• 대한기계학회논문집
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• 제13권5호
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• pp.938-946
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• 1989

본 연구에서는 CT시험편을 이용하여 소규모 항복조건하에서 하한계(near threshold)영역과 안전균열성장(제II)영역의 균열진전거동을 파악하고 피로균열 진전속도와 음향방출거동, 파단면 특성을 각각 비교, 고찰하여 각 파라미터간의 상관 관계 및 유용성을 검토하고자 한다.

• 한국해양공학회지
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• 제2권2호
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• pp.61-70
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• 1988

In order to consider the concept of the fitness for purpose'in fatigue design of offshore structure, fracture mechanics is applied to evaluate initial or weld defects. Generally, linear elastic fracture mechanics has been applied to tstimate initial fatigue crack propagation rate as well as long fatigue crack propagation rate. But, initial fatigue crack propagation rate in elasto-plastic notch field may not be characterized by application of stress intensity factor range .DELTA. K, because plastic effect due to stress concentration of notch may contribute to initial crack propagation. Therefore, to introduce the plastic effect into fatigue crack driving force, in this studty, the evaluating method of J-integral range .DELTA. J, was developed by willson was modified for application to notch field. In calculation of .DELTA. J obtained from the modified J-integral, stress gradient and crack closure behavior in the notch field were considered. The initial crack propagation rates in the notch fields of mild steels and high tensile strength steels were correlated to .DELTA. J. As the result, it was cleared that the present .DELTA. J is applicable to charachterize the fatigue crack propagation rates in both the elastic and elasto-plastic notch fields.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2003년도 춘계학술대회
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• pp.137-142
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• 2003

In this study, the propagation behavior of fatigue crack effected hole defects was investigated under mixed-mode I+II loading. To create mixed-mode stress field at crack tip, the compact tension shear (CTS) specimen and loading device were used in this tests. The propagation experiments of fatigue crack were performed by changing of the loading application angle(${\phi}$) and the distance(L) estimated from pre-crack tip to hole center located side by side by side with a pre-crack. As L changes, the variation for propagation aspect of fatigue crack, fatigue life and crack propagation rate were examined under mixed-mode loading. Under mixed-mode loading, the propagation rate of fatigue crack increased while the propagation direction changed dramatically because of the interference of hole defects.

• 한국생산제조학회지
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• 제9권6호
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• pp.82-88
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• 2000

The effect of the welding for the offshore structure in the TMCP steel on the fatigue crack propagation rate and crack opening-and-closure behavior was examined. The welding anisotropy of the TMCP steel and crack propagation characteristics of the excessive loading were reviewed. (1) It seemed that a heat which was generated by the welding made a compressive residual stress over the base metal, so fatigue crack propagation rate was placed lower than in case of the base metal. (20 In the base metal, an effect of the anisotropy which has an effect of fatigue crack propagation rate of the excessive load and the constant amplitude laos was not found but in the welding material case, fatigue crack propagation rate of the excessive load in the specimen of the width direction was located in the retard side as compared with a specimen rolling direction. (3) A crack opening ratio of the used TMCP stel in this study was not changed after excessive loading but a retard phenomenon of crack propagation was observed. Consequently, it was thought that all of the retard phenomenon of crack propagation did not only a cause of the crack opening-and-closure phenomenon.

• 한국안전학회지
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• 제12권2호
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• pp.57-64
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• 1997

Fatigue crack propagation behaviors and life prediction for SUS 321 plate and its electron beam weld metal were investigated using compact tension specimens. The larger the stress ratio is, the faster the crack propagates, but the variation of crack propagation rate decreases. The effect of stress ratio is greater in the slow crack propagation area than in the faster one. The crack propagation rate of electron beam weld metal is faster than that of base metal because of hardening, weld defect and residual stress in welding area. The crack propagation rate of transverse weld metal has a lower than that of base metal due to the effect of residual stress, but in the time of passing through welding area, has a higher rate. The crack propagation rate using $\Delta$K$_{eff}$ can be well plotted regardless of stress ratio. The fatigue life prediction method of considering crack closure more exactly predicts fatigue life than conventional one. conventional one.e.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 1997년도 추계학술대회 논문집
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• pp.759-764
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• 1997

