Explosion, Shock Wave and Hypervelocity Phenomena in Materials II

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Authors: Kazuyoshi Tateyama, Shigeru Itoh, Hironori Maehara
Abstract: In cases where a borehole has been dug in the ground and subjected to an explosive load, the soil around the borehole wall will be abruptly compressed and a cavity will then be created in the portion of the ground that is surrounded by the compressed soil wall. When this procedure is applied to the construction of tunnels or foundations, underground spaces can be created with minimum mucking and a thinner lining. The authors carried out some laboratory experiments in which small boreholes were expanded by blasting. The results of the experiments increase our knowledge and elevate the possibility of applying this procedure to underground space construction.
Authors: Kazuhito Fujiwara, Tetsuyuki Hiroe, Hidehiro Hata, Motoyasu Furukawa
Abstract: The thermal sterilization is limited to use for fungi and bacteria in some kinds of dry powdered foods because of the heat sensitivity of their flavor. The sterilization method using impulsive loads or shock waves has the characteristic to sterilize foods without heating. Higher shock pressure can shows higher disinfecting action, but has some problems such as the degradation of foods and the hardness of handling. The proper choice of energy sources is one of points to make the method push to the industrial level. Safety and facility are also important factors to develop the practical system. In this paper as the case of the lowest limit of the impact load, the powder was impacted by mechanical hammer. It was found that the iterative impacts showed the disinfecting effect although the efficiency was low at an impact. Several processing cycles were required to show the significant decreasing of bacteria, because the apparent colony number (not actual bacteria number) increased in the impact process. The numerical model to estimate the mechanical condition in sterilizing process is also presented in this paper.
Authors: Asuka Oda, Naoki Okamoto, Shigeru Itoh
Abstract: When an explosive in water is exploded, shock wave from the explosive propagates in water as underwater shock wave. Using a detonating fuse as an energetic source, an oblique underwater shock wave with high pressure is obtainable and possible to be utilized for various applications. It is expected that the use of water can inhibit the heating effect on the shock processed sample. In the present research, the authors are intended to use underwater shock wave for the food processing. After loading underwater shock wave against some foods, it is expected to show some advantageous effects for the food processing, such as, softening, improved permeability, and grinding foods. However, such advantageous effects are changed depending upon the condition of the received food. In this research, the foods containing high amount of water were treated by the underwater shock wave. Japanese radish and apple were used as food samples. The change in their hardness, permeability and so on were measured. These results were compared with the control sample in which the underwater shock wave was not applied.
Authors: Ayumi Takemoto, Toshiaki Watanabe, Hirofumi Iyama, Shigeru Itoh
Abstract: The sessile organism of the oyster and the barnacle, etc. causes friction between the surface of the ship and the water. Friction causes the deterioration of fuel cost. In addition, dry dock operation with putting the ship on the land or the diving operation, are needed for the removal of the sessile organism. These works require a very high cost. Various techniques for reducing friction resistance have been proposed. On the other hand, the method for the practical use is not popular still now. Authors tried to perform an experiment to remove the sessile organism on surface of the metal by using the underwater shock wave.
Authors: Igor A. Balagansky, Alexander Matrosov, Ivan Stadnichenko, A.I. Glumov, A.V. Samsonov
Abstract: We have investigated the influence of fluoroplastic, copper, and silicon carbide inert inserts on the process of detonation transmission through water. Active and passive HE charges were molded from Comp B. On the rear end of the passive HE charge an identification steel specimen was mounted, which detected presence or absence of detonation. Inert inserts were shaped as square prisms of varying lengths, and were contained between active and passive HE charges without any clearance on the way of initiating shock wave with partial overlap of HE cross sections. It is shown that preloading of a passive HE charge with a shock wave transmitted through copper or ceramic inserts causes considerable desensitization of the Comp B. Ceteris paribus, the crash distance of detonation transmission for copper was equal to 74%, and for silicon carbide – to 60% of the distance for fluoroplastic. While performing the experiments with ceramic inserts we have observed cumulation phenomenon, which manifested itself as a hole in identification steel specimen with depth of about 10 mm. The surface of specimen had typical temper colours that demonstrated presence of high temperatures.
