#01-7

Use of Sensitivity Analysis to Assess the Effect of Model

Uncertainty in Analyzing Accelerated Life Test Data

by

William Q. Meeker, Luis A. Escobar and Steve A. Zayac

Iowa State University and Louisiana State University

ABSTRACT

Accelerated life tests are used to obtain timely information on the durability and reliability of materials. Test units are subjected to higher than usual levels of “stress” and a model is used to estimate life at use conditions. Although it is desirable to use a physically-based model to justify the required extrapolation, in many practical situations, no such model is available or the physical basis for extrapolation is uncertain. In such situations, extra-polation is based on an empirical model. Sensitivity analysis tools then become important to access the effect of model departures and to allow engineers to make safe design decisions.

This paper presents models, methods, and a description of software tools for performing systematic sensitivity analysis to assess potential model error. These methods are illustrated by studying the results of an experiment that was conducted to determine if the fatigue life of a spring would meet a given specification.