This study primarily investigates the crashworthiness of Markforged 3D-printed hy-brid continuous fiber composite honeycomb, incorporating a hybridization of carbon andKevlar fibers. Through experimental and simulation analyses, the crashworthiness andfailure behaviors of hybrid composite honeycombs are examined. By characterizing thecrushing failure modes, the energy-absorbing mechanism is uncovered. Subsequently, thehybrid effect and mechanism are elucidated to illustrate the enhancements in crashworthi-ness. The key findings are summarized as follows.

To accurately observe and analyze failure behaviors, allexperiments were performed under quasi-static crushing loading conditions, with the rigidplate set at a constant speed of 5 mm/min.

Following the printing process, different fiber layers were thermally cured with high-strength epoxy resin to produce the final 3D-printed continuous carbon/Kevlar hybrid-fiber-reinforced composite honeycomb structures.

Figure 2 shows the design of composite honeycomb structures and the partialschematic diagram. As shown in Figure 2a, the single-fiber composite honeycomb struc-tures, specifically CFRP and KFRP, serve as the reference for comparative analysis. Forthe hybrid structures, in the CF/KFRP configuration, the carbon fiber layer is positionedon the exterior, while, in the KF/CFRP configuration, the Kevlar fiber layer occupies theoutermost position. This layup is informed by previous studies which have shown thatplacing the stiffer carbon fiber layers on the outside can enhance the structural stiffness andthat Kevlar layers on the exterior can improve impact resistance [ 31 ]. Due to the constraintsimposed by the Markforged 3D printer (Figure 1a), several Onyx layers are incorporated tosafeguard the fiber layers, as depicted in Figure 2b. Onyx, a composite material consistingof Nylon mixed with chopped carbon fibers, is known for its good mechanical propertiesand printability [32]. Consequently, interfaces between CFRP/Onyx, KFRP/Onyx, andOnyx/Onyx are formed and can be observed in the XOY coordinate system (CSYS), andthe properties and role of Onyx will be further elaborated in the subsequent section. Thepresence of Onyx layers provides a protective barrier that mitigates potential damage tothe fiber layers during the printing process [33].Moreover, in the YOZ coordinate system (CSYS), it is evident that the fiber layers areenveloped by Onyx on both sides along the thickness direction, as shown in Figure 2c.This encapsulation of fiber layers within Onyx can lead to improved load distributionand damage tolerance, as the Onyx layers help to absorb and dissipate energy undermechanical loading [ 34 ]. These detailed configurations and their implications on themechanical behavior of composite honeycomb structures will be comprehensively analyzedand discussed in the following sections, emphasizing the significance of the synergisticeffects of combining different fiber types.

Con-sequently, an integrated experimental and simulation approach is imperative to achievinga thorough understanding of the energy absorption characteristics of these advanced mate-rials and structures

By inte-grating these materials into a hybrid composite, it is possible to harness the advantages ofboth fiber types, potentially yielding structures with enhanced crashworthiness.

The advancement in additive manufacturing technologies has revolutionized thedesign and fabrication of complex structures, enabling the production of components withintricate geometries that were previously unattainable through traditional manufacturingmethods [ 1]. Fused Deposition Modeling (FDM) is a widely used additive manufacturingtechnique [ 2]. In FDM 3D printing, a thermoplastic filament is fed through a heatednozzle. The nozzle heats the filament to its melting point and then deposits it layer by layeraccording to the pre-designed model [3 ]. This layer-by-layer deposition process allows forthe creation of complex three-dimensional geometries. For continuous fiber composites inMaterials 2025, 18, 192 https://doi.org/10.3390/ma18010192Materials 2025, 18, 192 2 of 21FDM, it offers many unique advantages. The continuous fibers can be incorporated into thethermoplastic matrix during the extrusion process [4]. This enables the reinforcement of theprinted structure, enhancing its mechanical properties, such as strength and stiffness. Theability to precisely control the fiber orientation and distribution within each layer providesan opportunity to optimize the performance of the final structure. For example, by aligningthe fibers along the direction of the main stress, the load-bearing capacity of the structurecan be significantly improved. Additionally, FDM technology allows for relatively easycustomization and rapid prototyping, which is beneficial for fabricating complex structureswith different cell sizes and geometries to meet specific application requirements [5].