Experimental whole-field interferometry for transverse vibration of plates

Most of the work on vibration analysis of plates published in the literature are analytical and numerical and very few experimental results are available. Existing modal analysis techniques such as accelerometers and laser Doppler vibrometers are pointwise measurement techniques and are used in conjunction with spectrum analyzers and modal analysis software to characterize the vibration behaviour. In this study, a whole-field technique called amplitude-fluctuation electronic speckle pattern interferometry optical system is employed to investigate the vibration behaviour of square isotropic plates with different boundary conditions. This method is very convenient to investigate vibration objects because no contact is required compared to classical modal analysis using accelerometers. High-quality interferometric fringes for mode shapes are produced instantly by a video recording system. Based on the fact that clear fringe patterns will appear only at resonant frequencies, both resonant frequencies and corresponding mode shapes can be obtained experimentally using the present method. Two different types of boundary conditions are investigated in this study, namely free–free–free–free (FFFF, 27 modes) and clamped–clamped–clamped–clamped (CCCC, 12 modes). The numerical calculations by finite element method are also performed and the results are compared with the experimental measurements. Excellent agreements are obtained for both results of resonant frequencies and mode shapes.