• 대한용접접합학회:학술대회논문집
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• 대한용접접합학회 2001년도 춘계학술발표대회 개요집
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• pp.228-231
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• 2001

Elastic-plastic fracture toughness $J_{1c}$ can be used as an effective design criterion in elastic plastic fracture mechanics. Most of these systems are operated at high temperature and $J_{1c}$ values are affected by temperature. therefore, the $J_{1c}$ valuse at high temperature must be determined for use of integrity evaluation and designing of such systems. Elastic-plastic fracture toughness $J_{1c}$ tests were performed on SA516 carbon steel plate and test results were analyzed according to ASTM E 813-8, ASTM 1813-89. Safety and integrity are required for reactor pressure vessels vecause pthey are operated in high temperature. there are single specimen method, which used as evaluation of safety and integrity for reactor pressure vessels. In this study, elastic-plastic fracture toughness$(J_{1c})$ and $J-\Delta{a}$ of SA 516/70 steel used as reactor pressure vessel steel are measured and evaluated at room Temperature, $150^{\circ}C$, $250^{\circ}C$ and $370^{\circ}C$ according to unloading compliance method.

• 대한토목학회논문집
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• 제6권3호
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• pp.75-86
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• 1986

철도궤조(軌條) 용접연결부(鎔接連結部)는 용접(鎔接)에 의한 저인성(低靭性), 잔류응력(殘溜應力), 용접변형등(鎔接變形等)의 효과로 피로균열성장거동(疲勞龜裂成長擧動)의 복잡성을 나타낸다. 또한 철도궤조(軌條)의 장대화(長大化)로 용접연결(鎔接連結)이 불가피하며 용접연결부(鎔接連結部)에서는 피로파괴(疲勞破壞)가 빈번히 발생(發生)하고 있다. 이에 본(本) 연구(硏究)는 소재부(素材部), 가스압접부(壓接部), 테르밋트용접부(鎔接部)에 대하여 피로실험(疲勞實驗)을 행(行)하여 S-N 선도작성(線圖作成)의 기본적인 자료를 제시코져 하였다. 그 결과(結果), 소재부(素材部)가 용접부(鎔接部)보다, 또 가스압접부(壓接部)가 테르밋트용접부(鎔接部)보다 피로균열성장(疲勞龜裂成長)에 대한 저항성(抵抗性)이 좋으며, 이와같은 용접부(鎔接部)와 고강도(高强度)의 궤조강(軌條鋼)은 종래의 재료역학적(材料力學的)인 방법(方法)만으로 파괴(破壞)를 제어하는 것은 매우 위험하다는 것을 알 수 있었다.

• Composites Research
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• 제36권6호
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• pp.422-428
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• 2023

스택 체결압에 의해 접촉되는 분리판(BP)과 탄소펠트전극(CFE) 사이의 전기적 접촉저항은 상대적으로 낮은 바나듐 레독스 흐름전지(VRFB) 스택의 체결압 때문에 스택 효율에 큰 여향을 미친다. 본 연구에서는 이러한 접촉저항을 줄이고 셀 성능을 향상시키기 위해 국부 가열 접합 공정을 통해 폴리에틸렌(PE) 복합재료-CFE 하이브리드 BP 구조를 개발하였다. 탄소섬유 복합재료 BP의 PE 매트릭스를 국부적으로 녹여 CFE의 탄소 섬유와 BP의 탄소 섬유의 직접 접촉 구조를 만들어 전기 접촉 저항을 감소시겼다. PE 복합재료-CFE 하이브리드 BP의 성능을 평가하기 위해 면적비저항(ASR)과 기체투과도를 측정하였다. 또한 스택 신뢰성을 측정하기 위해 내산성 시험을 수행하였다. 최종적으로, 개발된 PE 복합재료-CFE 하이브리드 BP와 기존의 BP의 성능을 비교 분석하기 위하여 VFRB 단위셀 충/방전 시험을 수행하였다.

