EVENT DETAILS
Poking and Bulging of 2D Crystals
Nanshu Lu, Ph.D.
Temple Foundation Endowed Associate Professor
Department of Aerospace Engineering & Engineering Mechanics
Department of Electrical and Computer Engineering
Department of Mechanical Engineering
Department of Biomedical Engineering
Texas Materials Institute
The University of Texas at Austin
Abstract- In recent years, nano-tents and nano-bubbles formed by two-dimensional (2D) materials have seen a surge of interest because they are able to induce in-plane strain and strain gradient via easy-to-apply out-of-plane deformations. Our work has unveiled what sets the in-plane strains in terms of the shape characteristics of nano-tents and nano-bubbles. Moreover, out-of-plane poking or bulging, also known as indentation or blister tests, are popular methods for the measurement of in-plane elasticity of thin sheets. For linear elastic sheets, a load-cubic deflection relation has been frequently assumed so that the stiffness of the sheet could be readily extracted. However, we find that recent results of indentation and bulge tests on 2D materials do not follow this relation, which can be attributed to the slippage of atomically smooth 2D materials against their supporting substrates. Besides, the interfacial slippage could cause instabilities such as radial wrinkles in suspended region, with finite and predictable lengths. To gain a quantitative understanding, we assume constant interfacial shear traction and study the extent of the radial wrinkles and the effective stiffness of thin sheets upon poking and bulging. We identify a single dimensionless parameter governing these mechanical responses--the sliding number--defined by comparing the sheet tension (that drives the slippage) with the interfacial traction (that resists the slippage). We discuss several useful asymptotic behaviors emerging at small and large sliding numbers. These understandings are helpful for determining when the effect of the interfacial slippage (as well as other substrate-associated subtleties) can be neglected in these tests. We also propose a simple poking/bulging methodology immune to the complexities caused by slippage, pretension, Poisson's ratio, substrate roughness, etc., enabling a robust and accurate extraction of 2D material stiffness.
Bio- Dr. Nanshu Lu is currently Temple Foundation Endowed Associate Professor at the University of Texas at Austin. She received her B.Eng. from Tsinghua University, Beijing, Ph.D. from Harvard University, and then Beckman Postdoctoral Fellowship at UIUC. Her research concerns the mechanics, materials, manufacture, and human / robot integration of soft electronics. She is currently Associate Editor of Nano Letters and Journal of Applied Mechanics. She has been named 35 innovators under 35 by MIT Technology Review (TR 35) and iCANX/ACS Nano Inaugural Rising Star. She has received US NSF CAREER Award, US ONR and AFOSR Young Investigator Awards, 3M non-tenured faculty award, and most recently, the Thomas J.R. Hughes Young Investigator Award from the ASME Applied Mechanics Division. She has been invited to speak at the National Academy of Engineering Frontiers of Engineering Symposia and the National Academy of Medicine emerging leaders forum. She was selected as one of the five great innovators on campus and five world-changing women at the University of Texas at Austin. She is a highly cited researcher identified by Web of Science. For more information, please visit Dr. Lu's research group webpage at https://sites.utexas.edu/nanshulu/ and follow her Twitter: @nanshulu.
TIME Thursday May 26, 2022 at 10:00 AM - 11:00 AM
LOCATION B211, Technological Institute map it
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CONTACT Jeremy Wells jeremywells@northwestern.edu
CALENDAR McCormick - Mechanical Engineering