Biaxial cyclic hardening of annealed copper cylinders evaluated by deformation plasticity theories

Cycle-dependent hardening of annealed metals is by now a well known experimental phenomenon. The annealed metal, when cycled between equal tensile and compressive strain limits, develops increasing stresses with each strain reversal. However, all previous experimental work on cyclic hardening is restricted to uniaxial loading. In this investigation hollow and solid circular cylinders of annealed OFHC copper were subjected to cyclic proportional strain histories. The stress-strain histories for different strain paths were correlated on the basis of Tresca and Mises effective stresses and strains, and the correlations using Tresca definitions were shown to be more representative than those of Mises. However, a deformation plasticity theory corresponding to the Tresca yield condition and Tresca effective stresses and strains did not lead to accurate predictions of the stress histories. The predictive capability of a simplified plasticity theory, which assumed that proportional straining leads to proportional stressing, was evaluated. Although this simplifying assumption was not in qualitative agreement with experimental results, its accurate characterization of the load -torque histories of solid cylinders suggests that the greater computational effort required by the constitutive equations of incremental plasticity might not be justifiable for some cyclic proportional straining situations.Army Research Office, Durham, North Carolina 76/01 DAHC 04 74 G 0050 76/0