In this study, Fatigue behavior of laser weldment in heterogeneous materials was investigated. Fatigue strength test and fatigue crack propagation test were performed for specimens with laser weldment in heterogeneous materials, and hardness test was performed. From the fatigue strength test. it was observed that the difference of strength between heterogeneous materials had eflect on crack initiation position and fatigue limit. From the fatigue crack propagation test. it was observed that fatigue behavior of laser weldment in heterogeneous materials is different from that in same materials. The difference of strength between heterogeneous materials and laser weldment had effect on fatigue crack propagation rate.

• 한국정밀공학회지
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• 제18권9호
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• pp.131-139
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• 2001

The use of fracture mechanics has traditionally concentrated on crack growth under an opening mechanism. However, many service failure occur from cracks subjected to mixed mode loadings. Hence, it is necessary to evaluate the fatigue behavior under mixed mode loading. Under mixed mode loading conditions, not only the fatigue crack propagation rate is of importance, but also the crack propagation direction. The mode I and II stress intensity factors of CTS specimen were calculated using elastic finite element method. The propagation behavior of the fatigue crack of the STS304 steeds under mixed mode loading condition was evacuated by using stress intensity factors $K_I$ and $K_II. The MTS criterion and effective stress intensity factor were applied to predict the crack propagation direction and the fatigue crack propagation rate.

• 한국정밀공학회지
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• 제15권10호
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• pp.113-119
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• 1998

Ship structures and aircraft structures are consisted of thin sheet alloy, so it is very important to understand the characteristics of fatigue crack propagation of that material and to establish the data base. The data for fatigue crack propagation behavior scatter very much even under identical experimental conditions with constant loading. The behavior of fatigue crack propagation under regular and irregular cyclic loadings is known to be highly affected by complicated factors such as plastic zone developed at the vicinity of crack tip and reduction of cross sectional area. In this paper, the controlled stress amplitude and overload fatigue crack propagation tests have been conducted to investigate the effect of varying factors such as plastic zone size near the crack tip and area reduction factor (AF) on the fatigue crack propagation behavior A better simulation of fatigue crack propagation behavior is found to be obtainable by using Wheeler and Willenborg models with AF effect.

• 대한기계학회논문집
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• 제10권1호
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• pp.78-85
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• 1986

본 연구에서는 결함재의 결함선단에 발생 전파하는 피로거동을 검토하기 위해서 미소원공과 미소슬릿을 가공하고, 이것들의 피로한도를 기준으로 해서 이들 결함의 형상이 피로크랙 전파특성에 미치는 영향을 상세히 고찰하고자 한다.

• Journal of Advanced Marine Engineering and Technology
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• 제8권1호
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• pp.49-63
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• 1984

The 5086-H116 Al-Alloy plate specimens having an edge through-thickness notch were investigated to find out the characteristics of the corner crack propagation by the plane bending fatigue. The experiments were also carried out in order to clarify the change of the corner crack propagation behaviour due to the various materials and their thicknesses. In addition, the retardation effect of overload on the corner crack propagation was quantatively studied. Main results obtained are as follows; 1. In the case of estimating the crack propagation rate of the corner crack, it is more reasonable to consider the growth rate of fracture surface area than that of crack length. 2. The shape of the corner crack growing in the plane plate under the bending fatigue can be estimated. 3. The crack propagation rate increases with the increasing of the thickness and the decreasing of the Young's modulus of materials. 4. Regardless of a thickness and kind of materials of specimen, the characteristics of the corner crack propagation can be concluded. 5. The retardation effect of overload is distinct in the corner crack propagation.