Strength Of Carbon Fiber Composites Research Articles

Tensile Property of Carbon Reinforced Epoxy Composites for Different Directions

Due to higher chemical stability, higher strength/stiffness, lower density, and good corrosion resistance, carbon fiber-reinforced polymeric composites (CFRPs) have been increased numbers of areas such as aircraft industry, automotive industry, ship making and packing industry, turbines, compressors, wind blades besides implant applications. Epoxy based composites are developed using carbon fiber reinforcements by vacuum controlled resin transfer (VARTM) molding method by Twill carbon fiber [K3T] with 200 gr and Plain carbon fiber [K3P] with 200 gr. Composite plates are produced in the dimension of 500 mm x 500 mm with 0.8 mm thickness. According to the ASTM D3039, standard test samples are cut with CNC machine. Tensile tests are conducted at three different fiber directions like 00-450- 90o, respectively. Their mechanical properties are determined. Experimental results indicated that fiber direction significantly affected the tensile behavior of tested samples. Average tensile strength of CFRPs was obtained around 470 MPa for 0 degree to x-axis, and testing lasted about 44 s. For 90o direction, tensile strength of carbon fiber composites reached to 520 MPa, which is slightly higher than the previous one while trial period was around 50 s. For 45o tested samples, a completely different behavior was observed because stress-strain curve showed the elastic-plastic behavior. Its tensile strength measured was about 120 MPa average value while the trial lasted about 145 s.

Testing the Bending Strength of Carbon Fiber Composites using the vacuum infusion and vacuum bagging method on the UAV Skywalker 1900 Fuselage Material

The purpose of this study was to determine the bending strength of carbon fiber composite materials with lycal epoxy resin on the Skywalker 1900 UAV. Composites will be made for test specimens with carbon fiber combined with lycal resin using vacuum infusion printing and vacuum bagging methods. From these two methods a sample of specimens will be made for testing using a bending test using the three point bending method to determine the bending strength value of the fuselage material. As for another test, namely microphotos, the process of observing this microstructure can find out how the shape, size, and distribution of second phase particles have an important role in knowing the properties of the material itself. The results of the test specimens were compared between vacuum infusion printing and vacuum bagging and then the best value was sought between the two methods. The results were obtained after testing where the two methods of printing and micro-photos obtained the best results in vacuum bagging. In the vacuum bagging process, the highest value was found in specimen b2 with a bending stress value of 1201.90Mpa and the lowest yield was found in specimen i1 with a bending stress value of 1017.74Mpa. Then the micro photo test can be seen in the vacuum bagging printing process, the penetration of the resin in bagging to the fiber is better.

TİTANYUM DİOKSİT VE TALK'IN KOMPOZİT MALZEMELERİN ÇEKME DAYANIMI ÜZERİNE ETKİSİ

Epoxy was incorporated with titanium dioxide and talc at different concentrations (0, 0.5, 1, 2, and 4 wt%), and then that mixture was combined with carbon fiber via a hand lay-up process. The mechanical properties of the composites were determined using universal tensile testing. The tensile test results revealed that the mechanical properties of the polymer matrix composites were increased as a function of talc and titanium dioxide concentrations. The best tensile strength of the composite was obtained from the 0.5% talc and 1% titanium dioxide sides. Increasing the weight ratio of talc 1%, 2%, and 4% and 0.5%, 2%, and 4% of titanium dioxide in composite production doesn’t exhibit a significant difference. Tensile testing behavior of talc and titanium dioxide reinforced composite specimens shows better results compared to unreinforced carbon fiber composites. As a result, this study provides a detailed explanation of how to improve the strength of carbon fiber composites.

