• Journal of Welding and Joining
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• 제34권3호
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• pp.61-68
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• 2016

Characteristics of dissimilar metal welds between alloy steel ASTM A387 Gr. 91 and carbon steel ASTM A516 Gr.70 made with Flux cored arc welding(FCAW) have been evaluated in terms of microstructure, mechanical strength, chemical analysis by EDS as well as corrosion test. Three heat inputs of 15.0, 22.5, 30.0kJ/cm were employed to make joints of dissimilar metals with E91T1-B9C wire. Post-weld heat treatment was carried out at $750^{\circ}C$ for 2.5 h. Based on microstructural examination, tempered martensite and lower bainite were formed in first layer of weld metal. The amount of tempered martensite was decreased and the amount of lower bainite was increased with increasing heat input and layer. Heat affected zone of alloy steel showed the highest hardness due to the formation of tempered Martensite and lower Bainite. Tensile strengths of dissimilar welds decreased with increasing heat inputs. Dissimilar welds seemed to have a good hot cracking resistance due to the low HCS index below 4. The salt spray test of dissimilar metals showed that the corrosion rate increased with increasing heat inputs due to the increase of the amount of lower Bainite.

• Journal of Welding and Joining
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• 제35권3호
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• pp.68-74
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• 2017

Characteristics of dissimilar metal welds between alloy steel ASTM A387 Gr. 91 and carbon steel ASTM A516 Gr.70 made with Flux cored arc welding(FCAW) have been evaluated in terms of microstructure, mechanical strength, chemical analysis by EDS as well as corrosion test. Three heat inputs of 15.0, 22.5, 30.0kJ/cm were employed to make joints of dissimilar metals with E71T-1C wire. Post-weld heat treatment was carried out at $750^{\circ}C$ for 2.5 h. Based on microstructural examination, Intragranular polygonal ferrite and grainboundary ferrite were formed only in first layer of weld metal. Another layers consisted of acicular ferrite and $Widmannst{\ddot{a}}tten$ ferrite. The amount of acicular ferrite was increased with decreasing heat input and layer. Heat affected zone of alloy steel showed the highest hardness due to the formation of tempered martensite and lower bainite. Lower and upper bainite were formed in heat affected zone of carbon steel. Tensile strengths of dissimilar metal welds decreased with increasing heat inputs. Dissimilar metal welds showed a good hot cracking resistance due to the low HCS index below 4. The salt spray test of dissimilar metals welds showed that the weight loss rate by corrosion below 170 hours was decreased with increasing heat inputs due to the increase of the amount of acicular ferrite.

• Nuclear Engineering and Technology
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• 제56권10호
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• pp.4115-4126
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• 2024

The swelling behavior of ferritic/martensitic steels (FC92-B/-N, HT9, and Gr.92) was investigated following 3.5 MeV Fe⁺⁺ ion irradiation. Tested alloys were helium-pre-implanted up to the peak contents of 120 and 240 appm with He/dpa ratio of 1 appm/dpa at room temperature and then exposed to self-ion beam to the peak damage conditions of 120 and 240 dpa at 475 ℃. Field-emission transmission electron microscopy was used to characterize the cavity evolution. FC92-B exhibited the highest resistance to swelling among the irradiated alloys. The final volumetric swelling of FC92-B reached 1.3 % at 70 dpa and 2.9 % at 140 dpa. On the other hand, HT9 exhibited the highest swelling, reaching 7.4 % at 140 dpa. Comparing the present swelling results at 140 dpa/140 appm He with swelling data at 280 dpa/280 appm He from our previous study, it was observed that Gr.92 and FC92-N swelled more at 140 dpa/140 appm He than at 280 dpa/280 appm He. This negative correlation between swelling and dose in Gr.92 and FC92-N is primarily attributed to the helium-associated swelling suppression at higher helium concentration of 280 appm. A bimodal cavity size distribution appeared only in Gr.92 and FC92-N at 280 dpa/280 appm. This result demonstrates that the excess amount of helium over 200 appm promoted early-stabilization of new-born cavities, resulting in preferentially enhanced cavity nucleation, while impeding the growth of nucleated cavities. An inhibition in cavity growth possibly led to an extended duration of nucleation-dominant stages, finally suppressing swelling in ion-irradiated Gr.92 and FC92-N alloys.

• 대한안전경영과학회지
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• 제4권2호
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• pp.189-197
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• 2002

Composites have wide applications in aerospace vehicles and automobiles because of the inherent flexibility in their design lot improved material properties. Composite tubes in particular, are potential candidates for their use as energy absorbing elements in crashworthiness applications due to their high specific energy absorbing capacity and the stroke efficiency. Their failure mechanism however is highly complicated and rather difficult to analyze. This includes fracture in fibers, in the matrix and in the fiber-matrix interface in tension, compression and shear. The purpose of this study is to investigate the energy absorption characteristics of Gr/E(Graphite/Epoxy) tubes on static and impact tests. The collapse characteristics and energy absorption of a variety of tubes have been examined. Changes in the lay-up which increased the modulus increased the energy absorption of the tubes. Based on the test results, the following remarks can be made: Among CA15, CA00 and CA90 curves the CA90 tube exhibits the highest crush load throughout the whole crush process, and max load increases as interlaminar number increase. Among all the tubes type CC90 has the largest specific crushing stress of 52.60 kJ/kg which is much larger than other tubes.

