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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.

A modern combat aircraft uses considerable amount of advanced composite material in structure build for better flight performance, stealth requirement and higher payload. Combat aircrafts made using composite structure require large numbers of custom shims of various thickness and shapes throughout interface surface, which are presently prepared by suit on assembly process to fill gaps measured between sub-structure parts and skin. The scope of study is four plus generation combat aircraft like Indian Light combat aircraft. These gaps arise due to composite raw material characteristics, mould tool and manufacturing process which results in geometry variation. This research has focussed the delta wing integral fuel tank composite structure. However, these research findings can be applied in other wing shapes made by composite part within the scope. The shims, whether liquid or solid, are necessary to eliminate gaps, maintain structural performance and minimize pull-down forces required to bring the aircraft into engineering nominal configuration for aerodynamic efficiency. Customized shims amount to significant delays in production with much of the time being spent in the critical path of the aircraft assembly. In this research work, we present an alternative strategy for the use of designer solid shim, based on redesign of lay-up moulding tool (female type) and shims manufacturing with change in existing manufacturing value stream. The experimented method has reduced the manufacturing cost of wing assembly, shorten the shimming process cycle and improve the assembly efficiency, product quality and performance.

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.

Fiber reinforced polymer composites are often used as a replacement for metal alloys because of the superior strength to weight ratio. However, a major drawback of these materials is the lack of formability caused by the low strain to failure ratio that does not allow the material to follow tooling contours into deep drawn shapes or tight radii. Composite materials have a multiscale hierarchical structure where micro and meso scale effects (fiber and tow scales) contribute to the macro structural response (laminate scale). In particular, during forming, different deformation occurs simultaneously at every scale. Currently, the amount of quantifiable and comparable forming data for both continuous and discontinuous fiber reinforced polymer composites, including a multi-scale understanding of the deformation response, is limited because of the lack of a testing system. This article proposes a novel test method and an apparatus called “the forming fixture” for testing the tow formability of fiber reinforced polymer composites by determining the required load to form an uncured resin impregnated fiber tow sample into a stretch drawn profile. Test results from forming of Hexcel (Stamford, CT) IM7-G continuous carbon fiber impregnated with Huntsman (The Woodlands, TX) RDM 2019-053 resin system, in the temperature range of 21°C–121°C, are discussed to demonstrate the use of the proposed apparatus including representative data. Results showed consistency and repeatability, validating the reliability of the novel method. The test aided in defining the forming behavior of the material in real time both visually (e.g. sample failure location) and as forming load versus displacement curves. A novel forming metrics, relating the maximum drawing depth with no failure and the maximum forming load, is defined to compare and select different fiber and resin formulations. Widespread adoption of the forming fixture will reduce reliance on a “trial and error” approach during the the forming process.

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.

It is planned that the high voltage electrical insulation on the ITER feeder busbars will consist of interleaved layers of epoxy resin pre-impregnated glass tapes (‘pre-preg’) and polyimide. In addition to its electrical insulation function, the busbar insulation must have adequate mechanical properties to sustain the loads imposed on it during ITER magnet operation. This paper reports an investigation into suitable materials to manufacture the high voltage insulation for the ITER superconducting busbars and pipework. An R&D programme was undertaken in order to identify suitable pre-preg and polyimide materials from a range of suppliers. Pre-preg materials were obtained from 3 suppliers and used with Kapton HN, to make mouldings using the desired insulation architecture. Two main processing routes for pre-pregs have been investigated, namely vacuum bag processing (out of autoclave processing) and processing using a material with a high coefficient of thermal expansion (silicone rubber), to apply the compaction pressure on the insulation. Insulation should have adequate mechanical properties to cope with the stresses induced by the operating environment and a low void content necessary in a high voltage application. The quality of the mouldings was assessed by mechanical testing at 77 K and by the measurement of the void content.

The mechanical and tribological performances of glass-epoxy (GE) and carbon-epoxy (CE) pre-peg composites are presented in this paper. Composites were prepared from their respective pre-pegs using compression molding technique. The mechanical and three body abrasive wear tests were conducted as per ASTM standards. Evaluation of mechanical properties indicated that carbon-epoxy composites had superior properties compared to glass-epoxy composites except the tensile modulus and percentage elongation. The three body wear study has shown the considerable influence of sliding distance on wear rate. The sliding velocity and normal load have shown lesser influence on wear rate. This study has shown that pre-peg composites can be successfully prepared using compression molding technique and can be tested as per ASTM standards.

This paper approaches the design, modeling, and manufacturing process of the multipurpose steering wheel for a formula-style race car. The Multipurpose steering wheel is a device for lateral control of the formula student and also for changing the formula’s parameters. Steering wheel’s parts are designed with an aim to comfort, usefulness, manufacturability, and cost of prototype. Subsequently, the main body modular mold design and manufacturing process is presented, taken into the account the technology of production and material with suitable attributes selection. For the steering wheel, it is utilized the technology of pre-impregnated carbon fiber fabric reinforced polymer (CFRP) cured in an autoclave. Design of layers of composite material is described in the detail, followed by the material’s bend test. Custom internal parts made by 3D printing technology with a purpose of mounting electrical components and mechanical control components are demonstrated. The final product is part of formula student electric racing car SGT-FE18.

