Structural damage identification method based on curvature modal feature factor tomography

Abstract

The application discloses a structure damage identification method based on a curvature modal characteristic factor chromatography thought, comprising the following steps: setting curvature modal characteristic factor measuring points on all grid nodes of a composite material wall plate structure peripheral boundary, constructing a curvature modal characteristic factor sensing array; acquiring multiple groups of parallel virtual rays and curvature modal characteristic factor difference values corresponding to each group of rays, reconstructing a curvature modal characteristic factor change rate matrix about X and Y directions of a composite material wall plate unit center; obtaining a curvature modal factor distribution characteristic representing damage characteristics, realizing composite material wall plate damage positioning, imaging and damage scale identification; and measuring the curvature modal of the composite material wall plate according to actual application needs. When the method is used for internal damage of the composite material wall plate, the strain modal at the damage position will be changed, the correlation between the strain change and the strain modal change in position coordinates is established, damage identification and imaging are carried out, and the complexity of the monitoring system is effectively reduced.

Description

Technical Field

[0001] This invention relates to the field of structural health monitoring, and in particular to a structural damage identification method based on the concept of curvature modal characteristic factor tomography. Background Technology

[0002] Composite material structures, operating under thermo-coupling conditions for extended periods, are prone to damage such as matrix failure, fiber debonding or breakage, and interlaminar cracking due to performance differences between the matrix and reinforcing fibers, as well as interfacial effects. Furthermore, the inherent characteristics of composite structures and the complex nonlinear coupling factors present in composite joins make strength and failure mode analysis difficult. Moreover, the damage to composite materials is often concealed; many types of damage, such as impact-induced delamination and internal microcracks, cannot be assessed through external observation, severely impacting the safe operation of aerospace structures.

[0003] In actual service, composite structures are prone to damage under complex and harsh environments and loads, and such damage is often difficult to detect effectively in its early stages. Conventional damage identification methods often require densely deploying sensors on or inside the surface of composite structures. This "intrusive" layout not only adds extra weight to the structure and affects aerodynamic performance, but its leads, adhesives, etc., can also become new stress concentration points or potential sources of damage.

[0004] Therefore, conducting research on real-time online damage monitoring based on a "non-invasive mode" (i.e., no sensors are placed inside the monitoring area) for composite material structures of aircraft can provide a basis for making scientific maintenance decisions and significantly enhance the aircraft's adaptability and resistance to various risks throughout its service life. Summary of the Invention

[0005] The problem this invention aims to solve is to provide a structural damage identification method based on the tomographic concept of curvature modal characteristic factors. By constructing a curvature modal factor observation array based on the tomographic concept, it overcomes the limitation of conventional damage identification methods that require the placement of sensors within the structural monitoring area, thus reducing the complexity of the monitoring system. Based on the tomographic concept, it reconstructs the image features of curvature modal factors, solving the problem that conventional methods can only locate damage but cannot quantify the damage scale and contour features. This provides important assistance for further assessing the degree of damage to composite material structures, predicting residual strength, and formulating maintenance strategies.

[0006] This invention adopts the following technical solution: a structural damage identification method based on the curvature mode feature factor tomography idea, comprising the following steps:

[0007] Step 1: Set curvature modal characteristic factor measurement points on all grid nodes on the four outer boundaries of the composite material wall panel structure to construct a curvature modal characteristic factor sensing array;

[0008] Step 2: Obtain multiple sets of parallel virtual rays and the corresponding curvature mode characteristic factor differences between each set of parallel virtual rays, and reconstruct the curvature mode characteristic factor of the composite material wall panel unit mesh center with respect to the X and Y direction change rate matrix;

[0009] Step 3: Obtain the curvature mode factor distribution characteristics that characterize the damage features through reconstruction, and perform damage localization, imaging and damage scale identification of composite panel.

[0010] Step 4: According to the actual application requirements, measure the curvature mode of the composite material wall panel to obtain the strain mode and curvature mode of the composite material wall panel at the preset order.

