担当区分：筆頭著者   記述言語：日本語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Zairyo Journal of the Society of Materials Science Japan  

An applicability of pneumatic drive small disk bending test to fatigue strength assessment of resin materials was examined in this study. The effects of specimen thickness and air pressure on deformation behavior of epoxy resin were investigated using a finite element method to determine specimen geometry and test conditions. Then, the pneumatic drive bending fatigue testing apparatus with small disk-type specimen (8 mm in diameter) was designed. Fatigue test was carried out at a variety of maximum pressures of 0.25-0.73 MPa and frequency of 2 Hz using epoxy resin. The experimental results showed that the stable air pressure was alternately applied to both specimen surfaces. The change in the strain measured at the center of specimen surface using a strain gauge, followed well to the change in pressure. It was found the fatigue life, which was defined as the number of cycles to 10% drop in air pressure, decreased by attaching the strain gauge, because crack was initiated in the vicinity of strain gauge. It was revealed that there was a relatively good correlation between the applied pressure and the fatigue life.

DOI： 10.2472/jsms.74.96

Scopus

担当区分：筆頭著者   記述言語：日本語   掲載種別：研究論文（学術雑誌）   出版者・発行元：公益社団法人 日本材料学会  

We developed a small punch (SP) test system enables SP testing in a hydrogen atmosphere at elevated temperatures in order to utilize the SP testing for the remaining-life assessment of mechanical components used in advanced high-temperature hydrogen technologies, such as SOFC and SOEC. Type 304 stainless steel was subjected to the SP and SP creep tests with a small disk-type specimen. A small disk specimen with a diameter of 8 mm and thickness of 0.5 mm was tested in hydrogen and argon gases. The absolute gas pressure and temperature at which the SP test was carried out were 0.12 MPa and 600℃, respectively. The experimental results showed that the 0.2% proof stress and tensile strength in hydrogen and argon gases, which were predicted based on the SP test results, were consistent with those obtained from the tensile tests. The SP creep rupture time tended to be shorter in hydrogen gas than argon gas, and the equivalent fracture strain (rupture ductility) was slightly higher in hydrogen gas. The results obtained in the SP creep test were also qualitatively in agreement with those in the standard uniaxial creep test.

DOI： 10.2472/jsms.73.512

Scopus

CiNii Research

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Acta Materialia  

The hydrogen trapping and micromechanical behaviors of additively manufactured CoCrFeNi high-entropy alloy (HEA) using the laser powder bed fusion (L-PBF) technique in the as-built and pre-strained states were explored through nanoindentation and micro-tensile experiments combined with thermal desorption analysis. To analyze the influence of pre-straining, both global pre-strains, imposed using the interrupted tensile tests, and local strain levels, estimated using the digital image correlation measurements, were employed. It was revealed that pre-straining (which increases the dislocation density in the alloy) does not enhance the hydrogen effects on the micromechanical performance of the L-PBF HEA. To understand this, rather unexpected, result, we investigated the trapping behavior of diffusional hydrogen in detail, through thermal desorption analysis combined with the Ag decoration technique. The results are discussed in terms of the hydrogen contents and trapping sites in the L-PBF HEA.

DOI： 10.1016/j.actamat.2024.119886

Scopus

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Scripta Materialia  

Nanocrystalline (NC) dual-phase Al0.7CoCrFeNi HEAs containing face-centered cubic (FCC) and body-centered cubic (BCC) microstructural phases were fabricated by high-pressure torsion (HPT). The influences of hydrogen on the thermal desorption and nanoindentation responses of NC HEA were compared with the coarse-grained alloy. The plastic zone size and indentation size effects were carefully considered to identify the distinct contributions of the constituent phases to the hardness and its variation with hydrogen charging. Results show that the FCC phase is susceptible to a larger degree of hydrogen-induced hardening than the BCC phase. Such difference is negated in the NC samples. These results are discussed in terms of the distinct responses of FCC and BCC HEA phases to hydrogen and the governing deformation mechanisms in coarse grained and NC samples.

DOI： 10.1016/j.scriptamat.2021.114472

Scopus

担当区分：筆頭著者   記述言語：日本語   出版者・発行元：一般社団法人 日本鉄鋼協会  

In order to investigate the adaptability of small punch (SP) creep testing technique to the remaining-life assessment, the SP creep test was carried out with 2.25Cr-1Mo steel hot rehear steam piping, which had been actually used in a fossil power plant for long periods of time. The SP load (F) was converted to the stress (σ) by three different equations, which were derived based on the displacement to maximum load in the SP test (um) and the deflection to minimum deflection rate in the SP creep test (umin) for correlating the SP creep rupture data with the uniaxial ones. The experimental results showed that the SP creep rupture time of specimen removed at around outer surface of piping tended to be slightly shorter than those taken at around inner surface and center. It was also found that the SP creep rupture data were relatively in good agreement with the uniaxial ones by converting F to σ with the equations, and the creep remaining-life was well predicted by the extrapolation of short-term SP creep rupture data. The highest prediction accuracy was obtained by using the equation derived from the SP test result, that is, um. Consequently, it was confirmed that the SP testing technique could be a strong tool for creep remaining-life assessment of boiler piping.

DOI： 10.2355/tetsutohagane.tetsu-2021-077

Scopus

CiNii Research

開催年月日： 2024年11月

記述言語：日本語