Carbon fiber plate structure multi-material parameter measurement method based on ultrasonic guided waves

Abstract

The invention discloses a carbon fiber plate structure multi-material parameter measurement method based on ultrasonic guided waves, and belongs to the technical field of carbon fiber plate structure multi-material parameter measurement, and the method specifically comprises the steps: analyzing the propagation of the ultrasonic guided waves in a CFRP plate structure, solving a frequency dispersion curve at a plurality of propagation angles along the fiber direction, and calculating the multi-material parameter of the CFRP plate structure; different layering modes of the CFRP plate structure are distinguished according to the frequency dispersion curve; the method comprises the following steps: analyzing the influence of material parameters of a CFRP plate structure on a guided wave frequency dispersion effect at different propagation angles, establishing association between different modal propagation speeds of guided waves and the material parameters of the CFRP plate structure, and accordingly, adopting a machine learning algorithm, taking the different modal propagation speeds of the guided waves as input variables, taking the material parameters as output variables and endowing different weight coefficients to obtain the frequency dispersion effect of the guided waves. And establishing a CFRP plate structure multi-material parameter measurement model. According to the invention, the integrity and reusability of the CFRP structure can be ensured, simultaneous measurement of multiple material parameters of the CFRP plate structure can be realized, the test efficiency is high, the requirement on the test environment is not high, and the operation is simple and convenient.

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 a carbon fiber plate structure based on ultrasonic guided waves. Background Art

[0002] Carbon Fibre 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 industry, automotive industry 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 the stiffness matrix. If the CFRP structure in service is affected by external loads, ambient temperature and humidity changes, its actual material parameters will inevitably change, which will cause the material performance to no longer meet the use requirements and fail to achieve the expected function. Therefore, accurate measurement of the material parameters of the CFRP structure can be used to monitor the service status of the structure.

[0003] Traditional methods for measuring composite material parameters are mainly destructive measurements, such as tensile tests, compression tests, and shear tests. By stretching or applying compressive loads to the composite material, the stress-strain curve is measured to calculate parameters such as the elastic modulus and yield strength of the material. These destructive measurement methods will cause sample damage and cannot be reused, and the entire process usually takes a long time and is costly, limiting the economy and efficiency of material evaluation. In recent years, more and more research has begun to focus on non-destructive testing methods to achieve accurate evaluation of the mechanical properties of composite materials without destroying the material.

[0004] Among many non-destructive testing methods, guided wave testing technology has gradually become a hot topic of research at home and abroad due to its advantages such as high sensitivity, repeatability, non-invasiveness and non-pollution. Guided waves have multi-modal and dispersion characteristics, which make the signal contain rich information, so it has the potential to simultaneously measure multiple parameters of CFRP structures. At present, the material parameter measurement of CFRP plate structures based on ultrasonic guided waves focuses on the sensitivity of a certain guided wave mode to a single parameter, and it is difficult to measure multiple parameters at the same time; and most methods require the use of foreign media or in special environments, according to the waveform conversion when the sound wave is refracted and reflected at the interface of different media, to measure the material parameters. In actual measurement, ultrasonic waves may be lost when propagating in the medium, and there are certain restrictions 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 laying methods of the CFRP plate structure according to 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 modes of guided waves 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: According to the correlation between the propagation velocity of guided waves and the material parameters of the CFRP plate structure, a machine learning algorithm is used to take the propagation velocities of different modes of guided waves as input variables, and the material parameters as output variables and assign different weight coefficients to establish a multi-material parameter measurement model for the CFRP plate structure;

[0010] Step 4: Use simulation software to build a multi-material parameter measurement model for CFRP plate structure, 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, and according to the simulation results, obtain the modal propagation velocity group by time, angle and distance calculation, input the velocity group into the multi-material parameter measurement model of CFRP plate structure, and realize the material parameter measurement of CFRP plate structure.

