Fragmentation of a small celestial body entering the atmosphere of a planet

The interaction of a small celestial body passing through the atmosphere of a planet is considered. Equations of aerodynamic deceleration of the body and condition of its fragmentation are obtained. It is shown that the fragmentation is a multistep process with steps separated in space and time. The model developed allows one to estimate the number of steps in fragmentation of the body, the number of fragments, their dimensions, parameters of motion, coordinates, and energy release into the atmosphere. The model is illustrated using the examples of interaction of a small celestial body and Comet Schoemaker-Levy 9 with the Earth's and Jupiter's atmospheres, respectively. Translated fromFizika Goreniya i Vzryva, Vol. 35, No. 5, pp. 127–137, September–October 1999     

Hypothesis on the nature of the Tunguska meterorite

It is shown that all the specific features of the Tunguska catastrophe in 1908 can be explained by an explosion of a methane-air cloud which was initiated by a stony or iron meteorite whose mass was of the order of several tens of tons. The meteorite gently flied at an altitude of several kilometers with a velocity of 1–2 km/sec. A single ejection of 200 ktons of methane into the atmosphere is sufficient to form such a cloud. The meteorite fell several tens of kilometers from the epicenter of the explosion. Translated fromFizika Goreniya i Vzryva, Vol. 34, No. 1, pp. 120–122, January–February, 1998.     

Model for the Atmospheric Fragmentation and Scattering of a Small Celestial Body

This paper considers the interaction of a small celestial body with a planetary atmosphere, which is treated as a two-stage process: the first stage is the fragmentation of the parental body (a model for this stage was developed by the authors) and the second stage involves breakup and scattering of the fragments. A model for the second stage is proposed in which the breakup is treated as a two-phase process of macrodisplacement of the fragments resulting from the fracture of the parental body. In the first phase there is accelerated rotation of the fragments around their centers of mass with preservation of contact between them. By the moment the contact ceases, they acquire a transverse velocity and there comes the second phase — the dispersion of the fragments, which ends with their scattering on the ground. A feature of this model is that the breakup occurs by an aerodynamic mechanism. In an analysis of the first phase of breakup, a system of differential equations for the kinetostatics of the fragments is formulated. Calculations are performed using as an example the atmospheric breakup of the Sikhote Alin meteoroid and the scattering of its fragments on the ground. It is shown that along with the numerical method for solving the system, an approximate analytical method is also possible. Calculation results for both methods are close and are in good agreement with observations of the indicated phenomenon.__________Translated from Fizika Goreniya i Vzryva, Vol. 41, No. 3, pp. 121–132, May–June, 2005.     

Effect of the shape of a small object from outer space on its fragmentation in a planetary atmosphere

The fragmentation of a small object from outer space in the form of a rectangular parallelepiped in a planetary atmosphere is examined. The model for the interaction of an object with an atmosphere and its fragmentation developed by the authors is used in calculations of the Sikhote-Alin’ meteoroid as an example. The results are close to analogous calculations for a spheroidal meteoroid and agree satisfactorily with actual data. This suggests that the shape of a small object from outer space has little effect on its fragmentation in a planetary atmosphere.     

Numerical analysis for the abnormality of protective properties of a thin shield under oblique impact

A numerical analysis is performed to explain the abnormal effect observed in experiments investigating the protective properties of a thin shield under high-velocity impact at different angles. Within the framework of the model of a viscoelastic Maxwell-like body, in which fracture is taken into account, we solve three problems: the problem of perpendicular impact and that of impact at a 60° angle to the surface in the planar formulation, and the problem of perpendicular impact in the axisymmetrical case. The analysis has shown that under the given specific conditions the peculiarities of the projectile-target interaction in the case of the oblique impact give a decrease in the level of breaking loads as compared with the breaking loads appearing at the perpendicular impact and, as a consequence, lead to less fragmentation of the projectile. Ultimately, this decreases the protective properties of the shield. Lavrent'ev Institute of Hydrodynamics, Novosibirsk. Translated from Fizika Goreniya i Vzryva, Vol. 29. No. 6, pp. 81–87, November–December, 1993.     

