Amplifying damage signature in periodic structures using enhanced piezoelectric networking with negative resistance elements

Abstract

Spatially periodic structures, such as bladed disks, are widely used as components in rotating machines. The recent advent of blade-tip-timing sensing technique has allowed the extraction of vibratory response information of blades during rotation for damage detection purposes. The decision making in damage detection of a periodic structure based on such measurement, however, is difficult primarily because of the clustered natural frequencies and high modal density, which is further complicated by inevitable structural uncertainty/variation. Our underlying idea is to integrate piezoelectric transducers together with circuitry elements onto the periodic structure to alter its dynamic characteristics during the inspection stage to improve the sensitivity and robustness of vibration-based damage detection. In particular, it has been identified that a properly designed piezoelectric inductive circuitry can amplify the response anomaly under external excitation. Such amplification nevertheless diminishes as the mechanical damping in the periodic structure increases. In this research, it is shown that the adverse effect of mechanical damping to anomaly amplification can be effectively reduced, by incorporating negative resistance elements into the piezoelectric circuitry network. The negative resistance elements are synthesized using operational amplifier circuits and can offset the mechanical damping through the dynamic interaction between the piezoelectric circuitry and the host structure. The stability boundary of the negative resistance integration is identified, where the frequency-dependent inherent resistance of the piezoelectric transducer is taken into consideration explicitly. The effectiveness of the enhanced circuitry network for amplifying damage signature in periodic structures under large damping is illustrated with detailed case studies.