Method for predicting initial failure position of lap joint sandwich of trailing edge beam and core material of wind power blade

Abstract

The invention discloses a wind turbine blade trailing edge beam and core material lap joint sandwich initial failure position prediction method, and relates to the technical field of wind turbine blade structure damage failure prediction methods. Damage of a sandwich structure panel and a core material in a shear failure mode is characterized as a lap joint sandwich structure formed by combining a laminated plate area, a conventional sandwich area and an inclined plane lap joint sandwich structure area; respectively calculating the cross section bending rigidity of the conventional sandwich structure, the neutral layer position of the inclined plane lap joint sandwich structure and the cross section bending rigidity distribution of the inclined plane lap joint sandwich structure, and calculating the cross section bending rigidity distribution of the inclined plane lap joint sandwich structure on the basis of the neutral layer distribution function inflection point in the length direction of the inclined plane lap joint sandwich structure and the descending slope of the cross section bending rigidity distribution function; the initial failure position of the lap joint sandwich structure of the blade trailing edge beam and the trailing edge core material is predicted. The method provides an important theoretical basis for in-service wind power blade design, health prediction and repair decision making, and has great method innovation and engineering application values.

Description

Technical Field

[0001] The invention belongs to the technical field of wind turbine blade structure damage failure prediction, and in particular relates to a method for predicting the initial failure position of a lap sandwich between a trailing edge beam and a core material of a wind turbine blade. Background Art

[0002] As the key wind-catching structure of wind turbines, wind turbine blades have a decisive influence on the stable and safe operation of wind turbines. Predicting the initial failure position of complex damage in wind turbine blades is an important task to ensure the safe service life of blades. Due to the influence of environmental effects, wind conditions, and slender beam structures, blades are subject to the coupling effects of fatigue loads and extreme loads during their service life. With the development of large-scale wind turbine blades, new failure modes are increasing. A large number of shell bulges in the trailing edge area of ​​the blades were found on blades that had been in operation for about one year in a certain wind farm. Figure 8 ), accompanied by cracking and whitening of the blade inner skin shell ( Fig. 9 ), this damage involves many structural areas such as the trailing edge beam and trailing edge core material of the blade, and the damage occurs frequently, with a tendency to form large-scale damage, seriously threatening the safe operation of the blade.

[0003] In order to ensure the safe operation of wind turbine blades, the blades with internal and external damage on the trailing edge were cut along the cross section. After the section was cut open, it was found that the damage occurred in the overlapping sandwich structure area between the trailing edge beam and the trailing edge core material ( Fig.10 ). Since the blade design and development method is based on the safety factor method with no damage extension, and the safety failure verification of the sandwich structure is lacking in the design, certification and full-scale blade type tests, the failure analysis and failure prediction of the overlapping sandwich structure area of ​​the trailing edge beam and the trailing edge core material are basically blank in the existing blade damage research.

[0004] Since the damage of the trailing edge beam and the trailing edge core material in the overlapping sandwich area occurs on the inside of the sandwich structure, once it is characterized by visible external bulges or internal cracks on the blade, the damage to the trailing edge of the blade is already very serious, belonging to internal and external penetration. Therefore, it is very necessary to explore the initial failure position of this new damage mode of wind turbine blades, add the prediction of the initial failure position of the overlapping sandwich structure area of ​​the trailing edge beam and the trailing edge core material in the blade design stage, and strengthen the initial failure position in the design and blade manufacturing, so as to ensure that this complex damage no longer endangers the safe operation of the blade, and provide a crucial theoretical root and engineering application basis for blade design, healthy service and safe operation and maintenance. Summary of the invention

[0005] The technical problem to be solved by the present invention is to provide a method for predicting the initial failure position of the overlap sandwich between the trailing edge beam and the core material of a wind turbine blade in view of the above-mentioned existing deficiencies.

