Interactions of Impact Shock Waves in a Thin-Walled Explosive Container. I. Impact by a Flat-Ended Projectile

Interaction of impact shock waves that could detonate an explosive (Composition B) confined in a thin-walled container impacted by a cylindrical projectile is numerically studied, based on the Forest Fire explosive reaction rate model. After the impact, rarefaction waves from projectile periphery and front cover–explosive interface catch up the forward-moving shock fronts in the explosive as well as in the projectile. At a high impact velocity, the transmitted shock front induces detonation at the front cover–explosive interface. At an intermediate velocity, the rate of energy release from the shock-compressed volume in the explosive is such that the associated effects prevail over the effects caused by rarefaction waves, leading to detonation after the shock wave travels a certain distance in the explosive. There is a range of minimum impact velocities at which the effect of rarefaction waves prevails over the energy release; hence, the detonation is excited not behind the shock-wave front moving over the explosive but only after shock-wave reflection from the high-impedance back plate. It is suggested that, in interpreting the detonation behavior of an explosive confined by a high-impedance container, one should take into account the effects of shock-wave interaction with container walls.     

Effect of explosions on material with a defect-saturated structure

The influence of an explosive load on the structure of martensitic steel and of quickly quenched and amorphous alloys, i.e., materials a with a high density of crystal-lattice defects prior to explosive loading, is considered. The stability of such structures to the action of shock waves depends on the presence of a developed system of large-angle subboundaries. If the material has a high density of dislocations prior to explosive deformation but is not organized in blocks a with disordered boundaries, explosive loading transforms the structure so that such boundaries are created, analogously to structures after large degrees a of ordinary plastic deformation.Translated from Fizika Goreniya i Vzryva, Vol. 27, No. 6, pp. 134–139, November–December, 1991     

Shock-wave configuration in air gap on oblique collision of metal plates

With the aid of a 4-frame photorecorder operating with SNEF-4 electron-optical converters, shock waves in the air gap between colliding plates were photographed. We have demonstrated that in the movement of a plate within the gap an oblique shock wave is generated, and that the interaction of this shock wave with the lower plate occurs in the form of simple Mach wave reflection. The Mach wave arm moves faster than the detonation velocity of the explosive by a factor of 1.3.Warsaw. Novosibirsk. Translated from Fizika Goreniya i Vzryva, No. 2, pp. 128–130, March–April, 1991.     

Detonation of Secondary Explosives in a Vacuum Suspension

The existence of self–sustaining detonation in an evacuated suspension of the particles of a secondary explosive is shown experimentally. The experiments with HMX were performed in a vertical shock tube of diameter 0.07 m and length 7 m in the range of volume–average particle concentrations 0.32—0.9 kg/m³. It is shown that the vacuum–detonation velocity does not almost depend on the volume–average concentration of particles and it is (1750±50) m/sec and that the pressure profile of a vacuum–detonation wave is smooth. The data on the electric conductivity of vacuum–detonation products and the length of the reaction zone are given.     

Explosive generation of heterogeneous detonation waves in aerocolloids of a unitary fuel

The process of explosive initiation of spherical, heterogeneous detonation waves in monodisperse, homogeneous aerocolloids of a unitary fuel is modeled mathematically. It is shown that regimes of decaying and detonating combustion of the reacting disperse mixtures are possible, depending on the initial mass concentration and initial particle size in the mixture. It is established that the laws governing the mass transfer of burning particles have a significant influence on the patterns of explosive generation and propagation of detonation waves in unitary fuel aerocolloids. The critical (maximum) diameter of the unitary fuel particles, below which the shock initiation of heterogeneous combustion is possible, is determined as a function of the particular value of their relative mass concentration in the mixture.Institute of Mechanics of Multiphase Systems, Siberian Branch of the Russian Academy of Sciences. Translated from Fizika Goreniya i Vzryva, Vol. 31, No. 3, pp. 83–91, May–June, 1995.     

Shock Profiles Along a Specimen

The observation of shock waves in a block of plexiglass caused by a detonating high explosive charge shows the influence of air-gaps and cover-plates which are attached head on. The shock wave for high explosive charges without any cover plate gives a high maximum pressure which decays quickly. The detonating high explosive charge which is covered with a two millimeter thick disc of copper shows a shock wave which is constant over a certain time. An air-gap between the high explosive charge and the measuring plexiglass block always gives a weak shockwave at the beginning. In the case of an uncovered high explosive charge the expansion of the high explosive products gives a relatively smooth increasing blast or shock wave, and in the case of a covered high explosive charge a strong shock resulting from the following impact of the flying plate.     

