Continuous Carbon Fiber Research Articles

Comparison of properties of carbon reinforced plastic obtained on the basis of semicrystalline polyimideR‐BAPBand other high‐temperature‐resistant thermoplastic matrices

AbstractHeat resistant thermoplastic matrices offer potential advantages over thermoset polymers and represent a promising alternative in advanced composite applications. In the present work, the properties of carbon fiber reinforced plastics (CFRPs) based on the developed semicrystalline polyimide R‐BAPB were studied and compared with those of highly heat‐resistant thermoplastic polymers such as amorphous polyetherimide Ultem‐1000 and semicrystalline polyetherketone PEEK. To obtain CFRP, an approach was used basing on the uniform distribution of polymer powders on continuous carbon fibers by electrostatic spraying followed by their impregnation in heated calenders and hot pressing. The thermal and thermomechanical properties of CFRPs based on mentioned above polymers were studied. The effect of temperature on the mechanical behavior of CFRPs, including flexural properties and interlaminar fracture toughnessG1C, was investigated as well. CFRPs based on PEEK and R‐BAPB are found to have the highest thermal stability and heat resistance. The maximum flexural strength, which practically does not change in a wide temperature range from −50 to 180°C, is observed for CFRP based on R‐BAPB polyimide. Among the investigated CFRPs, the highest value of interlaminar fracture toughness is shown by CFRPs based on semicrystalline R‐BAPB.

Deformation behavior and mechanical properties of rolled carbon fiber reinforced Al-matrix composites via protection with Sn layer

How to break the restriction of elongation mismatch between the continuous carbon fibers and Al matrix in the rolling process has become a major obstacle for developing the rolled carbon fiber reinforced Al matrix (CF/Al) composites with high-performance. Herein, a strategy for liquid protection was proposed to overcome the damage of continuous CFs in rolling process of Al matrix by constructing the CF/Al composites with coating structure of Sn layer ([[email protected]]/Al composites). The design on the stress distribution and CFs damage in the rolling deformation of [[email protected]]/Al composites was optimized based on the numerical simulation. The micro-computed tomography (micro-CT) reconstruction indicated that the implantation of Sn can effectively release the stress concentration in CFs to prevent the CFs broken. After the heat treatment, the transition layer with eutectic Al-Sn structure (~550 nm) formed between the Al-matrix and CF-reinforcement, which can be used as weak boundaries, benefits to the load transfer to the CF-reinforcement with an with an increase of 23% in Vickers hardness. More importantly, the tensile strength of rolled [[email protected]]/Al composites can reach 256 MPa, which are 42.2% and 68.4% higher than that of rolled Al-matrix and rolled CF/Al composites (180 MPa and 152 MPa), respectively. This study could motivate the ingenious design of CFs damage protection for developing the advanced CF/Al composites in the automotive and aerospace industries.

A novel strategy for rapid fabrication of continuous carbon fiber reinforced (TiZrHfNbTa)C high-entropy ceramic composites: High-entropy alloy in-situ reactive melt infiltration

For the first time, dense continuous carbon fiber (Cf) reinforced (TiZrHfNbTa)C high-entropy ceramic (Cf/HEC) composites were rapidly prepared via in-situ reactive melt infiltration (RMI). A TiZrHfNbTa high-entropy alloy served as the cation source and carbon in Cf reinforced carbon matrix (Cf/C) preforms served as the anion source, and a (TiZrHfNbTa)C high-entropy ceramic phase with a near equimolar ratio was successfully formed. The results revealed that most of the TiZrHfNbTa high-entropy alloy reacted with the carbon matrix, and the harvested Cf/HEC composites exhibited an excellent bending strength (612.6 MPa) and low ablation rates. High reaction rates caused by ultra-high temperature and homogeneous distribution of elements in the high-entropy TiZrHfNbTa alloy significantly reduced the difference in reactivity with C among Ti, Zr, Hf, Nb, and Ta are considered to be the reasons for successful formation of (TiZrHfNbTa)C high-entropy ceramic with a near equimolar ratio in Cf/HEC composites.

