Strain detection method, device and equipment and storage medium

Abstract

The invention provides a strain detection method, device and equipment and a storage medium, which can be applied to the technical field of strain detection. The method comprises the following steps: determining parameters in a standard partial differential equation corresponding to a target structure according to a wave equation of the target structure under a strain effect; according to the parameters and the excitation signal data under the multiple strains, simulation under the multiple strains is carried out on a structure model corresponding to the target structure, simulation results under the multiple strains are obtained, and strain detection index values corresponding to the multiple strains are determined; performing excitation at a target position of the target structure by using the excitation signal, and receiving a time domain signal at a target point on a guided wave propagation path to obtain a frequency domain signal through fast Fourier transform processing so as to determine a target strain detection index value; and determining a target strain corresponding to the target strain detection index value from the fitted curve. According to the method, tedious calculation is avoided, the strain detection efficiency is greatly improved, and the problem of low strain detection precision is solved.

Description

Technical Field

[0001] The present application relates to the technical field of strain detection, and particularly to a strain detection method, device, equipment and storage medium. Background Art

[0002] Structural materials will generate strain distributions under loads, environmental changes or long-term use, and strains exceeding the material's bearing limit will cause the material to deform, crack or even be severely damaged. Therefore, regular strain detection of structural materials can prevent structural failure and ensure safety.

[0003] Although existing strain detection methods have their own characteristics, there are still problems such as a relatively single theoretical method and difficulties in practical applications. Currently, any existing method for detecting strain in any direction can only analyze the strain state within a closed curve and has low calculation efficiency; there is a method that can measure the strain of a specific structure, but its detection accuracy is low, and the change rate of the detection index is between 3‰ and 5‰ in the presence of strain. This method not only has high requirements for equipment but also has relatively strict requirements for the detection environment; there is a method that uses the transit time of ultrasonic body waves to analyze the strain of the structure to be measured, but its detection range is small, and the signals obtained between different target individuals of the same material vary greatly, resulting in poor detection effects for small strains. Summary of the Invention

[0004] In view of the above problems, the present application provides a strain detection method, device, equipment and storage medium.

[0005] According to a first aspect of the present application, a strain detection method is provided, including: determining parameters in a standard partial differential equation corresponding to the target structure according to the wave equation of the target structure under the action of strain; simulating the structure model corresponding to the target structure under multiple strains according to the parameters and excitation signal data of the target structure under multiple strains to obtain simulation results under the multiple strains; determining strain detection index values corresponding to each of the multiple strains according to the simulation results of the structure model under the multiple strains; using an excitation signal to excite at a target position of the target structure and receiving a time-domain signal corresponding to a target point at the target point on the guided wave propagation path; performing fast Fourier transform processing on the time-domain signal corresponding to the target point to obtain a frequency-domain signal corresponding to the target point; using the number of sideband peaks as a detection index, determining a target strain detection index value based on the number of sideband peaks in the frequency-domain signal corresponding to the target point, where the detection index is determined according to the wave equation; and determining a target strain corresponding to the target strain detection index value from a fitting curve, where the fitting curve is obtained by fitting the strain detection index values corresponding to each of the multiple strains.

[0006] According to an embodiment of the present application, taking the number of sideband peaks as the detection index, and determining the target strain detection index value based on the number of sideband peaks in the frequency-domain signal corresponding to the above target point includes: taking the logarithm of the ordinate value of the frequency-domain signal corresponding to the above target point and performing normalization processing to obtain the processed frequency-domain signal; determining the number of first sideband peaks in the processed frequency-domain signal that are between the preset threshold upper limit and the preset threshold lower limit; determining the number of second sideband peaks in the processed frequency-domain signal that are between the preset moving threshold and the preset threshold upper limit, where the preset moving threshold is between the preset threshold upper limit and the preset threshold lower limit; and determining the target strain detection index value according to the number of first sideband peaks and the number of second sideband peaks.

[0007] According to an embodiment of the present application, the above preset moving threshold includes a plurality of different moving thresholds, and the number of second sideband peaks includes the number of sideband peaks corresponding to each of the above plurality of different moving thresholds; the above determining the target strain detection index value according to the number of first sideband peaks and the number of second sideband peaks includes: for each of the above moving thresholds, determining a first initial strain detection index value according to the number of first sideband peaks and the number of sideband peaks corresponding to the moving threshold; and performing an averaging process on the first initial strain detection index values corresponding to each of the above moving thresholds to obtain the above target strain detection index value.

[0008] According to an embodiment of the present application, the wave equation of the above target structure under the action of strain is obtained through the following operations, including: for the detection point in the above target structure, determining the motion control expression of the above target structure according to the material parameters of the above target structure and the second derivative of the displacement of the above detection point; determining the expression of the Lagrangian strain tensor of the above detection point in the final state according to the position coordinates of the above detection point in the final state, where the initial state is the state after the natural state is subjected to stress and strain, the above natural state is the state without stress and without strain, the above final state is the state obtained after the above detection point fluctuates from the above initial state, and the position coordinates in the above final state are determined according to the applied strain and the position coordinates of the above detection point in the above natural state; determining the expression of the strain energy according to the expression of the Lagrangian strain tensor; determining the expression of the stress tensor in the presence of strain based on the expression of the Lagrangian strain tensor and the expression of the strain energy; and substituting the expression of the stress tensor into the motion control expression of the above target structure to obtain the wave equation of the above target structure under the action of strain.

[0009] According to an embodiment of the present application, determining the parameters in the standard partial differential equation corresponding to the target structure based on the wave equation of the target structure under the action of strain includes: comparing the wave equation with the standard partial differential equation to determine the parameters in the standard partial differential equation.

[0010] According to an embodiment of the present application, the simulation result is a time-domain signal corresponding to strain; determining the strain detection index values corresponding to the multiple strains according to the simulation results of the structural model under the multiple strains includes: performing fast Fourier transform processing on the time-domain signal corresponding to each strain to obtain a frequency-domain signal corresponding to each strain; taking the logarithm of the ordinate value of the frequency-domain signal corresponding to each strain and performing normalization processing to obtain a processed frequency-domain signal corresponding to each strain; determining the preset threshold upper limit and the preset threshold lower limit according to the processed frequency-domain signal corresponding to each strain; for the processed frequency-domain signal corresponding to each strain, determining the number of third sideband peaks in the processed frequency-domain signal corresponding to the strain that is between the preset threshold upper limit and the preset threshold lower limit; determining the number of fourth sideband peaks in the processed frequency-domain signal corresponding to the strain that is between the preset threshold upper limit and the preset moving threshold; determining the second initial strain detection index value corresponding to each moving threshold according to the number of third sideband peaks and the number of fourth sideband peaks; and determining the strain detection index values corresponding to the multiple strains based on the second initial strain detection index values corresponding to each moving threshold.

[0011] According to an embodiment of the present application, the excitation frequencies of the excitation signal include a first excitation frequency and a second excitation frequency; using the excitation signal to perform excitation at the target position of the target structure includes: using the excitation signal to excite a symmetric guided wave mode at the target position.

[0012] The second aspect of the present application provides a strain detection device, including: a first determination module, configured to determine parameters in a standard partial differential equation corresponding to the target structure according to the wave equation of the target structure under the action of strain; a first acquisition module, configured to perform simulations of the structure model corresponding to the target structure under the multiple strains according to the parameters and excitation signal data of the target structure under the multiple strains, and obtain simulation results under the multiple strains; a second determination module, configured to determine strain detection index values corresponding to the multiple strains respectively according to the simulation results of the structure model under the multiple strains; a receiving module, configured to use an excitation signal to perform excitation at a target position of the target structure and receive a time-domain signal corresponding to the target point at a target point on the guided wave propagation path; a second acquisition module, configured to perform fast Fourier transform processing on the time-domain signal corresponding to the target point to obtain a frequency-domain signal corresponding to the target point; a third determination module, configured to use the number of sideband peaks as a detection index, and determine a target strain detection index value based on the number of sideband peaks in the frequency-domain signal corresponding to the target point, where the detection index is determined according to the wave equation; a fourth determination module, configured to determine a target strain corresponding to the target strain detection index value from a fitting curve, where the fitting curve is obtained by fitting the strain detection index values corresponding to the multiple strains respectively.

[0013] The third aspect of the present application provides an electronic device, including: one or more processors; a memory, configured to store one or more computer programs, where the one or more processors execute the one or more computer programs to implement the steps of the above method.

[0014] The fourth aspect of the present application further provides a computer-readable storage medium, on which computer programs or instructions are stored, and when the computer programs or instructions are executed by a processor, the steps of the above method are implemented.

[0015] The fifth aspect of the present application further provides a computer program product, including computer programs or instructions, and when the computer programs or instructions are executed by a processor, the steps of the above method are implemented.

