1、李少凡教授学术报告题 目： A Multiscale Dislocation Pattern Dynamics -Towards an atomistic-informed crystal plasticity报告人： 李少凡 教授 University of California-Berkeley时 间： 7 月 7 日 10:00地 点： 江宁校区乐学楼 1116欢迎广大师生参加！河海大学力学与材料学院 计算力学研究所Abstract：Dislocations in a deformed crystal tend to aggregate into various dense format
2、ions separated by relatively dislocation free regions. These dense formations are called dislocation patterns that underlie most important crystal plasticity features such as work hardening and strain localization. In this work, we show that the previously developed multiscale crystal defect dynamic
3、s (MCDD) method (Li et al. (2015) Philosophical Magazine, 94,1414-1450. and Lyu and Li, (2017) Journal of Mechanics and Physics of Solids, 107, 379-410.) is actually a discrete dislocation pattern dynamics, in which we link the early pattern of the dislocation distribution, or the microstructure of
4、crystal defect in general, with that of original crystal lattices as part of material genome.The main developments of present work are: (1) Using the dislocation dynamics invariants and scaling laws, we demonstrated that the multiscale crystal defect dynamics is in fact a multiscale dislocation patt
5、ern dynamics; (2) The multiscale dislocation pattern dynamics may lead to an atomistically-informed crystal plasticity theory, and (3) It is shown that cyclic plastic responses of FCC crystals may be captured by MCDD simulations. The work is highlighted by the use of the hierarchical higher order Ca
6、uchy-Born rule approach, which models different dislocation patterns with different order of Cauchy-Born rules, so that it can capture the overall inelastic response of crystalline materials. In doing so, we have developed a MCDD based crystal plasticity finite element method (CPFEM) to simulate cry
7、stal slip and shear band formation in single crystals at sub micron scale.In this approach, coarse-grained models are adopted for both bulk media and material interphase or process zone. In bulk elements, the first order Cauchy-Born rule is adopted, so we can formulate an atomistic enriched continuu
8、m constitutive relation to describe the material behaviors. All the nonlinear deformations are assumed to be confined inside the process zone, and the process zone between the bulk elements is remodeled as a finite-width strip whose lattice constants and atomistic potential may be the same or differ
9、ent from those of the bulk medium. Inside the interphase zone, the higher order Cauchy-Born rules are adopted in process zones, and a higher order strain gradient-like coarse grain constitutive model is derived, which can capture the size-effect at the small scales. All interphase or process zones a
10、re constructed such that they are part (a subset) of slip planes in a lattice space. The multiscale crystal defect dynamics has been applied to simulate both dislocation motion and crack propagations in both single crystals and polycrystalline solids. Crack branching and void formation have been fou
11、nd possible for different element mesh stacking fault energies, which are dictated, by the effective lattice structure or microstructure in the process zone elements.Speakers BioDr. Shaofan Li is currently a full professor of applied and computational mechanics at the University of California-Berkel
12、ey. Dr. Li graduated from the Department of Mechanical Engineering at the East China University of Science and Technology (Shanghai, China) with a Bachelor Degree of Science in 1982; he also holds Master Degrees of Science from both the Huazhong University of Science and Technology (Wuhan, China) an
13、d the University of Florida (Gainesville, FL, USA) in Applied Mechanics and Aerospace Engineering in 1989 and 1993 respectively. In 1997, Dr. Li received a PhD degree in Mechanical Engineering from the Northwestern University (Evanston, IL, USA), and he was also a post-doctoral researcher at the Nor
14、thwestern University during 1997-2000.In 2000, Dr. Li joined the faculty of the Department of Civil and Environmental Engineering at the University of California-Berkeley. Dr. Shaofan Li has also been a visiting Changjiang Professor in the Huazhong University of Science and Technology, Wuhan, China
15、(2007-2013). Dr. Shaofan Li is the recipient of IACM (International Association of Computational Mechanics) Fellow Award 2017; Distinguished Fellow Award of ICCES 2014; ICACM Computational Mechanics Award 2013, USACM Fellow Award (2013), A. Richard Newton Research Breakthrough Award 2008, and NSF Career Award 2003. Dr. Li has published more than140 articles in peer-reviewed scientific journals (SCI) with h-index 42 (Google Scholar), and he is also the author of two research monographs/graduate textbooks.
