• 한국초전도ㆍ저온공학회논문지
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• 제15권4호
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• pp.10-14
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• 2013

We have clearly investigated with respect to the survival of the insulator at cryogenic temperature under the electrical stress. The breakdown and voltage-time characteristics of turn-to-turn models for point contact geometry and surface contact geometry using copper multi wrapped with polyimide film for an HTS transformer were investigated under AC and impulse voltage at 77 K. Polyimide film (Kapton) 0.025 mm thick is used for multi wrapping of the electrode. As expected, the breakdown voltages for the surface contact geometry are lower than that of the point contact geometry, because the contact area of the surface contact geometry is lager than that of the point contact geometry. The time to breakdown t50 decreases as the applied voltage is increased, and the lifetime indices increase slightly as the number of layers is increased. The electric field amplitude at the position where breakdown occurs is about 80 % of the maximum electric field value. The relationship between survival probability and the electrical stress at cryogenic temperature was evident.

• 한국구조물진단유지관리공학회 논문집
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• 제12권2호
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• pp.193-200
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• 2008

탄-소성론에 근거한 콘크리트나 토질과 같은 재료의 파괴 포락선은 주응력을 축으로 하는 공간 좌표계상에서 인장의 등압(hydrostatic stress)축을 향해 기울어진 형태를 가지며 소성흐름이 상관소성흐름 법칙(associated flow rule)에 따라 결정될 경우 콘크리트의 거동 예측시에 과도한 체적 팽창률을 나타내게 된다. 본 논문에서는 콘크리트의 다축응력 하에서의 거동을 예측하기 위하여 비균일 경화(nonuniform hardening)를 적용한 5계수 파괴 포락선과 등압축 방향 성분의 소성 흐름을 수정하는 비상관 소성흐름 법칙(non-associated flow rule)을 사용하여 비선형 유한요소해석 프로그램을 개발하였으며 신뢰성 있는 연구자의 다축응력 실험결과와 유한요소해석 프로그램의 해석결과를 비교하였다.

• International Journal of Aeronautical and Space Sciences
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• 제18권3호
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• pp.436-449
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• 2017

In this paper, the damage and failure behavior of triaxially braided textile composites was studied using progressive failure analysis. The analysis was performed at both micro and meso-scales through iterative cycles. Stress based failure criteria were used to define the failure states at both micro- and meso-scale models. The stress-strain curve under uniaxial tensile loading was drawn based on the load-displacement curve from the progressive failure analysis and compared to those by test and computational results from reference for verification. Then, the detailed failure initiation and propagation was studied using the verified model for both tensile and compression loading cases. The failure modes of each part of the model were assessed at different stages of failure. Effect of ply stacking and number of unit cells considered were then investigated using the resulting stress-strain curves and damage patterns. Finally, the effect of matrix plasticity was examined for the compressive failure behavior of the same model using elastic, elastic - perfectly plastic and multi-linear elastic-plastic matrix properties.

• 대한기계학회논문집A
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• 제26권3호
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• pp.471-478
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• 2002

In real structures, multi-spot welded joints are more frequently used than a single-spot welded joint. Most researches, however, have been focused to a single-spot welded joint until now. In this paper, the fatigue behavior of multi-spot welded joints are investigated using the finite element solutions of the multi-spot welded specimens. The local strain approach is used rather than the stress intensity factor approach to estimate the fatigue life since the former is quite simple and straightforward. It is found that the fatigue behavior of multi-spot welded joints is different from that of single-spot welded joints. The local strain approach is still applicable to multi-spot welded joints.

• 한국재료학회지
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• 제1권1호
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• pp.46-53
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• 1991

반도체 공정의 최종 보호막으로 주로 사용되는 PSG (Phosphosilicate class), USG (Undoped silicate glass) 및 SiN 막을 CVD 방식으로 deposition 하여 각 막의 스트레스를 막 두께 또는 대기중 방치시간의 함수로 조사하고 Al 배선의 stress-migration 관점에서 평가했다. 그 결과 PSG 막과 USG 막은 tensile stress를 나타내고 두께증가에 따라 스트레스가 증가하였고, SiN 막은 두께에 관계없이 일정한 compressive stress를 나타내었다. PSG 막은 현저한 스트레스 경시변화를 보여 대기중에 방치시 2일이내로 tensile stress가 compressive stress로 변화되었다. 그 주 원인은 PSG 막의 수분 흡수 때문인것이 FTIR 분석으로 밝혀졌고, $300^{\circ}C$에서 20분간 anneal 처리로 $2.5{\times}{10^9}\;dyne/cm^2$의 스트레스 회복이 가능하였다. PSG 막이 포함된 복합막의 경우, 복합막 stress는 PSG 막의 방치시간에 따라 변한다. 즉, 복합막의 스트레스는 복합막을 구성하고 있는 막들의 두께의 함수이다. 또 SiN 막의 강한 압축응력을 완화시켜주는 PSG, USG 막의 스트레스가 큰 인장응력을 나타낼수록 Al 배선의 stress-migration 에 대한 저항은 커진다.

