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배용탁(Yong Tak Bae),최성종(Sung Jong Choi),권재도(Jae Do Kwon) 대한기계학회 2004 대한기계학회 춘추학술대회 Vol.2004 No.8
The specific gravity of titanium alloy is 4.5 which is lighter than steel, however, its specific strength, heat and corrosion resistance are superior to steel. Therefore, it is used in spaceships, medicines, and so on. Ti-6Al-4V alloy is a kind of α+β phase titanium alloy, and mechanical properties are changed by alloy elements, shapes and distributions of microstructures. In this paper, the effect of microstructure on mechanical behavior for Ti-6Al-4V alloy was studied. Two different kinds of specimens are prepared under different heat treatments (rolled plate, 1050℃) in order to produce different microstructures. Various kinds of mechanical tests such as hardness, tensile, fatigue and fretting fatigue tests are performed for evaluation of mechanical properties with the changes of microstructures. Through these tests, the following conclusions are observed: 1) Microstructures are observed as equiaxed and widmanstatten microstructures respectively. 2) Impact absorbed energy is superior for the equiaxed microstructure, and the hardness and tensile strength are superior for the widmanstatten microstructure. 3) The fatigue endurance of widmanstatten microstructure shows higher value than that of the equiaxed microstructure. 4) The fatigue endurance in fretting condition was reduced about 50% from that of the non-fretting condition.
권재도,배용탁,최성종,Gwon, Jae-Do,Bae, Yong-Tak,Choe, Seong-Jong 대한기계학회 2000 大韓機械學會論文集A Vol.24 No.7
The degradation of a boiler header constructed by a material, 1Cr-0.5Mo steel in a fossil power plant is observed when the header is exposed for a long period to the high temperature and pressure. The present investigations are for evaluating the effect of the degradation on the material, such as its strength changes. Reheat-treated metal is used to compare the mechanical properties of the degraded and that of reheat-treated materials. Through the investigation, following results are obtained 1) the area ratio of ferrite in the reheat-treated material is larger than that of the degraded material, 2) the hardness and tensile strength of the degraded material are lower than that of the reheat-treated material, 3) the ductile-brittle transition temperature(DBTT) increased toward high temperature region, 4) the fatigue crack growth rate(FCGR) of the degraded material is higher than that of the reheat-treated material in the region of low ΔK value while FCGR of the both materials are similar in high ΔK region.
티타늄 합금(Ti-6Al-4V)의 조직변화에 따른 기계적 특성 평가
권재도,배용탁,최성종,Gwon, Jae-Do,Bae, Yong-Tak,Choe, Seong-Jong 대한기계학회 2002 大韓機械學會論文集A Vol.26 No.4
The characteristics of mechanical behavior are investigated for Ti-6Al-4V alloy. Four kinds of the specimens are prepared under different heat treatments in order to produce different microstructures. In the present investigations, impact, tensile and fatigue crack growth tests are performed for each test specimen. The results obtained through the investigations are compared. Additionally fr actal dimensions of crack pass are obtained using the box counting method. The results are, 1) the microstructures shows as equiaxed, bimodal and Widmanstatten microstructures respectively, 2) the impact energy and elongation are superior fur the bimodal microstructure, and the hardness and tensile strength are superior fur the Widmanstatten microstructure, 3) the fatigue crack growth rate is similar to all microstructures in low ΔK region while that of equiaxed microstructure is the largest, and that of Widmanstatten microstructure is the lowest in high ΔK region respectively, 4) the fractal dimension D of Widmanstatten microstructure shows higher value than that of the equiaxed and bimodal microstructures under 200 magnification view of the SEM micrographs.
INCONEL 600 과 690 합금의 프레팅 피로수명에 관한 연구
박대규(Dae Kyu Park),배용탁(Yong Tak Bae),최성종(Sung Jong Choi),우승완(Seung Wan Woo),권재도(Jae Do Kwon) 대한기계학회 2005 대한기계학회 춘추학술대회 Vol.2005 No.11
The fretting fatigue occurs at lower stress amplitude and at lower cycles of cyclic loading then plain fatigue. INCNEL 600 and 690 alloy are high-chromium nickel alloy having excellent resistance to many corrosive aqueous media and high-temperature atmospheres. In this paper, the effect of fretting damage on fatigue behavior for INCNEL 600 and 690 alloy were studied. Also, various kinds of mechanical tests such as hardness, tension and plain fatigue tests are per formed. Through these experiments, it is found that the fretting fatigue strength decreased about 40 ~ 70% compared to the plain fatigue strength in two materials. In fretting fatigue, the wear debris is observed on the contact surface and the oblique micro-cracks at on earlier stage are initiated.
최성종(Sungjong Choi),배용탁(Yongtak Bae),김종성(Jongsung Kim),최태규(Taegyu Choi),김구년(Gunyeon Kim) 한국자동차공학회 2006 한국자동차공학회 춘 추계 학술대회 논문집 Vol.- No.-
Fretting is a kind of surface damage mechanism observed in mechanically jointed components and structures. The initial crack under fretting damage occurs at lower stress amplitude and lower cycles of cyclic loading than that under plain fatigue condition. This can be observed in automobile and railway vehicle, fossil and nuclear power plant, aircraft etc. In the present study, railway axle material RSA1 used for evaluation of fretting fatigue life. Plain and fretting fatigue tests were carried out using rotary bending fatigue tester with proving ring and bridge type contact pad. Through these experiments, it is found that the fretting fatigue limit decreased about 35% compared to the plain fatigue limit. In fretting fatigue, the wear debris is observed on the contact surface, and oblique cracks at an earlier stage are initiated in contact area. These results can be used as useful data in a structural integrity evaluation of railway axle.