Research On The Thermo-visco-hyperelastic Constitutive Model Of NEPE Propellant Over A Large Range Of Strain Rates

NEPE propellant is a kind of high-energy composite solid propellants with high packing radio of solid particles. It is an important energy material, which is widely used in conventional weapons of rocket. As everyone knows, the propellant is under the loads with different strain rates and different temperatures during the process of storage and use. NEPE propellant belong to the composite materials, the mechanical properties of the composites always have obvious relevance of strain rate and temperature. In this paper, based on the strain rate range and temperature range in the using process of conventional weapons, the uniaxial compressive mechanical curves of NEPE propellant under different temperatures and strain rates were systematically researched, mainly includes the following contents:(1) The universal material testing machine was used to accomplish the uniaxial compression tests of NEPE propellant under low strain rates. The mechanical uniaxial compression curve of NEPE propellant under different low strain rates and ranging from temperature of233K to313K were obtained by the experiments. The influences of strain rate and temperature under low strain rates have been analyzed, and the static mechanical curves were determined.(2) The SHPB experimental setup and specimen were improved on account of the mechanical property of the NEPE propellant, meanwhile, the effectiveness of the test data obtained under high strain rate has been verified. An pioneering analysis has taken on the influence that the raising strain rate of SHPB test have on the test results of different materials under high strain rate, which further verified the availability of the high strain rate test results in this study.(3) The modified SHPB experimental setup and specimen were used to accomplish the uniaxial compression tests of NEPE propellant under high strain rates. The stress—strain curves at high strain rates of NEPE propellant ranging from temperature of233K to313K were obtained by the experiments. What calls for special attention is that the experimental results need to satisfy the requirements of SHPB test.(4) On the basis of the the mechanical property of NEPE propellant and the energy theory, a three-element visco-hyperelastic constitutive model was established. The model was used to express the uniaxial compression property of NEPE propellant under certain temperature, and the results convincingly implies that the model reliably expresses the mechanical property of NEPE propellant uniaxial compression under a wide range of stain rates, limits to50%strain level.(5) A temperature influence factor, which is strain-rate-dependent, was added into the visco-hyperelastic constitutive model to establish a thermo-visco-hyperelastic constitutive model. The model was used to express the uniaxial compression property of NEPE propellant under different strain rates and different temperatures, and the results convincingly implies that the model could reliably expresses the rate-dependent and temperature-dependent of NEPE propellant. It could also accurately predict the static mechanical curves at different temperatures.Through the study of this article, the issues about SHPB test were analyzed systematically and the uniaxial compression curves of NEPE propellant at different temperatures and over a large range of strain rates were obtained. A thermo-visco-hyperelastic constitutive model was established to describe the influences of strain rate and temperature to NEPE propellant. This provided a theoretical basis for future computer numerical simulation and the design of solid rocket motor.