Fatigue and fracture of structures often originate from the surface notch or crack. In this contribution, a Peierls type continuum model developed by Rice (1992) was employed to analyze the critical stress of dislocation emission from the surface notch/crack in the plane strain state in a unified manner. Both the stress field in a notched/cracked half-plane under mode-I loading and the stress field induced by an edge dislocation were obtained in closed forms using the Muskhelishvili method. Calculations were carried out to study the effects of the notch/crack depth and the root curvature radius on the dislocation emission. Results showed that the critical stress for dislocation emission depended greatly upon both of them. The shallower the surface notch/crack is, the higher the critical stress is. This depth dependence of the critical stress for the surface notch was more significant than that for the surface crack. Similarly, the dependence of the critical stress upon the slip plane orientation angle for the surface notch was relatively stronger than that for the surface crack. Within a certain range of the slip orientation angle, the critical dislocation emission stress for the surface notch with small root curvature radius was even less than that for the surface crack at the same depth. These results were helpful in understanding the ductile-brittle fracture behaviour of materials having surface notches or cracks.

Dislocation Emission From Surface Crack/Notch Under Mode I Loading and Its Size Dependence. M.Huang, Z.Li: International Journal of Damage Mechanics, 2010, 19[8], 883-97