Experimental and numerical looseness detection and assessment in flanged joints using vibro-acoustic modulation method

Flanged joints' looseness is among the common causes for the failure of industrial structures with flanged joints the timely detection of which can prevent the imposition of heavy financial losses and in some cases injuries. There are conventional methods for detecting this fault and each of them has its own drawbacks. For instance, torque control methods have high error of measurement, impedance-based measurement methods, have high expenses, and vibration or ultrasonic methods lack accuracy due to the use of linear phenomena in fault detection. Vibro-Acoustic modulation method is one of the nonlinear fault detection methods that can detect and assess looseness of flanged joints with high precision through the measurement of the intensity of the vibrational and ultrasonic signals modulation applied to the structure. This paper was an attempt to investigate the efficiency of the Vibro-Acoustic modulation method in the detection and evaluation of flanged joints numerically and experimentally. For this, a laboratory sample composed of two pipes connected with flanged joints is employed. It is revealed that this method can detect bolt looseness with 12.5% precision. In addition, the effect of parameters such as ultrasonic and vibrational frequency, amplitude of applied torque, sensors and actuators position, as well as excessive increase of torque have been examined and the method precision in the studied structure has been estimated.