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