• 한국전산구조공학회:학술대회논문집
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• 한국전산구조공학회 1991년도 가을 학술발표회 논문집
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• pp.29-32
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• 1991

It is well known that the fatigue damage process in composite materials is very complicated due to complex failure mechanisms that comprise debounding, matrix cracking, delamination and fiber splitting of laminates. Therefore, the residual strength, instead of a single dominant crack length, is chosen to describe the criticality of the damage accumulated in the sublaminate. In this study, two models for residual strength degradation established by Yang-Liu and Tanimoto-Ishikawa that are capable of predicting the statistical distribution of both fatigue life and residual strength have been investigated and compared. Statistical methodologies for fatigue life prediction of composite materials have frequently been adopted. However, these are usually based on a simplified probabilistic approach considering only the variation of fatigue test data. The main object of this work is to propose a fatigue reliability analysis model which accounts for the effect of all sources of variation such as fabrication and workmanship, error in the fatigue model, load itself, etc. The proposed model is examined using the previous experimental data of GFRP and it is shown that it can be practically applied for fatigue problems in composite materials.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2004년도 춘계학술대회
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• pp.394-399
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• 2004

In order to secure the safety of power steering system, it is necessary to perform the strength and the fatigue analysis of pulley in this paper. The applied stress distribution of the pulley subject to combined loads condition was obtained using finite element analysis. Based on these results, the fatigue life of the pulley with the variation of the fatigue strength was evaluated using durability analysis simulator. The optimal hole size to improved the safety of the pulley was investigated using parametric study. Moreover, the predicted fatigue life cycle with the simulator was verified by experimental tests.

• 한국주조공학회지
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• 제31권4호
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• pp.198-204
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• 2011

The present study was aimed to investigate the dependence of fatigue property on microporosity variation of low-pressure die-cast (LPDC) A356 alloy. The fatigue property of A356 alloy was evaluated through high cycle fatigue test, and the microporosity-terms used were the fractographic porosity measured from SEM observation on fractured surface and the volumetric porosity obtained through the density measurement using Archimedes's principle. The number of cycles to failure of A356 alloys depends obviously upon the variation of fractographic porosity, and can describe in terms of the defect susceptibility which depends on the microporosity variation at a given value of stress amplitude. The modified Basquin's equation was suggested through the combination of microporosity variation and static maximum tensile stress to fatigue strength coefficient. Using modified Basquin's equation, it could suggest that the maximum values of fatigue strength coefficient and exponent achievable in defect-free condition of A356 alloy are 265 MPa, -0.07, respectively.

• 대한기계학회논문집A
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• 제33권2호
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• pp.99-107
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• 2009

This study produced a design curve and fatigue limit for a variation in volume ratio and reduction ratio of TiNi/Al composites. In many cases, stress-life curve does not indicate fatigue limit, so it was presented by probabilistic-stress-life curve. Goodman diagram was used to analyze the fatigue strength of materials with a finite life determined by repeated load and the fatigue strength of endurance limit with an infinite life. The fatigue experiment was conducted using the scenk-type plane bending specimen in same shape. The result of the fatigue test, which had been conducted under consistent stress amplitude, was examined. (i) The optimal condition for TiNi/Al in accordance with hot pressing (ii) Impacts of fatigue limit caused by a variation in reduction ratio and volume ratio of TiNi/Al composites (iii) Probability distribution for fatigue limit of TiNi/Al2024 and TiNi/Al6061.

• 산업기술연구
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• 제23권A호
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• pp.139-147
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• 2003

The purpose of this study was to investigate and analyze the fatigue test data of pavement concrete. The static strength tests were carried out to check the compressive strength, flexural strength, and split tension strength at 56 days in order to minimize strength variation effect during test. The specimens were fabricated at twelves sections at a construction site of highway. The stress level and stress ratio of fatigue test were determined from static test results. The results are as follow: The flexural strength at 28 days mostly satisfied the criterion for design, but the compressive strength at 28 days were slightly below the criterion even though it satisfied at 56 days. The fatigue limit was 2 million cycles if the specimen was not failed to that cycles. The S-N curves were developed from the fatigue test results at each stress levels and each stress ratio. Then, the fatigue life of pavement concrete at a given stress level and fatigue strength of pavement concrete could be derived from these curves. Analysis using method No.2 was more acceptable because resulting of comparison and analysis using method No.2 was presented 2 sections were presented $R^2$ < 0.7, and other 2 sections were presented 0.7 < $R^2$ < 0.8, and the others 8 sections were $R^2{\geq}0.8$.

