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Biography


Prof. Sergei Alexandrov
A.Ishlinskii Institute for Problems in Mechanics of the Russian Academy of Sciences, Russia
Title:
Generation of Fine Grain Layers in the Vicinity of Friction Surfaces in Metal Forming Processes: Theory and Experiment.
Abstract:
It is well known that cracks can produce stress singularities in linear elastic materials. The stress intensity factor is one of the basic concepts in linear elastic fracture mechanics. This parameter appears in asymptotic analyses performed in the vicinity of a sharp crack-tip and is the coefficient of the singular term. In spite of the fact that the assumptions under which the stress intensity factor is determined are not satisfied in real materials (the crack-tip is not sharp and a region of inelastic deformation exists in its vicinity), this approach is effective in structural design. A similar concept in rigid plastic solids is the strain rate intensity factor. This parameter appears in asymptotic analyses performed in the vicinity of maximum friction surfaces and is the coefficient of the singular term in a series expansion of the equivalent strain rate. The stain rate intensity factor in plasticity can play a similar role to that of the stress intensity factor in elasticity. In particular, the strain rate intensity factor controls the magnitude of the equivalent strain rate in the vicinity of frictional interfaces. On the other hand, the equivalent strain rate is involved in many evolution equations for parameters that characterize material properties. Therefore, the strain rate intensity factor controls the intensity of physical processes in a narrow layer of material near frictional interfaces in processes of plastic deformation. Such layers (fine grain layers) actually appear in real metal-forming processes. This presentation concerns with general asymptotic analysis near maximum friction surfaces for several rigid plastic models which demonstrates the existence of the strain rate intensity factor. A number of available analytic solutions are used to reveal the effect of process and material parameters on the magnitude of the strain rate intensity factor. For the models described by hyperbolic systems of equations, the strain rate intensity factor is derived in characteristic coordinates. This significantly simplifies the calculation of the strain rate intensity factor by means of numerical methods. A numerical solution for the strain rate intensity factor in compression of a plastic layer between two rough plates is presented and compared to an approximate analytical solution. Finally, results of an extrusion test designed to generate a fine grain layer in the vicinity of the friction surface are discussed.
Biography:
Sergei Alexandrov is a Research Professor at the Laboratory for the Mechanics of Strength and Fracture of Materials and Structures at A. Ishlinskii Institute for Problems in Mechanics of the Russian Academy of Sciences. He received his Ph.D. in Physics and Mathematics in 1990 and D.Sc. in Physics and Mathematics in 1994. He worked as a Professor at Moscow Aviation Technology Technical University (Russia), a Visiting Scientist at ALCOA Technical Center (USA), GKSS Research Centre (Germany) and Seoul National University (South Korea), and was a Visiting Professor at Aveiro University (Portugal), University of Besancon (France) and Technical University of Malaysia (Malaysia). He is a member of the Russian National Committee on Theoretical and Applied Mechanics. Sergei Alexandrov has published more than 350 papers in journals, books and conference proceedings, including two monographs and around 190 papers in journals indexed in the Web of Science. He has participated in the scientific committee of several international conferences and served as a reviewer in a wide range of international journals. He is on the editorial board of several journals including Continuum Mechanics and Thermodynamics (Springer), Structural Engineering and Mechanics (Technopress), Scientific World Journal (Hindawi), and Journal of Applied Mathematics (Hindawi). His research areas are plasticity theory, fracture mechanics, and their applications to metal forming and structural mechanics. .
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