Deformation mechanisms and shock propagation in polymer particulate composites: Experimental study based on high speed visual and infrared imaging

Polymer bonded explosives are a class of polymer particulate composites with 80-95 % crystal and 5-20 % polymer binder by weight. The experimental study to understand the failure mechanism of such materials has been challenging due to the material's multiscale and heterogeneous deformation nature. Recently, using high-speed imaging, the shock propagation and deformation mechanisms at different loading conditions have been investigated. In this work, polymer-bonded sugar, a known mock material for polymer-bonded explosive, is subjected to impact loading, and its deformation mechanism and shock propagation characteristics are investigated. Different particle sizes and mass fractions are considered, and their effect on the deformation mechanism is investigated. It was shown that the crystal size affects the mechanical response in PBS; when the crystal size increases from 150 μm to above 650 μm, the ultimate compressive stress of the PBS decreases by 17 %. We also found that force chains are responsible for localized stress concentration in the material under impact loading, demonstrated by fracture of the crystals along the chain line. The nature of shock propagation in PBS was observed to be dissipative and can be associated with frictional heat dissipation caused by the fracture surface and crystals and the viscoelastic deformation of the polymer binder. The model composite's local temperature and deformation evolution reveal that the high relative movement between the crystal and the binder causes the highest local temperature rise. The temperature rise due to the relative movement of crystals and binder could be as high as four times higher than the temperature associated with other mechanisms such as the deformation of the binder, crystal fracture, and relative sliding of the fractured crystals.