XFEM fracture parameters are not unique for consistent global behavior in tensile, CT, and SENB specimen

This study investigates multiple sets of fracture parameters that yield the same global behavior for tensile, Compact Tension (CT) and Single Edge Notch Bending (SENB), using a cohesive zone model within the framework of the Extended Finite Element Method (XFEM) in Abaqus software. The cohesive zone model uses fracture energy and maximum principal strain as input parameters to determine damage initiation and crack propagation. By carefully balancing these two fracture parameters across different materials, it is possible to achieve comparable global responses in terms of fracture toughness. Crack Tip Opening Displacement (CTOD) and Crack Mouth Opening Displacement (CMOD) are used to evaluate fracture toughness for tensile, CT, and SENB specimens. Fracture behavior of specimens is presented through Force-CMOD and Force-CTOD curves for various sets of fracture parameters and compared for those sets, showing similar behaviors. The comparison includes an analysis of total crack length, cohesive damage area, and longitudinal strain (LE22) at different locations along the Force-CMOD curves where the CMOD values are identical. Additionally, this study examines the damage initiation location during crack propagation through maximum longitudinal strain perpendicular to the crack surface within region of interest. While the results show that multiple sets of XFEM fracture parameters can produce similar global Force-CMOD/CTOD responses, the local behavior around the crack tip differs significantly. For instance, the crack length varied by 10.46 % (tensile), 6.89 % (CT), and 4.96 % (SENB), and the maximum longitudinal strain near the crack surface changed by 20.80 %, 27.53 %, and 39.69 %, respectively. These findings reveal that global behavior alone is insufficient for selecting accurate XFEM fracture parameters and emphasize the need to also consider local behavior near the crack tip.