• Proceedings of the Korean Vacuum Society Conference
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• 2013.02a
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• pp.300-300
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• 2013

세계전자제품의 부품산업은 21세기 정보화 사회와 함께 IT 산업에서 급성장으로 인해 부품의 소형화, 경량화, 친환경화가 요구되고 있다. IT 산업에서 리드스크류(Leadsrew)는 마이크로 구동부품중의 이송장치를 구성하는 핵심 부품으로 탄소강과 합금강 및 스테인레스강 등이 사용되고 있다. 탄소강은 성형 가공성과 원가 절감에 최적의 소재로서 낮은 표면 경도로 인한 내마모성 저하와 부식 분위기에서의 내식성이 떨어지는 단점을 가지고 있다. 본 연구에서는 탄소강(S20C:${\oint}30{\times}h10$)을 이용하여 플라즈마 질화 표면처리를 통해 표면경도와 내마모성 향상 및 내식성을 높이는 연구를 수행하였다. 연구 방법으로 플라즈마 연질화 공정과 Post Oxidation 공정을 개발하였고, 질화 처리된 시험편에 대해 마이크로 비커스 경도, OEM&SEM, XRD 분석 및 염수분무(KS D 9502) 시험으로 특성을 분석하였다. 연구 결과로 탄소강(S20C)은 마이크로 비커스 경도 분석으로 표면 경도가 600Hv0.025 이상과 염수분무 시험으로 내식성은 24시간 이상의 결과를 얻었다.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.38 no.8
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• pp.899-904
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• 2014

Thickness profiled blank is designed using optimization techniques for maximizing the bulged heights during the free bulging of Inconel 718. The thickness of the blank was described by the Bezier curve and the locations of the control points were used as the design variables for optimization. The maximization of the bulged heights within the limited strain range served as the objective function and constraints for optimization. The equivalent static loads method for non-linear static response structural optimization (ESLSO) was used and the result of the optimization revealed 22 increased bulged heights. A free bulging test using a blank with an optimized profile was conducted to verify the optimization process. The results were compared with those of numerical analysis in terms of bulged height and deformed shape.

• Applied Chemistry for Engineering
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• v.21 no.5
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• pp.553-558
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• 2010

To solve the problems of the low combustion activity of Korean anthracite and the abundant loss of unburned carbon in fly ash, pellet coal was fabricated from coal fines and fly ash, and the mixed combustion of coarse coal with the pellet coal was examined in the circulating fluidized bed combustor of a 0.1 MW scale test unit. In the combustion of the raw coal only, the significant amount of coal fines was entrained, resulting in overheat at the top of the combustor. With the coarse coal that most fines were eliminated, however, the combustion temperature was maintained stable. The mixed combustion of coarse and raw coals was also feasible even though it often went unstable. The mixed combustion of the coarse coal with the pellet coal was as stable as the coarse coal combustion, showing a promise that the combustion of the Korean anthracite in commercial circulating fluidized bed boilers could be further enhanced.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.38 no.1
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• pp.65-70
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• 2014

This paper introduces a preform design method for a ring rolling process with an outer step. Underfilling is one of the general defects of the profile ring rolling process. It occurs when the deformation amount is small or step depth of the profiled region is large. To prevent underfilling, increasing the deformation amount or using a preform of size similar to that of the final product are required. Furthermore, the filling limit equation is suggested based on the shape factor and deformation ratio for preventing defects in the products. The filling limit equation has been derived through finite element analyses and production tests for four different cases. For verifying the suggested method, realsized profile rolling tests were performed, and test results were compared with the predictions of the equation.

• Design & Manufacturing
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• v.17 no.3
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• pp.55-60
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• 2023

The fiber-reinforced plastics and cellular injection molding process can be used to efficiently reduce the weight of battery housing components of mild hybrid electronic vehicles(MHEV) made of metal. However, the fiber orientation of fiber-reinforced plastics and the growth of foaming cells are intertwined during the injection molding process, so it is difficult to predict the mechanical properties of products in the design process. Therefore, it is necessary to evaluate the mechanical properties of the materials prior to the efficient stiffness design of the target product. In this study, a study was conducted to evaluated the mechanical properties of fiber reinforced cellular injection-molded specimens. Two types of fiber-reinforced plastics that can be used in the target product were evaluated for changes in tensile properties of cellular injection-molded specimens depending on the foaming ratio and position from the injection gate. The PP and PA66 specimens showed a decrease of tensile modulus and strength of approximately 30% and 17% depending on the foaming ratio, respectively. Also, the tensile strength decreased approximately 26% and 17% depending on the position from the injection gate, respectively. As a result, it was confirmed that the PP specimens have a significantly mechanical property degradation compared to the PA66 specimens depending on the foaming ratio and position.

