Shock induced pore collapse in energetic material simulant: Sucrose

Pore collapse under shock wave loading is considered to be one of the primary mechanisms of hotspot formation, which leads to ignition and shock to detonation transition (SDT) in energetic materials. In this study, X-Ray phase contrast imaging (XPCI) is employed to observe cylindrical pore collapse in sucrose when subjected to shock loading. Experiments were conducted at the European Synchrotron Radiation Facility (ESRF), France at the ID19 beamline. An imaging system consisting of three high speed cameras was used to record the subsurface time evolution of several phenomena, including cylindrical pore collapse, jetting, vortex generation and crack formation. A single-stage gas gun was used to generate shock pressures between 0.5 GPa and 6 GPa in the sucrose samples. Shock Hugoniot of sucrose was extracted from digital image correlation (DIC) analysis of the X-ray phase contrast images. In the case of vortex structures, simulations indicate that the post-collapse flow is influenced by shear strength, even though the collapse itself is predominantly hydrodynamic. This allows strength to be inferred at high pressures. Since these phenomena are controlled by dynamic strength of the material, they offer a promising approach to indirectly infer it.

Numerical simulations are performed to capture the shock velocity and observed phenomena such as jetting and vortex formation. Lagrangian finite element analysis using Abaqus proved to be inadequate for simulating such extreme events due to excessive mesh distortion. We conducted numerical simulations using the open-source code MFC, an Eulerian multi-component, multi-phase, and multi-scale compressible flow solver. A complete Mie-Gruneisen equation of state is implemented to model the volumetric behavior. The Johnson-Cook model is used to capture the viscoplastic deviatoric response of sucrose. The model accounts for specific heat variation over the temperature range, enhancing temperature prediction accuracy over the constant specific heat assumption. The MFC simulations reveal that the vortex structures are hotspots with temperature rising above 2000 K. Simulations show that material strength governs shock-induced pore collapse at lower shock pressures (< 2GPa), while the equation of state dictates material behavior at higher shock pressures.