Precise Investigation of the Theory of Damping by Transverse Thermal Currents

The frequency-dependence of internal friction of four α brass (62.5% Cu) reeds was measured at room temperature under conditions where contributions to the internal friction other than that arising from transverse thermal currents were small and assessable. Measurements were made by the free-decay method, at maximum strain amplitudes of 5×10−6. By using specimens of two different thicknesses, frequencies differing from the frequency of peak damping by nearly a factor of 20 were obtained by measurements in the range 7–370 cy/sec. The results, in conjunction with measurements of Young's modulus (1.06×1012 dynes/cm2±0.5%), coefficient of linear expansion (18.7×10−6/°C±0.5%), density (8.42 g/cc±0.2%), specific heat (0.088 cal/g/°C±2%), and thermal diffusivity (0.34 cm2/sec±5%), indicate that Zener's theory of damping by transverse thermal currents is probably valid exactly. From the position of the peak, the thermal diffusivity is found more precisely as 0.346 cm2/sec±1.5%.