The dynamic elastic behaviour of a fibre-reinforced composite sheet. I. The precise experimental determination of the principal elastic moduli

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Abstract
Precise measurements of the free-free resonant frequencies of specimens of unidirectional fibre-reinforced composite material are used to determine the principal elastic moduli and effective specimen moduli of the material. An iterative procedure is described incorporating the Timoshenko beam corrections (1937). A more precise approximation for the generalized torsional rigidity of an orthotropic material is presented. This allows a more direct method for the determination of the principal shear moduli. Discrepancies between the effective specimen shear moduli calculated from the corresponding torsional resonant frequencies and the results predicted using the principal elastic moduli are due to torsion-flexure coupling.