Cellulose nanofibrils (CNFs) have been proposed as reinforcement for thermoplastic polymers due to their potentially superior mechanical properties. However, it seems still uncertain how the reinforcement ability of CNFs compares to cheaper pulp fibres, and how the suspected potential of CNFs can be fully utilized in biocomposites. Therefore, this study presents a direct comparative investigation of kraft pulp fibres and their fibrillated materials as reinforcement of high- or low-density polyethylene. Besides the experimental investigations, the tensile properties of the corresponding biocomposites were predicted by using micromechanical analysis. It was shown that considering the same fraction of fibrous materials (pulp fibres vs CNFs), the experimental and modelling results revealed that the highest tensile strength was obtained from the pulp fibre-reinforced biocomposites. Regarding the CNFs-reinforced biocomposites, the compatibilizer content had to be up to 20 wt% to experimentally achieve the tensile strength predicted by the model.

Fatigue tests were carried out on a glass/epoxy cross-ply laminate under constant amplitude, two-stage repeated blocks and three different types of spectrum loadings. The damage evolution, in terms of transverse crack initiation, propagation and crack density evolution, was analysed. It was found that the linear damage accumulation rule, previously validated for long block loadings, is not suitable for a generic spectrum. Indeed, it leads to an underestimation of the number of cracks and their propagation rate. The results are discussed to identify the main spectrum features influencing the fatigue damage evolution. A theoretical framework is derived to interpret the results and predicting the crack density evolution under spectrum loadings.

Machine learning methods have been extensively explored for constitutive relation that is essential in material and structural analyses. However, most existing approaches rely on neural networks, which lack interpretability and treat stress–strain data as discrete values, disregarding their inherent continuous nature. Therefore, this paper proposes novel functional order-reduced Gaussian Processes emulators, which are more interpretable by leveraging Bayesian theory and account for the uncertainty arising from microstructural homogenization, providing the non-parametric probabilistic and continuous constitutive modeling of composite microstructure undergoing fracture/failure. Its most salient point is the capability of predicting the continuous and probabilistic stress–strain function only using limited (i.e., 400) samples, where the uncertain data is high-dimensional in large-scale composite (up to 250,000). An illustrative example demonstrates that the emulator accurately captures the probabilistic constitutive relation, providing insights into the maximum stress and strain values. Notably, the results highlight the significant variation in maximum stress due to fiber uncertainty. Moreover, the example showcases that as the fiber volume fraction increases from 0.4 to 0.6, the maximum stress tends to increase, while the maximum strain decreases, namely, more fiber results in higher strength and stiffness.

In this study, through structural design, thin film doping modification, and electrode preparation, a high-performance triboelectric nanogenerator (TENG) has been achieved, and an electromagnetic generator is incorporated as an energy supplement to construct a self-powered sensing system for gas alarm and environmental monitoring. The high porosity of NiO derived from MOFs, high charge accumulation, and the high charge carrier mobility of N-MWCNTs promote charge capture and transfer, greatly enhancing the output performance of the triboelectric nanogenerator. Under the optimal doping ratio, the open-circuit voltage can reach 860 V, and the maximum short-circuit current up to 47 μA, sufficient to power 600 LEDs lights, achieving a power density of 10.45 W/m2. Meanwhile, MXene/Carbon/Ecoflex electrodes were fabricated to enhance the contact efficiency between the thin film and electrodes, further obtaining an open circuit voltage of 1020 V. This work provides a viable solution for the design of high-performance hybrid nanogenerators.

In this work, micron scale GO20∼30 μm sheets were modified by five kinds of modifiers and co-dispersed with nano scale GO200 nm to promote their dispersion in epoxy resin. Meanwhile, ultra-thin carbon fiber technology was adopted to prepared carbon fiber reinforced polymer composites (CFRPs). Contrastive experiments were carried out to explore the influence of surface functionalization effect and synergistic dispersion effect of nano scale GO200 nm on the dispersibility of micron scale GO20∼30 μm and the “bridges” built by it between carbon fibers in the composites. The interlaminar and compression properties of CFRPs gained remarkable optimization due to the “bridges” built by micron scale GO20∼30 μm. Prominently, the lateral fiber bundle test (TFBT), the interlaminar shear strength (ILSS) and compressive strength of GO200 nm + GO20∼30 μm-D400/EP/CF24 mm composites reached 51.7 MPa, 86.9 MPa, 1397.9 MPa which were increased by 140.4 %, 31.4 % and 49.0 % respectively compared with GO20∼30 μm/EP/CF24 mm composites.

