A MICROMECHANICAL APPROACH TO THE VISCOELASTICITY OF UNIDIRECTIONAL HYBRID COMPOSITES

Combination of the well-known rule of mixtures and the classical theory of linear viscoelasticity leads to a stress/strain relation that effectively predicts the viscoelastic behaviour of hybrid composites in uniaxial extension. From this theory, it is shown that the rule of mixtures does not apply directly to the dynamic quantities E(d) and tan delta, whereas it can be used directly to correlate the storage and loss moduli of the composite to the properties of its components. The stress/strain relation is experimentally verified under isothermal conditions for a unidirectional, hybrid polyethylene-aramid/epoxy system both in constant strain rate and dynamic forced vibration experiments. The micromechanical model leads to numerical predictions which are in good agreement with experimental data on composite materials in various compositions.