Experiments on the nonlinear vibrations of postbuckled circular panels under harmonic excitation

The small deflection (static or dynamic) flexural response of a nominally flat panel is adequately described in terms of linear characteristics. However, for a (mildly) non-flat panel the situation is much more complex, whether the non-flatness is simply the natural consequence of imperfect geometry, or the result of an applied compressive loading (through heating, for example), i.e., a post-buckled state. A striking feature of many systems with non-trivial equilibrium configurations is bistability. Under quasi-static conditions it is possible to transition from one stable equilibrium configuration to another by applying some kind of external lateral force or disturbance. Furthermore, under dynamic excitation, for example placing the panel and it’s support on a shaker, for sufficiently large equivalent forcing conditions, the buckled system may not only jump between equilibria but tra-jectories can undergo persistent erratic behavior snapping around and between whatever equilibria are present. This paper considers such a system from an experimental perspective , and focuses attention on a geometry (a thin, circular, clamped plate) that is relatively simple. A key aspect of this work is the use of dynamic digital image correlation (DIC) to capture the complex dynamics of panels under various intensities of loading. Two panels with the same geometric properties but differing materials (one aluminum and one brass) are tested. Despite the simplicity of the system (in terms of geometry and harmonic forcing), and necessarily limited parameter variations in an experimental context, a wide variety of temporal and spatially complex behavior is encountered.