Dislocation Damping in Copper at Kilocycle and Megacycle per Second Frequencies

Abstract

A recent conclusion that the vibrating string model of dislocation motion cannot account for the magnitude of the observed amplitude-independent damping at kilocycle per second frequencies is shown to be not generally valid. In fact, it is shown that there are specimens for which the extrapolated values of the decrement from megacycle frequencies to 15 kc are higher than any previously measured values at 15 kc. This result shows that the model can easily account for the magnitudes observed in the kilocycle region, and contributes a substantial fraction, if not all, of the component of the damping at 15 kc, which can be removed by irradiation. Since it has been demonstrated for the megacycle measurements that the source of the damping is the dislocation-phonon interaction, the evidence is strong that the same mechanism contributes to the damping observed at 15 kc. The argument given does not depend on assumed values for dislocation parameters, but only on experimentally established relations. A critical experiment would now be a measurement of the frequency dependence in the kilocycle range of the component of the damping which can be removed by irradiation. Such a measurement, if feasible, should show whether or not other as yet unknown mechanisms also contribute to the damping at 15 kc.