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구상화율에 의한 구상 흑연주철재의 피로강도의 정량적 평가
윤명진(Yoon Myung-Jin) 한국공작기계학회 1999 한국공작기계학회지 Vol.8 No.5
Although the problems of defects and nonmetallic inclusion in metal fatigue are very complicated, it is particularly important to view these problems from the perspective that defects and inclusions are virtually equivalent to small cracks. This concept will help us to understand various fatigue phenomena caused by graphite of Ductile cast iron. Therefore, in this study, different ferrite-pearlite matrix structure and spheroidal ratio of graphite of 70%, 80% and 90%, GCD40, GCD45-l and GCD45-2 series, have been carried out rotary bending fatigue test, estimated the maxi-mum size of graphite, investigated correlation. It was concluded as follows; (l) in ductile cast iron which have various spheroidal ratio of graphite, the fatigue limit C series of 90% spheroidal ratio of graphite is the highest. While, A series of 70% spheroidal ratio of graphite is the lowest. (2) 삶tigue limit was predicted by vickers hardness(Hv) of matrix, of maximum size graphite inputting Murakami and Endo’s formula.
최대 및 평균 구상흑연크기에 의한 구상흑연주철재의 피로강도의 평가
윤명진(Myung-Jin Yoon) 한국기계가공학회 2012 한국기계가공학회지 Vol.11 No.1
For different ferrite-pearlite matrix structure, contain more than 90% spheroidal ratio of graphite, GCD 45-3, GCD 50, GCD 60 series and 70%, 80%, 90% spheroidal ratio of graphite, GCD 40, GCD 45-1, GCD 45-2 series, this paper has carried out rotary bending fatigue test, estimated maximum and mean size of spheroidal graphite, investigated correlation. It was concluded as follows. (1) Fatigue limit in 10?cycles and numbers of spheroidal graphite per 1㎟ was linear relation. (2) projection area of graphite can be used to predict fatigue limit of Ductile Cast Iron. The Statistical distribution of extreme values of projection area of defects may be used as a guideline for the control of inclusion size in the steelmaking processes.
윤명진(Myung-Jin Yoon) 한국기계가공학회 2010 한국기계가공학회지 Vol.9 No.6
Although the problems of defects and nonmetallic inclusion in metal fatigue are very complicated, it is particularly important to view these problems from the perspective that defects and inclusions are virtually equivalent to small cracks. This concept will help one to understand various fatigue phenomena caused by Ductile Cast Iron. For different ferrite-pearlite matrix structure, containing more than 90% spheroidal ratio of graphite, GCD 45-3, GCD 50, GCD 60 series and 70%, 80%, 90% spheroidal ratio of graphite, GCD 40, GCD 45-1, GCD 45-2 series, this paper has carried out image analyzer, estimated maximum and mean size of graphite, investigated correlation. It was concluded as follows. (1) A good quality of Ductile cast iron using in this experiment, the graphite was separated well. The effect of the interaction by graphite was verified by microscopic observation and by fracture mechanics investigation in surface, interior of the specimen. (2) √areamax of graphite can be used to predict fatigue limit of Ductile Cast Iron. The Statistical distribution of extreme values of √area may be used as a guide line for the control of inclusion size in the steel making processes.
구조용 압연강재와 스테인리스강재의 CO<sub>2</sub> 용접에 대한 기계적 특성연구
임종영,윤명진,김태현,김상윤,김태규,Lim, Jong Young,Yoon, Myung Jin,Kim, Tae Hyun,Kim, Sang Youn,Kim, Tae Gyu 한국결정성장학회 2013 韓國結晶成長學會誌 Vol.23 No.4
산업시설에는 용접된 구조물에 반복 하중이 발생하여 피로파괴가 발생하고 있는데 이 피로파괴를 줄이기 위해 일반구조용압연강재(SS400)와 스테인리스강(STS304)을 $CO_2$ 용접하여 기계적 특성 분석을 하였다. X-ray 촬영을 하여 결함검사를 하고 용접부에 결함이 없는 시험편으로 경도, 인장, 피로 시험을 하였다. 경도는 SS400과 STS304가 용접된 시험편이 SS304만 용접된 시험편보다 높게 나타났다. 그리고 인장강도와 항복강도는 반대로 SS304만 용접된 시험편이 높았으며 피로한도 또한 마찬가지였다. 따라서 $CO_2$ 용접을 할 경우 융점이 낮고 용접성이 좋은 SS400만으로 용접할 때 더 좋은 성능을 보여준다. It is well known that fatigue failure occur on welded structures in industrial application due to the repetitive load force. In order to decrease the fatigue failure, we analysed the mechanical properties based on their structural aspect, roll steel (SS 400) welded onto stainless steels (STS 304) by $CO_2$ gas as well as structure roll steel welded onto itself. We compared the hardness, tensile and fatigue properties with two kinds of samples which had no defects on the welding part observed by X-ray topographic analysis. It was recognized that the tensile and fatigue strength of SS 400 welded onto itself by $CO_2$ gas was higher than that of SS 400 welded onto STS 304.
알루미늄 합금(AI7050-T7451)의 반복 굽힘 하중하의 프레팅 피로거동 평가
김종성(Jong-Sung Kim),윤명진(Myung-Jin Yoon),최성종(Sung-Jong Choi),조현덕(Hyun-Deog Cho) 한국기계가공학회 2010 한국기계가공학회지 Vol.9 No.1
Fretting damage reduces fatigue life of the material due to low amplitude cyclic sliding and changes in the contact surfaces of strongly connected machine and structures such as bolt, key, fixed rivet and connected shaft, which have relative slip of repeatedly very low frequency amplitude. In this study, the fretting fatigue behavior of 7050-T7451 aluminum alloys used mainly in aircraft and automobile industry were evaluated. The plain fatigue test and fretting fatigue test under cyclic bending load carried out commercial bending fatigue tester and specially devised equipments to cause fretting damage. From these experimental work, the following results obtained: (1) The plain fatigue limit for stress ratio R=-l was about 151㎫. (2) In case of fretting fatigue, fatigue limit for stress ratio R=-l about 72㎫, the fatigue limit for R=0 about 81㎫, and the fatigue limit for R=0.3 about 93㎫. (3) The fatigue limit reduction rates by the fretting damage were about 52%(R=-1), 46%(R=0) and 38%(R=0.3) respectively. (4) The fatigue limit reduction rate decreased with stress ratio increase. In fretting bending test, as stress ratio increased, occurrence of initial oblique crack by fretting decreased or phased out, so that fracture surfaces were formed by plain fatigue crack occurrence, and such tendency was notable as stress amplitude increased. (5) Tire tracks and rubbed scars were observed in the fracture surface and contacted surface.