The study of fibre to matrix interface properties is crucial in understanding the failure mechanisms of fiber-reinforced composite materials. In this paper, a novel in-situ experimental approach, using micro-cantilever tests, was proposed to characterize a carbon-epoxy unidirectional composite system interface. Computational models were implemented to support the experimental campaign and identify the interface properties. The computational model was validated based on the experimental results, and then it was used to investigate the interface debonding behavior under both damage modes I and II. The validated model allows to investigate the effectiveness of the proposed experimental approach in consistently assessing the interface characterization. Overall, the proposed approach provides a valuable tool for the study of fiber-reinforced polymers and contributes to the development of more accurate predictive models for their behavior.

Generally, porous materials are good candidates for sound absorption and thermal insulation. However, low sound absorption coefficient under 1000 Hz, low mechanical stability and poor consistency of performance hinders the wide applications of porous materials. In this study, we develop a kind of aerogel (PAN@ZIF-8-Kevlar aerogel) with well-designed hierarchical and tortuous porous structures to consume the low-frequency sound, hinder thermal transmission. The sound absorption coefficient of the PAN@ZIF-8-Kevlar is as high as 0.99 at 500Hz; average sound absorption coefficient of the material at 250, 500, 750, and 1000 Hz reaches 0.73. In addition, the thermal conductivity of PAN@ZIF-8-Kevlar is similar to that of air, thermal conductivity is near that 24.61 mW m−1 K−1. Notably, the PAN@ZIF-8-Kevlar aerogels also exhibit durable and stable cycling performance. The material retains its structural stability and retains its original low frequency sound absorption properties after 500 compression cycles. The hydrophobic material provides them with good moisture resistance (the water contacts angle (WCA) of PAN@ZIF-8-Kevlar-90 wt% aerogel was 143.3°). These favorable properties indicate that the composite nanofibers aerogel has potential options for sound absorption, thermal insulation in vehicles, buildings, and indoor reverberation.

Flexible conductive composites have garnered significant interest as wearable strain sensors due to their potential in diverse application fields, such as next-generation robotics automation, electronic skin, and human body detection. Nevertheless, the practical usage scenarios often entail tear and fracture, posing a persistent challenge to their performance stability. Consequently, there exists a pressing demand to engineer conductive composites that not only exhibit flexibility, stretchability, and sensing capabilities but also demonstrate effective self-healing properties. This pursuit presents a formidable task, considering the complex requirements imposed on the materials. This study presents a novel methodology for fabricating a conductive silicone elastomer composite. The approach involves the initial utilization of an excess of amino-capped Polydimethylsiloxane (PDMS) to undergo a reaction with Toluene diisocyanate (TDI) and Isoflurane diisocyanate (IPDI), leading to the formation of amino-capped polyurea (TPU). Subsequently, the self-healing elastomer IPDI/TDI/TA (ITT) is synthesized through chain expansion with Terephthalaldehyde (TA) in tetrahydrofuran (THF). To complement the experimental investigations, all-atom molecular dynamics (AAMD) simulations are employed to develop a comprehensive model elucidating the mechanical characteristics and self-healing capabilities of the elastomers. To introduce hybrid fillers into the elastomer composite, MXenes are electrostatically modified with L-glutamine (negatively charged), while multi-walled carbon nanotubes (MWCNTs) are modified with cetyltrimethylammonium bromide (positively charged). These modified fillers self-assemble in water and are subsequently combined with the aforementioned rubber THF solution after drying. Through ultrasonication and drying, the ITT elastomers/MXene/MWCNT composite is successfully prepared. The formation of hydrogen bonds and dynamic imine bonds is verified using FT-IR and AAMD simulations. By maintaining a fixed ratio of TA to PDMS, we observe a positive correlation between TDI concentration and the fracture strength of the ITT elastomer, while the elongation at break decreases with increasing TDI. Furthermore, the successful modification of MXene and MWCNT is confirmed through FT-IR, XRD, and zeta potential measurements, and the resulting composites exhibit significant electrical conductivity and self-healing properties. Tensile and electrochemical measurements demonstrate that the composite possesses promising characteristics suitable for sensor applications, and its mechanical and electrical properties can recover after self-healing. Notably, the resulting composites exhibit a very low conductivity threshold (3.5 wt%). The composite system exhibits desirable tensile properties and efficient self-healing ability due to the reversibility of multiple hydrogen and imine bonds. Overall, this study aims to introduce a novel elastomer-based composite that possesses excellent properties in terms of self-healing, stretchability, sensing capability and flexibility.