[0016] A strain detection method, device, equipment and storage medium provided by the present application. Based on the wave equation of a target structure under strain, it can be determined that the target structure generates strain after being stressed. The propagation of the excitation signal in the target structure and the wave motion at the midpoint of the target structure will both exhibit non-linear characteristics, resulting in many sideband peaks in the received signal in the frequency domain. Moreover, since the sideband peaks can reflect the change in the material properties of the target structure, and the number of sideband peaks approximately linearly increases with the increase of strain in the elastic stage, the number of sideband peaks is selected as the detection index for the strain of the target structure. Based on the wave equation of the target structure, the parameters in the corresponding standard differential equation in the software for multi-physics field simulation can be determined, so as to perform simulations of the structure model corresponding to the target structure under different strains based on the parameter pairs under multiple strains, and thus the strain detection index values corresponding to multiple strains can be obtained, and the fitting curve can be obtained by fitting the strain detection index values corresponding to multiple strains respectively. In actual strain detection, an excitation signal is used to excite at the target position of the target structure, and the time-domain signal is received at the target point on the waveguide propagation path, and then the fast Fourier transform is performed on the time-domain signal to transform the time-domain signal into a frequency-domain signal, so that the target strain detection index value can be determined based on the number of sideband peaks in the frequency-domain signal, that is, the target strain corresponding to the target strain detection index value can be determined from the fitting curve based on the fitting curve obtained by simulation, realizing the strain detection of the target structure. Thus, in actual strain detection, the received time-domain signal is processed, and the evaluation of the strain of the target structure can be realized based on the fitting curve, avoiding cumbersome calculations and greatly improving the detection efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Through the following description of the embodiments of the present application with reference to the drawings, the above content and other objects, features and advantages of the present application will become clearer. In the drawings:

[0018] Figure 1 The application scenario diagram of the strain detection method according to the embodiment of the present application is shown.

[0019] Figure 2 The flowchart of the strain detection method according to the embodiment of the present application is shown.

[0020] Figure 3 The schematic diagram of transmitting and receiving signals to the target structure according to the embodiment of the present application is shown.

[0021] Figure 4 The schematic diagram of the space coordinate system established based on the target structure according to the embodiment of the present application is shown.

[0022] Figure 5 The schematic diagram of the two-dimensional cross-section for strain analysis according to the embodiment of the present application is shown.

[0023] Figure 6 A schematic diagram of the processed frequency-domain signal according to an embodiment of the present application is shown.

[0024] Figure 7 A schematic diagram of the second initial strain detection index values under different movement thresholds according to an embodiment of the present application is shown.

[0025] Figure 8 A schematic diagram of the strain detection index values under multiple strains according to an embodiment of the present application is shown.

[0026] Figure 9 A schematic diagram of the dispersion curve of the guided wave mode S0 according to an embodiment of the present application is shown.

[0027] Figure 10 A structural block diagram of the strain detection device according to an embodiment of the present application is shown.

[0028] Figure 11 A block diagram of an electronic device suitable for implementing the strain detection method according to an embodiment of the present application is shown. Detailed implementation manners

[0029] Hereinafter, embodiments of the present application will be described with reference to the accompanying drawings. However, it should be understood that these descriptions are merely exemplary and are not intended to limit the scope of the present application. In the following detailed description, for the sake of explanation, many specific details are set forth to provide a comprehensive understanding of the embodiments of the present application. However, it is obvious that one or more embodiments can also be implemented without these specific details. In addition, in the following description, descriptions of well-known structures and technologies are omitted to avoid unnecessarily confusing the concepts of the present application.

[0030] The terms used herein are merely for describing specific embodiments and are not intended to limit the present application. The terms "including", "comprising", etc. used herein indicate the presence of the described features, steps, operations, and / or components, but do not exclude the presence or addition of one or more other features, steps, operations, or components.

[0031] All terms used herein (including technical and scientific terms) have the meanings commonly understood by those skilled in the art, unless otherwise defined. It should be noted that the terms used herein should be interpreted as having a meaning consistent with the context of this specification and should not be interpreted in an idealized or overly rigid manner.

[0032] In cases where expressions such as "at least one of A, B, and C" are used, generally, it should be interpreted according to the meaning that those skilled in the art usually understand such expressions (for example, "a system having at least one of A, B, and C" should include, but not be limited to, a system having only A, only B, only C, having A and B, having A and C, having B and C, and / or having A, B, and C, etc.).

[0033] In the process of implementing this application, it is found that in fields such as aerospace, nuclear energy, and water conservancy, key components usually bear high strain states. Quantitative detection of strain distribution can help engineers evaluate material properties and timely detect potential risks; in equipment such as rotating machinery and bridges that require long-term detection, real-time strain detection can provide dynamic health data, which is helpful for preventive maintenance, reducing maintenance costs, and extending service life.

[0034] In addition, with the development of advanced manufacturing, strain detection also has guiding significance for improving manufacturing processes and optimizing design structures, that is, through strain distribution analysis, defects in the manufacturing process can be identified, and then the production process can be improved to achieve material lightweight and structural high-efficiency.

[0035] Therefore, strain detection is not only a means of safety guarantee and service life extension, but also a key means of improving the quality and efficiency of modern manufacturing.

[0036] In the prior art, different strain detection methods have their own characteristics. Among them, the strain gauge method is simple and easy to use and is suitable for surface strain detection. The X-ray diffraction method has high precision and is applicable to shallow surface strain measurement. The magneto-elastic method is suitable for non-contact strain detection of ferromagnetic materials. The ultrasonic strain detection method has unique advantages by virtue of the acousto-elastic effect, can non-destructively measure the strain inside and on the surface of materials, and is applicable to a wide range of materials, that is, it is not only applicable to metal materials, but also applicable to some non-metal materials, especially more advantageous in complex structure and deep strain analysis, making it play an important role in structural health detection in fields such as aerospace and construction. However, there are still certain limitations in the accuracy of ultrasonic detection, and the detection signal is easily affected by temperature and the microscopic structure of materials; for high-attenuation materials, such as porous or high-damping materials, the effect is limited.

[0037] In the prior art, there are also ultrasonic guided wave strain detection methods for cross-sections of arbitrary shapes, but the research is limited to a closed plane, and effective strain analysis cannot be carried out on irregular shapes and complex structures. Moreover, only the influence of biaxial strain states and different strain magnitudes on the phase velocity of ultrasonic guided waves is considered. Analyzing the axial strain of a circular tube structure based on the torsional mode of ultrasonic guided waves can have good signal performance, but restricted by the mode and theoretical ideas, the strain detection direction is relatively fixed, and radial and tangential strains cannot be analyzed. Strain detection can be carried out based on the semi-analytical finite element method, but the structure needs to be discretized, there are certain requirements for the structural boundary conditions, and the solution process is slow. The strain state can also be analyzed based on the global matrix method, but compared with the semi-analytical finite element method, this method is prone to losing solutions, resulting in incomplete solutions, and the guided wave mode is relatively fuzzy, without specifying the strain direction.

[0038] The above-mentioned strain detections are generally based on the weak nonlinear theory. However, when a structure is subjected to external forces, the material, boundary conditions, or large geometric deformations of the structure will exhibit nonlinear behaviors. Currently, there are also methods that use phase-matched lamb waves (elastic waves) to generate second harmonics to determine the acoustic nonlinear parameters and use the acoustic nonlinear parameters for strain detection, but this will be affected by other modal waves.

[0039] In summary, in terms of application, current strain detection technologies are often limited to the surface of the structure, and at the same time, the detection equipment has relatively strict requirements for the environment, which greatly limits the feasibility of strain measurement in industrial sites. Since ultrasonic guided waves have a high frequency and are not affected by on-site low-frequency vibrations, and the equipment structure is simple and can complete measurements in various extreme environments, most of the existing strain measurement methods combine the stress field with the sound field. However, stress is relatively difficult to measure, and often a complex calculation process is required to convert the external force into internal stress of the structure.

[0040] Therefore, the embodiments of the present application provide a strain detection method to overcome the problems of low calculation efficiency, low detection accuracy, and small detection range existing in the prior art for strain detection.

[0041] Figure 1 The application scenario diagram of the strain detection method according to the embodiments of the present application is shown.

[0042] As Figure 1 shown, the application scenario 100 according to this embodiment may include a server 101, a target structure 102, and a sensor 103.

[0043] Server 101 can determine the parameters in the standard partial differential equation corresponding to the target structure 102 according to the wave equation of the target structure 102 under the action of strain, so as to simulate the structure model corresponding to the target structure 102 under multiple strains based on the parameters and excitation signal data of the target structure 102 under multiple strains, obtain the simulation results under multiple strains, and thus can determine the strain detection index values corresponding to each of the multiple strains according to the simulation results of the structure model under multiple strains.

[0044] In actual strain detection, an excitation signal is used to excite at the target position of the target structure 102, and a sensor 103 is used to receive the time-domain signal corresponding to the target point at the target point on the guided wave propagation path, and then the received time-domain signal is sent to the server 101.

[0045] Server 101 can also perform fast Fourier transform processing on the time-domain signal corresponding to the target point to obtain the frequency-domain signal corresponding to the target point, and use the number of sideband peaks as the detection index. Based on the number of sideband peaks in the frequency-domain signal corresponding to the target point, determine the target strain detection index value, so that the target strain corresponding to the target strain detection index value can be determined from the fitting curve obtained by fitting the strain detection index values corresponding to each of the multiple strains.

[0046] It should be noted that the strain detection method provided by the embodiments of the present application can generally be executed by the server 101. Correspondingly, the strain detection device provided by the embodiments of the present application can generally be set in the server 101.

[0047] The following will be based on Figure 1 the described scenario, and through Figures 2 - 9 describe the strain detection method of the embodiments of the present application in detail.

[0048] Figure 2 shows a flowchart of the strain detection method according to the embodiments of the present application.

[0049] As Figure 2 shown, the strain detection method 200 includes operations S210 to S270.

[0050] In operation S210, according to the wave equation of the target structure 102 under the action of strain, determine the parameters in the standard partial differential equation corresponding to the target structure 102.

