#01-8

Estimation of Degradation-Based Reliability

In Outdoor Environments

By

Victor Chan and William Q. Meeker

Iowa State University

ABSTRACT

Some important reliability problems involve estimating a life distribution when failure is due to chemical degradation of materials or products that are exposed to the outdoor environment. There is a growing need to obtain timely predictions of such degradation behaviors on the basis of accelerated laboratory tests. Laboratory life tests provide information about degradation processes. Historical weather data are used to characterize the stochastic outdoor environment over time. A physical/chemical model for degradation rate is used as a basis for using these data to produce reliability estimates. We propose and illustrate the use of an evaluation/estimation method that involves time series modeling. The method is illustrated with an example involving the degradation of a solar-reflector material. We will also show how to construct approximate confidence intervals for important reliability.