Carbon Fiber Orientation Research Articles

Radially oriented functional thermal materials prepared by flow field-driven self-assembly strategy

Filler-reinforced polymer composites are widely applied in thermal management field on account of their promising heat transport ability, superior flexibility and excellent durability. Inside these composites, thermally conductive fillers are usually uniformly distributed or unidirectionally oriented in polymer matrix to improve thermal performances. However, the ever-shrinking and spatially distributed heat sources in three-dimensional, high-density packaged electronic devices have created the localized “hotspot” problem, which raises a new challenge and stricter requirement for the composite thermal materials. Inspired by the amazing radial microstructures in ginkgo leaf, we proposed a flow field-driven self-assembly strategy to fabricate functional thermal materials with radially oriented carbon fibers (CFs). To quantitively evaluate the orientation, an orientation algorithm based on microscale image identification was developed, and an evaluation criterion was proposed. The underlying orientation mechanisms of fillers under the driving of flow field were revealed by visual simulation of vacuum filtration. Thanks to the well-oriented fillers architecture, the composites demonstrated an ultrahigh in-plane thermal conductivity of 35.5 W/(m∙K) with a thermal conductivity anisotropy of 19.8, which enables rapid and efficient heat dissipation pathways towards localized hotspots. In addition, this flow field-driven self-assembly strategy provides a promising self-design ability that is expected to solve the heat dissipation of arbitrary-shape heat sources, and shed light on other application scenarios like efficient solar-thermal-electric conversion.

Estimation of the fiber orientation distribution of carbon fiber–reinforced plastics using small-angle X-ray scattering

• Carbon fiber orientation distributions in the CFRP were determined using their SAXS analysis. • Fast evaluation was achieved by introducing a calibration curve for integral width of the azimuthal direction. • Similar orientation distribution compared those obtained with X-ray CT could be obtained. The orientation of discontinuous carbon fibers (CFs) in CF-reinforced plastics (CFRPs) determines their properties, necessitating convenient evaluation methods. Herein, a fast and non-destructive method is proposed for the evaluation of the orientation distribution of CFs in CFRPs based on small-angle X-ray scattering (SAXS). The width of the equatorial streak in the SAXS pattern of (or azimuthal intensity distribution of scattering from) a CFRP depends on the orientation distribution of its CFs; a calibration curve for this relationship was derived by assuming the orientation distribution to be Gaussian. This calibration curve was used to determine the orientation distributions of CFRPs featuring CFs with different orientation distributions, which correspond well with the orientation distributions determined by X-ray computed tomography. Thus, the proposed method can be used to conveniently and quantitatively evaluate the orientation distribution of discontinuous CFs in CFRPs. Because this method is based on scattering from elongated nanovoids in CFs, it can be used to evaluate composite materials in which reinforcing fibers containing elongated scattering bodies, e.g., high-strength organic fibers containing fibrils, are preferentially oriented.

Investigation on electromagnetic shielding and mechanical properties of zirconia graded carbon fiber/epoxy nanocomposite

AbstractThe present study is on the fabrication of epoxy nanocomposites for electromagnetic interference (EMI) shielding in the X‐band and Ku‐band frequency range. Single‐layer unidirectional carbon fiber along with nano zirconia is used to achieve the required EMI shielding and mechanical strength. The microstructural study of the fabricated samples has revealed the good lamination of carbon fiber in epoxy matrix and the uniform dispersion nanoparticles provide a reduction of wettability. Dielectric parameter studies indicate an increase in permittivity and dielectric loss with the addition of zirconia nanoparticles. The shielding effectiveness (SE) shows as high as 25 dB when the electric field is parallel with the carbon fiber orientation. The addition of zirconia nanoparticles to the carbon fiber reinforced epoxy composite have enhanced the ability of microwave absorption shielding. Mechanical properties of the epoxy carbon fiber nano zirconia composites show an improvement in storage modules, activation energy, and impact resistance. It is realized that 3 wt% zirconia added epoxy carbon fiber composite shows high shielding effectiveness with good mechanical properties.

