• Journal of Advanced Marine Engineering and Technology
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• v.40 no.1
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• pp.10-16
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• 2016

Fatigue analysis for life extension of a ship is different from that of a newly constructed ship since the current corrosion margin and voyage routes of the past and future must be considered, thereby complicating the life extension procedure. This research introduces the fatigue analysis case for the life extension project of a moss LNG carrier using full spectral fatigue analysis, which has been previously used for newly constructed ships. It is expected that the fatigue analysis methodologies and full spectral fatigue analysis program used in this study will be applicable to other life extension projects.

• Proceedings of the Korean Nuclear Society Conference
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• 1996.05d
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• pp.188-194
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• 1996

현재 국내에서 관심이 고조되고 있는 원전 연장운전 방안의 일환으로, 주요 기기의 기술적 타당성 검토 대상기기 중 하나인 원자로 냉각재 배관 노즐의 피로수명 평가를 수행하였다. 본 노즐의 피로수명 평가는 원자로 냉각재 계통 노즐의 최종 설계문서에 제시된 응력해석 결과를 참조하여 ASME Code, Sec III의 절차에 따라 수행하였으며, 평가결과 이들 노즐의 설계수명 30년을 향후 40년 또는 그 이상 연장 운전할 경우에도 무리가 없는 것으로 판단된다.

• Proceedings of the Korean Nuclear Society Conference
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• 1997.05b
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• pp.509-514
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• 1997

원자력발전소 수명관리(Plant Lifetime Management, PLIM) 업무중 기기의 피로수명 평가는 중요하면서도 시간이 많이 소요되는 작업중의 하나이다. 고리원전 1호기 주요기기의 피로수명 평가를 위해 운전기간중 발생한 과도현상에 대한 운전기록을 일일이 분석하여 과도현상의 종류와 횟수를 기록하였다. 운전기간중 발생한 과도현상을 근거로 주요기기의 피로를 계산하여 설계피로계수와 비교ㆍ평가한 결과, 향후 발전소 수명연장운전을 위한 잔여피로수명은 충분한 것으로 판단되었다.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.35 no.1
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• pp.52-57
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• 2007

One of the hot issues in composite patching is to reduce the thermal residual stresses between composite patch and aluminum surface which occurs after bonding of composite patch. In this study, the edge crack patching is adopted for different curing cycles. For the analysis, three layer Mindlin plate elements are used, and Paris' law is adopted to predict the fatigue life of composite patch plate. The analysis results show a good agreement with the experimental fatigue life and this technique can be applied for the prediction of fatigue life of aircraft structures.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.37 no.7
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• pp.642-652
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• 2009

Most of lap jointed aircraft structures encounter the fretting damages, which provoke fretting cracks prematurely and lead to significant reduction of fatigue life. In the case of ageing aircrafts especially, this fretting fatigue problem is a fatal threat for the safety and airworthiness. Recently, as the service life extension program(SLEP) of ageing aircrafts has become a hot issue, the prediction of fretting fatigue life is also indispensable. On these backgrounds, a series of experimental tests of fretting fatigue on bolted lap joint specimens, were performed. And the fretting crack initiation and propagation life of each specimen were evaluated using existing and newly proposed prediction models with the fretting parameters obtained from the FEA results for elasto-plastic contact stress analyses. The validations of prediction models were also discussed, comparing the prediction results with experimental test ones.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.33 no.2
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• pp.60-66
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• 2005

Corrosion highly affects the lifetime and performance of machinery metallic components. The effects of shot peening on the fatigue life of Al 7075-T6 under corrosive environment are investigated in this paper. Experimental results show that the fatigue limit of shot peened specimen increases about 52%. That means the fatigue life of metallic components is highly extended by shot peening. The corrosion greatly reduces the fatigue strength depending on the corrosive condition from one week up to one year. In case of shot peened specimen, the corrosion does not reduce the fatigue strength and fatigue life up to six months. It means that the shot peening has superior effectiveness to reduce the influence of corrosion to the metallic materials.

