著者

蓮沼 将太 宮田 陽平 仁田 祐輝 小川 武史

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A編 (ISSN:18848338)

巻号頁・発行日

vol.78, no.786, pp.161-170, 2012 (Released:2012-02-25)

参考文献数

8

被引用文献数

8 8

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In this study, low cycle fatigue tests were conducted for carbon steel, STS410, low alloy steel, SFVQ1A and austenitic stainless steel, SUS316NG, in order to investigate surface and internal fatigue crack growth characteristics. The tests were conducted under repeated two-step variable amplitude straining conditions to appear beach marks of cracks on the fracture surface. In these tests, periodical surface removal was conducted to suppress surface fatigue cracks to be a main crack which led final fracture. STS410 specimen under surface removal test was not broken until its diameter became too small. There was a defect observed on the section of the specimen cut longitudinally. Cracks initiated from internal inclusion for SFVQ1A and SUS316NG and those fatigue lives were slightly larger under surface removal test compared to those under no surface removal tests. Internal crack growth rates calculated from beach marks were similar to those of surface cracks under the same crack driving force or J integral range, ΔJ.

著者

蓮沼 将太 小川 武史

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.84, no.863, pp.18-00151, 2018 (Released:2018-07-25)

参考文献数

33

被引用文献数

1

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In this study, the applicability of cumulative damage law for carbon steel, STS410, was investigated. In addition, prediction method of low cycle fatigue life based on small crack growth was researched. First, low cycle fatigue tests under two step variable loading condition were performed for STS410. Variation of cumulative damage UF at failure fell within general variation range, 0.7 to 1.4. The relationship between crack length and UF was corresponded under different conditions. Crack distribution was also corresponded under different strain range conditions. Therefore, cumulative damage law is available to evaluate the fatigue life of STS410. Next, crack initiation, growth and coalescence behavior of STS410 were modeled, and Monte Carlo simulation was carried out. Fatigue life and crack growth of simulation under strain range constant condition were similar to those of experimental results. In the case of two step loading simulation, simulation results show that UF at failure fell within variation range of strain range constant simulation. These results corresponded to experimental results. Crack length and distribution of simulation also corresponded to those of experiment. Therefore, good agreement can be seen in experiment and simulation, so low cycle fatigue lives of strain range constant and variable loading condition are able to be predicted using present model.

著者

倉光 貴之 藤井 達也 蓮沼 将太 小川 武史 禹 明勲 高梨 正祐

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.850, pp.17-00066-17-00066, 2017 (Released:2017-06-25)

参考文献数

12

被引用文献数

1

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The purpose of this study is to investigate low cycle fatigue (LCF) and high cycle fatigue (HCF) strengths, crack initiation and growth behaviors of Ni based castalloy 246. LCF and HCF tests are conducted under load controlled conditions. As the result of the observation of etched specimen, the grain size is from 3 mm to 5 mm. And the microstructure is mainly composed of dendritic structure. Growth orientation of dendritic structure varies in every grain. The result of elemental analysis, Si and Ti are detected at dendritic boundary. The results of LCF test show that small cracks initiate at the first cycle, followed by the crack growth along slip direction. Observation of fracture surface reveals that small cracks originate at casting defect or dendritic boundary. The results of HCF, on the other hand, show that small cracks initiate from subsurface casting defect under Δσ ≦ 600 MPa, while fracture origin becomes surface under Δσ > 600 MPa. The result of HCF test after introducing small crack on the surface shows that small crack on the surface does not affect on the fatigue life and the location of crack initiation. As the result of EBSD, the crack initiation site is near grain boundary and the crack grows along slip plane.