Prepreg Sheets Research Articles

Intelligent Material and Fluid Systems. Real-Time Measurement of Internal Strain in FRP Laminates with Optical Fiber Sensors in Autoclave Molding.

In the present study, real-time measurement of internal and residual strains in GFRP laminates with an optical fiber strain sensor was performed in an autoclave molding. An Extrinsic Fabry-Perot Interferometric (EFPI) type optical fiber strain sensor was embedded into prepreg sheets before the molding. The ion viscosity and the temperature of the epoxy resin matrix were also measured simultaneously with the internal strain measurement. The results of the experiments showed that the internal and residual strain of GFRP laminates during the molding could be monitored by the optical fiber sensor embedded in the parallel direction to the reinforcing fibers. It was also found that the circumstances around the embedded optical fiber strain sensor should be taken into account for the interpretation of the measured internal and residual strain.

繊維金属積層材の疲労き裂進展挙動に及ぼす初期切欠き長さおよび予ひずみの影響

Fatigue crack propagation was investigated in fiber metal laminates which have been developed as the aerospace materials. Two kinds of fiber metal laminates were prepared for the fatigue crack propagation test. One was the laminates in which an unidirectional aramid fiber/epoxy prepreg was sandwiched between aluminum alloy sheets, and another was the laminates of a glass fiber/epoxy prepreg and aluminum alloy sheets. The fatigue crack growth in aluminum alloy sheets is strongly influenced by the bridging behavior of unbroken fibers. The effects of difference in reinforcing fiber, initial notch length and pre-stretching were investigated. In comparison with conventional aluminum alloy sheet, the crack propagation rate was extremely small and the decrease in propagation rate was observed in spite of the K increasing test, depending on the initial notch length and the stress ratio. The glass fiber/aluminum alloy laminates showed the noticeable effect of pre-stretching on crack growth rate. The mechanism for the improvement in fatigue crack propagation was also investigated on the basis of the compliance variation with crack propagation and the stress distribution analysis of infrared spectra.

Modelling Flexible Sheets for Automatic Handling and Lay-up of Composite Components

Automating the manufacturing process associated with composite components from prepreg presents new engineering challenges. To design, implement and operate machinery to handle and lay-up prepreg sheet material requires a clear understanding of the processes involved. Manipulation of sheet material is an integral part of the lay-up procedure. This paper presents the main automation issues concerning the production processes and defines a mathematical model for predicting the shape of prepreg sheets for the purposes of manipulation. This provides an aid towards the control of shape during the process of lay-up. Critical mould parameters, which determine prepreg sheet shape, are presented. Lay-up trajectories for a multi-arm robotic system have been derived, utilizing the models formulated. Practical trials with an existing multi-arm robotic system have proved satisfactory control of the process.

Process for producing inorganic fibre-based prepreg sheet and process for producing insulating laminate: Yokoyama, H., Toyoshima, S. and Ibaraki, T. (Honshu Paper Co., Ltd, Tokyo, Japan)US Pat 5 328 566 (12 July 1994)

Process for producing inorganic fibre-based prepreg sheet and process for producing insulating laminate: Yokoyama, H., Toyoshima, S. and Ibaraki, T. (Honshu Paper Co., Ltd, Tokyo, Japan)US Pat 5 328 566 (12 July 1994)

A Vacuum and/or Pressure Forming System Using a Prepreg Sheet of FRP with a Gel Coat Layer

This paper introduces a new vacuum and/or pressure forming system using a prepreg sheet which consists of two thickened layers of unsaturated polyester, i.e., FRP (Fiber Reinforced Plastic) and gel coat layers, sandwiched by two stretchable films. The efforts were focused on the development of sheet construction, material properties and processing conditions. The difficulties in the development of this system are found in; 1. uneven thickness distribution in a molding 2. vaporization of vinyl monomer 3. gel coat cracks These difficulties were solved by the chemical modifications of resin such as; 1. unifying the apparent tensile modulus of each layer by controlling the viscosity 2. reducing the maximum exothermal temperature 3. shortening the gel time and by the physical modifications of processing conditions such as selection of an appropriate forming rate. The expected application area of this new system is also mentioned briefly.

