X-ray Phase Contrast Imaging of the Impact of a Single HMX Particle in a Polymeric Matrix

A complete understanding of the mechanisms by which high explosives (HEs) are shock initiated, especially at the particle scale, is still in demand. One approach to explain shock initiation phenomenon is hot spot theory, which suggests that distributed energy in energetic material is localized due to shock or impact to generate the high temperatures for ignition. This study focuses on the impact response of a HE polycrystalline particle, specifically HMX, in a polymer matrix. This represents a simplified analog of a traditional polymer-bonded explosive (PBX) formulation. A light gas gun, together with high-speed x-ray phase contrast imaging (PCI), was used to study the impact response of a single particle of production-grade HMX in a Sylgard-184® matrix. The high-speed x-ray PCI allows for real-time visualization of HE particle behavior. The experiments revealed that, at impact velocities of ∼200 m s ⁻¹ , the energetic particle was cracked and crushed. When the impact velocity was increased to 445 m s ⁻¹ , a significant volume expansion of the particle was observed. This volume expansion is considered to be the result of chemical reaction within the HE particle.