Mesoscale Modeling of Dynamic Failure of Shocked Single Crystals and Polycrystals
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Date
2019-04-05
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Abstract
A framework for dislocation-based viscoplasticity and dynamic ductile failure (CPDFE) has been developed to model high strain rate deformation and damage in single crystals and polycrystals. The rate dependence of the crystal plasticity formulation is based on the physics of relativistic dislocation kinetics suited for extremely high strain rates. The damage evolution is based on the dynamics of void growth, which are governed by both micro-inertia as well as dislocation kinetics and dislocation substructure evolution. An averaging scheme is proposed in order to approximate the evolution of the dislocation substructure in both the macroscale as well as its spatial distribution at the microscale. Additionally, a concept of a single equivalent dislocation density that effectively captures the collective influence of dislocation density on all active slip systems is proposed here. Together, these concepts and approximations enable the use of semi-analytic solutions for void growth dynamics, which greatly reduce the computational overhead that would otherwise be required. The resulting homogenized CPD-FE framework has been implemented into a commercially available finite element package, and a validation assessment against a suite of direct numerical simulations was carried out. The model is calibrated and validated against published experimental data of the stress-strain response of single crystals subject to dynamic loading conditions. Lastly, the model is utilized to study polycrystals at the mesoscale level through the explicit resolution of individual grains, i.e. resolving each individual grain’s size, shape, and orientation. A few thousand mesoscale calculations are carried out, systematically varying the misorientation angles of the grain boundaries (GB) in the computational microstructures. Despite the fact that the CPD-FE model neglects the possibility of variation in inherent GB weakness, the CPD-FE simulations agree favorably with experimental observations that have demonstrated a non-monotonic relationship between GB misorientation and the likelihood of failure initiation along said GB. The role played by mechanics, i.e. elastic and plastic anisotropy, in this non-monotonic trend is elucidated here.
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High rate, single crystal, polycrystal, intergranular, ductile, fcc