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[論文] 고강도 알미늄 합금재에 있어서 크랙열림점 평가에 관한 연구(I)
최병기(B. K. Choi) 한국자동차공학회 1993 오토저널 Vol.15 No.1
This paper aims to synthesize the research on fatigue fracture mechanisms of high strength aluminum alloys which are widely used in motorcars or airplanes to prevent accidents.<br/> To measure the data of crack opening ratio, the same materials and methods are used for evaluating the fatigue crack propagation rate as an effective stress intensity factor. But, many researchers have brought different results.<br/> An exact crack opening ratio was, therefore, proposed for getting a more accurate fatigue crack propa gation rate.<br/> The main. conclusions obtained are as follows.<br/> (1) As a result of the fatigue test, the value of the crack opening ratio is the same regardless of the stress ratio.<br/> (2) The value of crack opening ratio is different according to the measuring point.<br/> After measuring the crack propagation rate by using an effective stress intensity factor, the crack opening ratio value measured at the crack mouth by a clip gage, or measured rear of the specimen by a strain gage is more accurate than that by any other measuring test.
장경천(K.C. Jang),국중민(J.M. Kuk),최병희(B.H. Choi),정재강(J.K. Chung),최병기(B.K. Choi) 한국생산제조학회 2004 한국생산제조시스템학회 학술발표대회 논문집 Vol.2004 No.4
Effects of Nb(Niobium) contents and solution annealing on the strength and fatigue life of 18%Ni maraging steel commonly using in aircraft, space field, nuclear energy, and vehicle etc. were investigated. Also the fatigue life stress intensity factor were compared experiment result and FEA(finite element analysis) result. The more Nb content, the higher or the lower fatigue life on base metal specimens or solution annealed specimens showing that the fatigue life was almost the same. The maximum stresses of X, Y, and Z axis direction showed about 2.12×10²㎫, 4.40×10²㎫ and 1.32×10²㎫ respectively. The Y direction stress showed the highest because of the same direction as the loading direction. The fatigue lives showed about 7% lower FEA result than experiment result showing almost invariable error every analyzed cycle. Stress intensity factor of the FEA result was lower about 3.5~10% than that of the experiment result showing that the longer fatigue crack length, the higher error. It considered that the cause for the difference was the modeled crack tip having always the same shape and condition regardless of the crack growth.
C200 마르에이징강의 기계적성질에 미치는 Nb 첨가량 및 시효처리의 영향
장경천(K.C. Jang),최병희(B.H. Choi),최병기(B.K. Choi) 한국생산제조학회 2005 한국생산제조시스템학회 학술발표대회 논문집 Vol.2005 No.10
Objective of this study was effects of Nb(Niobium) contents and age hardening conditions on the strength of C200 maraging steel which are commonly using in aircraft, space field, nuclear energy, and vehicle etc. To investigate the effects, steel was manufactured by a VIM (Capacity: 30㎏f, Max Temp. : 1650℃, 10?³? Torr, 45 min/charge) added 0%, 0.03%, and 0.06% niobium with basic chemical compositions. And the steel was hot rolled automatically, solution annealed at 815℃ for I hour, and age hardened with 48%KNO₃+52NaNO₃ at 455℃, 482℃, and 510℃ for 1,2,4, and 8 hours each other. The most excellent condition for elongation was 0.03% Nb material aged at 455℃ for 1 hour having about 97% of base metal. The most excellent aging condition was 8 hours aged at 482℃ with 0.06% Nb content showing that the strength of the specimen increased twice more than that of the base metal.
