We will develop a multiscale molecular dynamics/material point method (MD/MPM) methodology for determining the response of PBXs to a wide range of loading conditions as a function of mesoscale structure with emphasis on accurate representation of interfacial physics. The initial material of choice will be HMX + DOA plasticized HTPB binder. Velocity-dependent grain-grain and viscoelastic grain-binder interfacial models as well as an improved viscoelastic model for the binder will be developed based upon non-equilibrium and Hugoniostat MD simulations. An array of representative mesoscale multiple grain elements (MGEs) will be generated using a Monte Carlo packing and growth (MCPG) methodology employing ellipsoidal particles for a range of configurations/formulations (grain size distributions/loading fractions). MGE generation will be biased to yield controlled degrees of grain-grain contact based upon previous experimental mesoscale structural analyses. MPM computational experiments (quasistatic loading and shock) performed on multiple MGEs with fully resolved grains, binder and interfaces will yield mesoscale structure-dependent properties (EOS and constitutive laws). These mesoscale structure-dependent properties will be employed in MPM simulations of bulk PBXs over a wide range of loading conditions and particle resolution with explicit mesoscale heterogeneity implemented through stochastic property seeding. Extensive hot spot analyses will be conducted and correlated with mesoscale structure.
Benefits: The objectives of this STTR project are of interest to the DOD, other government agency and industrial concerns interested in production of PBXs with controlled sensitivity as well as those interested in improving the safety of solid propellants. In addition to software licensing to interested users, success of this Phase I project will allow WMI to pursue patents and subsequent licensing and royalties for all developed materials where this is allowable.
Keywords: plastic bonded explosives, mesoscale structure, heterogeneous composites, multiscale modeling, material point method, molecular dynamics simulations, HMX, HTPB
