Prediction method for the initial failure position of the overlap sandwich between the trailing edge beam and the core material of a wind turbine blade

Abstract

The present invention discloses a method for predicting the initial failure position of the overlap sandwich structure between the trailing edge beam and the core material of a wind turbine blade, and relates to the technical field of wind turbine blade structure damage failure prediction methods. The present invention characterizes the damage of the sandwich structure panel and the core material shear failure mode as an overlap sandwich structure composed of a laminate area, a conventional sandwich area and an inclined overlap sandwich structure area, and calculates the cross-sectional bending stiffness of the conventional sandwich structure, the neutral layer position of the inclined overlap sandwich structure and the cross-sectional bending stiffness distribution of the inclined overlap sandwich structure respectively. 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, the initial failure position of the overlap sandwich structure between the trailing edge beam and the trailing edge core material of the blade is predicted. The present invention provides an important theoretical basis for the design, health prediction and repair decision-making of in-service wind turbine blades, and has great methodological innovation and engineering application value.

Description

Technical Field

[0001] The present 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 turbine generators, 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 of blades throughout their entire life cycle. Due to the influence of environmental effects, wind conditions, and slender beam structures, blades are subject to the coupling of fatigue loads and extreme loads during their service life. With the development of larger wind turbine blades, new failure modes are becoming more and more common. On blades that have been in operation for about one year at a certain wind farm, a large number of shell bulges in the trailing edge area of ​​the blades were found ( Figure 8 ), accompanied by cracking and whitening damage to the inner skin of the blade ( Figure 9 ), this damage involves many structural areas such as the blade trailing edge beam, trailing edge core material, and the damage occurs frequently, and there is a trend of forming large-scale damage, which seriously threatens the safety of blade operation.

[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 cross section was cut, it was found that the damage occurred in the overlapping sandwich structure area between the trailing edge beam and the trailing edge core material ( Figure 10 Because blade design and development methods are based on a safety factor approach with no damage expansion, and because design, certification, and full-scale blade type testing lack safety failure verification of the sandwich structure, existing blade damage research lacks the ability to analyze and predict failures in the sandwich structure where the trailing edge beam and the trailing edge core overlap.

[0004] Since the damage to 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 manifests as a visible bulge on the outside of the blade or an internal crack, the damage to the trailing edge of the blade is already very serious and is considered internal and external penetrating. Therefore, it is very necessary to explore the initial failure location of this new damage mode for wind turbine blades. In the blade design stage, the prediction of the initial failure location in the overlapping sandwich structure area of ​​the trailing edge beam and the trailing edge core material is added. In the design and blade manufacturing, the initial failure location is reinforced and implemented. This can ensure that this complex damage no longer endangers the safe operation of the blade, providing a crucial theoretical foundation 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 address the above-mentioned existing deficiencies and 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.

[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 core 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 overlapped sandwich structure between the trailing edge beam and the trailing edge core of the wind turbine blade; define the x-direction and y-direction along the length and thickness directions of the overlapped sandwich structure as the x-direction and y-direction along the width direction as the z-direction.

[0009] Step 2: The overlapped sandwich structure is divided 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. The laminated plates are laid out in the form of upper surface panels, trailing edge beams, and lower surface panels. The conventional sandwich structure area is laid out in the form of upper surface panels, core material, and lower surface panels. The inclined overlapped sandwich structure area is laid out in the form of upper surface panels, mitered sections with varying core material thickness, mitered sections with varying trailing edge beam thickness, and lower surface panels.

[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 relative 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, and 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, respectively; 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, i.e. 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 stipulated that h0=0, h n =h;

[0012] Step 5: Based on the calculation method of cross-sectional bending stiffness 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 layup design of the overlapped sandwich structure of the trailing edge beam and the trailing edge core material of the wind turbine blade into steps 3-5 to calculate the neutral layer position distribution and cross-sectional bending stiffness distribution of the overlapped sandwich structure of the wind turbine blade trailing edge beam and the trailing edge core material. 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 overlapped sandwich structure.

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

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

[0016] The upper and lower surface panels 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. In this case, the inclined surface segment can be approximately parallel to the surface panel. 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) 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;

[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 +E 41+E 42

[0024] D' can also be written as D'=D1+D2+D3+D4,

[0025] in:

[0026]

[0027] This invention provides a new approach that addresses the current lack of theoretical calculation basis for predicting the initial failure location of new damage modes in wind turbine blades. It has the following advantages:

[0028] 1. Since current blade design is based on the safety factor method with no damage expansion, and there is a lack of targeted structural analysis, experimental verification, and safety failure prediction for the overlapping sandwich structure area between the trailing edge beam and the trailing edge core material, large blades frequently suffer damage along the trailing edge area under complex working conditions. Since the bevel overlap sandwich structure area of ​​the overlapping sandwich structure between the trailing edge beam and the trailing edge core material involves bevel overlap sections of dozens of thick layers of 0° unidirectional fabric and variable thickness PVC core foam, due to the huge stiffness mutation and irregular shape of the sandwich structure, there is a lack of theoretical algorithms for failure prediction methods of this bevel overlap sandwich structure. This method proposes a high-precision prediction method for the initial failure position of the overlapping sandwich structure area between the trailing edge beam and the trailing edge core material with high precision and accuracy. This method can be transferred to the blade design stage to fill the design gap and has a very high theoretical method innovation.

