Modeling dislocation—grain boundary interactions through gradient plasticity and nanoindentation

By considering an interface energy term in gradient plasticity an “interfacial” yield criterion, indicating the stress at which the interface begins to deform plastically can be developed. From an experimental point of view interfacial yielding has been observed during nanoindentation on an Fe–2.2weight% 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 is fit to the nanoindentation 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 on the predicted values the internal length is physically related to the dislocation source distance.