[0006] In order to achieve the above technical objectives, the technical solution adopted by the present invention is:

[0007] A method for predicting the initial failure position of a lap sandwich between a trailing edge beam and a core material of a wind turbine blade comprises the following steps:

[0008] Step 1: Analyze the cross-sectional structure of the wind turbine blade and determine the coordinate system of the overlap sandwich structure of the trailing edge beam and the trailing edge core material of the wind turbine blade; define the x direction and y direction along the length direction and thickness direction of the overlap sandwich structure as respectively, and the z direction along the width direction.

[0009] Step 2: Divide the overlapped sandwich structure into laminated plates, conventional sandwich structures and inclined overlapped sandwich structures based on the structural distribution form in the x direction of the sandwich structure, wherein the plying form of the laminated plates is an upper surface panel, a rear edge beam, and a lower surface panel; the plying form of the conventional sandwich structure area is an upper surface panel, a core material, and a lower surface panel structure; the plying form of the inclined overlapped sandwich structure area is an upper surface panel, a mitered section with a changed core material thickness, a mitered section with a changed rear edge beam thickness, and a lower surface panel.

[0010] Step 3: The algorithm for calculating the cross-sectional bending stiffness of a conventional sandwich structure is: in, is the bending stiffness of the upper and lower surface panels of the conventional sandwich structure about their own neutral axis, is the bending stiffness of the upper and lower surface panels of the conventional sandwich structure to the overall neutral layer, is the bending stiffness of the core material of the conventional sandwich structure, E f is the elastic modulus in the x direction of the upper and lower surface panels, E c is the elastic modulus of the core material, b, t, c are the width of the conventional sandwich structure, the thickness of the upper and lower surface panels, and the thickness of the core material, d is the distance between the center lines of the opposite surfaces and d = t + c,

[0011] Step 4: The algorithm for calculating the neutral layer position of the inclined lap sandwich structure is: Where n represents the total number of layers of the inclined lap sandwich structure, that is, n = 4; i represents a certain layer; E i is the elastic modulus in the x direction corresponding to the i-th layer, h is the total thickness of the inclined lap sandwich structure, and h is specified 0 =0,h n =h;

[0012] Step 5: Based on the cross-sectional bending stiffness calculation method of conventional sandwich structures, the algorithm for calculating the cross-sectional bending stiffness of the inclined lap sandwich structure is: Where m represents the material number, j = 1 represents the bending stiffness of the material with respect to its own neutral layer, and j = 2 represents the bending stiffness of the material with respect to the overall neutral layer;

[0013] Step 6, substitute the geometry, material properties and ply design of the overlap sandwich structure of the trailing edge beam and the trailing edge core material of the wind turbine blade into steps 3-5, calculate the neutral layer position distribution and cross-sectional bending stiffness distribution of the overlap sandwich structure of the trailing edge beam and the trailing edge core material of the wind turbine blade, when the neutral plane offset reaches the maximum value, the position where the bending stiffness slope is close to zero is the predicted initial failure position of the overlap sandwich;

[0014] Step 7: Based on the actual case of wind turbine blade engineering, the predicted initial failure position of the lap joint core is compared through experimental verification and numerical simulation to verify the correctness of the proposed prediction method.

[0015] To optimize the above technical solutions, the specific measures taken also include:

[0016] The upper surface panel and the lower surface panel are both made of 1-2 layers of resin-based ±45° fiber cloth, the core material is PVC foam, and the trailing edge beam is made of dozens of layers of resin-based 0° unidirectional fiber cloth.

[0017] In step 4, the specific algorithm for calculating the neutral layer position of the inclined lap sandwich structure is:

[0018] (1) Take any micro-segment dx of the analysis structure that tends to 0 along the x direction of the sandwich structure. At this time, the inclined surface segment can be approximately parallel to the surface panel. At this time, the ply design of the micro-segment analysis structure is the upper surface panel, core material, trailing edge beam, and lower surface panel.

[0019] (2) Assume that the neutral plane is located at y = y 0 Based on the pure bending assumption, the micro-segment dx of the above analysis structure is only subjected to the bending moment M z , then the bending moment in the y direction is 0, and the equilibrium equation is Where σ is the normal stress and z is the z-axis coordinate value;

[0020] (3) Based on the assumption of cross-sectional strain continuity, the micro-segment dx of the above analysis structure satisfies Hooke's law within the linear elastic range, and the physical property equation is: Where ε is the strain and E is the elastic modulus.

