OPTIMAL-DESIGN OF PARTIALLY ACCELERATED LIFE TESTS FOR THE LOGNORMAL-DISTRIBUTION UNDER TYPE-I CENSORING

This paper considers optimal designs of partially accelerated life tests in which test items are first run simultaneously at use condition for a specified time, and the surviving items are then run at accelerated condition until a predetermined censoring time. For items having lognormally distributed lives maximum likelihood estimators (MLEs) of the location and scale parameters of the lifetime distribution at use condition, and the acceleration factor which is the ratio of the mean life at use condition to that at accelerated condition are obtained. The change time is determined to minimize either the asymptotic variance of MLE of the acceleration factor or the generalized asymptotic variance of MLEs of the model parameters.