Multiscale Composites Research Articles

Modeling and mechanical analysis of multiscale fiber-reinforced graphene composites: Nonlinear bending, thermal post-buckling and large amplitude vibration

In this paper, a mathematical model was developed to predict the effective material properties of graphene nanoplatelets/fiber/polymer multiscale composites (GFPMC). The large deflection, post-buckling and free nonlinear vibration of graphene nanoplatelets-reinforced multiscale composite beams were studied through a theoretical study. The governing equations of laminated nanocomposite beams were derived from the Euler–Bernoulli beam theory with von Kármán geometric nonlinearity. Halpin–Tsai equations and fiber micromechanics were used in hierarchy to predict the bulk material properties of the multiscale composite. Graphene nanoplatelets (GNPs) were assumed to be uniformly distributed and randomly oriented through the epoxy resin matrix. A semi-analytical approach was used to calculate the large static deflection and critical buckling temperature of multiscale multifunctional nanocomposite beams. A perturbation scheme was also employed to determine the nonlinear dynamic response and the nonlinear natural frequencies of the beams with clamped–clamped, and hinged–hinged boundary conditions. The effects of weight percentage of graphene nanoplatelets, volume fraction of fibers, and boundary conditions on the static deflection, thermal buckling and post-buckling and linear and nonlinear natural frequencies of the GFPMC beams were investigated in detail. The numerical results showed that the central deflection and natural frequency were significantly improved by a small percentage of GNPs. However, addition of GNPs led to a lower critical buckling temperature.

Self-assembled complexes of graphene oxide and oxidized vapor-grown carbon fibers for simultaneously enhancing the strength and toughness of epoxy and multi-scale carbon fiber/epoxy composites

Reinforcement of polymers with small addition of nanofillers has been intensively investigated. It has been suggested that combination of few-layer graphene nanoplatelets (GNPs) and carbon nanotubes (CNTs) is more effective than single nanofillers for polymer reinforcement. Herein, we report that the complexes of single-layer graphene oxide (GO) and oxidized vapor-grown carbon fibers (OVGCFs), with dimensionalities of 2 and 1, respectively, simultaneously improve the strength and toughness of epoxy and multi-scale carbon fiber reinforced composites at an extremely low content (∼0.2 wt%). The GO-OVGCF complexes are formed in water by the π-π stacking-induced self-assembly of OVGCFs and GO, and then rapidly transferred to a tertiary amine type epoxy oligomer for the preparation of epoxy and multi-scale composites. OVGCFs were observed to be wrapped by small GO sheets, which greatly improve the dispersion uniformity of OVGCFs in epoxy matrix and the filler-matrix interfacial interactions. The influences of the complexes with various GO-to-OVGCF ratios on the mechanical properties of epoxy and multi-scale composites were investigated systematically. At the optimized GO-to-OVGCF ratio, the complexes increase the mechanical properties of epoxy and multi-scale composites more significantly than previously reported individual nanofillers and the CNT-GNP hybrids.

Materials Engineering of High-Performance Anodes as Layered Composites with Self-Assembled Conductive Networks

The practical implementation of nanomaterials in high capacity batteries has been hindered by the large mechanical stresses during ion insertion/extraction processes that lead to the loss of physical integrity of the active layers. The challenge of combining the high ion storage capacity with resilience to deformations and efficient charge transport is common for nearly all battery technologies. Layer-by-layer (LBL/LbL) engineered nanocomposites are able to mitigate structural design challenges for materials requiring the combination of contrarian properties. Herein, we show that materials engineering capabilities of LBL augmented by self-organization of nanoparticles (NPs) can be exploited for constructing multiscale composites for high capacity lithium ion anodes that mitigate the contrarian nature of three central parameters most relevant for advanced batteries: large intercalation capacity, high conductance, and robust mechanics. The LBL multilayers were made from three function-determining components...

