Three Dimensional Printed Continuous Fiber‐Reinforced Foamed Composite Expansion Tubes With Radial Density Gradients for Enhanced Energy Absorption

ABSTRACT Polymer foams are attractive energy absorbers because of their low density and large deformation capacity, but homogeneous foams often have limited stiffness and inefficient material use. This study investigated the energy absorption and deformation mechanisms of 3D‐printed radially graded density tubes (RGDTs) made of continuous fiber‐reinforced foamed composites. The effects of printing temperature and layer height on foaming were examined to select appropriate printing parameters for each layer. At a layer height of 0.3 mm, temperatures of 190°C, 210°C, and 270°C produced densities of 0.88, 0.65, and 0.45 g/cm 3 for the outer, intermediate, and inner layers, respectively. Three separately printed tubes were then assembled concentrically, with density decreasing inward. Quasi‐static expansion tests assessed the effects of height gradients and interlayer connection methods on mechanical response. The results showed that the adhesively bonded height‐gradient RGDT achieved a specific energy absorption of 18.92 J/g, approximately 80% higher than the directly assembled equal‐height RGDT. Adhesive bonding reduced interlayer sliding and improved load transfer, while the height gradient promoted coordinated layer deformation. Under expansion loading, the continuous circumferential fibers carried tensile loads, while the foamed matrix was compressed and densified, allowing both components to absorb energy. Overall, the proposed RGDT combines low density with improved mechanical performance and energy absorption, providing a design strategy for lightweight impact protection in aerospace and transportation.