Monitoring of Bolted Joints with Electro- Mechanical Impedance Spectra and Acousto-Ultrasonics

A.-L. DREISBACH, P. KRAEMER, C.-P. FRITZEN

Abstract


Bolted connections are one of the most widely used types of joints in various fields of applications. Their functionality depends on the conservation of the preload in the bolt’s shaft, which implies the need to monitor it. This paper addresses a monitoring procedure of the preload. Therefore, two measurement techniques for the preload are compared: On one hand, a technique, which is based on Electro-Mechanical Impedance spectra, on the other hand, a technique, which is based on Acousto-Ultrasonics. Electro-Mechanical Impedance spectra are measured with the help of the Electro-Mechanical Impedance method. This method is deployed in a relative high frequency range and the resulting spectra represent the transfer function between the local excitation of the structure and its response. In the applied Acousto-Ultrasonics procedure a burst excitation is introduced into the bolt on its head and the response is measured in pitch-catch mode at the face side of its shaft. As both techniques make use of so-called piezoelectric wafer active sensors, three different types of these transducers were used in this study and have been compared. For the experiments, three bolts having a size of M72 × 380 are equipped with the required transducers. Subsequently, they are tightened stepwise with a custombuilt testing device for bolts. The several combinations of the measurement techniques and different types of piezoelectric wafer active sensors are then compared with focus on their sensitivity and variability. The most suitable combination in terms of preload monitoring is identified.


DOI
10.12783/shm2023/36778

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