Impact Location Method for Composite Material Plate Structures Based on Multidimensional Wave Velocity Reliability Weighting

Abstract

This invention discloses a fiber optic impact location method for composite material plate structures based on multidimensional wave velocity confidence weighting, belonging to the field of impact load identification in structural health monitoring. It includes the following steps: Step 1: Arranging a fiber optic FBG sensor network with four fixed supports on the plate surface; Step 2: Real-time signal acquisition using fiber optic FBG sensors; the impact signal undergoes wavelet transform, and the time delay of the impact signal is solved using generalized cross-correlation; Step 3: Measuring the stress wave velocity range of the composite material plate in multiple directions; determining the preliminary range of the impact point based on the time delay of arrival and the wave velocity range; Step 4: Setting the location deviation. e ,according to e Step 5: Calculate the confidence matrix of the horizontal and vertical coordinates of the eight sensor sets with respect to the grid nodes; Step 6: Weight the confidence of the grid nodes within the initial range of the impact point to determine the location of the impact point. The method described in this invention determines the location of the impact point on the anisotropic plate by weighting the confidence of multidimensional wave velocity. This invention is simple, convenient, and widely applicable.

Description

Technical Field

[0001] This invention belongs to the field of load monitoring technology for structural health monitoring, and specifically proposes an impact positioning method for composite material plate structures based on multidimensional wave velocity confidence weighting. Background Technology

[0002] With the rapid development of modern science and technology and industrial manufacturing technology, the performance of aircraft structures has been gradually improved. Modern aircraft structures are mainly made of metallic and non-metallic materials, with composite materials being the primary type of non-metallic material. The nose, wings, and fuselage, which are susceptible to impact, are currently mostly made of composite materials. However, composite materials have poor impact resistance; impact loads can easily lead to internal delamination, matrix cracking, and fiber breakage, reducing structural strength and stability. Real-time monitoring of low-speed impact loads is necessary to identify the location, magnitude, and energy of the impact load, enabling timely maintenance plans. This can reduce the cost of maintaining structural integrity to some extent, further improve structural safety, and extend the aircraft's service life.

[0003] Currently, research on low-speed impact positioning technology for large structures is extensive. Paul Tikalsky et al. from the University of Utah proposed a one-dimensional beam-focusing positioning algorithm, arranging a one-dimensional array of sensors facing each other at the edge of the structure. Impact positioning experiments on large structures yielded good results. Pratik Shrestha et al. used a linear array of six fiber optic grating sensors and an error anomaly estimation impact positioning algorithm to conduct low-speed impact positioning experiments on a 30cm×30cm aircraft wing structure, achieving an average positioning error of 2.9cm. Meng Yao et al. proposed a two-dimensional beam-focusing probabilistic imaging positioning algorithm based on a cross-shaped sensor arrangement. This algorithm generates a probability distribution map of the impact source in both the horizontal and vertical arrays, and then superimposes and fuses these probability distribution maps to obtain the impact location.

[0004] Some of the aforementioned methods require extensive prior knowledge to determine wave velocity, making the process cumbersome; others are only applicable to isotropic materials, limiting their applicability. Therefore, to address the shortcomings of current impact location methods for composite material plate structures, it is necessary to research new methods that are simple, fast, and highly practical, requiring no extensive prior knowledge. To this end, this invention proposes an impact location method for composite material plate structures based on multidimensional wave velocity confidence focusing. Summary of the Invention

[0005] Technical problem: The technical problem to be solved by this invention is to address the shortcomings of current impact positioning methods for composite material plate structures, and to propose an impact positioning method for composite material plate structures based on multidimensional wave velocity credibility focusing that does not require a large amount of prior knowledge and has wide applicability.

