• Proceedings of the Korean Society For Composite Materials Conference
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• 2001.10a
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• pp.43-48
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• 2001

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 fat developed have some brawbacks 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.

• Composites Research
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• v.27 no.1
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• pp.19-24
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• 2014

In this study, an investigation on mechanical properties of flax/vinyl ester natural fiber composite was performed as a precedent study on the design of eco-friendly structure using flax/vinyl ester composite. Vacuum Assisted Resin Transfer Molding(VARTM) manufacturing method was adopted for manufacturing the flax fiber composite specimen. The mechanical properties of the manufactured flax composites were compared with flax composite data cited from some references. Based on this, the experimental data showed that the flax/vinyl ester composite has some advantages when it is applied to environment-friendly structure.

• Composites Research
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• v.32 no.5
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• pp.249-257
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• 2019

In this paper, the buckling behavior of triaxially braided circular arch with monosymmetric open section subjected to three-point bending was studied experimentally and numerically. First, test specimens were manufactured using vacuum assisted resin transfer molding (VARTM). Then the specimen was tested under three-point bending to determine the ultimate buckling strength. Before performing the numerical analysis, effective material properties of the braided composite were obtained through micro-meso scale analysis virtual testing validated with available test results. Then linear buckling analysis and geometrically non-linear post buckling analysis, established to simulate the test setup, were performed to study the buckling behavior of the composite frame. Analysis results were compared with experimentally obtained ones for verification. The effect of manufacturing defects of tow misalignment, irregular surface and resin rich region, and uncertainties during test setup were studied using numerical models. From the numerical analyses performed it was observed that both manufacturing defect and uncertainties had effect on the buckling behavior and strength.

• Composites Research
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• v.28 no.4
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• pp.155-161
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• 2015

A composite structure was fabricated with embedded impact detection capabilities for applications in Structural Health Monitoring (SHM). By embedding sensor functionality in the composite, the structure can successfully perform impact localization in real time. Smart resin, composed of $Pb(Ni_{1/3}Nb_{2/3})O_3-Pb(Zr,\;Ti)O_2$ (PNN-PZT) powder and epoxy resin with 1:30 wt%, was used instead of conventional epoxy resin in order to activate the sensor function in the composite structure. The embedded impact sensor in the composite was fabricated using Hand Lay-up and Vacuum Assisted Resin Transfer Molding(VARTM) methods to inject the smart resin into the glass-fiber fabric. The electrodes were fabricated using silver paste on both the upper and bottom sides of the specimen, then poling treatment was conducted to activate the sensor function using a high voltage amplifier at 4 kV/mm for 30 min at room temperature. The composite's piezoelectric sensitivity was measured to be 35.13 mV/N by comparing the impact force signals from an impact hammer with the corresponding output voltage from the sensor. Because impact sensor functionality was successfully embedded in the composite structure, various applications of this technique in the SHM industry are anticipated. In particular, impact localization on large-scale composite structures with complex geometries is feasible using this composite embedded impact sensor.

• Composites Research
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• v.31 no.6
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• pp.379-384
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• 2018

This paper aims to study flow characteristics of epoxy resin w.r.t. the sizing agents treated on the carbon fibers which have the same surface morphologies before sizing treatment. Dynamic contact angle (DCA) was measured to evaluate wettability of a single carbon fiber. Wicking test and Vacuum Assisted Resin Transfer Molding (VARTM) were performed to find relation between DCA measurement results and impregnation characteristics. In addition, surface properties of the carbon fibers such as surface free energy and chemical compositions were measured and interfacial shear strength (IFSS) between the carbon fiber and the resin were experimentally characterized by using micro-droplet tests. According to these experimental results, the sizing agent for carbon fibers should have appropriate level of surface free energy and good chemical compatibility with the resin to reconcile resin flow characteristics and interfacial strength.

• Proceedings of the Computational Structural Engineering Institute Conference
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• 2006.04a
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• pp.15-20
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• 2006

Real time health monitoring system was studied to detect the . generation of defects in the composite structures during service life. The PZT sensors were embedded into the woven-glass/phenol composite plate during the fabrication. VARTM (Vacuum Assisted Resin Transfer Molding) process were used to fabricate the composite plate. A Teflon tape was embedded between glass fiber layers to mimic delamination induced during service. Normalized maximum amplitude and energy analyses were used for the acquired signals. Both amplitude and energy of acquired signals were extremely sensitive to the delamination. Therefore, it was successful to detect and to locate the defects in composite plate by monitoring signals from sensors and using the proposed method.

• 한국신재생에너지학회:학술대회논문집
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• 2007.11a
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• pp.378-381
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• 2007

탄소섬유가 중앙에 적층된 풍력발전용 블레이드 소재인 탄소 유리섬유 하이브리드 복합재료가 VARTM(Vacuum Assisted Resin Transfer Molding)공법을 이용하여 제작되었다. 아이조드 충격시험법을 이용하여 온도, 하이브리드화 비율 그리고 노치에 대한 충격강도의 영향을 연구하였다. 온도 감소 및 탄소섬유의 증가에 의해 충격강도는 감소하는 경향을 보였으며, 노치에 의해 하이브리드 복합재료는 약 $25{\sim}30$%가량의 충격강도 감소를 보였다. 그러나 단일 탄소섬유 복합재료의 경우 노치민감도는 없었으며, 이에 소량의 유리섬유 첨가로 인해 하이브리드화 하였을 경우 충격강도 향상 및 저온 충격강도 안정성을 확보 할 수 있었다.

• Korean Journal of Metals and Materials
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• v.50 no.10
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• pp.729-734
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• 2012

This study investigated the effect of water absorption on the tensile properties of carbon-glass/epoxy hybrid composites at room temperature and $-30^{\circ}C$. To investigate the effect of the position of glass fabric in the hybrid composite on the tensile properties, the stacking pattern of the fiber fabrics for reinforcing was created in three different ways: (a) glass fabrics sandwiched between carbon fabrics, (b) carbon fabrics sandwiched between glass fabrics and (c) alternative layers of carbon and glass fabrics. They were manufactured by a vacuum-assisted resin transfer molding (VARTM) process. The results showed that there was surprisingly little difference in tensile strength at the two different temperatures with dry and wet conditions. However, the water absorption into the hybrid system affected the tensile properties of the hybrid composites at RT and $-30^{\circ}C$. When the glass fabrics were at the outermost layers, the hybrid composite had the lowest tensile properties. This is attributed to the fact that the composite had a relatively high water absorption rate.

• Composites Research
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• v.31 no.5
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• pp.276-281
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• 2018

In this paper, elastic behavior of woven fabric composites with various fiber yarn structure were predicted through a theoretical calculation model. A representative volume elements (RVE) that can represent the mechanical properties of the woven composites were selected and crimp angle of the weave yarn was defined by several sinusoidal functions. The effective material properties of the woven composite such as young's modulus, shear modulus and poisson's ratio was predicted by classical laminate theory (CLT). The fiber volume fractions were calculated according to the shape and pattern (plain, twill weave) of the fiber yarn, and the elastic behavior of each woven composite was obtained through a theoretical calculation model. Also, to verify the theoretical predictions, woven composite specimens of plain and twill weave were fabricated by vacuum assisted resin transfer molding (VARTM) process and then mechanical test was conducted. As a results, a good correlation between theoretical and experimental results for the elastic behavior of woven composites could be achieved.