[0011] Furthermore, in the above step 1, the dispersion curve of the CFRP plate structure is solved at multiple propagation angles, and the method for distinguishing different plying methods is as follows: different plying forms of the CFRP plate structure include unidirectional plying, orthogonal plying and complex plying. For the CFRP plate structures with three plying forms, 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 CFRP plate structures with unidirectional and orthogonal plies, there are two guided wave modes in the dispersion curves along the fiber direction and perpendicular to the fiber direction in the low-frequency band; for CFRP plate structures with complex plies, there are three guided wave modes in the dispersion curves along the fiber direction and perpendicular to the fiber direction 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 in a certain frequency range; in contrast, 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 graph.

[0014] Furthermore, in the above step 2, 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 obviously affect the propagation velocity of S0 mode. In the same frequency range, the other elastic constants will not cause the change of S0 mode propagation velocity. Changing the frequency range, in the frequency band of 800kHz-4000kHz, 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 will basically not affect the propagation speed of S0 mode at 0° along the fiber direction; then change the propagation angle, in the direction of 0-90° along the fiber 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 will not affect the propagation speed of S0 mode at this propagation angle; in the direction of 90° along the fiber direction, the change of elastic modulus E2 and Poisson's ratio ν 12 , which 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; while the elastic modulus E1 and 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 plotted in the same way, changing the shear modulus G at 0-90° along the fiber direction. 13 , shear modulus G 23 The propagation velocity of the A0 mode will change significantly, and the change of other elastic constants will not affect the propagation velocity of the A0 mode. 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, and the relationship between density and S0 mode and A0 mode is analyzed. When the elastic constant remains unchanged, the change of density will cause the overall shift of the propagation speed of S0 and A0 modes in the dispersion curve diagram.

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

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

[0021] The material parameters of the CFRP plate structure are taken as output variables. Different weight coefficients are assigned to different material parameters according to the correlation between different waveguide modes and different material parameters of the CFRP plate structure at different propagation angles. The material parameters mainly related to the waveguide mode are assigned a larger weight coefficient, and 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 parameters 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 any angle along the fiber direction. According to the required material parameters to be measured, a set of ultrasonic guided wave excitation signals is selected within the corresponding frequency range.

[0025] The ultrasonic guided wave receiving signal is calculated and processed to obtain the propagation velocity groups 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 groups 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 require a high 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 three ply types of CFRP plate structures;

[0032] Figure 5The dispersion curves of the orthogonal ply and unidirectional ply of the CFRP plate structure 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] Fig. 9 The influence of the engineering elastic constant on the S0 wave group velocity at the propagation angle perpendicular to the fiber direction;

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

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

[0039] Fig.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] Fig.13 The influence of the engineering elastic constant on the A0 wave group velocity at the propagation angle perpendicular to the fiber direction;

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

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

[0043] Fig.16 Simulate the simulation results for the propagation of excitation signals;

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

[0045] Fig.18 The measurement results of material parameters E1, E2 and density of CFRP orthogonal laminated structural plate;

[0046] Fig.19 Flow chart 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 comprises the following steps:

[0048] Step 1: Analyze the propagation of ultrasonic guided waves in the laminate, and solve the dispersion curves of different CFRP plate structures at multiple propagation angles based on the theoretical basis of CFRP and the theory of Lamb wave propagation in CFRP plates; 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 CFRP plate structures with three layup forms, 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 mainly comes from the fact that the carbon fiber layers are often laid at different angles in practical applications. This laying method leads to significant differences in the physical properties of the material in various directions. In order to better understand and analyze the properties of CFRP plates, a three-dimensional coordinate system is used to describe them. Figure 2 is a three-dimensional schematic diagram of the CFRP plate, where the z-axis represents the thickness direction of the plate and the x-axis is consistent with the fiber direction of the CFRP plate. The stiffness matrix of the CFRP plate is a 6 by 6 matrix, as shown in formula (1), which describes the relationship between stress and strain of the material in different directions.

