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ECAP 강가공에 의한 마그네슘 AZ31합금의 결정립 미세화 및 미세조직 불안정성
김호경 ( H. K. Kim ),정강 ( K. Chung ),현창용 ( C. Y. Hyun ) 한국열처리공학회 2004 熱處理工學會誌 Vol.17 No.3
N/A Equal channel angular pressing (ECAP) technique had been adapted to the Mg alloy (AZ31) for achieving effective grain refinement through severe deformation. The average grain size of 2.5 ㎛ could be obtained after 4 passes. The stability of the ECAPed structure at elevated temperatures was examined by annealing the ECAPed materials over a wide range of temperature between 473 and 748 K. The average activation energy, Q, for static grain growth of 1, 2 and 3 passes was 33.7 kJ/㏖ (=0.25QL, activation for lattice diffusion). The abnormally low Q value in the lower temperature range may indicate that grain growth occurs in the unrecrystallized microstructure where non-equilibrium grain boundaries containing a large number of extrinsic dislocations exist. The yield stresses of the ECAPed alloys decreased whereas the elongations increased after the ECAP process. These results should be related to the modification of texture for easier slip on basal plane.
한병기,정강,유서열,Han, B.K.,Chung, K.,Yoo, S.Y. 대한기계학회 1991 대한기계학회논문집 Vol.15 No.1
Stiffened plate structure, which is generally used in the various structural design to develope the load carrying capacity, is classified in two groups; one is the plate stiffened with stiffeners, the other is corrugated plate. In the studies on those structures, the studies on the stiffened plates with stiffeners have been much studied with both quantities and qualities according to requirements of the minimum-weight structural design and the development in many industrial fields, especially automobile, ship and aerospace fields, but the studies on the corrugated plates are undeveloped in comparison with the stiffened plates, and also the analytical stiffness on the corrugated plates remains as the imperfect. In the present studies, the analytical method on the stiffness of corrugated plates made by folding is proposed, and the stiffness equation of corrugated plates with some angle is derived and generalized. The purpose of the present study is to contribute to the design of corrugated plates and to determine the optimum aspect ratio for parameters that decide the aspect of corrugated plates. 본 연구에서는 각이 지게 주름잡힌 주름판 구조물(산형, 사다리꼴형, 장방형 주름판)의 강성을 해석 하고, 이 강성식들을 일원화하여 한개의 식으로 표현하여 주고 자 한다. 이론 해석은, 연결부에서의 각도가 변형중에 변하지 않는다는 가정하에, 등가의 직교이방성판의 강성식을 유도하였다. 또한, 이론적으로 얻어진 강성치를 진 동해석에 적용시킴으로서, 직교이방성판으로서의 주름판의 고유진동수를 구하였다. 그리고 이를 진동실험에서 얻은 결과 및 PC용 슈퍼 SAP에서 얻은 수치결과와 비교함으로 서 이론의 신뢰성을 입증하였다.
ATM 망에서 ABR 서비스를 위한 혼잡회피 알고리즘에 관한 연구
정강화,진성호,임재홍 한국해양대학교 산업기술연구소 2001 연구논문집 Vol.18 No.-
In this paper, a congestion avoidance mechanism of rate based traffic algorithm for ATM(Asynchronous Transfer Mode) was studied. ATM is proposed to surpport B-ISDN that services various applications on a single network. To support various application's traffic characteristics, ATM Forum defined various service classes, such as CBR(Constant Bit Rate), VBR(Variable Bit Rate), ABR(Available Bit Rate), UBR(Unspecified Bit Rate). ABR service is to maximize link utilization and minimize cell loss rate. So it is important for ABR service to manage network traffic and congestion avoidance. In this paper, a studied ABR service traffic management algorithm is ER(Explicit Rate) mechanism. ER mechanism is composed of two algorithm, ERICA(Explicit Rate Indicate Congestion Avoidance), EPRCA(Enhanced Proportional Rate Control Algorithm), To study each algorithm, three switch simulation network model is composed and two ER mechanism, ERICA and EPRCA is compared.