Atomistic modeling of out-of-plane deformation of a propagating Griffith crack in graphene
MAN Dewapriya and SA Meguid, ACTA MECHANICA, 228, 3063-3075 (2017).
Linear elastic fracture mechanics concepts have been widely used to characterize the fracture of nanoscale materials. In these concepts, pre-existing cracks in two-dimensional problems are assumed to be planar during the crack propagation. However, a perfect planar configuration of atomically thin nanostructures is not achievable in many applications due to complex interatomic interactions at the atomic scale. Formation of ripples and wrinkles has been experimentally observed in freestanding two-dimensional materials such as graphene. In this study, we employ molecular dynamics simulations to investigate the influence of out-of- plane deformation of a propagating Griffith crack. A numerical nanoscale uniaxial tensile test of a graphene sheet with a central crack is conducted. Two main aspects of the study are considered. The first is devoted to examining the influence of the crack orientation and the out- of-plane deformation of the crack surfaces on the crack-tip stress field. The second is concerned with the influence of the out-of-plane deformation on the fracture resistance of graphene. The analysis of the crack-tip stress field reveals a remarkably high transverse compressive stress at the crack surfaces, which induces the out-of-plane deformation. Moreover, our results reveal that in the absence of the crack out-of-plane deformation, the fracture resistance of graphene approaches the value given by Griffith's criterion at a relatively smaller crack length as compared to the case involving out-of-plane deformation.
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