Unidirectional Carbon Fiber Prepreg Research Articles

BEHAVIOR OF BIKE HANDLEBARS MADE OF BRAIDED CARBON FIBRE

The mechanical design of a bike handlebar made of carbon fibre is presented. Usually carbon fibre handlebars are constituted by unidirectional (UD) carbon fibre prepreg. That configuration usually leads to a light design of the piece but fragile. The proposed design allows the handlebar to withstand as high efforts as a steel bar could. On the contrary the carbon handlebar presents a weight much lower. This can be achieved thanks to the selected carbon braiding. Design, manufacturing on cheap PolyLactic Acid (PLA) 3D printed moulds, FEM calculation and testing of the developed carbon fibre handlebar are shown in this paper. Keywords: handlebar, carbon fibre, numerical simulation, test, braiding

Investigation of the stress–strain state of a composite blade in ANSYS WorkBench

In this paper, the static strength of a UAV blade made of composite material was calculated. Composite materials have an advantage over traditional materials (metals and alloys) in the field of aviation - gain in weight, low sensitivity to damage, high rigidity, high mechanical characteristics. At the same time, the identification of vulnerabilities in a layered structure is a difficult task and in practice is solved with the help of destructive control. Composite materials available in the ANSYS materials library were used in the modeling: Epoxy Carbon Woven (230 Gpa) Prepreg woven carbon fiber in the form of a semi–finished prepreg impregnated with epoxy resin carbon fiber with Young's modulus E=230 GPa and Epoxy Carbon (230 Gpa) Prepreg is a unidirectional carbon fiber prepreg impregnated with epoxy resin with a Young's modulus E=230 GPa. Modern software products, such as ANSYS WorkBench, allow comprehensive investigation of the layered structure. Several variants of blade designs with different fillers as the median material were investigated. The forward and reverse destruction criteria based on the Tsai-Hill theory were used. The influence of gravity was not taken into account. It is shown that the developed blade design meets the requirements. Balsa wood, pine, aspen and polyurethane foam were chosen as the middle material of the blade. Pine and aspen wood were selected according to the criteria of their availability and having the lowest density. The materials library of the ANSYS WorkBench software package used does not have characteristics for all of them, so the characteristics of the selected materials (pines and aspens) were added manually. For modeling and calculations in the ANSYS WorkBench program, such characteristics as density, axial elastic modulus, Poisson's coefficients, shear modulus and tensile and compressive strength limits are required.

A study of a bio-inspired impact resistant carbon fiber laminate with a sinusoidal helicoidal structure in the mandibles of trap-jaw ants.

The majority of living organisms demonstrate remarkable attributes and have evolved effective mechanisms for synthesizing impact-resistant and damage-tolerant structures. One exemplary instance is the rapid mandible strikes exhibited by trap-jaw ants, which are a highly aggressive species of terrestrial social organisms. An impact-resistant sinusoidal helicoidal architecture is discovered in the mandibles of trap-jaw ants. The bioinspired laminate with a bi-sinusoidal helicoidal structure was manufactured using unidirectional carbon fiber prepreg by mold press forming. This study examines the impact resistance and damage tolerance of a bionic laminate through low velocity impact, computed tomography, and compression after impact tests. The results demonstrate that bionic laminates effectively limit damage propagation within the plane while enhancing energy dissipation capacity. The sinusoidal helicoidal configuration enhances cushioning capability against impact forces, retards penetration under higher loads, hinders crack propagation, and improves residual strength. Bionic laminates provide a valuable solution for damage tolerance through the resistance to through-the-thickness loads. STATEMENT OF SIGNIFICANCE: Helicoidal and sinusoidal helicoidal microstructures have been identified in the cross-section of the jaws of trap-jaw ants. The multiple waviness ratio parameters are designed for fabricating a sinusoidal helicoidal structure laminate using unidirectional carbon fiber prepreg through the mold press forming technique. This results in a damage-tolerant mechanism characterized by reduced delamination damage, which leads to a stiffer mechanical response. Meanwhile, it enhances resistance to crack propagation, leading to the formation of discontinuous delamination areas and the accumulation of sub-critical failures. Additionally, the sinusoidal helicoidal structure laminate combines the cushioning performance of bi-sinusoidal arrangements with the enhanced impact resistance of helical arrangements. This design delays penetration at higher loads, resulting in increased residual strength.

