Authors: Guoqiang Zhang | Huasong Qin | Yilun Liu
Source: Chinese Science Bulletin (Chinese Version) (article, 2024-04-24)
Field: Materials Science — Materials Chemistry

Strength of defective two-dimensional materials <p indent="0mm">Two-dimensional (2D) materials are increasingly utilized across various fields including energy, environment, electronic information, aerospace, and nanotechnology, owing to their distinctive physical and chemical characteristics. However, their complex lattice structures and inevitable defect configurations often result in non-uniform deformations and stress concentrations, leading to intricate deformation mechanisms and mechanical failures. Therefore, a comprehensive understanding of their failure mechanisms and the development of a unified strength criterion present significant challenges. This paper provides an overview of the methodologies employed to evaluate the mechanical properties of 2D materials, encompassing experiments, simulations, and theoretical analyses. Experimental techniques such as atomic force microscopy (AFM) nanoindentation, <italic>in situ</italic> scanning electron microscope (SEM) tensile testing, and substrate tension offer valuable insights into the mechanical properties of 2D materials. While, these methods may neglect various loading states and intrinsic defects, resulting in that the measured fracture strength and Young’s modulus are often lower than those of theoretical predictions. To overcome these limitations, molecular dynamics (MD) simulations and density functional theory (DFT) calculations are employed to examine the strength anisotropy under uniaxial tension along various directions, correlating these findings with fracture bond strength. Furthermore, the relationship between fracture strength and crack length aligns with the Griffith criterion, while increased defect density in GBs results in higher compressive residual stress, which can be explained by the disclination dipole model. Moreover, the dislocation-pileup model elucidates the pseudo/inverse Hall-Petch effect in polycrystalline graphene, though statistical theories suggest a decline in strength with decreasing grain size. Our recent investigations focus on elucidating the failure mechanisms of defective 2D materials under complex stress states. A unified strength criterion based on bond failure analysis is then proposed. Our findings indicate that the intrinsic bond strength is solely determined by the local chemical environment, but independent of loading states, defect types, and fracture bonds. This criterion, balancing intrinsic bond strength with the local stress state, offers a highly promising framework for the comprehensive assessment of the strength of defective 2D materials. Several pivotal aspects require attention, i.e., intrinsic invariants in various materials, the effect of temperature, and the prediction of crack propagation through the integration of theoretical frameworks and machine learning. This review synthesizes the existing theoretical, simulation-based, and experimental efforts focused on the failure mechanisms of defective materials, aiming to offer valuable insights for guiding the design and advancement of 2D materials with superior mechanical properties. Materials science Graphene research and applications ; Thermal properties of materials ; Additive Manufacturing and 3D Printing Technologies