Non-destructive real-time monitoring of bolt preload in wind turbine towers using FBG sensors on the nut

Bolt loosening in wind turbine towers often causes structural failures, leading to annual economic losses exceeding 100 million yuan. To address limitations of traditional monitoring methods, this study proposes a non-destructive, real-time preload monitoring technique using fiber Bragg grating (FBG) sensors. A mechanical model and finite element analysis reveal a strong linear correlation (<i>R</i>²>0.9996) between nut strain and applied torque. A dual-FBG differential compensation strategy effectively mitigates temperature-strain cross-coupling. The method demonstrates high accuracy and reliability, offering a feasible solution for structural health monitoring and early warning in wind turbine towers.