[0051] According to an embodiment of the present application, the target structure 102 can be a structure of any shape, such as a flat structure, a curved surface structure, a laminated structure, etc.; meanwhile, the material of the target structure 102 can be an isotropic material such as steel, aluminum, titanium, copper, alloy, etc. When the target structure 102 is subjected to stress, strain will be generated. By analyzing the strain suffered by the target structure 102, the wave equation of the target structure 102 under the action of strain can be obtained. Among them, the wave equation can be used to characterize the fluctuation process of a certain point in the target structure 102 under the action of strain with the excitation signal.

[0052] According to an embodiment of the present application, software for multi-physics field simulation can be used to perform simulations of the target structure 102 under multiple strains. The software for multi-physics field simulation includes a solver corresponding to the target structure 102, and the standard partial differential equation corresponding to the solver is the standard partial differential equation corresponding to the target structure 102. The standard partial differential equation corresponding to the solver can also be used to characterize the fluctuation process of the target structure 102 under the action of strain. Since the parameters in the standard partial differential equation are unknown and there is only a difference in the expression form between the standard partial differential equation and the wave equation, the parameters in the standard partial differential equation can be determined according to the wave equation of the target structure 102 under the action of strain, so that the parameters can be input into the software for multi-physics field simulation later to perform simulations of the target structure 102 under different strains.

[0053] In operation S220, according to the parameters of the target structure 102 under multiple strains and the excitation signal data, perform simulations of the structure model corresponding to the target structure 102 under multiple strains to obtain simulation results under multiple strains.

[0054] Among them, the multiple strains are multiple different strains.

[0055] According to an embodiment of the present application, first construct a structure model corresponding to the target structure 102 in the software for multi-physics field simulation. And since it is necessary to use the standard partial differential equation to characterize the fluctuation process of the structure model under the action of strain and it is necessary to use the excitation signal to simulate the external excitation received by the structure model, the parameters of the target structure 102 under multiple strains and the excitation signal data can be input into the software for multi-physics field simulation to perform simulations of the structure model under different strains according to the parameters of the target structure 102 under multiple strains and the excitation signal data.

[0056] Among them, when the stress received by the target structure 102 is different, the strain generated by the target structure 102 is also different. Then, for different strains received by the target structure 102, the parameter solutions in the standard partial differential equation are also different.

[0057] Among them, the excitation signal data may include numerical data simulating the time-varying external excitation source applied to the structural model and the frequency of the signal.

[0058] According to an embodiment of the present application, the dispersion curve corresponding to the target structure 102 can be solved according to the target structure 102 and the material properties of the target structure 102, so that the optimal excitation frequency, that is, the frequency of the signal included in the excitation signal data, can be determined according to the dispersion curve.

[0059] In operation S230, according to the simulation results of the structural model under multiple strains, the strain detection index values corresponding to the respective multiple strains are determined.

[0060] According to an embodiment of the present application, by simulating multiple strains on the structural model, the simulation results of the structural model under different strains can be obtained, that is, each strain corresponds to a simulation result. By analyzing the simulation results corresponding to each strain, the strain detection index values corresponding to each strain can be determined, that is, the strain and the strain detection index values are in one-to-one correspondence.

[0061] Among them, the properties of the target structure 102 and the structural model are isotropic.

[0062] In operation S240, using the excitation signal, excitation is performed at the target position of the target structure 102, and the time-domain signal corresponding to the target point is received at the target point on the guided wave propagation path.

[0063] According to an embodiment of the present application, in the process of actual strain detection of the target structure 102, the strain received by the target structure 102 is unknown, but through the above operations S210 to S230, the strain detection index values corresponding to the respective multiple strains can be obtained based on the simulation, that is, the one-to-one correspondence between the strain and the strain detection index values is obtained, so that the strain received by the target structure 102 can be determined by determining the strain detection index value of the target structure 102.

[0064] According to an embodiment of the present application, based on the wave equation of the target structure 102 under the action of strain, it can be determined that there will be a nonlinear effect after the target structure 102 is stressed and generates strain, so that the propagation of the excitation signal in the target structure 102 and the wave motion of the points in the target structure 102 will both exhibit nonlinear characteristics, that is, there will be more peaks in the received signal in the frequency domain. Therefore, the number of sideband peaks is selected as the detection index. Among them, the strain detection index values corresponding to the respective multiple strains determined in the above operation S230 are determined according to the number of sideband peaks.

[0065] Based on the above, at the target position of the target structure 102, excitation can be performed using an excitation signal, and a time-domain signal corresponding to the target point can be received at the target point on the guided wave propagation path, where the guided wave propagation path is the propagation path of the excitation signal in the target structure 102; the target position can be any position in the target structure 102; the target point can be any point on the guided wave propagation path.

[0066] Among them, the excitation signal data in the above operation S220 can be the data of the excitation signal in the operation S240.

[0067] In one example, the excitation signal can be generated by the excitation source 310, and the time-domain signal can be received at the target point through the sensor 103.

[0068] Figure 3 The schematic diagram of transmitting and receiving signals for the target structure according to the embodiment of the present application is shown.

[0069] As Figure 3 shown, taking the target structure 102 as a flat plate structure as an example, the excitation source 310 can be used to perform excitation at the target position of the target structure 102, and the sensor 103 can be used to receive the time-domain signal corresponding to the target point at the target point on the guided wave propagation path.

[0070] In operation S250, perform fast Fourier transform processing on the time-domain signal corresponding to the target point to obtain the frequency-domain signal corresponding to the target point.

[0071] According to the embodiment of the present application, since the sideband peak exists in the signal in the frequency domain, perform fast Fourier transform processing on the time-domain signal corresponding to the target point to convert the time-domain signal into a signal in the frequency domain, that is, obtain the frequency-domain signal corresponding to the target point, so as to determine the number of sideband peaks based on the frequency-domain signal subsequently.

[0072] In operation S260, taking the number of sideband peaks as the detection index, determine the target strain detection index value based on the number of sideband peaks in the frequency-domain signal corresponding to the target point.

[0073] Among them, the detection index is determined according to the wave equation.

[0074] According to the embodiment of the present application, since the number of sideband peaks is used as the detection index, the number of sideband peaks in the frequency-domain signal can be determined based on the frequency-domain signal corresponding to the target point, so that the target strain detection index value can be determined according to the number of sideband peaks in the frequency-domain signal, so as to evaluate the strain of the target structure 102 under the action of strain subsequently.

[0075] In operation S270, a target strain corresponding to the target strain detection index value is determined from the fitting curve, where the fitting curve is obtained by fitting the strain detection index values corresponding to multiple strains respectively.

[0076] According to the embodiments of the present application, by performing the above operations S210 to S230, the strain detection index values corresponding to multiple strains respectively can be obtained, and by fitting the strain detection index values corresponding to multiple strains respectively, a fitting curve is obtained, that is, there is a one-to-one correspondence between the strain and the strain detection index value in the fitting curve. Then, the target strain corresponding to the target strain detection index value is determined from the fitting curve to achieve the strain detection of the target structure 102.

[0077] According to the embodiments of the present application, based on the wave equation of the target structure 102 under the action of strain, it can be determined that when the target structure 102 is stressed, strain is generated, and both the propagation of the excitation signal in the target structure 102 and the wave motion at the midpoint of the target structure 102 will exhibit non-linear characteristics, resulting in more sideband peaks in the received signal in the frequency domain. Moreover, since the sideband peaks can reflect the change in the material properties of the target structure 102, and the number of sideband peaks approximately linearly increases with the increase of strain in the elastic stage, the number of sideband peaks is selected as the detection index for the strain of the target structure 102. Based on the wave equation of the target structure 102, the parameters in the corresponding standard differential equation in the software for multi-physics field simulation can be determined, so as to perform simulations of the structure model corresponding to the target structure 102 under different strains based on the parameters under multiple strains, thereby obtaining the strain detection index values corresponding to multiple strains respectively, and fitting the strain detection index values corresponding to multiple strains respectively to obtain a fitting curve. In actual strain detection, an excitation signal is used to excite at the target position of the target structure 102, and the time-domain signal is received at the target point on the waveguide propagation path, and then the time-domain signal is subjected to a fast Fourier transform to transform the time-domain signal into a frequency-domain signal, so that the target strain detection index value can be determined based on the number of sideband peaks in the frequency-domain signal, that is, based on the fitting curve obtained by simulation, the target strain corresponding to the target strain detection index value is determined from the fitting curve to achieve the strain detection of the target structure 102. Thus, in actual strain detection, the received time-domain signal is processed, and based on the fitting curve, the evaluation of the strain received by the target result can be realized, avoiding cumbersome calculations and greatly improving the detection efficiency.

[0078] According to an embodiment of the present application, the wave equation of the target structure 102 under the action of strain is obtained through the following operations, including: for the detection points in the target structure 102, determining the motion control expression of the target structure 102 according to the material parameters of the target structure 102 and the second derivative of the displacement of the detection points; determining the expression of the Lagrangian strain tensor of the detection points in the final state according to the position coordinates of the detection points in the final state; determining the expression of the strain energy according to the expression of the Lagrangian strain tensor; determining the expression of the stress tensor in the presence of strain based on the expression of the Lagrangian strain tensor and the expression of the strain energy; substituting the expression of the stress tensor into the motion control expression of the target structure 102 to obtain the wave equation of the target structure 102 under the action of strain.

[0079] Wherein, the initial state is the state after the natural state is subjected to stress and strain, that is, the state after the detection points are subjected to stress and generate strain; the natural state is the state without applied stress and without strain, and the final state is obtained after the detection points fluctuate from the initial state. The position coordinates in the final state are determined according to the applied strain and the position coordinates of the detection points in the natural state.

