Influence of deformation history on the yield locus and stress-strain behavior of aluminum and copper

Thin-walled tubular specimens of 1100-0 aluminum and OFHC copper were loaded biaxially through the application of simultaneous axial load and internal pressure. The effects of loading path and deformation history on the stress-strain and yield locus characteristics were studied at strains less than 2.0 pct. The observed plastic strains for both materials depended on the loading path to a given stress point, whereas the loading path during prestraining did not affect subsequent deformation. Deformation subsequent to prestraining depended on the prestraining magnitude and direction at strains less than 0.2 pct and only on the magnitude at larger strains. The resulting plastic response was, therefore, anisotropic at small strains and isotropic at large strains. The small strain behavior cannot be predicted by present continuum plasticity theories, whereas the large strain behavior agrees with the isotropic hardening rule. It was also found that a prestraining operation of sufficient plastic strain can erase some of the prior deformation history. Formerly with the Los Alamos Scientific Laboratory, Los Alamos, N. M.