Theoretically predicting the flame-spread limit of carbon-fiber-reinforced plastic

This work studied the flame-spread limit of carbon-fiber-reinforced plastic (CFRP) sheets and attempted estimating it theoretically. First, to measure the limiting oxygen concentration (LOC), the CFRP sheets with different carbon fiber (CF) orientations were combusted under variable opposed-flow velocity (Vg) and oxygen concentration. The flammability decreased as the CF orientation angle (θ) was increased. Increasing θ facilitated conductive heat losses sideways through the CFs, resulting in the low flammability. The LOC decreased with increased Vg. A flame leaned toward the solid surface as Vg was increased, leading to the high heat transfer rate from the flame. The increased heat transfer rate accelerated the flame spread to decrease the LOC. The decrease in the LOC was similar to the trend in the radiative regime for polymers. Next, the LOC was estimated via an equation that describes the radiative extinction. The calculated flame-spread limit, however, did not quantitatively agree with the measured LOCs, because that equation was derived from the conventional flame spread model that does not consider the solid-phase heat transfer. Nevertheless, the solid-phase heat transfer was dominant in the flame spread over the CFRP sheets. Then, a novel equation on the radiative extinction was formulated according to the flame spread model of CFRP. Although the response of the flame spread rate and the LOC to Vg was well simulated, a good agreement between the computed and measured LOCs was still not obtained. This is probably because the observed extinction of the CFRP sheets would not be governed by the radiative extinction, though both the radiative and blow-off extinctions are dominant. Therefore, to obtain the correct flame-spread limit, it is necessary to develop and solve an equation that considers both extinctions with true properties of the CFRP sheets.

Improving through-plane thermal conductivity of PDMS-based composites using highly oriented carbon fibers bridged by Al2O3 particles

Efficient thermal interface materials (TIMs) are urgently needed for heat dissipation of high-power density electronics. In this study, vinyl polydimethylsiloxane (PDMS) composites with the spatial alignment of carbon fibers (CFs) bridged by Al2O3 particles were fabricated by the flow field. The through-plane thermal conductivity (TPTC) of the composites with 24 vol% CFs and 47 vol% Al2O3 loading reached 38.0 W m−1 K−1. The oriented CFs bridged by Al2O3 acted as the efficient through-plane thermal conductive network. Furthermore, the effects of shape factor (b/a), spatial angle (γ) of CFs, and CF loading (Vf) on the TPTC were quantitatively discussed by steady-state finite element simulation combined with micro-computed tomography and machine learning. The positive contribution of the increased Vf to TPTC was in competition with the negative contribution of b/a and γ, both of which increased with the increase of Vf. Moreover, b/a exerted more negative effects than γ. The PDMS composites demonstrated excellent thermal stability (Td = 407.5 °C, CTE = −55.3 × 10−6 K−1), low compress modulus (1.71 MPa), and hardness (47 (Shore C)), which made them potential candidates for TIMs. This work offers a feasible method to prepare TIMs on large scale and refreshes the thermal conduction mechanism of TIMs by introducing the influencing factors (b/a and γ).

Continuous mapping of large surfaces with a quality inspection robot

This paper addresses the problem of mapping large surfaces with a moving sensor. In particular, it proposes image registration and mapping algorithms that enable to use in continuous motion sensors that need multiple shots to perform a measurement. These methods exploit the knowledge of the shape of the part to inspect in a both efficient and accurate fashion, thus allowing to obtain a measurement quality comparable to that of static measurements, while guaranteeing fast sensor motion and thus short scanning times. This work describes the application of these methods for the mapping of carbon fibre parts with an inspection robot equipped with a sensor estimating 3D carbon fibre orientation from multiple 2D images captured with different illumination. Experiments on carbon fibre preforms of complex 3D shape demonstrates that this system accurately reconstructs in real-time the 3D fibre orientations of the outer layer of carbon fibre parts. Accuracy assessments report small errors within the tolerances allowed by the automotive industry on flat and generic 3D surfaces. The inspection robot system presented in this paper has been demonstrated both as an in-line quality inspection robot for production of carbon fibre preforms and as a measurement device for improving the draping process in the prototyping of carbon fibre parts.

