In order to acquire the life information of the white organic light-emitting diode (OLED), Weibull distribution function was applied to describe the life distribution, whereas the least square method was employed to estimate the shape and scale parameters. The accelerated life equation was determined, and the statistics and analysis on constant-stress and step-stress test data were performed using the software developed by the authors. The numerical results indicate that Weibull distribution and the inverse power law are both consistent with the employed assumptions and that the accurately calculated acceleration parameters enable a rapid estimation of the white OLED life.

Constant-Step-Stress Accelerated Life Test of White OLED Under Weibull Distribution Case

In this paper, accelerated life tests of white organic light-emitting diodes (WOLEDs) are conducted to obtain failure data at normal operation conditions. The lognormal distribution function was applied to describe WOLED life distribution. Log mean and log standard deviation were determined by maximum likelihood estimation. The Kolmogorov-Smirnov test was performed, and the results further confirmed that WOLED life met the lognormal distribution. Numerical results indicated that WOLED life followed the lognormal distribution. It was also found that the acceleration model was consistent with inverse power law.

A Study of Accelerated Life Test of White OLED Based on Maximum Likelihood Estimation Using Lognormal Distribution

In order to acquire the reliability information of White Organic Light Emitting Display (OLED), three groups of OLED constant stress accelerated life tests (CSALTs) were carried out to obtain failure data of samples. Lognormal distribution function was applied to describe OLED life distribution, and the accelerated life equation was determined by Least square method (LSM). The Kolmogorov–Smirnov test was performed to verify whether the white OLED life meets lognormal distribution or not. Author-developed software was employed to predict the average life and the median life. The numerical results indicate that the white OLED life submits to lognormal distribution, and that the accelerated life equation meets inverse power law completely. The estimated life information of the white OLED provides manufacturers and customers with important guidelines.

Life prediction for white OLED based on LSM under lognormal distribution

Different estimation methods for exponentiated Rayleigh distribution under constant‐stress accelerated life test

The Accelerated Life Testing (ALT) has been used for a long time in several fields to obtain information on the reliability of product components and materials under operating conditions in a much shorter time. One of the main purposes of applying ALT is to estimate the failure time functions and reliability performance under normal conditions. This paper concentrates on the estimation procedures under ALT and how to select the best estimation method that gives accurate estimates for the reliability function. For this purpose, different estimation methods are used, such as maximum likelihood, least squares (LS), weighted LS, and probability weighted moment. Moreover, the reliability function under usual conditions is predicted. The estimation procedures are applied under the family of the exponentiated distributions in general, and for the exponentiated inverted Weibull (EIW) as a special case. Numerical analysis including simulated data and a real life data set is conducted to compare the performances between these four methods. It is found that the ML method gives the best results among other estimation methods. Finally, a comparison between the EIW and the Inverted Weibull (IW) distributions based on a real life data set is made using a likelihood ratio test. It is observed that the EIW distribution can provide better fitting than the IW in case of ALT. Copyright © 2015 John Wiley & Sons, Ltd.

Different Estimation Methods for Constant Stress Accelerated Life Test under the Family of the Exponentiated Distributions

In order to obtain the life information of vacuum fluorescent display (VFD) in a short time, four constant stress accelerated life tests (CSALT) are conducted with the cathode temperature increased. Lognormal function is applied for describing the life distribution of VFD. Assuming an Arrhenius model, the lognormal parameters are computed by using the maximum likelihood estimation. Furthermore, a self-developed software is employed in predicting the VFD life. The statistical analysis of the results indicates that the test design of CSALT is correct and feasible, that the average life of VFD is over 30,000 h, and that the life-stress relationship satisfies linear Arrhenius equation completely. The precise accelerated parameter is shown to be particularly useful to predict the VFD life within shorter time. Thus, this work provides significant guidelines to help engineers make decisions in design and manufacturing strategy from the aspect of reliability life.

Reliability Life Prediction of VFD by Constant Temperature Stress Accelerated Life Tests and Maximum Likelihood Estimation

In this brief, we propose an efficient asynchronous parallel expected improvement matrix-based (EIM) constrained multi-objective optimization approach with mixed models for analog circuit sizing. In contrast to other asynchronous methods for single-objective optimization, our method aims to solve multi-objective problems with multiple constraints. The proposed new asynchronous strategy can parallelize not only circuit simulations but also the process of building models. We introduce an EIM criterion for objectives as the acquisition function and build radial basis function models for constraints. The proposed method is based on prescreening instead of internal optimization to further reduce the computational cost of models. Experimental results on two real-world circuits illustrate that when the batch size is 15, our proposed method provides with better trade-off information and reduces the total runtime of the optimization by up to 92X compared with NSGA-II. There is a speedup of up to 8X and 4X compared with the state-of-the-art synchronous approach and asynchronous approach in terms of the runtime.

Rui-Tao Wang

Papers

Reliability Life Prediction of VFD by Constant Temperature Stress Accelerated Life Tests and Maximum Likelihood Estimation

Asynchronous Parallel Expected Improvement Matrix-Based Constrained Multi-Objective Optimization for Analog Circuit Sizing