Martensitic Transformation Effect on the Dislocation Emission from a Semi-infinite Crack Tip in Nanocomposites

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 method, 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∘\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${\vert }{\theta }{\vert }\approx 74^{\circ }$$\end{document} 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.