A method for measuring multi-material parameters of a carbon fiber plate structure based on ultrasonic guided waves

Abstract

The application discloses a kind of based on ultrasonic guided wave's carbon fiber plate structure multi-material parameter measurement method, belong to carbon fiber plate structure multi-material parameter measurement technical field, specifically including the propagation of ultrasonic guided wave in CFRP plate structure is analyzed, dispersion curve is solved under multiple propagation angles along fiber direction, and different layer modes of CFRP plate structure are distinguished according to dispersion curve;Analysis of the influence of material parameters of CFRP plate structure on guided wave dispersion effect under different propagation angles, the correlation between guided wave different mode propagation velocity and CFRP plate structure material parameters is established, accordingly, using machine learning algorithm, guided wave different mode propagation velocity is used as input variable, material parameter is used as output variable and is endowed with different weight coefficients, and CFRP plate structure multi-material parameter measurement model is established.The application can ensure the integrity and reusability of CFRP structure, can realize the simultaneous measurement of CFRP plate structure multi-material parameter, test efficiency is high, the requirement to test environment is not high, and operation is simple.

Description

Technical Field

[0001] The invention belongs to the technical field of multi-material parameter measurement of carbon fiber plate structures, and relates to a multi-material parameter measurement method of carbon fiber plate structures based on ultrasonic guided waves. Background Art

[0002] Carbon Fiber Reinforced Polymer (CFRP) has excellent properties such as high strength, high modulus, high temperature resistance, and corrosion resistance. It is widely used in aerospace, wind power, automotive, and civilian products. Material parameters such as density and elastic modulus are important indicators for measuring the mechanical properties of materials and for simulation modeling. CFRP has anisotropic characteristics, and multiple material parameters along different directions can be described by a stiffness matrix. If an in-service CFRP structure is affected by factors such as external loads, ambient temperature, and humidity changes, its actual material parameters will inevitably change, resulting in the material performance no longer meeting the requirements of use and failing to achieve the expected function. Therefore, accurately measuring the material parameters of CFRP structures can be used to monitor the service status of the structure.

[0003] Traditional methods for measuring composite material parameters primarily rely on destructive measurements, such as tensile, compression, and shear tests. These tests involve stretching or applying compressive loads to the composite material to measure its stress-strain curve and calculate parameters such as the material's elastic modulus and yield strength. These destructive measurement methods damage the sample, rendering it unreusable. Furthermore, the entire process is typically time-consuming and costly, limiting the economic and efficient nature of material evaluation. In recent years, a growing body of research has focused on non-destructive testing methods to accurately assess the mechanical properties of composite materials without damaging the material.

[0004] Among the many nondestructive testing methods, guided wave testing technology has gradually become a research hotspot both domestically and internationally due to its advantages such as high sensitivity, repeatability, non-invasiveness, and pollution-free nature. Guided waves have multimodal and dispersive characteristics, which allow the signal to contain rich information, thus possessing the potential to simultaneously measure multiple parameters of CFRP structures. Current ultrasonic guided wave-based material parameter measurements of CFRP plate structures focus on the sensitivity of a particular guided wave mode to a single parameter, making it difficult to measure multiple parameters simultaneously. Furthermore, most methods require the use of heterogeneous media or special environments, and measure material parameters based on the waveform transformation caused by refraction and reflection of sound waves at the interfaces of different media. In actual measurements, ultrasonic waves may experience losses when propagating through the medium, and there are certain limitations on the measurement environment. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to provide a method for measuring multi-material parameters of a carbon fiber plate structure based on ultrasonic guided waves, so as to perform multi-parameter measurement of the CFRP plate structure without the aid of foreign media.

[0006] A method for measuring multi-material parameters of a carbon fiber plate structure based on ultrasonic guided waves comprises the following steps:

[0007] Step 1: Analyze the propagation of ultrasonic guided waves in the CFRP plate structure, solve the dispersion curve at multiple propagation angles along the fiber direction, and distinguish different layup methods of the CFRP plate structure based on the dispersion curve;

[0008] Step 2: Analyze the influence of the material parameters of the CFRP plate structure on the guided wave dispersion effect at different propagation angles, and establish the correlation between the propagation velocity of different guided wave modes and the material parameters of the CFRP plate structure. The material parameters include density, elastic modulus, shear modulus, and Poisson's ratio.

[0009] Step 3: Based on the correlation between guided wave propagation velocity and CFRP plate material parameters, a machine learning algorithm is used to establish a multi-material parameter measurement model for CFRP plate structures, taking the guided wave propagation velocities of different modes as input variables and the material parameters as output variables with different weight coefficients assigned.

