Investigation of equivalent step-stress testing plans

Accelerated life testing (ALT) is a method for obtaining failure time data of test units quickly under more severe conditions than the normal operating conditions. Typical ALT plans require the determination of stress types, stress levels, allocation of test units to those stress levels, duration of the test and other test parameters. Traditionally, ALT is conducted under constant stresses during the entire test duration. In practice, the constantstress tests need more test unites and a long time at low stress levels to yield sufficient failure data. However, due to budget and time constraints, there are increasing necessities to design testing plans that can shorten the test duration and reduce the total cost while achieving the equivalent accuracy of reliability estimate. In this chapter, we develop an equivalent step-stress testing plan such that the reliability predictions at normal conditions using the results of this plan will be approximately “equivalent” to the corresponding constant-stress test plan but the test duration is significantly shortened. We determine the optimum parameters of the test plan through a numerical example and evaluate the equivalence of the test plans using simulation. We also investigate the sensitivity of the ALT model parameters.