In this work, we report a facile preparation of the composite resin with significantly enhanced high in-plane or through-plane thermal conductivity via controlling the layer thickness of digital light processing (DLP) 3D printing less than the lateral size of hBN. The thermal conductivity of the composite resin reaches up to 7.962 W∙m−1∙K−1 along the oriented direction at the content of 30 wt% hBN flakes with a lateral size of 25 μm under the 3D printing layer thickness of 15 μm, which is about 44 times greater than that of the pure resin. It is found that a lower thickness of the printing layer leads to a higher degree of the hBN flake orientation and higher thermal conductivity of the composite resin. Inspired by this method, the thermal conductivity prediction model based on the process parameters is established and has a higher accuracy than the traditional model. In addition, the 3D printed composite resin exhibits excellent thermostability, low water absorption and volume shrinkage, favorable mechanical properties, and great dielectric properties. This approach provides a new vision for the application of 3D printing in thermal management.

The mechanical properties of carbon nanofibers (CNFs) are always restricted by their disorganized crystal structures. Herein, this paper utilizes two typical hexagonal crystalline flake materials, nanoscale flake graphite (NG) and hexagonal nitride boron (BN), as nanofillers to optimize the crystal domains of CNFs and achieves enhancement in fiber strength, modulus and toughness. For this purpose, in situ polymerization technique is developed for the rapid and uniform mixing of nanofillers with polyacrylonitrile (PAN) precursors of CNFs. The nanofillers are exfoliated in this process and wrapped with PAN to prevent potential agglomeration. The obtained core–shell nanocomposites can be produced into composite CNFs via electrospinning, stabilization and carbonization. Based on the attraction effect, the dispersed nanofillers can organize PAN molecular chains into oriented crystalline fibrils in as-spun nanofibers and accelerate their transformation to more ladder structures in stabilized nanofibers. On this basis, NG is shown to act as the templating and nucleating agent to promote the formation, growth and compact stacking of graphitic planes in CNFs. BN also improves fiber crystallinity, while its limited templating effect leads to looser and finer crystal domains. As a result, NG-doped CNFs have significantly improved strength and modulus, and BN-doped CNFs possess simultaneously enhanced strength and toughness.

Broadband microwave absorption as a hot research topic plays important roles on electromagnetic compatibility, electromagnetic radiation protection and radar detection disguise. However, traditional molding method is difficult to fabricate large-size curving structures for broadband microwave absorption. Herein, the material extrusion with high-speed printing process was effective to manufacture large-size metastructures for broadband microwave absorption. The polylactic acid was mixed and extruded with nano pyrolytic carbon in high temperature to manufacture functional filaments with high dielectric loss. The printed metastructure integrated with 0.5 mm quartz fiber reinforced composite (QFRC) achieved −10 dB broadband microwave absorption in 3.03–18 GHz and effective load bearing performance in tensile and flexural tests. Severe impedance mismatch brought by QFRC was overcome by appropriate structure design and high-speed printing technique. The proposed design-manufacturing closed loop is a promising approach to fabricate aircraft skin with broadband microwave absorption performance and suitable aerodynamic properties for heavy unmanned aerial drones.

Herein, we present the mechanical and piezoresistive behavior of MWCNT/UHMWPE nanocomposites processed via selective laser sintering (SLS) under tensile, flexural and cyclic loadings. We show that the uniform dispersion of MWCNTs in UHMWPE enhances crystallinity (+10% for 0.5 wt.% MWCNT) and decreases porosity (as evidenced by μCT images), evincing the lowest porosity (∼ 1%) and the highest tensile strength of 20.3 MPa which is ∼45% higher than the maximum tensile strength of extant SLS processed UHMWPE and UHMWPE-based composites. The nanocomposite also exhibits superior piezoresistive characteristics, showing a sensitivity (in tension) of 0.6 and 2.6 in the elastic and inelastic regime, respectively. Furthermore, 2D-hexagonal nanocomposite lattices with a relative density of 50% reveal a linear piezoresistive response with a gauge factor of 1 and show consistent and stable strain sensing capability over 100 cycles. The results demonstrate the potential of MWCNT/UHMWPE nanocomposites for the development of smart biomedical devices.

Carbon nanotube yarns (CNTY) have the potential to serve as continuous reinforcement in functional-structural composite materials; however, there exists the insulation problem (or poor conductivity) of polymers that has hampered the development of CNT/polymer-based composite electronic devices. Herein, a strategy is proposed to develop CNT/polymer-based composite yarn with excellent electrical and mechanical properties by doping polyethyleneimine (PEI) polymer and then directional densification-stretching. The PEI polymer was well-infiltrated into intra- and inner CNT bundles to construct a consecutively conductive pathway, endowing an ultra-robust tensile strength (∼1207 MPa) and highly electrical conductivity (2.1 × 103 S cm−1) of composite yarn. The resulting CNT/PEI CYs also exhibit integrated performances of superior mechanical damping, anti-abrasive ability, extreme environment stability, and electrothermal properties. Additionally, they can act as stretchable conductors to maintain electrical stability during large-strain (100%) cyclic stretching. This engineering strategy provides novel insights into the development of continuous CNT/polymer-based composites for structural and functional composite materials.