[0011] As a preferred embodiment, step 1 includes:

[0012] First, obtain the curvature modal characteristic factor of the composite material structure, and define the r-th strain mode along the X direction of the damage-free composite panel as follows: The r-th strain mode along the X direction of the damaged composite wall panel is: The r-th strain mode along the Y direction of the damage-free composite panel is defined as follows: The r-th strain mode along the Y direction of the damaged composite wall panel is: ;

[0013] Then, the r-th order composite curvature modes of the undamaged and damaged composite wall panels along the X and Y directions are defined:

[0014] ;

[0015] In the formula, For the r-th order synthetic curvature mode of the non-damaging composite wall panel, The r-th order synthetic curvature mode of the damaged composite wall panel;

[0016] Definition of undamaged and damaged composite wall panels The difference of the r-th order synthetic curvature mode measured at each measuring point :

[0017] ;

[0018] In the formula, , The r-th synthetic curvature mode is measured at the i-th measuring point of the undamaged and damaged composite material wall panels.

[0019] Then, the synthesized curvature modes measured at the same measurement point at each natural frequency are normalized to obtain curvature mode characteristic factors. :

[0020] ;

[0021] In the formula, Indicates that the composite material wall panel has a total of First natural frequency;

[0022] Rate of change of curvature modal eigenvalues ​​with respect to the X and Y directions , for:

[0023] ;

[0024] In the formula, For curvature mode characteristic factors, , These are the coordinates corresponding to the X and Y directions.

[0025] As a preferred embodiment, step 1 further includes:

[0026] For a rectangular composite panel structure, the center of the panel is set as the origin. X-axis and Y-axis are established along the horizontal and vertical directions respectively. The panel is then evenly divided into sections along the X-axis and Y-axis respectively. Segment, generation Individual grid cells;

[0027] Curvature modal characteristic factor measurement points are set on all grid nodes along the four boundaries of the wall panel to construct a curvature modal characteristic factor sensing array. The measurement point at the lower left corner of the wall panel is taken as the first measurement point, and the measurement points are numbered counterclockwise. The curvature modal characteristic factor data sensed at the i-th measurement point is... , ;

[0028] Select the rate of change of curvature modal characteristic factors with respect to the X and Y directions. , Let be the quantities to be reconstructed, and set the rate of change of the curvature modal eigenfactors at the center of all element meshes with respect to the X and Y directions to be constant. Based on this, construct the matrix of the rate of change of the curvature modal eigenfactors at the center of each element mesh of the composite panel with respect to the X and Y directions. , .

[0029] As a preferred embodiment, step 2 includes:

[0030] For the matrix to be reconstructed , Reconstruct a two-dimensional function Integrating along lines at different angles yields the projection data:

[0031] ;

[0032] In the formula, For projection data from different angles, For the projection angle, For the projection distance, Dirac function; two-dimensional function It is the rate-of-change matrix of the curvature modal eigenfactors at the center of each unit grid of the composite panel with respect to the X and Y directions. , .

[0033] A virtual ray is generated between any two measurement points A and B in the curvature mode feature factor sensing array. Since the projection process of the curvature mode feature factor is a passive reception rather than an active transmission and reception, the projection data is rewritten as follows:

[0034] ;

[0035] The difference Δκ between the curvature mode eigenfactors measured at points A and B is used as the degree of attenuation of the virtual ray from point A to point B of the curvature mode eigenfactor field. The projection integral along different angles is expressed as:

[0036] ;

[0037] In the formula, , The curvature modal characteristic factor values ​​measured at measurement points A and B. For factor field Projection data;

[0038] The matrix to be reconstructed by combining the rates of change in the X and Y directions , ,Will The expression is rewritten as:

[0039] ;

[0040] ;

[0041] Obtain multiple sets of parallel virtual rays and the corresponding curvature mode characteristic factor differences between each set of parallel virtual rays.

[0042] As a preferred embodiment, step 2 further includes:

[0043] Based on the central slice theorem, the matrices to be reconstructed for the rates of change in the X and Y directions... , Refactor.

