Atomistically motivated interface model to account for coupled plasticity and damage at grain boundaries

Grain boundary (GB) characteristics play an important role in the determination and prediction of material behavior, especially when it comes to nanocrystalline metals and ceramics. The main goal of this work is to develop a general interface model to accurately incorporate grain boundary sliding as well as intergranular fracture as two main phenomena in characterizing the grain boundary. To gain a deeper insight into the behavior of different grain boundaries, molecular dynamics (MD) simulations are utilized for mode I and mode II loadings. By adding the unloading path to the MD simulations it was possible to differentiate between different active mechanisms at the GB. Current MD investigations motivate a model which accounts for anisotropic plasticity and damage within the grain boundary to capture the complex interface behavior. Therefore, a two-surface formulation is utilized in which damage and plasticity at the interface are coupled in a thermodynamically consistent way. The parameters for the introduced interface model are determined using the MD simulations based on an embedded atom potential. Finally, the calibrated interface model is implemented into a cohesive zone (CZ) element. In order to show the applicability of the proposed interface model, several numerical studies are carried out. A volume element is selected which depicts a point in an arbitrary polycrystalline material at the macroscale. The results of these studies reveal interesting behaviors of the selected volume element which can be used, e.g., to determine the parameters of a continuum damage model at the macroscale.