• Steel and Composite Structures
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• 제19권1호
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• pp.131-152
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• 2015

Easy detection and evaluation of defect in the tube structure is a continuous problem and remains a significant demand in tube inspection technologies. This study is aimed to automate defect detection using the pattern recognition approach based on the classification of high frequency stress wave signals. The stress wave signals from vibrational impact excitation on several tube conditions were captured to identify the defect in ASTM A179 seamless steel tubes. The variation in stress wave propagation was captured by a high frequency sensor. Stress wave signals from four tubes with artificial defects of different depths and one reference tube were classified using the autoregressive (AR) algorithm. The results were demonstrated using a dendrogram. The preliminary research revealed the natural arrangement of stress wave signals were grouped into two clusters. The stress wave signals from the healthy tube were grouped together in one cluster and the signals from the defective tubes were classified in another cluster. This approach was effective in separating different stress wave signals and allowed quicker and easier defect identification and interpretation in steel tubes.

• 한국안전학회지
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• 제29권5호
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• pp.88-96
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• 2014

Each year, it seems inevitable that major accidents will occur on construction sites. Industrial accidents, sometimes involving foreign laborers, have been constantly increasing. Construction laborers have higher hazard rates and higher work intensity than other industries, which means that they experience more job stress, as a result of the subcontracting structure. Therefore, this study performed an influence factor analysis on job stress and its relevance to industrial accidents involving Korean and foreign construction laborers, and proposed its effectiveness with the job stress and construction accident management measures based on the results of those. A questionnaire to measure job stress was performed targeting Korean and foreign laborers, and the results were analyzed. The results of this study can be utilized as important reference materials in efforts to reduce the job stress of foreign laborers on construction sites, and can be expected to contribute to preventing construction accidents related to job stress in the future.

• 대한기계학회논문집
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• 제8권2호
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• pp.127-132
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• 1984

본 연구에서는 상술한 점들을 고려하고 우선 다음과 같은 사항을 고찰하려고 노력하였다. 즉 슬롯 및 노치주위에는 어떤 응력들이 분포되며 응력분포거동은 어떤 인자에 의하여 좌우되는가, 어떤 응력이 응력집중을 지배하며 응력집중현상은 어떤 인 자에 의하여 좌우되는가를 주로 고찰하였다. 참고로 실험에서 노치 및 슬롯선단의 응력측정에는 실제로 기계나 구조물에 직접 사용할 수 있는 스트레인 게이지를 사용하 였고 측정치의 정도를 높이기 위하여 스트레인 게이지율 교정방법을 이용하였다. 참 고로 노치 및 슬롯주위에 발생하는 응력집중과 파괴거동과의 관계에 대해서는 다음에 보고하겠다.

• International Journal of Naval Architecture and Ocean Engineering
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• 제2권4호
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• pp.200-210
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• 2010

In this paper, different evaluation methods of Hot Spot Stresses (HSS) have been applied to four different welded structure details in order to compare them and to illustrate their differences. The HSSs at failure-critical locations were calculated by means of a series of finite element analyses. There was good overall agreement between calculated and experimentally determined HSS on the critical locations. While different methods and procedures exist for the computation of the structural hot-spot stress at welded joints, the recommendations within the International Institute of Welding (IIW) guideline concerning the 'Hot Spot Stress' approach were found to give good reference stress approximations for fatigue-loaded welded joints. This paper recommends and suggests an appropriate finite element modeling and hot spot stress evaluation technique based on round-robin stress analyses and experimental results of several welded structure details.

• Journal of Ship and Ocean Technology
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• 제11권3호
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• pp.14-23
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• 2007

Welding processes cause undesirable problems, such as residual stresses and deformations due to the thermal loads imposed by local heating, melting, and cooling processes. This paper presents a computational modeling technique to simulate the Gas Metal Arc Welding (GMAW) process, emphasizing the effect of the melting bead on the residual stress distribution. Both a three-bar analogy and a three-dimensional thermo-mechanical finite element analysis are carried out in order to explain the effect. Element (de)activation, enthalpy, and adjustment of the reference temperature of thermal strain are considered with respect to the effect of the weld filler metal added to the base metal during a thermo-elastic-plastic analysis. Stress distributions obtained by the present study are compared with measured values and available data from other studies. The effect of the melting bead on the residual stress distribution is discussed and demonstrated.

