A method for predicting the number of fatigue fractures of a wind turbine blade composite material

Abstract

The application discloses a method for predicting the fatigue fracture times of wind turbine blade composite materials, comprising the following steps: preparing a plurality of wind turbine blade composite material samples, each sample being prepared with two parallel test samples; taking one parallel test sample of each sample to perform a creep performance test under preset test conditions; taking another parallel test sample of each sample to perform a fatigue performance test; fitting the relationship between the creep strain and the fatigue fracture times; for the wind turbine blade composite material to be tested, performing a creep performance test under the same test conditions to obtain the creep strain, and according to the obtained relationship, obtaining the predicted fatigue fracture times of the wind turbine blade composite material. The method can complete the fatigue performance test and evaluation in a short time, establish a linear correlation model of creep and fatigue, calculate the fatigue fracture data by testing the creep strain data, and experimental results show that the theoretical calculation data is very close to the data obtained by the tensile fatigue performance test.

Description

Technical Field

[0001] This invention relates to the field of wind turbine blade technology, and specifically to a method for predicting the number of fatigue fractures in composite materials for wind turbine blades. Background Technology

[0002] With the continuous growth of global demand for renewable energy, wind energy, as a clean and sustainable energy form, is rapidly developing and becoming an important part of the energy structure. As the core equipment for wind energy utilization, the performance and reliability of wind turbine generators directly affect the efficiency and lifespan of wind power systems. However, the operating environment of wind turbine generators is complex and variable, subjecting them to the combined effects of wind loads, gravity loads, and environmental factors (such as temperature, humidity, and ultraviolet radiation) over long periods, leading to fatigue damage in their critical components, especially the blades.

[0003] Composite materials are widely used in wind turbine blade manufacturing due to their superior properties such as high specific strength, high specific stiffness, corrosion resistance, and designability. However, under long-term cyclic loading, composite materials are prone to fatigue damage, such as matrix cracking, fiber breakage, and interfacial debonding. These damages accumulate gradually, eventually leading to material failure and severely affecting the structural integrity and service life of the blades. Therefore, in-depth research on the fatigue behavior of wind turbine composite materials, revealing their fatigue damage mechanisms, and proposing effective fatigue-resistant design methods and life prediction models are of great significance for improving the reliability and economy of wind turbines.

[0004] In recent years, scholars both domestically and internationally have conducted extensive research in the field of composite material fatigue, achieving significant progress. However, the fatigue problem of wind turbine composite materials still faces many challenges. First, the load spectrum of wind turbine blades is complex, and the fatigue damage modes are diverse, making it difficult to accurately describe their fatigue behavior using a single theoretical model. Second, the fatigue performance of composite materials is affected by multiple factors, such as fiber type, matrix material, interfacial properties, and manufacturing process; the interactions between these factors further complicate the fatigue problem. Furthermore, environmental factors (such as temperature, humidity, and ultraviolet radiation) have a significant impact on the fatigue performance of composite materials and need to be considered in the design and evaluation processes.

[0005] Fatigue prediction for composite materials faces numerous challenges, primarily due to their complex structures and diverse damage mechanisms. The following are some key challenges:

[0006] 1. Anisotropy and Complexity of Composite Materials: Anisotropy: The mechanical properties of composite materials depend on the fiber orientation, and the fatigue behavior differs significantly in different orientations, increasing the difficulty of prediction. Multiphase Structure of Composite Materials: Composite materials consist of fibers, matrix, and interfaces, with large differences in the properties of each phase, resulting in complex fatigue damage modes.

[0007] 2. The diversity of damage mechanisms in composite materials: Fiber-reinforced composite materials exhibit multiple damage modes: during fatigue, various damages may occur, such as matrix cracking, fiber fracture, and interfacial debonding, and these damage modes influence each other. Furthermore, the accumulation and propagation of damage have nonlinear characteristics, making them difficult to describe with a single model.