[0050]

[0051] Where C' 11 Represents the elastic modulus along the fiber direction (x axis), that is, E1; C' 12 It represents the Poisson effect related to the fiber direction and the transverse direction (y axis), and Poisson's 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 Poisson's ratio ν 13 Related to the elastic modulus E1; C' 22 Represents the elastic modulus in the transverse direction (y axis), namely E2; C' 23 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 direction and the thickness direction, that is, 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 regarded as a transversely isotropic material, which means that there are only 9 elements of 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] In 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 transformed into a new matrix in the global coordinate system, as shown in formula (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] In the formula, 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 direction and the z direction; 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 the Lamb wave first contacts the CFRP plate, not all of its energy enters the plate and propagates, but a part of it will be reflected back to the original medium, and the remaining energy will penetrate the plate surface, enter the interior of the CFRP plate and continue to propagate. The Lamb wave entering the plate will be separated into three refracted waves in different directions due to the anisotropic characteristics of the CFRP plate. Therefore, when the Lamb wave is incident on the interface of the CFRP plate, it will generate refracted waves and reflected waves in different directions, three in each direction. Therefore, in the CFRP plate, the expression of 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 in x3 and 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 the CFRP plate 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; 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), the particle motion equation of the CFRP plate is obtained 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] In the formula, A, B, C, and D correspond to the coefficients of the constant term, quadratic term, quartic term, and sixth term, respectively.

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

[0078]

[0079] In the formula, 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] In the formula, the value of q is 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) in the CFRP plate and the layer above it 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. The specific form is shown in Equation (22).

[0091] |Hjk 6R×6R =0(22)

[0092] By solving the dispersion equation using mWorks software, the relationship between the phase velocity dispersion of the guided wave and the frequency and wave number can be determined. Through the conversion formula between wave number and group velocity and phase velocity, the dispersion curves of frequency-phase velocity and frequency-group velocity are also obtained accordingly. According to the dispersion diagram drawn by mWorks, the three laying methods of CFRP plate structure are analyzed, such as Figure 4 As shown in the dispersion curves of the unidirectional and orthogonal laminated 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 laminated 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 the CFRP plate structure is mainly related to the density and 9 independent elastic constants (E1, E2, E3, G 12 , G 13 , G 23 , ν 12 , ν 13 , ν 13). Taking the CFRP orthogonal laminate structure as an example, the present invention first analyzes the correlation between 9 independent elastic constants and the guided wave A0 and S0 modes. The single variable method is used to change one parameter each time, and the other parameters remain unchanged. The frequency-group velocity diagram of the A0 and S0 modes is calculated at different propagation angles by mWorks. Figure 6 , Figure 7 , Figure 8 , Fig. 9 , Fig.10 , Fig.11 , Fig.12 , Fig.13 As shown in Figure 2, it is found through analysis that: in terms of 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 in the low frequency band at any propagation angle along the fiber direction is mainly related to the elastic modulus E1, E2 and the 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 different modes of the guided wave at different angles, a connection 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. Fig.14 As shown in the figure, when the elastic constant remains unchanged, the change in density will cause the A0 and S0 group velocities 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. With a frequency range of 100-800KHz, 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 most of the weight coefficients of the remaining material parameters are 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: for the material parameters that cause the waveguide velocity to change, its weight coefficient is set to 1, and for the material parameters that do not cause the waveguide velocity to change, its weight coefficient is set to 0

[0095] Step 4: To verify the accuracy of the measurement method, the Abaqus simulation software was used to establish a CFRP orthogonal laminated structural plate model, and mWorks was used to generate a set of excitation signals with a frequency range of 100-800Khz, and a series of signal receiving points were established on the 0°, 45°, and 90° propagation paths. Fig.15 This is the simulation model of the CFRP orthogonal laminated structural plate. Fig.16 The simulation results of the propagation of the excitation signal are shown in Figure 2. According to the simulation results, mWorks is used to draw the envelope of the excitation signal and the envelope of 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. Fig.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 Fig.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 simplicity 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, and the proposed invention has a certain degree of versatility.