[0021] (4) Combining the above-mentioned ply form, geometric dimensions, equilibrium equation, and physical property equation of the analytical structure micro-segment dx, the neutral layer position of the analytical structure micro-segment dx is calculated as follows:

[0022] The specific algorithm for calculating the cross-sectional bending stiffness of the inclined lap sandwich structure is:

[0023] D'=E 11 +E 12 +E 21 +E 22 +E 31 +E 32 +E41 +E 42

[0024] D' can also be written as D'=D 1 +D 2 +D 3 +D 4 ,

[0025] in:

[0026]

[0027] The present invention provides a new idea, which makes up for the lack of theoretical calculation basis for predicting the initial failure position of new damage modes of wind turbine blades. It has the following advantages:

[0028] 1. Since the current blade design is based on the safety factor method with no damage extension, and there is a lack of targeted structural analysis, test verification and safety failure prediction in the overlapping sandwich structure area between the trailing edge beam and the trailing edge core material, large blades are frequently damaged along the trailing edge area under complex working conditions. Since the inclined overlapping sandwich structure area between the overlapping sandwich structure between the trailing edge beam and the trailing edge core material involves the inclined overlapping section of dozens of layers of 0° unidirectional fabric with large thickness and PVC core foam with variable thickness, due to the huge stiffness mutation and irregular shape of the sandwich structure, the failure prediction method of this inclined overlapping sandwich structure lacks a theoretical algorithm. This method proposes a high-precision prediction method for the starting failure position of the overlapping sandwich structure area between the trailing edge beam and the trailing edge core material with high precision and accuracy. The method can be transferred to the blade design stage to fill the design gap, and has a very high theoretical method innovation.

[0029] 2. In order to improve the correctness and engineering application value of this method, an actual case of an in-service wind turbine blade project was selected as the research basis. Through sample design, experimental research and numerical simulation research on the case, a comprehensive comparison was made with the prediction results of an algorithm based on the neutral layer position and cross-sectional bending stiffness distribution of the inclined lap sandwich structure to predict the initial failure position, verifying the high-fidelity prediction effect of this method. The proposed method can realize feedback design, provide a reinforcement plan for the trailing edge area from the design source, and provide strong theoretical support for the trailing edge operation damage prediction and repair technology of in-service blades, ensuring the precision and accuracy of the proposed method, and has great engineering application value. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 It is a flow chart of a calculation method for predicting the initial failure position of a lap sandwich structure;

[0031] Figure 2 It is a schematic diagram of the cross-sectional structure of a wind turbine blade;

[0032] Figure 3 It is the coordinate system and structural area division diagram of the overlapping sandwich structure of the trailing edge beam and the trailing edge core material;

[0033] Figure 4 This is a structural diagram of a conventional sandwich structure;

[0034] Figure 5 It is the structural form and calculation model diagram of the inclined lap sandwich structure;

[0035] Figure 6 It is the analysis structure and calculation result diagram of the actual case of wind turbine blade engineering;

[0036] Figure 7 It is a diagram of the experimental study and numerical simulation results of the analytical structure of an actual case of a wind turbine blade project;

[0037] Figure 8 It is a diagram of the shell bulge in the outer trailing edge area of ​​the blade in the prior art;

[0038] Fig. 9 It is a whitening image of cracks in the trailing edge area of ​​the blade in the prior art;

[0039] Fig.10 It is a shear damage pattern diagram of the overlapping sandwich structure area of ​​the trailing edge beam and the trailing edge core material in the prior art. DETAILED DESCRIPTION

[0040] In order to make the purpose, technical solutions and advantages of the present application clearer, the present application is described and illustrated below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and are not intended to limit the present application. Based on the embodiments provided in the present application, all other embodiments obtained by ordinary technicians in the field without making creative work are within the scope of protection of the present application.