Gas Diffusion Layer: The Critical Player in Gases Distribution in the Proton Exchange Membrane Fuel Cell

Within the last decades, fuel cells have become the center of attention of research community, industry, and the general public. This is due to the emphasis on the sustainability of the society and the emerging concept of a hydrogen economy. Proton exchange membrane fuel cells (PEM FCs) represent a mature and established fuel cell technology. The flexibility of operation, the high degree of fuel utilization, and the output power density make them suitable for mobile applications such as hydrogen-fueled vehicles or on-site energy generation. Membrane electrode assembly (MEA) is the mainstay of the PEM FCs. The MEA consists of the proton exchange membrane, catalytic layers, and gas diffusion layers (GDLs). Single MEAs are interconnected by bipolar plates with flow field channels homogenously distributing reactants and realizing easy removal of the generated water. Individual cells are compressed together, forming the fuel cell stack. The GDL plays a three-fold role in the performance of PEM fuel cells. It has to offer good electrical conductivity, ensure good reactant distribution along the reaction zone, and facilitate the removal of the water produced by the fuel cell operation. The optimal combination of these three aspects of GDL allows the FC to achieve high performance. Furthermore, the homogeneous distribution of the reactants is crucial for the durability and lifespan of the FC. The inhomogeneous reactants distribution leads to a local starvation of the electrode, leading to high local overvoltage and thus shortening the lifespan of overloaded parts. Although GDLs play a crucial role in the operation of PEM fuel cells, so far, they have received little attention. Hence, the objective of our study is to compare commercially available GDLs with respect to their properties, namely permeability under conditions close to the operating fuel cell.The approach of combining advanced mathematical modeling with extensive experimental characterization was used to achieve this task. Testing cells allowing precise determination of the in-plane permeability of various GDLs were designed based on the computational fluid dynamics modeling. According to the contemporary literature, two different carbon based GDLs were examined, namely carbon-cloth and carbon-paper, which principally differ in the carbon-fiber orientation in their internal structure. The investigated properties of GDLs thus include thickness, porosity, internal structure, and the presence or absence of microporous layer.The achieved experimental results show that at given compression, thicker carbon paper GDLs are superior to carbon cloth samples in terms of permeability and deformation resistance. The obtained permeability values of GLDs at different degrees of compression were compared with predictions based on the Carman-Kozeny equation to assess the accuracy of this semi-empirical prediction. Finally, the importance of the optimal flow field and GDL combination in terms of reactant distribution in the fuel cell stack of industrial conditions is documented via mathematical modelling based on the obtained experimental data.This work was supported by the European Regional Development Fund-Project “Fuel Cells with Low Platinum Content” (No. CZ.02.1.01/0.0/0.0/16_025/0007414).

Mechanical Properties of Carbon Fiber Reinforced Composites Filled with Carbon Microparticles

The aim of this work is to investigate the effect of carbon micro particles used as epoxy resin fillers, for the mechanical properties of reinforced composites unidirectionally oriented carbon fibers. The motivation for this work was expansion knowledge of the possibilities of improving the user properties of these materials at maintaining their weight, thus finding new areas for application recycled carbon fibers from composite waste, which would also contribute to the solution issues of recycling and subsequent use of today's mostly landfilled composites. This work deals with the influence of carbon fillers embedded in epoxy resin on tensile and flexural properties of carbon fiber reinforced epoxy (CFRE) composites. Samples were made from unidirectional carbon multifilaments, and epoxy resin modified with selected carbon fillers in 2.5weight% concentrations. Composites were subsequently examined using flexural and tensile tests. All specimen filled with carbon particles showed increase of both, flexural and tensile properties, if compared to neat epoxy composites.

