NUMERICAL STUDY ON YIELD CURVES OF FCC METALS BASED ON RATE-DEPENDENTCRYSTAL SLIPS

The macroscopic plastic deformation of polycrystalline metals, as reve aled 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 un der biaxial stress, which are equivalent to the yield curves in plasti city, are studied. The rate-sensitivity exponent in the rate-type cons titutive equation is closely related to the number of active slip syst ems on the yield curves. Hence, it is possible to examine the effect o f the number of active slip systems an the yield curve. The yield curv es of fee single crystals as well as fee polycrystalline metals are ca lculated. The shape of the obtained yield curve is dependent on the nu mber of active slip systems as well as the distribution of strain in p olycrystals. The direction of strain rate vectors is also discussed. A new model of polycrystals called the ''constant maximum shear strain rate model'' is proposed.