[0041] Obviously, the drawings described below are only some examples or embodiments of the present application. For ordinary technicians in this field, the present application can also be applied to other similar scenarios based on these drawings without creative work. In addition, it can also be understood that although the efforts made in this development process may be complicated and lengthy, for ordinary technicians in this field related to the content disclosed in this application, some changes in design, manufacturing or production based on the technical content disclosed in this application are just conventional technical means, and should not be understood as insufficient content disclosed in this application.

[0042] Reference to "embodiments" in this application means that a particular feature, structure, or characteristic described in conjunction with the embodiments may be included in at least one embodiment of the present application. The appearance of the phrase in various locations in the specification does not necessarily refer to the same embodiment, nor is it an independent or alternative embodiment that is mutually exclusive with other embodiments. It is explicitly and implicitly understood by those of ordinary skill in the art that the embodiments described in this application may be combined with other embodiments without conflict.

[0043] Unless otherwise defined, the technical terms or scientific terms involved in this application should be understood by people with ordinary skills in the technical field to which this application belongs. The words "one", "a", "a", "the" and the like involved in this application do not indicate a quantitative limitation, and may represent the singular or plural. The terms "include", "comprise", "have" and any of their variations involved in this application are intended to cover non-exclusive inclusions; for example, a process, method, system, product or device that includes a series of steps or units (units) is not limited to the listed steps or units, but may also include steps or units that are not listed, or may also include other steps or units inherent to these processes, methods, products or devices. The words "connect", "connected", "coupled" and the like involved in this application are not limited to physical or mechanical connections, but may include electrical connections, whether direct or indirect. The "multiple" / "several" involved in this application refers to two or more. "And / or" describes the association relationship of associated objects, indicating that there can be three relationships, for example, "A and / or B" can mean: A exists alone, A and B exist at the same time, and B exists alone. The character " / " generally indicates that the objects before and after are in an "or" relationship. The terms "first", "second", "third", etc. involved in this application are only used to distinguish similar objects and do not represent a specific ordering of the objects.

[0044] The present invention proposes a calculation method for predicting the initial failure position of the overlap sandwich between the trailing edge beam and the core material of a wind turbine blade. The specific process is as follows: Figure 1 As shown, it aims to solve the defects and gaps in the technical field of failure prediction methods for new forms of damage to wind turbine blades today, and provides a highly accurate solution for blade design, blade operation health prediction and blade damage repair.

[0045] Firstly, the overlap sandwich structure of the trailing edge beam and the trailing edge core material based on the blade profile structure is analyzed, such as Figure 2 As shown, the structural area to be analyzed is the overlapping transition area between the trailing edge beam and the trailing edge core material.

[0046] Then, the coordinate system of the overlapped sandwich structure of the trailing edge beam and the trailing edge core material is specified, such as Figure 3As shown, the length direction (corresponding to the chord length direction of the blade section) and the thickness direction of the sandwich structure are x and y, and the width direction (corresponding to the length direction of the blade) is z. Then, along the x direction of the sandwich structure, it is divided into the laminate area, the inclined overlap sandwich structure area and the conventional sandwich structure area based on the structural distribution form. At this time, the overlap sandwich structure is taken as the research object. This sandwich structure specifically includes three structures: upper and lower surface panels, trailing edge core material and trailing edge beam. Among them, the upper and lower surface panels are 1-2 layers of resin-based ±45° fiber cloth, the core material is PVC foam, and the trailing edge beam is dozens of layers of resin-based 0° unidirectional fiber cloth. At this time, the plying form of the laminate area along the x direction of the sandwich structure is the upper surface panel, the trailing edge beam, and the lower surface panel; the plying form of the conventional sandwich structure area is the upper surface panel, the core material, and the lower surface panel structure; the plying form of the inclined overlap sandwich structure area is the upper surface panel, the mitered section with varying core material thickness, the mitered section with varying trailing edge beam thickness, and the lower surface panel.

[0047] Secondly, in order to carry out research on the calculation method for predicting the initial failure position of the lap sandwich between the trailing edge beam and the core material of the wind turbine blade, and to achieve the purpose of feedback design and guiding engineering implementation, this calculation method is based on two basic assumptions, namely the pure bending assumption and the cross-sectional strain continuity assumption, which can realize the force and stiffness calculation of complex sandwich structure problems.