[0010] Step 4: Use simulation software to construct a multi-material parameter measurement model for CFRP plate structures. Select a set of excitation signals within the set frequency range for simulation. Establish a series of signal receiving points along the fiber direction, perpendicular to the fiber direction, and at any angle along the fiber direction. According to the simulation results, calculate the modal propagation velocity group through time, angle, and distance. Input the velocity group into the multi-material parameter measurement model of CFRP plate structures to realize the material parameter measurement of CFRP plate structures.

[0011] Furthermore, in step 1 above, dispersion curves of the CFRP plate structure are solved at multiple propagation angles. Different layup methods are distinguished as follows: different layup methods of the CFRP plate structure include unidirectional layup, orthogonal layup, and complex layup. For the three layup methods of the CFRP plate structure, the dispersion curves along the fiber direction, perpendicular to the fiber direction, and at any angle along the fiber direction are solved and analyzed respectively.

[0012] For unidirectional and cross-ply CFRP plate structures, the dispersion curves along and perpendicular to the fiber directions show two guided wave modes in the low-frequency band. For complex-ply CFRP plate structures, the dispersion curves along and perpendicular to the fiber directions show three guided wave modes in the low-frequency band.

[0013] In the dispersion curve of the orthogonal laminated CFRP plate structure at 30° along the fiber direction, the guided wave A1 mode and the S1 mode have an intersection within a certain frequency range; in contrast, in the dispersion curve of the unidirectional laminated CFRP plate structure within the same frequency range, there is no significant intersection between the guided wave A1 mode and the S1 mode in the graph.

[0014] Furthermore, in step 2 above, the method for analyzing the influence of the density, elastic modulus, shear modulus, and Poisson's ratio of the CFRP plate structure on the guided wave dispersion effect at different propagation angles includes:

[0015] The correlation between 9 engineering elastic constants and the propagation characteristics of different modes of guided waves is analyzed. The 9 engineering elastic constants include elastic modulus E1, elastic modulus E2, elastic modulus E3, shear modulus G 12 , shear modulus G 13 , shear modulus G 23 , Poisson's ratio ν 12 , Poisson's ratio ν 13 and Poisson's ratio ν 23 , the specific steps are as follows:

[0016] First, the dispersion curve of the S0 mode is drawn. Using the single variable method, one elastic constant is changed each time, and the other elastic constants remain unchanged. The discussion is carried out in different frequency ranges and different propagation angles. In the 0-800kHz frequency band along the fiber direction at 0°, the elastic modulus E1 and Poisson's ratio ν 12 The change of will significantly affect the propagation speed of the S0 mode. In the same frequency range, the other elastic constants will not cause the change of the propagation speed of the S0 mode. Changing the frequency range, in the 800kHz-4000kHz frequency band, changing the elastic modulus E3 and shear modulus G 13 , the propagation speed of the S0 mode will change significantly; the elastic modulus E2, shear modulus G 12 and shear modulus G 23 , Poisson's ratio ν 13 and Poisson's ratio ν 23 The change of , along the fiber direction 0 ° at basically no effect on the propagation speed of the S0 mode; then change the propagation angle, along the fiber direction 0-90 ° direction, the elastic modulus E1, elastic modulus E2, shear modulus G 12 and Poisson's ratio ν 12 The change will affect the S0 mode propagation speed in the 0-800kHz frequency band; the elastic modulus E3 and shear modulus G in the 800kHz-4000kHz frequency band. 13 and shear modulus G 23 The change of will cause the change of S0 mode propagation speed, Poisson's ratio ν 13 , Poisson's ratio ν 23The change of , at this propagation angle, will basically not affect the propagation speed of the S0 mode; in the 90° direction along the fiber direction, changing the elastic modulus E2 and Poisson's ratio ν 12 , will cause the S0 mode propagation velocity to change in the 0-800kHz frequency band; change the elastic modulus E3 and shear modulus G in the 800kHz-4000kHz frequency band 13 , the propagation speed of S0 mode will also change accordingly; and the elastic modulus E1, shear modulus G 12 , shear modulus G 23 , Poisson's ratio ν 13 and Poisson's ratio ν 23 The change of will not affect the propagation speed of S0 mode at this propagation angle;

[0017] Then, the dispersion curve of the A0 mode is drawn in the same way, and the shear modulus G is changed from 0 to 90 degrees along the fiber direction. 13 , shear modulus G 23 The propagation speed of the A0 mode will change significantly, and the changes of other elastic constants will not affect the propagation speed of the A0 mode. At 0° along the fiber direction, only the elastic modulus G 13 The change of will cause the change of A0 mode propagation velocity; while at 90° along the fiber direction, only the elastic modulus G 23 The change of will cause the change of A0 mode propagation speed;

[0018] Based on the above analysis, the density is changed at different angles along the fiber direction to analyze the relationship between density and the S0 mode and A0 mode. When the elastic constant remains unchanged, the change in density will cause the overall propagation speed of the S0 and A0 modes in the dispersion curve diagram to shift.

