Monitoring the looseness of a bolt through laser ultrasonic

Abstract

Abstract laser ultrasonic was applied to monitor the looseness of a bolt, aiming at the phenomenon that bolts can be loose after being assembled in a machine. We expound the experimental principle to monitor the bolt looseness by wave energy dissipation based on Hertzian theory of contact, taking only the asperity elastic deformation into account in our research. In the experiment, guided wave was induced by the laser, which was stimulated on the plate, to realize the goal of non-contact excitation. A piezoelectric sensor was used to receive the guided wave signal in the experiment. The distribution of guided wave power with frequency was observed by a Welch power spectral density (WPSD) image, and then the power of guided wave was calculated by power spectral density(PSD). We found that the power of guided wave is positively correlated with bolt torque. This conclusion is feasible for plates of different roughness (Ra0.5 ∼ Ra1.5), clamped by a bolt, verifying the efficiency of the method to monitor the bolt looseness through laser ultrasonic.This was verified by numerical analysis. Finally, the formula between power and bolt torque was fitted for bolted-joints in our experiment.