[0008] 3. The influence of load and environment: Complex loads: Loads in actual working conditions are often multi-axial and variable in amplitude, increasing the complexity of fatigue prediction. Environmental influences: Environmental factors such as temperature, humidity, and ultraviolet radiation can significantly affect the fatigue performance of composite materials and need to be considered in the prediction.

[0009] 4. Limitations of Experimental Data: Fatigue testing is costly, time-consuming, and difficult to cover all operating conditions. Furthermore, fatigue test data for composite materials is highly dispersed, increasing the difficulty of model validation.

[0010] 5. Limitations of fatigue models: Traditional empirical models (such as SN curves) cannot fully reflect the fatigue behavior of composite materials. While physical models based on damage mechanics can describe damage evolution, parameter acquisition is complex and computationally expensive. Multi-scale models: Although multi-scale models can consider microstructure, computation is complex and difficult to apply to practical engineering.

[0011] 6. Influence of interfacial properties The interfacial properties between fibers and the matrix have a significant impact on fatigue behavior, but interfacial properties are difficult to accurately characterize and model.

[0012] 7. Impact of manufacturing process: Defects such as pores and cracks generated during the manufacturing process can significantly affect fatigue performance, but these defects are difficult to accurately reflect in the prediction model.

[0013] 8. Uncertainty in lifetime prediction: Uncertainty exists in material properties, load conditions, environmental factors, etc., which increases the difficulty of lifetime prediction.

[0014] Chinese patent CN119023702A discloses a fatigue life prediction system for composite materials, including a material fatigue analysis platform, a material information unit, an appearance image unit, a defect influence unit, a real-time analysis unit, an information tracking unit, and a response display unit. Essentially, it predicts fatigue through defect analysis, requiring sophisticated instruments and complex testing procedures. Chinese patent CN112800624B discloses a composite material fatigue life prediction method based on a path planning algorithm. This method involves analyzing the failure process of composite materials to obtain their fatigue crack propagation characteristics, establishing a model simulating the random particle distribution in the composite material, and using Dijkstra's algorithm to simulate the fracture process. However, this process is complex and does not reduce the workload of composite material fatigue prediction. This invention, on the other hand, features shorter time requirements and simpler operation.

[0015] Therefore, developing a rapid, accurate, and effective method for evaluating the fatigue of wind power composite materials is of great significance for fatigue research and the development of the wind power industry. Summary of the Invention

[0016] To achieve the above objectives, the present invention provides a method for predicting the fatigue fracture count of composite materials for wind turbine blades, comprising the following steps:

[0017] Step (1): Prepare multiple wind turbine blade composite material samples, and prepare two parallel test specimens for each sample.

[0018] Step (2): Take one parallel sample from each sample and perform creep performance testing under preset test conditions to obtain the creep strain of each sample;

[0019] Step (3): Take another parallel sample from each sample and perform fatigue performance testing to obtain the actual number of fatigue fractures for each sample.

[0020] Step (4): Fit the relationship between the creep strain and the number of fatigue fractures;

[0021] Step (5): For the wind turbine blade composite material to be tested, creep performance test is carried out under the same test conditions as in step (2) to obtain its creep strain, and the predicted fatigue fracture number of the wind turbine blade composite material is obtained according to the relationship obtained in step (4).

[0022] Preferably, the relationship fitted in step (4) is that the number of fatigue fractures and the reciprocal of the creep strain are linearly related.

[0023] Preferably, the wind turbine blade composite material is a glass fiber reinforced epoxy resin composite material.

[0024] Preferably, the glass fiber content in the glass fiber reinforced epoxy resin composite material is 50 wt.% - 90 wt.%.

[0025] Preferably, the wind turbine blade composite material is a wind turbine beam plate prepared by pultrusion or a composite material prepared by vacuum infusion.

[0026] Preferably, the fiber orientation of the sample is arranged along its length direction, which is consistent with the loading direction of the creep performance test and the fatigue performance test.

