• International Journal of Highway Engineering
• /
• v.13 no.3
• /
• pp.65-73
• /
• 2011

Recently, researches to introduce the performance warranty contract are in progress for quality improvement of road pavements. The performance warranty contract is a type of contract in which contractors guarantee to maintain certain level of performance during a period from completion of construction. The contract use in Europe and the U.S is being increased because it has been known to contribute to improvement of structure quality, reduction of life cycle cost, development of construction techniques, and etc. The research on performance indicators, threshold values, and warranty durations is essential to effectively introduce the contract in Korea. In this study, literatures on the performance warranty contract for concrete pavements of the Minnesota, Indiana, and Florida of the U.S. were reviewed. Major distresses influencing the pavement performance were investigated and analyzed in the jointed concrete pavement sections of 21 Korean expressway routes to be compared to the performance indicators, threshold values, and warranty durations of the states. More accurate comparison is expected by investigation in planned sections for a long time.

• Proceedings of the Korean Reliability Society Conference
• /
• 2005.06a
• /
• pp.251-257
• /
• 2005

Software system which is essential in operating the computer has gradually become an indispensable element in many aspects of our daily lives and an important factor in numerous systems. In recent years, software cost sometimes exceeds the cost of maintaining the hardware system. In addition to the cost necessary to develop the new software system and to maintain the system, the penalty costs incurred due to software failures are even more significant. In this paper, a cost model incorporating the warranty cost, debugging costto remove each fault detected in the software system, and delivery delay cost is developed. A software reliability model based on non-homogeneous Poisson process(NHPP) is established and the optimal software release policies to minimize the expected total software cost are discussed. Numerical examples are provided to illustrate the results.

• Journal of Applied Reliability
• /
• v.16 no.3
• /
• pp.257-262
• /
• 2016

Recently, the subject of reliability attracts a great deal of domestic and international attentions and the extensive research activities are being conducted as well. Such trend exists mainly due to the fact that the research on the subject of reliability not only contributes to the theoretical developments, but also may find a wide range of applications in practice over several fields. In particular, the research regarding the maintenance policy incorporating certain types of warranty for repairable system and its application is being performed extensively by many researchers, and their efforts seem more concentrated on developing new maintenance policies which minimize the expected operating cost incurred for replacement and repair of the system, while keeping the system at high reliability. Effective maintenance policy may reduce the operating cost and decrease the downtime of the system during its mission period and consequently, increase the productivity of the system. In this article, the major areas of interest in the field of reliability and its historic perspectives are given briefly and the theoretical aspects in several fields of reliability including the maintenance and warranty policies is also discussed. Furthermore, the current domestic situation regarding the education and research on reliability is presented, along with the importance of reliability theory and the difficulty of training reliability personnel. Finally, the author's opinion for effective education system is proposed.

• International Journal of Reliability and Applications
• /
• v.1 no.1
• /
• pp.81-87
• /
• 2000

One of the most important quantities in reliability theory is the expected number of renewals of a system during a given interval. This quantity, the renewal function, is used to determine the optimal preventive maintenance policy and to estimate the cost of a warranty. In this paper we study a parametric approach for a renewal function. The simulation study is presented to compare the relative performance of the introduced estimators of a renewal function. And we show that the proposed parametric estimator performs well.

• International Journal of Reliability and Applications
• /
• v.17 no.1
• /
• pp.85-105
• /
• 2016

In this paper accelerated life testing is incorporated in quality control technique of acceptance sampling plan to induce early failures in high reliability products.Stress under accelerated condition can be applied in constant-stress, step-stress and progressive-stress or combination of such loadings. A ramp-stress results when stress is increased linearly (from zero) with time. In this paper optimum failure-censored ramp-stress accelerated life test sampling plan for log-logistic distribution has been formulated with cost considerations. The log-logistic distribution has been found appropriate for insulating materials. The optimal plans consist in finding optimum sample size, sample proportion allocated to each stress, and stress rate factor such that producer's and consumer's interests are safeguarded. Variance optimality criterion is used when expected cost per lot is not taken into consideration, and bilevel programming approach is used in cost optimization problems. The methods developed have been illustrated using some numerical examples, and sensitivity analyses carried out in the context of ramp-stress ALTSP based on variable SSP for proportion nonconforming.

