Carbon Fiber Length Research Articles

Green preparation of carbon fiber/liquid silicone rubber composites for flexible electrode

Stretchable flexible conductive polymer composites (flexible electrodes) had become a research hot spot. In this paper, two-component room-temperature vulcanized liquid silicone rubber (LRTV) and short carbon fibers (CFs) were mixed by mechanical blending without solvent to prepare a tensile self-reply composites with high conductivity. The relationships between the average length, length distribution and content of CFs and the performance of CFs/LRTV composites were investigated. When the CFs length was 100 μm, the composites achieved a high conductivity. The composites conductivity threshold was reached when the CFs content was 3 wt%. In addition, the composites could be used as a conductor to light the bulb when the CFs content reached 8 wt%. The conductivity remained stable during cyclic stretching with a strain of 8%. The breaking and reconstruction of the internal 3D conductive network in the composites during the stretching process were discovered. The obtained results revealed that CFs/LRTV composites can be used as highly effective, flexible, stretchable electrode materials for stretchable displays, electronic skin, personalized healthcare.

Mechanical Performance Optimization in Spray-Based Three-Dimensional-Printed Mortar Using Carbon Fiber

From the perspective of the features of effective vertical and overhanging construction, the spray-based three-dimensional (S-3D) mortar printing technology has promoted the application of 3D printing in construction fields. Carbon fibers were used to optimize the mechanical performance of S-3D printed mortar. The effects of carbon fiber volume (0%, 0.5%, 1.0%, 1.5%, and 2.0%) and length (3 and 5 mm) on the working properties, printing accuracy, mechanical properties, and microstructural properties of the S-3D printed mortar were studied comprehensively. The test results showed that the S-3D printed mortar with the 1.5 vol% and 3 mm length carbon fiber (L3-V1.5 specimen) showed optimal printing accuracy in the single-layer and accumulative thickness tests. The S-3D printed L3-V1.5 mortar had the maximum flexural strength, which increased by 53.06% and 39.96% at 7 and 28 days, respectively, more than those of its cast counterparts. In addition, the S-3D printing process enhanced the interlayer bonding strength, and the ultimate interlayer splitting strength of the S-3D printed L3-V1.5 mortar increased by 2.16% and 3.33% at 7 and 28 days, respectively, more than those of the cast mortar without carbon fibers. The S-3D printing process improved the carbon fiber alignment and compactness and, thus, the mechanical properties of the S-3D printed mortar.

Additive manufacturing and characterization of high temperature thermoplastic blends for potential aerospace applications

Here, we study the thermomechanical and microstructural properties of a carbon fiber (CF)-reinforced blend of poly ether ketone (PEEK) and polyether imide (PEI) used in the Fused Filament Fabrication (FFF) additive manufacturing (AM) process. The reinforced PEEK/PEI blend material was prepared by melt mixing in an extruder and used as filament feedstock for FFF printing and for the injection molding of test specimens for comparison purposes. The effect of the manufacturing process, CF reinforcement and mechanical testing temperature were investigated through mechanical tensile testing and microstructural analysis. Reinforced specimens printed in longitudinal direction demonstrated the highest modulus, 17.9 GPa, which was slightly more than the value of 16.9 GPa obtained for the injected specimens. The measured modulus was mostly constant up to 120 °C, while the ultimate tensile stress (UTS) showed an important drop from 129 MPa at 120 °C to 77.3 MPa at room temperature. Micro-tomography was executed, depicting porosity, carbon fiber length and orientation, for deeper understanding of the material microstructure and their effect on the mechanical performance. The microstructural analysis revealed that the porosity of the blend is ∼4%, the maximum fiber length is ∼600 μm, and the CFs are mainly aligned along the printing direction. According to our experimental measurements, our composite blend material shows a very strong potential for the aerospace sector, even for operating temperatures up to 120 °C.

