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The process of handling and bonding copper (Cu) and graphene inevitably creates defects. To use graphene/Cu composites as electronic devices with new physical properties, it is essential to evaluate the effect of such defects. Since graphene is an ultrathin anisotropic material having a hexagonal structure, an evaluation of graphene/Cu composites containing defects was conducted taking into account the inherent structural characteristics. The purpose of this study is to evaluate defects that may occur in the manufacturing process and to present a usable basic method for the stable design research and development of copper/graphene composites essential for commercialization of copper/graphene composites. In the future, when performing analytical calculations on various copper/graphene composites and defect shapes in addition to the defect conditions presented in this paper, it is considered that it can be used as a useful method considering defects that occur during application to products of desired thickness and size. Herein, density functional theory was used to evaluate the behavior of graphene/Cu composites containing defects. The density of states (DOS) values were also calculated. The analysis was implemented using three kinds of models comprising defect-free graphene and two- and four-layered graphene/Cu composites containing defects. DOS and Fermi energy levels were used to gage the effect of defects on electrical properties.

Type III vessels are used to store gases at high pressure and, for efficient use, should be as light as possible without compromising stability. However, since the fiber composite layer has a directional property, it causes different properties depending on the order of lamination and the direction of the layer, and it is necessary to evaluate various and complex variables because both the low and high lamination angles are used in the manufacturing process. Therefore, this study evaluated the composite material layer of type III high pressure storage vessels in a single layer pattern and a composite pattern, and evaluated the effects of the inherent characteristics of each angle and the increase or decrease in the stacking angle on the strength performance of the storage vessel. As a result of analysis, it was confirmed that the change of angle not only affects the strength performance, but also affects the location of storage vessel such as domes and cylinders. In addition, in the most optimized pattern, the stress of 79 MPa in the fiber direction and 20.35 MPa in the fiber orthogonal direction could be reduced.

This study analyzed the mechanical and fracture behavior of graphene/copper (Cu) composites with different Cu thicknesses by using molecular dynamics (MD) and representative volume element (RVE) analysis. Three graphene/Cu composite analytical models were classified as 4.8, 9.8, and 14.3 nm according to Cu thicknesses. Using MD analysis, zigzag-, armchair-, and z (thickness)-direction tensile analyses were performed for each model to analyze the effect of Cu thickness variation on graphene/Cu composite strength and delamination fracture. In the RVE analysis, the mechanical characteristics of the interface between graphene and Cu were evaluated by setting the volume fraction to 1.39, 2.04, and 4.16% of the graphene/Cu composite model, classified according to the Cu thickness. From their obtained results, whether the graphene bond is maintained has the greatest effect on the strength of graphene/Cu composites, regardless of the Cu thickness. Additionally, graphene/Cu composites are more vulnerable to armchair direction tensile forces with fracture strengths of 14.7, 8.9, and 8.2 GPa depending on the Cu thickness. The results of this study will contribute to the development of guidelines and performance evaluation standards for graphene/Cu composites.

To facilitate the widespread use of fuel cell vehicles, it is necessary to ensure the safety of high-pressure hydrogen storage vessels. Because the composite layer experiences the highest internal pressure, cracks in the carbon fiber reinforced plastic (CFRP) layer of type III high-pressure vessels directly affect their safety. In this study, we evaluate the crack behavior in a type III high-pressure hydrogen vessel using a ply modeling method and the extended finite element method. The failure criteria were determined from the maximum principal stress and displacement that exceed the allowable tensile strength, considering the fiber and the transverse directions of each ply. The weak point of the CFRP composite layers was in the transverse direction on the 17th ply at a helical winding angle of 35° in the boundary of the dome and the cylinder. The crack extension was resulted from exceeding the allowable transverse stress at 35° winding angle. These results may be valuable for ensuring the safety of high-pressure hydrogen vessels.