Self-reinforced prepregs and laminates of a poly(phenylene oxide)—polystyrene alloy with a liquid crystalline polymer

Extruded prepregs of a blend of a poly(phenylene oxide) (PPO)—polystyrene (PS) alloy with a liquid crystalline polymer (LCP) have been prepared for various concentrations and with different extension ratios. These prepregs have then been compression moulded into laminates with two orientations of the prepregs in the laminate. In one case, 16 prepreg sheets have been placed in unidirectional orientation. In the other, the 16 sheets have been placed in such a way that each subsequent sheet was at a 45° angle with respect to the preceding sheet, thereby yielding a quasi-isotropic orientation. The laminates have been prepared for each extension ratio with different reduction ratios. The unidirectional laminates have been tested for the tensile strength and secant modulus in the machine direction and the transverse direction. The quasi-isotropic laminates have also been tested for mechanical properties. The mechanical properties of the laminates have been compared to the values obtained for injection moulded blends of the same materials. Prediction of the mechanical properties of the quasi-isotropic laminates have been carried out based on the values obtained for the unidirectional laminates tested in the machine and transverse directions. The mechanical properties of the quasi-isotropic laminates with high extension and reduction ratios are either comparable to or higher than those obtained for the injection moulded blends of the same concentration tested in the machine direction. The morphologies of the prepreg sheets with various extension ratios have been studied in order to determine the nature of the LCP fibres in the prepregs. The morphologies of the quasi-isotropic laminates with various LCP concentrations have also been studied in order to determine the effect of orientation of the LCP fibres in the laminates. The studies have shown that this novel processing technique enables the preparation of self-reinforced laminates of LCP—thermoplastic blends, with controlled anisotropy and enhanced mechanical properties, when compared with the corresponding injection moulded blends.

スマートＣＦＲＰ構造開発を目的とした電気ポテンシャル法による層間はく離検出法の適用性検討

CFRP composite plate structures have been generally known as that those have high specific mechanical properties. The CFRP composite plate, therefore, has been widely applied to many kinds of aircraft structures. The composite plate structures, however, have a week point at interlamina strength. Since a delamination resistance of its plate is very low, delaminations easily yield by a low velocity impact loading or fatigue loading. For this reason, a smart structure to detect a delamination is desired now. In this study, therefore, an applicability of an electrical potential method to detect a delamination was examined experimentally from a stand point of a sensor for a smart structure. Effects of prepreg thickness, kind of electric current of electrical resistance bridge, loading mode and stacking sequence were all experimentally researched by using T 300/Epoxy. Mode I and II types of tests were conducted and the electrical resistance changes were measured by the electrical resistance bridge circuit. As a result, the followings were obtained. (1) In the case that there are many interlaminae by using thin prepreg sheet, the electrical resistance change is smaller than that of thick one because the electrical resistance to the plate thickness becomes large. (2) The AC is better for an electrical resistance bridge circuit than DC because it gave more stable results than those by DC. (3) Though the delamination crack surfaces contact with each other in the mode II tests. The electrical resistance change could be measured by the AC electrical resistance bridge method. (4) In the actual composite, plates, the nonlinear relations between the delamination crack growth and the electrical resistance of the specimen were obtained due to the delamination crack plane transition.

Thermal expansion coefficients of unidirectional carbon fiber/PEEK composite made of commingled yarns

