Bolt loosening detection using impedance based non-destructive method and probabilistic neural network technique with minimal training data

For centuries, bolted fastening has been widely used in aerospace, civil and mechanical engineering areas to achieve joining of parts. However, studies have shown that vibration occurs virtually in all dynamic systems such as in machines and structures which seems to be the main cause of bolt loosening. As this can significantly reduce the load bearing capacities of a system, it is important to monitor the state of bolts to ensure safety. In this study, piezoelectric transducer based technique method known as the electromechanical impedance (EMI) technique with probabilistic neural networks (PNN) was used to identify torque loss of bolts on three bolted structure specimens. The training data from the first specimen was used to predict torque loss of different specimens to evaluate the possibility of the proposed idea. Results show over 90% accuracy with the PNN algorithm designed for this work bringing one step close for the piezoelectric based non-destructive testing technique to be applied to real structures.