Step Down And The Sequence Down Stress Accelerated Life Testing

As for the importance of life testing, many scholars are researching on the methods for it. Zhang ChunHua [1],[2 ](2005) proposed a new life testing which is called step-down-stress accelerated life testing.Step-down-stress accelerated life testing (which is abbreviated to step- down-stress ALT) is a new type of life testing in which all the units are subjected to a group of step-down-stress. The stress is kept constant until a fixed time or a fixed number of units fail, and the un-failed units are put into the next experiment with lower stress. The experiment ends up till a fixed time or a fixed number of failure units.In order to improve the efficiency of the ALT, we carry out a research on the theory and method of step-down-stress ALT and common descending ALT, as well as the statistical analysis. In this paper we have the following results:Firstly, we compare the efficiency of step-down-stress ALT and step-up-stress ALT under cumulative exposure (CE) model on two-parameter Weibull distribution and two-parameter lognormal distribution occasions respectively by Monte-Carlo simulations. Thus we obtain the following conclusions:Ⅰ.Based on Weibull distribution (table 2-1, table 2-2)1. The step-up-stress ALT is better than the step-down-stress ALT by the results that we derive when 0 <β<1.5.2. The step-down-stress ALT is the same as the step-up-stress ALT in general when 1. 5≤β≤2.5.3. The step-down-stress ALT is better than the step-up-stress ALT by comparison. The advantage of the step-down-stress ALT is obvious while dealing with high-reliability and long-life products whenβ>2.5.4. If we use asymmetric and censored design ( r1 < r2<0.7.3. Asσbecomes larger, the efficiency of the step-down-stress ALT declines, but step-up-stress ALT will increase.4. When 0 <σ≤0.7, if we use asymmetric and censored design ( r1 < r2<