Staff publications (SoE)

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Browsing Staff publications (SoE) by Publisher "American Inst of Aeronautics and Astronautics"

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    Damage Tolerance and Fail Safety of Welded Aircraft Wing Panels
    (American Inst of Aeronautics and Astronautics, 2005-07-01T00:00:00Z) Zhang, Xiang; Li, Yazhi
    An investigation is presented on fatigue crack growth behavior and fail safety of integral stringer panels typified by welded aircraft fabrications. The stringer panel is made of aluminum alloy 2024-T351 and fabricated by the variable-polarity plasma-arc welding process. The sample simulates a part of the lower-wing skin structures. Based on the linear elastic fracture mechanics, numerical simulations are performed for two configurations, two-stringer and nine-stringer panels, and three damage scenarios, in which welding-induced longitudinal residual stresses are taken into account. A typical load spectrum for large transport aircraft is employed for the analysis. For the two-stringer panel life predictions have a reasonably good correlation with the test results. Based on this validation, large-scale nine-stringer panels with three manufacture options, that is, riveted, integrally machined, and welded integral, are simulated for a skin crack under a broken central stringer propagating to two-bay length. Useful comparisons are made among the three variants. Finally, remedies to improve damage tolerance and fail safety of integral stringer panels are explored. The incorporation of crack retarder straps bonded to the inner surface of an integral panel has greatly improved the fail safety behavior of the component with dramatically increased crack growth live.
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    Design and Modeling of Selective Reinforcements for Integral Aircraft Structures
    (American Inst of Aeronautics and Astronautics, 2008-09-01T00:00:00Z) Boscolo, M.; Allegri, Giuliano; Zhang, Xiang
    A numerical simulation is presented in this paper on the performance of crack retarders bonded to integral metallic structures. The work is described in two main parts. First, a novel modeling approach employing the finite element method has been developed for simulating the various failure mechanisms of a bonded structure and for predicting fatigue crack growth life. Crack growth in the substrate and the substrate/strap interface disbond failure are modeled in the framework of linear elastic fracture mechanics. A computer code interfacing with the commercial package MSC NASTRAN has been developed and validated by experimental tests. Second, the effectiveness of different strap configurations on crack growth retardation has been modeled; these include different strap materials, strap dimensions, and their locations on the substrate. The research has included two substrate materials and four strap materials, and at this stage the specimens were cured at room temperature. Strap stiffness and adhesive toughness are found to be the most influential parameters in designing crack retarders. A design tool has been developed based on the numerical simulation to achieve optimal crack retarder design in terms of prescribed fatigue life target and minimum structural weight added by the bonded reinforcement.