Fast loose rivet detection by using Scanning Laser Doppler Vibrometry

Until today, the manual inspection of riveted lab joints and detection of loose or damaged rivets is a time-consuming and costly task in the regular maintenance of civil aircraft. Many studies investigate the crack propagation in rivet holes or the influence of manufacturing parameters to the durability of riveted lab joints. However, no automated and digital in-situ quality assessment for loose and damaged rivets is explored so far. This work presents a study on a real aircraft fuselage panel in which Scanning Laser Doppler Vibrometer measurements enable the detection and distinction of loose, damaged and intact countersunk rivets. On the one hand, a chirp sine excitation allows the detection of loose rivets by a coherence analysis of the excitation signal and the measured vibration. On the other hand, damaged and intact rivets appear in the vibration analysis as so-called local defect resonances at low and high frequencies respectively. The presented work potentially leads to a digital, automated and full-field inspection method suitable for the application in an industrial environment like the regular aircraft maintenance.