Research Group "A02(d): Microdynamics Analysis on Advanced Materials
Containing Ultra-High Density Lattice Defects
- "Giant
Straining Process for Advanced Materials Containing Ultra-High Density
Lattice Defects, Program Leader Zenji Horita (Kyushu Universty)" -
- [Members]
-
Akihiro Nakatani (Osaka University) ... (Group Leader)
Tomotsugu Shimokawa (Kanazawa University)
Takashi Matsushima (Tsukuba University)
Toshihiro Kameda (Tsukiba University)
Ryosuke Matsumoto (Kyoto University)
Takahiro Kinoshita (Osaka University)
Ken-ichi Saitoh (Kansai University)
Yutaro Mukudai (Student of Osaka University)
- [Letter 1]
-
The purpose of this group is to clarify the emergent mechanism of
unique mechanical properties of giant-strained materials. The key
concept of the methodology is on the time evolution of those internal
structures consisting of ultra-high density lattice defects. We adopt
simulations based on discrete models in various space and time scales,
e.g., molecular dynamics, discrete dislocation dynamics, distinct
element method and quasicontinuum method. New multiscale
meso-plasticity models we develop here can seamlessly bridge between
large-scale molecular dynamics and coarse-grained models and also can
express the representative volume element and the elementary process
for plastic deformation of giant-strained materials. Using the
multiscale models, we determine the better internal structure of the
materials, e.g., grain arrangements in a bimodal structure and the
distribution of grain boundary characteristics, and propose design
principles in collaboration with experimental groups.
- [Letter 2]
- In ultra-grained materials, it is difficult to maintain
dislocation sources and form dislocation cells or sub-grains in the
grains; therefore, it can be presumed that the grain boundary becomes
an important dislocation source and sink. The right figure shows the
interaction between dislocations and the grain boundary dislocation
pile-up, dislocation absorption, and dislocation
transmission expressed by the multi-scale atomic simulations
[T. Shimokawa, et.al., Phys. Rev. B, Vol. 75, pp.144108(1-11) (2007)].
The influence of the grain boundary structures on the above
phenomenon is investigated, and the critical forces on the dislocation
in small-angle tilt grain boundaries for it to eject from the
boundaries are evaluated.
- [Letter 3]
- In the group A02(d) the mechanism of mechanical properties
observed in macroscopic point of view are studied through
understanding the microstructure and corrective behavior of lattice
defects. The members conduct not only analysing the time evolution of
geometrical structures in a framework of boundary value problem in
various scale levels, but linking the methodologies each other towards
multiscale analyses. The figure shows a stress distribution in the
vicinity of a grain boundary (GB) in which an extrinsic edge
dislocation is absorbed. The results obtained by both discrete
dislocation plasticity and quasicontinuum theory show good agreement
each other. The stress field of original GB composed of intrinsic
dislocation array at regular interval is short-ranged, but a
long-ranged stress field is formed in the GB-dislocation interacting
system (Y.Mukudai, T.Shimokawa and A.Nakatani, APCOM'07- EPMESC XI,
Dec.3-6, 2007 Kyoto, JAPAN). The discrete dislocation approach
substantiated by the atomistic simulation is expected as a powerful
tool for understanding the complex defect configuration which is
formed by severe plastic deformation.
- [Corresponding Person]
-
Prof. Akihiro Nakatani
Microdynamics Laboratory,
Department of Adaptive Machine Systems,
Osaka University
2-1 Yamadaoka, Suita, 565-0871 Osaka, JAPAN
nakatani@ams.eng.osaka-u.ac.jp
TEL:06-6879-7244
FAX:06-6879-7246