Effect of polymer-grafted carbon nanofibers and nanotubes on the interlaminar shear strength and flexural strength of carbon fiber/epoxy multiscale composites

Multiwalled carbon nanotubes (MWNTs) and vapor-grown carbon nanofibers (VGCNFs) were grafted with poly(styrene-co-maleic anhydride) (SMA) and poly(glycidyl methacrylate) (PGMA) by free radical polymerization, and used as the secondary reinforcing agent for multiscale carbon fiber (CF) reinforced epoxy composites. The polymer-grafted VGCNFs and MWNTs were simply suspended in ethanol and spray-coated onto the surface of CF fabrics to fabricate the multiscale composites. The structures of the polymer-grafted VGCNFs/MWNTs were characterized and their effect on the mechanical properties of multiple composites was compared. Interestingly, polymer-grafted VGCNFs with much larger diameters and lower grafting ratios are more effective than polymer-grafted MWNTs for the reinforcement; and SMA-grafted VGCNFs are more effective than PGMA-grafted VGCNFs. Addition of only 0.4 wt% (on the basis of CF fabrics) of SMA-grafted VGCNFs increases interlaminar shear strength (ILSS) by ∼73% and flexural strength by ∼21%. The increase of ILSS exceeds those of previously reported functionalized nanotubes/nanofibers, graphene oxide or organoclay nanoplatelets as the secondary reinforcement. The high straightness and large aspect ratio of SMA-grafted VGCNFs and the strong interaction with the matrix play the key roles in the reinforcement. This new and simple method simplifies the fabrication of high-performance multiscale composites for broad applications in the future.

Improved interfacial properties of PI composites through graphene oxide and carbon nanotubes on carbon fiber surface

Carbon nanotubes (CNTs) have been identified as excellent nanoreinforcements for carbon fiber (CF)–reinforced polymers regarding a wide range of engineering applications. The outstanding properties of CNTs, such as their large surface area, high mechanical strength, and low manufacturing cost bring them to be distinguished nanoreinforcements for carbon fiber–reinforced polymers to form multifunctional and multiscale composites. Electrophoretic deposition of graphene oxide for CNTs onto the CF surface was conducted. The presence of graphene oxide–CNTs may effectively increase both the roughness and wettability of the CF surface, resulting in an improvement to the interfacial bonding strength between the CF and the polyimide (PI).

Strong Anisotropy and Ultralow Percolation Threshold in Multiscale Composites Modified by Carbon Nanotubes Coated Hollow Glass Fiber

Inspired by biological materials, the use of combined fillers of different types and sizes has led to multiscale, hierarchical composites which are considered to be the multifunctional materials of the next generation. However, the effects of hierarchical architecture on the electrical properties and percolation behavior remain poorly understood. Here, a multiscale polymer‐based micro‐/nano‐composite with hollow glass fibers coated by carbon nanotubes (CNTs) has been produced based on a simple dip‐coating approach. Besides a significant increase in electrical performance, the composites exhibit a very strong anisotropy of electrical properties with the difference of 2–5 orders of magnitude in different directions. In the longitudinal direction of composites, an ultralow percolation threshold is found. These unique properties are shown to be related to the hierarchical morphology, which gives rise to the existence of two percolation levels with different thresholds: a local threshold in the nanoscale 2D CNT networks at the fiber‐polymer interfaces and a global threshold in 3D network formed by the fibers. This study helps to deeper understand the macroscopic electrical performance of the hierarchical composites, potentially opening up new ways for designing novel materials via flexible tailoring the orientation of fiber and the morphology of interfaces.

Cross-Sectional Design and Analysis of Multiscale Carbon Nanotubes-Reinforced Composite Beams and Blades

The present work addresses with the cross-sectional design and analysis of fiber-reinforced multiscale composite beams of general cross-sectional shape and arbitrary anisotropic material properties and investigates the effect of carbon nanotubes (CNTs) on their stiffness properties. The three-dimensional strain field was formulated in terms of one-dimensional strains and a three-dimensional warping displacement. The bulk material properties of the multiscale composite were predicted using Halpin–Tsai equations and fiber micromechanics. The carbon nanotubes were assumed to be uniformly distributed and randomly oriented throughout the polymer matrix. The variational asymptotic beam section (VABS) was used to numerically evaluate the stiffness and mass matrices of four test cases: strip, circular pipe, box beam and airfoil. The influence of CNTs weight percentage and volume fraction of fibers was investigated through a detailed parametric study. The numerical results indicate that the inclusion of a small weight percentage of carbon nanotubes in the polymer matrix is sufficient to induce a significant improvement in stiffness properties.

