• Composites Research
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• v.34 no.2
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• pp.88-95
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• 2021

VARTM (Vacuum-assisted resin transfer molding) process is a low-cost process technology and affiliated with OoA (Out of Autoclave). Besides, it has been widely used in various fields. However, because of its lower quality than the autoclave process, it isn't easy to apply the VARTM process to the aerospace industry, which requires high reliability. The main problem of the VARTM process is the loss of mechanical properties due to the low fiber volume fraction and high void content in comparison to the autoclave. Therefore, many researchers have studied to reduce void and increase fiber volume fraction. This study examines whether the method of controlling atmospheric pressure could increase the fiber volume fraction and reduce void during the resin impregnation process. Reliability evaluation was confirmed by compressive strength test, fiber volume fraction analysis, and optical microscopy. As a result, it was confirmed that increasing the atmospheric pressure step by step in the VARTM process of impregnating the preform with resin effectively increases the fiber volume fraction and reduces void.

• Design & Manufacturing
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• v.17 no.3
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• pp.28-33
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• 2023

The conventional FRP (Fiber Reinforced Plastic) manufacturing process used thermoset resins for ease of molding but faced the issue of non-recyclability. To address these shortcomings, a new process utilizing thermal plastic resin was developed. However, due to the high viscosity of thermal plastic resin, problems such as fiber deformation and a reduced fiber volume fraction occurred during the high-temperature, high-pressure process. In this study, to overcome the limitations of the conventional process, fiber-reinforced composite materials were manufactured through in-situ polymerization using PLA (Poly L-Lactide) resin in the VA-RTM (Vacuum Assistance Resin Transfer Molding) process. The fiber volume of the produced specimens was calculated, and resin impregnation and porosity were confirmed through optical microscopy. Additionally, molecular weight analysis using GPC (Gel Permission Chromatography) demonstrated improvements over the conventional process and emphasized the essential requirement of temperature control.

• 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.

• Carbon letters
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• v.25
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• pp.43-49
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• 2018

This study suggests the novel thermoplastic toughening agent, which can be applied in the monomer forms without increasing the viscosity of the epoxy resin and polymerized during the resin curing. The diazide (p-BAB) and dialkyne (SPB) compounds are synthesized and mixed with the epoxy resin and the carbon fiber reinforced epoxy composites are prepared using vacuum infusion process (VIP). Then, flexural and drop weight tests are performed to evaluate the improvement in the toughness of the prepared composites to investigate the potential of the novel toughening agent. When 10 phr of p-BAB and SPB is added, the flexural properties are improved, maintaining the modulus as well as the toughness is improved. Even with a small amount of polytriazolesulfone polymerized, due to the filtering effect of the solid SPB by the layered carbon fabrics during the VIP, the toughening and strengthening effect were observed from the novel toughening agent, which could be added in monomer forms, p-BAB and SPB. This suggests that the novel toughening agent has a potential to be used for the composites prepared from viscosity sensitive process, such as resin transfer molding and VIP.

• International Journal of Aerospace System Engineering
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• v.4 no.1
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• pp.9-12
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• 2017

In this study, an investigation on mechanical properties of flax natural fiber composite is performed as a precedent study on the design of eco-friendly structure using flax natural fiber composite. The Vacuum Assisted Resin Transfer Molding-Light (VARTML) manufacturing method is adopted for manufacturing the flax fiber composite panel. The VARTML is a manufacturing process that the resin is injected into the dry layered-up fibers enclosed by a rigid mold tool under vacuum. In this work, the resin flow analysis of VARTM manufacturing method is performed. A series of flax composite panels are manufactured, and several kinds of specimens cut out from the panels are tested to obtain mechanical performance data. Based on this, structural design of chemical storage tank for agricultural vehicle was performed using flax/vinyl ester. After structural design and analysis, the resin flow analysis of VARTM manufacturing method was performed.

• 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.17 no.3
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• pp.1-7
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• 2004

In the vacuum assisted RTM (VARTM) process that has become the center of attention for manufacturing massive composite structures, a good evacuation of air in the fiber preform is recognized as the prime factor. The microvoids, or the dry spots, are formed as a result of improper gate/vent locations and the mold geometry. The non-uniform resin velocity at the flow front leads to the formation of microvoids in the fibers, whereas the air in the microvoids can migrate along with the resin flow during mold filling. The residual air in the internal voids of a composite structure may cause a degradation of the mechanical properties as well as the structural failure. In this study, a unified macro- and micro analysis methods were developed to investigate the formation and transport of air in resin during VARTM process. A numerical simulation program was developed to analyze the three-dimensional flow pattern as well as the macro- and microscopic distribution of air in a composite part fabricated by VARTM process.

• Design & Manufacturing
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• v.18 no.2
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• pp.41-50
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• 2024

In this study, experimental design methods were used to derive optimal process conditions for improving the thickness uniformity of a 0.40 mm, 3.5 inch light guide panel. Process mapping and expert group analysis were used to identify factors that influence the thickness of injection molded products. The key factors identified were mold temperature, mold temperature, injection speed, packing pressure, packing time, clamp force, and flash time. Considering the resin manufacturer's recommended process conditions and the process conditions for similar light guide plates, a three-level range was selected for the identified influencing factors. L27 orthogonal array process conditions were generated using the Taguchi method. Injection molding was performed using these L27 orthogonal array to mold the 3.5 inch light guide plates. Thickness measurements were then taken, and the results were analyzed using the signal-to-noise ratio to maximize the CpK value, leading to the determination of the optimal process conditions. The thickness uniformity of the product was analyzed by applying the derived optimum process conditions. The results showed a 97.5% improvement in the Cpk value of 3.22 compared to the process conditions used for similar light guide plates.

• Journal of the Korean Ceramic Society
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• v.43 no.10 s.293
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• pp.607-612
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• 2006

In VARTM (Vacuum Assisted Resin Transfer Molding) process, the permeability generally controls the filling time of the resin and it also affects the void characteristics of the fiber composite. In this study, carbon and glass fiber inter-layered hybrid composites (carbon fiber centered stack) with an epoxy matrix were fabricated by VARTM process and evaluated the resin flow and macro void characteristics. The permeability of glass fiber was higher than that of carbon fiber used in this study. Using Darcy's equation, the permeability of hybrid composites could be predicted and experimentally confirmed. After curing, the macro void content of hybrid composites was investigated using image analyzer. The calculated filling time was well agreed with experimental result and the void content was significantly changed in hybrid composites.

• Korean Journal of Metals and Materials
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• v.50 no.2
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• pp.93-99
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• 2012

The mechanical properties of nano composites were evaluated for structural performance in order to enhance their applicability to the car and machine industrial fields. Carbon fiber reinforced plastics (CFRP) and GFRP were manufactured by vacuum-assisted resin transfer molding (VARTM) process with good mechanical properties. Tensile test was conducted to obtain the process factor of each composite. Also, carbon nano fiber (CNF) was dispersed in the composites and the relationship between the mechanical property and the CNF fraction was compared. The tensile strength and stiffness of 0/90 laminated CFRP were the best. CFRP/CNF (0.5 wt.%) was confirmed to be an excellent material for its elasticity and tensile strength.