Crystal Plasticity from First Principles

PI Vasily Bulatov, Lawrence Livermore National Laboratory
Project Description

With this INCITE project, researchers are using large-scale molecular dynamics (MD) simulations to settle two long-standing controversies in classical physical metallurgy: (1) the microscopic origin of strain hardening, and (2) the nature and geometric character of dislocation patterns. Widely divergent theories have been advanced about these two phenomena, some “classical” theories even being mutually contradictory. The disarray persists because scientists are unable to test crystal plasticity properties while simultaneously (in situ) observing the underlying dynamics of atoms and dislocations, which are line defects in the crystal lattice known to be responsible for crystal plasticity. 

At present, in situ microscopy observations are possible only in thin electron-transparent films — where neither strain hardening nor dislocation patterns are observed. MD simulations are currently the only means to permit, in principle, simultaneous mechanical testing of bulk crystal plasticity in silico and fully detailed in situ observation of the underlying atomic dynamics. Because of their immense computational cost, direct MD simulations of crystal plasticity had been regarded as impossible. However, the team, in applying a newly established simulation capability, has demonstrated that direct cross-scale MD simulations of plasticity and strength of tantalum metal are feasible.

The team’s approach combines very large MD simulations and detailed on-the-fly and post-processing analyses and characterizations of underlying events in the life of atoms and dislocations that, taken together, define crystal plasticity response. Their cross-scale simulations are simultaneously large enough to be representative of a macroscopic crystal plasticity and yet fully detailed tracing every “jiggle” of atomic motion. Ultimately, the team’s computations will provide definitive data on the origin of staged strain hardening and on the nature of dislocation patterns, while also increasing the understanding of material strength and other technologically relevant mechanical properties.