Design of optimum multiple-stress accelerated life testing plans based on proportional odds model

Accelerated Life Testing (ALT) is used to obtain failure time data quickly under high stress levels in order to predict product life and performance under the design stress. Most of the previous work on designing ALT plans is focused on the application of a single stress. However, as components or products become more reliable due to technological advances, it becomes more difficult to obtain significant amount of failure data within a reasonable amount of time using single stress only. Multiple-stress ALTs have been employed as a means of overcoming such difficulties. In this paper, we design optimum multiple-stress ALT plans based on the Proportional Odds (PO) model. The optimum combinations of stress levels and the number of test units allocated to each combination are determined such that the variance of the reliability prediction of the product over a pre-specified period of time is minimised. The proposed ALT plan is illustrated by a numerical example.