Papers by Author: Ning Hu

Abstract: Different types of defects can be introduced into graphene during material synthesis, and significantly influence the properties of graphene. In this work, we investigated the effects of structural defects, edge functionalisation and reconstruction on the fracture strength and morphology of graphene by molecular dynamics simulations. The minimum energy path analysis was conducted to investigate the formation of Stone-Wales defects. We also employed out-of-plane perturbation and energy minimization principle to study the possible morphology of graphene nanoribbons with edge-termination. Our numerical results show that the fracture strength of graphene is dependent on defects and environmental temperature. However, pre-existing defects may be healed, resulting in strength recovery. Edge functionalization can induce compressive stress and ripples in the edge areas of graphene nanoribbons. On the other hand, edge reconstruction contributed to the tensile stress and curved shape in the graphene nanoribbons.

Abstract: In order to improve the interlaminar mechanical properties of CFRP laminate, hybrid CFRP/VGCF laminates have been fabricated by newly-developed powder method. The critical load at crack growth Pc and fracture toughness GIC have been found to be increased with VGCF interlayer through double cantilever beam (DCB) tests. Fracture surfaces of DCB specimens have also been observed to interpret this improvement mechanism. Moreover, numerical simulations using finite element method (FEM) with cohesive elements have been carried out to analyze the delamination propagation. The numerically obtained interlaminar tensile strength of hybrid CFRP/VGCF laminates has also been verified to be higher than that of base CFRP laminates.

Abstract: In this paper, we have proposed a new cohesive model to stably and accurately simulate delamination propagations in composite laminates under transverse loads. In this model, we set up a pre-softening zone in front of the original softening zone. In this pre-softening zone, the initial stiffness is gradually reduced as the interface strength decreases. However, the onset displacement for starting the real softening process is not changed in this model. The fracture toughness of materials for determining the final displacement of complete decohesion is not changed too. This cohesive model is implemented in the explicit time integration scheme. A DCB problem is employed to analyze the characteristics of the present cohesive model. Moreover, an experimental example of laminates under impact loads is employed to illustrate the validity of the present method.

Abstract: Based on both molecular mechanics and computational structural mechanics, a three-dimensional (3D) equivalent beam element is developed to model a C-C covalent bond on carbon nanotubes (CNTs) whereas the van der Waals forces between atoms in the different walls of multi-walled CNTs are described using a rod element. The buckling characteristics of CNTs are conveniently analyzed by using the traditional finite element method (FEM) of a 3D beam and rod model, termed as molecular structural mechanics approach (MSMA). Moreover, to model the CNTs with large length or large diameter, the validity of Euler’s beam buckling theory and a shell model with proper properties defined from the results of MSMA is investigated. The predicted results by this simple continuum mechanics approach agree well with the reported experimental data.