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Marine ageing and fatigue of carbon/epoxy composite propeller blades

Abstract : The current document presents the long term seawater ageing effect on the fatigue properties of carbon fibre reinforced epoxy marine propeller blades. Seawater uptake in the resin and the composite was identified to correspond to a Fickian diffusion. Calculations of the mass to saturation of the composite based on that of the resin reveal the presence of water in the composite’s porosities.Accelerated ageing of the pure resin highlighted three ageing phenomena: oxidation, plasticization and physical ageing. The last two were mechanically characterized separately and coupled with one another. Above all, it was shown that the presence of seawater accelerated the physical ageing kinetics by reducing the relaxation time. The composite was studied under different quasistatic and cyclic loadings.Few effects of seawater have been found for tensile stresses on fibre oriented loadings. This was not the case for transversely loaded composite that showed a non-negligible decrease of the mechanical properties for both static and fatigue loadings. This was also the case for flexure loading which was studied under four-point flexure. This latter test method was particularly studied due to the particular induced damage. The composite was studied under two delamination loadings: crack opening and inplane shear. It was observed that seawater decreased the critical strain energy release rates for both load cases as well of the fatigue resistance of both crack modes. Finally, the effect of physical ageing on the composite was studied and found to be non-negligible, demonstrating the necessity of taking it into account for both ageing and mechanical design.
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Submitted on : Wednesday, May 20, 2020 - 12:09:22 PM
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Antoine Le Guen-Geffroy. Marine ageing and fatigue of carbon/epoxy composite propeller blades. Mechanical engineering [physics.class-ph]. Université de Bretagne occidentale - Brest, 2019. English. ⟨NNT : 2019BRES0104⟩. ⟨tel-02612622v2⟩

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