Shock-induced subgrain microstructures as possible homogenous sources of hot spots and initiation sites in energetic polycrystals

The purpose of this work is to assess the feasibility of a homogeneous—or defect-free—initiation mechanism for high energetic materials in which initiation is a direct consequence of the heterogeneity of crystal plasticity at the subgrain scale. In order to assess the feasibility of these mechanisms, we develop a multiscale model that explicitly accounts for three scales: i the polycrystalline structure at the macroscale, ii singlecrystal plasticity—including subgrain microstructure formation—at the mesoscale, and iii chemical kinetics at the molecular scale. An explicit construction gives the effective or macroscopic behavior of plastically deforming crystals with microstructure, and enables the reconstruction of optimal microstructures from the computed macroscopic averages. An intrinsic feature of the optimal deformation microstructures is the presence of highly localized regions of plastic deformation or slip lines. Temperatures, strain rates, and pressures in these slip lines rise well in excess of the average or macroscopic values. Slip lines thus provide a plentiful supply of likely initiation sites, or hotspots, in defect-free crystals. We have assessed this initiation mechanism by simulating a PETN plate impact experiment and comparing the resulting predictions with experimental pop-plot data. The computed characteristic exponents are in the ballpark of experimental observation.