Recently, 3D printing of fiber-reinforced composites has gained significant research attention. However, commercial utilization is limited by the low fiber content and poor fiber–resin interface. Herein, a novel 3D printing process to fabricate continuous fiber-reinforced thermosetting polymer composites (CFRTPCs) is proposed. In brief, the proposed process is based on the viscosity–temperature characteristics of the thermosetting epoxy resin (E-20). First, the desired 3D printing filament was prepared by impregnating a 3K carbon fiber with a thermosetting matrix at 130 °C. The adhesion and support required during printing were then provided by melting the resin into a viscous state in the heating head and rapidly cooling after pulling out from the printing nozzle. Finally, a powder compression post-curing method was used to accomplish the cross-linking reaction and shape preservation. Furthermore, the 3D-printed CFRTPCs exhibited a tensile strength and tensile modulus of 1476.11 MPa and 100.28 GPa, respectively, a flexural strength and flexural modulus of 858.05 MPa and 71.95 GPa, respectively, and an interlaminar shear strength of 48.75 MPa. Owing to its high performance and low concentration of defects, the proposed printing technique shows promise in further utilization and industrialization of 3D printing for different applications.

While carbon-fiber-reinforced polymers (CFRPs) are widely used in the aerospace industry, they are not able to disperse current from lightning strikes because their conductivity is relatively low compared to metallic materials. As such, the undispersed current can cause the vaporization or delamination of the composites, threatening aircraft safety. In this paper, finite element models of lightning damage to CFRPs were established using commercial finite element analysis software, Abaqus, with the user-defined subroutines USDFLD and HEAVEL. The influences of factors such as the structural geometry, laminate sequence, and intrinsic properties of CFRPs on the degree of damage to the composites are further discussed. The results showed that when a current from lightning is applied to the CFRP surface, it mainly disperses along the fiber direction in the outermost layer. As the length of the CFRP increases, the injected current has a longer residence time in the material due to the increased current exporting distance. Consequently, larger amounts of current accumulate on the surface, eventually leading to more severe damage to the CFRP. This damage can be alleviated by increasing the thickness of the CFRP, as the greater overall resistance makes the CFRP a better insulator against the imposed current. This study also found that the damaged area increased as the angle between the first two layers increased, whereas the depth of the damage decreased due to the current dispersion between the first two layers. The analysis of the electrical conductivity of the composite suggested that damage in the fiber direction will be markedly reduced if the conductivity in the vertical fiber direction increases approximately up to the conductivity of the fiber direction. Moreover, increasing the thermal conductivity along the fiber direction will accelerate the heat dissipation process after the lightning strike, but the influence of the improved thermal conductivity on the extent of the lightning damage is less significant than that of the electrical conductivity.

Tribological properties of glass fiber-reinforced polymer (GFRP) composites used in reciprocating contact should be improved to secure the efficiency and safety because of risks of abrasion, adhesion, and fatigue deficiency amidst fiber, matrix, or interphase. This paper investigates the influence of graphene reinforcement on the wear resistance of a GFRP composite. Graphene was integrated into a typical GFRP composite as the surface coating using a modified resin film infusion method with the percolating paper assisted. Dry reciprocating sliding tests were performed against a stainless steel ball moving in a direction 45 degrees to the fiber orientation. The morphology of the worn surface was observed, and the corresponding wear mechanisms are discussed. Results suggest that the prepared graphene coating improves the wear resistance of the GFRP composite. The protected GFRP laminates remained intact during the first 20 min of the wear test and only a small fraction of fibers were broken after 60 min test. Furthermore, abrasive debris and fiber breaks originating from composite were markedly reduced, likely owing to the formation of a protective transfer film between the surface of the modified composite and the rubbing counterpart.

Drilling of carbon fiber-reinforced plastics (CFRPs) is a challenging task in aviation and aerospace field. Damages, which can reduce the strength of the structure, often occur during secondary machining operations due to the applied cutting force and generated heat. The main objective of this study was to investigate the drilling performance and the deformation resistance of CFRPs subjected to cryogenic treatment based on glass transition temperature (Tg). Therefore, a cryogenic machining approach was adopted by fixing the workpiece inside a cryogenic box to drill CFRPs. The machining performance was briefly evaluated. Moreover, a through-hole drilling method was promoted to analyze the mechanism of different deformation mechanical properties. The results showed that the cryogenic machining approach improved the machining performance of CFRPs. Nevertheless, the residual intensity of cryo-treated specimen decreased (about 7.14%) due to the Tg-based viscoelasticity. These results demonstrate the great potential of this approach in advanced industrial applications and further pave the way for efficient secondary machining operation of CFRP components.