Method and device for measuring defects of plate-shaped specimens based on Lamb wave dispersion

Abstract

The present invention discloses a method and device for measuring defects of plate-like specimens based on Lamb wave dispersion, including: testing the plate-like specimen to obtain material parameters and basic equations of the plate-like specimen; using the state space method to establish a propagation model of Lamb waves on the plate-like specimen; obtaining the control equation of Lamb wave propagation through generalized displacement and stress solutions; obtaining the solution of the control equation according to the matrix index, and obtaining the dispersion relationship and modal vibration shape of Lamb wave propagation through the global transfer matrix method; using the obtained material parameters, dispersion relationship and modal vibration shape of the plate-like specimen, and establishing a finite element model for plate-like specimen detection according to Snell's law; calculating the vertical displacement of the signal according to the pre-placed monitoring point on the top surface of the plate-like specimen, thereby obtaining the position of the crack. The theoretical and numerical models of the present invention have the advantages of non-destructiveness, real-time monitoring, high sensitivity, applicability to complex structures and multi-modality, and provide a powerful method for structural analysis and evaluation.

Description

Technical Field

[0001] The invention belongs to the technical field of nondestructive testing, and in particular relates to a method for measuring defects of a plate sample based on Lamb wave dispersion. Background Art

[0002] With the acceleration of industrial modernization, non-destructive testing technology uses ultrasonic, magnetic powder, X-ray, eddy current and other technical means to detect hidden defects in structures with advantages such as non-destructive, safe and widely applicable, providing strong support for the safety, stability, reliability and durability of products and facilities in the fields of aerospace, automobile, construction, nuclear energy, etc. However, when using instruments to detect defects such as cracks, corrosion, holes, pores, fatigue damage, etc. in materials and structures, there are problems such as high equipment cost, technical specificity, sensitivity to surface conditions, experienced operators, and not applicable to all materials. Therefore, it is necessary to carry out theoretical and numerical research on non-destructive testing to reduce errors and difficulties in actual detection.

[0003] Ultrasonic nondestructive testing is an important indicator for the safety detection and evaluation of materials and structures. It not only directly reflects the stress state, thickness, and defects of materials and structures, but also can determine the safety of the use of structures, bearing capacity, and even the reliability life of structures. Lamb wave is the most commonly used waveguide form in ultrasonic nondestructive testing, and Lamb wave is an important basis for selecting wave modes. The principle of structural defect detection based on Lamb wave propagation theory is that when Lamb waves propagate in the structure, they will be reflected and transmitted at locations with obvious wave impedance in the medium (ends, defects, damage, etc.), and the damage in the materials and structures will be identified based on the changes in parameters such as the wave velocity and the time and phase of the Lamb wave arriving at the monitoring point. However, previous theoretical and numerical studies on structural damage identification based on Lamb wave propagation have been unable to overcome difficulties such as the anisotropy of materials, the complexity of wave mode recognition, the multi-physics coupling characteristics of structures, and the nonlinear effects under high-frequency amplitudes. Therefore, there is an urgent need for a theoretical and numerical model for structural defect detection based on Lamb wave propagation to solve the problems of dispersion relation of Lamb wave propagation in structures, numerical instability of modal parameters, and low detection accuracy of defect locations in existing models and methods. Summary of the invention

[0004] The purpose of the present invention is to provide an analytical method and a finite element model for measuring plate-shaped specimens based on Lamb wave dispersion, so as to solve the problems of numerical instability of the dispersion relation and modal parameters of Lamb wave propagation and the low detection accuracy of defect positions in existing numerical methods.

[0005] In order to achieve the above object, in the first aspect, the present invention adopts the following technical solution:

[0006] The method for measuring defects of plate specimens based on Lamb wave dispersion includes:

[0007] Step S1: testing the plate-shaped specimen to obtain material parameters and basic equations of the plate-shaped specimen;

[0008] Step S2: Based on material parameters and basic equations, a state space method is used to establish a propagation model of Lamb waves on a plate-like specimen;

[0009] Step S3: Based on the propagation model, the governing equations of Lamb wave propagation are obtained by generalized displacement and stress solutions;

[0010] Step S4: Obtain the solution of the control equation according to the matrix index, and obtain the dispersion relation and mode vibration shape of Lamb wave propagation through the global transfer matrix method;

[0011] Step S5: using the acquired material parameters, dispersion relation and mode vibration shape of the plate-shaped specimen and according to Snell's law, a finite element model for plate-shaped specimen detection is established;

[0012] Step S6: Calculate the vertical displacement of the signal according to the pre-placed monitoring points on the top surface of the plate-shaped specimen, so as to obtain the position of the crack.

