• Polymer(Korea)
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• v.31 no.1
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• pp.31-36
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• 2007

It has been reported that the surface properties of the plasma treated material were changed while maintaining its bulk properties. In this study, surface modification of nylon fiber by plasma treatment was tried to attain high water-repellency Nylon fiber was treated with RF plasma under a vacuum system using various parameters such as gas specious, processing time and processing power. Morphological changes by low pressure plasma treatment were observed using scanning electron microscopy (SEM) and atomic force microscopy (AFM). Moreover, the mechanical and inherent properties were analyzed by tensile strength, differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). The high water-repellency property of nylon fiber was evaluated by a water-drop standard test under various conditions in terms of aging effect. The results showed that the water-repellency of plasma-surface-treated nylon fiber was greatly improved compared to untreated nylon fiber.

• Composites Research
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• v.18 no.6
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• pp.1-8
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• 2005

The fiber-reinforced composite materials have been advanced for various applications because of their excellent mechanical and electromagnetic properties. On their manufacturing processes, however, thermo-curing inherently produces the undesired thermal deformation mainly from temperature drop from the process temperature to the room temperature, so called spring-back. The spring-back must be understood especially in the hybrid composites in order to design and fabricate desired shape. In this research, (glass fiber / epoxy) + (carbon fiber / epoxy) unsymmetric hybrid composites were fabricated under various conditions such as cure cycle, laminate thickness, stacking sequence and curing sequence. Coupons were made and spring-back were measured using coordinate measuring machine (CMM). Using the Classical Lamination Theory (CLT) and finite element analysis (ANSYS), the behavior of spring-back were predicted and compared with the experimental data. The results from CLT and FEA agreed well with the experimental data. Although, the spring-back could be reduced by lowering curing temperature, at any case, the spring-back could not be removed completely.

• Journal of Korean Society of Steel Construction
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• v.18 no.3
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• pp.331-337
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• 2006

Specimens with fillet-welded lap joints were fabricated from 20 mm, 60 mm, and 82 mm thick steel plates produced by Thermo Mechanical Control Process. The designed sizes of filet welds were betwen 6 mm and 16 m. The welds' axes were parallel with or perpendicular to the direction of loading or a combination of them. Specimens were axialy loaded in tension and the strength of fillet-welded joints were measured. Test results showed that the strengths of filet-welded joints are higher than the nominal strengths calculated for all the cases tested, and also approximately on the same level regardless of plate thickness and fillet weld size. Especially, the specimens with weld size les than that required by Korean design rules showed no visible defects on welds and also no str ength reduction.

• Tribology and Lubricants
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• v.32 no.1
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• pp.1-8
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• 2016

This paper focuses on the thermal deformation induced preload change in the tilting pad journal bearing, using a three-dimensional (3D) thermo-hydro-dynamic (THD) approach. Preload is considered as a critical factor in designing the tilting pad journal bearing. The initial preload measured under nil external load and nil thermal gradient is influenced by two factors, namely, the thermal deformation and elastic deformation. Thermal deformation is due to a temperature distribution in the bearing pads, whereas the elastic deformation is due to fluid forces acting on the pads. This study focuses on the changes induced in preload and film clearance due to thermal deformation. The generalized Reynolds equation is used to evaluate the force of the fluid and the 3D energy equation is used to calculate the temperature of the lubricant. The abovementioned equations are combined by establishing a relationship between viscosity and temperature. The heat transfer within the bearing pads, the lubricant, and the spinning journal is calculated using the heat flux boundary condition. The 3D Finite Element Method (FEM) is used in modeling the (1) heat conduction in the spinning journal and bearing pads, (2) thermal gradient induced thermal distortion of the spinning journal and pads, and (3) viscous shearing, and heat conduction and convection in a thin film. This evaluation method has an increased fidelity, and it can prove to be a cost-effective tool that can be used by designers to predict the dynamic behavior of a bearing.

• Tribology and Lubricants
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• v.30 no.3
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• pp.177-182
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• 2014

To stop a high speed train running at the speed of 300 km/h, the disc brake for the train should be able to dissipate enormous kinetic energy of the train into frictional heat energy. Sintered pin-type metals are mostly used for friction materials of high speed brake pads. A pad comprises several friction pins, and the topology, length, flexibility, composition, etc. have a great influence on the tribological properties of the disc brake. In this study, the topology of the friction pins in a pad was our main concern. We presented the optimization of the topology of a railcar brake pad with nine-pin-type friction materials by thermo-mechanical contact analysis. We modeled the brake pad with/without a back plate. To simulate a continuous braking, the pad or friction materials were rotated at constant velocity on the friction surface of the disc. We varied the positions of the nine friction materials to compare the temperature distributions on the disc surface. In a non-optimized brake pad, the distance between two neighboring friction materials in the radial direction from the rotational center of the disc was not equal. In an optimized pad, the distance between two neighboring friction materials in the radial direction was equal. The temperature distribution on the disc surface fluctuated more for the former than the latter. Optimizing the pad reduced the maximum temperature of the brake disc by more than 10%.

