Discrete dislocation dynamics (DDD) is a mesoscale modelling technique that simulates the motion and interaction of dislocations subjected to a state of stress. Unfortunately, the utility of DDD simulations for problems that involve grain boundaries (GBs) is limited because the physics of dislocation-grain boundary interactions is not well understood and hence is not included in DDD modelling. In this work, molecular dynamics (MD) simulations are used to study the interaction between an expanding dislocation loop and a grain boundary. Interaction details are examined via a new implementation of the atomic Nye Tensor, revealing that absorbed dislocation content is deposited at key structural locations within the GB plane. Motivated by these MD simulations, a mesoscale model for the stress field of a GB and its evolution due to dislocation transmission events is developed [1,2]. This model is based on an array of wedge disclination dipoles and is valid for symmetric tilt GBs whose stress field can be described by this type of line defect. DDD simulations using this model to describe the GB stress field and its evolution reveal that accumulated residual dislocation content from prior slip transmission events lowers the external driving stress required for subsequent slip transmission.