• International Journal of Aerospace System Engineering
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• v.3 no.1
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• pp.21-24
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• 2016

In this study, a optimal design on the hood automotive using eco-friendly natural fiber composites is performed. The hood of an automobile is determined by dividing the Inner panel shape through optimization phase to outer panel and inner panel. It was performed to optimize the size of the thickness of the inner panel and the outer panel by applying a flax/epoxy composite materials. The optimized shape was evaluated for weight-lightening, stability and the pedestrian collision safety. Through the resin flow analysis are confirmed to molding possibility judgment of product.

• 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.

• Advanced Composite Materials
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• v.17 no.2
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• pp.125-137
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• 2008

FBG (Fiber Bragg Grating) sensors and optical fibers were embedded into CFRP dry preforms before resin impregnation in VaRTM (Vacuum-assisted Resin Transfer Molding). The embedding location was the interface between the skin and the stringer in a CFRP-stiffened panel. The reflection spectra of the FBG sensors monitored the strain and temperature changes during all the molding processes. The internal residual strains of the CFRP panel could be evaluated during both the curing time and the post-curing time. The temperature changes indicated the differences between the dry preform and the outside of the vacuum bagging. After the molding, four-point bending was applied to the panel for the verification of its structural integrity and the sensor capabilities. The optical fibers were then used for the newly-developed PPP-BOTDA (Pulse-PrePump Brillouin Optical Time Domain Analysis) system. The long-range distributed strain and temperature can be measured by this system, whose spatial resolution is 100 mm. The strain changes from the FBGs and the PPP-BOTDA agreed well with those from the conventional strain gages and FE analysis in the CFRP panel. Therefore, the fiber-optic sensors and its system were very effective for the evaluation of the VaRTM composite structures.

• Composites Research
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• v.30 no.3
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• pp.202-208
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• 2017

Resin transfer molding (RTM) is a mass production process that allows the fabrication of composites ranging in size from small to large. Recently, fast curing resins with a curing time of less than about 10 minutes have been used in the automotive and aerospace industries. The viscosity of resin is bound up with the degree of cure, and it can be changed rapidly in the fast-cure resin system during the mold filling process. Therefore, it is advantageous to experimentally measure and evaluate the degree of cure because it requires much effort to predict the flow characteristics and cure of the fast curing resin. DMA and dielectric technique are the typical methods to measure the degree of cure of composite materials. In this paper, the resin flow and degree of cure were measured through the multi-channel dielectric system. A total of 8 channels of dielectric sensors were used and resin flow and degree of cure were measured and compared with each other under various pressure conditions.

• Transactions of Materials Processing
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• v.24 no.2
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• pp.101-106
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• 2015

Recently, silicone is being used for LED chip lens due to its good thermal stability and optical transmittance. In order to predict residual stresses, which cause optical birefringence and mechanical warpage of silicone, a finite element analysis was conducted for the curing of silicone during molding. For the analysis of the curing process, a dynamic cure kinetics model was derived based on the results of a differential scanning calorimetry (DSC) testing and applied to the material properties for finite element analysis. Finite element simulation results showed that a step cure cycle reduced abrupt reaction heat and showed a decrease in the residual stresses.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.56 no.3
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• pp.604-610
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• 2007

Injection molding is the most common method of shaping plastic resins for manufacturing a variety of parts. This injection molding is accomplished by injection molding machines (IMM) which consists of a hewer, a reciprocating screw, barrel assembly, and an injection nozzle. The plastic resin is fed to the machine through the hopper and it should be heated to the target melting temperature, which depends on material properties, as closely as possible with very small temperature overshoot in the barrel. Since the barrel, which has temperature dependent specific heat and thermal conductivity in the operating temperature range, is heated by the several electric heater bands, it is not an easy task to control the temperature of the barrel owing to the interference of neighboring heaters and its material properties. Though PID controller with auto-tuning capability is widely adopted in the nm, the auto-tuning process should be carried out whenever the operating temperature is changed significantly. Recently, though the predictive controller is developed and shows good performance, it has drawbacks: 1. Since the heat transfer modeling process is very complicated and should be carried out again when the barrel is changed, it is somewhat inappropriate in the field. 2. The controller performance is not validated in whole operating temperature range. In this paper, cascade type simple PI controller with input restriction is proposed to find the possibility of controlling the barrel temperature in the whole operating temperature range. It is shown by experiment that the proposed controller shows good performance. This result can be applied to design of PI controller with auto-tuning capability.

• 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.

• 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.

• Composites Research
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• v.15 no.6
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• pp.1-7
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• 2002

In VARTM process where a sacrificial medium is used to facilitate the resin flow, the velocity of resin varies drastically between the sacrificial medium and the fiber preform. Although the thickness-to-length ratio of a VARTM product is usually small, a 3-D analysis is prerequisite to analyze the lead-lag flow in the two different media. The problem associated with the full 3-D analysis is the CPU time. A full 3-D numerical mesh comprising large number of nodes requires an impractical CPU time on average computer platforms. In this study, a dual-scale analysis technique was developed. The flow analysis for the entire calculation domain was conducted in 2.5-D, and the 3-D analysis was performed for a small area of special concern. In some numerical examples, the local 3-D analysis could discover an eccentric flow pattern as well as the lead-lag flow that will inevitably be neglected in 2.5-D simulations. The global-local analysis technique practiced in this study can be used to analyze the intricate flow of resin through non-uniform media in affordable CPU times.

• Composites Research
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• v.28 no.6
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• pp.340-347
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• 2015

As resin impregnates through the fiber preform in vacuum assisted resin transfer molding process, the volume of fibers is changed by expansion of fiber mat according to filling time. It causes not only the change in dimension but also the decrease of mechanical properties of the composite product. Moreover, it results in the economic loss by increase of the used amount of resin especially in the large product such as wind turbine blade. In this study, the ways to control fiber volume fraction were investigated by both the experimental and theoretical analyses on the expansion of fiber preform as the preform was impregnated by resin in the VARTM process. Two kinds of swelling stage were observed as flow front progressed, which was analyzed by comparing the experimental and simulation results. The process parameters are expected to be optimized by investigating the swelling behavior of fiber preform in the manufacturing process of the composite product.