Institute of Metals Division - The Torsion Texture of Copper

THE preferred orientations, or textures, resulting from many of the various methods for testing and forming metals have been the subject of numerous investigations.1,2* Despite this large amount of work, however, only a few limited studies have been made of the texture that is developed by torsional deformation. Ono3 found that in severely twisted wires of copper and aluminum a [Ill] direction lies parallel and a [1101 direction perpendicular to the longitudinal axis of the wire. Sachs and Schiebold4 have reported that a double-fiber texture exists in a twisted aluminum wire with both the [Ill] and [loo] directions parallel to the axis of the wire. Twisted iron wires have also been examined by Ono.8 Both the [1101 and [1121 directions were reported as parallel to the axis of the wire. Goss5 concluded from a study of twisted rods of a low-carbon steel that the preferred orientation existing at fracture is quite complex, but that many grains have a [1101 direction parallel to the axis of the wire. In addition to the earlier experimental work, some suggestions have been made about the possible nature of the torsion texture. These suggestions are based on the results of many experiments which indicate that the cold-working texture of a particular metal is largely determined by the geometrical change in shape that the metal undergoes during plastic deformation.1,6 Hibbard and Yen7 have considered the problem of deformation textures and have presented an analysis which is able to explain why equivalent changes in shape should yield similar textures. Therefore, a knowledge of the principal strains associated with torsional deformation would seem helpful in the interpretation of the torsion texture. The necessary analysis has been made of the state of strain in an element of metal lying in the surface of a cylindrical rod or tube that has been subjected to pure torsion.8,9 This analysis shows that the directions of the principal normal strains rotate continuously within a torsion specimen while it is being twisted. After the first infinitesimal amount of twisting, these directions make angles of 45" with the longitudinal axis of the bar. They rotate from this position as twisting proceeds, and after an infinite amount of twisting, the direction of the principal tensile strain is perpendicular, and the direction