이종마찰압접재 계면의 기계·금속조직학적 거동 및 파면특성 : STS304와 SM15C재를 중심으로 For STS304 and SM15C

오환섭,박경식,박준건,오정국,백영남 慶熙大學校 材料科學技術硏究所 1998 材料科學技術硏究論集 Vol.11 No.-

In this study is behavior of crack propagation and fracture under static tensile load, shear load, rotary bending fatigue load in friction welded dissimilar materials. Crack was observed in fine ferrite zone of SM15C and heat affected zone of STS304. Plastic flow was occured by friction welding process, so direction of crack is inclined with welded surface. Fatigue fracture most occurred in SM15C heat affected zone around interface. Fibrous zone with the view of macroscope and dimple pattern with the view of microscope were observed at fracture surface. Result is more metal micrstructure dependence than stress dependence by mechanical and metallic mechanics.

中空丸奉材의 疲擧크랙擧動에 關한 硏究

吳煥燮 慶熙大學校 1980 論文集 Vol.10 No.-

The characteristic of the crack propagation behavior, crack growth rates and stress intensity factor under the rotary bending fatigue test have been studied. The equation dealing with fatigue crack propagation velocity and stress intensity factor based on this study has been confirmed in the test of cylindrical shell specimens having small-scale hole notch. In this study, the effects of stress gradient along with the bending by limitation of specimen to 1mm in thickness are not easily distinguishable to confirm the stress intensity factor and fatigue crack growth rates of specimen surfaces. Also, cylindrical one is just the same as in case of the round plane shaped by formming itself, so on the endless plane, the effect of cylindrical carvature and hole about the correction factor are considered respectively. Therefore, the equation of stress intensity factor is determined by K=k_1k_2σ√πℓ The stress intensity factor K concerned with dl/dN has been plotted in log-log diagrams, and here material constant C is obtained after order m is calculated.

表面微小缺陷을 갖는 低炭素鋼材의 疲勞限度擧動

吳煥燮 慶熙大學校 1986 論文集 Vol.15 No.-

Low-carbon steel was chosen as the material for this experiment since it has clear fatigue limit as well as the reason that the defect in the structure of the material does'nt effect to the fatigue fracture. This study has been made to investigate into the behavior of fatigue limit, of fatigue crack initiation, and of fatigue crack propagation under the condition ol rotating bending stress; specifically on the independency of stress-field as well as the crack behavior of surface micro-hole defect(MHD), which it made artificially the specimen. The results obtained can be summarized as follow; Fatigue limit of specimen with MHD is defined as a critical stress which is needed for repropagation of the crack around MHD. The behavior of non-propagating crack which is positioned around the MHD is found to be double of the size of MHD. The effect of MHD with regard to the fatigue limit and size of critical defect(dc) are depended on hardness and ferrite grain size.

압력용기의 설계기준 및 손상 평가

오환섭,정효진,박상필,손두익 한국공작기계학회 2005 한국공작기계학회 춘계학술대회논문집 Vol.2005 No.-

The damage of the pressure courage by degradation can become the reason of unexpected break down or failure accident and it is very important because safety accident, the production loss, environmental pollution, social problems are occur. Consequently The result to investigat of failure accident for domestic pressure vessel, the factor of degradation is SCC, Sorrosion, Cavity, Crack

이종접합재 접합 계면근방 균열의 응력 및 파괴특성

오정국,차용훈,오환섭,박준건,박경식 朝鮮大學校 機械技術硏究所 1998 機械技術硏究 Vol.1 No.1

현재까지 이종마찰압접재의 강도측정은 실험 (7)-(15)에 의해 구해져 왔다. 하지만 최근 이종마찰압접재의 효율성을 인정하여 여러 실용 부품에 응용하려는 연구가 한창 진행중이다. 이종마찰압접재에 대한 저자들(1)-(6)의 기초실험결과 일반적인 단종재와는 상이한 파괴거동(3)이 관찰되었고, 파괴역학적인 관점에서 정성적인 data 확보가 필요하게 되었다. 따라서 본 연구에서는 인장시험시 이종마찰압접재의 접합강도와 미소균열들에 의한 파괴거동을 파괴역학적 관점에서 해석적으로 고찰하여 보고자 경계요소법(BEM ; Boundary Element Method)을 이용하여 접합계면을 포함하는 접합부를 중심으로 계면상의 응력분포와 계면의 중앙에 결함이 균열로써 존재하는 경우의 응력분포와 인장시험시 열영향부에서 관찰된 균열의 모델링을 통한 균열선단에서의 응력해석을 행하였고, 그 결과 얻어진 중요한 내용을 요약하면 다음과 같다. 계면의 중앙에 균열이 존재하는 접합계면의 표면부에서 응력의 특이성이 발생하며 탄성계수의 비가 증가할수록 특이성이 증가함이 관찰되었다. 탄성계수의 비가 일정한 경우 균열의 크기가 변화하여도 계면의 표면부에서 발생하는 특이성은 거의 같은 값을 갖게 되며, 탄성계수의 비가 증가할수록 표면부의 응력 특이성의 크기는 증가한다. 이종마찰압접재의 인장시험시 관찰된 균열을 모델링 하여 해석한 결과 최대 응력 기준으로 살펴볼 때 인접한 균열선단에서의 응력분포는 균열을 합체시키는 방향으로 작용함을 알 수 있다. In this study stress distribution on the interface and stress near tip of the sub-interface crack in the dissimilar friction welded material is analyzed by using of BEM( Boundary Element Method). Stress singularity near surface of model to analyze is observed for various crack length and ratio of elastic modulus. Tensile and shear stress distribution near two neithbor sub-interface crack tips are analyzed. Existance of singularity near surface on the interface is particular situation so that we need to investigate for dissimilar friction welded materials by means of numerical analysis method.