[0027] Preferably, the creep performance test in step (2) is performed using a dynamic mechanical analyzer.

[0028] Preferably, the preset test conditions in step (2) are: test temperature of 80-100℃, constant tensile stress of 5 MPa, and test time of 3600 seconds.

[0029] Preferably, the dimensions of each parallel sample are: 55-60 mm in length, 15 mm in width, and 5 mm in thickness.

[0030] Preferably, the order of steps (2) and (3) can be interchanged.

[0031] The method for predicting the fatigue fracture count of wind turbine blade composite materials provided by this invention has the following technical advantages:

[0032] This method can evaluate both pultruded sheets and infused samples, and can complete the testing and assessment of fatigue performance in a short time. Specifically, it establishes a linear correlation model between creep and fatigue, and calculates fatigue fracture data by testing creep strain data. Experimental results show that the theoretically calculated data is very close to the data obtained by tensile fatigue performance testing. Attached Figure Description

[0033] Figure 1 The fatigue and creep relationship diagram of the pultruded composite sample provided by the present invention;

[0034] Figure 2 The diagram shows the fatigue and creep relationship of the infused composite sample provided by this invention. Detailed Implementation

[0035] This invention provides a method for predicting the fatigue performance of wind turbine blade materials. The wind turbine blade material is a glass fiber reinforced epoxy resin composite material. This composite material can be prepared using different processes, including but not limited to wind turbine main beams prepared by pultrusion, or composite materials prepared by vacuum infusion. The glass fiber content in the composite material can be between 50 wt.% and 90 wt%. The method involves testing the creep strain of the wind turbine blade composite material at a specific temperature (e.g., 90°C) within a temperature range of 80-100°C under a stress of 5 MPa. By testing the creep of different fatigue samples, it is found that the number of fatigue fractures and the reciprocal of the creep strain exhibit a linear relationship. A linear curve between creep and the number of fatigue fractures is fitted. Based on this, the advantage of rapid creep testing can be used to predict the number of fatigue fractures without having to break the sample every time.

[0036] The specific steps include:

[0037] Sample: Cut the sample obtained by injection or pultrusion into strips 55-60mm long, 15mm wide and 5mm thick, with the fibers arranged along the length of the sample.

[0038] Dynamic Mechanical Analyzer (DMA)

[0039] raw material:

[0040] Glass fiber and its fabrics TM2 468GS 2400 (Chongqing International Composite Materials Co., Ltd.), epoxy resin and curing agent (Dow Chemical Co., Ltd.).

[0041] Test method:

[0042] 1. Tensile strength, flexural properties, and impact resistance:

[0043] According to GB / T 2567-2008

[0044] 2. Glass transition temperature (Tg):

[0045] The glass transition temperature was obtained by testing the loss factor versus temperature curve using a dynamic mechanical analyzer (DMA), and the creep-temperature curve was calculated.

[0046] According to GBT 35465 fatigue testing method for polymer-based composite materials, pultruded samples with different fatigue properties obtained by pultrusion and injection were screened under 550N conditions. Glass fiber reinforced epoxy resin composite materials (wind power injection plates) were also cut into strips with a length of 55-60mm, a width of 15mm, and a thickness of 5mm. Tensile creep performance tests were conducted under stress conditions of 100℃ and 5MPa, with the load applied continuously for 3600 seconds, and creep strain-time data were obtained.

[0047] The tensile creep properties of pultruded composite specimens were tested using an MTS Landmark 370 testing machine, and cyclic tensile fatigue tests were conducted under a constant stress of 550 N.

[0048] The glass fiber reinforced epoxy resin composite material (wind power pultruded sheet) obtained by pultrusion was cut into strips with a length of 55-60 mm, a width of 15 mm, and a thickness of 5 mm. Tensile creep performance was tested under stress conditions of 100°C and 5 MPa. The load was applied continuously for 3600 seconds to obtain creep strain-time data.

