Speaker: Yong Zhu, Andrew A. Adams Distinguished Professor, Department of Mechanical and Aerospace Engineering, with affiliate appointments in Materials Science and Engineering, Biomedical Engineering, and electrical and computer engineering, at North Carolina State University (NCSU).
Abstract: Crystalline nanowires are not only important building blocks for a broad spectrum of applications such as flexible and stretchable electronics, but also an ideal platform to study fundamental nanomechanics. In this talk, I will start with recent advances in in-situ TEM nanomechanical testing based on microelectromechanical systems (MEMS), including high-temperature testing, high-strain-rate testing, and displacement-controlled testing with feedback control. Next, I will discuss several recent studies using MEMS-based in-situ TEM testing: 1) Effect of free surface and internal boundaries on the plasticity mechanisms (twinning vs. slip). We observed competition of twinning and slip in single-crystalline metallic nanowires – dependent on the cross-sectional shape of the nanowire – which was attributed to the change of surface energy associated with each mechanism. We also found that twin boundaries (either one or five) along the nanowire length direction can cause interesting recoverable plasticity and Bauscinger effect. 2) Brittle to ductile transition. We found that the crystalline Si nanowires under tension are brittle at room temperature but exhibit ductile behavior with dislocation-mediated plasticity at elevated temperatures. We revealed that unconventional ½<110>{001} dislocations become activated with increasing temperature. 3) Hydrogen embrittlement. We probed hydrogen embrittlement using metallic nanowires as a model system. We found increasing yield strength and brittle failure with the presence of hydrogen, which was attributed to the hydrogen-induced suppression of dislocation nucleation at the free surface. I will conclude the talk with a few applications of nanowires in soft electronics and robotics.
Bio: Yong Zhu is the Andrew A. Adams Distinguished Professor in the Department of Mechanical and Aerospace Engineering, with affiliate appointments in Materials Science and Engineering, Biomedical Engineering, and electrical and computer engineering, at North Carolina State University (NCSU). He received his B.S. degree from the University of Science and Technology of China, and his M.S. and Ph.D. degrees from Northwestern University. He was a postdoctoral fellow at the University of Texas at Austin before joining NCSU in 2007 as an Assistant Professor. His group conducts research at the intersection of solid mechanics and micro/nano-engineering, including nanomechanics, microelectromechanical systems, and nanomaterial-enabled stretchable electronics. His work has been recognized with a number of awards including James R. Rice Medal from the Society of Engineering Science, Bessel Research Award from the Alexander von Humboldt Foundation, ASME Gustus L. Larson Memorial Award and Sia Nemat-Nasser Early Career Award, Eshelby Mechanics Award for Young Faculty, and JSA Young Investigator Lecture Award from Society for Experimental Mechanics.
Webinar: https://iastate.zoom.us/j/91597257036?pwd=bVJSQk1YOUh4d3BCWENpTUlnb0U3QT09
Passcode: 698329