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

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.

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.

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.

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.

殘留應力을 考慮한 鎔接材의 疲勞龜裂 進展擧動에 關한 硏究

최병기,이을호,국중민,기준호,임선빈,정장만 朝鮮大學校 機械技術硏究所 2000 機械技術硏究 Vol.3 No.1

The effect of welding residual stress on the initiation and propagation of fatigue crack is investigated so as to study the fatigue behavior in welding residual stress field. Especially, the relation between welding residual stress and fatigue crack opening behavior is investigated and the redistribution of residual stress as a fatigue crack propagates is examined. Following results are obtained. 1) In case of the load range is constant, as the stress ratio is changing to 0.1, 0.33, 0.5 the propagation life is constant but the growth life decreases. And than, when maximum load or minimum load is constant, as the stress ratio increases the growth life and propagation life increase. 2) The fatigue crack propagations rate da/dN appears to accelerate when the stress intensity factor range ΔK is less than 15MPa-m^1/2. 3) The residual stress that is appeared by welding decreases after cutting. 4) Fatigue crack propagation ratio is affected by tensional and compressible residual stress at the initial time, but it's similar to the original in the more than 20mm of crack length.

Ti 鎔接材의 機械的 特性 및 殘留應力의 分布에 關한 硏究

최병기,장경천,국중민,정장만,구남열 한국산업안전학회 2003 한국안전학회지 Vol.18 No.1

The objective of this paper was to investigate the welding characteristics according to the restraint condition, the pass number, and the shield gas quantity with titanium commonly using in power stations, aircrafts, ships, and so forth. The residual stress distribution was measured under restraint and nonrestraint welding conditions. The tensile strength and elongation of the 4 pass welded specimen were shown higher about 10% and 30% than those of the 7 pass welded specimen at the same welding conditions respectably. Also, the more shield gas quantity and the shorter natural cooling time, the higher tensile strength and the lower elongation.

티타늄 용접재의 피로크랙 성장거동에 관한 연구

최병기,국중민 한국산업안전학회 2000 한국안전학회지 Vol.16 No.3

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 6.7 ㎜ 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.