ANALYSES OF ACCELERATED LIFE TEST DATA UNDER TWO FAILURE MODES

This paper proposes a method of estimating the lifetime distribution at use condition for constant stress accelerated life tests when an extrinsic failure mode as well as intrinsic one exists. A mixture of two distributions is introduced to describe these failure modes. It is assumed that the log lifetime of each failure mode follows a location-scale distribution and a linear relation exists between the location parameter and the stress. An estimation procedure using the expectation and maximization algorithm is proposed and specific formulas for Weibull distribution are obtained. Simulation studies are performed to investigate the properties of the estimates and the effects of stress level. Numerical comparisons with the masked data model are also performed.