[0019] Furthermore, the method for establishing a multi-material parameter measurement model for a CFRP plate structure includes:

[0020] In the 0-800kHz frequency band or the 800kHz-4000kHz frequency band, a certain interval value is selected and the propagation velocity corresponding to different modes of the guided wave is used as the input variable;

[0021] The material parameters of the CFRP plate structure are used as output variables. Different weight coefficients are assigned to different material parameters based on the correlation between different waveguide modes and different material parameters of the CFRP plate structure at different propagation angles. The material parameters that are mainly related to the waveguide mode are assigned larger weight coefficients, while the weight coefficients of the other material parameters are mostly zero or low. The larger and lower weight coefficients here are just a relative comparison number.

[0022] Using a machine learning algorithm, a measurement model for different material parameters is established based on the relationship between different modes of guided waves at different propagation angles and different material parameters of the CFRP plate structure, and then a multi-material parameter measurement model for the CFRP plate structure is obtained through integration.

[0023] 6. The method for measuring multi-material parameters of a carbon fiber plate structure based on ultrasonic guided waves according to claim 1 is characterized in that the material parameter measurement method for verifying the material parameter includes:

[0024] In the CFRP plate structure, a series of ultrasonic guided wave receiving points are arranged along the fiber direction, perpendicular to the fiber direction, and at arbitrary angles along the fiber direction. According to the required material parameters to be measured, a set of ultrasonic guided wave excitation signals are selected within the corresponding frequency range;

[0025] The ultrasonic guided wave received signal is calculated and processed to obtain a set of propagation velocities along the fiber direction, perpendicular to the fiber direction, and at any angle along the fiber direction. Each set of propagation velocities corresponds to a different material parameter. The propagation velocity sets along different fiber directions are input into the multi-material parameter measurement model of the CFRP plate structure.

[0026] According to the feedback results of the model, the same material parameters are averaged and finally the density, elastic modulus E1, elastic modulus E2, elastic modulus E3, shear modulus G are obtained. 12 , shear modulus G 13 , shear modulus G 23 , Poisson's ratio ν 12 , Poisson's ratio ν 13 and Poisson's ratio ν 23 The optimal solution of .

[0027] The beneficial effects of the present invention are as follows: the present invention does not require any destruction of the CFRP plate structure, can ensure the integrity and reusability of the CFRP structure, can realize the simultaneous measurement of multiple material parameters of the CFRP plate structure, has high test efficiency, does not have high requirements on the test environment, is easy to operate, and can be effectively implemented in actual application scenarios. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 There are three types of layup for CFRP laminates;

[0029] Figure 2 is a three-dimensional schematic diagram of the CFRP plate;

[0030] Figure 3 Schematic diagram of the Lamb wave propagation process between CFRP single layers

[0031] Figure 4 The dispersion curves along the fiber direction and perpendicular to the fiber direction of the three ply types of CFRP plate structures are shown;

[0032] Figure 5The dispersion curves of the CFRP plate structure with orthogonal ply and unidirectional ply at a propagation angle of 30° along the fiber direction;

[0033] Figure 6 is the effect of the engineering elastic constant on the S0 wave group velocity at the propagation angle along the fiber direction;

[0034] Figure 7 The effect of engineering elastic constant on S0 wave group velocity at a propagation angle of 30° along the fiber direction;

[0035] Figure 8 The effect of engineering elastic constant on S0 wave group velocity at a propagation angle of 45° along the fiber direction;

[0036] Figure 9 is the effect of the engineering elastic constant on the S0 wave group velocity at the propagation angle perpendicular to the fiber direction;

[0037] Figure 10 is the effect of the engineering elastic constant on the A0 wave group velocity at the propagation angle along the fiber direction;

[0038] Figure 11 The effect of the engineering elastic constant on the A0 wave group velocity at a propagation angle of 30° along the fiber direction;

[0039] Figure 12 The effect of the engineering elastic constant on the A0 wave group velocity at a propagation angle of 45° along the fiber direction;

