Article

# Testing for the validity of the assumptions in the exponential step-stress accelerated life-testing model

Zhejiang Gongshang University, Hangzhou, PR China; Received 27 March 2007. Revised 25 December 2008. Accepted 19 January 2009. Available online 24 January 2009.

Computational Statistics & Data Analysis (Impact Factor: 1.3). 01/2009; 53(7):2702-2709. DOI: 10.1016/j.csda.2009.01.008 Source: RePEc

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**ABSTRACT:**Copper-graphite composite is an important tribological material used in electrical sliding contact applications like electrical brushes in motors and generators. The electrical sliding contact experiences multiple stresses such as mechanical pressure and temperature. Traditional life tests under normal operating condition would be a time-consuming process due to the longer expected life of the composite. Accelerated wear testing was carried out to evaluate the life characteristics of the composite. This work focuses on evaluation of tribological performance of microwave-sintered copper-graphite composite using accelerated wear testing methodology using high temperature pin-on-disc tribometer. Microstructural studies of worn out surfaces were carried out using SEM with EDAX. Reliability and analysis on life characteristics were performed on the time-to-failure data using temperature-nonthermal-accelerated life-stress model. The obtained times-to-failure data from the accelerated wear testing was extrapolated to normal usage condition. Temperature and pressure are significantly affecting the wear performance. Self-lubricating action of graphite and improvement in wear resistance is helpful in extending the life of copper graphite composite. The life of the composite obtained through testing at mean and 99% reliability are 18,725 and 16,950 h, respectively.Journal of Materials Engineering and Performance 21(11). · 0.92 Impact Factor - [Show abstract] [Hide abstract]

**ABSTRACT:**In this article the parameter estimation method of Step-Stress Accelerated Life Testing (SSALT) model is discussed by utilizing techniques of Generalized Linear Model (GLM). A multiple progressive SSALT with exponential failure data and right censoring is analyzed. The likelihood function of the SSALT is treated as being a censoring variate with Poisson distribution and the life-stress relationship is defined by a log link function of a GLM. Both the maximum likelihood estimation and the Bayesian estimation of GLM parameters are discussed. The iteratively weighted least squares method is implemented to obtain the maximum likelihood estimation solution. The Bayesian estimation is derived by applying Jeffreys' non-informative prior and the Markov chain Monte Carlo method. Finally, a real industrial example is presented to demonstrate these estimation methods.IIE Transactions 08/2010; 42(8):589-598. · 1.29 Impact Factor - [Show abstract] [Hide abstract]

**ABSTRACT:**Lifetime performance assessment has been crucial to the manufacturing industry. In practice, a lifetime performance index CL is used to measure the larger-the-better type quality characteristics. Accelerated life test (ALT) has often been used to yield information quickly so that the life distribution of products can be estimated. This study constructs a maximum likelihood estimator (MLE) of CL for exponential products based on type II right censored data from the step-stress accelerated life test (SSALT). The MLE of CL is then utilized to develop the hypothesis testing procedure with the given lower specification limit L . This new testing procedure can be easily applied to assess whether the lifetime of products meets the requirements. Finally, we give two examples to explicate the proposed testing procedures.IEEE Transactions on Reliability 01/2013; 62(1):296-304. · 2.29 Impact Factor

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