For the development of vitrimer epoxy nanocomposites, this study employed covalent functionalization to specifically modify graphene oxide (GO) with 4-aminophenyl disulfide (4-AFD). To verify the functionalization of graphene oxide, Fourier transform infrared (FT-IR), Raman, and X-ray diffraction (XRD) analyses were conducted, while transmission electron microscopy (TEM) coupled with elemental analysis was employed to examine the surface morphology. Additionally, the dispersion of GO and 4-AFD functionalized graphene oxide (FGO) inside the vitrimer epoxy polymer matrix was examined through the use of field emission scanning electron spectroscopy (FE-SEM). By functionalizing GO, its tendency to agglomerate was reduced, thereby enhancing the dispersion of FGO within the polymeric matrix. The vitrimer epoxy/FGO nanocomposites developed in this study demonstrate outstanding self-healing and shape memory properties, attributed to the covalent adaptive network based on disulfide exchange. The findings of this study indicate that incorporating FGO-based nanofillers in vitrimer epoxy nanocomposites improves their self-healing properties, including shape memory, flexural strength, storage modulus, and loss modulus, compared to GO-filled counterparts. In addition, this significantly improved the thermal properties of vitrimer epoxy/FGO nanocomposites, such as glass transition temperature (Tg) and thermal degradation temperature. In particular, the Tg of vitrimer epoxy/FGO nanocomposites experienced a significant increase of 10 °C. Additionally, the thermal decomposition temperature saw substantial improvements, with a 5% increase of 15 °C and a 50% increase of 7 °C.

Multifunctional thermal management materials with high flexibility are urgently required to tackle the heat dissipation issues of highly integrated electronics. MXene is considered a promising two-dimensional (2D) material for preparing composite with high thermal conductivity. However, there still is a challenge to prepare highly aligned MXene composite for simultaneously achieving high thermal performance and excellent mechanical properties. Herein, a novel MXene composite film was synthesized by vacuum-assisted filtering MXene nano-sheets suspension containing non-toxic and pollution-free mannitol. Under the connection of mannitol, MXene nano-sheets in the MXene/mannitol composite film form a highly aligned structure, resulting in outstanding thermal and mechanical properties. In-plane and through-plane thermal conductivities are 36.3 and 1.06 W m−1 K−1 for the MXene/mannitol composite film prepared using MXene suspension with a mannitol content of 0.2 mol/L, which are higher by 172% and 193% than those of pure MXene film, respectively. As the heat sink for a high-power LED, the MXene/mannitol composite film also demonstrated an excellent heat dissipation efficiency outperforming pure MXene film. Moreover, the MXene/mannitol composite film exhibited noteworthy mechanical property and stable thermal conductivity after bending for 300 times. Our findings provide a promising approach to prepare high-performance heat spreader for the thermal management of modern electronic components.

The material anisotropy induced by the related additive manufacturing (AM) extrusion process and the geometric errors introduced into the unit lattices by the stair-stepping artifacts were coupled in the topology optimization model to ensure the accuracy and reliability of the optimal design for the fibre reinforced polymer lattice structures. The material properties of the 3D printed carbon fibre reinforced polymers (CFRP) were firstly systematically investigated by extensive tensile tests aided by the digital image correlation (DIC) system, through which the microscale material anisotropy was clarified. Moreover, the accurate orthotropic material models were introduced into the as-fabricated mesoscale unit lattices with geometric errors to obtain the effective mechanical properties. Finally, mechanical performance of the macroscale structures was optimized by the integration of the ideal and as-fabricated unit lattices with the homogenization-based topology optimization method. The AM process-induced material anisotropy and geometric errors result in significant deviations of the mechanical property of the topologically optimized macrostructures and more accurate topology optimization results can be achieved considering the microscale material anisotropy and the geometric error in the mesoscale unit lattice. The results obtained in this investigation indicate that it is essential to comprehensively consider the AM process-induced microscale material anisotropy and mesoscale geometric errors in the topology optimization of fibre reinforced polymer lattice structures to improve the accuracy and reliability of the optimal design.

Compressive failure in a notched cross-ply IM7/8552 carbon fiber reinforced polymer (CFRP) laminate is studied experimentally by time-lapse in-situ synchrotron radiation computed tomography (CT). The focus is on tracking and quantifying the fiber damage evolution in the 0° plies under compression for the first time via a specimen design that exhibits quasi-stable damage accumulation. A novel segmentation algorithm has been developed and applied to extract morphological features of interest including the kink band width, inclination angle, and the extent of propagation from the notch. In the four innermost 0∘ plies, shear-driven fiber fracture initiates from the notch tip and propagates as a single fracture plane inclined about 45° to the compression axis. This shear-driven fiber fracture transitions to a kink band at a distance of about 300μm from the notch, which propagates at a shallower angle. During the later stages of the test, the kink bands propagate in the reverse direction to areas that previously initiated by shear-driven fiber fracture, which may explain why post-mortem observations seldom reveal the fiber shear fracture mechanism. The fiber damage initiation and evolution appears distinctly different from the classical parallel plane kink bands formed by plastic microbuckling under uniaxial compression in that the dominant mechanism appears to be shear-driven fiber fracture.

