Step-stress life-testing with random stress-change times for exponential data

This paper studies statistical models in step-stress accelerated life-testi ng when the stress-change times are random. The marginal lifetime distribut ion of a test unit under a step-stress test plan when the stress change tim es are random variables is presented. Maximmum likelihood estimates for mod el parameters based on both the marginal and conditional life distributions are considered. An optimum test plan is explored for simple step-stress te st when the stress change time is an order statistic from the exponential l ifetime under the low-stress level.