[0013] Preferably, in step S1, the material parameters of the plate-like sample are tested and analyzed to obtain the density, elastic modulus and Poisson's ratio of the plate-like sample material, thereby deriving the basic equation of the plate-like sample material, which includes a constitutive equation, a geometric equation and a dynamic equation.

[0014] Preferably, in step S2, the state space method is used to process the basic equation of the plate-like sample material to establish a propagation model of Lamb waves in the plate-like sample, and its state equation is:

[0015]

[0016] Where: χ(x,z,t) is the state variable; M is the coefficient matrix.

[0017] Preferably, in step S3, the Lamb wave propagates in the plate-shaped sample along the x direction, and the wave behavior in the y direction is not considered, and the generalized solution of its state vector is:

[0018]

[0019] Where i is an imaginary number; k is the wave number in the x direction; ω is the angular frequency. The generalized solution transforms equation (1) into the governing equation in ordinary differential form, which is:

[0020]

[0021] Preferably, in step S4, equation (3) is solved by a matrix exponential function, and the dispersion relation of Lamb waves in the plate-like specimen is obtained by using a global transfer matrix method in combination with the interlayer continuity boundary condition, which is in the form of:

[0022] det[T 21 ]=0 (4)

[0023] Where T 21 for The dispersion relation includes the phase velocity and wave number. The vibration mode values ​​under different wave modes are obtained using equation (4).

[0024] Preferably, in step S5, the critical angle of the wave transmitted from the excitation region to the plate-shaped sample is calculated by using the phase velocity values ​​of the symmetric and antisymmetric wave modes in combination with Snell's law.

[0025]

[0026] Where: c p is the velocity of the incident wave in the wedge; c Lamb is the velocity of the refracted shear wave in the plate specimen; α is the incident angle of the incident wave in the wedge; β is the refraction angle of the refracted shear wave in the plate specimen. Based on the Lamb wave nondestructive testing device in engineering, a finite element model for plate specimen testing is established.

[0027] Preferably, in step S6, a time-domain explicit multi-physics interface is used to simulate the propagation of elastic waves in an elastic medium, and a finite element method and an explicit time integration method are used to solve the wave equation of the finite element model. When a crack exists in the plate-like specimen, the elastic wave hits the crack at a right angle, and a part of the wave will further propagate along the plate-like specimen, and the other part will be reflected back to the wedge, and the transmission and reflection signals are recorded at four preset monitoring points on the top surface of the plate-like specimen at equal distances before and after the crack.

[0028] In a second aspect, the present invention provides a device for measuring defects of a plate-shaped specimen based on Lamb wave dispersion, comprising:

[0029] A parameter acquisition module is used to test the plate-shaped specimen and obtain the material parameters and basic equations of the plate-shaped specimen;

[0030] Model building module, which is used to establish the propagation model of Lamb waves on plate-like specimens using the state space method based on material parameters and basic equations;

[0031] The equation acquisition module is used to obtain the governing equations of Lamb wave propagation through generalized displacement and stress solutions based on the propagation model;

[0032] The relationship acquisition module is used to obtain the solution of the control equation according to the matrix index and obtain the dispersion relation and mode vibration shape of Lamb wave propagation through the global transfer matrix method;

[0033] A model detection module is used to establish a finite element model for plate sample detection based on Snell's law using the acquired material parameters, dispersion relations and mode vibration shapes of the plate sample;

[0034] The position acquisition module is used to calculate the vertical displacement of the signal according to the pre-placed monitoring points on the top surface of the plate-shaped specimen, so as to obtain the position of the crack.

[0035] Preferably, the parameter acquisition module is specifically used to test and analyze the material parameters of the plate-like specimen to obtain the density, elastic modulus and Poisson's ratio of the plate-like specimen material, thereby deriving the basic equation of the plate-like specimen material, which includes the constitutive equation, geometric equation and dynamic equation.

[0036] Preferably, the model building module is specifically used to process the basic equation of the plate-like sample material using the state space method to establish a propagation model of Lamb waves in the plate-like sample, and its state equation is:

[0037]

[0038] Where: χ(x,z,t) is the state variable; M is the coefficient matrix.

