| Solid rocket motors(SRMs)have the characteristics of long-term storage and disposable use,and they are in the storage state during the most of whole life cycle from delivery,interim storage and ultimate disposal.Therefore,the storage life of SRMs is the main factor restricting the service life of missile weapon system,and it is also a key performance indicator of weapons and equipment.The storage life of SRMs depends largely on the storage performance of solid propellant.Traditionally,the life prediction of SRMs is mainly through the evaluation of aging performance of propellant billet.In a case-bonded SRM,solid propellant grains are subjected to a variety of strains after solidification by cooling,which are introduced during curing and cooling of the grains due to differential thermal expansion between the propellant and the case material.The failure mechanism of grains and propellant billet are different.Therefore,study on the aging mechanism storage performance of propellant under constant strain has more practical value,which is also the theoretical basis and model data sources of life prediction of SRMs.In this paper,the aging characteristics of HTPB propellant under constant strain were studied.The aging model of the maximum elongation and statistical damage constitutive equation were developed to analyze the effects of constant strain and temperature on model parameters.In addition,the assembly level accelerated storage test(ALAST)of SRMs were investigated,including the test mechanism,the determination and correction of test parameters,the monitoring and sampling during test process.Finally,the effect of curing strain on storage life of SRMs was investigated based on the viscoelastic stochastic finite element method(SFEM)and accelerated aging test of solid propellant,and the influence of different mechanical parameters of propellant and load conditions on the Von Mises strain of grian were analyzed.The main contributions of the dissertation are summarized as follows:1.The aging model of the maximum elongation under constant strain was developed.Results show that the change of maximum elongation was the combined actions of physical tension and chemical aging.The constant strain can increase the maximum elongation significantly during accelerated aging process,and the increasing amplitude exhibits a linear relationship with aging temperatures and constant strains.The chemical aging decreases the maximum elongation.The effect constant strain on chemical aging is related to a critical temperature _CT.Constant strains have almost no effect on the maximum elongation aging rate constant when aging temperature is below _CT,but they may promote decrease the maximum elongation aging rate constant at temperatures above _CT.2.A statistical damage constitutive model of propellant was established based on ZWT constitutive equation.The aging damage factor was introduced to quantify the damage degree caused by accelerated aging with constant strain.Further analysis indicated the damage effects caused by chemical aging and constant strain can be identified from the equation of aging damage coefficient.Chemical aging can not only influence the tensile strength of propellant in damage phase,but also change the shape characteristics of stress-strain curve.The constant strain only decreased the tensile strength in damage phase.3.Based on the conversion method,the comprehensive accelerated storage test(CAST)of SRMs which combined material level and assembly level was put forward.The test mechanism,the determination and correction of test parameters of CAST were introduced,and the multi-step correction method base on the double source data from propellant billet and SRMs was developed.The combustion chamber of a SRM was validated by methods of CAST.The solutions of performance monitoring and sampling during aging process were developed,and the monitoring device and sampling device were designed to solve the related problem.4.The effect of curing strain on the storage life of SRMs was investigated.The reliable life of the SRMs under different strain sensitivity coefficient was predicted with a reliability coefficient of 0.97.Results show that the reliable life is mainly depends on the strain sensitivity coefficient,and it increases as strain sensitivity coefficient increases.The influence of modulus on the Von Mises strain of grain almost remains unchanged.The influence of Poisson's ratio and internal pressure also remains unchanged in the first 15years,but the former gradually weakened in the following years and the latter just the opposite,and they were approximate complementary. |
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