Low-velocity Detonation Research Articles

Investigation of low detonation velocity emulsion explosives

Emulsion explosives (EEs) with detonation velocity up to 2–3 km/sec are considered. The compositions contain a large amount of hollow glass microspheres. Examples are given of the use of low detonation velocity EEs to clad metal plates with foils up to 0.1 mm thick and to weld a small-diameter tube to a steel collar in a parallel explosive welding arrangement.

Study on low velocity detonation phenomena in Nitromethane

In detonation of an explosive, there are two forms, high velocity detonation (HVD) and low velocity detonation (LVD). For example, it is known that the detonation velocities of methyl nitrate are 6700m/s in HVD and 2500m/s in LVD. In a liquid explosive, the highest pressure of LVD changes with the type of explosive and conditions, is a few GPa and has destructive power equivalent to HVD. It is important also for security to get to know the actual condition of LVD. Moreover, it is important that the performance of explosives is completely understood to control HVD, LVD, and deflagration, and to predict the behavior of the explosive.

Physical model of low-velocity detonation in plasticized HMX

A physical model of low-velocity detonation in plasticized HMX is considered. In this model, a low-velocity detonation wave is a combination of a weak leading shock wave and a subsequent compression wave. This combination is formed by the simultaneous effects of energy release and spreading of the reacting medium. The main features of low-velocity detonation observed in experiments are reproduced in two-dimensional calculations.

Detonation Behaviors of Nitromethane with Various Initiating Shock Pressure

Some liquid explosives have two different detonation behaviors: high velocity detonation (HVD) or low velocity detonation (LVD). The detonation behavior depends on the level of the initiating shock pressure. The detailed structure of LVD in liquid explosives has not yet been clarified. A physical model was proposed that LVD is not a self-reactive detonation, but rather a supported-reactive detonation from the cavitation field generated by precursor shock waves. In this study, high-speed photography was used to investigate the detonation behavior of nitromethane (NM) with the various initiating shock pressures. Stable LVD was not observed, only transient LVD was observed. A very complicated structure of LVD was observed: the interaction of multiple precursor shock waves, multiple oblique shock waves, and a cavitation field. Multiple shock waves propagating in non-detonating NM were observed for shock pressures below the range required for LVD, while above the LVD range HVD was observed.

Gas detonation in a channel with transverse ribs

Results of experiments on detonation propagation in a rectangular horizontal channel with high ribs on the lower wall are presented. The experiments were performed with acetylene-oxygen mixtures. An interval of initial pressures is found, in which low-velocity detonation with a steady velocity of 0.38–0.55 of the Chapman-Jouguet velocity without losses exists. This detonation wave is a system consisting of a shock wave and a flame. Owing to gas outflow to the layer occupied by the ribs, the flame is maintained at a constant distance from the shock wave, which is approximately equal to the free transverse size of the channel. This distance weakly decreases with increasing initial pressure and is almost independent of the burning rate of the gas at standard temperature.

Energy release of mixed explosives during propagation of a nonideal detonation under conditions similar to the operation conditions of a blasthole charge

Detonation experiments were performed in a specially developed explosive device simulating a blasthole using charges of fine-grained and coarse-grained (granular) 30/70 TNT/ammonium nitrate mixtures of identical density 0.89 g/cm3 in steel shells with an inner diameter of 28 mm and a wall thickness of 3 mm at detonation velocities of 4.13 and 2.13 km/sec, respectively. Despite significant differences in detonation velocity (pressure), identical expansion of the charge shells was observed. On the other hand, numerical simulations of detonation propagation in the explosive device with the corresponding velocities ignoring the possibility of energy release behind the shock front show that the expansion of the charge shell is always greater in the case of a high-velocity regime. It is concluded that under the conditions simulating detonation propagation and the work of explosion products in a blasthole, effective additional energy release occurs behind the low-velocity (nonideal) detonation front.

A Detonation Model of High/Low Velocity Detonation

AbstractA new detonation model that can simulate both high and low velocity detonations is established using the least action principle. The least action principle is valid for mechanics and thermodynamics associated with a detonation process. Therefore, the least action principle is valid in detonation science. In this model, thermodynamic equilibrium state is taken as the known final point of the detonation process. Thermodynamic potentials are analogous to mechanical ones, and the Lagrangian function in the detonation process is L=T−V. Under certain assumptions, the variation calculus of the Lagrangian function gives two solutions: the first one is a constant temperature solution, and the second one is the solution of an ordinary differential equation. A special solution of the ordinary differential equation is given.

