Health monitoring techniques using integrated sensors
Klaus Pfleiderer, R. Stoessel, Gerhard Busse · Proceedings of SPIE, the International Society for Optical Engineering/Proceedings of SPIE · 2003
Advanced high performance materials and components such as CFRP, GFRP and Smart Structures require improved testing techniques. The first part of our contribution deals with nonlinear vibrometry as a defect selective non-destructive testing method. This method uses higher harmonics (which are generated only at defects) to locate the defect by scanning across the surface of the sample with a laser interferometer. For input coupling of the elastic wave both an external (like ultrasound welding converters) or internal (integrated piezo actuators) excitation source can be used. The external detection tools are a microphone or a scanning laser vibrometer. With this technique, we characterized Smart Structures made of aerospace materials and composites with embedded piezoelectric actuators. The next part is about health monitoring techniques and diagnostics where integrated elements are used for excitation and detection. Thus, we monitored the transfer function over a large frequency spectrum and especially its changes caused e.g. by defects. Changes in the properties of structures by fatigue, impacts, and thermoplasticity have been successfully observed. Also the changes in reinforced plastics under tensile stress have been monitored. The results were correlated with destructive measurements. For health monitoring we also present the impedance analysis of embedded piezo ceramic sensors. A defect causes changes in the modal response of the hole structure and that effect can be detected using the phase angle of the electric impedance of the piezo element. Additionally some types of defects cause a non-linear behavior of the structure which was verified by extracting higher harmonics as a reaction to sinusoidal single frequency excitation.