Destruction of filled polymer targets by high-velocity impact

An analysis is made of experimental results on impact (at velocities of 0.6–6.26 km/sec) of projectiles made of Caprolon and polyethylene and compound projectiles (made of Caprolon with steel or aluminum spheres) on targets made of an epoxy resin with and without a filler (Al₂O₃) in a ballistic range. Impact on the edge surface of cylindrical targets with a characteristic size of 0.05 m is investigated. Complete fracture of the targets was recorded at velocities above 1 km/sec. The masses and dimensions of the collected fragments are subjected to statistical analysis. Average values of the fragment sizes and specific surface fracture energy are calculated. __________ Translated from Fizika Goreniya i Vzryva, Vol. 44, No. 2, pp. 129–138, March–April, 2008.     

Ignition of forests as a result of the explosion of the Tungusskii meteorite

Relying on the laws of the mechanics of multiphase reacting media, we construct a mathematical model of the ignition of forests by radiation emitted as a result of the explosion of the Tungusskii meteorite. The forest canopy is modelled by a multiphase porous reacting medium. The ignition regimes realized at different distances from the center of the explosion are analyzed. It has been established that the maximum radius of the ignition zone is 6–9 km for the forest canopy and 12–16 km for the ground cover, depending on the stock and moisture content of combustible forest materials. This corresponds to an explosion energy of 25·10¹⁶ J. V. V. Kuibyshev Tomsk State University, Tomsk. Translated from Fizika Goreniya i Vzryva, Vol. 29, No. 6, pp. 8–14, November–December, 1993.     

New approach to the application of multilayer superthin coatings. Effects of mixing

It is shown within the framework of molecular-dynamic modeling that the interaction of a nonlinear pulse with a free surface can result in the separation of an atomic plane. According to the results obtained upon colliding with the target, the separated fragments can form a multilayer coating. This has formed the basis of the proposed approach to the level-by-level application of thin coatings. It is shown that the change in the number of pulses and in the time for which they reach the surface of a “source” can significantly change the structure and composition of the coating at the target. Translated fromFizika Goreniya i Vzryva, Vol. 36, No. 4, pp. 137–139, July–August, 2000.     

Acoustic emission in investigation of the characteristics of fracture of complex viscose fibres and textile materials based on them

Acoustic emission methods were used to study deformation and fracture of viscose fibres, fabrics, and tricots. The effect of twisting and the frictional effect of the filaments in the complex fibre on the character of their fracture and acoustic spectrogram was demonstrated. The study of fracture of fabrics (in stretching and tearing) and tricots based on the character of the acoustic spectrograms revealed a significant difference in them determined by the characteristics of stretching and failure of individual fibres. The method of recording acoustic emission signals in deformation and failure of fibres, fabrics, and tricots combined with the strain diagram before break provides new information on the process of their fracture and the existence of defective structural elements — correspondingly filaments in the complex fibre or complex fibres in textile materials. Translated from Khimicheskie Volokna, No. 6, pp. 43–46, November–December, 1997     

Synthesis and Photoluminescence Property of Silicon Carbide Nanowires Via Carbothermic Reduction of Silica

Silicon carbide nanowires have been synthesized at 1400 °C by carbothermic reduction of silica with bamboo carbon under normal atmosphere pressure without metallic catalyst. X-ray diffraction, scanning electron microscopy, energy-dispersive spectroscopy, transmission electron microscopy and Fourier transformed infrared spectroscopy were used to characterize the silicon carbide nanowires. The results show that the silicon carbide nanowires have a core–shell structure and grow along <111> direction. The diameter of silicon carbide nanowires is about 50–200 nm and the length from tens to hundreds of micrometers. The vapor–solid mechanism is proposed to elucidate the growth process. The photoluminescence of the synthesized silicon carbide nanowires shows significant blueshifts, which is resulted from the existence of oxygen defects in amorphous layer and the special rough core–shell interface.     

