Nonlinear elasticity degrades monolayer fracture toughness

MXenes, a novel class of monolayer transition metal carbides and nitrides, have gathered significant attention in materials science for their exceptional properties. This study focuses on investigating the influence of atomic defects on the fracture toughness of MXenes and similar monolayers. Comprehensive understanding and modeling of the fundamental physical mechanisms that govern MXene defect-mediated fracture is largely unexplored. Here, molecular dynamics simulations and theoretical fracture mechanics are employed to investigate the role of slit vacancy defects in the toughness of Ti₂C MXene. The material is found to exhibit brittle fracture behavior, and compared to classic predictions, its strength is significantly degraded by short defects. Two physical mechanisms are proposed to model MXene fracture — the material nonlinear elasticity, and the quantization of the crack driving energy. Combining both effects, this model is in excellent agreement with the MXene simulated toughness and may find application in other materials exhibiting similar toughness degradation and nonlinear elasticity.