[0006] Step 1: Deployment of the fiber optic FBG sensor network on the four sides of the fixed plate surface; specifically:

[0007] A square strain monitoring area OABC is defined by a four-sided fixed composite material plate with side length l. A distributed fiber optic FBG sensor network, consisting of nine fiber optic FBG sensors, is arranged on the plate surface. The fiber optic FBG sensor at the center is numbered FBG0, and the fiber optic FBG sensors at the four surrounding positions are numbered FBGi, i∈(1,2,...8), where i is the number of each of the four surrounding fiber optic sensors. The central fiber optic sensor FBG0 is located at the geometric center of the plate surface, with its position coordinates set to (0,0). The surrounding fiber optic sensors FBGi are arranged at equal intervals around the central sensor, with a radius of l. On the circumference, the central angle of the adjacent four fiber optic sensors is 45°, and their position coordinates are (a i ,b i The central fiber optic sensor FBG0 and any one of the surrounding fiber optic sensors FBGi form a sensor pair, for a total of eight sensor pairs. The fiber optic FBG sensors are all pasted in a direction parallel to the X direction of the board surface to obtain the strain in a single direction on the board structure surface, thereby forming a fiber optic FBG sensor network on the board surface.

[0008] Step Two: The signal is acquired in real time using a fiber optic FBG sensor. The impact signal undergoes wavelet transform, and the time delay of the impact signal is solved using generalized cross-correlation. Specifically:

[0009] For a single impact, the signal received by the central fiber optic sensor FBG0 is m0, and the impact signals received by the surrounding fiber optic sensors FBGi are m... i The aforementioned signal is a non-stationary random signal with numerous frequency components and patterns. Wavelet transform is used to perform time-window analysis on the impulse signal, filtering out irrelevant frequency information and extracting the time-domain information of the desired dominant frequency signal. The dominant frequency signals obtained after wavelet transform are m′0 and m. i ′; where the wavelet basis functions are as follows:

[0010]

[0011] In the formula, a is the scaling factor, which represents the scaling of the mother wavelet function on the time axis. a>1 indicates expansion, and a<1 indicates contraction. b is the translation factor, which represents the left and right translation of the center position of the mother wavelet function. t is the time variable.

[0012] The formula for the continuous wavelet transform of any square-integrable function f(t) is as follows:

[0013]

[0014] W f (a,b) represents the continuous wavelet transform of the function f(t), R is the real number field, and ψ * Represents the complex conjugate operation; ψ a,b (t) represents the wavelet basis function generated after the mother wavelet function ψ(t) is adjusted by a and b;

[0015] The signals m′0 and m obtained by wavelet transform i The formula for performing a generalized cross-correlation operation with PHAT as the weighting function is as follows:

[0016]

[0017] Where τ is the time required for the stress wave generated by the impact to travel from the impact location to the fiber optic grating sensor; f is the frequency variable; and e is a mathematical constant, which is the base of the natural logarithm function.

[0018] The formula for calculating the time difference of arrival of the stress wave detected by the two sensors is as follows:

[0019]

[0020] Make The time delay of arrival (τ) at its maximum value is the time delay of arrival (T) for sensors FBG0 and FBGi, denoted as ΔT. 0i ;

[0021] Step 3: Determine the stress wave velocity range of the composite material plate under multiple directions. Based on the time-of-arrival delay and wave velocity range, determine the preliminary range of the impact point; specifically:

[0022] Five impact test points were set at the center and four corners of the composite material plate for impact testing. For each impact test point, nine stress wave velocities in different upward directions were obtained based on the specific time and location of the stress waves received by nine sensors. The maximum value of the five * nine stress wave velocities was taken as v. max The minimum value is taken as v min This allows us to obtain a rough range of stress wave velocities (v). min ,v max );

[0023] Divide the board surface into n×n, n∈[50,80] small square grids with side lengths of... Each grid point is considered a potential impact point; let the coordinates of any grid node M be (X... m ,Y mThe coordinates of the surrounding fiber optic sensor FBGi are (a i ,b i The coordinates of the central fiber optic sensor FBG0 are (0,0); the distances between each FBGi, FBG0 and the grid node M are defined as Ri and R0, respectively, and their calculation formulas are as follows:

[0024]

[0025] The difference between FBG0 and FBGi in the sensor pair with respect to the distance between grid nodes is defined as δ. 0i The calculation formula is as follows:

[0026] R i -R0=δ 0i (6)

[0027] According to the hyperbolic theory of distance, when the distance difference δ 0i When the value is constant, it can be determined that the impact point is located on the hyperbola determined by the central fiber optic sensor FBG0 and the surrounding fiber optic sensors FBGi, and the sensor position is the focus of the hyperbola.

