Micromechanics-based prediction of thermoelastic properties of high energy materials

High energy materials are used as propellants in solid rockets. Multiscale simulations of these materials require techniques that can bridge submicron scales and engineering scales. Micromechanics provides such techniques. The objective of this research is to investigate micromechanics approaches that can be used estimate the effective thermoelastic properties of high energy materials given the properties of the components.; In this research, rigorous bounds and analytical estimates for effective elastic properties are reviewed and applied to mock polymer bonded explosives and the explosive PBX 9501. A method of estimating three-dimensional elastic properties from two-dimensional finite element simulations is presented. Since detailed numerical simulations of PBXs are computationally expensive, two computationally inexpensive techniques are explored: the generalized method of cells and a renormalization-based approach called the recursive cell method.; Results show that rigorous bounds and analytical approximations provide inaccurate estimates of the elastic properties but reasonable estimates of the thermal expansion of PBX 9501. Finite element simulations of glass-estane composites overestimate the elastic moduli unless particle-binder debonding is included. Results for models of PBX 9501 show that the particle distribution, mesh discretization, and stress-bridging affect the estimated properties considerably. The generalized method of cells is shown to underestimate the elastic moduli because of inadequate consideration of stress-bridging and shear-normal coupling. The renormalization-based recursive cell method overestimates the effective properties unless large blocks of subcells are renormalized. Comparisons with exact relations provide useful checks of the accuracy of numerical methods. Detailed numerical simulations appear to be required for the accurate prediction of elastic properties of polymer bonded explosives.