Optimum Simple Bivariate Step-Stress Accelerated Life Test Plan for Cumulative Exposure Model

This paper presents a step stress accelerated life test for two stress variables to obtain optimal hold times. The lifetime of the items follows the Log-normal distribution. The lognormal life distribution is a very flexible model that can empirically fit many types of failure data. We model the effects of changing stress as a cumulative exposure function. The Fisher information matrix are obtained. The optimal test plan is determined for each combination of stress levels by minimizing the asymptotic variance of reliability estimate at a typical operating condition. Finally, simulation results are discussed to illustrate the proposed criteria. Simulation results show that the proposed optimum plan is robust, and the initial estimates have a very small effect on optimal values.