[0029] 2. To improve the accuracy and engineering application value of this method, an actual case study of an in-service wind turbine blade was selected as the research basis. Through prototype design, experimental research, and numerical simulation, the predicted results were comprehensively compared with those of a proposed algorithm that predicts the initial failure location based on the neutral layer position and cross-sectional bending stiffness distribution of the bevel-lap sandwich structure. This verified the high-fidelity prediction effect of this method. The proposed method can achieve feedback design, providing reinforcement solutions for the trailing edge area from the design source. It also provides strong theoretical support for the prediction and repair technology of the trailing edge of in-service blades, ensuring the precision and accuracy of the proposed method and having 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 location of a lap sandwich structure;

[0031] Figure 2 This 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 This is a diagram showing the experimental research and numerical simulation results of the analytical structure of an actual 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] Figure 9 This is a whitening image of the crack in the trailing edge area of ​​the blade in the prior art;

[0039] Figure 10 This is a shear damage pattern diagram of the overlapping sandwich structure area between 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 this application more clearly understood, the present application is described and illustrated below in conjunction with the accompanying drawings and examples. It should be understood that the specific embodiments described herein are merely used to explain this application and are not intended to limit this application. Based on the embodiments provided in this application, all other embodiments obtained by those of ordinary skill in the art without making any creative efforts are within the scope of protection of this application.

[0041] Obviously, the drawings described below are merely examples or embodiments of the present application. Those skilled in the art can, without inventive effort, apply the present application to other similar scenarios based on these drawings. Furthermore, it is also understood that, although the effort involved in such a development process may be complex and lengthy, for those skilled in the art related to the content disclosed in this application, changes in design, manufacturing, or production based on the technical content disclosed in this application are merely conventional technical means and should not be construed as an insufficiency of the content disclosed in this application.

[0042] References to "embodiments" in this application mean that a particular feature, structure, or characteristic described in connection with the embodiment may be included in at least one embodiment of the application. The appearance of this phrase in various places in the specification does not necessarily refer to the same embodiment, nor does it refer to independent or alternative embodiments that are mutually exclusive of other embodiments. It is understood, both explicitly and implicitly, by those skilled in the art that the embodiments described in this application may be combined with other embodiments unless there is a conflict.

[0043] Unless otherwise defined, the technical or scientific terms used in this application should have the ordinary meaning understood by a person of ordinary skill in the technical field to which this application belongs. The words "a", "an", "a", "the" and the like used in this application do not indicate a limit on quantity and may indicate the singular or plural. The terms "include", "comprise", "have" and any variations thereof used 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 that are inherent to these processes, methods, products or devices. The words "connect", "connected", "coupled" and the like used in this application are not limited to physical or mechanical connections, but may include electrical connections, whether direct or indirect. The words "multiple" / "several" used in this application refer to two or more. "And / or" describes the association relationship between associated objects, indicating that three relationships can exist. For example, "A and / or B" can mean: A exists alone, A and B exist at the same time, or 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 order for 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 the 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 types 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] First, the overlap sandwich structure of the trailing edge beam and the trailing edge core material based on the blade cross-section structure is analyzed, such as Figure 2 As shown, the structural area under analysis is the overlap transition area between the trailing edge beam and the trailing edge core material.

[0046] Then, the coordinate system of the 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 of the blade section) and the thickness direction of the sandwich structure are x and y, respectively, and the width direction (corresponding to the length direction of the blade) is z. Then, along the x direction of the sandwich structure, based on the structural distribution form, it is divided into the laminate area, the bevel overlap sandwich structure area, and the conventional sandwich structure area. In this case, 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. In this case, the layup form of the laminate area along the x direction of the sandwich structure is upper surface panel, trailing edge beam, lower surface panel; the layup form of the conventional sandwich structure area is upper surface panel, core material, lower surface panel structure; the layup form of the bevel overlap sandwich structure area is upper surface panel, bevel section with varying core material thickness, bevel section with varying trailing edge beam thickness, and 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, in order to achieve the purpose of feedback design and guidance of 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. In this case, 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 relative to the overall neutral layer and the bending stiffness of the core layer Composition, the cross-sectional bending stiffness of the conventional sandwich structure is calculated as

[0049] like Figure 5 As shown in the figure, the sloped-lap sandwich structure region is studied. Due to the large stiffness mutation and irregular shape of the sandwich structure, there is a lack of theoretical algorithms for failure prediction of this sloped-lap sandwich structure. Therefore, a discretization and step-by-step expansion method is used to calculate the neutral layer position and cross-sectional bending stiffness distribution of the sloped-lap sandwich structure region. The specific implementation steps of this method are as follows:

[0050] (1) Take any micro-segment dx of the analytical structure that approaches 0 along the x-direction of the inclined lap sandwich structure. In this case, the inclined segment can be approximately parallel to the panel layer. In this case, 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 trailing edge beam, and 1-2 layers of resin-based ±45° fiber cloth lower surface panel. It is also stipulated that the thickness vertices of the panel layer along the y-direction of each ply are h4, h3, h2, and h1 respectively, and the elastic modulus along the x-direction are E4, E3, E2, and E1 respectively).

