Nanofiller/elastomer nanocomposites as strategically important materials have attracted intensive attentions due to high elasticity{Liu, 2011 #46}. However, due to the limitation of conventional two-dimensional characterization methods, the multi-scaled dispersion structure of nanofiller in elastomer nanocomposites hasn’t been comprehensively understood. Here, we established a highly-objective method to comprehensively quantify the three-dimensional (3D)-dispersion of nanoparticle in elastomer matrix. 3D-scanning transmission electron microscope (STEM) was applied to get the intrinsic 3D-dispersion structure of nano-silica (SiO2) in solution-polymerized styrene-butadiene rubber (SSBR). Equivalent sphere and fractal branch models were created to further quantify the poly-dispersity, inner connectivity and morphology of SiO2. A two-stage agglomeration evolution schematic was proposed to elucidate the development of nanosized dispersion structure of SiO2. With the increase of SiO2 volume fraction (Φsilica), the number, size and branching degree of SiO2 simultaneously increase (namely, self-agglomeration). Further increase Φsilica, adjacent SiO2 interconnect with each other, leading to sharp increases of connectivity and branching degree of SiO2 (namely, external agglomeration). This two-stage agglomeration mode interprets the well-known “Payne effect” well, which has not been quantified by 3D dispersion structure parameters before.

In GFRP laminated composites, matrix-fiber delamination is almost unavoidable and a serious problem that significantly hampers the mechanical properties of the composites. This work presents the use of cost-effective silanized milled graphite nanoparticles (GrNPs) to mitigate matrix-fiber delamination in GFRP laminated composites. FESEM and TEM analysis of pristine GrNPs exhibit porous structure consisting of stacked and randomly oriented planes with a large number of defect sites. The silanization of GrNPs (SGrNPs) results in the covering of pores or defect sites and produces the rough surfaces. The SGrNPs (0.5 wt%) reinforced GRFP laminated composites reveal the enhancement in the mechanical properties such as tensile strength (∼33 %), tensile modulus (∼21 %), toughness (∼35 %), flexural strength (∼42.6 %), work of fracture (∼57 %), and short beam strength (∼23 %), respectively. The improvement in the mechanical properties of the composites is due to the mitigation of matrix-fiber delamination by SGrNPs.

Viscoelastically prestressed polymeric matrix composites (VPPMCs) are produced by subjecting fibres to tensile creep, the creep load being released prior to fibre moulding. Following matrix curing, the viscoelastically recovering fibres generate compressive stresses within the matrix which, from previous studies, can improve mechanical properties by up to 50%. This paper reports on the first study of thin flat-plate VPPMCs, using nylon 6,6 fibre-polyester resin to form cross-fibre composite plates (CCPs) with 0°/90° fibre layers and randomly distributed discontinuous fibre plates (RCPs). Drop-weight impact testing was performed on CCPs with impact velocities of 1.9 – 5.8 m/s and, compared with (unstressed) control samples, VPPMC damage depth was reduced by up to 29%; however, this difference decreased with impact velocity, indicating little improvement above 7.7 m/s. RCPs, tested at 3.0 m/s, showed a ∼30% reduction in VPPMC damage depth, compared with ∼20% for CCPs, but with no changes in debonded area.

This study examines a facile technology to manufacture food packaging alternatives with superior mechanical, ultra-flexible, gas barrier and self-clean properties, based on green and benign starting materials. A novel galactomannan (GM) was isolated from the sesbania cannabina seeds, which was used as matrix for the fabrication of GM-based films. Inspired by the brick-and-mortar structure of natural nacre, a facile method was adopted to fabricate an artificial nacre based on the self-assembly of GM and borate crosslinked graphene oxide (GO). These GM/GO composites are ultra-flexibile, which can be folded into various shapes. The tensile strength reached 135.54 MPa which is 2.4 times that of the pure GM film. In addition, after coating with the poly(dimethylsiloxane) (PDMS), these films became hydrophobic (WCA around 120°) with self-cleaning properties. Our study further revealed that the oxygen and water vapor permeabilities were improved with the introduction of GO and PDMS coating.

Utilizing high-performance cellulose nanopapers as 2D-reinforcement for polymers allows for realizing high-loading-fraction (80 vol.-%), high-performance (strength >150 MPa, modulus >10 GPa) laminated nanopaper reinforced epoxy composites. Such cellulose nanopapers are inherently dense, which renders them difficult to be impregnated with the epoxy-resin. High-porosity nanopapers facilitate better resin impregnation, truly utilizing the properties of single cellulose nanofibres instead of the nanofibre network. We report the use of high-porosity (74%) but low strength and modulus bacterial cellulose (BC) nanopapers, prepared from BC-in-ethanol dispersion, as reinforcement for epoxy-resin. High-porosity nanopapers allowed for full impregnation of the BC-nanopapers with epoxy-resin. The resulting BC-reinforced epoxy-laminates possessed high tensile modulus (9 GPa) and strength (100 MPa) at a BC loading of 30 vol.-%, resulting from very low void-fraction (3 vol.-%) of these papregs compared to conventional nanopaper-laminates (10+ vol.-%). Better resin impregnation of less dense nanocellulose networks allowed for maximum utilization of stiffness/strength of cellulose nanofibrils.

There is a lack of understanding on the damage tolerant design of bonded scarf joints, specifically when an existing bondline flaw affects the performance. This paper presents an improved progressive damage modelling methodology for assessing the damage tolerant performance of composite scarf joints containing artificial flaws in the bondline. The developed methodology is validated using an experimental study investigating the influences of design parameters on the strength of scarf joints under quasi-static tensile loading. The presented work gives excellent predictions of joint strength, and significant insight into the initiation, interaction and progression of damage. A new damage tolerant design approach is subsequently proposed for the application of bonded composite scarf joints, particularly in primary aerospace structures. The proposed design approach assesses the state of the stress at the failure-critical regions of adhesive and adherend to inform on damage-tolerant safe design loads, thus improving the future application of bonded composite scarf joints.

