Approches rhéologiques et mécaniques des matériaux composites à fibres courtes

Abstract : aThe aim of this work is to develop new composite materials on very short fibers which present at the same time good mechanical properties and a low viscosity of the liquid phase to be used for the molding of complex structures. To reduce the viscosity of the suspensions vacuum and treatment by ultrasound was used. It is shown, that the viscosity of a polymer material which exhibits shear thinning flow can be lowered substantially (up to 20%) by the addition of a small quantity of microspheres (<2%). The gain in fluidity is preserved for the mixtures studied. Consequently a material with higher content in fibers can be made having the same viscosity. For the applications of this discovery a patent was filed in 1997. The rheology of various mixtures with several resins had been studied. As a result two regions of different flow behavior are found : within the first regions the viscous flow essentially is determined by the matrix whereas in the second region the main contribution comes from the fiber-fiber interactions. Therefore a reduction of the viscosity of the matrix below a certain level does not yield a gain in fluidity of the suspension. Studies of the mechanical properties show that strong composites based on fibers of about 200?m only could be made if the matrix has an elevated Young's modulus. Twelve different epoxy resins (including 9 which were made especially for this study) are used in order to demonstrate the influence of the Young modulus and the strain of the matrix. Today based on the results mentioned above a composite material can be made from an epoxy resin and carbon fibers (30% in volume) which offers specific properties comparable to a standard aluminum : (Young's modulus ? 28GPa ; ultimate strength ? 220 Mpa; density ? 1400 kgm-3)
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Yves Schmitt. Approches rhéologiques et mécaniques des matériaux composites à fibres courtes. Autre [cond-mat.other]. Université Paul Verlaine - Metz, 1999. Français. ⟨NNT : 1999METZ005S⟩. ⟨tel-01775815⟩

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