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J2와 J3 불변량에 기초한 항복함수의 제안과 이방성 판재에의 적용
김영석,눙엔푸반,김진재 한국소성∙가공학회 2022 소성가공 : 한국소성가공학회지 Vol.31 No.4
The yield criterion, or called yield function, plays an important role in the study of plastic working of a sheet because it governs the plastic deformation properties of the sheet during plastic forming process. In this paper, we propose a novel anisotropic yield function useful for describing the plastic behavior of various anisotropic sheets. The proposed yield function includes the anisotropic version of the second stress invariant J_2 and the third stress invariant J_3. The anisotropic yield function newly proposed in this study is as follows. 〖F(J〗_2)+ αG(J_3 )+βH (J_2×J_3 )= The proposed yield function well explains the anisotropic plastic behavior of various sheets by introducing the parameters α and β, and also exhibits both symmetrical and asymmetrical yield surfaces. The parameters included in the proposed model are determined through an optimization algorithm from uniaxial and biaxial experimental data under proportional loading path. In this study, the validity of the proposed anisotropic yield function was verified by comparing the yield surface shape, normalized uniaxial yield stress value, and Lankford's anisotropic coefficient R-value derived with the experimental results. Application for the proposed anisotropic yield function to aluminum sheet shows symmetrical yielding behavior and to pure titanium sheet shows asymmetric yielding behavior, it was shown that the yield curve and yield behavior of various types of sheet materials can be predicted reasonably by using the proposed new yield anisotropic function.
J2와 J3 불변량에 기초한 비대칭 항복함수의 제안(II)
김영석,눙엔푸반,안정배,김진재 한국소성∙가공학회 2022 소성가공 : 한국소성가공학회지 Vol.31 No.6
The yield criterion, or called yield function, plays an important role in the study of plastic working of a sheet because it governs the plastic deformation properties of the sheet during plastic forming process. In this paper, we propose a modified version of previous anisotropic yield function (Trans. Mater. Process., 31(4) 2022, pp. 214-228) based on J2 and J3 stress invariants. The proposed anisotropic yield model has the 6th-order of stress components. The modified version of the anisotropic yield function in this study is as follows. The proposed anisotropic yield function well explains the anisotropic plastic behavior of various sheets such as aluminum , high strength steel , magnesium alloy sheets etc. by introducing the parameters α and β, and also exhibits both symmetrical and asymmetrical yield surfaces. The parameters included in the proposed model are determined through an optimization algorithm from uniaxial and biaxial experimental data under proportional loading path. In this study, the validity of the proposed anisotropic yield function was verified by comparing the yield surface shape, normalized uniaxial yield stress value, and Lankford's anisotropic coefficient R-value derived with the experimental results. Application for the proposed anisotropic yield function to AA6016-T4 aluminum and DP980 sheets shows symmetrical yielding behavior and to AZ31B magnesium shows asymmetric yielding behavior, it was shown that the yield locus and yielding behavior of various types of sheet materials can be predicted reasonably by using the proposed anisotropic yield function.
중국·중남미 경제협력 프레임워크와 수출경쟁력 변화 분석
김영석 국제지역학회 2019 국제지역연구 Vol.23 No.4
The purpose of this study is to analyze the impact of China on the competition structure and export competitiveness of Korea, China, Japan and the United States in the Latin America and the Caribbean (LAC) markets. In particular, this study analyzes the current status and characteristics of economic cooperation between China and LAC in the fields of trade, investment and finance under the "1+3+6 Cooperation Framework" as well as changes in the export competitiveness of the three East Asian countries(Korea, China and Japan) and the United States. This study shows that the trade, investment and financial flows from China into LAC has been unexpectedly decreased since 2015 when the “1+3+6 Cooperation Framework” was introduced by Chinese President Xi Jinping. This study also finds that the U.S. market share in LAC fell sharply due to China's growing market share, while Korea saw a slight increase and Japan saw a slight decrease. The Export Similarity Index (ESI) indicates that export competition between China and the U.S. has been intensified. The Revealed Comparative Advantage (RCA) Index shows that Korea and Japan has a comparative advantage in capital products, while China has been losing competitiveness in consumer products. 본 연구에서는 중국의 부상이 중남미 시장에서의 경쟁 구도와 수출경쟁력 변화에 미친 영향을 분석하였다. 특히, 중국의 대중남미 정책인 ‘1+3+6 협력 프레임워크’에 따른 무역, 투자, 금융 분야에서의 중국과 중남미의 경제협력 현황과 특징 그리고 한·중·일 동아시아 3국과 미국의 대중남미 수출경쟁력 변화에 대해 분석하였다. 분석 결과, 중국의 대중남미 경제협력 규모는 ‘1+3+6 협력 프레임워크’를 제시한 2015년 이후 오히려 둔화되었다. 중남미에서의 한·중·일 3국과 미국의 경쟁 구도와수출경쟁력에도 변화가 나타나고 있다. 특히 중국의 중남미 시장점유율 확대로 미국의 중남미 시장점유율이 가장 큰 폭으로 하락했으며, 한국은 소폭 증가 그리고 일본은 소폭 감소한 것으로 나타났다. 한중일 3국과 미국의 수출경합도(ESI)가 모두 증가했고, 특히 중국과 미국의 수출경합도가 가장 크게 증가한 것으로 분석됐다. 현시비교우위지수(SCA) 분석 결과, 한국과 일본은 자본재 부문에서 수출경쟁력을 유지하고 있으며, 중국은 소비재 부문의 수출경쟁력이 지속적으로 하락하고 있는 것으로 밝혀졌다.
탄소섬유를 이용한 600V 이하 저압 케이블의 전자파 차폐특성
김영석,김택희,김종민,송길목,김지연,김원석,곽동순,Kim, Young-Seok,Kim, Taek-Hee,Kim, Chong-Min,Shong, Kil-Mok,Kim, Ji-Yeon,Kim, Won-Seok,Kwag, Dong-Soon 대한전기학회 2017 전기학회논문지 Vol.66 No.1
This study used general carbon fibers(CF), which can be utilized for a low voltage cable screen, as well as metal-coated carbon fibers(MCF) to make cables and analyzed the properties of electromagnetic effectiveness. Both braid CF and MCF cables with 3,000 strands, 16 spindles, and braid density of 90% or over were adopted. The tape-type MCF specimens were spread into a tape(width: 15mm) using a hot melt to make a cable. The shield effectiveness was measured up to the 1GHz range in accordance with IEC 62153-4-6; braid shielded cables featured a superior shielding effect at 63dB than tape-type shielded cables. That was because the tape-type shielded cable has relatively more gaps and holes between carbon fibers than the braid type, resulting in a more inflow or emission of electromagnetic waves. In the case of braid cables, the characteristics of their electromagnetic waves were enhanced, with higher spindles and higher conductivity of carbon fibers. The shield effectiveness of the MCF shielded cable, however, was lower than that of tin-coated one.