纯铁在高应变率下的流动应力特征及其动态塑性本构关系

The characteristics of flow stress and dynamic constitutive model at high strain rates for pure iron

利用MTS材料试验机和分离式Hopkinson压杆实验装置，对锻造后经930℃下退火2h的纯铁材料进行压缩实验，测定纯铁在准静态条件（10^-3～10^0s^-1）和高应变率（650s^-1-8500s^-1）下的应力一应变曲线。实验结果表明，纯铁是应变率敏感材料，纯铁在高应变率条件下，具有应变率增强、增塑以及应变强化效应，高应变率下的塑性变形过程中产生的绝热升温对材料具有热软化作用。基于Johnson-Cook（J—C）本构模型，引入绝热温升软化项对模型进行修正，通过实验数据拟合得到了纯铁的动态塑性本构关系，模型计算结果和实验结果证明，该模型可以较好地预测纯铁在高应变率下的塑性流动应力。

The compression experiments for forged pure iron after annealing at 930℃ with 2h were carried out with materials testing system and split Hopkinson pressure bar apparatus, and the stress-strain curves of pure iron were measured at quasi-static condition （10^-3～10^0s^-1） and high strain rates （650s^-1-8500s^-1 ）. The experiment results show that the pure iron is sensitive materials to strain rate; it has the effects of strain rate strengthening and plasticity-increasing and strain work-hardening, and the adiabatic heating during plastic deformation at high strain rate lead to thermal weakening of pure iron. Based on the Johnson- Cook constitutive model, and taking into account of adiabatic heating to modify the model, the dynamic constitutive model of pure iron was obtained by fitting the experimental results. The model results were compared with experiment results. The results show that the present dynamic constitutive model can make a satisfied prediction to the plastic flow stress,