[0040] Figure 13 is the effect of the engineering elastic constant on the A0 wave group velocity at the propagation angle perpendicular to the fiber direction;

[0041] Figure 14 is the correlation between different modes of guided waves and density;

[0042] Figure 15 Abaqus simulation model of CFRP orthogonal laminated structural plate;

[0043] Figure 16 Simulate the simulation results for the propagation of the excitation signal;

[0044] Figure 17 Calculation of the S0 modal group velocity;

[0045] Figure 18 The graph shows the measurement results of the material parameters E1, E2 and density of the CFRP orthogonal laminated structural plate;

[0046] Figure 19 Flowchart of the multi-material parameter measurement method for carbon fiber plate structure. DETAILED DESCRIPTION

[0047] Example 1: Figures 1 to 19 As shown, a method for measuring multi-material parameters of a carbon fiber plate structure based on ultrasonic guided waves includes the following steps:

[0048] Step 1: Analyze the propagation of ultrasonic guided waves in the laminate. Based on the theoretical basis of CFRP and the theory of Lamb wave propagation in CFRP panels, solve the dispersion curves of different CFRP panel structures at multiple propagation angles; Figure 1 There are three common layup forms for CFRP laminates. Different layup forms of CFRP plate structures include unidirectional layup, orthogonal layup, and complex layup. For the three layup forms of CFRP plate structures, the dispersion curves along the fiber direction, perpendicular to the fiber direction, and at any angle along the fiber direction are solved and analyzed respectively.

[0049] The anisotropy of CFRP stems primarily from the fact that carbon fiber layers are often laid at varying angles in practical applications. This arrangement results in significant differences in the material's physical properties in various directions. To better understand and analyze the properties of CFRP panels, a three-dimensional coordinate system is used to describe them. Figure 2 is a three-dimensional schematic diagram of a CFRP plate, where the z-axis represents the thickness direction of the plate and the x-axis is aligned with the fiber direction of the CFRP plate. The stiffness matrix of the CFRP plate is a 6-by-6 matrix, as shown in Equation (1), which describes the relationship between stress and strain in different directions of the material.

[0050]

[0051] Where C' 11 represents the elastic modulus along the fiber direction (x axis), i.e. E1; C' 12 It represents the Poisson effect related to the fiber direction and the transverse direction (y axis), and is related to the Poisson ratio ν 12 Related to the elastic modulus E1; C' 13 It represents the Poisson effect related to the fiber direction and the thickness direction (z axis), and is related to the Poisson ratio ν 13 Related to the elastic modulus E1; C' 22 Indicates the elastic modulus in the transverse direction (y-axis), namely E2; C' 23 It represents the Poisson effect related to the transverse and thickness directions, and Poisson's ratio ν 23 Related to the elastic modulus E2; C' 33 Indicates the elastic modulus in the thickness direction (z axis), that is, E3; C' 44 Represents the shear modulus between the transverse and thickness directions, i.e. G 23 ; C' 55 Represents the shear modulus between the fiber direction and the thickness direction, that is, G 13 ; C' 66 Represents the shear modulus between the fiber direction and the transverse direction, that is, G 12 .

[0052] In practical engineering applications, each layer of the CFRP plate is considered as a transversely isotropic material, which means that there are only 9 elements in the stiffness coefficient matrix, namely elastic modulus E1, E2, E3, shear modulus G 12 , G 13 , G 23 , Poisson's ratio ν 12 、ν 13 、ν 23 , as shown in formula (2).

[0053]

[0054] During the research process, a global coordinate system is needed to fully understand the physical properties of the material. Using the stress axis formula and Bond transformation, the original stiffness coefficient matrix of the material is converted into a new matrix in the global coordinate system, as shown in Equation (3).

[0055] C ij =A*C i ' j *A T (3)

[0056] Where A is the transformation matrix, as shown in formula (4).

[0057]

[0058] Where θ is the laying angle of the carbon fiber layer.

[0059] According to formula (3), the stiffness matrix C ij The expression is shown in formula (5).

[0060]

[0061] Where C 11 represents the elastic modulus along the x direction in the global coordinate system; C 12 Represents the Poisson effect related terms in the x-direction and the y-direction; C 13 represents the Poisson effect related terms in the x-direction and the z-direction; C 16 represents the coupling term of shear deformation in the x direction and the xy plane; C 22 represents the elastic modulus along the y direction in the global coordinate system; C 23 Represents the Poisson effect related terms in the y and z directions; C 26 represents the coupling term of shear deformation in the y direction and the xy plane; C 33 represents the elastic modulus along the z direction in the global coordinate system; C 36 represents the coupling term of shear deformation in the z direction and the xy plane; C 44 represents the shear modulus in the xz plane; C45 represents the coupling term of shear deformation between xz plane and yz plane; C 55 represents the shear modulus in the yz plane; C 66 represents the shear modulus in the xy plane.