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.

Scrap is generated from the various manufacturing techniques of composites using prepregs. With the increasing amounts of composite waste generated, there are still no feasible techniques to re-use this scrap other than disposing it in landfills which implements concerns such as environmental and economic. Waste disposal charges are added to the cumulative manufacturing costs, which raises if the waste is categorized as hazardous in addition to the environmental duplications. With the current certain of growth, these factors have driven the development of recycling paths. This study focuses on investigating the compressive strength of carbon fiber reinforced polymer CFRP prepreg scrap from aerospace industries using compression molding. From this paradigm, we can define the potential applications they can be re-used for. Moreover, the newly developed scrap-based sample forms can help in leading several new business ideas for a more thorough vision in the industry. The process is demonstrated using prepreg scrap leftovers obtained from STRATA CFRP manufacturing processes used for aerospace purposes. The work frame followed in this study was to initially prepare the appropriate conditions and the material for the process, execute the compression molding, and then test the final samples for mechanical properties. The main parameters considered and evaluated in this study are the compressive strength and the modulus of elasticity of the samples, which are compared for applicability in the final phase of the study. This work offers a feasible and environment friendly solution to the increasing prepreg scrap waste problem in the composites industry, including an opportunity for the industry to redeem some original material cost. Furthermore, this process can later also be combined with other traditional processes for a more advanced improvement in properties.

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.

Preparation of natural fiber-reinforced thermoplastic prepreg tapes is impeded by two major challenges: 1) incompatibility between natural fibers and thermoplastic; and 2) difficulty impregnating thermoplastic into fibers, due to thermoplastics’ high viscidity. In this study, we investigated the reaction mechanisms associated with jute twines that were treated with alkali and laccase, to improve the compatibility of jute twine/ polypropylene (PP) tape. Simultaneously, PP with three melt flow indices (MFI, 10.9 g/10 min, 27.8 g/10 min, 50.0 g/10 min) was tested to determine optimal conditions for PP impregnation. The results showed that alkali and laccase treatment can effectively improve the interfacial bonding strength between jute twine and PP; although laccase treatment is milder than alkali treatment, and thus enabled more improvement in the prepreg tapes’ tensile and dynamic mechanical properties. The amount of PP impregnated into the jute twine increased as a function of increasing MFI. However, the impregnation effect must be balanced with the PP’s tensile strength. In summary, the prepreg tapes prepared by laccase-treated jute twine and PP with an MFI of 27.8 g/10 min exhibited the best tensile performance. Based on subsequent calculations, the nominal pressure of a pipe wound with laccase-modified jute twine prepreg tapes, can reach 2.88 MPa.

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.

In situ consolidation of pre-impregnated thermoplastic composite requires as much as possible intimate contact as well as an appropriate molecular diffusion across the interface where the intimate contact takes place. The last depends on the temperature that influences the molecular mobility. Thus, in order to evaluate the consolidation first we must describe accurately the composite surfaces and then, when placed in contact for manufacturing the laminate, a high-resolution simulation of the resulting thermal model must be accomplished to have access to the thermal history at the rough contact surface. In this paper based on a fractal description of the composite surface, the evolution of the intimate contact is performed by solving the flow equations during the compression. High-resolution thermal simulations based on the use of the proper generalized decomposition – PGD – are carried out on the geometrically evolving composite surface.

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.

A novel pre-preg coating method was used to improve the interlaminar fracture toughness in carbon fibre epoxy composite laminates, using reactive liquid rubber. The Epoxy Terminated Butadiene Nitrile (ETBN) liquid rubber incorporated between pre-pregs using automatic draw bar coating technique. Experimental test results reveal that by adding ETBN in small quantities in the range of 15.55–22.66 g/m2, inter laminar critical energy release rates (GIC and GIIC) can be improved up to 140% in mode-I loadings and 32% in mode-II loadings respectively. It was confirmed that the effect of ETBN rubber concentration in carbon epoxy pre-preg system on interlaminar fracture toughness under mode-I and mode-II loadings, was discussed by on the bases of fractographic observations and mechanism considerations using SEM.

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.

A study concerning the application of fiber laser to perforate thermoplastic pre-pregs is presented. An IPG fiber laser was used to drill arrays of holes in PEKK carbon-fiber composite pre-preg material. Perforated holes were of the order of 100μm. The effects of laser perforation process parameters including the number of pulses on the geometry of the resultant holes and the thermal damage to the matrix and fibres have been investigated. Dimensional analysis and experimental results have been used to construct the laser perforation process model. Keywords: Laser perforation; Fibre laser; Process modelling; Polymer matrix composites.

