Mechanism-based strain gradient (MSG) plasticity and the associated asymptotic crack-tip fields

The materials display strong size effect at the micron or sub-micron scale. The classical plasticity theories cannot explain this size dependence because they possess no internal material lengths. Based on the Taylor model in dislocation mechanics, the theory of Mechanism-based Strain Gradient (MSG) plasticity has been derived. It agrees very well with the available micro-scale experiments, such as micro-torsion, micro-bending and micro-indentation hardness experiments. The structure of the asymptotic crack tip fields associated with MSG plasticity is investigated. It is shown that the crack tip field associated with MSG plasticity does not have separable form of solutions. Its implication on the fracture criterion in MSG plasticity is also discussed.