Time Dependence of the Internal Friction in Alkali Halide Single Crystals

Recovery of the internal friction is studied theoretically where the string model for a dislocation has been used. It is considered that weak pinners of dislocations move from their original positions when an applied oscillating stress becomes high enough to produce full breakaway. This motion is caused by an elastic force which is arising from an interaction between weak pinners and the oscillating dislocation. The interaction is calculated rigorously and it shows that weak pinners localize at the maximum displacements of the oscillating dislocation. After switching off the oscillation, weak pinners return to their original positions by a similar elastic force. This process gives an aging law t 1/3 which agrees with an experiment on NaCl. Observed wave form of the electric potential difference caused by charged oscillating dislocations in NaCl is discussed also using this new model.