• Title/Summary/Keyword: critical experiment

검색결과 944건 처리시간 0.021초

항공기 주익구조물의 피로균열 진전 해석 및 실험을 위한 응력 스펙트럼 알고리즘 개발 (Stress Spectrum Algorithm Development for Fatigue Crack Growth Analysis and Experiment for Aircraft Wing Structure)

  • 천영철;장윤정;정태진;강기원
    • 대한기계학회논문집A
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    • 제39권12호
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    • pp.1281-1286
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    • 2015
  • 항공기는 다양한 임무를 수행함으로써 장기간 운영 시 비행시간 누적으로 인해 피로균열을 발생시킬 수 있다. 주익 구조물에 균열이 발생하면 수명단축 등 여러 문제점들이 발생할 수 있다. 이의 해결을 위해 피로임계위치(Fatigue critical location, FCL)에서의 균열진전 해석이 필요하다. 균열진전 해석을 위해서는 장시간의 응력 스펙트럼이 필요한데 실제 항공기에서 필요한 만큼의 데이터를 얻는 것은 막대한 시간과 비이 소요된다. 본 논문에서는 SwRI(South West Research Institute)보고서에 제시되어있는 임무별 단시간 하중배수 자료를 바탕으로 Peak-Valley Cycle Counting 을 진행하여 장시간의 응력 스펙트럼을 산출하는 알고리즘을 개발하였다.

전도냉각 고온초전도 SMES 시스템의 기초절연 특성 (Basic Insulation Characteristics of Conduction-Cooled HTS SMES System)

  • 최재형;곽동순;천현권;김상현
    • 대한전기학회논문지:전기물성ㆍ응용부문C
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    • 제55권8호
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    • pp.404-410
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    • 2006
  • Toward the practical applications, on operation of conduction-cooled HTS SMES at temperatures well below 40[K] should be investigated, in order to take advantage of a greater critical current density of HTS and considerably reduce the size and weight of the system. In order to take advantage of a greater critical current density of high temperature superconducting (HTS) and considerably reduce the size and weight of the system, conduction-cooled HTS superconducting magnetic energy storage (SMES) at temperatures well below 40[K] should be investigated. This work focuses on the breakdown and flashover phenomenology of dielectrics exposed in air and/or vacuum for temperatures ranging from room temperature to cryogenic temperature. Firstly, we summarize the insulation factors of the magnet for the conduction cooled HTS SMES. And Secondly a surface flashover as well as volume breakdown in air and/or vacuum with two kind insulators has been investigated. Finally, we will discuss applications for the HTS SMES including aging studies on model coils exposed in vacuum at cryogenic temperature. The commercial application of many conduction-cooled HTS magnets, however, requires refrigeration at temperatures below 40[K], in order to take advantage of a greater critical current density of HTS and reduce considerably the size and weight of the system. The magnet is driven in vacuum condition. The need to reduce the size and weight of the system has led to the consideration of the vacuum as insulating media. We are studying on the insulation factors of the magnet for HTS SMES. And we experiment the spacer configure effect in the dielectric flashover characteristics. From the results, we confirm that our research established basic information in the insulation design of the magnet.

크롬 및 구리로 치환한 L12 Titanium Trialuminides합금의 고온변형거동 (High Temperature Deformation Behavior of L12 Modified Titanium Trialuminides Doped with Chromium and Copper)

  • 한창석;진성윤;방효인
    • 한국재료학회지
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    • 제28권6호
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    • pp.317-323
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    • 2018
  • Crystal structure of the $L1_2$ type $(Al,X)_3Ti$ alloy (X = Cr,Cu) is analyzed by X-ray diffractometry and the nonuniform strain behavior at high temperature is investigated. The lattice constants for the $L1_2$ type $(Al,X)_3Ti$ alloys decrease in the order of the atomic number of the substituted atom X, and the hardness tends to increase. In a compressive test at around 473K for $Al_{67.5}Ti_{25}Cr_{7.5}$, $Al_{65}Ti_{25}Cr_{10}$ and $Al_{62.5}Ti_{25}Cu_{12.5}$ alloys, it is found that the stress-strain curves showed serration, and deformation rate dependence appeared. It is assumed that the generation of serration is due to dynamic strain aging caused by the diffusion of solute atoms. As a result, activation energy of 60-95 kJ/mol is obtained. This process does not require direct involvement. In order to investigate the generation of serrations in detail, compression tests are carried out under various conditions. As a result, in the strain rate range of this experiment, serration is found to occur after 470K at a certain critical strain. The critical strain increases as the strain rate increases at constant temperature, and the critical strain tends to decrease as temperature rises under constant strain rate. This tendency is common to all alloys produced. In the case of this alloy system, the serration at around 473K corresponds to the case in which the dislocation velocity is faster than the diffusion rate of interstitial solute atoms at low temperature.

