• International Journal of Reliability and Applications
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• 제2권3호
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• pp.189-197
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• 2001

The estimation of mean lifetimes in presence of interval censoring with mixed replacement procedure is examined when the distributions of lifetimes are exponential. It is assumed that, due to physical restrictions and/or economic constraints, the number of failures is investigated only at several inspection times during the lifetime test; thus there is interval censoring. The maximum likelihood estimator is found in an implicit form. The Cramor-Rao lower bound, which is the asymptotic variance of the estimator, is derived. The estimation of mean lifetimes for competing failures model has been expanded.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2001년도 추계학술대회 논문집 전기물성,응용부문
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• pp.165-167
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• 2001

Emitter injection efficiency of p+/n-buffer Junction with Gaussian impurity distribution is presented. This model takes into account the variation of the carrier lifetime with injection level which allows a unified interpretation of the injection efficiency for all injection level. The injected carrier density and injection efficiency of the anode are calculated as a function of the current density with the low level lifetime as a parameter for different thicknesses of the anode. The analytical results agree well with simulation.

• 한국신뢰성학회지:신뢰성응용연구
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• 제16권4호
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• pp.280-286
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• 2016

Purpose: Recently, Jiang defines the tradeoff B life to minimize a sum of life lost by preventive maintenance (PM) and corrective maintenance (CM) contribution parts and sets up an optimal replacement age of age replacement policy as this tradeoff life. In this paper, Jiang's model only considering the known lifetime distribution is extended by assigning different weights to two parts of PM and CM in order to reflect the practical maintenance situations in application. Methods: The new age replacement model is formulated and the meaning of a weight factor is expressed with the implied cost of failure under asymptotic expected cost model and also discussed with one-cycle expected cost criterion. Results: The proposed model is applied to Weibull and lognormal lifetime distributions and optimum PM replacement ages are derived with corresponding implied cost of failure. Conclusion: The new age replacement policy to escape the estimation of cost of failure in classical asymptotic expected cost criterion based on the renewal process is provided.

• 품질경영학회지
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• 제34권3호
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• pp.19-30
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• 2006

For highly reliable products, it is difficult to assess the lifetime of the products with traditional life tests. Accordingly, a recent approach is to observe the performance degradation of product during the test rather than regular failure time. This study compares performances of three methods(i.e. the approximation, analytical and numerical methods) to estimate the parameters and quantiles of the lifetime when the time-to-failure distribution follows Weibull and lognormal distributions under a random coefficient degradation rate model. Numerical experiments are also conducted to investigate the effects of model error such as measurements in a random coefficient model.

• Communications for Statistical Applications and Methods
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• 제24권4호
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• pp.397-419
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• 2017

A four-parameter extended fatigue lifetime model called the odd Birnbaum-Saunders geometric distribution is proposed. This model extends the odd Birnbaum-Saunders and Birnbaum-Saunders distributions. We derive some properties of the new distribution that include expressions for the ordinary moments and generating and quantile functions. The method of maximum likelihood and a Bayesian approach are adopted to estimate the model parameters; in addition, various simulations are performed for different parameter settings and sample sizes. We propose two new models with a cure rate called the odd Birnbaum-Saunders mixture and odd Birnbaum-Saunders geometric models by assuming that the number of competing causes for the event of interest has a geometric distribution. The applicability of the new models are illustrated by means of ethylene data and melanoma data with cure fraction.

• 대한산업공학회지
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• 제22권1호
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• pp.51-63
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• 1996

In this paper, we develop two replacement-type reliability acceptance sampling plans(RASPs) for the gamma lifetime distribution assuming that the shape parameter is known. The two plans are respectively based upon failure-free period and hybrid life tests. We then compare the plans in terms of expected test time to reach a decision, power, etc. Computational results indicate among others that the failure-free period RASP has a shorter expected completion time than the corresponding hybrid RASP when the true scale parameter is 'large'. Finally, sensitivity analyses reveal that the effects of the uncertainties involved in the assumed shape parameter on the producer and the consumer risks are in favorable directions for both parties for both types of plans.

• Communications for Statistical Applications and Methods
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• 제23권2호
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• pp.147-161
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• 2016

This paper introduces the four parameter new generalized inverse Weibull distribution and investigates the potential usefulness of this model with application to reliability data from engineering studies. The new extended model has upside-down hazard rate function and provides an alternative to existing lifetime distributions. Various structural properties of the new distribution are derived that include explicit expressions for the moments, moment generating function, quantile function and the moments of order statistics. The estimation of model parameters are performed by the method of maximum likelihood and evaluate the performance of maximum likelihood estimation using simulation.

• 한국강구조학회 논문집
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• 제14권5호통권60호
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• pp.627-639
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• 2002

교량의 건설은 여러 국가에서 거의 완료되었으며, 정부나 고속도로 관계기관은 유지관리쪽에 초점을 맞추고 있다. 교량을 효과적으로 유지관리하기 위해, 시스템 신뢰성을 이용한 교량의 잔존수명을 예측하는 것은 매우 시급하다. 그리고 시스템 신뢰성을 이용한 교량의 유지관리 모델을 개발하는 것은 필수적이다. 이 논문에서는 시스템 신뢰성과 생애함수를 이용하여 예방 (Preventive) 유지관리 와 사후 (Essential) 유지관리 모델을 개발하였다. 이 논문에서 개발된 유지관리 모델을 이용해서 현존하는 교량에 대해 최적의 유지관리 계획을 구하였다.

• 한국철도학회논문집
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• 제8권6호
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• pp.544-549
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• 2005

Nowadays, most of bridge networks are complete or close to completion. The biggest challenge railroad./highway agencies and departments of transportation face is the maintenance of these networks, keeping them safe and serviceable, with limited funds. To maintain the bridges effectively, there is an urgent need to predict their remaining life from a system reliability viewpoint. And, it is necessary to develop the maintenance models based on system reliability concept. In this paper, maintenance models are developed for preventive maintenance and essential maintenance by using system reliability and lifetime distributions. The proposed model is applied to an existing railroad bridge. The optimal maintenance strategy of this bridge is obtained in terms of services life extension and cumulative maintenance cost.

• 대한산업공학회지
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• 제25권2호
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• pp.204-216
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• 1999

Failure physics and statistical lifetime analysis constitute the two extreme ends of the reliability engineering spectrum, and studies that relate failure mechanisms to failure distributions have been near non-existent. This paper is an attempt to stimulate interest to fill the gap between the two extremes and proposes an approach of combining them through i) developing a failure mechanism model, ii) generating failure times by Monte Carlo simulation with the model, iii) deriving the failure time distribution and evaluating the product reliability, and iv) improving the product reliability by the sensitivity analysis. An application of the proposed approach to the BGA(Ball Grid Array) surface mount package is also provided.