Papers by Author: Toshiyuki Hashida

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Authors: Chang Sheng Ding, Hong Fei Lin, Kazuhisa Sato, Yoshifumi Tsutai, Mabito Iguchi, Toshiyuki Hashida
Abstract: Dense gadolinium doped ceria (GDC) electrolyte thin films were prepared on porous NiO-GDC substrates by spray coating process. Microstructure of the GDC thin films and effect of preparation process on the microstructure were examined. SEM results show that uniform and dense GDC thin films with a thickness of approximately 1 μm were successfully prepared on porous NiO-GDC anodes. Anode-supported single cell with the thin GDC electrolyte film was tested using humidified hydrogen as a fuel, and exhibited relatively high electrical performance at low operating temperature (the maximum power density of 135 mW/cm2 at 600 °C). This means that the thin GDC film may be applicable to an electrolyte for anode-supported SOFCs. The experimental results suggest that the spray coating method developed in this study may offer a useful route for preparing thin and dense electrolytes of SOFCs.
Authors: Mamoru Omori, A. Okubo, M. Otsubo, Toshiyuki Hashida, K. Tohji
Authors: Maribel L. Saucedo-Muñoz, Toshiyuki Hashida, Yutaka Watanabe, Tetsuo Shoji, Victor M. Lopez-Hirata
Abstract: Three types of austenitic stainless steels JK2, JJ1 and JN1 were isothermally aged at temperatures from 600 to 900°C for 10 to 1000 minutes in order to study the microstructural evolution and its effect on the fracture toughness at cryogenic temperatures. The Charpy V-Notch fracture energy at 77 K showed a significant decrease with aging time in JJ1 and JN1 steels because of their higher contents of C and N. In contrast, the fracture energy corresponding to the aged JK2 steel decreased gradually with aging time. The abundant intergranular precipitation of carbides and nitrides seems to be the responsible for the fracture toughness deterioration in the aged JJ1 and JN1 steels. On the other hand, the intergranular precipitation of carbides was less abundant in the aged JK2 steel. The scanning electron microscope fractographs of the CVN test specimens corresponding to the aged JJ1 and JN1 steels showed mainly an intergranular brittle fracture and its fraction increased with aging time and temperature. In general, the presence of a more abundant intergranular precipitation resulted in a more rapid decrease in toughness with aging time.
Authors: Peng Cheng Zhai, Gang Chen, Toshiyuki Hashida, Qing Jie Zhang
Abstract: The Small Punch Creep Tests (SP-C tests) are simulated by a Finite Element Method (FEM). The objective of the present study is to establish a foundation for the SP-C test method by investigating the deformation and stress state of the SP-C test specimen. The emphasis is placed on the dependence relation of the creep strain and the stress on the measurable quantities, such as applied loads and the central deflections. Simulation works are conducted for two different materials, one is the tungsten-alloyed 9% Cr ferritic steel and the other is 12Cr1MoV steel. The numerical results for the central deflection versus time curves are quantitatively similar to the experimental results obtained on tungsten-alloyed 9% Cr ferritic steels. From the numerical results, the relationship between the central deflection and the equivalent creep strain is approximately independent of load, temperature, and material properties. The magnitude of the equivalent stress in the central region of the SP-C specimen shows no significant change with respect to time at the secondary creep stage, an approximate equation is proposed for the assessment of the equivalent stress in the SP-C specimen. As a farther result, the high temperature creep properties of the 12Cr1MoV steel and tungsten-alloyed 9% Cr ferritic steel are appraised by numerical simulation. The results are in good agreement with the results from the standard test method. The results indicate that the small punch test technique is an effective method for the evaluation of the high-temperature creep properties of materials.
Authors: Kazushi Sato, Toshiyuki Hashida
Abstract: In this paper, cracking behavior of distributed microcracks is discussed using a numerical simulation. The microcracks are initially distributed in a rectangle region. The directions and locations of the cracks are chosen at random. Three kinds of length distributions are used, such as a uniform length, a random length distribution and a fractal length distribution. The crack propagations from the initially distributed cracks are analyzed under a uniaxial tensile load using liner elastic fracture mechanics. The global behaviors of various crack distribution are studied. Results obtained from the numerical calculations indicate that the effect of the crack length distribution is minor in term of the macroscopic behavior of the cracked body.
Authors: Takamasa Onoki, Kazuyuki Hosoi, Toshiyuki Hashida
Authors: Kazuhisa Sato, Toshiyuki Hashida
Abstract: The influence of residual stress, thermal stress and chemically induced expansion stress etc... on the fracture damage of solid oxide fuel cells (SOFCs) were investigated by using nondestructive testing method and numerical stress-strain analyses under operating conditions. In order to estimate stress-deformation behavior of cell/stack of SOFCs, mechanical properties of SOFC elements were evaluated under controlled high temperature and oxygen partial pressure conditions. In addition to deformation and mechanical damage behavior were observed by using acoustic emission method.
Authors: Takamasa Onoki, Toshiyuki Hashida
Abstract: A new hydrothermal method is proposed which enables us to prepare thin hydroxyapatite (HA) ceramic coatings on Ti substrates with a curved surface at low temperatures. The method uses double layered capsules in order to produce a suitable hydrothermal condition; the inner capsule encapsulates the coating materials and a Ti substrate, and the outer capsule is subjected to isostatic pressing under the hydrothermal condition. In this study, it is demonstrated that a pure HA ceramic layer with the thickness of 50 µm could be coated to a Ti cylindrical rod at the low temperature as low as 135°C under the confining pressure of 40 MPa. Pull-out tests were conducted to obtain an estimate for the adhesion properties of the HA coating prepared by the double layered capsule method. The shear strength obtained from the pull-out tests was in the range of 4.0-5.5 MPa. It was also shown that the crack propagation occurred within the HA coating layer, not along the HA/Ti interface in the pull-out tests.
Authors: Go Yamamoto, Toshiyuki Hashida, Mamoru Omori, Hisamichi Kimura
Abstract: Multi-walled carbon nanotube (MWCNT) reinforced alumina composites were prepared by spark plasma sintering using pristine MWCNTs and acid-treated MWCNTs. The effect of acid treatment on the structure and surface potential of the MWCNTs was examined by transmission electron microscopy (TEM) and zeta potential analyzer. It is demonstrated that with the acid treatment of the MWCNTs, we have deliberately introduced nanoscale defects and negatively charged functional groups on the surface of the MWCNTs. The average depths of the defects are typically 4.8-10.8 nm. Mechanical measurements revealed that surface modification of the MWCNTs is effective in improvement of bending strength and fracture toughness of the MWCNT/alumina composites. Only 0.9 vol.% acid-treated MWCNT addition results in 27% and 25% simultaneous increases in bending strength (689.6 MPa) and fracture toughness (5.90 MPa m1/2), respectively.
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