Enhanced longitudinal compressive strength of CFRP composites through matrix stiffening via flexible/rigid epoxide grafted silica: A combined analysis of simulation and experiments

An Epoxy matrix with a high elastic modulus is designed via flexible poly (ethylene glycol) diglycidyl ether (PEGDGE)/rigid cycloaliphatic epoxy (CE) grafted silica to fabricate carbon fiber composites with a high longitudinal compressive strength by theoretical and experimental methods. The relationship between the grafting chains on the silica surface and the interphase of silica reinforced resin matrix is derived from molecular dynamic (MD) simulations and experiments. The correlations of the interphase and matrix modulus with the longitudinal compressive strength of their carbon fiber composites are investigated by combining analytic models and experimental analysis. The results show that the stretched rigid CE chain on the silica surface induces inter-penetration and interfacial reaction of the grafting chains and epoxy matrix, leading to an enlarged thickness and enhanced modulus of interphase in the silica reinforced resin matrix. According to Yasser's assumption, the modified Halpin-Tsai model and experimental verification, the enhanced modulus of the interphase resulted in a higher elastic modulus of CE grafted SiO 2 (SiO 2 -CE) reinforced resin matrix. A further contribution is that the delay of fiber buckling and decline of fiber rotation in the kinking region are attained from the higher modulus matrix, thereby providing an improvement of longitudinal compressive strength of carbon fiber composites.

SiC Nanowire-Si3N4 Nanobelt Interlocking Interfacial Enhancement of Carbon Fiber Composites with Boosting Mechanical and Frictional Properties.

Carbon fiber composites composed of carbon fiber and pyrolytic carbon (PyC) matrix have great potential application in the brakes of aircrafts, where the combination of high mechanical strength and excellent frictional properties are required. In this work, two-component silicon-based interlocking enhancements were designed and constructed into carbon fiber composites for boosting the mechanical and frictional properties. Specially, silicon carbide nanowires (SiCnws) and silicon nitride nanobelts (Si3N4nbs) could form interlocking architectures, where SiCnws are rooted firmly on the carbon fiber surface in the radial direction and Si3N4nbs integrate the PyC matrix with carbon fibers together via a networked shape. SiCnws-Si3N4nbs not only refine the PyC matrix but also promote the bonding of the fiber/matrix interface and the cohesion strength of the PyC matrix, thus enhancing the mechanical and frictional properties. Benefiting from the SiCnws-Si3N4nbs synergistic effect and interlocking enhancement mechanism, the interlaminar shear strength and compressive strength of carbon fiber composites increased by 88.41% and 73.40%, respectively. In addition, the friction coefficient and wear rate of carbon fiber composites decreased by 39.50% and 69.88%, respectively. This work could open up an interlocking enhancement strategy for efficiently fabricating carbon fiber composites and promoting mechanical and frictional properties that could be used in the brakes of aircrafts.

High‐performance thermosets with tailored properties derived frommulti‐armstared vanillin and carbon fiber composites

AbstractVanillin, a rigid compound can be separated from lignin, is a promising sustainable candidate for industrial and high performance polymers, while synthesis of hexa‐epoxies is challenging. Meanwhile, carbon fiber reinforced bio‐based polymers combining high performance are more difficult to be achieved because of the contradictions of liquidity and high rigidity in the polymer structure and performance. In this paper, a novel hexa‐epoxy functionalized bio‐based epoxy resin (HPVIGEP) with a multi‐arm star structure, which simultaneously reduced the viscosity and improved thermo‐mechanical properties. The rheological behavior analysis results of HPVIGEP indicated that the viscosity was 3406.9 mPa·s at 25°C, which dramatically decreased by 75.8% compared to DGEBA (14,096 mPa·s), leading to excellent processability and adaptability. At the same time, the study on mechanical properties revealed that the cured HPVIGEP manifested 30.6%, 33.7% and 49.0% in higher tensile strength, tensile modulus and storage modulus (30°C) than of cured commercial epoxy, respectively. The tensile strength and flexural strength of carbon fiber composites which were applied HPVIGEP were increased by 9.3% and 10.9%, respectively. In a word, this work provides the promise for the application of environmentally friendly bio‐based composite materials.

