• 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.

• The Korean Journal of Rheology
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• v.11 no.1
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• pp.34-43
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• 1999

Flow-induced voids during resin impregnation and poor fiber wetting have known to be highly detrimental to the performance of composite parts manufactured by resin transfer molding(RTM) process. In this study, in order to overcome these serious problems encountered in RTM, the effects of surface modification by using silane coupling agent as a surface modifier on the flow characteristics, the wetting between resin and fiber, and void content were investigated. For the experiments of microscopic flow visualization and curing in a beam mold, glass fiber mats having plain weaving structure and epoxy resin were used. Modifying the fiber surface was found to result in a significant decrease of dynamic contact angle between resin and fiber and increase of wicking rate. Therefore, it was confirmed that the surface modification employed in this study could improve the wettability of reinforcing fibers as well as micro flow behavior. In addition, It was revealed that high temperature and low penetration rate of the resin are more favorable processing conditions to reduce the dynamic contact angle. However, surface modified fiber mat was found to have lower permeability than the unmodified one, which may be explained in terms of the decrease of contact time between resin and fiber owing to improvement of wetting. It was also exhibited that surface modification had a significant influence on void formation in RTM process, resulting in a decrease of overall void content due to the improvement of wetting in cured composite parts.

• 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.

• Design & Manufacturing
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• v.14 no.1
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• pp.1-7
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• 2020

In this study, the variation of the shrinkage in the thickness direction of the molded parts according to the gate size of the polymer core fabricated through the 3D printer using the SLS method was studied. The polymer cores are laser sintered and the powder material is nylon base PA2200. The polymer cores have lower heat transfer rate and rigidity than the metal core due to the characteristics of the material. Therefore, the injection molding test conditions are set to minimize the deformation of the core during the injection process. The resin used in the injection molding test is a PP material. The packing condition was set to 80, 90 and 100% of the maximum injection pressure for each gate size. The runner diameter used was ∅3mm, and the gates were fabricated in semicircle shapes with cross sections 1, 2, and 3 ㎟, respectively. Thickness measurement was performed for 10 points at 2.5 mm intervals from the point 2.5 mm away from the gate, and the shrinkage to thickness was measured for each point. The shrinkage rate according to the gate size tends to decrease as the cross-sectional area decreases as the maximum injection pressure increases. The average thickness shrinkage rate was close to 0% when the packing pressure was 90% for the gate area of 1mm2. When the holding pressure was set to 100%, the shrinkage was found to decrease by 3% from the standard dimension due to the over-packing phenomenon. Therefore, the smaller the gate, the more closely the molded dimensions can be molded due to the high pressure generation. It was confirmed that precise packing process control is necessary because over-packing phenomenon may occur.

• Journal of the Korea institute for structural maintenance and inspection
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• v.13 no.3 s.55
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• pp.188-196
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• 2009

In Concrete, shrinkages occur like plastic shrinkage and drying shrinkage in the early age because of evaporation and transfer of moisture. Within the country, the crack test standardized by KS is used to test the drying shrinkage of the concrete by using the restricted drying shrinkage of Dumbbell type mold, but this test is for the cracking-point and the restricted shrinkage stress. Thus it is difficult to valuate the crack quantitative test. In this study, it is intended to develop the Flat-ring type restrained test method for the shrinkage deformation movement of the concrete and to provide the quantitative data for evaluating the cracks in concrete. And it suggest the proper specimen diameter and quantitative test method about shrinkage crack properties on Flat-ring type restrained test method. And Verified the suitability.

• Journal of the Korean Ceramic Society
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• v.53 no.4
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• pp.386-392
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• 2016

Heat insulation plates of fumed silica were prepared by mixing fumed silica, SiC powder and chopped glass fiber by a high speed mixer followed by pressing of the mixture powder in a stainless steel mold of $100{\times}100mm$. Composition of the plates, particle size of SiC, and type of inorganic binder were varied for observation of their contribution to heat insulation of the plate. The plate was installed on the upper portion of an electric furnace the inside temperature of which was maintained at $400^{\circ}C$ and $600^{\circ}C$, for investigation of heat transfer through the plate from inside of the electric furnace to outside atmosphere. Surface temperatures were measured in real time using a thermographic camera. The particle size of SiC was varied in the range of $1.3{\sim}17.5{\mu}m$ and the insulation was found to be most excellent when SiC of $2.2{\mu}m$ was incorporated. When the size of SiC was smaller or larger than $2.2{\mu}m$, the heat insulation effect was decreased. Inorganic binders of alkali silicate and phosphate were tested and the phosphate was found to maintain the heat insulation property while increasing mechanical properties.