It is greatly important to shield the X-band electromagnetic radiation and meanwhile possess a high temperature resistant performance for the outer sealing materials of hypervelocity air aircrafts. In this work, novel ceramifiable electro-conductive polymer composites were prepared by incorporating glass powder (GP), mica powder (MP), organo-modified montmorillonite (OMMT), and short carbon fiber (SCF) into ethylene-vinyl acetate (EVA). The prepared EVA/GP/MP/OMMT/SCF displayed excellent electromagnetic interference (EMI) shielding performance before and after treating at 1000 ℃ and also had a high temperature resistant feature via the ceramization. For the EVA/GP/MP/OMMT/SCF composite with a weight ratio of 35/23/17/5/20, its EMI shielding effectiveness (SE) reached 36.0 dB at 2.6 mm thickness, and its ceramic formed at 1000 °C possessed about 30.0 dB of EMI SE. Moreover, the formed ceramic did not show any change during a vertical burning test. Mechanism for the high SE before and after high temperatures were revealed.

A novel phthalazinone-bearing epoxy resin, namely TEPZ, was designed and synthesized as functional modifier and prepreg agent for carbon fiber TGDDM epoxy composites by a “one pot two steps” method. Three-dimensional TEPZ/TGDDM/DDS system was constructed and optimized by modulating curing procedure and concentration of DDS to give thermosets with excellent thermal resistance and mechanical strength. The storage modulus and glass transition temperature (Tg) increased significantly with composition of 100 phr TGDDM, 30 phr TEPZ and 40 phr DDS as compared to those of TGDDM/DDS. The tensile strength, impact strength and flexural strength increased simultaneously. Afterwards, continuous unidirectional carbon fiber reinforced laminates were fabricated, followed by systematical investigation of their mechanical and interfacial properties. The interfacial study indicated that the polarity and wettability of TEPZ played an important role during the modification.

A micro-screw in-situ extrusion process was utilized to obtain high pressure for good impregnation and high fiber fraction of 3D printed continuous carbon fiber reinforced nylon (PA12) composites. Nylon pellets and different carbon fiber strand bundles (1K and 3K) were used as raw materials to print composites with different process parameters. Almost full impregnation for 1K continuous carbon fiber (CCF) reinforced PA12 composites (1K-CCF/PA12) with only 0.15% porosity and good impregnation for 3K continuous carbon fiber reinforced PA12 composites (3K-CCF/PA12) with 2.62% porosity achieved. Fiber volume fraction was dramatically improved from 31.9vol% for 1K-CCF/PA12 to 50.2vol% for 3K-CCF/PA12. Mechanical properties of different composites were measured systematically. Excellent longitudinal tensile strength and modulus of 735.7MPa and 79.5GPa, and simultaneously flexural strength and modulus of 772.6MPa and 85.3GPa for 3K-CCF/PA12 were obtained. This novel 3D printing of continuous fiber reinforced composite process realized the integration of composites preparation and formation with enhanced impregnation, high fiber fraction and mechanical performance which could expand the applications of this technology to more and more industry fields.

The insufficient interfacial bonding and low toughness of cellulosic fiber reinforced polypropylene (PP) composite remain limitations for advanced applications of the composite. Here we proposed to promote the interfacial adhesion by modifying the interfacial matrix crystal type and morphology, inducing the small β -PP spherulite from the dominated α-PP. Specifically, cellulose fiber was subjected to mechanical milling to improve the accessibility of hydroxyl groups, then pimelic acid, calcium carbonate and activated cellulose particles were mechanochemically reacted during solvent-free ball milling condition to prepare cellulose fillers with β nucleating sites for PP reinforcement. The nucleating effect and tensile properties of the composite were investigated. The results showed that the modified particles were effective for producing a large percentage of β crystals with smaller and more uniform spherulite, and the induced β phase crystal increased the tensile strength and elongation at break of the composite.

BC sheets can be prepared in two forms: direct press-drying of the as-synthesised BC pellicle or disintegrating the BC pellicle to create a homogenous BC-in-water suspension prior to producing the BC sheet. We found that BC sheet prepared from direct press-drying of pristine pellicle was more homogeneous due to its better BC network formation and possessed higher specific surface area (46 g m-2), better resin impregnation and mechanical properties compared to its disintegrated pellicle counterpart (21 g m-2). BC-poly(acrylated epoxidised soybean oil) (polyAESO) nanocomposites consisting of BC sheet prepared from pristine pellicle was optically transparent whilst BC-polyAEO nanocomposites consisting of BC sheet prepared from disintegrated pellicle was opaque. Whilst the tensile properties of BC-polyAESO nanocomposites from pristine pellicle were higher, the fracture toughness of BC-polyAESO composite consisting of BC sheet from disintegrated pellicle was better. The lack of resin impregnation in BC-polyAESO from disintegrated pellicle led to a laminated structure, which utilised the fracture toughness of BC sheet effectively.

How to obtain high strength while remain the good shielding performance of MXene film is a big challenge, which limits its further application. Herein, we report on fabrication of mechanically strong and high-performance EMI shielding Ti3C2Tx composite film by incorporating of poly(3,4-ethylenedioxythiophene)/poly(styrenesulfonate) (PEDOT/PSS) and then treatment with concentrated sulfuric acid to remove the insulating PSS. By introducing of 30 wt% PEDOT:PSS into Ti3C2Tx film and with acid post-treatment, the EMI SE of composite film with thickness of ∼ 6.6 μm is up to 40.5 dB while the tensile strength is 38.5 ± 2.9 MPa and the increment in tensile strength is as high as 155% when compared to that of pristine Ti3C2Tx film. It achieves a good balance between shielding performance and mechanical property, which has not been achieved in reported literatures. The combination of mechanical and shielding performances portfolio outperforms the counterpart of other polymers composite filled with MXene.

