时间：2019-06-06 15:00
地点：九里1号综合楼240
报告人：Qingda Yang
个人简介：
Dr. Qingda Yang is a full professor of the Department 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 joined the faculty of the Department of Mechanical and Aerospace Engineering at the University of Miami in 2006. Dr. Yang’s recent research has focused mainly on developing multi-scale methodologies that can lead to realistic virtual testing and designing of complex heterogeneous materials and structures under general and/or extreme thermal-mechanical loading environments. His research has attracted funding from many federal agencies and industrial companies. Dr. Yang is an author/coauthor of more than 90 peer-reviewed journal publications, 4 book chapters, and 30 refereed conference proceedings. He is an editorial board member for the Journal of Applied Composite Materials and the journal of Multifunctional Composites.
讲座内容：
The uncertainty associated with the long term safety of critical load-bearing composite structures such as airframes and wings remains a major challenge. Linear elastic fracture mechanics (LEFM) based approach has been used to guide the design of fatigue in composites. More recently, nonlinear fracture mechanics models such as the cohesive zone models (CZMs), coupled with experimentally established Paris Laws, have been developed for lifing assessment of such composites.
In this presentation I will give a detailed formulation of a recently developed, non-Paris-law based fatigue CZM. Currently the model uses well-established S-N curves for initiation indicators. For propagation, micromechanics based damage laws that can be calibrated from simple fracture tests are proposed. It will be demonstrated through comparisons with experimental data of several composites that the model can 1) predict Paris laws under pure fracture mode, 2) predict Paris laws for any mixed mode condition without the need of mode-mix dependent parameters, 3) faithfully predict crack initiation without starter crack and the ensuing propagation (Figure 1), and 4) the model predicts correctly the fast crack growth at small crack size limit (near threshold rapid crack growth), which is an open issue that has not been well understood in composites. Finally, I shall discuss issues associated with how to implement such a fatigue CZM into the A-FEM framework. Examples of validated fatigue simulation results on composite materials will be provided for discussion.
