Entire Torque Range Monitoring of Bolted Joints Via Nonlinear Electromechanical Impedance Spectroscopy (NEMIS)

Abstract

Abstract This paper proposes a Nonlinear Electro-mechanical Impedance Spectroscopy (NEMIS) methodology for the entire torque range monitoring of bolted joints. NEMIS utilizes a temporal interrogative signal to obtain the nonlinear impedance spectrum. It is capable of evaluating the structural resonance information as the conventional EMIS does and capturing the Contact Acoustic Nonlinearity (CAN) features simultaneously with only a single Piezoelectric Wafer Active Sensor (PWAS). A comparative illustration of the underlying mechanism behind the conventional EMIS, nonlinear ultrasonic techniques, and the proposed NEMIS was conducted. Subsequently, a reduced-order analytical model was established to simulate the variable rough interfaces of the bolted joints at different looseness stages. Parametric studies were carried out on the model to demonstrate the higher harmonics and vibro-acoustic modulation features from the bolt looseness. Ultimately, the experimental implementation of NEMIS for the entire torque range monitoring of a bolted joint was performed and compared with the conventional EMIS method. It was proved that NEMIS could detect both the incipient bolt loosening at an embryo stage and severe loosening of the bolted joints at the terminal period, combining the merits of the conventional EMIS and the nonlinear ultrasonic methodology. The paper finishes with summary, concluding remarks, and suggestions for future work.