Prepreg Resin Research Articles

Near Infrared Spectroscopy for On-line Monitoring of Alkali- Free Cloth /Phenolic Resin Prepreg During Manufacture

A NIR method was developed for the on-line monitoring of alkali-freecloth/phenolic resin prepreg during its manufacturing process. First, the sizing content ofthe alkali-free cloth was analyzed, and then the resin, soluble resin and volatiles content ofthe prepreg was analyzed simultaneously using the FT-NIR spectrometer. Partial leastsquare (PLS) regression was used to develop the calibration models, which for the sizingcontent was preprocessed by 1stDER MSC, for the volatile content by 1stDER VN, forthe soluble resin content by 1stDER MSC and for the resin content by the VN spectraldata preprocessing method. RMSEP of the prediction model for the sizing content was0.732 %, for the resin content it was 0.605, for the soluble resin content it was 0.101 andfor volatiles content it was 0.127. The results of the paired t-test revealed that there was nosignificant difference between the NIR method and the standard method. The NIRspectroscopy method could be used to predict the resin, soluble resin and the volatilescontent of the prepreg simultaneously, as well as sizing content of alkali-free cloth. Theprocessing parameters of the prepreg during manufacture could be adjusted quickly withthe help of the NIR analysis results. The results indicated that the NIR spectroscopymethod was sufficiently accurate and effective for the on-line monitoring of alkali-freecloth/phenolic resin prepreg.

The application of near infrared spectroscopy in the quality control analysis of glass/phenolic resin prepreg

During the manufacture of glass/phenolic resin prepreg cloth, the feasibility of near infrared (NIR) spectroscopy as a technique for the quality control analysis of the resin content, the volatile content and the resin pre-curing degree has been verified. The partial least square (PLS) regression was used to develop the calibration models by utilizing several different spectral pretreatments. The optimum models had determination coefficients (R2) of 98.29 for the resin content, of 99.50 for the volatile content and of 97.66 for the pre-curing degree, respectively. The root mean square errors of prediction (RMSEP) for the resin content, the volatile content and the pre-curing degree were 0.376%, 0.169% and 0.105%, respectively. The results of the paired t-test revealed that there was no significant difference between the NIR method and the standard method. In the manufacture process of the prepreg cloth, the NIR on-line monitoring results were used to be the instructions for the quality control.

On-line Monitoring of Resin Content and Volatile Content in Carbon/Phenolic Resin Prepreg Cloth by Near-Infrared Spectroscopy

Near-infrared (NIR) spectroscopy has been implemented for on-line monitoring of resin and volatile content during the manufacture of carbon/phenolic resin prepreg cloth. The calibration models were generated using partial least square (PLS) regression to relate the on-line spectral data to the components' content. The models had determination coefficients (R2) of 92.92 for the resin content and of 92.11 for the volatile content. The root mean square errors of prediction (RMSEP) were 0.861% and 0.273% for the resin and volatile content, respectively. The statistical results of the paired t-test revealed that there was no significant difference between the NIR method and the standard analysis method. The resin content and the volatile content were continuously monitored by NIR in the production of the carbon prepreg. The study indicates that NIR spectroscopy is a good alternative for monitoring the quality of carbon prepreg.

Avaliação da temperatura de transição vítrea de compósitos poliméricos reparados de uso aeronáutico

Este trabalho mostra a avaliação da temperatura de transição vítrea (Tg), por DMTA, de três famílias de compósitos poliméricos reparados, tendo como laminados base tecidos de fibras de carbono/resina epóxi modificada com elastômero (F584), vidro/resina epóxi (F161) e aramida/resina epóxi (F161). Os compósitos foram laminados manualmente por processo convencional e curados em autoclave de indústria aeronáutica. Posteriormente, danos foram simulados sendo, em seguida, reparados adotando-se a técnica de sobreposição de camadas de pré-impregnados de resina epóxi (F155), com adição de filme adesivo de epóxi (FM 73). As curvas DMTA mostram os efeitos da combinação de diferentes sistemas de resinas na Tg e, conseqüentemente, na temperatura de serviço do componente reparado. O material de reparo utilizado, baseado em pré-impregnados com resina epóxi F155 e filme adesivo de epóxi, provocou a redução da Tg dos compósitos reparados. Para os laminados base com tecido de fibras de carbono e vidro foram verificadas reduções de aproximadamente 30 °C na Tg. Este efeito foi mais pronunciado (redução de aproximadamente 40 °C) quando o laminado reparado de aramida foi submetido a condicionamento higrotérmico a temperatura e umidade elevadas. Esta redução na Tg dos laminados reparados é atribuída à migração do adesivo para o pré-impregnado de resina epóxi F155 utilizado no reparo, durante o processo de cura, e à plasticização do sistema polimérico pela água, durante o condicionamento higrotérmico. A redução da Tg leva a uma conseqüente redução da temperatura de serviço do compósito polimérico reparado.