[0028] If the stress wave velocity is consistent and constant at V in all directions on the plate surface, then the time delay ΔT0i of the FBG sensor receiving the impact signal is:

[0029] ΔT 0i =δ 0i / V (7)

[0030] By pairing the eight peripheral fiber optic sensors FBGi with the central fiber optic sensor FBG0, eight pairs of fiber optic FBG sensors can be obtained. If the ΔT0i and V of each sensor pair are known, the distance difference δ can be calculated according to equation (7). 0i ;

[0031] Due to the anisotropic nature of the composite material plate structure, the corresponding wave velocity V is an uncertain quantity, therefore the calculated distance difference δ 0i It is also an uncertain quantity, and its range is (δ 0imin ,δ 0imax );

[0032] Where δ 0imin and δ 0imax The values ​​are respectively:

[0033]

[0034]

[0035] In equation (8) v min ,v maxThe minimum and maximum values ​​of the stress wave velocity measured at the above 5 impact test points are respectively: in equation (9), t0 is the time interval between adjacent sampling points of the FBG sensor;

[0036] Based on the wave velocity V and wave arrival delay ΔT of the impact signal 0i The distance difference δ can be calculated from all of them. 0i The range; since the positions of sensors FBG0 and FBGi are fixed and known, based on the distance difference δ 0i The range within which the impact location can be preliminarily determined is defined as S. 0i ;

[0037] Since there are 8 pairs of fiber optic FBG sensors, the 8 initial impact ranges can be determined as S. 0i ,i∈(1,2,3,...,8);

[0038] Step 4: Set the positioning deviation e, and calculate the confidence matrix of the horizontal and vertical coordinates of the eight sensors with respect to the grid nodes based on e; specifically:

[0039] Since the x and y coordinates of the actual impact location (X,Y) and its nearest grid point must be less than or equal to half the grid side length, half the grid side length is defined as the positioning deviation e. For coordinates (a i ,b i The sensor pair consisting of the four surrounding sensors FBGi and the center sensor FBG0 at coordinates (0,0) measures the position of the sensor at grid node M(X). m ,Y m When the positioning deviation e is fixed, the distance deviations Δδx and Δδy required for this sensor group to generate the positioning deviation e are:

[0040]

[0041] Where Ri and R0 can be obtained from equation (5), and These are fiber optic sensor FBG0 and fiber optic sensor FBGi, respectively, to point (X). m +e,Y m The distance can be obtained from equation (11). and These are fiber optic sensor FBG0 and fiber optic sensor FBGi, respectively, to point (X). m ,Y m The distance of +e) can be obtained by equation (12);

[0042]

[0043]

[0044] Since the positioning deviation e is a fixed value, the larger the distance deviation Δδ, the better the sensor group's response to the distance difference δ. 0i The lower the accuracy requirement, the more reliable the sensor group is in determining the horizontal and vertical coordinates of grid point M. Furthermore, it is found from equation (10) that the distance deviations Δδx and Δδy of the grid nodes are related to the wave velocity V and the wave arrival delay ΔT. 0i It is irrelevant; the position is determined solely by the sensor's position and the coordinates of the grid nodes.

[0045] By performing calculations on all grid points on the board using the eight sets of sensors, according to equations (10), (11), and (12), the distance deviations Δδx and Δδy between the eight sets of sensors and all grid points can be obtained.

[0046] The confidence level K is defined as the distance deviations Δδx and Δδy of all grid nodes relative to different sensor pairs. x K y This yields eight sets of confidence matrices for the horizontal and vertical coordinates of all grid nodes on the board surface.