• Journal of Welding and Joining
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• 제31권6호
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• pp.1-7
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• 2013

In nuclear power plants, lined carbon steel pipes or PCCPs (pre-stressed concrete cylinder pipes) have been widely used for sea water transport systems. However, de-bonding of linings and oxidation of PCCP could make problems in aged NPPs (nuclear power plants). Recently at several NPPs in the United States, the PCCPs or lined carbon steel pipes of the sea water or raw water system have been replaced with HDPE (high density polyethylene) pipes, which have outstanding resistance to oxidation and seismic loading. ASME B&PV Code committee developed Code Case N-755, which describes rules for the construction of buried Safety Class 3 polyethylene pressure piping systems. Although US NRC permitted HDPE materials for Class 3 buried piping, their permission was limited to only 10-year operation because of several concerns including the quality of fusion zone of HDPE. In this study, various requirements for fusion qualification test of HDPE and some regulatory issues raised during HDPE application review in foreign NPPs are introduced.

• 마이크로전자및패키징학회지
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• 제21권1호
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• pp.1-6
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• 2014

고출력 LED 패키지의 열적 경로(thermal path)를 줄이기 위해 플립칩 본딩법에 대한 연구가 활발히 진행되고 있다. 본 연구에서는 Au-Sn 열압착 본딩 및 Sn-Ag-Cu(SAC) 리플로우 본딩을 이용하여 본딩 특성 및 열적특성을 비교 평가 하였다. Au-Sn 열압착 본딩은 50 N에서 $300^{\circ}C$의 접합온도로 본딩하였고, SAC 솔더는 솔더페이스트를 인쇄한 후 리플로우법으로 피크온도 $255^{\circ}C$에서 30 sec에서 본딩하였다. SAC 솔더를 사용한 LED 패키지의 전단강도는 $5798.5gf/mm^2$로 Au-Sn 열압착 본딩의 $3508.5gf/mm^2$에 비해 1.6배 높았다. 파단면과 단면분석 결과 Au-Sn, SAC 솔더 모두 LED 칩 내부에서 파단이 일어나는 것을 관찰하였다. 반면 Au-Sn 열압착 본딩 샘플의 열저항은 SAC솔더 접합 샘플에 비해 낮았으며, SAC 솔더 접합부 내부의 기공에 의해 열저항이 커짐을 알 수 있었다.

• Journal of Welding and Joining
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• 제20권6호
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• pp.30-30
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• 2002

It has been reported that the creep characteristics on weldment which is composed of weld metal(W.M), fusion line(F.L), heat-affected zone(HAZ), and base meta(B.M) could be unpredictably changed in severe service conditions such as high temperature and high pressure. However, the studies done on creep damage in power plant components have been mostly conducted on B.M and not the creep properties of the localized microstructures in weldment have been thoroughly investigated yet. In this paper, it is investigated the creep characteristics for three microstructures like coarse-grain HAZ(CGHAZ), W.M, and B.M in X20CrMoV121 steel weldment by the small punch-creep-(SP-Creep) test using miniaturized specimen(l0×10×0.5mm). The W.M microstructure possesses the higher creep resistance and shows lower creep strain rate than the B.M and CGHAZ. In the lower creep load the highest creep strain rate is exhibited in CGHAZ, whereas in the higher creep load the B.M represents the high creep strain rate. The power law correlation for all microstructures exists between creep rate and creep load at 600℃. The values of creep load index (n) based on creep strain rate for B.M, CGHAZ, and W.M are 7.54, 4.23, and 5.06, respectively and CGHAZ which shows coarse grains owing to high welding heat has the lowest creep loade index. In all creep loads, the creep life for W.M shows the highest value.

• Journal of Welding and Joining
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• 제20권6호
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• pp.754-761
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• 2002

It has been reported that the creep characteristics on weldment which is composed of weld metal(W.M), fusion line(F.L), heat-affected zone(HAZ), and base meta(B.M) could be unpredictably changed in severe service conditions such as high temperature and high pressure. However, the studies done on creep damage in power plant components have been mostly conducted on B.M and not the creep properties of the localized microstructures in weldment have been thoroughly investigated yet. In this paper, it is investigated the creep characteristics for three microstructures like coarse-grain HAZ(CGHAZ), W.M, and B.M in X20CrMoV121 steel weldment by the small punch-creep-(SP-Creep) test using miniaturized specimen($10{\times}10{\times}0.5mm$). The W.M microstructure possesses the higher creep resistance and shows lower creep strain rate than the B.M and CGHAZ. In the lower creep load the highest creep strain rate is exhibited in CGHAZ, whereas in the higher creep load the B.M represents the high creep strain rate. The power law correlation for all microstructures exists between creep rate and creep load at $600^{\circ}C$. The values of creep load index (n) based on creep strain rate for B.M, CGHAZ, and W.M are 7.54, 4.23, and 5.06, respectively and CGHAZ which shows coarse grains owing to high welding heat has the lowest creep loade index. In all creep loads, the creep life for W.M shows the highest value.