COMPOSITE MATERIALS FOR WIND POWER TURBINE BLADES

▪ Abstract Renewable energy resources, of which wind energy is prominent, are part of the solution to the global energy problem. Wind turbine and the rotorblade concepts are reviewed, and loadings by wind and gravity as important factors for the fatigue performance of the materials are considered. Wood and composites are discussed as candidates for rotorblades. The fibers and matrices for composites are described, and their high stiffness, low density, and good fatigue performance are emphasized. Manufacturing technologies for composites are presented and evaluated with respect to advantages, problems, and industrial potential. The important technologies of today are prepreg (pre-impregnated) technology and resin infusion technology. The mechanical properties of fiber composite materials are discussed, with a focus on fatigue performance. Damage and materials degradation during fatigue are described. Testing procedures for documentation of properties are reviewed, and fatigue loading histories are discussed, together with methods for data handling and statistical analysis of (large) amounts of test data. Future challenges for materials in the field of wind turbines are presented, with a focus on thermoplastic composites, new structural materials concepts, new structural design aspects, structural health monitoring, and the coming trends and markets for wind energy.

Characterization of epoxy prepreg SPX 8800 system by isothermal differential scanning calorimetry

AbstractIsothermal Differential Scanning Calorimetry (DSC) was used to study the curing behavior of epoxy prepreg SPX 8800 system, which contains DGEBA/DICY/Diuron (Diglycidyl ether of bisphenol A/Dicyandiamide/Diuron) reinforced by three layers of glass fibre. The rate curves from the DSC study agreed well with those obtained from the isothermal FT Near Infrared (FTNIR) study and similar activation energy was obtained in the range of 92.6 to 87.7 kJ/mol up to 50% total conversion. Modelling of the whole DSC trace with empirical equation dx/dt=kxm(A‐x)n gave relatively good fitting of the experimental curves (the error is lower than 15%.) in the whole studied cure temperature range (75‐110°C) and no significant difference in cure kinetics was observed for both epoxy prepreg and neat resin.

Repair of damaged RC columns using fast curing FRP composites

In this study, two fast curing resins were used to repair pre-damaged RC columns. They were 1.5-hour heat activated curing prepreg and 20-min ultraviolet curing resin. A 24-hour curing epoxy was also used for comparison purposes. A total of 24 steel reinforced φ 152.4 mm×609.6 mm small-scale concrete columns were designed, cast, cured, surface prepared, and pre-damaged. The damaged samples were repaired using the three types of E-glass fabric reinforced resins. An accelerated conditioning using boiling seawater and ultraviolet radiation was also conducted to investigate the hygrothermal durability of the repaired samples. Uniaxial compression test was conducted on both control samples and conditioned samples. The test results and cost/benefit analysis results show that the two fast curing resins can replace the currently used long-time curing resins in repairing damaged RC columns.

Smart autoclave processing of thermoset resin matrix composites based on temperature and internal strain monitoring

