Experimentally measuring weak fracture toughness anisotropy in graphene

Extended finite element analysis (XFEM) modeling the fracture process of
2D materials with anisotropic fracture toughness. Modification from the
classic XFEM, this updated script is based on the maximum energy release
rate criterion, and anisotropic fracture toughness in sine form
and hexagonal symmetry is included. By modifying the ratio of
maximum and minimum fracture toughness, model geometry, boundary
conditions, and pre-crack location and direction, the fracture patterns,
as well as the local fracture parameters including stress intensity
factors and energy release rate at the crack tip can be calculated.
Moreover, in this script, the distance of the crack extension at every
step is irrelevant to the mesh size of the geometry, thus accuracy and
computation efficiency is enhanced.