Raafat H. Guirguis

Ignition due to macroscopic shear

The energy dissipated by macroscopic shear when a thin explosive sample is squeezed between two parallel planes is quantified for a variety of boundary conditions and constitutive models. The viscous fluid model predicts the localization of energy dissipation near the edges, where ignition is usually observed.

Penetration Resistance in Granular Materials With and Without Fluid Injection

Investigating the different factors affecting the resistance of earth materials to penetration is important to both commercial and military applications. Friction and resistance to deformation are involved, but this paper focused on friction and the effectiveness of reducing it by injecting a fluid at the interface with the penetrator. Measurement of the coefficient of friction between Teflon or granular materials under pressure and a hardened steel surface are presented for sliding velocities between ∼0.01 m/s and ∼30 m/s. Pressures above and below the crushing strength of the grains were considered. Two types of granular materials were tested—sand and glass beads, the latter a model material that allows a highly uniform bed of particles. Measurements with dry beds were compared to those with a fluid injected through the sliding steel surface.

EFFECT OF PHASE TRANSITIONS OF INERT ADDITIVES ON DETONATION PROPERTIES OF POROUS EXPLOSIVES

One‐dimensional (1‐D) calculations are used to investigate the effect of phase transitions of chemically inert additives on the detonation properties of porous explosives. A shift in detonation velocity occurs when the initial density exceeds a threshold value at which the resulting pressures in the reaction zone correspond to a polymorphic phase transition of the additives. Phase transitions causing an increase (or decrease) in volume yield a positive (or negative) shift in velocity, that is augmented (or diminished) if the transition is exothermic (or endothermic).

Effects of late chemical reactions of the energy partition in non‐ideal underwater explosions

The bubble oscillation and the pressure pulse induced in the water due to the underwater detonation of nonideal explosives are calculated. In non‐ideal explosives, a substantial amount of energy could be released after the Chapman‐Jouguet surface, often after the bubble has expanded a few times the original charge size. The calculations were performed using a modified version of DYNA2D hydrocode in which a time‐dependent Jones‐Wilkins‐Lee equation of state was introduced in order to account for this late energy release. The effect of delaying the energy release on how the explosive chemical energy is partitioned between water and bubble is obtained.

Role of Radiation in Surface Burning of Melt Cast TNT

A thick pyrolysis zone regression model was developed to describe radiation driven surface burning of translucent homogeneous explosives and propellants. Radiation from the luminous flame penetrates deep beneath the surface and starts pyrolysis to an intermediate gas phase at randomly distributed germ nuclei. Pyrolysis is completed at the surface where the remaining porous solid is exposed to the decomposition products. The resulting gases then chemically react in the flame zone above the surface and release their energy. When radiation is dominant instead of conduction, the rate of regression mostly depends on the flame temperature, not the pressure.

MUNROE/CHANNEL EFFECT AND WEAK DETONATIONS

The detonation structure in tubular explosives is calculated. In these, a shock propagates through the air in the channel and ignites the explosive ahead of the detonation in the annulus, producing a weak detonation. If the channel is blocked, the shock reflection at the end of the cavity initiates forward and backward detonation waves that consume the explosive faster. In weak detonations, a plateau separates the Taylor wave from the front. In multiple-cavity tubular explosives, the pressure peaks resulting from detonation wave collisions oscillate around this plateau.