著者

橋本 翔 小俣 弘樹 松永 久生

出版者

一般社団法人 日本機械学会

雑誌

日本機械学会論文集 (ISSN:21879761)

巻号頁・発行日

vol.83, no.852, pp.16-00585-16-00585, 2017 (Released:2017-08-25)

参考文献数

17

被引用文献数

1

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Rolling contact fatigue (RCF) tests were conducted using rolling bearings with a micro-drilled hole on the raceway. In all the tests, fatigue crack initiated at the edge near the bottom of the hole, and then propagated by shear mode. Even in the unbroken specimens tested up to N = 1×108 cycles, a short fatigue crack was found at the edge. By using stress intensity factor (SIF) range calculated for initial defect size, fatigue life data were uniformly gathered inside a small band irrespective of the diameter and depth of the hole. In addition, it was found that the crack size dependency of threshold SIF range, which is well-known for mode I fatigue crack, also exists in mode II fatigue crack emanating under the rolling contact. The values of threshold SIF ranges obtained by the RCF tests were in good agreement with those obtained in the torsional fatigue tests under a static compression.

著者

松岡 三郎 古谷 佳之 竹内 悦男 蛭川 寿 松永 久生

出版者

一般社団法人 日本機械学会

雑誌

日本機械学会論文集 (ISSN:21879761)

巻号頁・発行日

vol.87, no.895, pp.20-00439, 2021 (Released:2021-03-25)

参考文献数

16

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In order to clarify the effect of internal hydrogen on the fatigue life properties of SUS304, SUS316 and SUS316L, tensile tests and low- and high-cycle fatigue life tests were carried out in air at room temperature using 10, 68 and 100 MPa hydrogen-charged specimens. High-cycle fatigue life tests demonstrated that S-N curve (i.e., relationship between stress amplitude, σa, and number of cycles to failure, Nf) of each steel was higher in hydrogen-charged specimen than in uncharged specimen. The increase in fatigue limit, Δσw, with internal hydrogen was 40 MPa in 100 MPa hydrogen-charged specimens, 20 or 30 MPa in 68 MPa hydrogen-charged specimens, and 0 or 10 MPa in 10 MPa hydrogen-charged specimens. Low-cycle fatigue life tests manifested that εta-Nf curve (i.e., relationship between total strain amplitude, εta, and number of cycles to failure, Nf) of 68 MPa hydrogen-charged specimen was nearly coincident with that of uncharged specimen in SUS316L, whereas 68 MPa hydrogen-charging markedly lowered εta-Nf curve in SUS304. The fraction of strain-induced martensite was measured on specimens fractured by tensile tests and low- and high-cycle fatigue life tests. The critical value of the martensite fraction below which 68~100 MPa hydrogen-charging does not cause hydrogen embrittlement, fmH, was 1 % in tensile tests. On the other hand, the fmH value was 9% in low- and high-cycle fatigue life tests. The increase in fatigue limit due hydrogen-induced solid solution strengthening, Δσw, in high-cycle fatigue life tests was expressed as Δσw (MPa) = 15.4 × 237H, where H is the hydrogen content (mass %). In addition, the hydrogen-induced strengthening of stress amplitude, Δσa, and 0.2% proof strength, Δσ0.2, in low-cycle fatigue life tests was expressed as Δσa+0.2 (MPa) = 15.4 × 296H. The results inferred that the contribution of hydrogen to solid solution strengthening was about 10 times larger than that of carbon and nitrogen when compared at the same mass concentration.