[0080] According to an embodiment of the present application, a spatial coordinate system corresponding to the target structure 102 can be established. The detection points can be any point on the target structure 102, and the relevant position coordinates of the detection points are all coordinates in this spatial coordinate system.

[0081] Figure 4 The schematic diagram of the spatial coordinate system established based on the target structure according to the embodiment of the present application is shown.

[0082] As Figure 4 shown, taking the target structure 102 as a flat plate structure as an example, the three axes of this spatial coordinate system are respectively 、 and .

[0083] According to an embodiment of the present application, the detection points can be any point in the target structure 102. Then, according to the material parameters of the target structure 102 and the second derivative of the displacement of the detection points, the motion control expression of the target structure 102 is determined, and this expression is shown in the following formula (1).

[0084] (1);

[0085] Wherein, can represent divergence, can represent the stress received by the target structure 102. The material parameters can include the density of the target structure 102, that is, can represent the density of the target structure 102, It can represent the second derivative with respect to the displacement of the detection point. It can be expressed as the displacement of the detection point.

[0086] According to the embodiments of the present application, when there is no force acting on the target structure 102, the detection point in the target structure 102 is in a natural state; when the target structure 102 is subjected to an external force, strain will be generated, and the detection point in the target structure 102 will change from the natural state to the initial state, that is, the detection point will change from the position coordinates in the natural state to the position coordinates in the initial state, which means the detection point has undergone displacement; when there is strain in the target structure 102, the target structure 102 can be excited by the ultrasonic guided wave sensor 103, and the detection point in the target structure 102 will fluctuate and change from the initial state to the final state, that is, the detection point will change from the position coordinates in the initial state to the position coordinates in the final state, which means the detection point has undergone displacement.

[0087] According to the embodiments of the present application, for small displacements of the detection point, the superposition principle can be used, that is, the final displacement of the detection point can be determined based on the initial displacement and the fluctuating displacement, and the final displacement of the detection point in the final state can be shown as the following formula (2).

[0088] (2);

[0089] Where, can be expressed as the initial displacement, that is, the displacement of the detection point from the natural state to the initial state; can be expressed as the fluctuating displacement, that is, the displacement of the detection point from the initial state to the final state, and this fluctuating displacement changes with time t. can be expressed as the final displacement, that is, the displacement of the detection point from the natural state to the final state.

[0090] According to the embodiments of the present application, based on the above formula (2), the Navier equation can be expressed as the following formula (3).

[0091] (3);

[0092] Where, and are Lame constants. The Lame constants are related to the material of the target structure 102, that is, the material parameters of the target structure 102 can also include the Lame constants. and ; can be expressed as the Laplace operator. can be expressed as the second-order spatial derivative of with respect to can be expressed as the second-order spatial derivative of with respect to can be expressed as the gradient; can represent the second derivative with respect to the initial displacement .

[0093] Among them, the above formula (3) is a complex representation of formula (1) and is used to introduce the Lamé constant and .

[0094] The acoustoelastic theory proposes that the strain can be defined by the Green-Lagrange tensor, and it is considered that the equilibrium occurs in the deformed configuration, that is, the material nonlinearity is taken into account in the strain detection. Thus, the Lagrangian strain tensor at the detection point in the final state can be as shown in the following formula (4).

[0095] (4);

[0096] where can be expressed as the Lagrangian strain tensor at the detection point in the final state, can be expressed as the identity matrix; can be expressed as the position coordinates of the detection point in the final state.

[0097] Assume that the third-order Murnaghan coefficient (Murnaghan coefficient) of the material of the target structure 102 is , and , , , , can be used to represent the material nonlinearity in classical acoustoelasticity, then the expression of the strain energy can be as shown in the following formula (5).

[0098] (5); where can be expressed as the tensor trace of the square of the Lagrangian strain tensor, that is, the sum of the main diagonal elements of this square tensor; det can be expressed as the determinant, can be expressed as taking the determinant of the Lagrangian strain tensor, that is, used to calculate the volume change caused by the deformation described by this tensor.

[0099] where the parameters , , , , are only related to the material of the target structure 102. Once the material is determined, these parameters are fixed, that is, the material parameters of the target structure 102 can also include the third-order Murnaghan coefficient .

[0100] Since the pre-strain loading method is adopted, in the nonlinearity of the target structure 102, the first-order Piola-Kirchhoff stress tensor (Piola-Kirchhoff stress tensor) P is more suitable for analyzing the deformation gradient of the material under actual stress. Then, the expression of the stress tensor P in the presence of strain can be shown as the following formula (6).

[0101] (6);

[0102] According to Hooke's law, the initial displacement of the detection point in the initial state , where can represent the magnitude of the strain to which the target structure 102 is subjected, that is, the magnitude of the strain to be detected; can represent the position coordinates of the detection point in the natural state.

[0103] Since the movement of the detection point in the target structure 102 is due to a dynamic perturbation superimposed on the initial state, and the dynamic perturbation is much smaller than the perturbation caused by the initial strain, the position coordinates of the detection point in the final state as shown in the following formula (7) can be obtained .

[0104] (7);

[0105] Based on the above formulas (1) to (7), formulas (4), (5), and (7) can be substituted into formula (6) to solve the stress tensor P. Since in formula (1) represents the stress tensor to which the target structure 102 is subjected, that is, the first-order Piola-Kirchhoff stress tensor , then the solved stress tensor P can be substituted into formula (1) to solve the wave equation of the target structure 102 under the action of strain.

[0106] According to the embodiments of the present application, the wave equation can be shown as the following formula (8).

[0107] (8);

[0108] Since the displacement of the detection point between the natural state, the initial state, and the final state is analyzed, the selection of the origin of the spatial coordinate system established based on the target structure 102 can be arbitrary, that is, the selection of the origin of the spatial coordinate system has no influence on the subsequent analysis to obtain the wave equation.

[0109] Taking the target structure 102 as a plate-like structure with a thickness of h as an example, as Figure 3 shown, when the excitation signal for measurement is inside the structure, in the case of the stress-free state, the free stress equation boundary conditions on the upper and lower surfaces of the plate-like structure can be shown as the following formula (9).

[0110] (9);

[0111] Wherein, is the unit vector of the normal of the upper and lower surfaces of the plate-like structure; The coordinate in the direction is

[0112] Wherein, the origin of the coordinate system is taken in the middle of the plate-like structure, and the distances from the upper and lower surfaces are both h / 2. Since the wave propagates in the direction, so = is used to describe that the normal stress in the boundary condition of wave propagation under no stress action is 0; refers to the positions of the upper and lower surfaces of the plate-like structure in the coordinate system.

[0113] Thus, in an infinite plate with a thickness of under no stress, the boundary conditions for the propagation of ultrasonic guided waves mainly involve the free boundary conditions of the plate surface (i.e., at ); and for the propagation of elastic waves, the boundary conditions are usually given by the free boundary conditions of stress, that is, the normal stress and shear stress are both zero on the free surface.

[0114] According to the embodiments of the present application, by analyzing the strain generated by the target structure 102 under stress, that is, based on the above formulas (1) to (7), the wave equation of the target structure 102 under the action of strain can be obtained. Thus, it can be known that after the target structure 102 is subjected to an external force and there is strain, there will be more sideband peaks in the received signal in the frequency domain. Therefore, the number of sideband peaks is selected as the detection index of strain for subsequent strain detection.

[0115] According to the embodiments of the present application, according to the wave equation of the target structure 102 under the action of strain, the parameters in the standard partial differential equation corresponding to the target structure 102 are determined, including: comparing the wave equation with the standard partial differential equation to determine the parameters in the standard partial differential equation.

[0116] According to an embodiment of the present application, since both the wave equation and the standard partial differential equation are used to characterize the dynamic response of the target structure 102 under the action of strain, except that the wave equation is derived for the target structure 102 and the standard partial differential equation is the equation corresponding to the target structure 102 in the software for multi-physics field simulation, both the wave equation and the standard partial differential equation can be used to represent the wave process of the target structure 102 under the action of strain. Therefore, by comparing the wave equation with the standard partial differential equation, each part in the wave equation and the standard partial differential equation can be corresponded, so as to determine the parameters in the standard partial differential equation.

[0117] According to an embodiment of the present application, the standard partial differential equation corresponding to the target structure 102 in the software for multi-physics field simulation can be shown as the following formula (10).

[0118] (10);

[0119] Wherein, can be expressed as the mass coefficient, can be expressed as the damping coefficient, can be expressed as the conserved flux, can be expressed as the source term.

[0120] According to an embodiment of the present application, the strain caused by the external force has been added to the wave equation of the target structure 102 under the action of strain, so the source term does not need to be considered in the standard partial differential equation , that is, the source term is set as ; the software for multi-physics field simulation is in a relatively ideal state and defaults to no damping, that is, the damping coefficient is set as .

[0121] According to an embodiment of the present application, on the basis of , , the wave equation can be compared with the standard partial differential equation to determine the parameters in the standard partial differential equation, wherein the parameters can include the mass coefficient and the conserved flux .

[0122] Taking Figure 4 the spatial coordinate system established based on the target structure 102 as an example, the research object is a flat plate structure.

[0123] In the above formula (7), the stress tensor P is a matrix. Based on the above formula (8) and formula (10), , , the conserved flux is composed of four numbers for each two-dimensional section in the spatial coordinate system.

[0124] Figure 5 A two-dimensional cross-sectional schematic diagram for strain analysis according to an embodiment of the present application is shown.