Unidirectional carbon fiber (CF)/poly(ether‐ether‐ketone) (PEEK) composite was manufactured from the commingled yarns composed of CF and PEEK filaments (this composite is named ‘‘commingled composite’’). The thermal expansion coefficient (TEC) of the commingled composite was measured and compared with that of CF/PEEK unidirectional composite made of prepreg sheets (this composite is named ‘‘prepreg composite’’). The minimum value of TEC’s parallel to the fiber direction was observed at around 150 °C for both specimens which were not thermally treated. This minimum disappeared after the thermal treatment at 230 °C for 30 min or the repeating measurements (0 °C→230 °C, 0 °C→230 °C,...). While the TEC of the prepreg composite was almost independent of temperature, that of the commingled composite showed a remarkable decrease at temperatures above the glass transition temperature (Tg) of PEEK. This could be interpreted in terms of the orientation distribution of carbon fibers in the commingled composite. The difference of longitudinal TEC’s between heating and cooling experiments was attributable to the temperature difference between the surface and the inner parts of the specimen. The TEC’s transverse to the fiber direction were scarcely influenced by the thermal history. The TEC’s increased slowly below 100 °C and increased rapidly above 100 °C with increasing temperature. Theoretical predictions based on the extended equivalent inclusion method and on the classical lamination theory exhibited good agreement with experimental data. However, it could not be predicted that the TEC’s parallel to the fiber direction were depressed at around 30 °C. The cause of this discrepancy was supposed due to the temperature dependence of TEC’s of the carbon fiber itself.

ＣＦＲＰと制振材料から構成される制振複合材料の曲げ振動減衰特性

New materials, that possess high damping capabilities and high strength properties, have been studied in carbon fiber reinforced plastics (CFRP). These materials are referred to in this article as CFRP/damping-material laminates. The CFRP/damping-material laminates investigated here are composed of a unidirectional carbon/epoxy prepreg sheet and a polyethylene based damping material sheet used as an interleaf. Cantilever beam tests revealed the high damping properties of these laminates. Loss factor values for these composites are 10 to 100 times as large as that for conventional CFRP. These values could be predicted by using the constrained layer damping theory, except for two specimens.

Mechanical Properties for CFRP/ Damping-Material Laminates

New materials that possess high damping capabilities and have high strength properties have been studied in carbon fiber reinforced plastics (CFRP). These materials are referred to in this article as CFRP/damping-matenal laminates The CFRP/damping-material laminates investigated here are composed of a unidirectional car bon/epoxy prepreg sheet and a polyethylene-based damping material sheet used as an in terleaf. Cantilever beam tests revealed the high damping properties of these laminates. Loss factor values for these composites are 5 to 50 times as large as that for conventional CFRP. These values could be predicted by using the analysis constrained layer damping treatment, except for two specimens. Also, the interleaving effect on tensile and compres sion strength are discussed here. Tensile test results for quasi-isotropic laminate based composites indicated that the damping material interleaf is effective for suppressing delamination and multiple splitting in the 0° angle layer. The ultimate load increase of 3 to 15 % was caused by this suppression effect. Compression test results suggest that the in terleaf is not very effective for the compression strength increment.

Silicon carbide/SRBSN composites

SUMMARYCeramic‐matrix composites have been produced using unidirectionally aligned Textron SCS‐6 fibres in a sintered reaction‐bonded matrix. A tape‐casting technique was used to produce a prepreg sheet that could be cut and stacked to form a layup. Al2O3 and Y2O3 were used as sintering aids, final sintering being carried out in a hot press at 1700°C.Matrix, fibre and interfacial microstructure has been characterized using analytical microscopical techniques. X‐ray mapping of the carbon and silicon distribution at the fibre–matrix interface was carried out, and evidence of reaction between the outer carbon‐rich layer of the fibre and the matrix was found.Micromechanical behaviour of interfaces has been investigated and compared with interfacial microstructure and macromechanical properties.

Thermal Expansion Coefficients of Unidirectional Carbon Fiber/PEEK Composite Made of Commingled Yarns

Unidirectional carbon fiber (CF)/poly(ether‐ether‐ketone) (PEEK) composite was manufactured from the commingled yarns composed of CF and PEEK filaments (this composite is named ‘‘commingled composite’’). The thermal expansion coefficient (TEC) of the commingled composite was measured and compared with that of CF/PEEK unidirectional composite made of prepreg sheets (this composite is named ‘‘prepreg composite’’). The minimum value of TEC’s parallel to the fiber direction was observed at around 150 °C for both specimens which were not thermally treated. This minimum disappeared after the thermal treatment at 230 °C for 30 min or the repeating measurements (0 °C→230 °C, 0 °C→230 °C,...). While the TEC of the prepreg composite was almost independent of temperature, that of the commingled composite showed a remarkable decrease at temperatures above the glass transition temperature (Tg) of PEEK. This could be interpreted in terms of the orientation distribution of carbon fibers in the commingled composite. The ...

