A HEURISTIC FOR DETERMINING OPTIMUM MULTIPLE STRESS ACCELERATED LIFE TEST PLANS

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 failure observation within reasonable time using single stress only multiple-stress ALTs have been employed as a means of overcoming Such difficulties. Furthermore, as is often the case, products are usually exposed to Multiple stresses in actual use such as temperature, humidity. electric current, electric field and various types of shocks and vibration. Attaining the most accurate extrapolations from these ALTs requires an optimal allocation of testing units to different stress combinations. In this paper, a heuristic is presented to determine the optimal ALT plan. The optirnum number of stress combinations, stress levels, and the number of test units allocated to each combination are determined to maximize the determinant of the Fisher information matrix (D-Optimality). The proposed heuristic is illustrated by numerical example utilizing the proportional odds model.