Fabrication and Out-of-Plane Compressive Behavior of 2.5D Equal-Wall-Thickness Carbon Fiber Honeycomb Composites

This study focuses on addressing the challenges of poor integrity and insufficient mechanical properties in carbon fiber honeycomb composites, which arise from weak interlaminar node connections and unequal free/bonded wall thicknesses. These issues are particularly critical in the field of satellite antennas, which require lightweight and high-load-bearing structures. To achieve continuous fibers and superior cell integrity in honeycomb materials, a honeycomb core structure with equal thicknesses for free walls and bonded walls was developed via 2.5D interlayer interlocking weaving technology. Honeycomb sandwich structure specimens with honeycomb cell side lengths of 5, 9, and 15 mm and equal-wall-thickness were fabricated. Additionally, comparison specimens with unequal wall thickness and 15 mm cell side length were prepared. Out-of-plane compression tests were conducted, combined with damage characterization using SEM, 3D profilometer, and high-definition video capture. A mesoscale-macroscale damage model was established, demonstrating good agreement between simulation and experimental mechanical responses. Analysis indicates that the small-cell-size equal-wall-thickness structure exhibits excellent out-of-plane compression performance, with a 296.88% strength increase compared to the large-cell-size equal-wall-thickness specimen. Notably, the equal-wall-thickness structure demonstrates a 63.6% strength improvement over the unequal-wall-thickness specimen under identical side wall length conditions. Simulation and experimental results reveal that the damage in honeycombs with equal wall thickness originates from microcracks in the matrix, progresses through fiber fracture and cell wall buckling, and ultimately leads to the progressive collapse of the honeycomb cells. This study provides an important theoretical and experimental basis for the design and optimization of high-performance honeycomb structures.