Unrecoverable Strain Hardening in Torsionally Strained OFHC Copper

Abstract

This paper investigates the recoverable and unrecoverable components of strain hardening in OFHC copper tubing subjected to torsional strain. Individual hardening components are classified and the magnitude of each is experimentally determined. Recoverable strain hardening is defined to be the difference between the final shear stress and the yield stress measured after recovery annealing. The recoverable hardening, due primarily to dislocation pileups, accounts for about 95.5 percent of the measured strain hardening at a shear strain of 1.9. Crystal lattice rotation during shear strain accounts for a portion of the unrecoverable hardening at shear strains less than .25, but becomes a strain softening effect at shear strains above .5. The evolution of the texture is measured experimentally and analyzed using both Taylor’s and Kochendorfer’s models. Texture evolution is also simulated up to a shear strain of 2.0 using Taylor’s model. This simulation yields similar results to the measured texture in determining strain hardening caused by rotation of the crystal lattice. The softening effect of crystalline reorientation accounts for a decrease in the observable hardening of 1.5 percent at a shear strain of 1.9.