Effects of Oxygen Plasma Treatments on Surface Functional Groups and Shear Strength of Carbon Fiber Composites

The morphology and chemical function of surfaces strongly influence adhesion at interfaces within carbon fiber composites (i.e., carbon fiber-reinforced polymer) and the mechanical strength of the ...

Enhancing functionalities in carbon fiber composites by titanium dioxide nanoparticles

Carbon fiber composite's high specific strength makes it incredibly useful for structural applications. However, their low strain-to-failure can be problematic in structural applications that can potentially see high strain conditions or high fatigue cycles resulting in sudden, catastrophic failure. This is further complicated by damage manifesting within the composite thus not showing damage indicators on the surface. Therefore, monitoring the structural integrity and strain history of the composite in application by itself―while maintaining positive composite performance―is vital to ensure safe operation. Here, a homogeneous dispersion of TiO2 nanoparticles on carbon fiber is demonstrated to generate a piezoresistive carbon fiber polymer matrix composite with enhanced self-sensing capabilities. The nanoparticle-embedded composites also exhibited superior strength and damping potential compared to the nanoparticle-free composites. The apparent interlaminar shear strength increased by up to 15% and the damping loss factor increased by an average of 150% while the piezoresistive sensitivity increased by up to 180% with the addition of a small weight fraction of nanoparticles to the fiber surface. These results demonstrate an approach to simultaneously improve the sensing capabilities, damping behavior and mechanical strength of carbon fiber composites by simply adding nanoparticles in the fiber sizing using a commercially scalable deposition method.

Experimental and analytical investigation on the interlaminar shear strength of carbon fiber composites reinforced with carbon nanofiber z-threads

This paper combines an experimental study of the interlaminar shear strength (ILSS) and fracture behavior of CFRPs reinforced with carbon nanofiber (CNF) z-threads (i.e., ZT-CFRPs) together with an analytical model to explain and predict the shear behaviors improved by the CNF z-threads. The ZT-CFRP prepreg was manufactured from resin film containing electrical-field-aligned CNFs by using a modified hot-melt flow-transfer process. The short-beam shear (SBS) test was conducted on the ILSS of ZT-CFRP laminates together with a microscopic morphology study to understand the roles of the CNF z-threads during the shear fracture process. The study revealed the significance of the alignment of the CNFs to increase the ILSS of CFRP laminates. It was shown that CNF z-threads statistically significantly increased the ILSS and the required shear fracture work of CFRPs when compared to the unmodified CFRP and the CFRPs reinforced with randomly dispersed CNFs due to energy transfer and mechanical interlocking from the CNF z-threads. Furthermore, calculations showed that CNF z-threads reduce unwanted stress concentrations, kIC during the double-notch shear (DNS) test. The analytical model helps to understand the interlaminar shear behavior of ZT-CFRPs further and is useful to predict additional experimental data and guide material design in the future.

Multi-scale structure construction of carbon fiber surface by electrophoretic deposition and electropolymerization to enhance the interfacial strength of epoxy resin composites

In order to improve the interfacial strength of carbon fiber composites, a simple and efficient carbon fiber/graphene oxide (GO)/polymer multi-scale reinforcement material was prepared by electrophoretic deposition (EPD) and in-situ electropolymerization technique. The effects of surface treatment on the microstructure of CF and the properties of composites were systematically studied. Microscopic image revealed a tight and uniform coverage of the GO/polymer, which significantly increased the physical and chemical binding sites of the fiber surface, thereby improving wettability and mechanical interlocking with epoxy resin. In addition, the GO/polymer multiscale structure on the fiber surface can be regulated by adjusting the electropolymerization time. The optimal interlaminar shear strength (ILSS) of the composites with an electropolymerization time of 120 s (CF-GO-EPI120s) was 61.9 MPa, which is 37.6% higher than that of original carbon fiber reinforced composites (45 MPa). Moreover, the tensile strength of carbon fiber monofilament was increased from 3.01 to 3.22 GPa. The failure surface of interlaminar shear strength test and dynamic mechanical properties of the composite confirmed the improvement of interface properties and formation of a good interfacial layer. This work shows that EPD of GO and electropolymerization is a simple and efficient method for the preparation of carbon fiber composites with good interfacial properties, and the process is simple and continuous, which is a potential application in industry.

