Akio Kira

An investigation on underwater explosive bonding process

In this paper, we propose a new explosive bonding method for bonding materials by using the underwater shock wave from the explosion of explosives in water. This method is especially suitable to bond the materials with thin thickness and largely dissimilar property. In bonding those materials, the shock pressure and the moving velocity of shock wave on the flyer plate should be precisely managed to achieve an optimum bonding conditions. In this method, the bonding conditions can be controlled by varying of the space distance between the explosive and the flyer plate or by inclining the explosive charge with the flyer plate. We made the experiment of this technique bond the amorphous film with the steel plate. A satisfactory result was gained. At the same time, numerical analysis was performed to investigate the bonding conditions. The calculated deformation of the flyer plate by the action of underwater shock wave was compared with the experimental recordings by high-speed camera under the same conditions. The comparison shows that the numerical analysis is of good reliability on the prediction of the experimental result. Furthermore, the numerical simulation also gives the deformations of the flyer and the base plate, and the pressure and its variation during the collision process.

Collection of Product Synthesized Using Extremely High Impulsive Pressure Generator

A new method has been developed to generate an extremely high impulsive pressure by using a metal jet that is discharged when a metal collides with another metal. The high pressure is used to synthesize a new material. When a metal plate was accelerated by the detonation of an explosive, it collides with the concentric circle of the conic surface of a conical concave metal block metal jets are discharged from all parts on the concentric circle. The metal jets fly toward the center while converging and collide with each other at the central axis. Because those collide at high-speed pressure becomes extremely high. The flight direction of the converged metal jet changes downward. The metal jet collides with the bottom of the block. A large hole is formed inside the bottom. The formation process of the hole was examined by the observation of the section of the block. A specimen powder that was rubbed to the conic surface is discharged with the metal jet and become the high pressure. The specimen powder is synthesized to a different material. The synthesized material is held inside the formed hole. The existence of cBN was confirmed by the X-ray diffraction of the synthesized material, in the case that BN was used as the specimen powder. Similarly, the existence of diamond was confirmed in the case of graphite powder.

Pressure Measurements and Numerical Simulation of Underwater Shock Wave for Food Processing

This study attempts to clarify underwater shock waves using a food container designed for food processing. The underwater shock wave is driven by a spark or wire explosion from a high-capacity condenser bank. Since the applied pressure must be known to control the experimental conditions, a numerical simulation was conducted and the results were compared with measurements using an elastic bar placed in the water.

Numerical Simulation of Oblique Collision of Flier Plate

The metal jet that is flowed out by the oblique collision between a metal flier plate and a metal block becomes a high velocity. We have been developing the device that makes a material extremely high pressure by using the metal jet. The flier plate of the previous device had been accelerated by using a high explosive. There were several problems in the collection and analysis of the material that had been made the high pressure. Therefore we thought up the new device of which the flier plate was accelerated by a powder gun. The collision process was examined by a numerical simulation because the collision process of the flier plate of this device differs from that of the previous device. LS-DYNA was used for a numerical simulation and the difference of the collision process was clarified.

Phase Transformation of Powdered Material by Using Metal Jet

The various techniques of phase transformation of the material have been proposed by many researchers. We have developed several devices to generate the ultrahigh pressure by using high explosive. One of them uses metal jets. It is expected that the ultrahigh pressure occurs by the head-on collision between metal jets, because the velocity of the metal jet is very high. By mixing a powdered material with metal jets, the pressure of the material becomes high. The purpose of this study is to transform the phase of the powdered material by using this high pressure. The powders of the graphite and hBN were applied. The synthesis to the diamond and cBN was confirmed by X-ray diffraction (XRD). In this paper, the mechanism of the generation of the ultrahigh pressure is explained and the results of the observation of the powder by using scanning transmission electron microscope (STEM) are reported.

Generation of Ultrahigh Pressure and Application of Ultrahigh Pressure to Formation of Diamond from Graphite Powder

The purpose of our research is to generate the ultrahigh pressure by using high explosive and to transform a phase of a material. The extremely high impulsive pressure generator that has been developed by us uses the head-on collision between metal jets. Because the velocity of the metal jet is very high, the ultrahigh pressure will generate. If a powdered material is mixed to metal jets, it is expected that the material is transformed to a high pressure phase by this ultrahigh pressure. A graphite powder was used to synthesize a diamond. The existence of the diamond was confirmed by X-ray diffraction (XRD). In this paper, the mechanism of the generation of the ultrahigh pressure is explained and the results of the observation of the powder by using scanning transmission electron microscope (STEM) are reported.

OBSERVATION OF METAL JET IN EXTREMELY HIGH IMPULSIVE PRESSURE GENERATOR

A new technique has been developed to generate an extremely high impulsive pressure by using an explosive. A metal jet, typically observed in explosive welding is used in this technique. The behavior of metal jet is crucial to the design of pressure generator. The experimental observation was made by the collision of metal jet on a metal block surface. Many craters formed by the collision of metal jets on the surface of the metal block were observed. The craters were overlapped and distributed in a wide range. The diameter of the largest crater was 0.5 mm. The quantity of the discharged metal jets was found to be a function of the quantity of explosive. The total area of the craters is considered as proportional to the quantity of the discharged metal jets and the experimental conditions for the formation of large craters was investigated.

Advanced Materials Synthesis and Microstructural Characterization Using Explosive at Sojo University

In the research center for advances in impact engineering established in Sojo university, advanced materials have been synthesized by using shock wave and their microstructure has been investigated. An extremely high shock pressure and a dynamic hot compaction technique were developed, and the synthesis of the advanced materials and composites was succeeded. Transmission electron microscopy observations revealed unique microstructures of such materials obtained by our original advanced technique.

Optical Observation of Extremely High Impulsive Pressure Generator Using Collision of High Velocity Metal Jets

A method to generate an extremely high impulsive pressure using a converging metal jet, has been developed as a purpose to achieve the high pressure above 1 TPa. The metal jet is discharged from the collision point, when a metal plate is accelerated by the detonation of an explosive and it collides with a conical concave metal block. The metal jet discharged on the concentric circle of the conical concave fly toward the center while converging and collide on the central axis, and the collided metal jets exhibit the extremely high pressure. In the present investigation, framing photographs were taken using an image converter camera to investigate the phenomenon occurred in the generator. The photographs show that the metal jets are discharged from the collision points between the metal flyer plate and conical concave block, and then, collided at the central axis. The maximum pressure obtained under vacuum was estimated about 0.83 TPa from the velocity calculated from the photographs, and the results were slightly lower than that evaluated theoretically.