Unidirectional spread‐tow carbon fiber/polypropylene composites reinforced with mechanically aligned multi‐walled carbon nanotubes and exfoliated graphite nanoplatelets

We investigated efficient methods to maximize the mechanical properties of carbon fiber/polypropylene (PP) composites by combining unidirectional spread‐tow carbon fibers (USCFs) and mechanically stretched PP films reinforced with aligned carbon nanomaterials (CNMs), such as multi‐walled carbon nanotubes (MWCNTs) and exfoliated graphite nanoplatelets (xGnPs). CNM/PP composite films were fabricated using film extrusion process, which resulted in tension‐induced orientation of CNMs. The influences of CNMs and their orientations in the films, the speed of the drawing rollers (take‐up speed), and the degree of crystallinity on the mechanical properties of nanocomposites were investigated. Multiscale hybrid composites (MHCs) consisting of USCFs and PP films reinforced with MWCNTs and xGnPs were manufactured by hot pressing. As compared with neat USCF/PP composites, USCF/PP composites containing 1 wt% aligned CNMs showed up to 18.3 and 77.3% increases in tensile modulus and strength, respectively, and 68.4 and 36.1% increases in flexural modulus and strength, respectively. In parallel, modeling and simulation of CNM/PP composite films and CNM/USCF/PP composites were performed to predict the tensile properties, taking into account the effects of CNM orientation. The mechanical properties of both nanocomposite films and MHCs were most dominantly affected by the degree of polymer crystallinity and CNM orientation. POLYM. COMPOS., 39:E1251–E1261, 2018. © 2018 Society of Plastics Engineers

Numerical study on the nonlinear resonant dynamics of carbon nanotube/fiber/polymer multiscale laminated composite rectangular plates with various boundary conditions

This work deals with the numerical investigation of the geometrically nonlinear resonant dynamics of carbon nanotube/fiber/polymer multiscale laminated composite (CNT-FPMLC) rectangular plates with different boundary conditions. It is assumed that a uniform distributed harmonic excitation load in the transverse direction is applied to the CNT-FPMLC plates. The material properties of multiscale composite are estimated by means of the fiber micromechanics and Halpin–Tsai relations. Furthermore, it is assumed that the carbon nanotubes (CNTs) are distributed uniformly and oriented arbitrarily through the epoxy resin matrix. Based upon the Mindlin plate theory and using the von Kármán hypotheses, the governing equations of motion for the in-plane and out-of-plane motions including the effects of geometric nonlinearity, rotary inertia and shear deformation are achieved by means of the Hamilton's principle. In the solution process, the nonlinear partial differential equations of motions and associated boundary conditions are discretized via the generalized differential quadrature (GDQ) and afterward converted into a Duffing-type nonlinear time-varying set of ordinary differential equations via a numerical Galerkin approach. Then, the time periodic discretization method and the pseudo-arc length continuation technique are employed to solve the obtained equations in order to achieve the frequency–response curves associated with nonlinear free and forced resonances for the CNT-FPMLC rectangular plates with various edge supports. Finally, the influences of important design parameters including the weight percentage of single-walled and multi-walled CNTs, volume fraction of fibers, CNT aspect ratio, plate geometry and boundary conditions on the nonlinear resonant dynamics and linear natural frequencies of CNT-FPMLC rectangular plate are investigated in the numerical results.

