Atomistic Activation Energy Criteria for Multi Scale Modeling of Dislocation Nucleation in FCC Metals
This study contributes to the development of a 'fundamental, atomistic basis' to inform macro scale models that can provide significant insights about the effect of dislocation microstructure evolution during plastic deformation. Within a mesoscale model, multi dislocation interactions can be studied which are capable of driving high stress effects such as dislocation nucleation under low applied stresses, due to stress concentration in dislocation pile ups at interfaces. This study establishes a methodology to evaluate a phenomenological model for atomic scale crystal defect interactions from molecular dynamics simulations, which is a critical step for mesoscale studies of plastic deformation in metals. Dislocations are affected by thermally activated processes that become energetically favorable as the stress approaches a threshold value. The nudged elastic band technique is ideal for evaluating the energetic activation parameters from atomic simulations. With this method, the activation energy and volume were obtained for the process of homogeneous nucleation of a full dislocation loop in pure FCC aluminum. Using the (atomistic) activation parameters, a constitutive mathematical model is developed for simulations at the mesoscale, to evaluate the critical (local) shear stress threshold. The constitutive model is effective for extrapolating from an atomistic timeframe of femtoseconds to experimentally accessible timespans of seconds.