Herein, magnetic Co/C composites were fabricated by room temperature stirring and high temperature pyrolysis processes. The results showed that the micromorphology of Co/C composites changed from flower-like shape to rhombic dodecahedron with the increase of methanol volume fraction. Furthermore, the electromagnetic absorption performance of Co/C composites could be regulated by changing the solvent composition, filler loading ratio and matching thickness. The attained Co/C composites exhibited the best electromagnetic absorption performance when the loading ratio was 37.5 wt%, i.e. the minimum reflection loss reached up to −82.19 dB at 16.16 GHz under a thin thickness of 1.85 mm. It was worth mentioning that the maximum absorption bandwidth of 6.56 GHz was achieved at a thickness of 2.01 mm. Additionally, the electromagnetic dissipation mechanisms were clarified. Therefore, this study could provide a reference for the preparation of magnetic carbon composites derived from metal organic frameworks as broadband and efficient electromagnetic absorbers.

The booming of modern communication and wearable electronics has greatly necessitated the development of films that could feature both electromagnetic interference shielding and thermal management capacity. Here we report a series of sandwich structured films prepared through freeze drying-laying-hot compression technology. Owing to the unique sandwich like structure, the resulting film has displayed not only EMI shielding performance (42 dB), but also enhanced absorption capacity (95 %). Meanwhile, strong anisotropic thermal conductive property that allows for satisfying in-plane thermal conductivity of 3.29 W m−1 K−1 was achieved. Benefiting from this, excellent electro-thermal conversion capacity that could enable fast de-icing under low voltage (4 V) was also acquired. Furthermore, those sandwich structured films possess sufficient flexibility to sustain repetitive bending, folding and shaping. Herein, this research has expanded the horizons in seeking both superior EMI shielding and heat dissipation capacity, which will further benefit the development of MXene‑based composites for high-performance electronic devices.

Unidirectional CFRP was treated by KrF laser in normal atmosphere, argon and underwater environments, before adhesive bonding. KrF laser removed the top resin layer and exposed the carbon fibres. Porosity and holes were generated around exposed carbon fibres after argon environment treatments and flakes-like-surface-structure was generated after underwater treatments with two-step method. KrF laser treatments increased Sq and Sdr values. Sdr was more influential for adhesive joint shear strength. These laser treatments in all environments transformed secondary and tertiary aliphatic amines to primary and secondary aliphatic amines, respectively. SLSS study confirmed that the highest shear strength of 35.78 MPa which was 45% higher than the untreated joint, was achieved after underwater treatment. Normal atmosphere and argon environment treatments resulted in 31.74 and 31.95 MPa, respectively. Adhesive failure which occurred after argon environment treatments, reduced after normal atmosphere treatments. Underwater treatments resulted in cohesive failure and thin layer cohesive failure.

MAX phase (Ti3AlC2) and its derivative MXene has brought the development of electromagnetic shielding and absorbing materials into a new stage. Herein, the MAX phase was creatively used to prepare microwave absorbing materials. The Ti3AlC2/liquid metal (TLM) hybrid micro-particles with multiple heterogeneous interfaces were prepared by simply liquid metal (LM) dotting on Ti3AlC2 surface and annealing at high temperature. When the mass fraction of liquid metal is 35 wt% and the sample is annealed for 2 h, the reflection loss (RL) value is −36.07 dB, and the maximum effective absorption bandwidth (EAB) is 7.2 GHz at a thickness of 2.5 mm. The electromagnetic wave loss ability of the TLM hybrid micro-particles comes from its special heterostructures, including multiple interfaces and defects caused by liquid metal etching.

This study presents a comprehensive analysis of conductive and hygroscopic nanocomposites using graphene oxide (GO), carbon nanotubes (CNT), and nano-silica. Nanocomposite suspensions for vacuum filtration were prepared by dispersion via ultrasonication in water. The dispersed phase of each nanomaterial was evaluated through ultraviolet absorbance, extinction coefficient, and zeta potential. The dispersion was performed at a ratio of CNT to GO well over 0.4 without any surfactants or additives because of the rich functional groups on the GO surface. In addition, the morphology of the fabricated nanocomposite generated after vacuum filtration, verified through scanning electron microscopy and Raman spectroscopy, showed a lamellar structure of GO and was easily separated as a membrane at composite-to-GO ratios of over 0.4. The fabricated membrane exhibited an excellent moisture collection ability and good responsivity as an environmental (humidity) sensor. This study supports the use of GO for the formation of well-dispersed nanocomposites for various applications.

