OHSAWA KAZUHITO
Organization
Research Institute for Applied Mechanics Division of Nuclear Fusion Dynamics Assistant Professor
Interdisciplinary Graduate School of Engineering Sciences Department of Interdisciplinary Engineering Sciences（Concurrent）
Interdisciplinary Graduate School of Engineering Sciences Department of Interdisciplinary Engineering Sciences（Concurrent）
Title
Assistant Professor
Contact information
Profile
1 Activation Energy for a Dislocation Loop
According to Vineyard’s theory, we estimate the activation energy of a dislocation loop. Our analytic solution shows that the activation energy is represented with elliptic integrals. Besides, plural saddle points with different energies simultaneously appear in the phase space in an appropriate condition. Therefore, the transition process of the dislocation loop can be regarded as a complicated bifurcation problem.
2 Relation between Peierls Stress and Slip System
Peierls stress τp, which is substantial crystal strength for plastic deformation, are widely distributed. For example, covalent crystal have the largest Peierls stress 10^-1, BCC metals' ones are 10^-3G and FCC metals' are 10^-5G, where G is shear modulus. The magnitude of Peierls stress is approximately determined from the crystal structure. Especially important parameter is h/b, where h is the width of slip plane and b is length of Burgers vector. We investigate the relation between the parameter h/b and Peiels stress with numerical simulations and obtained an exponential dependence τp/G = A exp(-h/b C).
3 Lattice Statics Green's Function
Lattice statics Green's function describes displacements of atoms induced by applied external force. Traditional elastic Green's function has a logarithmic divergence at the point where the external force is exerted. On the other hand, the lattice statics Green's function avoids such divergence. So it is very avaiable to calculate dislocation behaviors or crack expansions. Our developed Green's function is adjustable about lattice constant, elastic momulus to actual crystal and keeps the symmetry of stress tensor in the contimuun elastic limit. Besides, we calculate lattice Green' function for semi-infinite half space derived from Dyson's equation.
4 Flexible Boundary Condition for a Moving Dislocation
The displacement field around a dislocation is long-range one which decreases as r^-1. So, in a computer simulation, image force from the boundary often affects the results in a small simulation box. It is necessary to avoid or decrease such boundary effects. For this purpose, we introduce a flexible boundary condition, which changes associated with the state of dislocation core region. The equation of motion for the boundary condition is based on the principle of least action. Applied the boundary condition to a simulation of moving dislocation, we obtained expected results which do not strongly depend on model size.
5. Computer simulation in terms of first-principle calculation
Tungsten is used in fusion reactors. In particular, interaction of hydrogen with vacancy in the tungsten materials.
External link
Degree
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Physics
Research Interests・Research Keywords
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Research theme： hydrogen storage in vacancies in Fe-Al alloys controlled by accelerator irradiation
Keyword： hydrogen alloy storage
Research period： 2021.10 - 2023.3
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Research theme： Stabilization effect of impurities for vacancy-cluster growth in tungsten
Keyword： tungsten
Research period： 2018.4
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Research theme： Hydrogen absorption properities of depleted uranium intermetallics
Keyword： hydrogen absorption, depleted uranium
Research period： 2013.4
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Research theme： Study on interaction between BCC metals and hydrogen by first principles calculations
Keyword： BCC metals, hydrogen, first principles calculation
Research period： 2010.4
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Research theme： Study on radiation damage by first principle simulations
Keyword： radiation damage, first principle
Research period： 2008.4
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Research theme： Study on stress function for dislocation loops in anisotropic crystals
Keyword： stress function, dislocation, anisotropic crystal
Research period： 2007.1
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Research theme： Activation energy for dislocation loops
Keyword： dislocation、 saddle point、activation energy、Vineyard theory
Research period： 2003.9 - 2008.3
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Research theme： Flexible boundary condition for a moving dislocation
Keyword： Flexible Boundary Condititon
Research period： 1998.1 - 2002.3
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Research theme： Lattice statics Green's function
Keyword： elasticity, Green's function
Research period： 1996.1 - 2000.1
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Research theme： Study on the relation between Peierls stress and crystal structure
Keyword： Peierls stress、 plasticity
Research period： 1990.4 - 1996.3
Papers
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Configuration and binding energy of multiple hydrogen atoms trapped in monovacancy in bcc transition metals Reviewed International journal
Kazuhito Ohsawa, Keisuke Eguchi, HIDEO WATANABE, Masatake Yakaguchi, MASATOSHI YAGI
PHYSICAL REVIEW B 85 094102-1 - 094102-8 2012.3
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Trapping of multiple hydrogen atoms in a tungsten monovacancy from first principles Reviewed International journal
Kazuhito Ohsawa, Junya Goto, Masatake Yamaguchi, MASATOSHI YAGI
PHYSICAL REVIEW B 82 184117-1 - 184117-6 2010.11
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Activation Energy and Saddle Point Configuration of High-Mobility Dislocation Loops: a Line Tension Model Reviewed International journal
K. Ohsawa and E. Kuramoto
Phys. Rev. B 72 ( 5 ) 2005.8
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Analysis of the Thermal Activation of High-Mobility Dislocation Loops Reviewed International journal
Kazuhito Ohsawa and Eiichi Kuramoto
