By considering an interface energy term in gradient plasticity an “interfacial” yield criterion, indicating the stress at which the interface began to deform plastically could be developed. From an experimental point of view interfacial yielding was observed during nano-indentation on an Fe–2.2wt% Si bi-crystal and a Nb polycrystal. In the present study after illustrating the interaction of a grain boundary with the grain interior for a plastically deforming bi-crystal the theoretically determined interfacial yield stress expression was fit to the nano-indentation data for Fe–2.2% Si and Nb. This fit allows first estimates to be obtained for the internal length, a key material parameter that comes into play in all gradient theories. Based upon the predicted values the internal length was physically related to the dislocation source distance.

Modeling Dislocation-Grain Boundary Interactions through Gradient Plasticity and Nanoindentation. K.E.Aifantis, A.H.W.Ngan: Materials Science and Engineering A, 2007, 459[1-2], 251-61