| Kazuhito Ohsawa | Last modified date：2024.04.04 |
Graduate School
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Homepage
https://kyushu-u.elsevierpure.com/en/persons/kazuhito-ohsawa
Reseacher Profiling Tool Kyushu University Pure
Academic Degree
Physics
Country of degree conferring institution (Overseas)
No
Field of Specialization
lattice defects
Total Priod of education and research career in the foreign country
00years02months
Outline Activities
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.
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.
Research
Research Interests
- hydrogen storage in vacancies in Fe-Al alloys controlled by accelerator irradiation
keyword : hydrogen alloy storage
2021.10～2023.03. - Stabilization effect of impurities for vacancy-cluster growth in tungsten
keyword : tungsten
2018.04. - Hydrogen absorption properities of depleted uranium intermetallics
keyword : hydrogen absorption, depleted uranium
2013.04. - Study on interaction between BCC metals and hydrogen by first principles calculations
keyword : BCC metals, hydrogen, first principles calculation
2010.04. - Study on radiation damage by first principle simulations
keyword : radiation damage, first principle
2008.04. - Study on stress function for dislocation loops in anisotropic crystals
keyword : stress function, dislocation, anisotropic crystal
2007.01. - Activation energy for dislocation loops
keyword : dislocation、 saddle point、activation energy、Vineyard theory
2003.09～2008.03Activation Energy for a Dislocation Loop. - Flexible boundary condition for a moving dislocation
keyword : Flexible Boundary Condititon
1998.01～2002.03Flexible Boundary Condition for a Moving Dislocation. - Lattice statics Green's function
keyword : elasticity, Green's function
1996.01～2000.01Lattice Statics Green's Function. - Study on the relation between Peierls stress and crystal structure
keyword : Peierls stress、 plasticity
1990.04～1996.03Relation between Peierls Stress and Slip System.
Papers
Presentations
| 1. | Stress function for dislocation loops in anisotropic crystals. |
| 2. | Equilibrium structure and thermal activation of dislocation loops in BCC metals. |
Educational
Educational Activities
I belong to a laboratry of interdisciplinary graduate school of engineering sciences, so I study with gradurated students. They and I read scientific textbooks and solve problems as practice.
Social
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