Analytical modeling of chip formation mechanism in cutting unidirectional carbon fiber reinforced polymer

Fiber orientation of the unidirectional carbon fiber reinforced polymer (UD CFRP) dominates the chip formation in the cutting process owing to its anisotropy. Existing analytical cutting models focus on cutting force prediction based on the pre-defined chip formation modes obtained from experimental analyses at different fiber orientation ranges. This paper presents the analytical prediction of CFRP chip formation modes, including fiber tension, fiber compression, matrix tension, and matrix compression, based on the stress state in the chip formation region in the fiber orientation range of [0°,180°]. The chip formation angle and the stresses activating the material failure on the chip formation plane are predicted with the minimum cutting energy principle. The transition of the chip formation mode as the fiber orientation increases, and the variations of the chip morphology and cutting forces owing to the change of chip formation mode are predicted and analyzed. The chip formation angle, chip morphology, and cutting forces are compared between the simulations and the measurements through orthogonal cutting experiments of UD CFRP at different uncut chip thicknesses and fiber orientations.

Anisotropic tribological behavior of LSI based 2.5D needle-punched carbon fiber reinforced Cf/C–SiC composites

Cf/C–SiC composites were fabricated via liquid silicon infiltration with 2.5D needle-punched carbon fiber reinforced Cf/C composites. The effect of surface topography and carbon content of the Cf/C–SiC composites on the tribological properties was researched by the ball-on-disk reciprocating tribometer. The results indicate that different fiber layers and cross-section of the composites have various surface topography and show significant differences in the friction and wear properties. By the wear morphology and model analyses, the reason for the tribological anisotropy of the composites is that the distribution of carbon and SiC phases in the composites are inhomogeneous caused by the difference of the carbon fiber orientation and the relative content in each layer. Moreover, the wear rate of the short-cut fiber web layer was the lowest and there is an obvious linear decrease in coefficient of friction with increase of carbon content. The present work explains why the tribological properties of the composites are inconsistent and provides a way to adjust the friction properties of composite materials by optimizing the friction surface.

Non-destructive characterisation of out-of-plane fibre waviness in carbon fibre reinforced polymers by X-ray dark-field radiography

ABSTRACT Fibre waviness is a frequently encountered problem in composite design and manufacturing as it can severely influence mechanical properties of components. In this work, we propose a new method for the detection and quantification of out-of-plane fibre waviness in carbon fibre composites using Talbot-Lau grating interferometry. The sensitivity of X-ray dark-field imaging to the orientation of carbon fibres is exploited to visualise fibre waviness by radiographic imaging and reduce measurement times in comparison to full computed tomography scans. We show that fibre waviness can be qualitatively detected by single radiographic images providing a valid option, for example, for in-line monitoring of similar specimens. Furthermore, quantitative evaluation of fibre waviness angles can be performed by repeated radiographic imaging over an angular range of roughly 10°. Therefore, the number of required projection images can be reduced significantly. With this method, we evaluated wave angles at an error of less than ±1.5° compared to results achieved by full computed tomography scans.

3D Printing of Short-Carbon-Fiber-Reinforced Thermoset Polymer Composites via Frontal Polymerization.

3D printing of fiber-reinforced thermoset composites is desirable for rapid fabrication of 3D composite objects with minimal tooling. One of the main issues in 3D printing of thermoset composites is the low cure rates of matrix resins, which prevents rapid curing and rigidization of composite materials during the printing process and capturing the desired print geometry. Here, we demonstrate a new technique for in situ printing and curing of carbon-fiber-reinforced thermoset composites without any postcuring or postprocessing steps. Upon extrusion and deposition of the composite ink from a printing nozzle, the ink is cured via frontal polymerization, leading to rapid printing of high-quality composites. Tailoring the processing conditions allows for freeform or rapid, supported printing of 3D composite objects with zero void content and highly oriented carbon fiber reinforcements.

