Optimum simple step-stress accelerated life tests with censoring

The authors present the optimum simple time-step and failure-step stress accelerated life tests for the case where a prespecified censoring time is involved. An exponential life distribution with a mean that is a log-linear function of stress, and a cumulative exposure model are assumed. The authors obtain the optimum test plans to minimize the asymptotic variance of the maximum-likelihood estimator of the mean life at a design stress. Nomographs for the optimum time-step stress test are also given. Simple step stress test plans with censoring were studied. The optimum failure-step stress test plans are obtained in a closed form, whereas, for the time-step stress test, nomographs are given for finding the optimum plans on the basis of parameters. The parameters must be approximated from experience, similar data, or a preliminary test. For some selected values of the parameters, the effect of incorrect preestimates was studied in terms of the percentage of variance increase. The effect was found to be small