Hemispherical Molding Experiment and Simulation of Unidirectional Carbon Fiber Prepreg

To study the deformation law and forming defects of hemispherical molding of unidirectional carbon fiber reinforced polymer (UN-CFRP), hemispherical molding experiments were carried out, and a three-dimensional finite element model of single-ply UN-CFRP hemispherical molding was established. The results show that the established finite element model can accurately predict the molding deformation law and forming defects of UN-CFRP. The results indicate that the fiber at the top of the sample is uniformly distributed; the fiber on both sides of the sample top and parallel to the fiber direction is local dispersion; the fiber at both sides of the bottom is trapezoidal splitting. The results at the bending corner show that the bending quality is better when the angle between the fiber direction and the tangent of the circular bend is in the range of 70-90°; it is easy to produce extrusion wrinkling when the angle between the fiber direction and the tangent of the circular bend is 15-70°; it is easy to produce extrusion accumulation when the angle between the fiber direction and the tangent at the circular bending is in the range of 0-15°. The results of cross-ply UN-CFRP hemispherical molding show that the full spreading property is good, and there is no obvious fold in the bending part.

Experiment and analysis of mechanical properties of carbon fiber composite laminates under impact compression

Abstract Composite materials are more and more widely used in aircraft structural design, and impact damage is the most serious defect/damage form of aviation composite structures in service. Therefore, it is of great significance to study the impact resistance of composites with different materials and structural forms for aircraft structural design. In this article, the damage of reinforced fiber/resin composite laminates with unidirectional carbon fiber prepreg (UIN23100), carbon fiber woven fabric (W-3021FF), and carbon fiber-aramid fiber blended fabric (W-38211) under the same impact energy were studied. The impact damage area was scanned and analyzed by ultrasonic C-scan, and the impact resistance of the three laminates were obtained. Finally, the compression bearing capacity of carbon fiber laminates after impact was tested, and the compression failure mode of each material has been analyzed. The results show that the impact resistance of carbon fiber unidirectional prepreg was stronger than that of carbon fiber woven fabric; the compression bearing capacity of carbon fiber laminate after impact was higher than that of carbon fiber unidirectional prepreg; the post impact bearing capacity of W-38211 was higher than that of W-3021FF.

Mechanical Properties of the Carbon Nanotube Modified Epoxy-Carbon Fiber Unidirectional Prepreg Laminates.

The effect of plasma treatment of the multi-walled carbon nanotube (MWCNT) surface on the fracture toughness of an aerospace grade epoxy resin and its unidirectional (UD) carbon fiber prepreg laminates has attracted scientific interest. A prepreg route eliminates the possible risk of carbon nanotube filtration by unidirectional carbon fibers. X-ray photoelectron spectroscopy results suggested that oxygen atom concentration at the nanotube surface was increased from 0.9% to 3.7% after plasma modification of the carbon nanotubes. A low number (up to 0.5 wt.%) of MWCNTs was added to epoxy resin and their carbon fiber prepreg laminates. Transmission electron micrographs revealed that the plasma treatment resulted in a better dispersion and distribution of MWCNTs in the epoxy resin. Plasma-treated MWCNTs resulted in a more pronounced resistance to the crack propagation of epoxy resin. During the production of the reference and nanotube-modified prepregs, a comparable prepreg quality was achieved. Neat nanotubes agglomerated strongly in the resin-rich regions of laminates lowering the interlaminar fracture toughness under mode I and mode II loading. However, plasma-treated nanotubes were found mostly as single particles in the resin-rich regions of laminates promoting higher energy dissipation during crack propagation via a CNT pull-out mechanism.

