SUMMARY

The shock compression of inorganic powder mixtures is a process that is of great value to a range of technological applications (e.g., the chemical synthesis of aluminides and silicides, the consolidation of powders, and the design of structural-energetic material systems). An interesting phenomenon observed in experiments is the occurrence of high-yield chemical reactions within (or shortly behind) the shock front. At present, a fundamental understanding of these ultra-fast chemical reactions is incomplete because the mechanism of mass mixing that enables the reaction has not been explained. To address this problem, the proposed research focuses on the development of numerical models to simulate the shock-induced deformation and chemical reaction of inorganic powder mixtures at the length scale of the particles. First, a novel constitutive relation will be developed for the shear strength of the particles at the high rates of deformation encountered in the shock front. Next, a model of local heterogeneous chemical reactions in shocked powder mixtures will be constructed wherein the rate of reaction is limited by the rate of mass mixing. Finally, the thermomechanics of shock wave propagation in powder mixtures will be simulated using a finite element (FE) model that is resolved at the particle level. Local fields calculated in the FE model will be used in conjunction with the model of heterogeneous chemical reactions to simulate the initiation of shock-induced chemical reactions. In this work, the numerical models will be applied to micron-size Ni-Al powder mixtures. The proposed research is expected to yield models that provide insight to the mixing and chemical reactivity of Ni-Al powder mixtures during shock wave propagation. These models may be useful to those seeking to rationalize the mechanisms of shock-induced chemical reactions and those trying to design powder mixtures to achieve certain energy-release characteristics.