Nonlinear Electro-Mechanical Impedance Spectroscopy for fatigue crack monitoring

•Electromechanical impedance and nonlinear ultrasonics were hybridized.•Combined linear and nonlinear features facilitate comprehensive crack evaluation.•A single piezo transducer realized the nonlinear ultrasonic testing procedure.•Chaos information in the spectra fosters a baseline-free damage index.•The authors declare no conflict of interest.