Long Time-Scale Atomistic Modeling and Simulation of Deformation and Flow in Solids
Atom-based modeling and simulation are essential for the understanding and development of structural materials such as crystalline and amorphous metals. Classical molecular dynamics simulation enables the following of atomic-level structural evolution to elucidate the atomic processes underlying many macroscopic behaviors; however its predictive power is constrained by an intrinsic time-scale limitation. Here, we describe an alternative approach based on potential energy landscape modeling and transition state theory to probe the microscopic mechanisms controlling deformation and plastic flow observed in experiments. We survey several examples of slow deformation in crystals and metallic glasses to illustrate the computational algorithms used to perform the simulations and to reveal the underpinning elementary plastic processes that operate in crystalline and amorphous materials. We first show the evolution of dislocations and their interactions with obstacles over a wide range of strain rates and temperatures and discuss how they lead to macroscopic behaviors such as flow stress upturn and dislocation channeling. Then we turn to amorphous plasticity where discrete stress relaxation (avalanche) processes arise in serrated flow and creep in metallic glasses. A nonlinear interplay between nonaffine atomic displacement and local shear transformation distortion is revealed that provides a molecular explanation of the deformation-rate upturn.
The authors would like to take the opportunity to thank Sidney Yip for the instrumental discussions in outlining this chapter and for the edits. PC acknowledges the support from the US Department of Energy NEUP Grant DE-NE0008450. YF also acknowledges the support from the US Army Research Office Grant No. W911NF-18-1-0119.
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