报告人：Xijia Wu（吴犀甲），加拿大国家研究院（NRC）高级研究员
报告时间：2018年5月14日 下午14:00
报告地点：屏峰校区机械楼A311
摘要：
About one hundred seventy five years ago, a German scientist August 
found fatigue cracks on the surface of an axle of locomotive when he investigated the train crash incident in Versailles, France, 1842. Ever since, characterization of materials’ fatigue properties has been a major task in structural and component design, mostly through experimental work. Fatigue design curves are mostly expressed in terms of traditional engineering design parameters such as stress and/or strain amplitudes, e.g., S-N curve or e-N curve. On the other hand, fatigue crack growth behavior is characterized with the linear elastic fracture mechanics quantity, i.e., the cyclic stress intensity factor, DK. But, ASTM standard load-shedding fatigue crack growth rate testing introduced crack closure and “fatigue threshold” phenomena. The question remains whether fatigue threshold exists under service loading conditions (rather than load-shedding conditions), which has important implications for holistic structural integrity analysis.
Recently, the author has revisited the Tanaka-Mura model and corrected the dimensional error in the plastic strain of the dislocation pile-up, which resulted in a new theoretical formula calculating fatigue crack nucleation life based on material’s Burgers vector, elastic modulus and surface energy. A transgranular fatigue crack growth rate model has also been developed based on the restricted slip reversal (RSR) process. An integrated creep-fatigue theory (ICFT) is further developed to describe the constitutive behaviors of materials subjected to general thermomechanical loadingand damage accumulation consisting of surface/subsurface crack nucleation and propagation in coalescence with internally distributed damage.
In the above model, each type of damage is related to the mechanism strain derived from the constitutive equation for the responsible physical mechanism. The ICFT has been implemented in the finite element model (FEM) for component analyses subjected to prescribed boundary conditions and loading profiles. Examples are given to illustrate this physics-based holistic life prediction approach.
报告人简介：
Xijia Wu is currently a senior fellow in the Structures and Materials Performance Laboratory, Aerospace Research Centre in National Research Council Canada. He is also employed as adjunct professor in department of mechanics and aviation, Carleton University, Ottawa, Canada. He obtained his BS in department of modern mechanics, University of Science and Technology of China. He got MS in institute of mechanics, Chinese Academy of Sciences. He finished his PhD from department of engineering mechanics,University of Ottawa. After that, he did postdoctoral research in National Research Council Canada. He joined the Boeing Company for one year. After that, he joined the National Research Council Canada again as senior fellow since 1999. He received the National Research Council Canada Award in 1999, the Technical Cooperation Program Achievement Award in 2005, and Casey Baldwin Award in 2008. Xijia has published more than 72 journal papers and more than 52 conference papers on the research area of fatigue.
