## 2 Method  
### Structural Configurations and Modeling Strategies  
At present, the blades are made of two upper and lower shells and multiple shear webs by bonding using the most popular production technology of wind turbine blades. The thickness of the bonding area of the trailing edge is not constant due to the influence of geometric factors such as airfoils and relative thickness. Generally, bonding is of three types to ensure that the bonding thickness of the adhesive is controlled within a certain range. These bonding types are specified in Figure 2.  
Type A represents a case where the shell clearance of the trailing edge is large. In this case, the prefabricated bonding flange is required to control the bonding thickness. Type C represents a case where the shell clearance of the trailing edge is very small. In this case, adjusting the positioning of components (trailing-edge UD and staggering of layers) is necessary to control the bonding thickness. The shell clearance in the trailing edge of Type B is between that of Type A and Type C. The size of the prefabricated filler and the positioning of the components need to be considered comprehensively to control the bonding thickness in Type B. Under the same bonding width, the configurations that affect the bonding structure are roughly divided into four parts, which are shown in Figure 3. The bracketed content is the abbreviation of the model classification.  
1. Chamfer at the beginning of bonding line (BBL)
2. The position of trailing-edge UD (PUD)
3. Whether there are prefabricated components or blind bonding (PC)
4. Whether there is outer over-lamination at the end of bonding line (OL)  
The FEM method was used to simulate the bonding structure of the trailing edge so as to investigate the influence of these four configurations on the shear fatigue damage of the adhesive. [PERSON] [19] used layered shell elements to simulate the shell of the blade and the solid brick element to simulate the adhesive.  
Figure 2: Three types of tailing-edge bonding: (**a**) Profile of blade sections; (**b**) Type A: Prefabricated flange; (**c**) Type B: Prefabricated filler; (**d**) Type C: Blind bonding.  
A section with a chord length of 3 m and a relative thickness of 33% was selected to create the blade section model, which is shown in Figure 4.  
The section profile was obtained by interpolating NACA 63 series profiles. Figure 4a shows the model of the blade section and mesh in the ANSYS software package. The adhesive is divided into five layers of the solid element in the thickness direction. Figure 4b shows the shell elements, including the rendered shell thickness, while hiding the solid elements of the adhesive, prefabricated component, and outer over-lamination at the end of the bonding line.  
Three chamfering forms were set up to study the influence of chamfering on the shear fatigue damage of bonding, as shown in Figure 5. The influence of the prefabricated component on the adhesive shear fatigue damage was mainly considered in two cases: prefabricated flange and prefabricated filler. The effect of the outer over-lamination on shear fatigue was mainly investigated in two cases: outer over-lamination and no outer over-lamination. The distance between UD and the reference line was mainly considered to be 20, 30, and 40 mm. The average bonding width of the adhesive in all models was consistent.  
Figure 4: A cross-sectional view of the FEM model of the blade: (**a**) Local details of the trailing edge with the shell element; (**b**) Local details of the trailing edge without the adhesive, and bonding flange and shell element are shown with rendered thickness.  
Figure 3: Schematic diagram of four structural configurations.