Improving impact resistance and residual compressive strength of carbon fibre composites using un-bonded non-woven short aramid fibre veil

Laminar carbon fibre composites with weak ply interfaces were toughened with ultra-thin (less than 20 μm) un-bonded non-woven Short Aramid Fibre (SAF) veils in the form of home-made pre-pregs. The effects of SAF veil on impact behaviour and compressive strength after impact of Carbon Fibre Reinforced Polymer laminates with multiple ultra-thin SAF interfacial layers were investigated. Optical observation and X-ray micro-computed tomography were employed for intact inspection of external and internal damage after high energy penetration impact. 50.8% decrease in back-face deflection and inhibited in-plane delamination growth were seen when compared with unmodified laminates. Compression after impact tests were performed after low energy impact to assess damage tolerance. SAF veils increased the residual compressive strength by 38.6% and changed the damage mode from delamination dominated fracture to shear failure.

Bond strength of carbon fiber composites glued to concrete surface

This paper describes an analytical study about the bond between concrete and glued carbon fiber composites (CFCs) using data of 2 experimental researches. A total of 27 double compression‐tension tests were carried out on specimens with 2 concrete cubes (fixed and movable) connected by carbon fiber strips on opposite sides. The variables were concrete strength, with the evaluation of 9 specimens with strength of 20.5 to 38.1 MPa, with monotonic loading and smooth surface for all specimens, and 18 specimens with strength of 23.2 to 40.8 MPa, with monotonic loading and loading/unloading cycles and different concrete surfaces (smooth face and rough face). The test results showed that the ultimate bond stress slightly varies according to concrete strength in the analyzed zone. The strains of CFCs and concrete were measured, allowing the calculation of bond stress and the corresponding mean strain, which were compared with the values obtained by the expression given in the international codes. The prediction of the old expression applies to steel plates strengthening method, and the results of a more recent expression of CFC glued to concrete given by fib Bulletins and Model Code 2010 are compared with test results. The experimental results provided graphs and correlation curves for bond stress vs maximum strain, energy of fracture vs bond stress and a relationship between the mean shear strain and concrete strength. The expression for fracture energy given by fib Bulletins and Model Code 2010 varies with concrete strength fc and a reasonable agreement with test data was achieved.

Non-contact visualization of fiber waviness distribution in carbon fiber composites using eddy current testing

Fiber waviness is a process-induced defect that greatly decreases the compressive strength of carbon fiber composites. In this study, we developed eddy current techniques that enable non-contact visualization of waviness distribution. To visualize in-plane waviness in a carbon fiber composite, we visualized the path of eddy current flowing along the carbon fiber by measuring the magnetic field. Finite element analyses show that the shape of the in-plane waviness can be visualized in the distribution of the magnetic field from the eddy current. However, with increasing distance between the surface of the tested material and measurement plane, the visualization increasingly underestimates the in-plane waviness angle. To avoid this underestimation, we propose a magnetic imaging method that can reconstruct the magnetic field at the surface. The surface magnetic field was reconstructed by using the magnetic field data measured away from the surface. Experiments were performed on a cross-ply laminate with artificially induced in-plane waviness. The distribution of in-plane waviness can be successfully visualized from the measured magnetic field. Using this magnetic field imaging method to enable non-contact measurements, the angle of waviness can be measured with an error of only 1°.

Adhesive force measurement between HOPG and zinc oxide as an indicator for interfacial bonding of carbon fiber composites.

