• Proceedings of the Korean Society For Composite Materials Conference
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• 2004.04a
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• pp.246-249
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• 2004

When MWK (Multiaxial Warp Knitted Fabric) composites are applied for the structures, the connections of each component using mechanical fastening is needed. The local contact between the bolted joint and the composite laminates may induce high stress concentration or breakdown in the laminates for the mechanical joints. There for, it is strongly required to study the characteristics of mechanically joints of MWK composite laminates. In this study, stress analysis near the hole boundary of MWK composite laminate is conducted with various geometric factors under different loadings. In the case of multi-pin loaded MWK composite laminates, the results show that the types of loadings and geometric factors of mechanical joints have a significant influence on the joint performances.

• Journal of the Korea Institute of Military Science and Technology
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• v.2 no.2
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• pp.251-260
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• 1999

The stiffness of joint parts in the finite element beam model are corrected by the direct comparison between the modal test and analysis model. The corrected stiffness are reviewed according to the boundary conditions of modal testing. For the improved modal test/analysis correction, more modes measured than acceleration sensors are used to make a minimal order system model. In addition, the initial F.E. model is reduced to the degrees of freedom of a minimal order system model, keeping the dynamics of the initial model. Finally, for the parametric correction of the reduced model, the submatrices are used to model the initially assumed stiffness.

• Proceedings of the Korean Institute of Surface Engineering Conference
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• 2012.05a
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• pp.179-180
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• 2012

Back ferrule is a circular ring shaped metallic object which is used for fastening, joining or reinforcement during the tube fitting as well as to prevent leakage. Therefore, during tube fitting the leading edge of the back ferrule should be sufficiently hard enough to prevent leakage. In our research, we concentrated the improvement of two major factors. Firstly, to improve the surface hardness of the back ferrule made by AISI 316 Stainless Steel. Secondly, the enhancement of corrosion resistance of back ferrule after plasma treatment. Initially, the corrosion resistance and hardness of the back ferrule (both commercial and without treated) was not good enough for tube fitting but after applying plasma treatment with suitable conditions on ferrule, we improved the corrosion resistance and hardness of the back ferrule dramatically.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.46 no.10
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• pp.867-875
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• 2018

Conventional nylon wire cutting-type holding and release mechanisms (HRMs) are limited to securely hold the solar panel under launch environment as the size of the panel increases because the nylon wire is tightened directly on the surface of the solar panel. In this study, we proposed a nylon wire cutting-type HRM for 6U CubeSat's solar panel applying elliptic-shaped bracket with a Ball & Socket interface. The proposed HRM has the advantage of higher holding capability along in-plane and out-of plane directions of solar panel and simplicity in tightening process of nylon wire. The design drivers of structural design of CubeSat's solar panel with the proposed HRM were defined by structural analysis under launch loads. In addition, The design effectiveness of the proposed HRM was verified through the functional tests according to the thickness of nylon wire and the number of wire winding under various temperature conditions.

• Asia-Pacific Journal of Business Venturing and Entrepreneurship
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• v.11 no.4
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• pp.205-213
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• 2016

This study clarified the definition and interpretation of terms relating to SMEs Priority System. First, 'Domestic' is defined that the address of office is in our country. Second, 'Technology utilization capacity' is defined that the de facto capacity to technology commercialization and utilization. for example. development or production or sales activity of the production using national r&d performance. Third, 'priority' in priority consideration is defined that when there are many companies trying sign technology utilization contract, technology providers shoud provide the opportunity of signing contract to SMEs primarily. 'priority consideration' is defined that technology providers shoud try to do enough to sign a contract with SMEs. This study has significance in that raising the application of the current SMEs Priority System.

• Journal of the Korean Geosynthetics Society
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• v.15 no.3
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• pp.13-26
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• 2016

In this study, more economical than conventional reinforced soil retaining walls, we compared the behavior characteristic about the safety block type numerically for reinforced retaining wall. In this study, reinforced soil retaining wall, first, was integrated a wall putting shear key on the blocks. Second, construction reinforcement focused on the theoretical failure surface was satisfied with the stability of a retaining wall reinforced by a shear plane. when analyzing, element of using reinforcement was carried out a numerical analysis for the cable element and the strip element, and they were analyzed under the conditions according to the stiffener length, distance, with or without shear key. Analysis for the integration of the front wall was reinforced soil retaining walls by installing a larger displacement shear key confinement effect, if reinforced construction and reinforcement with 1 interval and 2 interval, the failure surface was bigger displacement constraints. Generating a deformation amount was smaller than the generation amount of deformation accrued during construction of AASHTO so that it was stable.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.21 no.9
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• pp.32-38
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• 2020

