• Journal of Applied Reliability
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• v.17 no.2
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• pp.103-111
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• 2017

Purpose: Accelerated degradation tests can speed time to market and reduce the test time and costs associated with long term reliability tests to verify the required service life of a product or material. This paper proposes a service life prediction method for components or materials using an accelerated degradation tests based on the relationships between temperature and the rate of failure-causing chemical reaction. Methods: The relationship between performance degradation and the rate of a failure-causing chemical reaction is assumed and least square estimation is used to estimate model parameters from the degradation model. Results: Methods of obtaining acceleration factors and predicting service life using the degradation model are presented and a numerical example is provided. Conclusion: Service life prediction of a component or material is possible at an early stage of the degradation test by using the proposed method.

• Journal of Korean Institute of Industrial Engineers
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• v.28 no.4
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• pp.407-414
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• 2002

The inherent reliability of a product is primarily determined in the design stage, and therefore, design engineers should be able to design reliability into the product in an efficient manner. Especially, the product should be designed such that its reliability is robust to various noise factors encountered in production and field environments. The Taguchi method can be effectively used for this purpose. However, there exist only a few attempts to integrate the Taguchi method with reliability design, and in addition, the existing works do not sufficiently consider the robustness and/or the distinction between noise and acceleration factors. This paper develops a unified approach to robust reliability design assuming that accelerated life tests are conducted at each combination of design and noise conditions. First, an experimental structure for assigning not only acceleration but also noise factors is presented. Second, the reliability at the use condition is estimated using the assumed accelerated life test model. Third, reliabilities are transformed into 'efforts' using an effort function which reflects the degree of difficulty involved in improving the reliability. Finally, an optimal setting of design parameters is determined based on the mean and standard deviation of the effort values. The above approach is illustrated with an example of a paper feeder design.

• Journal of Distribution Science
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• v.12 no.11
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• pp.101-111
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• 2014

Purpose - This study aims to verify the construct of the service quality suitable to the characteristics of the business center, to develop the scale that can measure the service quality objectively, compare the diverse business centers in Korea, and present desirable methods of business center management and operation. Research design, data, and methodology - In the first stage, literature research and focus group interviews with current users and actual business experts of business centers were conducted. In addition, 69 early stage scale items were derived. In the second stage, a Delphi survey was conducted on the experts of business and academic circles. The measurement items in the early stage were supplemented and revised. The content validity rate (CVR) of 69 measures was computed and then the experts' opinions were used. As a result, the business center service quality scale, made up of 9 organizing factors and 36 measurement items, was constructed. In the third stage, a survey was conducted on the occupants who were currently using the business center. It was to confirm if the developed business center service quality scale could be actually utilized. The data of 435 samples collected were used. To refine the scale items, the exploratory factor analysis (EFA) was conducted repeatedly. Results - The business center service quality scale, made up of 8 factors and 33 items, was developed again. The 8 factors are reliability, speed, kindness, specialty, responsibility, appearance, convenience, and public interest. The reliability coefficient (Cronbach's Alpha) of each factor is greater than .7. Thus, it was confirmed that there was reliability in the measurement items. Further, the model suitability was verified using the confirmatory factor analysis (CFA), and the convergent validity and the discriminant validity were verified. This proved the construct validity. Through this process, the Korea Business Center Service Quality Scale was developed. Based on factor analysis, the developed business center service quality (BCSQ) scale consists of 4 aspects, 8 factors, and 33 items, comprising the "process quality" aspect: reliability (3 items), speediness (4 items), kindness (3 items) factors, the outcome quality aspect: expertise (3 items), responsibility (5 items) factors, the environment quality aspect: appearance (5 items), convenience (3 items) factors, and the public interest aspect: public interest (7 items) factor. However, according to CFA, the BCSQ scale consists of a total of 4 aspects, 8 factors, and 33 items, comprising the "process quality" aspect: reliability (3 items), speediness (3 items), kindness (3 items) factors, the outcome quality aspect: expertise (2 items), responsibility (4 items) factors, the environment quality aspect: appearance (3 items), convenience (2 items) factors, and the public interest aspect: public interest (3 items) factor. Conclusions - The BCSQ scale could serve as a diagnostic tool that will allow business center managers to determine service areas that are weak and in need of attention, and to improve the service quality of the business center.

• Journal of the Korean Ceramic Society
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• v.46 no.2
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• pp.219-223
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• 2009

Effects of MgO or $R_2O_3$(R:Dy, Ho, Yb) on the capacitance aging behavior of multilayer ceramic capacitors (MLCCs) based on $BaTiO_3$ dielectrics under DC electrical fields has been studied. At a DC field of 1 $V{/\mu}m$, the capacitance of MLCC specimens dropped immediately in a very short period (<10 s, the first stage) and then decreased continuously with time (the second stage). Mn doping significantly increased the aging rate in the second stage. The addition of MgO or $R_2O_3$ notably decreased the second stage aging rate of Mn-doped specimens. Yb doping gives rise to the lowest aging rate in the second stage, which is due to the larger population of defect dipoles associated with oxygen vacancies.

