A Test of Viscous Dislocation Damping Theory

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Abstract
The amplitude‐independent dislocation damping of a series of dilute copper‐germanium single crystals has been studied as a function of composition and frequency. The measurements have been performed at room temperature on annealed and γ‐irradiated single crystals driven in longitudinal resonance at 80 and 240 kc/sec by means of the Marx piezoelectric oscillator. The results indicate that the Granato‐Lücke viscous damping analysis cannot account for the observed magnitude and composition dependence of the damping, although the damping is proportional to frequency in agreement with their theory. They further show that a γ‐ray dose of 2×108 rad is sufficient to suppress the damping to a composition‐independent value of 1×10−4 which does not decrease with further irradiation. There is evidence that the total damping consists of a composition‐dependent edge dislocation loss superposed on a composition‐independent screw dislocation loss.