Journal of the Society of Materials Science, Japan
Online ISSN : 1880-7488
Print ISSN : 0514-5163
ISSN-L : 0514-5163
Volume 68 , Issue 5
Showing 1-12 articles out of 12 articles from the selected issue
Techinical topic
Original Papers
  • Hideyuki KANAYAMA, Noritake HIYOSHI, Fumio OGAWA, Mie KAWABATA, Takamo ...
    2019 Volume 68 Issue 5 Pages 421-428
    Published: May 15, 2019
    Released: May 20, 2019
    JOURNALS FREE ACCESS

    This study presents creep damage assessment method for Mod. 9Cr-1Mo steel by sampling creep testing with thin plate specimen. Tensile creep rupture tests were performed using three different sizes of specimen under two different test environments to verify the creep testing with the thin plate specimen. Time to rupture of Mod. 9Cr-1Mo steel using three different sizes were almost same. In addition, there was no effect of environment on time to rupture. Pre-damaged thin plate specimens were machined from a bulk specimen’s gage section that pre-damage test was performed with. Pre-damage based on life fraction rule were 8%, 16% and 25%. No effect of the process of machining pre-damaged specimen on time to rupture was confirmed by verification tests in same test condition as pre-damage test. Stress acceleration creep rupture tests were performed to estimate creep damage assessment. Creep damage assessment by stress acceleration creep rupture tests was sufficiently accurate estimate. Creep damage assessments by Vickers hardness and lath width were compared with the assessment by stress acceleration creep rupture tests to study applicability of these methods.

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  • Hiroaki HASHIMOTO, Koji MIMURA, Isamu RIKU, Tsutomu UMEDA
    2019 Volume 68 Issue 5 Pages 429-435
    Published: May 15, 2019
    Released: May 20, 2019
    JOURNALS FREE ACCESS

    We experimentally investigated the dynamic buckling behavior of long strips in a wide range of loading velocities under three different end conditions; both ends clamped, clamped-supported, and both ends supported. To cover the wide velocity range in our experiments, we used a hydraulic loading device covering the loading velocities from 0.0001 to 0.1 m/s and a free fall drop-weight-type impact-testing device covering the loading velocities from 0.1 to 1 m/s. We chose A7075 aluminum alloy as the target material since it has a very high yield strength (it avoids plastic buckling) and relatively low elastic modulus (resulting in low Euler's buckling load). In the low-velocity range below 0.1 m/s, a dynamic buckling load was measured using a rod-type load cell connected to the piston rod of the hydraulic loading device. In the high-velocity range over 0.1 m/s, a load-sensing block was used to prevent disturbance in the load wave due to wave-reflection and interference. We measured the displacements of long strips using a high-speed magnetic-resistance device. From the relations between the buckling load and loading velocity, we found that there was a minimum velocity where the dynamic buckling load exceeded Euler’s buckling load, and that this velocity was dependent on the end conditions of the specimen and slenderness ratio λ. Based on these experimental results, we propose an empirical formula that can describe the velocity dependence of the dynamic buckling load in the loading-velocity range from 0.0001 to 1 m/s by taking into account various end conditions for long strips.

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  • Akihiro WADA, Tomohiro YAMASAKI, Kazuyoshi WASEDA
    2019 Volume 68 Issue 5 Pages 436-442
    Published: May 15, 2019
    Released: May 20, 2019
    JOURNALS FREE ACCESS

    Ultrasonic wave is applied to damage evaluation of GFRP laminate degraded by hot water from one surface. GFRP vessels have been used for storage of both acid solution and alkaline solution because of their excellent corrosion resistance. In these days, integrity evaluation of GFRP vessels has attracted much attention as the number of aged vessels increases. Although degradation proceeds gradually from the inner surface of vessels, sensors can only be attached on the outer surface. Then the through-thickness method for damage evaluation is required. In this research, GFRP plates are degraded by hot water from one surface, and through-thickness ultrasonic inspection is conducted to reveal the dependence of ultrasonic characteristics on damage state of the plates. Beside wave attenuation and velocity, characteristics of reflected waveforms from the degraded surface are analyzed. It is found that the envelope of echo from the degraded surface reflects damage propagation in the thickness direction, and it can be used as damage index of GFRP vessels.

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  • Hironori TOHMYOH, Akihiro FUKUDA, Yasuhiro KIMURA
    2019 Volume 68 Issue 5 Pages 443-449
    Published: May 15, 2019
    Released: May 20, 2019
    JOURNALS FREE ACCESS

    This paper reports on the relationship between the mechanical properties and the grain size of Cu microwires modified by Joule heating. The increase in yield strength as the grain size of a metal or alloy decreases is known as the Hall-Petch relation. Because the crystal grain size in thin metallic wires is fine, these have higher strength compared to their bulk counterparts. To improve the formability of 25 μm-thick Cu microwires, the wires were heat-treated at various temperatures by Joule heating, and the grain size of the wires was evaluated quantitatively by cross section method. Larger crystal grains grew at higher temperatures, and the wire heat-treated at the highest temperature of 600°C had a bamboo structure, in which the grain boundaries were only in the radial direction of the wire. Small-span, three-point bending tests were performed on the heat-treated Cu microwires to determine their mechanical properties. The Young’s modulus of the wires was found to be independent of grain size, with an average value of 86.4 ± 2.4 GPa. On the other hand, the yield stress of the wires clearly depended on the grain size. The yield stress of a Cu microwire that had not been subjected to Joule heating was 311 MPa, and this decreased to 75 MPa after heat treatment at 600°C. Finally, we confirmed that the Hall-Petch relation was applicable to the Cu microwires, except for those that, due to insufficient heat treatment, had crystal grain structures in which the grains were highly elongated in the axial direction of the wire.

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