Analysis of Explosive Bonding Parameters

Tantalum liners have been successfully bonded to the inside surface of an M242 Bushmaster barrel using a low-detonation velocity explosive. This report examines the governing equations of the explosive bonding process as they apply to this particular situation. The relevant properties of other high-strength tantalum alloys are investigated to see if they are suitable candidate materials. Parameters under consideration are the values of critical impact pressure, the critical flow transition velocity, the critical angle for jet formation, and the maximum flyer plate velocity. Plots are provided to indicate the bounds of the parameters that will make a strong mechanical bond.

Shock synthesis and densification of tungsten based heavy alloys

Tungsten heavy alloys have been traditionally manufactured by thermal sintering were the compaction is achieved by heating under pressure the pre-compacted powders, to elevated temperatures, up to 3000 °C. Additives such as dopants are usually incorporated in the original powder mixtures in order to control the grain sizes, and mechanical properties of the sintered microstructures. This process is capable of producing high-density tungsten heavy alloys but has its own limitations. Shock induced synthesis (SIS) and shock compaction (SC) or dynamic compaction (DC), are processes used for the manufacture of advanced materials. In shock synthesis high detonation velocity explosives are used for the synthesis, whereas in shock compaction low detonation velocity explosives, elevated temperatures and prior coating of the powders are used to generate the shock waves required for optimal densification. Due to the high shock wave velocity, the temperatures within the capsule raise above the melting points of some or all the elements present in the powder mixtures. The liquid mixtures are then quenched in microseconds, which results in novel phases. Shock compaction offers the possibility of producing high temperatures necessary for strong metallurgical bonding within the particle surface regions where they are most required, while the internal powder mass, within the particles remain at relatively lower temperatures. A novel approach for producing dense and fine grain tungsten heavy alloys has been investigated. This approach combines reaction synthesis and dynamic consolidation. By combining these two processes tungsten heavy alloys with 98% of the theoretical density have been produced. In this work four tungsten–iron–nickel heavy alloys and one tungsten–copper–nickel heavy alloy were manufactured by shock synthesis and densification. The elemental powders were mixed and pre-compacted at 20 °C by packing them in cylindrical steel capsules of 25 mm diameter. Ammonite with a detonation velocity of 3.6 km/s was used as the main explosive. The samples were preheated to temperatures between 300 and 1000 °C before the application of the shock wave. The specimens were then characterized by optical microscopy, SEM analysis, EDS quantitative analysis, quantitative image analysis, X-ray diffraction, hardness and microhardness testing. This paper will discuss the effects of the shock parameters on the microstructure and strength of these five tungsten heavy alloys and compares the results obtained with those of alloys of similar compositions manufactured by thermal sintering.

Simulation of explosive welding using the Williamsburg equation of state to model low detonation velocity explosives

Explosive welding is a process for producing bi-metallic plates and tubes. Whilst well established it has been essentially an empirical process. In most welding operations, low-speed explosives such as ammonium nitrate fuel oil (ANFO) mixtures, are used. Such explosives have a low velocity of detonation with an appreciable detonation zone. The usual Jones–Wilkins–Lee equation of state (EOS) is not valid. A more representative EOS is the Williamsburg EOS. Recent work to numerically model the process is described. A notable advance is the use of the finite difference engineering package AUTODYN with a Williamsburg-type EOS to model low detonation velocity ANFO explosive and perlite mixtures. In this work, the Williamsburg EOS was coded as a subroutine in the AUTODYN software package which was then used to simulate most aspects of the explosive welding process. The computed results were validated by explosive welding trials. The phenomenon of jetting and the interfacial waves usually observed in explosive welding were successfully reproduced.