Cure cycle optimization and process control for autoclave cure of thermoset resin matrix composites based on temperature and internal strain monitoring were studied. Cure of thermoset resin is usually an exothermic reaction, which causes temperature increase of composites during cure. Slowing down the temperature ramp rate is effective in lowering the peak temperature. However, the slower is the ramp rate, the longer the cure time becomes. Therefore, it is desirable to control the ramp rate in order to depress the peak temperature with prolongation of cure time minimized. Besides that, precise determination of cure completion is also required in order to minimize cure time. The procedure for smart processing described above was developed and tried on laminate of carbon fiber/epoxy resin prepreg. In this procedure, temperature ramp rate is controlled so that the peak temperature predicted by Springer's thermochemical model is kept below an allowable value. Cure completion is determined by a cure rate equation and internal strain monitoring with embedded EFPI optical fiber sensors. The internal strain is correlated with specific volume change of the matrix resin caused by cure shrinkage and thermal expansion/contraction. The authors found that the cure shrinkage terminates at a certain degree of cure, and EFPI sensors can detect this point. Although the degree of cure can be calculated by integrating the cure rate equation along temperature history, errors may be accumulated. Therefore, the degree of cure is corrected and integration of cure rate equation is restarted at the cure shrinkage termination point detected by EFPI sensors. Thus, cure completion is determined precisely. This smart autoclave processing procedure was able to depress the peak temperature and determine the end of cure.

ＣＦＲＰ硬化過程における光ファイバセンサによる内部ひずみモニタリングと硬化収縮

In the present study, internal strain monitoring and detection of cure shrinkage in matrix resins by using EFPI optical fiber sensors have been investigated for CFRP during autoclave cure. EFPI sensors were embedded into quasi-isotropic CFRP laminates composed of carbon fiber/heat-resistant tough epoxy resin prepregs for aircraft structures. In order to examine the monitoring ability of EFPI sensors, measured internal strains were compared with specific volume of matrix resins determined by PVT measurement during cure, which indicates their cure shrinkage and thermal expansion/contraction. The results show that the cure shrinkage terminates at a certain degree of cure before the resin cures completely, and the EFPI sensors can detect this phenomenon. From these results, it is found that the EFPI sensors can measure the internal strains corresponding to the specific volume change of the matrix resins after the degree of cure reaches approximately 30%.

耐熱タフエポキシ系ＣＦＲＰの硬化モニタリング

Autoclave curing processes of CFRP (carbon fiber reinforced plastics) laminates composed of carbon fiber/heat-resistant tough epoxy resin prepreg used as aircraft structure material were monitored by dielectric sensors. Then, monitored dielectric properties were compared with the degree of cure predicted by Springer's model and resin viscosity, Reciprocal dielectric loss factor (1/(ee0ω) or ion viscosity), which is considered to correspond to degree of cure, becomes constant at 30-40% degree of cure. And the ion viscosity before gelation does not correspond to resin viscosity. Besides, the exothermic reaction rate peak point shown as temperature overshoot does not correspond with the peak point of differential coefficient of ion viscosity. In the case of this particular resin we selected, motion of free charges or dipoles in the resin is presumed to become insensitive after the degree of cure reaches 30-40%.

A 13C NMR study of the methylol derivatives of 2,4′‐ and 4,4′‐dihydroxydiphenylmethanes found in resol phenol–formaldehyde resins

AbstractA total of 13 of the 16 possible methylol derivatives of 2,4′‐ and 4,4′‐dihydroxydiphenylmethane have been synthesized, isolated, and identified. These compounds are found as intermediates in the cure process of resol phenol–formaldehyde (PF) resins. Analysis of the 13C NMR spectra (in acetone‐d6) of these compounds provided a way to evaluate the seven methylolphenol ring types (methylol derivatives of 2‐hydroxyphenyl and 4‐hydroxyphenyl rings) found in typical resol PF resins using the ipso carbon region from 150 to 160 ppm. A simple diagnostic test was developed using the chemical shift values of the methylol methylene carbon atoms to identify the presence of intermediates containing either a 2‐hydroxyphenyl or a 4‐hydroxyphenyl ring. Using these data it is now possible to analyze the major components in extracted prepreg PF resins. Copyright © 2002 John Wiley & Sons, Ltd.

SCALED ANALYSIS OF COMPOSITE ADHESIVE INTERPHASE PROPERTIES1*

High-performance film adhesives are often employed in aerospace composite structures to provide adequate adhesion between substrates. This study was performed to evaluate the fracture properties of a commercial film adhesive and a carbon fiber prepreg material in both co-cured and bonded applications. In addition, the fundamental reasons for macroscopic fracture properties were evaluated on the microscale using interphase analysis and surface analysis techniques. From this information, it was possible to examine the commingling of prepreg and adhesive resins in the bond line interphase region. The information presented in this study points to a critical aspect of material selection and utilization that is often not considered in composite design: resin compatibility. *Dedicated to Prof. Francisco J. Baltá Calleja on the occasion of his 65th birthday.

