Advanced Durability Analysis. Volume 1. Analytical Methods

Abstract : Advanced durability analysis 'design tools' have been developed for metallic aircraft structures. These tools can be used to evaluate durability design requirements for functional impairments due to excessive cracking and fuel leakage/ligament breakage. The methodology accounts for the initial fatigue quality variation of structural details, the crack growth accumulation for a population of structural details under specified design conditions and structural properties. Step-by-step procedures are provided. This volume is limited to the analytical methods, technical aspects, concepts and philosophy for the durability analysis of metallic aircraft structures. The methodology reflects a probabilistic approach, a fracture mechanics philosophy and both deterministic and stochastic crack growth methods. It can be used to predict the probability of crack exceedance at any service time and/or the cumulative distribution of the time-to-crack initiation at any crack size. The methodology applies to the small crack size range associated with excessive cracking (e.g., <0.05-in.) and to large through-the-thickness cracks (e.g., 0.50-in-0.75-in.) associated with fuel leakage/ligament breakage. No matter what form, location or combination the as-manufactured flaws may have in fastener holes (e.g., scratches, burrs, microscopic imperfections, etc.) or whatever the source of fatigue cracking may be, a practical method of representing the reality of the as-manufactured condition is needed for durability analysis. This is taken care of by the equivalent initial flaw concept.