Seminar of Prof. Yoji Shibutani, from Osaka University (Japan), ” How far the defect interaction between dislocation and GB affects the inside of grain?”. September 1, at 12:00 pm in the Seminar Room.

The modeling of plastic deformation over the length scales has still been a challengeable problem. One of the most crucial defect interactions related to the plasticity is the reaction between the dislocation and GB, that is, GB strengthening of Hall-Petch law from the materials science view and also improvement of ductility due to the slip transfer across GB from the plastic forming process view. Both are mechanically trade-off and conjugate. To this problem, three approaches are demonstrated; one is from the millimeter-sized tensile testing with different grain sizes and different environmental temperatures. The H-P coefficient for the flow stress is linked to the plastic strain and discuss about the “Incorporation Effect” of the emitted dislocations in the grain adjacent to the grain with the piled-up dislocation via GB. The second is from nanometer-sized molecular dynamics simulation and energy landscape estimation method. The atomistic interactions of dislocation to GB were classified into several types of reactions and the critical interaction shear stress (CISS) for the “Slip Transfer across GB” and the activation volume of the reaction of dislocation to GB were estimated. The last one is from micrometer-sized crystal plasticity finite element method. The proposed constitutive law involves the above-mentioned two contributions of “Slip Transfer across GB” and “Incorporation Effect” and discussed about the localized plastic deformation around the three types of bicrystals with <112>-axis-symmetric tilt GBes of 35A, 11A and 77A. The parameters of constitutive law were determined by the micro-pillar testing using the selective single crystals of the materials, called “Mesotesting”. All the approaches are focused on the title of “How far the defect interaction between dislocation and GB affects the inside of grain?”.

Biographic note:
Prof. Yoji Shibutani graduated from Osaka University in 1981 and from Graduate School of Osaka University in 1983 with Master Degree of Engineering. He worked at Toshiba Corp. and was engaged in the Fusion Reactor Development in 1983 to 1988. After that, he returned to Osaka University as Assistant Professor and got Doctor of Engineering in 1992 from Osaka University. He stayed at The University of Pennsylvania in USA as a visiting researcher and collaborated with Profs. Vaclav Vitek and John L. Bassani in 1993 to 1995. After that, he was promoted as Associate Professor of Kobe University in 1995 and as Professor of Osaka University in 1999. His major is solid mechanics, especially the defect theory of materials and plasticity from multiscale view and the nondestructive observation technique, which has been originally developed as Scanning Electron-induced Thermal and Acoustic Microscope (SETAM), from multiphysics view among dynamical elasticity, non-Fourier heat conduction and piezo-electricity.