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A lot of researches on continuous carbon-fiber composite laminates have been conducted, but no scrutiny has been devoted to continuous carbon-fiber composite honeycomb sandwiches. This paper is aimed to assess the design and properties aspects of honeycomb sandwiches made of continuous carbon-fiber composite laminates. The applicability of the existing theoretical formulas for the mechanical properties of isotropic material honeycomb sandwich on continuous carbon-fiber composite honeycomb is examined by comparing the obtained results from the finite-element modeling and experimental results. The results reveal that the theoretical formulas of isotropic material honeycomb sandwich in density and out-of-plane compressive elastic modulus are suitable for continuous carbon-fiber composite honeycomb, while other performances cannot be achieved by theoretical formulas of isotropic material honeycomb sandwiches. The out-of-plane compression and shear properties of continuous carbon-fiber composite honeycomb can be evaluated by finite-element modeling. The effects of cell side length, wall thickness, and 45° ply content on the honeycomb density, out-of-plane compression properties and out-of-plane shear strength are researched. Subsequently, the out-of-plane compression experiments of honeycomb are carried out to show the accuracy of the finite-element modeling. Finally, a design approach for continuous carbon-fiber composites honeycomb structures is proposed. This methodology results in the design of honeycomb sandwiches with better performances. The chief innovation of this paper is to develop the concept of continuous carbon-fiber composite honeycomb sandwich structures. To this end, a honeycomb structure finite-element model of continuous carbon-fiber composite is established, and the mechanical properties of continuous carbon-fiber composite honeycomb sandwiches are explored. A methodology for the rapid design of honeycomb size parameters of continuous carbon fiber composite honeycomb sandwich is also proposed. [ABSTRACT FROM AUTHOR]

Bolted joints are commonly used for assembling carbon fiber/resin composite structures. Since drilling may generate defects at hole edges which affect mechanical properties, it is of great engineering significance to develop proper repair methods to restore the mechanical properties of the defective parts. However, there are few studies on hole edge defects and their repair methods. Therefore, a novelty short fiber filling repair method was proposed to repair defective holes in this study. The mechanical properties of intact, defective and repaired countersunk composite joints were compared and investigated. Experimental tensile tests showed that defective joints had lower initial stiffness and failure loads compared to intact joints, while the mechanical properties were effectively restored after repair. Three-dimensional finite element models were also established to analyze the damage process of the joints. Results of numerical modelling were consistent with the experimental results. The simulations showed that changes in contact behaviors and local deformations caused by hole edge defects led to the low initial stiffness and stiffness transition point of the joint, while this phenomenon was reduced after repair. Additionally, despite different joint types, laminate failure mainly occurred around the hole and countersink. [ABSTRACT FROM AUTHOR]

Cold expansion and interference fitting are two efficient methods for improving the fatigue life of open-hole structures. However, their combined effect on the fatigue behavior of aluminum-lithium lugs has barely been investigated. Therefore, this study aims to improve the fatigue life of 2297-T87 aluminum-lithium alloy lugs by utilizing cold expansion, interference fitting, and their combination, using experimental and numerical methods to determine the effects of these techniques. Scanning electron microscopy was employed for fracture analysis, three-dimensional finite element models were used to characterize cyclic loading–related stress histories and stress distributions around holes, and the Smith-Watson-Topper method was used to predict fatigue life. The combination of cold expansion with interference fitting achieved a 14.4-fold improvement of fatigue life, as determined by fatigue tests. Numerical modeling showed that the above combination decreases the mean stress and stress amplitude, outperforming other methods in terms of fatigue resistance, in agreement with experimental results. [ABSTRACT FROM AUTHOR]