STUDY ON INELASTIC CONSTITUTIVE EQUATIONS OF METALS CONSIDERING OF TEMPERATURE DEPENDENCY OF VISCOSITY AND AGING

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Many studies on rate dependency of plastic flow of metals have been reported. In most of those studies, strain rate dependence of flow stress is considered to be due to only viscosity. On the other hands, some special facts that a flow stress decreases as a strain rate increases were recognized experimentally for Alminum-alloys. From the author's systematical experiments, it is found that the current theory having only viscosity function like a so-called overstress constitutive model, is not available for explaining a transient phenomena in flow stress observed at a sudden change in strain rate, and that the viscosity function derived from flow stress properties does not necessarily coincide with the viscosity function obtained from relaxation properties. In the previous report, taking into consideration of aging-like effect as well as viscosity, authors proposed a new viscoplastic constitutive models with aging.Apparent decrease in strain rate dependence of plastic flow stress can be observed at elevated temperature up to 500K, but much more decrease in relaxation behavior. It is found that the reason exists in a decrease of aging effect, and that a real viscosity property so much changes due to temperature for SUS316 stainless steel. On the other hand, for Ti which showes no aging at room temperature, strain rate dependency also decreases with increase of temperature, but the reason exists differently in increasing of aging, and real viscosity does not so change. Inelastic constitutive expressions with viscosity and aging considering its temperature dependence were proposed for these metals and its reliabilities were confirmed by comparing simulation results with the corresponding experimental results.It is also found that rate dependence is larger in axial loading than that in tosional loading for SCM435 steel in room temperature.