On the delamination detection in composite beams with active piezoelectric sensors using non-linear ultrasonics

This paper investigates the potential of a novel SHM method for the detection of delamination cracks in composites which exploits the nonlinear ultrasonic response with in-situ d31 piezoceramic actuators and sensors. Composite beam specimens with artificially created delamination cracks are tested, entailing two piezoceramic actuator patches, the first to generate a low frequency, high power modal excitation and the second a high frequency acoustical wave, as well as a piezoceramic sensor. Nonlinearities induced at the high-frequency signal, such as sidebands at the spectral components as long as modulations at the measured sensory voltage are evaluated as damage indicators. Experimental results quantify the potential of the method in detecting small delamination cracks through spectral sideband components. The influence of high-frequency on the effectiveness of the method is shown. Additionally, the effect of the magnitude of applied voltage on the low frequency actuator on the formation of spectral components is investigated. Finally, the obtained results of the present method are compared with a guided wave based pitch and catch SHM method using the same actuator-sensor pair to excite and monitor the propagation of the first symmetric and asymmetric Lamb waves.