[0044] With matrix For example, perform a one-dimensional Fourier transform on each set of parallel virtual rays and the corresponding composite curvature difference between each set of parallel virtual rays:

[0045] ;

[0046] In the formula, It is a Fourier transform. It is angular frequency. The difference in curvature mode characteristic factors after Fourier transform;

[0047] The difference in curvature mode eigenfactors after Fourier transform is multiplied by a ramp filter. Perform filtering:

[0048] ;

[0049] The filtered result Perform a one-dimensional inverse Fourier transform to obtain the filtered projection. :

[0050] ;

[0051] In the formula, The function is the inverse Fourier transform;

[0052] According to the convolution theorem, the product in the frequency domain is equal to the convolution in the spatial domain, and the projection... Equivalent to:

[0053] ;

[0054] In the formula, It is a ramp filter The form of airspace.

[0055] because Non-integrable, can be solved by applying a window function. This enables the ramp filter To become an implementable filter:

[0056] ;

[0057] Integrating the filtered projections from all angles from 0 to π yields the rate of change matrix along the X-direction. :

[0058] ;

[0059] and The reconstruction process is similar, for By performing the same processing steps, the rate of change matrix of the central curvature mode characteristic factor of each unit grid of the composite material wall panel along the X and Y directions can be obtained. , .

[0060] As a preferred embodiment, step 3 includes:

[0061] The reconstructed matrix , Integrating along the X and Y directions yields the curvature mode characteristic factor field of the composite panel. :

[0062] ;

[0063] Based on the theory of composite material damage identification using curvature modes, the distribution of curvature mode factors characterizing damage features, obtained by reconstructing the above formula, can be used for damage localization, imaging, and damage scale identification of composite panel walls.

[0064] The specific methods for damage localization and scale identification are as follows:

[0065] Define the coordinates of the point where the damage factor of the composite panel is maximized as the location of the damage center:

[0066] ;

[0067] In the formula, The coordinates are the location of the damage center in the composite panel. The coordinates of the location where the curvature mode characteristic factor is maximized;

[0068] Based on the abrupt change characteristic contour of the curvature modal factor distribution cloud map, a damage discrimination threshold for the curvature modal characteristic factors of composite materials is defined. When the feature factor corresponding to a certain position is greater than or equal to the damage discrimination threshold When the location is determined to be within the damage area of ​​the composite material wall panel, it is determined that the location is within the damage area of ​​the composite material wall panel.

[0069] As a preferred embodiment, step 4 includes:

[0070] Measure the strain modal response at each node of the structure under test and calculate the strain frequency response function. As each element of the wall panel When a point is stimulated, at the 1st Strain response caused by each measuring point location:

[0071] ;

[0072] In the formula, It is the first Modal participation factor of the first mode, Composite material wall panels The measured point First displacement mode, It is the first composite material wall panel The measurement of the first measuring point First strain mode;

[0073] The strain frequency response function is transformed into:

[0074] ;

[0075] In the formula, Indicates in Excitation frequency of point input, It is the first First natural frequency, It is the damping ratio of the r-th mode. It is the first Stiffness of order;

[0076] When an excitation force is applied to a measuring point p at a random location on the wall panel surface, and the frequency is equal to the natural frequency corresponding to the t-th mode of the structure under test, the strain frequency response function can be rewritten as:

[0077] ;

[0078] For the non-compact mode case, the t-th mode plays a dominant role in the response, so the effects of other modes can be ignored, as shown in the above equation:

[0079] ;

[0080] in, It is the t-th natural frequency. It is the damping ratio of the t-th mode. It is the t-th order stiffness. Is the response point i at frequency The response amplitude at that point, Is the measurement point P at frequency The excitation amplitude at the location;

[0081] calculate Let be the t-th strain mode of measuring point P on the composite material wall panel:

[0082] ;

[0083] When a fixed measuring point p is excited at the t-th natural frequency, and the excitation force is constant, the modal parameters of the structure are all constant. The constant part is expressed as follows: :

[0084] ;

[0085] The formula Written as:

[0086] ;

[0087] By applying a preset order natural frequency excitation to the composite material wall panel, the strain modal response amplitudes acquired by the fiber optic grating sensor at different nodes are normalized and substituted into... The strain modes of the composite material wall panel at the preset order are obtained, and the curvature modes of the composite material wall panel at the preset order are calculated.

