COMPORTEMENT VISCOÉLASTIQUE DES COMPOSITES A RENFORT FILAMENTAIRE ET MATRICE POLYMÈRE

ABSTRACT The paper deals with the interpretation of the isothermous anisotropic viscoelastic characteristics of a unidirectional Kevlar 49 reinforced and epoxy matrix composite in the frame of the time temperature equivalence principle. Modulated tensile tests are carried out in the [10 -4 , 10 -1 Hz] x [200, 343 K] frequency temperature range. The classical networks of dynamical compliances and loss factors can be easily interpretad according to the equivalence principle and the hypothesis of linear viscoelastic behaviour. It appears that we need three different shift factors at least to interprete the temperature effects an the effective compliances of the orthotropic basis in a correct manner. This result shows that the reinforcement apparent behaviour in the matrix is thermorheologically simple. The two loss factors which are found by tensile tests performed in the direction and perpendicular to the direction of the fibers are characteristic of the predominant role respectively played by the reinforcement and the matrix. A tensile test carried out in an off axis direction shows that the equivalence principle can reduce the viscoelastic compliances of the composite in any orthonormal basis without being incompatible with the tensorial invariance of the dynamical compliances. We conclude that the time temperature principle is an intrinsical feature of the viscoelastic behaviour of the composite although it is not a thermorheologically simple material.