The Explosive Dispersal of Heterogeneous Systems Surrounding High-explosive Charges PDF Download

Author: Bradley Marr
Publisher:
ISBN:
Category :
Languages : en
Pages :

Get Book Here

Book Description
"The explosive dispersal of a heterogeneous medium, specifically a saturated or unsaturated particle bed, surrounding a high-explosive burster charge generates a complex multiphase flow. The developing cloud of particles and/or liquid droplets tend to have a non-uniform density distribution and can lead to the formation of jet-like structures. The tendency to form these jets in the dispersal of an unsaturated system has been seen to depend on the explosive loading and the material properties of the particles. Particles comprised of brittle ceramics or soft-ductile metals are more susceptible to forming jets, whereas particles with moderate hardness and high compressive strength are less prone to jet formation. The dominant mechanisms governing the generation of these jets has been a topic of debate amongst researchers.This thesis presents experimental and computational data supporting the theory that shock consolidation, dependent upon the characteristic material strengths of the medium, within a dispersed unsaturated particle bed is the governing mechanism responsible for the jetting phenomenon. After the formation of the consolidate, the dispersal events depend on the fracture and fragmentation of the particle shell. Mesoscale simulations using the EDEN hydrocode show that during the compaction and subsequent expansion of a layer of brittle ceramic particles, fractures emanate from the inner surface of the consolidate, propagate radially outward and bifurcate, consistent with the bimodal fragment size distribution observed in radiographic films obtained during experiments of the explosive dispersal of a silicon carbide particle bed. In contrast, mesoscale simulations of explosively dispersed ductile metal particles exhibit the typical shear and brittle fracture behaviour usually associated with the fragmentation of a metal casing, supporting the monomodal fragment size distribution observed in radiographic films from the dispersal of an aluminum particle bed. In addition to the main topic concerning the dispersal of an unsaturated particle bed comprised of a single particle type, two supplementary, closely-related problems are examined: (i) the explosive dispersal of unsaturated binary mixtures, and (ii) the explosive dispersal of saturated particle beds. The explosive dispersal of binary mixtures, containing both “jetting” and “non-jetting” particles, produces a particle cloud with features consistent with the superposition of the behaviour observed during the dispersal of the individual components. The effect of the particle bed configuration on the superposition behaviour is examined in the binary mixtures, by varying the volumetric ratio of the two types of particles and the charge loading. In saturated particle beds, the effects of heterogeneous cavitation at particle-liquid interfaces are examined through varying the morphology of the particles in the charge. Estimates of the initial velocities of the dispersed particle layers are also obtained from high-speed video records of the experimental tests. These results are compared with both the classical and porous Gurney models, and reasonable agreement is observed between the models and the experimental results, within the error estimates of the experimental velocities"--