[0088] Compared with the prior art, the present invention, employing the above technical solution, has the following technical effects:

[0089] 1. This invention proposes a structural damage identification method based on the curvature modal feature factor tomography idea. By constructing a curvature modal factor observation array based on the tomography idea, it overcomes the limitation of conventional damage identification methods that require the placement of sensors in the structural monitoring area, and effectively reduces the complexity of the monitoring system.

[0090] 2. The curvature modal factor image features reconstructed based on the tomographic principle of the present invention can not only accurately locate the damage center, but also quantify the damage scale and contour features, providing important assistance for further assessing the damage degree of composite material structures, predicting the remaining strength, and formulating maintenance strategies. Attached Figure Description

[0091] Figure 1 This is a flowchart of the structural damage identification method of the present invention.

[0092] Figure 2 This is a perceptual array diagram of curvature mode feature factors.

[0093] Figure 3 The graph shows the rate of change matrix of the curvature mode characteristic factors in the X and Y directions.

[0094] Figure 4 This is a structural model diagram of a composite panel containing delamination damage.

[0095] Figure 5 A comparison diagram of the first-order curvature modes of undamaged and damaged composite panel models.

[0096] Figure 6 The image shows a comparison of the second-order curvature modes of the composite panel models with and without damage.

[0097] Figure 7 The image shows a comparison of the third-order curvature modes of the composite panel models with and without damage.

[0098] Figure 8 A comparison diagram of the fourth-order curvature modes of undamaged and damaged composite panel models.

[0099] Figure 9This is a distribution map of curvature mode characteristic factors in the monitoring area of ​​the composite panel corresponding to single-damage and double-damage conditions. Detailed Implementation

[0100] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of the application will be further described in detail below with reference to the accompanying drawings. The described embodiments are only a part of the embodiments involved in this invention. All non-innovative embodiments based on these embodiments by other researchers in the art are within the protection scope of this invention. Furthermore, the step numbers in the embodiments of this invention are only set for ease of explanation and do not limit the order of the steps. The execution order of each step in the embodiments can be adaptively adjusted according to the understanding of those skilled in the art.

[0101] In one embodiment of the present invention, a structural damage identification method based on the curvature mode feature factor tomography concept is provided, such as... Figure 1 As shown, it includes the following steps:

[0102] Step 1: Obtain the curvature mode characteristic factor of the composite material and define the first characteristic factor of the non-damaging composite material wall panel. The strain mode along the X direction is Damaged composite wall panel The strain mode along the X direction is Define the first non-damaging composite material wall panel The strain mode along the Y direction is Damaged composite wall panel The strain mode along the Y direction is Composite panel structure model with delamination damage, such as Figure 4 As shown.

[0103] Define the r-th order synthetic curvature mode of the undamaged / damaged composite panel along the X and Y directions:

[0104] (1)

[0105] In equation (1), For the r-th order synthetic curvature mode of the non-damaging composite wall panel, The r-th order synthetic curvature mode of the damaged composite wall panel.

[0106] Let the non-damaging composite material wall panel be the first The r-th order synthetic curvature mode measured at each measuring point is: Damaged composite wall panel The r-th order synthetic curvature mode measured at each measuring point is: Then the composite wall panel with no damage and with damage is the first The difference in the r-th order synthetic curvature mode measured at each measuring point can be expressed as:

[0107] (2)

[0108] Since there are large numerical differences between the synthetic curvature modes of different orders in composite wall panel structures, the synthetic curvature modes measured at the same measurement point at each natural frequency can be normalized and defined as curvature mode characteristic factors, which can be used to locate internal damage and identify damage scale in composite wall panels.

[0109] Composite material wall panel The characteristic factors are obtained by normalizing the synthesized curvature modes measured at each natural frequency at each measurement point. The expression is:

[0110] (3)

[0111] In equation (3), Indicates that the composite material wall panel has a total of The first natural frequency.