[0039] Beneficial effects of the present invention:

[0040] Compared with the prior art, the technical solution provided by the present invention has the following beneficial effects: the Lamb wave propagation model established by the state space method has the advantages of simple and intuitive analysis process, convenient program compilation and easy standardization; the dispersion relationship and modal vibration shape obtained by the matrix index and global transfer matrix method have the characteristics of high precision and fast convergence, and can be widely used in plate-like specimens of metal materials, non-metallic materials, composite materials, elastic media and porous media; the finite element model for plate-like specimen detection established in combination with theoretical results has a simple detection process for defects in plate-like specimens and a clear test method, and can accurately measure the position of defects in plate-like specimens and the modal diagram during wave propagation; the established method and model can accurately capture the dynamic solution of Lamb waves propagating in piezoelectric, piezomagnetic, temperature field and other multi-field coupled materials and structures.

[0041] The features, advantages and technical effects of exemplary embodiments of the present invention are described below through drawings and examples. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] Figure 1 The present invention is a flow chart of a method for measuring defects of a plate-shaped specimen based on Lamb wave dispersion.

[0043] Figure 2 The present invention is a flow chart for solving the dispersion relation of Lamb waves propagating in a plate-like sample.

[0044] Figure 3 This is a dispersion relationship diagram of the Lamb wave propagating in a plate-like sample according to the present invention.

[0045] Figure 4 It is the modal vibration shape diagram under fixed wave number of the present invention.

[0046] Figure 5 Figure 2 is a diagram of wave refraction at the wedge / test sample boundary of the present invention.

[0047] Figure 6 This is the finite element model of Lamb wave nondestructive testing of the present invention.

[0048] Figure 7 It is a cross-sectional view of a mode propagating at a fixed frequency and symmetrical with respect to the sagittal plane according to the present invention.

[0049] Figure 8 The vertical displacement of the monitoring point before the defect (left) and after the defect (right) of the present invention. DETAILED DESCRIPTION

[0050] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments in the present invention, all other embodiments obtained by ordinary technicians in the field without making creative work are within the scope of protection of the present invention. In the description of this specification, the description of the reference terms "one embodiment", "some embodiments", "examples", "specific examples", or "some examples" means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representation of the above terms does not necessarily target the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any one or more embodiments or examples in a suitable manner. In addition, in the absence of mutual contradiction, those skilled in the art can combine and combine the different embodiments or examples described in this specification and the features of different embodiments or examples.

[0051] In order to solve the problems in the prior art, the present invention provides a method for measuring defects in plate specimens based on Lamb wave dispersion, so as to solve the problems of dispersion relation of Lamb waves propagating in structures, numerical instability of modal parameters, and low detection accuracy of defect locations in existing models and methods.

[0052] It should be noted that the method for measuring defects of plate-shaped specimens based on Lamb wave dispersion provided in the embodiment of the present invention can be applied to electronic devices. In practical applications, the electronic device can be: a smart phone, a tablet computer, a laptop computer and other devices, which is all reasonable.

[0053] The following is combined with Figure 1-8 The present invention is further described in detail, but is not intended to limit the present invention.

[0054] The method for measuring defects of plate specimens based on Lamb wave dispersion includes:

[0055] Step S1: testing the plate-shaped specimen to obtain material parameters and basic equations of the plate-shaped specimen;

[0056] Step S2: Based on material parameters and basic equations, a state space method is used to establish a propagation model of Lamb waves on a plate-like specimen;

[0057] Step S3: Based on the propagation model, the governing equations of Lamb wave propagation are obtained by generalized displacement and stress solutions;

[0058] Step S4: Obtain the solution of the control equation according to the matrix index, and obtain the dispersion relation and mode vibration shape of Lamb wave propagation through the global transfer matrix method;

[0059] Step S5: using the acquired material parameters, dispersion relation and mode vibration shape of the plate-shaped specimen and according to Snell's law, a finite element model for plate-shaped specimen detection is established;

[0060] Step S6: Calculate the vertical displacement of the signal according to the pre-placed monitoring points on the top surface of the plate-shaped specimen, so as to obtain the position of the crack.

