Materials Selection for Airframes: Assessment Based on the Specific Fatigue Behavior

Structural weight reduction is a major driver to improve the transportation efficiency particulary in aeronautics. However the lightweight structural designs can be too costly. Indeed, minimum-weight designs are frequently too costly to manufacture, whereas less expensive and easy to fabricate and assemble designs are often much heavier. The most efficient design on the basis of both cost and weight often lies between these two extremes. The current trend in structural materials selection, by the principal commercial aircraft producers, consists of the extensive use of composite materials in the airframe, as in the last generation of twin aisle aircrafts. Composite materials have high specific strength, are less prone to fatigue crack initiation and provide enhanced flexibility for structural optimization compared to the aluminum alloys. On the other hand, aluminum alloys display higher toughness and better damage tolerance in the presence of defects. In order to improve the material selection and the comparison of airframe materials, this chapter presents an weight assessment based on the specific weight for different damage scenarios taking into account their damage tolerant properties.