X-Mechanics: An Endless Frontier

Yang Wei

Zhejiang University

Abstract: In contrast to the conventional wisdom that mechanics is a relatively mature subject, the new manifestation of mechanics in an extended or crossed form is unfolding. Mechanics is now powering all subjects, from physical sciences, life sciences to social sciences. We name this new phase for the development of mechanics X-Mechanics. The present talk outlines the contents of X-Mechanics from four aspects: cross media, cross scales, cross compliances, and cross cyber/physical spaces. X-mechanics constitutes an endless frontier of science and technology. Examples related to bio-mechanics will be discussed, including bio-compatible hydrogels and their derivatives; cross-scale simulation and experimentation, flexible electronics and soft electro-mechanical fishes. From another aspect, solids in nano-scales may exhibit extreme strength and elasticity. The nano-scaled specimen can be made by diamond, ice or high entropy alloy. For the case of single crystal natural diamond, the nano-pillars that deplete interior defects and with superior surface finishing can be produced, and the nano-pillar could withstand bending up to 13.4% elastic stretch at the surface. Translated with a non-linear elastic relation facilitated by ab initio calculation, we are able to achieve an extraordinary tensile strength of 125GPa, quite close to the theoretical strength of diamond. We are able to drive a very clean cleavage crack through the diamond nano-pillar and that gives rise to the blade of a sharp “Atomic Knife” of diamond, with an edge radius of only 1nm. The atomic wedge can be used as a sweeper to cut metals (such as gold). For ice fibres of sub-micron diameter, an extreme elastic strain of 10.9% is acquired, far exceeding the previous record of 0.3%. For high entropy alloy in nano-scale, an extreme elastic strain of about 10% can be achieved. Tension-induced melting for crystalline metals, as envisaged by Lindemann, is realized. These results indicate ample room for upgrading the mechanical behaviour of solids in nano-scales.

Bio: Yang Wei was graduated from Northwestern Polytechnic University in 1976. He received a M.S. in Engineering from Tsinghua University in 1981 and a Ph.D. in Engineering from Brown University in 1985. Yang Wei started his career at the Department of Engineering Mechanics of Tsinghua University, and became a professor in 1989. He chaired the Academic Committee of Tsinghua University (2004-2006). From 2004 to 2006, he served as the Director-General of the Academics Degrees Committee of the State Council of China. From 2006 to 2013, he took the position of the President of Zhejiang University. Since 2013, he has been appointed as the President of the National Natural Science Foundation of China (NSFC). Prof. Yang made contributions in Fracture, Micromechanics and X-Mechanics. Yang Wei was elected as a member of the Chinese Academy of Sciences (CAS) in 2003. He is also a member of TWAS since 2004, a foreign member of NAE since 2017. Yang Wei’s honors include the Calvin Rice Lecture Award, ASME, 2012; Eric Reissner Medal, ISES, 2011 and W. T. Koiter Medal, ASME, 2015. He currently chairs the review for Sceince & Technology Award of Macau.