Production of Thermoplastic Composite Filaments for Additive Manufacturing using Recycled Carbon Fibers

AbstractThe present work reports the use of recycled carbon fibers (rCF), obtained from pyro‐gasification treatment of carbon fibers reinforced polymers (CFRP), to produce a thermoplastic composite filament for additive manufacturing, in particular fused deposition modeling (FDM) process. Polylactic acid (PLA), a thermoplastic biobased and biodegradable polymer, is used as matrix for the composite filament, as it is the most common plastic used in FDM due to its good mechanical properties, stiffness, and strength. Upon production process optimization, filaments with rCF loadings of 5 and 10% wt are produced and analyzed. A particular attention is devoted to the evaluation of the production process on the carbon fibers (CFs) length and the study of the thermal and mechanical properties of the obtained composite materials.

Investigation of mechanical behavior and fracture energy of fiber-reinforced concrete beams and panels

This study quantifies the role of carbon fibers as micro-reinforcement in round panels to prevent and slow the formation of cracks. While carbon fiber-reinforced concrete (CFRC) has drawn considerable attention for use in pavements, the majority of CFRC performance assessment is limited to laboratory-scale samples which do not conform to the predominant failure mechanism, yield-line theory, for concrete pavements. In this study, the effects of carbon fiber content and length on flowability, fiber-matrix bond, and mechanical properties were studied and compared to polypropylene fiber. Analysis of the quadratic polynomial fitted surface plot helped to find the most effective fiber content and length. Composite theory was used to predict the flexural strength, and the result were compared to that of experimental results. The last phase consisted of concrete round panels tested under center-point bending in which the failure mechanism under yield line theory was analyzed. Analysis of Variance (ANOVA) model was finally adopted to compare the calculated modulus of rupture in beams and panels. The results showed beneficial effect of CFRC on pre-crack energy absorption, and their role as crack retarders was justified when the absorbed energy was compared to non-fibrous mixes. The residual flexural strength was also improved in beams and round panels reinforced with carbon fibers. Using the composite theory, the experimental-to-predicted flexural strength ratios in PAN-based carbon fibers were in the range of 1.11–1.34. However, the predicted strengths of mixtures with polypropylene and pitch-based carbon fibers were significantly higher than the experimental values.

Effect of Carbon Fiber Admixture and Length on Microwave Deicing Efficiency of Airport Road Surface Concrete

In order to improve the microwave deicing efficiency of airport road surface concrete, the method of incorporating carbon fiber materials of different doping amounts and lengths into concrete is proposed. The test method is optimized by using a fiber-optic temperature sensor and a self-developed open microwave deicing vehicle, and the effect of the coupling effect of different carbon fiber doping and length on the microwave deicing efficiency of concrete is studied. The results of the study show that the appropriate amount of carbon fiber blended into the concrete can significantly improve the microwave deicing efficiency, and the reasonable use of carbon fiber-modified concrete can achieve the purpose of efficient deicing of the airport road surface. By analyzing the temperature rise curve, temperature rise rate curve, deicing effect, and infrared thermography of the microwave deicing process, combined with the “heat generation-heat dissipation” theory, the microwave deicing is divided into four stages: concrete wave absorption, water layer formation, ice thinning, and ice breaking and ice melting. In the process of microwave deicing of concrete, changing the length of carbon fiber and the amount of doping will have a greater impact on the rate of temperature rise and deicing range, but the shape of deicing remains basically the same, mainly spindle-shaped. When the length of carbon fiber is short, it is not conducive to the absorption of microwave by concrete, and with the increase of fiber length and doping amount, the wave absorption performance of carbon fiber-modified concrete on the airport road surface is gradually improved; when the fiber length is 0.6 cm and the fiber doping amount is 2‰, the wave absorption performance is the best, and the deicing rate is 1.82 times of ordinary concrete, and the deicing area is 1.2 times of ordinary concrete.

