Description: XFEM allows you to model crack growth without remeshing the crack surfaces since it does not require the mesh to match the geometry of the crack. A user-defined damage initiation criterion is now supported. User subroutine UDMGINI provides a very general capability for implementing a user-defined damage initiation criterion. You can specify more than one failure mechanism in an enriched element, with the most severe one governing the actual failure.

The XFEM capability can be used to simulate a discrete crack growth along an arbitrary path subjected to a sub-critical cyclic loading based on the principles of linear elastic fracture mechanics (LEFM) in a low-cycle fatigue analysis using the direct cyclic approach. The fracture energy release rates at the crack tips in the enriched elements are calculated based on the modified VCCT technique. The onset and crack growth are characterized by using the Paris law, which relates the relative fracture energy release rates to crack growth rates. A low-cycle fatigue step can be the only step, can follow a general static step, or can be followed by a general static step. Multiple low-cycle fatigue analysis steps can be included in a single analysis. If a fatigue analysis is performed in a model without a pre-existing crack, a static step proceeded by the fatigue step can be used to nucleate a crack.

XFEM is now available for second-order stress/displacement tetrahedron elements.