이종마찰압접재의 변형 및 균열 성장 거동 : STS304 와 SM15C재를 중심으로 For STS304 and SM15C

오정국,오환섭,박준건 조선대학교 동력자원연구소 1997 動力資源硏究所誌 Vol.19 No.1

In this study, behavior of crack growth and fracture under static tensile load in friction welded dissimilar materials, and necking phenomenon occuring at tensile yeilding point is shown. Crack is observed in heat affected zone including fine ferrite region of SM15C and heat affected zone of STS304. Plastic flow was occured by friction welding process, so direction of crack is inclined with welded surface. Fracture behavior of similar material is subject to joint of void, but dissimilar material is liable to joint of micro crack. Fibrous zone with the view of macroscope and dimple pattern with the view of microscope is observed at fracture surface.

疲勞크랙의 發生 및 傳播擧動에 對하여 : 素面크랙을 中心으로 Through Surface Crack

吳煥燮 慶熙大學校 1982 論文集 Vol.11 No.-

In recent days, there are many reports about fatigue crack behavior mostly connected with reciprocal relations combined crack propagation velocity and stress intensity factor. And applications of fracture mechanics of macro crack have been generalized, but analysis of the mechanics of micro crack which are contained in steel structures have very some important problems as follows; in case that fatigue cracks would be initiate and propagate in the region of interstitial compound and micro notch, the fatigue crack progress symmetry and the fatigue crack growth propagation velocity round the compound under same repeated stress cycle each other. In this paper, a rotary bending fatigue test was done with micro hole notched specimen of rolled low carbon steel, and then the crack initiation behavior on the crack tip, propagation behavior of front and rear of the crack and latency phenomenon during the crack propagation process, is present.

人工缺陷을 갖는 炭素鋼材의 微小疲勞크랙擧動

吳煥燮 慶熙大學校 材料科學技術硏究所 1989 材料科學技術硏究論集 Vol.2 No.-

This study has been made to investigate into the behavior of fatigue crack propagation under the condition of rotating bending stress. The results obtained can be summarized as follow; In the case of single surface defect, fatigue crack produce semi-elliptical crack contour which has the ratio of crack length in the radial direction to the half crack length on the surface at 0.85 in the neighbored double surface defect, the behavior of fatigue crack propagation has the effect of delay as well as the interference effect. In the view of small crack propagation rate (da/dN), the size of single surface defect depends upon stress intensity factor (k)

이종재 브레이징 계면에서의 균열거동 해석

오환섭,김시현,김성재,양인수 한국공작기계학회 2002 한국생산제조학회지 Vol.11 No.6

Applications of brazing in the studying fields such as high-speed machining are very increasing in various industry fields. Therefore, applying to the fracture mechanics by numerical analysis method is very important to analyse the crack problem dissimilar materials in brazed interface. In this study, stress intensity factor(SIF) is analysed to investigate crack behavior on the crack tip of dissimilar materials in brazed interface such as a hardmetal and a HSS by two dimensional(2-D) BEM. Kelvin's solution was used as a fundamental solution in BEM analysis and stress extrapolation method was used to determine SIF.

BEM을 이용한 크랙전파 해석 및 수명예측에 관한연구

吳煥燮,結城良治 慶熙大學校 材料科學技術硏究所 1992 材料科學技術硏究論集 Vol.5 No.-

Stress analysis of surface crack tips becomes very important in the recent development of leak-before-break(LBB) concepts. In this study the stress intensity falter k analyzed by considering the fatigue fracfure process which is characterized by interface coalesence and growth. Criteion parameters derived from the stress intensity factor obtained from the boundary element method(BEM) are used to predict the fatigue life. We develop the surface crack growth analysis system using the stress intensity factor data base and also fatigue crack growth law. The results are obtained as some kind of fatigues.