Weak impacts on high explosives (HE) can give rise to either violent reactions or harmless fracture and material dispersal. Predicting this response or the state of damage in the material remains an unsolved technical challenge. In situ mesoscale insights to anisotropic dislocation-mediated plasticity, phase transitions, and damage are needed to quantify fundamental structure-property relationships, inform theory, and enable high fidelity simulations.
Laser-driven shock, gas gun, and split-Hopkinson pressure bar experiments have been performed to span multiple orders of strain rate, using synchrotron and X-ray free electron laser radiation to measure time-resolved X-ray diffraction (XRD) and phase contrast imaging (PCI) in situ for single crystal and plastic bonded explosive.
Multiphase single crystal plasticity models have been developed. They consist of non-linear thermo-elasticity, Orowan expressions for slip rate using the Austin-McDowell model for dislocation velocity, and multiphase equations of state (EOS) imposing phase transitions through Gibbs free-energy. Constitutive equations were parameterized with density functional theory and atomistic calculations for EOS and elastic constants along with experimental measurements of anisotropic deformation mechanisms and rates. These models are capable of predicting anisotropy, grain size, and pressure dependent effects remarkably well.
Combining the new capabilities, mesoscale thermomechanics can be investigated from the average lattice response up to PBX microstructures. For the first time, XRD quantify average lattice response and allows for direct comparison of experiments and simulations through measured and computed diagnostics. Using the experimentally validated models, simulation can be compared to PCI of heterogeneous micorstructure effects such as void collapse and grain boundaries.
