Low-velocity Detonation Research Articles

Bubble detonation in a channel with elastic walls

One-dimensional flow of a gas-liquid system with an active gas phase in a channel with elastic walls is investigated. The structure problem is solved, i.e., a stationary solution of the equations of the joint motion of a bubbly liquid and a membrane has been found which connects two different equilibrium states and which contains a shock with an energy release in the front. Since in the obtained solution the pressure decreases in the channel ahead of the shock, it can be used in a qualitative description of a cavitation mechanism of low-velocity detonation in liquid explosive films on an elastic carrier.

Detonation of a highly diluted explosive

Detonation of mixtures of PETN with quartz sand with a 10–30% content of the explosive was investigated experimentally. Such systems are characterized by a low pressure and detonation velocity. The mass velocities of the solid filler and gas of the detonation products were measured by the electromagnetic method. With an explosive content of more than 15% the process is carried out by the leading shock wave and on the whole is single-velocity. The effects of a two-phase state are substantial with a low explosive content.

Method for the Determination of the Critical Diameter of High Velocity Detonation by conical geometry

AbstractA critical diameter exists for both high velocity (HVD) and low velocity detonation (LVD). No relationship exists between these two diameters, however they are both dependent upon the temperature, confinement, contaminants, type of detonation and, most importantly, geometry. In cylindrical geometry, the critical diameter is determined by go/no go tests which are relatively expensive and time consuming. In this respect, there is a need for a method by which the critical diameter can be determined quickly and reliably.A relatively simple procedure which can also be performed in the field is proposed in this article where the critical diameter is determined in principle by a single test through the application of conical geometry. However, on account of “overdrive”, the values always fall below those obtained by cylindrical geometry. Metal plating is proposed as a method of indication. The results are then compared simultaneously by optical and electrical measurements. The temperature dependence of the critical diameter of the HVD of pure nitromethane was also demonstrated by conical geometry and was compared to the values of cylindrical geometry.The method was originally proposed as a joint US/German effort between Dr. Mallory of NSWC, China Lake, and Dr. Leiber of BICT. Since Dr. Mallory has recently passed away, the question is therefore open as to whether or not this test can be approved internationally.

Detonation transformations in an aerated liquid

In this work the DEGDN was obtained by the standard method [4] from diethylene glycol (pure grade) and gelled with a small quantity (3%) of KNh colloxylin (12% N). The nitromethane (PNR production) was used without additional purification: special experiments established that the critical diameter of detonation of the mixture of purified nitromethane with colloxylin (3%) is the same as that of the unpurified compound (13  0.5 mm). The degree of aeration was characterized by the "porosity" m = 1 -- ~, ~ = 0o/0, where 0o and p are the densities of the sample and homogeneous liquid. Aeration of the gelled DEGDN up to a porosity of ~0.5 was carried out by foaming it with an addition of a small quantity of OP-7 surfactant with amechanical mixer in two variants: i) with a constant number of rotations of the mixer (45 rps) and a surfactant content of -1% the starting porosity was fixed by the mixing time; 2) for constant mixing time (30 min) and a somewhat lower rate of rotation of the mixer (25-30 rps) ~he required density was obtained by varying the surfactant con=ent (from 0.04 to i.1%). In =he case of nitromethane (for which a surfactant could not be chosen) the density after gelling was varied hy introducing microspheres consisting of phenol formaldehyde resin (liquid density of 0.243 g/cm 3) 0.04 mmindiameter; conglomerates of microspheres up to 0.2 ran in size were also present. To obtain DEGDN porosity of less than 0.5 it was mixed with porous phenol formaldehyde resin with mipora. With a mipora content of 30% it was possible to obtain a mixture whose density equalled only 0.13 g/cm s (m = 0.91). Experiments on the determination of the critical diameter and detonation velocity were performed in glass tubes with walls 1 mm thick, and a charge length of up to 20 cm (in all cases not less than ten diameters of the charge). The detonation velocity was determined with the help of SFR-2 apparatus. DETONATION VELOCITY The ideal velocity and other detonation characteristics were calculated by the method of [5]. The parameters at the Jouguet point were determined by minimizing the dependence of the detonation velocity D on the pressure p on the detonation adiabat, and the composition of the products were determined by minimizing the Gibbs energy of the products, whose equation of state was determined from the collection of the most reliable shock-wave and detonation measurements. The computational results for homogeneous and porous liquids are presented in Tahie i. The dependence D(po) (Fig. i) is nearly linear. The small break in the case of DEGDN (Fig. la) at po = i g/cm 3 is linked with the formation of condensed carbon in the detonation products. For d = 16-17 mm and in a steel tube the value of D is close to the computed value. As d decreases the difference between the theory and experiment increases. For d ~ 5 mm the detonation velocity increases as p~ increases, passes through a maximum, and then decreases substantially. For Po = 1.2-1.3 g/cm ~ for DEGDN and Po = 0.95-1.05 g/cm ~ for nitromethane the process crosses over to the low-velocity detonation regime (D = 2.0-2.5 km/sec).

