Experiments on the symmetry-breaking effect of orientation on a pair of connected cantilevers

It is well established that axial loads tend to influence lateral stiffness and hence natural frequencies of slender structural components. For very slender structures, the axial loading can be caused by self-weight (in a gravitational field), and these effects influence equilibrium configurations and dynamic behavior. In some applications, for example solar sails, attached cables provide an additional complication. This paper will focus attention on a specific form of double cantilever beam system, i.e., two cantilevers sharing a common hub. Two specific cases are considered, in which the two ends of the cantilevers are connected by a cable under a given tensile load. The key observation is the effect that orientation (with respect to gravity) has on breaking the inherent symmetry in the vibration modes shapes of the systems studied. Although theoretical results are available for both a single cantilever pulled by a cable attached to its tip, together with results on the effect of gravity, the focus of the current paper is on the natural frequencies and mode shapes of two-beam systems from an experimental modal analysis perspective.