• Structural Engineering and Mechanics
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• 제13권4호
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• pp.455-464
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• 2002

There is a growing demand to assess the remaining strength and endurance of existing composite steel and concrete bridge beams due to the aging infrastructure, increases in permissible vehicle weights and increases in their frequencies. As codes are generally dedicated to the design of new structures, new procedures are required to aid in the assessment of existing bridges to ensure that they are utilised to the full. In this paper, simple expressions are presented to perform partial-interaction analyses directly from full-interaction analyses, so that the beneficial effect of partial-interaction on the shear forces on the shear connectors can be utilised in assessment to extend the fatigue life of simply supported bridge beams and to determine the effect of remedial work if necessary. Use of the assessment technique is described by way of an illustrative example.

• 한국초전도ㆍ저온공학회논문지
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• 제6권4호
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• pp.22-26
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• 2004

For practical applications, the evaluation of reliability or endurance of HTS conductors is necessary. The mechanical properties and the critical current, Ie, of multifilamentary Bi-2223 superconducting tapes, externally reinforced with stainless steel foils, subjected to high cycle fatigue loading in the longitudinal direction were investigated at 77K. The S-N curves were obtained and its transport property was evaluated with the increase of repeated cycles at different stress amplitudes. The effect of the stress ratio, R, on the Ie degradation behavior under fatigue loading was also examined considering the practical application situation of HTS tapes. Microstructure observation was conducted in order to understand the Ie degradation mechanism in fatigued Bi-2223 tapes.

• 한국철도학회:학술대회논문집
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• 한국철도학회 2002년도 춘계학술대회 논문집
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• pp.399-403
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• 2002

The transmission system of high speed train serve in the severe condition compared with those of other trains, namely, they have to transmit high power to run with high speed and they have to make maximum use of the limited space. To clarify the strength of gear for Korea High-Speed Train, a bending fatigue test of gear specimen is performed and compare with actual gear's. From this result, specimen test is useful to infer S-N curve and endurance limit of actual gear that much time and expense are consumed.

• 한국축산식품학회지
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• 제31권1호
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• pp.61-65
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• 2011

Acanthopanax senticosus, a member of the Araliaceae used as an invigorant in traditional Korean medicine, is known to relieve physical fatigue. The principal objective of this study was to evaluate the effects of eggs laid by hens fed on Acanthopanax senticosus extracts on physical endurance and reproductive parameters. Male Sprague-Dawley rats at 4 wk of age were divided into 3 groups of 15 rats each: group A (14% egg yolk powder from hens fed with Acanthopanax senticosus extracts+86% AIN-93G), group B (14% plain egg yolk powder + 86% AIN-93G) and group C (7% fat source + 93% AIN-93G), and studied for 5 wk. The rats' physical endurance was measured via forced swimming tests. According to the results, 53.3% rats of group A swam for longer than 20 min, in group B and C, only 48.9% and 46.7% of the rats achieved this. In terms of reproductive parameters, sperm motility was significantly higher in group A than in groups B and C (p<0.05). However, no differences in sperm count were detected among the groups. Additionally, the serum testosterone levels of groups A and B were higher than that of group C. Our findings suggest that rats fed with egg yolk powder from hens fed on Acanthopanax senticosus extracts may improve athletic endurance and reproductive parameters in rats.

• 한국구조물진단유지관리공학회 논문집
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• 제9권4호
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• pp.209-216
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• 2005

본 연구에서는 피로시험을 통해 H형 및 Channel형 복공판의 성능을 검토하였다. 이 시험을 통하여 균열의 발생원인과 구조체의 거동의 상관성을 분석하였다. H형 복공판은 백만회 이상의 반복하중에서도 안정적으로 거동하였다. Channel형 복공판의 경우 시험체 모두 대략 십만회에서 피로파괴가 발생하여 공용하중을 사용하는데 있어 내구 수명의 확보에 문제점이 있음을 알 수 있었다.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2004년도 추계학술대회 논문집 Vol.17
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• pp.345-348
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• 2004

For practical applications, the evaluation of reliability or endurance of HTS conductors is necessary. The mechanical properties and the critical current, $I_c$, of multifilamentary Bi-2223 superconducting tapes, externally reinforced with stainless steel foils, subjected to high cycle fatigue loading in the longitudinal direction were investigated at 77K. The S-N curves were obtained and its transport property was evaluated with the increase of repeated cycles at different stress amplitudes. The effect of the stress ratio, R, on the $I_c$ degradation behavior under fatigue loading was also examined considering the practical application situation of HTS tapes. Microstructure observation was conducted in order to understand the L degradation mechanism in fatigued Bi-2223 tapes.

