Resonant frequency study of tensile and shear elasticity moduli of carbon fibre reinforced composites (CFRC)

The dynamic elastic properties are important characteristics of composite m aterials. They control the vibrational behaviour of composite structures an d are also an ideal tool for monitoring of the development of CFRCs' mechan ical properties during their processing (heat treatment, densification). Th e present studies have been performed to explore relations between the dyna mic tensile and sheer moduli and some structural features (viz., fibre frac tion, fibre type, porosity, weave pattern of woven reinforcement) of variou s unidirectional or bi-directional fibre reinforced carbon/carbon composite s, made out of PAN- or pitch-based fibres as reinforcements and phenolic re sin or coal tar pitch as matrix precursors. The dynamic tensile and in-plan e shear moduli were determined from resonant frequencies of a beam with fre e ends. The longitudinal dynamic Young's modulus of unidirectional CFRC com posites - besides its dependence on the original fibre modulus and fibre vo lume contents - also reflects changes induced in matrix and fibres by heat treatment. The in-plane shear modulus does not depend on the fibre type but there exists its distinct tendency to increase with increasing fibre fract ion. For bi-directionally reinforced composites, the longitudinal tensile m odulus is more sensitive to the fabric weave pattern than to the fibre type . Tensile modulus of diagonally cut specimens and in-plane shear modulus of longitudinally cut ones are mutually con-elated and, therefore, simultaneo usly controlled by densification steps and graphitisation heat treatment. ( C) 2000 Elsevier Science Ltd. All rights reserved.