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

关于金属塑性流动速率依赖性的研究已有许多报道。在大多数研究中，流变应力的应变率依赖性被认为是由于只有粘度。另一方面，对于铝合金，实验上也发现了流变应力随应变速率增加而减小的一些特殊事实。作者通过系统的实验发现，目前的理论仅具有所谓的过应力本构模型那样的粘度函数，不能解释应变率突变时所观察到的流变应力的瞬态现象，而且由流变应力性质导出的粘度函数与由松弛性质导出的粘度函数并不一定一致。在前人的研究中，考虑了类时效效应和粘性效应，提出了一种新的考虑时效的粘塑性本构模型，在500K的高温下，塑性流变应力的应变速率依赖性明显降低，但松弛行为明显降低。发现其原因在于时效效应的降低，以及SUS316不锈钢的真实的粘度特性因温度而发生如此大的变化。另一方面，对于在室温下未显示出老化的Ti，应变速率依赖性也随温度的升高而降低，但原因在老化的增加中存在不同，并且真实的粘度没有如此变化。通过与实验结果的比较，验证了该模型的可靠性，并发现SCM435钢在室温下轴向加载时的速率依赖性大于扭转加载时的速率依赖性。

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.