Search

In this paper, we describe how to analyze and design the accelerated life test plans to improve the quality and reliability of the item. We focus on estimating the costs of maintenance service poli...

In this paper, a step-stress accelerated life test with two stress variables for Weibull distribution under progressive type-I censoring is considered. The stress-life relationship as a log-linear function of stress levels, and for each combination of stress levels, a cumulative exposure model is assumed. The maximum likelihood and Bayes estimates of the model parameters are obtained. The optimum test plan is developed using variance-optimality criterion, which consists in finding out the optimal stress change time by minimizing asymptotic variance of the maximum likelihood estimates of the log of the scale parameter at the design stress. The proposed study illustrated by using simulated data.

This paper studies the problem about how to design a Bayesian sampling plan (BSP) for two exponential distributions linked by the cumulative exposure model through a simple step-stress accelerated ...

In this paper, we consider a two-stage sequential estimation procedure to estimate the parameters of a cumulative exposure model under an accelerated testing scenario. In particular, we focus on a step-stress model where the stress level changes after a pre-specified number of failures occur, which is also random. This is termed as a 'random stress change time' in the literature. We further aim to estimate these parameters using maximum precision and hence use a certain variance optimality criteria. Our proposed two-stage estimation procedures follow interesting efficiency properties and their applicability is seen through extensive simulation analyses and a pseudo-real data example from reliability studies.

Consider estimating data of failure times under step-stress partially accelerated life tests based on adaptive Type-I hybrid censoring. The mathematical model related to the lifetime of the test units is assumed to follow Rayleigh distribution. The point and interval maximum-likelihood estimations are obtained for distribution parameter and tampering coefficient. Also, the work is conducted under a traditional Type-I hybrid censoring plan (scheme). A Monte Carlo simulation algorithm is used to evaluate and compare the performances of the estimators of the tempering coefficient and model parameters under both progressively hybrid censoring plans. The comparison is carried out on the basis of mean squared errors and bias.

This article describes how a step-stress accelerated life test (SSALT) can be designed for testing the fatigue life and reliability of structural components with a single failure mode. With simple numerical simulations of the crack’s propagation in the notched area of the structural part for different loading levels, the slope of the S-N curve for a structural component is initially estimated. Then, a very few fatigue-life experiments are carried out in the high-cycle domain to determine the intercept of the structure’s S-N curve. By considering the scatter from the material’s P-S-N curve, different SSALT designs for the structural component can be composed and checked for their expected acceleration factor. The procedure is experimentally validated for the case of a notched specimen and two different SSALT designs. From the results it can be concluded that the predicted durations of the SSALT experiments correlate well with the real experiments.

In this article, we mainly focus on the meta-analysis of several simple step-stress experimental data sets. It is assumed that independent data sets are obtained from s simple step-stress experimen...

In accelerated life testing, the products are tested under high stress conditions and the results are used to draw inferences about the product lifetime under the normal stress condition using a re...

For highly reliable products and devices, conducting the life tests at normal usage conditions demands a great deal of time and cost, which can result in missed opportunities to introduce the produ...

With the engineering technology and manufacturing processes continuously improving, modern products and devices are becoming more sophisticated and reliable. On the other hand, conducting tradition...

This paper considers a step-stress accelerated dependent competing risks model under progressively Type-I censoring schemes. The dependence structure between competing risks is modeled by a general...

The competing risks problem is ubiquitous in different areas of life science, in engineering and science where failure of one component causes to fail all the system. Studying life testing experiment of a product or material, usual requires long period of time to monitoring. For the purpose of reducing the testing period, test units may be presented under conditions more severe than normal circumstances, which is called accelerated life tests (ALTs). More precisely, this procedure makes the lives shorter than would be spotted or monitored under normal conditions. Burr XII model has increasingly important in engineering statistics than other model. So, within this paper, maximum likelihood and Bayesian estimations will be discussed under the type-II censored Burr XII life time data. The Burr XII parameters as well as accelerated factor under competing risks model will be estimated. Also, the asymptotic confidence intervals under normality theory and credible intervals are obtained from MCMC sampling method will be drawn. Finally, the maximum likelihood and Bayesian estimations will be considered and a simulation investigation is described and reported by comparing the two approaches.

In reliability analysis and life-testing experiments, the researcher is often interested in the effects of changing stress factors such as “temperature”, “voltage” and “load” on the lifetimes of the units. Step-stress (SS) test, which is a special class from the well-known accelerated life-tests, allows the experimenter to increase the stress levels at some constant times to obtain information on the unknown parameters of the life models more speedily than under usual operating conditions. In this paper, a simple SS model from the exponentiated Lomax (ExpLx) distribution when there is time limitation on the duration of the experiment is considered. Bayesian estimates of the parameters assuming a cumulative exposure model with lifetimes being ExpLx distribution are resultant using Markov chain Monte Carlo (M.C.M.C) procedures. Also, the credible intervals and predicted values of the scale parameter, reliability and hazard are derived. Finally, the numerical study and real data are presented to illustrate the proposed study

In this paper, step-stress accelerated life testing is studied when the lifetime of test units follows power generalized Weibull distribution (PGW). Maximum likelihood estimates (MLEs) and Bayes estimates (BEs) of the model parameters are obtained under type-II progressive censoring. Moreover, the approximate and credible confidence intervals of the parameters are derived. Also, simulation studies are conducted to check the precision of the MLEs and BEs for the parameters of PGW distribution. Finally, some interesting conclusions are obtained.

