Many engineering structures are held together by arrays of closely mounted bolts. For the safety of e.g. wind turbine towers, it is essential that all bolts are properly tightened. Currently many resources are spent at mandatory regular checks of bolt tightness. For the inspectors the work can take a long time, be monotonous, physically demanding, and risky, e.g. with heavy hydraulic tools at elevated height.
Funded by a grant from The Danish Council for Independent Research, this 3-year research project aims at exploring new ways for testing critical bolt connections in engineering structures. In a collaboration with Karlsruhe Institute of Technology and the company Brüel & Kjær Sound & Vibration, assoc. prof. Jon Juel Thomsen from MEK, along with a postdoc and a PhD student, will explore why a well-tightened bolt sounds differently from a looser bolt, when stroke by a hammer [
listen to audio clip], and how this can be used to check critical bolted joints faster, cheaper, more accurately, and with less physical effort than using conventional tools.
We aim at quantifying the difference in sound/vibration, so as to estimate bolt tension from measured vibrations, by using advanced mathematic modelling and analysis, and suitable measurement equipment and signal processing. Our pilot studies indicate a strong correlation between various features of vibrations and bolt tension, but also reveals difficult obstacles, which will be addressed in the project.