COLLABORATIVE RESEARCH: NANOMESO: A NSF-EC Cooperative Activity in Computational Research to Study Nano/Meso Length Scale Effects on Crystal Plasticity

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TECHNICAL EXPLANATION This collaborative award is made in response to proposals submitted to the FY05 NSF-EC Cooperative Activity in Computational Materials Research. The project involves the Ohio State University, Stanford University and Los Alamos National Laboratory in the US and collaborating institutions in Switzerland, Germany and the Netherlands. The aim of this cooperative activity is to develop and validate a computational approach to understand and predict unique plasticity phenomena at the nano and sub-micron scales. In recent years, a combination of advances in synthesis, characterization, and computational techniques has revealed striking plasticity phenomena that are not explained by traditional crystal plasticity theories or even more recent strain gradient theories. These phenomena are associated with shrinking sample size to the sub-micron regime and decreasing structural length scales such as grain size to the nano-scale regime. An exciting prospect is that new deformation regimes have been identified which, if understood, could enable the development of materials with unrivaled strength. Thus, the primary impact of the proposed work is an understanding of material strength at length scales not addressed by current plasticity theories. Such an activity is expected to impact our understanding of strength and work hardening in thin films and guide our understanding of appropriate material parameters for small-scale devices used in MEMS.The high intellectual merit of this project derives from a goal to address the fundamental nature of plasticity posed by sub-micron and nano-scale samples, and from the creative process by which ab initio, atomistic, and Peierls approaches to computational materials science are used to support a direct comparison between dislocation dynamics level modeling and novel micro-pillar and in-situ x-ray diffraction verification techniques. The inadequacies of current plasticity theories, including strain gradient formulations, will be addressed via a systematic approach in which the kinetics of cross slip and role of free surfaces and grain boundaries as sources and sinks will be systematically studied. An exciting premise in this investigation is that sub-micron and nano-scale samples may derive extraordinary strength from "dislocation-starvation." A principle outcome is that the proposed, focused interaction among several computational techniques will provide the basis for a new plasticity theory for sub-micron and nano-scale components.The broader impact of the project draws from the current industrial and scientific thrusts to understand the properties of small devices. The research is aimed at enabling small mechanical device design and development, by providing a computational tool base with which to predict the mechanical properties of components as size and structure are diminished to the sub-micron and nano-scale. Our computational and experimental findings will be packaged into an open web site for use by the academic and industrial communities - particularly those in the US and EC - and will set a precedent for comprehensive, accessible computational materials results at the sub-micron scale.The educational impact will be enhanced by investigators who are commited to participation from under-represented groups, the unique educational exchange offered by an international collaboration, and a proposed series of web-based lectures to teach the basis of each of the computational materials methods to be used in this program.NON-TECHNICAL EXPLANATIONThis collaborative award is made in response to proposals submitted to the FY05 NSF-EC Cooperative Activity in Computational Materials Research. The project involves the Ohio State University, Stanford University and Los Alamos National Laboratory in the US and collaborating institutions in Switzerland, Germany and the Netherlands. The aim of this cooperative activity is to develop and validate a computational approach to understand and predict unique plasticity phenomena at the nano and sub-micron scales. In recent years, a combination of advances in synthesis, characterization, and computational techniques has revealed striking plasticity phenomena that are not explained by traditional crystal plasticity theories or even more recent strain gradient theories. These phenomena are associated with shrinking sample size to the sub-micron regime and decreasing structural length scales such as grain size to the nano-scale regime. An exciting prospect is that new deformation regimes have been identified which, if understood, could enable the development of materials with unrivaled strength. Thus, the primary impact of the proposed work is an understanding of material strength at length scales not addressed by current plasticity theories. Such an activity is expected to impact our understanding of strength and work hardening in thin films and guide our understanding of appropriate material parameters for small-scale devices used in MEMS.The high intellectual merit of this project derives from a goal to address the fundamental nature of plasticity posed by sub-micron and nano-scale samples, and from the creative process by which ab initio, atomistic, and Peierls approaches to computational materials science are used to support a direct comparison between dislocation dynamics level modeling and novel micro-pillar and in-situ x-ray diffraction verification techniques. The inadequacies of current plasticity theories, including strain gradient formulations, will be addressed via a systematic approach in which the kinetics of cross slip and role of free surfaces and grain boundaries as sources and sinks will be systematically studied. An exciting premise in this investigation is that sub-micron and nano-scale samples may derive extraordinary strength from "dislocation-starvation." A principle outcome is that the proposed, focused interaction among several computational techniques will provide the basis for a new plasticity theory for sub-micron and nano-scale components.The broader impact of the project draws from the current industrial and scientific thrusts to understand the properties of small devices. The research is aimed at enabling small mechanical device design and development, by providing a computational tool base with which to predict the mechanical properties of components as size and structure are diminished to the sub-micron and nano-scale. Our computational and experimental findings will be packaged into an open web site for use by the academic and industrial communities - particularly those in the US and EC - and will set a precedent for comprehensive, accessible computational materials results at the sub-micron scale.The educational impact will be enhanced by investigators who are commited to participation from under-represented groups, the unique educational exchange offered by an international collaboration, and a proposed series of web-based lectures to teach the basis of each of the computational materials methods to be used in this program.