• 품질경영학회지
• /
• 제36권1호
• /
• pp.31-39
• /
• 2008

This paper proposes a method of estimating the lifetime distribution at use condition for constant stress accelerated life tests when an infant-mortality failure mode as well as wear-out one exists. General limited failure population model is introduced to describe these failure modes. It is assumed that the log lifetime of each failure mode follows a location-scale distribution and a linear relation exists between the location parameter and the stress. An estimation procedure using the expectation and maximization algorithm is proposed. Specific formulas for Weibull distribution are obtained. An illustrative example and the simulation results are given.

• International Journal of Reliability and Applications
• /
• 제15권1호
• /
• 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.

• 지역사회간호학회지
• /
• 제14권2호
• /
• pp.263-273
• /
• 2003

Objectives: The purpose of this study was to identify the family phenomenon and characteristics by ICNP such as family shape, life standard. area, and development stage. Method: 1. Sample size was 115. 2. Data analysis method included frequency analysis including ratio. Results: 1. On the distribution of the family phenomena by family shape, the nuclear family showed a higher ratio on the distribution in family communication and the unhealthy life style. The nuclear family was related to children andhad a higher ratio on the inadequate care management of the sick member. The extended family showed the highest ratio on the inadequate care management of sick member. 2. On the distribution of the family phenomena by family life standard, the family with medium life standard showed a higher ratio on the inappropriate family coping, whereas the family with lower life standard appeared to have a higher ratio on the inadequate care management of the sick member. 3. On the distribution of the family phenomena by area. the large city area showed the highest ratio on the inappropriate family coping, the medium and small city area appeared to have the highest ratio on the unhealthy life style. The county area showed the highest ratio on the inadequate care management of sick member. 4. On the distribution of the family phenomena by development stage, the family in rearing period showed a higher ratio on the inappropriate family coping and the lack of family intimacy. Families with preschool children showed a higher ratio on the unhealthy life style, and families with school age children showed the highest ratio on the inappropriate family coping. Families with adolescents appeared to have the highest ratio on the disturbance in family communication, and families with launching young adults showed the highest ratio on the inadequate care management of sick member. 5. On the distribution of the family characteristics by family shape, the nuclear family showed a higher ratio on the family characteristics such as less communication chances among family members and neglect of general child rearing, whereas the third generation family appeared to have a higher ratio on the characteristics such as overburden of housewife's role and short of caring among family members. 6. On the distribution of the family characteristics by family life standard, the family of medium life standard showed higher ratio on the family characteristics such as a few communication chance among family and overburden of housewife's role, and the family of lower life standard appeared to higher ratio on the family characteristics such as short of caring among family members. 7. On the distribution of the family characteristics by area. the large city area showed a higher ratio on the family characteristics such as overburden of housewife's role and neglect of general child rearing. The medium and small city area appeared to have a higher ratio on the family characteristics such as less communication chancec among family members. The county area showed a higher ratio on the family characteristics such as short-term care among family members. 8. On the distribution of the family characteristics by development stage, the family with rearing period showed a higher ratio on the family characteristics such as neglect of general child rearing. Families with preschool children showed a higher ratio on the family characteristics such as less communication chancec among family members. Families with school age children showed a higher ratio on the family characteristics such as overburden of housewife's role. Families with adolescents appeared to have a higher ratio on the family characteristics such as less communication chances among family members. Families with launching young adults showed a higher ratio on the family characteristics such as less communication chances and short-term care among family members.

• 품질경영학회지
• /
• 제23권1호
• /
• pp.15-28
• /
• 1995

We consider a step-stress life testing which is devised for a two-component parallel system with considerably long life time. To describe such a system, we use an exponential distribution as the survival function. The lift distribution is assumed between the log mean life time and the stress with the cumulative exposure model. The criterion for optimality is to minimize the sum of the variances of the maximum likelihood estimators of the mean life times of each part under the normal stress.

• 대한산업공학회지
• /
• 제14권1호
• /
• pp.103-117
• /
• 1988

Replacement demand plays an important role to forecast the total demand of durable goods, while most of the diffusion models deal with only adoption data, namely initial purchase demand. This paper presents replacement demand forecasting models incorporating repurchase rate, multi-ownership, and dynamic product life to complement the existing diffusion models. The performance of replacement demand forecasting models are analyzed and practical guidelines for the application of the models are suggested when life distribution data or adoption data are not available.

• 대한기계학회논문집
• /
• 제18권8호
• /
• pp.2053-2061
• /
• 1994

The static and fatigue tensile tests have been conduted to predict the fatigue life of 8-harness satin woven and plain woven carbon/epoxy composite plates containing a circular hole. A fatigue residual strength degradation model, based on the assumption that the residual strength for unnotched specimen decreases monotonically, has been applied to predict statistically the fatigue life of materials used in this study. To determine the parameters(c, b and K) of the residual strength degradation model, the minimization technique and the maximum likelihood method are used. Agreement of the converted ultimate strength by using the minimization technique with the static ultimate strength is reasonably good. Therefore, the minimization technique is more adjustable in the determination of the parameter and the prediction of the fatigue life than the maximum likelihood method.

• 한국공작기계학회:학술대회논문집
• /
• 한국공작기계학회 1997년도 추계학술대회 논문집
• /
• pp.265-270
• /
• 1997

Helical gear system is utilized to transmit motion between parallel shafts. The axial thrust loads on the shafts are existed. On each of the support shafts, at least one of the bearings should be able to support the axial loads. The reliability and life analysis are based on the two-parameter Weibull distribution lives of the component gears and bearings. The computer calculates the system lives and dynamic capacities of the components and their system. The system life is defined as the life of the component or the helical gear system at an output torque at which the probability of survival is ninety percent.

• 대한기계학회:학술대회논문집
• /
• 대한기계학회 2007년도 춘계학술대회A
• /
• pp.1848-1853
• /
• 2007

In this study, we are to analyze the life and the main failure mode of pneumatic valves that are usually applied to the factory automation line. Pneumatic valves have complicated failure cause since they are organized as a complex of various elements. Therefore, in this paper, we analyzed the main failure mode of pneumatic valves, and then performed life test and performance test according to the international standards. On the basis of these processes, we estimated a shape parameter that is the main factor for the calculation of test time for the reliability of pneumatic valves by analyzing life distribution data.

• 대한기계학회:학술대회논문집
• /
• 대한기계학회 2007년도 춘계학술대회A
• /
• pp.1842-1847
• /
• 2007

In this study, we are to analyze the life and the main failure mode of flexible tubes fitting for pneumatic that are usually applied in the factory automation line. Flexible tubes fitting for pneumatic have complicated failure cause because they are organized as a complex of various elements. Therefore, in this paper, we analyzed the main failure mode of flexible tubes fitting for pneumatic, and then performed life test and performance test according to the international standards. On the basis of these processes, we estimate shape parameter that is the main factor for the calculation of test time for the reliability of flexible tubes fitting for pneumatic and their data analysis of life distribution.

• 대한산업공학회지
• /
• 제19권2호
• /
• pp.15-21
• /
• 1993

This paper considers the optimal design of accelerated life test in which the stress is linearly increased. It discusses the special case when the life distribution under constant stress follows an exponential distribution and the accelerated equation satisfies the inverse power law. It is assumed that cumulative damage is linear, that is, the remaining life of test units depends only on the current cumulative fraction failed and current stress(cumulative exposure model). The optimization criterion is the asymptotic variance of the maximum likelihood estimator of the log mean life at a design stress. The optimal increasing rate is obtained to minimize the asymptotic variance. Table of sensitivity analysis is given for the prior estimators of model parameters.