In order for these carbon nanostructures to be used as reinforcing constituents in the advanced composite materials and structures, one needs to assess their structural performance subject to various loading conditions. Such structure performance can be evaluated by mechanical properties such as stiffness, maximum stress and strain to failure, etc. Among numerical analytical work to predict the mechanical properties of the carbon-based molecular architectures, widely and promisingly used are an atomistic modeling, such as molecular dynamic (MD) simulations [1, 2], tight binding MD , density functional theory , classical continuum mechanics  and structural mechanics approach, etc. While many aspects of the carbon nanostructures have been discussed in literature, only a few study has been conducted to predict their mechanical strength subject to various modes of loading such as tension, compression and shear loads, especially for the complicated 3-D carbon nanostructures.
In the current study, we have developed a computational method to predict the mechanical strength of various carbon nanostructures, such as CNTs, graphene sheets, CNT-graphene and CNT-CNT junctioned nanostructures, and have identified their critical failure modes. The prediction method is based on combined molecular mechanics and atomistic molecular dynamics simulations by ensuring a global energy minimum at a given loading level. We have applied the present method to various carbon nanostructures including carbon nanotubes (CNTs), graphene, CNT with defects, CNT-graphene junctioned 3-D nanostructures and pillared graphene nanostructures. We have identified the maximum stress and strain at failure of these carbon nanostructures as well as their critical failure modes. Further, the failures due to defects in mixed chirality carbon nanotubes are also predicted.
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