Evaluation of the Amplitude-Dependent Internal Friction of Materials under Inhomogeneous Strain

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Abstract
The phenomenology of the internal friction experiments is examined with special attention to the influence of the distribution of vibrational strain. A method is presented for the determination of the strain dependence of internal friction from the data obtained under inhomogeneous strain. It is shown that measured values of internal friction, expressed usually as a function of the maximum strain amplitudesεm, are dependent on the strain distribution and that the strain-amplitude dependence of internal friction can be obtained by plotting the measured values against the average strain amplitudeεa, given byεa=Kεm. The factorKcan be calculated from the mode of vibration. The result for a cylindrical specimen of common materials shows thatK=0.8165 for torsion, 0.8660 for a free longitudinal mode and 0.6059 for a free transverse mode.