Tailorable mechanical and energy absorption behaviors of 3D printed continuous hybrid fiber reinforced composites

Abstract3D printing of continuous fiber‐reinforced thermoplastic composites (CFRPCs) has expanded potential structural application in recent years. However, it is still challenging to tailor the mechanical and energy absorption properties of 3D‐printed composites to fulfill the requirements for critical application conditions. Herein, hybrid fiber (HF) reinforced composites have been prepared by 3D printing of CFRPCs and investigated on the mechanical and energy absorption behaviors. Continuous virgin carbon fibers (CF), Kevlar fibers (KF) (130 Deniers (D), and 200 Deniers (D)) and E‐glass fibers (GF) were used as reinforcing fibers to produce hybrid and non‐hybrids composites. Hybrid composites with different combination of CF + GF, CF + 130D KF, and CF + 200D KF showed tailorable behaviors, such as flexural modulus (16,691.74, 20,372.38, and 19,017.44 MPa), tensile modulus (15,022.6, 16,269.41, and 15,320.58 MPa). And energy absorption behaviors of CF + 130D KF and CF + 200D KF were tailored in both tensile (18,865.25 and 20,302.07 N‐mm, respectively) and bending (3594.54 and 3570.80 N‐mm, respectively) tests compared to other composites which will be ideal for energy absorption applications. Moreover, CF + GF showed tailored strength which could be used in the need of high stiffness. SEM images were providing strong evidence to resist the fracture and breakage patterns, by tailoring the stiffness and elongation properties of fibers in hybrids specimens. Furthermore, positive hybrid effects of CF + KF hybrids in tensile and bending tests were also showing an ideal match of toughness and flexibility. In future, these cost and weight effective hybrids will have potential to apply in aerospace and automobile.

Fabrication of continuous carbon fiber reinforced polypropylene composites by injection compression molding with self‐resistance electric heating

AbstractInjection compression molding technique with self‐resistance electric heating provides an effective way to fabricate continuous carbon fiber reinforced thermoplastics (cCFRTs) components, but it may also have a significant impact on the properties of the components by inducing undesirable effects. It is necessary to understand the manufacturing process and minimize the introduction of undesirable factors. Thus, this work is to investigate the influence of process parameters (i.e., melt temperature, current intensity, holding pressure, and holding time) on the impregnation quality and mechanical properties of cCFRTs. The results show that fiber fabrics cannot be uniformly distributed in all cCFRTs, resulting in a thick polymer layer on the top of all cCFRTs. Moreover, the fiber distribution shows insensitive to the processing parameters. The increase of melt temperature, the decrease of current intensity and the extension of holding time are conducive to reduce void content and the frequency of macro void; While excessive holding pressure cannot reduce void content due to serious overflow of resin. Meanwhile, the effect of processing parameters on the mechanical properties and fracture morphology of the sample was also determined. The findings show that the flexural strength of the sample is 106.7 ± 0.8 MPa using the optimal processing parameters.

Influence of post-consolidation on continuous carbon-fibre reinforced additively manufactured specimens in bending

Continuous carbon-fibre (CCF) additive manufacturing of composites has significant potential for production of optimised structures. However, stiffness and strength in parts are often significantly lower than manufacturer material data. For thermoset-impregnated CCF, post-consolidation of specimens has greatly increased strength. In this contribution, the effect of post-consolidation for thermoplastic CCF material is presented. Specimens were manufactured on a commercial AM CCF printer and post-consolidation was performed by rapid compression moulding. Porosity was evaluated by X-ray Computed Tomography (CT) and a significant reduction from 5.3vol.% to 1.1vol.% was yielded.Experimental testing is performed in four-point bending with as-printed and post-consolidated samples. Bending stiffness and strength data was obtained. The results show that the bending strength was below expectations in as-printed specimens. Finite Element Analysis indicates that snap-buckling of a small number of outer layers can lead to such a reduced apparent bending strength, and CT scans of fracture surfaces of as-printed specimens reveal the presence of interlaminar debonding. It is shown that post-consolidation highly improves the interlaminar bond, yielding experimentally obtained strength values close to nominal material strength, and the expected kink-band compressive failure is achieved.

