Vibrations for estimating bolted joint integrity (VEBJI) project: Challenges and results

Bolted joints are one of the oldest and widely-used means of connecting parts of technical installations. For mission-critical and expensive assets, periodic inspection of bolted joints is the conventional way of ensuring the assets' structural integrity, and hence their safe operation. Currently, the inspections require hours of physically demanding and monotonic work, as in practice it often means re-tightening the bolts. Thus, the asset maintenance units will benefit from a simpler and less demanding technique, which would allow checking the correct bolt tightening and notifying if a bolt is loose. For the last three years, a joint research team led by the Technical University of Denmark in collaboration with Brüel & Kjær and Karlsruhe Institute of Technology was conducting a project, where vibrations, artificially induced in a bolted joint, were utilized for estimation of the static axial force acting in the bolt. The presented paper provides an overview of the project, lists the numerous challenges the project had to deal with and describes what was learned and achieved.