[0125] As Figure 5 shown, taking the target structure 102 with a thickness of h as an example, in order to save calculation time, a plane formed by and is intercepted as the analysis object, considering that the shift derivative in the direction is set to 0, and the conserved flux for the plane formed by and includes four numbers , , and .

[0126] According to an embodiment of the present application, it can be as shown in formula (11) below.

[0127]

[0128] Among them, in the software for multi-physics simulation, the strain magnitude in the direction is , the strain magnitude in the direction is the strain magnitude in the direction is ; and are Lame constants, related to the material of the target structure 102; u1x, u1y, u3x, u3y are the displacement components of a certain point in the target structure 102 excited by the excitation signal in the two-dimensional cross-section formed by and .

[0129] According to an embodiment of the present application, based on the wave equation, the parameters in the standard partial differential equation can be determined so as to input the parameters under different strains into the software for multi-physics simulation to realize the simulation of the structural model under different strains.

[0130] According to an embodiment of the present application, based on the simulation results of the structural model under multiple strains, determining the strain detection index values corresponding to the multiple strains respectively includes: performing fast Fourier transform processing on the time-domain signal corresponding to each strain to obtain the frequency-domain signal corresponding to each strain; taking the logarithm of the ordinate value of the frequency-domain signal corresponding to each strain and performing normalization processing to obtain the processed frequency-domain signal corresponding to each strain; determining a preset threshold upper limit and a preset threshold lower limit according to the processed frequency-domain signal corresponding to each strain; for the processed frequency-domain signal corresponding to each strain, determining the number of third sideband peaks between the preset threshold upper limit and the preset threshold lower limit in the processed frequency-domain signal corresponding to the strain; determining the number of fourth sideband peaks between the preset threshold upper limit and the preset moving threshold in the processed frequency-domain signal corresponding to the strain; determining the second initial strain detection index value corresponding to each moving threshold according to the number of third sideband peaks and the number of fourth sideband peaks; and determining the strain detection index values corresponding to the multiple strains respectively based on the second initial strain detection index value corresponding to each moving threshold.

[0131] Wherein, the simulation result is the time-domain signal corresponding to the strain received by the structural model.

[0132] According to an embodiment of the present application, by using software for multi-physics field simulation to perform simulation on the structural model under multiple strains, the time-domain signal corresponding to the excitation signal data received by the structural model under different strains can be obtained. Since the number of sideband peaks needs to be used as the detection index subsequently, the time-domain signal needs to be processed by fast Fourier transform to obtain the frequency-domain signal.

[0133] According to an embodiment of the present application, since the value corresponding to the ordinate of the frequency-domain signal is relatively small and the peaks in the frequency-domain signal obtained by fast Fourier transform are not obvious, the logarithm of the ordinate value of the frequency-domain signal is taken to make the peaks in the signal obvious, which is convenient for determining the number of sideband peaks subsequently. At the same time, since the preset threshold upper limit, the preset threshold lower limit and the preset moving threshold need to be determined subsequently, after taking the logarithm of the ordinate value of the frequency-domain signal, normalization processing is performed to unify the ordinate value of the frequency-domain signal to between 0 and 1, which is convenient for determining the preset threshold upper limit, the preset threshold lower limit and the preset moving threshold.

[0134] Figure 6 The schematic diagram of the processed frequency-domain signal according to the embodiment of the present application is shown.

[0135] As Figure 6As shown, the abscissa is Frequency and the ordinate is Normalized log(FFT, Fast Fourier Transform), that is, the value of the ordinate of the frequency-domain signal after normalization processing. Strains of 0.001, 0.002, 0.003, and 0.004 are taken as examples. Figure 6 shows the processed frequency-domain signals corresponding to strains of 0.001, 0.002, 0.003, and 0.004 respectively.

[0136] Among them, Figure 6 the circles shown in represent a sideband peak in the frequency-domain signal.

[0137] According to the embodiments of the present application, based on the distribution of sideband peaks in the processed frequency-domain signals corresponding to each strain, the upper limit of the preset threshold and the lower limit of the preset threshold can be determined, that is, the value range of the moving threshold is determined.

[0138] Taking Figure 6 the frequency-domain signal shown in as an example, the selection of the upper limit of the preset threshold and the lower limit of the preset threshold can be mainly based on the range where the sideband peaks in the processed frequency-domain signals under different strains are relatively concentrated, but the fundamental frequency cannot be selected, and it should be smaller than the value of the ordinate corresponding to the fundamental frequency. For example, the value of the ordinate corresponding to the fundamental frequency is in the range of 0.8 - 1, but most of the range of the circles is at the ordinate of 0.2 - 0.6, that is, most of the sideband peaks are located in the range of 0.2 - 0.6; at the same time, try to include all the sideband peaks corresponding to the same abscissa, or none of the sideband peaks corresponding to the same abscissa, to avoid affecting the calculation of the strain detection index value.

[0139] Based on Figure 6 the processed frequency-domain signals under multiple strains shown in, under different strains, the total number of sideband peaks in the processed frequency-domain signals changes. High strain will increase the nonlinearity of the target structure 102. Therefore, only looking at the total number of sideband peaks cannot reflect the nonlinearity, and the proportion can better reflect the nonlinearity.

[0140] According to the embodiments of the present application, for the processed frequency-domain signals corresponding to each strain, the number of third sideband peaks located between the upper limit of the preset threshold and the lower limit of the preset threshold in the processed frequency-domain signals corresponding to the strain can be determined first, and then the number of fourth sideband peaks located between the upper limit of the preset threshold and the preset moving threshold in the processed frequency-domain signals corresponding to the strain can be determined.

[0141] Among them, the preset movement threshold is located between the preset threshold upper limit and the preset threshold lower limit. The preset movement threshold may include multiple movement thresholds, and the multiple movement thresholds may be multiple thresholds equally spaced between the preset threshold upper limit and the preset threshold lower limit. That is, the number of fourth sideband peaks may include the number of sideband peaks corresponding to each movement threshold.

[0142] According to an embodiment of the present application, for the processed frequency-domain signal corresponding to each strain, according to the number of third sideband peaks and the number of sideband peaks corresponding to each movement threshold, the second initial strain detection index value corresponding to each movement threshold can be determined.

[0143] According to an embodiment of the present application, the second initial strain detection index value corresponding to each movement threshold can be obtained through the following formula (12).

[0144] (12);

[0145] Wherein, can be expressed as the second initial strain detection index value, can be expressed as the number of sideband peaks between the preset threshold upper limit and the preset threshold lower limit, that is, the number of third sideband peaks, can be expressed as the number of sideband peaks between the movement threshold and the preset threshold upper limit, that is, the number of sideband peaks corresponding to the movement threshold.

[0146] Figure 7 Shows a schematic diagram of the second initial strain detection index value under different movement thresholds according to an embodiment of the present application.

[0147] As Figure 7 shown, the abscissa is the frequency threshold, that is, the range of the preset threshold lower limit and the preset threshold upper limit determined by Figure 6 , which is also the value range of the movement threshold. Then the value range of the abscissa is 0.2~0.6; the ordinate is the second initial strain detection index value .

[0148] In Figure 7 , for the threshold range 0.2~0.6, multiple movement thresholds are obtained by dividing with 0.01, and based on the above formula (12), the second initial strain detection index value corresponding to each movement threshold is obtained.

[0149] According to an embodiment of the present application, based on the second initial strain detection index value corresponding to each movement threshold, the strain detection index value corresponding to the strain can be obtained, that is, the second initial strain detection index value corresponding to each movement threshold can be averaged to obtain the strain detection index value corresponding to the strain.

[0150] Figure 8A schematic diagram showing strain detection index values under multiple strains according to an embodiment of the present application.

[0151] As Figure 8 shown, for Figure 7 each line shown in , the strain detection index value corresponding to the strain is obtained by calculating the average value of the second initial strain detection index values corresponding to each movement threshold under the corresponding strain Figure 8 , and the strain detection index values corresponding to multiple strains are fitted, and the obtained fitting curve is as

[0152] shown. Figure 7 For example, taking the line corresponding to the strain of 0.001 shown in

[0153] as an example, it can be determined that the strain detection index value corresponding to the strain of 0.001 is 0.480.

[0154] According to an embodiment of the present application, based on the time-domain signals under multiple strains obtained by simulation, and using the number of sideband peaks as the detection index, the strain detection index values corresponding to different strains can be determined in advance and fitted to obtain a fitting curve, so that in actual strain detection, the strain suffered by the target structure 102 can be determined based on the fitting curve by determining the strain detection index value.

[0155] Based on the Figure 8 fitting curve shown above, it can be seen that when there is a strain in the target structure 102, the change rate of the strain detection index value of the present application is obvious, so that the detection accuracy can be improved when determining the strain suffered by the target structure 102 based on the fitting curve. Moreover, using the number of sideband peaks as the detection index of the strain instead of the time difference between the transmitted and received signals improves the detection effect on the small strain suffered by the target structure 102, and each point in the fitting curve can be used for the strain detection of the target structure 102, expanding the detection range of the strain suffered by the target structure 102; and, the fitting curve obtained by simulation in the present application can be used for strain detection of the target structure 102 without measuring baseline data.

