Solid material failure is a fundamental and critical problem, and strength criteria are often viewed as a measure of such failure. The family of two-dimensional (2D) materials, including graphene, hexagonal boron nitride, transition metal dichalcogenides, and others, exhibit a wide range of lattice structures and defect configurations, leading to complex deformation mechanisms and mechanical failure behaviors[1, 2]. However, there is currently no universally accepted criterion that accurately describes the mechanical failures of these materials under complex stress states. This talk introduces two strength criteria of defective 2D materials and their theoretical application. As a preliminary exploration, we present a strength criterion of graphene GBs under complex stress states that the bond stretch stress generated by external load exceeds any bond strength of the hexagon–heptagon defect. While, the residual stress is solved by disclination dipole theory containing multiple geometric parameters so it cannot describe the failure behavior of other defects. For 2D materials composed of covalent bonds, the origin of mechanical failure is bond fracture, based on which a unified strength criterion may be established. Herein, we demonstrate the existence of intrinsic bond strength as the local tensile stress of the bond at the fracture point, solely dependent on the local chemical environment of the bond and is independent of loading states, defect types, and fracture bonds. Subsequently, a unified strength criterion that considers the balance between the intrinsic bond strength and the local stress state for any 2D material is proposed. The strength criterion can accurately predict the failure of various 2D materials with different types of defects, including voids, cracks, grain boundaries, and hydrogenation. Furthermore, this unified strength criterion can also be extended to the three-dimensional stress state and describe the mechanical failure of diamane GBs. REFERENCES [1] Y. Wei, J. Wu, H. Yin, X. Shi, R. Yang, M. Dresselhaus, The nature of strength enhancement and weakening by pentagon–heptagon defects in graphene, Nature Materials, 11(9): 759-763, 2012. [2] O.V. Yazyev, Y.P. Chen, Polycrystalline graphene and other two-dimensional materials, Nature Nanotechnology, 9(10): 755-767, 2014.