Carbon Fiber Epoxy Composite Material Research Articles

Enhancement of the bearing strength of pinned-joint composite materials

In this study, a different approach is used to enhance the bearing strength in continuous carbon fiber epoxy composite materials. In order to enhance the bearing strength, metal washers are inserted between laminae of composite material in the region of the pin. Two types of washer, one is stainless steel and the other is aluminum, are used in the preparation of specimens to carry out the bearing strength tests. In addition, three metal washer inserting configurations, as embedding one, two, or three washers in between carbon fiber layers, are tested in each group of specimens. The results show that the first bearing strength values obtained from the specimens with stainless steel washers increase considerably with respect to specimens with aluminum washers and the specimens without washers. The maximum strength of the specimens reinforced with one, two, and three stainless steel washers is approximately 185%, 405%, and 390% higher than the reference specimen, respectively. It is also observed that the maximum strength of the specimens reinforced with one, two, and three aluminum washers is 265%, 285%, and 320% higher than the reference specimen, respectively.

A comparative study of mechanical and machining performance of polymer hybrid and carbon fiber epoxy composite materials

Fiber-reinforced plastics are known as advanced composite materials thanks to their high strength and lightweight features. Carbon fiber reinforced polymers (CFRPs) are one of the high-performance and high-cost fiber-reinforced polymer (FRPs) materials. They are used in several high-performance engineering applications such as motorsports, marine, aviation, energy and defense industry. The cost of carbon fiber is higher compared to many other materials, more competitive and cost-effective productions will spur the demand for composite parts exponentially. Thus, hybrid laminate composite containing carbon and glass fiber materials were manufactured as an alternative for CFRP materials. Because using glass fiber prepreg instead of carbon fiber prepreg will lead the material to become cheaper. However, machining of the FRP materials is still an important issue. For this reason, the present study is focused on the mechanical and machining performance of the polymer hybrid and carbon fiber epoxy composites.

Experimental Investigation of Open-Hole Compression Strength of Carbon Epoxy Composite Material and Determination of Localized Strains Using Digital Image Correlation Technique

The biggest application of the fiber-reinforced composites are in the field of military and commercial aircrafts. Carbon fibers either alone or with the Kevlar 49 fibers, are widely used as main material in many aero plane wing, fuselage and empennage components. Composites materials have wide applications in different industries because of it has very different properties from the metals and polymers. In the drilling of Carbon/Epoxy Composites the cut surface quality is very much dependent on the drilling parameters set during drilling which further effect the strength of the hole during extension/compression loading. In this research, Carbon Fiber Epoxy Composite material is drilled with the standard carbide drill bit and Open Hole Compression (OHC) tests are performed on the Universal Testing Machine. The Digital Image Correlation (DIC) technique is used to find out the strain distribution around the hole during compression loading. From the experimental method and DIC, maximum strength of carbon epoxy composite is achieved by drilling at 1600-2400 mm/min in presence of notch. It was also observed that failure of the structure is dependent on the drilling feed rate and 1600-2400 mm/min was the optimized drilling range.

Catalytic, aerobic depolymerization of epoxy thermoset composites

Fully cured carbon fiber-epoxy composite materials are recycled by a manganese and aluminum catalyzed, aerobic catalysis process specifically designed for high-performance amine-linked epoxy materials commonly used in aerospace manufacturing.

Numerical evaluation of the elastic properties of carbon fiber reinforced composite material at elevated and lowered temperatures

The effect of elevated and lowered temperatures on the elastic properties of carbon fiber-epoxy composite material was studied using multi-phase unit cell (MPUC) numerical model. Evaluation of the elastic properties of carbon fiber-epoxy composite material is based on the finite element method. Obtained results confirmed that elevated and lowered temperature has noticeable influence on elastic properties of carbon fiber-epoxy composite material. As demonstrated, this fact has considerable influence on accurate evaluation of generated thermal stresses in real laminated composite structures, exposed to extremely high or low operating temperatures.

Damage-Reporting Carbon Fiber Epoxy Composites

The ability to detect early damage is of great significance in load bearing composite materials used for high performance applications. Microdamages if left unchecked can grow under subsequent stress, leading to catastrophic structural failure. The sensing of early stage damage via nondestructive methods is therefore critically important for the safe use of these materials. Herein a supramolecular approach to self-diagnosis of early stage damage in a carbon fiber epoxy composite material, via the incorporation of a CB[8] based ternary complex as an additive is reported. The complex comprising a fluorescent probe and a quencher encapsulated by the CB[8] is introduced into the epoxy resin of the composite as a supramolecular cross-linking agent, whose stress-induced dissociation results in the turn on of fluorescence of the probe. In this way, detection of irreversible mechanical strain and fatigue at an early stage is attainable, enabling the assessment of microdamage in the material.

