotted as a function of temperature. Finally, the theoretical results, compared with some experimental observations, are shown to be able to qualitatively explain observed deviations from simple Debye type behaviour.