Cette thèse est essentiellement consacrée à la caractérisation et à l’analyse des propriétés mécaniques de matériaux composites constitués d’un renfort taffetas verre et d’une résine acrylate (Elium®). Avant l’apparition de la résine Elium® sur le marché en 2013, les polymères acrylates n’étaient pas utilisés dans l’industrie des composites fibres longues. Dans le volet expérimental de la thèse, nous nous intéressons principalement à l’influence de l’ensimage (traitement de surface appliqué aux fibres pour favoriser l’adhésion de la matrice) sur le comportement mécanique de nos composites. En complément de différents essais mécaniques macroscopiques « classiques » (traction, flexion etc.), nous avons utilisé des techniques d’analyse locales fines (mesures de champ cinématique, microtomographie X, Microscopie Électronique à Balayage, nanoindentation…) qui nous ont permis de caractériser et d’étudier certains mécanismes locaux de déformation et d’endommagement. L’influence de l’ensimage sur les propriétés en fatigue a été mise en évidence grâce à des mesures d’autoéchauffement pour lesquelles nous avons développé un traitement original des données. A l’issue de nos investigations, nous avons pu quantifier le bénéfice qui résulte de l’utilisation d’un ensimage spécifiquement conçu pour favoriser l’adhésion d’un polymère acrylate sur des fibres de verre. Dans le volet « simulation numérique » de la thèse, nous avons modélisé le comportement mécanique de nos composites taffetas verre/matrice acrylate grâce au solveur spectral CraFT (Composite response and Fourier Transforms). Le détail des champs de contrainte et de déformation a été obtenu à l’échelle de la mésostructure et révèle une structuration périodique induite par la présence du renfort tissé. Une analyse quantitative a permis de vérifier que les champs de déformation qui ont été obtenus grâce au solveur CraFT sont en très bon accord avec des mesures réalisées par corrélation d’images. A partir du champ de contrainte, nous avons mis en évidence les régions de la mésostructure qui subissent les plus fortes sollicitations mécaniques. En visualisant par microtomographie X la structure interne d’éprouvettes précédemment déformées, nous avons pu établir le lien entre la localisation de l’endommagement au sein de la mésostructure et les régions de concentration de contrainte que la simulation numérique avait mises en évidence / This thesis is devoted to the characterization and the analysis of the mechanical properties of composite materials made of a plain weave glass fiber reinforcement and an acrylic resin (Elium®). Before the commercialization of the Elium resin in 2013, acrylics polymers were not used in the composite industry. In the experimental part of this thesis, we mainly focused on the sizing effect (surface treatment of the fibers to enhance the bonding between the matrix and the fibers) on the mechanical behavior of our composites. The characterizations were carried out through classical macroscopic mechanical tests (tensile, bending, shearing…) but using metrological tools for local analysis (full-field strain measurements, X ray micro-tomography, Scanning Electron Microscopy, Nano-indentation etc.). We were able to study strain and damage phenomena at local scales. Fatigue properties of the sizing were highlighted by heat build-up experiments. To analyze these measurements, an original data treatment has been developed which makes clear the benefit of an acrylic sizing in order to enhance the bonding between glass fibers and our acrylic matrix. In the theoretical part of this thesis, we studied the mechanical behaviour of our glass fiber plain weave/acrylic resin composite through a numerical simulation based on the CraFT spectral solver (Composite response and Fourier Transforms). Local stress and strain fields were obtained at the mesoscopic scale. The strain field analysis shows a periodic structure induced by the presence of the plain weave reinforcement. By a quantitative study, a good agreement between the numerical strain field obtained by CraFT and the 3D-DIC experimental strain measurements was found. The numerical stress field analysis reveals regions were a high local stress occurs. Comparing with X ray micro-tomography observationsof the internal structure of previously loaded composite sampleswe noticed that the damages occurring inside the mesostructure are totally correlated with the local stress concentration revealed by CraFT numerical simulations

This work correlates the chemistry of phenol-formaldehyde (PF) resins, its functionalities with their microstructural and mechanical properties in composite materials. The main focus is put on the development of the pores in dependence on the chemical composition of the resins and their influence on the structure of the material. Chemical characteristics of the synthesized resins are analyzed and physical/mechanical properties of the matrices based on PF resins are determined. Differences in the chemical properties are detected e.g. by FT-IR and NMR spectroscopy. They indicate the existence of similar molecular basic structure units, but different network conditions of the resins. DSC investigations point on different reaction mechanisms and temperatures; they reveal also their changed thermal behavior. The bulk matrix behavior differs from that of the composite based on the same resin due to the three dimensional stress and strain fields in the composites. The structure of the CFRP composites is strongly depended on the fiber/matrix interaction. The fiber matrix bonding (FMB) strength controls the load transfer via shear forces and therefore the segmentation of the fiber bundles.

