The boundary conditions of the present models, illustrated in Figure 1, are implemented in such a way that the grain boundaries can slide freely without separation. Nodes at the grain-boundary triple points are pinned together to meet strain compatibility conditions. Symmetry boundary conditions, and , are applied on sides OF and OA of the cell OACF, respectively. This unit cell forms a larger cell when reflected about OA and OF, and repetition of this process builds a representative bulk material sample. Nodes on cell boundary AC are constrained to have the same y displacement, u, while nodes on boundary CF are constrained to have the same z displacement, v, at all times.
External stress is maintained constant all the time.
A detailed discussion of the problem formulation and method of analysis is given in Reference 25 . It is evident from Figure 4 that the presence of the 2 grain at the center of the unit cell leads to a stress concentration at the triple point K. Similar stress concentration, with a bigger zone, results in the presence of grain-boundary sliding, as seen from Figure 5b. Figure 6a shows the normalized axial stress distribution in the fully lamellar model in the absence of grain-boundary sliding. As observed in the case of creep deformation, it is found that the 2 laths that are more closely aligned with the applied stress direction redistribute more stress to the adjacent laths. Figure 6b illustrates the normalized axial stress distribution in the same model in the presence of grain-boundary sliding.