• 대한안전경영과학회지
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• 제2권2호
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• pp.71-83
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• 2000

This paper presents accelerated life tests for Type I censoring data under probabilistic stresses. Probabilistic stress, $S_j$, is the random variable for stress influenced by test environments, test equipments, sampling devices and use conditions. The hazard rate, ,$theta_j$, is the random variable of environments and the function of probabilistic stress. Also it is assumed that the general stress distribution is uniform, the life distribution for the given hazard rate, $\theta$, is exponential and inverse power law model holds. In this paper, we obtained maximum likelihood estimators of model parameters and the mean life in use stress condition.

• 한국건설관리학회논문집
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• 제17권4호
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• pp.57-65
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• 2016

본 연구에서는 신뢰성 개념을 도입하여 최근 10년간의 한국도로공사 관할의 교량부재별의 유지보수 이력 데이터를 기반으로 적합한 모수적 수명 분포를 찾고 최대우도법으로 구해진 모수를 이용하여 교량 부재별 평균수명 및 신뢰도를 산정하는 방안을 제안하였다. 교량 부재별의 수명 데이터를 가장 잘 설명하는 모수적 수명 분포형태를 찾기 위해 많이 활용되는 지수분포, 와이블분포, 대수정규분포를 대상으로 분석한 결과 대수정규분포와 와이블분포가 해당 수명 데이터의 특성을 가장 잘 설명하는 것으로 나타났다. 이 때 모수 추정을 위해서 최대우도법을 사용하였으며, 적합성 검정을 위해서는 AD통계량을 이용하였다. 추정된 모수를 기반으로 교량 부재별 평균수명을 산정한 결과, 강교도장이 18.51년으로 가장 길었으며, 바닥판이 17.56년으로 그 다음 순이었다. 배수시설과 교량받침의 경우 평균수명이 각각 12.27년, 12.57년으로 가장 짧았다. 또한 교량의 평균수명일 때 추정된 신뢰도 지표는 현재 교량 부재별 유지보수 시점이라고 할 수 있다. 교량받침, 바닥판, 하부구조, 배수시설의 경우 다른 부재보다 빠른 시기에 유지보수를 하는 것으로 분석되었다.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2003년도 춘계학술대회
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• pp.445-450
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• 2003

This study was performed 10 develop the accelerated life test method using Weibull-IPL(Inverse Power Law) model for mechanical components. Weibull-IPL model is concerned with determining the assurance life with confidence level and the accelerated life test time From the relation of weibull distribution factors and confidence limit, the testing times on the no number of failure acceptance criteria arc determined. The mechanical components generally represent wear and fatigue characteristics as a failure mode. IPL based on the cumulative damage theory is applied effectively the mechanical components to reduce the testing time and to achieve the accelerating test conditions. As the actual application example, accelerated life test method of agricultural tractor transmission was described. Life distribution of agricultural tractor transmission was supposed to follow Weibull distribution and life test time was calculated under the conditions of average life (MTBF) 3,000 hours and 90% confidence level for one test sample. According to IPL, because test time call be shorten in case increase test load test time could be reduced by 482 hours when we put the load 1.1 times of rated load than 0.73 times of rated load that is equivalent load calculated by load spectrum of the agricultural tractor. This time, acceleration coefficient was 11.7.

• 대한기계학회논문집A
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• 제24권9호
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• pp.2353-2360
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• 2000

Statistical fatigue properties of metallic materials are increasingly required for reliability design purpose. In this study, static and fatigue tests were conducted and the normal, log-normal, two -parameter Weibull distributions at the 5% significance level are compared using the Kolmogorov-Smirnov goodness-of-fit test. Parameter estimation were compared with experimental results using the maximum likelihood method and least square method. It is found that two-parameter Weibull distribution and maximum likelihood method provide a good fit for static and fatigue life data. Therefore, it is applicable to the static and fatigue life analysis of the spheroidal graphite cast iron. The P-S-N curves were evaluated using log-normal distribution, which showed fatigue life behavior very well.

