Abstract
In this paper, both the modal testing method and amplitude-fluctuation (AF) electronic speckle pattern interferometry (ESPI) were used to measure the resonant frequencies, mode shapes, phase distribution and whole-field displacements of composite plates with and without defects. Square- and circular-shape defects of two different sizes were used in the composite plates. Two different stacking sequences of the composite plates were adopted, i.e. [0/90]3S and [±45]3S. Composite plates containing simulated defects located from the 3rd to 6th layer numbering from the top of the plates were fabricated, respectively. It was found that both the anomaly of the AF-ESPI fringe pattern around the defect and the decrease of resonant frequencies due to the defect are feasible ways to detect the existence of the defect. To explain the local effect of the defect at higher frequencies, vibration theory of thin plate with fixed ends for the square shape defect was employed.
