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报告内容摘要：
    With the rapid increasing usage of advanced composites as primary load-support components in civilian and military vehicles and as protective armor solutions, the safety and durability of such materials has become an issue of paramount importance. However, the complex material and structural response of composites under such conditions have not been fully understood despite decades of extensive research. An outstanding unresolved question is how those “non-critical” damage events, which may develop under fairly low load levels, will conspire to form major, critical damage events that lead to catastrophic structure failure. As a result, costly and time-consuming experimental testing programs are needed to establish design allowables, and large safety margins have to be applied to cope with the associated uncertainty. In the past several years, my collaborators and I have been working to establish high-fidelity numerical prediction capabilities (i.e., virtual testing capabilities) in partial replacement of the costly physical experiments.
    This presentation will start with a brief summary of the most recent experimental findings on progressive composite damage processes using 3D X-ray Computer Tomography with specimens loaded in situ. The purpose is to highlight the urgent need of multiscale numerical platforms that can explicitly resolve both the small scale discrete damage events and their explicit effects on structural integrity. This will be followed by a brief comment on existing numerical approaches based on continuum damage mechanics (CDM), linear elastic fracture mechanics (LEFM), cohesive zone models (CZMs), and messless methods. The pros-and-cons and their insufficiency in coping with the complex material heterogeneity and the multiple, coupled damage events will be reviewed.
    After this introduction, I shall present the recent success in developing our top-down multiscale approach for virtual testing of composites. Focus will be on the numerical platform based on our augmented finite element method (A-FEM). It will be shown that the A-FEM is capable of modeling both the multiscale material heterogeneity and the multiple arbitrary cracking systems in composites, which is achieved by incorporating explicit descriptions of multiple damage processes and allowing for cohesive cracks to be initiated at any locations where an initiation criterion is met. Successful examples using this method to deduce the progressive failure process of several composite materials based solely on their constituent matrix, fiber, and interface properties (i.e., no need for any other failure parameters) will be given to demonstrate the virtual testing capability. The perspective of using A-FEM for fatigue and high-velocity impact loading environment will also be discussed. Finally, I shall introduce a much enhanced new A-FEM formulation currently under development within my group, which we believe will be the next generation finite element solution for arbitrary cracking problems.

报告人简介：
    Dr. Qingda Yang is an associate professor of Mechanical and Aerospace Engineering at the University of Miami (Coral Gables, FL). He obtained his B.S. (Engineering Mechanics, 1991) and M. S. (solid mechanics, 1994) from Zhejiang University, China, and a PhD (Mechanical Engineering, 2000) from University of Michigan at Ann Arbor. Prior to joining University of Miami, Dr. Yang worked for Rockwell Scientific Company (formerly known as Rockwell Science Center) as a solid mechanics scientist from 2000 to 2006.
   Dr. Yang’s primary research areas include the mechanical and thermal related issues in engineering materials and structures with emphasis on failure and damage assessment of engineering composites and biomaterials. His recent research focus has been on developing multi-scale methodologies that can lead to realistic virtual testing and designing of complex heterogeneous materials. Dr. Yang is an author/coauthor of more than 50 journal publications and book chapters. He is a member of the editorial board for the Journal of Applied Composite Materials, and is currently serving as the Chair of the Composite and Heterogeneous Materials Committee in ASME, and as an executive committee member of Aerospace Division (ASD) in ASCE.
    Dr. Yang is an award recipient of several professional and academic societies, including the Alan Gent best student paper award from Adhesion Society (1999); the Ivor K. McIvor Award (1999) and the Doris Caddell Award (2000) from University of Michigan; Technical Excellence awards from Rockwell Scientific (Golden Award, 2001; Purple Award, 2004; and Best IR&D award, 2005), and the Eliahu I. Jury Award (2007) for excellence in research from the College of Engineering at University of Miami.