Oshikawa Wataru

写真a

Title

Professor

Researcher Number(JSPS Kakenhi)

80224228

Current Affiliation Organization 【 display / non-display

  • Duty   University of the Ryukyus   Faculty of Engineering   School of Engineering_Energy and Environment Program   Professor  

Academic degree 【 display / non-display

  • The University of Tokyo -  Doctor of Engineering

External Career 【 display / non-display

  • 2005.07
     
     

    University of the Ryukyus, Faculty of Engineering, Department of Mechanical Systems Engineering, Engineering Materials,Design and Processing, Associate Professor  

Research Areas 【 display / non-display

  • Nanotechnology/Materials / Material processing and microstructure control

Published Papers 【 display / non-display

  • Cracking Process in Delayed Fracture of High-Strength Steel after Long Atmospheric Exposure

    Homma T.

    ISIJ International ( 一般社団法人 日本鉄鋼協会 )  62 ( 4 ) 776 - 787   2022.04

    Type of publication: Research paper (scientific journal)

     View Summary

    <p>This paper is the first microscopic observation of the entire cracking process in delayed fracture of high-strength steel bolt after long-term atmospheric exposure. A sufficiently fresh fracture surface exhibits the initiation of the propagating crack in a thin zone beneath the screw groove, resulting from the merging of multiple cracks nucleated therein. The fracture morphology is initially intergranular, exhibiting the three-dimensional shape of prior austenite grains, but the stress and strain states at the nucleation sites are not uniquely specified. The fracture morphology alters as the crack extends from intergranular to quasi-cleavage and fine dimples, associated with increasing stress intensity under a constant-displacement condition. The change from inter- to trans-granular fracture is continuous, implying affinity among different morphologies associated with the increased density and the distribution of potential crack nucleation sites in the crack front. The crack propagation in the quasi-cleavage and fine dimple regions is step-wise of about 50 <i>µ</i>m per step. Recent studies about the function of hydrogen in embrittlement are referred to in respect of the accumulation of strain-induced damage. The enhanced generation of strain-induced vacancies is the presumable function of hydrogen compatible with the present findings.</p>

  • Evaluation of corrosion properties of steel with Zn-30mass% Al thermal-spray coating using accelerated atmospheric exposure test

    Nakano A.

    MATERIALS TRANSACTIONS ( 公益社団法人 日本金属学会 )  62 ( 7 ) 1001 - 1008   2021.07

    Type of publication: Research paper (scientific journal)

     View Summary

    <p>A four-year atmospheric exposure test was performed on steel with a Zn–30 mass%Al thermal-sprayed coating using an accelerated atmospheric exposure test, and then the atmospheric corrosion properties were evaluated. X-ray diffraction results showed that the corrosion products formed on the coating owing to the accelerated atmospheric exposure test were the same as those formed in a typical atmospheric exposure test. The corrosion weight loss of the thermally sprayed coatings in the accelerated atmospheric exposure test was promoted by approximately 1.5 to 2.0 times compared to the atmospheric exposure test.</p><p> </p><p>This Paper was Originally Published in Japanese in Zairyo-to-Kankyo <b>68</b> (2019) 187–193.</p>

  • Evaluation of Galvanic Current Property of ACM Type Corrosion Sensor Consisting of the Fe-C galvanic Couple

    Nakatsu Michiyo, Oshikawa Wataru, Shinohara Tadashi

    Zairyo-to-Kankyo ( Japan Society of Corrosion Engineering )  68 ( 8 ) 212 - 219   2019.08

    Type of publication: Research paper (scientific journal)

     View Summary

    <p>We fabricated the ACM sensor consisted of a Fe/C-galvanic couple and investigated the sensor output behaviors in outdoor exposure test or in constant humidity test. In the exposure tests of Fukui and Okinawa, the FeC sensor output is almost the same as the FeAg sensor output, but decreases when several days after the start of exposure and during rain period. The FeC sensor output in the <i>I</i>-<i>RH</i> calibration curve increases with increasing an amount of deposited sea salt and a humidity, and is the same as FeAg sensor output when W<sub>s</sub> is in the range of 0.01 to 1 g/m<sup>2</sup> and RH is 30 to 90%. The <i>I</i><sub>gal</sub> of the FeC sensor in an artificial seawater drops to 90μA, which is less than 1/3 of that of the FeAg sensor. The cathode current density of the C electrode in an artificial seawater is lower than that of the Ag electrode. By analysis impedance spectrum of the C electrode, the change transfer resistance, <i>R</i><sub>ct</sub> increased and the electric double layer capacitance, <i>C</i><sub>dl</sub> reduced than that of the Ag electrode. It is considered that the C electrode/liquid interface has reactive resistance to electron transfer in the reduction reaction of dissolved oxygen.</p>

  • Evaluation of Corrosion Properties of Steel with Zn-30mass% Al Thermal-Spray Coating Using Accelerated Atmospheric Exposure Test

    Nakano Atsushi, Oshikawa Wataru, Yonezawa Noboru

    Zairyo-to-Kankyo ( Japan Society of Corrosion Engineering )  68 ( 7 ) 187 - 193   2019.07

    Type of publication: Research paper (scientific journal)

     View Summary

    <p>A four-year atmospheric exposure test was performed on steel with Zn-30mass%Al thermal-spray coating using the accelerated atmospheric exposure test, and atmospheric corrosion properties was evaluated. X-ray diffraction results showed that the corrosion products which formed on the coating film as a result of the accelerated atmospheric exposure test were the same as those which formed in a typical atmospheric exposure test. The amount of corrosion of the spray-coated film in the accelerated atmospheric exposure test was promoted by approximately 1.5 to 2.0 times compared to the atmospheric exposure test.</p>

  • Ⅳ. Electrochemical Measurements in Various Environments―ACM Type Corrosion Sensor―

    Oshikawa Wataru

    Zairyo-to-Kankyo ( Japan Society of Corrosion Engineering )  67 ( 7 ) 273 - 279   2018

    Type of publication: Research paper (scientific journal)

     View Summary

    <p>The measurement method of the ACM sensor under the atmospheric corrosion environment was described with actual samples. By analyzing the sensor output and humidity data obtained every 10 minutes, it is possible to estimate the wetting time and sea salt attachment amount, and by correcting the sensor output during rainfall, corrosion rate in the outdoor can be estimated.</p>

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