Numerical and Experimental Analysis of the Mode I Interlaminar Fracture Toughness in Multidirectional 3D-Printed Thermoplastic Composites Reinforced with Continuous Carbon Fiber.

It is well known that the use of continuous reinforcing fibers can largely improve the typical low in-plane mechanical properties of 3D-printed parts. However, there is very limited research on the characterization of the interlaminar fracture toughness of 3D-printed composites. In this study, we investigated the feasibility of determining the mode I interlaminar fracture toughness of 3D-printed cFRP composites with multidirectional interfaces. First, elastic calculations and different FE simulations of Double Cantilever Beam (DCB) specimens (using cohesive elements for the delamination, in addition to an intralaminar ply failure criterion) were carried out to choose the best interface orientations and laminate configurations. The objective was to ensure a smooth and stable propagation of the interlaminar crack, while preventing asymmetrical delamination growth and plane migration, also known as crack jumping. Then, the best three specimen configurations were manufactured and tested experimentally to validate the simulation methodology. The experimental results confirmed that, with the appropriate stacking sequence for the specimen arms, it is possible to characterize the interlaminar fracture toughness in multidirectional 3D-printed composites under mode I. The experimental results also show that both initiation and propagation values of the mode I fracture toughness depend on the interface angles, although a clear tendency could not be established.

Multiplanar continuous fiber reinforcement in additively manufactured parts via co-part assembly

PurposeMany additively manufactured parts suffer from reduced interlayer strength. This anisotropy is necessarily tied to the orientation during manufacture. When individual features on a part have conflicting optimal orientations, the part is unavoidably compromised. This paper aims to demonstrate a strategy in which conflicting features can be functionally separated into “co-parts” which are individually aligned in an optimal orientation, selectively reinforced with continuous fiber, printed simultaneously and, finally, assembled into a composite part with substantially improved performance.Design/methodology/approachSeveral candidate parts were selected for co-part decomposition. They were printed as standard fused filament fabrication plastic parts, parts reinforced with continuous fiber in one plane and co-part assemblies both with and without continuous fiber reinforcement (CFR). All parts were loaded until failure. Additionally, parts representative of common suboptimally oriented features (“unit tests”) were similarly printed and tested.FindingsCFR delivered substantial improvement over unreinforced plastic-only parts in both standard parts and co-part assemblies, as expected. Reinforced parts held up to 2.5x the ultimate load of equivalent plastic-only parts. The co-part strategy delivered even greater improvement, particularly when also reinforced with continuous fiber. Plastic-only co-part assemblies held up to 3.2x the ultimate load of equivalent plastic only parts. Continuous fiber reinforced co-part assemblies held up to 6.4x the ultimate load of equivalent plastic-only parts. Additionally, the thought process behind general co-part design is explored and a vision of simulation-driven automated co-part implementation is discussed.Originality/valueThis technique is a novel way to overcome one of the most common challenges preventing the functional use of additively manufactured parts. It delivers compelling performance with continuous carbon fiber reinforcement in 3D printed parts. Further study could extend the technique to any anisotropic manufacturing method, additive or otherwise.

Assessing the shear viscous behavior of continuous carbon fiber reinforced PEKK composites with squeeze flow measurements

Out-of-autoclave processes of carbon fiber thermoplastic composites are gaining interest as they can drastically reduce the economic cost. To optimize consolidation, the flow behavior of these highly filled composites has to be characterized. Here, we propose to measure viscosity of carbon fiber/polyetherketoneketone through squeeze flow experiments in a rheometer. A modified Stefan's law assuming a power law fluid behavior with full anisotropy is developed for square and circular geometries to model the data. Values of the power law parameters K and n are obtained, on the order of 15,000 Pa.sn and 0.02 at 1 bar. Though as expected independent of the samples' geometry and tapes' stacking, K and n depend on the applied pressure and plate size. This is due to localized shear which results in a shear-banding-like phenomenon. Finally, squeeze flow is compared to dynamic measurements and invalidate the Cox-Merz rule for such materials.

