A Theory of the Hysteretic Contribution to Internal Friction; Thermomechanical Unpinning of Dislocations

The thermomechanical unpinning and repinning of dislocation lines pinned at equidistant points are analyzed. The hysteretic type of internal friction which results from this unpinning is calculated using a computer program which allows an examination of the effects of stress, temperature, frequency, dislocation-pin interaction energy, dislocation loop length, and density of pinning points. It is shown that the internal friction due to thermomechanical unpinning is a function of the above variables. The hysteretic damping exhibits a maximum as a function of temperature, frequency, and stress, and the characteristics of these peaks are examined. A brief comparison of the calculated damping with the experimental results is made and it is shown that the theory can qualitatively account for the features of deformation produced damping peaks such as the Bordoni and Hasiguti peaks.