The Internal Friction of Rock Salt Single Crystals

Abstract

The internal friction of rock salt crystals is markedly decreased by mild x-irradiation. This is interpreted as the pinning of dislocations by cation vacancies liberated from vacancy pairs on the trapping of photo-electrons. Very small applied stresses are capable of breaking the pinning points. Under some conditions, such breakage under the vibrational stress of measurement may lead to a doubly valued dependence of internal friction on strain amplitude. A variety of other phenomena occur, most of them being qualitatively explainable on the basis of damping by moving dislocations.