• Fibers and Polymers
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• v.4 no.2
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• pp.77-83
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• 2003

The cell modeling homogenization method to derive the constitutive equation considering the microstructures of the fiber reinforced composites has been previously developed for composites with simple microstructures such as 2D plane composites and 3D rectangular shaped composites. Here, the method has been further extended for 3D circular braided com-posites, utilizing B-spline curves to properly describe the more complex geometry of 3D braided composites. For verification purposes, the method has been applied for orthotropic elastic properties of the 3D circular braided glass fiber reinforced com-posite, in particular for the tensile property. Prepregs of the specimen have been fabricated using the 3D braiding machine through RTM (resin transfer molding) with epoxy as a matrix. Experimentally measured uniaxial tensile properties agreed well with predicted values obtained for two volume fractions.

• Journal of the Korean Wood Science and Technology
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• v.35 no.3
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• pp.29-35
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• 2007

This research investigates the composites reinforced with fiberglass to wood and commercial particleboard using VARTM process to enhance the mechanical properties. Specimens were prepared from lumbers from thinning crop-trees and commercial particleboard. Matched specimen were reinforced on both sides with one layer of unidirectional fiberglass roving. Fiberglass reinforcement to wood and particleboard using VARTM process improved mechanical properties.

• Proceedings of the Korean Society For Composite Materials Conference
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• 2002.10a
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• pp.280-283
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• 2002

In the manufacturing of large scale composite structures, the cost-effective processing and the enhancement of structural performance are critical. One of the most effective ways for this purpose is to use stitched multiaxial warp knitted (MWK) perform in the resin transfer molding process. This study reports the effect of stitching on the mechanical properties of MWK composites, and the feasibility processing of the thick U-beam structure utilizing the stitched preforms. Permeability of the preform, viscosity and cure property of the epoxy resin have been measured. The results of resin flow analysis has been used in determining the gate/vent locations of the RTM mold. Cross-sectional observation of the channel beam prototype demonstrated that the resin impregnation was almost complete, except for some surrounding area of stitched yarns.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.25 no.8
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• pp.1294-1301
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• 2001

In order to reduce the time and cost for assembly, automobile speaker grills have been injection molded with door trims or map pockets in one piece recently. However, several defects such as short shots or air traps can easily occur due to the decreased fluidity of the melting polymer according to the excessive heat transfer to the mold. Therefore, it is necessary to optimize the resin feed system and predict possible defects by CAE analysis. However it is not possible to obtain exact analysis results for the speaker grill by using general shell elements since the heat transfer in the thickness direction which is the dominant factor of the filling stage can not be considered. Therefore, there have been several efforts to simulate the injection molding nature of the speaker grill by using shell elements with an effective thickness which is smaller than the actual thickness of the part. Two empirical values have been recommended for the effective thickness in real practice. One is 50∼70% of the thickness of the speaker grill and another is the gap distance between the adjacent holes. In this paper, CAE analyses of a map pocket with a speaker grill were conducted using shell elements with both of these recommended effective thicknesses, and the predicted flow fronts were compared with the findings from injection molding experiments. The commercial code MOLDFLOW was used for injection molding analysis and an 850 ton injection molding machine was used for experiments.

• 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 Urban Science
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• v.11 no.2
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• pp.25-30
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• 2022

