1,721,005 research outputs found
Binary mixture rule for predicting the dielectric properties of unidirectional E-glass/epoxy composite
No full textSince the electromagnetic properties of fiber reinforced polymeric composite can be tailored effectively by adjusting its composition, the polymeric composite is a plausible material for fabricating the radar absorbing structures (RAS) of desired performance. In order to design the effective electromagnetic wave (EM) absorber with the fiber reinforced polymeric composite, the electromagnetic characteristics of its constituents are required in the target frequency band with respect to the content of each component of composite. In this study, the dielectric characteristics of unidirectional E-glass fiber reinforced epoxy composites were tested with the free space method, from which theoretical models and mixture equations for estimating its dielectric constant were proposed with respect to the fiber volume fractions. From the investigation, it was found that the suggested binary mixture rules agreed pretty well with the experimental results. (c) 2005 Elsevier Ltd. All rights reserved
Laminating rule for predicting the dielectric properties of E-glass/epoxy laminate composite
No full textSince the electromagnetic properties of fiber reinforced polymeric laminate composite can be tailored effectively by adjusting its composition and regulating the stacking sequence, it is plausible material for fabricating the radar absorbing structures (RAS) of desired performance. In order to design the effective electromagnetic wave (EM) absorber with the fiber reinforced polymeric laminate composite, its electromagnetic characteristics should be available and could be regulated easily in the target frequency bands. In this study, dielectric characteristics of the E-glass/epoxy laminate composites were measured by the free space method in the X-band frequency (8.2-12.4 GHz). In order to describe the dielectric behavior of laminate composites of arbitrary stacking sequences, the equivalent circuit model and the laminating equations for estimating dielectric properties were proposed, and experimentally verified. From the comparison of the predicted and measured data, the proposed method predicted well the experimentally measured data. (c) 2005 Elsevier Ltd. All rights reserved
Development of the trenchless rehabilitation process for underground pipes based on RTM
No full textIn order to overcome the disadvantages of conventional excavation technology for repairing and replacing worn-out under,Ground pipes, Various trenchless technologies have been developed and tried. But trenchless technologies so far developed have some drawbacks such as high cost and inconvenience of operation. In this study a rehabilitation process for underground pipes has been developed using vacuum assisted resin transfer molding (VARTM) with glass fiber fabric preform to overcome the disadvantages of present trenchless technologies. For the reliable operation of the developed method, a simple method to apply pressure and vacuum to the reinforcement was devised with a flexible mold technology. From the investigation, it has been found that the developed process requires shorter operation time and lower cost with smaller and simpler operating equipments than those of the conventional trenchless technologies. (c) 2004 Elsevier Ltd. All rights reserved
Development of the composite RAS (radar absorbing structure) for the X-band frequency range
No full textSince the EM properties of fiber reinforced polymeric composites can be tailored effectively by adjusting its composition, they are plausible materials for fabricating the radar absorbing structure (RAS) of desired performance. In this study, the composite RAS which has superior load bearing capacity and EM absorption characteristics has been developed by blending the conductive carbon black with the binder matrix of the E-glass/polyester composite, and its EM absorption characteristics has been measured by the free space method in the X-band frequency range (8.2-12.4 GHz). The composite RAS was designed so as to have the optimal performance for the X-band centered at 10 GHz. From the investigation, it was found that the composite RAS of 2.93 mm thickness with the conductive carbon black absorbed more than 90% of incident EM wave throughout the entire X-band frequency range. (c) 2005 Elsevier Ltd. All rights reserved
Binary Mixture Rule for Predicting the Dielectric Properties of Unidirectional E-glass/Epoxy Composite
No full textCharacterization of electromagnetic properties of polymeric composite materials with free space method
No full textThe introduction of microwave radars during the second World War altered the air defense scenario significantly, and this led to the development of the "stealth" techniques. By reducing the detectability of aircrafts or warships, of which the radar cross section (RCS) is a measure, they could evade radar detection, which affected not only the mission success rate but also survival of them in the hostile territory. In the very early stage of the research on stealth techniques, many researches were mainly concentrated on the reduction of RCS and development of radar absorbing materials (RAM), but nowadays studies on investigating the radar absorbing structures (RAS) using fiber reinforced polymeric composite materials are becoming popular research field. In this study, electromagnetic characteristics of unidirectional E-glass fiber reinforced epoxy composites were tested with free space methods, which can overcome drawbacks of conventional cavity and waveguide methods. Complex relative permittivities of low-loss composite were measured with respect to the angle between the fiber orientation and the electric field vector of EM wave in X-band frequency range. From the experimental data, empirical relation between the dielectric properties of composites and test variable was suggested and verified. (C) 2004 Elsevier Ltd. All rights reserved
EM characteristics of the RAS composed of E-glass/epoxy composite and single dipole FSS element
No full textFrom the methods to reduce radar cross section (RCS) such as shaping of the target, radar absorbing material (RAM), and radar absorbing structure (RAS), the RAS composed of frequency selective surface (FSS) screens and low-loss composite materials is used widely because the FSS screen transmits or reflects electromagnetic (EM) waves selectively and the composite material withstands external loads. In this study, the RAS composed of the E-glass/epoxy composite and single dipole FSS element was fabricated by printed circuit board (PCB) manufacturing process, and their EM transmission characteristics, such as a resonant frequency, a minimum transmission loss, and a transmission bandwidth, were measured in the X-band frequency range by the free space method with respect to the size of dipole element and its periodicity of array. (C) 2006 Elsevier Ltd. All rights reserved
Repair of underground buried pipes with resin transfer molding
No full textRepairing and replacing of worn-out underground pipes, such as sewer pipes, water-supply pipes, gas pipes, and communication cables by excavating not only cause traffic congestion but also produce large amount of waste. Also, the operation requires heavy equipments and longer operating time and high cost. In this study, the repairing-reinforcing process of underground pipes with glass fiber fabric polymer composites using resin transfer molding (RTM) which overcomes the problems of present trenchless technologies has been developed. The developed process requires shorter operation time and lower cost with smaller and simpler operating equipments than conventional trenchless technologies. For the faultless operation. a simple method to apply pressure and vacuum to the reinforcement was developed. The resin wetting and void removal during RTM process for very large and long-composite buried pipes were experimentally investigated, and the efficient void removal method was suggested. Cure status and resin filling were monitored with a commercial di-electrometry cure monitoring system, LACOMCURE. From the investigation, it has been found that the developed repair technology with appropriate process parameters and on-line cure monitoring has many advantages over conventional methods. (C) 2002 Published by Elsevier Science Ltd
Prediction of crack length and crack growth rate of adhesive joints by a piezoelectric method
No full textAs adhesive joints have been widely used for fastening thin adherends, the damage tolerance design of adhesive joints has become important, and the estimation of initiation and propagation of a fatigue crack in the adhesive has become necessary. However, the measurement of crack length of tubular joints has been difficult because the observation of crack initiation and growth in the adhesive layer by conventional methods is not easy. In this work, a prediction method for the fatigue crack length in the adhesive layer of tubular single-lap adhesive joints was developed by the piezoelectric method. In order to obtain the relationship between the fatigue crack length and the piezoelectric signal, finite element analysis was conducted and verified by experiments. The damage of the adhesive joints was monitored by the piezoelectric method during torsional fatigue tests on tubular single-lap adhesive joints. Using the damage monitoring signals and the relationship between the fatigue crack length and the piezoelectric signal, a method for predicting fatigue crack growth in the adhesive layer of tubular single-lap adhesive joints was developed
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