• 수산해양기술연구
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• 제54권2호
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• pp.97-106
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• 2018

The objective of this study was to estimate physical properties and fishing performances of net twine with improved PBS copolymer resin (Bio-new), the existing PBS/PBAT blending resin (Bio-old) and commercial Nylon (Nylon). The tensile strength of Bio-new monofilament was equal to Bio-old and the elongation of Bio-new was about 6 % higher than that of Bio-old in wet condition. The physical properties tests were carried out to estimate breaking load and stiffness in dry and wet conditions, respectively. In the results, the breaking load of Nylon netting was the highest whereas the elongation of Bio-new was 1.4 times higher than that of Nylon netting in wet condition. The breaking load of Bio-old netting was about 9.2 % higher than that of Bio-new netting. However, the elongation of the Bio-new netting was about 3% higher than that of Bio-old. The stiffness of the Bio-new compared to Bio-old was improved about 34 % in dry condition and about 32 % in wet condition. The filed experiments of the fishing performance were conducted with three kinds of drift nets with different netting materials in the coastal sea of Jeju. The each experimental drift net made of different materials showed the similar fishing performance. Bio-old drift net yielded less catches of small sized yellow croaker than other drift nets. The netting materials affected the fishing performance and length distribution of catches in the drift nets.

• Elastomers and Composites
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• 제46권2호
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• pp.138-143
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• 2011

EPDM에 카본블랙과 더불어 무기 충전제인 탈크, 탄산칼슘, 혹은 클레이를 함께 혼합하여 EPDM 배합물과 가황물을 제조하여, 무기 충전제가 EPDM 배합물과 가황물의 특성에 미치는 영향을 조사하였다. 무기 충전제를 추가해도 결합 고무 함량(bound rubber content)에는 큰 차이가 없었다. 무기 충전제 함량이 높을수록 큰 입자로 존재함을 확인하였다. 무기 충전제를 추가하면 가교 시간은 전반적으로 증가하는 경향을 보였으며, 델타 토크(delta torque)는 감소하였다. 무기 충전제를 추가하면 모듈러스는 전반적으로 감소하였으나, 신율과 인장강도 그리고 인열강도는 증가하였다. 모듈러스의 감소와 신율의 증가는 가교밀도의 감소로 설명하였으며, 인장강도와 인열강도의 증가는 신율의 증가로 설명하였다. 무기 충전제의 첨가에 의해 보강성은 증가하지 않았고 가교밀도는 감소하였다.

• 한국수자원학회논문집
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• 제42권9호
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• pp.691-702
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• 2009

본 연구에서는 집수평면의 신장도에 대한 검토와 함께 자연유역의 자기유사성 및 자기상사성을 고려하여 Hack의 법칙에 대한 체계적인 접근을 수행하여 보았다. DEM으로부터 추출된 대상유역의 집수평면들은 Hack의 법칙에 대한 두 가설이 상호작용을 할 경우 나타날 수 있는 유역 형상들에 대한 모집단처럼 나타났다. 유역면적에 따른 집수평면 신장도의 변화를 도시해 본 결과 유로연장을 기반으로 한 고전적인 지형인자들보다는 관성적률을 기반으로 한 신장도가 보다 직관적인 결과를 줄 수 있을 것으로 판단되었다. Hack의 법칙에 대한 지수 h는 Gray (1951)의 연구결과와 유사하게 산정됨을 확인할 수 있었다. 하지만 대상유역들에 대한 Hurst의 지수 H는 0.96으로 나타나 본 연구에서 고려한 집수평면들은 규모에 따라 등방성 성장률을 가지고 있는 것으로 사료되었다. 이로부터 본 연구의 대상유역들의 형상은 집수평면의 자기유사성보다는 유로연장의 자기상사성에 더 영향을 받는 것으로 추론할 수 있었다.

