Cohesive zone modeling for crack propagation in polycrystalline NiTi alloys using molecular dynamics

Nickle-titanium (NiTi) alloys are widely accepted to be one of the most favored engineering materials for use in the structural community. In this work, the formulation and application of a multiscale approach combined with cohesive zone model (CZM) and molecular dynamics (MD) were proposed to investigate the crack propagation of NiTi alloys. The Voronoi tessellation was employed to represent microstructures of such polycrystalline materials. MD simulations were performed to achieve the traction-separation law in the CZM with various initial micro-cracks. The resultant characteristic parameters were embedded in cohesive elements along grain boundaries and in grains, and in turn both intergranular and transgranular fracture were simulated by implementing the finite element analysis with failure criteria. Consequently, the stress intensify factor of compact tension specimens was predicted, and further the relationship between the microstructure and fracture toughness was explored. The results show that there is a reasonable agreement between numerical results and published experimental data, highlighting the adequacy of the new analytical method for reproducing the cracking behavior across micro-, meso-, and macro-scales.