Evaluation of a Damage and an Interfacial Bonding on Composites from the Viewpoint of Viscoelastic Property

The viscoelasticity of a composite material is influenced especially by the strength of adhesive bonding between resin and fiber. The viscoelastic properties are investigated from the viewpoint of interfacial properties of composites. A significant concept named 'balance stress', which reflects viscoelastic properties of a composite, is introduced. While balance stress indicates the strength of adhesive bonding in the interface, interfacial bonding is evaluated strength creep behavior of the material, analysed with a three element model of the material into viscoelastic coefficients. On the other hand, the three viscoelastic coefficients have strong relation to fatigue process of a composite material, reflecting fatigue damage. Some experimental results for composites are shown and discussed on the basis of viscoelastic properties. The viscoelasticcoefficients proved to be a helpful measure to estimate both interfacial properties and fatigue damages of composite material.