Carbon Fiber Rovings Research Articles

First Conclusions on Damage Behaviour of Recycled Carbon Staple Fibre Yarn Using X-ray and Acoustic Emission Techniques.

This paper presents the first results on the characterisation of the damage behaviour of recycled carbon fibre (rCF) rovings manufactured into unidirectionally (UD) reinforced plates. In the first step, the mechanical properties of several material combinations were determined by mechanical tests (tensile, flexural, compression). This proves the usability of the material for load-bearing structures. For example, a tensile modulus of up to 80 GPa and a tensile strength of 800 MPa were measured. Subsequently, the fracture surface was analysed by scanning electron microscopy (SEM) to characterise the fibre-matrix adhesion and to obtain first indications of possible failure mechanisms. Despite the high mechanical properties, poor fibre-matrix adhesion was found for all matrix systems. In situ X-ray microscopy tests were then performed on smaller specimens under predefined load levels as transverse tensile and bending tests. The results provide further predictions of the failure behaviour and can be compared to the previous test results. The three-dimensional scan reconstruction results were used to visualise the failure behaviour of the staple fibres in order to detect fibre pull-out and fibre or inter-fibre failure and to draw initial conclusions about the damage behaviour in comparison to conventional fibre composites. In particular, a benign failure behaviour in the transverse tensile test was demonstrated with this procedure. In addition, first concepts and tests for the integration of AE analysis into the in situ setup of the X-ray microscope are presented.

Placement defects in thermoset‐impregnated rovings deposited along curved paths

AbstractWet Fiber Placement (WFP) is a novel process for manufacturing complex shaped parts from continuous fiber‐reinforced polymers without semi‐finished products. Here, dry fiber bundles (rovings) are in‐line impregnated with a thermoset resin, followed by almost tension‐free deposition. The freshly impregnated and limp rovings allow for placement in radii. Due to the lack of compression in deposition, subsequent consolidation, for example, via vacuum bagging, is required. However, this consolidation cannot compensate for defects already present in the deposited lay‐up as they will typically occur when depositing rovings along curved paths. In this study, we deposited two carbon fiber rovings in radii between 5 and 2000 mm by WFP. The occurring defects were visually evaluated. Three main defects were observed: Fiber waviness, up‐folding and twists. The extent of the defects was evaluated using image analysis techniques. Results show, that up‐folding and twists are dominant for radii <100 mm, while for greater radii fiber waviness is the main defect. Up‐folding and twists almost completely disappear for radii >500 mm, but a slight waviness is still observed. However, the effect of fiber waviness on the longitudinal stiffness is estimated to be small for radii >500 mm and perhaps acceptable for some applications.

Influence of Roller Configuration on the Fiber–Matrix Distribution and Mechanical Properties of Continuously Produced, Mineral-Impregnated Carbon Fibers (MCFs)

The article at hand is envisaged to enumerate significant technological parameters for the successful impregnation of carbon fiber rovings having 50,000 (50 K) filaments, each within a fine-grained, cementitious suspension. Parameters such as the number of rollers as well as the influence of roller deflection and rotation have been investigated and discussed with regard to the quality of the related impregnation and mechanical properties resulting therefrom. Morphological analysis disclosed distinct differences in the fiber matrix distribution, which are particularly reflected in the flexural performance of the mineral-impregnated carbon fibers (MCFs) produced. Moreover, with the best fiber matrix distribution, uniaxial tensile tests on MCFs demonstrated superior tensile strengths, moduli of elasticity, and elongations at rupture.

Impact damage detection in glass fibre reinforced polymers via electrical capacitance measurements on integrated carbon fibre bundles

Impact damages are critical for fibre reinforced polymers, as they can lead to large delaminations that strongly influence the structural integrity of the components. Therefore, reliable detection of impact damages through structural health monitoring is desired. This paper demonstrates a method for the detection and size estimation of impact damages in glass fibre reinforced polymers using capacitance measurements on integrated carbon fibre bundles. Therefore, individual rovings of glass fibre fabrics are replaced by carbon fibre rovings. After infusion of the laminate, the electrical capacitance is measured between the carbon fibre bundles. Damage in the form of matrix cracks or delaminations results in incorporated air that changes the permittivity of the material and, therefore, can be detected as a capacitance decrease. Considering the magnitude of capacitance decrease, a size estimation of the impacts is possible. Consequently, the presented method can be used for in-situ monitoring of damages in glass fibre reinforced polymers.

