EFFECT OF COLD-DRAWING ON THE YIELD AND FLOW BEHAVIOR OF OFHC COPPER UNDER COMBINED STRESS

Tests under combinations of tension, torsion and internal pressure have been performed at constant stress ratio on oxygen-free high-conductivity (OFHC) copper, previously annealed and then subjected to progressive reductions in the plug-drawing process. The influence of cold-drawing was investigated by means of six reductions in area up to 81 percent and this showed marked changes in the creep behavior. Logarithmic creep no longer occurred and, in contrast to the annealed material, creep was observed at stresses well below yield when the latter is defined by the backward extrapolation method. The creep rate accelerated rapidly as the yield stress was approached and the creep strain became large compared with the instantaneous strain. Under axial tension-internal pressure, symmetrical yield loci tending progressively towards the Tresca criterion were found for reductions up to 42. 4 percent.