Modelling grain-boundary resistance in intergranular dislocation slip transmission

We investigate the resistance on the glide of lattice dislocations between adjacent crystal grains due to the presence of a grain boundary (GB). Applying a combination of molecular dynamics (MD) simulations and a line tension (LT) model we identify the geometrical parameters that are relevant in the description of this process. In the MD simulations we observe slip transmission of dislocation loops nucleated from a crack tip near a series of pure tilt GBs in Ni. The results are rationalized in terms of a LT model for the activation of a Frank-Read source in the presence of a GB. It is found that the slip transmission resistance is a function of only three variables: firstly, the ratio of resolved stress on the incoming slip system to that on the outgoing slip system, secondly, the magnitude of any residual Burgers vector content left in the GB and, thirdly, the angle between the traces of the incoming and outgoing slip planes in the GB plane. Comparison with the MD simulations and experimental data shows that the LT model captures the essential energetics of slip transmission and suggests relatively simple functional relationships between the GB geometry and loading conditions on the one hand and slip transmission resistance on the other.