• Proceedings of the Korean Reliability Society Conference
• /
• 2002.06a
• /
• pp.273-273
• /
• 2002

In this paper, we investigate a software release policy with software reliability growth factor during the warranty period by assuming that the software reliability growth is assumed to occur after the testing phase with probability p and the software reliability growth is not assumed to occur after the testing phase with probability 1-p. The optimal release policy to minimize the expected total software cost is discussed. Numerical examples are shown to illustrate the results of the optimal policy. And we consider a Bayesian decision theoretic approach to determine an optimal software release policy. This approach enables us to update our uncertainty when determining optimal software release time, When the failure time is Weibull distribution with uncertain parameters, a bayesian approach is established. Finally, numerical examples are presented for illustrative propose.

• Journal of Families and Better Life
• /
• v.25 no.3 s.87
• /
• pp.119-135
• /
• 2007

The purpose of this study is to find out the level of digital stress that people experience and to investigate the effects of socio-economic variables on that. To collect data, structured questionnaire was developed and 1,200 questionnaires were distributed through internet. There were 2 dimensions in this study to examine digital stress. First dimension was about the devices themselves: computers and the other digital goods. Second dimension was about the time digital stress occurring in consumers' decision-making process: purchasing and using. Based on Yeo&Kim(2004), sub-dimensions of purchasing and using aspects were chosen. 5 sub-dimensions in purchasing side were new technology, cost, variety of alternatives, warranty service, and informational problem 6 sub-dimensions in using field were mal(or impaired)-functioning. physical aspects, immaturity in use, pressure to use, addiction to use, and informational problem. As independent variables, sex, age, educational level, digitalization acceptability and computer usability were used. The overall level of digital stress was around the average point which was not as high as expected. Digital stress of purchasing was higher than that of using. First, in purchasing aspects, the level of digital stress was relatively high in cost, variety of alternatives and warranty service. Hence, clear communications with consumers about the distinctive aspects and cost of digital devices in market are needed. Secondly, in using side, mal-functioning and physical aspects were relatively more powerful stressors. In the other words, the more serious problems were not from the characteristics of individual consumers but from those of products. Producers should put their best efforts to reduce imperfection (defectiveness) and develop user-friendly digital devices. Also, users' individual efforts to overcome the problems that can be solved privately are necessary. Finally, it was discovered that sex and computer usability were very important variables on digital stress. To extend computer usability of consumers and get over digital illiteracy, it is essential to expand the paths to give chances for people to contact with computers and other digital goods. Still there are lots of people whore computer-illiterate or low-skilled at computers. In policies or educational programs made by government, communities, or schools, more attention should be paid to the digitally vulnerable groups.

• Journal of the Korean Society of Industry Convergence
• /
• v.21 no.3
• /
• pp.141-147
• /
• 2018

In a time when product development cycles are getting shorter and shorter, many companies are making efforts to develop products with high reliability in a short period of time, accelerated life test is widely used as a method to quickly evaluate reliability. Accelerated life test reduces the test life or the life of the product from the observed data by shortening the lifetime of the product or abruptly lowering the performance under the worse condition than the actual condition in order to shorten the test cost or the test time. In this paper, BL3640A-06P+RB35, DC12V model, which is used in the support device of an automatic rotation type digital signage, which display various information such as textures and images on a display screen in a public place or a commercial space, BLDC motors were subjected to a constant stress test and at the rotational speed of 1rpm, $180^{\circ}$ rotation and reverse rotation under actual use conditions, the stress was imposed on the rotating speed of 2rpm and the weight of the actual installed product from 22.2kgf to 10kgf were installed. The lifetime of the actual use environment condition is 23,545 hours and the rotation speed is accelerated. The life time of the acceleration condition with the additional weight is 1,380 hours. The acceleration factor is calculated as 17.06, the one year guarantee test day is 235 days to 14 days, of the period from 470 days to 28 days, and the third year from 704 days to 42 days. The test date of the BLDC motor was tested on the shortened test date, and the rotational speed and the current value were measured. It is found that there is no defect even if it operates as the test date corresponding to the specified one year warranty period and the 3 year accelerated life test which is experimented. Using the statistical technique of the regression analysis the expected time for the motor to defect to #4 samples was 20 years.