[0062] Due to the anisotropy and multi-layer structure of CFRP plates, the propagation characteristics of Lamb waves become particularly complex. In order to simplify the analysis, each layer of the CFRP plate is regarded as a basic model. Figure 3 Schematic diagram of the Lamb wave propagation process between CFRP single layers. Figure 3 It can be seen that when a Lamb wave first contacts a CFRP plate, not all of its energy enters the plate and propagates. Instead, a portion is reflected back into the original medium, while the remaining energy penetrates the plate surface, enters the interior of the CFRP plate, and continues to propagate. Due to the anisotropic properties of the CFRP plate, the Lamb wave entering the plate is separated into three refracted waves with different directions. Therefore, when a Lamb wave is incident on the CFRP plate interface, it generates three refracted waves and three reflected waves with different directions. Therefore, in the CFRP plate, the expression for the acoustic field particle displacement (u1, u2, u3) is shown in Equation (6).

[0063] (u1,u2,u3)=(1,V,W)exp[iβ(x1+αx3-ωt / β)]U(6)

[0064] Wherein, the amplitude of u1 is U; the ratio of the amplitude of u2 to u1 is V; the ratio of the amplitude of u3 to u1 is W; the wave number is β; the ratio of the wave vector components at x3 to x1 is α; the phase velocity of the Lamb wave along the x1 direction is c; the angular velocity is ω; x1 represents the fiber direction of the carbon fiber plate, and x3 represents the thickness direction of the carbon fiber plate.

[0065] According to the strain-displacement relationship of the material and the generalized Hooke's law, without considering the body force, the propagation mechanism of Lamb waves in CFRP plates can be simplified as shown in Equations (7) and (8).

[0066] σ ij =C ijkl e kl (7)

[0067]

[0068] In the formula, the values ​​of k and l are 1, 2 and 3 respectively; σ ij represents the component of the stress tensor; C ijkl Represents the fourth-order tensor form of the elastic stiffness matrix; e kl represents the component of the strain tensor; u k,l and u l,k represents the components of the displacement gradient tensor;

[0069] Substituting Equations (7) and (8) into Equation (6), we obtain the particle motion equation of the CFRP plate as shown in Equation (9), and the corresponding linear equation system is shown in Equation (10).

[0070]

[0071] Where, the elastic stiffness matrix of the CFRP plate is C ijkl ; The density is ρ; the values ​​of m and n are 1, 2 and 3.

[0072] To ensure that the equation (10) has a non-zero solution, the determinant of its coefficient matrix must be zero, as shown in equation (11).

[0073] |Kmn(α)=0(11)

[0074] After expansion, it is shown in formula (12).

[0075] Aα 6 +Bα 4 +Cα 2 +D=0(12)

[0076] Where A, B, C, and D correspond to the coefficients of the constant term, quadratic term, quartic term, and sextic term, respectively.

[0077] After obtaining the solution of formula (12), the displacement ratio is further calculated using V r and W r It is represented as shown in Equation (13) and Equation (14).

[0078]

[0079] Wherein, r=1, 2, 3, 4, 5 and 6.

[0080] If the influence of nonlinear effects inside the solid is not considered, the displacement and stress components at any point in the plate can be regarded as the result of the linear superposition of six waves, as shown in Equations (15)-(17).

[0081]

[0082] In the formula, the values ​​of i and j are 1, 2 and 3. The matrix equation of stress and particle displacement in the CFRP plate is shown in formula (18).

[0083]

[0084] Er=exp(iα r ,x3)(19)

[0085] Where D1q 、D 2q and D 3q As shown in formula (20).

[0086]

[0087] Where q takes the values ​​of 1, 3, and 5.

[0088] If the upper and lower surfaces of the CFRP plate are not constrained by external stress and the interaction between the plates is transmitted through elastic force, the displacement and stress boundary condition expressions between the Rth layer (where R ranges from 1 to n-1) and the layer above it in the CFRP plate are shown in Equation (21).

[0089]

[0090] By combining the displacement equation and the stress equation, the dispersion equation of the multilayer CFRP plate can be calculated, and the specific form is shown in Equation (22).

