Experiments that demonstrate the basic quantitative and qualitative aspects of the cyclic plasticity of metals are presented in Part 1. Three incremental plasticity kinematic hardening models of prominence are based on the Prager, Ziegler, and Mroz hardening rules, of which the former two have been more frequently used than the latter. For a specimen previously fully stabilized by out of phase cyclic loading the results of a subsequent cyclic nonproportional strain path experiment are compared to the predictions of the above models. A formulation employing a Tresca yield surface translating inside a Tresca limit surface according to the Mroz hardening rule gives excellent predictions and also demonstrates the erasure of memory material property.

Extensive experiments were conducted on annealed copper under cyclic nonproportional strain histories. After cyclically stabilizing the material by uniaxial cycling, out-of-phase axial-shear strain cycling for the same effective strain range caused additional increases in stress amplitudes to restabilized levels. Following cyclic stabilization of the material under out-of-phase cycling, a cycle whose effective strain amplitude was comparable to those of previous cycles resulted in stress-strain behavior unique to that cycle and independent of prior stable deformation. The experimental verification of this material property, which has been the subject of much conjecture, allowed the design of a fundamental class of experiments that determined the subsequent yield surface and strain hardening behavior from only one specimen.

An experimental investigation was undertaken to evaluate anisotropic plasticity theories which have been proposed in the literature. Three different metals in the form of 2.5-in-dia bars were considered: SAE 1020 steel preloaded in tension to a strain of 8 percent, copper alloy 360 (free-cutting brass) preloaded in tension to a strain of 3 percent, and 2024-T351 aluminum alloy as received. All metals had approximately the same properties in the radial and circumferential directions with greatly different properties in the axial direction. Tension and compression tests were conducted on specimens having directions of axial, circumferential, and 45 deg to the axis. Hollow torsion tests were conducted on axial specimens. Biaxial tests were conducted on thin-walled cylinders. All loading was monotonic and proportionate and extended well into the plastic region. Anisotropic plasticity theories were evaluated by comparing theoretical and experimental yield curves for each material and by comparing theoretical load-deformation curves with experimentally determined curves for tension and compression specimens at 45 deg to the axis, for hollow torsion specimens, and for biaxial loading. In most cases, good agreement was found between theory and experiment.