Stress and plastic strain partitioning behaviors and those contributions to martensitic transformation of retained austenite in medium manganese and transformation-induced plasticity-aided bainitic ferrite steels

Hojo, Tomohiko*; Koyama, Motomichi*; Kumai, Bakuya*; Zhou, Y.*; Shibayama, Yuki; Shiro, Ayumi*; Shobu, Takahisa; Saito, Hiroyuki*; Ajita, Saya*; Akiyama, Eiji*

ISIJ International, 65(2), p.284 - 296, 2025/02

https://doi.org/10.2355/isijinternational.ISIJINT-2024-268

Biofilm-mediated interactions between plastics and radiocesium in coastal environments

Battulga, B.; Nakanishi, Takahiro; Atarashi-Andoh, Mariko; Otosaka, Shigeyoshi*; Koarashi, Jun

Environmental Science and Pollution Research, 31, p.60080 - 60092, 2024/10

https://doi.org/10.1007/s11356-024-35164-y

A ubiquitous distribution of plastic debris has been reported in aquatic and terrestrial environments; however, the interactions between plastics and radionuclides and the radioactivity of environmental plastics remain largely unknown. Here, we characterize biofilms developing on the surface of plastic debris to explore the role of plastic-associated biofilms as an interaction medium between plastics and radiocesium (Cs) in the environment. Biofilm samples were extracted from plastics (1-50 mm in size) collected from two contrasting coastal areas in Japan. The radioactivity of plastics was estimated based on the Cs activity concentration of the biofilms and compared seasonally with surrounding environmental samples (i.e., sediment and sand). Cs traces were detected in biofilms with activity concentrations of 21-1300 Bq kg biofilm (dry weight), corresponding to 0.04-4.5 Bq kg plastic (dry weight). Our results reveal the interaction between Cs and plastics and provide evidence that organic and mineral components in biofilms are essential in Cs retention in environmental plastics.

Dynamics and functions of microbial communities in the plastisphere in temperate coastal environments

Battulga, B.; Nakayama, Masataka; Matsuoka, Shunsuke*; Kondo, Toshiaki*; Atarashi-Andoh, Mariko; Koarashi, Jun

Water Research, 264, p.122207_1 - 122207_12, 2024/10

https://doi.org/10.1016/j.watres.2024.122207

Growing attention has been given to microbial attachment and biofilm formation on microplastics (MPs; sizes: 5 mm) in the environment. Here, we explore the microbial communities in the plastisphere to improve our understanding of microbial ecology as well as their impacts on aquatic ecosystems. Using the amplicon sequence of 16S and ITS genes, we identified bacterial and fungal community composition and diversity on MPs, surface waters, bottom sediments, and coastal sands in two contrasting coastal areas of Japan. Significantly different microbial diversity and taxonomic composition were detected depending on sample types and research sites. This research highlights the microbial metabolic functions in MP-associated biofilm, which could be the key to uncovering the true impact of plastic debris on the global ecosystem.

Multi-modal 3D image-based simulation of hydrogen embrittlement crack initiation in Al-Zn-Mg alloy

Higa, Ryota*; Fujihara, Hiro*; Toda, Hiroyuki*; Kobayashi, Masakazu*; Ebihara, Kenichi; Takeuchi, Akihisa*

Materials Transactions, 65(8), p.899 - 906, 2024/08

https://doi.org/10.2320/matertrans.MT-L2024007

It is indispensable to suppress hydrogen embrittlement (HE) to develop the strength of the Al-Zn-Mg alloy. Because intergranular fracture (IGF) is mainly observed when HE occurs in the alloy, we need to understand the IGF initiation to suppress HE. In the present study, we investigated the stress, strain, and H concentration, which influence the IGF initiation, in actual fractured regions by simulation of a crystal plasticity finite element method and H diffusion analysis in a 3D image-based model, which was created based on 3D polycrystalline microstructure data obtained from X-ray imaging technique. Combining the simulation and in-situ observation of the tensile test sample by X-ray CT, we examined the stress, strain, and H concentration, and discussed the IG crack initiation condition. As a result, it is revealed that stress normal to grain boundary induced by crystal plasticity dominates IG crack initiation while the accumulation of H due to stress has little impact on it.

Hierarchical deformation heterogeneity during Lders band propagation in an Fe-5Mn-0.1C medium Mn steel clarified through scanning electron microscopy

Koyama, Motomichi*; Yamashita, Takayuki*; Morooka, Satoshi; Yang, Z.*; Varanasi, R. S.*; Hojo, Tomohiko*; Kawasaki, Takuro; Harjo, S.

Tetsu To Hagane, 110(3), p.205 - 216, 2024/02

https://doi.org/10.2355/tetsutohagane.TETSU-2023-052

Unstable stress-triaxiality development and contrasting weakening in two types of high-strength transformation-induced plasticity (TRIP) steels; Insights from a new compact tensile testing method

Matsuno, Takashi*; Fujita, Taiki*; Matsuda, Tomoko*; Shibayama, Yuki; Hojo, Tomohiko*; Watanabe, Ikumu*

