Abstract: In order to shorten test time further and realize rapid evaluation of the reliability of products, based on the rules of optimum design plan of accelerated life test(ALT) and constant-stresses ALT, the minimum variance of the product life estimate under normal stress level is defined as object and the total stress levels and the corresponding change time are determined as variables. Applying maximum likelihood estimation theory and Nelson failure model, the optimum design plan of step-stress ALT is modeled. Compared the optimized results of electrical connectors’ step-stress ALT with the constant-stresses ALT and on the condition that the precision of statistic is almost same, the sample can be reduced by 2/5 and the test time can be reduced by 1/3.

Key words: Accelerated life test, Optimum design, Step-stress