Young’s and Shear Moduli of Unidirectional Composites by a Resonant Beam Method

The resonant frequencies of unidirectional graphite epoxy com-posite beams were found to deviate markedly from classical beam theory predictions at higher modes of vibration. Timoshenko beam theory was used to account quantitatively for the dependence of ex-perimental resonant frequencies on mode of vibration, length/thickness ratio, and the ratio of Young’s modulus/shear modulus of the com-posite beam. By using reasonable values for the longitudinal-trans-verse shear moduli, the longitudinal Young’s modulus of anisotropic composite beams under vibration agreed well with values determined by static tests and became independent of mode of vibration and L/t. The vibrating beam test method was employed for the deter-mination of E11, E22, and G12