Multiscale enhancement behavior of nano‐silica modified CF/PEEK composites prepared by wet powder impregnation

The mechanical performance of modified multiscale carbon fiber (CF) reinforced poly(ether‐ether‐ketone) (PEEK) composites is improved through wet powder impregnation. The complex PEEK suspension is prepared by mixing nano‐silica and PEEK powders in water homogeneously. The CFs are pulled through the complex PEEK suspension, and the modified multiscale PEEK prepregs and composites are prepared by a series of drying and consolidation process. The increasing energy storage, decreasing tan δmax and the area under the tan δ curve in the dynamic mechanical tests indicate strong interface interactions of modified multiscale CF/PEEK composites. The interlaminar shear strength increases by 15.6% from 72.2 to 83.5 MPa for 2.5 wt% nano‐silica addition, showing significant improvement in resisting the delamination damage. Besides, the same addition makes the flexural strength and modulus increase by 13.9 and 8.6%, respectively. The modified multiscale CF/PEEK composites exhibit higher flexural strength and modulus at elevated temperature than the pristine composites. Furthermore, the enhancement mechanisms for the modified multiscale CF/PEEK composites are proposed and illustrated, which contributes to future research on multiscale enhancement for conventional composites. POLYM. COMPOS., 40:1187–1197, 2019. © 2018 Society of Plastics Engineers

Tunable mechanical properties of MWCNT–glass fiber fabric reinforced epoxy composites by controlling MWCNTs dispersing conditions

A novel, simple and cost-effective method, which is capable of easily tailoring the dispersion of multi-walled carbon nanotubes (MWCNTs), was developed here to fabricate the MWCNT–glass fiber fabric (MWCNT–GFf) multiscale composites with tunable mechanical properties. MWCNTs were dispersed into the commercial GFfs through the combined effect of the ultrasound and amino silane (AS) firstly, followed by a resin infusion process. By tuning the ultrasonic power and AS concentration, it is possible to control the MWCNTs dispersion level and subsequently mechanical properties of resultant composite. Making use of optimal dispersion conditions, which involves the optimal combination of ultrasonic power and AS concentration, the interlaminar shear strength of MWCNT–GFf reinforced composites was dramatically increased by 40.5%, and the storage modulus in the glassy region and rubbery region was improved by 27.7% and 125.0%, respectively. The work demonstrates the great promise of this novel method toward practical, industrial application in manufacturing fiber-reinforced composites with superior mechanical properties.

Preparation and properties of carbon nanotubes/carbon fiber/poly (ether ether ketone) multiscale composites

The carbon nanotubes/carbon fiber/poly (ether ether ketone) (CNTs/CF/PEEK) multiscale composites with excellent properties were prepared by introducing treated CNTs (t-CNTs) into CF/PEEK composites using prepreg spraying method. The effect of t-CNTs content on the mechanical performance of composites such as interlaminar shear strength (ILSS), flexural strength and flexural modulus were investigated. The results indicated that the ILSS, flexural strength and flexural modulus of CNTs/CF/PEEK composites were increased by 35.8%, 25.4% and 23.7% after 0.5 wt% t-CNTs introducing. The surface of prepregs and cross-section of the composites displayed evenly t-CNTs dispersion and strong fiber-resin adhesion by scanning electron microscope observation. With the addition of t-CNTs, the electrical conductivity and thermal conductivity of CNTs/CF/PEEK composites were also markedly improved, in comparison with that of CF/PEEK composites. This suggested that the prepreg spraying method was an effective approach to coat t-CNTs on CF/PEEK prepregs and enhance the performance of CNTs/CF/PEEK composites.