Materials Transactions 46 ( 3 ) 457 - 462 2005.3
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Flexible boundary condition for a moving dislocation Reviewed International journal
K. Ohsawa and E. Kuramoto
Journal of Applied Physics 86 ( 1 ) 179 - 185 1999.7
Presentations
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Characteristics of Hydrogen Configuration in Tungsten Monovacancy International conference
Kazuhito Ohsawa, Takuya Yamamoto, Hideo Watanabe, Masatake Yamaguchi, Masatoshi Yagi
International Conference on Fusion Reactor Materials 2011.10
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Stress function for dislocation loops in anisotropic crystals International conference
Kazuhito Ohsawa, Masatoshi Yagi, Hirokazu Koizumi, and Eiichi Kuramoto
Dislocations 2008 2008.10
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Equilibrium structure and thermal activation of dislocation loops in BCC metals International conference
Kazuhito Ohsawa and Eiichi Kuramoto
3rd international conference of multiscale materials modeling 2006.9
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鉄空孔周辺の銅原子の安定構造
大澤一人、外山健、渡邊英雄
日本金属学会 2025.3
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Interaction of vacancy trapping H or He to impurity in iron
大澤一人
富山大学研究推進機構水素同位体科学研究センター「一般共同研究成果報告会」 2025.3
Professional Memberships
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日本金属学会
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日本物理学会
Academic Activities
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ポスター審査員
材料照射研究会 （ Japan ） 2022.12
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ポスター審査員
日本金属学会 （ Japan ） 2021.3
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座長（Chairmanship）
日本金属学会 （ Japan ） 2020.9
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Screening of academic papers
Role(s)： Peer review
2020
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座長
日本金属学会 （ Japan ） 2019.9
Research Projects
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空孔－溶質結合エネルギーの高精度直接測定と原子炉圧力容器鋼照射組織形成機構の解明
Grant number：24K01396 2024.4 - 2027.3
Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research (B)
外山 健, 大澤 一人
Grant type：Scientific research funding
原子空孔-溶質原子の結合エネルギーは、原子力材料をはじめとする材料研究における最も基礎的な物理量である。本研究では、新しい実験手法（空孔-溶質が1対1で結合した空孔-溶質複合体のみを欠陥として含む試料を作製し、先端手法で空孔-溶質複合体を観察する）により、鉄中の銅などの重要溶質に関して、空孔-溶質結合エネルギーを直接実測しようとする。得られた空孔-溶質結合エネルギーを用いて、原子炉圧力容器鋼について、照射による微細組織形成機構を解明する。本研究で得られる空孔-溶質結合エネルギーの実験値は、今後期待される計算機を活用した原子力材料の研究開発など、幅広い材料研究で活用されることが期待される。
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加速器照射を利用した規則型Fe-Al合金中の空孔制御による多量水素貯蔵に関する研究
2021.10 - 2023.3
若狭湾エネルギー研究センター（日本）
Authorship：Coinvestigator(s)
加速器によるイオン照射によって金属材料に空孔を導入した試料を作成し、その空孔中に貯蔵される水素に関する研究を行う。
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第一原理計算による金属空孔中の水素に関する研究
2018.6 - 2019.3
Joint research
Authorship：Principal investigator Grant type：Other funds from industry-academia collaboration
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Grant number：17K06993 2017 - 2020
Japan Society for the Promotion of Science Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research (C)
Ohsawa Kazuhito
Authorship：Principal investigator Grant type：Scientific research funding
Tungsten shows promise as structural material used in fusion reactors in the future. Tritium used in the reactor as fuel is radioisotope and we are worried about its large amount of retention in the tungsten specimen. Vacancy and vacancy cluster in tungsten are main trap sites of the hydrogen isotope. So, their stable structures and growth process in tungsten specimen are studied by numerical simulations. As a result, impurities in the metal contribute to the stabilization of the vacancy clusters. In particular, oxygen play an important role in the stabilization.
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第一原理計算による金属空孔中の水素に関する研究
2016.6 - 2017.3
Joint research
Authorship：Principal investigator Grant type：Other funds from industry-academia collaboration
Class subject
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プログラミング基礎、シミュレーション物理学基礎
2020.4 - 2020.9 First semester
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プログラミング基礎、シミュレーション物理学基礎
2019.4 - 2019.9 First semester
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プログラミング基礎、シミュレーション物理学基礎
2018.4 - 2018.9 First semester
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プログラミング基礎
2015.4 - 2015.9 First semester
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金属物理工学
2009.10 - 2010.3 Second semester
Visiting, concurrent, or part-time lecturers at other universities, institutions, etc.
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2021 福岡工業大学 Classification:Part-time lecturer
Semester, Day Time or Duration：前期、火曜日、２限
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2020 福岡工業大学 Classification:Part-time lecturer Domestic/International Classification:Japan
Semester, Day Time or Duration：前期、火曜日、２限
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2019 福岡工業大学 Classification:Part-time lecturer Domestic/International Classification:Japan
Semester, Day Time or Duration：前期、火曜日、２限
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2018 福岡工業大学 Classification:Part-time lecturer Domestic/International Classification:Japan
Semester, Day Time or Duration：前期、火曜日、２限
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2017 福岡工業大学 Classification:Part-time lecturer Domestic/International Classification:Japan
Semester, Day Time or Duration：前期、火曜日、２限
Outline of Social Contribution and International Cooperation activities
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Attendance of Technical meeting of the international atomic and molecular code centre network on simulation of plasma-material interaction experiments hold in Vienna, Austria, from 29 to 31 July 2015
Social Activities
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写真の提供
学術図書出版社 2004.8
Travel Abroad
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2009.7
Staying countory name 1：France Staying institution name 1：Institut d'Etudes Politiques
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2008.11
Staying countory name 1：France Staying institution name 1：南パリ大学
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2000.1 - 2000.3
Staying countory name 1：United States Staying institution name 1：UCLA