In this paper, a multiple step-stress model is designed and analyzed when the data are Type-I censored. Lifetime distributions of the experimental units at each stress level are assumed to follow a two-parameter Weibull distribution. Further, distributions under each of the stress levels are connected through a tampered failure-rate based model. In a step-stress experiment, as the stress level increases, the load on the experimental units increases and hence the mean lifetime is expected to be shortened. Taking this into account, the aim of this paper is to develop the order restricted inference of the model parameters of a multiple step-stress model based on the frequentist approach. An extensive simulation study has been carried out and two real data sets have been analyzed for illustrative purposes.

In this paper, the likelihood estimation of model parameters and acceleration factor are considered under step-stress partially accelerated life test using adaptive type-II progressive hybrid censoring scheme, when the lifetime of the test units follows Exponentiated Pareto distribution. The numerical values of Maximum likelihood estimators are obtained using the Newton–Raphson technique. The performance of model parameters and acceleration factor in terms of mean square errors and biases are evaluated using the Monte-Carlo simulation technique.

In reliability analysis, different stress techniques are used to know the lifetime and performance of electrical devices via accelerated life testing. One of these stress technique is the step stress, which combines the traditional reliability testing and over-stress testing; with this method, it is easy to obtain the failure time in a short time. Nonetheless, the analysis of step-stress data can be difficult, and the specialist has usually have to trust on shortcuts or estimations to obtain reliability information from step-stress data. In this paper, a model based on Weibull distribution, inverse power law, cumulative damage model and step-tress technique is proposed to analyze the behavior of electronic devices under a voltage step-stress scenario. The parameters of the model were analyzed via a maximum likelihood. A case of study is based on DC motors is presented in this paper. The results obtained in this paper helped to design department in order to improve the lifetime and performance of the device under analysis.

To increase the optical output of a lighting system, high power Light Emitting Diodes are requested to operate at high currents; however, the maximum drive current is limited by the reliability of the devices. With this work we report on the effects of step stress carried out at increasing bias up to extreme current levels. By means of optical, electrical and photoluminescence analysis we hypothesize that the optical power decrease is related a degradation of the current transport layers of the devices and that an accurate control of the current crowding is crucial in extending the operating range of high power devices.

The inverse piezoelectric effect and trap effect in GaN HEMTs under the high electric field by reverse-bias step stress at cryogenic temperature (CT, 77K) have been investigated. It is found that the inverse piezoelectric effect is suppressed while the trap effect is enhanced at CT. Due to the lower tensile stress in the as-grown AlGaN barrier at CT, the amplitude of the critical voltage related to inverse piezoelectric effect increases from 75V at 300K to 100V at CT, mitigating the irreversible degradation of the devices. The inverse piezoelectric effect dominates the degradation of reverse gate leakage, which is weakened at CT. However, the devices suffer from more degradation of Id (decreases by 94.38%) and Gm,max (decreases by 95.15%) at CT in the dark, induced by the serious trap effect due to the longer emission time. UV-light-assisted stress measurements have been utilized to identify the contribution of the two mechanisms to the degradation of device characteristics at CT. The degradation of Id(Gm, max) is only 0.82% (3.31%) for the piezoelectric effect and 93.56% (91.84%) for trap effect at CT, respectively.

Purpose The purpose of this paper is to consider the general k level step-stress accelerated life test with the Rayleigh lifetime distribution for units subjected to stress under progressive Type-I censoring. Design/methodology/approach The parameter of this distribution is assumed to be a log-linear function of the stress, and a tampered failure rate model holds. The progressive Type-I censoring reduces the cost of testing. Due to constrained resources in practice, the test design must be optimized carefully. A numerical study is conducted to illustrate the optimum test design based on several four optimality criteria under the constraint that the total experimental cost does not exceed a pre-specified budget. Findings This paper compares unconstrained and constrained optimal k level step-stress test. Based on the results of the simulation study, the cost constraint reduces cost and time of the test and it also, in the most cases, increases the efficiency of the test. Also, the T-optimal design is lowest cost and time for testing and it is found more optimal in both conditions. Originality/value In this paper, various optimization criteria for selecting the stress durations have been used, and these criteria are compared together. Also, because of affecting the stress durations on the experimental cost, the author optimize under the constraint that the total experimental cost does not exceed a pre-specified budget. The efficiency of the unconstrained test in comparison with constrained test is discussed.

Dans le present article, le critere T-IPH (Type-I Progressive Hybrid censoring) est avec ont combines le SS-PALT test (Step-Stress Partially Accelerated Life Test). Les deux criteres sont combines pour la la premiere fois dans la litterature. Par consequent, il n'y a pas de travaux disponibles jusqu'a present concernant la mise en commun de ces deux elements. Ici, la distribution de Rayleigh a un parametre est utilisee comme modele sous-jacent aux inferences. Sur la base de donnees reelles et simulees, les resultats de cette approche sont discutees.

Cross-linked polyethylene (XLPE) insulation DC voltage endurance coefficient (VEC) is an important basis in the selection of DC cable insulation design and factory test parameters. Studies on the degradation of XLPE insulation performance under DC electric field can also provide technical support for the reliability evaluation of cable operation. The step stress method as an efficient electrical life test method is widely used to obtain VEC. The parameters of step stress method present considerable influences on VEC. An analytical method based on the trajectory of the damage curve and equivalence between step stress test and constant stress test within zone division is proposed in this paper. According to the proposed method, several sets of step stress tests with different test parameters have been carried out. The accuracy of the test results has been confirmed via analyzing test data. The experimental results show that the VEC (n=12.0) obtained by the step stress test whose parameters are selected by proposed method has good equivalence with the result (n=12.2) under constant-stress method.

This article considers the statistical analysis of dependent competing risks model with masked causes of failure in step-stress accelerated life test, where the failure times of the competing risks...