Micromechanics Of Composite Solid Propellant Viscoelastic Damage Constitutive Model

In this dissertation,a nonlinear viscoelastic constitutive model for composite soild propellant including particles-reinforced and dewetting damage effects has been established at microlevels. The main achievements are summarized as following:1.Based on the irreversible thermodynamics and the internal variable theroy,a generalized viscoelastic constitutive law has been derived for the matrix of composite soild propellant with distinct viscoelasticity.2. The Eshbely's equivalent inclusion micromechanics theroy is extended to investigate viscoelastic constitutive equations of composite soild propellant. The constitutive law is related to constituent properties (fillers and matrix) in a considerable simple form. The result shows that composite soild propellant's constitutive formula is equal to that of its matrix multiplied by a reiforced factor. The particles' filled-status and the matries' nonliner viscoelasticity have been discussed. An equivalent filler volume fraction has been discovered.3.The microscopic stress distribution in particle-filled material has been studied by axisymmetric finite element method. The numerical results indicate that interface debonding has a strong tendency while the rigidity and volume fraction of particle are getting higher. As the result,interface dewetting becomes the dominant mode of microdamage for composite soild propellant. Also,based on an energy criterion,the effects of particle volume fraction,the size distribution,loading rate and relaxation time are discussed.4. The damage evolution due to distributed microcracks growing has been studied. Based on the Taylor model,compliance tensor increment induced by single penny-shaped microcrack is derived under complex loadings,both the closure and frictional sliding effects of microcrack are considered. The mixed-mode fracture criterion is applied to estblish the control equation of mcriocracks extending under three-dimensional tensile loading. In order to describe the damage evolution state,the concept of microcracks growth domain (MOD) are introduced and defined as the union of all possible orientations and sizes of propagated microcracks after a loading path. The evolution of MGD as well as the overall effective compliancetensor of damaged materals is formulated. By this MGD,the damage state can be described more exactly and clearly and the problem of complex loadings can be solved expediently. That three-dimensional damage model is applied to uniaxial tension to reveal the anisotropic properties of materials due to microcracks damage.5.Based on MGD model,a damage evolution equation for composite soild propellant has been determined under uniaxial tension. Material constants are determined by one set of constant tension rate experiment. Thus,the constitutive equations found include the effects of constituents and micro-dewetting damage. The consistency between theory and experiment is pretty good,and the rationality of the model has been confirmed.We hope and believe that the conclusions of this thesis will be useful to the structure analysis and design of soild motors.