Shaokai Wang

It has long been desired to achieve mechanical enhancement and structural health monitoring by introducing carbon nanotubes (CNTs) into traditional carbon fiber (CF) composites. Herein, the initiation of micro-damage and crack propagation has been investigated by utilizing in situ electrical resistance changes in interlaminar hybrid CNT network/CF composites during the shear loading process. The results show a clear relationship between the crack propagation and the electrical resistance response particularly when approaching the failure of the single-layer CNT network hybrid composites. Furthermore, the chemically modified CNT network exhibits evident enhancement on main mechanical properties of the CF composites, superior to the thermoplastic toughening method. The characterizations manifest that the multiscale interlayered CNT/CF structure can simultaneously resist the crack propagation along both the in-plane direction and the cross-plane direction, which consequently enhances the flexural and compressive strengths of the composite material. This discovery provides a novel idea for the potential application of CNT network/CF hybrid composites in the integration of mechanical reinforcement and structural health monitoring, namely, that the CNT network acts not only as a reinforcing phase but also as a sensor for the structural health monitoring of the composites.

The effect of Z‐pin on the impact property of carbon fiber reinforced epoxy resin composite was investigated. Carbon fiber Z‐pin and aramid fiber Z‐pin were used to improve the impact property of composite laminate. The impact property and damage mode of the composite were studied under low‐velocity and high‐velocity impact. The low‐velocity impact was conducted by a drop hammer machine, and high‐velocity was carried out on a modified Hopkinson bar system. The maximum impact load, absorbed energy, impact damage area, and failure morphology of composites with and without Z‐pin were evaluated from impact experiments. It demonstrates that the damage modes of the composite under low‐velocity and high‐velocity are similar, while the matrix damage, fracture, and delamination damages are the dominant failure mode under high‐velocity and low‐velocity damage, respectively. The effects of Z‐pin on low‐velocity and high‐velocity impact depend on impact energy and the damage mode of Z‐pin. Carbon fiber Z‐pin shows better enhancement on impact property due to more energy absorption through its damage under the low impact energy range with both low and high velocity impact. Aramid fiber Z‐pin performs with higher efficiency when the impact energy reaches a high level, due to strong energy dissipation by its fracture and pull‐out failure. Especially, high impact energy from high‐velocity impact promotes aramid fiber Z‐pin to pull out, resulting in an excellent enhancement effect. It denotes that the type of fiber used in Z‐pin needs to be chosen based on the levels of impact velocity and energy, and a suitable failure mode of Z‐pin is the key for improvement of the impact property.Highlights: The low‐velocity and high‐velocity impacts under the same boundary were conducted. Matrix damage, fracture, and delamination are dominant failure modes under impact. Carbon fiber Z‐pin shows better enhancement in impact property under low energy. Aramid fiber Z‐pin performs a higher effect on impact property under high energy.

This paper developed a carbon nanotube (CNT)-coated aramid fiber sensor, which was successfully used to monitor the resin flow front and sense the fluid pressure difference during the (VARI) process. The electrical resistance change of the CNT-coated fiber sensor was compared with that of buckypaper materials. The results show that the electrical resistances of CNT sensors show rapid growth successively along the infusion direction once the flow front reaches the sensor position during resin infusion in the VARI process. The electrical resistance of CNT-coated fiber sensors may increase by as much as 12 times after full impregnation. For the thicker preform, the resistance change ΔR/R₀ of sensors on the top surface is closely related to fluid pressure, and bigger fluid pressure close to the inlet may result in a larger ΔR/R₀. Two competitive factors affecting the electrical resistance of a CNT-coated sensor are revealed: aramid fiber tow swelling due to resin impregnation, and the compaction effect arising from resin pressure on the CNT network. In addition, the sensors on the top surface show a bigger ΔR/R₀ than the bottom ones, and as the preform thickness decreases, these sensors tend to show smaller ΔR/R₀.

Carbon nanotube (CNT) film is favored in structural health monitoring of advanced composite materials, primarily due to its commendable mechanical properties and piezoresistive properties. Nonetheless, floating catalytic chemical vapor deposition (FCCVD) is an attractive method for fabrication of CNT films, and the electrical response to strain of FCCVD‐prepared CNT films is impeded by high aspect ratio and lamellar packing structure. For this purpose, FCCVD CNT films were modified by HCl dissolving Fe impurities, nano‐SiO₂ particles doping and freeze‐drying in combination to increase the spacing between CNTs and its networks as well as their strain sensitivities. It showed that the gauge factor (GF) according to the variation of resistance (ΔR/R₀) of the co‐modified film (CNT‐HCl‐SiO₂ film) was up to 15.6 for the tensile strain at the bottom surface of unidirectional carbon fiber reinforced plastic (CFRP) laminates during the process of bending tests. The bending cycle experiment of the CFRP showed relatively stable changes of ΔR/R₀ with the strains for CNT‐HCl‐SiO₂ film, while that of the pristine CNT film (CNT‐HCl‐0 film) displayed unstable non‐monotonic changes and that of HCl purified CNT film (CNT‐HCl‐10 film) revealed a gradual declining tendency. Moreover, the ΔR/R₀ of CNT‐HCl‐SiO₂ film exhibited excellent sensitivity to the strains of multiple bistable‐deformations of cross‐ply CFRP laminates. Strain gauge analysis indicated that a 51% increase of ΔR/R₀ of CNT‐HCl‐SiO₂ film at the 90° layer surface corresponded to the average strain of 434 με, meanwhile a 37% increase of ΔR/R₀ of the CNT film at the 0° layer surface corresponded to the strain of averagely −173.9 με, and both exhibited super high GFs of 1175 and 2108, respectively. Based on this high sensitivity, CNT‐HCl‐SiO₂ film also had the ability to predict the release of residual stress during the demoulding process of CFRP.Highlights: Even SiO₂ dispersion in CNT film, increased the pristine film thickness by 10 times GF of CNT‐HCl‐SiO₂ film increased by 68% than CNT‐HCl‐0 film and by 164% than CNT‐HCl‐10 film SiO₂ doping significantly improved the stability of the CNT film's ΔR/R₀ with temperature and strain CNT‐HCl‐SiO₂ film has the ability to monitor the deformation and residual stress of CFRP

With the rapid development in information, communication, energy, medical care, and other fields, the demand for light, strong, flexible, and stable materials continues to grow. Carbon nanotube (CNT) films possess outstanding properties, such as flexibility, good tensile properties, low density, and high electrical conductivity, making them promising materials for a wide range of applications. This paper reports an effective strategy that combines stretching treatment, laser etching, and electron beam deposition to fabricate an iron-deposited CNT film, which can serve as a counter electrode (CE) of quantum-dot-sensitized solar cells. The study also investigates the influences of processing parameters, such as stretching ratio and iron-depositing thickness on the film's stacking structure, electrical conductivity, and catalytic activity. Under optimized stretching ratios and depositing thicknesses, the catalytic activity of the reacted deposited layer and the high electrical conductivity of the flexible film basis can be fully utilized, allowing the photoelectric conversion efficiency (PCE) of the solar cells to reach approximately 4.58%. Additionally, the CE exhibits flexibility, light transmission, and good stability, with its primary properties remaining above 97% after nearly 50 days. Thus, this research provides innovative material options and development strategies for the development of electrode materials.