Journal of Materials Processing Technology, 322, p.118174_1 - 118174_16, 2023/12

https://doi.org/10.1016/j.jmatprotec.2023.118174

The impact of high stress triaxiality on work hardening in transformation-induced plasticity (TRIP) steel has been widely acknowledged, particularly through measurements of the austenite fraction. Understanding this TRIP behavior is crucial for predicting material fracture in press-forming processes. However, the actual flow stresses under high-stress-triaxiality conditions remain largely undetermined. To address this gap, we developed a new tensile testing method using tiny notched round bars to investigate stress-triaxiality-induced work hardening in TRIP steels. The specimens were analyzed using two-dimensional micrometry to allow finite element analyses to identify the flow stress. Additionally, we conducted in situ tensile tests in which their crystal lattice stresses were monitored using synchrotron X-ray diffraction (XRD) to realize mechanism analyses of the unexpected work-hardening behavior identified by the developed tensile testing method. Our combined approach revealed a mutual, unstable increase in the flow stress and stress triaxiality in the TRIP-aided bainitic ferrite steel, which reduced the hardening exponent coefficients and thus induced a higher stress triaxiality. In contrast, the TRIP-aided martensitic steel exhibited a weakening behavior, characterized by a significant decrease in the hardening exponent coefficients in the case of the sharpest notch. XRD analyses showed that microstructural heterogeneity led to an extraordinarily high hydrostatic stress in the austenite phase, accounting for these contrasting behaviors. This finding challenges the established consensus on TRIP steels and suggests the need for a revised framework for their application in press-forming, taking into account stress-triaxiality conditions.

Measurement methods for the radioactive source distribution inside reactor buildings using a one-dimensional optical fiber radiation sensor (Contract research); FY2021 Nuclear Energy Science & Technology and Human Resource Development Project

Collaborative Laboratories for Advanced Decommissioning Science; Nagoya University*

JAEA-Review 2022-033, 80 Pages, 2022/12

JAEA-Review-2022-033.pdf:4.08MB

The Collaborative Laboratories for Advanced Decommissioning Science (CLADS), Japan Atomic Energy Agency (JAEA), had been conducting the Nuclear Energy Science & Technology and Human Resource Development Project (hereafter referred to "the Project") in FY2021. The Project aims to contribute to solving problems in the nuclear energy field represented by the decommissioning of the Fukushima Daiichi Nuclear Power Station (1F), Tokyo Electric Power Company Holdings, Inc. (TEPCO). For this purpose, intelligence was collected from all over the world, and basic research and human resource development were promoted by closely integrating/collaborating knowledge and experiences in various fields beyond the barrier of conventional organizations and research fields. The sponsor of the Project was moved from the Ministry of Education, Culture, Sports, Science and Technology to JAEA since the newly adopted proposals in FY2018. On this occasion, JAEA constructed a new research system where JAEA-academia collaboration is reinforced and medium-to-long term research/development and human resource development contributing to the decommissioning are stably and consecutively implemented. Among the adopted proposals in FY2019, this report summarizes the research results of the "Measurement methods for the radioactive source distribution inside reactor buildings using a one-dimensional optical fiber radiation sensor" conducted from FY2019 to FY2021. Since the final year of this proposal was FY2021, the results for three fiscal years were summarized. The present study aims to develop an optical fiber type radiation sensor that can measure the radiation distribution one-dimensionally along the fiber under a high radiation field for the decommissioning of 1F. Based on the conventional time-of-flight method, we found several promising sensor candidates for the radiation distribution measurement under high dose rate and many scattered gamma-rays.

Hierarchical deformation heterogeneity during Lders band propagation in an Fe-5Mn-0.1C medium Mn steel clarified through scanning electron microscopy

Koyama, Motomichi*; Yamashita, Takayuki*; Morooka, Satoshi; Yang, Z.*; Varanasi, R. S.*; Hojo, Tomohiko*; Kawasaki, Takuro; Harjo, S.

ISIJ International, 62(10), p.2043 - 2053, 2022/10

https://doi.org/10.2355/isijinternational.ISIJINT-2022-098

Constraint effect on fracture mechanics evaluation for an under-clad crack in a reactor pressure vessel steel

Shimodaira, Masaki; Tobita, Toru; Takamizawa, Hisashi; Katsuyama, Jinya; Hanawa, Satoshi

Proceedings of ASME 2020 Pressure Vessels and Piping Conference (PVP 2020) (Internet), 7 Pages, 2020/08

https://doi.org/10.1115/PVP2020-21441

In JEAC 4206 which prescribes the methodology for assessing the structural integrity of reactor pressure vessels (RPVs), an under-clad crack (UCC) at the inner surface of RPV is postulated, and it is required that the fracture toughness of RPV steels is higher than stress intensity factor for at the crack tip during the pressurized thermal shock event. In the present study, to investigate the effect of cladding on the fracture toughness, we performed three-point bending fracture toughness tests and finite element analyses (FEAs) for an RPV steel containing an UCC or a surface crack, and the constraint effect for UCC was also discussed. As the result, we found that the fracture toughness for UCC was considerably higher than that for surface crack. On the other hand, the FEAs showed that the cladding decreased the constraint effect for UCC.

Environmental measurement using plastic scintillation fiber after the accident at the Fukushima Daiichi Nuclear Power Plant

Sanada, Yukihisa

Kogaku, 45(8), p.300 - 305, 2016/08

http://ci.nii.ac.jp/naid/40020939422

For the purpose of environmental radiation measurement, decontamination effect and detection of leakage of radionuclide plastic scintillation fiber (PSF) had been used for the wide area as technique to measure radiation distribution quickly after the Fukushima Daiichi Nuclear Power Plant accident that occurred in March, 2011. The PSF can easily measure radiation distribution due to position sensing of radiation source. The PSF was used for the measurement before and after the decontamination by considering features that PSF obtained many point data at one time. The PSF was used for the measurement of radiocesium concentration in sediment of irrigation pond by considering features that PSF has high water resistance. This paper described the principle of PSF and the application example after the accident at the Fukushima Daiichi Nuclear Power Plant.