• 한국압력기기공학회 논문집
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• 제6권1호
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• pp.16-22
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• 2010

Cast austenitic stainless steel(CASS) is used in the primary cooling piping system of nuclear power plant for it's relative low cost, corrosion resistance and easy of welding. However, the coarse-grain structure of cast austenitic stainless steel can strongly affect the inspectability of ultrasonic testing. The major problems encountered during inspection are beam skewing, high attenuation and high background noise of CASS component. So far, the best inspection performance involving CASS components have been achieved using low frequency TRL(Transmitter/Receiver side-by-side L wave) angle beam probe. But TRL technique could not detect shallow defect and it contains an uncertainty for sizing capability. Currently, most of researchers are studying to overcome these challenge issue. In this study, low-frequency phased array TRL technique used to detect and sizing the flaws in CF8A cast austenitic stainless steel.As conclusion, we could detect and size not only axial flaw but also circumferential flaw using low frequency phased array technique.

• 대한용접접합학회:학술대회논문집
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• 대한용접접합학회 2001년도 춘계학술발표대회 개요집
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• pp.220-223
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• 2001

In this study, CT specimens were prepared hem ASTM SA516 which was used for pressure vessel plates for room and low temperature service. And we got the following characteristics from fatigue crack growth test carried out in the environment of room and low temperature at $25^{\circ}C$, -3$0^{\circ}C$, -6$0^{\circ}C$, -8$0^{\circ}C$, -l$0^{\circ}C$ and -l2$0^{\circ}C$ and in the range of stress ratio of 0.1, 0.3 by means of opening mode displacement. At the constant stress ratio, the threshold stress intensity factor range ΔK$_{th}$ in the early stage of fatigue crack growth ( Region I ) and stress intensity factor range ΔK in the stable of fatigue crack growth ( Region II) was increased in proportion to descend temperature. It assumed that the fatigue resistance characteristics and fracture strength at low temperature is considerable higher than that of room temperature in the early stage and stable of fatigue crack growth region. The straight line slope relation of logarithm da/dN - ΔK in Region II, that is, the fatigue crack growth exponent m increased with descending temperature at the constant stress ratio. It assumed that the fatigue crack growth rate da/dN is rapid in proportion to descend temperature in Region H and the cryogenic-brittleness greatly affect a material with decreasing temperature.e.greatly affect a material with decreasing temperature.

• Nuclear Engineering and Technology
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• 제50권1호
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• pp.116-125
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• 2018

Modified 9Cr-1Mo ferritic steel is a preferred material for steam generators in nuclear power plants for their creep strength and good corrosion resistance. Austenitic stainless steels, such as type 316LN, are used in the high temperature segments such as reactor pressure vessels and primary piping systems. So, the dissimilar joints between these materials are inevitable. In this investigation, dissimilar joints were fabricated by the Shielded Metal Arc Welding (SMAW) process with Inconel 82/182 filler metals. The notch tensile properties and Charpy V-notch impact toughness properties of various regions of dissimilar metal weld joints (DMWJs) were evaluated as per the standards. The microhardness distribution across the DMWJs was recorded. Microstructural features of different regions were characterized by optical and scanning electron microscopy. Inhomogeneous notch tensile properties were observed across the DMWJs. Impact toughness values of various regions of the DMWJs were slightly higher than the prescribed value. Formation of a carbon-enriched hard zone at the interface between the ferritic steel and the buttering material enhanced the notch tensile properties of the heat-affected-zone (HAZ) of P91. The complex microstructure developed at the interfaces of the DMWJs was the reason for inhomogeneous mechanical properties.