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마하피닝 처리에 의한 기계구조용 합금강의 피로균열전파 지연효과
김민건,임복규,박홍기,황중각 강원대학교 산업기술연구소 2006 産業技術硏究 Vol.26 No.B
Mach peening treatment is one of the various kinds of techniques to improve the fatigue properties. The mach peening process gives high-level work hardening and compressive residual stress near the surface layer, improving the fatigue strength. In addition, this treatment reduces slip bands that initiate the fatigue cracks near the surface. During impingement, a plastic indentation surrounded by a plastic zone is formed. Mach peening treatment characteristic is less energy consumption and is an environmental friendly processing methods that is not accompanied by pollution. It is machining process that can prevent fatigue fracture beforehand in structure using already as well as process of production. The test results showed that fatigue crack propagation delay appeared by drilling type 43%, mach peening type 110%.
저사이클 피로수명에 영향을 미치는 구상흑연주철의 흑연입자수의 영향
김민건,이병현,유병호 강원대학교 산업기술연구소 2000 産業技術硏究 Vol.20 No.B
Low cycle fatigue life of spheroidal graphite cast iron is determined by the morphological parameters of internal graphite. The aim of this study is to clarify the effect of the number of nodular grain of spheroidal graphite cast iron on low cycle fatigue life. Two specimens that have identical average nodular grain size by changing nodular grain volume fraction and different number of nodular grain count was tested. In this paper, the parameter governing fatigue life through fatigue test, the number of nodular grain seriously affect fatigue life and nodular grain size is no longer governing parameter of it.
곡률을 갖는 셀프-피어싱 리벳 접합시편의 피로수명 평가
김민건,조석수,김동열,Kim, Min-Gun,Cho, Seok-Swoo,Kim, Dong-Youl 한국생산제조학회 2010 한국생산제조학회지 Vol.25 No.3
One of methods that accomplish fuel-efficient vehicle is to reduce the overall vehicle weight by using aluminum structure typically for cross members, rails and panels in body and chassis. For aluminum structures, the use of Self Piercing Rivet(SPR) is a relatively new joining technique in automotive manufacture. To predict SPR fatigue life, fatigue behavior of SPR connections needs to be investigated experimentally and numerically. Tests and simulations on lap-shear specimen with various material combinations are performed to obtain the joining strength and the fatigue life of SPR connections. A Finite element model of the SPR specimen is developed by using a FEMFAT SPR pre-processor. The fatigue lives of SPR specimens with the curvature are predicted using a FEMFAT 4.4e based on the liner finite element analysis.
시간에 따라 변화하는 장기기억의 동태적 특성 분석: 코스피 주요 2차 산업을 중심으로
김민건 한국금융공학회 2012 한국금융공학회 학술발표회 Vol.2012 No.-
본 연구는 그 동안 연구되어져 왔던 정태적인 장기기억 특성을 보완하기 위해 동태적으로 변화하는 장기기억 특성에 대해 살펴봄으로써 그 특성에 대한 설명력을 높이고, 다양한자산수익률 예측력을 높이기 위함에 목적을 두고 있다. 이를 위해 본 연구에서는 코스피 시장의 2차 산업(화학, 철강 및 금속, 기계, 전기가스업,건설업, 제조업)의 일별 수익률자료를 사용하여 Hurst exponent 측정하였으며, 또한 시간에 따라 동태적으로 변화하는 Hurst exponent를 찾기 위해 표본이동평균법을 이용하였다. 특히 본 연구에서는 504개, 756개, 1008개의 시간창을 이동시켜 그 변화정도까지비교해봄으로써 보다 세밀한 연구를 하였다. 이 연구를 통해 글로벌 금융위기가 코스피의 2차 산업의 시계열에 영향을 주었으며, 효율성을 악화시키는 원인이 그에 있음을 알아보았다. 연구 결과 글로벌 금융위기로 인하여 코스피의 주요 2차 산업에서 장기기억의 특성이 존재하였고, 특히 장기기억의 특성이 시간에 따라 가변적으로 변화함을 발견했다. 또한 시간창을 달리 한 표본이동평균법으로 시간 가변적 장기기억의 특성이 달리 표현된다는 연구결과를 이용하여 향후 단기적인 등락을 예측하느냐 혹은 장기적 추세를 예측하느냐에 따라 시간창을 달리한다면 보다 정확한 예측력을 가질 수 있을 것임을 발견하였다.
김민건,서봉원 강원대학교 산업기술연구소 2000 産業技術硏究 Vol.20 No.B
In order to observe the pattern forming of copper plate and chemical corrosion reaction, a study on the effect of the process parameters on the formation of micro-pattern by a photochemical etching of copper plate was carried out. The results are as follows : 1) Etching rate increases as the concentration of etchant increases under the regular condition of the temperature by the increasing of diffusion rate to surface. 2) Etching rate increases as the temperature of etchant increases by the fast acting of the material delivery of diffusion to surface under the regular condition of concentration. 3) It was found that etching speed increases as the material delivery of convection rising increased when the aeration speed of etchant increases. This result was from the fact acted by the material delivery of convection rising rather than material delivery of diffusion to the surface.
페라이트-마르텐사이트 복합 조직강의 피로한도에 미치는 마르텐사이트 조직형태의 영향
김민건,지정근 강원대학교 산업기술연구소 2000 産業技術硏究 Vol.20 No.B
A study has been made on the behavior of microscopic fatigue crack growth at the stress level of the fatigue limit with ferrite-martensitic structures. For the above purpose, two types of the microstructures were prepared ; one is the microstructure having the ferrite encapsulating the islands of second phase martensite(FEM), the other is the microstructure with the martensite encapsulating the islands of ferrite(MEF). It has been pointed out that the fatigue limits of these microstructures are related to the critical stress at which the microcrack in the MEF microstructure in which the critical crack length would be restricted within the second phase spacing in contrast with the FEM microstruture. However, the fatigue tests shows that no appreciable difference of the fatigue limits among them were recognized. Also, it turned out from the metallographic observations that the micro crack path is very much affected by the microstructures, so that the microcracks grow according to the 3-dimentional situation of its microstructures.
SNCM강의 피로균열의 발생 및 전파속도에 미치는 질화처리의 영향
김민건,이상호 강원대학교 산업기술연구소 2003 産業技術硏究 Vol.23 No.A
Effect of nitriding on fatigue crack imtiation and growth rate has been studied on SNCM. Specunens were nitnded for 15 hr at 860℃. The fatigue limit of nitrided specunens was superior to that of annealed(860℃. 15 hr) specimens. Based on detailed observations of slip band and micro crack initiation, it is concluded that the excellent fatigue limit of nitrided specunens is attnbuted to improved slip initiation resistance by nitriding The charactenstic of fatigue crack growth rate of nitrided specimens was investigated and compared with those of annealed specunens It was found that by nitriding the crack growth rate was markedly decreased and the threshold stress intensity factor range was improved. It is concluded that the excellent fatigue limit of nitnded specunens is also attributed to unproved fatigue crack growth rate and threshold stress intensity factor range by nitriding