A Modal Analysis of Submerged Composite Plates Using Digital Speckle Pattern Interferometry

An experimental analysis of the modal vibrations of laminated composite plates with free and cantilever boundary conditions is described in this thesis. The vibrations of the plates are studied in air and when submerged in a water tank to examine the effects of fluid loading on the plates. The experiments were also performed on similar homogeneous aluminum plates to illustrate the effects of anisotropy in the composites. The analysis was performed with the experimental technique of Digital Speckle Pattern Interferometry (DSPI) which is like holographic interferometry with the exception that a video camera and digital image processor are used to collect and process the holographic images. DSPI provides full-field, non-intrusive, out-of-plane displacement measurements of vibrating structures, and produces mode shapes in the form of speckle correlation fringe patterns. In addition, the drive point mobilities of the plates were determined with the aid of a laser Doppler vibrometer. The results of the experiments showed that the composites exhibited unpredictable modal behavior due to anisotropy in the plates. For this reason, DSPI proved to be efficient technique for acquiring mode shapes. In addition, the use of vibrometry in conjunction with DSPI provided an accurate experimental modal analysis system.