Dry Fibre Placement: The Influence of Process Parameters on Mechanical Laminate Properties and Infusion Behaviour.

Within the dry fibre placement (DFP) process, spread and pre-bindered carbon fibre rovings are automatically processed into dry textile preforms using 2-D and 3-D laying systems. The aim was to automate existing hand lay-up processes, reducing the complexity, increasing robustness, and facilitating the handling of the DFP technology. Process reliability, low waste rates, and flexible production are demonstrated. In this publication, the influences of the process parameters, 2 mm wide gaps and the percentage of 90° plies in the laminate, are investigated with regard to the mechanical properties, the permeability, and the infusion times in the preform z-direction (thickness). The effects on stiffness and strength are compared for several use cases. An approach to determine the infusion times as a function of the laminate thickness, the ply structure, and 2 mm wide gaps is demonstrated and analysed using vacuum-assisted process (VAP) infusion tests. The investigations are performed with carbon fibre tows (24 k), a reactive epoxy-based binder system, and a thermoset infusion resin system.

Investigating the feasibility of using carbon fiber tapes as reinforcement for 3D concrete printing

AbstractThe main advantages of textiles as concrete reinforcement are high corrosion resistance, allowing for thin concrete covers, high drapability, and high strength. Due to these advantages, textiles are particularly suitable as reinforcement for 3D printed concrete, where thin elements and freeform geometries are possible. In this article, a new type of textile reinforcement for the integration into 3D concrete printing is investigated: unidirectional carbon fiber tapes. Carbon fiber tapes are made from carbon fiber rovings by spreading. Three carbon fiber tapes are produced and used as reinforcement in concrete specimens subjected to four‐point bending tests. The results show that for a spreading factor of 2.2 (areal weight 136 g/m2), the flexural strength of the beams is increased by 125% compared to reference beams reinforced with unspread rovings. Further increase of the spreading factor does not increase flexural strength further as the failure mode changes from rupture to spalling.

Enhancement of mechanical behavior of resin matrices and fiber reinforced polymer composites by incorporation of multi-wall carbon nanotubes

Herein, to enhance the toughness of resins and tensile strength of fiber-reinforced polymers (FRPs), multi-wall carbon nanotubes (MWCNTs) were incorporated as a toughening material into resin matrices. The effects of the MWCNT addition on the fracture toughness (KIC) and mechanical properties of epoxy and vinyl ester resins, and the tensile strength (σr) and stiffness of impregnated basalt, carbon, and glass fiber rovings were systematically examined. The enhancement mechanism was studied by scanning electron microscopy (SEM). The enhancement in the tensile strength of the FRPs was predicted. The results showed that as compared to pure epoxy resin, the 0.3 wt% MWCNT-modified epoxy resin exhibited elevated KIC, tensile strength (σt), flexural strength (σf), and impact strength (αcU). Similar improvements were discovered for the MWCNT-modified vinyl ester resins. Concentrated tortuous textures due to the bonding and bridging effects of MWCNTs were observed on the fracture surface by SEM. The σr of the basalt, carbon, and glass rovings obviously increased with the addition of MWCNTs, owing to the combined action of restricted crack propagation and the promoted co-stress of fibers. Additionally, the σr of MWCNT-modified basalt and carbon rovings exhibited a lower dispersion, resulting in a higher guaranteed strength. The modification method proposed above can effectively improve the mechanical properties and design strength of FRP.