[0091] |Hjk 6R×6R =0(22)

[0092] By solving the dispersion equation using mWorks software, we can determine the relationship between the phase velocity dispersion of the guided wave and the frequency and wave number. Through the conversion formula of wave number, group velocity and phase velocity, the frequency-phase velocity and frequency-group velocity dispersion curves are also obtained accordingly. Based on the dispersion diagram drawn by mWorks, the three lay-up methods of CFRP plate structure are analyzed, such as Figure 4 As shown in the dispersion curves of the unidirectional and cross-ply CFRP plate structures along the fiber direction and perpendicular to the fiber direction, there are obviously two guided wave modes in the low frequency range. In the dispersion curves of the complex ply CFRP plate structure along the fiber direction and perpendicular to the fiber direction, there are obviously three guided wave modes in the low frequency range. Figure 5 As shown in the dispersion curve of the orthogonal laminated CFRP plate structure at a propagation angle of 30° along the fiber direction, the guided wave A1 mode and the S1 mode have an intersection in a certain frequency range in the diagram, while in the dispersion curve of the unidirectional laminated CFRP plate structure in the same frequency range, the guided wave A1 mode and the S1 mode have no significant intersection in the diagram.

[0093] Step 2: The dispersion effect of CFRP plate structure is mainly related to density and 9 independent elastic constants (E1, E2, E3, G 12 , G 13 , G 23 、ν 12 、ν 13 、ν 13) is related. Taking the CFRP cross-laminated plate structure as an example, the present invention first analyzes the correlation between 9 independent elastic constants and the guided wave A0 and S0 modes. Using the single variable method, one parameter is changed each time, and the other parameters remain unchanged. The frequency-group velocity diagrams of the A0 and S0 modes are calculated at different propagation angles by mWorks. Figure 6 、 Figure 7 、 Figure 8 、 Figure 9 、 Figure 10 、 Figure 11 、 Figure 12 、 Figure 13 As shown in the figure, it is found through analysis that: in the propagation angle along the fiber direction, the group velocity of the S0 mode in the low frequency band is mainly related to the elastic modulus E1, and the group velocity in the high frequency band is mainly related to the elastic modulus E3 and the shear modulus G 13 The A0 modal group velocity is mainly related to the shear modulus G 13 At the propagation angle perpendicular to the fiber direction, the group velocity of the S0 mode in the low frequency band is mainly related to the elastic modulus E2, and the group velocity in the high frequency band is mainly related to the elastic modulus E3 and the shear modulus G 13 The A0 modal group velocity is mainly related to the shear modulus G 23 The group velocity of the S0 mode at any propagation angle along the fiber direction in the low frequency band is mainly related to the elastic modulus E1, E2 and shear modulus G 12 The group velocity in the high frequency band is mainly related to the elastic modulus E3 and the shear modulus G 13 , G 23 The A0 modal group velocity is mainly related to the shear modulus G 13 , G 23 It can be seen that there is a certain correlation between the 9 independent elastic constants of the CFRP plate structure and the different modes of the guided wave at different angles. According to the dispersion effect of the different modes of the guided wave at different angles, a relationship can be established with the required measured elastic constants. Then the influence of density on the dispersion effect of different modes of the guided wave is analyzed, and the control variable method and mWorks software are also used. Figure 14 As shown in Figure 2, when the elastic constant remains unchanged, the change in density will cause the group velocities A0 and S0 to shift as a whole on the dispersion curve.

[0094] Step three, based on the analysis results, the present invention takes the correlation between the S0 modal group velocity and the CFRP orthogonal laminate structure as an example. Taking 100-800KHz as the frequency range, the S0 group velocity is selected as the input variable, the density and 9 elastic parameters are selected as the output variables, and different weight coefficients are assigned to the material parameters according to the correlation between the CFRP plate structure material parameters and the waveguide propagation velocity at different angles. For the S0 mode, E1, E2 and density are assigned with larger weight coefficients, and the weight coefficients of the remaining material parameters are mostly zero or low, and a database corresponding to the S0 modal group velocity of the CFRP orthogonal laminate structure plate in the propagation directions of 0°, 45°, and 90° is constructed. The random forest algorithm is used to train a multi-material parameter measurement model for the CFRP orthogonal laminate structure plate in the propagation directions of 0°, 45°, and 90°. The weights are assigned according to the accuracy of the model and integrated into the optimal parameter measurement model. The specific weight coefficient assignment method is: the material parameter that causes the waveguide velocity to change has its weight coefficient set to 1, and the material parameter that does not cause the waveguide velocity to change has its weight coefficient set to 0

