The Genome of Size-Dependent Plasticity in Metals
Jaafar El-Awady (Johns Hopkins University)
Discrete Dislocation Plasticity
Mon 4:20 - 5:40
Barus-Holley 157
The realization of a size-dependent physically-based constitutive model that accurately predicts strength and plastic deformation of single- and poly-crystals remains missing. Over the last decade microscale experimental studies, limited to a very small subset of starting initial dislocation densities, suggest that such a unified model is nonexistent and that the deformation at the microscale is completely different than at bulk scales. In this talk we reanalyze discrete dislocation dynamics (DDD) simulations on Ni micro-crystals having sizes spanning over two orders of magnitude, and having initial dislocation densities spanning five orders of magnitude. These simulations show for the first time that the microstructural features controlling plasticity of micro-sized crystals do not differ much from the response of bulk crystals. These simulations also reveal the existence of a size dependent critical dislocation density at which the strength of the crystal is minimum. Above this critical density Taylor hardening is recovered while below it the flow strength increases with decreasing dislocation density through a power law relationship. We will also reanalyze recent microscale experiments and show a clear validation of these simulations. Based on these simulation and experimental results we develop a new unified size-dependent constitutive model for crystal plasticity. We show that this new model accurately predicts the experimentally observed Hall-Petch effect in polycrystals without any further assumptions.