Size effect in uncracked and pre-cracked reinforced concrete beams shear-strengthened with composite jackets

The paper deals with the size effect on shear behaviour of reinforced concrete beams strengthened with fiber reinforced polymer jackets. Continuous U-jackets were made of glass or carbon fiber fabrics and epoxy composite materials. Twelve uncracked or pre-cracked strengthened reinforced concrete beams and six beams without strengthening, all of them in 6 different sizes, were tested. The results indicate that fabric-epoxy continuous U-jackets have reduced the brittleness of the shear failure of beams, tensile strains in stirrups, and, in a significant way, also the width of shear cracks at the failure state. Although similar strengthening was used for both, uncracked and pre-cracked beams, activation of jackets significantly differed. While jacket strains and their strengthening effectiveness were affected by the sizes of uncracked, retrofitted beams, they remained almost constant in pre-cracked, repaired beams of varying sizes. In contrast to repaired beams, stirrups in retrofitted beams did not yield at failure. Degree of strengthening, defined as the ratio of strengthened-to-unstrengthened beam shear capacities, was studied. It was found out that consideration of the degree of strengthening would provide relations reflecting real behaviour of reinforced concrete beams strengthened with fiber reinforced polymer U-jackets or U-jacketed strips.

Design and biomechanical performance analysis of a user-friendly orthotic device

Material selection and proper design are essential for developing a new product, especially biomedical devices. Stance-control-orthosis (SCO) are walking assistive device for the patients with weak quadriceps. This manuscript presents the development of a prefabricated SCO with suitable material and design. It is 45% lighter than commercially available prefabricated device. It contains some adjustable features to make it competent for wide range of patients in terms of height (153–183cm) and weight. Finite element analysis (FEA) was used for selecting the best material and optimizing weight of different components of this device. Basic structures the device were made of aluminum alloy 7075-T6. Carbon-fiber epoxy composite material was used for fabricating the support braces of the device and a polypropylene made foot part was included. Components were fabricated according to FEA results and had been evaluated by mechanical tests. Almost similar results of FEA were found during mechanical tests. The device gait performance was assessed and compared with commercially available prefabricated SCO. The results revealed a better gait. Proper material selection and design made this orthotic device light, structurally stable, functionally suitable and cosmetically acceptable to users.

Use of FBG Strain Gages on a Pipeline Specimen Repaired With a CFRE Composite

Laboratory tests were conducted to understand and describe how the reinforcement layers of a carbon fiber epoxy composite material can enable a steel line pipe specimen with a metal loss defect to withstand pressure loading, and to compare the test results with those predicted by mechanics of materials and by finite element numerical solutions developed previously. Hydrostatic burst tests were performed on three pipe (API 5L X65 ERW) specimens: one with metal loss defect, one without metal loss defect, and one with metal loss defect but repaired with a carbon-fiber-reinforced epoxy composite system. Fiber Bragg grating strain gages were used during the tests of the repaired specimen. The strain gages were bonded either directly on the surface of the defect, or were inserted in between some of the composite layers in order to show the reinforcement’s effective contribution to the strength of the repaired pipes. The analytical and numerical results agreed very satisfactorily with experimentally determined burst pressures and pressure–strain curves, showing that the behavior of composite reinforced pipelines can be well predicted by using simple mechanics of materials or sophisticated finite element solutions.

Application of the Experiment Design Method in Modelling the Temperature Effect on the Behaviour at a Low Velocity Impact Damage of Epoxy Matrix Reinforced with Unidirectional Carbon Fiber Composite

The present study was carried out to evaluate the temperature effect on the mode II interlaminar fracture be- haviour of two unidirectional carbon fiber composite materials subject to low velocity impact damage. Before testing, the specimens were exposed at positive and negative temperatures. The delamination crack energy was calculated at the maximum loading point according to the directed beam theory, to the corrected beam theory and to the compliance calibra- tion. Two types of carbon fiber epoxy composite materials were investigated of denominations AS4/8552 and AS4/3501-6. Unidirectional panels of 32 plies were fabricated according to the prepreg manufacturers. A thin film of PTFE was intro- duced between the mid-planes of the panels in order to provide an artificial starter crack of length 60 mm. Of each materials, five specimens were tested at the statically and the dynamical mode II at the temperatures of:-30,-15, 0, 15, 30, 45 and 60°C. From the experimental results, we conclude that the two composites have a similar behaviour, with a slightly effect of a temperature. The experimental design method was used to obtain a mathematical model describing the effect of the tem- perature on the crack delamination energy. The compliance calibration method gives conservative values of the crack delamination energy.

