When 10:30 AM - 11:30 AM Dec 04, 2020
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Behaviors of Structural Materials away from Equilibrium: a Tale of Two Solids by Hovering Over the Energy Landscape

Yue Fan
Assistant Professor, U-M Mechanical Engineering

An improved fundamental understanding of materials performance at extreme environments far from equilibrium has become a compelling need in many important applications. I will introduce the microstructural evolutions in two kinds of solid systems (crystals and glasses) under complex environments. I will demonstrate the seemingly different systems can be understood within the same framework by combining the transition state theory and potential energy landscape (PEL)-based atomistic modeling.

In particular the first part of this talk concerns the mechanisms of interactions between dislocations and obstacles in crystalline alloys, under various temperatures and very wide range of strain rate conditions (from 10-6s-1—107s-1 ) far beyond the accessibility of regular MD simulations. It is demonstrated that, due to the multiple co-existing pathways in the PEL and their different susceptibilities to external stimuli, the same unit interaction could lead to qualitatively different microstructural evolution mechanisms and consequently, different mechanical consequences. In the second part of the presentation, I will discuss the deformation mechanisms in metallic glasses, where there are no longer well-defined topological defects due to the disappearance of lattice periodicity. It is demonstrated that deformation modes (localized vs cascade) depend on the density of local minima of the materials underlying PEL: higher density would enable more efficient energy dissipation and yield better ductility. The implications of these examples, as well as the broad impacts on other important problems, are also discussed.