NEPE推进剂低高应变率下改进的黏-超弹本构模型

为研究低高应变率条件下NEPE推进剂的力学特性，通过电子万能试验机和分离式霍普金森杆装置，对NEPE推进剂进行了准静态和冲击实验，得到了不同应变率下（1.667×10?4～4 500 s?1）的应力-应变曲线。实验结果表明NEPE推进剂具有明显的非线性弹性和应变率敏感性，随着应变率的增加，材料的强度、屈服应力和弹性模量显著增加，与低应变率相比，高应变率条件下材料的应变率敏感性更高。在高速冲击下材料内部瞬间产生大量热量无法及时散发出去，使得材料内部温度升高，导致材料出现软化效应，力学性能降低。本文建立了一个非线性黏超弹本构模型，其中采用Rivlin应变能函数来描述稳态超弹响应部分，采用积分型本构模型来描述材料的动态黏弹性响应部分，考虑到松弛时间具有应变率相关性，本文采用了一个率相关松弛函数来替代传统的Prony级数形式。使用极慢速压缩实验数据对本构模型中的超弹部分进行拟合获得超弹参数，然后用准静态和动态实验数据对本构模型进行拟合得出其他参数。不同应变率下的预测曲线与实验曲线具有较好的重合度，证明了该模型可以很好地描述低高应变率下NEPE推进剂的力学特性。

An improved visco-hyperelastic constitutive behaviour of NEPE propellant at low and high strain rates

In order to study the mechanical properties of NEPE propellant at low and high strain rates, the quasi-static and impact eperiments of NEPE propellant were carried out by the electronic universal testing machine and split Hopkinson bar, and the stress-strain curves of NEPE propellant under different strain rates (1.667×10?4?4 500 s?1) were obtained by processing the experiment data. By analyzing the stress-strain curve of low and high strain rates experiment, it can be found that NEPE propellant has obvious nonlinear elasticity and strain rate sensitivity. With the increase of strain rate, the strength, yield stress and elastic modulus of the material increase significantly. Compared with low strain rate, the strain rate sensitivity of the material at high strain rate is higher. Under the high speed impact, a large amount of heat is generated inside the material and cannot be released in time, which makes the internal temperature of the material rise, leading to softening effect of the material and reduction of mechanical properties. In this paper, a nonlinear visco-hyperelastic constitutive model is established to describe the mechanical properties of NEPE propellant at low and high strain rates, in which the Rivlin strain energy function is used to describe the static hyperelastic behaviour, and an integral constitutive model is used to characterize the dynamic response of the material. Considering that the relaxation time has strain rate correlation, a rate-dependent relaxation function is adopted in this paper to replace the traditional Prony series. The hyperelastic parameters were obtained by fitting the hyperelastic part of the constitutive model with extremely slow compression experiment data, and then the other parameters were obtained by fitting the constitutive model with quasi-static and dynamic experiment data. It was proved that the model could well describe the mechanical properties of NEPE propellant at low and high strain rates by the good coincidence degree between the prediction curve and the experiment curve under different strain rates.