• Korean Journal of Materials Research
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• v.10 no.2
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• pp.128-137
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• 2000

A study has been made to investigate the effects of hot isostatic pressing(HIPing) on the microstructure and high temperature fatigue lives of the IN738LC, Ni-base superalloy used in turbine blades, with emphasis on the elimination of casting microporosity and fatigue damage through HIP treatments. Microstructure was observed using OM, SEM and the fatigue life was investigated with rotate bending fatigue tester. The results show that the fatigue lives of properly HIP-processed specimens could be extended be extended by a factor of about sixty. In contrast, no comparable life improvement was achieved with heat treatment only. The repetitive HIP treatment was shown to be very effective as a means of rejuvenating the fatigue life of intentionally fatigue-damaged IN738LC by restoration of the initial alloy microstructure and additional removal of fine casting defects which remained in the HIP-processed material.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.33 no.2
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• pp.821-831
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• 2013

As a result of recent research, it is reported that the periodic replacements criterion of rails is able to extend as grinding rail surface and using the continuous welded rail (CWR). In this study, we carried out fatigue tests on existing laid rails. Based on the test results, an S-N curve expressing the remaining life of laid rails at a fracture probability of 50% was obtained using weighted probit analysis suitable for small-sample fatigue data sets. As rails used for testing had different histories in terms of accumulated tonnage, the test data were corrected to average out the accumulated tonnage. We estimated the remaining service lives for laid rails on the urban railway using equations developed in the past to estimate rail base bending stress and that surface irregularities into consideration. Therefore, estimating the remaining service life of laid rails showed that the rail replacement period could be extended over 200 MGT, although it is necessary to remove longitudinal rail surface irregularities at welds by grinding. Also, the fatigue test results under fatigue limit, Haibach's rule appling half slope of S-N curve under the fatigue limit was considered more reasonable than modified Miner's rule for estimating rail fatigue life.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.33 no.8
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• pp.842-848
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• 2009

Fatigue failures are often occurred at welded joints where stress concentrations are relatively high due to the joint geometry. Although employing good detail design practices by upgrading the welded detail class enables to improve the fatigue performance, in many cases, the modification of the detail may not be practicable. As an alternative, the fatigue life extension techniques that reduce the severity of the stress concentration at the weld toe region, remove imperfections and introduce local compressive welding residual stress, have been applied. These techniques are also used as definite measures to extend the fatigue life of critical welds that have failed prematurely and have been repaired. In this study, a hammer peening procedure for using commercial pneumatic chipping hammer was developed, and the effectiveness is quantitatively evaluated. The pneumatic hammer peening makes it possible to give the weld not only a favorable shape reducing the local stress concentration, but also a beneficial compressive residual stress into material surface. In the fatigue life calculation of non-load carrying cruciform specimen treated by the pneumatic hammer peening, the life was lengthened about ten times at a stress range of 240MPa, and fatigue limit increased over 65% for the as-welded specimen.

• Computational Structural Engineering
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• v.5 no.1
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• pp.11-14
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• 1992

최근 교량공학자들의 공통관심사는 초대형 구조물을 가설하고, 적절한 유지관리에 의해 기존 구조물의 공용수명을 연장시키는 것 등을 들 수 있다. 고성능 컴퓨터 산업의 발달로 인한 구조해석의 정밀화, 경량골재 및 고강도 재료의 개발, 용접성과 시공법의 발달 및 초대형 크레인과 같은 건설기자재의 개발 등으로 인하여 초대형 구조물의 가설은 외국에서 뿐만 아니라 국내에서도 가능하게 되었다. 그리고 구조물의 공용수명을 연장하기 위해서 최근에는 첨단계측장비와 신호처리기술, 신뢰성이론, 피로파괴이론 및 system identification technique 등의 발달로 인해 비교적 정확하게 교량구조물의 손상부위와 손상정도의 파악이 가능하게 되었다. 그리하여 가까운 시일내에 100년 이상의 공용수명을 갖는 초대형 교량이 출현될 것으로 전망된다. 따라서 교량 공학자들은 앞으로 장대교량의 설계와 시공 및 유지관리의 완전 국산화를 위한 연구에 더욱 박차를 가해야 할 것이다.