Coupling Grain Scale and Bulk Mechanical Response for PBXs Using Numerical Simulations of Real Microstructures

Abstract

PBXs are complex composites geometrically (irregularly shaped grains vary greatly in size), and constitutively (grains are anisotropic, twin and fracture). Heterogeneity at the grain scale results in localized damage and the creation of hot spots. To develop accurate, quantitative and predictive models it is imperative to develop a sound physical understanding of the grain scale material response. Numerical simulation is a useful tool to further model development. Here an inherent advantage of a particle method in discretizing geometrically complex materials is exploited to import three-dimensional material configurations from x-ray microtomography data, i.e. "real" microstructures. Numerical simulations determine representative volume element size and generate statistics on grain scale strain heterogeneity. These statistics calibrate the Stochastic Transformation Field Analysis bulk constitutive model.

Nanoscale Characterization of Mock Explosive Materials Using Advanced Atomic Force Microscopy Methods

“…Tentatively, we identify the harder crystalline-like material on the left region of the image as crystalline Ba(NO3) 2 , and the higher modulus locations in the granular region on the right is identified as Pentek. These sub-10-micrometer elastic modulus heterogeneities of the different components may be relevant for informing computational models of explosives [7,8], which often assume homogeneity in these properties.…”

“…Previous models of explosive materials either treated the binder [4][5][6] or the ''dirty binder'' (binder with fine crystals) [7,8] as homogenous. A direct measurement of the physical properties at the submicrometer level can inform advanced computational models, which may be used to better predict the behavior of composite explosive systems.…”

Simulations of Deformation Processes in Energetic Materials

“…Constitutive equations are obtained for implementation into the DYNA3D nonlinear, explicit finite element code for solid and structural mechanics (DYNA3D). An example of the second approach is the construction of a continuum constitutive model based on homogenization procedures applied to realistic 2-D or 3-D representative volume element microstructures obtained, for instance, from digital images of cross sections (De & Macri, 2006) or X-ray microtomography (Bardenhagen et al, 2006) of a PBX. An example of the third approach is the direct simulation at the mesoscale of the propagation of a shock wave through randomly packed crystal ensembles (Baer & Trott, 2002).…”

Visualisation of the three-dimensional structure of energetic polymer composite materials

“…Therefore there is demand for representative structural images for mesoscale models. Mesoscale modelling is becoming increasingly commonplace as a tool to validate our understanding [3][4][5][6]. The observation that PBX microstructures can evolve during the manufacturing process [7] means that it is necessary to make measurements on consolidated samples, rather than use predicted PBX structures based on measurements of the properties of their raw materials.…”