Soutenance de thèse de Gianluca Auteri

Textile cord-elastomer composites are essential structural elements in pneumatic tires and numerous elastomeric products, where they provide a combination of strength and flexibility under complex service loading conditions. Their fatigue behavior is difficult to characterize due to the coupling of multiscale phenomena between individual filaments, cord architecture, adhesive interfaces, and the surrounding matrix. Applications in tires impose cyclic loading involving both compression and tension on textile cords, which can activate different damage modes related to filament rupture, elastomer cracking, and interface degradation. Understanding how these mechanisms interact with each other during fatigue degradation is crucial for designing more fatigue-resistant reinforced elastomeric structures. This PhD thesis, carried out in collaboration with Michelin, investigates the fatigue behavior of textile cord–elastomer composites under service-representative cyclic loading conditions. A multiscale approach is developed to relate local deformation and damage mechanisms at the filament and cord scales to the macroscopic response of composite structures and tires. The mechanical response of textile cords embedded in an elastomer matrix is analyzed using a filament-scale finite element framework, Multifil, that accounts for cord architecture, frictional contact interactions and manufacturing induced geometry. This approach enables the investigation of deformation mechanisms that are challenging to capture with homogenized models. In particular, the compressive behavior of cords is examined, leading to the first characterization of helical buckling in multi-filament textile cords embedded in rubber. Combining in situ X-ray tomography and numerical modeling, the three-dimensional deformation of cords under compression is revealed, and the influence of matrix stiffness and cord twist on buckling amplitude and load redistribution is quantified. The role of the adhesive coating surrounding textile cords is also investigated, as it governs stress transfer and damage initiation. A dedicated modeling strategy is proposed to represent the mechanical contribution of the adhesive layer without explicitly resolving microscale details. The approach is validated against experimental bending tests and highlights the stiffening effect of the adhesive as well as its influence on frictional dissipation and internal deformation mechanisms. To link these local mechanisms to fatigue behavior under realistic conditions, a dedicated laboratory fatigue test, the Extension–Compression–Uniaxial (ECU) test, has been developed. This setup enables independent control of tensile and compressive strains and temperature, allowing for the decoupling of the respective effects on fatigue degradation. The ECU test allows systematic investigation of a wide range of parameters, including cord architecture, filament nature, and elastomer matrices, under controlled and repeatable conditions. Mechanical measurements combined with tomography and microscopy observations provide insight into damage mechanisms, follow their fatigue evolution and allow direct comparison with damage observed in tires.

Composition du jury :

• M. Eric MAIRE : Directeur de recherche, Laboratoire MatéIS - INSA Lyon. Rapporteur
• Mme Emmanuelle VIDAL-SALLÉ : Professeure des universités, Laboratoire LaMCoS - INSA Lyon. Rapporteure
• M. Peter DAVIES : Ingénieur de recherche, Ifremer, Examinateur
• M. Valter CARVELLI : Professeur des universités, Dipartimento di Architettura, Ingegneria delle Costruzioni e Ambiente Costruito - Politecnico di Milano. Examinateur
• M. Simon NUYTTEN : Ingénieur de recherche, MFP Michelin. Examinateur
• M. Florent BOUILLON : Ingénieur de recherche, SAFRAN GROUP. Examinateur