Health Monitoring Technique for Truss Structure with PZT Patches. Estimation of Fastening Condition of Bolts and Damage Indices.

This work presents a study on development of a practical and quantitative technique for assessment of the structural health condition by piezoelectric impedance-based technique associated with longitudinal wave propagation method. A truss structure constructed by aluminum beams and piezoelectric patches is investigated experimentally for estimation of the fastening condition of bolts which is supposed to be a kind of infancy damage. The bolt fastening condition is adjusted by torque wrench. In order to estimate the damage condition numerically, three damage indices, impedance peak frequency shift ΔF, peak amplitude ratio δ and quality factor ratio γ, are proposed in this paper. Furthermore, an assessment method is described for estimation of the damage by using these three damage indices. As an example, estimation of fastening torques on the bolt is illustrated. With a plenty of experiment results, the damage indices proposed in this work are validated useful for assessment not only of the looseness of bolts and also for any other structural infancy damage, such as the concentrated stress, small crack and so on.