In order to study the mechanical properties of the heterogeneous core plate of the wind turbine blade, a modeling method of the core plate based on displacement field variables is proposed. Firstly, the wind turbine blade core plate was modeled according to the theory of modeling heterogeneous material characteristics. Secondly, the three-point bending finite element model of the wind turbine blade core plate was solved by the display dynamic equation to obtain the deformation pattern and force-deformation relationship of the core plate. Finally, the three-point bending static test was conducted to compare with the finite element analysis. The test results show that: the damage form of the wind turbine blade core plate includes elasticity, yield, and failure stages. The main failure modes are plastic deformation, core material collapse, and panel-core delamination. The failure load measured by the test is 1.59 kN, which is basically consistent with the load-displacement result obtained by the simulation, with a difference of only 1.9%, which verifies the validity and reliability of the model. It provides data references for wind turbine blade structure design.

According to the outline of the 14th Five-Year Plan and the proposal for 2035, China will be vigorously developing renewable energy and environmental protection industries accordingly. Wind power plays an important part of renewable energy’s irreplaceable role in modern society [

At present, scholars at home and abroad have done a great deal of research on heterogeneous solid modeling methods. Kumar et al. [

To solve the aforementioned problems, a heterogeneous solid model was established for the core material of wind turbine blades based on the displacement field theory. A three-point bending test was carried out on the wind power blade core plate sample to observe the distribution of strength, stress, and deformation. By comparing the load-displacement curve and deformation shape obtained from the experiment, the reliability of the modeling method for the displacement field of the heterogeneous material of wind turbine blade core plate the core can then be verified; it provides a theoretical data reference for the overall parameter performance of the wind turbine blade.

The blade core plate exists in the leading edge, trailing edge, and web, which has an irreplaceable role in increasing the strength of the structure, reducing the local instability, and improving the blade load resistance [

The core material property set are

Concerning the material function of the distance, the material standard form is obtained by repeating the integral or differential transformation of L. The material function is known to be used to control the shear modulus,

Due to the uncertainty of environmental factors in the core plate field manufacturing, it is far from sufficient to explicitly define core plate’s material properties, and only represent the distance standard form locally. The original function can only be approximated by ignoring the remainder term. To reduce the error, define the unknown function

The upper and lower panels in the core plate are laminate structures composed of glass fibers, whose properties are mainly determined by the glass fiber monolayers’ mechanical properties, geometry, and boundary conditions [

The positive axis stiffness matrix

Convert the main direction of the single-layer glass fiber composite material with the ply angle of 45° to the overall coordinate system XYZ, and obtain the coordinate conversion matrix of each layer:

Among them,

The stress correspondence for each glass fiber layer is:

Using the same method, the strain-stress relationship under coordinate transformation can be found as follows:

The in-plane stiffness coefficient of the upper and lower panels is calculated as:

In-plane flexibility

The modulus of elasticity in the x-direction of the panels after regularization is:

As shown in

The blade core layup needs to add material properties, build a model, define the coordinate tool system, and define the direction selection set and layup parameters. It is set in the ACP-Pre module of the finite element analysis software Ansys workbench. Firstly, material properties were added. The orthotropic anisotropic glass fiber monomorphic strip material and heterogeneous solid material properties were added to the model. The material parameters are detailed in

Glass fiber | Resin | |
---|---|---|

Density/t⋅mm^{−3} |
0.6e‐9 | 1.15e‐9 |

E_{X}/MPa |
68 | 2900 |

E_{Y}/MPa |
68 | 2900 |

E_{Z}/MPa |
68 | 2900 |

PR_{XY} |
0.4 | 0.25 |

PR_{XZ} |
0.4 | 0.25 |

PR_{YZ} |
0.4 | 0.25 |

G_{xy}/MPa |
24.3 | 1160 |

G_{XZ}/MPa |
24.3 | 1160 |

G_{YZ}/MPa |
24.3 | 1160 |

In _{R} is Poisson’s ratio; G is shear modulus; X, Y, Z respectively represent the three directions of the material coordinate system.

After the material properties were added, it created a cloth layer; and gave its glass fiber and core unit thickness. That thickness is thoroughly detailed in

Specimen section | Panel fiber cloth laying angle | Panel thickness |
The thickness of the core material h/mm | Core material width b/mm |
---|---|---|---|---|

+45°/−45° | 2.00 | 24.00 | 33.00 |

The explicit dynamic algorithm solved the finite element model of the three-point bending structure. The finite element model was pre-processed [

Numerical simulation of three-point bending structure was carried out after the composite material was laminated. The ACP preprocessing module and explicit dynamics were associated and shared in Ansys workbench to solve. For the analysis of three-point bending, referring to the work of Fries et al. [

The material parameters are shown in

Name | Parameters |
---|---|

Tensile strength/Mpa | 980 |

Yield strength/Mpa | 835 |

Modulus of elasticity/Gpa | 206 |

Poisson’s ratio | 0.272 |

Secondly, set the contact relationship. The contact relationship between the indenter and the core plate was “surface-to-surface” friction contact, and the friction coefficient was 0.2. The contact relationship between the support and the core plate was frictionless contact. Since the fineness of meshing greatly influence the results of finite element analysis, high-quality mapped meshes were used for meshing. Its total number of nodes was 51813 and the total number of cells was 44905.

