• Proceedings of the Korea Society for Industrial Systems Conference
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• 2009.05a
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• pp.107-113
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• 2009

This paper deals with noninformative priors for such as Jeffres' prior, reference prior and probability matching prior for scale parameter of exponential distribution when the data are collected in multiple step stress accelerated life tests. We find the noninformative priors for this model and show that the reference prior satisfies first order matching criterion. Using artificial data, we perform Bayesian analysis for proposed priors.

• Journal of Korean Society of Industrial and Systems Engineering
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• v.23 no.61
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• pp.75-87
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• 2000

This paper proposes a procedure for designing an accelerated test using SMAT(Stress, (failure) Mechanism and Test) model describing the relation among stress, failure mode/mechanism and test method. In SMAT model the stresses to be applied are derived from the environmental factor analysis, the relative importance of those stresses can be estimated using AHP(Analytic Hierarchy Process) and failure mode/mechanism and test method are derived from the fields failure information and FMEA(Failure Mode and Effect Analysis). By applying the procedure we can make a selection of major factors to cause the failure of assembly and design the accelerated test using DOE(Design of Experiments) The procedure is illustrated with an qualification test case study of washing machine shaft assembly in "A" electric appliance company.

• Journal of Korean Society for Quality Management
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• v.23 no.4
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• pp.13-27
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• 1995

This paper considers the design of life test sampling plans based on Type II censored accelerated life tests. The lifetime distribution of products is assumed to be exponential. An estimator of acceleration factor between use condition stress and an accelerated level of stress higher than use condition stress is assumed to be known. The critical value for lot acceptance and the number of failure before censoring which satisfy the producer's and consumer's risk requirements are determined. The properties of the proposed life test sampling plans are investigated.

• Journal of Applied Reliability
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• v.9 no.1
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• pp.47-58
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• 2009

In this paper, an accelerated life test procedure for a vacuum cleaner motor is proposed. We investigate the failure mechanism of the motor and select some accelerating factors and determine the orifice size as a key accelerating factor. Three stress levels of orifice size are tested and the failure data with censored data are analyzed. The modified accelerating test will reduce the test time in design phase by using the accelerating factor.

• International Journal of Reliability and Applications
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• v.13 no.1
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• pp.19-35
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• 2012

This paper presents an optimum design of step-stress partially accelerated life test (PALT) plan which allows the test condition to be changed from use to accelerated condition on the occurrence of fixed number of failures. Various life distribution models such as exponential, Weibull, log-logistic, Burr type-Xii, etc have been used in the literature to analyze the PALT data. The need of different life distribution models is necessitated as in the presence of a limited source of data as typically occurs with modern devices having high reliability, the use of correct life distribution model helps in preventing the choice of unnecessary and expensive planned replacements. Truncated distributions arise when sample selection is not possible in some sub-region of sample space. In this paper it is assumed that the lifetimes of the items follow Truncated Logistic distribution truncated at point zero since time to failure of an item cannot be negative. Optimum step-stress PALT plan that finds the optimal proportion of units failed at normal use condition is determined by using the D-optimality criterion. The method developed has been explained using a numerical example. Sensitivity analysis and comparative study have also been carried out.

• Journal of Korean Society for Quality Management
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• v.24 no.4
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• pp.14-28
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• 1996

We consider optimal designs of partially accelerated life testing which is deviced for parallel systems with the considerably long life time. In partially step-stress life testing, test items are first run simultaneously at use condition for a specified time, and the surviving items are then run at accelerated condition until a predetermined censoring time. In partially constant-stress life testing, test items are run at either use or accelerated condition only until a specified censoring time. The optimal criterion for each test is to minimize either the generalized asymptotic variance of maximum likelihood(ML) estimators of the hazard rates at use condition and the acceleration factors or the asymptotic variance of the ML estimators of the acceleration factors.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.38 no.11
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• pp.1221-1229
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• 2014

This paper proposes an approach for predicting the fatigue life of a propeller shaft of a forklift truck by an accelerated life test method. The accelerated life test method adopted in this study is the calibrated accelerated life test, which is highly effective in the prediction of the lifetime and enables significant reduction of the test time as well as a quantification of reliability in the case of small sample sizes. First, the fatigue test was performed under two high stress levels, and then, it was performed by setting low stress levels in consideration of the available test time and extrapolation. Major reliability parameters such as the lifetime, accelerated power index, and shape parameter were obtained experimentally, and the experimentally predicted lifetime of the propeller shaft was verified through comparison with results of an analysis of load spectrum data under actual operating conditions.

• Journal of Applied Reliability
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• v.17 no.2
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• pp.136-142
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• 2017

Purpose: In this paper, we propose a test method for evaluating the life time of the inverter which is one of the main internal configuration systems in order to evaluate the life time of the power supply for the vehicle. Methods: The performance and failure criteria required for the development of the accelerated life test method were established and the Taguchi method was used to derive the stress factors affecting performance and reliability. Results: The major stress of the product degradation were considered to be high temperature. Conclusion: The acceleration factor was estimated through a two-level high temperature test and a test methods was designed to guarantee the accelerated life time of the inverter.

• Journal of Korean Institute of Industrial Engineers
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• v.34 no.1
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• pp.23-31
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• 2008

This paper presents accelerated degradation test plans considering adoption of tightened critical values. Under arandom coefficient degradation rate and log-linear acceleration models, the asymptotic variance of an estimatorfor a lifetime quantile at the use condition as the optimization criterion is derived where the degradation ratefollows a lognormal and Reciprocal Weibull distributions, respectively and then the low stress level andproportions ofunits allocated to each stress level are determined. We also show that the developed test plans canbe applied to the multiplicative model with measurement error.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.34 no.3
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• pp.273-281
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• 2010

In this paper, a method to predict the fatigue life of an axle drive shaft by the calibrated accelerated life test (CALT) method is proposed. The CALT method is very effective for predicting lifetimes, significantly reducing test time, and quantifying reliability. The fatigue test is performed by considering two high stress and one low stress levels, and the lifetime at the normal stress level is predicted by extrapolation. In addition, in this study, the major reliability parameters such as the lifetime, accelerated power index, shape parameter, and scale parameter are determined by conducting various experiments. The lifetime prediction of the axle drive shaft is verified by comparing the experimental results with load spectrum data. The results confirm that the CALT method is effective for lifetime prediction and requires a short test time.