Abstract
An investigation of the free vibration characteristics for a set of extensiontwist coupled thin-walled single-cell composite beams with optimal and near-optimal coupling is performed using an analytical model, a finite element simulation, and testing. It is found that, despite the relatively large beam slenderness ratio, the applicability of the analytical model is limited to the first bending modes, for which excellent agreement with the finite element and experimental results is obtained. For analytically predicted higher order modes, increasingly significant in-plane warping is shown by the corresponding finite element results, and an increasingly large variance is observed between the two sets of results. The occurrence of shell modes that cannot be captured by the analytical model is also shown by the finite element results. Test data confirm finite element calculations as well as low modes predicted by the analytical method. The sensitivity of natural frequencies to lay-up perturbation angle is established over a frequency range of interest, providing insight into the robustness of the modal characteristics for the global and the local optima, respectively.