Planning step-stress life-test with a target acceleration-factor

A sequential approach is presented to plan a multiple-steps step-stress accelerated life test (SSALT) with type-I censoring so as to achieve a pre-specified acceleration factor. An initial optimal plan for a simple SSALT, where one not only has to determine the optimum hold-time under low stress but also the optimum low stress level, is obtained by solving a constrained nonlinear program. A backward recursion scheme generates the subsequent optimal low-stress levels and hold-times for multiple-step SSALT. An illustration using a 3-step SSALT is presented. The relative efficiency of the 2-step and 3-step SSALT is investigated. A numerical example illustrates the method under 2-step and 3-step SSALT.