S. Van der Veen, Alcan Aerospace, Issoire, France; J. Boselli, Alcoa Incorporated, Alcoa Center, PA; A. Murphy, P. Wang, Queen's University Belfast, Belfast, United Kingdom

Summary:

The upper wing structure of commercial transports is largely driven by compression stability requirements. For these applications, integral structure has a theoretical advantage over conventional riveted design because the quadratic section moment can be maximised and sections can more easily be tailored across the wing span. However, the post-buckling collapse of this kind of sturdy structure is sensitive to both the Young's modulus and the yield strength (plastic buckling). Since high strength 7xxx-series aluminium alloys are invariably quench-sensitive, the properties of thick plate for integral upper wing applications are never as good as those of the strongest 7xxx-alloys in gauges used in riveted designs. To unlock the potential of integral upper wing design, Alcan Aerospace has developed a processing method that significantly improves the properties of high strength 7xxx-plate for integral upper wing designs. The processing method and resulting properties will be discussed, along with some advanced concepts making full use of the new higher properties. One of these concepts aims at delaying the onset of buckling (local buckling of the skin) by integrating small, weight-neutral stiffeners in between the main stiffeners. This solution has been verified in compression tests of sub-scale stiffened panels that have proven the desired performance gains. The concept and test results will be presented.