Particle segregation during explosive dispersal of binary particle mixtures

Abstract

Abstract. The explosive dispersal of a layer of solid particles surrounding a spherical high explosive charge generates a turbulent, multiphase flow. The shock-compacted particle layer typically fractures into discrete fragments which move radially outwards on ballistic trajectories. The fragments shed particles in their wakes forming jet-like structures. The tendency to form jets depends on the mass-ratio of the particles to explosive and the type of particles. Brittle or soft, ductile particles are more susceptible to forming jets during compaction and dispersal, whereas particles that are comprised of material with moderate hardness, high compressive strength and high toughness are much less prone to forming jets. Experiments have been carried out to determine the degree of particle segregation that occurs during the explosive dispersal of a uniform, binary mixture containing both "jetting" (silicon carbide) and "non-jetting" (steel) particles with various mass fractions of each particle type. During the dispersal of mixtures that contain predominantly non-jetting (steel) particles, the steel particles form a stable layer whereas the jetting (silicon carbide) particles rapidly segregate and form jets which are confined within the shell of steel particles. As the fraction of silicon carbide particles increases, the jet structures dominate the particle motion and the steel particles are entrained into the jet structures.

Explosively driven hierarchical particle jetting

“…10(b)). It has long been suspected that it is the localized densification during the shock interaction that is responsible for the fragmentation of the particle shell and the ensuing particle jetting (Frost et al, 2017a(Frost et al, , 2017bLoiseau et al, 2018). Nevertheless our simulations which don't take into account of thermal effects find that the shock compaction doesn't necessarily lead to the non-trivial localized densification.…”

“…Extensive experimental observations via either high-speed photography or radiography all elaborate that the formation of the explosively driven particle jetting occurs on the timescale of shock interaction (Milne et al, 2010;Milne et al, 2014;Ripley and Zhang, 2014;Frost et al, 2017a;2017b;Loiseau et al, 2018;Pontalier et al, 2018). Thus it is of essence to understand how the particle layers evolve while being subjected to multiple shock and rarefaction waves related with the detonation of the confined explosive.…”

“…Previous experimental studies argue that it is a certain form of shock consolidation (sintering) resulted from the primary shock interaction with particles that leads to the brittle fracture of the particle shell upon the release of the rarefaction wave (Loiseau et al, 2018;Frost et al, 2017b;2017a). This hypothesis is schematized in Fig.…”

“…Particle jetting during the explosive or shock dispersal of particles has been widely observed in nature and many military applications, such as volcanic eruption (Kieffer, 1981), explosion of landmines (Rigby et al, 2018), thermobaric explosion (Ritzel et al, 2009;Bai et al, 2018), high-speed intruder striking granular media, and particle jets impacting targets (Shi et al, 2017;Huang et al, 2010), etc. A typical configuration involves particle rings or shells dispersed by the explosion of central charges (Milne et al, 2010;Ripley et al, 2011;David et al, 2012;Xue et al, 2013;Milne et al, 2014;Ripley and Zhang, 2014;Frost et al, 2017aFrost et al, , 2017bBai et al, 2018;Loiseau et al, 2018;Pontalier et al, 2018;Marr et al, 2018). The resultant expanding cloud of disseminated materials comprises of large particle agglomerates which rapidly protrude to finger-or spike-like particle jets as shown in Fig.…”

“…The Rayleigh-Taylor instability (and other hydrodynamic instabilities such as Richtmyer-Meshkov or Kelvin-Helmholz) has been excluded as a possible candidate owing to the inconsistence between the theoretically predicted characteristic timescale and that derived experimentally (Milne et al, 2010;Milne et al, 2014;Ripley and Zhang, 2014). Loiseau et al (2018) and Frost et al (2017b) conjectured a brittle fracture model which is based on the assumption that the explosive shock compaction of particles is so strong that intense particle bonding (sintering) enables the particles achieve near solid density. Although this argument is seemly supported by the aluminum fragments collected after the explosive dispersal of aluminum powder layer (Frost et al, 2017a), it is quite contentious to apply this model to the particles with high melting temperatures during quite short shock passage duration.…”