Microlevel manufacturing process simulation of carbon fiber/epoxy composites to analyze the effect of chemical and thermal induced residual stresses

A micromechanical implicit finite element analysis using Samcef/Mecano was performed to analyze the effect of process-induced deformations and stresses on a unidirectional carbon fiber–epoxy composite material (G1157/RTM6). During the manufacturing process, chemical and thermal shrinkage deformations occur and lead to internal stresses. In this article, several effects on the level of stress on the microscale will be discussed, which address the nonlinear behavior of the polymer matrix material. A parametric study was done on the influence of these effects on residual stresses including temperature dependency of the young’s modulus, thermal expansion coefficient, nonlinear thermomechanical stress–strain behavior, microyielding, microdegradation, and viscoelasticity. Several experiments have been carried out to investigate the thermomechanical behavior of the matrix material and to derivate constitutive equations. The derived equations and the discussed effects are integrated into an analysis model of a squared unit cell and used to perform a coupled curing thermomechanical simulation. As a result, the development of process-induced stresses is presented with the integration of nonlinear local material effects. Assessment of these effects is one of the key aspects for interpretation of process-induced stresses on the macroscale.

Construction of constant fatigue life diagram for a carbon fiber composite

Using the constant amplitude fatigue data at various stress ratios, the constant fatigue life (CFL) diagram was constructed for the CFC material which is useful in prediction of fatigue life under variable amplitude fatigue loads. A quasi-isotropic lay-up sequenced carbon fiber-epoxy composite (CFC) laminate was fabricated by resin infusion technique. The tensile and compression tests were carried out to determine the static strength of the material. About 175 mm long, constant rectangular cross-sectioned fatigue test specimens were cut and prepared from the laminate. The stress-controlled, constant-amplitude fatigue tests were conducted in a 100 kN servo-hydraulic test machine, at room temperature and in lab air atmosphere. All the fatigue tests were performed with a sinusoidal waveform and a frequency of 1–3 Hz. The fatigue tests were conducted at four different stress ratio, R = σmin/σmax, Viz., 0.7,0.5 (tension-tension), −1.0 (tension-compression), and 4.0 (compression-compression). Anti-buckling guide was employed during the fatigue tests which involved compressive load cycles. The CFL Diagrams are material specific with predictive capability for any designed levels from selective experimental data.

하이브리드 샤프트 설계 파라미터 변화에 따른 특성 연구

The carbon fiber epoxy composite material and aluminum have many advantages over other materials because of their high specific stiffness and good fatigue characteristics. Basically, the propeller shaft of automobile requires bending frequency of higher than 2,700 Nm and high natural frequency of higher than 9,200 rpm occurred by fast revolution. For this reason, natural frequency and torsion torque characteristics of hybrid shaft was studied in variation of its outer-diameter and thickness. Vibration and torque characteristics of hybrid shaft were compared by torsion tester, natural frequency experiments and FE analysis. Designed hybrid shaft satisfied its vibration and torque characteristics when its outer-diameter was 60 mm and thickness was 5 mm. Therefore, hybrid material enables to manufacture one piece structure hybrid propeller shaft rather than current two piece structure.

炭素繊維複合材料への超高速衝突による損傷領域と残存強度について

炭素繊維複合材料への超高速衝突による損傷領域と残存強度について

Reduction of fabricational thermal residual stress of the hybrid co-cured structure using a dielectrometry

In this work, cure control system using dielectrometry for co-cured metal/composite hybrid structures was devised to reduce the fabricational thermal residual stress of the bonding layer between metal and composite material. The cure kinetic model of carbon fiber epoxy composite materials was developed by curve fitting the differential scanning calorimetry (DSC) data. The relationship between start of cure and gelation points of epoxy resin and the dissipation factor were investigated. The degree of cure was obtained by comparing the dissipation factor from the dielectric properties to the degree of cure from the DSC. Also, the curvature experiment of co-cured steel/composite strip and the static lap shear tests of the co-cured steel/composite lap joints were measured to investigate the effect of cure cycle on the thermal residual stress of the co-cured hybrid structures. From these results, the cure control algorithm using the dielectrometry for reduction of thermal residual stress was devised and verified under various temperature profiles.

