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

Abstract

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.