LAUSR

Twinning is an important deformation mechanism of crystalline materials. A deformation twin blocked at the grain boundary may lead to microcrack nucleation and seriously deteriorate the mechanical properties of materials. In this paper, a theoretical model is proposed to study the microcrack nucleation from a blocked twin at the grain boundary. The deformation twin is simulated with the wedge disclination quadrapole model. Inspired from the recent molecular simulation results, the microcrack is assumed to have two sharp tips and nucleate from the tensile stress of one of the negative wedge disclinations. The characteristics of the nucleated crack are then revealed with the distributed dislocation method. The influence of the remote disclination dipole on the crack nucleation is discussed. It is found that for twins with large aspect ratios, the disclination dipole model is sufficient to simulate the crack nucleation behavior. The opening profile of the nucleated crack is calculated and is comparable with the atomistic simulation result in the literature. The numerical results indicate that for a specific deformation twinning, there exists a critical twin thickness for the microcrack to nucleate. The critical thickness of the twin can be predicted with the proposed model.