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Carbon fiber reinforced polymers (CFRPs) are increasingly used in the aerospace industry because of their robust mechanical properties and strength to weight ratio. A significant drawback of CFRPs is their resistance to formability when drawing continuous CFRPs into complex shapes as it tends to bridge, resulting in various defects in the final product. However, CFRP made from Stretch Broken Carbon Fiber (SBCF) aims to solve this issue by demonstrating superior formability compared to conventional continuous CFRPs. To study and validate the performance of SBCF, a statistical design of the experiment was conducted using three different types of CFRPs in tow/tape form. Hexcel (Stamford, CT, USA) IM7-G continuous carbon fiber impregnated with Huntsman (The Woodlands, TX, USA) RDM 2019-053 resin system, Hexcel SBCF impregnated with RDM2019-053 resin, and Montana State University manufactured SBCF impregnated with Huntsman RDM 2019-053 resin were tested in a multitude of forming trials and the data were analyzed using a statistical model to evaluate the forming behavior of each fiber type. The results show that for continuous fiber CFRP tows forming, Fmax and Δmax do not show statistical significance based on temperature fluctuations; however, in SBCF CFRP tows forming, Fmax and Δmax is dominated by the temperature and geometry has a low statistical influence on the Fmax. The lower dependence on tool geometry at higher temperatures indicates possibly superior formability of MSU SBCF. Overall findings from this research help define practical testing methods to compare different CFRPs and provide a repeatable approach to creating a statistical model for measuring results from the formability trials.

El presente artículo analiza las propiedades tensiles de un material compuesto polimérico reforzado con fibras de carbono empleado en la fabricación del monoplaza para competición Fórmula SAE. Para ello se manufacturaron compuestos a partir de preimpregnados con diferentes orientaciones de fibra mediante un proceso de curado al vacío. Se evaluó el efecto de la orientación de las fibras sobre la resistencia y la rigidez de los compuestos formulados. Se instrumentaron las probetas de tracción con extensómetros biaxiales para obtener un registro real de la deformación y posterior determinación del módulo de Young. Los resultados experimentales fueron comparados con los resultados analíticos obtenidos a partir de la Teoría Clásica de Laminados mediante software especializado. Se desarrolló también un análisis microscópico de la región fracturada de las probetas para evaluar el efecto del proceso de manufactura. El conjunto de información generada a partir de los resultados experimentales y analíticos proporciona un entendimiento de la anisotropía de los materiales compuestos Epoxi-Carbono que permitirá tomar decisiones de diseño en futuros desarrollos dentro del proyecto Fórmula SAE.

A thermoplastic-penetrated natural fiber belt was developed for potential application in filament winding. Discontinuous sisal fiber bundles were impregnated with high density polyethylene and then connected into continuous pre-pregs via hot-pressing. The interfacial bonding was improved by treating the fibers with sodium hydroxide (NaOH) and three types of coupling agents (NH2C3H6Si(OC2H5)3, C2H3Si(OC2H5)3 and C51H112O22P6Ti). Tensile properties of the fiber bundles, pre-pregs, and annular specimens were determined. The fiber surface microstructure and the pre-preg interfacial bonding were evaluated via scanning electron microscopy and Fourier transform infrared spectroscopy. Among the four treatments, 2% C2H3Si(OC2H5)3 yielded the most significant improvement in the tensile properties of the pre-pregs and annular specimens. The fiber bundle was less damaged by the coupling agents treatment comparing to NaOH treatment. When the overlap at the end of the sisal fibers was >11 mm, the presence of the joint had no effect on the tensile strength of the pre-preg. The pre-preg belt containing treated fibers, which was evaluated based on the requirements of filament winding applications, exhibited a high performance.