[0061] In this embodiment, the Lamb wave propagation model established by the state space method has the advantages of simple and intuitive analysis process, convenient program compilation and easy standardization; the dispersion curves and modal vibration shapes obtained by the matrix index and global transfer matrix method have the characteristics of high precision and fast convergence, and can be widely used in plate specimens of metal materials, non-metallic materials, composite materials, elastic media and porous media; the finite element model for plate specimen detection established in combination with theoretical results has a simple detection process for defects in plate specimens and a clear test method, and can accurately measure the location of defects in plate specimens and the modal diagram during wave propagation; the established method and model can accurately capture the dynamic solution of Lamb waves propagating in piezoelectric, piezomagnetic, temperature field and other multi-field coupled materials and structures.

[0062] It is understandable that after testing and analyzing the material parameters of the plate-like specimen, different parameters can be obtained, thereby deriving the constitutive equation, geometric equation and dynamic equation of the material. For example, the density, elastic modulus, Poisson's ratio, etc. of the material can be obtained. For example, the Young's modulus, Poisson's ratio and density of the plate-like specimen can be 202 GPa, 0.3 and 7800 kg / m respectively. 3 .

[0063] Exemplarily, in step S2, the state space method is used to process the basic equation of the material to establish a propagation model of Lamb waves in a plate-shaped specimen, and its state equation is:

[0064]

[0065] Where: χ(x,z,t) is the state variable; M is the coefficient matrix.

[0066] For example, in step S2, the state space method is used to establish the propagation model of Lamb waves in the plate-shaped specimen. The state equation in the example is:

[0067]

[0068] In step S3, Lamb waves propagate in the plate-like specimen along the x direction, and the wave behavior in the y direction is not considered. In this example, the generalized solution of the state vector is:

[0069]

[0070] Specifically, it can be:

[0071]

[0072] Where i is an imaginary number; k is the wave number in the x direction; ω is the angular frequency. The generalized solution transforms equation (11) into the governing equation in ordinary differential form, which is:

[0073]

[0074] In step S4, equation (3) is solved by matrix exponential function, and the dispersion relation of Lamb wave in the plate specimen is obtained by global transfer matrix method in combination with interlayer continuity boundary conditions.

[0075] det[T 21 ]=0(4)

[0076] Where T 21 for The dispersion relation includes phase velocity and wave number, where the dispersion relation is as follows: Figure 3 As shown. Using equation (4), the normalized displacement and stress vibration mode diagrams under fixed wave number are obtained, as shown in Figure 4 shown.

[0077] In one implementation, in step S5, the critical angle of the wave transmitted from the excitation region to the sample is calculated by using the phase velocity values ​​of the symmetric and anti-wave modes in combination with Snell's law.

[0078]

[0079] Where: c p is the velocity of the incident wave in the wedge; c Lamb is the velocity of the refracted shear wave in the sample; α is the incident angle of the incident wave in the wedge; β is the refraction angle of the refracted shear wave in the plate sample. Based on the Lamb wave nondestructive testing device in engineering, a finite element model for sample testing is established.

[0080] The content of step S5 is further explained in combination with specific numerical values. For example, in step S5, the wave number and phase velocity curve in the theoretical model, the phase velocity values ​​of the symmetric and anti-wave modes are used to estimate the velocity v of the A0 mode at the center frequency f0 = 200 kHz of the source signal. Lamb =2300m / s. The finite element model is established in combination with Snell's law, such as Figure 5 As shown. The critical angle of the wave transmitted from the excitation area to the plate sample is:

[0081]

[0082] The velocity c of the incident wave in the wedge in the example p =2080m / s; incident angle α=65°; refraction angle β=90°; since the incident angle of the selected wedge is greater than the critical angle, the wave emitted through the wedge will be refracted into the desired mode in the plate-mounted sample.

[0083] In one implementation, in step S6, a time-domain explicit multiphysics interface is used to simulate the propagation of elastic waves in an elastic medium, and the wave equation of the model is solved using a finite element method and an explicit time integration method. When a crack exists in a plate-like specimen, the elastic wave hits the crack at a right angle, and part of the wave propagates further along the plate, while part of the wave is reflected back to the wedge, and the transmission and reflection signals are recorded at four monitoring points on the top surface of the plate at equal distances before and after the crack.

[0084] As an example, assume that there is a crack in the specimen with a size of half the thickness and width of the plate. The crack is oriented so that the guided wave hits it at right angles, part of the wave propagates further along the plate and the other part is reflected back to the wedge. The transmitted and reflected signals are recorded at four listening points located on the top surface of the plate at equal distances before and after the crack. The profile of the mode of Lamb wave propagation and the vertical displacement of the signal calculated by the placed listening points are shown in Figure 7 and Figure 8 shown.