[0112] Define the rate of change of curvature modal eigenvalues ​​with respect to the X and Y directions. , for:

[0113] (4)

[0114] Taking a rectangular composite material wall panel structure as an example, the center of the wall panel is set as the origin, and X-axis and Y-axis are established along the horizontal and vertical directions respectively. The wall panel is then evenly divided into sections along the X-axis and Y-axis respectively. Segment, generation Each cell grid has curvature modal characteristic factor measurement points set on all grid nodes on the four boundaries of the outer perimeter of the wall panel to construct a curvature modal characteristic factor sensing array.

[0115] The measuring point at the lower left corner of the wall panel is set as the first measuring point. The measuring points are numbered counter-clockwise. The curvature mode characteristic factor data sensed at the i-th measuring point is... , ;like Figure 2 As shown.

[0116] Select the rate of change of curvature modal characteristic factors with respect to the X and Y directions. , Let be the quantities to be reconstructed, and set the rate of change of the curvature modal eigenfactors at the center of all element meshes with respect to the X and Y directions to be constant. Based on this, construct the matrix of the rate of change of the curvature modal eigenfactors at the center of each element mesh of the composite panel with respect to the X and Y directions. , ,like Figure 3 As shown, its expression is as follows:

[0117] (5)

[0118] Step 2: Analyze the variation rate matrix of the central curvature modal eigenfactors of the composite panel element mesh with respect to the X and Y directions. , Reconstruction can transform a two-dimensional function Integrate along lines at different angles to obtain projection data:

[0119] (6)

[0120] In equation (6), For projection data from different angles, For the projection angle, For the projection distance, This is the Dirac function.

[0121] Two-dimensional function It is the rate-of-change matrix of the curvature modal eigenfactors at the center of each unit grid of the composite panel with respect to the X and Y directions. , .

[0122] Assuming a virtual ray S is generated between any two measurement points A and B in the curvature mode feature factor sensing array, since the projection process of the curvature mode feature factor is a passive reception rather than an active transmission and reception, equation (6) needs to be rewritten as:

[0123] (7)

[0124] Assume the curvature modal characteristic factor measured at measurement point A is... The curvature mode characteristic factor measured at measuring point B is... The difference in curvature modal characteristic factors measured at measurement points A and B is... This can be understood as the degree to which the curvature mode characteristic factor of the virtual ray attenuates as it travels from point A to point B.

[0125] The expression for the projection integral of the curvature mode characteristic factor field κ along different angles is:

[0126] (8)

[0127] Combining equation (4), equation (8) can be rewritten as:

[0128] (9)

[0129] (10)

[0130] To reconstruct the rate of change matrix along the X and Y directions , It is necessary to obtain multiple sets of parallel virtual rays and the curvature mode characteristic factor difference between each set of parallel virtual rays in advance.

[0131] According to the central slice theorem: two-dimensional functions At angle Projection below The corresponding one-dimensional Fourier transform , equal to a two-dimensional function Two-dimensional Fourier transform In the frequency plane upper edge angle A slice whose direction passes through the origin has the following expression:

[0132] (11)

[0133] Based on the central slice theorem, the rate of change matrices in the X and Y directions... , Reconstruct the matrix using the rate of change in the X direction. For example, the reconstruction steps are as follows:

[0134] Perform a one-dimensional Fourier transform on each set of parallel virtual rays and the corresponding composite curvature difference between each set of parallel virtual rays:

[0135] (12)

[0136] Multiply the difference in curvature mode eigenfactors after Fourier transform by a ramp filter:

[0137] (13)

[0138] Perform a one-dimensional inverse Fourier transform on the filtered result to obtain the filtered projection. :

[0139] (14)

[0140] According to the convolution theorem, the product in the frequency domain is equal to the convolution in the spatial domain. Therefore, equations (12)-(14) are equivalent to:

[0141] (15)

[0142] In equation (15), ramp filter The form of airspace.

[0143] because It is not integrable and requires a window function. (such as Ram-Lak, Shepp-Logan, Hann window), making it an implementable filter. .

[0144] Integrating the filtered projections from all angles from 0 to π yields the rate of change matrix along the X-direction. :

[0145] (16)

[0146] and The reconstruction process is similar. Through the above steps, the rate of change matrix of the curvature modal characteristic factor of each unit grid of the composite material wall panel along the X and Y directions can be obtained. , .