Explosion of a cylindrical charge above a rigid surface

We investigated the explosion of a cylindrical charge, which lies on a rigid surface or is positioned at some height above it. The explosion is modeled by the jump between the background and the region occupied by gas at a high pressure, density, and temperature. In an analogous formulation, the explosion from the Tunguska meteorite impact [1–4] was modeled by spherical and cylindrical explosive waves which consider the gravitational back pressure. Explosions from charges with nontraditional shapes have been studied [5–8]. Reflections of an explosive wave from a point charge from a rigid surface have been examined [9–10]. A more complete review of investigations on the spatial effects of forming propagating explosive waves can be found in [11].Moscow. Translated from Fizika Goreniya i Vzryva, Vol. 27, No. 6, pp. 131–134, November–December, 1991     

Time Dependence of the Fracture Energy of Metals in Spallation

The form of the time dependence is analyzed in the 10^–6 — 10^–13 sec range of maximum stretching stresses in spallation and at the specific (per unit surface) fracture energy on the basis of experimental spallation data for geometrically similar specimens of a number of metals and for steel (St. 3) specimens in shock rarefaction waves. Strong scale effects of power nature were observed in metals upon spallation fracture.     

Interactions of Impact Shock Waves in a Thin-Walled Explosive Container. II. Impact by a Cone-Nosed Projectile

Interaction of impact shock waves that could detonate an explosive (Composition B) confined in a thin-walled container impacted by a cone-nosed projectile is numerically studied, based on the Forest Fire explosive reaction rate model. The normal impact on the container by a small projectile with a conical nose is considered. Depending on the cone angle of the nose part of the projectile, the zone of interaction of initiating shock waves can be remote from the central axis of the impact. The off-the-central-axis detonation is interpreted from the viewpoint of different interaction modes in the explosive container, which are reflected from the cassette wall, change their directions, and superimpose onto each other, leading to explosive detonation.     

Transition from Mach to regular reflection and domains of various mach reflection configurations

Conclusions We have investigated different reflection configurations associated with the quasisteady reflection of shock waves from a plane corner in a shock tube.We have shown that a necessary condition for the inception of the transition configuration of Mach reflection and double Mach reflection is the existence of supersonic (relative to the triple point) flow behind the reflected shock wave.For strong shock waves the transition from Mach to regular reflection proceeds through the double Mach configuration. We have analyzed the transition process and proposed a strong-shock transition model.Graphs are presented, describing the inception of the various reflection configurations for shock waves in air and in nitrogen as a function of the impingent-wave Mach number and corner angle.Institute of High Temperatures, Academy of Sciences of the USSR, Moscow. Translated from Fizika Goreniya i Vzryva, Vol. 13, No. 1, pp. 102–110, January–February, 1977.     

Desensitization of pressed RDX/paraffin and HMX/paraffin compounds by multiple shock waves

Multiple shock initiation of detonation in pressed RDX/paraffin and HMX/paraffin compounds is studied. If the explosive is preshocked by a weak shock wave, the effect of desensitization is observed, which is detectable by two features. First, a weak reaction appears behind the second shock wave. Second, the run to detonation increases by 100% for pressed RDX. Experiments with the samples of pressed RDX show that the run to detonation in preloaded explosive can be estimated from the distance at which the second shock wave overtakes the first weak shock; the run to detonation expected for the second shock wave, from Pop-plot data.Novosibirsk. Translated from Fizika Goreniya i Vzryva, Vol. 31, No. 2, pp. 114–124, March–April, 1995.     

Symmetry and some cumulative phenomena during explosions in water

The general features of the development of cumulative phenomena in systems with diverging shock waves are examined. It is proposed that the latter can be converted into converging shocks for the purpose of producing cumulative effects if special shaping elements are included in the structure of the explosive device. Experimental confirmation of this proposition is presented. Symmetry is shown to play an important role in the development of cumulative effects.Scientific Research Institute of Technical Physics, 454070 Chelyabinsk. Translated from Fizika Goreniya i Vzryva, Vol. 30, No. 3, pp. 143–146, May–June, 1994.     

Initiation and propagation of detonation in dry and water-filled explosive charges of small diameter

Experiments are conducted to study the initiation and propagation of detonation in dry and water-filled detonating fuses. The structure of the detonation front is studied by electromagnetic methods and high-speed photography of luminescence at the end of the fuse. It is shown that moistening of the charge suppresses nonideal detonation regimes. Such regimes account for the sensitivity of the explosive to the formation of weak shock waves.Lavrent'ev Institute of Hydrodynamics, Siberian Branch, Russian Academy of Sciences, Novosibirsk 630090. Translated from Fizika Goreniya i Vzryva, Vol. 30, No. 4, pp. 164–166, July–August, 1994.     

The maximum effective explosive cylinder lenght in the projection of plates using opposing detonation waves

An empirical dependence is presented of the maximum effective explosive cylinder length on a number of basic factors in the projection of plates by opposing detonation waves. This dependence was obtained on the basis of experimental investigations. The obtained length may be twice the length of the limiting effective length of an explosive cylinder which is initiated only in the direction from the launched plate. In addition, a range of explosive cylinder lengths is established in which, compared to the initiation in the direction only from the plate, the opposing initiation provides a gain in plate energy by a factor of 1.3.Chelyabinsk. Translated from Fizika Goreniya i Vzryva, Vol. 28, No. 2, pp. 104–106, March–April, 1992.     