• Journal of Energy Engineering
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• v.21 no.4
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• pp.427-434
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• 2012

The fuel characteristics and combustion behaviors of bituminous (Anglo) and sub-bituminous (Tanito) coals used in 500MW coal fired power plant have been investigated. With ashes of those coals, the ash fusibility is characterized with thermo mechanical analyzer, and the advanced ash slagging propensity, BHEL index, has been obtained. The melting-down of tanito coal ash happened in the temperature range of 1,200 to $1,250^{\circ}C$, and for anglo coal ash it occurred near $1,550^{\circ}C$. BHEL indices for two coals gives the high slagging propensity, and these are compared with the existing traditional indices which give different tendencies.

• Journal of Korea Society of Industrial Information Systems
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• v.23 no.1
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• pp.31-41
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• 2018

This paper discusses a structure design and thermal analysis of cryogenic conduction cooling system for a high current HTS DC reactor. Dimensions of the conduction cooling system parts including HTS magnets, bobbin structures, current leads, support bars, and thermal exchangers were calculated and drawn using a 3D CAD program. A finite element method model was built for determining the optimal design parameters and analyzing the thermo-mechanical characteristics. The operating current and inductance of the reactor magnet were 1,500 A, 400 mH, respectively. The thermal load of the HTS DC reactor was analyzed for determining the cooling capacity of the cryo-cooler. Hence, we carried out the operating test of conduction cooling system of the 1st stage area with high current flow. The cooper bars was cooled down to 40 K and HTS leads operated stably. As a experiment result, the total heat load of the 1st stage area is 190 W. The study results can be effectively utilized for the design and fabrication of a commercial HTS DC reactor.

• Proceedings of the Korean Powder Metallurgy Institute Conference
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• 1997.10a
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• pp.7-7
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• 1997

During sintering of very porous green bodies, as obtained by compaction of hard powders - such as tungsten carbide or ceramics - or by injection moulding, important shrinkage occurs. Due to heterogeneous green density field, gravity effects, friction on the support, thermal gradients, etc., this shrinkage is often non-uniform, which' may induce significant shape changes. As the ratio of compact dimension to powder size is very high, the mechanics of continuum is relevant to model such phenomena. Thus numerical techniques, such as the finite element method can be used to simulate the sintering process and predict the final shape of the sintered part. Such type of simulation has much been developed in the last decade firstly for hot isostatic pressing and next for die compaction. Finite element modelling has been recently applied to free sintering. The simulation of sintering should be based on constitutive equations describing the thermo-mechanical behaviour of the material under any state of stress and any temperature which may arise within the sintering body. These equations can be drawn either from experimental data or from micromechanical models. The experiments usually consist in free sintering and sinter-forging tests. Indeed applying more complex loading conditions at high temperature under controlled atmosphere is delicate. Micromechanical models describe the constitutive behaviour of aggregates of spheres from the deformation of two-sphere contact either by viscous flow or grain boundary diffusion. Such models are not able to describe complex microstructure and mechanisms as observed in real materials but they can give some basic information on the formulation of constitutive equations. Practically both experimental and theoretical approaches can be coupled to identify the constitutive equations. Such procedure has been performed for modelling the sintering of compacts obtained by die pressing of a mixture of tungsten carbide and cobalt powders. The constitutive behaviour of this material during sintering has been described by a linear viscous constitutive model, whose functions have been fitted from results of free sintering and sinter-forging experiments. This model has next been introduced in ABAQUS finite element code to simulate the sintering of heterogeneous green compacts of various geometries at constant temperature. Examples of simulations are shown and compared with experiments.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.43 no.5
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• pp.432-439
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• 2015

MEMS solid thruster module is composed of solid thruster and its control board. It was developed for the purpose of an academic research. Therefore, thermo-mechanical design and verification for space usage were not considered in the design phase. To mount it on a cube satellite without any design modification, technical efforts at the system level structure design is required. In this study, we proposed a structural design concept to mount the MEMS thruster module by using brackets for guaranteeing structure safety under launch loads and easier mating and de-mating of MEMS thruster module during test phase. The effectiveness of the design has been verified through structural analysis and vibration test. In addition, electrical connection method using spring pins between MEMS thruster and control board is effective for guaranteeing the structural safety under launch vibration loads.

• Polymer(Korea)
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• v.34 no.5
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• pp.480-484
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• 2010

A series of poly(amic acid)s(PAAs) was prepared by reacting 4,4'-(4,4'-isopropylidenediphenoxy) bis(phthalic anhydride)(BPADA) as the anhydride monomer and 2,2'-bis(trifluoromethyl) benzidine (TFB), bis(3-aminophenyl)sulfone (APS), 4,4'-methylenebis-(2-methylcyclohexylamine) (MMCA), or bis[4-(3-aminophenoxy) phenyl] sulfone (BAPS) as the amine monomer with 5 mol% melamine in N,N-dimethylacetamide (DMAc). Colorless and transparent polyimide (PI) films were obtained by casting the PAAs at various heat treatment temperatures. The thermo-mechanical properties and optical transparency of the PI films were investigated. The thermal properties of the PI films were examined using differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), and thermomechanical analysis (TMA), and their optical transparency were measured by spectrophotometry. The coefficient of thermal expansion (CTE) and yellow index (YI) values of all samples were in the range of $48.53-64.24ppm/^{\circ}C$ and < 3.0, respectively.