Pre-preg and non-crimp-fabric composite single lap bonded joints were manufactured and investigated to characterise the bond quality and static failure behaviour. A two-part epoxy adhesive was employed to bond composite laminates. The composite panels, which were treated with low pressure oxygen plasma, were bonded in a hot drape former and then cut to manufacture single lap bonded joints. The joints were examined using X-ray microtomography to evaluate the bond quality achieved in the hot drape former. Quasi-static tensile tests were conducted on the pre-preg and non-crimp-fabric composite single lap bonded joints. The fracture surfaces were examined using optical and scanning electron microscopy. The static failure behaviour and failure patterns observed in the two joint types were compared and discussed.

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.

This paper presents a novel approach to toughen the otherwise brittle unsaturated polyester resin (USP) in the polymer matrix biofiber composites. In contrast to the conventional method of incorporating the toughening agent in the matrix resin, the method used in the present investigation consisted in treating the biofiber (OPF) with the toughening resin before impregnating with USP resin. Accordingly biofiber was first impregnated with toughening resin, acrylonitrile-butadienne-styrene (ABS) to produce a pre-preg. The pre-preg was then impregnated with USP resin containing free radical initiator. The ABS content in the biofiber pre-preg was varied from 5 to 25%. Unsaturated polyester was reinforced with the pre-preg and cured in presence of MEKP to produce “hybrid composite”. The physical and mechanical properties of the composites were determined.

The most common commercial processes for manufacturing pre-pregs for electronic applications use solvent-based epoxy systems. Solvents are environmentally unfriendly and contribute to voids in the pre-preg and laminate. Voids cause product variability, which is a major source of scrap in board shops. In this paper, we use chemo-rheological and kinetic measurements to identify a potential epoxy-based resin system for a solventless process that is based on injection pultrusion. Differential scanning calorimetry and rheological data show that the candidate system does not react appreciably without catalyst up to temperatures of 170 °C or with catalyst at temperatures

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.

A design method is studied for effective one- and two-layer-type wave absorbers to be installed on circular cylinders using lossy dielectric materials. Design charts based on this design method are presented for each type of wave absorber. One-layer-type cylindrical absorbers are fabricated and measured results for absorbed amounts are presented.

Shape memory alloys (SMA) exhibit functional properties associated with the shape memory effect, responsible of the SMA shape recovery after a cycle of deforming-heating and of a simultaneous generation of mechanical work. Composite systems incorporating SMA wires have the ability to actively change shape and other structural characteristics. The functional properties of such adaptive composites are related to the martensitic transformation in the SMA elements and to the constraining behaviour that the composite matrix has on the SMA wires. In this work the behaviour of a shape memory alloy hybrid composite (SMAHC) is numerically and experimentally investigated. A plate was fabricated using prestrained SMA wires embedded in an epoxy resin pre preg glass fibres composite system. Upon calorimetric and mechanical material characterization, a finite element model was used in order to predict the structural behaviour of the SMAHC. In the experimental tests, the plate was clamped at one side and actuated via electrical heating. Temperature and displacement data were collected and compared with the prediction of the finite element model. The results show that the model is able to capture the shape change in the actuation region, although a thorough description of the SMAHC behaviour requires further modelling work, including the simulation of the SMA loading history during composite manufacturing.

The presence of sharp, “pointed” features on Printed Circuit Board (PCB) power planes and their contribution to increased plane-to-plane electric fields is studied as a potential root cause for PCB level dielectric breakdown. The results of this study are used to gauge the propensity for heat generation due to current leakage through pre-preg. A first order approximation for the E-field between a power and ground plane is Ê = V/d (1) where Ê is the electric field, V is the potential across the planes, and d is the separation between the planes. While this first order approximation is correct for infinite parallel planes, simulations show that second and third order effects that exist on real boards can multiply the effective Ê by more than 100x. The second order effects are primarily dependent on the local sharpness of planar shapes, and plane-to-plane separation. This amplified Efield could potentially breakdown pre-preg locally and initiate current leakage. Leakage through prepreg can grow over time as a leakage path becomes established and can wreak havoc with power rails or create a local ohmic conduction path that can lead to board level failures. A test platform and a series of experiments were developed to understand and quantify the various parameters that contribute to these failures. Tests revealed that given an ambient temperature of 70C, the presence of pointed features in planes reduces the breakdown voltage by at least 75%. It is suspected that under the right conditions, a breakdown will occur on a sharp shape if given sufficient duration of exposure to even low voltages.

A new pre‐impregnated (pre‐preg) ceramic‐based electrical insulation system capable of surviving high superconductor reaction temperatures has been developed for use in superconducting magnets. The use of Nb3Sn superconductors holds great promise for increased magnet performance for high energy physics, fusion, and other applications. A robust, cost‐effective manufacturing process is critical to the successful implementation of these coils. Due to its embrittlement after the high temperature reaction cycle, Nb3Sn cable is usually insulated and wound into the coil prior to heat treatment. An earlier ceramic‐based insulation system, applied using wet‐winding or vacuum impregnation, has been successfully used in the “wind and react” fabrication process. Use of the new pre‐preg system will further simplify the manufacturing process while improving control over the insulation properties. Pre‐preg insulation offers several advantages including improved dimensional control of the insulation, controllable and uni...