Browsing by Author "Teklal, Fatiha"

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    Mesoscopic Defects of Forming and Induced properties on the Impact of a Composite Glass/Polyester
    (2019-12-30) Kacimi, Bachir; Teklal, Fatiha; Djebbar, Arezki
    Forming processes induce residual deformations on the reinforcement and sometimes lead to mesoscopic defects, which are more recurrent than macroscopic defects during the manufacture of complex structural parts. This work contributes to the experimental study of the effect of mesoscopic buckles defect and shear deformation of the reinforcement, which result from forming, on the low velocity impact behavior of a composite laminate. The material studied is a glass/polyester composite with three layers of mat and one layer of taffeta fabric. To assess the properties induced on the final composite, plates with different amplitudes of calibrated defects and deformations were manufactured. First, the healthy material, which serves as a reference, was subjected to three levels of impact energy to observe the evolution of its behavior and damage mechanisms. Results of the impact tests and observations performed on the materials with calibrated defects identified a negative effect of buckling on elastic parameters and revealed greater damage relative to the healthy material. The reinforcement shear had a beneficial effect on the impact properties of the laminate, which was attributed to the increase in local fiber density.
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    Micromechanics of Stress Transfer across the Interface fiber-matrix bonding
    (2019-12-30) Teklal, Fatiha; Kacimi, Bachir; Djebbar, Arezki
    The study and application of composite materials are a truly interdisciplinary endeavor that has been enriched by contributions from chemistry, physics, materials science, mechanics and manufacturing engineering. The understanding of the interface (or interphase) in composites is the central point of this interdisciplinary effort. From the early development of composite materials of various nature, the optimization of the interface has been of major importance. While there are many reference books available on composite materials, few of them deal specifically with the science and mechanics of the interface of fiber reinforced composites. Even more important, the ideas linking the properties of composites to the interface structure are still emerging. A number of experimental techniques have been devised to measure the mechanical properties of the fiber-matrix and laminar interfaces in composites. A number of analytical solutions have been proposed in order to better understand the stress transfer mechanism across the interfaces between the fiber and the matrix. In our study, we need a direct characterization of the interface; the micromechanical tests we are addressing seem to meet this objective and we chose to use two complementary tests simultaneously. The microindentation test that can be applied to real composites,and the drop test, preferred to the pull-out because of the theoretical possibility of studying systems with high adhesion (which is a priori the case with our systems). These two tests are complementary because of the principle of the model specimen used for both the first "compression indentation" and the second whose fiber is subjected to tensile stress called the drop test. Comparing the results obtained by the two methods can therefore be rewarding.
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    RÔLE DES INTERFACES DANS DES COMPOSITES A MATRICES ORGANIQUES, SOLLICITATIONS HORS AXES
    (UNIVERSITE MOULOUD MAMMERI DE TIZI OUZOU, 2023-12-16) Teklal, Fatiha
    : L’objectif principal de cette thèse est de comprendre le comportement micromécanique des interfaces dans des matériaux composites à matrice polymère en utilisant le test d’arrachement (pull-out).Il est donc nécessaire de caractériser le comportement mécanique de la zone interfaciale de manière aussi détaillée que possible. Afin de résoudre le problème d’identification de la force de décohésion permettant la rupture de la liaison entre fibre et matrice. Dans ce but nous avons proposé différents modèles d'éléments finis qui a été construire à l’aide du code de calcul Abaqus. L’interface est représentée à l’aide d’éléments cohésifs (MZC). Ces modèles sont développés pour étudier le comportement force-déplacement lors d’un essai d'arrachement des fibres dans des composites renforcés de fibres continues. Une étude paramétrique a été menée pour étudier la sensibilité de la ténacité de l'interface, comme le coefficient de frottement, l'épaisseur de la zone interfacial, et les conditions au limites…. Les modèle éléments finis ont été validé par comparaison avec les modèles analytique et les résultats expérimentaux. Le comportement charge-déplacement prédit par le modèle analytique et le modèle d’éléments finis s’est révélé similaire pour divers paramètres étudiés dans cette étude. La réponse du matériau à des sollicitations statiques (flexion, traction) ou dynamiques (Choc Charpy) permet de bien cerner la part jouée par l’interface fibre/matrice dans le comportement du matériau. Dans ce contexte des éprouvettes sont découpées à différents angles de 0°, 5°, 15°, 30°,45° et 90° par rapport à la direction principale du renfort. Nous avons convenus d’appelle ces essais « hors axes ». Pour ces essais hors-axe, nous avons pu mettre en évidence l’effet de l’anisotropie du matériau composite à renfort unidirectionnel, et l’influence prépondérante de l’orientation des fibres sur les caractéristiques mécaniques….