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[Lecture] Theory of controlled fragmentation in cold drawing

DEC . 24 2021

Speaker:
Huajian Gao
Distinguished University Professor, College of Engineering, College of Science, Nanyang Technological University, Singapore
Scientific Director, Institute of High Performance Computing, Agency for Science, Technology and Research, Singapore

Host: Prof. Yang Wei, PKU College of Engineering

Time: 10:00-11:30 am, Dec. 24, 2021, Beijing Time

Venue:
Zoom Meeting ID: 944 0326 9736 Passcode: 420565

Abstract:

Cold drawing is a mature and widely adopted technique in the shaping of metallic and polymeric materials inindustry. Interestingly, cold drawing of a ductile cladding containing abrittle core wire or a ductile substrate with a deposited brittle film has recently emerged as a method to produce micron sized rods and ribbons through controlled fragmentation induced by local necking. While this method shows potential in providing an economic yet efficient technological platform forlarge-scale manufacturing of structures at the micro- and nanoscale, there is so far no theoretical guideline on how to control the size of the fragmented components. Here, we develop a theory of controlled fragmentation in colddrawing of both axisymmetric core-cladding and plane-strain film-substrate systems. The theory reveals that the process is governed by a reverse shear lag effect which gives rise to a peak tensile stress leading to controlled fragmentation near the necking zone. Of particular interest is that the fragmentation size is predicted to depend on the interfacial shear strength,geometrical dimension and stiffness of the brittle material, and therefore can be reduced via increasing the strength of interfacial interactions and/or decreasing geometrical dimensions such as the core radius or film thickness.

Biography:

Huajian Gao received his B.S. degree from Xian Jiaotong University in 1982, and his M.S. and Ph.D. degrees in Engineering Science from Harvard in 1984 and 1988, respectively. He served on the faculty of Stanford from 1988-2002, as Director at the Max Planck Institute for Metals Research from 2001-2006 and as Walter H. Annenberg Professor of Engineering at Brown from 2006-2019. At present, he is a Distinguished University Professors at Nanyang Technological University and Scientific Director of the Institute of High Performance Computing in Singapore. Professor Gao’s research has been focused on the understanding of basic principles that control mechanical properties and be haviors of materials in both engineering and biological systems. He is the Editor-in-Chief of Journal of the Mechanics and Physics of Solids. His list of honors includes election to National Academy of Sciences and National Academy of Engineering in USA, and numerous awards such as the Timoshenko Medal from American Society of Mechanical Engineers.

Source:
College of Engineering