Solid Explosives Research Articles

Investigation of shear stress on a shock front in solid high explosives (HE)

This article gives results of an experimental investigation of the dependence of the critical shear stress at the shock front in cast TNT and in a cast TH 50/50 composite on the magnitude of the shock compression pressure in a range to 4.0 GPa (e.g. to the beginning of excitation of the explosive transformation). The principal stresses were measured by manganin sensors located in the high explosive under investigation in two mutually perpendicular directions in the tests. Stationary shocks were produced in the explosive specimens under investigation by using an explosive apparatus of the ''laminate'' type. It is determined that the magnitude of the shear stress grows linearly for the cast explosives investigated as the pressure grows, and exceeds considerably the static values of the shear strength.

A microscopic theory of compressive wave-induced reactions in solid explosives

A simple physical model is developed for the interaction of molecules with compressive waves in condensed explosives. Multiphonon excitation of the internal vibrational levels of the molecules is shown to be possible and to exceed thermal dissociation rates. A calculation of the threshold condition for which a self-sustaining reaction can occur is given.

Chemical energy release in self-sustaining detonation waves in condensed explosives

The nonequilibrium Zel'dovich-von Neumann-Doring (ZND) model of a one-dimensional detonation wave is applied to condensed phase (solid and liquid) explosives in this paper. In condensed explosives, the detonation wave is assumed to consist of four main zones: a narrow leading shock wave; a much thicker induction zone in which the intra- and intermolecular vibrational degrees of freedom rapidly equilibrate and the rate-determining endothermic bond-breaking reaction then proceeds at a rate governed by the equilibrium von Neumann spike conditions; a narrow chemical reconstitution zone in which the unreacted explosive rapidly decomposes and recombines into highly vibrationally excited reaction products; and another thick relaxation zone in which the reaction products expand and approach thermal equilibrium at the Chapman-Jouguet (CJ) state. Gruneisen-type equations of state are used to calculate the energy release in several condensed explosives at various initial densities. Along with kinetic and chemical energy release, the release of potential or cold compression energy in the exothermic chemical reconstitution and vibrational deexcitation zones sustains the leading shock front. The conditions for amplification of transverse pressure waves in the zone of highly vibrationally excited reaction products are shown to exist for condensed explosives. The effects of the resulting complex cellular structure of detonation waves on the energy release in homogeneous (liquid) and heterogeneous (solid) explosives are qualitatively discussed.

Effect of initial particle size on the DDT of pressed solid explosives

AbstractThe effect of the initial particle size on the deflagration to detonation transition (DDT) of pressed, confined explosives has been studied. The explosives examined were ground tetryl, RDX, picric acid, waxed RDX, and waxed HMX. The ground tetryl was studied over the range of 61%−90% theoretical maximum density (TMD); most of the rest of the comparisons were made at 70% TMD. It was found that the initial particle size (or particle size distribution) δ affected the predetonation column length ℓ, the relative time to detonation, and even the apparent mechanism of DDT. Available data in the literature in conjunction with the present results indicate that the curves ℓ versus %TMD at constant δ, and ℓ versus δ at constant %TMD both exhibit a minimum.

Simulation of detonation waves in solid explosives

Simulation of detonation waves in solid explosives

Transition from convective combustion to detonation for an aerocolloidal suspension of a unitary fuel

