Colloquium attented

5月14日工学院力学与空天技术系学术报告

题目一： Pressing Issues in Reliability and Durability of Aerospace Composites and Modeling Strategy
题目二： Direct Multiscale modeling for Coupled Multiple Damage Evolution in Structural Composites
报告人： Dr. Qingda Yang （杨庆大）
Dept. Mechanical & Aerospace Engineering, University of Miami

主持人：苏先樾 教授
时 间：5月14日（周一）下午2:30
地 点：力学楼434会议室

欢迎广大师生光临！要求力学系没课的研究生必须参加。
联系人：刘才山，62756177

EDUCATION:
Ph. D. University of Michigan, Ann Arbor, Michigan, 2000
M.S. Zhejiang University, Hangzhou, P. R. China, 1994
B. S. Zhejiang University, Hangzhou, P.R. China, 1991
RESEARCH:
Multi-scale, multidisciplinary failure/damage analysis of engineering and biological materials, linear and nonlinear fracture mechanics, structural composite design and analysis; nonlinear fluid-structure interaction.
EXPERIENCE:
2006-present: Assistant Professor, University of Miami
2000-2006: Member of Technical Staff,Rockwell Science Center (RSC)
2000 Spring: Postdoctoral research fellow, University of Michigan (Ann Arbor)
1994-1996: Research Engineer, Institute of Special Engineering Mechanics, Zhejiang University
HONORS:
1) Best IR&D Project Award, Division of Materials Technology, RSC, 2005.
2) Purple Award for excellent performance in a DUST program, RSC, 2004.
3) Golden Award for excellent performance an IR&D program, RSC, 2001.
4) Doris Caddell Award for outstanding student research achievements, Dept. MEAM, University of Michigan, 2000.
5) Ivor K. McIvor Award for outstanding scholastic performance in applied mechanics, College of Engineering, University of Michigan, 1999.
6) A run-up for Alan Gent Best Student Paper Award in the 22nd Annual Meeting of Adhesion Society, 1999.
ABSTRACT
The ever-increasing fuel cost has driven aerospace industry to use more extensively fiber reinforce composites (FRCs) in replace of traditionally used metals. FRCs have long been advocated as excellent alternatives to metals that can offer major weight-savings (efficiency), better damage tolerance (longer service time with less maintenance), stronger resistance to environmental attacks (endurance), and more flexibility in component design. However, despite a huge body of literature on composite studies some key issues remain unresolved, with the most critical ones being 1) lack of proven test methodologies, 2) no reliable durability assessment techniques, and 3) no established certification procedures to satisfy governmental regulation authorities. The primary cause of such significant shortfalls is the lack of understanding of the interplay among the multiple damage processes (matrix cracking, matrix/fiber shear splitting, delamination, local fiber rupture or kinking, etc.) that co-evolve in response to environmental changes and external loading. These damage modes occur in various materials scales at different load levels and are strongly coupled to each other. It is this strongly coupled nonlinear damage evolution that dominates the macroscopic composite properties. To achieve realistic damage tolerance design, the key question of how damage transfers from a lower level scale to a higher one has to be answered. Neither traditional continuum mechanics based composite theories nor micro-mechanics based models are likely to meet the challenge because they cannot address the full spectrum of damage modes occurring at various materials and structural scales. There is an urgent demand from aerospace industry for new approaches that encompass a multi-scale, multi-disciplinary methodology to address the multiple damage evolution in a unified self-consistent way, upon which a realistic damage tolerance design methodology can be established.
In first part of this two-session presentation, the current start-of-art design in composite materials will be reviewed. Focuses will be on the recently developed/developing advanced PMCs and CMCs with 3D integral features. This will be followed by a discussion of the material length scale issues in FRCs and their close relation to various damage modes. Major challenges that must be resolved to achieve realistic damage tolerance design will be highlighted. Existing analytical and computational models will be briefly reviewed and their pros and cons discussed.
In the second part of the presentation, a multi-scale approach the presenter has been developing in an effort to address the coupled damage evolution in aerospace composite materials will then be introduced. The necessity of using nonlinear fracture mechanics models and seeking explicit representation of discrete damage modes will be emphasized and strategies of how to implement explicitly such damage models into standard simulation tools will be presented. Applications of the approach to two common classes of aerospace FRCs, i.e., textile composites and laminate composites will be presented and discussed. It will be demonstrated that with this approach the nonlinear coupling among different damage/fracture modes becomes a nature outcome of the analysis, and results obtained for some important composite problems are far more superior than those obtained using existing methods. For textile composites wherein fiber architecture (interlacing pattern) plays a key role in mechanical performance, a scheme called Binary Model (BM) is developed to explicitly include the spatial fiber tow architecture into the formulation. Failure prediction of BM is achieved through the use of micromechanics-based gage-averaging scheme. The BM formulation and gage-averaging scheme and their successful application to several textile composites will be presented. Finally, future improvement of the multi-scale approach and its possible extension to other engineering and biological materials shall also be discussed before the presentation is concluded.