Capacitance measurements on integrated conductors for detection of matrix cracks in GFRP

For the reliable and cost-efficient application of glass fibre polymer composites in structural applications, knowledge of the damage state of the material during operation is necessary. Within this work, a structural health monitoring method based on in-situ electrical capacitance measurements is presented, which enables damage monitoring in glass fibre reinforced polymers. For this purpose, individual glass fibre rovings in a non-crimp fabric were replaced by carbon fibre rovings at regular intervals. Additionally, specimens with solid or stranded copper conductors were manufactured to gain insights into the influences of conductor material and composition. The modified fabrics were implemented as 90 ∘ layers of [0/904]s glass fibre polymer cross-ply laminates. To monitor the progressive damage, conductive rovings were contacted, forming the capacitor walls of interleaved capacitors. Carbon fibre conductors show higher sensitivity of the capacitance to crack formation than solid or stranded copper conductors. Capacitance decrease measured in-situ during tensile tests on specimens with carbon fibre conductors shows a high correlation with crack initiation, further crack formation and speed of crack evolution. An analytical model can describe the correlation based on the assumptions of an ideal plate capacitor. Thus, the structural health monitoring method developed in this work can reveal in-situ knowledge of the material damage state.

Oxygen plasma modification of carbon fiber rovings for enhanced interaction toward mineral-based impregnation materials and concrete matrices

The insufficient bond strength of carbon fibers (CFs) towards cementitious matrices limits at present their prospective application as CF-reinforcement in construction. In this investigation an oxygen plasma modification process was utilized to tailor the surface properties of CF rovings in achieving higher affinity towards mineral-based aqueous suspensions. A systematic study on various process parameters was performed to outline expedient treatment regimes. X-ray photoelectron spectroscopy, single fiber tensile tests, and Weibull-analysis delivered insights on the effects of plasma modification on the carbon fibers’ properties.Mineral-impregnated carbon fiber (MCF) reinforcement bars were produced and characterized by means of pullout tests. It was found that short plasma treatment time, high oxygen flow rates, low pressure, and long pulse duration improved the shear strengths of the MCF bonds on being extracted from the concrete matrix. Morphological analysis revealed that a higher oxygen concentration enables better wetting behavior towards the mineral matrices and, hence, yields higher bond strength.

Reinforcing carbon fibers as sensors: The effect of temperature and humidity

We investigated how temperature and relative humidity affects the electrical resistance of reinforcing carbon fibers in polymer composites. We used hybrid composites in which a tight, carbon fiber roving was laminated inside glass fiber-reinforced epoxy specimens. The electrical resistance of the carbon fibers was monitored continuously while the temperature or relative humidity was varied. The specific resistance was calculated in order to compare the different effects acting on the resistance of the carbon fiber. We found a relationship between temperature or relative humidity and specific resistance. As a result, carbon fibers can be used in different applications (for example in cure process monitoring). On the other hand, the effects should be compensated for when the resistance of the carbon fiber is measured in a health monitoring application (e.g. as an elongation sensor).

Technological Development of a Yarn Grip System for High-Speed Tensile Testing of High-Performance Fibers

Abstract Particularly in terms of carbon fiber (CF) rovings and further high performance fibers, it is a highly demanding task to clamp technical yarns with low elongations at break during high-speed tensile tests due to their sensitivity to shear stress. For fibers to be tested, a low elongation at break results in short testing times and requires high acceleration. In this paper, four different yarn grips that can be applied with various test machines will be introduced and compared to a wedge screw grip. By using most sensitive CF rovings, advantages and disadvantages of these gripping devices will be qualitatively evaluated by means of testing machines with test speeds of up to 20 m/s and strain rates of up to 200 s−1, respectively. Hence, the reproducibility and precision of test results were considerably enhanced by optimizing the geometry and mass of yarn grips. Moreover, theoretical approaches and calculations for the design of yarn grips suitable for test speeds of up to 100 m/s will be presented.

Mechanical properties of geopolymers reinforced with carbon and aramid long fibers

The paper presents the results of the study of geopolymer composites reinforced with carbon and aramid fibers. Geopolymers were made on the basis of fly ash activated with 10 mole sodium hydroxide solution with an addition of aqueous sodium silicate solution. The fibers were introduced in the form of a roving. Carbon fibers 800 tex and aramid fibers 805 tex were used. Additionally, to compare the influence of the number of fibers on the properties of geopolymer composites for carbon fiber, 1600 tex fiber was also used. The flexural strength of composites made with the fibers was tested. Fiber reinforced geopolymer composites showed a higher value of flexural strength than unreinforced ones. The higher value was noted for carbon fiber reinforced composites (800 tex) compared to aramid fiber roving composites (805 tex). The study also showed that the application of higher fiber mass in the case of carbon fiber roving does not bring the expected increase in mechanical properties of the composites. The use of carbon fiber roving (1600 tex) resulted in a lower flexural strength than in the case of 800 tex roving. Double increase of fiber mass in the composite caused a decrease in strength parameters.

