• 한국전기전자재료학회논문지
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• 제33권1호
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• pp.50-55
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• 2020

Porcelain insulators have been used for a long time in 154 kV power transmission lines. They are likely to be exposed to sudden failure because of product deterioration. This study was conducted to evaluate the quality of porcelain insulators. After stresses were applied, the damaged regions of aged insulators were investigated in terms of chemical composition, material structure, and other properties. For porcelain insulators that were in service for a long time, the mechanical failure load was 126 kN, whereas the average mechanical failure load was 167.3 kN for new products. It was also determined that corrosion occurred at the metal pin part due to the penetration of moisture into the gap between the pin and the ceramic. Statistical analyses of failure were performed to identify the portion of the insulators that were broken. Cristobalite porcelain insulators fabricated without alumina additives had a high failure rate of 54% for the porcelain component. In the case of the addition of Alumina (Al₂O₃) to the porcelain insulators to improve the strength of the ceramic component, a more frequent damage rate of the cap and pin of 73.3% and 27%, respectively, was observed. This study reports on the material component of SiO₂ and the percentage of alumina added, with respect to the mechanical properties of porcelain insulators.

• 한국신뢰성학회지:신뢰성응용연구
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• 제18권3호
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• pp.220-228
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• 2018

Purpose: The purpose of this study is to investigate the tail behavior of the life distribution which exhibits an increasing failure rate or other positive aging effects after a certain time point. Methods: We characterize the tail behavior of the life distribution with regard to certain reliability measures such as failure rate, mean residual life and reliability function and derive several stochastic properties regarding such life distributions. Also, utilizing an L-statistic and its asymptotic normality, we propose new nonparametric testing procedures which verify if the life distribution has an increasing tail failure rate. Results: We propose the IFR-Tail (Increasing Failure Rate in Tail), DMRL-Tail (Decreasing Mean Residual Life in Tail) and NBU-Tail (New Better than Used in Tail) classes, all of which represent the tail behavior of the life distribution. And we discuss some stochastic properties of these proposed classes. Also, we develop a new nonparametric test procedure for detecting the IFR-Tail class and discuss its relative efficiency to explore the power of the test. Conclusion: The results of our research could be utilized in the study of wide range of applications including the maintenance and warranty policy of the second-hand system.

• Geomechanics and Engineering
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• 제25권2호
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• pp.135-142
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• 2021

This study provided a new research perspective for processing and analyzing AE data to evaluate rock failure. Cluster method and information entropy theory were introduced to investigate temporal and spatial correlation of acoustic emission (AE) events during the rock failure process. Laboratory experiments of granite subjected to compression were carried out, accompanied by real-time acoustic emission monitoring. The cumulative length and dip angle curves of single links were fitted by different distribution models and distribution functions of link length and directionality were determined. Spatial scale and directionality of AE event distribution, which are characterized by two parameters, i.e., spatial correlation length and spatial correlation directionality, were studied with the normalized applied stress. The entropies of link length and link directionality were also discussed. The results show that the distribution of accumulative link length and directionality obeys Weibull distribution. Spatial correlation length shows an upward trend preceding rock failure, while there are no remarkable upward or downward trends in spatial correlation directionality. There are obvious downward trends in entropies of link length and directionality. This research could enrich mathematical methods for processing AE data and facilitate the early-warning of rock failure-related geological disasters.

• 산업경영시스템학회지
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• 제40권4호
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• pp.96-104
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• 2017

A one-shot system (device) refers to a system that is stored for a long period of time and is then disposed of after a single mission because it is accompanied by a chemical reaction or physical destruction when it operates, such as shells, munitions in a defense weapon system and automobile airbags. Because these systems are primarily related with safety and life, it is required to maintain a high level of storage reliability. Storage reliability is the probability that the system will operate at a particular point in time after storage. Since the stored one-shot system can be confirmed only through inspection, periodic inspection and maintenance should be performed to maintain a high level of storage reliability. Since the one-shot system is characterized by a large loss in the event of a failure, it is necessary to determine an appropriate inspection period to maintain the storage reliability above the reliability goal. In this study, we propose an optimal inspection policy that minimizes the total cost while exceeding the reliability goal that the storage reliability is set in advance for the one-shot system in which periodic inspections are performed. We assume that the failure time is the Weibull distribution. And the cost model is presented considering the existing storage reliability model by Martinez and Kim et al. The cost components to be included in the cost model are the cost of inspection $c_1$, the cost of loss per unit time between failure and detection $c_2$, the cost of minimum repair of the detected breakdown of units $c_3$, and the overhaul cost $c_4$ of $R_s{\leq}R_g$. And in this paper, we will determine the optimal inspection policy to find the inspection period and number of tests that minimize the expected cost per unit time from the finite lifetime to the overhaul. Compare them through numerical examples.

