Katsuhiko Takahashi

Development of pressure gauge using PVDF copolymer for underwater shock measurement

In order to realize pressure gauge which can sustain underwater shock pressure higher than 100 MPa, we developed new type of pressure gauge using two materials as sensing element, PVDF and PVDF copolymer. Within 1.8 to 6.7 of the scaled distance, measurements of underwater shock profile were performed using new type of pressure gauge and compared with the results obtained by pressure gauge using tourmaline. Measured peak pressure using new type of pressure gauge presents good agreement with that using tourmaline. As the results of development of the sensor system with buffer amplifier, underwater shock wave profile was successfully measured using new gauge with PVDF copolymer. Experimental results using PVDF copolymer presents good agreement with that using tourmaline. On the other hand, measured duration time of underwater shock wave using PVDF is shorter than that using tourmaline because discharge time of PVDF is very short compared with time scale of underwater shock wave.

Formation of Fe-Al Intermetallic Compound Film on Carbon Steel by Shot Peening and Heat Treatment

The formation of an Fe-Al intermetallic compound film on carbon steel by shot lining and heat treatment was investigated. In the experiment, a centrifugal-type peening machine with an electrical heater was employed. The shot medium was high-carbon cast steel. The substrate was a commercial carbon steel, and the sheet was commercially available pure aluminum. The shot lining process of carbon steel with an aluminum sheet was carried out at 300 °C in air using a peening machine. Heat treatment was performed at diffusion temperatures from 600 to 1050 °C in vacuum. The lined substrates exhibited a harder layer of Al-rich intermetallics, such as Fe2Al5, in the diffusion temperature range of 650 to 900 °C. When the temperature of the lined substrates was more than 930 °C, the surface was covered with thicker and highly anticorrosive layers of Fe-rich intermetallics, such as FeAl and Fe3Al. We found that the present method could be used for the formation of functional films on carbon steel.

Underwater Shock and Bubble Pulse Loading against Model Steel Cylinder

The importance of the underwater explosion tests is increasing to assess the vulnerability of ships and underwater structures against the underwater explosion phenomena. The near-field underwater explosion causes severe fluid-structure interaction on a target; shock wave contact, resulting fluid cavitation formation and closure, and finally bubble expansion and collapse leading possibly to water jet impact. A series of the near-field underwater explosion tests were performed to investigate the response of model target during underwater shock and bubble pulse loading. The relation between deformation of model target and the underwater shock and bubble pulse loading was obtained.

Surface Modification of Magnesium Alloy by Shot Lining and Laser Heating

Magnesium alloy has a wide range of application prospects in the automobile and electronic industries. However, peeling of the coating material may occur under harsh environments such as high and low temperatures and high humidity with the conventional coating techniques. The authors have proposed a lining process of metals with thin aluminium foils using shot peening. In this method, the foil can be bonded to the workpiece surface bringing about large plastic deformation. The pressure generated by the hit of many shots is utilized for the bonding. In the present study, to improve the surface characteristics of magnesium alloy, the formation of an Fe-Al intermetallic compound film on magnesium alloy by compound treatment combining shot lining method and heat treatment was mainly investigated. Shot peening was performed with a centrifugal-type machine using cast steel ball. The lined sheet is aluminum foil with pure iron powders, and the workpiece was the commercial magnesium alloys. The lined workpieces are heat treated by laser in air. The Vickers hardness test was performed with a microhardness tester. It was confirmed that the present method could be used for the formation of functional films on the magnesium alloy.

Formation of Fe-Al Intermetallic Compound Film on High-Speed Tool Steel by Shot Lining and Heat Treatment

Shot peening is widely utilized to improve the fatigue property of mechanical parts for transportation equipment such as cars and airplanes. Also, this technology is being applied as a film-forming technology in order to improve surface quality. The authors have recently proposed new joining methods using shot peening, shot lining. In this method, the metals are bonded with the dissimilar metal by applying plastic deformation and the pressure. The thin foil can be joined to the substrate surface by the pressure generated by the hit of the shots. In this study, the formation of an Fe-Al intermetallic compound film on high-speed tool steel by shot lining and heat treatment was investigated. In the experiment, a centrifugal-type peening machine with an electrical heater was employed. The shot medium was high-carbon cast steel. The substrate was a commercial high-speed tool steel JIS-SKH51, and the foil was commercially available pure aluminium. The shot lining process of tool steel with an aluminium foil was carried out at 573K in air using a peening machine. Heat treatment was performed at diffusion temperatures from 923 to 1573K in vacuum. The lined substrates exhibited a harder layer of aluminium-rich intermetallics in the diffusion temperature range of 923 to 1173K. When the temperature of the lined substrates was more than 1273K, the surface was covered with thicker and highly anticorrosive layers of iron-rich intermetallics. We found that the present method could be used for the formation of functional films on high-speed tool steel.

Densification During Spark Plasma Sintering of Ni Powder Containing Dispersed MgO Particles

It is known that metal powders containing dispersed oxide particles are difficult to sinter by the conventional process. Spark Plasma Sintering (SPS) method was tried for making the dense sinter tablets from Ni powders containing MgO. The high–temperature hardness of the sinter tablets were examined from room temperature to 1173 K. The results were summarized as the follows. The relative density of the tablets increased with an increase in sintering temperature. The relative density of more than 97 was obtained at higher temperature than 1273 K with MgO contents of 0, 2.5, 5 and 10. The Vickers hardness of the sinter tablets increased with an increase in MgO contents and an increase in sintering temperature. The maximum hardness of about 270 Hv, which corresponded to more than 2.5 times of pure Ni, was obtained with 10MgO at 1273 K sintering. These high relative density and hardness can be obtained by SPS method but not by the conventional sintering. The high–temperature hardness decreased with an increase in the temperature. Plotting the logarithm of hardness against the temperature, two straight lines were obtained. The reflection point which showed the change in deformation mode was shifted to high–temperature side by the dispersion of MgO particles. The high–temperature hardness straightly increased against a reciprocal of a space between MgO particles.