Structure Damage Detection Based On Weak Signal Enhancement

For structure damage detection, the pivotal procedure is to define the feature signal that brings the damage information. Usually the feature signal is rather weak or submerged in heavy background noise and proper methods must be applied to process or enhance the weak signals. The paper explores how to improve the structure damage detection from the viewpoint of weak signal enhancement.Firstly, the paper addresses the improvement of the stochastic resonance (SR) approach to enhance the effectiveness of weak signal detection through a circuitry system. The multiscale noise tuning through a filter array is explored to enhance the performance of a classical SR circuitry system. The experiment exhibits that the multiscale noise tuning greatly widens the noise intensity range suited for the SR effect in comparison with white noise tuning. Furthermore a practical weak signal detection approach is proposed by combining the multiscale noise tuning SR (MSTSR) with the traditional synchronous demodulation (SD) detector. The study shows that the combination could detect weak signal in extremely heavy background noise while the signal-to-noise ratio (SNR) is lower than-50dB and it has more stable output and higher output SNR than the SD detector.Secondly, the paper explores the structure damage detection based on the ultrasonic guided wave with the sparse piezoelectric actuator/transducer array. Precise measurement of time of the flight (TOF) of the propagating signal plays a pivotal role in structure damage localization. In this paper, a time-frequency analysis method, Wigner-Ville Distribution (WVD), is applied to calculate the TOF of signal based on its excellent energy distribution property in the time-frequency domain. The true energy distribution is beneficial to reliably locate the position of damage. Experimental studies are demonstrated for damage localization of one-dimensional and two-dimensional structures. In comparison with traditional Hilbert envelope and Gabor wavelet transform methods, the proposed WVD-based method has better performance on the accuracy and the stability of damage localization in one-dimensional structure. In addition, the proposed scheme is validated to work effectively for damage imaging of a two-dimensional structure.Finally, the paper explores the structure damage detection based on the nonlinear ultrasonic effect. Vibro-Acoustic Modulation (VAM) has been studied to detect the micro or close crack in structure but there are many problems to be explored. The paper combines the VAM effect with the tristable SR mechanical system. Through the experimental studies, the scheme is verified to realize the micro crack detection with the excitation frequency out of the resonance range of the structure and the applicable frequency range is much wider than the traditional VAM methods. The scheme has great potentials to improve the structure damage detection at a very early stage.