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하중작용각도와 균열닫힘수준에 따른 피로균열성장 특성 변화
서기정(Kijeong Seo),송삼홍(Samhong Song),이정무(Jeongmoo Lee) 한국자동차공학회 2005 한국자동차공학회 춘 추계 학술대회 논문집 Vol.2005 No.5_2
Crack tip displacement behavior depends on combined types of different two stress components under mixed-mode loading conditions (MMLC). Crack closure level(CCL) is estimated with crack tip displacement behavior. The crack closure level is calculated from the information of crack tip displacement under MMLC. This information has been obtained from the high resolution optical microscope in direct observations of crack displacement behavior at the crack tip. Observed crack tip displacement is analyzed by using CTD vector to determine crack opening load. The various effects of MMLC on the crack closure are explained using crack opening ratio with crack length and mode mixture. The effective stress intensity factor considering crack closure is also discussed.
피로파면의 기하학적 형상을 바탕으로 한 응력진폭 변화와 혼합모드 하중관계에 관한 연구
서기정(Kijeong Seo),송삼홍(Samhong Song),이정무(Jeongmoo Lee) 한국자동차공학회 2004 한국자동차공학회 춘 추계 학술대회 논문집 Vol.- No.-
Most cracks in the structure occur under mixed mode loading and those fatigue crack propagation behavior depends on the stress ratio. Hence. it is necessary to study the fatigue behavior under mixed-mode loading as the stress ratio changes. In this paper, the fatigue crack behavior was respectively investigated at stress ratio 0.33, 0.50 and we changed the loading application angle into 0°, 30°, 45°, 60° to apply various loading mode. These experimental results were evaluated by the shape of fatigue fracture surface using 2D or 3D images obtained from the C-scan method. As stress ratio and mode mixity change, the change of effective stress intensity factor and crack closure have effect on the fatigue behavior of cracks. The variation of fatigue crack behavior caused by the change of stress ratio and loading application angle could be explained by using the shape of fatigue fracture surface.
직접측정법과 벡터 CTD해석을 통한 샤시 프레임용 강재의 하중작용각도 변화에 따른 피로균열 전파거동
서기정(Kijeong Seo),송삼홍(Samhong Song) 한국자동차공학회 2004 한국자동차공학회 춘 추계 학술대회 논문집 Vol.- No.-
Occuring on fatigue crack surface crack closure effect is a major cause of crack growth rate decreasing. For fatigue crack propagations, especially under mixed-mode loading one is closely difficult to estimate without crack closure effect. Single mode acting only tensile loading component and mixed-mode acting tensile loading component at the same time shear loading component must be analyzed differently the crack closure effect. To measurement crack opening displacement by tensile loading component and crack sliding by shear loading component under mixed-mode loading we used the direct measuring method. Data through direct measuring method was studied using the vector crack tip displacement method. In result, we can correct Paris's equation considering crack closure effect under mixed-mode loading.
모드 Ⅰ 및 혼합모드 Ⅰ/Ⅱ 의 파단면에 대한 프랙토그래피의 정량화
서기정(Kijeong Seo),이정무(Jeongmoo Lee) 대한기계학회 2005 대한기계학회 춘추학술대회 Vol.2005 No.11
Fracture surface roughness and asperity in fatigue crack propagation vary with changes in various loading parameters. Especially loading modes in the parameters have influence on crack driving force. As we know, if under Mixed-mode Ⅰ/Ⅱ, the crack driving force become decreasing more than under Mode Ⅰ, resulting in fracture surface roughness are improved. The aspects of the fracture surface roughness and asperity result from loading modes have been mostly confirmed or defined by SEM farctography. In this study fracture surfaces under Mode Ⅰ and Mixed-mode Ⅰ/Ⅱ observed using the C-scan and calculated contour area roughness parameter. We know conveniently that the aspects of the fracture surface with loading modes as a result of this.
혼합모드 하중 하에서의 균열성장 중 피로파단면 마찰과 균열닫힘효과의 상호관계
서기정(Kijeong Seo),송삼홍(Samhong Song),이정무(Jeongmoo Lee) 대한기계학회 2004 대한기계학회 춘추학술대회 Vol.2004 No.11
Crack tip behavior of single mode loading condition(mode I)depend on tensile loading component but one of mixed mode loading condition(mode I+II) have influenced on shear loading component like the practical structure. Because crack closure is caused by shear loading component under mixed-mode loading a research on the behavior in the stage of crack initiation and propagation require to be evaluate about crack closure effect by fatigue crack surface friction. For that reasion we examined the behavior at the crack tip by direct measuring method. Measured behavior at the crack tip was analyzed through vector crack tip displacement. As a result, crack propafation equation was corrected by considering with crack closure effect. In addition we compared fatigue fracture crack surface and crack closure level.
서기정(Kijeong Seo),한승우(Seungwoo Han),김완두(Wandoo Kim),이학주(Hakjoo Lee),이현우(Hyunwoo Lee),신재호(Jaeho Shin),이재준(Jaejoon Lee) 대한기계학회 2006 대한기계학회 춘추학술대회 Vol.2006 No.6
The mechanical properties and the fatigue-life behavior of two layers thin copper foils onto elastic polyimide substrates were characterized for two different products, namely a rolled copper foil (18 ㎛ thick Cu/25 ㎛ thick PI) and a electrodeposited (ED) copper foil (12 ㎛ thick Cu/20 ㎛ thick PI). The results indicated that the ultimate tensile strength σ<SUB>u</SUB> and the life cycles to failure N<SUB>f</SUB>, under both monotonic tensile and tensile-tensile high cycle fatigue conditions, are lower for the rolled foil than for the ED foil.