Residual stresses and failure behavior of 3/2 GFRP/Al-Li laminates after single and Multiple shot’s indentation under quasi-static condition were investigated to better reveal the characteristics of residual stresses after shot-peening forming. Single shot’s indention behavior was analyzed with the finite element model using the Johnson-Cook material model and customize damage initiation criterion then validated by experiments of single shot’s indentation. Results indicated that the fiber layers hindered the deformation of aluminum-lithium layer. Moreover, the layup of fiber layers and the shot diameter (more than 2mm) affected the shape of the crater which reflected characteristics of residual stresses around the crater. In addition, the pressing depth of shot was related to GFRP/Al-Li laminates’ failure. Residual stresses increased with the pressing depth of shot. Excessive residual stresses led to the FMLs’ failure. Depth of failure (the pressing depth of shot when failure occurred) was affected by shot size and the corresponding failure form changed with the shot size. Based on the results on single shot’s indentation, the residual stress field of the FMLs under multiple shot’s indentation was simulated and the forming curvatures of the FMLs with different shot peening coverage were calculated. The prediction values were consistent to the experimental results with the overall error being about ±10%.

Conductive polymer composites for use as stretchable strain sensors have recently been developed for use in wearable electronic devices capable of detecting various stimuli such as human body motion. In this work, we report the development of a flexible strain sensor based on conductive thermoplastic vulcanizate (TPV) by the incorporation of conductive carbon black (CCB). By adopting special processing conditions, the percolation threshold of the CCB could be minimized to a value as low as ∼4wt% as compared to a value of 10 wt% for conventional TPV. Under static and cyclic loading, the strain sensing behavior of the conductive TPV depended on the morphology and filler content. The result also revealed that interconnected TPV exhibited superior piezoresistive characteristics with good sensitivity. Therefore, the good strain sensing performance of this conductive TPV can be considered as a promising material for use in wearable human-motion and wearable strain sensors.

Flexible electromagnetic shielding composite material has good deformation ability and stable electromagnetic shielding performance. In this paper, [email protected]/sodium alginate/polydimethylsiloxane flexible composites are prepared by infiltrating PDMS polymer into [email protected]/sodium alginate sponge skeleton. Nano-scale Au particles coated on CNT surface can effectively improve the electrical conductivity and electromagnetic shielding performance of the composite. The experimental results show that the log function values of conductivity and electromagnetic shielding performance obey a quasi linear relationship. After 10% elastic tensile strain, the conductivity of all samples are remain unchanged, which indicate a stable electromagnetic shielding performance under strain. Combined with the multi-scale model analysis, the mechanism of electrical stability and the effect of Au sizes and cladding rate are discussed. Calculation results show that the electromagnetic shielding performance of the flexible composite sample could reach more than 60 dB. These flexible shielding composites with stable performance under strain may have good application potential, such as for wearable smart electronics.

The brilliant electromagnetic wave (EMW) absorbers are urgent with the extensive attention of electromagnetic pollution. Herein, the binary Fe3O4/MoS2 composites are successfully synthesized via a facile hydrothermal method, where the different morphologies of 3D MoS2 nanoflowers decorated with the monodispersed Fe3O4 particles by tailoring the molar ratio of Fe3O4 to MoS2. Moreover, we find that the dielectric/magnetic loss and good impedance matching have dramatically contributed to the enhanced EMW absorption ability for binary Fe3O4/MoS2 composites compared to pristine Fe3O4 nanoparticles. Meanwhile, the effective absorption bandwidth (EAB, RL< -10 dB, > 90% absorption) of 6.1 GHz at thin thickness of 2.0 mm could be obtained while it exhibits the strongest minimum reflection loss (RLmin) of -64.0 dB with ultra-thin thickness of 1.7 mm. Noticeably, even for the low frequency of C (4-8 GHz) and X (8-12 GHz) bands, the 100% frequency occupy ratio can be realized while the RL intensity is still not severely deteriorated, which is superior than most of MoS2-based absorbers that have been reported so far. Hence, it can be expected that the Fe3O4/MoS2 composites in this work featured with strong absorption intensity, selectable wide bandwidth (especially for 100% coverage both for C and X bands) as well as ultra-thin thickness (EAB of 6.1 GHz at 2.0 mm) will ensure it an attractive EMW absorber.

Stretchable sensors based on conductive polymer composites (CPCs) are attracting considerable interest from both academia and industry. For CPCs consist of elastomeric substrates with dispersed conductive fillers, a strain-induced conductivity-drop phenomenon (negative piezo-conductivity effect) is often observed in previous reported studies. Herein, CPCs with unconventional positive piezo-conductivity effect were prepared by employing a facile and low-cost fabrication process based on thermoplastic polyurethane (TPU) and conductive metal particles (nickel/iron particles). For the first time, a strongly stretch-induced conductive networks formation phenomenon was observed under tensile strain, contributing to the electrical resistivity of the composites decreases by more than 6 orders of magnitude under 20 % tensile strain. The evolution of conductive networks and resistivity under uniaxial strain were studied with scanning electron microscope (SEM) and a modified mathematic model, respectively. Furthermore, these CPCs exhibits temperature sensing capability between 30-60 oC, indicating such method could be used to fabricate multi-functional sensors.

Automation of fabric preforming for resin transfer moulded composite parts motivates the need to characterize the response of dry fabric, which is required for the development of simulation models to predict potential draping defects. In this study, the in-plane tensile-shear response of a heavy-tow unidirectional non-crimp fabric (UD-NCF) subjected to bias tensile loading was investigated. Challenges associated with fabric surface texturization and associated strain measurement through digital image correlation was addressed by using a mixture of oil-based paint and mineral spirits to create a suitable speckle pattern. Custom clamps were also designed to prevent the test specimen from damaging or sliding from the grips. Strain maps revealed that the off-axis extension tests induced combined shear, tensile and compressive strains in the fabric test specimens. The fabric deformation response and proposed methods are relevant aspects for characterizing unbalanced UD-NCFs and calibrating corresponding draping simulation models.