• Journal of the Korean Society of Manufacturing Technology Engineers
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• v.18 no.3
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• pp.285-293
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• 2009

Thermal infrared cameras have been conducted actively in various application areas, such as military, medical service, industries and cars. Because of their characteristic of sensing the radiant heat emitted from subjects in the range of long-wavelength($3{\sim}5{\mu}m$ or $8{\sim}12{\mu}m$), and of materializing a vision system, when general optics materials are used, they don't react to the light in the range of long-wavelength, and can't display their optic functions. Therefore, the materials with the feature of higher refractive index, reacting to the range of long-wavelength, are to be used. The kinds of materials with the characteristic of higher refractive index are limited, and their features are close to those of metals. Because of these metallic features, the existing producing method of optical systems were direct manufacturing method using grinding method or CAD/CAM, which put limit on productivity and made it difficult to properly cope with the increasing demand of markets. GASIR, a material, which can be molded easily, was selected among infrared ray optics materials in this study, and the optical system was designed with two Aspheric lenses. Because the lenses are molded in the environment of high temperature and high pressure, they require a special metallic pattern. The metallic pattern was produced with materials with ultra hardness that can stand high temperature and high pressure. As for the lens mold, GMP(Glass Molding Press) of the linear transfer method was used in order to improve the productivity of optical systems for thermal infrared cameras, which was the goal of this paper.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.28 no.4
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• pp.433-440
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• 2004

Since the numerical analysis was adopted in the mold design, lots of computational methods have been proposed for the simulations of casting processes for the various shaped molds. Today, it is possible to simulate the filling and solidification processes of most casts using the VOF technique. Though the three-dimensional numerical model based on the Cartesian coordinate system can be applied to any shape of cast, it becomes very inefficient when the three-dimensional model is applied to the cast of axi-symmetrical shape since the control volume includes at least 11 of the physical model. In addition, the more meshes should be distributed along the circumferential boundaries of curved shape in the Cartesian coordinate system fur the better results, while such curved circumferential boundary does not need to be considered in the two-dimensional cylindrical coordinate system. This motivates the present study i.e. developing a two-dimensional numerical model for the axi-symmetrically shaped casts. The SIMPLER algorithm, the VOF method, and the equivalent specific heat method have been adopted in the combined algorithm for the flow calculation, the free surface tracking, and the phase change heat transfer, respectively. The numerical model has been applied to the casting process of a pulley, and it was proven that the mesh and time effective calculation was accomplished comparing to the calculation using three-dimensional model.

• Journal of the Korean Society of Clothing and Textiles
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• v.30 no.6 s.154
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• pp.851-858
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• 2006

The human have constantly pursued the beauty through the history. Especially, the pursuit for the beauty of the human's body means that the subject is at one with the object pursued by Ire subject, which so called as the most active behavior of searching far the beauty. However it sometimes shows that human have tried excessively to search for the beauty of the human's ideal body in the history, and to the degree of hurting the body. For example, the corset was eagerly worn by women with the hope of a satisfied silhouette because the slender waist and the busty bosom were demanded as the woman's ideal body at 18C and 19C(the age of Victorian). The purpose of this study was to investigate the corset fashion in 18C, 19C, one of the most aggressive fashions out of the unreasonable fads, using narcissism that Freud mentioned as inside energy called libido. And the reason why to use the theory of narcissism in this study was that fashion as social outcome is thought to be influenced by the environment but the wearing behavior is considered totally private, it is particularly when focused on the excess ive energy, and the scope was limited to the investigation into the source of the energy binding the own body to hurting. The analysis about this craze of a corset with the view of the theory of narcissism as follows. First, women could mold the ideal concretely in surroundings that ideal woman was constituted just to focus on the appearance, moreover, the mother reinforced the narcissism of their offsprings. Also, the society demanded women to be chaste, and did not allowed for women to reveal libido to the external. As a result of this, libido should be ended up concentrating on ego. With this process, it to be difficult for 'ideal ego' impossible for attainment to transfer to compromising product, ego ideal. That is, women did not think entirely to be out of the question to reach the ideal ego, which meant the energy to tight waists was given women.

• 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.