실험계획법을 이용한 인공위성 주반사경 플렉셔 마운트의 최적 설계 (Optimal Design of the Flexure Mounts for Satellite Camera by Using Design of Experiments)

  • 김현중;서유덕;윤성기;이승훈;이덕규;이응식
    • 대한기계학회논문집A
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    • 제32권8호
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    • pp.693-700
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    • 2008
  • The primary mirror system in a satellite camera is an opto-mechanically coupled system for a reason that optical and mechanical behaviors are intricately interactive. In order to enhance the opto-mechanical performance of the primary mirror system, opto-mechanical behaviors should be thoroughly investigated by using various analysis procedures such as elastic, thermo-elastic, optical and eigenvalue analysis. In this paper, optimal design of the bipod flexure mounts for high opto-mechanical performance is performed. Optomechanical performances considered in this paper are RMS wavefront error under the gravity and thermal loading conditions and 1st natural frequency of the mirror system. The procedures of the flexure mounts design based on design of experiments and statistics is as follows. The experiments for opto-mechanical analysis are constructed based on the tables of orthogonal arrays and analysis of each experiment is carried out. In order to deal with the multiple opto-mechanical properties, MADM (Multiple-attribute decision making) is employed. From the analysis results, the critical design variables of the flexure mounts which have dominant influences on opto-mechanical performance are determined through analysis of variance and F-test. The regression model in terms of the critical design variables is constructed based on the response surfaceanalysis. Then the critical design variables are optimized from the regression model by using SQP algorithm. Opto-mechanical performance of the optimal bipod flexure mounts is verified through analysis.

변형경화형 시멘트 복합체를 사용한 프리캐스트 끼움벽판의 내진성능 (Seismic Performance of Precast Infill Walls with Strain-Hardening Cement Composite)

  • 김선우;전에스더;김윤수;지상규;장광수;윤현도
    • 한국콘크리트학회:학술대회논문집
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    • 한국콘크리트학회 2008년도 추계 학술발표회 제20권2호
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    • pp.89-92
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    • 2008
  • 최근 빈번하게 발생되는 지진으로 인해 내진규정이 강화된 바 있으며, 국내에서도 인접 국가들의 지진피해 발생으로 인해 지진에 대한 안전지대가 될 수 없다는 인식이 고조되어 건축구조설계기준에 서의 내진규정이 강화되었다. 그러나 기존 비내진상세를 갖는 건축물을 해체하여 요구성능을 얻고자 하는 경우 경제적, 환경적 손실이 크므로 비내진상세를 갖는 라멘구조물을 끼움벽을 통해 보강하는 것이 합리적일 것이라 판단된다. 따라서 본 연구에서는 변형경화형 시멘트 복합체인 SHCC를 끼움벽에 적용하였으며, 일반배근 및 대각보강근에 따른 내진성능을 정량적으로 평가함으로써 SHCC 적용에 따른 배근상세 감소 및 시공성 향상을 꾀하고자 한다. 실험체는 1/3 축소모형의 프리캐스트 끼움벽으로 제작되었으며, 실험결과 다수의 미세균열이 발생하여 기존 콘크리트에서 발생되는 명확한 전단균열 및 급격한 내력저하는 발생하지 않았다. 이는 SHCC 내 혼입된 PVA 및 PE 섬유의 가교작용에 의한 것으로 벽체에 전달되는 횡하중에 의한 응력을 재분배했기 때문인 것으로 사료된다.

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장기운영 항공기 주익 구조물 피로임계부위의 손상허용평가 (Damage Tolerance Assessment for Fatigue-Critical Locations of Wing Structure of Aged Aircraft)

  • 천영철;김원철;진지원;정태진;강기원
    • 대한기계학회논문집A
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    • 제41권2호
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    • pp.129-136
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    • 2017
  • 본 연구의 목적은 항공기 주익 구조물에 대한 피로균열진전 해석 및 실험을 통하여 운영 기간에 따른 장기 운영 항공기의 손상허용성을 평가하는 하는 것이다. 이를 위하여 주익 구조물의 피로임계부위 2 곳을 대상으로, 선행 연구에서 개발된 알고리즘을 기반으로 산출된 피로응력 스펙트럼 및 상용 코드인 NASGRO 를 이용한 피로균열진전해석을 수행하고 그 결과를 참고문헌의 결과와 비교하여 피로응력 스펙트럼 및 균열진전해석방법의 타당성을 확인하였다. 또한 실제 주익 구조물에서 채취한 시험편 및 이와 동일 재료로 가공된 시험편을 대상으로 위의 피로응력 스펙트럼을 적용한 피로균열진전시험을 실시하고 그 결과를 이용하여 운영 기간에 따른 주익 구조물의 손상허용성을 평가하였다.