V diplomskem delu smo naredili pregled literature o kompozitih, laminatih in lahkih sendvič panelih. Raziskali smo tri tehnološke postopke izdelave lahkih strukturnih sendvič plošč in njihov vpliv na kakovost izdelave. Ugotavljali smo vplive parametrov izdelave na upogibno trdnost in debelino sendvič kompozita. Testiranje je potekalo z dvema materialoma polnila, peno in satjem, obdana z enoslojno prepreg (pred-impregnirano) tkanino iz ogljikovih vlaken na vsaki strani. Iz posamezne serije plošč so bili izrezani standardni vzorci katere smo stehtali, premerili in stestirani s tri-točkovnim upogibnim preizkusom. Ugotovili smo, da se v območju med 0 in 5 barov delovnega tlaka v avtoklavu postopno zmanjšuje debelina sendvič plošče. Še posebej izrazito se je to pokazalo pri vzorcih iz pene, ki ima slabšo tlačno trdnost od satja. Po drugi strani pa smo ugotovili manjši padec debeline z naraščanjem tlaka pri vzorcih iz satja, v tem primeru je porušitev sledila šele pri najvišjih tlakih. Na upogibnem preizkusu se je najbolje obnesel vzorec iz satja pri tlaku 2 barov, najslabše pa sta se obnesla vzorca izdelana, sicer z zelo pogosto uporabljenim postopkom v industriji, naknadnim lepljenjem. Vzorci iz satja so dosegli tudi največje razmerje med maksimalno napetostjo in težo. Z mikroskopiranjem smo nato želeli rezultate dodatno ovrednotiti in ugotovili, da je je najbolj dominantna porušitev pri vzorcih, ki so lepljeni naknadno, delaminacija, pri ostalih pa kombinacija porušitve sredice in prekinitev vlaken pod točko obremenitve zaradi uklona na tlačni strani. In the thesis we have reviewed the literature on composites, laminates and light sandwich panels. We learned about three processes of making a very light structural sandwich panels, which we later used in the research with the desire to optimize the manufacturing process. With different parameters we wanted to observe the impact on bending strength and thickness. The testing was carried out with two core materials, foam and honeycomb, surrounded by a single-layer prepreg carbon fibre fabric on each side. Standard samples were cut out of each series of plates, which were weighed, measured and tested with a three-point bending test. We found that in the range of 0 to 5 bar working pressure in the autoclave gradually reduces the thickness of the sandwich plate. This was particularly pronounced in the samples of foam, which has a less compressive strength than a honeycomb. On the other hand, we found a slight decrease in thickness with an increase in pressure in honeycomb samples, in which case the failure was followed only at the highest pressures. The bending test results were the best of honeycomb at a pressure of 2 bar, and the worst was the panel produced, otherwise with a very commonly used industry process, subsequent gluing. Honeycomb samples also achieved the maximum ratio of bend strength compared to weight. With microscopy, we then wanted to further evaluate the results and found that the most dominant failure in samples glued afterwards is delamination, while in others the combination of core failure and the break of the fibres below the load point.

peer-reviewed This study investigates a device for in-line continuous spreading of carbon fibre/thermoplastic pre-preg tape for potential application in the Laser-Assisted Automatic Tape Placement (LATP) laminate manufacturing process.The spreading device allows variable tape width to be achieved locally during lay-up. Integration of this device in the LATP process would remove gap and overlap manufacturing defects in variable angle tow (VAT) laminates and complex curvature components. During trials different width tapes were produced using the novel spreading device. Three different width increases were investigated, viz. 15%, 30% and 45%, and were compared with as-received tape. Initial trials indicate that it is possible to achieve a tape width increase of 62%. Preliminary charac-terisation tests show that the spreading process does not adversely affect the properties of the tapes. Physical properties including cross-sectional area,fibre volume fraction and void content remain similar to as-received tape. Furthermore, differential scanning calorimetry data show that levels of crystallinity increase due to spreading, improving related mechanical properties.