Quantitative determination of size and properties of interphases in carbon nanotube-based multiscale composites

Experimental investigations are carried out to quantify the effect of filler composition, filler diameter and carbon nanotube (CNT) grafting on the properties of interphase in epoxy matrix composites. To this end, epoxy is reinforced with stainless steel (SS) wire, brass wire(s) and carbon fiber (CF) before and after CNT growth on their surface. Surface morphology, elemental composition and thickness of interphase in unsized (ar) and CNT grafted composites is studied using scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS). The size and mechanical properties of the interphase are evaluated through nanoindentation and pull-out tests. It is observed that interphase properties depend on material and geometry of reinforcing filler. Moreover, CNT grafting on the filler surface improves the size and stiffness of interphase and increases the interfacial shear strength (IFSS). The relative improvement in interphase properties and IFSS due to grafting of CNTs on the surface of wires and carbon fiber found to be a function of interfacial chemistry between reinforcement and epoxy. SEM analysis of pulled out wires and fibers reveals that the interface fails differently in the presence and absence of CNTs on their surface. Moreover, increase in CNT growth time from 15 to 30 min inside chemical vapor deposition (CVD) reactor increases the interphase thickness but has an adverse effect on the IFSS in CF/epoxy composites. It is shown that the size and composition of reinforcement and grafting of CNTs on their surface are the variables which provide a handle to suitably design the interphase in multiscale composites.

Fracture behavior of the carbon nanotube/carbon fiber/polymer multiscale composites under bending test – A stochastic finite element method

ABSTRACTThe behavior of L-shaped samples made of multi-scale carbon nanotube/carbon fiber reinforced polyethylene under the bending test is investigated by using the extended finite element method. The mechanical properties of the multi-scale composite are obtained by a stochastic finite element mode. Initially, molecular dynamics simulations are used to compute the mechanical properties of nanotubes at the nanoscale. Then, by using the finite element method, the properties of the carbon nanotube/polyethylene nanocomposite are obtained. Considering the mechanical properties of the matrix as the properties of nanotube reinforced polyethylene, the carbon fibers are included into the composites in the next scale.

Effect of carbon nanotube grafting on the wettability and average mechanical properties of carbon fiber/polymer multiscale composites

An experimental investigation is performed to relate the wetting behavior of unsized and carbon nanotube (CNT) grafted carbon fibers to the average mechanical properties of unsized and CNT grafted carbon fiber/polymer multiscale composites. Contact angle measurements and single fiber pull out tests show that the choice of polymer matrix plays a crucial role in determining whether the incorporation of CNTs on the fiber surface enhances or degrades the wettability and hence average mechanical properties of carbon fiber/polymer composites. CNT grafting leads to a significant improvement in interfacial shear strength as well as flexural and tensile response of carbon fiber/polymer composites with the epoxy resin. However, incorporation of CNTs on fiber surface has no significant effect on the average mechanical properties of carbon fiber/polyester composites. Moreover, it is recorded that the relative enhancement in properties after CNT grafting depends on the fiber orientation in CNT grafted carbon fiber/epoxy composites. POLYM. COMPOS., 39:E1184–E1195, 2018. © 2018 Society of Plastics Engineers

Nanocomposites for new Functionalities in Multiscale Composites

This work describes the developing of multiscale composites with inherent health monitoring functionality. Nanotubes tend to form electrically conductive networks when embedded even at low concentrations in traditional insulating polymers. By dispersing nanotubes it is possible to obtain a class of polymers that show a piezoresistive behavior. By using that kind of piezoresistive polymer as matrix in fiber reinforced composites, it is possible to develop multiscale composites with an inherent health monitoring functionality. Two different approaches have been developed to obtain a multiscale composite able to monitor the tensional states of composites. In a first manner has been used a thermosetting resin filled with a mixture of nanotubes and graphene and a specific method has been developed to impregnate carbon fiber fabrics with that nanocharged resin. A second idea was to insert a thermoplastic nanocharged thin film into a glass fiber reinforced composites.

Vibration analysis of an axially moving multiscale composite plate subjected to thermal loading

This study investigated the effects of temperature on free vibrations and critical transport speeds of an axially moving multiscale composite plate. On the basis of the frequency-temperature equivalence principle, a linear mathematical model of the moving multiscale composite plate is derived in the complex frequency domain. Fractional standard rheological model of the plate material as the function of reduced frequency depended on the temperature is determined. In numerical investigations carbon nanotubes- and graphene-reinforced copper plate was taken into account.. To describe thermomechanical properties of the plate material, the investigation results obtained from the molecular dynamics studies and the experimental characteristic of beryllium copper in low temperatures presented in literature is taken into account.. The effects of temperature, transport speed, and internal damping on natural frequencies and critical transport speed are analyzed. The critical transport speeds of the graphene-reinforced multiscale composite are higher than both carbon nanotubes-reinforced composite as well as the comparable copper alloy.