Production of flexible metal matrix composites reinforced with continuous Si-Ti-C-O fibers by atmospheric plasma spraying

An investigation of the production of aluminum matrix composite sheet reinforced with continuous Si-Ti-C-O fibers was performed by a plasma spraying method. The unidirectionally reinforced Si-Ti-C-O fiber/Al prepreg sheet (300 by 3000 mm, 0.1 to 0.15 mm thick, with 40 vol. % Fiber) was fabricated by plasma spraying under atmospheric conditions. The depth of the oxidation layer formed on the surface of the metal matrix composite (MMC) prepreg sheet was found to be about 200 A, and this value is almost independent of the atmosphere during plasma spraying. The fibers homogeneously disperse and do not contact each other in the matrix of the MMC prepreg. No damage on the surface of the extracted fibers from the MMC prepreg sheet can be observed. The MMC prepreg sheet was used to produce MMC plate by hot pressing at 640 to 680 °C under 9.8 MPa. The flexural strengths in the longitudinal and transverse directions of the MMC plate pressed at 660 °C were 1.0 and 0.25 GPa, respectively.

Prepreg sheet for flake lining and lining process using the same : Inuzuka, T., Hasegawa, T., Tomikawa, M. and Aoki, S. (Nippon Glass Fiber Co, Ltd, Tsu and Chiyoda Corporation, Yokohama, Japan) US Pat 4 889 766 (26 December 1989)

Prepreg sheet for flake lining and lining process using the same : Inuzuka, T., Hasegawa, T., Tomikawa, M. and Aoki, S. (Nippon Glass Fiber Co, Ltd, Tsu and Chiyoda Corporation, Yokohama, Japan) US Pat 4 889 766 (26 December 1989)

Design of an opposing pair magnet system for ASTROMAG

A magnet system comprising a pair of self-supporting disk-shaped coils has been designed for the ASTROMAG facility on the space station Freedom. The coils are connected in a quadrupole configuration in order to eliminate their dipole moment. One of the primary requirements of this design is that the magnet coils must have near-perfect structural integrity. To this end, each coil would be manufactured as a monolithic composite in which the superconducting wire is incorporated as one of the components. By utilizing a precision X-Y numerically controlled wiring machine, the coil can be built up in pancake layers by alternating prepreg sheets of fiber/epoxy (e.g. carbon or Kevlar fiber) with a layer of NbTi wire that spirals from OD to ID in one layer, from ID to OD in the next. and so on. Each disk magnet will have an ID of 0.4 m and an OD of 1.7 m. The peak field at the winding will be 7.2 T. The system is to operate at 1.8 K. and I/sub op//I/sub c/=0.5. Results of magnetic field and force calculations are presented, and the structural characteristics of the system are described.

Resistance to transverse tension of a commingled carbon fiber/poly(ether ether ketone) composite.

Resistance to transverse tension of the unidirectional carbon fiber/Poly(ether ether ketone) (PEEK) composites was examined by uniaxial tensile and cleavage tests. Three types of unidirectional carbon fiber/PEEK composites were fabricated from: (a) prepreg sheet, (b) plain weave cloth (warp: commingled yarn of 1800d of carbon fiber with PEEK fiber, weft: PEEK yarn of 70d), or (c) 5-shaft sateen weave cloth (warp: carbon yarn of 1800d, weft: PEEK yarn of 900d). The initial Young's modulus and the breaking strength measured by the transverse tensile tests were the highest on the specimen (a). Those of the specimen (c) were the lowest because of the lack of the carbon fiber/PEEK interfacial adhesion. On the other hand, the mode I intralaminar fracture toughness estimated from the cleavage test was the highest on the specimen (b). The interfacial adhesion between the carbon fiber and PEEK resin was also investigated by scanning electron microscopic observation of the fractured surface after transverse tensioning. For specimen (b) the fracture surface was rough and irregular, and the fibers were twisted with one another. The fracture surface of specimen (a) was flat and smooth, and the fibers were parallel to one another. It was concluded that the undulation and twisting of the carbon fibers enhanced the fracture toughness of specimen (b).

