Composites Science and Technology最新文献

Significant enhancement in out-of-plane thermal conductivity of carbon fiber/epoxy laminated composites without sacrificing mechanical strength is of great challenge for advanced composites. In this study, a novel graphene-based hierarchical structure was constructed by combining graphene foams (GrFs) with graphene nanoplatelets (GNPs) together and laminating with carbon fiber (CF) fabrics. The GrFs acted as thermally-conductive skeletons in bridging CF fabrics together to remarkably increase out-of-plane thermal conductivity of composites, while the GNPs were helpful to further increasing heat-transfer paths and effectively transferring stress between continuous CFs for high mechanical reinforcement. The hierarchical composites exhibited extremely high out-of-plane thermal conductivity of 2.64 W/m·K, increasing by 158.8 % than that of CF/Ep composites, and they also showed satisfactory tensile, flexural, and interlaminar shear strength. Such high performance is mainly due to the hierarchical structure, continuous heat-transfer paths, synergetic enhancement of GrFs with GNPs, and strong interfacial interactions between components for high-efficiency heat and stress transfer.

Artificial muscles, designed to replicate the movements of natural biological muscles, hold significant promise in the fields of robotics and prosthetics. Recent advancements have led to the development of fiber-reinforced actuators, drawing inspiration from biological tissues. Dielectric elastomer actuators (DEAs) are a type of electroactive artificial muscle. It is possible to enhance the uni-axial deformation of DEAs by constraining and applying pre-stretch on the actuator membrane. This can be achieved through uni-directional fibers bonded to the DEA that lead to transversely isotropic properties. However, combining membrane pre-stretch and fiber reinforcement may lead to instabilities such as fiber buckling due to the compressive load of the pre-stretched membrane or due to wrinkling during actuation. Understanding these instabilities is crucial as they can significantly impact the performance. A novel model taking into consideration these instabilities is established and experimentally validated. By calculating the force in the fiber direction, the buckling profile such as the wavelength and amplitude can be predicted. The validation of the model presented along with an extensive experimental investigation allow for a comprehensive analysis to explore the impact of fiber buckling on the performance and the force of uni-axial DEAs.

Smart materials with high thermal conductivity are expected to have greatly application potential in thermal management for future electronic equipment. However, actual applications often require multifunctional properties of materials, such as high thermal conductivity (TC), good mechanical properties, and suitable electrical insulation performance. It is still a challenge to obtain such polymer composites with good comprehensive properties. Herein, the rational assembly of two-dimensional (2D) nanofillers of boron nitride nanosheets (BNNS) and graphene nanosheets (GNs) in nanofibrillated cellulose matrix is reported. The film shows 53.76 W m⁻¹ K⁻¹ of TC and 87.88 MPa of tensile strength. Meanwhile, the flexible film has the ability of response deformation by sensing the environmental temperature, which is promising for soft materials with excellent heat dissipation.

To further decrease the mass and thickness of multifunctional wideband microwave absorption metamaterials (MAMs), this study applies photonic crystal principles to the field of microwave absorption. Drawing inspiration from the structural coloration regulation of Morpho Menelaus scales, a novel integrated bioinspired MAM named MM is designed. MM possesses low drag coefficient, hydrophobicity, mechanical load-bearing capacity, and wideband radar stealth functionality. Utilizing PA6@CF filaments and material extrusion 3D printing technology, mechanical test specimens and MM specimens optimized through particle swarm optimization (PSO) are rapidly fabricated at low cost. Reflectivity tests at normal incidence reveal that MM (with a thickness of 8 mm) achieves an effective absorption bandwidth (EAB) of 33.4 GHz within the 2–40 GHz frequency range. Under transverse magnetic polarization and 60° oblique incidence conditions, MM demonstrates a coverage rate of 98.5 % for EAB. Furthermore, three-point bending tests demonstrate MM's excellent deformation capabilities (up to 50 mm) and mechanical load-bearing performance (bending strength reaching 78 MPa), laying the groundwork for its application on complex surfaces. Lastly, targeting the application of microwave absorption metamaterials on high-speed moving objects, comparative analysis of MM and five typical MAMs reveals that MM exhibits the lowest drag coefficient (C_d = 0.132). In summary, this study offers a straightforward and replicable method for designing, optimizing, fabricating, and evaluating MAMs, while suggesting aerodynamic performance as a novel metric for assessing their multifunctional capabilities.

The mechanical reinforcement of rubber by carbon black (CB) depends strongly on its the size and topography of CB clusters. However, the underlying mechanisms remain largely unexplored. This study uses atomic force microscopy (AFM) to probe interfacial properties at the nanoscale to elucidate the influence of the CB topological structure on macroscopic mechanical properties. A substantial amount of high-modulus bound rubber is found inside the CB aggregates, particularly in highly branched ones. This phenomenon plays a critical role in reinforcement, as corroborated by quantitative AFM nanomechanics, chain segment motion results and theoretical calculations. A quantitative analysis of the filler network reveals that the branched chain structure effectively reduces the packing spacing and improves the stress transfer efficiency.