[0047] Step 5: Weight the grid nodes within the initial range of the impact point to determine its location; specifically:

[0048] For the eight preliminary impact ranges S obtained in step three 0i For each i ∈ (1,2,3,...,8), the grid nodes contained therein are assigned the confidence level K from step four. x K y Substitute the values ​​into the equations and weight them accordingly; as shown in equation (13), if grid point M is located in S... i When the determined impact point range is reached, the weight Q is... xi Q yi For credibility K xi K yi Otherwise, it is 0;

[0049]

[0050] The total weight Q of grid node M x Q y for:

[0051]

[0052] The confidence weight of all grid points on the composite material plate is calculated, and the total weight value Q of the horizontal and vertical coordinates of each grid point is obtained. x Q y The coordinates of the one with the largest weight can be determined as the corresponding coordinates of the impact judgment point, thereby realizing the impact positioning.

[0053] Beneficial effects

[0054] A method for impact location determination of composite material plate structures based on multidimensional wave velocity reliability focusing is proposed. This method identifies the applied load location by measuring the load response signal through a fiber Bragg grating (FBG) sensor network arranged on the plate structure. This invention is applicable to engineering applications such as load identification of four-sided fixed composite material plate structures. Its advantages include: requiring only nine fiber optic FBG sensors to form the sensor network, resulting in simpler wiring and stronger resistance to electromagnetic interference compared to traditional sensing methods. Wavelet transform is used to perform low-frequency denoising on the original impact response signal to filter out irrelevant parts, and generalized cross-correlation is used to obtain the arrival time delay of the FBG sensor response signal. Secondly, considering the anisotropic nature of composite material plates, this invention treats the stress wave velocity generated by the impact as a range quantity, eliminating the need for precise wave velocity measurement. Furthermore, considering the low sampling rate of the fiber optic FBG sensors, the initial impact range is determined by the arrival time delay and the stress wave velocity range. Finally, setting up multiple sensor groups and performing gridded reliability weighting further improves the load location accuracy. Attached Figure Description

[0055] Figure 1 This is a diagram showing the arrangement of a fiber Bragg grating sensor with a composite material plate structure.

[0056] Figure 2 This is a schematic diagram of one-dimensional wave velocity focusing.

[0057] Figure 3 This is a preliminary impact range map determined by FBG1 and FBG0 groups.

[0058] Figure 4 This is a flowchart of the load identification process; Detailed Implementation

[0059] Step 1: Deployment of the fiber optic FBG sensor network on the four sides of the fixed plate surface; specifically:

[0060] A square strain monitoring area OABC is defined by a four-sided fixed composite material plate with side length l. A distributed fiber optic FBG sensor network, consisting of nine fiber optic FBG sensors, is arranged on the plate surface. The fiber optic FBG sensor at the center is numbered FBG0, and the fiber optic FBG sensors at the four surrounding positions are numbered FBGi, i∈(1,2,...8), where i is the number of each of the four surrounding fiber optic sensors. The central fiber optic sensor FBG0 is located at the geometric center of the plate surface, with its position coordinates set to (0,0). The surrounding fiber optic sensors FBGi are arranged at equal intervals around the central sensor, with a radius of l. On the circumference, the central angle of the adjacent four fiber optic sensors is 45°, and their position coordinates are (a i ,b iThe central fiber optic sensor FBG0 and any one of the surrounding fiber optic sensors FBGi form a sensor pair, for a total of eight sensor pairs. The fiber optic FBG sensors are all pasted in a direction parallel to the X direction of the board surface to obtain the strain in a single direction on the board structure surface, thereby forming a fiber optic FBG sensor network on the board surface.

