3D-printed continuous carbon fiber reinforced thermoplastic matrix composites: Mechanical behavior, interfacial bonding, and energy absorption mechanism

MD simulations quantify intermolecular interactions governing microphase separation. • TPU/PLA blending resolve the rigidity-flexibility trade-off and reduce pore defects. • Component/interface tuning contributes to mixed failure mechanism of C/T 3.0 P 1 . • Process optimization induces composite multiscale dissipation to widen damping range. • Custom composite realizes reusable NS structure with novel reversible energy absorption. To develop lightweight reusable protective structures for aerospace and marine heavy equipment, single thermoplastics fail to balance stiffness and ductility. Here, a series of gradient Thermoplastic Polyurethane/Polylactic Acid (TPU/PLA) ratio (TPU, PLA, T 1.5 P 1 –T 3.5 P 1 ) systems and 3D printed continuous carbon fiber(CCF)-reinforced TPU/PLA composites are fabricated, and their molecular interactions, interfacial morphology, mechanical performance, and negative stiffness(NS) energy absorption are systematically investigated. Molecular dynamics(MD) simulations were conducted on CCF-reinforced resin systems to elucidate compatibility and mechanism across ratios within the 235–255 °C processing window. Combined with physical chemistry and morphological characterization, the intrinsic reasons for the interface bonding state, mechanical properties, and structural characteristics are also explained at the microscopic mechanism level. The X-ray Computed Tomography(XCT) shows that the volume porosity of C/PLA, C/TPU, C/T 2.0 P 1 , and C/T 3.0 P 1 is 0.126%, 0.411%, 1.261%, and 1.056%, respectively. Under the optimal process parameters, C/T 3.0 P 1 presents a unique brittle-ductile coupling fracture mode, with the comprehensive mechanical properties being the best, and its fracture elongation rate being 6.52 ± 0.21%. Its tensile strength(120.96 ± 12.30 MPa) and Young's modulus (4.88 ± 0.27GPa) are respectively 22.60% and 39.03% higher than those of C/TPU, and its bending strength(80.67 ± 6.00 MPa) and bending modulus(5.95 ± 0.04GPa) are 139.23% and 74.30% higher, respectively. The Dynamic Mechanical Analysis(DMA) test confirms that the multi-phase composite system builds multiple energy- dissipation paths, significantly expanding the wide-temperature damping stable interval. Finally, 3D-printed composite large-scale NS structures and periodic honeycomb were prepared, and impact and cyclic load-unload tests reveal C/T 3.0 P 1 achieves EA = 712.36 mJ(134.71%, 22.11% higher than C/TPU, C/PLA) and SEA = 0.239 mJ mm −3 , retaining 70.47% initial EA(501.99 mJ) after 10 cycles. TPU/PLA synergy overcomes the stiffness-ductility trade-off. This work fills the research gap of 3D-printed large-scale aerospace/marine protective components, reusable NS energy-absorbing structures.