The in-plane elastic properties of materials can be determined using an experimental-numerical procedure based on the resonant frequencies of thin beams and plates. The objective of this paper is to study the accuracy of the material constants obtained with this technique. The procedure is presented and the parameters affecting its accuracy are identified. Specimens of epoxy reinforced with carbon fibers and 6082-T6 aluminum alloy were produced and experimental work was developed to obtain resonant frequencies in free-free boundary conditions. A numerical procedure based on FEM was developed replicating the experimental procedure and was used for a sensitivity analysis on the numerical and physical parameters. A great sensitivity relative to geometry was found, which emphasizes the need for ideally shaped specimens and accurate measurements. The influence of elastic properties on resonant frequencies is comparatively lower and varies quite considerably with geometry. The accuracy of experimental frequencies and specific mass was found to have a great impact on material constants.
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