The need to investigate the transition of aerocolloidal suspensions of unitary fuels {solid propellants and high explosives) from convective combustion to detonation has been recognized lately in connection with safety-engineeri ng problems. Various techniques exist for the initiation of combustion and detonation of aerocolloidal suspensions. In this article we discuss the initiation of combustion by ignition without an increase in the pressure. A distinctive feature of unitary-fuel systems is the liberation of a large quantity of gaseous reaction products during the combustion process. These products form a convection front, which moves under the action of the pressure drop created in the gas liberation process, entraining new particles in the combustion process. We have previously [ 1, 2] developed an asymptotic theory of the initial stage of propagation of convective combustion in aerocolloidal suspensions, during which time the velocity of motion is strongly subsonic and the particles are still unable to be entrained in the motion of the gas. In this case the condition of uniformity of the pressure p =p(t) (or homobaricity) holds in the region of the hot gases, and the gas flow is a simple Riemann wave ahead of the convection front. Within the framework of this approach it is possible to determine the law governing the motion of the convective combustion front up to the time of formation of a weak shock in the flow. In this study we obtain a numerical solution of the problem of transition from convective combustion to detonation for act.colloidal suspensions within the framework of the complete system of equations of the mechanics of multiphase reacting media [3]. We describe the evolution of convective combustion of aerocolloidal suspensions up to the formation of a strong shock in the flow, behind which particle combustion takes place, followed by the transition of this shock into the steady Chapman-Jouguet detonation regime [4]. We note a recent attempt [5] to analyze the combustion-to-de tonation transition in a porous solid propellant under shock excitation and an investigation [6] of the transition to steady detonation in a gas-droplet medium as the result of a point explosion. Fundamental Equations; Statement of the Problem. Let us consider the planar one-dimensional motion of a monodisperse aerocolloid in the presence of a heterogeneous chemical reaction. We assume for simplification that the chemical reaction is initiated by heating of the particle surface to the dissociation temperature T s (p) and continues as an equilibrium process at a temperature equal to T s, so that all the heat admitted to the particle is used for its gasification and the chemical reaction obeys the simple equation A---B, where A and B are the symbols for the chemical elements; the thermodynamic properties of the reaction products and the gas carrier are the same, the gas is calorically ideal, and the particles are incompressible. The equations of motion of the aerocolloids under the stated assumptions have the form [2, 3]

Buildup to detonation in solid high explosives during plane shock initiation: Some comparisons

The predictions of two models for the initiation process are compared with results of experimental studies of initiation of detonation by sustained shock waves in the two high explosives, PBX-9404 (HMX-based) and PBX-9502 (TATB-based). First, critical examination of the model known as single-curve buildup is made. Several comparisons are made with experimental results for the two explosives. The model describes the observed shock trajectories moderately well, although it has some limitations. These are manifested by an examination of the relation between input pressure and distance-of-run to detonation. Second, the data are also compared with the solution for a model which assumes that the initiation process is a self-similar flow. The model can fit the experimental shock trajectory reasonably well, but difficulties are encountered in attempting to complete the solution for the entire flow field. For PBX-9404, published pressure-time profiles are examined for self-similar character. The measured profiles show substantial disagreement with the similarity model.

Phenomenological model of shock initiation in heterogeneous explosives

An ignition and growth concept is used, within the framework of a one-dimensional Lagrangian hydrodynamic code, to model the shock initiation of heterogeneous solid explosives. The leading shock wave of an initiating pulse is assumed to ignite a small fraction of the explosive at localized heated regions. These ignited regions then grow as material is consumed at their boundaries. The growth rate for a particular material is assumed to have the characteristic pressure dependence of high-pressure laminar burning experiments. Results of the model calculations are in good quantitative agreement with recent manganin pressure gage and particle velocity gage measurements of the buildup of the initiating shock front to detonation for both sustained and short duration pulses in four solid explosives: PBX−9404, TATB, cast TNT, and PETN. The predicted run distances to detonation as functions of shock pressure at various initial densities and the predicted reaction zone lengths of the fully developed detonation waves also correlate well with experimental data for these four solid explosives.

Thermal instability of the axial deformation of a plastic layer and estimation of the critical pressures of impact initiation of solid he (high explosive)

