Papers by Author: Yuji Wada

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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.
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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.
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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.
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Authors: Tei Saburi, Shiro Kubota, Yuji Wada, Masatake Yoshida
Abstract: A multidimensional analysis code for reactive shocks (MARS), which is developed to solve various problems in the physical hazard analysis of high energetic materials, has been applied to such complex problems as multi-material problem and sympathetic problem because it can employ various types of equations of state and a materials database. However, it was difficult to meet a growing demand for large-scale analysis and fluid-structure interaction (FSI) analysis. To address these issues, this study reports a parallelization of the code and an implementation of the functional capability of FSI analysis, and performance results for sample problems were also shown.
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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.
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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.
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Authors: Woo-jin Jung, Shiro Kubota, Yuji Wada, Yuji Ogata, Hideki Shimada, Kikuo Matsui
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Authors: Yuji Ogata, Woo-jin Jung, Shiro Kubota, Yuji Wada
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Authors: Kana Nishino, Shiro Kubota, Yuji Wada, Yuji Ogata, Norio Ito, Masayuki Nagano, Satoki Nakamura, Takuya Taguchi, Atsuya Fukuda
Abstract: The crack on the reinforced concrete wall generated by the explosion of several grams of Composition C4 explosive was investigated. A series of the single-shot blast experiment were conducted. The structural specimens for the reinforced concrete wall () were used for estimation of the crater size. The diameter of the borehole was fixed 16 mm, and the depth was varied to generate the various size of crater. The amount of explosive was also varied from 2.0 to 3.5 g. The effect of the depth of the borehole to the crater depth was examined, and the optimum charge condition for making the large crater at borehole side was clarified. For the case in which the fragmentation at the back side was allowed, the optimum charge condition was also found. High-speed photography was used to observe the growth process of the surface cracks. As the results, it was predicted that the crater was generated at 2 ms after explosion at least. The strain measurements were also conducted.
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Authors: Atsumi Miyake, Yuji Ohtagaki, Takayuki Abe, Yuji Wada, Yoshio Nakayama, Terushige Ogawa
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