Prof. Khanh Chau Le, Ruhr University Bochum, Germany

Dr. Khanh Chau Le is an extraordinary professor at the Ruhr University Bochum, Germany. He also serves as the co-director of the Master Program in Computational Engineering at the Vietnamese German University, Vietnam. He is a member of editorial boards of two international journals in mechanics (International Journal of Plasticity and Archive of Applied Mechanics).
His first scientific results relate to applications of the variational-asymptotic method in the theory of high-frequency vibrations of elastic shells and rods. He developed also the theories of low- and high-frequency vibrations of piezoelectric shells and rods. Variational-asymptotic method and its applications in the theory of vibrations of shells and rods was summarized in his monograph “Vibrations of shells and rods”, Berlin, Springer Verlag, 1999. He wrote later two other books entitled “Introduction to Micromechanics” and “Energy Methods in Dynamics”
Dr. Le’s recent research interests are in the field of nonlinear dynamics, fracture mechanics, crystal plasticity, crack nucleation, and continuum dislocation theory. His results in these areas are presented in leading scientific journals and at various conferences (nearly 130 publications, with the total impact factor 160). According to Google Scholar, the number of citations of his paper is 1240, with the h-index being 20, and the i10-index being 38.

Speech Title: Dislocation Mechanism of Microstructural Changes in Ductile Single Crystals

Abstract: The present paper considers three problems: i) martensitic phase transition involving dislocations, ii) formation of grain boundaries during severe plastic deformations, iii) thermal softening effect and shear band formation. The two first problems turn out to be non-convex variational problems of energy minimization that will be solved within the continuum dislocation theory (CDT). In the first problem it will be shown that the coexistence of phases having piecewise constant plastic slip in laminates is possible for the two-well free energy density. The jumps of the plastic slip across the phase interfaces determine the surface dislocation densities at those incoherent boundaries. The number of phase interfaces should be determined by comparing the energy of dislocation arrays and the relaxed energy minimized among uniform plastic slips. In the second problem we interpret the grain boundary as surfaces of weak discontinuity in placement but strong discontinuity in plastic slip. The set of governing equations and jump conditions are derived for the energy minimizers admitting such surfaces of discontinuity from the variational principle. By constructing energy minimizing sequences having piecewise constant plastic and elastic deformation in two examples of ductile single crystals deforming in plane strain simple shear or uniaxial compression, it is shown that the formation of lamellae structure with grain boundaries is energetically preferable. The number of lamellae is estimated by minimizing the energy of grain boundaries plus the energy of boundary layers. The third problem will be solved by the thermodynamic dislocation theory (TDT) developed recently by J. Langer and the author of this talk.