[0095] Step 4. To verify the accuracy of the measurement method, Abaqus simulation software was used to establish a CFRP orthogonal laminated structural plate model. mWorks was used to generate a set of excitation signals with a frequency range of 100-800 kHz, and a series of signal receiving points were established on the 0°, 45°, and 90° propagation paths. Figure 15 This is the simulation model of the CFRP orthogonal laminated structural plate. Figure 16 The simulation results of the excitation signal propagation are shown in Figure 2. Based on the simulation results, mWorks is used to draw the envelope of the excitation signal and the received signal at different frequencies. The group velocity group of S0 in the low frequency band is obtained by calculating the time, angle and distance, as shown in Figure 2. Figure 17 The calculated group velocity group is input into the optimal parameter measurement model to measure the material parameters E1, E2 and density of the CFRP orthogonal laminated structure plate. The measurement results are shown in Figure 18 shown.

[0096] Through the above description of the embodiments in combination with the accompanying drawings, technical personnel in the relevant field can understand that for the convenience and brevity of description, only the division of the above-mentioned functional modules is used as an example. In actual applications, the required measurement parameters and objects can be adjusted as needed. The proposed invention has a certain degree of versatility.

Claims

1. A method for measuring multi-material parameters of carbon fiber plate structures based on ultrasonic guided waves, characterized in that: The following steps are involved: Step 1: Analysis CFRP The propagation of ultrasonic guided waves in plate structures is solved at multiple propagation angles along the fiber direction, and the dispersion curves are used to distinguish CFRP Different laying methods of plate structure; Step 2: Analyze different propagation angles CFRP The influence of the material parameters of the plate structure on the dispersion effect of the guided wave is established, and the propagation speed of different modes of the guided wave is established. CFRP Correlation of plate structure material parameters, including density, elastic modulus, shear modulus, and Poisson's ratio; Step 3: According to the waveguide propagation speed and CFRP The correlation between the material parameters of the plate structure is established by using a machine learning algorithm, taking the propagation speed of different modes of guided waves as input variables and the material parameters as output variables with different weight coefficients. CFRP Multi-material parameter measurement model for plate structures; Step 4: Use simulation software to build CFRP The multi-material parameter measurement model of the plate structure selects a set of excitation signals within the set frequency range for simulation, and establishes a series of signal receiving points along the fiber direction, perpendicular to the fiber direction, and at any angle along the fiber direction. According to the simulation results, the modal propagation velocity group is calculated by time, angle, and distance, and the velocity group is input into the CFRP Multi-material parameter measurement model of plate structure, realizing CFRP Measurement of plate structure material parameters.

2. The method for measuring multi-material parameters of a carbon fiber plate structure based on ultrasonic guided waves according to claim 1, characterized in that: In step 1, solve at multiple propagation angles CFRP The dispersion curve of the plate structure and the method of distinguishing different laying methods are as follows: CFRP Different layup forms of plate structures include unidirectional layup, orthogonal layup and complex layup. CFRP For plate structures, the dispersion curves along the fiber direction, perpendicular to the fiber direction and at any angle along the fiber direction are analyzed respectively; For unidirectional and cross-ply CFRP In the dispersion curves of the plate structure along the fiber direction and perpendicular to the fiber direction, there are two guided wave modes in the low frequency band; for complex plies CFRP For the plate structure, in the dispersion curves along the fiber direction and perpendicular to the fiber direction, there are three guided wave modes in the low frequency band; Orthogonal ply at 30° along the fiber direction CFRP In the dispersion curve of the plate structure, the guided wave A 1 modal and S 1 Mode has an intersection point within a certain frequency range.