Belt-Press Tape Forming of Carbon-Fiber-Reinforced Thermoplastic

A new tape placement device that incorporates the double belt press mechanism was developed for carbon-fiber-reinforced thermoplastic composites. A unidirectional carbon fiber prepreg tape, impregnated with PA6 at volume fraction fiber of 50%, was heated to the melting temperature by the heating roller, compressed on the base tape by the pressing roller, and cooled by the cooling roller. During this process, the prepreg tape was sandwiched between the base tape and the thin stainless belt surrounding the rollers. The combination of the pressing roller and the stainless belt provides a longer pressing and cooling region than that of the device without stainless belt. For the first trial of the device, a 10-layered ring with a diameter of 100 mm and a width of 18 mm was formed by applying a constant load using the six-axis robot. The specimen cut from the ring exhibited the flexural strength of 550 to 600 MPa and the good consolidation quality. For the second trial, a front heater was developed to elevate the temperature of the base tape, and a spiral tube was formed by manipulating the robot in the axial direction. The flexural strength was in the range of 500 to 600 MPa. The tape was compacted in width direction during the forming.

Mechanical performance of carbon-glass hybrid composite joints in quasi-static tension and tension-tension fatigue

The ever increasing size of wind turbines has given rise to a need for robust glass to carbon joint designs. This study investigates the effect of different ply layups on the static and fatigue behaviour of hybrid glass/carbon fibre composite joints. Uni-directional carbon fibre prepreg was co-cured to 8H glass prepreg using an overlap to thickness ratio of 20:1, where four joint designs were examined: scarf, interleaving and two forms of double scarf. The joints were tested statically in uniaxial tension and dynamically in tension-tension fatigue. Finite element analysis has been performed to provide insight into stress distributions within each joint. The double scarf joint (with glass on the outside) was found to perform best in fatigue and static tension, while the interleaving joint performed second best in fatigue in static tension but poorest in fatigue. For joint designs that will be used under highly stressed cyclic loading conditions, the current study indicates that static tests alone are a poor indicator of the joint performance and fatigue tests are required.

Development and verification of a finite element model for double diaphragm preforming of unidirectional carbon fiber prepreg

A finite element (FE) model for double diaphragm preforming of a unidirectional (UD) carbon fiber prepreg was developed. In the model, a hyperelastic constitutive model considering the effect of temperature was used to describe the nonlinear large deformation behavior of the diaphragm in the preforming process. The prepreg lamina was characterized by a transverse isotropy elastic model. The interfacial behavior between prepreg laminate was characterized by a previously developed analytical three-stage inter-ply slipping model which considers the effects of preforming temperature and pressure. Double diaphragm preforming experiments of the UD carbon fiber prepreg laminates over a C-type mold were implemented and then simulated by using the proposed FE model. Comparisons between experimental results and simulation data verified the numerical model. The proposed FE model provides a numerical tool for processing simulation and optimization for double diaphragm preforming of prepregs.

Prediction of degree of impregnation in thermoplastic unidirectional carbon fiber prepreg by multi-scale computational fluid dynamics

A multi-scale simulation approach was proposed to predict the degree of impregnation (DoI) in thermoplastic unidirectional carbon fiber prepreg (UD-CFP). The multi-scale approach included a two-dimensional (2D) micro-scale computational fluid dynamics (CFD) in a representative elementary volume (REV) of carbon fiber (CF) tow, a 3D macro-scale CFD of an entire impregnation die with 15 sliding CF tows, and a process-scale simulation assembling data from the micro- and macro-scale CFDs. In the macro-scale steady-state CFD, thermoplastic resin injection and CF tow insertion were considered for an impregnation die 10 cm in width. In the micro-scale transient CFD, impregnation mechanisms of resin into CF filaments 7 μm in diameter were identified in terms of surface coverage, capillary permeation, and penetration through CF filaments. The DoI as a function of pressure and time was obtained from the micro-scale CFD within a range of pressures found in the macro-scale CFD. In the process-scale simulation, the cumulative DoI of the 15 tows was predicted along the impregnation die length with the aid of the micro- and macro-scale CFD results. Combining the multi-scale models gives a potential to predict the uniformity of the transverse resin amount in the final UD-CFP product.

