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최성종(Sungjong Choi),김종성(Jongsung Kim),최태규(Taegyu Choi) 한국자동차공학회 2007 한국자동차공학회 지부 학술대회 논문집 Vol.- No.-
Fretting damage 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 test, the following results are obtained: 1) it is found that the fretting fatigue limit of standard specimen decreased about 37% compared to the plain fatigue limit. 2) The early crack of Shinkansen type specimens initiated in contact area and final fractured below σamp=214 ㎫. 3) The early crack of all TGV type specimens initiated in rounded area and fractured. 4) Tire tracks and rubbed scars were observed in the oblique crack region and fatigue crack growth region of fracture surface. 5) 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.
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.
최성종(Sungjong Choi),최태규(Jongsung Kim),김종성(Taegyu Choi),권종완(Jongwan Kwon) 한국자동차공학회 2007 한국자동차공학회 지부 학술대회 논문집 Vol.- No.-
Fretting damage can be observed in automobile and railway vehicle, fossil and nuclear power plant, aircraft etc. In the present study, railway axle material RSA 1 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 test, the following results are obtained: 1) it is found that the fretting fatigue limit of standard specimen decreased about 37% compared to the plain fatigue limit. 2) The early crack of Shinkansen type specimens initiated in contact area and final fractured below σamp=289 MPa. 3) The early crack of all TGV type specimens initiated in rounded area and fractured. 4) 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.
HVOF용사 코팅한 SM490B용접재의 피로크랙성장에 미치는 후 열처리의 영향
윤명진(Myungjin Yoon),최성종(Sungjong Choi) 한국자동차공학회 2007 한국자동차공학회 지부 학술대회 논문집 Vol.- No.-
High velocity oxygen-fuel thermal spray coating of the WC-Co cermet material is a well-established process for modifying the surface properties of the structural components exposed to the corrosive and wear attacks. In this study, HVOF coated SM490B are prepared to evaluation of the effect of coating and post-heat treatment on fatigue crack growth behavior. The pre-crack of the fatigue crack growth test specimens machined at deposited material area, heat affected zone and boundary, respectively. Through these test, the following results are obtained: 1) The fatigue crack of coated specimens propagated more rapidly than non-coated specimen in all specimens. 2) In the same coating thickness specimens, the specimens with pre-crack at boundary more rapidly propagated than the specimens with pre-crack at HAZ and deposited material area. This is probably because whereas the structure of the deposited material zone is very strong thanks to evenly distributed minute carbide or minute martensite, the structure of the edge is highly unstable and contains diverse defects. 3) In three type specimens, the fatigue crack growth rate of post-heat treatment specimen decrease in near-threshold value, while it was about the same in intermediated region and high growth rate region. These results can be used as basic data in a structural integrity evaluation of rolled SM490B weldments considering HVOF coating.
티타늄 합금(Ti-6Al-4V)의 조직변화에 따른 피로수명 평가
권재도(Jaedo Kwon),최성종(Sungjong Choi),배용탁(Yongtak Bae) 한국자동차공학회 2004 한국자동차공학회 춘 추계 학술대회 논문집 Vol.- No.-
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. Three different kinds of specimens are prepared under different heat treatments (rolled plate, 980℃, 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: I) Microstructures are observed as equiaxed, bimodal and lamellar microstructures respectively. 2) Impact absorbed energy is superior for the bimodal microstructure, and the hardness and tensile strength are superior for the lamellar microstructure. 3) The fatigue endurance of lamellar structure shows higher value than that of the equiaxed and bimodal structures. 4) Fractal dimension depend on maximum stress and heat treatment temperature.