[0156] According to an embodiment of the present application, using the number of sideband peaks as a detection index, based on the number of sideband peaks in the frequency-domain signal corresponding to the target point, determining the target strain detection index value includes: taking the logarithm of the ordinate value of the frequency-domain signal corresponding to the target point and performing normalization processing to obtain the processed frequency-domain signal; determining the number of first sideband peaks in the processed frequency-domain signal that are between the preset threshold upper limit and the preset threshold lower limit; determining the number of second sideband peaks in the processed frequency-domain signal that are between the preset moving threshold and the preset threshold upper limit; and determining the target strain detection index value according to the number of first sideband peaks and the number of second sideband peaks.

[0157] Wherein, the preset moving threshold is between the preset threshold upper limit and the preset threshold lower limit.

[0158] According to an embodiment of the present application, taking the logarithm of the ordinate value of the frequency-domain signal corresponding to the target point and performing normalization processing can obtain the processed frequency-domain signal, so as to better determine the number of first sideband peaks in the processed frequency-domain signal that are between the preset threshold upper limit and the preset threshold lower limit and determine the number of second sideband peaks in the processed frequency-domain signal that are between the preset moving threshold and the preset threshold upper limit, and thus the target strain detection index value can be determined according to the number of first sideband peaks and the number of second sideband peaks.

[0159] According to an embodiment of the present application, in actual strain detection, using the number of sideband peaks as a detection index, based on the number of first sideband peaks and the number of second sideband peaks determined by the frequency-domain signal, the target strain detection index value can be determined, so that the target strain corresponding to the target strain detection index value can be directly determined from multiple strains based on the strain detection index values corresponding to multiple strains obtained through simulation, realizing the strain detection of the target structure 102.

[0160] According to an embodiment of the present application, determining the target strain detection index value according to the number of first sideband peaks and the number of second sideband peaks includes: for each moving threshold, determining a first initial strain detection index value according to the number of first sideband peaks and the number of sideband peaks corresponding to the moving threshold; and performing an averaging process on the first initial strain detection index values corresponding to each moving threshold to obtain the target strain detection index value.

[0161] Wherein, the preset moving threshold may include multiple different moving thresholds, and the number of second sideband peaks may include the number of sideband peaks corresponding to each of the multiple different moving thresholds.

[0162] According to an embodiment of the present application, for each movement threshold, based on the number of first sideband peaks and the number of sideband peaks corresponding to the movement threshold, a first initial strain detection index value is determined. That is, based on the number of first sideband peaks and the number of sideband peaks corresponding to the movement threshold, through the above formula (12), the first initial strain detection index value can be obtained. Then, by averaging the first initial strain detection index values corresponding to each movement threshold, the target strain detection index value can be obtained.

[0163] According to an embodiment of the present application, since the strain detection index values at multiple strains have been obtained through simulation, in actual strain detection, by obtaining the target strain detection index value, the target strain corresponding to the target strain detection index value can be directly determined from multiple strains, thereby realizing the strain detection of the target structure 102.

[0164] Based on the strain detection index values at multiple strains obtained through simulation, if the determined target strain detection index value is not among the strain detection index values obtained through simulation, the target strain corresponding to the target strain detection index value can be solved through the linear relationship between two adjacent strain detection index values obtained through simulation. Among them, the target strain detection index value is located between these two adjacent strain detection index values.

[0165] Take Figure 8 as an example. If the target strain detection index value is between 0.001 and 0.002, then based on Figure 8 the relationship between the strain and the strain detection index value between 0.001 and 0.002, the target strain corresponding to the target strain detection index value can be determined.

[0166] Meanwhile, take Figure 8 the strain from 0.001 to 0.002 shown in

[0167] as an example. The change range of the strain detection index value corresponding to the strain change from 0.001 to 0.002 exceeds 10%, which improves the accuracy of determining the target strain based on the target strain detection index value.

[0168] Among them, the excitation frequencies of the excitation signal include a first excitation frequency and a second excitation frequency.

[0169] According to an embodiment of the present application, the excitation signal can adopt the side-incidence method, which can selectively excite specific guided-wave modes, such as the symmetric guided-wave mode. In the actual application process, the excitation of the excitation signal can be achieved through a variety of ultrasonic sensors, such as magnetostrictive sensors. In order to improve the detection sensitivity, the first excitation frequency and the second excitation frequency are used, and the interaction of the two frequency waves generates a wave with a new frequency, and the wave with the new frequency is very sensitive to micro-damage (such as micro-cracks, plastic deformation, etc.) in the target structure 102. In order to make the measurement signal, that is, the received time-domain signal, have a non-linear effect with sufficient signal-to-noise ratio to improve the detection sensitivity, the excitation signal needs to generate high-order harmonics with a cumulative effect. And in order to meet the cumulative effect of the high-order harmonics, the first excitation frequency and the second excitation frequency need to satisfy the principle of phase matching, that is, the phase velocity of the high-order harmonics is the same as the phase velocity of the fundamental frequency mode (excitation signal).

[0170] Figure 9 The schematic diagram of the dispersion curve of the guided-wave mode S0 according to an embodiment of the present application is shown.

[0171] As Figure 9 shown, taking the target structure 102 as a flat plate structure as an example, when the excitation signal is a mixed signal modulated by a Gaussian window with frequencies of and , the high-order harmonics caused by the excitation signal and the excitation signal approximately satisfy the phase matching condition, that is, when the excitation frequency of the excitation signal is and in the case of the mixed frequency, the high-order harmonics can be strengthened.

[0172] Among them, the first excitation frequency can be , and the second excitation frequency can be , is the wave number of the fundamental frequency wave, is the wave number of the second harmonic, = , = ; = , = .

[0173] According to an embodiment of the present application, since the dispersion curve is related to the shape of the target structure 102, when the target structure 102 is a curved surface structure or a laminated structure, it will affect the generated dispersion curve. Then, in order to meet the phase matching, it is necessary to re-find the position of phase matching and determine the first excitation frequency and the second excitation frequency.

[0174] According to an embodiment of the present application, since the excitation frequency of the excitation signal is dual-frequency, symmetric waveguide modes can be excited at the target position, which can avoid some non-linear signals inside the target structure 102 and make the received time-domain signal more accurate.

[0175] Based on the above, when the target structure 102 is subjected to a strain effect, non-linear effects will be generated in the ultrasonic guided wave used to excite the target structure 102 in the target structure 102. Exciting ultrasonic guided waves with different frequencies on the target structure 102 will enhance the non-linear phenomenon of the guided wave in the material, generate high-order harmonics, and increase the number of independent harmonics available for material non-linear measurement. Therefore, the number of sideband peaks can be used as a detection index to quantitatively describe the non-linearity of the target structure 102.

[0176] Moreover, the present application combines an easily measurable strain field with a general form of partial differential equation, gives the wave equation under strain action, and based on the wave equation, proposes that the number of sideband peaks in the frequency-domain signal be used as an index in strain detection to achieve non-linear measurement of the structure under strain in any direction. Accordingly, a fitting relationship between strain and non-linear index can be constructed, and then the measurement of structural strain can be realized; at the same time, by changing the parameters in the standard partial differential equation, the non-linearity of the target structure 102 under different magnitudes and directions of strain can be calculated, which is applicable to any structure where the sensor 103 can be arranged; in the case of determining the strain detection index values under multiple strains through simulation, only the received time-domain signal needs to be processed to evaluate the strain, avoiding cumbersome calculations and greatly improving the detection efficiency.

[0177] In some embodiments, based on the above strain detection method, the present application also provides a strain detection device. The following will be combined with Figure 10 to describe this device in detail.

[0178] Figure 10 The structural block diagram of the strain detection device according to an embodiment of the present application is shown.

[0179] As Figure 10 shown, the strain detection device 1000 of this embodiment includes a first determination module 1010, a first acquisition module 1020, a second determination module 1030, a reception module 1040, a second acquisition module 1050, a third determination module 1060, and a fourth determination module 1070.

[0180] The first determination module 1010 is used to determine the parameters in the standard partial differential equation corresponding to the target structure according to the wave equation of the target structure under strain action. In one embodiment, the first determination module 1010 can be used to perform the operation S210 described above, which will not be elaborated here.

[0181] The first acquisition module 1020 is configured to perform simulations of a structural model corresponding to a target structure under multiple strains based on parameters of the target structure under multiple strains and excitation signal data, and obtain simulation results under multiple strains. In one embodiment, the first acquisition module 1020 may be configured to perform the operation S220 described above, which will not be elaborated here.

[0182] The second determination module 1030 is configured to determine strain detection index values corresponding to respective multiple strains according to simulation results of the structural model under multiple strains. In one embodiment, the second determination module 1030 may be configured to perform the operation S230 described above, which will not be elaborated here.

[0183] The receiving module 1040 is configured to use an excitation signal to perform excitation at a target position of the target structure, and receive a time-domain signal corresponding to a target point at the target point on a guided wave propagation path. In one embodiment, the receiving module 1040 may be configured to perform the operation S240 described above, which will not be elaborated here.

[0184] The second acquisition module 1050 is configured to perform fast Fourier transform processing on the time-domain signal corresponding to the target point to obtain a frequency-domain signal corresponding to the target point. In one embodiment, the second acquisition module 1050 may be configured to perform the operation S250 described above, which will not be elaborated here.

[0185] The third determination module 1060 is configured to use the number of sideband peaks as a detection index, and determine a target strain detection index value based on the number of sideband peaks in the frequency-domain signal corresponding to the target point, where the detection index is determined according to a wave equation. In one embodiment, the third determination module 1060 may be configured to perform the operation S260 described above, which will not be elaborated here.

[0186] The fourth determination module 1070 is configured to determine a target strain corresponding to the target strain detection index value from a fitting curve, where the fitting curve is obtained by fitting strain detection index values corresponding to respective multiple strains. In one embodiment, the fourth determination module 1070 may be configured to perform the operation S270 described above, which will not be elaborated here.