Multi-scale computational fluid dynamics of impregnation die for thermoplastic carbon fiber prepreg production

A multi-scale computational fluid dynamics (CFD) model of a pultrusion process was proposed for unidirectional carbon fiber (UD-CF) prepreg production. Polyamide 6 (PA6) and polyacrylonitrile-based CF were used as the thermoplastic polymer matrix and reinforcement, respectively. The non-Newtonian viscosity of PA6 was expressed by Carreau's model. A micro-scale CFD model was constructed to obtain a proper resin permeability to CF filaments, while the tow domain was treated as sliding porous media in the macro-scale CFD. The resin velocity profile showed a similar shape to the relative resin amount experimentally measured in the UD-CF prepreg. The uniformity index of the resin velocity (UIv) on the outlet surface was calculated for 45 case studies with several tow speeds and resin flow rates. The tow speed showing a maximum UIv was remarkably well expressed as a linear function of the slip velocity, which is the difference between the tow speed and resin velocity.

A new unidirectional carbon fiber prepreg using physically modified epoxy matrix with cellulose nano fibers and spread tows

A new unidirectional carbon fiber prepreg was successfully developed, whose epoxy matrix was physically modified with cellulose nano fibers (CNF). Two different types of prepreg were fabricated using regular carbon fiber (CF) and spread CF tows to identify the effect of prepreg thickness on the mechanical performance including fatigue of quasi isotropic laminates using these prepregs while the thickness of each layer was kept the same (120μm). The effect of CNF modification of epoxy matrix on the fatigue life is quite significant if thin prepregs were used. It increases greater than 10 times than the fatigue lives of laminates fabricated by regular CF tows/unmodified EP or regular CF tows/modified EP. Uniformly dispersed CNF in the epoxy matrix increases the interfacial strength between CF and matrix.

Experimental and Numerical Study on the Tensile Behaviour of UACS/Al Fibre Metal Laminate

A new fibre metal laminate fabricated with aluminium sheets and unidirectionally arrayed chopped strand (UACS) plies is proposed. The UACS ply is made by cutting parallel slits into a unidirectional carbon fibre prepreg. The UACS/Al laminate may be viewed as aluminium laminate reinforced by highly aligned, discontinuous carbon fibres. The tensile behaviour of UACS/Al laminate, including thermal residual stress and failure progression, is investigated through experiments and numerical simulation. Finite element analysis was used to simulate the onset and propagation of intra-laminar fractures occurring within slits of the UACS plies and delamination along the interfaces. The finite element models feature intra-laminar cohesive elements inserted into the slits and inter-laminar cohesive elements inserted at the interfaces. Good agreement are obtained between experimental results and finite element analysis, and certain limitations of the finite element models are observed and discussed. The combined experimental and numerical studies provide a detailed understanding of the tensile behaviour of UACS/Al laminates.

