Full lifecycle quantitative monitoring and early warning of bolt loosening based on acoustic emission

Bolted joints are a critical fastening method widely used in mechanical structures, and monitoring their loosening, particularly in the early loosening, is crucial for ensuring structural safety and reliability. This article presents a method for full lifecycle quantitative monitoring and early warning of bolt loosening based on acoustic emission (AE) technology. Variational mode decomposition is applied to the AE signals from the bolted joint interface to extract the energy characteristics of the intrinsic mode functions (IMFs). The IMFs most sensitive to changes in preload force are then selected as the characteristic mode. Segmented fitting equations are developed for the relationship between the energy of this characteristic mode and the bolt preload force across three key stages of loosening: early loosening, intermediate loosening, and late loosening. These equations enable effective monitoring and quantitative assessment of bolt loosening. This method not only allows for full lifecycle monitoring of bolted joints from fastening to loosening but also provides effective early warnings during the initial loosening phase.