LXV. On the theory of the low-temperature internal friction peak observed in metals

Recent data by Niblett and Wilks on polycrystalline copper suggest that the low-temperature internal friction mechanism in metals first observed by Bordoni is determined by intrinsic properties of dislocations. This is contrary to an explanation by Mason according to which the activation energy of the process should depend on the impurity content of the material and the separation between dislocation nodes. A mechanism proposed elsewhere seems to account for all the major features of the experimental results. The relaxation phenomenon is thought to be due to dislocations which are confined by the Peierls stress to certain crystallographic directions. Under the combined action of thermal fluctuations and the applied stress they may form pairs of kinks. Internal friction peaks are observed if the frequency of the applied alternating shear stress is equal to the frequency of the formation of these kink pairs. The Peierls stresses deduced from the experimental results are rather large, being of the order of one thousandth of the shear modulus.