Simulation of explosive welding using the Williamsburg equation of state to model low detonation velocity explosives

Simulation of explosive welding using the Williamsburg equation of state to model low detonation velocity explosives

Pressure diffusivity and low-velocity detonation

The mechanism controlling occurrence of the low-velocity denotation in obstacle-laden systems is discussed. A quasi-one-dimensional model where the impact of obstacles is accounted for through a drag-force term is explored. It is shown that the hydraulic resistance gives rise to a powerful agency (diffusion of pressure) capable of driving the combustion wave both at fast subsonic and at supersonic velocities. The latter mode is identified with the so-called choking regime often observed in obstacle-affected detonations.

Propagation and quenching of detonation waves in particle laden mixtures

Propagation and quenching of curved detonation waves in particle laden mixtures were investigated analytically and numerically using the square wave model and quasi-steady state assumption, respectively. An analytical expression describing the combined effects of heat and momentum losses because of the interaction between the particle and gas phases, as well as the effect of wave curvature on detonation velocity, was obtained. Detonation quenching and multiple detonation regimes were examined. Numerical simulation of the detonation wave structure was also made. The results showed that particle heat loss, momentum loss and wave curvature considerably reduce the detonation speed and cause detonation quenching. It is also shown that, for fixed particle volume fractions, smaller particles cause a larger heat loss from the gas phase and result in a lower detonation velocity and narrow detonation limit.

Deformational structure and properties of Cu-Mo explosive compacts

Mixtures of fine powders of copper and molybdenum were subjected to ball milling before shock-wave consolidation. The degree of previous plastic working by milling was varied by varying the milling time. The shock-wave pressure was varied by using different explosives. The microstructure, conduction and porosity of the resulting compacts were investigated. The shock-consolidated powders have extensively deformed particle interiors. The characteristics of the deformed structures of each composite were studied using X-ray diffraction line broadening. It was found that the previous milling produces micro-deformation in the particles which is proportional to the milling time. Additionally, compaction using low detonation velocity explosives increases the micro-strains. With intense prior milling with subsequently higher detonation velocity explosives results in lower micro-strains. Also, crystal defects form sub-boundaries, so a dispersed sub-grain structure results. The particle bonding is improved by intense milling followed by explosive loading, this is shown by measurements of conduction.

Transient development of friction-induced low-velocity detonations

Detonation velocities as low as 20% of the Chapman-Jouguet (C-J) values are observed in tubes with a dense array of obstacles. The present study attempts to investigate these low-velocity detonations (LVDs) through the use of a friction factor to account for the momentum losses due to the interactions with the flow obstacles. The present study investigates the asymptotic approach to the LVD solution from a transient solution of a detonation initiated via a strong blast wave. Pulsating detonations are obtained asymptotically even for cases when the activation energy is below the stability limit for the case without friction. The result indicates that friction tends to increase the effective activation energy and thus renders the detonation more unstable. Following the previous studies of Zel'dovich, Gelfand et al., and so forth, it is found that the generalized C-J criterion can be used to obtain steady solutions for the detonation structure. However, below a certain velocity, the generalized C-J criterion breaks down. On the basis of the nonsteady solution, a different criterion of zero particle velocity (absolute) at the chemical equilibrium plane can be used to continue the solution further to the low-velocity regime with very high friction. However, the non-steady analysis gives highly unstable pulsation detonations with no meaningful averages that can be ascribed to these steady-state LVD solutions for realistic values of the activation energy.

Low-velocity detonation limits of gaseous mixtures

Low-velocity detonation regimes in acetylene-oxygen mixtures are studied experimentally. Data are obtained on the kinematics of detonation waves and on the boundaries of the high-velocity, galloping, and low-velocity detonation regions. In lean mixtures, the lower pressure limit for the detonation regimes in narrow channels is found to be an order of magnitude lower than assumed previously under the assumption that the limiting detonation is always spin detonation. The major structural characteristics of low-velocity detonations are calculated. The boundary between low-velocity and galloping detonation is found to correspond almost exactly to equality between the induction time in a particle and the time for it to move from shock wave to flame. Nearly harmonic oscillations of the flame are observed with periods that are related to the longitudinal size of low-velocity detonation waves.

