Kyushu University Academic Staff Educational and Research Activities Database
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Kazuhito Ohsawa Last modified date:2017.12.15



Graduate School


E-Mail
Academic Degree
Physics
Field of Specialization
lattice defects
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.
Research
Research Interests
  • 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.
Academic Activities
Papers
1. Kazuhito Ohsawa, Keisuke Eguchi, HIDEO WATANABE, Masatake Yakaguchi, MASATOSHI YAGI, Configuration and binding energy of multiple hydrogen atoms trapped in monovacancy in bcc transition metals, PHYSICAL REVIEW B, 85, 094102, 2012.03.
2. Kazuhito Ohsawa, Junya Goto, Masatake Yamaguchi, MASATOSHI YAGI, Trapping of multiple hydrogen atoms in a tungsten monovacancy from first principles, PHYSICAL REVIEW B, 82, 184117, 2010.11.
3. K. Ohsawa and E. Kuramoto, Activation Energy and Saddle Point Configuration of High-Mobility Dislocation Loops: a Line Tension Model, Phys. Rev. B, 72, 5, Vol. 72 No. 2 (2005) p. 054105., 2005.08.
4. Kazuhito Ohsawa and Eiichi Kuramoto, Analysis of the Thermal Activation of High-Mobility Dislocation Loops, Materials Transactions, 46, 3, Vol. 46 No. 3 (2005) pp. 457-462, 2005.03.
5. K. Ohsawa and E. Kuramoto, Flexible boundary condition for a moving dislocation, Journal of Applied Physics, 86, 1, Vol 86 p. 179, 1999.07.
Presentations
1. Stress function for dislocation loops in anisotropic crystals.
2. Equilibrium structure and thermal activation of dislocation loops in BCC metals.
Educational
Social
Professional and Outreach Activities
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.