• 한국원자력학회:학술대회논문집
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• 한국원자력학회 1998년도 춘계학술발표회논문집(2)
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• pp.324-329
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• 1998

본 연구는 주증기배관으로 사용되고 있는 SA106. Gr.C의 모재와 용접계에 대해서 파괴인성에 미치는 온도와 하중속도의 영향을 살펴보기 위해서 다양한 온도와 하중속도에서 J-R 시험 및 인장시험을 수행하였다. 두 재료 모두 동적변형시효의 영향을 받고 있는 온도영역에서 약 40% 정도의 파괴인성 감소가 관찰되었으며, 하중속도에 따른 파괴인성 감소영역은 serration과 인장강도 증가 영역의 하중속도 의존성과 일치하였다. 원자력발전소 운전온도에서 모재와 용접재 모두 하중선변위속도가 4.0mm/min 일 때 파괴인성치의 최저를 보였으며, 하중속도가 증가함에 따라 증가하여 동적하중속도(800, 40mm/min)일 때 최대를 보였다. 모재와 용접재를 비교하면 용접재에서 serration이 뚜렸했고, 보다 넓은 온도영역에서 관찰되었다. 또한 인장강도의 증가가 보다 고온에서 형성되었다. 이러한 특성은 용접재가 모재에 비해 냉각률이 크고 미세한 결정입으로 이루어져있으며, 망간의 함량이 높기 때문으로 판단된다.

• 한국잡초학회지
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• 제17권4호
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• pp.431-438
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• 1997

유해(有害)한 활성산소종(活性酸素種)들을 생성하는 환경 stress에 대한 식물의 적응과정(適應過程)을 파악하기 위한 일환으로서, 호박을 식물재료로 공시하고 Mg이 결핍(缺乏)된 영양액(營養液)에서 재배하여 산화적(酸化的) stress 조건을 부여하였을 때, 나타나는 과산화(過酸化)의 피해정도와 항산화효소(抗酸化酵素)들의 활성변동(活性變動)을 조사하였다. 충분한 양의 Mg이 공급된 영양액에서 재배된 호박의 잎에서는 Mg, 엽록소(葉綠素), 단백질(蛋白質) 함량(含量) 및 항산화효소(抗酸化酵素)들의 활성(活性)이 다소 증가 되었거나 거의 일정하게 유지되었다. 그러나 Mg이 결핍(缺乏)된 영양액(營養液)에서 재배된 호박의 잎에서는 Mg, 엽록소(葉綠素), 단백질(蛋白質) 함량(含量)은 현저히 감소된 반면, 항산화효소(抗酸化酵素)인 AP, GR 및 SOD의 활성(活性)이 크게 증가되었다. 본 연구에서 얻어진 결과들은 식물에서 Mg의 결핍(缺乏)으로 이하여 해로운 활성산소종(活性酸素種)이 생성되며 동시에 이들 활성산소종(活性酸素種)의 유해(有害)한 작용을 소거(消去)하기 위한 항산화효소(抗酸化酵素)의 활성(活性)도 유도(誘導)되는 것을 시사한다.

• 한국안전학회지
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• 제13권4호
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• pp.96-101
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• 1998

J-R curve tests were performed on 1T compact specimens of SA516 Gr. 70 carbon steels under reverse cyclic loading. A Direct-Current Potential Drop (DCPD) method, one of the nondestructive techniques to detect flaw of structure, is being increasingly used for monitoring crack initiation and stable crack growth in typical fracture mechanics specimens for J-R testing. In many aspects this method is simpler than the unloading compliance method. The objective of this paper is to evaluate the J-R Curve according to the crack length measurement techniques under reverse cyclic loading. In order to prove the reliability and repeatability of the DCPD method, the crack length measured by using DCPD method was compared to one determined from unloading compliance. Consequently, this DCPD method correlated well with J-R curves and crack extension measurements determined from unloading compliance method.