[0061] Step Two: The signal is acquired in real time using a fiber optic FBG sensor. The impact signal undergoes wavelet transform, and the time delay of the impact signal is solved using generalized cross-correlation. Specifically:

[0062] For a single impact, the signal received by the central fiber optic sensor FBG0 is m0, and the impact signals received by the surrounding fiber optic sensors FBGi are m... i The aforementioned signal is a non-stationary random signal with numerous frequency components and patterns. Wavelet transform is used to perform time-window analysis on the impulse signal, filtering out irrelevant frequency information and extracting the time-domain information of the desired dominant frequency signal. The dominant frequency signals obtained after wavelet transform are m′0 and m. i ′; where the wavelet basis functions are as follows:

[0063]

[0064] In the formula, a is the scaling factor, which represents the scaling of the mother wavelet function on the time axis. a>1 indicates expansion, and a<1 indicates contraction. b is the translation factor, which represents the left and right translation of the center position of the mother wavelet function. t is the time variable.

[0065] The formula for the continuous wavelet transform of any square-integrable function f(t) is as follows:

[0066]

[0067] W f (a,b) represents the continuous wavelet transform of the function f(t), R is the real number field, and ψ * Represents the complex conjugate operation; ψ a,b (t) represents the wavelet basis function generated after the mother wavelet function ψ(t) is adjusted by a and b;

[0068] The signals m′0 and m obtained by wavelet transform i The formula for performing a generalized cross-correlation operation with PHAT as the weighting function is as follows:

[0069]

[0070] Where τ is the time required for the stress wave generated by the impact to travel from the impact location to the fiber optic grating sensor; f is the frequency variable; and e is a mathematical constant, which is the base of the natural logarithm function.

[0071] The formula for calculating the time difference of arrival of the stress wave detected by the two sensors is as follows:

[0072]

[0073] Make The time delay of arrival (τ) at its maximum value is the time delay of arrival (T) for sensors FBG0 and FBGi, denoted as ΔT. 0i ;

[0074] Step 3: Determine the stress wave velocity range of the composite material plate under multiple directions. Based on the time-of-arrival delay and wave velocity range, determine the preliminary range of the impact point; specifically:

[0075] Five impact test points were set at the center and four corners of the composite material plate for impact testing. For each impact test point, nine stress wave velocities in different upward directions were obtained based on the specific time and location of the stress waves received by nine sensors. The maximum value of the five * nine stress wave velocities was taken as v. max The minimum value is taken as v min This allows us to obtain a rough range of stress wave velocities (v). min ,v max );

[0076] Divide the board surface into n×n, n∈[50,80] small square grids with side lengths of... Each grid point is considered a potential impact point; let the coordinates of any grid node M be (X... m ,Y m The coordinates of the surrounding fiber optic sensor FBGi are (a i ,b i The coordinates of the central fiber optic sensor FBG0 are (0,0); the distance between each FBGi, FBG0 and the grid node M is defined as R. i And R0, the formula for its calculation is as follows:

[0077]

[0078] The difference between FBG0 and FBGi in the sensor pair with respect to the distance between grid nodes is defined as δ. 0i The calculation formula is as follows:

[0079] R i -R0=δ 0i (6)

[0080] According to the hyperbolic distance theory, when the distance difference δ0i is a constant, it can be determined that the impact point is located on the hyperbola determined by the central fiber optic sensor FBG0 and the surrounding fiber optic sensors FBGi, and the sensor position is the focus of the hyperbola.

[0081] If the stress wave velocity is consistent and constant at V in all directions on the plate surface, then the time delay ΔT0i of the FBG sensor receiving the impact signal is:

[0082] ΔT 0i =δ 0i / V (7)

[0083] By pairing the eight peripheral fiber optic sensors FBGi with the central fiber optic sensor FBG0, eight pairs of fiber optic FBG sensors can be obtained. If the ΔT0i and V of each sensor pair are known, the distance difference δ can be calculated according to equation (7). 0i ;

[0084] Due to the anisotropic nature of the composite material plate structure, the corresponding wave velocity V is an uncertain quantity, therefore the calculated distance difference δ 0i It is also an uncertain quantity, and its range is (δ 0imin ,δ 0imax );

[0085] Where δ 0imin and δ 0imax The values ​​are respectively:

[0086]

[0087]

