This article presents multi-step stress accelerated life tests based on type I censoring. It is assumed that the lifetime at design stress has the Weibull Poisson distribution. The scale parameter of the Weibull Poisson failure time at constant levels is assumed to have an inverse power law of the stress levels. Under the assumption of a cumulative exposure model, the maximum likelihood method is used to obtain the estimators of the model parameters. The optimal design of the accelerated life tests is studied according to the A-optimality criterion to specify the optimal stress change time and the optimal censoring time. Finally, the numerical studies are performed to illustrate the proposed procedures. Keywords : Cumulative Exposure Model, Lifetime Distribution, Step Stress ALT, Optimal Test Plan, A-Optimality.
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