Dynamic behaviour of postbuckled composite plates under acoustic excitation
Simple single-mode formulae are derived to present a general and straightforward understanding of the non-linear static and dynamic behaviour of postbuckled plates. The Rayleigh-Ritz method is used for multi-degrees-of-freedom analysis of postbuckled plates. A finite-element method using 16-nodes rectangular element is applied to postbuckling analysis of a composite plate with a central square hole. The magnitudes of multimodal linear response to random excitation are predicted using a simple formula based on results obtained by the Rayleigh-Ritz method and the trends of non-linear random responses are estimated using the single-mode formulae. Experimental techniques used include the Shadow Moire method to measure static displacement patterns, a point excitation test to find resonance frequencies and mode shapes, and acoustic testing to obtain random structural responses to sound pressure levels up to 163 dB. Experimental results were obtained for Aluminium alloy plates with two types of boundary conditions. These were compared with results from CFRP plates with similar types of boundary conditions. Finally, the acoustic response of a CFRP plate with a central square hole was examined. It was found that at high levels of acoustic exacitation, snap-through motion of amplitude larger than the oscillatory motion component can occur in the postbuckled plates and the overall r.m.s. strain value is comparable to the static strain value. In summary, the buckling of the plate changes the dominant deformations in the in-plane direction from those of in-plane effects to those of bending effects, whereas the large acoustic excitation changes the dominant dynamic deformations in the transverse direction from those of bending effects to those of in-plane effects.