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Non-Local Modeling of the Compressive Strength of Composite Structures

Abstract : The compressive failure of long carbon fiber composites is due to complex mechanisms. The knowledge of these mechanisms is important for the design of composite structures because the compressive strength and stiffness of laminates are assumed less than their tensile strength. Further, compressive failure is a mechanism of non-local ruin that depends on the composite structure (layer thickness, load gradient) which makes it a peculiarity. The mechanism has been described and modelled in the literature with suitable numerical tools and experiments that accounted for this effect. There are many articles in the literature regarding the modelling of composites compressive behavior, particularly the microbuckling phenomenon / local instability. But only a few researchers modelled the mechanism at the structural/mesoscopic scale. For example, Drapier et al., [D3] proposed a 2D homogenized model, which takes into account fiber initial alignment defects, matrix plasticity and structural parameters. The model is successful in predicting the elastic microbuckling modes and to predict the failure. But the model is built for 2D unidirectional laminates and assumes microbuckling is periodic in the fiber direction, just one gradient in the thickness direction is taken into account and the influence of the misalignment is not completely described [D4]. Therefore, to extend the developments of these works ([D1],[D3],[G1],[G4]), new non-local finite element models are developed: one with using ABAQUS® in-built structural elements, named Beam Non-Local (BNL) model and the other with User Element (UEL) subroutine of ABAQUS®, named Homogenized Non-Local Model (HOMNL), implemented in the user element (NL U32), which can be applied with the aim to predict the compressive strength of unidirectional plies/laminates and also for woven composites (2D and 3D). Both the non-linear geometrical and material effects are taken into account in this model. With the BNL model, it is possible to capture the mechanism in 2D and 3D space for laminates of unidirectional composites. Results of the bibliography have been confirmed and new results are presented, for example, the elastic mode in 3D or the mechanism under bending. The width and angle of the kink band are determined by this model. In the framework of more general, the validation of the NL U32 element has been performed with respect to ABAQUS® classical elements for both linear and non-linear (geometry and material) cases. The classical (elastic and plastic) and non-local material properties (elastic) are identified by comparison to the responses of a Representative Volume Element (RVE) of full heterogenous microstructures. Some results have been validated with the bibliography. The developed non-local user element (NL U32) is 2D in this thesis and it can be extended easily to a 3D case, which remains one of the future perspectives.In this work, ABAQUS® v2017, DAKOTA v6.10.0, PARAVIEW v5.8.0 are the softwares used and FORTRAN, Python are the programming languages used.
Keywords : Non-local model
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Anil Bettadahalli Channakeshava. Non-Local Modeling of the Compressive Strength of Composite Structures. Other. ISAE-ENSMA Ecole Nationale Supérieure de Mécanique et d'Aérotechique - Poitiers, 2020. English. ⟨NNT : 2020ESMA0018⟩. ⟨tel-03166430⟩

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