Preparation of pre-impregnated continuous carbon fiber reinforced nylon6 filaments and the mechanical properties of 3D printed composites

The addition of continuous fibers as the reinforcement is considered to be an effective option to promote the mechanical properties of 3D printed parts. In this paper, different types of prepreg continuous fiber filaments for 3D printing were prepared, and the effects of fiber types and content on the tensile strength of filaments were investigated. Moreover, the prepared filaments were also applied to 3D printing continuous fiber reinforced composite parts. The effects of the infiltration degree on the properties and its strengthening mechanism were studies by failure morphologies. The results showed that the strength of filament was influenced by both internal infiltration degree and resin content, at the same fiber content, the tensile modulus of the filament increases with resin content, and the maximum tensile force can reach 0.21 MPa (3k-0.68). The tensile strength of the sample is negatively correlated with the fiber content in the filament, while the shear strength is positively correlated with the fiber content. At the printing temperature of 280 °C, the printed samples show better tensile and shear properties of 189 MPa and 29 MPa, respectively.

Two‐scale elastic property prediction of 3D printed continuous carbon fiber reinforced thermoplastic composite based on micro‐computed tomography

AbstractA two‐scale method combined with micro‐CT is presented for the prediction of 3D printed continuous fiber reinforced thermoplastic composites. The proposed method is verified by tensile experiments. The distribution of voids and fibers is reconstructed and quantified by two micro‐CT scans with different resolutions. Then the two‐scale models are established according to the scanned data. Effective properties of fiber‐rich region are predicted by the micro‐scale analysis of the representative volume element, and then transferred into the meso‐scale analysis. In meso‐scale analysis, the high‐fidelity generalized method of cells is applied to predicted elastic parameters of the printed samples. While maintaining the overall fiber volume fraction, the fiber volume fraction in the fiber‐rich region is very important for the accuracy of prediction.

Thermally assisted extrusion-based 3D printing of continuous carbon fiber-reinforced SiC composites

A novel method for the three-dimensional (3D) printing of continuous carbon fiber-reinforced SiC composites is proposed. A thermally assisted extrusion-based 3D printing system was developed to simultaneously print a thermoplastic SiC ink, which exhibited shear-thinning properties at high temperatures and underwent rapid solidification at room temperature, and continuous carbon fiber bundles. The viscosity, thixotropy, and printability of the thermoplastic ink were optimized by varying the content of SiC whiskers. Furthermore, the established correlation between the ink composition, nozzle structure, and printability demonstrated that fiber deviations in filaments could be minimized by selecting an appropriate whisker content and coaxial nozzle. A trade-off between the dimensional accuracy and mechanical properties of the printed materials was achieved by optimizing the ink composition and nozzle structure. Finally, PIP was combined for composite densification; the final specimens exhibited a maximum bending strength of 149.1 ± 8 MPa and fracture toughness of 5.32 ± 0.4 MPa·m1/2.