모의 수업 실행 과정에서 나타난 초등 예비 교사의 과학 탐구 수업에 대한 인식 (Examining Pre-service Elementary Teachers' Views on Science Inquiry Teaching during Peer Teaching Practice)

  • 윤혜경;정용재;김미정;박영신;김병석
    • 한국초등과학교육학회지:초등과학교육
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    • 제31권3호
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    • pp.334-346
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    • 2012
  • For teachers' conceptions and understandings are critical to their decision making and classroom practice, this study attempts to understand pre-service elementary teachers' views and practices of science inquiry during peer teaching practice. Fifteen 4th year university students in teacher education program participated in peer teaching practice. Their teaching and reflective discussion were video and audio recorded and written lesson plans were collected for data analysis. Five science teacher educators individually looked into the data and shared their comments and interpretations on pre-service teachers' views and practice. The study findings suggest that pre-service teachers emphasized the importance of providing students with motivating resources in the beginning of lesson, employing certain inquiry teaching models, the process of predicting and dis/proving via experiment, and teachers' minimal intervention as the important features of inquiry teaching. Science teacher educators emphasized that it is critical to help children understand inquiry questions in the beginning of inquiry process, to be mindful of children's problem solving and critical thinking rather than following instruction models or simply going through prediction and test process. They also commented that teachers' guidance could lead a good inquiry process in classroom practice, not always interfering students' inquiry. Based on the findings, the study suggests science teacher educators need to understand what and how pre-service teachers view and practice science inquiry teaching and consider these as useful resources where they can start effective teaching for pre-service teachers at the university level.

통계적 논증활동을 강조한 통계수업의 효과에 대한 사례연구 (A Case Study on Effect of Statistics Class focusing on Statistical Argumentation)

  • 강현영;송은영;조진우;이경화
    • 대한수학교육학회지:수학교육학연구
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    • 제21권4호
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    • pp.399-422
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    • 2011
  • 현대 사회에서는 실생활의 양적 정보를 합리적으로 다루는데 필요한 능력이 요구된다. 최근에는 시대적 요구에 적절하고 의미 있는 통계 교육의 필요성에 따라 '통계적 소양'이 주목을 받고 있으며 많은 논의가 되고 있다. 특히 그 중에서도 비판적 사고능력과 통계적 의사소통 능력의 개발이 강조되고 있다. 이에 따라 본 연구에서는 학생들에게 통계적 논증에 따른 의사소통이 일어나도록 과제를 개발, 제공하였다. 그리고 학생들의 논증활동 과정에서 나타나는 주장에 대한 정당화 및 과제를 해결하는 과정에서 나타나는 관점의 변화나 개념의 형성을 분석하고 통계적 소양의 발전이나 변화가 있는지를 알아보았다.

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An experimental study on shear mechanical properties of clay-concrete interface with different roughness of contact surface

  • Yang, Wendong;Wang, Ling;Guo, Jingjing;Chen, Xuguang
    • Geomechanics and Engineering
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    • 제23권1호
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    • pp.39-50
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    • 2020
  • In order to understand the shear mechanical properties of the interface between clay and structure and better serve the practical engineering projects, it is critical to conduct shear tests on the clay-structure interface. In this work, the direct shear test of clay-concrete slab with different joint roughness coefficient (JRC) of the interface and different normal stress is performed in the laboratory. Our experimental results show that (1) shear strength of the interface between clay and structure is greatly affected by the change of normal stress under the same condition of JRC and shear stress of the interface gradually increases with increasing normal stress; (2) there is a critical value JRCcr in the roughness coefficient of the interface; (3) the relationship between shear strength and normal stress can be described by the Mohr Coulomb failure criterion, and the cohesion and friction angle of the interface under different roughness conditions can be calculated accordingly. We find that there also exists a critical value JRCcr for cohesion and the cohesion of the interface increases first and then decreases as JRC increases. Moreover, the friction angle of the interface fluctuates with the change of JRC and it is always smaller than the internal friction angle of clay used in this experiment; (4) the failure type of the interface of the clay-concrete slab is type I sliding failure and does not change with varying JRC when the normal stress is small enough. When the normal stress increases to a certain extent, the failure type of the interface will gradually change from shear failure to type II sliding failure with the increment of JRC.

단일채널 내 임계영역 이산화탄소 가열과정의 열유동 특성에 관한 실험적 연구 (Experimental Studies on Thermal-Fluidic Characteristics of Carbon Dioxide During Heating Process in the Near-Critical Region for Single Channel)

  • 최현우;신정헌;최준석;윤석호
    • 설비공학논문집
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    • 제29권8호
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    • pp.408-418
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    • 2017
  • Supercritical carbon dioxide ($sCO_2$) power system is emerging technology because of its high cycle efficiency and compactness. Meanwhile, PCHE (Printed Circuit Heat Exchanger) is gaining attention in $sCO_2$ power system technology because PCHE with high pressure-resistance and larger heat transfer surface per unit volume is fundamentally needed. Thermo-fluidic characteristics of $sCO_2$ in the micro channel of PCHE should be investigated. In this study, heat transfer characteristics of $sCO_2$ of various inlet conditions and cross-sectional shapes of single micro channel were investigated experimentally. Experiment was conducted at supercritical state of higher than critical temperature and pressure. Test sections were made of copper and hydraulic diameter was 1 mm. Convective heat transfer coefficients were measured according to each interval of the channel and pressure drop was also measured. Convective heat transfer coefficients from experimental data were compared with existing correlation. In this study, using measured data, a new empirical correlation to predict near critical region heat transfer coefficient is developed and suggested. Test results of single channel will be used for design of PCHE.