ACCELERATED DEGRADATION TESTS - MODELING AND ANALYSIS

High reliability systems generally require individual system component s having extremely high reliability over long periods of time. Short p roduct development times require reliability tests to be conducted wit h severe time constraints. Frequently few or no failures occur during such tests, even with acceleration. Thus, it is difficult to assess re liability with traditional life tests that record only failure times. For some components, degradation measures can be taken over time. A re lationship between component failure and amount of degradation makes i t possible to use degradation models and data to make inferences and p redictions about a failure-time distribution. This article describes d egradation reliability models that correspond to physical-failure mech anisms. We explain the connection between degradation reliability mode ls and failure-time reliability models. Acceleration is modeled by hav ing an acceleration model that describes the effect that temperature ( or another accelerating variable) has on the rate of a failure-causing chemical reaction. Approximate maximum likelihood estimation is used to estimate model parameters from the underlying mixed-effects nonline ar regression model. Simulation-based methods are used to compute conf idence intervals for quantities of interest (e.g., failure probabiliti es). Finally we use a numerical example to compare the results of acce lerated degradation analysis and traditional accelerated life-test fai lure-time analysis.