[0088] In equation (8) v min ,v max The minimum and maximum values ​​of the stress wave velocity measured at the above 5 impact test points are respectively: in equation (9), t0 is the time interval between adjacent sampling points of the FBG sensor;

[0089] Based on the wave velocity V and wave arrival delay ΔT of the impact signal 0i The distance difference δ can be calculated from all of them. 0i The range; since the positions of sensors FBG0 and FBGi are fixed and known, based on the distance difference δ 0i The range within which the impact location can be preliminarily determined is defined as S. 0i ;

[0090] Since there are 8 pairs of fiber optic FBG sensors, the 8 initial impact ranges can be determined as S. 0i ,i∈(1,2,3,...,8);

[0091] Step 4: Set the positioning deviation e, and calculate the confidence matrix of the horizontal and vertical coordinates of the eight sensors with respect to the grid nodes based on e; specifically:

[0092] Since the x and y coordinates of the actual impact location (X,Y) and its nearest grid point must be less than or equal to half the grid side length, half the grid side length is defined as the positioning deviation e. For coordinates (a i ,b i The sensor pair consisting of the four surrounding sensors FBGi and the center sensor FBG0 at coordinates (0,0) measures the position of the sensor at grid node M(X). m ,Y m When the positioning deviation e is fixed, the distance deviations Δδx and Δδy required for this sensor group to generate the positioning deviation e are:

[0093]

[0094] Where R i R0 can be obtained from equation (5). and These are fiber optic sensor FBG0 and fiber optic sensor FBGi, respectively, to point (X). m +e,Y m The distance can be obtained from equation (11). and These are fiber optic sensor FBG0 and fiber optic sensor FBGi, respectively, to point (X). m ,Y m The distance of +e) can be obtained by equation (12);

[0095]

[0096]

[0097] Since the positioning deviation e is a fixed value, the larger the distance deviation Δδ, the better the sensor group's response to the distance difference δ. 0i The lower the accuracy requirement, the more reliable the sensor group is in determining the horizontal and vertical coordinates of grid point M. Furthermore, it is found from equation (10) that the distance deviations Δδx and Δδy of the grid nodes are related to the wave velocity V and the wave arrival delay ΔT. 0i It is irrelevant; the position is determined solely by the sensor's position and the coordinates of the grid nodes.

[0098] By performing calculations on all grid points on the board using the eight sets of sensors, according to equations (10), (11), and (12), the distance deviations Δδx and Δδy between the eight sets of sensors and all grid points can be obtained.

[0099] The confidence level K is defined as the distance deviations Δδx and Δδy of all grid nodes relative to different sensor pairs. x K y This yields eight sets of confidence matrices for the horizontal and vertical coordinates of all grid nodes on the board surface.

[0100] Step 5: Weight the grid nodes within the initial range of the impact point to determine its location; specifically:

[0101] For the eight preliminary impact ranges S obtained in step three 0i For each i ∈ (1,2,3,...,8), the grid nodes contained therein are assigned the confidence level K from step four. x K y Substitute the values ​​into the equations and weight them accordingly; as shown in equation (13), if grid point M is located in S... i When the determined impact point range is reached, the weight Q is... xi Q yi For credibility K xi K yi Otherwise, it is 0;

[0102]

[0103] The total weight Q of grid node M x Q y for:

[0104]

[0105] The confidence weight of all grid points on the composite material plate is calculated, and the total weight value Q of the horizontal and vertical coordinates of each grid point is obtained. x Q y The coordinates of the one with the largest weight can be determined as the corresponding coordinates of the impact judgment point, thereby realizing the impact positioning.

