Experimental Nonlinear Dynamics of a Post-buckled Composite Laminate Plate

Composite laminate materials are prevalent in the aerospace industry as programmable high-strength structural options. An increased focus on high-speed and space flight demands an understanding of composite materials subject to extreme combined thermal, aeroelastic and acoustic loading. Under such conditions constrained composite panels may buckle, thus exhibiting nonlinear structural behavior. This study focuses on a unidirectional carbon fiber epoxy composite laminate plate, a surrogate for more complex composite structures, with four stable static equilibria under fixed-fixed, free-free boundary conditions. The experiment includes pre- and post-buckled modal analysis as well as characterization of the nonlinear response due to transverse excitation. An electrodynamic shaker excites the plate at varying frequencies and loading amplitudes. The dynamic response of the post-buckled plate is measured with the 3D dynamic digital image correlation (DIC) technique combined with a laser vibrometer. The results show single-well and coexisting responses for the four stable equilibria along with chaotic snap through between equilibria. The experimental results of the pre-buckled plate modal analysis are compared to an analytical solution based on classical laminate plate theory (CLPT) and the equation of motion for transverse vibration of laminated plates. Future efforts include modeling and analyzing carbon fiber laminates with respect to damage initiation and material degradation due to high-stress snap through response.