著者

ケビンサニー 岡﨑 三郎 髙桑 脩 松永 久生 船越 裕亮 沖田 耕一

出版者

一般社団法人 日本機械学会

雑誌

M&M材料力学カンファレンス 2019 (ISSN:24242845)

巻号頁・発行日

pp.OS0319, 2019 (Released:2020-05-25)

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Tension-compression fatigue tests were conducted on non-charged and hydrogen-charged additively manufactured Ni-based superalloy 718 to investigate the effect of solute hydrogen on the fatigue strength properties of the material. The surface condition of the specimens was either as-built or mechanically-polished, aiming to clarify the effect of process-induced defects and roughness on the property. Fractographic observations using a scanning electron microscope manifested that process-induced defects existed at the fracture origin of as-built specimens, whereas such defects were not observed in the mechanically-polished specimens. However, both the fatigue life and the fatigue limit of the specimens were neither affected by surface condition nor by hydrogen. The results revealed that (1) the defects were not detrimental to the fatigue strength of the material due to its large defect-size tolerance accounted to its coarse-grained microstructure, based on comparison with previous studies conducted on forged Alloy 718, and (2) hydrogen caused no remarkable influence on both crack growth rate and crack growth threshold of the material.

著者

松岡 三郎 松永 久生 山辺 純一郎 濱田 繁 飯島 高志

出版者

一般社団法人 日本機械学会

雑誌

日本機械学会論文集 (ISSN:21879761)

巻号頁・発行日

vol.83, no.854, pp.17-00264-17-00264, 2017 (Released:2017-10-25)

参考文献数

29

被引用文献数

19

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Considering in design by analysis, four types of tests, slow-strain-rate tensile (SSRT), fatigue life, fatigue crack-growth (FCG), and elasto-plastic fracture toughness (JIC) tests, were conducted with low-alloy steels, JIS-SCM435 and JIS-SNCM439, in 115 MPa hydrogen gas and air at room temperature (RT). In addition to above tests at RT, the SSRT tests were also conducted in 115 MPa hydrogen gas and air at 120 oC and in 106 MPa hydrogen gas and 0.1 MPa nitrogen gas at -45 oC. The low-alloy steels used in this study had tensile strengths (σB) ranging from 824 to 1201 MPa with fine and coarse tempered-martensitic microstructures. In the SSRT and fatigue life tests, the tensile strength and fatigue limit were not degraded in hydrogen gas. The FCG tests revealed that the FCG rate (da/dN) was accelerated in hydrogen gas; however, there existed an upper bound of the FCG acceleration, showing the FCG rate in hydrogen gas was about 30 times larger than that in air, when σB was lower than 900 MPa. The JIC tests demonstrated that the fracture toughness (KIC) in air was 207 MPa·m1/2 at σB = 900 MPa, whereas the hydrogen-induced crack-growth threshold (KI,H) was 57 MPa·m1/2 at σB = 900 MPa. Based on these results, we proposed advanced guidelines on the use and design for SCM435 and SNCM439 on design by analysis in 115 MPa hydrogen gas, which enable to design the storage cylinders used in 70 MPa hydrogen station with lower cost without compromising safety.

著者

橋本 翔 小俣 弘樹 松永 久生

出版者

一般社団法人 日本機械学会

雑誌

日本機械学会論文集 (ISSN:21879761)

巻号頁・発行日

vol.83, no.852, pp.16-00584-16-00584, 2017 (Released:2017-08-25)

参考文献数

19

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It has been shown that rolling contact fatigue (RCF) test using specimen having a small drilled hole is a useful method for evaluating the effect of small defect on flaking strength of steels. In this study, RCF tests of rolling bearings having a small drilled hole were carried out. The flaking failure was considered as a problem of shear-mode fatigue crack emanating from the small defect. As a first step to quantify the crack-growth threshold on the basis of fracture mechanics, mode II stress intensity factor range, ΔKII, of a ring-shaped crack emanated around the edge of a drilled hole under the passing of a rolling element was analyzed by using finite element method. And then, the obtained values were correlated with the ΔKII values of penny-shaped cracks in an infinite body under uniform shear through the intermediary of a correlation factor, fdrill. The stress intensity factor of the ring-shaped crack was uniformly correlated with that of the penny-shaped crack by the single factor fdrill irrespective of hole diameter, d, depth of hole edge, h’, and maximum contact pressure, qmax, within the ranges: d = 0.05 ~ 0.2 mm, h’ = 0.05 ~ 0.345 mm and qmax = 2.0 ~ 3.0 GPa. The obtained results will be applied for the quantification of RCF test results shown in the subsequent paper.