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Mécanismes microstructuraux impliqués dans la fatigue des fibres thermoplastiques

Abstract : High performance polyamide and polyester thermoplastic fibres find wide use in technical applications such as structural reinforcements, belting, geotextiles .... These various different uses subject the fibres to a wide range of sever mechanical, thermal and environmental conditions. The present study has explored the effects of different mechanical loading conditions and in particular cyclic fatigue loading, over a wide range of temperatures from 20 to 180°C, which included the glass transition temperatures of the fibres.
The mechanical testing used throughout this study was performed on single fibres with diameters from 18
to 27μm as well as on bundles of fibres. Tests included tensile, creep and fatigue tests on single fibres as well
as fatigue tests on bundles. The microstructural mechanisms involved were revealed by the use of a variety of observational techniques (SEM, optical microscopy, ultra-microtomy), microstructural analysis (small and wide angle X-ray diffraction) and themomechanical characterisation (DSC, DMTA).
Observations at different levels of resolution have revealed an overall evolution of the fibre structure and
an increase of structural orientation during fatigue testing. Coincidently with a resulting overall improvement of properties, local damage, due to a fatigue mechanism, was observed which resulted in the development of distinctive fatigue cracks in the fibres. The loading parameters and in particular the minimum cyclic load, governing fatigue failure, have been studied in conjunction with an examination of the energy dissipation mechanisms occurring during cyclic loading. The initiation of crack growth has been seen to be associated with the presence of solid inclusions in the fibres as well as a skin/core macrostructure.
Cyclic loading above the glass transition temperature was shown to produce an additional mode of crack
growth leading to previously unrecognised fatigue fracture morphologies. This type of failure at high
temperature of single fibres has been seen to correspond to fracture morphologies observed with fibres removed from complex structures which have undergone cyclic loading.
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Submitted on : Monday, July 23, 2007 - 4:22:11 PM
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  • HAL Id : tel-00164759, version 1

Citation

Christophe Le Clerc. Mécanismes microstructuraux impliqués dans la fatigue des fibres thermoplastiques. Mécanique [physics.med-ph]. École Nationale Supérieure des Mines de Paris, 2006. Français. ⟨tel-00164759⟩

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