[0049] Table 1: Mechanical properties and fatigue / creep data of pultruded composite materials

[0050]

[0051] Data from pultruded composite materials show that five samples (samples 1-5) with similar static mechanical properties exhibit significant differences in fatigue performance, indicating a weak correlation between static mechanical properties and fatigue. By performing linear fitting on the creep data of these five samples with large fatigue differences, the fatigue of any sample with varying creep data can be calculated. The results are close to the actual fatigue data (based on a comparison of the measured and calculated values ​​for sample 6). This method can be used for rapid testing and calculation of fatigue data, greatly saving fatigue testing time.

[0052] Table 2: Mechanical properties and fatigue and creep data of the cast-in-place composite material

[0053]

[0054] Data from the infused composite materials show that five samples (samples 1-5) with similar static mechanical properties exhibit significant differences in fatigue performance. By performing linear fitting on the creep data of the five different fatigue samples, it can be calculated that the fatigue of any other sample with obtained creep data is close to the actual fatigue data (through a comparison of the measured and calculated values ​​of sample 6). This method can be used to quickly test and calculate fatigue data.

Claims

1. A method for predicting the number of fatigue fractures in composite materials for wind turbine blades, characterized in that, Includes the following steps: Step (1): Prepare multiple wind turbine blade composite material samples, and prepare two parallel test specimens for each sample. Step (2): Take one parallel sample from each sample and perform creep performance testing under preset test conditions to obtain the creep strain of each sample; Step (3): Take another parallel sample from each sample and perform fatigue performance testing to obtain the actual number of fatigue fractures for each sample. Step (4): Fit the relationship between the creep strain and the number of fatigue fractures; Step (5): For the wind turbine blade composite material to be tested, creep performance test is carried out under the same test conditions as in step (2) to obtain its creep strain, and the predicted fatigue fracture number of the wind turbine blade composite material is obtained according to the relationship obtained in step (4).

2. The method for predicting the number of fatigue fractures in wind turbine blade composite materials according to claim 1, characterized in that, The fitted relationship in step (4) is that the number of fatigue fractures and the reciprocal of creep strain are linearly related.

3. The method for predicting the number of fatigue fractures in wind turbine blade composite materials according to claim 1, characterized in that, The wind turbine blade composite material is a glass fiber reinforced epoxy resin composite material.

4. The method for predicting the number of fatigue fractures in wind turbine blade composite materials according to claim 3, characterized in that, The glass fiber content in the glass fiber reinforced epoxy resin composite material is 50 wt.% - 90 wt.%.

5. The method for predicting the number of fatigue fractures in wind turbine blade composite materials according to claim 3, characterized in that, The wind turbine blade composite material is either a wind turbine beam plate prepared by pultrusion or a composite material prepared by vacuum infusion.

6. The method for predicting the number of fatigue fractures in wind turbine blade composite materials according to claim 1, characterized in that, The fiber orientation of the sample is arranged along its length direction, which is consistent with the loading direction of the creep performance test and the fatigue performance test.

7. The method for predicting the number of fatigue fractures in wind turbine blade composite materials according to claim 1, characterized in that, The creep performance test in step (2) is performed using a dynamic mechanical analyzer.

8. The method for predicting the number of fatigue fractures in wind turbine blade composite materials according to claim 1, characterized in that, The preset test conditions in step (2) are: test temperature of 80-100℃, constant tensile stress of 5 MPa, and test time of 3600 seconds.

9. The method for predicting the number of fatigue fractures in wind turbine blade composite materials according to any one of claims 1-8, characterized in that, The dimensions of each parallel sample are: 55-60 mm in length, 15 mm in width, and 5 mm in thickness.

10. The method for predicting the number of fatigue fractures in wind turbine blade composite materials according to claim 1, characterized in that, The order of steps (2) and (3) can be reversed.

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