Recycling of Reinforced Plastics

This work has shown is that it is possible to recycle continuous and short fibre reinforced thermosetting resins while keeping almost the whole of the original material, both fibres and matrix, within the recyclate. By splitting, crushing hot or cold, and hot forming, it is possible to create a recyclable material, which we designate a Remat, which can then be used to remanufacture other shapes, examples of plates and tubes being demonstrated. Not only can remanufacturing be done, but it has been shown that over 50 % of the original mechanical properties, such as the E modulus, tensile strength, and interlaminar shear strength, can be retained. Four different forms of composite were investigated, a random mat Glass Fibre Reinforced Plastic (GFRP) bathroom component and boat hull, woven glass and carbon fibre cloth impregnated with an epoxy resin, and unidirectional carbon fibre pre-preg. One of the main factors found to affect composite recyclability was the type of resin matrix used in the composite. Thermoset resins tested were shown to have a temperature range around the Glass Transition Temperature (Tg) where they exhibit ductile behaviour, hence aiding reforming of the material. The high-grade carbon fibre prepreg was found to be less easy to recycle than the woven of random fibre laminates. One method of remanufacturing was by heating the Remat to above its glass transition temperature, bending it to shape, and then cooling it. However, unless precautions are taken, the geometric form may revert. This does not happen with the crushed material.

Thermal Residual Stress and Tensile Strength of UACS/Al Laminate with Different Slit Angles

This paper focus on the investigation of tensile strength and thermal residual stress in UACS/Al laminates. The UACS (unidirectionally arrayed chopped strands) is made by cutting parallel slits on unidirectional carbon fiber prepreg. Thus all of the carbon fibers in the cut prepreg are 25 mm in length. Six cases of UACS prepregs are prepared with different slit angle θ, which is the angle between slit and fiber direction, including 5.7o, 11.3o, 16.7o, 31o, 45o and 90o. A UACS/Al laminate consists of one UACS layer with four UACS plies and two aluminum layers, such as [Al/UACS4/Al]. Four pieces of UACS prepreg with alternate slit angle [θ/-θ/θ/-θ] are stacked together in the same fiber direction. Then stacked UACS/Al laminate are cured using an autoclave. Tensile tests are performed to investigate the thermal residuals stress using the yielding-point-shift method. Experiment results show that thermal residual stress is reduced in the case of UACS/Al compared with conventional CFRP/Al. Among all the cases, specimen with slit angle of 11.3o is the most impressive one with 37.7% reduction of thermal residual stress.

Mode-II Fracture at the Interface between a Base and a Repair Graphite/Epoxy Laminates

Experimental investigation of the characteristics of the interface between a base laminate [08] T and a repair laminate [08] T was carried out through Mode II fracture tests, compliance calibration tests, and microscopic observations. The material used for manufacturing the test samples is unidirectional carbon fiber prepreg (Newport Composites NCT-301 graphite/epoxy). The laminate lay-up used in all experiments was [016] T.The specimens were subjected to variations in the autoclave pressure in the repair curing cycle. A standard sample (reference) was subjected to the manufacture recommended cure cycle. The repair samples were subjected to the manufacturer recommended curing cycle (for temperature) with different values for pressure. Results show a significant effect of pressure. However, the effect of the magnitude of the pressure is not significant after some threshold values. More than 28% drop in the fracture toughness is experienced by the lack of bonding between the older previously cured matrix and the newly added composite laminate. There is some difference between the Mode-II test and compliance calibration test, but no preference, in terms of accuracy, can be given to what method to be used to obtain Mode II fracture toughness.

The Effect of Phenylethynyl Terminated Imide Oligomer Molecular Weight on the Properties of Composites

As part of a program to develop high temperature/high performance structural resins for applications on a Mach 2.4 high speed civil transport, a phenylethynyl terminated imide oligomer designated PETI-5 has been under investigation. The oligomer was prepared at a calculated number average molecular weight of about 5000 g/mol and has exhibited good processability and excellent mechanical properties upon thermal cure at 350-371°C for 1 hr. However in the fabrication of complex composite structures, primarily skin stringer structure, a resin with improved flow and equivalent or better mechanical properties was desired. To improve melt flow (i.e., processability or compression moldability), 1250 and 2500 g/mol molecular weight versions of PETI-5 were prepared and their solutions used to prepare supported adhesive film and unidirectional carbon fiber prepreg. Imide powder of the oligomers was used for characterization of melt flow behavior and the fabrication of neat resin moldings. The PETI-5 oligomers were fabricated into titanium adhesive specimens and IM-7 carbon fiber laminates under 0.3-1.4 MPa for 1 hr at 350-371°C. The lower molecular weight oligomers exhibited improved processability, and when cured, higher T g s and better retention of mechanical properties at elevated temperature without significantly sacrificing toughness (damage tolerance) than the higher molecular weight oligomer. The neat resin, adhesive and composite properties of the cured polymers are discussed.