Prepreg platelet molded composite (PPMC) is derived from compression molded pieces of chopped unidirectional prepreg tape. The properties of a stochastic PPMC arise from the meso-structure that develops during processing. This paper describes an integrated methodology for analysis of stochastic PPMC to develop process-structure-property relationships. Flow-induced fiber orientation distributions were predicted using an anisotropic viscous constitutive model implemented in a nonlinear, explicit finite element (FE) solver. The predicted orientation state was validated by CT-based orientation measurements and optical microscopy. A computational framework for simulation of tensile property distributions of a stochastic PPMC by progressive failure analysis is presented. The probabilistic simulation results were statistically validated against experimental data. A FE analysis was developed with an explicitly modeled platelet meso-structure wherein the platelets are treated as a homogeneous orthotropic medium using continuum damage mechanics to model the intraplatelet failure and a cohesive zone model for interlaminar disbonding. Panels were molded using partial charge coverage to induce flow alignment of the fibers. Tensile coupons were excised from the molded panels both along (parallel) and transverse (perpendicular) to the preferential fiber direction to compare the composite effective properties with those reported in the literature for planar random orientation states. The composite tensile properties were found to be strongly dependent on the global orientation state.

The material removal mechanism of Cf/SiC composites in brittle regime is more complex than that of single-phase materials. Variable loading nano-scratch tests of unidirectional Cf/SiC composites along different fiber orientations were carried out. According to different fracture mechanism of fibers, the brittle regime of Cf/SiC composites can be subdivided into micro brittle fracture regime and macro brittle fracture regime. In micro brittle fracture regime, cracks were initiated under the extrusion of the indenter, and propagated between the graphite crystallites, resulting in material removal. The scratched surface of fibers was rough. The thickness of fiber subsurface damage layer was the largest when scratching along transverse fibers, and was the smallest when scratching along across fibers. In macro brittle fracture regime, fibers occurred debonding and flexural deformation under the extrusion of the indenter, which caused bending-induced fracture. The scratched surface fluctuated greatly, but the fractures or the surface of fibers were smooth.

Highly conductive and flexible materials have many applications in the electrical and electronic fields, while the realization of high electrical/thermal conductivity by a green, simple and efficient approach is still challenging. Herein a simple method was proposed to construct three-dimensional Ti3C2Tx (3D-MXene) skeleton without using adhesive agents. After incorporated into polydimethylsiloxane (PDMS) matrix, the resultant 3D-MXene/PDMS nanocomposites exhibited excellent electrical conductivity of 5.5 S/cm, which was nearly 14 orders of magnitude higher than that of the neat PDMS. On the other hand, the nanocomposites show a thermal conductivity enhancement of about 220% at a low MXene content of 2.5 vol% in comparison with neat PDMS. Moreover, the output current of 3D-MXene/PDMS based triboelectric nanogenerators (TENGs) was greatly enhanced because of the significantly decreased electrical resistance. This finding can be applied to TENGs with capacitor structures and can also widen the practical applications of MXene in the field of thermal management, sensors and energy harvesters.

The recent rise of metacomposites offered a new research strategy for electromagnetic shielding materials owing to their negative electromagnetic parameters, such as negative permittivity. Herein, we prepared silver/silicon nitride (Ag/Si3N4) metacomposites with tunable negative permittivity by a facile impregnation-calcination process, and explored their electrical conductivity, permittivity and electromagnetic shielding properties. As the Ag content increased, formative metal networks in the composites rendered their conductivity characteristic changing from a hopping conductivity to a metal-like conductivity. Tunable negative permittivity behavior combined with enhanced shielding effectiveness (SE) was observed at 2-18 GHz in the metacomposites with high Ag contents. The plasma-like negative permittivity was accounted for by a low frequency plasmonic state of free electrons in the inductive Ag networks, and the frequency band and absolute magnitude of negative permittivity could be adjusted by controlling Ag content, which was well described by Drude model. The average total SE of our obtained metacomposite could reach ∼30 dB, and the reflection was the primary shielding mechanism, which was attributed to the intense impedance mismatching stemmed from the negative permittivity. Our work opens up the possibility of designing metacomposites for promising electromagnetic shielding materials, promoting their application in microwave field.

It is generally accepted that composites with thinner fillers would show more refined pore structure, so currently the uses of nano materials including nano graphene-based additives (NGAs) to fabricate functional cement composites are quite popular. However, the effects of NGAs on the pore structure of cement composites are far from being fully understood. In this work, we investigated the pore structure of cement composites blended with graphene oxides (GOs) and graphene nanoplatelets (GNPs), which show the similarly layered structure but different sizes and chemico-physical properties. Results reveal that both GOs and GNPs will not significantly alter the hydration products of cement. Both GOs and GNPs can make the material matrix denser by depressing the meso pores; and GOs tend to coarsen the macro pores due to the laminar agglomerations. The findings of this study help better tailor the pore structure of cement composites with NGAs for future materials design and manufacture.

A promising novel composite coating based on compound pigment of zinc phosphate and polypyrrole (PPy) functionalized graphene (ZGP) was reported for carbon steel in 3.5 wt% NaCl solution. Two ratios of PPy functionalized graphene oxide (GO-PPy) nanocomposites were prepared by in-situ polymerization of pyrrol (Py) on the surface of graphene oxide (GO). PPy film deposited on the surface of graphene oxide guaranteed excellent dispersion in the coating owing to hydrophilic groups. Embedding a small amount of ZGP-2 composite pigment (mPy/mGO=2:1) into the waterborne epoxy coating significantly improved corrosion protection of the prepared composite coating. The corrosion protection mechanism of the desirable coating was attributed to the synergistic protection of impermeable GO-PPy nanosheets and passivation function of zinc phosphate, which was proved by the identification of corrosion products. Therefore, this work may provide a new direction for further study on compound pigments composed of functional graphene nanomaterials and inorganic salt inhibitors.

Inspired by metal forming tests, the conventional forming limit diagram (FLD) was employed to characterize the forming properties of the Glass Fiber Reinforced Polypropylene (GFRP) composite in this study. The strain history of GFRP specimens was captured by using a 3D digital image correlation (DIC) system. Since the conventional metal FLD is established by major and minor strains only, which is inadequate to characterize the formability of different components in the pre-consolidated woven composites. Therefore, this study proposes a new notch design, where the specimens have two long notches with different aspect ratios on the both sides, to ensure that the failure is dominated by fiber breakage mode while retaining the fiber continuity in specimens. For comparison, the conventional hourglass specimens and the newly-proposed notch specimens with different widths were both tested through a series of stamping experiments to investigate the formability of the GFRP materials. The equivalent fiber strains based FLD from the conventional narrow hourglass specimens with 45°,-45° shows an abnormal value of equivalent fiber strain around 40% in the shear deformation region, which was far beyond the tensile limit of glass fibers. On contrary, the FLD from the proposed notch specimens presented a limiting strains around 5%, involving all possible deformation modes. Thus, the FLD of the notch specimens was established in the form of parallel line here, which can be used as a criterion to characterize the formability of GFRP in which the fiber breakage was a dominant failure mode. Note that this criterion takes into account the influence of different components on the formability of GFRP and combined deformation history with failure mechanism, implying more suitable for GFRP. This study provided an effective way to establish the design criteria and FLD for other woven pre-consolidated GFRP materials.

