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Comportement à l'impact et post-impact d'un composite lin/polyamide 11 élaboré par thermocompression

Abstract : This PhD work deals with the impact and post-impact behavior of a fully bio-based composite made of flax fibresand Polyamide 11. The first goal was to optimize the hot press moulding parameters for manufacturing this composite. Two types of unidirectional flax fabrics (A and B) and two forms of Polyamide 11 (powder or film) were tested. At first, the pressure and temperature process values were optimized using a first set of composites made of flax A and Polyamide 11 in the form of powder. Then, an optimization of material components was conducted using a second set of composites. All the manufactured composites were tested by means of tensile tests, DMA and porosity measurements. Finally, an optimum configuration was determined: the composite flax B/PA 11 film manufactured with a temperature value of 210 °C and with gradual levels of pressure until 65 bars. Moreover, damage mechanisms were evaluated by acoustic emission and SEM observations during tensile tests. Four mechanisms were identified for the [0]4 and [90]4 composites and five for [±45]s composites. The second goal of this study was to study the effect of an impact of 3.6 J on the compression and tensile behaviors of four stacking sequences of this composite: unidirectional [0]8, alternated [0/90]2s, sandwich [02/902]s and multidirectional [45/0/- 45/90]s. The damage created by the impact in these four lay-ups was characterized thanks to different techniques: visual observations, topographic and C-scan measurements, and micro-tomography. It has been shown that the configurations with the smallest damage were the alternated and multidirectional composites. Then, impacted composites were tested by tensile and compressive loadings, and results were compared with the properties of non- impacted composites. Acoustic emission and digital image correlation were used to identify the damage and strain mechanisms of each type of composites. The results showed that, thanks to the presence of the ±45° plies, the multidirectional composite has the best post-impact behavior. Finally, a finite element model has been developed for simulating the post-impact behavior. As a first approach, a lower value of modulus has been implemented in the impacted area. It has allowed us to compare numerical and experimental strain fields for the different stacking sequences.
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Submitted on : Friday, January 27, 2017 - 8:35:07 AM
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yann Lebaupin. Comportement à l'impact et post-impact d'un composite lin/polyamide 11 élaboré par thermocompression. Autre. ISAE-ENSMA Ecole Nationale Supérieure de Mécanique et d'Aérotechique - Poitiers, 2016. Français. ⟨NNT : 2016ESMA0017⟩. ⟨tel-01447572⟩



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