Azide polyether propellant is a new type of highenergy solid propellant with broad application prospects. In order to measure the mechanical properties of azide propellant, tensile tests of propellant under different loading conditions were carried out, and compression test pieces of azide propellant of different sizes were designed and tested, and the tensile and compressive stress-strain curves of azide propellant were obtained. Through qualitative and quantitative analysis, the influence law of loading rate and temperature on the mechanical properties of propellant was obtained, the linear variation law of mechanical properties parameters with logarithmic strain rate was analyzed, and the mathematical relationship between propellant stiffness and strength was found. The master curve of the compressive initial modulus and maximum strength of the azide propellant was drawn. The test results can provide theoretical basis for the performance research of azide propellant and the nondestructive testing of this type of engine.
The application of pressure cure molding technology can effectively reduce the structural integrity problems of casting solid rocket motors. In order to describe the curing and cooling process under this new technology more realistically, it is decomposed into two processes, pressurization curing, and pressure relief cooling and a time‐varying segmented solid propellant intrinsic equation applicable to the pressure cure molding technology is proposed. The constitutive equation takes into account the change in material properties caused by the change in the state of the propellant during the curing process. In order to accurately model the changes in mechanical properties of the propellant during curing, the present constitutive equations for this process are rewritten in incremental form and implemented in the user subroutine UMAT of the finite element analysis platform ABAQUS. The detailed derivation steps of the constitutive equation are introduced in this paper, and the subsequent application analysis is carried out with reference to the star‐shaped grain. The final stress and strain state of the propellant after cooling is used as the main analytical index. The results show that the pressure cure molding technology can effectively reduce the residual stress and the residual strain on the inner surface of the propellant grain. The pressure cure effect on the outer surface of the grain is relatively small compared to the overall reduction. The time‐varying constitutive model provides technical support for a more accurate description of the pressure cure process.
To further investigate the fracture response in propellant grain, numerical methodology is proposed to cope with crack propagation simulation especially for the mixed mode condition. The numerical discrete scheme of the propellant linear viscoelastic constitutive model is proposed, which provides a key means for the simulation of crack propagation. In order to simulate the cohesive traction distribution on the new crack surface, the extrinsic Park-Paulino-Roesler (PPR) cohesive zone model (CZM) is introduced. To let the crack propagate along any direction determined, element splitting technique and its corresponding topological operations are proposed step by step. Then, computational simulation implementation process is explained in greater detail. Typical fracture problem, single edge-notched tension test (SENT) is solved to demonstrate the efficiency and accuracy of the proposed method. In addition, double edge-notched tension test (DENT) as well as plate tension test with a slant crack is conducted to show the special fracture characters in viscoelastic solid propellant, like time dependence. Computational results reveal that the method proposed can be utilized in further fracture investigation in solid propellant combined with the experimental findings.
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