The traction-separation cohesive behavior approach is described in detail in “Modeling moving cracks with the cohesive segments method and phantom nodes” in “Modeling discontinuities as an enriched feature using the extended finite element method,” Section 10.7.1 of the Abaqus Analysis User's Guide. You can specify the material properties that define the evolution of damage leading to eventual failure. You apply the material to the section that is assigned to the crack domain. You can choose to associate a normal behavior contact interaction property with the XFEM crack that defines the contact of cracked element surfaces. For detailed information, see “Specifying a contact interaction property for XFEM,” Section 31.3.6. To assist convergence as the material fails, you can introduce localized damping using the viscous regularization technique. For more information, see “Damage stabilization” in “Defining damage,” Section 12.9.3.

The linear elastic fracture mechanics (LEFM) approach uses the modified Virtual Crack Closure Technique (VCCT) to calculate the strain energy release rate at the crack tip. The approach is more appropriate for brittle fracture problems and is described in detail in “Modeling moving cracks based on the principles of linear elastic fracture mechanics (LEFM) and phantom nodes” in “Modeling discontinuities as an enriched feature using the extended finite element method,” Section 10.7.1 of the Abaqus Analysis User's Guide. To use this approach, you must create a fracture criterion contact interaction property, as described in “Specifying fracture criterion properties for crack propagation” in “Defining a contact interaction property,” Section 15.14.1. If you specify localized damping in the contact interaction property, Abaqus will use the viscous regularization technique to assist convergence as the material fails. For more information, see “Specifying fracture criterion properties for crack propagation” in “Defining a contact interaction property,” Section 15.14.1.