Abstract A mathematic model is proposed for predicting the dynamic properties of fiber reinforced plastic composites （FRP） with interphase. Dynamic properties mainly include loss factors and elastic moduli. The results of elastic moduli fi＇om the present model are compared with other models. Elastic moduli Ell, E22, G12, G23 and loss factors ηll, η22, ηl2 and η23 of FRP are calculated and a study of the effect of elastic modulus Ej and loss factor rh ofinterphase on dynamic properties in FRP is carried out here. In this paper, E11 linearly increases with El, but the growth rate is slow. E22, G12, G23 increase rapidly for lower value of EI. The longitudinal loss factor E1 decreases with the increase of El in the case of rh 〈 0.0026. But η11 linearly increases with E1 in larger range of η1, η1 〉 0.0026. On the contrary, transverse loss factor η22, transverse shear loss factors r/23 and longitudinal shear loss factors η12 increase with increase of E1 in the case of lower value of η1, but decreases at larger value of ηl. And they also show insensitivity to E1 at higher value.
