Initiation Of Detonation In Explosives Research Articles

Line-imaging velocimetry for observing spatially heterogeneous mechanical and chemical responses in plastic bonded explosives during impact

A line-imaging velocity interferometer was implemented on a single-stage light gas gun to probe the spatial heterogeneity of mechanical response, chemical reaction, and initiation of detonation in explosives. The instrument is described in detail, and then data are presented on several shock-compressed materials to demonstrate the instrument performance on both homogeneous and heterogeneous samples. The noise floor of this diagnostic was determined to be 0.24 rad with a shot on elastically compressed sapphire. The diagnostic was then applied to two heterogeneous plastic bonded explosives: 3,3(')-diaminoazoxyfurazan (DAAF) and PBX 9501, where significant spatial velocity heterogeneity was observed during the build up to detonation. In PBX 9501, the velocity heterogeneity was consistent with the explosive grain size, however in DAAF, we observed heterogeneity on a much larger length scale than the grain size that was similar to the imaging resolution of the instrument.

Initiation of detonation in explosives on an U-70 proton accelerator

Detonation initiation in a composite explosive based on HMX and TATB loaded by a divergent shock wave was studied on a U-70 proton accelerator using proton radiography. Density distributions behind the initiating shock front at various times were obtained. Detonation failure due to collision of shock and detonation waves was studied for a plastic-bonded TATB sample using radiography. Characteristic features of the explosive transformation under shock-wave loading were determined from the images obtained.

Defect and surface asperity dependent yield during contact loading of an organic molecular single crystal

The onset of plastic deformation was investigated using nanoindentation in single crystals of the explosive cyclotrimethylene trinitramine (RDX). Cleavage and habit planes were tested revealing a range of yielding behaviors. Smooth habit planes of unprocessed single crystals exhibited distinct yield points near the theoretical shear strength; planes produced by cleavage yielded at lower applied stresses. Cumulative probability distributions of maximum shear stresses at yield were used to illustrate the representative yielding behavior for samples prepared by the different methods. A statistically significant difference was observed for cleavage and habit planes. This suggested that structural defects, such as dislocations from growth and sample preparation, were being probed and nanoindentation can be used to correlate the mechanical response of organic molecular crystals with defect density. This capability may help explain the observed range of measurement differences in fundamental properties in this class of materials, such as sensitivity to the initiation of detonation in explosives, and disparate tablet integrity and stability responses in polymorphs of some pharmaceutical materials.

English

This paper presents a study of initiation of detonation in explosives by the impact ofprojectiles. The shock wave produced by the impact of projectiles has been considered as thestimulus for initiation of detonation. Three types of projectiles, namely (i) flyer plate, (ii) flatendedrod, and (iii) round-ended rod or a shaped charge jet, have been considered to impact andproduce a shock wave in the explosives. Deriving relations for the parameters of impact-generatedshock wave in the explosives and projectiles, and the sound velocity in the compressed explosives,it has been shown that the difference of kinetic energy of the flyer plate before and after theimpact, which is equal to the total energy of the shock wave in the explosives, leads to criticalenergy criterion for shock initiation of explosives. In this study, the critical criterion has beenused to derive the relations for initiation of explosives by a shaped charge jet, Vj2 D = K0 , whereV j and D denote the velocity and diameter of the jet, and K0 is a constant of the explosive.

On hydrodynamic effects of exothermic power in condensed explosives

The initial flow produced in an explosive by the impulsive action of a constant velocity rear-boundary is considered to provide a better understanding of the coupling between hydrodynamic flow and chemical reaction and the shock initiation of detonation in explosives impacted by flying plates. Equations determining the initial shape of the reactive shock are derived from the equations of motion for an arbitrary specific energy-pressure-specific volume-extent of reaction equation of state and an arbitrary energy release rate. These expressions for the flow derivatives define the relationship between hydrodynamic flow and energy release rate induced by a constant velocity rear boundary, and demonstrate the dependence of the shock initiation process on the equation of state of an explosive and its energy release rate. The equations for the first derivatives show that the shock accelerates with a positive particle velocity gradient; those for the second derivatives show that the wave can develop with a positive, negative, or zero pressure gradient and account for the flows observed by Bernier, Wackerle and Johnson, and Kennedy respectively. The equation determining the pressure gradient was used to check the results of numerical studies of initiation and to determine the relationship between the pressure gradient and the initial shock pressure for a series of condensed explosives. Calculations on cast TNT, PBX9404, and Composition B based on reasonable assumptions about their equations of state and energy release rates predict that the sign of the initial pressure gradient in these explosives will change from negative to positive as the initial shock pressure is increased in a series of shock initiation experiments.

Some considerations on the mechanism of initiation of detonation in explosives

Various ways of initiating detonation in explosives (initiation by burning at various conditions, transmission of detonation over distance by the action of shock) are considered. The main cause of initiation of detonation seems to be a sudden rise in pressure, occurring when a suspension of an explosive in the gaseous products of burning is formed and exploded. Different ways of formation of such a suspension are discussed.