Internal friction due to crystal lattice imperfections

Abstract

This dissertation is concerned with internal friction due to crystal lattice defects. Particular attention is given to losses involving dislocation motion which are observed in metals. Five characteristic types of loss are distinguished experimentally. These are i) the Bordoni Peaks, ii) the Hasiguti Peaks iii) a damping observed at high temperatures which increases exponentially with temperature, iv) a damping which is independent of the stress amplitude at which it is measured, providing this is small, end which is also dependent on the frequency of the stress wave, and v) a damping which is dependent on the measuring stress amplitude but independent of the measuring frequency. An attempt is made to relate each of these five losses to a specific dislocation damping mechanism. The individual damping mechanisms ere based on one or other of three general processes by which energy may be lost from an oscillating length of dislocation. These were firstly a relaxation process, secondly a damped resonance process end thirdly a static hysteresis process. Internal friction measurements are found to give information on, for example, the nature and distribution of point defects and dislocations, the interaction between point defects and dislocations, the magnitude of the Peierls stress and the dynamics of dislocation motion. In connection with the latter the string model of dislocation motion is compared with the kink model.