Martensitic Transformation Eflfect on the Dislocation Emission from a Semi-infinite Crack Tip in Nano composites

A theoretical model is established to investigate the effect of martensitic transformation particle on the dislocation emission from a crack tip in ceramic-matrix nanocomposites. Using the model of dislocation-based strain nucleus and the Green's function met hod, the expressions of complex potentials and stress fields are derived in closed form. The critical stress intensity factors for the first-lattice dislocation emission and the maximum number of emitted dislocations are well calculated. The effects of important parameters such as the size of transformation particle, the dislocation emission angle and the distance from the crack tip to the transformation particle on dislocation emission are discussed in detail. The results reveal that the transformation particle shows a significant shielding effect on the dislocation emission from the crack tip, and the shielding effect enhances with an increase in the size of transformation particle. On the other hand, the results also imply that the emission of edge dislocations is closely related with the dislocation emission angle, and there exists a probable angle |θ|≈ 74° making the dislocation emission easiest. Besides, the remarkable crack blunting induced by the dislocation emission is quite difficult for small grain size but easy for the growth of crack.

Interaction between a screw dislocation and a circular nano-inhomogeneity with a bimaterial interface

The problem of a screw dislocation interacting with a circular nano-inhomogeneity near a bimaterial interface is investigated. The stress boundary condition at the interface between the inhomogeneity and the matrix is modified by incorporating surface/interface stress. The analytical solutions to the problem in explicit series are obtained by an efficient complex variable method associated with the conformal mapping function. The image force exerted on the screw dislocation is also derived using the generalized Peach–Koehler formula. The results indicate that the elastic interference of the screw dislocation and the nano-inhomogeneity is strongly affected by a combination of material elastic dissimilarity, the radius of the inclusion, the distance from the center of inclusion to the bimaterial interface, and the surface/interface stress between the inclusion and the matrix. Additionally, it is found that when the inclusion and Material 3 are both harder than the matrix（ μ1 〉 μ2 and μ3 〉 μ2）, a new stable equilibrium position for the screw dislocation in the matrix appears near the bimaterial interface; when the inclusion and Material 3 are both softer than the matrix（ μ1 〈 μ2 and μ3 〈 μ2）, a new unstable equilibrium position exists close to the bimaterial interface.