• 대한안전경영과학회지
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• 제4권3호
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• pp.59-66
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• 2002

This paper presents accelerated life tests for Type I censoring data under probabilistic stresses. Probabilistic stress, S, is the random variable for stress influenced by test environments, test equipments, sampling devices and use conditions. The hazard rate, $\theta$ is a random variable of environments and a function of probabilistic stress. In detail, it is assumed that the hazard rate is linear function of the stress, the general stress distribution is a gamma distribution and the life distribution for the given hazard rate, $\theta$is an exponential distribution. Maximum likelihood estimators of model parameters are obtained, and the mean life in use stress condition is estimated. A hypothetical example is given to show its applicability.

• Communications for Statistical Applications and Methods
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• 제26권2호
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• pp.131-148
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• 2019

Constant stress partially accelerated life tests are studied according to exponentiated Weibull distribution. Grounded on multiple censoring, the maximum likelihood estimators are determined in connection with unknown distribution parameters and accelerated factor. The confidence intervals of the unknown parameters and acceleration factor are constructed for large sample size. However, it is not possible to obtain the Bayes estimates in plain form, so we apply a Markov chain Monte Carlo method to deal with this issue, which permits us to create a credible interval of the associated parameters. Finally, based on constant stress partially accelerated life tests scheme with exponentiated Weibull distribution under multiple censoring, the illustrative example and the simulation results are used to investigate the maximum likelihood, and Bayesian estimates of the unknown parameters.

• 한국정밀공학회지
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• 제16권6호
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• pp.100-107
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• 1999

This paper describes a probabilistic remaining life assessment program for the creep crack growth. The probabilistic life assessment program is developed to increase the reliability of life assessment. The probabilistic life assessment involves some uncertainties, such as, initial crack size, material properties, and loading condition, and a triangle distribution function is used for random variable generation. The resulting information provides the engineer with an assessment of the probability of structural failure as a function of operating time given the uncertainties in the input data. This study forms basis of the probabilistic life assessment technique and will be extended to other damage mechanisms.

• 한국신뢰성학회:학술대회논문집
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• 한국신뢰성학회 2004년도 정기학술대회
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• pp.129-137
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• 2004

This paper presents an accelerated life test for burnout of tungsten filament of incandescent lamp. From failure analyses of field samples, it is shown that their root causes are local heating or hot sports in the filament caused by tungsten evaporation and wire sag. Finite element analysis is performed to evaluate the effect of vibration and impact for burnout, but any points of stress concentration or structural weakness are not found in the sample. To estimate the burnout life of lamp, an accelerated life test is planned by using quality function deployment and fractional factorial design, where voltage, vibration, and temperature are selected as accelerating variables. We assumed that Weibull lifetime distribution and a generalized linear model of life-stress relationship hold through goodness of fit test and test for common shape parameter of the distribution. Using accelerated life testing software, we estimated the common shape parameter of Weibull distribution, life-stress relationship, and accelerating factor.

• KEPCO Journal on Electric Power and Energy
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• 제8권2호
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• pp.79-86
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• 2022

Recently, the amount of maintenance is increasing due to the aging of power facilities, but the budget is constrained. Therefore, the importance of asset management that selects replacement priorities based on the failure probability and enhances investment effects is increasing. Because the number of distribution transformers is very large, the proportion of investment cost is very high. Therefore, it is important to select the investment priority by evaluating the reliable remaining life based on the failure probability. This paper evaluates the statistical expected life using the failure data of distribution transformers for the last 11 years and the current operation data. The hazard rate of distribution transformer and MV cable was compared with each other and the adequacy of early failure removal was reviewed and the statistical expected life corresponding to the cumulative failure probability B3% was calculated.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2007년도 춘계학술대회A
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• pp.1667-1672
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• 2007

In order to assess the reliability of the exhaust bellows for automobiles, accelerated life test model and procedure are developed. By using this method, failure mechanism and life distribution are analyzed. The main results are as follows; i) the main failure mechanism is crack or breakage of inner flexible tube by shaken displacement at shear direction. ii) temperature is a second factor to affect a failure. iii) the life distribution of exhaust bellows is fitted well to Weibull life distribution and the shape parameter is 13.3 on condition of shaken displacement and $600^{\circ}C$