Modeling Plasticity in Metals at Atomistic and Mesoscopic Length Scales
Douglas E. Spearot, Associate Professor
Department of Mechanical and Aerospace Engineering
Department of Materials Science & Engineering (affiliate)
Recent efforts towards accurate modeling of plastic deformation in metals via integration of atomistic and discrete dislocation dynamics (DDD) simulations will be discussed. Following a brief introduction to atomistic simulation and DDD methods, two coupled research tasks will be discussed in detail. (1) An atomistic framework to study the geometry of dislocation shear loops will be presented. Energy minimization methods are used to determine the stabilizing shear stress of dislocation loops as a function of loop radius. Then, the computational algorithm is extended to molecular dynamics simulations and used to determine the average dislocation loop lattice friction stress as a function of temperature. (2) Atomistic simulations are used to determine the dependence of the Peierls stress and dislocation mobility on dislocation segment character angle and local stress state. The Peierls stress is calculated based on the change in the internal energy, which is an invariant measure of the dislocation driving force. For screw and 60o dislocations, the Peierls stress versus pressure relationship has maximum values associated with stacking fault widths that are multiples of the Peierls period. For edge dislocations, the Peierls stress decreases with increasing pressure from tension to compression. Ultimately, it is shown that both character angle and local stress dependent properties must be incorporated into DDD simulations to model the behavior of nanoscale dislocation loops. This is quantified by measuring dislocation junction formation rates in the early stages of plastic deformation in DDD simulations.
Dr. Spearot is an Associate Professor in the Department of Mechanical & Aerospace Engineering at the University of Florida. He also has an affiliate appointment in the Department of Materials Science & Engineering. From 2005-2015, Dr. Spearot was a faculty member in the Department of Mechanical Engineering and a member of the Institute for Nanoscience and Engineering at the University of Arkansas. His research focuses on the mechanical and thermodynamic behavior of materials, with particular focus on dislocations and interfaces in metallic materials, using atomistic and mesoscale simulation techniques. In addition, his research group develops computational tools necessary to extract experimentally relevant material metrics from simulation generated data. Dr. Spearot was awarded the 2010 NSF CAREER Award to study vapor deposited microstructures and to develop coupled atomistic/mesoscale models for predictive process modeling. As a faculty member at the University of Arkansas, he received the 2014 College of Engineering Imhoff Outstanding Teaching Award and the 2014 Arkansas Alumni Association Rising Teaching Award for classroom excellence. Originally from Bloomfield Hills, Michigan, Dr. Spearot received his B.S. in Mechanical Engineering from the University of Michigan. He completed his M.S. and Ph.D. degrees in Mechanical Engineering from the Georgia Institute of Technology.