Self-sustaining detonation in liquids with bubbles of explosive gas

The authors have the goal of explaining the properties and conditions of excitation of detonation in relation to the value of beta and the physiochemical composition of the bubble medium. It was shown that a detonation wave propogates in the above-examined bubble systems by the mechanism of microexplosions: bubbles compressed in the pressure field expolde and send out shock waves to the surrounding liquid. These shock waves in turn compress and ignite bubbles located upstream. A similar mechanism was examined previously to describe the excitation of low-velocity detonation in liquid explosives.

Approximative quantitative aspects of a hot spot

To understand the phenomena of initiation and low velocity detonation in liquids an approximate generalized description of bubble motion is suggested. Within this framework it is essential for any detonation to have a two-phase system of high and low compressibility of the components. The dynamic activated high compressibility component (bubble or void, cluster of chemical reaction) always has a phase-locked conservative radiation loss, and in addition, dissipative losses. These force a chemical decomposition in reactive liquids, so that a pressure-coupled chemical reaction is possible. In media of poor reactivity a decoupling may also occur, and, if the radiation loss dominates, even a nonchemical “detonation”, in the sense of a shock wave amplification, becomes possible. The dissipative loss at the boundary of a bubble or void is governed by the medium's viscosity, and is, under some circumstances, the controlling factor. Questions concerning Bowden's hot spots are discussed, and another suggestion, that initiation should occur via dynamic bubble surface instabilities, is explored.

Sensitivity of nitromethane for low velocity detonation

AbstractRecently the occurrence of a low velocity detonation (LVD) in nitromethane has been demonstrated. In the present study this phenomenon has been further investigated by mapping the shock loading regime in which a stable LVD can develop. A confinement geometry has been chosen that earlier appeared to be able to sustain the LVD. A calibrated shock donor system has been used, so that loading shock strengths were known. The critical shock strengths for the occurrence of both high and low velocity detonation could thus be determined. Including LVDs, nitromethane appears to have a sensitivity comparable to that of relatively sensitive high explosives. The results also indicate that the geometries of some standard shock sensitivity tests are not fully adequate to detect an LVD in nitromethane.

Low-velocity detonations in cast and pressed high explosives

A model of low velocity detonations in charges of cast and pressed high explosives confined in metal tubes with thin walls is suggested. An analytical solution is obtained and velocities and pressures of stationary LVD waves are calculated as functions of the parameters of the wall confinement. The fraction of the total chemical energy transferred to maintain the shock wave and the average rate of reaction in the wave are estimated and the dynamics of transient predetonation processes are analysed. An explanation of the causes of the secondary shock wave formation in the transition from deflagration to normal detonations is suggested and the delay of this secondary wave is calculated and compared with experimental data.

Stability of ?low-velocity detonation? in powdered solid explosives

Stability of ?low-velocity detonation? in powdered solid explosives

Effect of the casing of the charge on the stability of low-velocity detonation in powdered trotyl

Effect of the casing of the charge on the stability of low-velocity detonation in powdered trotyl

The role of cavities in the initiation and growth of explosion in liquids

A study has been made of the growth of explosion in thin films and also three-dimensional charges of liquid explosives including nitroglycerine, nitromethane‒nitric acid mixtures, hydrogen peroxide‒ethanol mixtures and diethyleneglycol dinitrate (DEGDN). Observation was by high-speed photography at microsecond framing rates. In the thin film experiments burning was initiated at the centre of the film by the rapid discharge of a condenser across a spark gap. The transition from deflagration to much faster reaction (low velocity detonation) was found to depend on the production and collapse of cavities ahead of the reaction front. Experiments with inert liquids showed that the cavitation generated in the thin film arrange­ment was produced by a surface wave propagating on the liquid/solid interface. In other ex­periments air bubbles of chosen size were deliberately inserted into the thin films. Cavities and bubbles were observed to cause transition to fast reaction in nitroglycerine and then help sustain it by various processes, namely: (i) adiabatic collapse of cavities by pressure waves from the deflagration front; (ii) presentation, of a larger burning surface to the deflagration front as it entered the cavitated liquid, (iii) jetting during the collapse which dispersed liquid droplets in the heated cavity or produced high impact pressures. The delay before transition in nitroglycerine, and the dominant process causing it, depended on the acceleration of the deflagration front and the cavity size when the front and cavities inter­acted. Transitions did not take place in the other liquid explosives with the confinements and for the propagation distances considered. In these cases the deflagration front never accelerated sufficiently to reach cavitated liquid but always propagated into homogeneous liquid in which cavities had been ‘sealed’ by pressure waves from the front. In three-dimensional charges it was possible to propagate a deflagration front into homo­geneous liquid; the reaction then progressed throughout as a deflagration. When cavities were introduced by pre-shocking, transitions to faster reaction occurred with velocities which depended on cavity size.