3. The method for measuring multi-material parameters of a carbon fiber plate structure based on ultrasonic guided waves according to claim 1, characterized in that: In step 2, analyze the different propagation angles CFRP Methods for studying the effects of plate structure density, elastic modulus, shear modulus, and Poisson's ratio on guided wave dispersion include: Analyze the correlation between 9 engineering elastic constants and different modal propagation characteristics of guided waves. The 9 engineering elastic constants include elastic modulus E 1. Elastic modulus E 2. Elastic modulus E 3. Shear modulus G 12 , shear modulus G 13 , shear modulus G 23 , Poisson's ratio ν 12 , Poisson's ratio ν 13 and Poisson's ratio ν 23 , the specific steps are as follows: First, draw S The dispersion curve of mode 0 is obtained by using the single variable method. One elastic constant is changed each time, and the other elastic constants remain unchanged. The discussion is carried out in different frequency ranges and different propagation angles. In the 0-800kHz frequency band along the fiber direction at 0°, the elastic modulus is E 1 and Poisson's ratio ν 12 The changes will affect S The propagation velocity of the 0 mode, in the same frequency range, the other elastic constants will not cause S 0. Change of modal propagation velocity; change of frequency range, in the 800kHz-4000kHz frequency band, change of elastic modulus E 3 and shear modulus G 13 , S The propagation speed of the 0 mode will change significantly; the elastic modulus E 2. Shear modulus G 12 and shear modulus G 23 , Poisson's ratio ν 13 and Poisson's ratio ν 23 The change of 0° along the fiber direction will not affect S 0 mode propagation speed; then change the propagation angle, in the direction of 0-90° along the fiber direction, the elastic modulus E 1. Elastic modulus E 2. Shear modulus G 12 and Poisson's ratio ν 12 Changes will affect the 0-800kHz frequency band S 0 modal propagation velocity; elastic modulus in the frequency band of 800kHz-4000kHz E 3. Shear modulus G 13 and shear modulus G 23 The changes will cause S 0 Change in mode propagation velocity, Poisson's ratio ν 13 , Poisson's ratio ν 23 The change of S 0 mode propagation speed; changing the elastic modulus in the 90° direction along the fiber direction E 2 and Poisson's ratio ν 12 , which will cause S 0 Modal propagation velocity changes; changes in elastic modulus in the 800kHz-4000kHz frequency band E 3 and shear modulus G 13 , S The propagation speed of the 0 mode will also change accordingly; and the elastic modulus E 1. Shear modulus G 12 , shear modulus G 23 , Poisson's ratio ν 13 and Poisson's ratio ν 23 The change of S 0 mode propagation speed; Then draw in the same way A Dispersion curve of mode 0, changing the shear modulus at 0-90° along the fiber direction G 13 , shear modulus G 23 The propagation speed of the shear modulus A0 mode will change significantly, while the changes in the other elastic constants will not affect A The propagation velocity of the 0 mode; at 0° along the fiber direction, there is only the elastic modulus G 13 The changes will cause A 0 modal propagation velocity changes; while at 90° along the fiber direction, only the elastic modulus G 23 The changes will cause A 0. Change in mode propagation velocity; Based on the analysis, the density is changed at different angles along the fiber direction, and the density and S 0 modal and A 0 mode correlation; when the elastic constant remains unchanged, the change of density will make S 0 modal and A The propagation velocity of the 0 mode in the dispersion curve diagram is overall shifted.

4. The method for measuring multi-material parameters of a carbon fiber plate structure based on ultrasonic guided waves according to claim 1, characterized in that: Establish CFRP The methods for measuring the multi-material parameter model of plate structures include: In the 0-800kHz frequency band or the 800kHz-4000 frequency band, select a certain interval value and use the propagation speed corresponding to different modes of guided waves as input variables; CFRP The material parameters of the plate structure are used as output variables. Different weight coefficients are assigned to different material parameters based on the correlation between different waveguide modes and different material parameters of the CFRP plate structure at different propagation angles. The weight coefficient assignment method is as follows: the material parameter that causes the guided wave velocity to change is set to 1, and the material parameter that does not cause the guided wave velocity to change is set to 0. Using machine learning algorithms, different modes of guided waves under different propagation angles are CFRP The relationship between different material parameters of the plate structure, the establishment of different material parameter measurement models, and the integration of CFRP Multi-material parameter measurement model for plate structures.

5. The method for measuring multi-material parameters of carbon fiber plate structure based on ultrasonic guided waves according to claim 1, characterized in that: Verification of material parameters Material measurement methods include exist CFRP In the plate structure, a series of ultrasonic guided wave receiving points are arranged along the fiber direction, perpendicular to the fiber direction, and at any angle along the fiber direction. According to the required material parameters to be measured, a set of ultrasonic guided wave excitation signals are selected within the corresponding frequency range; Calculate and process the ultrasonic guided wave receiving signal to obtain the propagation velocity group along the fiber direction, perpendicular to the fiber direction and at any angle along the fiber direction. Each propagation velocity group corresponds to different material parameters. The propagation velocity group is input along different directions of the fiber. CFRP Multi-material parameter measurement model for plate structures; According to the feedback results of the model, the same material parameters are averaged and the density and elastic modulus are finally obtained. E 1. Elastic modulus E 2. Elastic modulus E 3. Shear modulus G 12 , shear modulus G 13 , shear modulus G 23 , Poisson's ratio ν 12 , Poisson's ratio ν 13 and Poisson's ratio ν 23 The optimal solution of .

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