Jetting formation of the explosively loaded powders

The formation of jet-like structures is widely reported in the explosive dispersal of powders surrounding high explosive charges. The jetting of powder beds initiates upon the shock wave reaches the outer edge of the charge. Opposed to the interface instability theory, a hollow sphere based bulk fragmentation model is established to account for the jetting of powders. A two-phase process, namely the nucleation and free expansion of hollow spheres, corresponds to the unloading process of the powder compact caused by the rarefaction waves which governs the fragmentation of the powders. The separation between adjacent hollow spheres dictates the size of the particle clusters, which would evolve into particle jets in later times. The predicted breakup time and the size of particle jets agree well with the experimental results. The increased moisture content in powders results in an increased number of particle jets. This moisture effect can be understood in light of the varied energy distribution due to the incompressibility of the interstitial liquids trapped inside the inter-grain pores. The portion of shock energy which is not consumed in the shock compaction of the wet powders would be dissipated through the viscous shear flows during the unloading of the wet powder compact. The excessive viscous energy requires to activate more localized shear flows, accordingly leading to an increased number of particle jets.