• 한국철도학회:학술대회논문집
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• 한국철도학회 2007년도 추계학술대회 논문집
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• pp.352-364
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• 2007

It is essential to reduce track maintenance costs and to extend the periodic replacements of continuous welded rails based on accumulated passing tonnage. As recently train load decrease and rail joints wear down less, the periodic replacements of continuous welded rails can be extended. There are many kinds of rail damage like squat, head-check and corrugation. These can be taken nondestructive or naked eye test. So the periodic replacements of continuous welded rails based on accumulated passing tonnage were examine with focusing on a crack of rail bottom of continuous welded rail. Therefore, this study measure dynamic response of track by metro train load, it compute impact coefficient and track spring coefficient for estimating a condition of actual track system. Also, it is converted the measured stress waveform into stress frequency histogram by the rain-flow counting methods, and then the equivalence of stress is calculated. As apply s-n curve of a new welded rail, accumulated fatigue damage ratio of laid rail and remaining service lives is estimated. This study suggest a plan of the periodic replacements of continuous welded rails based on accumulated passing tonnage classified by the types of track system.

• 한국기계가공학회지
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• 제18권6호
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• pp.9-18
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• 2019

This study derives load characteristics and analyzes the safety of plowshares operating in dry fields. We mounted a three-blade, reversible plow on a 23.7 kW tractor and measured the plow's tractive force as well as the torque from the engine output shaft on the rear axle under various working speeds (L4, M1, M2, M3). We chose a Korean test site of Seomyeon, Chuncheon with sandy soil texture, as determined using the USDA method. We constructed the load spectrum for torque and tractive force using measured data and derived the fatigue life of the plowshare from a stress-cycle (S-N) curve of the plow material. Our results show that the M3 gear maximizes the driving shaft torque loads and, applying the tractive force load spectrum, creates a cumulative damage sum of $4.14{\times}10^{-5}$. Considering sampling time, we estimate a fatigue life of 805 hours while using the M3 gear. When using the other working speeds, however, all of the stress levels fell within the endurance limits and, therefore, our model predicts infinite plowshare lifetimes. For this analysis, we used a yield strength of 1,079 MPa for the plowshare and static safety factors, analyzed using the maximum stress, between 6.83 and 8.63 under each working speed.

• 한국자동차공학회논문집
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• 제11권6호
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• pp.101-107
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• 2003

Since stainless steel sheets have good mechanical properties, weldability, appearance and corrosion resistance, they are commonly used as one of the structural materials of the railroad cars or the commercial vehicles which are manufactured by the spat welding. Among the many kinds of spot welded lap joints, it can be found that multi-lap joints are employed in their body structure. But, fatigue strength of these joints is lower than that of base metal due to high stress concentration at the nugget edge of spot weld and is considerably influenced by welding conditions as well as the mechanical and geometrical factors. Thus, it is necessary to establish a reasonable and systematic design criterion for the long life design of the spot-welded body structures. In this paper, the stress distribution and deformation around the spot-welded multi-lap joints subjected to tensile shear load was numerically analyzed. Also, the $\Delta$P-Nf curve was obtained by fatigue tests. Using these results, $\Delta$P-Nf curves were rearranged in to the ${\Delta}{\sigma}$-Nf relation with the maximum stress at nugget edge of spot weld.

• 한국해양공학회지
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• 제4권2호
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• pp.100-111
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• 1990

In this paper, fatigue tests were carried out at stress test levels of 461 MPa, 441 MPa, and 431 MPa by using smooth specimen of$2_{1/4}$ Cr-1 Mo steel with the stress ratio(R) of 0.05. The initiation, growth and coalescense process of the major cracks and sub-cracks among the fatigue cracks on the smooth specimen are investigated and measured under each stress level at a constant cycle ratio by the replica technique with optical microscope. Some of the important results are as follows: In spite of the difference of stress levels, the major crack data gather into a small band in the curve of surface crack length and crack depth against cycle ratio N/Nf. The sub-crack data, however, deviate from the band of the major crack. The growth rates, da/dN, of major and sub-crack plotted against the stress intensity factor range, ${\Delta}K$, have the tendency to be compressed on a relatively small band. But it is more effective to predict fatigue life through major cracks. The propagation behavior of surface microcracks on the smooth specimens coincides with that of the specimen having an artificial small surface defect or through crack.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2003년도 봄 학술발표회 논문집
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• pp.555-560
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• 2003

Fatigue strength of concrete is ususlly presented by the Wohler Curve. But, new dimension T(time) from the view point of cyclic creep concept should be considerd. This paper presented four variable F-N-T-R relationship, this four variable relationship simultaneously accounts for the time effect and the effect of load rate. And analytical models are presented to predict fatigue strength of R/C beam strengthened with steel plate and carbon fiber sheet. Also, the correlation between the ratio of stress and the fatigue life was investigated.

• 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.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2003년도 춘계학술대회 논문집 유기절연재료 방전 플라즈마연구회
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• pp.15-18
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• 2003

In this paper, We explained the best shape design of electrode for discharge on the water. Electrode with rounding was reduced maximum electric field of over 40% to electrode without rounding for discharge on the water and the best shape of electrode for discharge on the water designed when shape of electrode had a curve radius of over $60^{\circ}$ at electrode's face to electrode's face with minimum distance and a curve radius of under $120^{\circ}$ at electrode's side face to electrode's front face. And When dielectric beads are used between electrodes, the life of electrodes is improved by lower stress of electric field on surface of electrodes.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2007년도 춘계학술대회A
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• pp.1734-1739
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• 2007

The materials characteristics and lifetime evaluation are very important in design procedure to assure the safety and reliability of rubber components. This paper discusses the failure mechanism and material test were carried out to predict the useful life of NBR and EPDM rubber mount for compression motor which is used in refrigerator. In order to investigate the heat-aging effects on the materials properties, stress-strain curve were obtained from the results of material tests. Compression set results changes as the threshold are used for assessment of useful life and the time were plotted against reciprocal of absolute temperature to give the Arrhenius plot.

• 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.

• 마이크로전자및패키징학회지
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• 제9권4호
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• pp.61-68
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• 2002

지금까지 전자 디바이스의 솔더접합부에 대한 신뢰성 평가에 있어서는 열충격시험에 의한 평가가 주류를 이루었다. 그러나 최근 모바일 제품이 소형화/다기능화되고 고밀도실장에 대한 요구가 증가함에 따라 BGA/CSP와 같은 솔더볼을 사용하는 패키지가 표면실장의 주류를 이루게 되었으며, 솔더접합부에 대한 메커니컬 스트레스 수명이 요구되어지고 있다. BGA/CSP의 솔더접합부에 대한 신뢰성 평가는 하중을 가한 상태에서 데이지체인 패턴의 전기적 저항변화와 스트레인 게이지에 의한 스트레스-스트레인 커브에 의해 행해진다. 본 연구에서는 자체 개발한 PCB만능시험장치의 응용과 솔더접합부에 대한 메커니컬 스트레스의 동적거동을 평가한 소니의 실험자료를 소개하도록 한다.