Authors: Satoshi Kimura, Hidehiro Hata, Tetsuyuki Hiroe, Kazuhito Fujiwara, Hideaki Kusano
Abstract: In this study, an explosion combustion phenomenon of ammonium nitrate (ρ=1.7kg/cm3) was used instead of the explosive PETN and the ultra-high-speed destruction phenomenon of aluminum cylinder was analyzed. The mix powder obtained by mixing aluminum powder (ρ=2.7kg/cm3) and ammonium nitrate was used instead of the explosive PETN, and an explosive combustion phenomenon was generated using copper wire explosion by high-voltage capacitor bank (40kV, 12.5 /F). Ammonium nitrate and aluminum powder are kneaded in a combination ratio of 5 : 1 in mass. An aluminum cylinder was destroyed by the phenomenon. The experiments were conducted using various diameters of ammonium nitrate particle and the photographs of the phenomenon were taken by the high-speed camera (IMACON468) and the high-speed video camera (HPV-1). The fragments of aluminum cylinder were collected and their dimensions were measured. The explosion phenomenon and fragments were compared with the result by explosive PETN. This paper presents these experiments and analysis result. And, hydro codes have been applied to simulate the deformation behavior of the aluminum cylinder.
Authors: Masaharu Fujiwara, Kazuhito Fujiwara, Tetsuyuki Hiroe, Hidehiro Hata
Abstract: High explosives are useful material to generate great amount of energy in short time. Since controlling their releasing energy is hard, the use of explosive is limited to breaking and crushing the tough structures and processing of bulk materials. However, the reduction of mass of the explosive powders in a process and the arrangement of pellets with constant intervals provide us the safe handling, and then those lead the new utility of the explosion, while there are some difficulties encountered when a small amount of explosive powder is used, such as the initiation regularity of explosives and the protection of mechanical parts from impact damages. In this paper, the successive initiation of small explosive was tested by means of the wire explosion that is generated by the instant release of electric energy from high volt capacitors, and the successful results were obtained under the controlled condition. The damages of surrounding devices were avoided by using of the initiating head of the device that had small chamber isolated from the outer atmospheric environment.
Authors: Masahiko Otsuka, Naoki Okamoto, Shigeru Itoh
Abstract: In this study, the destruction of concrete block using underwater shock wave generated by high current is studied. A metal wire was connected to an electrode and a high voltage impulsive current was passed through it to generate the underwater shock wave. The underwater shock wave was investigated by optical observation using a high-speed camera and pressure measurement. A comparison was made on the shock wave generated from the electrode with and without connecting it to a metal wire. The underwater shock wave generated from electrode without metal wire showed the existence of many shock waves by continuous plasma within discharge duration, and the duration of the pressure pulse was long in this case. The peak pressure of underwater shock wave generated from metal wire explosion was higher than the previous case due to the reaction of metal vapor and water, whereas the pressure duration was less. The concrete block was efficiently destructed by the effect of underwater shock pressure of high impulse. The high peak pressure and long duration are necessary for the destruction of concrete block. It is suggested that high pressure induces crack to the structure, and the long pulse duration destructs the structure.
Authors: S. Kawabe, Hidetoshi Sakamoto, Masahiro Himeno, T. Ono, Shigeru Itoh
Abstract: The high-speed fracture mechanism of glass bottles by using underwater shockwave and the recycling process by crushing the glass bottles were discussed. The proposed crushing process of the glass bottles can decrease the recycle cost by generating small fragments called "Cullet" and by executing the washing process at the same time as the crushing process. In this study, the relations between the "Cullet" sizes and various explosive conditions, that is, the distance from explosive, the amount, the velocity and the shapes of explosive, were clarified by using beer bottles, and the influence of the serial and concentric arrangements of two or more bottles on "cullet" sizes were examined. Moreover the behaviors of the underwater shockwave were observed by framing photograph method, shadowgraph method, illumination photography method and the FEM simulation was executed in order to make clear the high speed fracture mechanism.
Authors: Tetsuyuki Hiroe, Kazuhito Fujiwara, Hidehiro Hata, K. Watanabe, Mitsuharu Yamamoto
Abstract: Explosive driven rapid fracture in a structural body will be preceded by a compression process, and the compression effects on mechanical properties of the materials are clearly important to understand shock-induced failure such as spall or fragmentation phenomena. In this study, incident shock waves in plate specimens of aluminum A2017-T4 and 304 stainless steel are generated by plane detonation waves in the high explosive PETN initiated using wire-row explosion techniques, and the compressed specimens are successfully recovered without severe damages due to the reflected expansion waves with use of momentum trap method. A hydro code, Autodyn-2D is applied to determine test conditions: thicknesses of explosives, attenuators, specimens and momentum traps and to evaluate experimental results, simulating time-histories of stress waves in the layers of the test assembly. Microhardness distributions in cross-sections, tensile strength, fracture ductility and yield stress are measured for the recovered specimens, using miniature tensile and compression test pieces machined from them. They are compared with those of virgin specimens, showing significant increase of hardness, tensile and yield strength and remarkable reduction of elongation and ductility for shocked specimens. The results are taken into consideration for evaluation of experimental fragmentation energy in cylinder explosion tests.

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