[0085] With respect to the above method embodiment, the present application embodiment provides a device for measuring defects of a plate-shaped specimen based on Lamb wave dispersion, and the device may include:

[0086] A parameter acquisition module is used to test the plate-shaped specimen and obtain the material parameters and basic equations of the plate-shaped specimen;

[0087] Model building module, which is used to establish the propagation model of Lamb waves on plate-like specimens using the state space method based on material parameters and basic equations;

[0088] The equation acquisition module is used to obtain the governing equations of Lamb wave propagation through generalized displacement and stress solutions based on the propagation model;

[0089] The relationship acquisition module is used to obtain the solution of the control equation according to the matrix index and obtain the dispersion relation and mode vibration shape of Lamb wave propagation through the global transfer matrix method;

[0090] A model detection module is used to establish a finite element model for plate sample detection based on Snell's law using the acquired material parameters, dispersion relations and mode vibration shapes of the plate sample;

[0091] The position acquisition module is used to calculate the vertical displacement of the signal according to the pre-placed monitoring points on the top surface of the plate-shaped specimen, so as to obtain the position of the crack.

[0092] In this embodiment, the Lamb wave propagation model established by the state space method has the advantages of simple and intuitive analysis process, convenient program compilation and easy standardization; the dispersion relationship and modal vibration shape obtained by the matrix index and global transfer matrix method have the characteristics of high precision and fast convergence, and can be widely used in plate specimens of metal materials, non-metallic materials, composite materials, elastic media and porous media; the finite element model for plate specimen detection established in combination with theoretical results has a simple detection process for defects in plate specimens and a clear test method, and can accurately measure the location of defects in plate specimens and the modal diagram during wave propagation; the established method and model can accurately capture the dynamic solution of Lamb waves propagating in piezoelectric, piezomagnetic, temperature field and other multi-field coupled materials and structures.

[0093] Optionally, the parameter acquisition module is specifically used to test and analyze the material parameters of the plate-like specimen to obtain the density, elastic modulus, and Poisson's ratio of the plate-like specimen material, thereby deriving the basic equations of the plate-like specimen material, which include constitutive equations, geometric equations, and dynamic equations.

[0094] Preferably, the model building module is specifically used to process the basic equation of the plate-like sample material using the state space method to establish a propagation model of Lamb waves in the plate-like sample, and its state equation is:

[0095]

[0096] Where: χ(x,z,t) is the state variable; M is the coefficient matrix.

[0097] Alternatively, the Lamb wave propagates along the x-direction in the plate-like specimen, ignoring the wave behavior in the y-direction, and its state vector generalized solution is:

[0098]

[0099] Where i is an imaginary number; k is the wave number in the x direction; ω is the angular frequency. The generalized solution transforms equation (1) into the governing equation in ordinary differential form, which is:

[0100]

[0101] Optionally, the relationship acquisition module is specifically used to solve equation (3) through a matrix exponential function, and in combination with the interlayer continuity boundary condition, use a global transfer matrix method to obtain the dispersion relationship of Lamb waves in the plate-like specimen, which is in the form of:

[0102] det[T 21 ]=0 (4)

[0103] Where T 21 for The dispersion relation includes the phase velocity and wave number. The vibration mode values ​​under different wave modes are obtained using equation (4).

[0104] Optionally, the model detection module is specifically used to calculate the critical angle of the wave transmitted from the excitation region to the plate-shaped sample by using the phase velocity values ​​of the symmetric and antisymmetric wave modes in combination with Snell's law.

[0105]

[0106] Where: c p is the velocity of the incident wave in the wedge; c Lamb is the velocity of the refracted shear wave in the plate specimen; α is the incident angle of the incident wave in the wedge; β is the refraction angle of the refracted shear wave in the plate specimen. Based on the Lamb wave nondestructive testing device in engineering, a finite element model for plate specimen testing is established.

[0107] Optionally, the position acquisition module is specifically used to simulate the propagation of elastic waves in elastic media using a time-domain explicit multi-physics field interface, and to solve the wave equation of the finite element model using a finite element method and an explicit time integration method. When there is a crack in the plate specimen, the elastic wave hits the crack at a right angle, and part of the wave will further propagate along the plate specimen, while the other part will be reflected back to the wedge, and the transmitted and reflected signals are recorded at four preset monitoring points on the top surface of the plate specimen at equal distances before and after the crack.