[0187] According to an embodiment of the present application, the third determination module 1060 includes a first acquisition unit, a first determination unit, a second determination unit, and a third determination unit.

[0188] The first acquisition unit is configured to take the logarithm of the ordinate value of the frequency-domain signal corresponding to the target point and perform normalization processing to obtain a processed frequency-domain signal.

[0189] The first determination unit is configured to determine a first number of sideband peaks in the processed frequency-domain signal that is between a preset threshold upper limit and a preset threshold lower limit.

[0190] A second determination unit, configured to determine a second sideband peak number in the processed frequency-domain signal that is between a preset movement threshold and a preset threshold upper limit, where the preset movement threshold is between the preset threshold upper limit and the preset threshold lower limit.

[0191] A third determination unit, configured to determine a target strain detection index value according to the first sideband peak number and the second sideband peak number.

[0192] According to an embodiment of the present application, the preset movement threshold includes a plurality of different movement thresholds, and the second sideband peak number includes sideband peak numbers respectively corresponding to the plurality of different movement thresholds; the third determination unit includes a determination subunit and an obtaining subunit.

[0193] The determination subunit is configured to, for each movement threshold, determine a first initial strain detection index value according to the first sideband peak number and the sideband peak number corresponding to the movement threshold.

[0194] The obtaining subunit is configured to perform an averaging process on the first initial strain detection index values corresponding to each movement threshold to obtain the target strain detection index value.

[0195] According to an embodiment of the present application, the strain detection device 1000 further includes a fifth determination module, a sixth determination module, a seventh determination module, an eighth determination module, and a third obtaining module.

[0196] The fifth determination module is configured to determine a motion control expression of the target structure according to the material parameters of the target structure and the second derivative of the displacement of the detection point.

[0197] The sixth determination module is configured to determine an expression of the Lagrangian strain tensor of the detection point in the final state according to the position coordinates of the detection point in the final state, where the initial state is the state after stress is applied to the natural state to cause strain, the natural state is the state without stress application and without strain, the final state is obtained after the detection point fluctuates from the initial state, and the position coordinates in the final state are determined according to the applied strain and the position coordinates of the detection point in the natural state.

[0198] The seventh determination module is configured to determine an expression of the strain energy according to the expression of the Lagrangian strain tensor.

[0199] The eighth determination module is configured to determine an expression of the stress tensor in the presence of strain based on the expression of the Lagrangian strain tensor and the expression of the strain energy.

[0200] The third obtaining module is configured to substitute the expression of the stress tensor into the motion control expression of the target structure to obtain a wave equation of the target structure under the action of strain.

[0201] According to an embodiment of the present application, the first determination module 1010 includes a fourth determination unit.

[0202] The fourth determination unit is configured to compare the wave equation with a standard partial differential equation to determine the parameters in the standard partial differential equation.

[0203] According to an embodiment of the present application, the simulation result is a time-domain signal corresponding to strain; the second determination module 1030 includes a second acquisition unit, a third acquisition unit, a fifth determination unit, a sixth determination unit, a seventh determination unit, an eighth determination unit, and a ninth determination unit.

[0204] The second acquisition unit is configured to perform fast Fourier transform processing on the time-domain signal corresponding to each strain to obtain a frequency-domain signal corresponding to each strain.

[0205] The third acquisition unit is configured to take the logarithm of the ordinate value of the frequency-domain signal corresponding to each strain and perform normalization processing to obtain a processed frequency-domain signal corresponding to each strain.

[0206] The fifth determination unit is configured to determine a preset threshold upper limit and a preset threshold lower limit according to the processed frequency-domain signal corresponding to each strain.

[0207] The sixth determination unit is configured to determine the number of third sideband peaks between the preset threshold upper limit and the preset threshold lower limit in the processed frequency-domain signal corresponding to each strain for the strain.

[0208] The seventh determination unit is configured to determine the number of fourth sideband peaks between the preset threshold upper limit and a preset moving threshold in the processed frequency-domain signal corresponding to the strain.

[0209] The eighth determination unit is configured to determine a second initial strain detection index value corresponding to each moving threshold according to the number of third sideband peaks and the number of fourth sideband peaks.

[0210] The ninth determination unit is configured to determine a strain detection index value corresponding to each of the multiple strains based on the second initial strain detection index value corresponding to each moving threshold.

[0211] According to an embodiment of the present application, the excitation frequencies of the excitation signal include a first excitation frequency and a second excitation frequency; the receiving module 1040 includes an excitation unit.

[0212] The excitation unit is configured to use the excitation signal to excite a symmetric guided wave mode at a target position.

[0213] According to an embodiment of the present application, any one or more of the first determination module 1010, the first acquisition module 1020, the second determination module 1030, the receiving module 1040, the second acquisition module 1050, the third determination module 1060, and the fourth determination module 1070 may be combined and implemented in one module, or any one of them may be split into multiple modules. Alternatively, at least part of the functions of one or more of these modules may be combined with at least part of the functions of other modules and implemented in one module. According to an embodiment of the present application, at least one of the first determination module 1010, the first acquisition module 1020, the second determination module 1030, the receiving module 1040, the second acquisition module 1050, the third determination module 1060, and the fourth determination module 1070 may be at least partially implemented as a hardware circuit, such as a field programmable gate array (FPGA), a programmable logic array (PLA), a system on a chip, a system on a substrate, a system on a package, an application specific integrated circuit (ASIC), or may be implemented by any other reasonable means such as integrating or packaging circuits, etc., in hardware or firmware, or implemented in any one of the three implementation manners of software, hardware, and firmware, or in an appropriate combination of any several of them. Alternatively, at least one of the first determination module 1010, the first acquisition module 1020, the second determination module 1030, the receiving module 1040, the second acquisition module 1050, the third determination module 1060, and the fourth determination module 1070 may be at least partially implemented as a computer program module, and when the computer program module is run, it can execute corresponding functions.

[0214] Figure 11 FIG. shows a block diagram of an electronic device suitable for implementing a strain detection method according to an embodiment of the present application.

[0215] As Figure 11 shown, the electronic device 1100 according to an embodiment of the present application includes a processor 1101, which can perform various appropriate actions and processes according to a program stored in the ROM 1102 or a program loaded from the storage section 1108 into the RAM 1103. The processor 1101 may include, for example, a general microprocessor (such as a CPU), an instruction set processor, and / or a related chipset, and / or a dedicated microprocessor (such as an application specific integrated circuit (ASIC)), etc. The processor 1101 may also include on-board memory for caching purposes. The processor 1101 may include a single processing unit or multiple processing units for performing different actions of the method flow according to an embodiment of the present application.

[0216] In the RAM 1103, various programs and data required for the operation of the electronic device 1100 are stored. The processor 1101, the ROM 1102, and the RAM 1103 are connected to each other via a bus 1104. The processor 1101 performs various operations of the method flow according to the embodiments of the present application by executing the programs in the ROM 1102 and / or the RAM 1103. It should be noted that the programs may also be stored in one or more memories other than the ROM 1102 and the RAM 1103. The processor 1101 may also perform various operations of the method flow according to the embodiments of the present application by executing the programs stored in the one or more memories.

[0217] According to an embodiment of the present application, the electronic device 1100 may further include an input / output (I / O) interface 1105, and the input / output (I / O) interface 1105 is also connected to the bus 1104. The electronic device 1100 may further include one or more of the following components connected to the input / output (I / O) interface 1105: an input portion 1106 including a keyboard, a mouse, etc.; an output portion 1107 including, for example, a cathode ray tube (CRT), a liquid crystal display (LCD), etc. and a speaker, etc.; a storage portion 1108 including a hard disk, etc.; and a communication portion 1109 including a network interface card such as a LAN card, a modem, etc. The communication portion 1109 performs communication processing via a network such as the Internet. A drive 1110 is also connected to the input / output (I / O) interface 1105 as needed. A removable medium 1111, such as a magnetic disk, an optical disk, a magneto-optical disk, a semiconductor memory, etc., is installed on the drive 1110 as needed so that a computer program read from it can be installed into the storage portion 1108 as needed.

[0218] The present application also provides a computer-readable storage medium, which may be included in the device / apparatus / system described in the above embodiments; or may exist alone without being assembled into the device / apparatus / system. The above computer-readable storage medium carries one or more programs, and when the one or more programs are executed, the method according to the embodiments of the present application is implemented.

[0219] According to an embodiment of the present application, the computer-readable storage medium may be a non-volatile computer-readable storage medium, for example, it may include but is not limited to: portable computer disks, hard disks, random access memories, read-only memories, erasable programmable read-only memories (EPROM or flash memories), portable compact disk read-only memories (CD-ROMs), optical storage devices, magnetic storage devices, or any suitable combination of the above. In the present application, the computer-readable storage medium may be any tangible medium that contains or stores a program, and this program can be used by or in combination with an instruction execution system, apparatus, or device. For example, according to an embodiment of the present application, the computer-readable storage medium may include one or more memories other than the above-described ROM 1102 and / or RAM 1103 and / or ROM 1102 and RAM 1103.

[0220] An embodiment of the present application further includes a computer program product, which includes a computer program, and the computer program contains program code for executing the method shown in the flowchart. When the computer program product runs in a computer system, the program code is used to enable the computer system to implement the strain detection method provided by the embodiment of the present application.