[0147] Step 3, reconstruct the results , Integrating along the X and Y directions yields the curvature modal characteristic factor field of the composite panel. for:

[0148] (17)

[0149] Based on the theory of composite material damage identification using curvature modes, the distribution of curvature mode factors that characterize damage features, obtained by reconstructing from equation (17), can be used for damage localization, imaging, and damage scale identification of composite panel walls.

[0150] In this embodiment, the specific damage localization and scale identification method is as follows:

[0151] The coordinates of the point where the damage factor of the composite panel is maximized are defined as the location of the damage center, expressed as:

[0152] (18)

[0153] In equation (18), The coordinates are the location of the damage center in the composite panel. The coordinates are the location coordinates where the curvature mode characteristic factor is at its maximum.

[0154] Based on the abrupt change characteristic contour of the curvature modal factor distribution cloud map, a damage discrimination threshold for the curvature modal characteristic factors of composite materials is defined. When the feature factor corresponding to a certain location is greater than or equal to the damage discrimination threshold... This means that the location was determined to be within the damaged area of ​​the composite panel. Modal analysis using the Lanczos method was employed to obtain the first to fourth curvature modes of the undamaged and damaged composite panel models. The comparison results of the first, second, third, and fourth curvature modes of the undamaged and damaged composite panel models are as follows: Figure 5 , Figure 6 , Figure 7 and Figure 8 As shown.

[0155] The following example uses the identification results of single-damage and dual-damage conditions, combined with... Figure 9 This illustrates the effects of the present invention.

[0156] Depend on Figure 9 As shown in (a), under the single-damage condition, there is a significant curvature mode characteristic factor mutation region in the monitoring range of the composite panel, indicating that there is significant damage at the mutation location.

[0157] According to the damage localization method of the present invention, the location of the damage is calculated to be (56.2mm, 206.4mm), and the absolute error of damage localization is 7.44mm. According to the damage scale identification method, by setting the damage threshold ρ to 0.5, the equivalent diameter of the damage can be calculated to be 24mm, and the absolute error of damage scale identification is 4mm.

[0158] Depend on Figure 9 As shown in (b), under the dual-damage condition, there are two obvious curvature mode characteristic factor abrupt change regions in the monitoring area of ​​the composite panel, indicating that there is obvious sub-damage at both abrupt change locations.

[0159] According to the damage localization method of the present invention, the first damage location is calculated to be (103.4mm, 221.7mm), with an absolute damage localization error of 3.8mm; the second damage location is calculated to be (226.2mm, 57.2mm), with an absolute damage localization error of 6.8mm. The damage threshold is then set... With the value set to 0.5, the equivalent diameter of the first damage was calculated to be 12.4 mm, and the absolute error of damage scale identification was 2.6 mm; the equivalent diameter of the second damage was 28.7 mm, and the absolute error of damage scale identification was 3.7 mm.

[0160] Step 4: In practice, measuring the strain modal response at each node requires normalization to obtain the r-th strain mode of the structure. The principle can be briefly described as follows:

[0161] Calculate the strain frequency response function The function is calculated by the following formula:

[0162] (19)

[0163] Its value can be used as the value of each element in the panel. The strain response at measurement point i when the point is excited.

[0164] The strain frequency response function in equation (19) is transformed into:

[0165] (20)

[0166] In equation (20), Indicates in Excitation frequency of point input, , , It is the r-th natural frequency. It is the damping ratio of the r-th mode.

[0167] When the frequency of the excitation force applied to a random point p on the wall panel is equal to the natural frequency corresponding to a certain order of the structure, taking the excitation of the t-th modal frequency as an example, equation (20) can be rewritten as:

[0168] (twenty one)

[0169] For the non-compact mode case, the t-th mode plays a dominant role in the response, so the effects of other modes can be ignored. From equation (21), we can obtain:

[0170] (twenty two)

[0171] From equation (22), we can obtain:

[0172] (twenty three)

[0173] From equation (23), it can be seen that when the structure is excited at a fixed measuring point p with the t-th natural frequency, the modal parameters of the structure are all constant when the excitation force is fixed as a constant. Let the constant part for:

[0174] (twenty four)

[0175] Therefore, equation (24) can be written as:

[0176] (25)

[0177] By applying a certain order of natural frequency excitation to the composite wall panel, normalizing the strain mode response amplitudes obtained by the fiber optic grating sensor at different nodes, and substituting them into equation (24), the strain mode corresponding to that order of the composite wall panel can be obtained.