Claims

1. A method for measuring multi-material parameters of carbon fiber plate structure based on ultrasonic guided waves, characterized in that: The following steps are involved: 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 laying methods of the CFRP plate structure according to the dispersion curve; 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 modes of guided waves and the material parameters of the CFRP plate structure. The material parameters include density, elastic modulus, shear modulus and Poisson's ratio. Step 3: According to the correlation between the propagation velocity of guided waves and the material parameters of the CFRP plate structure, a machine learning algorithm is used to take the propagation velocities of different modes of guided waves as input variables, and the material parameters as output variables and assign different weight coefficients to establish a multi-material parameter measurement model for the CFRP plate structure; Step 4: Use simulation software to build a multi-material parameter measurement model for CFRP plate structure, 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, and according to the simulation results, obtain the modal propagation velocity group by time, angle and distance calculation, input the velocity group into the multi-material parameter measurement model of CFRP plate structure, and realize the material parameter measurement of CFRP plate structure.

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, the dispersion curve of the CFRP plate structure is solved at multiple propagation angles. The method of distinguishing different plying methods is as follows: the different plying forms of the CFRP plate structure include unidirectional plying, orthogonal plying and complex plying. For the CFRP plate structures with three plying forms, 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; For CFRP plate structures with unidirectional and orthogonal plies, there are two guided wave modes in the dispersion curves along the fiber direction and perpendicular to the fiber direction in the low-frequency band; for CFRP plate structures with complex plies, there are three guided wave modes in the dispersion curves along the fiber direction and perpendicular to the fiber direction in the low-frequency band; In the dispersion curve of the orthogonal laminated CFRP plate structure at 30° along the fiber direction, the guided wave A1 mode and S1 mode have an intersection in 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, 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: 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: 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 affect the propagation speed of S0 mode. In the same frequency range, the other elastic constants will not cause the change of S0 mode propagation speed. Changing the frequency range, in the frequency band of 800kHz-4000kHz, changes 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 will basically not affect the propagation speed of S0 mode at 0° along the fiber direction; then change the propagation angle, in the direction of 0-90° along the fiber 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 23 The change of will not affect the propagation speed of S0 mode at this propagation angle; in the direction of 90° along the fiber direction, the change of elastic modulus E2 and Poisson's ratio ν 12 , which 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; while the elastic modulus E1 and 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; Then, the dispersion curve of the A0 mode is plotted in the same way, changing the shear modulus G at 0-90° along the fiber direction. 13 , shear modulus G 23 The propagation velocity of the A0 mode will change significantly, and the change of other elastic constants will not affect the propagation velocity of the A0 mode. 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; Based on the analysis, the density is changed at different angles along the fiber direction, and the correlation between density and S0 mode and A0 mode is analyzed; when the elastic constant remains unchanged, the change in density will cause the overall shift of the propagation speed of S0 and A0 modes in the dispersion curve diagram.

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: The method of establishing a multi-material parameter measurement model for CFRP plate structure includes: In the frequency band of 0-800kHz or 800kHz-4000, a certain interval value is selected, and the propagation velocity corresponding to different waveguide modes is used as the input variable; the material parameters of the CFRP plate structure are used as the output variable, and different weight coefficients are assigned to different material parameters according to the correlation between different waveguide modes and different material parameters of the CFRP plate structure at different propagation angles; the material parameters mainly related to the waveguide mode are assigned a larger weight coefficient, and the weight coefficients of the other material parameters are mostly zero or low; 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.

5. 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: Verification of material parameters Material measurement methods include 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 any angle along the fiber direction. According to the required material parameters to be measured, a set of ultrasonic guided wave excitation signals is selected within the corresponding frequency range. The ultrasonic guided wave receiving signal is calculated and processed to obtain the propagation velocity groups 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 groups along different fiber directions are input into the multi-material parameter measurement model of the CFRP plate structure. 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 .

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