23 September 2010
Venue: Arts Lecture Theatre, Arts Building, Mile End Campus
Recently discovered behaviour of dependent flow characteristics of initially defect free single nanocrystals allows heretofore unavailable insight. The study involves in-situ transmission electron microscopy of single-crystal silicon nanopillars and nanospheres. First, surface mediated dislocation nucleation can be identified. Second, we demonstrate an experimental dislocation dynamics relationship from direct measurements of dislocation velocities. With both molecular dynamics and experimental measurements of activation volumes, these lead to a phenomenological relationship for both yield strength and work hardening. While this may be mostly applicable to initially low density crystal structures, it is suggested as a route for more multi-scale modeling approaches to follow, using discretized dislocation density analysis. From the dislocation nucleaton and their velocities, key parameters are measured. With these, the modeling ensues. The implication is that both strain-rate and length scale effects on flow characteristics can be accounted for in a model with testable parameters.
William W. Gerberich, a professor at the University of Minnesota, Department of Chemical Engineering and Materials Science-Minneapolis, was honoured for his major contributions to the field of mechanical behaviour of materials and his mentoring of students for over 35 years.
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