First review of capacitance-based self-sensing in structural materials

This is the first review of the emerging field of capacitance-based self-sensing in structural materials. Capacitance-based self-sensing is rich in both science and applications. It is applicable to materials ranging from insulators to conductors, whereas the longstanding resistance-based self-sensing is only applicable to conductors. The attributes sensed include the stress/strain, temperature and damage. The stress/strain sensing exploits piezopermittivity, which is typically positive. The temperature sensing exploits pyropermittivity, which is typically positive. The damage sensing exploits the fact that defects reduce the permittivity. The dielectric behavior of highly conductive materials is consistent with the 1999 theoretical prediction by Jonscher concerning charge-carrier polarization and the consequent “giant polarizability”. The materials for which capacitance-based self-sensing has been shown include 3D-printed polymer, asphalt (bitumen-based material), cement-based materials (without or with conductive admixture), continuous carbon fiber polymer-matrix composite, carbon-carbon composite, steel and aluminum. For the conductors, the polarization hinges on the carrier-atom interaction. For the electronic conductors (carbons and metals), the carriers are electrons. For the ionic conductors (cement-based material without conductive admixture), the carriers are ions. For the nonconductors (3D-printed polymer and asphalt), the molecules present align to cause polarization. This work is focused on the ordinary frequencies (such as kHz). For the conductors, the capacitance measurement using an LCR meter needs to be performed with a dielectric film between the specimen and an electrode. For determining the permittivity, the capacitance should be measured for three or more different values of the inter-electrode distance, so that the specimen volumetric capacitance and the interfacial capacitance of the specimen-electrode interface are decoupled.

Improved fibre placement in filament-based 3D printing of continuous carbon fibre reinforced thermoplastic composites

This study investigates the mechanism of fibre deposition in conventional 3D printing and presents an aligned fibre deposition (AFD) method to improve the fibre placement. The deposition mechanism reveals that the cracking of the filament in the transition zone and the torsional deformation during the steering path are the main cause of the defects in the conventional printing process. The AFD method is shown to reduce and mitigate the fibre waviness and twisting, hence producing smooth filament deformation, introducing less air voids and fibre breakage during printing. It is found that the AFD method improves the fibre alignment angle from ±25° to ±12° and reduces the void content to 0.27 % during straight-line deposition. During curved-line printing at a large radius of curvature, tow shearing instead of fibre folding is produced by AFD method, resulting in smooth edges with less fibre breakage.

3D printing and modelling of continuous carbon fibre reinforced composite grids with enhanced shear modulus

Within this research, continuous carbon fibre (CCF) reinforced polyamide (PA) composite grids were topologically-tailored and 3D printed to show enhanced shear modulus. Based on the 3D printing trajectories, a new numerical scheme to predict the elastic responses and behaviours of the 3D printed CCF/PA composite grids was developed. To verify the design and the numerical model, specifically created shearing tests were performed. By comparison, the modelled data agrees well with the experiments. Reinforced by CCFs, the effective shear modulus of 3D printed PA specimens was found to increase by 641.3%, 437.6% and 723% for basic structural configurations with material volume fractions of 20 vol-%, 40 vol-% and 60 vol-%, respectively. Even more, an index for evaluating the CCF reinforcement efficiency, independent of the design of the reinforced structure, was proposed and applied, indicating that the effective shear modulus can be maximally enhanced by 40.5 MP once the CCF volume content is increased by 1%. This study innovatively provides a systematic approach by integrating topological design, modelling and experimental methods for creating engineering grid structures with enhanced shear modulus, and thus proving the efficiency of using continuous fibres as structural reinforcements in 3D printing for engineering applications.

4D printing of continuous fiber-reinforced electroactive smart composites by coaxial additive manufacturing

In this study, a coaxial additive manufacturing process was developed for four-dimensional (4D) printing with continuous carbon fiber-reinforced shape memory polymers (SMPs). These materials have potential applications in the aerospace, automotive, and biomedical industries due to their high strength-to-weight ratio and shape memory properties. The mechanical and thermal properties of the SMPs were evaluated and the effects of printing parameters on printability and carbon fiber volume fraction were analyzed to determine optimal printing conditions. It was found that even a small amount of carbon fiber significantly improved the mechanical properties of the 4D printed samples. The shape memory properties of the printed samples were also examined, and it was found that the structure was able to recover the original shape quickly at low-temperature programming, making it suitable for load-bearing structures. At high-temperature programming, the structure retained the programmed shape well, but recovery of the original shape was slower and incomplete. The use of continuous carbon fiber reinforced SMPs also allows for Joule heating to be used for shape recovery, with the applied voltage able to control the shape recovery process. A high level of deformation recovery (95%) was also achieved in highly deformed structures.

