Materials Science & Engineering, MIT
"Unit Process" Mesoscale Mechanical Modeling for Metallic Glasses and Nanocrystalline Metals
Location: EB II Room 1231
Monday, February 4th 2013 - 11:00 am
Metallic glasses and nanocrystalline metals represent young classes of engineering materials. Their unique engineered structures give rise to appealing mechanical properties, e.g., high yield strength (~ GPa), as well as unique deformation physics at the microscopic level. In particular, for metallic glasses, the shear transformation zone (STZ), originally proposed theoretically and further observed in atomistic simulations, has been widely accepted as a "unit process". And for nanocrystalline metals, molecular dynamics simulations have identified a process of dislocation nucleation or depinning from grain boundaries as a "quantized" unit process that controls the evolution of plastic strain. But how do these unitary microscopic processes connect to the fascinating and potentially useful macroscopic responses for which these materials are proposed? This talk will present meso-scale models that propose to bridge the scales and make this connection. Fundamentally similar, they combine "quanta" of localized deformation in a finite-element framework, and allow collective phenomena to emerge under the action of applied boundary conditions (stress, temperature, etc). They are termed the "STZ-dynamics" model for metallic glasses, and the "quantized crystal plasticity model" for nanocrystalline metals. These meso-scale models are able to establish insightful connections and bridge the disparity in length and time scales between atomistic simulations and physical experiments.
Lin Li is currently a postdoctoral associate in the Department of Materials Science and Engineering at Massachusetts Institute of Technology. She holds a BEng from Zhejiang University, China (2005), MS and PhD degrees in Materials Science and Engineering from The Ohio State University (2011).