Composites Science and Technology最新文献

Unidirectional carbon/polyamide-6 (CPA6) is a thermoplastic composite with attractive properties for many industrial applications. However, shortage of experimental data may hinder the development of reliable material models. This paper is the first to provide a complete dataset for the tensile behaviour of unidirectional CPA6, including the longitudinal, transverse, in-plane shear, and off-axis response, at different temperatures and (quasi-static) strain rates. The oblique end tab design, already proven in the literature for off-axis testing of composites at room temperature, was successfully extended to the elevated temperature of 120 °C. The use of cardboard tabs and fast-curing adhesive greatly simplified the tab manufacturing and application for all the combinations of fibre angles, temperatures and strain rates. Digital image correlation (DIC) was performed through the window of the temperature chamber to verify the homogeneous strain field produced by the oblique tabs. The in-plane shear behaviour was extracted from the off-axis tests, allowing to estimate the shear modulus and shear strength. Finally, the robustness of the experimental results generated in this study was demonstrated with well-established analytical models that could excellently predict the elastic modulus, Poisson’s ratio, and failure stress at different fibre angles.

High-performance aramid papers are ideal insulating materials in the electric industry, due to their superior mechanical strength and insulation capabilities. However, when subjected to prolonged high-voltage and high-power operations, these papers are prone to electrical damage, such as breakdown or corona aging. Unfortunately, most damaged aramid papers are viewed as mere waste, discarded through landfill or other unsustainable disposal methods. It is not only contrary to circular economy principles but also poses a significant environmental threat due to the potential for pollution. Herein, a closed-loop recycling strategy is proposed that efficiently and effectively reclaims electrically damaged meta-aramid papers. Using the DMAc/LiCl deprotonation system, waste aramid papers are completely decomposed into molecular chains, exposing carbon residues resulting from electrical breakdown. These carbon residues are removed through a step-by-step purification process. A reprotonation treatment is then applied to regenerate new meta-aramid papers by reforming the intermolecular hydrogen bonds. This approach not only fully restores the original honeycomb-like structure but also ensures the crystallization and hydrogen bond content, maintaining both electrical and mechanical properties at above 90 % of their original values. Notably, our recycling method is also compatible with aramid-based composites, achieving exceptional recycling efficiency.

Carbon fiber composites have poor impact resistance that constrains their wider application in advanced engineering structures, and hybridizing carbon fibers with Kevlar fibers is an effective method to enhance their impact resistance. The ballistic impact resistance can be optimized through regulating the hybridization layout and hybrid ratio, which requires systematically exploration on the inherent failure mechanism. In this work, the ballistic impact behavior of hybrid carbon/Kevlar fiber reinforced epoxy laminates against flat-head projectile are systematically investigated. Hybrid specimens with different thicknesses and hybridization ratios are designed, tested and compared. The results reveal the strong correlation between thickness and ballistic impact performance. When laminates are relatively thin, Kevlar fiber layers at the back surface impart superior impact resistance. In contrast, the opposite result is observed when the thickness is beyond a threshold value. With an increase in the Kevlar fiber hybridization ratio, this threshold value will occur in thinner laminates. Further analysis indicates that this phenomenon is related to a shear plugging effect that dominates the different modes of impact failure.

A novel 3D viscoelastic–viscoplastic and viscodamage constitutive model is proposed to predict the viscous effects due to dynamic loading conditions of unidirectional carbon fibre-reinforced polymer laminates at the meso-scale level. The present model is developed under continuum damage mechanics and the thermodynamics of irreversible processes framework. The viscoelastic response is modelled using the generalised Maxwell model, while an overstress model is employed to address the viscoplastic strain. The onset of the viscodamage mechanisms is based on experimental expressions, and their propagation is defined as a function of the corresponding fracture toughness. The mechanical response of the present constitutive model under pure longitudinal shear loading conditions at different strain rates is presented. The higher the strain rate is, the stiffer the responses in the viscoelastic and viscoplastic regions are. Additionally, the onset of viscodamage increases with higher strain rates. Off-axis compressive experimental data at two different strain rates are employed to demonstrate the capabilities of the present model with good predictions being obtained.