Claims

1. A method for composite panel structure fiber impact location based on multi-dimensional wave velocity credibility weighting, characterized in that, The method comprises the following steps: Step one: arranging a four-side fixed plate surface optical fiber FBG sensor network; specifically, A four-side fixed composite plate with side length l is taken as a square strain monitoring area OABC, and a distributed fiber Bragg grating (FBG) sensor network is arranged on the plate surface, which is composed of 9 FBG sensors. Among them, the center FBG sensor is numbered as FBG0, and the four surrounding FBG sensors are numbered as FBGi, i∈(1, 2,...8), i is the number of each surrounding FBG sensor. The center FBG sensor FBG0 is located at the geometric center of the plate surface, and its position coordinates are set as (0, 0). The surrounding FBG sensors FBGi are arranged in equal intervals on the circumference with the center sensor as the center and the radius of The central angle of adjacent surrounding FBG sensors is 45°, and the position coordinates are (a i ,b i ). Among them, the center FBG sensor FBG0 and any one surrounding FBG sensor FBGi form a sensor pair, and there are eight sensor pairs in total. The above FBG sensors are pasted in the direction parallel to the X direction of the plate surface to obtain the single direction strain of the plate structure surface, thereby forming a plate surface FBG sensor network. Step two: collecting signals in real time by using the optical fiber FBG sensor, and solving the time delay of the impact signal by using wavelet transform and generalized cross-correlation; specifically, For single impact, the signal received by the center fiber sensor FBG0 is m0, and the impact signals received by each of the four surrounding fiber sensors FBGi are m i ; the above signals are non-stationary random signals with many frequency components and patterns; wavelet transform is used for time window analysis of the impact signal, irrelevant frequency information is filtered out, and the time domain information of the required main frequency signal is extracted. The main frequency signal obtained after wavelet transform is m′0 and m i ′; wherein the wavelet base function is as follows: In the formula, a is a stretching factor, representing the stretching of the mother wavelet function on the time axis, a>1 represents stretching, and a<1 represents contraction; b is a translation factor, representing the left and right translation of the center position of the mother wavelet function; t is a time variable; The continuous wavelet transform formula of an arbitrary square integrable function f(t) is as follows: W f (a,b) is the continuous wavelet transform of the function f(t), R is the field of real numbers, ψ * denotes the complex conjugate operation; ψ a,b (t) denotes the wavelet basis function resulting from the adjustment of the mother wavelet function ψ(t) by a, b. The generalized cross-correlation with PHAT as the weighting function is performed on the wavelet-transformed signals m'0and m i The formula is as follows: Where τ is the time required for the stress wave generated by the impact to be transmitted from the impact position to the optical fiber grating sensor; f is a frequency variable; e is a mathematical constant, which is the base of the natural logarithm function; The formula for calculating the time difference of the arrival of stress waves detected by the two sensors is as follows: So that The τ when the maximum value is the wave arrival time delay of the sensor FBG0 and the sensor FBGi, recorded as ΔT 0i ; Step three: determining the stress wave velocity range of the composite material plate in multiple directions, and determining the preliminary range of the impact point according to the time delay and the wave velocity range; specifically, In the center of the composite material plate and the four corners, a total of 5 impact test points are set for impact. For each impact test point, the stress wave velocity in 9 different directions is obtained according to the specific time when the stress wave is received by the 9 sensors and the specific position of each sensor. The maximum value of the 5*9 stress wave velocities is taken as v max , and the minimum value is taken as v min , and then the rough stress wave velocity range (v min , v max ) is obtained. The plate surface is divided into n x n, n ∈ [50, 80] small square grids, and the side length is Each grid point is regarded as a potential impact point; assuming that the coordinates of an arbitrary grid node M are (X m ,Y m ), the coordinates of the four surrounding fiber sensors FBGi are (a i ,b i ), and the coordinates of the central fiber sensor FBG0 are (0, 0); the distances between each FBGi, FBG0 and the grid node M are defined as Ri and R0, and the calculation formula is as follows: The difference in distance between the sensor and the FBG0 and FBGi with respect to the grid nodes is defined as δ 0i The formula for