拉伸变形应变速率敏感性指数的力学涵义及其规范测量

鉴于建立超塑性变形定量力学解析理论的重要性，从分析Backofen超塑性拉伸的本构方程出发，讨论了方程中的材料参数k和应变速率敏感性指数m的力学涵义。提出了恒应变ε、恒速度υ和定载荷F三种典型变形路径条件下应变速率敏感性指数的规范测量公式。对每种变形路径又提出应变速率敏感性指数的传统测量方法和计算机模拟精确测量方法，并作了精度对比分析。给出了典型超塑Zn-5%Al合金在常态（18℃）和超塑状态（340℃）时三种变形路径下应变速率敏感性指数m ε、m υ和m F的实测结果。由于三者之间不但存在大的偏差，而且随ε的变化规律也各异。这就从试验上判明，即使在相同的应力状态下，应变速率敏感性指数也与变形路径密切相关。由此便向力学理论提出新的问题，要求从理论上解答偏差和变化规律不同的原因，进而揭示其力学本质。

MECHANICAL MEANING OF STRAIN-RATE SENSITIVITY INDEX AND CRITERION OF IT'S MEASUREMENT UNDER TENSION CONDITION

Due to the importance of establishing the quantitative　mechanical　analysis　theory　of superplastic deformation， the mechanical meanings of material parameter k and strain-rate sensitivity index m in Backofen′s constitutive equation are discussed. The canonical measurement formulae and methods of m value under constant strain ε，constant velocity v and constant load F3 typical deformation routes are given. Moreover， the precision of traditional measurement method is compared with that of computer simulation under each typical deformation route. Under the above deformation routes， the strain-rate sensitivity indexes mε，mv and mF of typical superplastic alloy Zn-5%A1 for room temperature (18℃) and superplastic state(340℃) are obtained bythe experiments. The results indicate that there exist large deviation among mε，mv and mF，they have different variational rule with strain rate ε respectively. These prove that the strain-rate sensitivity index depends tightly on the deformation route from experiment，even on the condition that those stress-state are similar. So new problem emerges， it requires giving the explanation in theory why there exist deviation and different variational rule with strain rate respectively， and further disclose the mechanical essence of mε，mv and mF.