[0178] Substituting the measured strain modes of the composite wall panel along the X and Y directions into equation (1) respectively, the curvature modes of the composite wall panel at that order can be obtained.

[0179] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A structural damage identification method based on the idea of curvature modal feature factor tomography, characterized in that, Includes the following steps: Step 1: Set curvature modal characteristic factor measurement points on all grid nodes on the four outer boundaries of the composite material wall panel structure to construct a curvature modal characteristic factor sensing array; Step 2: Obtain multiple sets of parallel virtual rays and the corresponding curvature mode characteristic factor differences between each set of parallel virtual rays, and reconstruct the curvature mode characteristic factor of the composite material wall panel unit mesh center with respect to the X and Y direction change rate matrix; Step 3: Obtain the curvature mode factor distribution characteristics that characterize the damage features through reconstruction, and perform damage localization, imaging and damage scale identification of composite panel. Step 4: According to the actual application needs, measure the curvature mode of the composite material wall panel to obtain the strain mode of the composite material wall panel at the preset order and the curvature mode of the composite material wall panel at the preset order. Step 1 includes: Obtain the curvature modal characteristic factor of the composite panel structure, and define the r-th strain mode along the X direction of the undamaged composite panel as... The r-th strain mode along the X direction of the damaged composite wall panel is: The r-th strain mode along the Y direction of the damage-free composite panel is defined as follows: The r-th strain mode along the Y direction of the damaged composite wall panel is: ; Define the r-th order composite curvature modes of undamaged and damaged composite wall panels along the X and Y directions: ； wherein is the rth order synthetic curvature mode of the undamaged composite panel, is the rth order synthetic curvature mode of the damaged composite panel; Computing non-damaged and damaged composite wallboard rth order difference of the synthetic curvature mode measured at the rth measurement point : ； wherein , is the rth modal shape of the undamaged composite panel measured at the rth measurement point. The normalized curvature modal of the same measuring point measured at each order natural frequency is obtained : ； In the formula, Indicates that the composite material wall panel has a total First natural frequency; Curvature modal characteristic factor about X, Y direction change rate , is: ； In the formula, is a curvature modal characteristic factor, , are coordinate positions corresponding to the X and Y directions. For a rectangular composite panel structure, the center of the panel is set as the origin. X-axis and Y-axis are established along the horizontal and vertical directions respectively. The panel is then evenly divided into sections along the X-axis and Y-axis respectively. Segment, generation Individual grid cells; Curvature modal characteristic factor measurement points are set on all grid nodes along the four outer boundaries of the wall panel to construct a curvature modal characteristic factor sensing array. The measurement point at the lower left corner of the wall panel is taken as the first measurement point, and the measurement points are numbered counterclockwise. The curvature mode feature factor data sensed at each measurement point are as follows: , ; Select the curvature modal characteristic factor about X, Y direction change rate , The to-be-reconstructed quantity is the curvature modal characteristic factor about X, Y direction change rate of each unit grid center of the composite wall panel , : ； In the formula, to , to are the curvature modal characteristic factors of each unit grid center along the X and Y directions, respectively.

2. The structural damage identification method of claim 1, wherein Step 2 includes: reconstructing the matrix to be reconstructed , reconstructing the matrix to be reconstructed integrating the two-dimensional function along lines of different angles to obtain projection data: ； wherein is projection data at different angles, is a projection angle, is a projection distance, is a Dirac function; A virtual ray is generated between any two measurement points A and B in the curvature modal feature factor sensing array, and the projection data is rewritten as follows: ； The difference between the curvature modal eigenvalue measured at points A and B The degree to which the curvature modal eigenvalue measured at point A by a virtual ray decays to point B, for a field of curvature modal eigenvalues The projection integral is performed at different angles, and the expression is ； In the formula, , The curvature modal characteristic factor values ​​measured at measurement points A and B. For factor field Projection data; The matrix to be reconstructed by combining the rates of change in the X and Y directions , ,Will The expression is rewritten as: ； ； Obtain multiple sets of parallel virtual rays and the corresponding curvature mode characteristic factor differences between each set of parallel virtual rays.

