TENSILE STRENGTH OF CUBIC CRYSTALS UNDER PRESSURE

The face-centered cubic crystal contains four nonparallel planes over which slip or plastic deformation may occur; these planes are determined to within discrete parallel displacements by the crystalline structure and if slip is realized over any plane, it must take place along one or the other of three possible directions in the plane. With SR denoting the magnitude of the shearing stress on a slip plane P resolved in one of its slip directions X, it is usually stated that slip will occur over the plane P in the direction X when SR attains a critical value independent of the normal stress on the plane. I find this difficult to understand in view of Bridgman's data on the tensile strength of solids under hydrostatic pressure.' Indeed, the lack of any relationship between slip and pressure in a crystal would appear to contradict, at the crystal level, all of Bridgman's important observational results concerning the effect of hydrostatic pressure on the flow and fracture characteristics of solids. In this note I have derived a possible formula for the tensile strength of a face-centered cubic crystal based on the crystallographic analogue of the slip condition which I have used in a previous article2 to explain Bridgman's results on the tensile strength of steel cylinders subjected to hydrostatic pressure, namely