[0048] like Figure 4 As shown in the figure, the conventional sandwich structure area of ​​the lap sandwich structure is taken as the research object, and E is specified. f is the elastic modulus in the x direction of the resin-based ±45° fiber cloth of the upper and lower surface panels, and t is the thickness of the surface panel; E c is the elastic modulus of the core material, c is the thickness of the core material; b is the width of the sandwich structure area, d is the distance between the center lines of the opposite surfaces and d = t + c. At this time, the cross-sectional bending stiffness of the conventional sandwich structure is the bending stiffness of the upper and lower surface panels about their own neutral axis. Bending stiffness of the upper and lower surface panels to the overall neutral layer and the bending stiffness of the core layer The cross-sectional bending stiffness of the conventional sandwich structure is calculated as

[0049] like Figure 5 As shown in the figure, the area of ​​the inclined overlap sandwich structure is taken as the research object. Due to the huge stiffness mutation and the irregular shape of the sandwich structure, the failure prediction method of this inclined overlap sandwich structure lacks a theoretical algorithm. Therefore, the neutral layer position and cross-sectional bending stiffness distribution of the inclined overlap sandwich structure area are calculated by discrete and step-by-step expansion. The specific implementation steps of this method are:

[0050] (1) Take any micro-segment dx of the analytical structure that tends to 0 along the x direction of the inclined lap sandwich structure. At this time, the inclined segment can be approximately parallel to the panel layer. At this time, the top-down ply design of the micro-segment analytical structure is 1-2 layers of resin-based ±45° fiber cloth upper surface panel, core material PVC foam, dozens of layers of resin-based 0° unidirectional fiber cloth rear edge beam, and 1-2 layers of resin-based ±45° fiber cloth lower surface panel. And it is stipulated that the thickness vertices of each ply layer along the y direction are h 4 、h 3 、h 2 、h 1 , the elastic moduli along the x direction are E 4 、E 3 、E 2 、E 1 ).

[0051] (2) Assume that the neutral layer is located at y = y 0 Based on the pure bending assumption, the micro-segment dx of the above analysis structure is only subjected to the bending moment M z , then the bending moment in the y direction is 0, and the equilibrium equation is The further balanced equation is:

[0052]

[0053] Right now:

[0054]

[0055] Where h is the thickness of the structure and dA is the area element.

[0056] Apparently is a constant, then the equation can be simplified to:

[0057]

[0058] (3) Based on the assumption of cross-sectional strain continuity, such as Figure 5 As shown, the strain is continuous with its distance to the neutral plane within the linear elastic range. The micro-segment dx of the above analysis structure satisfies Hooke's law within the linear elastic range. The physical property equation is: You can get:

[0059]

[0060] where y * is the y-coordinate of the neutral axis, and ρ is the radius of curvature of the neutral layer.

[0061] Because the structure is composed of multiple materials, the elastic modulus varies along the y-axis and can be written as E(y), that is:

[0062]

[0063] And because:

[0064]

[0065] In this way, we can get a solution with only unknown number y 0 Solving the equation, we can get the position of the neutral layer as follows:

[0066]

[0067] For an n-layer structure, it is stipulated that:

[0068]

[0069] The neutral layer can be obtained as:

[0070]

[0071] Among them, n represents the total number of layers, that is, n=4; i represents a certain layer; and h is the total thickness.

[0072] (4) Based on the cross-sectional bending stiffness calculation method of conventional sandwich structures, the cross-sectional bending stiffness D' of the micro-segment dx of the above analysis structure is calculated as:

[0073] D'=E 11 +E 12 +E 21 +E 22 +E 31 +E 32 +E 41 +E 42

[0074] The subscript E mj , m represents the material number, and j is represented by:

[0075]

[0076] D' can also be written as D'=D 1 +D 2 +D 3 +D 4 ,

[0077] in:

[0078]

[0079] (5) Based on the calculation results of the neutral layer position and cross-sectional bending stiffness of the above-mentioned structural micro-segment dx, the neutral layer position distribution function and cross-sectional bending stiffness distribution function of the inclined lap sandwich structure are obtained by integrating along the length segment of the inclined lap sandwich structure.

