Frictional Stress Acting on a Moving Dislocation in an Otherwise Perfect Crystal

Abstract

The problem of the frictional stress suffered by moving dislocations in otherwise perfect crystals is investigated. This is done without calculating the core energies of dislocations, but by considering stresses and strains on the slip plane. The level of frictional stresses obtained is much higher than reported previously. Since common glide dislocations in metals with close packed structures apparently do not suffer significant frictional stresses, mechanisms are discussed which tend to reduce their effect. A new such mechanism is discovered. It is based on the idea that the positions of dislocation axes are not defined with precision, but only within one to a few times the average displacement of the oscillating atoms. The expected result of this is a depression of the frictional stress for close packed metals even at very low temperatures, almost no effect on dislocations in crystals with diamond structures, and a temperature dependence proportional to $e^{-\frac{\mathrm{const}T}{T_M}}$ for NaCl type salts and, probably, for bcc metals.