Heat-induced structural changes in magnesium alloys AZ91 and AZ31 investigated by in situ synchrotron high-energy X-ray diffraction

Liu, X. J.*; Xu, P. G.; Shiro, Ayumi*; Zhang, S. Y.*; Shobu, Takahisa; Yukutake, Eitaro*; Akita, Koichi*; Zolotoyabko, E.*; Liss, K.-D.*

Journal of Materials Science, 57(46), p.21446 - 21459, 2022/12

https://doi.org/10.1007/s10853-022-07917-y

In situ diffraction characterization on microstructure evolution in austenitic stainless steel during cyclic plastic deformation and its relation to the mechanical response

Kumagai, Masayoshi*; Akita, Koichi*; Kuroda, Masatoshi*; Harjo, S.

Materials Science & Engineering A, 820, p.141582_1 - 141582_9, 2021/07

https://doi.org/10.1016/j.msea.2021.141582

Feasibility study on application of synchrotron radiation CT imaging to alloy steel for non-destructive inspection of inclusions

Shimamura, Yoshinobu*; Matsushita, Shinya*; Fujii, Tomoyuki*; Togo, Keiichiro*; Akita, Koichi*; Shobu, Takahisa; Shiro, Ayumi*

Metals, 9(5), p.527_1 - 527_9, 2019/05

https://doi.org/10.3390/met9050527

Strain measurement in Ti layers of CFRP/Ti laminates by synchrotron X-ray diffraction

Akita, Koichi; Nakatani, Hayato*; Ogihara, Shinji*; Shobu, Takahisa; Shiro, Ayumi*; Igawa, Naoki; Shimojo, Yutaka

SPring-8/SACLA Riyo Kenkyu Seikashu (Internet), 6(1), p.105 - 108, 2018/01

http://doi.org/10.18957/rr.6.1.105

no abstracts in English

Detection of fatigue damage in stainless steel by EBSD analysis; Applicability of EBSD pattern quality

Kuroda, Masatoshi*; Kamaya, Masayuki*; Yamada, Teruaki*; Akita, Koichi

Nihon Kikai Gakkai Rombunshu (Internet), 83(852), p.17-00072_1 - 17-00072_7, 2017/07

https://doi.org/10.1299/transjsme.17-00072

In order to assess the fatigue damage of austenitic stainless steels by electron backscatter diffraction (EBSD) method more simply and easily, it should be more preferable to use a commercially available general-purpose EBSD analysis software rather than to employ an in-house developed EBSD analysis programme. In the present study, EBSD measurement was performed for Type 316 austenitic stainless steels subjected to cyclic loading, and the applicability of the EBSD parameter relevant to the pattern quality, which could be obtained by the commercial software, to the fatigue damage assessment was discussed by comparing the other EBSD parameter of the averaged local misorientation (Mave), which could be calculated by the in-house developed programme. As a result, the EBSD parameter relevant to the pattern quality, which signified the full width at half maximum (FWHM) of the histogram distribution of the image quality (IQ), was saturated at the beginning stage of the fatigue cycles, while Mave was increased monotonically with the cycles. This suggested that the FWHM of IQ could be useful to detect the initial stage of the fatigue damage, while Mave was suitable for the quantitative evaluation of the fatigue damage. XRD measurement was also carried out for the same samples employed in the EBSD measurement, and the XRD data was compared with the EBSD data to discuss the crystallographic mechanism of the change in the FWHM of IQ. As a result, it was found that the FWHM of the (111) XRD peak correlated well with the FWHM of IQ. Because the (111) plane in fcc metal such as austenitic stainless steel was most preferable for slip system, this implied that the change in the distribution of the pattern quality generated by the fatigue loading could be due to the slip deformation.

