| To meet the remote requirements of the solid rocket weapon system, the rocket motor grain design is progressing toward large length-diameter ratio (L/D ratio), big modulus of grain and high loading density. However, grain’s structural integrity problems will be more severe. Meanwhile, propellant have a high nonlinear viscoelastic mechanical property, then the linear viscoelastic theory and numerical simulation technology can’t content with the engineering application. Therefore, it will be necessary to modeling the constitutive model and numerical simulation method based on macromechanics behavior of materials such as the solid propellant which will support the grain design of solid rocket motor (SRM). The main jobs of this dissertation were as follows:(1) For the shortcomings of lower accuracy of relaxation modulus for viscoelastic materials, a fitting method based on Prony series was proposed based on the static relaxation tests and linear viscoelastic theory. The method can get more accuracy results and more convenience in data processing that can been verified by the constant tensile tests and relaxation tests. Further more, according to TTSP, the relaxation modulus under unsteady temperature state can be obtained by defining the reduced time as a function of shift factor aT and "zero time t0=t0(T)". And the method for obtaining the relaxation modulus under unsteady temperature state was verified by contrast with experiment results.(2) Extensive research of the TTSP in the nonlinear mechanics of the propellant have been done by establishing a series of stress-reduced time master curves under different strain levels. We can calculate the mechanical behavior of material which have a good repeatability with the tests results, by making use of the stress-reduced time master curves. The master curve of ultimate strength was built, and the ultimate strength of the propellant under different temperatures and different loading conditions can be forecasted.(3) Have a research on the damage evolution theory of elastic material based on the thermodynamic theories, and expend the model for viscoelastic materials according to the elastic-viscoelastic correspondence principle, then, the nonlinear constitutive model of the propellant which including the damage model was established. Then the model was expended to consider the temperature effect by defining the parameter α, which reflect the damage evolution rate, as a exponential function of temperature.(4) Numerical implementation of the nonlinear constitutive model was done based on the ABAQUS user subroutine (UMAT), and stress update equation and stiffness matrix were obtained, and the constitutive model was applied in numerical simulations. The model and the user subroutine were verified by the constant tensile tests and complex stress state tests, the results show that the constitutive model can describe the mechanical behavior of the propellant under various loading conditions.(5) The grain’s structural integrity of a case-bonded casting SRM was simulated by the constitutive model and the numerical method that established in this dissertation, and the mechanical behavior of case, lining and grain were obtained. Further more, the influence of structural parameters of stress release device and the modulus of grains were studied, the result show that:circumferential stressσ22and maximum principal strain εmax on the internal surface of the grain reduced along with the increment in thickness of lining in the end, while radial strain ε11and the mechanical response in tail end of artificial debond layer increased. The mechanical response on the internal surface of the grain and the tail end of artificial debond layer increased along with the grain’s modulus.Through the research of this dissertation, establish the thermo-viscoelastic constitutive model and the numerical simulation method, discuss the structural mechanics issues of SRM under temperature shock loading, lay a foundation for the study of grain’s structural integrity. |
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