Numerical study on yield curves of FCC metals based on rate-dependent crystal slips

The macroscopic plastic deformation of polycrystalline metals, as revealed by features such as yield surface under multiaxial stress or the normality rule, is related to the microscopic slips in grains. In the present paper, a rate-type constitutive equation and a constant stress model of polycrystals are adopted and the equal-strain-rate curves under biaxial stress, which are equivalent to the yield curves in plasticity, are studied. The rate-sensitivity exponent in the rate-type constitutive equation is closely related to the number of active slip systems on the yield curves. Hence, it is possible to examine the effect of the number of active slip systems an the yield curve. The yield curves of fee single crystals as well as fee polycrystalline metals are calculated. The shape of the obtained yield curve is dependent on the number of active slip systems as well as the distribution of strain in polycrystals. The direction of strain rate vectors is also discussed. A new model of polycrystals called the ''constant maximum shear strain rate model'' is proposed.