COMPARISON OF DISLOCATION-STRUCTURES AT SMALL STRAINS IN COPPER DEFORMED IN TENSION AND IN TORSION

OFHC copper specimens of 39 mu m grain size were deformed in tension (to 8% tensile strain) and in pure torsion (to 8% shear strain) at 300 K, and the resulting dislocation Burgers vectors, distributions, and densities were determined using transmission electron microscopy. Employing the von Mises yield criterion and the total plastic work hypothesis, good agreement was obtained between the tension and torsion test results for equivalent stress versus equivalent strain curves, the dislocation Burgers vectors, distribution, and density as a function of the equivalent strain, and the equivalent stress as a function of the square root of the dislocation density. These results imply that in the unidirectional straining of copper there results a constant dislocation structure for a given amount of plastic work, irrespective of whether the deformation is in tension or torsion. However, equally good correlations were obtained on the basis of maximum shear stress and maximum shear strain, and therefore a positive decision between the two yield criteria could not be made.