  Strain gradient plasticity theories are being widely used for fracture
assessment, as they provide a richer description of crack tip fields by
incorporating the influence of geometrically necessary dislocations.
Characterizing the behavior at the small scales involved in crack tip
deformation requires, however, the use of a very refined mesh within microns to
the crack. In this work a novel and efficient gradient-enhanced numerical
framework is developed by means of the extended finite element method (X-FEM).
A mechanism-based gradient plasticity model is employed and the approximation
of the displacement field is enriched with the stress singularity of the
gradient-dominated solution. Results reveal that the proposed numerical
methodology largely outperforms the standard finite element approach. The
present work could have important implications on the use of
microstructurally-motivated models in large scale applications. The non-linear
X-FEM code developed in MATLAB can be downloaded from www.empaneda.com/codes.