Investigation the CF Based Conductive Asphalt Mixtures for Anti-icing

In recent years, researchers have been working on a new type of pavement called electrically conductive asphalt to be anti-icing. In this study, hot mix asphalt (HMA) stone mastic asphalt (SMA) specimens were prepared by adding carbon fiber (CF) in three different lengths (5-10-15 mm) and five different percent (0.1-0.2-0.3-0.4 and 0.5% by weight). Volume resistivity measurement and temperature changes of the specimens under constant voltage (20 V) were determined for each of the specimens. As a result of the study, it was determined that the CF properties and aggregate gradation difference were quite effective on the electrical conductivity, and the electrical conductivity properties also changed depending on the CF length and percentage in the mixtures. According to the electrical conductivity test results, it was concluded that 5 mm long CF specimens were more suitable for use in electrically conductive asphalt concretes (CAC), one of the lowest volumetric resistivity values in the literature was obtained. In addition, it was concluded that aggregate gradation is also effective on electrical conductivity.

Strengthening Effect of Short Carbon Fiber Content and Length on Mechanical Properties of Extrusion-Based Printed Alumina Ceramics.

Extrusion-based ceramic printing is fast and convenient, but the green body strength is too low, and the application prospect is not high. An extrusion-based printing method of alumina ceramics toughened by short carbon fiber is reported in this paper. The bending strength and fracture toughness of 3D-printed alumina ceramics were improved by adding short carbon fiber. The toughening effects of four carbon fiber lengths (100 μm, 300 μm, 700 μm, and 1000 μm) and six carbon fiber contents (1, 2, 3, 4, 5, and 6 wt%) on ceramics were compared. The experimental results show that when the length of carbon fiber is 700 μm, and carbon fiber is 5 wt%, the toughening effect of fiber is the best, and the uniform distribution of fiber is an effective toughening method. Its bending strength reaches 33.426 ± 1.027 MPa, and its fracture toughness reaches 4.53 ± 0.46 MPa·m1/2. Compared with extrusion-based printed alumina ceramics without fiber, the bending strength and fracture toughness increase by 55.38% and 47.56%, respectively.

Effect of de-sizing on the structural and mechanical properties of carbon fiber reinforced polypropylene composites molded by the novel direct fiber feeding injection molding technology

Carbon fiber reinforced thermoplastic composites are rapidly emerging as alternative materials for auto parts due to recyclability, excellent stiffness, and strength to weight ratio. In the present study, the influence of carbon fiber de-sizing on the structural and mechanical properties of the sized and de-sized Carbon Fiber Reinforced Polypropylene (CFPP) composites molded by the recently developed novel Direct Fiber Feeding Injection Molding technology was studied. The effect of carbon fiber de-sizing on the structural properties was studied from the fiber dispersion status, fiber orientation factor, fiber volume fraction, and the fiber length. The surface morphology of the sized and de-sized carbon fibers was studied from the Scanning Electron Microscopy (SEM) and Atomic Force Microscope images. The static mechanical properties were studied based on the tensile tests at different loading rate and temperature. The Dynamic Mechanical Analysis tests were conducted to analyze the dynamic viscoelastic behavior of the sized and de-sized CFPP composites. The SEM images were used to observe the failure mechanism. The preliminary results indicated that de-sized composites had better fiber dispersion as compared to the sized CFPP composites. It was found that de-sizing the carbon fiber surface does not significantly affect the carbon fiber length, fiber volume fraction, and fiber orientation in the CFPP composites. Also, the de-sized composites showed better static and thermodynamic mechanical properties caused by the enhanced fiber matrix interaction in CFPP composites as compared to the sized CFPP composites. [Formula: see text]

An Investigation of the Properties of Expanded Polystyrene Concrete with Fibers Based on an Orthogonal Experimental Design.

