EXPERIMENTAL AND FINITE-ELEMENT ANALYSIS OF PULTRUDED GLASS-GRAPHITE EPOXY HYBRIDS IN AXIAL AND FLEXURAL MODES OF VIBRATION/

The effects of hybridization on the extensional and flexural dynamic p roperties of pultruded composite materials are reported in this paper. The composite materials considered were made up of unidirectional gla ss, graphite fibers in an epoxy matrix, and hybrids of glass-graphite/ epoxy produced by the pultrusion manufacturing process. The dynamic st orage modulus and loss factor of the rectangular and circular cross-se ction samples were first evaluated using the nondestructive impulse-fr equency response vibration technique. The long and slender flat specim ens were analyzed in both extensional and flexural modes of vibration in a free-free test configuration, whereas the thicker round specimens were analyzed only in the axial model of vibrations. The properties o f the monofiber type glass/epoxy and graphite/expoxy composites were u sed as input to the finite element model for predicting and experiment al validation of various pultruded (and hypothetical) glass-graphite/e poxy hybrid combinations. The modal strain energy method was used for computing the structural loss factors of the hybrid specimens based on the element stiffness matrices and estimated mode shapes in the funda mental mode of vibration. Results of this investigation showed excelle nt agreement between experimental data and numerical predictions for t he dynamic extensional properties of both flat and round specimens. Th e numerical results for dynamic flexural properties of flat specimens were found to have a similar trend as that obtained from the experimen tal technique. Small variations in flexural properties could be attrib uted to the irregular shapes (which were not taken into account in the finite element model) of layers in the hybrid combinations formed dur ing the pultrusion manufacturing process. Results also demonstrated th at while the extensional properties were independent of the fiber loca tion and fiber packing geometry, the flexural properties were highly d ependent upon these two factors. Previously reported data (which was o btained by testing these hybrid specimens in the flexural model of vib ration in a clamped-free boundary condition) were re-analyzed using th e free-free configuration and modal strain energy method, yielding mor e reasonable results.