[0108] The embodiment of the present application also provides an electronic device, including a processor, a communication interface, a memory and a communication bus, wherein the processor, the communication interface and the memory communicate with each other through the communication bus.

[0109] Memory, used to store computer programs;

[0110] The processor is used to implement the method for measuring defects of a plate-shaped specimen based on Lamb wave dispersion provided in an embodiment of the present application when executing the program stored in the memory.

[0111] The communication bus mentioned in the above terminal can be a Peripheral Component Interconnect (PCI) bus or an Extended Industry Standard Architecture (EISA) bus, etc. The communication bus can be divided into an address bus, a data bus, a control bus, etc. For ease of representation, only one thick line is used in the figure, but it does not mean that there is only one bus or one type of bus.

[0112] The communication interface is used for communication between the above terminal and other devices.

[0113] The memory may include a random access memory (RAM) or a non-volatile memory, such as at least one disk memory. Optionally, the memory may also be at least one storage device located away from the aforementioned processor.

[0114] The above-mentioned processor can be a general-purpose processor, including a central processing unit (CPU), a network processor (NP), etc.; it can also be a digital signal processor (DSP), an application specific integrated circuit (ASIC), a field programmable gate array (FPGA) or other programmable logic devices, discrete gate or transistor logic devices, discrete hardware components.

[0115] In another embodiment provided in the present application, a computer-readable storage medium is also provided, wherein a computer program is stored in the computer-readable storage medium, and when the computer program is executed by a processor, the method for measuring defects of a plate-shaped specimen based on Lamb wave dispersion as described in any of the above embodiments is implemented.

[0116] In another embodiment provided in the present application, a computer program product including instructions is also provided, which, when executed on a computer, enables the computer to execute the method for measuring defects of a plate-shaped specimen based on Lamb wave dispersion as described in any of the above embodiments.

[0117] In the above embodiments, it can be implemented in whole or in part by software, hardware, firmware or any combination thereof. When implemented using software, it can be implemented in whole or in part in the form of a computer program product. The computer program product includes one or more computer instructions. When the computer program instructions are loaded and executed on a computer, the process or function described in the embodiment of the present application is generated in whole or in part. The computer may be a general-purpose computer, a special-purpose computer, a computer network, or other programmable device. The computer instructions may be stored in a computer-readable storage medium, or transmitted from one computer-readable storage medium to another computer-readable storage medium, for example, the computer instructions may be transmitted from a website site, computer, server or data center by wired (e.g., coaxial cable, optical fiber, digital subscriber line (DSL)) or wireless (e.g., infrared, wireless, microwave, etc.) mode to another website site, computer, server or data center. The computer-readable storage medium may be any available medium that a computer can access or a data storage device such as a server or data center that includes one or more available media integrated. The available medium may be a magnetic medium, (e.g., a floppy disk, a hard disk, a tape), an optical medium (e.g., a DVD), or a semiconductor medium (e.g., a solid-state drive Solid State Disk (SSD)), etc.

[0118] It should be noted that, in this article, relational terms such as first and second, etc. are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Moreover, the terms "include", "comprise" or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device. In the absence of further restrictions, the elements defined by the sentence "comprise a ..." do not exclude the existence of other identical elements in the process, method, article or device including the elements.

[0119] Each embodiment in this specification is described in a related manner, and the same or similar parts between the embodiments can be referred to each other, and each embodiment focuses on the differences from other embodiments. In particular, for the device embodiment, since it is basically similar to the method embodiment, the description is relatively simple, and the relevant parts can be referred to the partial description of the method embodiment.

[0120] The above description is only a preferred embodiment of the present application and is not intended to limit the protection scope of the present application. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application are included in the protection scope of the present application.