Fibre path defects are detrimental to the structural integrity of composite components and need to be minimised through process optimization. This requires understanding of the uncured pre-preg material, which is influenced by multiple process parameters, and sophisticated multi-scale modelling tools. Even though the capabilities of process modelling techniques have been improved over the past decades, the occurrence of localised wrinkles remains challenging to predict. One of the processes known to influence the formation of fibre path defects is the consolidation of laminates manufactured by automated fibre placement. The particular focus of this paper is to understand how out-of-plane wrinkles form during debulking and autoclave curing of laminates with embedded gaps and overlaps between the deposited tapes. Predictions are made using a novel modelling framework and validated against micro-scale geometry characterisation of artificially manufactured samples. The paper demonstrates the model’s ability to predict consolidation defects for the latest generation of toughened pre-pregs.

This article presents the analysis of the tensile properties of a carbon fiber reinforced polymer composite used in the manufacture of the single-seater for Formula SAE competition. Composites were manufactured from pre-pregs with different fiber orientations by a vacuum curing process. The effect of the fiber orientation on the strength and rigidity of the formulated composites was evaluated. The tensile specimens were instrumented with biaxial extensometers in order to obtain a real record of the deformation and subsequent determination of the Young's modulus. The experimental results were compared with the analytical results obtained from the Classical Laminate Theory using specialized software. A microscopic analysis of the fractured region of the specimens was also developed to evaluate the effect of the manufacturing process. The set of information generated from the experimental and analytical results provides an understanding of the anisotropy of Epoxy-Carbon fiber composites that will allow design decisions to be made in future developments within the Formula SAE project., El presente artículo analiza las propiedades tensiles de un material compuesto polimérico reforzado con fibras de carbono empleado en la fabricación del monoplaza para competición Fórmula SAE. Para ello se manufacturaron compuestos a partir de preimpregnados con diferentes orientaciones de fibra mediante un proceso de curado al vacío. Se evaluó el efecto de la orientación de las fibras sobre la resistencia y la rigidez de los compuestos formulados. Se instrumentaron las probetas de tracción con extensómetros biaxiales para obtener un registro real de la deformación y posterior determinación del módulo de Young. Los resultados experimentales fueron comparados con los resultados analíticos obtenidos a partir de la Teoría Clásica de Laminados mediante software especializado. Se desarrolló también un análisis microscópico de la región fracturada de las probetas para evaluar el efecto del proceso de manufactura. El conjunto de información generada a partir de los resultados experimentales y analíticos proporciona un entendimiento de la anisotropía de los materiales compuestos Epoxi-Carbono que permitirá tomar decisiones de diseño en futuros desarrollos dentro del proyecto Fórmula SAE.

Pre-preg material has been widely-used in the industry of the aerospace, the wind power, which has many advantages on manufacture process, and can be chosen as an effective complementary insulation method for the Wet-winding and Vacuum Pressure Impregnation technology in the field of superconducting fusion magnets. ASIPP undertaken many engineering tasks on the superconducting coil and busbar design and manufacture for the large fusion device, the pre-preg material and the relevant curing technology were researched as a new method for the high voltage potential components in ITER Feeders, such as the busbars and current leads. Two types of Chinese industrial glass fiber pre-preg insulation composite material were studied and pre-qualified using vacuum bag and silicone rubber assistance technique in ASIPP. The mechanical properties including the ILSS and UTS at 77 K, and void content of this composites were measured and discussed in this paper in detail.

This study concerns the effect of AFP process-induced microstructure and imperfections on the failure response of composite laminates subjected to out-of-plane tensile loading. Microstructure-based description and analysis of automated layup and forming of laminates are firstly conducted by experimental observation. Further, two failure modes are experimentally obtained for understanding the fracture mechanisms of the AFP laminates under out-of-plane tensile loading. In order to capture transition zones of the random gaps and their developments, a two-step approach for constructing a more realistic geometrical model is presented, thereby establishing an AFP random gap model to account for the deformation and failure mechanisms of the out-of-plane tensile specimens. Numerical results show a good agreement with experiments in terms of material modulus and strength and in predicting the failure behavior. In addition, parametric studies show significant knockdown in out-of-plane tensile properties due to gaps, specifically with larger gap sizes showing higher knockdown.