Expanded polystyrene (EPS) concrete is commonly used as the core material of commercial sandwich panels (CSPs). It is environmentally friendly and lightweight but has poor strength. Adding fibers can improve the microstructure of EPS concrete and reduce the weakening effect of EPS beads on the mechanical properties of concrete. An orthogonal experimental design (OED) was used in this paper to analyze the influence of length and content of polypropylene fiber (PF), glass fiber (GF), and carbon fiber (CF) on the physical and mechanical properties and micromorphology of EPS concrete. Among them, CFs have the most apparent impact on concrete and produce the most significant improvements in all properties. According to the requirements of the flexural performance of CSPs, the splitting tensile strength was taken as the optimization index, and the predicted optimal combination (OC) of EPS concrete with fibers was selected. The variations in the material properties, mechanical properties, and microstructure with age were analyzed. The results show that with increasing age, the dry density, compressive strength, and splitting tensile strength of concrete are markedly improved relative to those of the CSP core material and the control case (CC), and even the degree of hydration is improved.

Understanding the Role of Carbon Fiber Skeletons in Silicone Rubber-Based Ablative Composites.

At present, silicone rubber-based ablative composites are usually enhanced by carbon fibers (CFs) to protect the case of solid rocket motors (SRMs). However, the effect of the CFs’ length on the microstructure and ablation properties of the silicone rubber-based ablative composites has been ignored. In this work, different lengths of CFs were introduced into silicone rubber-based ablative composites to explore the effect of fiber length, and ceramic layers of various morphologies were constructed after ablation. It was found that a complete and continuous skeleton in ceramic layers was formed by CFs over 3 mm in length. In addition, the oxyacetylene ablation results showed that the linear ablation rate declined from 0.233 to 0.089 mm/s, and the maximum back-face temperature decreased from 117.7 to 107.9 °C as the length of the CFs increased from 0.5 to 3 mm. This can be attributed to the fact that successive skeletons concatenated and consolidated the ceramic fillers as well as residues to form an integrated, robust, and dense ceramic layer.

The effect of length and inclination of carbon fiber reinforced polymer laminates on shear capacity of near‐surface mounted retrofitted reinforced concrete beams

AbstractThis study undertakes a comprehensive investigation of the shear behavior of reinforced concrete (RC) beams strengthened by near surface mounted (NSM) carbon fiber reinforced polymer (CFRP) laminates. Different strengthening configurations were employed by varying the length and inclination angle of the CFRP laminates. Results indicated that NSM‐CFRP strengthening increased the load‐carrying capacity, ductility, stiffness, and toughness from 8% to 41%, 9% to 78%, 24% to 159%, and 22% to 254%, respectively. Results also confirmed that as the CFRP laminate length decreases, the efficacy of the strengthening process increases, where the load‐carrying capacity, ductility, stiffness, and toughness improved from 8% to 19%, 10% to 21%, 8% to 68%, and 26% to 119%, respectively. Also, the comparative results revealed that specimens strengthened with 45°‐inclined CFRP laminates versus those strengthened with vertical laminates had higher load‐carrying capacity (2%–10%), ductility (1%–35%), stiffness (24%–40%), and toughness (13%–32%). Two analytical formulations to predict the contribution of the possible distinct NSM‐CFRP shear strengthening configurations for the shear resistance of RC beams were considered. Results indicated an agreement between the experimental and the analytical results for both formulas, where the average values for the safety factor, k, were 0.80 and 0.73, with corresponding values of standard deviation of 0.195 and 0.125, respectively.

Study of the Residual Length of Discrete Carbon Fibers in Polyetherimide Based Composites for 3D-Printing

The influence of the multiplicity of extrusion and melt viscosity on the residual length of discrete carbon fibers in composites based on polyetherimide for 3D-printing is estimated. A technique for measuring the residual length of carbon fibers in composites is proposed. The residual length of carbon fibers in composites containing from 10 to 40% fibrous filler with different initial linear dimensions has been determined. It was found that the addition of a melt viscosity modifier to a carbon-filled composite helps to maintain the linear dimensions of the fiber filler particles, thereby increasing the physical and mechanical properties of the material.