[0080] like Figure 6 As shown in the figure, the geometry, material properties and ply design of the structural area of ​​the trailing edge beam and the trailing edge core material of the actual case of the wind turbine blade engineering are determined based on the ply thickness of the upper and lower surface panels of the blade outer skin and inner skin, the trailing edge beam, the trailing edge core material and the overlapping sandwich structure of the trailing edge beam and the trailing edge core material, the elastic modulus in the x direction of the material, the miter ratio, and the length, thickness and width of the analysis structure:

[0081] E 1 =E 4 ,Pick b=80mm

[0082] but,

[0083] (x is the coordinate of the specimen in the length direction, and x=0 at the center of the specimen)

[0084] At this time, the neutral layer position and cross-sectional bending stiffness distribution of the sandwich structure of the lap joint between the trailing edge beam and the trailing edge core are calculated as follows: Figure 6 Based on the inflection point of the neutral layer distribution function along the length direction of the inclined overlap sandwich structure and the descending slope of the cross-sectional bending stiffness distribution function, it is confirmed that the initial failure position of the overlap sandwich structure of the trailing edge beam and the trailing edge core material is x=109mm, and the initial failure position of the overlap sandwich structure of the trailing edge beam and the trailing edge core material of the blade is predicted.

[0085] like Figure 7 As shown in the figure, in order to verify the correctness of the prediction method, the actual case of the wind turbine blade project mentioned above was taken as the research object, and the lap sandwich structure was designed based on the failure mode. The three-point bending static test and the finite element numerical simulation method were used respectively. The initial failure position of the lap sandwich structure of the trailing edge beam and the trailing edge core material was determined to be x=109mm through the test and numerical simulation. Compared with the initial failure position determined by the prediction method, the correctness of the proposed prediction method was verified.

[0086] The beneficial effects achieved by the present invention are as follows: First, the present invention provides a calculation method combining theoretical calculation with engineering verification for the starting failure position of a new type of damage form required for wind turbine blade design, blade operation health prediction, and blade damage repair technology. Second, the present invention fills the gap in the safety verification of the lap sandwich structure of the trailing edge beam and the trailing edge sandwich that is not considered in blade design, and realizes the application of failure prediction of actual damage in wind turbine blade engineering to feed back design defects, providing a theoretical implementation basis for the design, with very high theoretical innovation, and greatly improving the design accuracy and safety. Third, the present invention adopts theoretical calculation, experimental design and experimental implementation of actual engineering cases, and numerical analysis of actual engineering cases, and verifies each other, thereby achieving high fidelity and high accuracy of the calculation method of the present invention, and the method proposed thereby is more in line with actual engineering applications.

[0087] It can be understood that the above specific description of the present invention is only used to illustrate the present invention and is not limited to the technical solution described in the implementation of the calculation method of the present invention. Ordinary technicians in the field should understand that the present invention can still be modified or replaced by equivalents to achieve the same technical effect; as long as the requirements of the calculation method are met, they are all within the protection scope of the present invention.