Thermally conductive silicone rubber composites with vertically oriented carbon fibers: A new perspective on the heat conduction mechanism

The continual increase in power density and consumption of modern electronic devices calls for high-performance thermal interface materials (TIMs). In this work, silicone rubber composites with vertically oriented magnetic carbon fibers (o-MCF/SR) were successfully prepared via the cast molding and filler orientation upon uniform magnetic field in a vacuum environment. The through-plane thermal conductivity of o-MCF/SR composites showed an unusual power-law growth with increasing MCF loading. At a 9 vol% MCF loading, the o-MCF/SR composite exhibited a maximum through-plane thermal conductivity of 4.72 W/(m·K) with 2045.5 % TCE, about 3.55 W/(m·K) higher than that of SR composites with randomly dispersed MCF (λ = 1.17 W/(m·K), TCE = 431.8 %). To reveal the underlying through-plane heat conduction mechanism of o-MCF/SR composites, finite element simulation combined with classical effective medium theory model and machine learning method was used. A homogeneous unit fiber-filled composite (HUFC) was modelled, and a new parameter influencing the through-plane thermal conductivity, i.e., shape factor (b/a), was introduced here for the first time. Theoretically, this shape factor was dependent on the filler content and indirectly reflected the assembly of matrix and 1D filler in HUFC fit to a parallel-series hybrid model. Furthermore, a decrease of b/a was practically found with increasing MCF loading, and the dominant series-type assembly gradually transformed to parallel-type assembly of the o-MCF/SR composites. This work not only developed a method to fabricate desirable TIMs that hold great promise for advanced thermal management, but also introduced a new parameter to reveal the underlying mechanism for heat conduction capacity of polymer composites.

Measuring orientation dynamics of carbon fibers by dielectric anisotropy in shear flows

Measuring orientation dynamics of carbon fibers is important for manufacturing high-performance composite materials, however, conventional methods fail to timely and non-destructively measure due to destructive sample preparation or complicated data processing from numerous fibers. Herein, we report a timely and non-destructive method that uses two pairs of interdigital electrodes to record dielectric anisotropy induced by carbon fibers orientation. As a proof-of-concept, orientation dynamics of carbon fibers is successfully characterized, the accuracy of which in measuring the final degree of orientation and dynamic orientation process is evidenced by theoretical calculations and optical observations. Experimental results reveal that increasing the fiber aspect ratios, viscosities of solvents and shear rates, could shorten orientation time or increase the final degree of orientation. Meanwhile, a modified model is proposed to explain orientation dynamics with a maximum error of 4.7%. This method has the potential for measuring the orientation dynamics of carbon fibers in the complex structure during processing.

K‐Means Clustering for Prediction of Tensile Properties in Carbon Fiber‐Reinforced Polymer Composites

The application of computer algorithms to identify patterns in data is referred to as machine learning. The algorithms are used to learn complex relationships and build models for various predictions. Herein, the k‐means method is used, one of the unsupervised learning methods in machine learning, to predict Young's modulus and ultimate tensile strength (UTS) of carbon‐fiber‐reinforced polymers (CFRPs), and their experimental Young's modulus and UTS values are compared. The k‐means method categorizes CFRP into four colors: carbon fiber, epoxy resin matrix, defects, and contamination. The prediction of Young's modulus and UTS of CFRP with different porosities and carbon fiber orientation demonstrates the effectiveness of the k‐means method. Furthermore, the experimental values of Young's modulus and UTS of commercial CFRP plate are closer to the predicted values than the catalog values. These results suggest that the k‐means method can predict Young's modulus and UTS of CFRP accurately, instantly, and automatically. The k‐means method is promising as a new technique to accurately and instantly understand the mechanical and physical properties of CFRPs without any material test.

Non-destructive characterization of out-of-plane fiber waviness in carbon fiber reinforced polymers by X-ray dark-field radiography

Fibre waviness is a frequently encountered problem in composite design and manufacturing as it can severely influence mechanical properties of components. In this work we propose a new method for the detection and quantification of out-of-plane fibre waviness in carbon fibre composites using Talbot-Lau grating interferometry. The sensitivity of X-ray dark-field imaging to the orientation of carbon fibres is exploited to visualize fibre waviness by radiographic imaging and reduce measurement times in comparison to full computed tomography scans. We show that fibre waviness can be qualitatively detected by single radiographic images providing a valid option, e.g. for in-line monitoring of similar specimens. Furthermore, quantitative evaluation of fibre waviness angles can be performed by repeated radiographic imaging over an angular range of roughly 10°. Therefore, the number of required projection images can be reduced significantly. With this method, we evaluated wave angles at an error of less than ±1.5° compared to results achieved by full computed tomography scans.