A numerical model of the viscosity of an epoxy prepreg resin system

AbstractThe development of the viscosity of a thermoset material during processing is complicated because of the dependence of the initial material state and the kinetic rate of conversion from a liquid to a solid material. Uncured thermoset materials typically have a low enough viscosity such that the consumption of energy to generate flow is relatively low. However, as the curing process advances, the flow mechanisms become hindered by the development of a network gel during crosslinking. Once the resin has reached the appropriate degree of cure for gelation, the resin system is incapable of large fluid‐like deformations. In this research, the rheological properties of an epoxy resin system used in laminate processing were measured and numerically fit with a modification to the dual Arrhenius model to predict the progression of the viscosity during cure. The numerical results were compared with the experimental measurements, and it was found that the model predicts the experimental observations quite well. It was found that the initial degree of cure of the prepreg is not as significant a factor as the temperature rate dependence on the processing time between the point of flow onset and gelation. However, the minimum viscosity during processing is strongly influenced by the initial degree of cure of the prepreg system.

The effect of fabric tension and the number of impregnation rollers on woven fabric prepreg quality and cured laminates

The effects of fabric tension and number of impregnation rollers used during hot-melt prepreg processing were investigated as they relate to woven fabric prepreg and final composite part quality. Specifically, the processing parameters varied in a design of experiments (DOE) were applied fabric tension and the number of impregnation rollers, while maintaining the same impregnation force. Six experimental prepregs were characterized in terms of prepreg thickness, resin content, tack, and morphology. The results show that fabric tension had a large influence on the prepreg characteristics due to more cylindrical tow shapes and a ridged fiber bed. The number of impregnation rollers was found to affect only the characteristics of the prepregs manufactured with no tension. To investigate the effects of tension on cured composites, six ply laminates were made with each experimental prepreg. Two cure cycles, differing only in consolidation pressures, were used to examine the void content and morphology in the cured laminates. The laminates made with prepregs manufactured with high tension and cured only under vacuum had a greater void content than laminates made with prepregs manufactured with no tension. In both cure cycles, the tow shape in the laminates made from the prepreg manufactured with high tension remained in almost the same shape as in the uncured prepreg. The void content, however, was negligible for all laminates cured at higher consolidation pressure.

Development and hot‐melt impregnation of a model controlled flow prepreg system

AbstractA controlled‐flow epoxy‐based model prepreg resin system was developed. The formulation of the model controlled‐flow resin was designed from performance information obtained from a commercially available controlled‐flow resin, presently used in the aircraft industry. Thermoanalytical techniques including rheometry were used to provide the necessary information to develop the model system along with a formulation methodology developed by Seferis and co‐workers. The model resin formulation, which was a combination of tetraglycidyl ether of methylenedianiline (TGMDA), diglycidyl ether of bisphenol‐A (DGEBA), carboxyl‐modified butadiene/acrylonitrile rubber (CMBN), carboxyl‐terminated butadiene/acrylonitrile rubber (CTBN), bisphenol‐A (BPA), diaminodiphenyl sulfone (DDS), and dicyandiamide (DICY), was hot‐melt impregnated into unidirectional carbon fibers on a laboratory scale hot‐melt prepreg machine. A two‐parameter, three‐level design of experiments was performed on the prepreg processing parameters in which impregnation temperature and pressure were varied. Thus, a total of nine different experimental prepregs were produced and characterized by resin content, extent of impregnation, and tack. The results from the characterization of the nine experimental prepregs are compared with the effects of the prepreg processing conditions. These results are also compared with the results generated for the commercial controlled‐flow resin. Collectively, this work provides a fundamental basis by which the analysis and rational utilization of controlled‐flow matrix prepregs can be effected.