Additive manufacturing of silicone composite structures with continuous carbon fiber reinforcement

AbstractAs a relatively new material deployed in additive manufacturing (AM), silicone and its composites have the potential to realize tunable functionality and heterogeneous, architected properties for a number of applications requiring low modulus, elastic materials. Continuous fiber reinforced composites have been developed for AM to achieve various complex structures that are lightweight with high mechanical properties. AM of silicone‐based composites with direct ink writing (DIW) technology has potential application in medical devices, gasket components, flexible soft electronics, and food packaging. However, DIW printed materials have mechanical anisotropy since the extrusion‐based printing process creates small changes in geometry during the material deposition process. In addition, silicone elastomers are relatively low modulus in tension and can be reinforced with woven cloth or fibers. In this work, a continuous fiber AM machine is developed to manufacture silicone composite structures with continuous fiber reinforcing the printed silicone. Tensile tests show that the anisotropic property of the perpendicular printed specimens, relative to the tension direction, has been significantly improved by continuous carbon fiber reinforcements. This continuous fiber silicone reinforcement printing technique can be applied to tune fiber volume ratios and orientations for different silicone composite structures to meet the desired strength and stiffness.

Turning-angle optimized printing path of continuous carbon fiber for cellular structures

Turning-angle optimized printing path of continuous carbon fiber for cellular structures

Influence of Fibre Fill Pattern and Stacking Sequence on Open-Hole Tensile Behaviour in Additive Manufactured Fibre-Reinforced Composites

Additive manufacturing has revolutionised the field of manufacturing, allowing for the production of complex geometries with high precision and accuracy. One of the most promising applications of additive manufacturing is in the production of composites, which are materials made by combining two or more substances with different properties to achieve specific functional characteristics. In recent years, the use of Continuous Filament Fabrication (CFF) in additive manufacturing has become increasingly popular due to its ability to produce high-quality composite parts which have fibres with a complex orientation and high curvature. This paper aims to investigate the influence of fill pattern and stacking sequence on the open-hole tensile strength of composites manufactured using CFF and made of an innovative matrix composed of nylon and short carbon fibres, i.e., Onyx, and with continuous carbon fibre as reinforcement. By systematically varying the fill pattern and stacking sequence, we aim to identify the optimal combination that can achieve the highest open-hole tensile strength in these composites. The results of this study will provide valuable insights into the design and manufacture of high-strength composites using additive manufacturing. Open-hole strength and elastic properties are strongly influenced by the infill strategy and stacking sequences adopted, and show different failure modes. The results also point out a technological issue characterising the process and indicate some guidelines for designing and manufacturing 3D printing composites.

Characterization of the tensile behavior of continuous carbon fiber reinforced polyamide 6 under self‐resistance electrical heating

AbstractThe stamping molding with self‐resistance electric (SRE) heating is advantageous for the mass production of carbon fiber reinforced thermoplastic (CFRT) because of its short production cycle and energy efficiency. The mechanism of SRE heating is different from traditional oven heating. The impact on CFRT laminates under loading is ambiguous. In this article, the tensile testing systems with SRE heating and traditional heating were designed. The temperature distribution, mechanical response, strain, and failure mode of carbon fiber reinforced polyamide 6 (CFR‐PA6) laminates under SRE heating are studied and contrasted with traditional heating. Specifically, to measure the full‐field strain distribution, digital‐image correlation (DIC) technique and high‐speed camera were introduced. It is found that the electric resistance fluctuates in tensile test with SRE heating and shown temperature sensitivity. Temperature distribution of the specimen under SRE heating is relatively uniform. Besides, the mechanical properties (i.e., tensile strength and elastic modulus) of CFR‐PA6 seem to be insensitive to heating mode. DIC results show that deconsolidation phenomenon makes the specimen fracture randomly. Inversely, heating method has an obvious influence on failure modes. To be specific, there are more shearing damage in traditional heating during high temperature. High current under SRE heating causes corrosion on fiber surface and destroy the fiber‐resin matrix interface.