• Proceedings of the KWS Conference
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• 2010.05a
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• pp.62-62
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• 2010

PVC(Polyvinyl Chloride)와 HDPE(High-density Polyethlene) 하수도관은 수많은 고분자 재료 중에도 높은 기계적 강도를 가지며, 광범위하게 사용되고 있다. 하지만, PVC와 HDPE 하수관을 연결하기 위해 소모 접착제나 고무링 이용한 소켓 방법 이음 방법은 낮은 수밀성과 기계적 강도로 오 폐수의 누수가 발생되고, 이것이 흙에 스며들어 지하수, 하천 및 토양을 오염시키고 있다. 따라서, 대안으로 최근에는 열판을 이용한 맞대기 융착 용접을 PE 하수도 관에 제한적으로 적용하여 시공하고 있다. 그러나, PVC 하수관은 열을 가할 시 열에 의한 민감한 거동으로 인해 맞대기 융착 용접법이 적용되지 못하고 있는 실정이다. 따라서 본 연구에서는 하수도 관 중, 국내에서 가장 많이 사용되고 있는 내 충격 PVC 하수도관과 HDPE 이중 벽관의 DSC(Diffential Scanning Calorimeter), TGA(Thermogravimetric analyzer), TMA(Thermomechanical Analysis), DMA(Dynamic Mechanical Analysis) 분석으로 온도에 따른 열적 거동을 분석하여, 적절한 융착 온도 조건을 제시하였다. 또한 접합강도 향상을 위한 이음부 설계를 제안하여, 융착 용접 특성을 평가하였다.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.37 no.11
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• pp.1379-1386
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• 2013

The present work reports the mismatch limit loads for a V-groove welded pipe for a circumferential crack using finite element (FE) analyses. To integrate the effect of groove angles on mismatch limit loads, one geometry-related slenderness parameter was modified by relevant geometric parameters including the groove angle, crack depth, and root opening based on plastic deformation patterns in the theory of plasticity. Circumferential through-wall cracks are located at the centre of the weldments with two different groove angles ($45^{\circ}$, $90^{\circ}$). With regard to the loading conditions, axial (longitudinal) tension and bending are applied for all cases. For the parent and weld metal, elastic-perfectly plastic materials are considered to simulate and analyze under- and over-matching conditions in plasticity. The overall results from the proposed solutions are found to be similar to the FE results.

• Journal of the Korean Society of Marine Environment & Safety
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• v.21 no.2
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• pp.194-199
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• 2015

In this study, experiments of welding deformation considering dog-pieces setting were performed to assess the effect of dog-pieces on welding deformations quantitatively and an analysis method of welding deformations considering dog-pieces was proposed. Experimental results show the relationship between welding deformations and dog-pieces setting quantitatively. The maximum reduction of welding deformation was measured as 74%. The proposed numerical analysis method to predict welding deformations is one of thermal elasto-plastic analyses using a circular heat flux and finite elements model and has been verified through experiments of welding deformation. The proposed analysis method is expected to be used in a variety of fields as an analysis tool to assess or establish guidelines for a proper use of dog-pieces.

• Journal of Korean Society of Steel Construction
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• v.10 no.3 s.36
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• pp.497-508
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• 1998

The objective of this study is to examine fatigue behavior of as-welded butt-welded joints with incomplete penetration from fatigue tests. The test results are the following. In static tests, tensile strength and yield strength of butt-welded joints are constant regardless of incomplete penetration. And in fatigue tests, fatigue strength of fully penetrated butt-welded joints satisfies fatigue limits, prescribed in Korean Specifications and JSSC, respectively. The results show that as the magnitude of incomplete penetration increases, fatigue strength decreases. In fractured surfaces, full and incomplete penetration specimen show different shapes, it is because that stress concentration factor vary with structural geometry in bead toe and root tip, and certify in FEM analysis. This study suggests that defects such as incomplete penetration from welding must be avoided in order to attain the sufficient life of steel structures.

• Proceedings of the KWS Conference
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• 2000.04a
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• pp.235-238
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• 2000

• Proceedings of the KWS Conference
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• 2001.05a
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• pp.94-97
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• 2001

• Transactions of the Korean Society of Mechanical Engineers A
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• v.36 no.9
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• pp.1047-1052
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• 2012

Primary water stress corrosion cracking (PWSCC) instances have been reported in the Alloy 600 reactor pressure vessel head penetration nozzle and the Alloy 82/182 dissimilar metal butt weld nozzle in several PWRs. Therefore, in-service inspection programs have been adopted worldwide to prevent failure at the weld region. If a PWSCC is observed at the dissimilar metal weld region during inspection, its structural integrity should be evaluated; however, this requires considerable time and effort, and this might lead to a decrease in the plant utilization coefficient. To prevent this, KHNP-CRI have established integrity assessment criteria and developed a computer program for the fast evaluation and judgment of PWSCC. In this paper, the results and current status of the same are presented. Through this study, criteria for the structural integrity evaluation of PWSCC have been established, and a computer program has been developed to realize technical means for the evaluation of PWSCC structural integrity.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.37 no.5
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• pp.649-655
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• 2013

During welding, the dissimilar metal butt welds of nuclear piping are typically subjected to repair welding in order to eliminate defects that are found during post-weld inspection. It has been found that the repair weld can significantly increase the tensile residual stress in the weldment, and therefore, accurate estimation of the weld residual stress due to repair weld, especially for dissimilar metal welds using Ni-based alloy 82/182 in nuclear components, is of great importance in order to assess susceptibility to primary water stress corrosion cracking. In the present study, the stress distributions of dissimilar metal butt welds in nuclear reactor piping subjected to repair weld were investigated based on detailed nonlinear finite element analyses. Particular emphasis was placed on the variation of the stress distribution in the dissimilar metal butt weld according to the finite element welding analysis sequence for the repair welding process.

• Journal of Korean Society of Steel Construction
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• v.10 no.3 s.36
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• pp.423-435
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• 1998

In this paper fatigue strength reduction of butt weld with penetration defect, which can be seen frequently in the steel bridge, was assessed quantitatively. S-N curves were derived and investigated through the constant amplitude fatigue test of fully or partially penetrated welded specimen made of SWS490 steel. The fracture mechanical method was applied in order to calculate the remaining fatigue life of the partially penetrated butt welds. The fatigue limit of the fully penetrated butt welds was higher than that of category A in AASHTO's fatigue design curves, and the slope of S-N curves with 5.57 was stiffer than that of other result for welded part generally accepted as 3. The fatigue strength of the partially Penetrated butt weld was strongly influenced by the size of lack of penetration, D. It decreased drastically with increasing D from 3.9 to 14.7mm. Fracture behaviour of the partially penetrated butt weld is able to be explained obviously from the beach mark test that a semi-elliptical surface crack with small a/c ratio initiates at a internal weld root and propagates through the weld metal. To estimate the fatigue life of the partially penetrated butt weld with fracture mechanics, stress intensity factors K of 3-dimensional semi-elliptical crack were calculated by appling finite elements method and fracture mechanics parameters such as C and m were derived through the fatigue test of CT-specimen. As a result, the fatigue lives obtained by using the fracture mechanical method agreed well with the experimental results. The results were applied to Sung-Su bridge collapsed due to penetration defects in butt weld of vertical member.

• Proceedings of the KWS Conference
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• 2000.10a
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• pp.21-23
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• 2000