• Journal of Energy Engineering
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• v.24 no.1
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• pp.17-23
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• 2015

Electrical door system is one of the most essential items for the successful commercial operation of the railway vehicles. Nowadays, reliability values of electrical door system have a tendency to be included in technical requirements for design and manufacturing of rolling stocks. Manufacturer shall meet the reliability target values of electrical door system which is proposed by railway operator in procurement contract book. Railway operator shall approve the supplier's the reliability target values based on maintenance operation data. Railway operators are in the transition stage from the framework of maintenance interval based on time to the framework of maintenance interval based on distance. In this study, failure rates of the electrical door system currently used in railway vehicles are collected from maintenance field data. Failure rates are analyzed by using Minitab. Several kinds of plan for improving reliability are also suggested. It is necessary to keep studying on reliability prediction methodology, applying it in the field and implementing on improvement of reliability through feedback as well. Further, it will be useful for determining new maintenance policies or changing maintenance intervals for existing railway vehicles.

• Nuclear Engineering and Technology
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• v.55 no.6
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• pp.2047-2052
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• 2023

Risk-informed approach has been widely applied in the safety design, regulation, and operation of nuclear reactors. It has been commonly accepted that risk-informed design optimization should be used in the innovative reactor designs to make nuclear system highly safe and reliable. In spite of the risk-informed approach has been used in some advanced nuclear reactors designs, such as Westinghouse IRIS, Gen-IV sodium fast reactors and lead-based fast reactors, the process of risk-informed design of nuclear reactors is hardly to carry out when passive system reliability should be integrated in the framework. A practical method for new passive safety reactors based on probabilistic safety assessment (PSA) and passive system reliability analyze linking is proposed in this paper. New three-dimension frequency-consequence curve based on risk concept with three variables is used in this method. The proposed method has been applied to the determination optimization of design options selection in a 10 MWth lead-based research reactor(LR) to obtain one optimized system design in conceptual design stage, using the integrated reliability and probabilistic safety assessment program RiskA, and the computation resources and time consumption in this process was demonstrated reasonable and acceptable.

• The KIPS Transactions:PartD
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• v.10D no.5
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• pp.837-844
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• 2003

The software reliability have to be improved as one major method to enhance the quality of developed software, and its defect is detected and modified through testing as a direct way to meet the purpose before releasing. Once its reliability grows up to the target and it is released to public. there nay be operational reliability problem. The operational software reliability trend nay be different depending on the condition whether it is universal or dedicated. And its reliability estimation is changed based on the condition if it follows uniform testing efforts or Weibull testing efforts. I study the operational reliability trend of dedicated software, applying two case testing efforts for the released item.

• Nuclear Engineering and Technology
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• v.51 no.1
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• pp.45-53
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• 2019

Thermal-hydraulic passive safety systems (PSSs) are incorporated into many advanced reactor designs on the bases of simplicity, economics and inherent safety nature. Several factors among which are the critical parameters (CPs) that influence failure and reliability of thermal-hydraulic (t-h) passive systems are now being explored. For simplicity, it is assumed in most reliability analyses that the CPs are independent whereas in practice this assumption is not always valid. There is need to critically examine the dependency influence of the CPs on reliability of the t-h passive systems at design stage and in operation to guarantee safety/better performance. In this paper, two multivariate analysis methods (covariance and conditional subjective probability density function) were presented and applied to a simple PSS. The methods followed a generalized procedure for evaluating t-h reliability based on dependency consideration. A passively water-cooled steam generator was used to demonstrate the dependency of the identified key CPs using the methods. The results obtained from the methods are in agreement and justified the need to consider the dependency of CPs in t-h reliability. For dependable t-h reliability, it is advisable to adopt all possible CPs and apply suitable multivariate method in dependency consideration of CPs among other factors.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.21 no.1
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• pp.300-307
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• 2020

This study examines the reliability evaluation concept and procedure of bulletproof materials (BRP: Bulletproof Reliability Program). ASRP, RAM analysis tasks were utilized for the study. Based on this analysis, the concept, method, performance system, and procedure of BRP were examined. The BRP task execution procedure consists of the following four steps. First, the business (evaluation) planning stage establishes the evaluation plan every year. Second, there is a testing stage that performs the general inspection, functional test, and operational test according to the established plan. Thirdly, there is an evaluation/analysis phase to synthesize/analyze the results and to judge the appropriate grade considering the performance of bulletproof materials. Finally, the follow-up step of each group according to the result. The following criteria are suggested for BRP implementation: BRP testing capability, development of BRP evaluation method, and recognition of the importance of BRP business.

• Journal of the Korea Institute of Building Construction
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• v.10 no.2
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• pp.133-138
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• 2010

Conceptual cost is estimated with insufficient information at an early stage of a building construction project, resulting in an inevitable gap between conceptual estimated cost and real constructed cost. For a project to be successful, this gap must be managed to be lower than a reliable level. Therefore, the purpose of this study is to propose a structural process for managing the reliability of conceptual cost estimates at an early stage of a building construction project. In researching this study, conceptual cost estimate experts were interviewed,and a risk management process was studied. Reliability assessment and a review process for improving the quality of conceptual cost estimate and the planning strategy of reliability management based on previous similar projects were added to the present estimate process. The proposed reliability management process will improve the chances of a successful project, by helping to decrease the risk of conceptual estimated cost.