Flexural properties of carbon fibre reinforced plastics (CFRPs) with multi-layer interfacial reinforcement of hierarchically structured aramid pulp (AP) fibres were measured at −40 and −100 °C under three-point bending (3 PB) together with unreinforced CFRPs. After curing, the ‘interleaf’ thicknesses were 3.3, 5.6 and 12.2 μm for three different AP areal densities of 0.8, 1.6 and 3.2 g/m2, respectively. 3 PB tests of control and AP reinforced CFRPs were also performed at 20 °C to compare the AP strengthening effects and their variations from ambient temperature to −100 °C. The flexural strength increased up to 30.6% at −100 °C for specimens with 1.6 g/m2 AP in comparison to 24.5% enhancement at room temperature. This finding proves that a proper composite design, i.e. adding tough and flexible short fibres into the brittle-fibre and brittle-matrix system, can indeed enhance the structural performance of CFRPs. The small-scale in-house ‘pre-preg’ fabrication adopted in this study shows that the ultra-thin layers of AP fibres can be potentially incorporated into a large-scale pre-preg production so that the extra step of inserting the interleaving layers can be removed from the composite forming process. In other words, end users can use the AP toughened pre-pregs just like any carbon fibre pre-pregs currently in use without the trouble of interleaving.

International audience; Automated tape placement - ATP - is a recent manufacturing technology for composite materials. Therefore, a correct modeling of the multi-physical process is critical in order to make possible in-situ consolidation. In this work, we propose an accurate modelling framework and an efficient simulation procedure of physics occurring during the process with the aim of studying the influence of material and process parameters into the material consolidation evolution. For that purpose, an accurate description of the prepreg surface becomes compulsory, justifying the use of a multi-resolution description of it based on the use of wavelets.

Gaps and overlaps between pre-preg plies represent common flaws in composite materials that can be introduced easily in an automated fibre placement manufacturing process and are potentially detrimental for the mechanical performances of the final laminates. Whereas gaps and overlaps have been addressed for full composite material, the topic has not been extended to a hybrid composite material such as Glare, a member of the family of Fibre Metal Laminates (FMLs). In this paper/research, the manufacturing, the detection, and the optical evaluation of intraply gaps and overlaps in Glare laminates are investigated. As part of an initial assessment study on the effect of gaps and overlaps on Glare, only the most critical lay-up has been considered. The experimental investigation started with the manufacturing of specimens having gaps and overlaps with different widths, followed by a non-destructive ultrasonic-inspection. An optical evaluation of the gaps and overlaps was performed by means of microscope image analysis of the cross sections of the specimens. The results from the non-destructive evaluations show the effectiveness of the ultrasonic detection of gaps and overlaps both in position, shape, width, and severity. The optical inspections confirm the accuracy of the non-destructive evaluation also adding useful insights about the geometrical features due to the presence of gaps and overlaps in the final Glare laminates. All the results justify the need for a further investigation on the effect of gaps and overlaps on the mechanical properties.

peer-reviewed The weight saving benefits of fiber-reinforced composite materials in structural applications are well established. However, there is an increasing requirement to develop processing techniques that can produce highly repeatable and accurate components more efficiently than using autoclave processing; Laser-assisted Automated Tape Placement (LATP) in-situ consolidation of thermoplastic composites has significant potential to fulfil this requirement. In addition, LATP can process layers with Variable Angle Tow (VAT), an advanced tailoring option that allows modification of load paths within the laminate to result in more favorable stress distributions and improved laminate performance. Studies of VAT laminate manufacture using dry fiber placement and thermoset pre-preg tape placement have been previously reported. This work examines the ability to produce VAT laminates from carbon fiber/PEEK pre-preg tapes using LATP. A VAT laminate was successfully manufactured which had three steering radii of 800 mm, 600 mm and 400 mm with little defects. Characterization and mechanical testing were completed on steered samples to examine the effect of lay-down speed and radius on bond strength of steered tapes. Measurements showed that the width and thickness of the carbon fiber/PEEK tapes were changed during steering. Mechanical testing showed that bond strength was a function of lay-down speed, yet the effect of steering radius was inconclusive due to undesired failures.

