Three-Dimensional BEM and FEM Submodelling in a Cracked FML Full Scale Aeronautic Panel
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Three-Dimensional BEM and FEM Submodelling in a Cracked FML Full Scale Aeronautic Panel R. Citarella & G. Cricrì
# Springer Science+Business Media Dordrecht 2014
Abstract This paper concerns the numerical characterization of the fatigue strength of a flat stiffened panel, designed as a fiber metal laminate (FML) and made of Aluminum alloy and Fiber Glass FRP. The panel is full scale and was tested (in a previous work) under fatigue biaxial loads, applied by means of a multi-axial fatigue machine: an initial through the thickness notch was created in the panel and the aforementioned biaxial fatigue load applied, causing a crack initiation and propagation in the Aluminum layers. Moreover, (still in a previous work), the fatigue test was simulated by the Dual Boundary Element Method (DBEM) in a bidimensional approach. Now, in order to validate the assumptions made in the aforementioned DBEM approach and concerning the delamination area size and the fiber integrity during crack propagation, three-dimensional BEM and FEM submodelling analyses are realized. Due to the lack of experimental data on the delamination area size (normally increasing as the crack propagates), such area is calculated by iterative three-dimensional BEM or FEM analyses, considering the inter-laminar stresses and a delamination criterion. Such three-dimensional analyses, but in particular the FEM proposed model, can also provide insights into the fiber rupture problem. These DBEM-BEM or DBEM-FEM approaches aims at providing a general purpose evaluation tool for a better understanding of the fatigue resistance of FML panels, providing a deeper insight into the role of fiber stiffness and of delamination extension on the stress intensity factors. Keyword DBEM . BEM . FEM . FML . Submodelling . Delamination . Crack propagation
1 Introduction Nowadays the Fiber Metal Laminate (FML) technology is optimized for fatigue and damage tolerance properties; Glare is an example of such hybrid material and is used for cargo floor of Boeing 777 airplanes, for the lower wing panels of the Fokker 27 and for the skin panels of the upper side of the A380 aircraft fuselage. Fatigue crack propagation in FML is a subject of great interest that has only recently reached a well-defined theory. Since the early days of the investigation, the importance of the R. Citarella (*) : G. Cricrì Department of Industrial Engineering, University of Salerno, Salerno, Italy e-mail: [email protected]
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Fig. 1 Crack propagation in the aluminium ply (left), with highlight of the delaminated area and related bridging effect (right)
bridging effect, i.e. an alternate load path offered by the intact fibers, has been highlighted [1]. In particular, the crack propagation in the Aluminum ply is highly connected to the debonding of the glass fibers by the so-called bridging effect, enabling a significant load transfer to the
Fig. 2 A330/300 aircraft fuselage barrel
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Fig. 3 Test panel scheme, with highlight of strain gage and rosette configuration on
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