Prévision de la résistance en compression des composites à fibres longues : approche structurelle du microflambage plastique

Abstract : The low compressive strength of the long fibre composites is now a penalizing factor for the structure design. This weakness is generally related to a fibre instability, called microbuckling, which depends especially on the fibre misalignment defect in the initial state and on the plastic matrix behaviour. But experimentally, one can observe that the compressive strength also depends on some parameters at structure scale (tested ply thickness sequence and apllied loading). The few models able to account for the effect of all these parameters are very heavy to use. We aim at proposing a specific numerical tool which permits to conduct a parametric study and which can then be suited for industrial use. From a bidimensional homogenized model established in a perfect framework by Grandidier - Gardin - Potier-Ferry, the plastic microbuckling problem including defect is set. In order to minimize the computations costs, this problem is formulated at ply scale by using double-scale kinematics. Remarking that microbuckling is a cellular instability, the solution is sought on a reduced domain thanks to a peculiar finite element. With this specific code, the complete response of plies is determined in a few minutes. The study of the microbuckling mechanism confirm the importance, on the strength, of the misalignment defect. This latter can be defined by the angle between the fibre and its theorical axis, for the wavelengths close to the elastic critical wevelength. The computations also show that the compressive strength strongly depends on the loading and on the ply position in the laminate, especially when the thickness decreases. Finally, the comparison between our predictions and the experimental results is quite good, facing that the defect is the only main parameter which is difficult to evaluate experimentally
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Sylvain Drapier. Prévision de la résistance en compression des composites à fibres longues : approche structurelle du microflambage plastique. Autre. Université Paul Verlaine - Metz, 1996. Français. ⟨NNT : 1996METZ024S⟩. ⟨tel-01777136⟩

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