C200 마르에이징강의 기계적성질에 미치는 Nb 첨가량 및 시효처리의 영향
장경천(K.C. Jang),최병희(B.H. Choi),최병기(B.K. Choi) 한국생산제조학회 2005 한국공작기계학회 추계학술대회논문집 Vol.2005 No.-
Objective of this study was effects of Nb(Niobium) contents and age hardening conditions on the strength of C200 maraging steel which are commonly using in aircraft, space field, nuclear energy, and vehicle etc. To investigate the effects, steel was manufactured by a VIM (Capacity: 30㎏f, Max Temp. : 1650℃, 10?³? Torr, 45 min/charge) added 0%, 0.03%, and 0.06% niobium with basic chemical compositions. And the steel was hot rolled automatically, solution annealed at 815℃ for I hour, and age hardened with 48%KNO₃+52NaNO₃ at 455℃, 482℃, and 510℃ for 1,2,4, and 8 hours each other. The most excellent condition for elongation was 0.03% Nb material aged at 455℃ for 1 hour having about 97% of base metal. The most excellent aging condition was 8 hours aged at 482℃ with 0.06% Nb content showing that the strength of the specimen increased twice more than that of the base metal.
다품종 슬리브 양산을 위한 복합금형 제작기술개발에 관한 연구
장경천(K.C. Jang),이동길(D.G. Lee),김기풍(K.P. Kim),정민관(M.G. Jung),최병기(B.K. Choi) 한국생산제조학회 2007 한국생산제조시스템학회 학술발표대회 논문집 Vol.2007 No.10
The objective of this paper is to study the suitability of design and capability analysis for the multi-type CIM(Ceramic Injection Molding) that can mass-produce three-type sleeves using in a mold by conduct the experiments as well as the flow analysis. 11 minutes and 40 seconds that was about 29% of general exchange way was required to exchange 8-cavity cores and center pins on the average, and the accuracy dispersion was only ±6㎛. Therefore the mold design and manufacturing was very excellent for multi-type sleeve produce in large quantities. Yield that is more than gravity 6.0 that establish by target as result that analyze gravity of products at investigated injection conditions was each 97.88%, 92.65%, 90.32% from 8SC-OLC-OSC/LC, 6SC-ILC-ISC/LC and 4SC-2LC-2SC/LC cavity combination. The measured results of the SC, LC, and SC/LC sleeve products showed 5.46㎛, 11.41㎛, and 13.05㎛ on concentricity and 3.43㎛, 6.74㎛, and 4.16㎛ on roundness respectively.
200 Grade 마르에이징강의 기계적성질 향상을 위한 연구
장경천(K.C. Jang),국중민(J.M. Kuk),이동길(D.G. Lee),최병기(B.K. Choi) 한국생산제조학회 2004 한국생산제조시스템학회 학술발표대회 논문집 Vol.2004 No.10
Hardness value decreased about 3% for annealed specimens and increased about 60% for one hour aged specimens. But the values of the other specimens aged two hours or more showed almost the sane. The yield strength was the highest about 1,800㎫ in 0.06%Nb specimen having twice as much as the base metal specimen. Also, the elongation was the highest in 0.03%Nb specimen showing the same as base metal specimen. The higher aging temperature and the longer aging titre, the higher fatigue life. On the other hand, the 0.03%Nb specimen showed the highest fatigue life which increased about 12% more than base metal specimen. 0.06% Nb specimen aged at 482℃ for 8 hours simultaneously satisfied the 250 grade strength and an grade elongation having the most superior mechanical properties.
Ni-Co 합금강의 기계적 특성에 대한 탄소함량의 영향
장경천(K.C. Jang),국중민(J.M. Kuk),정장만(J.M. Jung),권택용(T.Y. Kwon),최병기(B.K. Choi) 한국생산제조학회 2004 한국생산제조시스템학회 학술발표대회 논문집 Vol.2004 No.4
This study was to evaluate the effect of carbon content on metallic change and fatigue characteristics with Fe-29%Ni-17%Co, low heat expansion alloy, widely using electronic components, precision machines, and sealing with glass and metal etc. The steels were fabricated with variation of carbon content, 0, 0.03, 0.06, 0.1, and 0.20% with VIM and tensile test and fatigue test were performed to achieve the above purpose. The more carbon content, the higher hardness value and yield strength. But elongation of 0.03%C, 0.06%C, and 0.10%C specimen decreased about 2.2%, 1.5% and 0.8% respectively more than that of the base metal. Especially the strength and elongation of 0.20%C specimen increased simultaneously about 14.4% and 7.5%. Fatigue life of 0.03%C specimen decreased but the more carbon content, the higher fatigue life over 0.06% carbon content more than that of base metal.