This paper introduces an experimental and numerical investigation into hollow cylindrical thin-walled glass fibre reinforced epoxy matrix composite shafts produced by using both pre-preg wrapping and filament winding methods. The filament wound samples were manufactured with four different helix angles ([±30]FW, [±45]FW, [±60]FW, and [±75]FW ), whereas [0, 90]PP pre-pregs was utilised for producing the wrapped kind of samples. In order to assess the quasi-static failure responses, the samples were subjected to increasing amount of torsional load at a fixed angular rotation speed. The experimental findings of [±30]FW, [±45]FW, and [±60]FW samples were found to be very compatible with those obtained via Finite Element Analysis (FEA). Contrarily, the numerical model were not able to describe accurately the load—displacement behaviour of [±75]FW and [0, 90]PP with the exception of the initial loading phase. [±45]FW was found as the most favourable option for designers in terms of torsional stiffness. Whereas, those characterised by [±30]FW, and [±60]FW exhibited very close torsional resistances in a difference range of only 5%. [0, 90]PP exhibited the lowest average torsional failure resistant and stiffness but the highest average rotation angle before rupture.

The content of the scientific work is to evaluate the properties of matrix pre-preg systems of composite materials suitable for the production of high performance composite parts, for example for automotive or aerospace industry. The research work introduces composite materials, types, properties and fields of use of matrices and fibres. The main part deals with the description of the pre-preg production, the description of the state of the material conversion with a focus on the B-state of the resin, including the technologies for the production of composite materials from pre-preg systems. The practical part is focused on the testing of matrices intended for the manufacture of pre-preg systems of composite materials, it compares different types of epoxy matrix and glass fiber in several layers. The aim of the work is to evaluate the tested composite systems suitable for pre-preg applications, to compare the properties and parameters of the given application with the focus on the recommended production methods. The result of the work can then be used as the most suitable production application according to the customer's requirements for the product.

The purpose of this study was to evaluate the adhesion properties of phenol formaldehyde-prepreg oil palm veneers that have potential for plywood manufacture. Phenol formaldehyde (PF) resin of three different molecular weights (i.e. 600 (low), 2,000 (medium), and 5,000 (commercial)) were used to pre-treat the veneers. The veneers were soaked in each type of PF resin for 20 seconds, pressed between two rollers, and pre-cured in an oven maintained at 103 ± 2 °C for 24 hours. The volume percent gain (VPG), weight percent gain (WPG), pH, buffering capacity, and contact angle of the phenolic pre-preg veneers were determined. The bonding shear was also evaluated according to British Standard European Norm BS EN 314. The results show that veneers from both inner and outer layers treated with low molecular weight PF (LMwPF) resin had significantly higher VPG and WPG compared to the other PF resins. The pH values of all of the veneers were slightly acidic (6.5 to 6.8) except for those that were treated with commercial molecular weight PF resin (7.8). A buffering capacity study revealed that untreated veneer had a greater resistance toward alkali, but was unstable under acidic conditions, while the phenolic pre-preg veneer behaved differently. This effect was more prominent as the molecular weight of the PF resin increased. An examination of the veneer surfaces demonstrated that phenolic treatment had increased the contact angle of the OPS veneer surfaces significantly. The bonding properties of plywood made from pre-preg palm veneers were found to be superior to those of commercial palm plywood.