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2015 年 05 月 06 日
Seminar - The surface eigenstress model and size-dependent Young’s modulus and ultimate tensile strength* By Prof. Tong-Yi ZHANG

Date: 06 May 2015 (Wednesday)

Time: 11:00 am – 12:00 pm

Venue: N002, The Hong Kong Polytechnic University

Abstract:

This talk will include two parts. In the first part the development of innovative
methods for characterizing the mechanical properties of nanowires, nanobelts and
ultrathin films will be introduced. In the second part the fundamental understanding of
deformation mechanisms of a thin film multilayered structure under mechanical loading
and its removal characteristics involved in abrasive machining will be discussed.

The surface eigenstress model was developed to study surface-induced size-dependent Young’s modulus and ultimate tensile strength. Surface eigenstress gauges the born surface stress of a nanomaterial that still maintains the dimensions as that without free surfaces. In general, tensile (or compressive) surface eigenstress renders a lager (or smaller) nominal modulus of a thin film or a nanowire and thus results in the thinner-the harder (or softer) elastic behaviour. Nonlinear scaling laws were also developed for the thickness-dependent Young’s modulus under tension/compression and bending; and for the size-dependent ultimate biaxial tensile strength of thin films. First principles calculations and molecular dynamics (MD) simulations verified the theoretical predictions from the surface eigenstress model and put insights into the surface induced strengthening or weakening mechanism.

Bio-sketch:

Tong-Yi Zhang, PhD in 1985 in materials physics from University of Science and Technology Beijing, China, is Fang Professor of Engineering and Chair Professor of Mechanical and Aerospace Engineering at Hong Kong University of Science and Technology. He is Associate Editor-in-Chief of Science China: Technological Science and the Fracture and Continuum Mechanics Subject-Editor of Theoretical and Applied Fracture Mechanics; and a vice president of the International Congress on Fracture (ICF) and a vice president of The Far East and Oceanic Fracture Society. He was a recipient of two Second Prizes of State Natural Science Award, China, and the 1988 National Award for Young Scientists, China. He became ICF Fellow in 2013, Fellow of the Hong Kong Academy of Engineering Sciences in 2012, member of Chinese Academy of Sciences in 2011, Senior Research Fellow of Croucher Foundation, Hong Kong, in 2003, Fellow of ASM International, USA, in 2001.

 

* The work was supported by a General Research Fund (622312) from the Hong Kong Research Grants Council.