• 한국기계가공학회지
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• 제14권3호
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• pp.131-140
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• 2015

The purpose of this study is to predict the fatigue life of a planet carrier of a slewing reducer for a tower crane. To predict the fatigue life of the carrier, the inertia endurance test was carried out, and then the input torque profile for the reducer was obtained. The load profile acting on the planet pins that assembled the carrier was calculated from the measured input torque profile using commercial gearbox analysis software. The stress profiles of the carrier weak points were analyzed from the calculated load profile and boundary conditions using commercial FE software, and the stress cycles were determined using the rainflow counting method. Finally, the fatigue life of the carrier was predicted using the equivalent stress range by considering the effect of mean stress, and an S-N curve was drawn up using the GL guideline and the cumulative damage law.

• 산업기술연구
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• 제30권B호
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• pp.17-23
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• 2010

Since the propagation of a short fatigue crack is directly related to the large crack which causes the fracture of bulk specimen, the detailed study on the propagation of the short crack is essential to prevent the fatigue fracture. However, a number of recent studies have demonstrated that the short crack can grow at a low applied stress level which are predicted from the threshold condition of large crack. In present study, the threshold condition for the propagation of short fatigue crack is examined with respect to the micro-structure and cyclic loading history. Specimens employed in this study were decarburized eutectoid steels which have various decarburized ferrite volume fraction. Rotating bending fatigue test was carried out on these specimens with the special emphasis on the "critical non-propagating crack length" It is found that the reduction of the endurance limit of their particular micro-structures can be due to the increase of the length of critical non-propagating crack, and the quantitative relationship between the threshold stress ${\sigma}_{wo}$ and the critical non-propagating crack length $L_c$ can be written as ${\sigma}_{wo}{^m}{\cdot}L_c=C$ where m,C is constant. Further experiments were carried out on cyclic loading history on the length of critical non-propagating crack. It shown that the length of critical non-propagating crack is closely related to cyclic loading history.

• 한국도로학회논문집
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• 제16권6호
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• pp.115-120
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• 2014

PURPOSES : This research describes how to predict the life cycles of fatigue cracking based on NCHRP Report 704 as well as modified harmony search (MHS) algorithm. METHODS : The fatigue cracking regression model of NCHRP Report 704 was used in order to calculate the ESAL (Equivalent Single Axle Load) numbers up to pavement failure, based on using material parameters, composite modulus, and surface pavement thickness. Furthermore, the MHS algorithm was implemented to find appropriate material parameters and other structural conditions given the number of ESALs, which is related to pavement service life. RESULTS : The case studies show that the material and structural parameters can be obtained, resulting in satisfying the failure endurance of asphalt concrete structure, given the number of ESALs. For example, the required ESALs such as one or two millions are targeted to satisfy the service performance of asphalt concrete pavements in this study. CONCLUSIONS : According to the case studies, It can be concluded that the MHS algorithm provides a good tool of optimization problems in terms of minimizing the difference between the required service cycles, which is a given value, and the calculated service cycles, which is obtained from the fatigue cracking regression model.

• 한국구조물진단유지관리공학회 논문집
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• 제7권1호
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• pp.165-172
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• 2003

The fatigue problem of Prestressed Concrete(PSC) bridges are more serious than the other type of concrete bridges, because the cross sectional area and self weight of PSC bridges are smaller. The endurance of strengthening methods for PSC bridges are tested in this study. Glass fiber sheeting and external post-tensioning methods were applied. 1/5 scale PSC beams were made for fatigue test, same as static test. The range of repeated load is from 10% to 80% of yielding load with sine curve. The experimental results show that the failure cycle of strengthened members are increased compare to non-strengthened members. The members strengthened with glass fiber show better enhancement in fatigue problem than the members strengthened with external post-tensioning method, though the adhesion of glass fiber and concrete is failed, as increase of crack. With these experimental results, it can be said that the strengthening methods used in this study are efficient at extending the life time of aged PSC bridges.