Key Takeaways & Executive Findings
- •• • Wet twisting of continuous carbon fiber (CCF) significantly enhances mechanical properties of CCF/PLA/PVDF composites, with failure mode shifting from fiber pull-out to characteristic fiber breakage, indicating improved interfacial adhesion. • • The optimized G-code and contour bias path redirect force distribution, enabling effective utilization of CCF properties in 3D-printed structures. • • Abaqus simulations confirm the deformation process and energy absorption mechanisms of the CCFRTP cosine beam structure, validating its feasibility for energy-absorbing applications. • • The double-cell array configuration validates the negative stiffness honeycomb structure's potential for large deformation energy absorption, with performance strongly influenced by interface properties and structural parameters.
Abstract
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.
1. Introduction
Conventional energy-absorbing structures rely on plastic deformation, ceramic fragmentation, or viscoelastic dissipation, each with inherent drawbacks. Plastic deformation, common in automotive bumpers and ceramic composite armor, offers high specific energy absorption but suffers from destructive, non-reusable deformation. Viscoelastic structures, such as those in helmet protectors, allow multiple cycles but exhibit rate-dependent performance, underperforming at low-speed, low-frequency loads. These limitations drive the search for structures that combine high energy absorption with repeatability.
Negative stiffness (NS) structures, leveraging multi-stable mechanisms and flexural step effects, present a promising alternative, achieving large deformations while maintaining reusability. However, existing NS implementations are constrained by material and manufacturing limitations, hindering load-bearing capacity and energy absorption efficiency. This study addresses these bottlenecks by employing continuous carbon fiber reinforced thermoplastic polymers (CCFRTP) and 3D printing to fabricate NS structures with cosine beam cells. A wet twisting method for continuous carbon fiber enhances mechanical properties and interfacial adhesion, while a one-stroke path planning model optimizes the structure's bistability. This approach aims to overcome prior limitations and validate the feasibility of CCFRTP-based NS honeycomb structures for demanding aerospace and naval applications.
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Yaru Zhang, Wenkai Zheng, Wenhua Guo, Yuzhong Wang, Kaiyue Ma, Qianyu Ji, Yuhang Xue, Bingheng Lu (2026). Performance enhancement, negative stiffness structural characterization, and energy absorption mechanisms of 3D-printed continuous carbon fiber reinforced composites. SCIENCE CHINA Materials. https://doi.org/10.1007/s40843-025-3616-8
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Frequently Asked Questions
What specific mechanical property improvements were observed in wet twisted CCF/PLA/PVDF composites compared to untreated counterparts?
The wet twisted prints exhibited significant increases in mechanical properties, with failure analysis showing characteristic fiber breakage due to improved interfacial adhesion, in contrast to untreated prints which displayed fiber pull-out and irregular fracture morphologies.
How does the one-stroke path planning model contribute to the bistability and energy absorption of the cosine beam structure?
The one-stroke path planning model optimizes the G-code and implements a contour bias path to redirect force distribution, effectively utilizing CCF properties. This enables the structure to exhibit bistable behavior and efficient energy absorption, as confirmed by displacement-controlled experiments and Abaqus simulations.
What are the energy absorption characteristics of the CCFRTP cosine beam structure in energy-locked and repetitive modes?
Displacement-controlled loading/unloading experiments assessed energy absorption in both modes. The structure's performance was significantly influenced by interface properties and structural parameters, with differences observed between energy locking and repetitive energy absorption modes.
How was the feasibility of the negative stiffness honeycomb structure validated?
A dual-unit assembly structure was fabricated and tested, demonstrating overall deformation and energy absorption properties. This validated the feasibility of the negative stiffness honeycomb structure for large deformation energy absorption applications.
What are the potential applications of this CCFRTP-based negative stiffness structure?
The structure shows considerable potential for aerospace and naval applications requiring efficient energy absorption under large deformation and high loading conditions.
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