The Dynamic Properties of Unidirectional Carbon and Glass Fiber Reinforced Plastics in Torsion and Flexure

Specimens of polyester resin reinforced with unidirectional R. A. E. Type 1 (high modulus) carbon fibers or E-glass were subjected to torsional and flexural vibration. For both types of fibers the damping was independent of, or only weakly dependent on, the cyclic stress amplitude in the range covered. E 11 and G 12 were measured and neither was affected by stress amplitude. The longitudinal flexural modulus for both CFRP and GFRP was slightly lower than as predicted by the law of mixtures. This may be attributed to lower compressive modulus than tensile modulus of these composites. The longitudinal shear modulus was very close to the theoretically predicted value if the anisotropy of the carbon fibers is assumed. The damping decreased as the volume fraction was increased and specimens made from both fibers gave very similar results.