Three-dimensional Finite Element Analysis Of The Structural Strength Of Large Composite Wind Turbine Blade

Since 2005,wind power industry has been developed in China on a large scale.By the end of 2017,the cumulative installed capacity of wind power of China has exceeded one third of the world.At present,the production of wind turbine blades mainly uses glass fiber composite materials and adopts the molding process of vacuum perfusion.Firstly,suction side and pressure side and shear webs are all forming seperately.Then each sub-component is bonded together by adhesives.As a key component of energy absorption of wind turbine,composite blades are subjected to severe and complex dynamic loads.The researches show that the adhesive bonded joints of blade at the leading edge,trailing edge and spar cap are prone to crack and debonding under severe and complex dynamic loads.According to the analysis of the failure section of the blade by relevant scholars,the failure of the blade shows the coupling effect of various failure modes and behaviors,including blade buckling,composites fracture,adhesive debonding,fatigue damage and so on.It's difficult to determine the root cause of blade failure due to the complex composite structure and variable service load of blades.So it's of great academic value and engineering significance to study the structural strength of large wind turbine blades based on their dangerous sections.In chapter 2,the SNL 100-meter blade designed by the Sandia Renewable Energy Laboratory in US was selected as the research object.According to the aerodynamic profile data and the composite laminated structure of the blade at the dangerous section,a full 3D FE model of the blade segment including the adhesive bonded joints was established with ANSYS.In combination with the bilinear cohesion model,the formation and expansion of the adhesive debonding under the flapwise and edgewise loads were analyzed,and then the failure analysis of the material was carried out using the Tsai-Wu failure criterion.The results show that adhesive debonding appears at the buckling area of trailing edge under edge-wise load,and buckling is the driving factor of adhesive debonding.By comparing the initial failure loads of each part of the blade segment under the flapwise and edgewise loads respectively,it is found that composites failure occur first,then adhesive debonding,and finally adhesive fails.In the process of blade production,it is difficult to accurately control the quality of adhesive joints,and inevitably there will be adhesive defects at the joints,such as lack of glue,surplus structural glue,structural glue containing bubbles and slag inclusion on the adhesive surface,etc.In the service period of the blade,the defects in the adhesive joint are easy to form cracks.Therefore,chapter 3 carried out a research on the adhesive cracks,and analyzed the influence of the location of the adhesive cracks on the adhesive debonding,material failure and trailing edge buckling.It was found that when there were adhesive cracks at different positions of the blade,the debonding was determined by the buckling of trailing edge.The locations of the adhesive cracks have no effect on the initial failure load of the material,but has an effect on the propagation process of the material failure.The buckling waveform and amplitude of the trailing edge are different with the location of the defect.Under the edgewise load,when the adhesive cracks is located at the trailing edge,the buckling amplitude of the trailing edge is also the largest.As the trailing edge buckling is the driving factor for the adhesive debonding,in chapter 4,the trailing edge of the blade is taken as the research focus.And adhesive cracks of different lengths are set in the middle of the TE adhesive joint to study the influence of cracks length on adhesive debonding,material failure and trailing edge buckling.Under flapwise load,the change of crack length has no obvious effect on the failure of the material.The increase of the crack length will not change the initial failure load of the material,but accelerate the process of failure propagation.With the increase of the crack length,the larger the buckling amplitude is,the more serious the failure is.In this paper,the formation and expansion rules of debonding of wind turbine blade adhesive joints under flapwise and edgewise loads are explored.Also the initial failure loads and failure positions of composite materials and adhesives are analyzed.And the buckling of trailing edge is also analyzed.It is hoped that this paper can be of some help to the relevant blade structure designers.