Study On The Mechanical Properties Of Wind Turbine Blade Root

In recent years,the development of wind power at home and abroad is an upward trend,and wind turbines convert wind energy into electricity without pollution.Wind turbine blade is a thin shell structure made of fiber reinforced composite,consisting of roots,shells and girders.Blade root is a key part of connection of the blade and the wind turbine rotor hub.Under a complex combination of shear,extrusion,bending and twisting effect,so the blade root connection parts must have enough mechanical strength and bend torsion stiffness.The connection of blade bolt and blade root is usually connected by the embedded blade root bolt sleeve and the blade root T bolt type.This paper mainly studies the mechanical properties of the blade root.The paper gets the broken pattern,the ultimate bearing capacity,stress load curve and displacement load curve of blade root through test and validates blade root whether meet the design requirements.The typical blade root is a cylinder structure,and the experimental subject is 3/92 of the cylinder structure.The experimental model is established by using large-scale finite element software ANSYS 17.0.The axial stress and stress cloud images are acquired from ANSYS.According to the calculated results,the strain points are selected and the experimental scheme was developed.Based on the structural design method,the paper designs experimental model.The experimental model is subjected to axial tensile test to complete the test data acquisition and the test observation.According to the failure modes and ultimate tension observed in the experiment,the failure pattern of the specimen and the average value,the standard value,the standard deviation and the coefficient of variation of the specimen are classificated calculated.In this paper,the difference between the test strain of blade bolts and blade layer,the test displacement of blade root and the calculating value from ANSYS numerical simulation is analyzed.The Von Mises equivalent stress and the first principal stress of blade bolts and blade layer are calculated and the corresponding intensities are evaluated through the establishment of a blade root mechanical properties analysis model and local model.The paper studies the bolt necking static strength,the static strength of the glass steel under the nut,the compression strength of the glass steel under the nut,the bending strength of the nut from blade root under different pretension force,and analyzes the influence of the strength under different pretensionforce.Through the experiment,it is found that the blade bolt is subjected to the period of elasticity,reinforcement,contraction and two kinds of failure pattern of the blade root is the blade bolt contraction failure and the embedded blade root bolt failure.The blade bolt contraction failure is plastic failure and the embedded blade root bolt failure is brittle failure.There is a failure phenomenon include two kinds of failure pattern.The maximum percentage reduction of area of the blade bolt is 35.24%,and blade bolt has good plastic properties.The average value of the specimen is 1050 kN.The standard value is of the specimen 1019.89 kN.The standard deviation and the coefficient of variation are small and the difference between the individual and the overall average also is small,so the test data reliability is high.In this paper,the test data and the calculation data error are small through the comparison of the test strain of blade bolts and blade layer,the test displacement of blade root and the calculated strain and calculated displacement of ANSYS numerical simulation,so the reliability of numerical simulation of blade root is high.The maximum axial stress,the maximum Von Mises equivalent stress and the maximum first principal stress of the blade bolt under pretension force of 250 kN and350kN are in the range of bolt elastic stress.Blade bolt meet the design requirement.The greater pretension force,the lower safety of the static strength of the bolt necking static strength,the more favorable to the load safety of the bolt necking static strength.The pretension force has no effect on the static strength of the glass steel under the nut.The greater pretension force,the lower safety of the static strength and the load safety of the compression strength of the glass steel under the nut.The greater pretension force,the lower safety of the static strength and the load safety of the bending strength of the nut.Safety coefficient of the static strength and load of the blade root is more than 1,so the structure is safe.