Explosion, Shock Wave and Hypervelocity Phenomena in Materials II

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Authors: Hitoshi Miyoshi
Abstract: The SPH (Smoothed Particle Hydrodynamics) solver of the AUTODYN-3D was utilized to demonstrate a remarkable numerical simulation of shaped charges, specifically the process of jet formation and target penetration. A shaped charge consists of an explosive, a case and a conical liner. The Euler solver has been generally utilized for the simulation of the liner collapse process. Though the axi-symmetric modeling of the liner usually is selected, the actual jet formation process is never so idealistic. When we choose options consistent with live fire experiments, the SPH solver produces a more accurate solution over the Euler approach. The SPH method is capable of dealing with problems, including the free surface, deformable boundaries, moving interface and extremely large deformation. Calculated hypervelocity particles using the SPH method precisely represented the actual observed jet formation profiles of shaped charge characteristics. Accurate representations of the jet velocities, a velocity gradient with the tip traveling much faster than the trail and phase changes of the liner material were demonstrated. Using the calculated jet particles from the SPH method, the penetration process was simulated. The calculation was very time-consuming and the results did not conform to the traditional theories of the penetration. We have been investigating this discrepancy.
Authors: Hiroaki Miura, Akiko Matsuo
Abstract: The effects of the friction between the projectile and launch-tube wall in a single-stage gun are examined by the interior ballistics simulations. The solid/gas two-phase flow code for two-dimensional axisymmetric calculation is used in the simulations. In this study, one-dimensional quasi-steady-state elastic relations are applied to the projectile in the estimation of the friction force. The calculation method is validated by the comparison of the simulated results with the experimental data such as the histories of the breech pressure and the projectile acceleration. The simulated results reveal that the impact of the shock waves to the base increases the friction force acting on the projectile. The large friction force in the tight fit case decelerates the projectile, consequently intensifying the chamber pressure. The muzzle velocity decreases with the increase of the projectile diameter, and this appears strongly in the low chamber pressure case.
Authors: Mehdi Zohoor, A. Mehdipoor
Abstract: Underwater explosive compaction is a modified explosive compaction process that is used for manufacturing of parts by compaction of hard powders such as tungsten powder. In the present research work, equation of state (EOS) for tungsten powder was determined by a theoretical method and numerical simulation of the underwater explosive compaction process for tungsten powder was done using LS-DYNA program. The simulation results were utilized for the optimization of die design setups, which were used in our experimental test. Several experiments for compaction of tungsten amorphous powder with a mean grain size about 5 microns were performed using C4 explosive with a detonation velocity about 8.2 km/s. The hardness and density of consolidated samples were determined. The fragmented surfaces of samples were analyzed by scanning electron microscope (SEM). The experimental results indicated the usefulness of computer simulation for optimization of die design and the process parameters. In addition, the results indicated that the tungsten parts without cracks and with a high relative hardness and density could be obtained by underwater explosive compaction method.
Authors: Stanislav Rolc, Vladislav Adamík, J. Buchar, L. Severa
Abstract: This paper deals with the dynamic response of clamped plate to the loading following from the detonation of buried explosive charge. The cylindrical explosive charges of 8 kg mass has been considered. The numerical analysis is carried out using the LS DYNA finite element code. Numerical results exhibit reasonable agreement with results of controlled explosion experiments. The study is oriented mainly on the effects of structure representations (solids or shells) and of computational mesh size on evaluation of the structure response.
Authors: Zhi Yue Liu, Muhamed Suceska
Abstract: The cookoff of explosives is of great concern for the safety assurance of explosive devices in storage, transportation and handling. It may occur in the situation that explosive devices are subjected to the external heating stimuli such as fire or high-temperature surrounding. In order to gain ever-increasing knowledge toward the cookoff explosion of explosives, we establish numerical program to predict the cookoff explosion of explosive in a metal container. The computational formulation and methods are given in detail. The thermal decomposition and temperature variation in the interior of explosive were found corresponding to several typical external heating conditions. The results demonstrate that the method is beneficial to the future study on this subject.
Authors: Ki Hong Kim, Jai Ick Yoh
Abstract: We present an innovative method of multi-physics application involving energetic materials. Energetic materials are related to reacting flows in extreme environments such as fires and explosions. They typically involve high pressure, high temperature, strong non-linear shock waves, and high strain rate deformation of metals. We use an Eulerian methodology to address these problems. Our approach is naturally free from large deformation of materials that makes it suitable for high strain-rate multi-material interaction problems. Furthermore we eliminate the possible interface smearing by using the level sets. We have devised a new level set based tracking framework that can elegantly handle large gradients typically found in reacting gases and metals. We show several work-in-progress applications of our algorithm including the Taylor impact test, explosive venting and additional confined explosion problems of modern interest.
Authors: Atsumi Miyake, Hidefumi Kobayashi, Hiroshi Echigoya, Katsumi Katoh, Shiro Kubota, Yuji Wada, Yuji Ogata, Terushige Ogawa
Abstract: To obtain a better understanding of detonation properties of ammonium nitrate (AN) and activated carbon (AC) mixtures, steel tube test with several diameters was carried out for various compositions of powdered AN and AC mixtures and the influence of the charge diameter on the detonation velocity was investigated. The results of test indicated that the detonation velocity increased with the increase of the charge diameter. The experimentally observed values were far below the theoretically predicted values made by the thermohydrodynamic CHEETAH code and they showed so-called non-ideal detonation. The extrapolated detonation velocity of stoichiometric composition to the infinite diameter showed a good agreement with the theoretical value.
Authors: Atsumi Miyake, Hiroshi Echigoya, Hidefumi Kobayashi, Katsumi Katoh, Shiro Kubota, Yuji Wada, Yuji Ogata, Terushige Ogawa
Abstract: To obtain a better understanding of detonation properties of ammonium nitrate (AN) and activated carbon (AC) mixtures, steel tube test was carried out for stoichiometric composition of powdered AN and AC mixtures and the detonation velocity and the pressure profile were measured. Based on the results obtained the relation between the detonation velocity and the peak pressure was discussed with the theoretically predicted values which were obtained by the thermohydrodynamic CHEETAH code with the BKWC equation of state. The measured detonation velocity and peak pressure were far below the theoretically predicted values and the non-ideal detonation behaviour was confirmed.
Authors: Rolf Prümmer, A. Witt
Abstract: Hot isostatic pressing (HIP) is the established procedure to process Udimet 700 Powder by Powder Metallurgy (P/M) techniques. In this paper the method of hot explosive pressing (HEP) was applied. Its main feature is the direct method of explosive pressing. To avoid any reaction beforehand, the heating device and the explosive compaction device are separated and brought together very rapidly just a few milliseconds before ignition of the explosive charge. Udimet 700 bulk samples are obtained and investigated by metallographic and mechanical testing.
Authors: Akira Chiba, Yoshihito Kawamura, Minoru Nishida
Abstract: Recently, a number of amorphous alloys that possess high glass-forming ability and a wide supercooled liquid region before crystallization have been discovered. Especially, bulk metallic glasses, which are made in bulk form with a thickness of ~10 mm at slow cooling rates of the order of 1~100 K/s, have been noted as an industrial application. Hence the welding of bulk metallic glasses to other materials is very important. Explosive welding of most popular Zr41.2Ti13.8Cu10Ni12.5Be22.5 bulk metallic glass to crystalline pure Ti and SUS304 plates is investigated in this paper. The BMGs was found to retain the amorphous structure and the original mechanical properties. The sound bonding with other materials is expected to push forward the application of bulk metallic glass for industrial usage.

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