[0051] (2) Assuming that the neutral layer 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 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] Obviously 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 and its distance to the neutral plane is within the linear elastic range. The micro-segment dx of the above analysis structure satisfies Hooke's law within the linear elastic range, and 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 linear equation with only the unknown variable y0. Solving the equation, we can get the position of the neutral layer as:

[0066]

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

[0068]

[0069] The neutral layer can be obtained as:

[0070]

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

[0072] (4) Based on the calculation method of cross-sectional bending stiffness 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, j is expressed as:

[0075]

[0076] D' can also be written as D'=D1+D2+D3+D4,

[0077] in:

[0078]

[0079] (5) Based on the calculation results of the neutral layer position and cross-sectional bending stiffness of the micro-segment dx of the above analysis structure, 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 layup design of the structural area of ​​the trailing edge beam and the trailing edge core material in an actual wind turbine blade project are determined based on the layup thickness, material elastic modulus in the x-direction, and miter ratio 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 overlap sandwich structure of the trailing edge beam and the trailing edge core material, as well as the length, thickness and width of the analyzed structure.

[0081] E1=E4, take 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 trailing edge beam and the trailing edge core material are calculated as follows: Figure 6 Based on the inflection point of the neutral layer distribution function along the length direction of the inclined plane overlap sandwich structure and the decreasing slope of the cross-sectional bending stiffness distribution function, the initial failure position of the overlap sandwich structure of the trailing edge beam and the trailing edge core material is confirmed to be x = 109 mm, thus achieving the prediction of the initial failure position of the overlap sandwich structure of the trailing edge beam and the trailing edge core material.

[0085] like Figure 7 As shown in the figure, in order to verify the correctness of the prediction method, the actual case of the above-mentioned wind turbine blade project was taken as the research object, and the overlap sandwich structure was designed based on the failure mode. The three-point bending static test and the finite element numerical simulation method were adopted respectively. Through the test and numerical simulation, the initial failure position of the overlap sandwich structure of the trailing edge beam and the trailing edge core material was determined to be x = 109mm. 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 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 to achieve high fidelity and high accuracy of the calculation method of the present invention. The method proposed thereby is more in line with actual engineering applications.

[0087] It is understandable 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 this field should understand that the present invention can still be modified or replaced by equivalents to achieve the same technical effects; as long as the requirements of the calculation method are met, they are within the scope of protection of the present invention.

Claims

1. A method for predicting the initial failure position of a sandwich core 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 overlapped 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 overlapped sandwich structure as respectively, and the z-direction along the width direction; Step 2: The overlapped sandwich structure is divided 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 laminated plates have a plywood layer consisting of an upper surface panel, a trailing edge beam, and a lower surface panel; the conventional sandwich structure region has a plywood layer consisting of an upper surface panel, a core material, and a lower surface panel; and the inclined overlapped sandwich structure region has a plywood layer consisting of an upper surface panel, a mitered section with varying core material thickness, a mitered section with varying trailing 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 relative 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, and 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, respectively; 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, i.e. 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 stipulated that h0=0, h n =h; Step 5: Based on the calculation method of cross-sectional bending stiffness of conventional sandwich structures, the algorithm for calculating the cross-sectional bending stiffness of the inclined lap sandwich structure is: j = 1, 2, where m represents the material number, j = 1 represents the bending stiffness of the material relative to its own neutral layer, and j = 2 represents the bending stiffness of the material relative to the overall neutral layer; Step 6: Substitute the geometry, material properties, and layup design of the overlapped sandwich structure of the trailing edge beam and the trailing edge core material of the wind turbine blade into Steps 3 to 5 to calculate the neutral layer position distribution and cross-sectional bending stiffness distribution of the overlapped sandwich structure of the wind turbine blade trailing edge beam and the trailing edge core material. 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 overlapped sandwich structure. Step 7: Based on the actual case of wind turbine blade engineering, the predicted initial failure position of the lap sandwich 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 trailing 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 analytical structure that approaches 0 along the x direction of the sandwich structure. In this case, the inclined surface segment is approximately parallel to the surface panel. The layup design of the micro-segment analytical 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: 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' or D'=D1+D2+D3+D4, in:

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