This grant provides funding for research on maintenance strategies for engineered systems that explicitly consider the environmental conditions in which the systems operate. The current state of the art derives inspection/repair/replacement times from lifetime distributions based on laboratory data. There are several limitations to the use of lifetime data in maintenance planning. For highly reliable devices, expensive devices, and devices where accelerated testing is not feasible, lifetime data can be sparse. More importantly, operating conditions are often quite different from strictly controlled laboratory conditions. In the field, devices degrade in response to uncontrolled (random) phenomena, such as electrical transients, heat and cold cycles, vibrations, and collisions. Consequently, lifetime estimates derived from laboratory data may have little value in establishing effective maintenance practices. This work will develop and analyze theoretical and empirical models for system degradation driven by exogeneous random phenomena. The following activities will be performed as part of this research: (1) computable expressions will be developed to describe the performance of maintained systems in random environments; (2) improved maintenance strategies will be developed for these systems; (3) stochastic process models of equipment degradation due to random environments will be developed and analyzed; (4) methods to estimate nominal life from lifetime data and degradation models will be developed. The goal of this research is to improve maintenance practice. If successful, the results of this research will lead to improvements in the operation of engineered systems and reductions the life-cycle costs assignable to system failure and repair. The results of this effort will be useful to maintenance practitioners as well as to device and equipment manufacturers who must make reliability characterizations of their products. The research will also contribute to the available theoretical tools and methodologies for studying system deterioration as a result of random environmental effects.