3. The structural damage identification method of claim 2, wherein Step 2 also includes: Based on the central slice theorem, the matrices to be reconstructed for the rate of change in the X and Y directions are... , Reconstruction based on matrix For each set of parallel virtual rays and the corresponding composite curvature difference between each set of parallel virtual rays, perform a one-dimensional Fourier transform: ； wherein is the Fourier transform, is the angular frequency, is the Fourier transformed curvature modal feature factor difference; the curvature modal feature factor difference after fourier transform is multiplied by a ramp filter , filtering is performed: ； on the filtered result performing an inverse one-dimensional Fourier transform on the filtered projection : ； wherein the function is the inverse Fourier transform; According to the convolution theorem, the product in the frequency domain is equal to the convolution in the spatial domain, the projection is equivalent to: ； wherein is a spatial form of a ramp filter ; by a windowing function makes the slope filter an implementable filter: ； Integrating the filtered projections from all angles from 0 to π yields the rate of change matrix along the X-direction. : 。 4. The structural damage identification method of claim 3, wherein The central slice theorem describes a two-dimensional function. At angle Projection below The corresponding one-dimensional Fourier transform , equal to a two-dimensional function The two-dimensional Fourier transform F along the angle in the frequency plane A slice passing through the origin, the formula is: 。 5. The structural damage identification method of claim 3, wherein Step 3 includes: The reconstructed matrix is obtained , The composite wallboard curvature modal characteristic factor field is obtained by integrating along the X and Y directions : ； Damage localization, imaging, and damage scale identification of composite panel are performed, and the coordinates of the point where the damage factor of the composite panel is maximum are defined as the damage center location. ； In the formula, The coordinates are the location of the damage center in the composite panel. The coordinates are the location coordinates of the maximum curvature mode feature factor; when the feature factor corresponding to a certain location is greater than or equal to the preset damage discrimination threshold... When the location is determined to be within the damage area of ​​the composite material wall panel, it is determined that the location is within the damage area of ​​the composite material wall panel.

6. The structural damage identification method of claim 5, wherein Step 4 includes: Measure the strain modal response at each node of the structure under test and calculate the strain frequency response function. As each element of the wall panel When a point is stimulated, at the 1st Strain response caused by each measuring point location: ； wherein is the modal participation factor of the rth order mode, is the rth displacement modal measured at the i th measured at the i th strain modal measured at the i th The strain frequency response function is transformed into: ； wherein represents the input of the excitation frequency at the point represents the input of the excitation frequency at the point is the rth natural frequency, is the rth modal damping ratio, is the rth stiffness; When an excitation force is applied to a random measuring point p on the surface of the composite material panel, and the frequency is equal to the natural frequency corresponding to the t-th mode of the structure under test, the strain frequency response function can be rewritten as: ； For the non-compact mode case, the t-th mode plays a dominant role in the response: ； Among them, w t It is the t-th natural frequency. It is the damping ratio of the t-th mode. It is the t-th order stiffness. It is the first Each measurement point at frequency w t The response amplitude at that point, The measurement point P is at frequency w t The excitation amplitude at that point, It is the t-th displacement mode measured at measuring point P; is the tth strain modal of the composite panel measurement point P: ； When the fixed point p is excited at the tth natural frequency, the modal parameters of the structure are constant when the exciting force is constant, and the constant part is represented as : ； will be written as: written as: ； By applying a preset order natural frequency excitation to the composite material wall panel, the strain modal response amplitudes acquired by the fiber optic grating sensor at different nodes are normalized and substituted into... The strain modes of the composite material wall panel at the preset order are obtained, and the curvature modes of the composite material wall panel at the preset order are calculated.

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