EFFECTIVE THERMOVISCOELASTIC PROPERTIES OF FIBROUS COMPOSITES WITH FRACTAL INTERFACES AND AN INTERPHASE

Our recent atomic force microscopy studies of surfaces of several adva nced reinforcing fibers have revealed their self-similar fractal prope rties over a scale range from nanometres to micrometres. The fractal n ature of fiber surfaces implies a fractal morphology for the interface s in composites. Fiber composites with fractal interfaces and transiti onal layers between the fibers and matrix are addressed. Simple models for the effective elastic, viscoelastic, and thermal properties of a unidirectional composite in axial and transverse directions are develo ped. A general scaling relationship for effective properties is derive d with the thickness of an interlayer as a scale parameter. Variation of elastic and transport properties, expansion coefficients, viscoelas tic loss and creep factors with the thickness of the transitional laye r are analysed for different fractal dimensions of the interface. Stro ng effects of the fractal dimension on mechanical properties are obser ved. The importance of fractal characterization and design of interfac e regions in composites is emphasized. (C) 1997 Elsevier Science Limit ed.