Strength of Metal Single Crystals

Abstract

IN the course of some experimental work on single crystals of cadmium, which I have been carrying out under Prof. E. N. da C. Andrade, I have found that the condition of the surface exercises a surprisingly large effect on the initial strength of the crystal. It is well known that glide commences in a single crystal when the shear stress on the glide plane, and in the glide direction, reaches a certain value, known as the critical shear stress. Thus in a series of crystals grown from cadmium (glide plane, hexagonal base; glide direction, axis of digonal symmetry), which proved to contain 0·15 per cent of lead and 0·15 per cent of zinc, this critical shear stress lay within the comparatively narrow range of 50–59 gm. wt. per sq. mm., while the angles which the hexagonal planes made with the axis of the wire varied from 8° to 72°.