Papers by Author: Yuji Ogata

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Authors: Shiro Kubota, Zhi Yue Liu, Masato Otsuki, Yoshio Nakayama, Yuji Ogata, Masatake Yoshida
Authors: Shiro Kubota, Yuji Ogata, Yuji Wada, Tei Saburi, Kunihito Nagayama
Abstract: The behaviors of the high explosive near the critical conditions for shock initiation of detonation are investigated by high speed photography and pressure measurements in gap tests. The sample is RDX base explosive, and the inner diameter of donor and acceptor charges is 26 mm. Gap material is PMMA. Near the critical condition, the results under the following conditions have been discussed. 1) Shock to detonation transition (SDT) take place in acceptor, 2) The SDT does not occur, but the reaction wave affects the leading shock front in acceptor, and 3) The gap length in which the effect of the reaction wave to shock front almost disappears. These results are very useful to construct the initiation model for solid explosive.
Authors: Tei Saburi, Shiro Kubota, Masatake Yoshida, Ganda M. Simangunsong, Yuji Wada, Yuji Ogata
Abstract: This paper presents the design of a compact size projectile accelerator, and its application. To meet the various needs such as a compact body size to use under various experimental conditions, an easy maintenance for repetitive experiments during a certain period, and a capability of the velocity control, the compact accelerators were newly designed with a direct explosive drive method. Two different types of accelerator were designed: a PMMA accelerator and a metal accelerator. The pictures of the projectile shoot using the designed accelerators were recorded by SHIMADZU HyperVision HPV-1 high-speed video camera. As a result, it was recognized that the PMMA accelerator was failed to accelerate the projectile, while the metal accelerator succeeded to accelerate it effectively. The accelerating performance of the metal accelerator was further investigated. The explosives for projectile acceleration were Emulsion explosive and Composition C4 explosive weighing 5 to 35g. It was found that the metal accelerator has the capability to control the projectile velocity adjusting the weight of the explosives, and there is an approximate linear correlation between them in our experimental range. A series of impact tests on 5052S aluminum alloy targets was examined using the accelerator.
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: Shiro Kubota, Tei Saburi, Yuji Ogata, Kunihito Nagayama
Abstract: The purpose of this study is to reconstruct the equation of state (EOS) whose parameters can be applied for high energetic material of arbitrary initial density without any modification. The simulation for detonation propagation in arbitrary initial density was proposed as the new method for obtaining the information of the EOS for detonation products of arbitrary initial density. At the same time, to collect the experimental data which verify the applicability of the numerical simulation, the detonation velocity for the system consisting of the pellet explosives and air gaps were conducted. The thickness of the 20 mm diameter pellet explosive was 10 mm, and air gaps were varied 0.5 mm to 2.0 mm. The relationship between detonation velocity and experimental condition was clarified for composition A5. The proposed one dimensional simulation was also conducted. The relationships between the pressure and the specific volume for detonation products were extracted from the proposed simulation
Authors: Shiro Kubota, Tei Saburi, Katsumi Katoh, Tomotaka Homae, Yuji Ogata, Mitsuaki Iida
Abstract: The development study of blast containment vessels for anti-terrorism has been conducted. The goal of this study is to develop safe disposal vessel for 10 kg of explosives. Considering of the use at the airport or railroad stations, it needs to be more compact compared with the conventional explosion chamber. By introducing both the internal structure and attenuation technology in the vessel, sufficient blast proof ability to contain internal explosion is realized. The blast containment vessel can be used repeatedly by exchanging the internal structure. To realize these concepts, model experiments were carried out using high speed photography, strain and pressure measurements. By introducing these technologies, the vessel for the 1 kg of explosive materials has been made, and the experiments employing 1 kg C4 explosive have been conducted. Finally, the compact blast containment vessel for 10 kg explosives was made, and its blast proof ability was shown by the internal blast test.
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: Tei Saburi, Toshiaki Takahashi, Shiro Kubota, Yuji Ogata
Abstract: The dynamic strain distribution behavior of a mortar block blasting was experimentally investigated. A small-scale blasting experiment using a mortar block with well-defined property was conducted and the dynamic strain distribution on the mortal block surface was analyzed using a Digital Image Correlation (DIC) method to establish the effective method for investigating the relationship between blast design and fracture mechanism. The block was blasted by simultaneous detonation of Composition C4 explosive charges with an electric detonator in two boreholes. The behavior of the block surface was observed by two high-speed cameras for three-dimensional DIC analysis and it was also measured by a strain-gauge for comparison. The three-dimensional displacements of the free surface of the block were obtained and dynamic strain distributions were computed. A point strain profile extracted from the analyzed strain distribution data was compared with a directly observed strain profile by the strain gauge.
Authors: Ganda M. Simangunsong, Shiro Kubota, Tei Saburi, Katsumi Katoh, S. Yoshino, Yuji Wada, Yuji Ogata
Abstract: To design a cylindrically-shape explosion container, the experiment of a high explosive charge detonating in a steel pipe has been performed. The charges, composition C4, were positioned at the geometrical centre of the steel pipe. Two kinds of measurements were performed on the steel pipe: circumferential strain and outside diameter. The strain-time history shows that the pipe structure vibrates and the vibration is decaying. It has been reported that this type of response is explained as the mechanism of strain growth, and this problem is taken up to verify computer simulation in this study. This simulation code could be strong tool to estimate the geometries of the explosion container. The relationship among the pipe parameter, explosive charge and pipe’s final deformation is proposed as practical guidance for predicting radius and thickness of the pipe correspond to the level of internal blast loading.
Authors: Woo-jin Jung, Shiro Kubota, Yuji Wada, Yuji Ogata, Hideki Shimada, Kikuo Matsui
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