calculating this is: |R i - Ro| = δ 0i (6) According to the hyperbolic theory of distance, when the distance difference δ 0i is a constant value, it can be judged that the impact point is located on the hyperbola determined by the central fiber sensor FBG0 and the four surrounding fiber sensors FBGi, and the sensor position is the focus of the hyperbola. If the stress wave velocity in all directions of the plate surface is consistent and constant as V, the time delay AT of the impact signal received by the central FBG sensor of the sensor is 0i is: ΔT 0i = δ 0i / V (7) Eight four-week fiber sensors FBG1 are respectively paired with the center fiber sensor FBG0, and eight groups of fiber FBG sensor pairs can be obtained. If the ΔT 0i and V are known, the distance difference δ 0i can be obtained according to formula (7). Due to the anisotropic nature of the composite material plate structure, the corresponding wave velocity V is an uncertain quantity, therefore the calculated distance difference δ 0i It is also an uncertain quantity, and its range is (δ 0imin ,δ 0imax ); where δ 0imin and the values of δ 0imax are respectively: v in formula (8) min v in formula (8) max respectively the minimum and maximum values of the stress wave velocity measured at the above five impact test points: t0 in formula (9) is the time interval of adjacent sampling points of the FBG sensor; According to the wave velocity V and the time delay ΔT of the impact signal 0i Both the distance difference δ 0i The range of the impact position can be preliminarily determined according to the distance difference δ 0i The range of the impact position can be preliminarily determined according to the distance difference δ 0i ; Since there are 8 groups of fiber Bragg grating sensor pairs, 8 preliminary impact ranges S 0i i∈(1,2,3,...,8); Step four: setting a positioning deviation e, and calculating the horizontal and vertical coordinate reliability matrix of the eight groups of sensors with respect to the grid nodes according to e; specifically, Since the horizontal and vertical coordinates of the real impact position (X, Y) and its nearest grid point are less than or equal to half of the grid length, half of the grid length is defined as the judgment deviation e, For the four surrounding sensors FBGi with coordinates (a i ,b i ) and the center sensor FBG0 with coordinates (0, 0), the distance deviations Δδx, Δδy required by the sensor group to generate the judgment deviation e are measured respectively under the condition that the judgment deviation e of the grid node M (X m ,Y m ) is fixed. wherein Ri and R0 can be obtained from equation (5), and respectively the distance of the fiber-optic sensor FBG0 and the fiber-optic sensor FBG1 to the point (X m + e, Y m ) can be obtained from equation (11), and respectively the distance of the fiber-optic sensor FBG0 and the fiber-optic sensor FBG1 to the point (X m + e, Y m ) can be obtained from equation (12); Since the position error e is a fixed value, the greater the distance error Δδ, the lower the accuracy requirement of the sensor group for the distance difference δ 0i ; further illustrating that the sensor group has higher reliability for the horizontal and vertical coordinate position determination of the grid point M; meanwhile, it is found from equation (10) that the distance error Δδx, Δδy of the grid node is irrelevant to the wave speed V and the time delay ΔT 0i , and is only determined by the position of the sensor pair and the coordinates of the grid node; According to formula (10), formula (11), and formula (12), the horizontal and vertical coordinate distance deviations Δδx and Δδy of the eight groups of sensors with respect to all the grid points on the plate surface can be obtained; The distance deviation of all grid nodes relative to different sensor pairs is defined as the credibility K x , K y , and eight groups of credibility matrices of the horizontal and vertical coordinates of all grid nodes on the board are obtained. Step five: performing reliability weighting on the grid nodes in the preliminary range of the impact point, and determining the position of the impact point; specifically, For the 8 preliminary impact ranges S obtained in step three 0i , i∈(1, 2, 3, …, 8), the grid nodes contained therein, the credibility K x , K y in step four are substituted and weighted respectively; as shown in formula (13), if the grid point M is in the impact point range S i determined, then the weight Q xi , Q yi is the credibility K xi , K yi ; otherwise, it is 0; The total weight Q of the mesh node M x , Q y is: The total weight value Q of the horizontal and vertical coordinates of each grid point is calculated by weighting all grid points on the surface of the composite material plate x , Q y ; the coordinates of the maximum weight value are determined as the corresponding coordinates of the impact determination point, thereby achieving impact determination.

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