We formulate a homogenized thermo-chemical model to simulate the manufacturing of unidirectional composites made of carbon fibers embedded in a thermosetting dicyclopentadiene (DCPD) matrix using frontal polymerization (FP). The reaction-diffusion model is then solved using the finite element method to investigate the evolution of the temperature and degree of cure during the fabrication process. The results reveal two different processing regimes: At lower fiber volume fractions, the polymerization front speed increases with the fiber volume fraction due to the increase in the effective thermal conductivity of the composite. At higher fiber volume fractions, the front velocity decreases with increasing fiber content due to the reduced heat source generated by the exothermic reaction. The 1-D simulations are complemented with 2-D studies that include heat losses to the surroundings. The model predictions are validated with experiments conducted on carbon/DCPD composite panels manufactured through frontal polymerization.

In this paper, an elastoplastic-damage coupling constitutive model for unidirectional fiber-reinforced polymer matrix composites (UD FRPs) is presented, which both considers the plastic-hardening and damage-softening processes. Tension-compression asymmetry and shear strength increase due to transverse compression are observed under off-axis tensile/compressive tests of UD E-glass/YPH-200. Therefore, a four-parameter plastic yield criterion considering these two effects is proposed. Applying this model to predict the off-axis tensile/compressive responses of present tests provides good agreement with experimental curves. In addition, we give a novel definition of shear damage variable based on Puck failure theory and discuss it in detail. Further, we develop a four-parameter matrix failure criterion for UD FRPs and exactly predict the off-axis failure strength.

This article investigates electrical conductivity and piezoresistivity of carbon nanotube (CNT)-polymer nanocomposites using an efficient analytical model. The effects of chopped carbon fibers on the electrical conductivity and percolation behavior of multiscale polymer-based nanocomposites containing CNTs are examined at various maximum angular orientations and different polymer matrix barrier heights. The multiscale nanocomposite (MSNC) electrical conductivity and percolation onset are found to be dependent on the carbon fiber and CNT geometry and dispersion. The tunneling effect is discussed as an important mechanism to explain the low percolation threshold and nonlinear electric behavior of MSNC. A comparison between nanocomposites filled with CNTs and MSNC reinforced with CNTs and chopped carbon fibers demonstrates different percolation behaviors. Moreover, the influences of CNT position and orientation changes on the piezoresistivity of polymer nanocomposites are studied. Resistance change ratio as a function of applied strain demonstrates a non-linear behavior due to tunneling resistance change between CNTs.

Process-induced residual stresses in 3D woven carbon-epoxy composites are studied by blind hole drilling experiments interpreted with finite element (FE) modeling. It is assumed that residual stresses are primarily caused by the difference in thermal expansion coefficients of the constituents which are modelled as temperature-dependent linear elastic solids. The impact of residual stresses is quantified by drilling blind holes in the composite panels and mapping the resulting in-plane surface displacements by electronic speckle pattern interferometry. Mesoscale finite element models are used to correlate these surface displacements with the volumetric distribution of the residual stresses in the composite. This is done by determining the effective temperature drop ΔTeff that results in the same predictions for the surface displacements as experimentally measured. The effective temperature drop approach allows to use linear elastic models while approximately accounting for various nonlinear effects occurring in the material during processing. The models are also used to establish the sensitivity of the predicted results to the exact location of a hole and its depth.

The advent of 3D printing has enabled the rapid prototyping of complex structures with relatively shorter production times and lower material wastage. Despite these advantages, it is still a challenge to fabricate nanofiller-reinforced lattices using 3D printing. Here, we report for the first time, the successful 3D printing of graphene-polymer octet-truss lattices using the stereolithography (SLA) technique. The factors influencing the mechanical properties of the printed graphene-polymer composite, such as filler concentration, solvent addition and post-fabrication baking temperature and duration were investigated in detail. Our results showed that stereolithographic 3D printing can confer the same improvement in material modulus with ~ 10 times less graphene concentration compared to other processing techniques reported in literature. Our calculations suggest that this was due to a unique characteristic of stereolithography, which enabled the selection and incorporation of aligned graphene platelets into the polymer matrix during the 3D printing process. These exceptional mechanical properties of SLA fabricated polymer-graphene composites are indicative of their potential for use in various applications such as aerospace, automotive and sports equipment.

In this work, thermoplastic polyurethane based conductive polymer composites containing carbon nanotubes (CNTs) and synthesized silver nanoparticles (AgNPs) were used to fabricate highly elastic strain sensors via fused deposition molding. The printability of the materials was improved with the introduction of the nanofillers, and the size and content of the AgNPs significantly influenced the sensing performance of the 3D printed sensors. When the CNTs:AgNPs weight ratio was 5:1, the sensors exhibited outstanding performance with high sensitivity (GF = 43260 at 250% strain), high linearity (R2 = 0.97 within 50% strain), fast response (∼57 ms), and excellent repeatability (1000 cycles) due to synergistic effects. A modeling study based on the Simmons' tunneling theory was also undertaken to analyze the sensing mechanism. The sensor was applied to monitor diverse joint movements and facial motion, showing its potential for application in intelligent robots, prosthetics, and wearable devices where customizability are usually demanded.

