MRS Bulletin

Technical Feature

Technical Feature

The Mechanics and Physics of Defect Nucleation

Ju Li

Abstract

The following article is based on the Outstanding Young Investigator Award presentation given by Ju Li on April 19, 2006, at the Materials Research Society Spring Meeting in San Francisco. Li received the award “for his innovative work on the atomistic and first-principles modeling of nanoindentation and ideal strength in revealing the genesis of materials deformation and fracture.”

Defect nucleation plays a critical role in the mechanical behavior of materials, especially if the system size is reduced to the submicron scale. At the most fundamental level, defect nucleation is controlled by bond breaking and reformation events, driven typically by mechanical strain and electronegativity differences. For these processes, atomistic and first-principles calculations are uniquely suited to provide an unprecedented level of mechanistic detail. Several connecting threads incorporating notions in continuum mechanics and explicit knowledge of the interatomic energy landscape can be identified, such as homogeneous versus heterogeneous nucleation, cleavage versus shear-faulting tendencies, chemomechanical coupling, and the fact that defects are singularities at the continuum level but regularized at the atomic scale. Examples are chosen from nano-indentation, crack-tip processes, and grain-boundary processes. In addition to the capacity of simulations to identify candidate mechanisms, the computed athermal strength, activation energy, and activation volume can be compared quantitatively with experiments to define the fundamental properties of defects in solids.

Ju Li is an assistant professor in the Department of Materials Science and Engineering at the Ohio State University. He received his bachelor's degree in physics from the University of Science and Technology of China in 1994, and his PhD degree in nuclear engineering from the Massachusetts Institute of Technology in 2000. He was a postdoctoral associate and a research scientist at MIT before joining the faculty at Ohio State in the fall of 2002.

Li's research focus is the development of robust analytical and computational approaches to the modeling of the structural and functional properties of materials, including Ni- and Ti- based superalloys, fuel cell catalysts, ultrahigh-temperature ceramics, hydrogen storage materials, electroactive polymers, and metallic glasses. In these endeavors, Li is leading the rapidly growing multiscale modeling effort in bridging continuum, atomistic, and electronic scales at the interface of nanoscience and mechanics.

He has more than 60 peer-reviewed publications and is the author of the molecular visualization software AtomEye. Li won an MRS Graduate Student Silver Award in 1999 and was the recipient of the Presidential Early Career Award for Scientists and Engineers (PECASE) 2005.

Li can be reached by e-mail at li.562@osu.edu.

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