Design of a vane mixer with controlled extensional/shear strength ratio and its application for carbon fiber/polyamide 6 composites

AbstractIn this work, a novel melt mixing method and its corresponding mixing device are developed. The extensional/shear strength ratio of the device can be controlled by adjusting its eccentricity. The structure and working principle of the device are introduced in detail. Carbon fiber (CF)/polyamide 6 (PA6) composites are prepared via this novel mixing device. The influences of eccentricity and mixing time on the morphology, CF length, thermal, mechanical, and electrical properties of CF/PA6 composites are studied. Scanning electron microscopy results show that CFs uniformly disperse in the matrix and interfacial adhesion between CFs and PA6 is improved. It is observed that CF length and its distributions can be optimized by changing eccentricity. The maximum average fiber length is about 351 μm. Differential scanning calorimetry results exhibit that the Xc increases 6.5% when eccentricity is 2 mm. Mechanical test results show tensile strength and modulus increase first and then decrease with the increasing eccentricities or mixing time. Electrical property measurement shows an obvious increase when eccentricity is 2 mm due to good fiber dispersion and long fiber retention length. The experimental results indicate that the novel mixing method and its corresponding apparatus provide an environment‐friendly and effective way to prepare polymer‐based composites.

Effect of Carbon Fiber on Microwave Deicing Efficiency of Pavement Concrete

Snow and icing on roads in winter will bring serious consequences to traffic safety. Microwave deicing, as a new type of environmentally friendly road surface deicing method, has the characteristics of environmental protection, pollution-free, and high ice removal rate, but its low deicing efficiency limits its use. Carbon fiber has good electrical and thermal conductivity, wear resistance, etc., and can provide a new composite material for road surface deicing. Taking carbon fiber concrete as the research object, the effect of different carbon fiber length on the microwave heat absorption efficiency of concrete is studied. The results found that: as the length of carbon fiber increases, the temperature rise at the same time increases exponentially, the higher the efficiency of carbon fiber concrete for absorbing and heating.

Effects of A, B, and S components on fiber length distribution, mechanical, and impact properties of carbon fiber/ABS composites produced by different processing methods

AbstractCarbon fiber/ABS composites with different acrylonitrile, butadiene, and styrene components were produced via extrusion/injection and long fiber thermoplastic (LFT)/injection molding processes, respectively. The effect of the components on fiber length distribution, tensile, flexural, impact, and dynamic mechanical properties of the composites was investigated. The properties of carbon fiber/ABS composites produced using 12 mm‐long LFT pellets were markedly higher than those produced using extruded pellets made with 12 mm‐long chopped carbon fibers. Uses of LFT pellets were preferable to enhancing the mechanical properties of carbon fiber/ABS composites. The tensile, flexural, and dynamic mechanical properties were increased in order of ABS750sw > ABS720 ≥ ABS780 > ABS740, whereas the impact strength was increased in order of ABS740 > ABS780 > ABS720 ≈ ABS750sw. Less carbon fiber damages and less carbon fiber length degradation upon LFT processing resulted in longer fiber length distribution and higher fiber aspect ratio in the composites with LFT pellets, indicating a beneficial reinforcing effect, which was responsible for the increased mechanical properties of ABS composites, particularly with ABS750sw. The results were agreed with each other, significantly depending on the A, B, and S components, being supported by fiber length distribution, fiber aspect ratio, and fracture surfaces.