In this work, pre-impregnation techniques including Dr. Ernst Fehrer (DREF) spinning and electrostatic powder coating were used to negate the poor impregnation of highly viscous thermoplastics. The DREF spun hybrid yarns and electrostatic spray coated towpregs were woven into 2D and 3D fabrics and subsequently consolidated to yield two variations of 2D and four variations of 3D composites including 3D angle inter-lock and 3D orthogonal weave. The 2D composites possessed higher tensile and flexural strength than the 3D composites. However, better notch impact properties were observed for 3D orthogonal weave. The closer wrapping in 3D orthogonal slightly improves the shock absorption capability of the composite than the angle interlock composite. Composites made from powder coated towpregs performed better than composites made from DREF spun hybrid yarns, minimizing the effect of the weave pattern. Porosity was a common feature of composites manufactured from DREF spun yarns as observed from micro-CT images.

This paper addresses the challenge of reconstructing nonuniformly orientated fiber-reinforced polymer composites (FRPs) with three-dimensional (3D) geometric complexity, especially for fibers with curvatures, and proposes a framework using micro X-ray computed tomography (μXCT) images to quantify the fiber characteristics in 3D space for elastic modulus prediction. The FRP microstructure is first obtained from the μXCT images. Then, the fiber centerlines are efficiently extracted with the proposed fiber reconstruction algorithm, i.e., iterative template matching, and the 3D coordinates of the fiber centerlines are adopted for quantitative characterization of the fiber morphology. Finally, Young's modulus is predicted using the Halpin-Tsai model and laminate analogy approach, and the fiber configuration averaging method with the consideration of the fiber morphology. The new framework is demonstrated on both injection-molded short and long carbon fiber-reinforced polymer composites, whose fiber morphology and predicted mechanical properties are validated through previous pyrolysis and quasi-static tensile tests, respectively.

The nano-porous structure of CNT film severely limits the penetration of polymer resin for advanced composites. To solve this critical issue, we propose a method which could not only uniformly infiltrate resin into CNT films along thickness direction but also ensure sufficient polymer penetration for the fabrication of CNT film/epoxy composites. The resultant composites revealed an outstanding improvement of 352% and 664% accordingly for tensile strength and Young’s modulus. It also showed 8 times enhancement of tensile toughness compared to that of the pristine CNT film. Furthermore, the high sensitivity (gauge factor ∼ 4.6) with a linear piezo resistive response within a large strain (∼ 5%) and the stable sensing reversibility, demonstrated the excellent strain sensing properties of the produced composites. Therefore, our study innovatively proposes this vacuum-assisted filtration method to obtain the strong fibre-matrix interface interaction inside the dense CNT assemblies as well as other nanomaterials.

Prepregs with discontinuous resin patterns facilitate air removal and impart robustness to vacuum-bag-only processing of composites. However, optimal pattern characteristics have not yet been identified. A geometric model was developed to guide the fabrication of prepregs with various discontinuous patterns and laminates with different orientations and ply counts. The model was used to evaluate metrics related to gas transport: projected surface area exposed, sealed interfaces, and tortuosity. Statistical analysis revealed that single layer surface area exposed and ply count had the greatest effect on projected surface area exposed; orientation had the greatest effect on sealed interfaces and tortuosity. From these insights, prototype prepregs were fabricated to measure through-thickness permeability. Prepregs with a large percentage of sealed interfaces and high tortuosity exhibited lower permeability. The study demonstrated a methodology to differentiate/screen patterns for gas transport efficiency. The model can guide prepreg design and support robust production of composites via out-of-autoclave manufacturing.

Composite materials are increasingly used in the aeronautical field. The assembly of structures requires usually drilling of composite parts. Drilling of composite materials generates defects, mainly delamination at the exit of the hole. This major defect diminishes the structure strength. Delamination is directly related to the drilling thrust force. Minimizing this force reduces the defects. Adding a woven glass ply at the exit of the hole is found to be another adequate solution to reduce the defects. In this paper, the drilling of carbon/epoxy thick composite structures with a woven glass ply at the exit of the hole is considered. An analytical model is developed to determine for a given tool geometry the critical delamination forces as function of the number of non-drilled plies remaining beneath the tool. The results are validated experimentally. These results show that adding a woven glass ply at the exit of the hole reduces delamination.

The large deformation tensile stress-strain response of graphene nanocomposites was investigated, whereby Polyvinyl alcohol (PVA) - graphene oxide (GO) nanocomposites with different GO concentrations were prepared, and subjected to quasi-static tension. Test results indicate that the normal stress on the GO filler phase does not increase for global strains beyond about 0.05. This was confirmed by subjecting specimens to different degrees of tension and examining them via Raman spectroscopy. The change in stress of GO filler is attributed to interfacial slip between the filler and matrix. Adoption of the Mori-Tanaka (M-T) simulations at the microscale is unable to reproduce the experimental stress-strain response of the nanocomposites when slip between the matrix and filler occurs, since perfect bonding between them is assumed in the M-T perspective. Consequently, an interfacial slip model was formulated and incorporated into the M-T method, and good agreement between the modified model and experiments was observed.

An effective and facile method was developed to construct the thermal conductive path way in BNNSs-NH2/epoxy/polyetherimide (PEI) ternary blends via reaction-induced phase separation (RIPS). The well dispersed BNNSs-NH2 in the blends was prepared by the urea-functionalization process, which built a bridge to each other at the interface between epoxy and PEI phases. The through-plane thermal conductivity (TC) of composites is enhanced by 83% at low content of 1 wt% BNNSs-NH2. Filler thermal conductive efficiency (η) of BNNSs-NH2 reaches 189 and 83 based on volume fraction and weight fraction, respectively. In addition, the BNNSs-NH2 shows a critical impact on the kinetic of RIPS, which promotes the curing reaction (coarsening process) of epoxy phase. The glass transition temperatures (Tg) of epoxy and PEI were both enhanced due to the amino group of BNNSs and its selective distribution.

A custom-built test device was developed to measure the inter-ply shear resistance of dry carbon woven fabrics as well as prepregs at different temperatures, consolidation pressures, and forming rates typical to those used in autoclave processing. A quantitative understanding of the nature of the shear forces encountered during fabric consolidation was established, suggesting the strong dependence of these forces on the process conditions along with the dominance of a mixed lubrication regime. Among the most influential state variables, the resin viscosity and distribution of the resin on the prepreg surface, as well as the surface roughness of the reinforcing fibers could be identified.