One of the conceptions of the deformation rupture of plastic bodies is based on the representation of the instability of the deformation process because of spoilage of the balance between the growth rates of the stress state of the specimen and of material hardening (see e.g., [1]). It permits the satisfactory explanation of the presence of a maximal load in the majority of tests by testing the strength under comparatively slow (quasistatic) loading rates when dissipative heating of the substance because of plastic deformation can be neglected. The deformation conditions approach the adiabatic in high-speed (dynamic) tests, hence, the case can be mentioned when the temperature of the specimen under load can be raised considerably and reaches the melting point at individual sections (principally on the slip planes). If it is taken into account that heating of the materiaI is ordinarily accompanied by a substantial increase in its plasticity, then the deduction is easiIy made that a state when the carrying capacity of the specimen becomes spontaneously diminished (its rupture sets in) can be achieved under sufficiently rapid loading conditions. In contrast to the deformational type, the rupture mechanism considered can be called thermal. However, such a classification is provisional since specimen rupture ordinarily takes place in practice because of loss of deformation stability in both the mentioned mechanisms. It should be noted that the thermal strain instability considered for the plastic material recalls, in many ways, the phenomenon of the loss of thermal stability of viscous fluid pressure flow [2] or of viscoplastic medium [3]. The question posed is related to the problem of the response of solid explosives (HE) to mechanical effects. It is known [4, 5] that the strength rupture of a HE charge by impact is the reason for its initiation under definite conditions. Briefly, the following are these conditions: the stress state in the deformable specimen should satisfy the rupture condition (strength), the pressure at the time of rupture should be so great that the melting point of the HE would reach the value of the critical temperature (resulting in an explosion). The physical meaning of the initiation mechanism of a solid HE is the development of heating loci because of dissipative heat liberation on the charge rupture planes [4-6]. In this paper, we present an approximate solution of the axisymmetric problem of thermal stability of the deformation of a thin plastic layer in the gap between solid colliding surfaces. The results obtained are used for a quantitative estimate of the magnitudes of the critical pressures exciting the explosion of solid HE under impact. Let us assume that a deformable material is chemically inert and that the dissipatable heating is distributed uniformly over its volume, where the temperature of the interlayer depends only on the magnitude of its axial deformation. To determine the stress state of the interlayer, we use the results of solving the axisymmetric problem of the deformation of a thin disc of incompressible rigidly plastic material placed in the gap between shifting rough stamps. Under conditions of developed plastic flow the pattern of the stress state of the disc is almost hydrostatic [7]. For the case of inertialess motion, the magnitude of the axial stress p averaged over the area of the disc is evaluated by the formula p = ~(Fx + l),

Evaluation of hazards from industrial activities near nuclear power plants — deterministic and probabilistic studies

Among the potential hazards which could arise from industrial activity near nuclear power plants, fires and explosions of dangerous products are of particular concern. Indeed, thermal radiation from an adjacent fire could endanger the resistance of a plant's structures. Likewise, an accidental explosion would induce an overpressure wave which could affect buildings' integrity. This paper presents the methodology developed by Electricite de France to evaluate the consequences of accidents affecting: • - Industrial facilities: refineries, chemical and petrochemical plants, storage areas, pipelines of gaseous, liquid and liquefied materials. • - Transportation routes (roads, railways, inland waterways) used to carry dangerous substances (solid explosives, liquid, gaseous or liquefied hydrocarbons). Probabilistic methods have been developed by analysis of actual accident statistics (e.g. risks induced by transportation routes) and realistic and representative accident scenarios have been set up. Five sequences have been identified: • - Formation of a fluid jet at a breach. • - Evaporation and possible formation of a liquid layer. • - Atmospheric dispersion and drift of a gaseous cloud. • - Heat radiation from fire. • - Unconfined explosion of a gaseous cloud. This paper gives an overview of the methods and the main assumptions used to deal with each sequence. Those methods, presently applied by Electricite de France, provide a coherent and realistic approach for the evaluation of the risks at nuclear power plants induced by industrial activity.

Heating and flaming of solid explosives under conditions of dry friction with abrasion

Heating and flaming of solid explosives under conditions of dry friction with abrasion

The diffraction of a planar detonation wave at an abrupt area change

Previous experimental work on the diffraction of a detonation wave at a large and abrupt area change in a tube, has shown that every system is characterized by a critical tube diameter at which quenching of the detonation occurs. Zeldovich, Kogarko & Simonov (1956) established that the critical tube diameter, for the oxy-acetylene system with varying dilution of nitrogen, lies between 500 and 700 times the one-dimensional induction zone length. Later, Mitrovanov & Soloukhin (1964) discovered that, for the same system, the critical diameter is 10 or 13 times the transverse wave spacing for a flat channel and cylindrical tube respectively. The two results are shown to be equivalent and are confirmed by further experiments in a 75 × 6 mm channel in which the flow is two-dimensional.Smoked foil and schlieren records show that, for supercritical waves, re-ignition occurs at sites along the wedge formed by the head of the expansion from the diffracting aperture and criticality is attained when the site is located at the apex of the wedge. A universal feature of re-initiation, which is also observed in liquid and solid explosives, is the sudden appearance of a transverse detonation which sweeps through the compressed, but unreacted, gas of the dissociated shock-reaction zone regime; this is signalled by the appearance of fine triple-point writing on smoked-foil records.A criterion for re-initiation is formulated by equating the critical velocity gradient which characterizes the decay of the wavefront in a cell, to that obtaining in the diffracted shock front at the head of the expansion fan; an expression for the latter is derived from Whitham's (1957) theory for non-reactive shocks. The prediction of the criterion is in good agreement with observation.