Design and manufacture of a carbon fiber epoxy rotating boring bar

High speed boring operations of deep holes with steel or tungsten boring bars are often hindered by the chatter vibration of boring bars because of their low dynamic stiffness and natural frequencies. The chatter is a self-excited vibration that occurs in metal cutting if, either the chip width is too large with respect to the dynamic stiffness of the system, which is proportional to the damping and static stiffness of the boring bar, or the rotating speed of the boring bar approaches one of its natural frequencies, which is proportional to the specific stiffness ( E/ ρg) of the material used. In this study, a rotating boring bar was designed and manufactured with high stiffness pitch-based carbon fiber epoxy composite to meet the requirements of boring at high rotating speed because carbon fiber epoxy composite materials have a much higher specific stiffness and higher damping than conventional boring bar materials. The optimum design parameters for the composite boring bar were experimentally determined with respect to material types and dimensions of the boring bar through vibration tests. The dynamic characteristics of the composite boring bar developed were measured by the boring operation of aluminum engine blocks. From experiments, it was found that the dynamic stiffness of the composite boring bar was about 30% higher than that of the tungsten carbide boring bar. Also, chatter did not occur up to the ratio of length to diameter ( l/ d) of 10.7, which is about a 30% improvement compared to the tungsten boring bar of l/ d of 8.0.

Composite wrist blocks for double arm type robots for handling large LCD glass panels

Recently, robot structures handling liquid crystal display (LCD) glass panels are increased in size as the size of LCD is increased. In order to handle large LCD panels, the robot structures should have high stiffness to reduce the deflection of robot end effector under the weights of LCD. The LCD manufacturing industries have a trend to employ double arm type robots rather than single arm type robots to increase productivity. Currently, two aluminum wrist blocks that have different configurations not to interfere with each other are mounted on the robot arms. The aluminum wrist block becomes one of the largest deflection sources as the size of the robot structures increases. Since the size of the wrist block can not be increased indefinitely to increase the stiffness due to the limitation of driving motor power, the best way to increase the stiffness of the wrist block is to employ carbon fiber epoxy composite material for structural material of the wrist block because the carbon fiber epoxy composite material has much higher specific stiffness and damping than aluminum. In this work, the two wrist blocks for the double arm type robot for handling large LCD glass panels were designed and manufactured using foam core sandwich structure. Finite element analysis was used along with an optimization routine to design the composite wrist blocks. Box type sandwich structures were employed to reduce shear effect arising from the low modulus of polyurethane foam core. The weight reduction of the composite wrist blocks was more than 50% compared to those of comparable aluminum wrist blocks and found that the composite wrist blocks had much improved performances compared to those of the aluminum wrist blocks from the static and dynamic tests.

Performance of high speed air spindle motor equipped with composite squirrel cage rotor

The dynamic characteristics of a built-in motor type air spindle system can be improved by the reduction of mass of squirrel cage rotor because the critical whirling vibration frequency of a high speed air spindle system is highly dependent on the rotor mass of motor and the spindle specific bending modulus. In this paper the rotor of an AC induction motor was manufactured using magnetic powder containing epoxy composite whose density is half of conventional metal rotor and the motor shaft was made of high modulus carbon fiber epoxy composite material. In order to enhance the magnetic flux of the composite squirrel cage rotor of the motor, a steel core was inserted into the composite rotor. The magnetic behavior of composite squirrel cage rotor was analyzed with respect to shapes and positions of the conductor bars and the steel core of the rotor, and the optimal configuration for the dynamic performance of the rotor system was proposed.

Damping characteristics of composite hybrid spindle covers for high speed machine tools

In order to improve the vibration characteristics of a spindle cover made of 2 mm thick steel plate for high speed machine tools, the cover was reinforced with carbon fiber epoxy composite material. Considering the mounting conditions and the vibration mode shape of the spindle cover, the stacking sequence and the thickness of the reinforced composite laminate were determined through finite element analysis. The relationship between the loss factor and the stacking sequence was also investigated. The steel-composite hybrid spindle cover was fabricated by co-cure bonding in an autoclave and its dynamic characteristics were tested. From the tests, it was found that damping improvement of the composite hybrid spindle cover was substantial over a wide frequency range.

Manufacture of composite screw rotors for air compressors by RTM process

Screw rotors, the key parts of screw compressors, are widely used in compressing air and refrigerant due to their high productivity, compact size, low noise and easy maintenance. In general, a screw compressor unit is composed of female and male rotors of complex geometric shape. The manufacturing cost and time of the screw rotors are high because the complicated helical shapes of the screw rotors are manufactured usually by dedicated machine tools. In this study, to reduce the production cost and weight of screw rotors, the screw rotors for air compressors were manufactured with chopped carbon fiber epoxy composite materials by the RTM (resin transfer molding) process using separable four-piece molds for easy demolding of helical shape screw rotors.