평가 방법에 따른 피로균열 성장속도에 관한 연구

국중민(Jung-min Kuk),권택용(Tack-yong Kwon),최병기(Byung-ki Choi) 한국생산제조학회 1998 한국공작기계학회 춘계학술대회논문집 Vol.1998 No.-

Al 2024-T3재의 Crack Opening Point의 평가에 관한 연구

최병기(Byung-Ki Choi),국중민(Jung-Min Kuk) 한국생산제조학회 2002 한국공작기계학회 춘계학술대회논문집 Vol.2002 No.4

유동 및 응고 시뮬레이션을 활용한 회전자 패밀리 금형의 오버플로우 설계 방안

정재민 ( J M Jung ),김창완 ( C W Kim ),( Tam Nguyen Van ),이경민 ( K M Lee ),국중민 ( J M Kuk ),진현기 ( H G Jin ),홍성길 ( S K Hong ) 한국주조공학회 2013 한국주조공학회지 Vol.33 No.5

The family mold casting have advantages which are able to make products with different shapes and dimensions simultaneously in a single mold. In this study, the design of the 4 cavity rotor family mold was used by “Anycasting” software, the defects occurred during die casting were predicted and suggested the best optimization conditions for sound products. The result of the experiment were that the optimum overflow design was needed for gas emission and control of residual oxides. It was clear that the defects positions formed by diecasting were agreed with nearly them predicted by simulation.

표면활성화법에 의한 이종재료의 저온접합에 관한 연구

국중민,임언택,권택용,최병기 朝鮮大學校 機械技術硏究所 1998 機械技術硏究 Vol.1 No.1

본 논문은 서로 다른 재료를 표면활성화법을 이용하여 저온에서 접합할 목적으로 이들 재료의 접합 가능성을 검토하고 이들 접합계면에서의 접합 메카니즘을 검토할 목적으로 연구하였으며 연구 결과는 다음과 같다. 1) 10-7 Torr대의 진공도에서도 알루미늄은 알루미나, 질화 알루미늄, 질화규소, 지르코늄 등의 세라믹스와 양호한 접합이 가능하였다. 2) 알루미늄, 동, 은은 같은 금속끼리의 접합이 가능하고, 또 알루미늄과 동의 이종재료의 접합도 가능하였다. 3) 실리콘은 알루미늄, 동, 은, 금 등의 실험결과 모든 금속과 접합이 가능하였다. In this paper considered it possible to bone different materials in low temperature using surface activated method. To do so, It was examined the possibility of bonding different materials and applied the bonding mechanism on the bonding surface. The followings are the result. 1) It was possible that Aluminum could be bonded well with ceramics such as alumina, nitrification aluminum, nitrification silicon, and zirconium at the vaccum level of 10-7 Torr. 2) It was possible that aluminum, copper, and copper could be bonded with each other and aluminum and copper could be bonded with other metals. 3) Silicon was bonded with aluminum copper silver, and gold which were tested before.

18Ni 마르에이징강의 피로특성 및 유한요소해석

장경천,국중민,최병희,정재강,최병기 한국공작기계학회 2004 한국공작기계학회 춘계학술대회논문집 Vol.2004 No.-

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 2.12×10²MPa, 4.40×10²MPa and 1.32x10²MPa 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.

200 Grade 마르에이징강의 기계적성질 향상을 위한 연구

장경천,국중민,이동길,최병기 한국공작기계학회 2004 한국공작기계학회 추계학술대회논문집 Vol.2004 No.-

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 1,800MPa 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 time, 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 200 grade elongation having the most superior mechanical properties.

Al 2024-T3재의 Crack Opening Point의 평가에 관한 연구

최병기,국중민 한국공작기계학회 2002 한국공작기계학회 춘계학술대회논문집 Vol.2002 No.-

This paper aims to synthesize the research on fatigue mechanisms of high strength aluminum alloys which are widely used in motorcars or airplanes to prevent accidents. 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. An exact crack opening ratio was, therefore, proposed for getting a more accurate fatigue crack propagation rate.