• Human Ecology Research
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• 제53권4호
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• pp.391-404
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• 2015

This study examined job satisfaction and relevant variables for multi-cultural family home-visiting educators. The selected study subjects were 192 home-visiting educators who work at Multi-Cultural Family Support Centers in the Seoul, Gyeonggi-do, and Chungcheongnam-do areas. Data analysis was conducted using SPSS ver. 18.0. The main results were as follows. First, the job satisfaction level in multi-cultural family visiting educators stood at 3.29 points, subjects' age, averagely monthly income, marital status, and activity career were shown to influence generally upon job satisfaction, self-efficacy, job stress, and cultural competency. Job satisfaction was high in groups with: a high age, small career, low averagely monthly income, and married. Second, self-efficacy and job stress were big in the job satisfaction of multi-cultural family visiting educators. The same outcome as the existing prior research was indicated. Cultural competency was not significant. Third, an examination of relative influence upon job satisfaction in home visiting educators indicated that the explanation power was 29.0%. Significant influential variables included academic background, marital status, self-regulation, and role ambiguity. Self-regulation was greater for those with lower academic backgrounds and unmarried. Job satisfaction was higher in the lower role ambiguity. Thus, the same outcome as the existing prior research was indicated. Cultural competency wasn't indicated to be significant. This has significance in having shown characteristics of job satisfaction in multi-cultural family visiting educators.

• Smart Structures and Systems
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• 제15권1호
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• pp.99-117
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• 2015

The Stonecutters Bridge (SCB) in Hong Kong is the third-longest cable-stayed bridge in the world with a main span stretching 1,018 m between two 298 m high single-leg tapering composite towers. A Wind and Structural Health Monitoring System (WASHMS) is being implemented on SCB by the Highways Department of The Hong Kong SAR Government, and the SCB-WASHMS is composed of more than 1,300 sensors in 15 types. In order to establish a linkage between structural health monitoring and maintenance management, a Structural Health Rating System (SHRS) with relevant rating tools and indices is devised. On the basis of a 3D space frame finite element model (FEM) of SCB and model updating, this paper presents the development of an SHR-oriented 3D multi-scale FEM for the purpose of load-resistance analysis and damage evaluation in structural element level, including modeling, refinement and validation of the multi-scale FEM. The refined 3D structural segments at deck and towers are established in critical segment positions corresponding to maximum cable forces. The components in the critical segment region are modeled as a full 3D FEM and fitted into the 3D space frame FEM. The boundary conditions between beam and shell elements are performed conforming to equivalent stiffness, effective mass and compatibility of deformation. The 3D multi-scale FEM is verified by the in-situ measured dynamic characteristics and static response. A good agreement between the FEM and measurement results indicates that the 3D multi-scale FEM is precise and efficient for WASHMS and SHRS of SCB. In addition, stress distribution and concentration of the critical segments in the 3D multi-scale FEM under temperature loads, static wind loads and equivalent seismic loads are investigated. Stress concentration elements under equivalent seismic loads exist in the anchor zone in steel/concrete beam and the anchor plate edge in steel anchor box of the towers.

• 대한전자공학회:학술대회논문집
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• 대한전자공학회 2008년도 하계종합학술대회
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• pp.455-456
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• 2008

New CMOS ROM cell is reported in this paper, distinguished from conventional ones in that it can be re-programmed by multi-times. It uses the comparator offset as the physical storage quantity and the MOSFET FN stress effect for offset programming. It demands very low offset for read, and works well in very low voltage. It can become a promising ROM solution for various SoC systems.

• Journal of Forest and Environmental Science
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• 제14권1호
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• pp.89-100
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• 1998

본 연구는 제지 원료의 효율적 이용 및 기능의 최적화를 위한 수단으로 사용되고 있는 다층구조화에 따른 종이의 내부응력 및 물성의 변화를 조사하기 위하여 수행되었다. 또한 최근 사용량이 급증되고 있는 재생섬유를 다층구조에 도입할 경우 수반되는 종이의 물성 변화도 조사되었다. 펄프의 고해처리는 단층지의 내부응력을 증가시켜준 반면 충전제의 사용은 내부응력을 감소시켰다. 종이의 다층구조화는 인열지수를 제외한 대부분의 종이물성과 내부응력을 감소시켰으며, 이러한 변화는 사용된 펄프의 종류, 고해수준, 원료의 배합 방법에 따라 다양하게 나타났다. 충전시에는 충전제를 외층 또는 내층에 사용함으로써 단층지보다 우수한 내부응력 및 종이물성을 얻을 수 있었다. 재생섬유를 사용할 때는 다층구조화를 통하여 투기도와 빳빳이의 개선이 가능하였으나, 파열지수가 감소되었다.

• 콘크리트학회논문집
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• 제14권5호
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• pp.726-733
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• 2002

수축대는 큰 부재를 공사기간 중 일정기각 동안 몇 개의 부분으로 나누어 부재내의 인장 응력을 유발시키지 않으면서 상당량의 건조수축이 발생하도록 하여 건조수축으로 인한 응력을 감소시키는 역할을 하는 일시적인 조인트이다. 본 연구에서는 시공단계와 크리프에 의한 응력완화 효과를 고려한 건조수축응력해석 방법을 바탕으로 수축대의 효과를 해석할 수 있는 방법을 제안하였다. 제안된 해석방법을 10층 규모의 예제 구조물에 적용하여 얻은 결과는 다음과 같다. 수축대의 응력감소효과는 수축대가 설치된 층에만 적용되며 다른 층 슬래브에는 오히려 건조수축응력을 다소 증가시키게 된다. 수축대의 메움시기 변화에 따른 건조수축응력 감소효과는 콘크리트모델의 건조수축변형량의 시간에 따른 변화와 유사한 양상을 보이고 있으며 수축대를 메우기 전에 발생한 건조수축변형량이 많을수록 수축대의 응력감소효과가 증가한다.