Surface modification with micro/nanostructures is a common approach for enhancing the performance of flexible pressure sensors. However, the current fabrication of the singular functionality of instruments and redundancy of processes increase the complexity of the sensor manufacturing process. In this study, we developed a multilayer microstructure-enhanced flexible capacitive pressure sensor based on the multimodal electrohydrodynamic jet (E-jet) printing technology. The experimental results demonstrate that the sensors incorporating the microstructure-sensitized electrode layer and the polyvinyl alcohol/graphene/polydimethylsiloxane dielectric layer exhibit the following characteristics: high sensitivity (0.3139 kPa⁻¹/0–2 kPa), low limit of detection (∼100 mg), and stable performance even after 10,000 cycles. Moreover, microstructure-enhanced sensors have considerable potential for human behavior detection, such as detecting fluid flow, tracking muscle movements, and measuring pulse rates. Finally, microstructure-enhanced sensors fabricated using the E-jet printing method present a novel approach for designing sensitized structures in capacitive pressure sensors.

With the demand for further miniaturization and higher frequency operation of electronic devices, polymer films with high thermal conductivity and electromagnetic interference (EMI) shielding effectiveness (SE) are urgently required. Herein, polyimide (PI)/boron nitride nanosheets (BNNS) aerogels with oriented porous structure are fabricated by unidirectional-freezing and freeze-drying methods. Subsequently, hierarchical PI/BNNS/Ti₃C₂T_x composite films with consecutively electrically and thermally conductive networks are successfully prepared via a unidirectional PI/BNNS aerogels-assisted immersion and hot-pressing strategy. Owing to the three-dimensional conductive dual networks of BNNS and Ti₃C₂T_x, the composite film exhibits excellent thermal conductivity with the maximum in-plane value of 4.73 W/(m·K), increased by 456 % compared to pure PI film. Moreover, the conductive network of Ti₃C₂T_x is conducive to the excellent EMI shielding performance, endowing the PI/BNNS/Ti₃C₂T_x composite film with an outstanding EMI SE value of 49.2 dB at 8.2 GHz with a low MXene content of 6 wt% and thickness of 300 μm. Furthermore, the composite film shows the superior Joule heating performance with fast thermal response and sufficient reliability. Therefore, the resulting composite film exhibits excellent thermal conductive, EMI shielding and Joule heating performance, which enables the potential application of multifunctional composites for thermal management and EMI shielding.

The high jeopardy of prosthesis joint infection demands urgent development of an in-situ drug delivery joint material, while achieving sustained antimicrobial activity remains a challenge. Herein, a sedimentary rock-like “cross-bedded” drug delivery structure was constructed in the ultrahigh molecular weight polyethylene (UHMWPE) joint material. Epigallocatechin gallate (EGCG), a representative tea polyphenol, was employed as a substitute of antibiotics with antimicrobial activity. Delivery pathways composed of EGCG were highly aligned and cross-bedded with the UHMWPE matrix under the strong flow field offered by solid-state extrusion. The EGCG pathlength was thus increased in a longitudinal section, attenuating burst release and prolonging the release time of EGCG. The release of EGCG in the “cross-bedded” structure was restricted to a low concentration at the initial stage yet subsequently extended 2–3 times compared to that in the massive structure. The prolonged release ratio is nearly equivalent to the EGCG pathlength increment as calculated via a simplified mathematical model. The quantitative relationships between release behavior and antimicrobial performance proved that the cross-bedded structure was efficient in maintaining sustained antimicrobial activity. These findings offer a paradigm to achieve sustained drug therapy in UHMWPE joint material, which is constructive for treating prosthetic bacterial infections in clinical trials.

