Experimental investigation of damage detection in composite material structures using a laser vibrometer and piezoelectric actuators

An experimental investigation to detect embedded delamination and other forms of damage in heterogeneous structures using smart materials and a laser vibrometer is presented. Typically, piezoelectric actuators and sensors have been used for characterizing the presence of damage in composite structures. However, the interpretation of vibration responses in identifying damage using such a procedure is strongly dependent upon the numbers and types of sensors and actuators used. The use of Vibration Deflection Shapes (VDSs), which are the actual vibration patterns of a structure undergoing steady-state vibration, is an alternative approach that is investigated in this paper. Experiments are conducted on composite structures with piezoelectric actuator patches and embedded delaminations, using the VDS method and a Scanning Laser Doppler Vibrometer. The laser vibrometer provides a dense pattern of measurements of the structural response, which effectively increases sensor density compared to the widely spaced piezoceramic sensors used in other techniques. A series of experiments is performed on composite plate-beams with various sizes, ply-level locations and placement of delaminations to comprehensively evaluate the performance of the laser technique. The VDSs are shown to be sensitive to structural parameter variations, and hence can be used to detect and located damage in large composite structures, including a woven fiberglass curved plate and a honeycomb intertank panel. The successul experimental demonstration of the procedure using different test articles shows that the VDS method can become an effective and time saving tool for structural health monitoring, particularly for detection of damage in composites.