Tailored fibre placement of carbon fibre rovings for reinforced polypropylene composite part 1: PP infusion of carbon reinforcement

Tailored fibre placement was utilised to create carbon fibre composite preforms, the preforms were impregnated with polypropylene (PP) through different methods and then was heat pressed into the final composite form. This part of the research focussed on three impregnation techniques; layered melt infusion, use of comingled rovings and PP dispersion using a PP emulsion product, the mechanical properties of the resultant composites were assessed. It was found that melt infusion of PP layers under the processing conditions did not allow satisfactory migration of PP through the preform, and that this had a strong negative effect on the bending strength of these composites. It was observed that preforms made using comingled yarns had a lower void volume. Composites with a combination of comingled rovings and emulsion deposited PP showed the highest bending strength. Interestingly the highest tensile strength was shown from composites made from pure carbon fibre rovings (i.e. not comingled) and emulsion PP deposit.

Bending load capacity of carbon fiber reinforced concrete beams as a function of fiber performance index (FPI)

Over the past several decades, textile reinforced concrete (TRC) materials have been developed due to their superior mechanical properties, corrosion resistance, lightweight application, and high load-bearing capacity. In this study, the effect of three main factors on bending load capacity of carbon fiber reinforced concrete (CFRC) beams is investigated; the number of reinforcements (carbon-fiber rovings), penetration of the cement within the fibers, and the post-cracking factor. The second and third factors are defined as the fiber performance index (FPI) for evaluating bending load capacity of CFRC beams. The best FPI for a different number of reinforcements was estimated using empirical values of bending load capacity of CFRC beams. The results were indicative of the efficiency and accuracy of the proposed FPI for a wide range of roving numbers, namely 2–24 with 800 tex as the titer. The post-cracking factor was suggested as 2.67 for TRCs and CFRCs materials, which are reinforced by rovings. In order to improve the FPI, the roving was impregnated partially with epoxy, which increased the maximum load capacity and displacement of the beams up to 26.68 and 23.24%, respectively. In addition, the impacts of roving numbers, the first factor, on the failure mode, load-bearing capacity, ductility, and toughness of the CFRC beams were investigated.

Wet Fiber Placement: A novel manufacturing technology for continuous fiber reinforced polymer composites

The novel Wet Fiber Placement process enables in-line resin impregnation of fiber rovings and direct placement with defined length, position, and orientation. Therefore, the main challenge is the conveying of the impregnated roving, which is limp and provides little friction. For this, a special arrangement of rollers exploiting belt friction is used. In this study, a prototype system is presented and used to give a first impression on the potential of the approach. Therefore, a 24 k carbon fiber roving, saturated with oil, is conveyed at different speeds while varying the winding scheme, the pre-tension, and the test time in order to investigate their influence on the force development, roving slip and fiber/matrix–volume ratio. It could be proven that even at speeds of 15 m/min and at pre-tensions of 60 N in-line impregnation as well as conveying is securely possible, with the slip being below 3%. Therefore, the number of windings and the winding scheme have the greatest influence, whereas pre-tension and conveying velocity have few/no influence on the process results. With an optimized arrangement, a fiber/matrix–volume ratio around 55% is possible.

Process development for the manufacture of fiber reinforced wood composites (FRWC)

In this study, the reinforcement of wooden beams with fiber-reinforced plastics (FRP) for restorative and constructive purposes was investigated. Two application-oriented processes were developed and evaluated for the production of static as well as dynamic highly stressed fiber reinforced wood composites (FRWC). For that purpose, spruce wood (Picea abies Karst.) was reinforced with carbon fiber and basalt fiber rovings and the static short-run behavior was tested by a four-point bending test. The results show a significant increase in bending stiffness (66%) and bending strength (54%) even for a small degree of reinforcement (3% and 6% by cross section). A parametric simulation model of the four-point bending test was established to predict the bending stiffness as well as to simulate both material and geometry parameters. The simulated and experimental results show good correlations.

