FBG Sensor Bonding Process And Application In Wind Turbine Blade Damage Monitoring

As the only high-altitude dynamic bearing operation part of wind turbines,wind turbine blades are subject to alternating fatigue loads for a long time,and the leading edge of the blade tip and the blade root are easily damaged.Optical fiber strain monitoring is one of the commonly used in-service health monitoring methods for wind power blades.However,wind power blades are mostly installed in mountainous areas and offshore.The large temperature difference between day and night and high humidity in the service area will cause condensation water to adhere to the inside of the blade.At the same time,small cracks and micropore will cause water accumulates inside the blade,so the surfacemounted Fiber Bragg Grating(FBG)sensor will be in a high temperature and high humidity environment during use.The harsh environment will affect the bonding effect of the sensor,so that the sensor will be fatigued and debonded during the long-term dynamic monitoring process.If the maintenance is not carried out in time,the sensor will even be broken,causing other sensors welded to it to fail,thus affecting the monitoring effect.Aiming at the unreliable operation of the FBG sensor due to the failure of the paste during the operation process,the paper explores the paste process,and performs static and dynamic verification of the sensing characteristics.Finally,the paste process is applied to the single blade fatigue and wind field monitoring process.The main research contents of the thesis include the following aspects:First,based on GB/T 7124-2008,four adhesives,502 glue,5210 glue,353 ND glue and LOCTITE glue,were selected for curing under different humidity conditions.The LOCTITE glue with the maximum shear modulus was selected,and then the optimal bonding length and width of 11 mm for wind turbine blade monitoring were selected through numerical calculation and simulation.Second,equal-strength beam samples were fabricated,followed by strain transmissibility verification for adhesive,bond length,and width based on strain gauge monitoring data.The cantilever beam experiment verified that under static load,the FBG sensor pasted with LOCTITE glue with a length of 100 mm and a width of 11 mm has good strain transfer characteristics.After 10,000 times of dynamic fatigue loading,the transmissibility is maintained at 96.1%,which has good strain transmission characteristics and adhesion reliability.Third,the prefabricated tensile samples with different crack lengths were produced,and the strain load law was analyzed to find that the greater the percentage of crack damage,the greater the strain under the same load and the accelerated rate of increase.Single leaf fatigue test using the explored bonding process found that the blade strain increased from the initial strain to 108% and was maintained for a long time,indicating the occurrence of blade damage.Finally,the damage inside of the blade in service is monitored online.The monitoring results showed that the range of strain change was ±6.5%under different wind conditions,and the monitoring data was basically stable during longterm monitoring.