In this study, a triple-layered coaxial fibre structure was fabricated for strain sensor applications. The core consisted of melt-spun poly (ethylene terephthalate) (PET) where in a subsequent step carbon black (CB) particles were coated onto the surface of the PET fibre to build the conductive pathways by a dissolving-coating method. For the outer protective sheath, a thermoplastic polyurethane (TPU) with a thickness of about 7 μm was generated using a layer-by-layer assembly technique. Compared with other investigated CB-coated fibres, the novel triple hierarchic PET/CB/TPU composite fibres exhibit a high Young’s modulus and tensile strength, as well as a doubled sensing range. The fabrication process can be directly used in the textile industry for the production of wearable and flexible sensors due to its efficacy and low cost. Moreover, a model based on tunnelling theory utilizing only two adjustable parameters was modified based on the actual experimental data, which could precisely describe the relative change of resistance upon the applied strain. Meanwhile, an empirical equation was first proposed and this model offers an effective but simple approach towards quantitative analysis of strain sensors.

In this study, graphene nanoplatelet (GNP)/nano-carbon aerogel (NCA) hybrids were used to reinforce epoxy/carbon fiber composite (CFRP) laminates to investigate the environmental aging effect on their mechanical properties. Different amounts (i.e., 0, 0.25, 0.5, 0.75, and 1.0 wt.%) of the GNP/NCA (1:1) hybrids were dispersed in epoxy resin to prepare GNP/NCA/CFRP laminates. The mechanical properties of these reinforced laminates were investigated under three different environmental aging conditions (i.e., 25 °C, 65% relative humidity (RH); 25 °C, 85% RH; and 85 °C, 85% RH). Furthermore, the micro-mechanisms were examined under the environmental aging conditions for improved mechanical properties of the GNP/NCA/CFRP laminate. The impacts of various environmental parameters, i.e., temperature and moisture, were discussed. The reinforced laminates showed better mechanical properties than neat laminates under all three environmental aging conditions. Based on the published results and the experimental results obtained herein, the mechanisms of the GNP/NCA hybrid-reinforced CFRP laminate were defined.

Zeolitic imidazolate framework-8 (ZIF-8) was synthesized and used as a flame retardant in polyvinyl alcohol (PVA) aerogels. The introduction of ZIF-8 increased the roughness of the cell walls due to attachment of the ZIF-8 particles. The ZIF-8 also promoted the thermal degradation of PVA, but increased the residue yield. The limiting oxygenation index (LOI) increased from 19.5% for pure PVA aerogel to 24.0% for the ZIF-8/PVA hybrid aerogel. The self-extinguishing behavior of ZIF-8/PVA hybrid aerogel was observed in the UL-94 vertical burning test, while the PVA aerogel burned out finally. The peak heat release rate (PHRR) and total heat release (THR) of the ZP3 hybrid aerogel were 44.2% and 12.8% lower than pure PVA aerogel, respectively. The decomposition of ZIF-8 to zinc oxide enhanced the barrier effect of the residues, which accounted for the suppressed PHRR and THR. This study demonstrated that incorporation of ZIF-8 can result in tunable flame retardancy for fire safety application.

Surface modification of carbon fiber is a traditional research field and many techniques have been developed to improve the adhesion force between fiber and the polymer matrix. However, most studies were focused on the carbon fibers with standard modulus. The surface of high-modulus carbon fiber (HMCF) is difficult to be activated due to the highly inert structure after graphitization. A convenient and effective surface modification method that can simultaneously improve the content of function groups with containing oxygen and nitrogen on the surface of HMCF was developed in this paper. The surface of HMCF was first anodized to be activated by electrochemical oxidation, and then the diethylenetriamine (DETA) was grafted by electrochemical grafting. The effect of the type of electrolyte on the electrochemical grafting of DETA was studied by the addition of NH4HCO3 and (NH4)2SO4, respectively. The results indicated that the addition of NH4HCO3 electrolyte in DETA solution will promote the grafting and increase the grafted amount on HMCF surface. Moreover, the addition of (NH4)2SO4 electrolyte can not only promote the grafting, but also oxidize the surface of the fibers further to generate more oxygen-containing groups. In addition, the interfacial performance of HMCF composites was significantly improved after modification by this method. Especially, when (NH4)2SO4 was added to DETA solution, the inter-laminar shear strength (ILSS) of HMCF/epoxy composites reached 97.5 MPa, which was 257.1% higher than that of untreated HMCF.

Ternary heterogeneous MWCNT@TiO2-C wave absorbent was firstly prepared, using glucose, MWCNT, and titanium isopropoxide as raw materials, through the solvothermal process followed by post-heat treatment. Afterwards, MWCNT@TiO2-C/silicone rubber wave-absorbing composites were fabricated via solution casting and subsequent curing process. XRD, Raman, XPS, and TEM analyses demonstrated the MWCNT@TiO2-C fillers were successfully synthesized with TiO2 and amorphous carbon coated on the surface of MWCNT. When the MWCNT@TiO2-C/silicone rubber wave-absorbing composites contained 25 wt% MWCNT@TiO2-C fillers and with the thickness of 2.5 mm, it displayed the minimum reflection loss of −53.2 dB and an effective absorption bandwidth of 3.1 GHz. Remarkable wave-absorbing performances for MWCNT@TiO2-C/silicone rubber composites could be attributed to the synergetic effect of interfacial polarization loss and conduction loss.

Polyphenylene sulfide (PPS) fiber is widely used in flame-retardant fabrics, high-temperature filter bags, among other applications. It has excellent heat and corrosion resistance. However, the fibers were characterized by weak photo-stability. Herein, an unique strategy based on second component induced shielding effect for constructing organic-inorganic hybrid nanocomposites were developed by using multi-walled carbon nanotubes (MWCNTs) as effective stabilizers. The photo-stability of PPS/MWCNTs composite fibers were investigated by Xenon-lamp weather resistance test chamber. Moreover, the mechanism for photo-stability enhancement was analyzed by Fluorescence spectrometer, differential scanning calorimeter and thermogravimetric analysis. Compared with neat PPS fiber, it was showed significant improvement in photo-stability of PPS/MWCNTs composite fibers resulting to increased strength retention ratio from 57.8% for neat PPS to 77.3% for PPS/MWCNTs-1.0 fiber. It was finally concluded that the mechanism for enhanced photo-stability of PPS fiber was based on efficient quenching of optically generated excitons by MWCNTs resulted from steady-state fluorescence spectroscopy.