The present study aims at investigating the delamination behavior of laminated composites in different loading modes within a homogenization theory of mixtures. The delamination damage phenomenon is introduced at the bulk level by eliminating the explicit representation of interfaces. Potential delamination planes are identified according to the developed interfacial stresses, and damage evolution is computed for each mode independently through a stress-based formulation. An arc-length strategy is employed to solve equilibrium equations owing to the snap-back effects. Reliability of the adopted mixing theory, as a framework for integrating the delamination theory into, is assessed by comparing the results with the ones obtained from micromechanical models in a fiber metal laminate structure. Considering delamination, a good agreement is observed in mode I, mode II and mixed mode configurations by evaluating the results against available numerical and experimental data in thermoset and thermoplastic composite systems. The present method has the capability to be used in the conventional finite element codes with the number of elements kinematically needed in the thickness, regardless of the number of layers, which dramatically reduces the computational cost in modeling composites with large number of layers. The proposed approach is not intended to replace other exact methods at the coupon scale, however, its main application would be in modeling delamination on large scale systems with minimum loss of accuracy.

To improve the sensitivity and broaden the range of flexible pressure sensors, we proposed a high-performance flexible pressure sensor based on ordered double-level nanopillar array films. In this work, polypyrrole/multi-walled carbon nanotube/polyurethane (PPy/MWCNT/PU) conductive films with double-level nanopillar array microstructures were prepared by continuously adjusting the oxidation and pore expansion parameters of a porous anodic alumina template (AAO), where the high pillar height was 1243.0 ± 7.0 nm, and the low pillar height was 868.0 ± 4.70 nm. We studied the influence of the structural characteristics of ordered double-level nanopillar array conductive films and a flexible pressure sensor on the sensing performance using finite element simulations, the establishment of sensing mechanism, and sensor performance measurements. The results showed that the pressure was positively correlated with the change rate of strain and the surface microstructure contact area of the ordered double-level nanopillar array films. The sensor sensitivity reached 208.353 kPa−1, and its range was extended by 267%. In addition, the sensor, which could monitor vocalization, drinking pulse and finger movements, could be used in a wide range of applications, including wearable medical monitoring and smart sign language textiles.

Structural supercapacitors are multifunctional devices able to bear mechanical load while storing electrical energy. Carbon fibres can be used as a bifunctional component within structural supercapacitors, acting both as current collector and mechanical reinforcement. A promising route to such devices is to increase the surface area of carbon fibres, which can be achieved by the deposition of active materials, and embed them into a structural electrolyte. A highly sulfonated, high porosity hypercrosslinked polymer was deposited onto carbon fibres by electrophoretic deposition from an aqueous suspension. We investigated the effect of polymer and binder concentration in the deposition suspension on the electrochemical properties of the coated carbon fibre electrodes. Multifunctional structural composite supercapacitors had a fibre volume fraction of only 21% and possessed a tensile strength and Young's modulus of 495 MPa and 49 GPa, respectively. A specific capacitance of 1.2 F/g was reached, comparable to graphene coated carbon fibre electrodes. At room temperature and ambient humidity an energy density of 39 mWh/kg and a power density of 15 W/kg were measured. We demonstrate that moisture plays a major role in the energy storage mechanism in these SCs.

Tensile strength models for unidirectional composites require scaling of fiber strength distributions to small length scales in the range of the fiber radius to the ineffective length (5–200 μm). No test methods currently exist to measure and validate fiber strength at these length scales. In this paper, a novel continuous fiber bending test method is developed to measure the size and spatial distribution of defects in S-glass fibers. For this test method, a single glass fiber was placed between Kapton film and tape, and the sample is subjected to a sequence of controlled radii of curvatures ranging from 350 μm to 25 μm in a confocal microscope. From the bending tests, the number of defects and spacings between the defects over 780 mm length of fiber are obtained for each level of flexural stress. The Kapton film confines the fiber fragments and maintains fiber alignment allowing the same sample to be tested at lower radius of curvature (higher flexural strain/stress). The associated defect size is calculated using fracture mechanics. These results are used to map the size- and spatial-distribution of critical defects on the tension surface of a glass fiber. A methodology is presented to map additional defects around the circumference of the fiber, while maintaining the size and spatial distribution obtained from the bending tests. The results show that the lognormal distribution best fits the spatial distribution of defects along the fiber axis. The results also indicate that extrapolating the Weibull strength distribution (be it bimodal or unimodal) to gage lengths less than 200 μm leads to serious errors in fiber strength prediction.

