Abstract
In a remarkable series of experiments, Elssner, Korn and Ruehle (Scripta Metall. Mater. 31 (1994) 1037) observed cleavage fracture in ductile materials, a phenomenon that cannot be explained by classical plasticity theories. In this paper we present a study of fracture by the theory of mechanism-based strain gradient (MSG) plasticity (Gao et al., J. Mech. Phys. Solids 47 (1999b) 1239); Huang et al., J. Mech. Phys. Solids 48 (2000a) 99). It is established that, at a distance much larger than the dislocation spacing such that continuum plasticity is applicable, the stress level in MSG plasticity is significantly higher than that in classical plasticity near the crack tip. The numerical results also show that the crack tip stress singularity in MSG plasticity is higher than that in the HRR field, and it exceeds or equals to the square-root singularity. This study provides a means to explain the observed cleavage fracture in ductile material.
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