Staff publications (SoE)

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Browsing Staff publications (SoE) by Author "Allegri, Giuliano"

Now showing 1 - 4 of 4
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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.
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    Fail-Safe Design of Integral Metallic Aircraft Structures Reinforced by Bonded Crack Retarders
    (Elsevier Science B.V., Amsterdam., 2009-01-01T00:00:00Z) Zhang, Xiang; Boscolo, M.; Figueroa-Gordon, Douglas J.; Allegri, Giuliano; Irving, Phil E.
    This paper presents an investigation on the effectiveness of crack growth retarders bonded to integral metallic structures. The study was performed by both numerical modelling and experimental tests. It focuses on aluminium alloy panels reinforced by bonded straps made of carbon-epoxy, glass-epoxy composite materials or a titanium alloy. The goal was to develop a fail-safe design for integrally stiffened skin-stringer panels applicable to aircraft wing structures. The modelling strategy and finite element models are presented and discussed. The requirements that the models should meet are also discussed. The study has focused on establishing the extent of crack retarder benefits, in terms of fatigue crack growth life improvement, by numerical simulation and experimental tests of various crack retarders. The results of predicted fatigue crack growth retardation have been validated by tests of laboratory samples. This study concludes that by bonding discrete straps to an integral structure, the fatigue crack growth life can be significantly improved.
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    On the delamination suppression in structural joints by Z-fibre pinning
    (Elsevier Science B.V., Amsterdam., 2007-04-01T00:00:00Z) Allegri, Giuliano; Zhang, Xiang
    The main objective of this paper is to investigate the benefits of Z-fibre pinning to improve the bonding strength of composite joints. The problem is addressed from a design point of view in order to develop a simulation methodology that can be employed to predict the strength of Z-fibre pinned joints. Firstly, an efficient and accurate computational approach is presented using the well established finite element method in conjunction with a constitutive model of Z-fibre response behaviour under mixed mode loading condition. The Z-fibre bridging model previously developed by the authors is summarised in the paper. Secondly, the computational approach is demonstrated via the analysis of two structural joints, namely a conventional T-joint and a novel cruciform joint. Comparison with test data confirms the model’s predictive capabilit
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    On the inverse power laws for accelerated random fatigue testing
    (Elsevier Science B.V., Amsterdam., 2008-06-01T00:00:00Z) Allegri, Giuliano; Zhang, Xiang
    This paper addresses the usage of inverse power laws in accelerated fatigue testing under wide-band Gaussian random loading. The aim is not at predicting an absolute value of fatigue life but assessing the fatigue damage relative accumulation. The widely accepted inverse power scaling laws in fatigue damage assessment is discussed, reviewing the engineering standards and pointing out their inherent limitations. A physically consistent general scaling law is obtained by rigorous mathematical analysis in the framework of random vibration theory and the rules of safe-life fatigue analysis. Simplifications of the general scaling rule are presented, highlighting conditions under which the current standard practice could provide a correct an acceptable estimation of the relative fatigue damage accumulation.