In this study, we propose a versatile two-scale approach for thermo-viscoelastic analysis of the curing of composite laminates. Cure-induced residual stresses and part distortion significantly affect the quality and assembly of composite parts. An accurate computational tool for process optimization is required to replace time consuming and expensive experimental trial and error. The proposed method accounts for the different behaviors of fiber and resin during the curing process in terms of heat transfer and mechanical deformation. In particular, the evolved resin properties are described by a cure kinetics model and a cure-dependent viscoelastic constitutive model, which can be characterized directly from experiments. These microscopic mechanisms are concurrently used to reproduce the induced macro deformation. By virtue of the Direct FE2 implementation, the two-scale modeling only requires a single finite element analysis, where the macro laminate and the micro RVEs are coupled through multi-point constraints. Finally, this approach was employed to predict process-induced distortions of flat and curved composite parts subject to a typical two-dwell cure cycle. The results are verified by direct numerical simulations and typical residual deformations such as warpage and spring-in are well captured.

Experimental results, obtained from digital volume correlation (DVC) analysis are reported for the damage initiation of a single-edge notched cross-ply [90/0/90] laminate loaded in tension. The DVC data was obtained from images that did not require the addition of a foreign agent to create an internal speckle pattern. From the DVC results, it was observed that the damage initiation mode was delamination of one of the interfaces at approximately 24% of the ultimate load in a small region near the tip of the notch. This delamination of the first interface led to a stress redistribution that quickly caused other damage modes, thereby establishing the sequence of the progressive failure that occurred. These results are useful for establishing and validating progressive failure analysis models for fiber reinforced composite laminates.

Continuous carbon fibres can greatly improve the properties of 3D-printed polymer parts made by material extrusion. However, like all laminated composites, 3D-printed parts are susceptible to delamination damage. In addition, the printing process does not include a consolidation at high temperatures and pressure, unlike conventional manufacturing methods, which can lead to poor interlayer cohesion. Due to the combination of the susceptibility to delamination and a weak interface, the assessment of the interlaminar properties of 3D-printed parts is critical. This work experimentally investigates the delamination behaviour of carbon fibre-reinforced polyamide laminates under mode I, mode II and mixed mode I-II loading, using the double cantilever beam (DCB), end-loaded split (ELS), end-notched flexure (ENF) and mixed-mode bending (MMB) tests. An interlaminar fracture toughness at crack initiation of 1.5 kJ/m2 was found in mode I, 2.1 (ELS) and 1.8 (ENF) kJ/m2 in mode II, and 1.0 kJ/m2 in mixed mode I-II with GII/Gtotal = 0.5. Several analytical and numerical models are employed to validate the experimental results. Scanning electron microscopy revealed the micro-mechanical origins of the crack in the different loading configurations.

Architecture design enables multi-mechanism coordination of strengthening and toughening to overcome the strength-ductility trade-off in particulate reinforced metal matrix composites (PRMMCs). Here we introduce high-density stacking faults (SFs) in aluminum composites with a heterogeneous architecture consisting of micro/nano particles and ultrafine/coarse grains. It was demonstrated that the in-situ formed, uniformly dispersed MgO nanoparticles (n-MgO) can act as “vehicles” to carry interfacial-stress-induced SFs. The size and dispersion of n-MgO could be tailored by means of flake powder metallurgy to effectively manipulate SFs across the matrix. As a result, for the first time, SFs with a density as high as ∼ 5.7 × 1015 m−2 were obtained in the heterogeneous PRMMCs with the incorporation of micro- and nanoparticles. It is supposed that the SF-dislocation interactions promote dislocation storage and strain hardening, and such heterogeneous architectures provide a well-balanced combination of tensile strength (472 MPa) and ductility (8.9%).

Cold-sprayed composites' inherent brittleness, caused by the weak interface bonding and plastic depletion, limits their wide application. Friction stir processing (FSP) as a post-treatment method was used in this paper to improve the comprehensive properties of cold-sprayed Cu-Ti3SiC2 composite. After FSP, the microstructure evolution, electrical conductivity and mechanical properties of the samples were investigated. The results showed that the composite was composed of ultrafine grains (UFG) with an average size of 0.58 μm (Cu) and 0.16 μm (Ti3SiC2). The defects such as micro holes and cracks were reduced, and the particle boundaries changed from opened inter-splat boundaries to closed inter-splat boundaries. The FSP samples exhibited good electrical conductivity (85.6 %IACS), high tensile strengths (397 MPa) and elongation (18.7%). In conclusion, FSP is a simplified and efficient method for improving the toughness and electrical conductivity of cold-sprayed Cu-Ti3SiC2 composite.