• Journal of Advanced Marine Engineering and Technology
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• 제19권2호
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• pp.36-46
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• 1995

In this paper, fatigue crack propagation behaviors were investigated experimentally for the materials, carbon steel forgings (SF45A, SF50A, SF60A) which are used in the marine propeller shaft. The results obtained are as follows: The number of cycles required to grow crack length 1.30mm from microcrack initiation was about 60% of the total fatigue life. Fatigue crack propagation rate was expressed by the equation d(2a)/dN_B 2a/$N_f$ and the result was agreed well with the experimented data. And the equation d(2a)/dN=$C{\sigma}_a^m(2a)^n$ was evaluated also. Obtained material property m and n are 3~5 and 1-1.5 respectably, and the result was reasonably agreed to the data obtained from experiments.

• 한국공작기계학회논문집
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• 제15권3호
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• pp.120-126
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• 2006

In this paper, we investigated the characteristics of fatigue fracture on TB(Tailored Blank) weldment by comparing the fatigue crack propagation characteristics of base metal with those of TB welded sheet used for vehicle body panels. We also investigated the influence of center crack on the fatigue characteristic of laser weld sheet of same thickness. We conducted an experiment on fatigue crack propagation on the base metal specimen of 1.2mm thickness of cold-rolled metal sheet(SPCSD) and 2.0mm thickness of hot-rolled metal sheet(SAPH440) and 1.2+2.0mm TB specimen. We also made an experiment on fatigue crack propagation on 2.0+2.0mm and 1.2+1.2mm thickness TB specimen which had center crack. The characteristics of fatigue crack growth on the base metal were different from those on 1.2+2.0mm thickness TB specimen. The fatigue crack growth rate of the TB welded specimens is slower in low stress intensity factor range$({\Delta}K)$ region and faster in high ${\Delta}K$ region than that of the base metal specimens.

• 대한기계학회논문집
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• 제10권6호
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• pp.898-905
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• 1986

본 논문에서는 강의 피로균열진전거동과 미시조직과의 관계를 밝히기 위한 연 구의 일환으로 제이상 마르텐사이트 중에 모상 페라이트가 존재하는 복합조직강을 준 비하여 이들 강의 제이상 경도변화에 따른 피로균열진전저항을 균열휨과 균열닫힘을 통하여 검토하였다.

• Journal of Welding and Joining
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• 제12권4호
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• pp.117-126
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• 1994

APAL (Aramid Patched ALuminum alloy) was manufactured, which was a material that was consisting of a A12024-T3 aluminum alloy plate bonded to single-side of it with aramid/epoxy laminates. The aramid/epoxy laminates were bonded to it in condition of 1, 2 ply and fiber orientation of .+-.45, 0.deg./90.deg. Fatigue crack propagation tests were performed at stress ratio R-0.2, 0.5 with Al 2024-T3, APAL 45-1P, APAL 0/90-1P, APAL 45-2P, APAL 0/90-2P specimens to examine behavior of retardation in fatigue crack propagation. All the APAL specimens showed superior fatigue crack resistance. Number of cycle spended for crack to propagate from $a_{M}$=37 to $a_{M}$=65 mm in case of APAL 0/90-2P specimen was half that of Al 2024-T3 specimen. Fatigue crack propagation rate of APAL 0/90 specimens were retarded more compared to APAL 45 specimens and the amounts of retardation at R=0.5 were larger than that at R=0.2. It was found that the retardation in fatigue crack propagation was caused by intact fibers in the wake of crack.ack.

