• Journal of Aerospace System Engineering
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• v.13 no.6
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• pp.52-59
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• 2019

The rotor blade is a key component that generates the lift, thrust, and control forces required for helicopter flight by the torque transmitted through the hub and the blade pitch angle control, and should be designed to factor vibration characteristics so that there is no risk of resonance with structural safety. In this study, the structural design of the main rotor blade for MPUH(Multi-Purpose Unmanned Helicopter) was conducted and the sectional stiffness measurement of the fabricated blade was performed. The evaluation of the vibration characteristics of the main rotor system was then conducted factoring the measured stiffness distribution. The interior of the rotor blade comprised of the skin, spar, and torsion box, and carbon and glass fiber composites were applied. The Ksec2D program was applied to predict the stiffness of blade, and the results were compared to the measured data. CAMRADII, a comprehensive rotorcraft analysis program, was applied to investigate the natural frequency trends and resonance risks due to the rotor rotation.

• Journal of the Korean Society for Advanced Composite Structures
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• v.5 no.1
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• pp.1-8
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• 2014

Pultruded glass fiber reinforced polymeric plastic (PFRP) and FRP member manufactured by sheet molding compound (SMC) have superior mechanical and physical properties compared with those of conventional structural materials. Since FRP has an excellent corrosion-resistance and high specific strength and stiffness, the FRP material may be highly appreciated for the development of floating-type photovoltaic (PV) power generation system. In this paper, advanced floating PV generation system made of PFRP and SMC is designed. In the design, it includes tracking solar altitude by tilting photovoltaic arrays and tracking solar azimuth by spinning structures. Moreover, the results of the finite element analysis (FEA) are presented to confirm stability of entire structure under the external loads. Additionally, installation procedure and mooring systems in the Hap-Cheon Dam are discussed and the measurement of strain under the actual circumstances is conducted for assuring stability of actually installed structures. Finally, by comparison with allowable stress, appropriate safety of structure is confirmed to operate the system.

• Composites Research
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• v.15 no.1
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• pp.21-31
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• 2002

To overcome the disadvantages of conventional excavation technology various trenchless (or excavation free, or no-dig) repair-reinforcement 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 repairing-reinforcing process for underground pipes with glass fiber fabric polymer composites using VARTM (Vacuum Assisted Resin Transfer Molding) has been developed. The developed process requires shorter operation time and lower cost with smaller and simpler operating equipments than those of the conventional trenchless technologies. For the reliable operation of the developed method, a simple method to apply pressure and vacuum to the reinforcement was devised and flexible mold technology was tried. Also, resin filling and cure status during RTM process were monitored with a commercial dielectrometry cure monitoring system, LACOMCURE. From the investigation, it has been found that the developed repairing-reinforcing technology with appropriate process variables and on-line cure monitoring has many advantages over conventional methods.

• Journal of the Korean Society for Advanced Composite Structures
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• v.3 no.3
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• pp.1-8
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• 2012

Recently, underground pipes are utilized in various fields of applications such as sewer lines, drain lines, water mains, gas lines, telephone and electrical conduits, culverts, oil lines, etc. Most of pipes are installed for long-term purposes and they should be safely installed in consideration of installation conditions because there are unexpected various terrestrial loading conditions. In this paper, we present the result of investigation pertaining to the structural behavior of glass fiber reinforced thermosetting polymer plastic (GFRP) flexible pipes buried underground. The mechanical properties of the GFRP flexible pipes produced in the domestic manufacturer are determined and the results are reported in this paper. In addition, ring deflection is measured by the field tests and the finite element analysis (FEA) is also conducted to simulate the structural behavior of GFRP pipes buried underground. From the field test results, we predicted long-term, up to 50 years, ring deflection of GFRP pipes buried underground based on the method suggested by the existing literature. It was found that the GFRP flexible pipe to be used for cooling water intake system in the nuclear power plant is appropriate because 5% ring deflection limitation for 50 years could be satisfied.

• The Journal of Korea Robotics Society
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• v.8 no.2
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• pp.136-142
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• 2013

In nature, many small insects are using jumping as a survival strategy. Among them, fleas jump in a unique method. They use an elastomer, 'Resilin', an extensor muscle and a trigger muscle. By contracting the extensor muscle, the elastic energy, that makes a flea to jump, is stored in the resilin. After storing energy, the trigger muscle begins contracting and pulling the extensor muscle. When the extensor muscle crosses the rotational joint, direction of torque generated from the extensor muscle reverses, 'torque reversal mechanism'. Simultaneously, the elastic energy stored in the resilin releases rapidly and is converted into the kinetic energy. It makes a flea to jump 150 times its body length. In this paper, miniaturized jumping robot using flea-inspired catapult mechanism is presented. This mechanism is based on the 4-bar linkage and the reversal joint and is actuated by Shape Memory Alloy (SMA) coiled springs describing the flea's muscle. The robot prototype is fabricated by SCM process using glass fiber prepregs and a sheet of polyimide film. The prototype is 20mm link length, 34mm width and 2.0g weight and can jump 103cm.

