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AUTOMATED UNIT-CELL MODEL GENERATION FOR MICRO-MECHANICAL SIMULATIONS OF 3D REINFORCED COMPOSITES

par Pierreux, Gerrit
Président du jury Guillaume, Patrick
Promoteur Massart, Thierry,Jacques ;Van Hemelrijck, Danny
Publication Non publié, 2018-12-03

Thèse de doctorat

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Résumé :

3D reinforced composites are favored for aerospace, automotive and wind turbine applicationbecause of their high specific stiffness and strength in the in-plane and out-ofplanedirections. In these composites, pins, stitching yarns and binder yarns are insertedthrough-the-thickness of the in-plane fiber-reinforced regions. Binder parameters as diameter,content, pattern and tensioning can further be varied to regulate the out-of-planeproperties. However, the insertion of these binders distorts the reinforcement which furthercan affect the global and local mechanical behaviour. Unit-cell models offered avaluable approach to assess the effect of the distortions on these mechanical features.An approach is presented to include the main geometrical features of pinned, stitchedand 3D woven composites into mesoscopic unit-cell models. Discretised lines, whichrepresent the main geometrical features, are hereby gradually shaped by geometrical operationswhile a geometrical contact treatment account for line interactions. The localfiber volume fraction and fiber direction distributions are afterwards modelled on crosssectionsin a post-processing step. Tools are further proposed to automatically transformthe geometrical models into finite element models. The effect of distortions, local fibervolume fraction and fiber direction, and typical geometrical features for each 3D reinforcedcomposite, on the stiffness and damage initiation stress levels is investigated bymeans of elastic finite element (FE)-computations.The shape of geometrical features corresponding to the different binder parameters couldautomatically be generated and the dimensions of features could be controlled by the parametersof the geometrical operations. The stiffness of a 3D reinforced composite havebeen observed to be either decreased or increased (dependent on the stacking sequence,the binder type and the loading direction). Early damage initiation in the FE-modelswas observed to take place near the binder locations, which was mainly caused by transverseand shear cracking in the fiber-reinforced regions. Local fiber volume fraction andfiber direction have shown to affect damage initation mechanisms and stress levels, andshould therefore be properly included in the models. In future work, the possibility ofthe framework to generate unit-cells including voids and micro-vascular networks canbe investigated and the finite element models can be extended with damage and crackpropagation mechanisms for damage and failure computations.