Vertically aligned zinc oxide (ZnO) nanowires have recently been utilized as an interphase to increase the interfacial strength of carbon fiber composites. It was shown that the interaction between the carbon fiber and the ZnO nanowires was a critical parameter in adhesion; however, fiber based testing techniques are dominated by local defects and cannot be used to effectively study the bonding interaction directly. Here, the strength of the interface between ZnO and graphitic carbon is directly measured with atomic force microscopy (AFM) using oxygen plasma treated highly oriented pyrolytic graphite (HOPG) and an AFM tip coated with ZnO nanoparticles. X-ray photoelectron spectroscopy analysis is used to compare the surface chemistry of HOPG and carbon fiber and to quantify the presence of various oxygen functional groups. An indirect measurement of the interfacial strength is then performed through single fiber fragmentation testing (SFF) on functionalized carbon fibers coated with ZnO nanowires to validate the AFM measurements. The SFF and AFM methods showed the same correlation, demonstrating the capacity of the AFM method to study the interfacial properties in composite materials. Additionally, the chemical interactions between oxygen functional groups and the ionic structure of ZnO suggest that intermolecular forces at the interface are responsible for the strong interface.

Engineered Interface Chemistry to Improve the Strength of Carbon Fiber Composites Cured by Electron Beam

A reactive sizing was designed to achieve high levels of interfacial adhesion and improved mechanical properties with a carbon fiber–acrylate system cured by electron beam (EB). The sizing was made of a partially cured epoxy sizing with a high density of pendant functional groups (acrylate functionality) to facilitate covalent bonding with the matrix. The interlaminar shear strength improved from 61 to 81 MPa (+33%) without postprocessing, reaching a shear strength similar to that of the same system cured by a thermal treatment. Observation of the fracture profiles clearly highlighted a change in the fracture mechanism from a purely adhesive failure to a cohesive failure. To the best of our knowledge, such improvements of the mechanical properties of carbon fiber composites cured by EB, without any postcure, have not been reported previously. This constitutes a breakthrough for the industrial development of EB curing of composites.

Effect of sizing agent on interfacial shear strength of carbon fibre composites

The influence of two types of sizings (3#, 4#) on the surface of carbon fibres, and interface of carbon fibre composites were investigated. It was found that the surface topography of carbon fibres studied appeared to consist of grooves along the fibre axial direction. Sizing decreased the roughness of fibres surface, and the surface roughness value (Ra) for the 3# sized fibre was higher than that of the 4# sized fibre. X-ray photoelectron spectroscopy (XPS) result shows that the percentages of functional group –C–OH or –C–OR on the 4# sized fibre was less than that of 3# sized fibre, but the percentages of functional group containing oxygen -C = O on the 4# sized fibre was more than that of 3# sized fibre. The 4# sizing can improve the soakage of LY-1 epoxy resin to carbon fibre when compared to the 3# sizing. In addition, the IFSS of 4# sized fibre/LY-1 epoxy resin monofilament composite was 44·66 MPa, presenting 120% higher than 3# sized fibre. Therefore, 4# sized fibre has a stronger bond with the resin matrix compared with 3# sizing fibre.

Reliability-based design of blast-resistant composite laminates incorporating carbon nanotubes

Research efforts have reported on the ability of carbon nanotubes (CNTs) to enhance the stiffness and strength of carbon fiber composites. Systematic design of blast-resistant composites requires considering CNTs–carbon composites characteristics and the uncertainty of blast events. This article suggests a systematic reliability-based design approach where system reliability is used to compute the probability of failure of a composite laminate. A case study for the design of a five-layer composite laminate incorporating CNTs and subjected to uncertain blast event is demonstrated. 0.5–1% CNTs contents by weight seem capable of significantly reducing the composite probability of failure during blast.

A method for the chemical anchoring of carbon nanotubes onto carbon fibre and its impact on the strength of carbon fibre composites

This article proposes an alternative way to use carbon nanotubes to improve the performance of carbon fibre-reinforced composites. A chemical process, based on esterification of surface groups, is used to anchor nanotubes onto carbon fibre surface. Anchored nanotubes form a network surrounding the carbon fibres. After CNT anchoring, the tow is impregnated with an epoxy resin and tensile tests are performed on this minicomposite sample. By enhancing matrix properties and fibre/matrix interface, the CNT network has a significant influence on the composite strength.