• Journal of Electrical Engineering and Technology
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• 제13권2호
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• pp.918-927
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• 2018

Based on the actual operating environment of transformer, the aging tests of nitrile butadiene rubber (NBR) were conducted systematically under four conditions: in air, in transform oil, under compression in air and under compression in transform oil to studythe effect of high temperature, transform oil and compression stress simultaneously on the thermal aging behaviors of nitrile butadiene rubber and predict the lifetime. The effects of liquid media and compression stress simultaneously on the thermal aging behaviors of nitrile butadiene rubber were studied by using characterization methods such as IR spectrosc-opy, thermogravimetric measurements, Differential Scanning Calorimetry (DSC) measurements and mechanical property measurements. The changes in physical properties during the aging process were analyzed and compared. Different aging conditions yielded materials with different properties. Aging at $70^{\circ}C$ under compression stress in oil, the change in elongation at break was lower than that aging in oil, but larger than that aging under compression in air. The compression set or elongation at break as evaluation indexes, 50% as critical value, the lifetime of NBR at $25^{\circ}C$ was predicted and compared. When aging under compression in oil, the prediction lifetime was lower than in air and under compression in air, and in oil. It was clear that when predicting the service lifetime of NBR in oil sealing application, compression and media liquid should be involved simultaneously. Under compression in oil, compression set as the evaluation index, the prediction lifetime of NBR was shorter than that of elongation at break as the evaluation index. For the life prediction of NBR, we should take into account of the performance trends of NBR under actual operating conditions to select the appropriate evaluation index.

• Corrosion Science and Technology
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• 제2권6호
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• pp.283-288
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• 2003

The cathodic protection method is being widely used in marine structural steel, however a high tensile steel like RE 36 steel for marine structural steel is easy to get hydrogen embrittlement due to over protection during cathodic protection as well as preferential corrosion of HAZ(Heating Affected Zone) part. In this paper, corrosion resistance and mechanical properties such as elongation and hydrogen embrittlement were investigated with not only in terms of electrochemical view but also SSRT(Slow Strain Rate Test) method with applied constant cathodic potential, analysis of SEM fractography in case of both As-welded and PWHT(Post-Weld Heat Treatment) of $550^{\circ}C$. The best effect for corrosion resistance was apparently indicated at PWHT of $550^{\circ}C$ and elongation was increased with PWHT of $550^{\circ}C$ than that of As-welded condition. On the other hand. Elongation was decreased with applied potential shifting to low potential direction which may be caused by hydrogen embrittlement, however the susceptibility of hydrogen embrittlement was decreased with PWHT of $550^{\circ}C$ than that of As-welded condition and Q.C(quasi cleavage) fracture mode was also observed significantly according to increasing of susceptibility of hydrogen embrittlement. Eventually it is suggested that an optimum cathodic protection potential range not causing hydrogen embrittlernent is from -770 mV(SCE) to -850 mV(SCE) in As-welded condition while is from -770 mV(SCE) to -875 mV(SCE) in PWHT of $550^{\circ}C$.

• 한국수산과학회지
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• 제32권5호
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• pp.664-668
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• 1999

생분해성이며 가식성 alginate 필름을 가공하기 위하여 추출용 액의 $Na_2CO_3$ 농도와 추출시간을 달리하여 alginate를 추출하고, 동 alginate로 제조한 alginate 필름의 수증기 투과율과 장력성의 변화를 측정하였다. 추출용액중의 $Na_2CO_3$ 농도의 증가 및 추출시간의 연장과 더불어 alginate의 점도와 중합도는 감소하였다. 저점도 alginate로 만든 alginate 필름은 높은 수증기투과율을 보였다. 가소제로서 사용된 sorbitol과 polyethylene glycol 첨가는 필름의 수증기투과율과 인장강도를 현저히 낮추는 효과를 보였다. Alginate의 추출시간은 alginate필름의 수중기투과율과 신장성에 미치는 영향이 적었으나 alginate 중합도는 인장강도에 직접적으로 영향을 미쳤다.

