Application of a simple and cost-effective method for detection of bolt self-loosening in single lap joints

One of the major advantages of bolted joints (BJs) over welded, riveted and adhesively bonded joints is the disassembling option. This option facilitates the manufacturing and transportation of large-scale structures that are commonly formed as assemblage of various large structural components. However, this option is not always problem free, in that, during the life cycle of such structures, the bolts used to fasten the joints may become loosened. Although several techniques have been developed to mitigate bolt self-loosening (BSL), nonetheless, development of a methodology for detecting BSL has consumed considerable attention in recent years. As a result, several researchers have been seeking simple and reliable methods for detecting bolt-loosening in BJs, without compromising their stability. In this study, piezoelectric sensors are used to collect the vibration signals of a laboratory-scale single lap joint, joining two steel plates with three bolts. The acquired signals are then processed using the empirical mode decomposition method and the energies of the respective signals are calculated. A recently developed effective method is then employed to establish the so-called energy damage index, evaluated based on the energy stored in certain modes of the collected signal, in both the damaged and healthy states of the system. This method is found to be quite effective in detecting bolt loosening and the progression of self-loosening.