This work correlates the chemistry of phenol-formaldehyde (PF) resins, its functionalities with their microstructural and mechanical properties in composite materials. The main focus is put on the development of the pores in dependence on the chemical composition of the resins and their influence on the structure of the material. Chemical characteristics of the synthesized resins are analyzed and physical/mechanical properties of the matrices based on PF resins are determined. Differences in the chemical properties are detected e.g. by FT-IR and NMR spectroscopy. They indicate the existence of similar molecular basic structure units, but different network conditions of the resins. DSC investigations point on different reaction mechanisms and temperatures; they reveal also their changed thermal behavior. The bulk matrix behavior differs from that of the composite based on the same resin due to the three dimensional stress and strain fields in the composites. The structure of the CFRP composites is strongly depended on the fiber/matrix interaction. The fiber matrix bonding (FMB) strength controls the load transfer via shear forces and therefore the segmentation of the fiber bundles.:1 Introduction 2 Theoretical Overview 2.1 Phenol-Formaldehyde Resins 2.1.1 Overview 2.1.2 Reactions of phenol-formaldehyde resin 2.1.2.1 Addition reaction 2.1.2.2 Condensation reaction 2.1.2.3 Curing 2.1.3 Application of phenol-formaldehyde resin 2.2 Carbon-Fiber 2.2.1 PAN type carbon fiber 2.2.2 Pitch type carbon fiber 2.2.3 Application of carbon fiber 2.3 Composites 2.3.1 Carbon fiber composites 2.3.2 Matrix 2.3.3. Interfaces 2.3.3.1 Carbon fiber side interface between carbon fiber and matrix 2.3.3.2 Matrix side interface between carbon fiber and matrix 2.3.3.3 Toughening of fiber-reinforced polymer 3 Goal and Works 3.1 Problem and Motivation 3.2 Objective and Works plan 4 Experiments and Methods 4.1 Materials 4.1.1 Chemical reagents 4.1.2 Carbon fiber weave 4.2 Synthesis of Resin 4.3 Fabrication of Matrix 4.4. Measurement methods and Experimental approach 4.4.1 Chemical analysis 4.4.2 Microstructure characterization 4.4.3 Mechanical test 5 Chemical characterization of modified phenol-formaldehyde resin 5.1 Fourier Transformed Infrared spectroscopy (FT-IR) 5.1.1 Introduction 5.1.2 Preparation and Measurement 5.1.3 Results and Discussion 5.2 Nuclear Magnetic Resonance spectroscopy (NMR) 5.2.1 Liquid 13C Nuclear Magnetic Resonance spectroscopy 5.2.1.1 Introduction 5.2.1.2 Preparation and Measurement 5.2.1.3 Results and Discussion 5.2.2 Solid 13C CP-MAS Nuclear Magnetic Resonance spectroscopy 5.2.2.1 Introduction 5.2.2.2 Preparation and Measurement 5.2.2.3 Results and Discussion 5.3 Simultaneous Thermal Analysis (STA) 5.3.1 Introduction 5.3.2 Preparation and Measurement 5.3.3 Results and Discussion 5.3.3.1 Simultaneous Thermal Analysis 5.3.3.2 Different Scanning Calorimetry 5.4 Conclusion 6 Microstructural Characterization 6.1 Porosity 6.1.1 Introduction 6.1.2 Preparation and Measurement 6.1.3 Results and Discussion 6.1.3.1 Density 6.1.3.2 Porosity 6.2 Morphology 6.2.1 Introduction 6.2.2 Preparation and Measurement 6.2.3 Results and Discussion 6.2.3.1 Optical Microscopy 6.3.3.2 Scanning Electron Microscopy 6.3.3.2.1 Observation of the bulk matrix 6.2.3.2.2 Structural observation of the composite 6.3 Conclusion 7 Mechanical Properties 7.1 Hardness test 7.1.1 Introduction 7.1.2 Preparation and Measurement 7.1.3 Results and Discussion 7.2 Micro-bending test 7.2.1 Introduction 7.2.2 Preparation and Measurement 7.2.3 Results and Discussion 7.3 Conclusion 8 Summary and Conclusion 8.1 Summary 8.2 Conclusion 9 References