Abstract
LONDON
Royal Society, June 7. G. I. TAYLOR: (1) The mechanism of plastic deformation of crystals. Plastic strain is chiefly due to the sliding of one plane of atoms over its immediate neighbour in such a way that the perfect crystal structure is re-formed after each atomic jump. Slipping occurs over limited lengths of the slip plane, and this type of plastic strain necessarily gives rise to elastic stresses near the two dislocations which occur at the two ends of each of these lengths. The assumption that such dislocations will migrate through the crystal, owing perhaps to temperature agitation, under the influence of even the smallest shear stress, leads to a definite picture of the mechanics of plastic distortion. (2) The strength of rock salt. Experiment shows that plastic strain in rock salt is the main factor determining the strength of well annealed crystals. A recent theory of the strength of metals is applied to rock salt and shown to lead to a parabolic relationship between tensile stress and plastic strain. It is concluded that the strain in rock salt occurs in the crystalline parts of the structure where the crystal order is perfect, and that the strength is determined by the mean free path of the centres of dislocation. The latter, which is of the order of 10˜4 cm., is determined by the distance apart of the faults and by the temperature. The theory therefore assigns a definite function to the faults in determining the strength of crystals irrespective of their actual crystallographic or atomic nature. C. A. BEEVERS and H. LIPSON: The crystal structure of copper sulphate pentahydrate, CuSO4.5H2O. The copper atoms lie on the special positions (000) and (JJO) and the sulphur upon the general position (0-01 0-29 0-64). Four of the waters are arranged in squares around the coppers, and two oxygens make with these approximate octahedra. The fifth water is not co-ordinated, but is in contact with two oxygens and two waters. All the waters show two oxygen bonds each, in accordance with recent ideas.
Article PDF
Rights and permissions
About this article
Cite this article
Societies and Academies. Nature 133, 922–924 (1934). https://doi.org/10.1038/133922a0
Issue Date:
DOI: https://doi.org/10.1038/133922a0