• Proceedings of the Korean Nuclear Society Conference
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• 1998.05a
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• pp.818-823
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• 1998

Three Mile Island Unit-2 (TMI-2)의 사고 후 OECD-NEA 주관의 연구에 의하면 압력용기 하부의 노즐이 국부열점(hot spot) 영역의 경우 거의 압력용기 바닥까지 용융되었음이 조사되었다. [1]. 이러한 재배치된 용융노심의 열속에 의하여 압력용기의 외부와 통하는 penetration tube weld(노즐 용접부)가 파손된다면 내부의 고압상태로 인해 penetration tube ejection 사고 및 이에 따르는 용융노심의 압력용기 외부로의 유출 가능성까지 배제할 수 없을 것이다. 본 연구의 출발점은 중대사고시 이러한 압력 및 열속에 따르는 노즐 용접부의 파손확률을 결정하는데 있다. 크리프 파출시 기존의 해석에서 쓰인 deterministic approach를 개선하여 probabilistic approach를 개발하였다. 또한 기존의 해석에서 쓰인 단순한 안전 여유도(margin-to-failure)의 개념과 비교하여 용접부에서의 파손확률을 계산하였다.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 1995.04b
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• pp.353-357
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• 1995

교반기나 펌프등의 회전기계에서의 트러블은 베어링 부분의 파손이나 결함보다는 미케니컬시일(이하 시일이라 한다)의 이상상태로 인한 액이나 기체의 누설에 의한 경우가 많다. 기계 또는 설비의 가동중에 이 실일의 고장은 단순히 시일 자체뿐만 아니라 설비 전체의 파손을 야기하고 시스템의 가동 중단으로 생산 계획에 막대한 차질을 가져오기 때문에 시일이 장착된 시스템에서는 시일의 이상상태에 대한 관리, 감시가 중요한 문제가 되고 있다. 본 연구에서는 온도와 토오크의 출력변화를 온라인 센싱 하고이들 센싱정보를 통합처리하여 시일의 이상 상태를 진단하는 방법에 대해 검토하였다. 센싱정보의 통합처리 모델로는 예측기능을 갖는 다충신경회로망을 이용하였다.

• Transactions of the Korean Society of Mechanical Engineers
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• v.16 no.4
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• pp.707-722
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• 1992

Fracture of a cutting tool is one of the most serious problems in machining systems. Therefore, several methods have been proposed so far to detect cutting tool fracture. However, most of them have some problems from the viewpoint of practical applications. In this study, the feasibility of using acoustic emission and cutting force signals for the detection of massive tool breakages as well as small fracture of cutting tools were investigated. Turning experiments were performed using conventional carbide inset tools under realistic cutting conditions and the SM45C steel and heat treated SM45C steel were used as a workpiece. And the sensitivities of the AE and cutting force signals to the fracture of cutting tools were illustrated. Finally, a detection algortithm for the fracture of cutting tools was developed through the analysis of these dual signals in the several types of tool fracture.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.31 no.4D
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• pp.555-564
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• 2011

More than sixty percentages of the highway constructed by concrete pavements in South Korea and over half of the concrete pavements were twenty years or older. The most of South Korea road is hard to provide a bypass in conditions of network of roads. Asphalt concrete overlay has been used for the overlay of aged concrete pavement. However, the cost of maintenance and rehabilitation in an asphalt overlay is expensive by early damage. Therefore, bonded concrete overlay was recently attempted in South Korea as an alterative method of rehabilitation for aged concrete pavement. Hence, it needed to investigate the factors to find performance of the bonded concrete overlay life. However, there is no performance data of the concrete overlay in South Korea. This study was to make a database of an affecting of the pavement life and draws statistical analysis of the performance data on the LTPP (Long Term Pavement Performance) database of U.S.A.

• International Journal of Highway Engineering
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• v.13 no.1
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• pp.207-221
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• 2011

More than sixty percentage of highway in South Korea were constructed by concrete pavements and more than half of the concrete pavements were twenty years or older. The most of highway have difficulty in providing detour due to the traffic and road condition of South Korea. So far, asphalt concrete has been used for the overlay of aged cement concrete pavement. However, the frequent early damage and maintenance of typical asphalt overlay due to repetitive maintenance causes inconvenience of road users and expensive costs. It is necessary to investigate the factors affecting the performance of asphalt concrete overlay to improve the performance of asphalt overlay. However, the performance data of asphalt concrete overlay in South Korea does not exist. In this research, to investigate on the factors affecting the life of asphalt concrete overlay was attempted based on statistical analysis of the performance data of asphalt concrete overlay included in LTPP (Long-Term Pavement Performance) Database of U.S.A.