Vitrimers with dynamic covalent bonds combine the merits of thermosets and thermoplastics, opening up new opportunities for science and industry. The attainment of enhanced mechanical performance without compromising dynamic reprocessability poses a significant obstacle to vitrimer materials. Designing vitrimer nanocomposites from interfacial and structural aspects is promising to solve this problem. Herein, strengthening and toughening of hard epoxy vitrimer using nanosilica have been successfully achieved by introducing interfacial covalent binding and microphase separation. Performing interfacial covalent binding between epoxide-modified silica nanoparticles and hard epoxy vitrimer matrix improves interfacial compatibility and nanoparticle dispersion. Controlling the proportion of silica nanoparticles yields two types of microstructures, including a uniformly dispersed material at low nanoparticle loadings and unique microphase separation at high nanoparticle loadings. Particularly, silica reinforcement accompanied with phase separation exhibits a substantial enhancement in Young's modulus, tensile strength, and fracture toughness while achieving good stretchability. In addition, the silica-epoxy vitrimer nanocomposites preserve excellent reprocessability not inferior to the pristine vitrimer. The resulting nanocomposites show potential applications in bonding, recycling, and shape morphing. The concepts and methodologies presented in this work will enlighten future vitrimer material design and functional applications.

To match the increasing miniaturization and integration of electronic devices, higher requirements are put forward for the electromagnetic wave absorption (EWA) and thermal conductivity (T_c) of heat conduction-microwave absorption integrated materials (HCMWAIMs) to overcome the problems of electromagnetic wave (EMW) pollution and heat accumulation. Herein, a simple and efficient shear force induction technique is used to construct a carbon/magnetic isolation network within the silicone resin matrix, where ferrite particles are well dispersed in vertically oriented SiC-coated carbon fibers array. Benefiting from the orderly interconnection of CFs@SiC in the array, the prepared composites have a high T_c of 7.86 W m⁻¹ K⁻¹. The introduction of magnetic ferrite particles within the CFs@SiC array can induce electrical-magnetic coupling, optimize impedance matching, and enhance EMW attenuation. This synergy of V-CFs@SiC/ferrite isolation network structure gives the composites an excellent effective absorption bandwidth (EAB) of 5.88 GHz and a minimal reflection loss (RL_min) of −47.5 dB at a thickness of 1.5 mm. Moreover, the as-prepared composites exhibit outstanding elastic compressibility of 43.2 % and rebound rate of 45.1 % under a pressure of 35psi. This strategy offers a distinguishing understanding of preparing high-performance HCMWAIMs in modern electronic devices.

This study aims to investigate the damping behaviors of unidirectional and laminated flax fiber reinforced composites (FFRCs) under various frequencies and moisture absorption conditions. The damping performances of unidirectional (0°, 45°, 90°), orthotropic and symmetric angle-ply composites were evaluated by the cantilever percussion free-decay method to establish the relationship between frequency, hygroscopicity and damping ratio. To elucidate the frequency- and moisture-dependent damping mechanisms, the glass-transition temperature and modal analysis were examined using dynamic mechanical analysis and a 3D scanning laser Doppler vibrometer respectively. To predict the frequency- and moisture-dependent damping behaviors for hierarchical FFRC laminates, a finite element model subject to the damping test was developed by integrating laminate theory and the complex eigenvalue method in a user-defined material subroutine. The findings indicate that moisture absorption leads to an increase in the damping ratio and changes the frequency-dependent trend. The distinct hierarchical structures of flax yarns result in strong frequency- and moisture-dependent damping performances in FFRC laminates. A significant agreement between the experimental modal frequency, damping ratio, mode of vibration of all composites and those values derived from the established modelling was achieved. It offers a foundational parameter for precisely predicting the damping properties of FFRC laminates with complex stacking sequences and designing safe and reliable FFRC structures integrating load-bearing and damping functionalities.