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Estimation accélérée des performances en fatigue de matériaux et structures composites thermoplastiques par le suivi de leur auto-échauffement

Abstract : This thesis is part of the study on the fatigue of composite materials. It consists in estimating the fatigue performance of a thermoplastic composite woven material, made of carbon fibres and PA66 matrix, by self-heating tests. Following a characterization of the damage to the material under monotonous loading by acoustic, thermal and optical monitoring, a fatigue test campaign is carried out on two material configurations, at 0° and 45°. Several methods for modelling the S-N curve are proposed to determine the fatigue limit of the material. It is shown that the estimation of this limit and its confidence interval is complicated by the large dispersion of experimental data. Self-heating tests are then carried out, consisting of applying a fatigue load over a limited number of cycles, increasing the maximum stress applied step by step. Signal processing tools are developed to determine a threshold stress and its confidence interval at which the heating accelerates. However, this threshold stress remains conservative in comparison to the fatigue limit. Another approach is then developed, consisting in monitoring the amplitudes of the thermal signal. New signal processing tools are being developed to map the specimen from the harmonic amplitudes. It is then shown that it is possible to obtain the same curves as the selfheating curves by monitoring the amplitudes of the harmonics, and this for only a hundred cycles. A new self-heating test protocol is then implemented, based on a hundred steps of only a few hundred cycles, allowing harmonics to be monitored with almost continuous final curves in a minimum of time.
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Laura Muller. Estimation accélérée des performances en fatigue de matériaux et structures composites thermoplastiques par le suivi de leur auto-échauffement. Mécanique des solides [physics.class-ph]. École centrale de Nantes, 2019. Français. ⟨NNT : 2019ECDN0035⟩. ⟨tel-02464971⟩

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