The Interaction Problem Between a Crack and a Wedge Disclination Dipole With Irwin Plastic Zone Correction

In this work, the multiple defects interaction problem is studied. A crack located near an inclusion is influenced by a wedge disclination dipole. Stress field induced by the disclination affects the crack tip field and yield behavior of the crack. With varying the wedge disclination dipole properties, including strength, position to the crack tip, arm length, etc., the plastic zone size (PZS), the crack tip opening displacement (CTOD) and the stress intensity factor (SIF) are estimated with the generalized Irwin model. Numerical results showed that the wedge disclination dipole arm length and strength can significantly increase or decrease the values of the CTOD and PZS, depending the disclination dipole positions. The maximum values of the CTOD and the PZS were explored with the change of disclination position.

Coupled effect of grain boundary sliding and dislocation emission on fracture toughness of nanocrystalline materials

This paper establishes a theoretical model to explore the coupled effect of grain boundary (GB) sliding deformation and crack tip dislocation emission on the critical stress intensity factor (SIF) for crack growth in ultrafine-grained and nanocrystalline materials (NCMs). The model postulates that the stress concentration near a crack tip initiates GB sliding. It is found that GB sliding leads to the formation of wedge disclination dipole at the triple junctions of grain boundaries. Under the external load and stress fields produced by wedge disclinations, dislocations are emitted from crack tips but will stop at the opposite GBs. The influence of the wedge disclination dipole and the dislocation emitted from crack tip on the critical SIF for crack growth is investigated. The model prediction shows that the critical SIF varies with the decrement of grain size, and that there is a critical grain size corresponding to a minimum value of SIF. Compared with the pure brittle fracture in NCMs at the grain sizes of tens of nanometers, the combined deformation mechanisms can bring an increase of the critical SIF for crack growth.