A Comparative Study of Pellet-Based Extrusion Deposition of Short, Long, and Continuous Carbon Fiber-Reinforced Polymer Composites for Large-Scale Additive Manufacturing

Abstract Pellet-based extrusion deposition of carbon fiber-reinforced composites at high material deposition rates has recently gained much attention due to its applications in large-scale additive manufacturing. The mechanical and physical properties of large-volume components largely depend on their reinforcing fiber length. However, very few studies have been done thus far to have a direct comparison of additively fabricated composites reinforced with different carbon fiber lengths. In this study, a new additive manufacturing (AM) approach to fabricate long fiber-reinforced polymer (LFRP) was first proposed. A pellet-based extrusion deposition method was implemented, which directly used thermoplastic pellets and continuous fiber tows as feedstock materials. Discontinuous long carbon fibers, with an average fiber length of 20.1 mm, were successfully incorporated into printed LFRP samples. The printed LFRP samples were compared with short fiber-reinforced polymer (SFRP) and continuous fiber-reinforced polymer (CFRP) counterparts through mechanical tests and microstructural analyses. The carbon fiber dispersion, distribution of carbon fiber length and orientation, and fiber wetting were studied. As expected, a steady increase in flexural strength was observed with increasing fiber length. The carbon fibers were highly oriented along the printing direction. A more uniformly distributed discontinuous fiber reinforcement was found within printed SFRP and LFRP samples. Due to decreased fiber impregnation time and lowered impregnation rate, the printed CFRP samples showed a lower degree of impregnation and worse fiber wetting conditions. The feasibility of the proposed AM methods was further demonstrated by fabricating large-volume components with complex geometries.

Application of Secondary Carbon Fiber for Reinforcing Composite Material Based on Alkali-Activated Blast-Furnace Slag

The potential for using secondary carbon fiber, recovered from aviation carbon fiber wastes, for reinforcing composite materials based on blast-furnace slag activated by a sodium silicate solution is evaluated. The influence of the concentration and length of the secondary carbon fiber on the structure, physicomechanical properties, and nature of the fracture of dispersion-reinforced composites was investigated.

Experimental investigation on mechanical properties of clay soil reinforced with carbon fiber

Using environmentally friendly, durable, and effective measures to reinforce clay soil are important in geotechnical engineering. This study investigated the mechanical performance of clay soil reinforced with carbon fibers (CF). Unconfined compressive strength tests were performed on soil samples under their optimum water content. The effects of CF length and content on shear strength, failure mode and stress–strain behavior of the reinforced soil samples were examined. The influence of CF on the cohesion and internal friction angels of specimens were also analyzed. Besides, the microstructures of the composite before and after the shear tests were examined by the scanning electron microscopy (SEM). The tests results demonstrated that the addition of CF can significantly improve the shear strength and cohesion of clay soil. Among all the samples, it is believed that using 3 wt% content of 6 mm CF can offer the best effect on strength improvement as the fibers can be uniformly dispersed in soil specimens and their length is long enough to create an interlocking network between soil particles that restrained the soil movement when subjected to external loads.

Flexural Properties and Low-Cycle Bending Fatigue of Anisotropic Carbon Fiber Mat Reinforced Composites

The carbon fiber/polypropylene (CF/PP) nonwoven fabrics were manufactured by carding process, lay-up process and needle punched process. After hot pressing the nonwoven fabrics, the CF/PP composites were mold. CF/PP composites with carbon fiber lengths of 50 mm and 70 mm was prepared respectively. The 3-point bending test and the low-cycle bending fatigue test (LCBF) at constant stress of 55%, 70% and 85% of original flexural strength were performed. The results showed that the ratio of transverse direction (TD)/machine direction (MD) flexural modulus of CF50 and CF70 was 1.55 and 2.35, which indicated the composites exhibited anisotropic property. The longer the fibers were, the easier they were to be oriented. The effect of low cycle bending fatigue (LCBF) with 55% and 70% stress level on flexural properties was not obvious. The LCBF of 85% stress level has an obvious influence, and some samples have broken before reaching 30 times of fatigue. Optical observation shows that with the increase of fatigue stress level, the crack becomes deeper, and the bending modulus and strength decrease obviously.