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The ultrasonic logarithmic decrement and modulus defect in high purity copper crystals was measured at 10, 30 and 50 MHz in the temperature interval 5-373 K. The samples were deformed at room temperature in the 3-20% range along the 111 crystallographic direction. The experimental data were fitted over the whole interval of temperatures, assuming the contribution of two kink mechanisms: (i) relaxation by kink pair formation with diffusion in the dislocation line and (ii) overdamped resonance of the kink chain with a temperature dependent number of kinks in the dislocation lines. With this procedure both primary and secondary properties of the high frequency Bordoni peak could be satisfactorily explained. Numerical data are reported for peak parameters and for the kink diffusion coefficient.

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An atomistic calculation of the Peierls stress in Al and Cu is undertaken in order to assess consistency with experiments. The measured yield stress extrapolated to 0 K results at least one order of magnitude smaller than the Peierls stress commonly derived from internal friction data. On the theoretical side, some calculations for Al are already available (using different approaches than presently) however none is for Cu. The simulations employ semi-empirical many-body interatomic potentials, fitted here to the generalized stacking fault energy surface (calculated elsewhere with ab initio electronic structure methods), as well as others from the literature. After a critical assessment, reasonable agreement is demonstrated between our results and the Peierls stress values derived from internal friction experiments within the framework of the kink pair formation model.

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