• 한국정보전자통신기술학회논문지
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• 제9권4호
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• pp.351-358
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• 2016

과학기술이 급속하게 발전함에 따라 더 강력한 소프트웨어 기능의 급속한 발전과 함께 소프트웨어의 복잡성이 크게 증가함으로써 소프트웨어 테스트 및 신뢰성 평가의 어려움이 증가하고 있다. 소프트웨어 고장분석을 위한 비동질적인 포아송 과정에서 결함당 고장발생률이 상수이거나, 단조 증가 또는, 단조 감소하는 패턴을 가질 수 있다. 본 논문에서는 결함의 기대값을 가정하는 유한고장 소프트웨어 NHPP 모형과 수리시점에서도 고장이 발생할 상황을 반영하는 무한고장 NHPP 모형들을 상호 비교 제시하였다. 소프트웨어 신뢰성 분야에서 많이 사용되는 어랑분포에 근거한 유한고장과 무한고장 소프트웨어 신뢰성 모형에 대한 신뢰도 성능을 비교 분석하였다. 그 결과 유한고장 모형이 무한고장 모형보다 효율적으로 좋게 나타났으며, 이 과정에서 모수추정법은 최우추정법을 이용하였다. 본 연구결과를 통하여 소프트웨어 개발자들에게 소프트웨어 고장현상을 파악하는데 도움을 줄 수 있을 것으로 판단된다.

• 한국안전학회지
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• 제31권5호
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• pp.95-101
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• 2016

This study proposes a multi-scale dynamic system reliability analysis of control system as a method of quantitative evaluation of its performance in probabilistic terms. In this second paper, we discuss the control effect of the viscous damper on the seismic performance of the structure-level failure. Since the failure of one structural member does not necessarily cause the collapse of the structural system, we need to consider a set of failure scenarios of the structural system and compute the sum of the failure probabilities of the failure scenarios where the statistical dependence between the failure scenarios should be taken into account. Therefore, this computation requires additional system reliability analysis. As a result, the proposed approach takes a hierarchial framework where the failure probability of a structural member is computed using a lower-scale system reliability with the union set of time-sequential member failures and their statistical dependence, and the failure probability of the structural system is again computed using a higher-scale system reliability with the member failure probabilities obtained by the lower-scale system reliability and their statistical dependence. Numerical results demonstrate that the proposed approach can provide an accurate and stable reliability assessment of the control performance of the viscous damper system on the system failure. Also, the parametric study of damper capacity on the seismic performance has been performed to demonstrate the applicability of the proposed approach through the probabilistic assessment of the seismic performance improvement of the damper system.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2007년도 춘계학술대회A
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• pp.1848-1853
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• 2007

In this study, we are to analyze the life and the main failure mode of pneumatic valves that are usually applied to the factory automation line. Pneumatic valves have complicated failure cause since they are organized as a complex of various elements. Therefore, in this paper, we analyzed the main failure mode of pneumatic valves, and then performed life test and performance test according to the international standards. On the basis of these processes, we estimated a shape parameter that is the main factor for the calculation of test time for the reliability of pneumatic valves by analyzing life distribution data.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2003년도 춘계학술대회 논문집
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• pp.133-136
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• 2003

In these days, the reliability analysis and prediction are applied for many industrial products and many products require guaranteeing the quality and efficiency of their products. In this study reliability prediction for core units of machine tools has been performed in order to improve and analyze its reliability. ATC(Automatic Tool Changer) and interface Card of PC-NC that are core component of the machine tools were chosen as the target of the reliability prediction. A reliability analysis tool was used to obtain the reliability data(failure rate database) for reliability prediction. It is expected that the results of reliability prediction be applied to improve and evaluate its reliability. Failure rate, MTBF (Mean Time Between Failure) and reliability for core units of machine tools were evaluated and analyzed in this study.

• 한국철도학회논문집
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• 제9권6호
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• pp.725-731
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• 2006

Hot Standby sparing system detecting faults by using software, and being tolerant any faults by using Hardware Redundancy is difficult to perform quantitative reliability prediction and to detect real time faults. Therefore, this paper designs Hot Standby sparing system using hardware basis self checking logic in order to overcome this problem. It also performs failure mode analysis of Hot Standby sparing system with designed self checking logic by using FMEA (Failure Mode Effect Analysis), and identifies reliability assessment of the controller designed by quantifying the numbers of failure development by using FTA (Fault Tree Analysis)

• 한국군사과학기술학회지
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• 제9권2호
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• pp.51-59
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• 2006

The purpose of this paper is to present reliability analysis procedures for repairable systems and apply the procedures for assessing the reliabilities of two subsystems of a specific group of military equipment based on field failure data. The mean cumulative function, M(t), the average repair rate, ARR(t), and analytic test methods are used to determine whether a failure process follows a renewal or non-renewal process. For subsystem A, the failure process turns out to follow a homogeneous Poisson process, and subsequently, its mean time between failures, availability, and the necessary number of spares are estimated. For subsystem B, the corresponding M(t) plot shows an increasing trend, indicating that its failure process follows a non-renewal process. Therefore, its M(t) is modeled as a power function of t, and a preventive maintenance policy is proposed based on the annual mean repair cost.