Comparative Study of Estimated and Experimental Values for Weatherability Strength and Elastic Modulus of CFRP Subjected to Accelerated Exposure.

CFRP specimens have been exposed under accelerated exposure apparatus. The specimens are made of epoxy resin and the unidirectional carbon fiber prepreg having the fiber orientation angles of 0.45 and 90 degree, respectively. In order to clarify the dependence of the exposure period on the weatherability strength, the complicated accelerated exposure test is continued to 20 cycles. The variations of flexural strengths, flexural moduli, matrix volume fractions and thicknesses to the exposure period are reported in this paper. Furthermore, the experimental results of flexural strength and modulus for CFRP are compared with their estimated values calculated from the results of accelerated exposure of epoxy resin.

促進暴露を受けるＣＦＲＰ材の耐侯性曲げ強度とその非破壊的予測

CFRP specimens have been tested under accelerated exposure experiments. The specimens were made of epoxy resin and unidirectional carbon fiber prepreg to the fiber orientation angles of 0, 45 and 90 degrees. In order to clarify the dependence of the exposure period on the weatherability strength, the accelerated exposure of complex testing is continued through 20 cycles and the relation of thier flexural strengths and moduli, etc. to the number of cycle are examined. The variations of flexural strengths, flexural moduli, matrix volume fractions, hardnesses, hydrolytic decomposition of polymer chains and absorbance peak of infrared spectrums with the exposure period are reported in this paper. Furthermore, the non-destructive estimation for weatherability of flexural strengths have reached the estimated values by making full use of the flexural modulus and cycle number data. It has been confirmed that the estimated results are in good agreement with the experimental ones of accelerated exposure for CFRP.

Processing and Properties of IM7/LARCTM-SCI Composite

LARCTM-SCI (Langley Research Center - Semi-Crystaline polyImide) is an aromatic polyimide based on 3,4′-oxydianiline and 3,3′,4,4′-biphenyl tetracarboxylic dianhydride. This polyimide was synthesized and evaluated for use as a neat resin and a matrix resin for advanced composites. Three 30% w/w solids polyamic acid/ N-methypyrrolidone solutions were prepared using 2, 3 and 4% stoichiometric imbalances end-capped with phthalic anhydride to provide polyimides with theoretical number average molecular weights of approximately 22 800, 15 100 and 11 400 g mol−1 respectively. Unidirectional IM7 carbon fibre prepreg was prepared from these three resins using the Langley multipurpose tape machine. Thermal and rheological properties and the solvent/volatile depletion rates along with crystallization kinetics were characterized for the resin scraps taken from the prepreg tapes. Processing characteristics of the LARCTM-SCI resin were thoroughly understood from these results, and a workable moulding cycle was designed for this composite. Composite laminates were moulded at 410 °C at either 200 or 300 psi, which consistently yielded good consolidation and high-quality panels as measured by C-scan, acid digestion and optical photomicrography. The composite mechanical properties were also obtained. Short beam shear strength was 15 ksi at RT. Longitudinal flexural strength was 295 ksi at RT and 200 ksi at 177 °C. Excellent fracture toughness of 6.9 in-lb/in2 was obtained. Excellent values of transverse flexural strength and longitudinal tensile strength indicated a good translation of fibre properties into the composite. Un-notched longitudinal compression strength of 163 ksi was comparable to typical thermoplastic composites. An open hole compression strength of 55 ksi suggested good damage tolerance for this composite.