A methodology to model arbitrary holes and material interfaces (inclusions) without meshing the internal boundaries is proposed. The numerical method couples the level set method (Osher and Sethian, 1988) to the eXtended Finite Element Method (X-FEM) (Mo es et al., 1999). In the X-FEM, the nite element approximation is enriched by additional functions through the notion of partition of unity. T...