Continuous fiber-reinforced polymers (FRPs) are important lightweight structural materials, yet predicting their damage and failure remains difficult. Bottom-up multiscale approaches emphasize understanding microscale mechanisms, particularly for semi-crystalline thermoplastics like PEEK, whose spherulites - similar in scale to the fiber diameter - and possible transcrystalline layers complicate the extrapolation of neat matrix properties to composites. Because matrix microstructure depends strongly on processing-induced thermal history, this thesis examines how PEEK crystallinity affects its mechanical response and the early deformation and damage mechanisms in PEEK/carbon fiber composites.
PEEK matrices processed under three distinct processing methods were first characterized to quantify overall crystallinity. The microstructure of the crystallized matrix was then examined, but limited access to inter-fiber regions led to the fabrication of model samples with only a few fibers. Polarized light microscopy revealed distinct crystalline morphologies, which were analyzed for crystallinity and lamellar organization. Structures of different dimensions exhibited different degrees of crystallinity, linked to variations in lamellar stack density. Variations in lamellar stack density were also observed within the crystalline morphologies.
In-situ mechanical properties of matrix pockets processed under different conditions were then measured, along with those of individual crystalline entities in the model samples. Indentation modulus and hardness varied with processing conditions, the dimension of the crystalline morphology, and even within single crystalline structures.
Finally, deformation and failure of unidirectional PEEK/carbon fiber composites with different microstructures were studied from the specimen scale down to inter-fiber zones. A multiscale DIC approach combined with in-situ testing enabled detailed strain-field measurements, linking matrix crystallinity to strain-localization mechanisms and providing data for micromechanical model validation.
Membres du jury :
Prof. Thomas Pardoen (UCLouvain)(Promoteur)
Prof. Bernard Nysten (UCLouvain)(Promoteur)
Prof. Grégoire Winckelmans (UCLouvain) (Président)
Prof. Alain Jonas (UCLouvain) (Secrétaire)
Dr. Jérémy Chevalier (UCLouvain)
Dr. Lucien Laiarinandrasana (Ecole des Mines Paris)
Prof. Christophe Tromas (Université de Poitiers)
Prof. Véronique Michaud (Ecole Polytechnique Fédérale de Lausanne)
Soutenance publique également accessible par visio-conférence via le lien (TEAMS) :
https://teams.microsoft.com/meet/37625385824253?p=luC5bfApg79b5d9QBi
