Factors Affecting the Ductility and Strength of NaCl Single Crystals Tested in Flexure

Abstract

An experimental investigation has revealed that the initial deformation of NaCl single crystals is anelastic rather than Hookean. This anelastic deformation is manifested by a low slope foot in the load-deflection curve. The magnitude of the foot is dictated by the pretreatment given the specimen. Treatments which increase or decrease the fresh dislocation density respectively increase or decrease the length of the initial anelastic foot. The order of increasing ductility and strength with specimen pretreatment was found to be (1) heated at 135°C, (2) as cleaved, (3) coated with silver, (4) heated at 135°C and then water polished, (5) water polished and then coated with silver, (6) water polished, (7) water polished and then heated at 135°C, (8) annealed at 700°C, and (9) annealed at 700°C and then water polished. The experimental results have been discussed in terms of the role played in deformation and fracture by surface cracks, grown-in dislocations, and fresh dislocations.