• Steel and Composite Structures
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• 제7권5호
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• pp.391-404
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• 2007

This paper presents push-out tests of stud shear connectors to examine their fatigue behavior for developing a new composite bridge deck system. The fifteen push-out specimens of D16 mm stud welded on 9 mm steel plate were fabricated according to Eurocode-4, and a series of fatigue endurance test and residual strength test were performed. Additionally, the stiffness and strength variations by cyclic loading were compared. The push-out test, when the stiffness reduction ratio of the specimens was 0.95 under cyclic load, resulted in the failure of the studs. The stiffness variation of the push-out specimens additionally showed that the application of cyclic loads reduced the residual strength. The fatigue strength of the shear connectors were compared with the design values specified in the Eurocode-4, ASSHTO LRFD and JSSC codes. The comparison result showed that the fatigue endurance of the specimens satisfies the design values of these codes.

• 한국해양공학회지
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• 제6권1호
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• pp.113-121
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• 1992

In this study, the variation of fatigue strength in CF/PEEK and CF/EPOXY, the matrix and interfacial strength of which differ from each other, has been studied from the viewpoint of microfracture behavior. The results obtained are as follows; According as the fatigue strength moves from the lower cycle range to the higher cycle range, that of CF/PEEK shows higher curve than that of CF/EPOXY does. In the early stage of fatigue life, the characteristic of fatigue crack in CF/PEEK is mainly the fracture of longitudinal fiber, while that in CF/EPOXY is the fracture of transverse fiber. The difference of fatigue strength in these materials can be explained by the fracture criteria of transverse fiber and longitudinal fiber.

• 대한기계학회논문집A
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• 제24권4호
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• pp.1055-1064
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• 2000

First, various specimen geometries, namely, coupon type, waisted type and dog-bone type, were examined to determine appropriate fatigue specimen of thermoplastic composite material AS4/PEEK and the n, fatigue strength of smooth and notched specimens of AS4/PEEK [-45/0/+45/90]2s was investigated. Fatigue tests were performed under load controlled condition at a stress ratio of 0. 1 at a frequency of 5Hz. Stiffness degradation of specimens with fatigue cycling was monitored using an automated unloading compliance technique. The waisted type specimen is found appropriate for smooth fatigue specimen geometry of AS4/PEEK. As for the effect of stress concentration, it is found that fatigue strength is higher for a 2mm-diameter hole notched specimen than a 5mm-diameter one. Fatigue notch factor decreases with the increase of fatigue life. These results are far different from the trend of fatigue strength of metallic materials. The stiffness variation of smooth specimen was only 4% at maximum until final fracture. On the other hand, the stiffness of hole notched specimen was reduced by 45% at maximum. Notched fatigue strength was compared between thermoplastic composite AS4/PEEK and thermosetting composite Graphite/Epoxy. In long-life fatigue (>104), the AS4/PEEK composite shows superior fatigue strength, but in short-life fatigue, the fatigue strength of the Graphite/Epoxy composite is nearly equal or somewhat higher than that of the AS4/PEEK composite.

• Journal of Welding and Joining
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• 제22권3호
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• pp.50-55
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• 2004

S-N fatigue tests were conducted to investigate the fatigue strength of small diameter socket and butt welded joints made of carbon steels. Experimental parameters were pipe diameter, throat depth, shape of socket welds and welding procedure. Filler metals used in SMAW and GTAW procedure were E9016-G with diameter of 4.0 m and ER70S-G with diameter of 2.4 m. API 5L Gr.B pipes were adopted as a small diameter branch pipes. All socket fittings were machined from ASTM A105 carbon steel. Tensile strength was not affected by the welding procedure. Fatigue strength in socket weld joints increased with increasing pipe diameter, area of weld metal and weld leg length of pipe side.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2003년도 추계학술대회
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• pp.1051-1055
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• 2003

Aluminum carbody for rolling stocks is light and perfectly recycled, but includes severe defects which are very dangerous to fatigue strength. Structural integrity assessment for the carbody by static load test has been performed up to date. In this study, to evaluate fatigue strength of the aluminum carbody of urban transit unit. a testing method to simulate dynamic loading condition was proposed and the fatigue strength of the carbody was evaluated. The dynamic load test results showed that the alternating stress ranges were different from the estimated ranges based on the static test results. Excessive stress ranges at the center are thought to come from the flexible motion of the carbody. published fatigue test data for aluminum components, but variation of alternating acceleration along the length due to flexibility of carbody yielded unexpected results. Because fatigue strength based on the static test results may be overestimated at the center, modification of testing method is necessary.