EFFECT OF PRESTRAIN AND STRAIN RATE ON VISCOPLASTIC PROPERTIES AND ON STRAIN AGEING OF METALS ( Experimental and theoretical investigation on viscoplastic properties including stress relaxation of steel)

摘要

Although many studies on viscoplasticity of metals have been reported, these do not necessarily succeed in unitive interpretation of viscoplastic behavior, for example, strain rate inverse-dependency of plastic flow stress and ununitive properties in both flow stress and stress relaxation. In this study, authors have succeeded to interpret unitively viscoplastic behavior of metals including both creep and stress relaxation behavior by investigating strain ageing properties under plastic flow of metals quantitatively. In the previous report, an experimental method is successfully presented to get both a viscosity dependency and a strain ageing dependency of viscoplastic flow stress of metals separately. In this report, both an increasing strain ageing during stress relaxation in which strain rate decreases gradually, and temporal over-hardening in reloading are estimated quantitatively. It is shown that the proposed viscoplasric constitutive model including strain ageing effect has a good applicability to an inelastic behavior having a stress-relaxation.