Characterizing dynamic failure around shock-loaded voids via high-speed x-ray imaging and digital image correlation

Dynamic collapse of voids plays a key role in hot spot formation and the shock-to-detonation transition (SDT) in energetic materials. To better understand the dynamic material response which leads to hot spot formation, here we quantitatively characterize the kinematic fields around collapsing cylindrical holes under extreme loading conditions (i.e., high pressures and strain rates). PMMA and sucrose (which is a common energetic simulant) were subjected to impact induced shock wave loading; the subsequent dynamic pore collapse was observed with x-ray phase contrast imaging (PCI) at synchrotron x-ray facilities. Digital Image Correlation (DIC) was employed to extract the dynamic displacement and strain fields at micron resolution in space and sub-microsecond resolution in time. Experiments explored the transition between the strength dominated and hydrodynamic regimes of pore collapse, producing a variety of phenomena such as shear cracking, jetting, secondary shock waves, and hydrodynamic vortex formation. To provide further insights into the phenomena, thermomechanical simulations have been carried out through both a Lagrangian approach as well as using the Multi-Component Flow Code (MFC), which is an Eulerian multi-component, multi-phase, and multi-scale compressible flow solver. Thermomechanical models are calibrated by the experimental data. Successful comparison of the model predictions and experimental observations allows the models to be extended to finer length and time scales that are not experimentally accessible at present.