Papers by Author: Tetsuyuki Hiroe

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 specific fields and industries. However, the reduction of the explosive powder mass uses at a time makes the handling safe. And use of explosives in a continuous producing process leads the new utility of the explosion. Based on this concept, we enclosed small mass explosives with a polyethylene sheet and initiate them by using metallic foil explosion. We have also developed the system that can generate small explosion continuously. Since it was not easy to initiate a small amount of explosive steady, we had initiated them by metallic foil explosion using a power-supply unit of capacitor bank with 2500J (20kV). In present study, we tested the initiation of a small amount of explosive using a comparatively small power-supply unit of capacitor bank with 4.5J (600V) and that of 2J (1kV) to apply to the general use. In this paper, result of experiments and the conclusions are shown. We observed the perfectness of explosion by using omnidirectional microphone. It is concluded that initiation of explosives enclosed with polyethylene sheet by small power supply unit at 2J (1kV) is possible, while the explosion was not perfect.

Abstract: One-dimensional symmetrical explosive loadings are applied to expand structural components: tubular cylinders, spherical shells and rings of 304 stainless steel and double and single walled cylinders of an aluminum alloy, A5052 to fragmentation, and the effects of wall thicknesses, explosive driver diameters and the constant proportionality of the in-plane biaxial stretching rates are investigated on the deformation and fracture behavior of three types of single walled structures and shatterproof behavior for double walled cylinders experimentally and numerically. In the cylinder tests, the driver is a column of high explosive PETN, inserted coaxially into the bore of a cylinder and initiated by exploding a fine wire bundle at the column axis using a discharge current. In case of the ring tests, ring specimens are placed onto a cylinder charged with the PETN as an expansion driver, and for sphere tests, a specimen filled with the PETN is also initiated by exploding a fine copper wire line with small length located at the central point. Observation results of deformation have shown the final maximum in-plane stretching rate order of , and fracture evaluations on recovered fragments are discussed indicating the need of modified fragmentation model for the structural components. In the double walled cylinder tests, only for lowermost amount of the explosive the outer cylinder has almost caught the fragments of inner cylinder, revealing that the damage phenomena are much different from those for single walled ones.

Abstract: Explosive loading techniques are applied to expand tubular cylinders, spherical shells and rings of 304 stainless steel to fragmentation, and the effects of wall thicknesses, explosive driver diameters and the constant proportionality of the in-plane biaxial stretching rates are investigated on the deformation and fracture behavior of three basic structures experimentally and numerically. In the cylinder tests, the driver is a column of high explosive PETN, inserted coaxially into the bore of a cylinder and initiated by exploding a fine wire bundle at the column axis using a discharge current from a high-voltage capacitor bank. In case of the ring tests, ring specimens are placed onto a single cylinder filled with the PETN as a expansion driver, and for sphere tests, specimens filled with the PETN are also initiated by exploding a fine copper wire line with small length located at the central point. Two types of experiments are conducted for every specimen and test condition. The first type uses high speed cameras to observe the deformation and crack generation of expanding specimens showing the final maximum in-plane stretching rate of above , and the second uses soft capturing system recovering typically most fragments successfully. The fragments are measured and investigated using a fragmentation model. The effects of test parameters on the deformation and fracture behavior for three types of structures are discussed in need of modified fragmentation model for shell structural elements.

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.

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.

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.

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.