Study of Hall effect on laminated carbon fibre-epoxy composite

Conductive polymer composites are important materials for many technical applications. These materials can be used as solar cells, resistors, semiconductor elements, antistatics and electromagnetic shielding materials [1-4]. In our previous publications we attempted to study the electrical characteristics of different polymer composites, at low and high frequency (microwave) range with respect to different types of fillers under different conditions [5-8]. The reported results indicate that the conductivity behaviour of carbon fibre filled polymer composites is governed by complex charge transfer mechanisms such as tunnelling, hopping and interconnecting between fibres. The rate of crosslinking depends on the fibre concentration and their distribution [9, 10]. However, there have been few investigations into the type of majority charge carriers that could be presented in the bulk. For example, it was thought that laminated carbon fibreepoxy composite is likely to exhibits interesting electrical properties. The present work is concerned with calculation of the charge carrier concentration in unidirectional epoxy-laminated carbon fibre composite using the Hall effect concept. We applied the Hall effect technique because it is controlled by surface states. We believe that this technique is practically suitable for materials that have conduction mechanism controlled by hopping or tunnelling processes. Furthermore, this technique was used successfully to measure the compliance of some orientated polymers [11]. The samples used in this study were epoxy composite containing 10, 25 and 36 layers of unidirectional carbon fibres. The prepreg epoxy resin was provided by DuPont (Italy). The physical parameters of this epoxy are given elsewhere [7]. The laminated sheet composites were prepared by embedding carbon fibre layers in epoxy matrix using curing hot pressing techniques. Samples in the form of parallelpipeds were cut from each composite sheet. The electrodes were made of copper evaporated on both sides of the specimen for Hall effect measurements. The measurements were performed at room temperature under constant magnetic field. A conventional Hall effect experimental set-up

Research and development on polymer composites in BIAM

This paper reports the research and development of polymer composites in Beijing Institute of Aeronautical Materials. A series of resin matrices and prepregs were developed. The exploration for toughened matrices was emphasized. Many kinds of processes were studied and inter-related equipment installed. With co-cured process, carbon fiber composite rudder and airfoil with integral fuel tank were made. In addition, using developed electromagnetism wave transmission materials and RTM process, a few type of radomes and radar antenna in aircraft were manufactured.

Recent Trend of Carbon Fiber Technology from Mesophase Pitch (Part 3)

High performance pitch-based carbon fiber that makes ingenious use of the mesophase phenomenon that appears in highly refined pitch (optically anisotropic pitch) has been improved in quality in recent years, particularly in Japan. A process is now established for manufacturing high performance carbon fiber with a high strength of 4.0 GPa and a small diameter of 7μm.Development of applications for the new carbon fiber is focused here. The carbon fiber is used as primary fabricated products, such as resin compounds and resin prepregs, and as new composites, such as high-stiffness industrial rolls, high-capacity and high-speed press cross bars, various construction materials, rolling stock parts (body, truck and brake lining parts), and automoble propeller shafts. Railroad, automotive, aerospace, marine and shipbuilding, civil engineering and construction, energy, nuclear power, medical and other industrial applications in which the carbon fiber is expected to find increasing usage are also described.

Thermal Analysis for plastics and rubber engineering

A survey of the possibilities of Thermal Analysis (TA) in the plastics and rubber industry is presented. As well as giving examples from research (liquid crystalline main and side chain polymers) and construction (laminates of carbon fibre reinforced epoxy resin prepregs), the field of quality assurance and material characterization is specially discussed. The correlation between TA-characteristics such as the degree of crystallinity and mechanical properties (e.g. hardness or green strength) is demonstrated. The application of thermogravimetry for a precise compositional analysis of compounded rubbers is shown. In practice, Thermal Analysis is most important for failure analysis and the characterization of processing parameters during the production of moulded parts as TA-methods are usually much faster than traditional standard methods. Moreover, the increasing importance of combining TA-methods with other techniques of instrumental analysis is demonstrated. An example of this combination is the TG-DSC-MS coupling which is invaluable in the area of environmental protection especially in the production, application and recycling of moulded parts from polymeric materials.

Repair of Composite Aircraft Parts: An Operator's Viewpoint

This paper discusses the problems of repair experienced by aircraft operators and some actual repairs are mentioned. The use of cold-setting adhesives is compared with the hot-setting pre-pregs recommended by the manufacturers. A need is then shown for more mechanical and physical property data on both the original pre-preg resins and the cold-setting resins that may be used for repair when the provision of hot-curing is difficult.