Etude du comportement en fatigue d’un composite à matrice polyamide renforcé d'un tissu de fibres de verre pour application automobile

Abstract : This study is focused on a woven glass-fibre-reinforced composite (2/2 twill) with a polyamide 6,6 matrix. From the perspective of its future integration in automotive parts, the fatigue behavior of this material is investigated. The aim is to develop a fatigue model able to predict the fatigue life of the composite studied. The PA66 behaviour is highly influenced by the moisture content, thus, it is necessary to take this parameter into account. Hence, three conditionings are studied: RH0, RH50 andRH100 which correspond respectively to the dry-as-moulded, the ambient and the water-saturated state.Three different stacking sequences are used in order to study the influence of fibre orientation: [(0/90)3],[(90/0)3] and [(±45)3]. First, the influence of moisture on microstructural and mechanical properties formonotonic tensile tests is studied. The plasticizing effect of water on PA66 has been highlighted. A damage scenario has been determined for every configuration studied by using acoustic emission technique during monotonic tensile tests and post-mortem SEM observations. Then, tension-tension fatigue tests are performed for all sample configurations. The results have been used to set up two phenomenological fatigue life models: the constant life diagrams and the two-parameter model based onS-N curves. The latter has been enhanced by including the relative humidity in order to be able to predict the fatigue life of the material for any conditioning. In general, this model estimates quite well the fatigue life of the material for different testing conditions. Finally, the two-parameter model has been used for fatigue life prediction of both open-hole samples and a mini-structure in order to evaluate its capability to be used in an industrial context.
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Amélie Malpot. Etude du comportement en fatigue d’un composite à matrice polyamide renforcé d'un tissu de fibres de verre pour application automobile. Autre. ISAE-ENSMA Ecole Nationale Supérieure de Mécanique et d'Aérotechique - Poitiers, 2017. Français. ⟨NNT : 2017ESMA0002⟩. ⟨tel-01505589⟩

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