Nonlinear Electro-Mechanical Impedance Spectroscopy for fatigue crack monitoring

Abstract

This article presents a Nonlinear Electro-Mechanical Impedance Spectroscopy (NEMIS) methodology for fatigue crack monitoring. Different from the conventional Electro-Mechanical Impedance Spectroscopy (EMIS) implemented in the frequency domain, the proposed NEMIS employs a temporal chirp interrogating signal to obtain the impedance spectra, and simultaneously captures the Contact Acoustic Nonlinearity (CAN) features. To develop an insight into the mechanism behind the NEMIS method, a comparative investigation between the conventional EMIS and the two-phase NEMIS algorithm was conducted. Numerical studies were carried out on a 1-D transitional-bilinear CAN model to demonstrate the chirp-induced higher harmonics and nonlinear mixed-frequency response features. Furthermore, finite element (FE) simulations were conducted to demonstrate the feasibility of the NEMIS. A baseline-free damage index was subsequently developed to quantify the severity of the fatigue crack. Finally, experimental validation of the NEMIS method was performed. The experimental results validated the feasibility and accuracy of the chirp-based impedance spectra. It was also shown that NEMIS successfully captured the nonlinear impedance spectra, obtaining higher harmonics and wave modulation features to manifest the existence of the fatigue crack. Quantification on the severity of the crack was conducted via the nonlinear damage index, which presented a consistent, monotonic trend with the increasing severity of the fatigue crack. The experiment demonstrated the capability of NEMIS for detecting and quantifying fatigue cracks. The article finishes with summary, concluding remarks, and suggestions for future work.