Multiscale damage modeling of solid propellants: Theory and computational framework

The present work provides a theoretical and computational framework for modeling the macroscopic/microscopic behavior and interfacial decohesion of grains during propellant loading. The micro-scale is characterized by a unit cell, which contains micro-constituents (grains) dispersed in a polymeric blend. We have used a packing algorithm, treating the ammonium Perchlorate (AP) as spheres or discs, which enables us to generate packs which match the size distribution and volume fraction of actual propellants. Then a novel technique to characterize the pack geometry suitable for meshing is described and a powerful mesh generator is employed to obtain high quality periodic meshes with refinement zones in the regions of interest. The proposed numerical multiscale framework, based on the mathematical theory of homogenization, is capable of predicting non-homogeneous microfields and damage nucleation and propagation along the particle matrix interface, as well as the macroscopic response and mechanical properties of the damaged continuum. Examples are considered involving simple unit cells in order to illustrate the multiscale algorithm and demonstrate the complexity of the underlying physical processes.