Extrusion and dispersion of metals under the action of short-time dynamic pressures

It is shown that extrusion and dispersion of metals under the action of short-time dynamic pressures are, in principle, possible. Anomalously short delay times of inflammation of aluminum dispersing in a rarefied atmosphere and in air were recorded. It is shown that this process is accompanied by explosive combustion. Central Scientific-Research Institute of Chemical Machine Building, 115487 Moscow. Translated from Fizika Goreniya i Vzryva, Vol. 29, No. 6, pp. 107–110, November–December, 1993.     

Rotational components of deformation in metal bodies under dynamic loading

The plane problem of an initially quiescent cylinder subjected to a gradient flow of a highly viscous fluid is solved. It is shown that the cylinder is brought into rotation with angular velocity ω=−εé, where εé in the shear-strain rate of the medium. The solution is used to analyze flows under high-rate loading of metallic bodies that occurs at the level of the microstructure. The appearance of rotation is associated with the presence of fragments in the structure of the substance (grains, fragments, cells, and inclusions) that are unable to change their shape under the given loading conditions and, consequently, begin to rotate in the process of shear strain. Rotations that occur at the microlevel during joint deformation of solid bodies lead to transfer of oxide, hydroxide, and other surface films into the depth of the material, and this contributes to formation of a bond. Translated fromFizika Goreniya i Vzryva, Vol. 34, No. 2, pp. 129–133, March–April, 1998.     

Specific features of the nanoscopic spalling fracture near the grain boundary

The spalling fracture in a copper crystallite with a specific intergrain boundary under pulsed loading is modeled numerically. It is found that the grain boundary changes the parameters of nonlinear waves generated by loading and significantly affects the character of the spalling fracture. Translated fromFizika Goreniya i Vzryva, Vol. 36, No. 5, pp. 126–129, September–October, 2000.     

Mechanism of metal ignition due to fracture

A mechanism of ignition of compact metal samples during their fracture in oxygen is proposed. Ignition is assumed to be initiated by microfragments of the fractured sample at the moment when a crack passes through the volume of the metal, and the limiting stage of interaction is dissociative chemical adsorption of oxygen molecules on the surface of microfragments, which defines the dependence between the capability of materials to ignite during fracture and the pressure of the oxygen-containing medium. __________ Translated from Fizika Goreniya i Vzryva, Vol. 43, No. 4, pp. 39–48, July–August, 2007.     

On Compressive Brittle Fragmentation

Dynamic brittle fragmentation is typically described using analytical and computational approaches for tensile stress‐states. However, most fragmentation applications (e.g., impact, blast) involve very large initial compressive stresses and deformations. In this study, the compressive fragmentation of brittle materials is investigated experimentally across a range of materials: silicon carbide, boron carbide, spinel, basalt and a stony meteorite. Analysis of our experimental results suggests that there exists two different regimes in the fragment size distributions, based on two brittle fragmentation mechanisms. The first is a mechanism that produces larger fragments and is associated with the structural failure of the sample being tested. This mechanism is influenced by the loading conditions (rate, stress state) and sample geometry. The second fragmentation mechanism produces comparatively smaller fragments and arises from the coalescence of fractures initiating and coalescence between defects in regions of large stresses and contact forces (e.g., between two fractured surfaces from the larger fragments). A framework is developed for comparing experimental compressive fragmentation results with tensile fragmentation theories. The compressive experimental results are shown to be adequately described by the theories using the new framework.     

Development of Ni–YSZ cermet anode for solid oxide fuel cells by electroless Ni coating

Nickel–Yttria-stabilized zirconia (Ni–YSZ) cermet (ceramic–metal composite) anodes have been prepared from a simple electroless Ni bath without hypophosphite. Ni–YSZ powder having varying amounts of Ni has been prepared. The effect of two different reducing agents has been evaluated with respect to stability of the bath. Hydrazine can be effectively used as a reducing agent up to 30 vol.% Ni. However beyond 30% Ni, the hydrazine bath loses its stability. Formaldehyde is found to be a very effective reducing agent for higher Ni concentration. The Ni–YSZ powder obtained is characterized by SEM and XRD. When the powder is oxidized for calculating actual amount of Ni deposited, it turns to complete green due to the formation of NiO. The XRD results also show distinct peaks of NiO. The powder is pressed and sintered in air and reduced in hydrogen atmosphere to convert NiO back to Ni. The sintered microstructure shows a well-defined network of Ni around YSZ particles and the fracture surface shows porosity. These features indicate the effectiveness of the technique in producing the essential microstructural elements necessary for effective functioning of the anode.     

