Optimum constant-stress accelerated life-test plans

This paper deals with optimal design of four-level constant-stress accelerated life test plans with various censoring times. The optimum plans choose the stress levels, test units allocated to each stress, and censoring times to minimize the asymptotic variance of the MLE of the mean (log) life at design stress and test length. A FORTRAN-77 program was written to calculate the optimum plan. This paper compares the test plans with existing three-level test plans, and concludes that: the mean number of failures at the two mid-stresses before the optimum censoring times are the least, and slightly greater than the prescribed least mean number of failures; the censoring times at stresses except the lowest stress are almost equal, and much shorter than that at the lowest stress; the test plans require a shorter test length than existing three-level test plans to achieve the same precision; and the test plans are more robust than the three-level best-compromise test plans