• Journal of the Korean Wood Science and Technology
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• v.47 no.5
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• pp.655-662
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• 2019

This study evaluated the multi-bonding performances of timbers as well as those of reinforcement and timber to obtain data for preparing guidelines regarding the use of timbers as large structural members. For the multi-bonding performances of timbers, four types of bonding surfaces were prepared according to the pith position. For the bonding performances of FRP (fiber-reinforced plastic)/steel plate and timber, a total of 11 types of specimens were produced for the selection of the appropriate adhesive. The bonding performances of the produced specimens were evaluated through a water soaking delamination test, a water boiling delamination test, and a block shear strength test. The test results showed that the bonding strength of the bonding surface according to the pith position was highest in the specimen for which the two sections with the pith at the center of the cross-section on timber and between the bonding surfaces (the tangential and radial sections were mixed) were bonded. Furthermore, the specimens for which the section (radial section) with the pith on the bonding surface of the timber was bonded showed a high delamination percentage. The results of the block shear strength test showed that the bonding section did not have a significant effect on the shear strength, and that the measured wood failure percentage was higher than the KS standard value. The PVAc adhesive showed the highest bonding strength between larix timber and GFRP (glass FRP). Furthermore, the epoxy and polyurethane adhesives showed good bonding strength for CFRP (carbon FRP) and structure steel, respectively.

• Clean Technology
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• v.16 no.4
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• pp.245-253
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• 2010

Optimum conditions for UV-radiated photopolymerization of unsaturated polyester that could be used as protecting layer of large diameter pipe were investigated in this paper. UV photopolymerization method was selected to solve the problems, arising when thermal polymerization by organic peroxide was used, such as the instability of peroxide initiator, the evolution of volatile organic compound, and thermal deformation of product. Two of the photo-initiators (Irgacure 819 and Darocure 1173) well known for its penetrating ability deep into the polymer layer were selected, and the optimum conditions for photopolymerization (1.5 phr initiator content, 1:1.2 initiator ratio, Ga lamp for UV source) were found from the thermal and mechanical test results of the resultant UP polymers. In addition, composite materials containing UP polymer and glass fiber were tested for hardness, impact strength, and flexural strength to find that the impact strength of composite significantly improved.

• Restorative Dentistry and Endodontics
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• v.45 no.4
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• pp.49.1-49.11
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• 2020

Objectives: The aim of this study was to perform a clinical and radiographic analysis of endodontically treated teeth (ETT) restored with cast metal posts (CMPs) or prefabricated glass fiber posts (GFPs) and crowns. Materials and Methods: Fifty ETT were restored with 25 CMPs and 25 GFPs at a private dental clinic between 2001 and 2016. The restorations consisted of 12 all-ceramic crowns, 31 metal-ceramic crowns, and 7 composite resin crowns. Demographic data, type of teeth, type of post-and-core system, time of placement, crown restorations, the number of proximal contacts, the type of antagonist, and reports of any complications after post-and-core placement were recorded for each patient. Assessments were performed at baseline (radiographic) and follow-up (radiographic and clinical). Data were analyzed by the McNemar test, the Pearson χ² test, and Kaplan-Meier survival curves (α = 0.05). The mean follow-up was 67.6 months. Results: No significant difference was observed for any of the radiographic parameters when the baseline and final radiographs were compared. In the clinical evaluation, anatomical form (p = 0.009) and occlusion (p = 0.001) showed significant differences according to the type of crown restoration; specifically, metal-ceramic and all-ceramic crowns outperformed composite resin crowns. Conclusions: CMPs and GFPs showed favorable results for restoring ETT after 6 years of follow-up. All-ceramic and metal-ceramic crowns showed higher survival rates and better clinical outcomes.

• Steel and Composite Structures
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• v.49 no.2
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• pp.161-180
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• 2023

In the previous research, the axial compressive capacity models for the glass fiber-reinforced polymer (GFRP)-reinforced circular concrete compression elements restrained with GFRP helix were put forward based on small and noisy datasets by considering a limited number of parameters portraying less accuracy. Consequently, it is important to recommend an accurate model based on a refined and large testing dataset that considers various parameters of such components. The core objective and novelty of the current research is to suggest a deep learning model for the axial compressive capacity of GFRP-reinforced circular concrete columns restrained with a GFRP helix utilizing various parameters of a large experimental dataset to give the maximum precision of the estimates. To achieve this aim, a test dataset of 61 GFRP-reinforced circular concrete columns restrained with a GFRP helix has been created from prior studies. An assessment of 15 diverse theoretical models is carried out utilizing different statistical coefficients over the created dataset. A novel model utilizing the group method of data handling (GMDH) has been put forward. The recommended model depicted good effectiveness over the created dataset by assuming the axial involvement of GFRP main bars and the confining effectiveness of transverse GFRP helix and depicted the maximum precision with MAE = 195.67, RMSE = 255.41, and R2 = 0.94 as associated with the previously recommended equations. The GMDH model also depicted good effectiveness for the normal distribution of estimates with only a 2.5% discrepancy from unity. The recommended model can accurately calculate the axial compressive capacity of FRP-reinforced concrete compression elements that can be considered for further analysis and design of such components in the field of structural engineering.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.11 no.4
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• pp.1361-1366
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• 2010

This research aims to develop polymer composites which can be used for PEMFC separators by injection molding process. Considering the moldability and stiffness, we used PPS(Poly(phenylene sulfide)) and PP(Polypropylene) as base resin. In order to improve electrical conductivity and physical properties, we chose glass fiber, carbon fiber, carbon black, and both expanded graphite and synthetic graphite. The 3 type composites are prepared for injection molding of PEMFC separators. and CAE(Computer Aided Engineering) analysis was conducted to optimize injection processing parameters(injection pressure, heat time, mold temperature etc.). We did successfully fabricate the separators by injection molding, and measure the electrical conductivity of the samples by using four point probe device. Conclusively, PP/SG/CB composite showed better both electrical conductivity and moldability than the others.