• 열처리공학회지
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• 제36권1호
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• pp.7-14
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• 2023

We investigated the effect of multiple tempering on the microstructure and mechanical properties of AISI 4340 steel. The austenitized and quenched AISI 4340 steels were tempered at 550, 600, and 650℃ for 1, 2, and 4 h by single-tempering (ST). The multiple tempering was conducted for 4 h by double-tempering (DT, 2 h + 2 h), and quadruple-tempering (QT, 1 h + 1 h + 1 h + 1 h). As tempering temperature increases, yield strength and ultimate tensile strength decrease and elongation increases due to recovery and recrystallization of martensite and coarsening of carbides. At 550℃, as the number of tempering cycles increases, the yield strength and tensile strength decrease at the expense of fracture elongation. At 600 and 650℃, the yield strength and tensile strength increase with increasing the number of tempering cycles while fracture elongation maintains similar values. The multiple tempering at the same tempering time of 4 h improves the modulus of toughness at all tempering temperatures, which is presumed to be due to the change in carbide precipitation behavior by multiple tempering.

• 소성∙가공
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• 제33권3호
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• pp.161-168
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• 2024

Aluminum alloy sheets, compared to conventional steel sheets, face challenges in press forming due to their lower elongation. To enhance their formability, extensive research has focused on forming technologies at elevated temperatures, specifically warm forming at around 300℃ and hot forming at approximately 500℃. This study proposes that the formability of aluminum alloy sheets can be significantly enhanced using a multi-stage hot forming technique. The research also investigates whether the strength of the A6061 aluminum alloy, known for its precipitation hardening, can be maintained when formed below the precipitate solid solution temperature. In the experiments, the A6061-T6 sheet underwent heating and rapid cooling between 250 and 500℃. The mechanical properties were evaluated at each stage of the process. The findings revealed that when the initial heat treatment was below 350℃, the strength of the material remained unchanged. However, at temperatures above 400℃, there was a noticeable decrease in strength coupled with an increase in elongation. Conversely, when the secondary heat treatment was conducted at temperatures of 350℃ or lower, the strength remained comparable to that of the initial heat treated material. However, at higher temperatures, a reduction in strength and an increase in elongation were observed.

• E2M - 전기 전자와 첨단 소재
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• 제6권1호
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• pp.34-39
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• 1993

본 논문에서는 폴리프로필렌 박막에 대하여 연신이 그 시편의 미세적 구조변화와 물성에 미치는 영향이 조사되었다. 이축연신으로 인해, 이축연신폴리프로필렌의 절연내역은 결정화도의 증가와 미세구조의 변화때문에 증가하는 것이 관찰되었다.

• 한국식품과학회지
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• 제39권2호
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• pp.158-163
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• 2007

본 연구는 curdlan 복합필름을 제조하고 물성을 비교하기 위해 수행되었다. 우선 low set 방식과 high set 방식 중 적절한 방식을 선정하였고, 순차적으로 AMG나 oleic acid 중에서 적절한 방습소재를 선정하였으며, PB와 PIB 중에서 적절한 물성개량제를 선정하고자 하였다. 그 결과 high set 필름이 low set 필름보다 신장율은 다소 작지만 인장강도가 높고 수증기 투과도가 낮기 때문에 curdlan 복합필름 제조에는 high set 방법이 더 적합하며 이때 PEG는 2.0g 첨가하는 것이 유리할 것으로 판단하였다. 또한 oleic acid 첨가군이 AMG 첨가군보다 인장강도와 신장율이 더 크고, 수증기투과도는 더 낮은 편이며 특히 oleic acid 0.3g 첨가한 경우 신장율과 수증기 차단성 면에서 유리하므로 방습소재로서 oleic acid를 0.3g 첨가하는 것이 적합할 것을 판단하였다. PIB 첨가군이나 PB 첨가군 모두 인장강도와 수증기투과도는 비슷하나 신장율의 경우는 PIB 첨가군이 PB 첨가군보다 더 큰 것으로 나타났으므로 유연성과 관련된 물성개량 측면에서는 PIB 첨가가 더 유리할 것으로 판단하였다. 종합적으로 curdlan에 가소제 PEG와 방습소재 oleic acid와 물성개량제 PIB를 첨가하는 것이 유연성과 관련된 물성 면에서 가장 유리할 것으로 판단하였다.