The sensitisation of thin films of nitroglycerine

High speed photography techniques have been used to study the sensitising effects of air bubbles volume a few mm 3) within thin films of spark-ignited nitroglycerine. The collapse of the bubble is shown to lead to an increase in sensitivity of the liquid explosive, by (a) locally increasing the deflagration velocity and (b) generating a pressure pulse which is capable of producing hot spots at cavitation sites within the liquid. If several gas bubbles are included, cooperative effects are observed which lead to increased sensitiveness. The results support a distributed hot spot model for low velocity detonation.

Heat release in the low-velocity detonation regime

Heat release in the low-velocity detonation regime

Effect of initial temperature on the low detonation velocity in nitroglycerine

Effect of initial temperature on the low detonation velocity in nitroglycerine

The elastic wave in a thin-walled vessel and its role in relation to the low-velocity detonation regime

The elastic wave in a thin-walled vessel and its role in relation to the low-velocity detonation regime

Initiation and development of detonation as a result of the action of weak shock waves on liquid explosives

Clearly, in handling liquid explosives safely it is important to take into account, among other things, their actual physical state. Whereas for most liquid explosives the initiating pressures for simple homogeneous compression are high (60–120 kbar); in the presence of cavitation the same liquids exploded at relatively low pressures (about 0.1–10 kbar) and, in their sensitivity to waves shock, resemble (or may even be inferior to) powdered explosives (according to [16] the initiating pressure for PETN at a density of 1.0 g/cm3 is 2.5 kbar). Under favorable conditions, especially if the vessel is capable of conducting elastic disturbances, the development of explosion in liquids leads to a low-velocity detonation which may subsequently resolve into normal detonation. In this respect, the propagation of low-velocity regimes in liquids is very similar to the propagation of low-velocity detonation in powdered explosives. Our present lack of definite ideas, about the specific reaction initiation mechanism associated with the collapse of cavities in liquids places considerable diffculties in the way of any quantitative analysis of the experimental data on the excitation and propagation of explosions.

Low-velocity detonation of cast explosives

Low-velocity detonation of cast explosives

Low-velocity detonation of powdered explosives

Low-velocity detonation of powdered explosives

Low-velocity detonation of cast charges of TNT and DINA

Certain liquid [1-4], plastic [5], a n d i n low-density chargespowdered [6] explosives are capable under certain conditions of so-called low-velocity (1-2 km/sec) detonation, which differs significantly from ordinary high-velocity detonation with respect to the mechanism of initiation and propagation of the reaction in the detonation wave. This paper describes experiments in which stable lowvelocity detonation was also obtained in cast charges. The experiments were performed on TNT and (to a lesser degree) on DtNA in the form of cast charges in steel (St. 3) tubes 7-15 mm in inside diameter, 16-36 mm in outside diameter and up to 300 mm long. Explosive heated 10 ~ ~ above the melting point was poured into a preheated tube and, as it cooled, melt was added to the shrink hole. In some experiments the charges were prepared separately by pouring explosive into a metal mold or glass tubes, usually cooled with water. The charges obtained had a density of 1.57-1.61 g/em s (TNT), were free of visible cavities, pores and other inhomogeneities, and usually consisted of radially oriented needlelike erystats up to 7 mm long and about 0.8 mm thick. As initiators we used ED-8-56 and ED-202 electric detonators, and also a mixture of fine RDX and sodium chloride (average particle size about 8~ forRDX and 0.2 mm for the NaC1)placed in glass tubes 3 1 cm in diameter and 5 cm long. At a density of 1.3-1.4 g/era the detonation velocities of this mixture were 1.3, 2.2, 3.4, and 4.8 kin/see for RDX contentsof 1O, 20, 30, and 40 percent, respectively. The process was photographed and the detonation velocity determined by means of an SFR-2 high-speed photorecorder using tubes with radial holes 2-3 mm in diameter drilled in the walls at intervals of I-3 era.

The structure of low-velocity detonation waves

In an attempt to clearly define the structure of low-velocity reaction waves, a number of liquid explosives known to undergo low-velocity detonation were examined using both high-speed photography and flash radiography. Owing to experimental limitations, low-velocity detonations could not be induced in all of the systems investigated. However, near sonic and supersonic reactions were observed in all the explosives investigated. When the reactions were clearly supersonic, the leading edge of the reaction zone consisted of a gradually curved shock front, concave in the direction of propagation, followed by an apparently unperturbed region. Behind this region, pockets of lower X-ray absorbency developed throughout the body of the fluid; undoubtedly, these pockets were reacting cavities in late stages of growth. Thus, these observations offer support for a previously postulated model for low-velocity detonation. The radiographic observations also indicate that fluid cavitation may play an essential role in the propagation of subsonic reactions.