PAN and Pitch-Based Carbon Fiber-Reinforced Polyethernitrile Composites

A new engineering thermoplastic resin (ID300) was combined with con tinuous carbon fiber (CF) to produce an advanced composite material. Both polyacryloni trile (PAN) and pitch-based carbon fiber were investigated as reinforcements. Impregna tion was accomplished directly from the powder form to a well-consolidated prepreg sheet. No fiber degradation even for the pitch carbon-fiber system was experienced. The mechanical properties measured included flexural strength, compressive strength and short beam shear strength. The ID300 materials compare quite favorably to conventional thermoplastic and ther moset material systems. The prepreg sheet was utilized in the diaphragm sheet forming method to produce hemispherical geometries from laminates of [0/90] s and [0/45/-45/90] s configurations. The laminates exhibited excellent formability

Die-Less Forming of Thermoplastic- Matrix, Continuous-Fiber Composites

A die-less forming process is described which is intended to be an eco nomical method for manufacturing large, complex-shaped components from thermoplastic matrix, continuous-fiber composite materials. The concept is specialized to tapered shapes which are singly curved, long in their straight direction, and of arbitrary variable cross section along their length. An array of universal, computer-controlled rollers generates such shapes from initially flat laminates or stacks of prepreg sheet. Heating and bending of the material are strictly local operations occurring only within a small active zone at any one instant, thereby eliminating the need for fixed tooling and for large autoclaves or presses. The rollers are controlled using a "kinematically admissible bending" algorithm which requires interply sliding only in the local hot zone. Despite the fact that all of the regions not being formed are cold and rigid, the fibers of the composite are not forced to change length. Experimental verification to date includes: (1) rapid, local, through-thickness induction heating of carbon fiber, polymer matrix composite workpieces, and (2) kinematically- admissible bending of preconsolidated thermoplastic matrix laminates to simple singly- curved shapes, using a "near-term demonstration" forming machine. Tension superim posed during such bending operations has been shown to be useful for maintaining good fiber alignment.

混繊糸および交織布を用いた一方向炭素繊維／ＰＥＥＫ複合材の試作と横方向引張り特性

Three types of unidirectional carbon fiber/PEEK composites are fabricated from : (a) prepreg sheet, (b) plain weave cloth ; warp : commingled yarn (1800 d) of carbon fiber with PEEK fiber, weft : PEEK yarn (70 d), (c) 5-shaft sateen weave cloth ; warp : carbon yarn (1800 d), weft : PEEK yarn (900 d). The transverse tensile properties are measured and compared with the theoretical predictions based on the perfect adhesion and interfacial slippage models. The transverse Young's moduli of the composites fabricated from (a) and (b) are in good agreement with the theoretical values based on the perfect adhesion model at the fiber/matrix interface. On the other hand, Young's modulus of the composite from (c) rather coincides with the prediction by the interfacial slippage model. The wettability and the interfacial adhesion between the carbon fiber and the PEEK resin are also investigated by the SEM observation of the fracture surface.

横等方性繊維を用いた一方向繊維複合材への界面すべりモデルの適用

In a preceding paper, the interfacial slippage model of the unidirectional fiber composite was developed assuming that the fiber and the matrix were both isotropic. By the use of this model, the elastic moduli and the stress distribution in the transverse cross-section of the composite can be predicted. In this paper, the interfacial slippage model has been extended to the composite reinforced with transversely isotropic fiber. The predicted transverse Young's moduli of the unidirectional carbon fiber/PEEK composites are compared with the experimental results. In the experiment, two types of unidirectional carbon fiber/PEEK composites are prepared : (a) from prepreg sheet and (b) from the cloth woven using the warp of carbon fiber and the weft of PEEK fiber. The transverse Young's modulus of the specimen (a) coincides with the theoretical results assuming the perfect adhesion at the carbon fiber/PEEK interface. On the other hand, the experimental result, of specimen (b) rather coincides with the theoretical prediction based on the interfacial slippage model.