Bauschinger effect by torsion of copper wires

Abstract

If a metal is deformed in one direction and afterwards deformed in the opposite direction, the yield value has decreased. This decrease is called the Bauschinger effect (RE.). This effect has been measured by many investigators for polycrystalline metals 1) and single crystals 2).For polycrystalline metals it is usually explained by the production of internal stresses in the metal during unloading, caused by the different orientation of the grains 3). The B.E., however, has also been measured for-single crystals. This may be explained by the back-stresses produced by the mutual repulsion between piled-up dislocations 4). Zen e r 3) makes the interesting prediction, that the RE. should be removed to a large extent by low-temperature annealing.If a wire is twisted. an extra RE. is introduced. caused by the inhomogeneous deformation. The B.E. as due to the different deformation of the grains in the polycrystalline metal and to the twisting has been calculated by R a h I f s and 11 a sin g 1) under certain simplifications.We have studied the influence of the amount of deformation, the temperature and preliminary stretching on the RE. for copper wires with the aid of a torsion apparatus. The measurements have been carried out on wires of about 44 rom length and about I mm diameter of electrolytic copper (99.98%). Initially these wires have been annealed for It hour at 550°C in vacuo, and in most experiments this has been followed by a prestrain of 8% by stretching.The results are shown by plotting the shear stress T in the outer -100-