Claims

1. A method for predicting the initial failure position of the overlap sandwich between the trailing edge beam and the core material of a wind turbine blade, characterized by: The following steps are involved: Step 1: Analyze the cross-sectional structure of the wind turbine blade and determine the coordinate system of the overlap sandwich structure of the trailing edge beam and the trailing edge core material of the wind turbine blade; define the x direction and y direction along the length direction and thickness direction of the overlap sandwich structure as respectively, and the z direction along the width direction. Step 2: Divide the overlapped sandwich structure into laminated plates, conventional sandwich structures and inclined overlapped sandwich structures based on the structural distribution form in the x direction of the sandwich structure, wherein the plying form of the laminated plates is an upper surface panel, a rear edge beam, and a lower surface panel; the plying form of the conventional sandwich structure area is an upper surface panel, a core material, and a lower surface panel structure; the plying form of the inclined overlapped sandwich structure area is an upper surface panel, a mitered section with a changed core material thickness, a mitered section with a changed rear edge beam thickness, and a lower surface panel. Step 3: The algorithm for calculating the cross-sectional bending stiffness of a conventional sandwich structure is: in, is the bending stiffness of the upper and lower surface panels of the conventional sandwich structure about their own neutral axis, is the bending stiffness of the upper and lower surface panels of the conventional sandwich structure to the overall neutral layer, is the bending stiffness of the core material of the conventional sandwich structure, E f is the elastic modulus in the x direction of the upper and lower surface panels, E c is the elastic modulus of the core material, b, t, c are the width of the conventional sandwich structure, the thickness of the upper and lower surface panels, and the thickness of the core material, d is the distance between the center lines of the opposite surfaces and d = t + c, Step 4: The algorithm for calculating the neutral layer position of the inclined lap sandwich structure is: Where n represents the total number of layers of the inclined lap sandwich structure, that is, n = 4; i represents a certain layer; E i is the elastic modulus in the x direction corresponding to the i-th layer, h is the total thickness of the inclined lap sandwich structure, and it is specified that h0=0, h n =h; Step 5: Based on the cross-sectional bending stiffness calculation method of conventional sandwich structures, the algorithm for calculating the cross-sectional bending stiffness of the inclined lap sandwich structure is: Where m represents the material number, j = 1 represents the bending stiffness of the material with respect to its own neutral layer, and j = 2 represents the bending stiffness of the material with respect to the overall neutral layer; Step 6, substitute the geometry, material properties and ply design of the overlap sandwich structure of the trailing edge beam and the trailing edge core material of the wind turbine blade into steps 3-5, calculate the neutral layer position distribution and cross-sectional bending stiffness distribution of the overlap sandwich structure of the trailing edge beam and the trailing edge core material of the wind turbine blade, when the neutral plane offset reaches the maximum value, the position where the bending stiffness slope is close to zero is the predicted initial failure position of the overlap sandwich; Step 7: Based on the actual case of wind turbine blade engineering, the predicted initial failure position of the lap joint core is compared through experimental verification and numerical simulation to verify the correctness of the proposed prediction method.

2. The method for predicting the initial failure position of the overlap sandwich between the trailing edge beam and the core material of a wind turbine blade according to claim 1 is characterized by: The upper surface panel and the lower surface panel are both made of 1-2 layers of resin-based ±45° fiber cloth, the core material is PVC foam, and the rear edge beam is made of dozens of layers of resin-based 0° unidirectional fiber cloth.

3. The method for predicting the initial failure position of the overlap sandwich between the trailing edge beam and the core material of a wind turbine blade according to claim 1 is characterized by: In step 4, the specific algorithm for calculating the neutral layer position of the inclined lap sandwich structure is: (1) Take any micro-segment dx of the analysis structure that tends to 0 along the x direction of the sandwich structure. At this time, the inclined surface segment can be approximately parallel to the surface panel. At this time, the ply design of the micro-segment analysis structure is the upper surface panel, core material, trailing edge beam, and lower surface panel. (2) Assuming that the neutral plane is located at y = y0, based on the pure bending assumption, the micro-segment dx of the above analysis structure is only subjected to the bending moment M z , then the bending moment in the y direction is 0, and the equilibrium equation is Where σ is the normal stress and z is the z-axis coordinate value; (3) Based on the assumption of cross-sectional strain continuity, the micro-segment dx of the above analysis structure satisfies Hooke's law within the linear elastic range, and the physical property equation is listed as follows: Where ε is the strain and E is the elastic modulus. (4) Combining the above-mentioned ply form, geometric dimensions, equilibrium equation, and physical property equation of the analytical structure micro-segment dx, the neutral layer position of the analytical structure micro-segment dx is calculated as follows:

4. The method for predicting the initial failure position of the overlap sandwich between the trailing edge beam and the core material of a wind turbine blade according to claim 3 is characterized by: The specific algorithm for calculating the cross-sectional bending stiffness of the inclined lap sandwich structure is: D'=E 11 +E 12 +E 21 +E 22 +E 31 +E 32 +E 41 +E 42 D' can also be written as D'=D1+D2+D3+D4, in:

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