Research On Microstructural Damage And Its Numerical Simulation Method For Composite Solid Propellant

Composite solid propellant is a kind of energetic material with very high volume fraction of particles in binder matrix, and therefore its macroscopic mechanical behavior strongly depends on its microstructure. Under external loads, the micro structure of cohesive interface will be damaged by the microcracks propagation, voids growth and localized stress concentration, leading to particle/matrix interfacial dewetting, thereby affecting the macroscopic mechanical properties. In this dissertation, a research has been systematically explored on the microstructural damage characteristics and its numerical simulation method for composite solid propellant. The main content is as follows:(1) Experimental research on correlation between mesoscopic damage and macroscopic mechanical properties of composite propellant is developed. The dewetting damage evolution at different tensile rates is carried out, using uniaxial tension and CCD optical microscope. The correlation between interface dewetting morphology with the stress-strain curve, strain rates and Poisson’s ratio is discussed. Then the microscopic reasons are analyzed to interpret the developing of mechanical properties.(2) The microstructure model of composite solid propellants is established. The geometric model of energetic particles and microstructure features are analyzed. Using random sequential algorithm (RSA), a simple and effective two-dimensional three-dimensional microstructure model is programmed to generate. The cell model for particle/matrix interfacial characteristics is also established, and the setting of boundary condition is implemented.(3) The mechanical properties and the constitutive model of the matrix material is studied. To describe the properties of HTPB crosslinked specimen, by means of uniaxial tension test, the stress response characteristics under loading are studied. Mooney-Rivlin and Ogden hyperelastic constitutive model are established. Experimental data is fitted to acquire hyperelastic constitutive parameters, and then analyzed the applicability and fitting accuracy of two models. Visco-hyperelastic characteristics of HTPB/IPDI specimen are analyzed.(4) Numerical simulation of mesoscopic damage evolution in composite propellant is studied. The particle/matrix interface damage is simulated using cohesive elements; the mechanical response is governed by using the bilinear constitutive relation. A microstructure model to simulate the damage evolution of composite propellant subjected to finite deformation is established. The damage nucleation, propagation mechanisms and non-uniform distribution of microstructural stress-strain fields, particularly, the effect of interface properties and particle sizes on the mechanical response, are obtained. Combined with experimental observations, the internal reasons of the changes in the macromechanical properties are further analyzed, and the mesoscopic failure mechanisms of composite propellant are discussed.Through experiments research and numerical framework based on micro structure model, the correlation between the microstructure state and macroscopic mechanical properties is studied. It has an important significance on predicting the trend of macromechanical properties, mesoscopic failure mechanism, and the law of damage evolution in composite propellant.