Solid-sate-bonding techniques have been widely used and investigated in welding and joining community, and also recently in novel nanomanufacturing processes. Nevertheless, it is well known in the community of mechanics of materials that crack healing, an opposite process to Griffith fracture, does not usually take place at ambient conditions except for extremely flat surfaces. Traditionally, the solid-state-bonding mechanisms are believed to be dominated by atomic interdiffusion across the interface. In contrary, we propose that both lateral diffusion along the interface and creep deformation of surrounding materials dominate the gap closure and thus dictate the kinetics of bonding. Additionally, the competition between these two processes defines a length scale, on which various solid-state-bonding techniques find their characteristic parametric space. Our model has been applied to friction stir welding and related techniques, where an additional technical hurdle on the interface stick-slip behavior has been solved. Details can be found in Papers #142, #158, and #165 at https://gao.utk.edu.

报告人简历:

Yanfei Gao is currently a Professor at Department of Materials Science and Engineering, University of Tennessee, USA. He received his BS degree in Engineering Mechanics (advised by Prof. Zhenhan Yao) and a dual BS degree in Computer Science from Tsinghua University (Beijing, China) in 1999, and PhD from Princeton University (advised by Prof. Zhigang Suo) in 2003. After a two-year post-doctoral training at Brown University, he joined the University of Tennessee in 2005. He was also a Joint Faculty with Oak Ridge National Laboratory in 2005~2018. His research activities have been focusing on mechanical metallurgy. He and his PhD students have solved a number of key engineering problems for advanced manufacturing and petrochemical industries; one of such works has led to a R&D100 Award. He has published more than 160 journal papers, many of which are in Journal of the Mechanics and Physics of Solids and Acta Materialia. He belongs to the 2% world top scientists from a Stanford University study and has a Web of Science H-index of 39. He is a former champion in hammer throw in Tsinghua University campus games.