Non-isothermal crystallization kinetics of polypropylene/short glass fibre/multiwalled carbon nanotube composites.

The non-isothermal crystallization kinetics of polypropylene (PP) reinforced with multiwalled carbon nanotubes (MWCNTs) and short glass fibres (GF) was studied by differential scanning calorimetry (DSC). The glass fibre concentration was maintained at 20 wt% and the MWCNT content ranged from 1 to 5 wt% in the PP matrix. The crystallization studies performed by DSC showed an increase in crystallization rate and a decrease in half time of crystallization of PP in the presence of micro and nano fillers. The Avrami, Ozawa, and Mo models were applied to analyze the non-isothermal crystallization behavior of PP multiscale composites. The Avrami model could very well describe the crystallization behavior of PP to 70% of the completion of crystallization. Beyond that level, it deviated significantly for all composites. On the other hand, the kinetics of crystallization could be well described by the Mo model. The strongest nucleating effect and the lowest activation energy were obtained for the composite with 2 wt% MWCNT and 20 wt% glass fibre. The X-ray diffraction analysis showed a significant reduction in the average crystal size in accordance with the amount of MWCNTs added.

Thermal effects on nonlinear dynamic characteristicsof polymer-CNT-fiber multiscale nanocomposite structures

In the present study, nonlinear dynamic response of polymer-CNT-fiber multiscale nanocomposite plate resting on elastic foundations in thermal environments using the finite element method is performed. In this regard, the governing equations are derived based on Inverse Hyperbolic Shear Deformation Theory and von Karman geometrical nonlinearity. Three type of distribution of temperature through the thickness of the plate namely, uniform linear and nonlinear are considered. The considered element is C1-continuous with 15 DOF at each node. The effective material properties of the multiscale composite are calculated using Halpin-Tsai equations and fiber micromechanics in hierarchy. The carbon nanotubes are assumed to be uniformly distributed and randomly oriented through the epoxy resin matrix. Five types of impulsive loads are considered, namely the step, sudden, triangular, half-sine and exponential pulses. After examining the validity of the present work, the effects of the weight percentage of SWCNTs and MWCNTs, nanotube aspect ratio, volume fraction of fibers, plate aspect, temperature, elastic foundation parameters, distribution of temperature and shape of impulsive load on nonlinear dynamic response of CNT reinforced multi-phase laminated composite plate are studied in details.

Enhanced electromagnetic interference shielding properties of carbon fiber veil/Fe3O4 nanoparticles/epoxy multiscale composites

The multiscale approach has been adapted to enhance the electromagnetic interference shielding properties of carbon fiber (CF) veil epoxy-based composites. The Fe3O4 nanoparticles (NPs) were homogeneously dispersed in the epoxy matrix after surface modification by using silane coupling agent. The CF veil/Fe3O4 NPs/epoxy multiscale composites were manufactured by impregnating the CF veils with Fe3O4 NPs/epoxy mixture to prepare prepreg followed by vacuum bagging process. The electromagnetic interference shielding properties combined with the complex permittivity and complex permeability of the composites were investigated in the X-band (8.2–12.4 GHz) range. The total shielding effectiveness (SET) increases with increasing Fe3O4 NPs loadings and the maximum SET is 51.5 dB at low thickness of 1 mm. The incorporation of Fe3O4 NPs into the composites enhances the complex permittivity and complex permeability thus enhancing the electromagnetic wave absorption capability. The increased SET dominated by absorption loss SEA is attributed to the enhanced magnetic loss and dielectric loss generated by Fe3O4 NPs and multilayer construction of the composites. The microwave conductivity increases and the skin depth decreases with increasing Fe3O4 NPs loadings.