• International Journal of Korean Welding Society
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• 제5권1호
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• pp.29-34
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• 2005

Finite element analysis (FEA) and experimental studies on an elastic bending method have been performed in order to control the angular distortion at the fillet weldment for curved panel. Process parameters for the elastic bending method such as clamping span and release time were analyzed with reference to welding condition and geometric effect of the curved panel, which can minimize or prevent the angular distortion by producing a proper skin stress to the fillet weldment. The amounts of the angular distortion decrease almost in a linear manner with an increase in the skin stress. The skin stress required for non-angular distortion at the fillet weldment is strongly dependent on the plate thickness, not the heat intensity applied. The clamping span for obtaining uniform skin stress was defined as functions of the plate thickness and length of the free edge. Clamp should be removed after the fillet weldment is cooled down to room temperature for non-angular distortion. Effectiveness of the elastic bending method established was verified by its application to an actual curved panel.

• Composites Research
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• 제12권4호
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• pp.1-7
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• 1999

비선형 하중/변위 거동을 나타내는 모재 지배 복합재료의 피로수명 예측을 이론과 실험에 의해 연구하였다. 재료의 비선형성을 고려하기 위해 초기 피로계수와 탄성계수의 관계를 나타내는 응력함수를 도입하였다. 피로계수와 참고계수 개념을 기반으로 하여 새로운 피로수명 예측식이 가한 하중 수위의 함수로 유도되었다. 예측 결과는 직교이방성 탄소섬유/에폭시 적층판을 사용한 원통형 시편의 비틀림 피로 실험과 비교되었으며, 제안된 식은 실험치와 잘 일치하였다.

• 한국안전학회지
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• 제22권2호
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• pp.22-27
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• 2007

To assess a creep life of elevated temperature plant components, inspections and analysis are usually focused on the critical locations. In this study, stress analysis of a weld region in branch part of Y-piece was conducted by using a three-dimensional finite element analysis. The stresses at the inner and outer surface in the weld part were estimated by using elastic and elastic-creep analysis. For the elastic-creep analysis two kinds of elastic-creep analysis was conducted. The one was assumed that base and weld material properties were same and the other was that material properties were different between base and weld metal. The material properties of base and weld metal were used from reference data. The results showed the stress relaxation level and its location. The result stresses are also compared with elastic stresses.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 1998년도 봄 학술발표회 논문집(I)
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• pp.211-216
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• 1998

Parameter analysis of mass concrete structures of two types subjected to heat of hydration and surface heat transfer is presented. Thermal stress analysis is conducted through the 3D FEM program. Thermal and mechanical properties of concrete, for example, conductivity, heat capacity, density, thermal expansion coefficient are varied from 80% to 120% of a reference value, and the change of thermal stress against the parameter is achieved respectively. As a result of the analysis, the parameter affecting thermal stress most significantly is an adiabatic temperature rise in the case of wall-type structure, and an initial temperature of concrete in the case of slab-type structure, respectively.

• International Journal of Safety
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• 제10권1호
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• pp.1-4
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• 2011

The fuel cell is one of the green energy receiving a lot of attention. Among the fuel cells, it is generally referred to SOFC(solid oxide fuel cell) which is made up composites of a solid. SOFC has excellent merits in the side of environment and energy. However because of the high operating temperature, it has economic loss by the using of expensive materials and problems of structural instability by thermal stresses. Therefore, this study aims to the effect of analysis by the FEMLAB. The results have deformations and the maximum stresses from the variation of the thickness of vulnerability spots. The deformation shows expansion as 0.82% and the stress ${\sigma}_{xx}$ is 392MPa in electrolyte and -56.31MPa in anode. When increasing or decreasing the thickness to 50% of the reference thickness about the electrolyte which is vulnerable spots.