Bolted joint loosening detection by using laser excitation

In this paper, the authors propose a finite element model of a simple single bolt joint that undergoes loosening in order to verify characteristic changes due to bolt loosening and develop a loose-bolt detection system. The model is created using 3D solid elements and surface-to-surface contact elements between head/nut and flange interfaces. Pretension effects and contact behavior between flanges to be joined are also taken into account. In order to validate the finite element model by experiment, vibration testing method based on non-contact impulse excitation by high-power YAG pulse laser which can produce an ideal impulse is conducted. The characteristic changes due to the bolt loosening in high frequency region can be extracted by the present laser excitation system. Finally, an approach of loose bolt detection is demonstrated by applying statistical evaluation of Recognition-Taguchi (RT) method to a six bolt cantilever which has loose bolt.