Reverse yield experiments and internal variable evolution in polycrystalline metals

Abstract In this work, sequences of reverse yield experiments are used to measure the evolution of the directionally-dependent contribution to strain-hardening in OFHC copper. It is shown that based upon a 50 microstrain offset definition of yielding, a strength asymmetry commonly known as the Bauschinger effect develops and increases with prestrain. From the perspective of macroscale isotropic/kinematic hardening models, these data imply an increase in the kinematic hardening component of the yield strength. Hardening model parameters are determined by integrating the evolution equations and correlating the experimental data. Consistency between these modeling results and other data on the same heat of OFHC copper is then explored. It is found that while the reverse yield tests show the kinematic hardening variable, α , increasing in magnitude for uniaxial strains up to 20%, the tensor must very quickly change direction in stress space when the straining path is altered. Stress relaxation experiments were conducted and strain rate effects including the decomposition of the rate dependence between the flow rule and the evolution equations are investigated.

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