Characterization of dislocation networks under varying boundary conditions in the discrete to continuum transition regime

The formation and evolution of dislocation networks governs the plastic response and the mechanical properties of crystalline materials, influencing yield strength, strain hardening and ductility. However, identifying representative dislocation network features that can be transferred to continuum formulations such as crystal plasticity is challenging due to the complexity of the evolving dislocation structures.
In this study, we employ three-dimensional discrete dislocation dynamics (DDD) simulations of face-centered cubic (fcc) single crystalline metals to explore how dislocation networks affect plasticity under homogeneous (tension, shear) and gradient-induced (bending, torsion) boundary conditions. Our analysis reveals three fundamental dislocation network characteristics: (i) the dislocation link length distribution, (ii) the degree of link pinning, and (iii) the proximity of links to free surfaces. From the physics of bow-out and lengthening we derive an exponential envelope probability that captures the long tail of the link length distribution and is independent of the imposed boundary condition. We report pinning mechanisms due to successive dislocation interactions between links on different slip systems impeding subsequent link motion. ... mehrBy analyzing pre-strained inhomogeneous dislocation networks generated by a strain path change, we reveal that these pinning mechanisms selectively enhance or suppress dislocation multiplication demonstrating how prior deformation reshapes subsequent plasticity.
Ultimately, we embed the derived dislocation network descriptors in a probabilistic dislocation-based plasticity model. The proposed model predicts dislocation multiplication, plastic shear and strain hardening for various crystal orientations, reproduces size effects and demonstrates the importance of dislocation network characteristics for continuum modeling.