Functional reliability design and evaluation methodology: A systems approach

Traditionally, reliability activities have focused on the evaluation and assessment of reliability of products by analyzing actual test data or field data. These methods are costly and 'after-the-fact'. Further, classical reliability evaluation of systems is based on the assumption that the components comprising the system work independently and their failures are assumed to be statistically mutually independent events. In reality this assumption of independence does not hold true in most system/product designs.;This research was motivated by the need to address these fundamental inadequacies in current reliability design theory and the lack of implementation of product reliability at the early design phase of a product. The primary goal of this research was to develop a technique to link system functional performance to component failures by introducing a new design concept called Multilevel Hierarchical (MLH) modeling. Reliability models were developed in the MLH framework. The model was expanded by extending the MLH theory to incorporate the effect on system reliability due to dependent failures of sub-systems. Next, a cost benefit analysis approach was introduced to enable evaluation of system designs from a cost of failure perspective. The author then extended the reliability assumption of binary failure to a multi-state and continuous-state component performance characteristic and the system functional reliability model was developed in this context.;This methodology is practically feasible, applicable to engineering design problems and is explained through practical examples and applications. This research also puts focus on improving reliability by design evaluation and improvement at concept design stage (before test) rather than a test-and-fix approach.;Contributions to the field of reliability in this dissertation are: (1) Establishing reliability models and estimation method for systems based on system functions and sub-system performance; (2) Deepening the knowledge of dependent failures and their impact on system/product reliability; (3) Establishing functional reliability design evaluation and improvement methods that utilize design conceptual weakness and vulnerability identification techniques; (4) Developing a practical reliability framework to implement functional reliability design and cost of failure analysis in complex systems at concept design.