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김엄기,차동진 한밭대학교 생산기반기술연구소 2002 생산기반기술연구소 논문집 Vol.2 No.1
In this research, we developed the δ_5 clip gage based on strain gage application and the adaptor which keep the ends of clip on two marked positions during test. The results of research are following: The δ_5 clip gage with gage length of 5㎜ and the calibrator were developed. The adaptor for the attachment of δ_5 clip gage to the specimen was developed. The accuracy and repeatability of δ_5 clip gage turns out to be good in comparison with those of conventional clip gages.
Study of Al-Alloy Foam Compressive Behavior Based on Instrumented Sharp Indentation Technology
Kim Am-Kee,Tunvir Kazi The Korean Society of Mechanical Engineers 2006 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.20 No.6
The stress-strain relation of aluminum (Al) alloy foam cell wall was evaluated by the instrumented sharp indentation method. The indentation in a few micron ranges was performed on the cell wall of Al-alloy foam having a composition or Al-3wt.%Si-2wt.%Cu-2wt.%Mg as well as its precursor (material prior to foaming). To extract the stress-stram relation in terms of yield stress ${\sigma}_y$, strain hardening exponent n and elastic modulus E, the closed-form dimensionless relationships between load-indentation depth curve and elasto-plastic property were used. The tensile properties of precursor material of Al-alloy foam were also measured independently by uni-axial tensile test. In order to verify the validity of the extracted stress-strain relation, it was compared with the results of tensile test and finite element (FE) analysis. A modified cubic-spherical lattice model was proposed to analyze the compressive behavior of the Al-alloy foam. The material parameters extracted by the instrumented nanoindentation method allowed the model to predict the compressive behavior of the Al-alloy foam accurately.
Study on Erosion of Carbon Fiber Reinforced Plastic Composite
김엄기(Kim, Am-Kee),김일현(Kim, Il-Hyun) 한국산학기술학회 2008 한국산학기술학회논문지 Vol.9 No.2
일방향 탄소섬유 강화 복합재료(CFRP)의 고체입자 마식 거동을 다양한 충돌각도 (α), 속도 (V) 및 섬유 방향 (β)에 대하여 연구하였다. 실험결과 30。 충돌각도에서 최대 마식률을 나타내었고, 마식률은 멱함수 법칙 Eoc Vⁿ에 따라 충돌속도에 크게 의존하였다. 본 연구에서는 이상의 결과로부터 일방향 탄소섬유 강화 복합재료의 마식률을 충돌속도, 충돌각도 및 섬유방향 각도로부터 예측하는 방법을 제안하였다. The solid particle erosion behaviour of unidirectional carbon fiber reinforced plastic (CFRP) composites was investigated. The erosive wear of these composites was evaluated at different impingement angles (30°, 45°, 60°, 90°), different impact velocities (40, 55, 60, 70㎧) and at three different fiber orientations (0°, 45°, 90°). The erodent was SiC sand with the size 50-100㎛ of irregular shapes. The result showed ductile erosion behaviour with maximum erosion rate at 30° impingement angle. The fiber orientations had a significant influence on erosion. The erosion rate was strongly dependent on impact velocity which followed power law Eoc Vⁿ. Based on impact velocity (V), impact angle (α) and fiber orientation angle (β), a method was proposed to predict the erosion rate of unidirectional fiber reinforced composites.
김엄기(Am-Kee Kim),남승훈(Seung-Hoon Nahm),고성위(Sung-Wi Koh) 한국해양공학회 1996 韓國海洋工學會誌 Vol.10 No.4
A fractal analysis on fracture surface of aluminium-particulate SiC composites was attempted. As the volume fraction of SiC in composites increases, the fractal dimension tends to increase. However, no correlation between the fractal dimension and the fracture toughness in terms of critical energy release rate was observed. Since the fractal dimension represents the roughness of fracture surface, the fracture toughness would be a function of not only fracture surface roughness but also additional parameters. Thus the applicability of fractal analysis to the estimation of fracture toughness must depend on the proper choice and interpretation of additional parameters. In this paper, the size of characteristic structural unit for fracture was considered as an additional parameter. As a result, the size appeared to be a function of only volume fraction of SiC. Finally, a master curve for fracture toughness of aluminium-particulate SiC composites was proposed as a function of fractal dimension and volume fraction of SiC.
이방성 자기저항측정을 이용한 NiO / NiFe 박막의 교환결합연구
김종기(Jong-Kee Kim),김선욱(Sun-Wook Kim),이기암(Ky-Am Lee),이상석(Sang-Suk Lee),황도근(Do-Guwn Hwang) 한국자기학회 2002 韓國磁氣學會誌 Vol.12 No.4
We report an experimental evidence of coexistence of the strong and weak exchange couplings in unidirectional NiO/NiFe (antiferromagnetic/ferromagnetic) bilayer thin films. The exchange bias was measured by VSM and AMR techniques and then, analyzed into the strong and weak exchange couplings by means of a regression method. In NiO(60 ㎚)/NiFe(10 ㎚) film, the ratio of the weak exchange coupling field over the average exchange coupling field was found to be almost unchanged within a range from 0.2 to 0.4 irrespective to the strength of an applied field. However, the ratio increased among the samples with decreasing the average exchange coupling field due to the increment of the weak exchange coupling area.