• Proceedings of the Korean Vacuum Society Conference
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• 2007.08a
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• pp.373-373
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• 2007

• Proceedings of the Korean Powder Metallurgy Institute Conference
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• 2006.09a
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• pp.99-100
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• 2006

Cellular metals based on Iron have been intensively investigated during the last two decades. Because of the significant decreasing of the structural density of Iron based cellular structures, numerous technologies have been developed for their manufacturing. Besides the tremendous weight reduction a combination with other properties like energy and noise absorption, heat insulation and mechanical damping can be achieved. This contribution will give an overview about the latest state in Iron based cellular materials, including technologies in manufacturing, properties and potential applications.

• Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
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• 1999.11a
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• pp.225-232
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• 1999

The effect of manufacturing parameters such as molding and curing conditions on friction characteristics of friction materials was studied using a pad-on-disk type friction tester. Friction materials containing 15 ingredients were investigated for an optimal manufacturing condition for the best friction characteristics employing Taguchi robust experimental design. The main effects were different for mechanical properties and friction characteristics and were strongly influenced by manufacturing conditions. An optimum manufacturing condition was obtained to achieve the best friction characteristics concerning mechanical properties(hardness, porosity, wear resistance), friction stability, and change of rotor temperature.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.21 no.5
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• pp.1-8
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• 2022

Fused deposition modeling (FDM), based on stacking a continuous filament of polymer or composite materials, is well matured and is thus widely used in additive manufacturing technology. To advance FDM-based 3D printing technology, the mechanical properties of additively manufactured composite materials must be improved. In this study, we proposed a novel FDM 3D printing process using metal wire-polymer composites, enabling enhanced mechanical properties. In addition, we developed a new type FDM filament of copper wire wrapped in nylon material for stable 3D printing without thermal damage during the printing process. After FDM printing of the copper wire-nylon composite filament, we conducted a tensile test to investigate the mechanical behavior of the printed composite materials. The experimental results confirmed that the tensile strength of the 3D-printed metal wire-polymer composites was higher than that of the conventional single polymer material. Thus, we expect that the FDM printing process developed in this study may be promising for high-load-bearing applications.

• Transactions of Materials Processing
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• v.23 no.5
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• pp.303-310
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• 2014

Functionally graded properties are characterized by the gradual variation in composition and structure through the volume of the material, resulting in corresponding gradation in properties of the material. Direct laser melting (DLM) is a prototyping process whereby a 3-D part is built layer-wise by melting metal powder with laser scanning. Studies have been performed on the functionally graded properties induced by direct laser melting of compositionally selected metallic powders. For the current study, quadrangle structures were fabricated by DLM using Fe-Ni-Cr powders having variable compositions. Hardness and EDX analysis were conducted on cross-sections of the fabricated structure to characterize the properties. From the analysis, it is shown that functionally graded properties can be successfully obtained by DLM of selected metallic powders with varying compositions.

• Journal of Aerospace System Engineering
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• v.14 no.4
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• pp.25-31
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• 2020

The development of manufacturing technology for braided composites has led to farther extension of the applications in aerospace structures. Since the mechanical characteristics of braided composites are affected by various materials and manufacturing parameters, it is important to determine the parameters required to appropriately design the braided composite structures. In this study, we proposed a geometric model of RUC (repeating unit cell) for 2D braided composites, and predicted the mechanical properties according to the change of fiber volume fraction, fiber filament size, braiding angle, and gap between adjacent yarns by the yarn slicing technique and stress averaging method. Finally, we analyze the characteristics of mechanical properties according to each manufacturing parameter of the braided composite material.

• Current Optics and Photonics
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• v.3 no.2
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• pp.164-171
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• 2019

Photoluminescence (PL) properties of GaN-based light-emitting diodes (LEDs) were analyzed to study the effects of carrier leakage on the luminescence properties at room temperature. The electrical leakage and PL properties were compared for LEDs showing leakages at forward bias and an LED with an intentional leakage path formed by connecting a parallel resistance of various values. The leakages at the forward bias, which could be observed from the current-voltage characteristics, resulted in an increase in the excitation laser power density for the maximum PL efficiency (ratio of PL intensity to excitation power) as well as a reduction in the PL intensity. The effect of carrier leakages on PL properties was similar to the change in PL properties owing to a reduction of the photovoltage by a reverse current since the direction of the carrier movement under photoexcitation is identical to that of the reverse current. Valid relations between PL properties and electrical properties were observed as the PL properties deteriorated with an increase in the carrier leakage. The results imply that the PL properties of LED chips can be an indicator of the electrical properties of LEDs.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.21 no.9
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• pp.85-91
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• 2022

The demand for electric vehicles has increased because of environmental regulations. The lithium-ion battery, the most widely used type of battery in electric vehicles, is composed of a cathode, an anode, and an electrolyte. It is manufactured according to the pole plate, assembly, and formation processes. To improve battery performance and increase manufacturing efficiency, the manufacturing process must be optimized. To do so, simulation can be used to reduce wasted resources and time, and a finite-element method can be utilized. For high simulation quality, it is essential to reflect the material properties of the electrode by considering the pores. However, the material properties of electrodes are difficult to derive through measurement. In this study, the representative volume element method, which is a homogenization method, was applied to estimate the representative material properties of the electrode considering the pores. The representative volume element method assumes that the strain energy before and after the conversion into a representative volume is conserved. The method can be converted into one representative property, even when nonhomogeneous materials are mixed in a unit volume. In this study, the material properties of the electrode considering the pores were derived. The results should be helpful in optimizing the electrode manufacturing process and related element technologies.

• Journal of the Korean institute of surface engineering
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• v.56 no.5
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• pp.309-319
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• 2023

Non-woven fabric is a textile product made by spinning thermoplastic polymers without manufacturing processes such as stretching, doubling, twisting, weaving, and knitting to form a sheet-shaped web in which fibers are tangled with each other, and then combining them by mechanical and physical methods. In addition, the non-woven fabric manufacturing process has various raw material choices, high productivity, so it is a textile manufacturing technology that can have various uses and increase added value. This study was conducted to control the shape and physical properties of products by improving the manufacturing method of melt-blown non-woven fabrics using process technology that easily changes the shape of non-woven fabrics and improves mechanical properties. In particular, it is considered that a non-woven fabric with a thin material shape and improved mechanical properties will be easily applied to a continuous secondary battery manufacturing industry such as roll to roll operation.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.26 no.5
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• pp.813-821
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• 2002

Glass fiber reinforced PET matrix composite was manufactured by rapid press consolidation technique as functions of temperature, pressure and time in pre-heating, consolidation and solidification stages. The optimal manufacturing conditions for this composite were discussed based on the void content, tensile, interlaminar shear and impact properties. In addition, the levels of crystallinity with various manufacturing conditions were measured using differential scanning calorimetry to investigate the mechanical properties of this composite material as a function of crystallinity. Among many processing parameters, the mold temperature and the cooling rate after forming were found to be the most critical factors in determining the level of crystallinity and mechanical properties. The level of crystallinity affects the tensile properties to some degree. However, impact properties are affected much more. It also affects the degree of ductility, which determines the impact energy of this material.