Influence de la qualité de l’interface fibre de verre / matrice sur le comportement mécanique monoaxial et biaxial de plaques et de tubes en matériaux composites

Abstract

Composites, bi-phasic materials made up of a fibre reinforced organic matrix, have very attractive mechanical and physical assets. Although their properties mainly depend on those of each phase (fibre and matrix), the quality of the fibre/matrix interface also plays an essential role in the definition of their characteristics. In order to reveal this role, The Department of Polymers and Composites Technology of the Ecole des Mines de Douai has investigated the behaviour of composite samples, differing only by the interface quality, under the laws of loading, which are used most in industrial fields:– monoaxial tension with monitoring of acoustic emission spectra,–interlaminar shear,–crack initiation and crack growth in mode I,–viscoelasticity in bending,–biaxial monotonic tension, cyclic loading with increasing amplitude and dynamic fatigue.Biaxial tests were carried out on industrial tubing systems under internal pressure, the other tests on standard flat test pieces. In tension and interlaminar shear, fibre/matrix adhesion has only little influence on the behaviour of the material. In return, the incidence of this parameter appears to be more pronounced through mode I fracture mechanics and viscoelasticity studies. Initiation and growth energies thus can be influenced by the interface quality by up to 50%. In the same way, variations of 45% on the modulus loss and of 70% on the damping at glass transition temperature are noticed. Concerning the study of tubing system, the level of sensitivity to the interface quality is dependent on the type of load applied and the end of life criteria which have been chosen, weeping or threshold of non-linearity. Under monotonic loading one can observe maximum divergences of 17% on the values of weeping pressures; these gaps increase considerably if first damage pressures are considered, and can reach 30%. In terms of circumferential stresses, these differences are still more pronounced and can go as high as 45%. The fatigue lifetime is also very strongly affected by the nature of the fibre/matrix interface, which can make it possible to multiply the lifetime by 30.