Effect of carbon fiber winding layer on torsional characteristics of filament wound composite shafts

Composite materials are promising candidates as structural materials and substituting metals in extensive applications. Shafts are used in aerospace and automotive structures and hence replacing conventional shafts with composite material shafts is a viable option. Hollow shafts can be manufactured using filament winding technology employing hoop and helix winding layers. Filament winding technology offers several advantages such as continuous filaments through structure and capability for continuous manufacturing. Previously researchers have investigated composite shafts; however, this research elaborates the significance of type of winding layer on torsional characteristics. This paper reports the effects of carbon fiber winding layer on torsional characteristics of filament wound composite hollow shafts. Shafts were manufactured using filament winding technology with continuous carbon fiber roving and epoxy matrix material and tested using the torsional testing machine. The finite element (FE) simulations have been carried out with a general purpose commercial FE code, ABAQUS, to demonstrate shafts in torsional loading. The results revealed that values from torsional test correlate with developed finite element model. It was concluded that helix winding layer offers high hardness and more resistance to torsional forces as compared to hoop winding layer in filament wound composite shafts.

Improvement of high-velocity impact properties of anisogrid stiffened composites by multi-walled carbon nanotubes

The present study represents the influence of adding different weight fractions (0, 0.1, 0.25 and 0.4 wt.%) of multi-walled carbon nanotubes (MWCNT) on the high velocity impact behavior of anisogrid stiffened composite (AGSC) plates. AGSC plates were fabricated through hand lay-up method where E-glass woven fabrics and unidirectional carbon fiber rovings were used as fibrous reinforcement of ribs and skin, respectively. High velocity impact test was performed on these plates by cylindrical projectile with conical nose. Obtained results revealed that the maximum improvement of the high velocity impact properties of AGSC plates were obtained through addition of 0.4 wt.% of MWCNTs. Field emission scanning electron microscopy (FESEM) examinations of the fracture surfaces clearly indicated the improvement in the interfacial adhesion between the fibers and epoxy matrix in the case of the nanocomposite specimens. Also, it was observed that the addition of MWCNTs to the AGSC specimens led to reduce the damage area and increased the damage tolerance, considerably.

Mineral-Based Coating of Plasma-Treated Carbon Fibre Rovings for Carbon Concrete Composites with Enhanced Mechanical Performance.

Surfaces of carbon fibre roving were modified by means of a low temperature plasma treatment to improve their bonding with mineral fines; the latter serving as an inorganic fibre coating for the improved mechanical performance of carbon reinforcement in concrete matrices. Variation of the plasma conditions, such as gas composition and treatment time, was accomplished to establish polar groups on the carbon fibres prior to contact with the suspension of mineral particles in water. Subsequently, the rovings were implemented in a fine concrete matrix and their pull-out performance was assessed. Every plasma treatment resulted in increased pull-out forces in comparison to the reference samples without plasma treatment, indicating a better bonding between the mineral coating material and the carbon fibres. Significant differences were found, depending on gas composition and treatment time. Microscopic investigations showed that the samples with the highest pull-out force exhibited carbon fibre surfaces with the largest areas of hydration products grown on them. Additionally, the coating material ingresses into the multifilament roving in these specimens, leading to better force transfer between individual carbon filaments and between the entire roving and surrounding matrix, thus explaining the superior mechanical performance of the specimens containing appropriately plasma-treated carbon roving.

Multimetallic Electrodeposition on Carbon Fibers

Efficient lightweight design requires intelligent materials that meet versatile functions. One approach is to extend the range of properties of carbon fiber reinforced plastics (CFRP) by plating the fiber component. Electroplating leads to metalized layers on carbon fibers. Herein only cyanide-free electrolytes where used. Until now dendrite-free layers were only obtained using current densities below 1.0 A dm-2. In this work, dendrite-free tin and copper coatings were achieved by pre-metalizing the carbon fiber substrates. Furthermore, applying a combination of two metals with different sized thermal expansion coefficient lead to a bimetallic coating on carbon fiber rovings, which show an actuatory effect.