Static and fatigue behavior of a carbon‐fiber SMC‐R composite under combined tensile and shear stresses

AbstractRandomly oriented short fiber reinforced sheet molding compound composites (SMC‐R) are among the most commonly used composites for automotive and many non‐automotive structural applications. Many studies have reported the static and fatigue properties of SMC‐R composites under uniaxial stress conditions. However, there are many applications in which they may be subjected to biaxial stress conditions and their biaxial properties have not been reported in literature. The current study considers the static and fatigue characteristics of a randomly oriented carbon fiber SMC‐R under both uniaxial and biaxial loading conditions with various combinations of tensile and shear stresses. A butterfly shaped Arcan specimen was used to conduct the biaxial stress tests. Since both static strength and fatigue life data exhibited significant variability, statistical analysis was conducted using Weibull distribution to analyse the variations in these properties of the material. In biaxial conditions in which a shear stress is imposed along with a tensile stress, the tensile strength of the material decreases with increasing shear stress. A failure envelope drawn based on von Mises equation shows reasonable agreement with the experimental results. As a percentage of the static strength, the fatigue strengths at 1 million cycles in tension and combined equal tension and shear are significantly higher than the fatigue strength in pure shear.

Mode Tracking of Unidirectional Carbon-Based Composite Structures Using Modified Mode Shape Vectors

A comparison of mode shapes in isotropic structures can be efficiently performed using the modal assurance criterion (MAC) to determine the similarity between mode shape vectors. However, the unidirectional, carbon-based composite (UCBC) structure shows different dynamic characteristics according to the carbon fiber orientation, even for the same structural configuration. The MAC of a certain mode may result in a poor value for the CBC structures in the case of the existence of the distorted mode shape vector from reinforced carbon fibers. In this study, the mode tracking of the UCBC structure is proposed using the MAC value only under the modified mode shape vector to enhance the MAC value between relevant modes. Because the mode shape vectors of the UCBC structure are altered from those of the isotropic structure owing to the reinforced stiffness along the carbon fiber orientation, the modified mode shape vectors are calculated by multiplying the original vectors with the proposed modification window. The proposed method was verified for simple UCBC structures with five different carbon fiber orientations, from 0° to 90°. The UCBC structures were tracked for five modes, three bending and two torsional, and the results were discussed with reference to earlier study results.

Experimental Characterization and Modeling of 3D Printed Continuous Carbon Fibers Composites with Different Fiber Orientation Produced by FFF Process.

The development of 3D printed composites showing increased stiffness and strength thanks to the use of continuous carbon fibers has offered new prospects for Fused Filament Fabrication (FFF) technique. This work aims to investigate the microstructure and mechanical properties of 3D printed CCF/PA composites with various layups, and also to apply predictive models. The mechanical properties of the printed parts were directly related to the adopted laminate layup as well as to the microstructure and defects induced by the FFF process. The highest stiffness and strength were reported for longitudinal composites, where the fibers are unidirectionally aligned in the loading direction. In addition, it was found that the reduction in tensile properties obtained for cross-ply and quasi-isotropic laminate layups can be described by using the Angle Minus Longitudinal. A step-like failure with extensive fibers breakage and pull-out was observed for the longitudinal composites. By contrast, the rupture mode of the quasi-isotropic laminates mainly exhibited debonding between beads. Moreover, the predictions obtained using the Volume Average Stiffness method and Classical Laminate Theory were in good agreement with the tensile test results. This work could help engineers to design complex laminates with specific mechanical requirements by tailoring the orientation of continuous carbon fibers.

Evaluation of Effective Thermal Conductivity by 2d Image Simulation And The Effect of Orientation of Copper-Plated Carbon Fiber on Effective Thermal Conductivity of Fe-Based Composites

Evaluation of Effective Thermal Conductivity by 2d Image Simulation And The Effect of Orientation of Copper-Plated Carbon Fiber on Effective Thermal Conductivity of Fe-Based Composites