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The double‐ended slip line model is considered on the basis of previous experimental results [1]. It represents a plane mobile array emitted by a source, that gives rise to dislocation pairs of opposite signs. Several source models have been considered. Integration is done by the Adams scheme using a computer. Parameters are determined at which the results calculated coincide with the experiment. An analysis of the results shows that the stress concentrators are the most likely sources that produce slip lines and the interactions of dislocations with the explicit obstacles are to be taken into consideration in several cases.

A stress relaxation method is employed to obtain internal and effective stresses in NaCl single crystals at various strain rates before and after a γ‐irradiation. The conditions are found at which dislocation mobility estimated from the plastic strain rate during relaxation coincides with the velocity of individual dislocations measured by a direct method.

NaCl polycrystals, produced by press forging of single crystals at 275°C, are deformed in compression at room temperature. The dislocation structure is analysed by transmission electron microscopy as a function of the flow stress. Macroscopic yield of the polycrystals occurs at a stress that is equivalent to the flow stress of single crystals deforming in single glide at a comparable dislocation density. During deformation, a three‐dimensional dislocation structure is observed to form within the grains. This structure bears strong resemblance with that observed in [111]‐ orientated NaCl single crystals. Consistently, the high flow stress of the polycrystals arises due to the activation of considerable glide in subsidiary glide systems. This activation is necessary to accomodate the plastic incompatibilities that occur at the grain boundaries of the polycrystals.