Effect of solid propellant failure at intermediate strain rate on structural integrity of solid rocket motor grain

Under the condition of low temperature ignition of solid rocket motor, the grain is subjected to the combined effect of low temperature and internal pressure load, and the structural integrity is easily damaged. For NEPE solid propellant, uniaxial tensile mechanical performance tests were conducted under low temperature and intermediate strain rate conditions. The tensile mechanical properties and the failure envelopes dependent on temperature and strain rate were obtained from experimental results, and the law of translation of the failure envelopes was revealed. Based on the homogenization theory of nonlinear viscoelastic composite materials, a temperature and strain rate dependent nonlinear viscoelastic constitutive model is developed for solid propellants. The developed constitutive model and propellant failure criterion are applied to the grain structural integrity analysis. The results show that 100 MPa/s is the optimum pressurization rate of the propellant, and the safety margin of the structural integrity of the low temperature ignition is the largest at this time. The results of this investigation have significance for assessing the NEPE propellant’s structural integrity.