OPTIMUM CONSTANT-STRESS ACCELERATED LIFE-TEST PLANS

This paper deals with optimal design of 4-level constant-stress accele rated life test plans with various censoring times. The optimum plans choose the stress levels, test units allocated to each stress, and cen soring times to minimize the asymptotic variance of the MLE of the mea n (log)life at design stress and test length. A FORTRAN-77 program was written to calculate the optimum plan. This paper compares the test p lans with existing 3-level test plans, and concludes that: the mean nu mber of failures at the 2 mid-stresses before the optimum censoring ti mes 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 str ess, the test plans require a shorter test length than existing 3-leve l test plans to achieve the same precision, the test plans are more ro bust than the 3-level best-compromise test plans.