August 28th, 2017

ISE Welcomes Ill Ryu

Size dependent mechanical behaviors in metals: Defects make materials interesting

Seminar by Ill Ryu, Assistant Professor

Mechanical Engineering, University of Texas at Dallas

Thursday, August 31st  from 11:00am – 12:00pm

210E Baker Systems, 1971 Neil Avenue

Nanotechnology attracts much attention due to not only its useful engineering applications, but also their superior material performances. As the dimensions of the devices become smaller and smaller, however, understanding the mechanical properties of materials at sub-micron length scales becomes more challenging. This is driven by the knowledge that many mechanical properties at the sub-micron scale differ from those at the macroscopic scale and, in addition, mechanical deformations are coupled with other concurrent physical phenomena, such as diffusion, chemical reaction, and phase transformation. For the reliable design of MEMS or NEMS devices, nanotechnology has always called for an understanding of the mechanical behaviors of materials at small length scales. In this talk, size dependent plasticity in metallic micropillars will be discussed in terms of dislocation mechanics. Considering dislocation sources from the surface, micropillar plasticity will be analyzed using three dimensional dislocation dynamics model to understand how dislocation behavior relates to mechanical response in metals. In addition, we also have performed dislocation dynamics simulation to investigate the size effect in bi-crystalline FCC micropillars, taking account for the role of the grain boundary as both a source and a sink. Our simulation results show the smaller size effect in bi-crystalline micropillars, showing hardening for larger samples, softening in smaller samples due to the existence of grain boundary.

Ill Ryu is currently an assistant Professor in Mechanical Engineering at University of Texas at Dallas. Ill Ryu received his Ph.D. degree in Materials Science and Engineering with minor in Mechanical Engineering from Stanford University. After completing his Ph.D., Dr. Ryu continued his research as a postdoctoral research fellow and lecturer at Brown University. His research interests include multi-scale computational material science, materials mechanical size effect, mechanics of energy materials, and multi-physical modeling of materials science. Especially, his research focused on fundamental understanding of deformation mechanism, which is necessary to design robust and reliable devices from MEMS/NEMSs (Micro-/Nano-Electromechanical Systems) devices at small length scales to Airplane at large length scales.