Abstract: Aiming at the identification problem of bolt fracture damage in flange section of wind turbine tower, taking a 1.5 MW wind turbine as an example, the theoretical derivation, simulation analysis and damage identification index correction of bolt fracture damage identification were studied. The vibration differential equation and strain mode theory of beam were established by using the method of continuum vibration differential equation. ANSYS software was used to analyze the vibration mode of the tower, and the changes of displacement and strain mode shapes under different bolt fracture conditions were studied. The absolute deviation of strain was taken as the damage identification index, numerical simulation was used to verify the effect of wind turbine tower damage identification under different working conditions. The results show that there is no obvious mutation in displacement mode shapes under different damage conditions, while the strain mode shapes appear significant mutation at the fracture of tower flange bolt, and the strain index is more sensitive to damage. The modified strain absolute deviation damage identification index weakens the influence of high strain value in undamaged area on damage identification, and then improves the sensitivity of damage identification. The damage identification based on strain mode analysis can provide reference for damage monitoring and health maintenance of large wind turbine tower.
Key words:  wind turbine tower; strain mode; bolt breaking; damage identification; identification correction

ZHANG Ze-rong, LI Peng-fei, HAN Tong-tong, et al. Fracture damage monitoring of wind turbine tower flange bolt based on strain mode analysis［J］.Journal of Mechanical & Electrical Engineering, 2021,38(10):1348-1354.