“…In Wagner et al (2001), a computational model for rigid particles in Stokes flow was proposed, whereas moving phase boundary problems have been modeled using the coupled extended finite element and level set methods (Merle and Dolbow, 2002;Ji et al, 2002;Chessa et al, 2002). Dolbow and Nadeau (2002) investigated the use of effective properties for fracture analysis in functionally-graded systems, whereas Sukumar et al (2003b) adopted the X-FEM as a fracture tool to study the competition between intergranular and transgranular modes of crack growth through a material microstructure. In other related studies, Wells and Sluys (2001) used the Heaviside step function to model the displacement discontinuity within a finite-element based cohesive crack model, whereas Wells et al (2002) used partition of unity enrichment to alleviate volumetric locking during plastic flow.…”