Effect of Pretreatment Atmosphere on CuO/TiO2 Activities in NO + CO Reaction

Using TiO₂ as carrier, CuO/TiO₂ catalysts with different CuO loading were prepared by the impregnation method. The catalytic activities in NO+CO reaction were examined with a micro-reactor gas chromatography reaction system and the methods of TPR, XPS and NO-TPD. It was found that the catalytic activities were affected by pretreatment atmosphere, i.e. H₂ atmosphere > reduction–reoxidation > 10%CO/He > reaction gas (fresh sample). NO decomposition was better by low-valence Cu species than by high-valence Cu species, i.e. Cu⁰>Cu⁺>Cu²⁺. The XPS results indicated that Cu species on CuO/TiO₂ were Cu⁰, Cu⁺, normal Cu²⁺(Cu²⁺(I)) and chain-structured Cu²⁺(Cu²⁺(II)) as –Cu–O–Ti–O–. The activities of Cu²⁺(II) were much higher than that of Cu²⁺(I), but both species were very unstable in the reaction atmosphere and easily reduced by CO, which accounted for the variable activities of fresh catalysts with increasing reaction temperature. In NO+CO reaction, the redox process was a cycle of Cu⁺–Cu²⁺(I) at low reaction temperature but was a cycle of Cu⁰–Cu⁺ at high reaction temperature. As shown by NO-TPD, high catalytic activities could be attributed to the following factors, e.g. oxygen caves on the catalyst’s surface after pretreatment with H₂ and reduction–reoxidation, formation of Cu⁰ after pretreatment with H₂, and increment of Cu species dispersion and formation of Cu²⁺(II) after pretreatment with reduction–reoxidation.     

Effect of the strain rate on the tensile strength of a copper shaped-charge jet

The data on the penetration depth of a rotating shaped-charge jet were used to estimate the strength of the material of a copper jet formed from a “low” conical linear with an apex angle of120° under the action of centrifugal forces. The estimates0.07–0.15 GPa obtained are close to the static yield point of deformed copper. The jet strength, which is estimated using the length of the fragments formed upon breakup of a rotation-free jet owing to the axial velocity gradient, attains1–1.5 GPa at a strain rate of ≌2·10⁴ sec⁻¹. Lavrent’ev Institute of Hydrodynamics, Siberian Division, Russian Academy of Sciences, Novosibirsk 630090. Translated from Fizika Goreniya i Vzryva, Vol. 33, No. 1, pp. 111–118, January–February, 1997.     

Effect of propionitrile nitramine salts on the thermal decomposition of HMX

The thermal decomposition of HMX with additives of metal salts of propionitrile nitramine is studied. The process goes with acceleration by a complex mechanism, in which the interaction of HMX with propionitrile imine and its oligomer formed in the reaction plays an important role. The initial rate of HMX decomposition correlates with the mass fraction of the anion in the salt. Translated fromFizika Goreniya i Vzryva, Vol. 36, No. 5, pp. 74–77, September–October, 2000.     

Production and service of high-alumina ceramic castables. 1. Ramming mixtures based on modified bauxite HCBS

The prospects of using bauxite-base HCBS in the production of high-quality ramming mixtures for lining blast furnace spouts are considered. A system of Chinese bauxite (filler) and bauxite HCBS (binder) is shown to give a ramming mixture with a porosity of 18 – 22% and σ_c of 120 MPa. The effect of some process factors on the properties of the new refractory material is considered. The life of the mixture in the main hearth spout is shown to be 70 – 90 thousand tons cast iron before the first repair at a consumption of 0.53 – 0.63 kg mixture per one ton cast iron. The processes that occur in the interaction between the material and blast furnace slags of various chemical compositions is considered. The characteristics of the developed mixture are compared with those of the standard ones. Translated from Ogneupory i Tekhnicheskaya Keramika, No. 3, pp. 37–41, March, 2000.