순수티타늄 용접재의 피로크랙 진전거동에 관한 연구

최병기,국중민,장경천,권택용 朝鮮大學校 機械技術硏究所 2001 機械技術硏究 Vol.4 No.1

본 연구에서는 원자력 발전소의 터빈장치에 사용되는 순수티타늄 용접재의 피로수명과 크랙성장속도 등을 열영향부, 용접부 그리고 모재부를 각각 비교하기 위하여 시험편을 크게 용접된 4개의 시험편(Specimen1∼4 ; 초기노치에서 2∼3mm 떨어진 부분이 각각 H.A.Z, 본드부, 용접부, 모재부 등에 위치함)과 모재 시험편으로 나누어 피로시험을 수행한 결과 다음과 같은 결론을 얻을 수 있었다. 1) 순수티타늄 용접재 중 Specimen-2가 모재 시험편에 비해 피로수명이 약 700%로 가장 크게 나타났다. 2) 초기 크랙이 1mm로 성장하는데 걸리는 평균 크랙진전속도를 조사한 결과 Specimen-2가 모재에 비하여 약 30배로 가장 낮은 크랙진전속도를 나타내고 있었으며, 초기 크랙진전속도가 최종 파단 수명에 매우 큰 영향을 미치고 있음을 알 수 있었다. 3) 시험편 중 피로수명이 가장 큰 Specimen-2 시험편은 노치 선단으로부터 H.A.Z까지 거리가 약 6.7mm로 전체 파단길이의 약 25%를 차지하고 있었다. 4) da/dN과 ΔK를 고찰한 결과 용접으로 인해 생긴 두 개의 기울기로 인하여 Paris 법칙에 적용하기에는 부적당함을 알 수 있었다. In this study, Specimens were classified four welded specimens and a base metal to investigate fatigue life and crack growth rate of pure titanium welding materials, and Ti was used in turbine equipment of nuclear power generation, etc. The summarized results are as follows ; 1) Specimen-2 was bigger 712% than base metal, when it was compared with other welding materials. 2) As the result of specimens data. Specimen-2 crack Behavior rate was lower 30 times than base metal, and so total fracture life was very influenced by it 3) Notch tip of Specimen-2 was offsetted 6.7mm from boundary H.A.Z, and it formed 25% in total fracture length. 4) As the considering of da/dN and ΔK, Paris' law is incongruous in this study, because two inclines were on one date.

Ni-Co 합금강의 기계적 특성에 대한 탄소함량의 영향

장경천,국중민,정장만,권택용,최병기 한국공작기계학회 2004 한국공작기계학회 춘계학술대회논문집 Vol.2004 No.-

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.

순수티타늄 용접재의 피로수명 예측에 관한 연구

최병기,국중민,장경천 朝鮮大學校 機械技術硏究所 2001 機械技術硏究 Vol.4 No.1

본 연구에서는 순수티타늄를 TIG용접하여 모재와 용접재의 피로시험을 수행하여 피로크랙 진전거동을 고찰하고, Nisitani가 제안한 역학적 변수에 의해 재료상수를 구한 후 그 적용성을 검토해 보았으며 얻어진 결과는 다음과 같다. 1. 동일한 하중비 조건에서 피로수명은 모재에 비해 Specimen-A, B, C는 각각 약 481%, 751%, 562% 크게 조사되었다. 2. 동일한 조건의 시험편에서 피로수명은 하중비 0.01에 비해 0.1과 0.2는 평균적으로 129%, 180% 크게 나타났다. 3. 모재 시험편를 제외한 용접재 시험편에서 피로크랙이 3mm 진전되는데 소모된 반복수는 전체피로수명의 약 90%를 차지하였으며, 이후에는 급속파단이 일어났다. 4. 본 재료에 실험으로부터 얻어진 재료상수를 이용하여 Nisitani의 피로크랙 전파속도 예측식에 적용하여 피로수명을 예측한 결과 노치의 위치 및 하중비에 관계없이 약 5% 내외의 낮은 오차를 보이며 잘 일치함을 알 수 있었다. In this study, the fatigue test was carried out with pure titanium and TIG welded material using in chemical plants and airplane frames etc.. The fatigue the propagation behavior and the fatigue life were investigated at 190% (400 kgf) of fatigue limit of base metal. Then, we compared and reviewed the result of experimented values and predicted values with the fatigue crack propagation equation reported by Nisitani in the present study. The summarized results are as follows; 1. The fatigue life of specimen B was showed to be about 751% longer than that of the base material at same load ratio. 2. The average fatigue lives at R=0.1 and 0.2 were respectably showed to be about 129% and 180% longer than that at R=0.01 at the same condition. 3. The fatigue life of the welded specimen was consumed about 90% of the whole fatigue life to grow 3mm fatigue crack length and then, the rupture was occurred rapidly. 4. The fatigue lives were predicted with the formula of the fatigue crack propagation, da/dN = C_2a^p_2, and compared with the experimented results, the results were shown good and in agreement within 5.0% error regardless of the notch position.