Effect of Crystal Size on the Failure Mechanics of Polymer-Bonded Explosives

Polymer-bonded explosives (PBXs) contain explosive crystals bonded together by a polymeric binder and are widely used in extreme loading conditions such as rocket propellants and explosive munitions because of their high performance and low sensitivity. PBXs typically constitute 80–95% of energetic crystals and 5–20% of a soft polymer binder. The particle size of crystals has a significant effect on the mechanical properties of most polymer particulate composites. In this paper, the effect of particle size on the deformation behavior of PBX under dynamic loading is investigated. This study involves testing polymer-bonded sugar (PBS) samples, a well-known mechanical simulant of PBXs, with four different crystal sizes – coarse, intermediate, fine, and superfine – with corresponding crystal sizes of 600–850 μm, 425–600 μm, 212–425 μm, and 100–212 μm, respectively. A dynamic compression load is applied to these samples using a split Hopkinson pressure bar (SHPB). The macroscale and local dynamic deformation of the samples are captured by taking a series of images of the samples as they deform using a high-speed camera. From the macroscale experiment, it was observed that as the crystal size increases from superfine crystal size to coarse crystal size, the ultimate compressive stress of the PBS decreases. The mesoscale experiment shows that the local von Mises strain field of PBS for different crystal size specimens is different. The von Mises strain field in higher crystal size specimens such as coarse crystal size specimens is highly localized in the polymer-rich regions while more dispersed across the specimens with lower crystal size, particularly superfine crystal size. This study would give an in-depth knowledge and understanding of how the crystal size affects the deformation mechanics of energetic and other particulate polymer composites.