Resin Transfer Molding FRP (RTM FRP) is a fiber reinforced polymeric plastic which is manufactured by applying pressure to fibers, injecting resin into a mold, and then impregnating it. RTM FRP is a new construction material suitable for producing non-continuum structural elements such as sole plate because it has excellent strength and can produce many members in a short time. In this study, experiments were conducted to estimate the capacity of the bolted connection of RTM FRP. First, a tensile test was conducted to confirm the mechanical properties such as the tensile strength of the RTM FRP to be used for the bolted connection experiments. In addition, experiments were conducted on the bolted connection with the thickness of the RTM FRP and the edge distance of the bolt as variables. In the first experiment, F4.8 bolts were used, and shear failure of the bolt occurred before the RTM FRPs were failed. The F4.8 bolt is a general structural bolts used for the sole plate of a bridge bearing, and it was confirmed that the RTM FRP has a higher bold bearing strength than the shear strength of a F4.8 bolt. In the second experiment, G12.9 bolts were used, and shear failure of the bolt and bearing failure of the RTM FRP occurred simultaneously. In addition, as the thickness of the RTM FRP and the edge length of the bolt increased, the strength of the joint increased. When analogized with the bearing fracture equation of steel plate, the bolted connection of RTM FRP showed a bearing strength coefficient of 0.420 to 0.549 compared to the tensile strength, and it is considered that further research is needed.

• Proceedings of the Korean Society For Composite Materials Conference
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• 2000.11a
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• pp.249-252
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• 2000

To overcome problems of excavation technology far repairing or replacing underground buried pipes which are worn out or damaged, various trenchless repair-reinforcement technologies have been invented. But these trenchless technologies also have many problems in the aspect of economy and convenience of operation. In this research, the repair-reinforcement process using RTM (Resin Transfer Molding) which can solve problems of present trenchless technologies was developed. The resin wetting and void removal during RTM process to form large composite structures inside of buried pipes were experimentally investigated. From the experiment, it was found that the new technology had advantage over conventional methods by employing appropriate process parameters and void removal vents.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.23 no.1
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• pp.34-37
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• 2010

0.25 mm thickness super thin surface mounted device LED Lamp is developed with PCB type lead frame in which BT (Bismaleimide Triazine) resin is used. BT resin is removed by a laser beam in order to reduce the thermal resistance below $1\;^{\circ}C/W$ and transfer molding is used with silicone. Compared to conventional 0.4 mm thickness LED lamp, the developed LED lamp can be derived in high current and the luminance of the LED lamp is increased up to 240 mA.

• Composites Research
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• v.33 no.2
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• pp.39-43
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• 2020

Recently, fabrication process of thermoplastic polyamide-based composites with recyclability as well as impact, chemical, and abrasion resistance have been widely studied. In particular, thermoplastic reactive resin transfer molding (TRTM) in which monomer with low viscosity is injected and in-situ polymerized inside mold has received a great attention, because thermoplastic melts are hard to impregnate fiber preform due to their very high viscosity. However, it is difficult to optimize the processing conditions because of high reactivity and sensitivity to external environments of the used monomer, ε-caprolactam. In this study, viscosity as an important process parameter in TRTM was measured during in-situ anionic polymerization of ε-caprolactam and the solutions for problems caused by high polymerization rate and sensitivity to moisture and oxygen were suggested. Reliability of the improved measurement technique was verified by comparing the viscosity behavior at various environmental conditions including humidity and atmosphere, and it is expected to be helpful for optimization of TRTM process.

• Composites Research
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• v.35 no.1
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• pp.42-46
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• 2022

In this study, when the carbon fiber composite was manufactured, the correlation between the porosity and mechanical properties according to the number of glass fiber felts laminated together and the stacking sequence was confirmed. The carbon fiber composite was manufactured by stacking glass fiber felts, which are highly permeable materials, and using vacuum assisted resin transfer molding (VARTM). Porosity was measured by photographing the cross-section of the specimen with an optical microscope and then using porosity calculation code of MATLAB, and mechanical properties were measured for tensile strength, modulus by tensile test. Furthermore, Pearson correlation coefficient between porosity and mechanical properties was calculated to confirm the correlation between two variables. As a result, the number of glass fiber felt increased and the distance from the center of laminated composites increased, the porosity increasing were confirmed. In addition, tensile strength/modulus showed a weak positive correlation with porosity. Also, in order to confirm the effect of only porosity on tensile strength and modulus, mechanical properties calculated by CLPT (Classical Laminate Plate Theory) and experimental values were compared, and the difference in tensile strength showed a strong positive correlation with porosity and the difference in modulus showed a weak positive correlation with porosity.