Fracture and buckling behavior of graphene-bridged vertically aligned carbon nanotube nanocomposites

Abstract Covalently integrated graphene-carbon nanotube (CNT) nanocomposites hold substantial potential, yet their fracture mechanics remain incompletely understood. Herein, molecular dynamics simulations investigate the quasi-static mechanical behavior of vertically aligned CNTs (VACNTs) covalently bridged by bilayer graphene. The results show that the nanocomposite exhibits anisotropic tensile fracture behavior. Fracture initiates at the heptagonal topological rings at the graphene-CNT junctions, propagating along the CNT axial direction (forming zigzag edges) under armchair-direction tension and along the annular interface (forming numerous carbon–carbon single chains) under zigzag-direction tension. However, as CNT height increases, the fracture difference between the two directions gradually diminishes, as longer CNTs reduce interfacial constraints and enhance deformation coordination within the graphene layers. Additionally, increasing inter-CNT spacing ( L ) enhances stiffness and strength by reducing defect density, but compromises fracture strain, with L ≈ 25 Å as the optimal spacing to maximize fracture energy. Under compression, failure modes transition with the CNT aspect ratio, leading to a three-stage evolution of the compressive strain energy density. These findings reveal the structural parameter-dependent mechanical behaviors of Graphene/VACNTs nanocomposites and offer guidelines for designing novel nanocomposites for advanced engineering applications.