Short-duration shock-wave initiation of solid explosives

Abstract In the study of the initiation of solid, polycrystalline explosives by short-duration (thin) shock waves, several investigators have found that the relationship between initial pressure (P) and shock duration (τ) can be described with the equation P2τ = const. Different mechanisms have been proposed to explain this relationship. However, the possibility that the relationship arises from the hydrodynamics of the overtake of the shock wave by a rarefaction from the rear has not been considered. I have investigated five simple models, three analytic and two numerical models, to examine the relationship between the entry time of the rarefaction and the time of its overtaking the initiating shock wave in a solid explosive. The purpose of this study is not to define a new quantitative model, but is to explore what effects changes in the wave profile and sustained-shock parameters have on the interaction of the rarefaction and the shock front. One of the analytic models fits the experimental data for the explosive PBX 9404 exceptionally well, but the very simplicity of the analytic model argues that transit time data on fixed-length samples are not sufficient to verify a proposed model for the initiation of solid explosives by thin shock waves. The analytic models show, in a simple manner, how the sustained-shock initiation parameters can influence the thin-shock initiation. The two numerical models, neither of which are intended to model reality, could be forced to fit the experimental sustained- and thin-shock data. They also illustrate some of the additional data that will be required before a realistic model can be developed. Given a more realistic model for the hydrodynamic conditions behind the shock front, this study indicates that a model based on rarefaction overtake is apparently adequate to describe thin-shock initiation.

A separated two-phase flow analysis to study deflagration-to-detonation transition (DDT) in granulated propellant

A two-phase reactive flow model is derived and solutions are applied to the analysis of the unsteady convective heat transfer in initially packed beds of granulated solid propellant or explosives. The resulting pressure wave and flame spreading event is considered the physical process that may provide for, deflagration-to-detonation transition (DDT) in such granulated beds. Discussions are included as to the appropriate constitutive laws required to complete the hydrodynamic model. The paper concludes with a brief assessment regarding both the limitations of the model and another possible DDT mechanism.

Heat and mass transfer during an explosion in solids

Heat and mass transfer during an explosion in solids

The Propagation of Blasts from Solid Explosives to two‐phase media

AbstractThe aim of this investigation is to determine the influence of the energy release from a combustible two‐phase media on the blast wave generated by an explosive charge, during the first stages of the process. For this purpose ball charges of “Composition B” were detonated in air, in pure nitrogen containing suspended solid particles of carbon, and in pure oxygen containing particles of aluminum and carbon. The blast wave's velocity was measured in all the media using fast frame camera 300,000 f.p.s. and streak photography at 2 mm/μs. The influence of release or absorption of energy by the medium was investigated by comparing experiments done in inert media with those conducted in combustible media while other parameters are kept constant.Kozorezov's triple isentrope model was compared to the results, and good agreement is found. The article contains detailed information on the experiments and the calculations performed.

The State of the Detonation Products of Solid Explosives

AbstractThe polytropic equation, together with the detonation relations, provides practicable values for all the quantities characterizing the detonation products of solid, high explosives apart from the temperature. Its application, however, is restricted to material at absolute zero, that is to solids possessing purely potential energy. Thus polytropic detonation products have the characteristics of solids although their state of aggregation is gaseous.In fact the polytropic equation can be derived by assuming a solid under an internal, expansive pressure sufficient to break all atomic bonds. In terms of the Debye theory this represents an approximation which is valid in the absence of the thermal energy contribution from atomic vibrations. This requirement is satisfied by the detonation products of solid explosives of sufficiently high density since their heat of detonation is completely absorbed by the breakage of atomic bonds or the sublimation of the atomic lattice.The sublimation process in the course of the reaction also allows the Chapman‐Jouguet temperature of the detonation products to be determined from the equilibrium between the phases. In addition the fracture theory provides material data which assign a metallic character to the polytropic detonation products and indicate that they form a conducting plasma.

Creating an explosion: The theory and practice of detonation and solid chemical explosives

Recently in Physics in Technology we described the advances in containment of undesirable explosions. Here we look more closely at the physical phenomena of detonation and explosion, and how they can be tailored to practical advantage.

Relaxation mechanism of local heating of solid high explosives under mechanical effects

Relaxation mechanism of local heating of solid high explosives under mechanical effects

Mechanism of heating up and ignition of solid explosives due to external friction as a result of mechanical stimulations

Mechanism of heating up and ignition of solid explosives due to external friction as a result of mechanical stimulations