Optimum Test Plan for 3-Step, Step-Stress Accelerated Life Tests
Volume 10, Number 1, January 2014 - Paper 1 - pp. 3-14
N. CHANDRA1, MASHROOR AHMAD KHAN1 and M. PANDEY21 Department of Statistics, Ramanujan School of Mathematical Sciences, Pondicherry University, Pondicherry-605 014, INDIA
2 Ex. Professor in Biostatistics, Department of Zoology and DST Centre of Interdisciplinary Mathematical Sciences, Banaras Hindu University, Varanasi 221 005, INDIA
(Received on November 13, 2012, revised on June 15, and August 23, 2013)
In this paper we obtain the optimum time for changing the stress level in 3-step, step stress accelerated life testing under the cumulative exposure model. The lifetimes of test units are assumed to follow a two-parameter Lomax distribution. The scale parameter of the Lomax failure time distribution at constant stress level is assumed to be a log-linear function of the stress level. We also assume that there may exist a quadratic relationship between the log mean failure time and stress. As an extension of the results for the linear model, the optimum plan for a quadratic model is also proposed. We derive the optimum test plans by minimizing the asymptotic variance of the maximum likelihood estimator of the mean life at a design (use) stress.
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