Reliability and Risk Assessment Methods for Redundant Structures.

Abstract : This report summarizes developments of new reliability analysis methods resulting from research under Air Force Contract F33615-70-C-1131. The historical background of risk assessment activities concerning the USAF fleet is reviewed and the flaw-growth and wear-out approaches to material behavior are discussed to place the present work in perspective. A new definition of two categories of risk assessment probability calculation is proposed. The second category, which estimates risk due to strength degradation in an aging structure, is shown to require accounting for mechanical redundancy if accurate assessments are to be made. A new probability modelling procedure is presented. The new procedure accounts for mechanical redundancy by combining a new generalization of Daniels' fiber bundle theory with matrix structural analysis methods. Several example analyses are presented. The results of some related preliminary investigations on the effects of complexity in components and application of redundant models to time-to-failure calculations are discussed. (Author)