• Journal of the Korean Geotechnical Society
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• v.18 no.4
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• pp.147-157
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• 2002

In this paper, the testing cell and the related theory far the interpretation of constant rate of strain (CRS) consolidation test results in case of radial drainage were developed. The proposed method makes it possible to evaluate consolidation characteristics of clayey soil rapidly and accurately. To investigate the application of the developed testing device and theory, CRS consolidation tests and incremental loading(IL) tests in radial drainage condition with remolded and undisturbed samples were performed. Comparisons of consolidation parameters from consolidation curves including coefficient of consolidation values show the applicability and the reliability of the suggested method. The experimental data were compared with additional vertical drainage CRS tests and IL tests, and then were analyzed considering the effect of the drainage direction. In addition, the effect of excess pore water pressure generated during CRS consolidation test was investigated.

• Composites Research
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• v.14 no.3
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• pp.10-17
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• 2001

A reseach was peformed to develop composite pressure vessels in conjunction with design, fabrication, and test. Fiber pattern and angels were decided by CADFIL software and they were [$liner/15^{\circ}/15^{\circ}/90^{\circ}/18^{\circ}/90^{\circ}/21^{\circ}/21^{\circ}/90^{\circ}$]. Fabrication of bottles were done by 5-axis filament winding machine. During fabrication fiber optic sensors were embedded to measure the strain at points when internal pressure was applied by water pump. Conventional strain gage instrumentation showed the stable test results. The test results were compared to finite element analysis results and they were close each other in strain values. One can see the successful design and fabrication of single boss composite vessels.

• Fire Science and Engineering
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• v.25 no.5
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• pp.69-75
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• 2011

It was performed to test the combustive properties of low density polyethylene and ethylene vinyl acetate (LDPE-EVA) composite by the addition of magnesium hydroxide. Flame retardant of natural magnesium hydroxide was added to the mixture of LDPE-EVA in 40 to 80 wt% concentration. The composite was compounded to prepare specimen for combustive analysis by cone calorimeter (ISO 5660-1). Comparing with virgin LDPE-EVA, the specimens including the magnesium hydroxide had lower flashover possibility. It is supposed that the combustive properties in the composites decreased due to the endothermic decomposition of magnesium hydroxide. The specimens with magnesium hydroxide showed both the lower total heat release rate (THR) and lower CO production rate than those of virgin polymer. As the magnesium hydroxide content increases, the total smoke release (THR) and smoke extinction area (SEA) decreased.

• Geotechnical Engineering
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• v.2 no.1
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• pp.15-26
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• 1986

Consolidated undrained standard triaxial tests for two remoulded clays and one undisturbed clay were carried out in order to find out the relationship between excess pore water pressure and axial strain in mortally consolidatated saturated clays during undrained shear. Tests were performed with isotropically-normally consolidated specimens by strain controlled and stress controlled loading. As the result of this stud!'a hyperbolic function expressing the relationship between pore water pressure and strain was found out, and it showed the same form as the Kondner's hyperbolic function for stress·strain behaviour. Two parameters used for the function can be obtained by CU-triaxial test.

• Journal of the Korea institute for structural maintenance and inspection
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• v.22 no.3
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• pp.84-89
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• 2018

Recently, study on self-healing materials have been performed to increase the life by repairing the damage of structures themselves, which are difficult to repair or require high maintenance costs. A water permeability test has been widely used for the evaluation of self-healing performance. However, in the self-healing performance test method, the initial crack width of the concrete greatly affects on the self-healing performance but it does not have a consistent standard. Therefore, in this study, the correlation between crack and permeability and that between time and permeability were analyzed based on crack width and permeability. In addition, since the initial crack width measured by optical microscope is not reliable, the value is derived from the Poiseuille flow and the tendency of time-permeability and time-crack width are analyzed.