Fatigue strength of carbon fibre composites up to the gigacycle regime (gigacycle-composites)

Knowledge of the fatigue strength is necessary for design purposes also at very high numbers of load cycles. While static properties and fatigue strength curves in the low, medium and high cycle fatigue regime 1 1 Definitions of the different fatigue regimes are here used as follows: low cycle, 1−5×10 4; medium cycle, 5×10 4–5×10 6; high cycle, 5×10 6–5×10 7; gigacycle, 5×10 7–1×10 9; run out, 1×10 9. are well investigated, only few data beyond 5×10 6 cycles (gigacycle fatigue regime) are available. In a first part of this paper, the fatigue strength for various laminates of a carbon fibre reinforced thermoplastic material (AS4/APC-2) was investigated experimentally up to 10 9 cycles. The specimen shape was optimised for tensile, compression and bending load cases to get significant fatigue data. Various candidates of fatigue damage indicators have been evaluated and monitored continuously during these fatigue tests. A general trend of the fatigue strength reduction could be observed for the majority of laminates and loading conditions beyond 5×10 6 load cycles. A fatigue limit (endurance limit) was not found. Significant changes of the stiffness, resonance frequency and temperature could be measured. However, a correlation between these signals and the final failure of the specimen could not be found. In a second part, a fatigue design procedure was developed, which allows predicting the fatigue life of a typical structural detail under bending loads. Various failure criteria used in the static mode have been extended to fatigue loads. In a verification test program, the fatigue strength of a waisted beam has been assessed for bending loads and compared with the predicted fatigue life.

Here Comes Hypercar!

Despite the fact that the price of gasoline seems stuck around $2.00 per gallon, gas-guzzling SUVs and pickups remain as popular as ever among Americans. The United States produces 25% of the world’s greenhouse gas emissions; cars and light trucks account for around 20% of the nation’s energy-related greenhouse gas emissions, according to the U.S. Energy Information Administration. It would appear that a gas-saving, nonpolluting car for the U.S. masses will need to be something that even car enthusiast magazines could applaud. It will need to equal or beat conventional cars in handling, performance, size, safety, and amenities, and do so at a competitive cost. It’s a tall order, but Amory Lovins, chief executive officer of the nonprofit Rocky Mountain Institute (RMI) in Snowmass, Colorado, thinks he may have just the car to meet it: the Hypercar®. The latest version of Lovins’s Hypercar concept is a detailed virtual design illustrating an SUV crossover vehicle that would fully compete with today’s midsize entry-level luxury SUVs. Powered by a hybridized hydrogen fuel cell, the concept, dubbed Revolution, would achieve Environmental Protection Agency mileage ratings equivalent to 108 miles per gallon (mpg) of gasoline; as a Prius-like gasoline hybrid, 62 mpg, and with a good nonhybrid gasoline engine, 45 mpg, according to extensive RMI simulations. The gasoline hybrid version could sell profitably for $40,000–45,000 (in year 2000 dollars), at standard markups based on what Lovins calls extensive supplier price quotations for 82% of the components, plus bottom-up cost modeling by RMI and independent consultants for technologies not yet in production. Further development could pare the price to about $35,000. But Lovins’s concept goes beyond transportation. A national fleet of fuel cell–powered Hypercar-class vehicles could contribute to the national electricity grid when they are parked—which averages about 96% of the time, according to the Population Reference Bureau. And according to RMI, if Hypercars captured half of the world’s market by 2020, global carbon dioxide emissions from cars and trucks would fall 25%, instead of rising by 12%. (This estimate assumes that the efficiency of conventional cars improves by 25%, and vehicle miles traveled increases by 50%.)