• Polymer(Korea)
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• v.32 no.5
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• pp.440-445
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• 2008

The failure mechanism and failure morphology of linear low density polyethylene (LLDPE) tubing under hydrostatic pressure were investigated. Microscopic observations using video microscope and scanning electron microscope indicate that the failure mode is a brittle fracture including cracks propagated from inner wall to outer wall. In addition, oxidation induction time and Fourier transform infrared spectroscopy results show the presence of exothermic peak and the increase in carbonyl index on the surface of fractured LLDPE tubing, due to thermal-degradation. An accelerated life test methodology and testing system for LLDPE tubing are developed using the relationship between stresses and life characteristics by means of thermal acceleration. Statistical approaches using the Arrhenius model and Weibull distribution are implemented to estimate the long-term life time of LLDPE tubing under hydrostatic pressure. Consequently, the long-term life time of LLDPE tubing at the operating temperature of $25^{\circ}C$ could be predicted and also be analyzed.

• Journal of Welding and Joining
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• v.22 no.5
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• pp.4-8
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• 2004

• KSCE Journal of Civil and Environmental Engineering Research
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• v.33 no.4
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• pp.1651-1664
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• 2013

Precise analysis on deterioration processes of road pavements is not so simple matter due to severe uncertainty originated from a lot of explanatory variables engaged in. For those reasons, most analytical models for pavement deterioration prediction have often preferred to probabilistic approaches than deterministic models. However, the general probabilistic approaches that treat overall characteristics of population or entire sample would not be suitable for providing detail or localized information on their changing process. Considering the aspects, this paper aimed to suggest a stochastic disaggregation method to analyze the localized deterioration speeds and its variances changed by time and condition states. In addition, life expectancies and their uncertainty were estimated by probabilistic algorithm using the disaggregated stochastic process. For an empirical study, pavement inspection data (crack) accumulated from 2003 to 2010 from Korean national highway network was applied. This study can contribute to securing reliability of life cycle cost analysis, which is one of the primary analyses in road asset management, with much advanced deterioration forecasting functions. In addition, it would be meaningful trials as fundamental research for preventive maintenance strategy that demands essential understanding on changing process of the deterioration speed of pavement.

• Composites Research
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• v.29 no.2
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• pp.66-72
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• 2016

Porosity in polymer matrix composites increases rapidly during thermochemical decomposition at high temperatures. The generation of pores reduces elastic moduli and failure strengths of composite materials, and gas pressures in internal pores influence thermomechanical behaviors. In this paper, micromechanical finite element analysis is carried out by using two-dimensional representative volume elements for unidirectionally fiber-reinforced composites with porous matrix. According to the state of the pores, effective elastic moduli, poroelastic parameters and failure strengths of the overall composites are investigated in detail. In particular, it is confirmed that the failure strengths in the transvers and through-thickness directions are predicted much more weakly than the strength of nonpored matrix, and decrease consistently as the porosity of matrix increases.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.23 no.11 s.170
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• pp.2022-2032
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• 1999

In recent years, the subject of remaining life assessment has drawn considerable attention in the power generation industry. In power generation systems a variety of structural components, such as steam pipes, turbine rotors, and superheater headers, typically operate at high temperatures and high pressures. Thus a life prediction methodology accounting for fracture and rupture is increasingly needed for these components. For accurate failure assessment, in addition to the single parameter such as K or J-integral used in traditional fracture mechanics, the second parameter like T-stress describing the constraint is needed. The most critical defects in such structures are generally found in the form of semi-elliptical surface cracks in the welded piping-joints. In this work, selecting the structures of surface-cracked plate and straight pipe, we first perform line-spring finite element modeling, and accompanying elastic-plastic finite element analyses. We then present a framework for including constraint effects (T-stress effects) in the R6 failure assessment diagram approach for fracture assessment.