• 한국자동차공학회논문집
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• 제5권1호
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• pp.129-135
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• 1997

Previous studies has shown that the curve of low-cycle fatigue life was not expressed with the single line subjected to Manson-Coffin's law type and bent to short life in low ${\Delta}{\varepsilon}_p$ region. The main cause of this phenomenon has been considered that the localization of plastic strain in the crack initiation process fosters the crack initiation. In this study, the low-cycle fatigue life was investigated for each specimens omitted crack initiation process and it was found that fatigue life curve in log(${\Delta}{\varepsilon}_p$)-log($N_f$)was bent in low ${\Delta}{\varepsilon}_p$ region as ever. Therefore, the main cause of appearance of knee point in fatigue life curve is not found in the crack initiation process but in the crack propagation process. In the crack propagation process, the localization of the plastic strain in the vicinity of crack tip and the influence of test environment on the crack propagation rate were observed and these inclinations were more remarkable in low ${\Delta}{\varepsilon}_p$ region. Hence, it was concluded that these two phenomena in the crack propagation process were proved to the main cause which accelerates the crack propagation in low ${\Delta}{\varepsilon}_p$ region and bent the fatigue life curve in result.

• 대한기계학회논문집A
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• 제21권5호
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• pp.842-849
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• 1997

The aim of this study is an investigation of the interaction of two micro hole defects affecting fatigue crack initation life and propagation behavior. The locatio of two micro hole defects was considered as an angle of alignment and the distance between the centers of two micro hole defects. The fatigue cracking behavior is experimented under bending. When micro defects are located close to each other, the fatigue crack initiation lives are varied with their relative locations. In the experiments, the area of local plastic strain strongly played a role in the fatigue crack initiation lives. Therefore we introduce a parameter which contains the plastic deformation area at stress concentrations and propose a fatigue crack initiation life prediction curve. In addition, the directions and propagation rates of fatigue cracks initiated at two micro hole defects are studied experimentally.

• 대한기계학회논문집
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• 제14권5호
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• pp.1193-1199
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• 1990

본 연구에서는 가공경화지수 (n)가 서로 다른 몇가지 재료를 선택하고 과대하 중의 비 (%PL)를 달리하는 단일 과대하중 피로 시험을 행하여 재료의 가공경화지수가 피로 균열 진파의 지연거동에 미치는 영향과 아울러 균열닫힘현상과의 관계를 구명하였다.

• 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.

• Structural Engineering and Mechanics
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• 제35권3호
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• pp.283-299
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• 2010

This paper addresses the numerical simulation of fatigue crack growth in arbitrary 2D geometries under constant amplitude loading by the using a new finite element software. The purpose of this software is on the determination of 2D crack paths and surfaces as well as on the evaluation of components Lifetimes as a part of the damage tolerant assessment. Throughout the simulation of fatigue crack propagation an automatic adaptive mesh is carried out in the vicinity of the crack front nodes and in the elements which represent the higher stresses distribution. The fatigue crack direction and the corresponding stress-intensity factors are estimated at each small crack increment by employing the displacement extrapolation technique under facilitation of singular crack tip elements. The propagation is modeled by successive linear extensions, which are determined by the stress intensity factors under linear elastic fracture mechanics (LEFM) assumption. The stress intensity factors range history must be recorded along the small crack increments. Upon completion of the stress intensity factors range history recording, fatigue crack propagation life of the examined specimen is predicted. A consistent transfer algorithm and a crack relaxation method are proposed and implemented for this purpose. Verification of the predicted fatigue life is validated with relevant experimental data and numerical results obtained by other researchers. The comparisons show that the program is capable of demonstrating the fatigue life prediction results as well as the fatigue crack path satisfactorily.

• 대한기계학회논문집A
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• 제33권8호
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• pp.707-719
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• 2009

The variables relating to the fatigue behavior have uncertainty and are random. The fatigue crack propagation is, thus, stochastic in nature. In this study, fatigue experiments are performed on the specimen of the magnesium alloy AZ31. The data of the fatigue life are scattered even in the same experimental condition. It is necessary to determine the probability distribution of the fatigue crack propagation life for the reliability analysis as well as the design and maintenance of structural components. Therefore the statistics and the probability distribution for the fatigue crack propagation life are investigated and the best fit probability distribution of that is proposed in this paper.