Study on shot peened residual stress distribution under cyclic loading by numerical analysis

Ikushima, Kazuki*; Kitani, Yuji*; Shibahara, Masakazu*; Nishikawa, Satoru*; Furukawa, Takashi*; Akita, Koichi; Suzuki, Hiroshi; Morooka, Satoshi

Yosetsu Gakkai Rombunshu (Internet), 35(2), p.75s - 79s, 2017/06

http://www.jweld.jp/quarterly/v35/visual/35_75s.pdf

Numerical analysis of residual stress distribution on peening process

Ikushima, Kazuki*; Shibahara, Masakazu*; Akita, Koichi; Suzuki, Hiroshi; Morooka, Satoshi; Nishikawa, Satoru*; Furukawa, Takashi*

Welding in the World, 61(3), p.517 - 527, 2017/05

http://doi.org/10.1007/s40194-017-0430-4

In this study, first, an analysis method to predict the behaviour of residual stress distribution on shot peening process was proposed. In the proposed method, the load distribution on the collision of shots was modelled, and it was integrated with the dynamic analysis method based on the idealized explicit FEM (IEFEM). The accuracy of the proposed analysis system was confirmed by comparing the stress distribution on the collision of a single shot with the results analyzed by ABAQUS. The thermal elastic plastic analysis method using IEFEM was applied to the analysis of residual stress distribution of multi-pass welded pipe joint. The calculated residual stress distribution was compared with the measured residual stress distribution using X-ray diffraction (XRD). As a result, it was shown that the both welding residual distribution agree well with each other. Considering the calculated welding residual stress distribution, the modification of stress distribution due to shot peening was predicted by the proposed analysis system. As a result, the similar stress distribution with measurement by XRD was obtained in case that a large number of collisions are considered.

Non-destructive damage assessment in CFRP/Ti laminates by synchrotron radiation laminography

Nakatani, Hayato*; Kajiwara, Kentaro*; Akita, Koichi; Ogihara, Shinji*

Proceedings of 14th Japan International SAMPE Symposium & Exhibition (JISSE-14) (USB Flash Drive), 6 Pages, 2015/12

Internal stress distribution for generating closure domains in laser-irradiated Fe-3%Si(110) steels

Iwata, Keiji*; Imafuku, Muneyuki*; Suzuki, Kanki*; Shobu, Takahisa; Orihara, Hideto*; Sakai, Yusuke*; Akita, Koichi; Oya, Shinichi*; Ishiyama, Kazushi*

Journal of Applied Physics, 117(17), p.17A910_1 - 17A910_4, 2015/03

https://doi.org/10.1063/1.4916183

Internal stress distribution for generating closure domains occurring in laser-irradiated Fe-3%Si(110) steels was investigated using high-energy X-ray analysis and domain theory based on the variational principle. The measured triaxial stresses inside the specimen were compressive and the stress in the rolling direction became more dominant than stresses in the other directions. The calculations based on the variational principle of magnetic energy for closure domains showed that the measured triaxial stresses made the closure domains more stable than the basic domain without closure domains. The experimental and calculation results reveal that the laser-introduced internal stresses result in the occurrence of the closure domains.

Relaxation behavior of laser-peening residual stress under tensile loading investigated by X-ray and neutron diffraction

Akita, Koichi; Hayashi, Kengo*; Takeda, Kazuya*; Sano, Yuji*; Suzuki, Hiroshi; Moriai, Atsushi; Oya, Shinichi*

Mechanical Engineering Journal (Internet), 1(4), p.SMM0029_1 - SMM0029_8, 2014/08

https://doi.org/10.1299/mej.2014smm0029

Compressive residual stresses induced by peening techniques improve the strength properties of steels, such as fatigue and stress corrosion cracking. However, the compressive residual stress might be reduced owing to thermal and mechanical loading in-service. In this study, the behavior of surface and internal residual stresses of a laser-peened ferritic steel under quasi-static tensile loading was investigated by X-ray and neutron diffraction. The complementary use of these diffraction techniques provided decisive experimental evidence for elucidating the relaxation process. The critical applied stress of peened samples subjected to a tensile loading can be estimated from the von Misses yield criterion with the maximum tensile residual stress inside the sample.