Application of Reliability Growth Model in Step-Down Stress Accelerated Storage Test

Step-down accelerated storage test is equalled to reliability growth, a method of step-down stress accelerated storage test based Army Materiel System Analysis Activity (AMSAA) model is proposed, according to the step-down stress, the mean time between failures (MTBF) under normal stress can be obtained, by using the AMSAA model. First, through the product’s cumulative failure time, cumulative failure numbers and based on AMSAA model, the product’s instantaneous MTBF is shown. Then the step-down stress is divided into n ladders, and there is only one fault under each stress, the joint probability density function is shown by the cumulative failure time of each step-down stress, and the parameters of the AMSAA model are estimated by the maximum likelihood estimation, then the point estimation of the product’s instantaneous MTBF is got. By choosing instantaneous MTBF of certain accelerated stresses and combined respective physical accelerated model, the product’s storage lifetime is estimated. Finally, a case study is performed using this method. The effectiveness of this method is shown, for the point estimation of each parameter is little different. Thus it provides a new evaluation method for step-down accelerated storage test.