Claims

1. A method for measuring defects of plate-shaped specimens based on Lamb wave dispersion, characterized in that: include: Step S1: testing the plate-shaped specimen to obtain material parameters and basic equations of the plate-shaped specimen; Step S2: Based on material parameters and basic equations, a state space method is used to establish a propagation model of Lamb waves on a plate-like specimen; Step S3: Based on the propagation model, the governing equations of Lamb wave propagation are obtained by generalized displacement and stress solutions; Step S4: Obtain the solution of the control equation according to the matrix index, and obtain the dispersion relation and mode vibration shape of Lamb wave propagation through the global transfer matrix method; Step S5: using the acquired material parameters, dispersion relation and mode vibration shape of the plate-shaped specimen and according to Snell's law, a finite element model for plate-shaped specimen detection is established; Step S6: Calculate the vertical displacement of the signal according to the pre-placed monitoring points on the top surface of the plate-shaped specimen, thereby obtaining the position of the crack; In the step S1, the material parameters of the plate-like sample are tested and analyzed to obtain the density, elastic modulus, and Poisson's ratio of the plate-like sample material, thereby deriving the basic equation of the plate-like sample material, which includes a constitutive equation, a geometric equation, and a dynamic equation; In step S2, the state space method is used to process the basic equation of the plate-like sample material, and a propagation model of Lamb waves in the plate-like sample is established, and its state equation is: Where: χ(x,z,t) is the state variable; M is the coefficient matrix; In step S3, Lamb waves propagate in the plate-like sample along the x direction, and the wave behavior in the y direction is not considered. The generalized solution of the state vector is: Where i is an imaginary number; k is the wave number in the x direction; ω is the angular frequency. The generalized solution transforms equation (1) into the governing equation in ordinary differential form, which is: In step S4, equation (3) is solved by matrix exponential function, and the dispersion relation of Lamb wave in the plate-like specimen is obtained by global transfer matrix method in combination with interlayer continuity boundary conditions, which is in the form of: it[T 21 ]=0 (4) Where T 21 for The dispersion relation includes phase velocity and wave number. The vibration mode values ​​under different wave modes are obtained using equation (4). In step S5, the critical angle of the wave transmitted from the excitation region to the plate-shaped sample is calculated by using the phase velocity values ​​of the symmetric and antisymmetric wave modes in combination with Snell's law. Where: c p is the velocity of the incident wave in the wedge; c Lamb is the velocity of the refracted shear wave in the plate-like specimen; α is the incident angle of the incident wave in the wedge; β is the refraction angle of the refracted shear wave in the plate-like specimen. Based on the Lamb wave nondestructive testing device in engineering, a finite element model for plate-like specimen testing is established; In step S6, the time-domain explicit multi-physics field interface is used to simulate the propagation of elastic waves in the elastic medium, and the finite element method and the explicit time integration method are used to solve the wave equation of the finite element model. When there is a crack in the plate-like specimen, the elastic wave hits the crack at a right angle, and part of the wave will further propagate along the plate-like specimen, and the other part will be reflected back to the wedge. The transmission and reflection signals are recorded at four preset monitoring points on the top surface of the plate-like specimen at equal distances before and after the crack.

2. A device for measuring defects of plate-shaped specimens based on Lamb wave dispersion, characterized in that: The method for measuring defects of a plate-shaped specimen in claim 1 comprises: A parameter acquisition module is used to test the plate-shaped specimen and obtain the material parameters and basic equations of the plate-shaped specimen; Model building module, which is used to establish the propagation model of Lamb waves on plate-like specimens using the state space method based on material parameters and basic equations; The equation acquisition module is used to obtain the governing equations of Lamb wave propagation through generalized displacement and stress solutions based on the propagation model; The relationship acquisition module is used to obtain the solution of the control equation according to the matrix index and obtain the dispersion relation and mode vibration shape of Lamb wave propagation through the global transfer matrix method; A model detection module is used to establish a finite element model for plate sample detection based on Snell's law using the acquired material parameters, dispersion relations and mode vibration shapes of the plate sample; The position acquisition module is used to calculate the vertical displacement of the signal according to the pre-placed monitoring points on the top surface of the plate-shaped specimen, so as to obtain the position of the crack.

3. The device for measuring defects of plate-shaped specimens based on Lamb wave dispersion according to claim 2, characterized in that: The parameter acquisition module is specifically used to test and analyze the material parameters of the plate-like sample to obtain the density, elastic modulus, and Poisson's ratio of the plate-like sample material, thereby deriving the basic equations of the plate-like sample material, which include constitutive equations, geometric equations, and dynamic equations.

4. The device for measuring defects of plate-shaped specimens based on Lamb wave dispersion according to claim 3, characterized in that: The model building module is specifically used to process the basic equation of the plate-like sample material using the state space method to establish a propagation model of Lamb waves in the plate-like sample, and its state equation is: Where: χ(x,z,t) is the state variable; M is the coefficient matrix.

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