Aligning microfibers along a user-specified direction is important to fabricate polymer-matrix composite materials with tailored properties, including anisotropic electrical and thermal conductivity and high strength-to-weight ratio. Building on our earlier work, we employ ultrasound directed self-assembly to align carbon microfibers along user-specified directions in photopolymer resin and use stereolithography to cure the resin and 3D print composite materials. We quantify macro- and microscale alignment of microfibers in the matrix as a function of weight fraction and dimensionless ultrasound transducer separation distance and input power. Multiple regression analysis expresses microfiber alignment as a function of the fabrication process parameters and shows that microscale alignment is primarily determined by microfiber weight fraction, whereas macroscale alignment is a function of microfiber weight fraction, dimensionless ultrasound transducer separation distance and input power. Relating microfiber alignment to the fabrication process parameters is a crucial step towards 3D-printing polymer-matrix composite materials with tailored material properties.

Tannic acid (TA), natural phenolic compounds abundant in many plants, exhibit low flammability and good absorbility because of multidentate properties. Based on it, a novel intumescent flame retardant (IFR) system (AGT) that consists of ammonium polyphosphate (APP)/TA functionalized graphene (TGE) presents synergistic flame retardant and smoke suppression for natural rubber (NR) due to the dual flame retardant functions of each component. The novel IFR (AGT ) system is of interest to a variety of fields because of its distinct flame retardant and relatively good mechanical properties in comparison to traditional IFR system. Cone calorimeter results reveal that the AGT system could clearly change the decomposition behavior of NR and form a strong a highly graphitized and phosphorous-containing carbonaceous structure char layer on the surface of the composites, consequently resulting in synergistic effects on the flame retardancy and smoke suppression properties. Moreover, TGE endows NR composite excellent mechanical properties within an effective additive mass of AGT system.

This paper presents an explicit finite element methodology for predicting fatigue delamination in composite laminates using twin cohesive models and a combined static & fatigue cohesive formulation; one model is loaded under the peak-load envelope, whilst the other model is loaded under the trough-load envelope. The twin models contain pairs of twin cohesive interface elements that predict delamination growth by exchanging data at every time increment. The cohesive formulation evaluates fracture mechanics parameters, e.g. the local minimum to maximum fracture energy ratio via local information associated with the twin cohesive elements, without the need to know the global loading information, e.g. the global R ratio. The method allows predicting the mechanical condition of a laminate at both the peak and trough loads. This method is validated by multiple test cases with varying mode mixities and R ratios, showing a high computation efficiency.

Phase change materials (PCMs) applied in the energy storage and temperature control system are crucial for energy conservation and environmental protection. In this work, boron nitride (BN)@chitosan (CS) scaffolds with three-dimensional (3D) porous structures were fabricated. And effective thermal conductive pathways could be created in the resultant scaffolds. By introducing polyethylene glycol (PEG) into the BN@CS scaffolds, composite PCMs with large latent heat of fusion and excellent shape-stability were obtained. In particular, a high thermal conductivity up to 2.77 W m−1 K−1 could be reached at a relatively low content of BN (27 wt%). Moreover, they also exhibited a satisfactory energy storage density of 136 J g−1. This work demonstrated a facile and environmentally friendly strategy to simultaneously achieve enhancement of thermal conductivity, high energy storage density, shape stability and outstanding thermal repeatability for composite PCMs, which held promising potential in waste heat recovery, cooling system and temperature control system.

Commercial ethylene propylene diene monomer (EPDM) rubber grafted with maleic anhydride (EPDM-g-MA) was thermoreversibly crosslinked by silane modified silica. EPDM-g-MA was first modified with furfurylamine to obtain furan functionalized EPDM (EPDM-g-FA) which was then crosslinked with 3-methacryloxypropyltrimethoxysilane (as electron-poor agent) modified silica via a Diels-Alder reaction. The as-formed rubber network could be broken at high temperature and reconstructed by thermal annealing, which were proven by differential scanning calorimetric analysis and solubility testing. The mechanical strength of the resulting EPDM/silica composites could be tailored by the amount of modified silica and were superior to the previously reported EPDM rubber crosslinked by low molecular organic agents. More importantly, the rubber composites showed good thermal reprocessability and self-healing behavior, by which the crosslinked composites could be recycled to use with comparable mechanical property as the original composites.

A considerable collection of VARTM choices for composite manufacturing techniques can be both found in literature as well as in industry. Each manufacturing process provides different benefits that must be carefully considered depending on the final application of the desired composite. Here, we present a performance comparison in terms of process effectiveness related to fibre volume fraction, the magnitude of thickness variation, and void contents of 16 laminated composites manufactured by different variants of VARTM (DBVI, VAP, and CAPRI) as well as HIPRTM. Non-crimp carbon textile reinforcements and five-harness satin woven carbon textile reinforcements with a PRISM® EP2400 resin system as base constituents are used to produce composite panels. After manufacturing 16 composite panels, an evaluation of the pros and cons of the processing vs properties/performance obtained with each of them is discussed.

Highly thermally conductive form-stable phase change materials (PCMs) possessing shape memory are designed based on covalent-noncovalent interpenetrating polymer network and boron nitride. The matrix network relies on the composition of two functional species, cured mesogenic epoxy (EO) and polyethylene glycol (PEG). It is demonstrated that the covalent network of EO can trap PEG by forming hydrogen bond with PEG chains. On the basis of EO/PEG networks, by incorporating boron nitride, the thermally conductivity of the PCMs can reach to 2.962 W m-1 K-1. The prepared composites show satisfied thermal energy storage capability and good shape stability when undergo long time heating at 80 °C. In addition, the prepared composite exhibits excellent shape memory function. Diverse functions of the PCMs might produce new applications in thermal energy storage or thermal management fields.