Détection de l'endommagement dans un composite tissé PA66,6/Fibres de verre à l'aide de techniques ultrasonores en vue d'une prédiction de la durabilité de pièces automobiles

Abstract : The present study is focused on the experimental study of a polyamide 66/6 based composite reinforced by a 2/2 twill weave glass fabric. The aim is to propose Non Destructive Evaluation (NDE) methods based on ultrasound that can efficiently distinguish different damage state. In order to do so, an investigation of the damage mechanisms induced by different type of mechanical solicitations. Tension along and off the axis of the fibers was considered as well as the case of drop weight impact. Those solicitations were shown to induce different damage mechanisms. The latter were characterized by means of Scanning Electronic Microscopy (SEM) and X-Ray tomography mostly. The decreasing of the elastic modulus and the void volume fraction evolution were shown to be more significant for the samples loaded in tension off-axis. During the drop weight impact tests, the energies were considered in order to remain close to the Barely Visible Impact Damage (BVID) regime in order to experience the capability of the ultrasound based NDE methods. Two NDE methods investigated during this study deserve to be highlighted. Firstly, the stiffness tensor was estimated by means of phase velocities measurements in different propagation direction. Damage indicators based on results from this method were proposed. They were found to give results similar with the one from the evaluation of damage discussed earlier on. Secondly, a study of the damage detection using guided waves was performed. No mode conversion effect was observed from this investigation. Consequently, the signal energy was proposed as damage indicator and was found to be suitable to detect damage induced by tension but not by impact. The measure of time shift allowed obtaining a localization and evaluation of the damage induced by impact.
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Pascal Pomarede. Détection de l'endommagement dans un composite tissé PA66,6/Fibres de verre à l'aide de techniques ultrasonores en vue d'une prédiction de la durabilité de pièces automobiles. Mécanique des matériaux [physics.class-ph]. Ecole nationale supérieure d'arts et métiers - ENSAM, 2018. Français. ⟨NNT : 2018ENAM0024⟩. ⟨tel-01932575⟩

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