Cargo train braking uses the pressure changes in the air braking pipe to operate the braking tightening and releasing service repeatedly. Air-braking release failure means partial braking caused by a failure of the variable load valve after the driver handling the brake release. This phenomenon causes wheel flaws while driving a wagon, resulting in wheel breakage or train derailment. This study developed the air-braking release failure proof valve considering the technical requirements of the railway operation corporations. In addition, a durability test of the valve was carried out using a braking performance simulator, and its operating performance was evaluated from the pneumatic history under cyclic braking conditions. The warranty life of this valve was assessed by performing 160,000 cycles of testing of 12 prototypes in accordance with the zero-failure test method, considering the number of braking cycles while driving the wagon. During the durability test, the pneumatic input time, output time, and release velocity were almost constant. The warranty life of this valve was 59,860 times the 95% confidence level, which means that it can be operated without trouble for four years when the valve is installed in the bogie of the wagon.

• Journal of the Korean Geotechnical Society
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• v.31 no.9
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• pp.29-38
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• 2015

In this study, track dynamic interaction characteristics caused by the vehicle running through transitional section such as bridge abutments were studied using the finite element analysis program. The geometric condition of track was generated by trigonometric function and allowable maximum track irregularity is determined by KORAIL track maintenance criteria. The sub-infrastructure under rail fastener system was modelled by 3D solid elements. To reduce computational cost only half track line is numerically considered and the roller boundary condition was applied to each side of model. In this study, the vehicle-track dynamic interaction analysis was carried out for standard Korean transition section of concrete track and the dynamic behaviors were investigated. The dynamic characteristics considered are wheel load variation, vertical acceleration at body, and maximum Mises stress at each part of transitional section.

• 한국신재생에너지학회:학술대회논문집
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• 2011.05a
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• pp.97.1-97.1
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• 2011

저온에서 양이온 고분자막을 사용하는 고분자 연료전지의 경우 뛰어난 성능과 다양한 응용분야로 인해 많은 연구와 실증이 이루어지고 있지만 공기극에서의 느린 산소 환원반응으로 인해 백금과 같은 귀금속의 사용이 불가피하고 백금의 제한된 매장량과 높은 가격으로 인해 상용화가 늦어지고 있다. 그래서 많은 연구자들이 합금 촉매 또는 비귀금속 촉매를 이용한 전극 개발에 집중하고 있다. 알칼리 분위기에서 저가의 전이 금속들이 백금과 비슷한 활성을 보이고 고체 음이온 교환막이 개발됨에 따라 최근 알칼리 연료전지가 다시금 큰 주목을 받고 있다. 그러나 고분자 연료전지와는 달리 아직 촉매나 전해질막, 이오노머의 특성 및 메커니즘에 관해 별로 알려진 것이 없다. 본 연구에서는 직접 개발한 세공충진막 형태의 탄화수소계의 음이온 교환막과 비귀금속 공기극 촉매를 이용하여 막전극접합체(MEA)를 개발하였고 촉매 및 이오노머 함량과 같은 전극 조성, 막전극접합체의 제조 및 체결, 가습이나 가스조성 등의 단위전지 운전조건과 같은 다양한 변수에 대해에 최적 조건을 도출하고자 하였다. 공기극 촉매는 Cu-Fe/C를 이용한 상용 촉매를 이용하였고 이오노머의 경우는 탄화수소계의 상용 제품을 사용하였으며 음이온 교환막에 전극층을 형성하기 위해서는 스프레이 공정을 이용하였다. 단위전지를 통해 성능을 확인하였고 임피던스 및 CV를 통해 전기화학적인 특성을 규명하였다. 조건의 최적화를 통해 상당한 성능 향상을 이루었으나 추가적인 성능 향상 및 내구성 확보 등에 대해 계속적인 실험을 진행할 예정이다.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.42 no.3
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• pp.439-448
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• 2022

Recently, domestic small and medium-sized subcontractors participating in the overseas construction market are suffering from the continuous loss and damage due to the insufficient recognition of the importance of risk Sub-Clauses among conditions of subcontracts. Therefore, the need to derive risk Sub-Clauses for conditions of the subcontract has been raised, but until now, previous studies have been conducted focusing on deriving risk Sub-Clauses for standard conditions of contract for construction between the Employer and the Contractor. In this study, 52 risk Sub-Clauses were derived on the basis of the influence size of the Sub-Clauses through the Delphi technique targeting 94 Sub-Clauses of conditions of standard subcontract for construction edition 2011, issued by the International Federation of Consulting Engineers (FIDIC) and In addition, 33 key risk Sub-Clauses were finally derived through the PI Risk Matrix by Probability and Impact. The results of this study provide will useful information on key risk Sub-Clauses that need to be reviewed in advance to minimize contractual risks at the stage of bidding and signing contracts for overseas subcontract construction projects.