**4. Numerical Study**

In this study, a double-cantilever-beam (DCB) specimen containing a level cohesive crack was numerically simulated by the above four different enrichment schemes in order to examine their accuracy and convergence performance. This configuration was taken from the literature [29]. The boundary conditions and dimensions of this case study are provided as a sketch in Figure 7. Uniformly distributed forces were applied on the left side of the beam, and the plane stress condition was assumed to hold. The Young's modulus was 36.5 GPa and the Poisson's ratio was 0.18, which are the material properties of common concrete.

**Figure 7.** A sketch of the dimensions and boundary conditions of the double-cantilever beam.

Six finite element meshes were used in the convergence studies (17 × 9, 31 × 15, 61 × 31, 121 × 61, 301 × 151, and 601 × 301 grids of quadrilateral elements). The meshes were created by making the element length in the x and y directions approximately equal, with the number of elements being odd, such that the crack tip lies within an element. The mesh size h was represented by the square root of the area of an element.