The double explosive layer cylindrical compaction method

The standard cylindrical configuration for shock compaction is useful for the compaction of composite materials which have some plastic behavior. It can also be used to densify hard ceramics up to about 85% of the theoretical density (TMD), when low detonation velocity explosives (2-4 km s-1) are used. In order to attain higher densities, higher pressures will be needed. With the aid of computer simulations, it is shown that this can be realized without the risk of tensile rarefaction waves, by using two layers of explosives having different detonation velocities. This method has already resulted in a homogeneous B4C compact (87% TMD). After infiltration with Al, a B4C composite having a hardness ranging from 15 to 18 GPa could be obtained with this method. © 1999 Elsevier Science S.A. All rights reserved.

The Normal Detonation Shock Velocity–Curvature Relationship for Materials with Nonideal Equation of State and Multiple Turning Points

We present a model and a simple-to-implement numerical procedure that obtains the normal detonation shock velocity (Dn)–curvature (κ) relationships for an explosive material with nonideal equation of state and an arbitrary reaction rate law. In addition we illustrate numerically (for a nonideal equation of state) and analytically (for an ideal equation of state with a large activation energy rate law) that for sufficient rate-state–sensitive explosives, the corresponding Dn, κ-response curve can have two turning points, at Dn, κ,-pairs [(Dn)1, κ1], [(Dn)2, κ2], such that κ1 > κ2 > 0 for DCJ ≥ (Dn)1 ≥ (Dn)2, and such that the curve has a Z-shape. The top branch of the Z response curve has been previously associated with detonation extinction at a critical curvature. The bottom branch can be possibly associated with low-velocity detonation and rapid change from low-order detonation to high-order.

Can Snake Oils Become Panaceas?

At just about any time during the course of recent history, in the "oil patch," there have been processes or "technologies" which for one reason or another did not fit the paradigm of the time, and in many cases were branded as radical, extreme, unwarranted or even dangerous, as they had not either been sufficiently developed or tested to everyone's satisfaction. In many cases, some were even considered "snake oil," as they seemed to work, but no one could say why, and in many cases the results were short-term or not at all. And so it goes, in the ever present struggle by producers to increase field productivity. So many possibilities, all of which would take a part of the profits from current production, while promising future increases. For many of these technologies, success and acceptability came from the acceptance of the process by some forward thinking, established service company which decided to invest in the process, and even to improve or develop it through genuine research projects, lack of such acceptance resulted in failure and obscurity. Such is the case even today, with many applications which can and in many cases do, improve productivity substantially, using unconventional or even unorthodox methodology. In all of the problems faced daily by producers, two of the major ones in the current market are: formation/perforation damage, and waxing and scaling. Formation/perforation damage which occurs to the formation from initial drilling and fluid invasion thereby reducing effective porosities and permeabilities, or damage which occurs from perforating, such as reduced core flow efficiencies, have always been problems, which have required many different approaches in as many situations. However there now appears to be a consistent application which can help. Historically, explosive stimulation has always been treated as one of those "snake oil" methods which worked in many cases, and not in just as many, with no real way of telling where it would or would not. In too many cases, not only did it not, but many times it also caused significant and irreversible damage in the process. Little Wonder in the Lack of Faith by the Industry In recent years, however, significant scientific investigation, and improvements both in the method and materials (low detonation velocity epoxies) have significantly increased the efficiency of propellant stimulation technology. More important still, the ability to model and simulate the stimulation technique have been developed and refined, and high speed impact resistant data recorders have been developed which can measure and record the event. By simulating the event and using precisely calculated amounts of propellant, and by analysing the data recorded, an effective, repeatable stimulation can be obtained. With this sort of control and predictability, many companies have decided to use propellant stimulation, in a variety of applications, rom heavy oil perf clean up and sand-arch collapse, to prefrac treatments of sandstones and carbonates, all with a good deal of success.

Possibility of determining the velocities of turbulent and laminar flames at high initial temperatures

A low-velocity detonation regime without self-ignition is discovered in which turbulent flame is held at a distance of several channel diameters behind the leading-shock wave due to gas “suction” to the turbulent boundary layer at the tube wall. The structure of such a detonation agrees principally with the structure of low-velocity detonation in a capillary with a laminar boundary layer. Calculation results for the distance from the shock wave to the flame agree with the experimental data. It is proposed to use the experimental value of the distance to determine flame velocities in a nonturbulent shock-heated gas under conditions of extremely short ignition delays. The domains of existence of the initial pressures of multiheaded and low-velocity detonations partially overlap.