北京大学力学与工程科学学院

力学系学术报告

报告人  Yannis F. Dafalias教授

University of California, Davis

时  间：7月24日（周四）下午14:00

地  点：工学院1号楼210会议室

报告摘要：

The motivation stems from the need to address the design of tall buildings under wind loading enhanced in both intensity and duration due to climate change and causing significant ratchetting due to plastic deformation. For this purpose, the Bounding Surface (BS) plasticity model for metals is enhanced by a novel modification of the original proposition by Burlet, Cailletaud, and Delobelle (BCD) for the kinematic hardening of a classical Armstrong/Frederick (AF) model. An additional new constitutive feature is provided by the free-to-choose kinematic hardening of the BS. The new model achieves two objectives: first, it maintains the inherent feature of BS for decoupling plastic modulus and direction of kinematic hardening, and second, allows for a greater flexibility as to the relative kinematic hardening direction without altering the value of the plastic modulus. The new model exhibits a dramatically improved capability to simulate multiaxial ratcheting (MR), because it affects directly the changing flow rule direction during complex multiaxial loading, without sacrificing accurate simulations under uniaxial ratcheting (UR). The new model, named SANIMETAL-BCD, is shown to yield superior simulations of UR and very complex MR experimental data for three Carbon Steel specimens, in comparison with other models, within a much simpler constitutive framework.  Shortcomings and future necessary improvements are discussed in detail.

报告人简介：

Dr. Yannis F. Dafalias is Distinguished Professor Emeritus in the Department of Civil and Environmental Engineering of the University of California at Davis, and Emeritus Professor at the Department of Mechanics, School of Applied Mathematical and Physical Sciences, of the National Technical University of Athens (NTUA), Greece. He is currently a Senior Researcher at the Institute of Thermo-mechanics of the Czech Academy of Sciences. He received his Ph.D. in Engineering Sciences, 1975, from the University of California at Berkeley, his M.S. in Engineering Mechanics, 1971, from Brown University, and his Diploma of Civil Engineering, 1969, from NTUA.

Y. F. Dafalias main research focuses on the development and implementation of constitutive models for metals, sands, clays, concrete, polymers, biomaterials etc. He developed the concepts of bounding surface in plasticity theory that has become a standard tool of constitutive modeling, and the plastic and constitutive spins that introduced new aspects of theoretical formulation in large inelastic deformations and rotations theories. Recent research topics include turbulence in fluid dynamics, biomechanics, DEM investigations and the development of a novel fabric-enhanced Anisotropic Critical State Theory in soil mechanics. 

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