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불균질 취성재료 파괴인성에 미치는 두께효과의 확률적 연구
김엄기,고성위,정규동,Kim, Am-Kee,Koh, Sung-Wi,Jung, Gyoo-Dong 대한기계학회 1996 大韓機械學會論文集A Vol.20 No.4
Fracture toughness of heterogeneous brittle materials such as poly crystalline ceramics used to present the size (thickness) effect as well as statistically distributed results. There is belief that both(size effect and scatter) must be associated with each other. However, no generally accepted theory has been established so far. Using statistical approach, a probabilistic modeling for the fracture toughness which describes the thickness effect was attempted in this paper, Weibull distribution of specific fracture energy(SFE)at local areas and Griffith criterion are applied to the model. In addition, the newly developed model was verified with experimental results of alumina.
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.
미소 비커스경도에 의한 Cr-Mo-V강의 경년열화 평가
김정기,남승훈,김엄기 ( Jung Ki Kim,Seong Hoon Nahm,Am Kee Kim ) 한국열처리공학회 1998 熱處理工學會誌 Vol.11 No.1
Since Cr-Mo-V steel has excellent fracture and creep properties at elevated temperature, they are extensively used as steam turbine components such as the turbine rotor. However, the turbine rotor steel used to suffer material degradation during long term service. Therefore, the assessment of the safety and residual life of the turbine rotor is periodically required during service. One of the most convenient techniques for that is the hardness method mainly due to its simplicity and nondestructive characteristics. In this research, six specimens with different aging times of turbine rotor steel were artificially prepared by an isothermal heat treatment at 630℃. The micro Vickers hardnesses of specimens were measured at room temperature. The relationships between the fracture properties and the hardness ratio were investigated. And also an indirect method to evaluate the residual life of degraded turbine rotor was proposed based on the micro Vickers hardness measurement.
CTOD 측정용 δ<sub>5</sub> Clip Gage 설계
박태현,남승훈,김엄기,Park, Tai-Heoun,Nahm, Seung-Hoon,Kim, Am-Kee 대한기계학회 2004 大韓機械學會論文集A Vol.28 No.4
The flaw assessment method based on ${delta}_5$ parameter was recently proposed and put to the practical use. However: since it is almost impossible to measure the ${delta}_5$ by the existing commercial clip gager, we need to develope the specially designed gages which are suitable for that purpose. In this research, a double cantilever type ${delta}_5$ clip gage with the traveling distance of 4mm was developed by the finite element analysis and the construction of Wheatstone bridge circuit including strain gages. The linearity of developed ${delta}_5$ clip gage was evaluated by the MTS extensometer calibrator with the proper adapters which allow the 6s clip gage to sit on the calibrator. Consequently, the 6s clip gage revealed the good linearity between the output voltage and the traveling distance of gage.
CFRP 복합재료의 층간파괴인성치에 미치는 수분의 영향
김형진(Hyung-Jin Kim),김종훈(Jong-Hoon Kim),고성위(Sung-Wi Koh),김엄기(Am-Kee Kim) 한국해양공학회 1996 韓國海洋工學會誌 Vol.10 No.4
Polymeric composites can be subjected to a wide variety of environmental conditions in practical use. One of most important conditions to be considered in the structural design using such materials is the moisture environment. Thus the moisture effect on interlaminar fracture toughness G<SUB>ⅠC</SUB> and G<SUB>ⅡC</SUB> of CFRP(Carbon fiber reinforced plastic) composed of carbon fibers and epoxy resin is studied in this paper. Specimens were first processed in 25, 50, 80℃ flesh water and 25℃ sea water for various periods of time. After that, the water absorption and fracture toughness tests were performed under laboratory atmosphere. As result, the specimen processed in 80℃ flesh water indicates the highest moisture absorbing capability, the second in 50℃ flesh water, the third in 25℃ sea water, and the specimen in 25℃ flesh water does the lowest. The interlaminar fracture toughness G<SUB>ⅠC</SUB> increases, approaches to the maximum, and decreases as the immersion time increases. In case of interlaminar G<SUB>ⅡC</SUB>, the value of the specimen processed in 80℃ flesh water turns out to be higher than others. In addition, the scanning electron micrographs(SEM) of fracture surfaces were also examined in order to explain the mechanism of fracture.