• International Journal of Reliability and Applications
• /
• v.6 no.1
• /
• pp.31-39
• /
• 2005

An economic life test sampling plan for products with exponential lifetime distribution is developed. To reduce test time, a test plan with curtailed Type II censoring is considered. A cost model is constructed which involves three cost components; test cost, accept cost, and reject cost. Determination of optimal plan minimizing the expected average cost per lot is discussed with a constraint related to consumer's risk. Some numerical examples are provided.

• Journal of Applied Reliability
• /
• v.18 no.2
• /
• pp.122-129
• /
• 2018

Purpose: This article develops an optimal reliability acceptance sampling plan for the case where the degradation quantity of the performance characteristic follows Weibull distribution. Method: For developing reliability acceptance sampling plans, the sample size and the acceptance constant are determined based on the accelerated characteristic of the test condition and the product. Results: The sample size and the acceptance constant are provided such that the constraints of the producer and the consumer risks are satisfied. Conclusion: Reliability acceptance sampling plans based on the accelerated degradation test method can be used for the quality control within a resonable amount of cost and time. In this article. an optimal reliability sampling plans are newly developed for this purpose.

• Journal of Applied Reliability
• /
• v.12 no.1
• /
• pp.47-56
• /
• 2012

Reliability demonstration tests with zero-failure acceptance criterion are most commonly used in the field of reliability application since they require fewer test samples and less test time compared to other test methods that guarantee the same reliability with a given confidence level. For products with lognormal lifetime distribution, an economic zero-failure test plan is developed that minimizes the total cost related to perform a life test to guarantee a specified reliability of a product with a given confidence level. A numerical example is provided to illustrate the use of the proposed test plan.

• Journal of Korean Society for Quality Management
• /
• v.30 no.1
• /
• pp.74-96
• /
• 2002

The objectives of this study is to suggest the rectifying sampling inspection plan considering quality cost. Limiting quality level(LQL) plans(also called LTPD plans) and outgoing quality(OQ) plans are considered. The Hald's linear cost model is discussed with and without a beta prior for the distribution of the fraction of nonconforming items in a lot. It is assumed that the sampling inspection is error free. We consider the design of reliability acceptance sampling plan (RASP) for failure rate level qualification at selected confidence level. The lifetime distribution of products is assumed to be exponential. MIL-STD-690C and K C 6032 standards provide this procedures. But these procedures have some questions to apply in the field. The cost of test and confidence level(1-$\beta$ risk) are the problem between supplier and user. So, we suggest that the optimal life test sampling inspection plans using simple linear cost model considering product cost, capability of environment chamber, environmental test cost, and etc. Especially, we consider a reliability of lots that contain some nonconforming items. In this case we assumed that a nonconforming item fail after environmental life test. Finally, we develope the algorithm of the optimal sampling inspection plan based on minimum costs for rectifying inspection and RASP. And computer application programs are developed So, it is shown how the desired sampling plan can be easily found.

• Journal of the Korea Safety Management & Science
• /
• v.6 no.4
• /
• pp.139-153
• /
• 2004

Korea Railroad Research Institute(KRRI) has developed the rubber-tired AGT system from 1999 to 2004. The rubber-tired AGT vehicle is now on test for its performance and function in the Gyeong-San test line. In this paper, we provide the reliability management plan to assure required the RAMS(reliability, availability, maintainability 8t safety) of the AGT vehicle system.

• Communications for Statistical Applications and Methods
• /
• v.17 no.5
• /
• pp.725-731
• /
• 2010

Economic Reliability test plans(ERTP) are proposed considering that the life time of the submitted items follow the Pareto distribution of the second kind. For various specified acceptance number, sample size and producer's risk, a minimum test termination time is obtained. A comparison of proposed plan has been made with the existing plan developed by Aslam et al. (2010). The results are explained by tables and example.

• International Journal of Reliability and Applications
• /
• v.15 no.1
• /
• pp.23-50
• /
• 2014

This paper deals with formulation of optimum multi-objective modified step-stress accelerated life test (ALT) plan for Burr type-XII distribution under type-I censoring. Since it is impractical to estimate only one objective parameter after conducting costly ALT tests; also, it is not desirable to assume instantaneous changes in stress levels because of limited capacity of test equipments and the presence of undesirable failure modes, therefore, an optimum multi-objective modified step-stress ALT plan has been designed. The optimal test plan consists in determining the optimum low stress level and optimal time at which stress starts linearly increasing from low stress by minimizing the weighted sum of the asymptotic variances of the maximum likelihood estimator of quantile lifetimes at design constant stress. The method developed has been illustrated using an example. Sensitivity analysis has been carried out. Comparative study has also been done to highlight the merits of the proposed model.

• Journal of Applied Reliability
• /
• v.13 no.3
• /
• pp.165-174
• /
• 2013

Thruster break for aerogenerator performs a role that is stopping the rotor in case of emergency such as strong wind, system abnormality or maintenance check. In this study, failure analysis and test evaluation on the thruster break for aerogenerator are proposed, and the entire process to improve reliability of the product through design improvement is presented. The typical failure case is fatigue and wear, and failure cause on these are identified and improvement plan is presented. Lastly, reliability improvement is established to analyse test results before after the life test.

• Journal of the Korea Safety Management & Science
• /
• v.9 no.2
• /
• pp.123-134
• /
• 2007

This paper focuses on the in-house reliability assurance plan for the bulk materials of each company. The reliability assurance needs in essence a long time and high cost for testing the materials. In order to reduce the time and cost, accelerated life test is adopted. The bulk sampling technique was used for acceptance. Design parameters might be total sample size(segments and increments}, stress level and so on. We focus on deciding the sample size by minimizing the asymptotic variance of test statistics as well as satisfying the consumer's risk. In bulk sampling, we also induce the sample size by adapting the normal life time distribution model when the variable of the lognormal life time distribution is transformed and adapted to the model. In addition, the sample size for both the segments and increments can be induced by minimizing the asymptotic variance of test statistics of the segments and increments with consumer's risk met. We can assure the reliability of the mean life and B100p life time of the bulk materials by using the calculated minimum sample size.

• Journal of Applied Reliability
• /
• v.7 no.2
• /
• pp.57-72
• /
• 2007

This paper suggests an approach for using ALTA 7 PRO to design accelerated life test plans. Conducting a accelerated life test requires finding life distributions at different stress levels and determining an appropriate life-stress relationship. Moreover, a test plan needs to be developed. In its optimal test plan, stress levels are determined and the proportions of test units are assigned at each stress level so that asymptotic variance of the maximum likelihood estimate of a (log) percentile of the life distribution at the design stress is minimized. Examples are presented for usage.