Study On Acoustic Emission Behavior Of Composite Adhesive Joints Of Wind Turbine Blade

Duo to the fact of common bonding defects of composite adhesive joints of wind turbine blade, Acoustic emission(AE) technology was used to monitor the whole damage process of composite blade adhesive joints and Metal/FRP cylinder-shell adhesive joints under loading in real time. According to the results of Finite element analysis(FEA) and experiments, the mechanical properties and AE behavior were investigated. An AE new method to evaluate adhesive joints of wind turbine blade was proposed.The mechanical properties, failure characteristics of interface, AE responses, and FEA of adhesive specimens were studied, respectively. Through investigations contrasts, the following conclusions are obtained:(1) AE technology was used to monitor the tensile failure of adhesively bonded single-lap composite joints with defects and no defects in real time. Results show that the load-bearing capacity of adhesively bonded single-lap composite joint reduces due to defects in the adhesive layers. Adhesion failure is the major failure mode, and the damage mainly occurs at the edge of the adhesive layers and defects in the adhesive layer, where stress is concentrated. For the adhesive joint with defects, AE signals with the amplitude from 60 to 80 dB increase at the evolution stage.(2) AE technology was used to monitor the damage initiation and propagation of adhesive joints in mode I and II loading in real time. Results show that adhesion failure is found to be the dominant failure mode for both mode I and II specimens, and with the cohesive failure and fiber break. Furthermore, higher load-bearing capacity, higher AE amplitude and relative energy, and more cumulative hits are connected with the damage process of specimen with longer overlapped length.(3) AE technology was used to monitor the torsion failure of Metal/fiber-reinforced polymer(FRP) cylinder-shell with different overlapping lengths and different diameters of bolt under torsion test in real time. The results of FEA and the experiment show that increasing the overlapping length and diameter of bolt can effectively improve the load-bearing capacity of adhesive joints, nevertheless the average shear stress decreases with the increasing of the overlapping length. It was found that the cohesive failure is the major failure mode, and with the fiber break. As the overlapping length and diameter of bolt increases, more AE signals with the amplitude from 60 to 80 dB increased at the evolution stage, and more AE signals with the amplitude above 80 dB increased at the failure stage.(4) AE technology was used to monitor the tensile failure of Metal/FRP cylinder-shell with different overlapping lengths under tensile test in real time. Results show that adhesion failure is the major failure mode and damage mainly occurs at the edge of the adhesive layers, where stress is concentrated. The higher load-bearing capacity, higher AE amplitude and relative energy, and more cumulative hits are connected with the damage process of adhesive joint with longer overlapped length.As a result, AE parameters are related to the failure process, especially the amplitude distribution. AE Behaviors can be used to study the damage mechanisms of adhesive joints, and can provide evidences for early health monitoring and security evaluation of composite adhesive joints of wind turbine blade.