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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.
우창수(Changsu Woo),김완두(Wandoo Kim),권재도(Jaedo Kwon) 대한기계학회 2005 대한기계학회 춘추학술대회 Vol.2005 No.5
Fatigue life prediction methodology of the vulcanized natural rubber was proposed by incorporating the finite element analysis and fatigue damage parameter determined from the fatigue tests. Nonlinear finite element analysis of the 3-D dumbbell specimen of natural rubber was performed based on a hyperelastic material model determined from the tension, compression and shear tests. The Green-Lagrange strain at the critical location determined from the FEA was used for evaluating the fatigue damage parameter of natural rubber. Fatigue tests were formed using the 3-D dumbbell specimens with different levels of maximum strain and various hardness. Fatigue life curves can be effectively represented by a following single function using the Green-Lagrange strain. Predicted fatigue lives of the rubber component agreed fairly well the experimental fatigue lives.
우창수(Changsu Woo),김완두(Wandoo Kim),김완수(Wansoo Kim),권재도(Jaedo Kwon) 한국자동차공학회 2004 한국자동차공학회 춘 추계 학술대회 논문집 Vol.- No.-
The interest of the fatigue life of rubber components such as engine mounts is increasing according to the extension of warranty period of the automotive components This paper discusses a fatigue life prediction of the 3-dimensional dumbbell specimens and rubber components considering the effects of maximum strain. Displacement controlled fatigue life tests were performed using specimens with different levels of maximum strain and various hardness. The basic mechanical properties test and the fatigue test of rubber specimen were executed. A procedure to predicted the fatigue life of vulcanized natural rubber components based on the maximum strain method was proposed, and then this curve was in good agreement with fatigue test data less than 200% error range.
우창수(Changsu Woo),김완두(Wandoo Kim),김완수(Wansoo Kim),권재도(Jaedo Kwon) 한국자동차공학회 2003 한국자동차공학회 춘 추계 학술대회 논문집 Vol.- No.-
The interest of the fatigue life of rubber components such as engine mounts is increasing according to the extension of warranty period of the automotive components. Automotive engine mounts get damaged due to thermal and mechanical loadings. Rubber component was aged during its life and the aging phenomena depended upon thermal condition. Thermal aging under engine room temperature and fluctuating mechanical loading by vehicle dynamic motion have affected the fatigue life of engine mount.<br/> The experimental works were carried out to evaluate the effects of thermal and mechanical loadings on the fatigue lives of rubber engine mounts. The basic mechanical properties test and the fatigue test of aged rubber specimen under normal and elevated temperature were executed. The several load-life curves considering aging conditions and test temperature were obtained. The procedure to unify these curves to one curve was proposed. Also, the equation of the unified load-life curve was induced. This curve was in good agreement with fatigue test data less than 200% error range.
압전 구동기를 이용한 인코넬 690 튜브의 프레팅 마멸시험
정일섭(Ilsup Chung),이명호(Myungho Lee),박기홍(Kihong Park),이정훈(Junghoon Lee),권재도(Jaedo Kwon) Korean Society for Precision Engineering 2009 한국정밀공학회지 Vol.26 No.2
A fretting wear test rig for dry ambient condition, which employs a piezoelectric actuator, has been developed. It is driven and loaded in a very simple manner with acceptable experimental accuracy By using the rig, Inconel 690 tube has been tested under the normal load of 10 and 15N with sliding amplitude of less than 100j..lm during 106cycles. The wear resistance of the material has been characterized in terms of the wear coefficient based on the work rate model. SEM micrographs show the complex structures of the scars, which consist of risen peaks, plate-type thin layers and locally exposed bare surfaces. The cracks spread over the layers give clue to the fretting wear mechanism of the material.