Detonation propagation in thin explosive layers with inert partitions

This paper describes the experimental results in the study of detonation transfer in thin layers of a PVV-12M plastic-bonded explosive (90% of RDX and 10% of bond) through solid and perforated partitions. The critical thicknesses of steel or Plexiglas partitions, exceeding which makes detonation transfer impossible, are determined for the explosive layers with a thickness of 2–12 mm. It is shown that shock waves in the plates, which bound the explosive charge, can stay ahead of the initiating shock wave in the passive part of the explosive charge and load the explosive charge from the lateral surface. Thus, the peripheral desensitized layers of the explosives are formed, which reduce the layer thickness of the detonable explosive and complicate the detonation transfer. Detonation transfer through the partitions whose thickness is greater than the critical thickness can be carried out with the use of holes in the partition, closed by thin plates. The plate thicknesses at which detonation propagates through the hole either in forward and reverse directions or in the forward direction only, are determined.     

The Use of Utilizable Explosives to Increase the Efficiency of an Explosion

The possibility of using the utilizable explosives to increase the efficiency of an explosion of industrial high–explosive (HE) charges is studied under laboratory and working conditions. To do this, the explosive charges were used as linear initiators of the elongated charges of industrial HE. It is shown that the placing of an NB–40 ballistite powder rod of diameter 10 mm in a bulk–density TNT charge of diameter 40 mm increases the velocity of acceleration of an aluminum shell by 14% (the ratio between the detonation velocities of the powder and TNT is 1.8 : 1.0). The use of ShZ–1 TNT–based and ShZ–2 RDX–based hose charges in well charges of industrial HE, such as 79/21 Grammonit (79% granular ammonium nitrate/21% scale–shaped TNT), 30/70 Grammonit (30% granular ammonium nitrate/70% granular TNT), and ammonium nitrate, as linear initiators leads to a decrease in the output of bulky rock by 15—20% and allows one to increase the grid of the wells of diameters 160 and 220 mm by 20—25% with preservation of the rock output. The ratio of the detonation velocities of ShZ–1 and ShZ–2 and industrial HE charges is within 1.5—1.7 in the case of 79/21 Grammonit and 2.2—2.6 in the case of ammonium nitrate. The results obtained are explained by the fact that the detonation of a linear initiator from utilizable materials changes the form of the detonation wave front of the basic charge; as a result, it arrives at the surface of an ambient medium at a large angle and a more intense shock wave enters the medium compared to the case without a linear initiator.     

Wettability of aluminosilicate refractories with molten steel

Conclusions An increase in the Al₂O₃ content of the base causes the wetting angle of steel 10kp to increase with an increase in the temperature from 1490 to 1620°C.Chromium-nickel steel wets refractories to a greater degree than rimmed steel. In this case the wetting angle is largest on mullite-corundum refractories containing 75–78% Al₂O₃.The introduction of small amounts of modifying additives in the form of MgO and Cr₂O₃+ ZrSiO₄ into mullite-corundum and corundum refractories causes the wetting angle to increase by 7–10° and helps to increase the resistance of the refractory materials to the action of rimmed steel.Translated from Ogneupory, No. 4, pp. 53–56, April, 1978.     

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.Lavrent'ev Institute of Hydrodynamics. Siberian Branch, Russian Academy of Sciences, 630090 Novosibirsk. Translated from Fizika Goreniya i Vzryva, Vol. 30, No. 3, pp. 124–130, May–June, 1994.     

Spalling Kinetics over a Wide Range of Shock-Wave Amplitude and Duration

The paper reports results of metallographic studies of specimens of St. 3 steel and M1 copper loaded by shock waves of various intensity (p 2 – 30 GPa) and duration ( 10^–6 – 10^–7 sec). The kinetics of spalling fracture of materials under these conditions is discussed. Key words: metals, shock waves, fracture, kinetics, modeling.     

Effect of Shock–Wave Loading Conditions on the Behavior of a PETN–Based Plastic Explosive

The paper reports results of investigation of the spallation and initiation of an explosive transformation in the plastic explosive formulation TP–83 under shock–wave loading. In the first case, specimens 20 mm thick were impacted by explosive driven steel plates 1.0 and 1.6 mm thick at velocities of 120—420 m/sec, and in the second case, the impact velocity was 430—580 m/sec. In addition, in the second case, specimens 5 mm thick were impacted by copper plates with a thickness of 0.10—0.28 mm accelerated to velocities of 590—1250 m/sec. The loading conditions were calculated in an elastoplastic formulation. The relationships between the loads leading to shock–induced spallation and explosive transformation of the explosive formulation are obtained and represented analytically.