Surface defects in highly-filled wood polymer composites (WPCs) are mapped in single-screw extrusion via inline optical spectral analysis for the first time. The effects of wood fiber content and drying on the dynamics of surface defects are spatio-temporally resolved via space–time inline optical imaging. Surface tearing appeared from the lowest shear rates investigated followed by a gradual decay in spectral intensity with increasing shear rates/slip velocities. This is accompanied by broadening of the surface tearing characteristic frequency while the average wavelength is estimated to remain constant within the experimental conditions. Increasing shear rates, drying and increasing wood fiber content showed mitigating effects on surface tearing. However, surface tearing in undried samples was still present even at the highest shear rates and high wall slip velocities. A regime where the extrudate surface is dominated by bubbles at high shear rates and low wood fiber contents in undried WPCs was identified.

In order to reduce the damage to people's health from diseases that attack the respiratory system such as COVID-19, asthma, and pneumonia, it is desired that patients' breathing can be monitored and alerted in real-time. The emergence of wearable health detection sensing devices has provided a relatively good response to this problem. However, there are still problems such as complex structure and poor performance. This paper introduces a laser-induced graphene (LIG) device that is attached to PDMS. The LIG is produced by laser irradiation of Nomex and subsequently transferred and attached to the PDMS. After being tested, it has demonstrated high sensitivity, stable tensile performance, good acoustic performance, excellent thermal stability, and other favorable properties. Notably, its gauge factor (GF) value can reach 721.67, which is quite impressive. Additionally, it is capable of emitting an alarm sound with an SPL close to 60 dB when receiving signals within the range of 5–20 kHz. The device realizes mechanical sensing and acoustic functions in one chip, and has a high application value in applications that need to combine sensing and early warning.

Mesoscale simulations of woven composites using parameterized analytical geometries offer a way to connect constituent material properties and their geometric arrangement to effective composite properties and performance. However, the reality of as-manufactured materials often differs from the ideal, both in terms of tow geometry and manufacturing heterogeneity. As such, resultant composite properties may differ from analytical predictions and exhibit significant local variations within a material.We employ mesoscale finite element method simulations to compare idealized analytical and as-manufactured woven composite materials and study the sensitivity of their effective properties to the mesoscale geometry. Three-dimensional geometries are reconstructed from X-ray computed tomography, image segmentation is performed using deep learning methods, and local fiber orientation is obtained using the structure tensor calculated from image scans. Suitable approximations to composite properties, using analytical unit cell calculations and effective media theory, are assessed. Our findings show that an analytical geometry and sub-unit cell geometry provide reasonable approximations of the full-scale predictions for the effective thermal properties of a multi-layer production composite.

In this study, a novel approach based on the maximum penetration-biased (MPB) algorithm is proposed to rapidly generate representative volume elements (RVEs) for advanced composites. This method is capable of handling various microstructural features such as nonuniform distribution of high-volume fractions, concave or convex inclusions and the control of inter-inclusion distances. Statistical functions from short-range to long-range demonstrate that the resulting microstructures are complete spatial random, and the microstructures observed in realistic composites can be reproduced by the proposed algorithm. Accurate prediction for the elastic properties and transverse isotropy of the generated microstructures with varying inclusion shapes using homogenization method further verify the validity of the developed method. A nonlinear damage study compared to the circular inclusion reveals that the capsule shape leads to a reduction of strength of unidirectional fiber reinforced composites under transverse tension or compression while the lobular inclusion presents a deterioration of strength under tension but an enhancement of strength in compression. The MPB algorithm provides an effective tool for micromechanical assessment, quantitative research and data-driven studies such as machine learning of composites.

Basalt fiber has been widely used in a variety of industries due to its unique properties and relatively low cost. However, the nature of electrical insulation of basalt fiber limits its application in the field of functional composite materials such as electromagnetic interference (EMI) shielding materials. Laser-induced graphene (LIG) is a form of three-dimensional carbon nanomaterial, which could be generated by scribing a laser on many carbonaceous precursors. In this work LIG film obtained by double-sided etching Polyimide (PI) paper was embedded in the basalt fiber laminates to fabricate multi-functional basalt fiber composites. The effects of LIG film insertion on Mode I and Mode II fracture toughness and out-of-plane ballistic impact resistance of basalt fiber laminates were investigated. The basalt fiber laminates with LIG inserted retain their original mechanical properties in terms of fracture toughness and impact resistance. While the conductivity and electromagnetic shielding performance of basalt fiber laminate after LIG insertion have been greatly improved. The EMI shielding effectiveness of the basalt fiber laminates is increased to ∼20 dB after one layer of LIG was inserted, and to ∼50 dB after three layers of LIG were inserted, for the X-band frequency range. The damage localization of the basalt fiber laminates was demonstrated by arraying the rectangular LIG strips in the shape of hash key and in-situ monitoring the electric resistance changes.

