Performance enhancement, negative stiffness structural characterization, and energy absorption mechanisms of 3D-printed continuous carbon fiber reinforced composites
Negative stiffness (NS) structures exploit multi-stable mechanisms to achieve energy absorption, yet their practical application is limited by material and manufacturing constraints that compromise load-bearing capacity, reusability, and energy absorption efficiency. This study addresses these limitations by employing continuous carbon fiber reinforced thermoplastic polymers (CCFRTP) and three-dimensional (3D) printing to fabricate NS structures with cosine beam cells. A wet twisting method for continuous carbon fiber (CCF) was developed to enhance mechanical properties and elucidate failure behaviors and interfacial adhesion mechanisms. The resulting CCF/PLA/PVDF composites exhibited significant improvements in mechanical properties compared to untreated counterparts, with failure analysis revealing characteristic fiber breakage due to enhanced interfacial adhesion, as opposed to fiber pull-out and irregular fracture in untreated samples. A one-stroke path planning model was used to investigate bistability principles and energy absorption mechanisms. Displacement-controlled loading/unloading experiments assessed energy absorption in both energy-locked and repetitive modes. A dual-unit assembly structure was fabricated to validate the feasibility of a negative stiffness honeycomb structure. Composite layup simulations via Abaqus confirmed the deformation process and energy absorption mechanisms. The findings demonstrate that CCFRTP-based NS structures offer considerable potential for large deformation energy absorption applications in aerospace and naval fields.