• 한국초지조사료학회지
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• 제5권2호
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• pp.93-99
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• 1985

1984년도(年度) 초지조성(草地造成) 대상지(對象地) 10,077ha에 대한 환경조건(環境條件)과 토양(土壤)의 이화학적(理化學的) 특성(特性)을 조사(調査)하여 초지조성(草地造成) 및 시책자료(施策資料)를 제공(提供)코자 수행(遂行)한 결과(結果)는 다음과 같다. 1. 신분류체계(新分類體系)에 의한 토양분류단위(土壤分類單位)는 일(日) 4, 아목(亞目) 7, 대군(大群)11, 아군(亞群)28 및 통(統) 105개로 분류(分類)되었다. 2. 초지조성면적(草地造成面積) 3.0ha이하로 경영(經營)하는 농가(農家)는 70.8%로 면적(面積)은 35.9%였으며, 불경운(不耕耘) 초지조성면적(草地造成面積)이 71.3%였다. 3. 초지조성(草地造成) 대상지(對象地)는 구릉지(丘陵地)와 산여지(山麗地)에 82.0% 분포(分布)하였고 경사(傾斜) 30%이하(以下)가 66.9%였다. 4. 조립질토양(粗粒質土壤)이 85.0, 유효토심 20cm이하(以下)이 97.8, 그리고 석력함량(石礫含量) 35%이상(以上)이 1.6%였다. 5. 초지토양(草地土壤)의 적성등급(適性等級) 구분(區分)은 1등급(等級)이 67.32 등급(等級) 29.7 그리고 3등급(等級) 3.0%였다. 6. 표토(表土)의 평균(,平均) pH는 5.6, 유효인산 31ppm, 유기물(有機物) 3.2%, 그리고 Ca, Mg 및 K는 각각(各各) 2.23, 1.05 및 0.37me/100gr였다.

• 한국잡초학회지
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• 제16권3호
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• pp.210-220
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• 1996

Oxyfluorfen에 내성(耐性) 벼 3품종(品種)과 감수성(感受性) 벼 4품종(品種) 및 피를 공시하여 $10^{-6}M$ 농도로 처리하여 24시간 암배양(暗培養)하고 광(光)에 0, 2, 4, 6시간 노출 후에 항산화효소(抗酸化酵素)의 활성 차이와 항산화효소(抗酸化酵素)의 isozyme 변화를 조사하였다. 1 내성(耐性) 및 감수성(感受性) 벼품종(品種) 자체의 APOX, CAL, POX, NR, GR, MDAR 및 SOD의 항산화효소(抗酸化酵素) 활성(活性)은 차이가 없었으나, 감수성(感受性)인 피는 다른 벼품종(品種)들보다 활성(活性)이 아주 낮았다. 그리고 lipoxygenase는 내성(耐性) 벼품종(品種)들보다 감수성(感受性) 벼품종(品種)과 피에서 활성(活性)이 다소 높은 경향이었다. 2. Oxyfluorfen 처리 후 항산화효소(抗酸化酵素)인 MDAR, POX, GR 및 SOD는 내성(耐性) 벼품종(品種)들이 감수성(感受性) 벼품종(品種)들과 피보다 활성(活性)이 높았다. 3. Oxyfluorfen 처리 후 POX 동위효소(同位酵素)변화는 처리농도가 증가할수록 내성(耐性) 벼품종(品種)들에서 C band 활성(活性)이 증가하였으나, 감수성(感受性) 벼품종(品種)에서는 활성(活性)증가가 없었다. 감수성(感受性) 피에서는 B band가 $10^{-4}M$ 처리에서 활성(活性)이 다소 감소하였다. 4. Oxyfluorfen 처리에 따른 GR, SOD 및 AO 동위효소(同位酵素)는 내성(耐性)과 감수성(感受性) 벼품종(品種)들간에 각 band 활성(活性)은 차이가 없었으나, GR 동위효소(同位酵素)는 $10^{-4}M$ 처리시 감수성(感受性)인 피에서 C band가 소실되었다. 5. Oxyfluorfen 처리에 따른 esterase 동위효소(同位酵素)의 변화는 B, C 및 D band에서 내성(耐性) 벼품종(品種)보다 감수성(感受性) 벼품종(品種)에서 활성(活性)감소가 컸으며, 감수성(感受性)인 피는 $10^{-4}M$ 처리시 A band가 소실되었다.

• Nuclear Engineering and Technology
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• 제54권4호
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• pp.1414-1420
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• 2022

High dose rate (HDR) brachytherapy treatment planning usually involves optimization methods to deliver uniform dose to the target volume and minimize dose to the healthy tissues. Four optimizations were used to evaluate the high-risk clinical target volume (HRCTV) coverage and organ at risk (OAR). Dose-volume histogram (DVH) and dosimetric parameters were analyzed and evaluated. Better coverage was achieved with PGO (mean CI = 0.95), but there were no significant mean CI differences than GrO (p = 0.03322). Mean EQD₂ doses to HRCTV (D₉₀) were also superior for PGO with no significant mean EQD₂ doses than GrO (p = 0.9410). The mean EQD₂ doses to bladder, rectum, and sigmoid were significantly higher for NO plan than PO, GrO, and PGO. PO significantly reduced the mean EQD₂ doses to bladder, rectum, and sigmoid but compromising the conformity index to HRCTV. PGO was superior in conformity index (CI) and mean EQD₂ doses to HRCTV compared with the GrO plan but not statistically significant. The mean EQD₂ doses to the rectum by PGO plan slightly exceeded the limit from ABS recommendation (mean EQD₂ dose = 78.08 Gy EQD₂). However, PGO can shorten the treatment planning process without compromising the CI and keeping the OARs dose below the tolerance limit.