The shape memory effect allows stimuli-responsive materials to generate programmable morphing when subjected to external stimuli, facilitating the creation of active origami with 2D-to-3D shape transformation capabilities. However, the current active origami made of polymer-based stimuli-responsive materials exhibits poor mechanical performance due to the inherent low stiffness of materials, which hinders their exploration and engineering application. This work reported a novel fabrication and design method to construct 3D continuous fiber-reinforced self-locking Miura-ori (SLMO) composites with high energy absorption and cyclability by 4D printing of shape memory composites. The SLMO structure consists of a Miura-ori unit and a highly stretchable bottom stopper panel, where the Miura-ori unit actively morphs and locks into a predetermined configuration under external stimuli and the constraint of the stopper panel. Incorporating continuous fibers enhanced the strength of the Miura-ori facets, synergizing with the highly stretchable characteristic of the bottom panel to enable the SLMO structure to exhibit a push-to-pull deformation mode under compressive load. Structural analysis of the SLMO, stress-stretch behavior of the bottom panel, and buckling criteria of the Miura-ori facets were theoretically investigated to describe the push-to-pull deformation behavior of the SLMO structure and the conditions necessary for its realization. Moreover, the compressive behavior of the SLMO structure with different design parameters was investigated through experiments and theoretical analysis. By optimizing design parameters, it was demonstrated that the SLMO structure can sustain more than 10 cycles of 50% compressive strain. This approach broadens the practical and functional applications of active origami.

Resistance welding of thermoplastic composites often suffers from quality issues due to high-pressure requirements and nonuniform heating, leading to nonbonding at the overlap edge. This study proposes an ultrasonic-assisted resistance welding method aimed at enhancing joint quality while operating at lower welding pressures. Results indicate that in traditional welding, reducing pressure tends to create voids near the weld line, whereas increasing pressure results in nonbonding at the overlap edge due to reduced temperatures. Introducing ultrasonic during the final phase of the welding process efficiently raises the temperature at the overlap edge and enhances the uniformity across the joint. Moreover, applying ultrasonic facilitates the squeeze flow of the polymer melt, extending the melt front and enlarging the effective bonding area. An improved squeeze flow reduces void formation caused by trapped air, diminishing the need for high pressure. The ultrasonic effects are more pronounced with increasing welding pressure. Consequently, glass fiber reinforced polyphenylene sulfide joints exhibit a 12 % increase in the maximum lap shear strength (LSS) compared to those welded without ultrasonic. Additionally, the use of ultrasonic achieves a 27 % reduction in pressure while maintaining an LSS comparable to the maximum values of the joints welded without ultrasonic.

This study aims at obtaining an effective structural design strategy for stronger and more reliable Unidirectional glass fiber (UD-GF) composites by in-situ formed cross-linking from randomly distributed nano-/micro- Aramid pulp (AP) fibers. The flexural strength and stiffness have shown substantial improvements in both the transverse and longitudinal directions due to the AP cross-linking and the “brick-slurry” structure. With AP of 8 g/m², up to 60–70 % improvement in flexural strengths (both transverse and longitudinal directions) and up to 20–37 % improvement in “effective modulus” have been observed. The noticeable longitudinal improvements have been attributed to the resin reinforcement and interlayer cross-linking provided by ultra-thin AP interlayers, and the resultant improvement in micro-buckling resistance under compression. Since sparsely distributed nano-/micro-AP can be readily incorporated in pultrusion and pre-preg manufacturing processes, this study is not only important for micro-mechanism study, but also provides a plausible improvement in manufacturing.

Polymer-based dielectric film capacitors are essential energy storage components in high-power energy storage devices benefiting from their high breakdown strength (E_b) and ultra-fast charge storage/release capability. However, the state-of-the-art commercial capacitor, biaxially oriented polypropylene (BOPP), exhibits limited energy storage density primarily due to low dielectric constant, which hinders the advancement of the film capacitor industry. Introducing high-permittivity (high-k) nanofillers into PP matrix to improve polarization is a promising method but poor filler dispersion leads to a remarkable decrease of E_b, while various strategies to enhance dispersion of fillers typically require sophisticated process involving toxic procedure and consuming significant time and cost. Herein, we show that a novel and scalable surface grafting method for high-k fillers can be achieved by a facile and short-period microwave irradiation with the assistance of silane coupling agent (KH560). As a demonstration, the KH560 is effectively grafted onto the surface of barium titanate (BT), achieving a high grafting ratio of 4.91 % at a yield of 85.1 % within a short time (40s). Furthermore, the surface modified BT nanofillers are introduced into PP matrix and then biaxially stretched. The as-prepared film exhibits excellent dispersion and superior compatibility, resulting in a remarkable enhancement of tensile strength (from 82 MPa to 115.4 MPa), breakdown strength (from 200 MV/m to 254 MV/m), and energy density (from 1.49 J/cm³ to 2.21 J/cm³). This work proposes a new strategy for constructing homogeneous polymer-based dielectric film by microwave activating high-k fillers and is crucial for the design of next-generation energy storage devices.