Shape memory hydrogels are widely used in soft robots and other fields. However, it is difficult to realize multiple-shape memory hydrogels with high strength and simple driving modes. The mechanical properties of a hydrogel were improved in this study through the creation of a double network hydrogel using a combination of gelatin and PAAm. Additionally, hydrogen bonding was introduced into the structure of the hydrogel through the incorporation of acryl 11-aminodecanoic acid (A11AUA). The helical structure of gelatin and the semi-crystalline segment of A11AUA provide enabling the hydrogels to realize a triple shape memory effect at different temperatures. In addition, we found that the hydrogel could also complete shape memory behavior in the FeCl3 solution due to the carboxyl group in A11AUA. And we prepared composite hydrogel to realize remote infrared driving by introducing nano Fe3O4. We believe that this triple-shape memory hydrogel with high mechanical property and multiple stimulus responses can expand the application of hydrogel in soft robots, sensors, and other fields.

Exploring and adjusting the migration pathway of photogenerated electron-hole pairs in novel semiconductor composites is vital to enhance the charge separation efficiency and transferability in photocatalytic environmental governance and hydrogen generation performance. Herein, an electrostatic self-assembly combining with a low-temperature hydrothermal strategy for forming the Ti-O-Mn bond was designed to rationally construct the S-scheme Pt-MnO2/TiO2@Ti3C2Tx composite. Through the systematic characterization and density functional theory calculations, the metastable marginal Ti atoms and the electrostatic adsorbed Mn2+ ions on Ti3C2Tx surface are oxidized and in situ form TiO2/MnO2 nanoparticles (NPs) due to its fitted lattice energy and low adsorption energy, which are intercalated on the conductive Ti3C2Tx multilayer surfaces and construct a new-fashioned S-scheme TiO2/MnO2 heterojunction via the Ti-O-Mn bond, for affecting the density of charge states, promoting the charge separation and shortening migration carrier distance. Also, Pt NPs as the cocatalyst is selectively decorated on MnO2/TiO2@Ti3C2Tx surface for further improving the charge carrier transfer and visible light absorption. Benefiting from the extraordinary composition and structure, the obtained Pt-MnO2/TiO2@Ti3C2Tx composite exhibits high photocatalytic degradation of organic pollutants (more than 90%), hydrogen generation activity (3610 μmol g−1 h−1) and wonderful cycle stability.

Compared with the traditional 3D needled composites with non-woven structure, the composites with twill layers have an extremely complex mesostructure. Three representative regions are divided based on the mesostructure observation of 3D needled twill composites. At the same time, the needling process of the 3D preform is simulated based on the digital element method, and the fiber deflection formulas in the needled region are built. Considering the distribution of different needling points, the periodic unit cell models of 3D needled twill composites that include three representative regions are established to predict the mechanical properties. It is verified that the results predicted by the proposed model agree well with the experimental data. Moreover, the effects of different needling angles and needling points on the mesostructure and mechanical properties of the composites are further studied, which helps guide the design and manufacture of 3D needled twill composites.

The development of temperature-insensitive stretchable conductors has significant implications for a wide range of applications, including wearable electronics, flexible sensors, and stretchable circuits in different environments, while resistances of conductive polymer composites are generally temperature dependent. In this study, we develop a novel and facile approach to achieve stable electrical conducting under stretching and temperature variation by incorporating a hierarchical wavy graphene foam (wGF) with a double-layer conductive framework formed by coating highly conductive poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) on interior graphene struts. The resulting wGF/PEDOT:PSS/PDMS composites exhibit exceptional resistance stabilities during stretching within a wide temperature range of -30-145 °C. The synergistic effects of the unique composite structure, including the macroscopic wavy structures, microscopic compacted conductive skeletons, and more ductile double-layer graphene/PEDOT:PSS frameworks, contribute to the excellent stretchable conducting properties and temperature-insensitive performance. The developed temperature-insensitive stretchable conductor holds great promise for reliable performance in various environmental conditions, opening up new opportunities for advanced flexible and wearable electronic devices.