The finite element model obtained after meshing is shown in

By analyzing the working conditions involved, it became understood that the contact surface between the indenter and the blade core plate was the force-bearing surface. Finally, an external load was applied, a speed of 5 m/s was set, the direction was positioned to be straight down, and the end time was 0.04 s. There were only degrees of freedom to move in regarding of speed. In the analysis process, the rate of the indenter in the finite element analysis was much greater than the speed of the indenter movement in the experiment. The purpose was to eliminate the inertial force caused by the increase in speed. Perform dynamic solution after setting according to parameters.

After the finite element was pre-processed and solved, post-processing was then performed. The accuracy of the numerical simulation results was also verified according to the grid independence [

To study the bending mechanical properties of the wind turbine blade core plate, the relationship between the mid-span deflection of the blade core plate and the loading load was measured through a three-point bending test. The test consisted of an Instron5969 universal testing machine, a PC terminal, and an image acquisition system; those test parameters are shown in

Name | Parameters |
---|---|

Maximum working pressure/kN | 100 |

Maximum power/kW | 3 |

Measurement range | 2%−100% FS |

Force sensor model/T | LC4C/20 |

No-load speed/(mm/min) | 24 |

Indenter speed/(mm/min) | 5 |

Position accuracy/μm | 0.00268 |

Frame stiffness/(kN/mm) | 180 |

Acquisition frequency/Hz | 50 |

Indenter diameter/mm | 10 |

Span/mm | 260 |

Specimen length/mm | 300 |

The PC terminal had the work of designing the control algorithm, collecting data, as well as storing and displaying the strain curve. The test site is shown in

At the end of the test, the load-displacement curves fed back by the digital image system and the force sensor are shown in

Original number | Specimen number | Span/mm | Maximum bending force F/N |
---|---|---|---|

2-30-2-A | 1 | 260 | 1493 |

2-30-2-B | 2 | 260 | 1545 |

2-30-2-C | 3 | 260 | 1587 |

2-30-2-D | 4 | 260 | 1604 |

2-30-2-E | 5 | 260 | 1609 |

The deformation of the core board is shown in

The first stage was the elastic stage. The load-displacement curve increased linearly and the core plate did have elastic deformation. The deformation of the core plate could restore to its original state after unloading.

The second stage was the yield stage, in which the load remained stable and did not change obviously with the displacement increase. The upper ultimately plate completely failed and the core layer near the upper panel was gradually compacted.

The third stage was the destruction stage, which showed that the upper panel had a sizealy local deformation, and the core material was compacted in the indenter area. The responses of each stage of the panel, core material, and the interface layer were not synchronized, and face-core delamination occurred.

By comparing the results of the finite element analysis of the core plate with the test results, the correctness of the simulation analysis method was verified from the core plate deformation form and load-displacement curve. From the deformation profile of the core plate shown in

Data name | Simulation value/kN | Measured value/kN | Deviation/% |
---|---|---|---|

Comparison of simulation test results | 1.62 | 1.59 | 1.9 |

This paper took the wind turbine blade core board as the research object and proposed a modeling method for displacement field variables of heterogeneous materials. Furthermore, it established a heterogeneous solid model of blade core plate, performed finite element analysis on it, and conducted static force tests. The main conclusions are as follows:

The shear modulus of the core board and the glass fiber panel was expressed by establishing a heterogeneous model of the core board of the wind turbine blade. Based on the established model, the finite element method was used to analyze the displayed dynamics, and the failure load of the core plate was 1.62 kN. And the deformation shape of the core board was obtained through simulation.

The failure modes of the core plate included elasticity, yield, and failure stages. In the elastic stage, the deformation of the core board could restore to its original state; in the yield stage, the glass fiber panel yielded, and the core layer near the upper panel was gradually compacted; in the failure stage, the upper panel was partially deformed, and the central area of the core layer was compacted.

The main failure modes of the core board were plastic deformation, core material collapse and delamination of the panel-core material interface. The indenter expanded along the surface-core interface on both sides during delamination, and bending deformation was more likely to occur at the delamination position.

The three-point bending test was verified by building a test platform, and the test measured the damage load of 1.59 kN, with a difference of 1.9%. The load-displacement curve obtained by the numerical simulation was basically consistent with the experimental results, and the finite element analysis’s deformation patterns were consistent with the experimental results. The validity and reliability of the displacement field variable modeling were verified. It has important guiding significance for the design of wind power blades and related structures, and at the same time provides detailed experimental control data for related numerical simulation work.