[0221] When the computer program is executed by the processor 1101, it executes the above functions defined in the system / apparatus of the embodiment of the present application. According to an embodiment of the present application, the above-described systems, apparatuses, modules, units, etc. can be implemented by computer program modules.

[0222] In one embodiment, the computer program may rely on tangible storage media such as optical storage devices and magnetic storage devices. In another embodiment, the computer program may also be transmitted and distributed in the form of a signal on a network medium, and be downloaded and installed through the communication part 1109, and / or be installed from the removable medium 1111. The program code contained in the computer program can be transmitted by any suitable network medium, including but not limited to: wireless, wired, etc., or any suitable combination of the above.

[0223] In such an embodiment, the computer program can be downloaded and installed from the network through the communication part 1109, and / or be installed from the removable medium 1111. When the computer program is executed by the processor 1101, it executes the above functions defined in the system of the embodiment of the present application. According to an embodiment of the present application, the above-described systems, devices, apparatuses, modules, units, etc. can be implemented by computer program modules.

[0224] In accordance with embodiments of the present application, program code for executing the computer programs provided by the embodiments of the present application may be written in any combination of one or more programming languages. Specifically, these computing programs may be implemented using high-level procedural and / or object-oriented programming languages, and / or assembly / machine languages. Programming languages include, but are not limited to, such as Java, C++, Python, the "C" language, or similar programming languages. The program code may be executed entirely on the user's computing device, partially on the user's device, partially on a remote computing device, or entirely on a remote computing device or server. In cases involving a remote computing device, the remote computing device may be connected to the user's computing device through any type of network, including a local area network (LAN) or a wide area network (WAN), or it may be connected to an external computing device (e.g., by connecting through the Internet using an Internet service provider).

[0225] The flowcharts and block diagrams in the accompanying drawings illustrate the possible architectures, functions, and operations of systems, methods, and computer program products according to various embodiments of the present application. In this regard, each block in the flowchart or block diagram may represent a module, a program segment, or a part of code, and the above-mentioned module, program segment, or part of code contains one or more executable instructions for implementing the specified logical function. It should also be noted that in some alternative implementations, the functions marked in the blocks may occur in a different order than that marked in the accompanying drawings. For example, two consecutive blocks shown may actually be executed substantially in parallel, and they may sometimes be executed in the reverse order, depending on the functions involved. It should also be noted that each block in the block diagram or flowchart, and the combination of blocks in the block diagram or flowchart, may be implemented by a dedicated hardware-based system for performing the specified functions or operations, or may be implemented by a combination of dedicated hardware and computer instructions.

[0226] Those skilled in the art can understand that the features described in the various embodiments of the present application can be combined and / or combined in various ways, even if such combinations or combinations are not explicitly described in the present application. In particular, without departing from the spirit and teachings of the present application, the features described in the various embodiments of the present application can be combined and / or combined in various ways. All such combinations and / or combinations fall within the scope of the present application.

[0227] The above describes the embodiments of the present application. However, these embodiments are for illustrative purposes only and are not intended to limit the scope of the present application. Although the embodiments are described separately above, this does not mean that the measures in each embodiment cannot be used advantageously in combination. Without departing from the scope of the present application, those skilled in the art can make various substitutions and modifications, and all such substitutions and modifications should fall within the scope of the present application.

Claims

1. A strain detection method, characterized in that: The method comprises: Determining parameters in a standard partial differential equation corresponding to the target structure according to a wave equation of the target structure under strain; According to the parameters of the target structure under multiple strains and the excitation signal data, a structural model corresponding to the target structure is simulated under the multiple strains to obtain simulation results under the multiple strains; Determining strain detection index values ​​corresponding to each of the plurality of strains according to simulation results of the structural model under the plurality of strains; Using an excitation signal, excitation is performed at a target position of the target structure, and a time domain signal corresponding to the target point is received at the target point on the waveguide propagation path; Performing fast Fourier transform processing on the time domain signal corresponding to the target point to obtain a frequency domain signal corresponding to the target point; Taking the number of sideband peaks as a detection index, determining a target strain detection index value based on the number of sideband peaks in the frequency domain signal corresponding to the target point, wherein the detection index is determined according to the wave equation; A target strain corresponding to the target strain detection index value is determined from the fitting curve, wherein the fitting curve is obtained by fitting according to the strain detection index values ​​corresponding to each of the plurality of strains.

2. The method according to claim 1, characterized in that The method of using the number of sideband peaks as a detection index and determining a target strain detection index value based on the number of sideband peaks in a frequency domain signal corresponding to the target point includes: Taking the logarithm of the ordinate value of the frequency domain signal corresponding to the target point, and performing normalization processing to obtain a processed frequency domain signal; Determining the number of first sideband peaks between a preset upper threshold and a preset lower threshold in the processed frequency domain signal; Determine the number of second sideband peaks in the processed frequency domain signal that are between a preset moving threshold and an upper limit of the preset threshold, wherein the preset moving threshold is between the upper limit of the preset threshold and the lower limit of the preset threshold; The target strain detection index value is determined according to the number of the first sideband peaks and the number of the second sideband peaks.

3. The method according to claim 2, characterized in that The preset movement threshold comprises a plurality of different movement thresholds, and the second sideband peak number comprises the sideband peak numbers corresponding to each of the plurality of different movement thresholds; The determining the target strain detection index value according to the first sideband peak number and the second sideband peak number includes: For each of the movement thresholds, determining a first initial strain detection index value according to the first sideband peak number and the sideband peak number corresponding to the movement threshold; The first initial strain detection index value corresponding to each of the movement thresholds is averaged to obtain the target strain detection index value.

4. The method according to claim 1, characterized in that: The wave equation of the target structure under strain is obtained by the following operations, including: For the detection points in the target structure, Determining a motion control expression of the target structure according to material parameters of the target structure and a second-order derivative of the displacement of the detection point; According to the position coordinates of the detection point in the final state, determining the expression of the Lagrangian strain tensor of the detection point in the final state, wherein the initial state is a state after stress is applied to the natural state and strain occurs, the natural state is a state where no stress is applied and no strain occurs, the final state is obtained after the detection point fluctuates from the initial state, and the position coordinates of the final state are determined according to the applied strain and the position coordinates of the detection point in the natural state; Determine an expression for strain energy according to the expression for the Lagrangian strain tensor; Determine an expression for a stress tensor in the presence of strain based on the expression for the Lagrangian strain tensor and the expression for the strain energy; The expression of the stress tensor is substituted into the motion control expression of the target structure to obtain the wave equation of the target structure under the action of strain.

5. The method according to claim 4, characterized in that Determining parameters in a standard partial differential equation corresponding to the target structure according to a wave equation of the target structure under strain includes: The wave equation is compared with the standard partial differential equation to determine the parameters in the standard partial differential equation.

6. The method according to claim 3, characterized in that The simulation result is a time domain signal corresponding to the strain; and determining the strain detection index value corresponding to each of the multiple strains according to the simulation results of the structural model under the multiple strains includes: Performing fast Fourier transform processing on the time domain signal corresponding to each strain to obtain the frequency domain signal corresponding to each strain; Taking the logarithm of the ordinate value of the frequency domain signal corresponding to each strain, and performing normalization processing to obtain a processed frequency domain signal corresponding to each strain; Determining the preset upper threshold value and the preset lower threshold value according to the processed frequency domain signal corresponding to each strain; For the processed frequency domain signal corresponding to each strain, Determine the number of third sideband peaks located between the preset upper threshold and the preset lower threshold in the processed frequency domain signal corresponding to the strain; Determining the number of fourth sideband peaks located between the preset upper threshold value and the preset moving threshold value in the processed frequency domain signal corresponding to the strain; Determining a second initial strain detection index value corresponding to each movement threshold according to the third sideband peak number and the fourth sideband peak number; Based on the second initial strain detection index value corresponding to each movement threshold, a strain detection index value corresponding to each of the plurality of strains is determined.

7. The method according to claim 1, characterized in that The excitation frequency of the excitation signal includes a first excitation frequency and a second excitation frequency; and the excitation at the target position of the target structure using the excitation signal includes: A symmetric guided wave mode is excited at the target position by using the excitation signal.

8. A strain detection device, characterized in that: The device comprises: A first determination module is used to determine parameters in a standard partial differential equation corresponding to the target structure according to a wave equation of the target structure under strain; A first acquisition module is used to simulate a structural model corresponding to the target structure under the multiple strains according to the parameters of the target structure under the multiple strains and the excitation signal data, so as to obtain simulation results under the multiple strains; A second determination module is used to determine the strain detection index value corresponding to each of the multiple strains according to the simulation results of the structural model under the multiple strains; A receiving module, used to excite at a target position of the target structure using an excitation signal, and receive a time domain signal corresponding to the target point at the target point on the waveguide propagation path; A second acquisition module is used to perform fast Fourier transform processing on the time domain signal corresponding to the target point to obtain a frequency domain signal corresponding to the target point; a third determination module, configured to determine a target strain detection index value based on the number of sideband peaks in the frequency domain signal corresponding to the target point, using the number of sideband peaks as a detection index, wherein the detection index is determined according to the wave equation; The fourth determination module is used to determine the target strain corresponding to the target strain detection index value from the fitting curve, wherein the fitting curve is obtained by fitting according to the strain detection index values ​​corresponding to each of the multiple strains.

9. An electronic device, comprising: one or more processors; a memory for storing one or more computer programs, It is characterized in that the one or more processors execute the one or more computer programs to implement the steps of the method according to any one of claims 1 to 7.

10. A computer-readable storage medium having a computer program or instruction stored thereon, characterized in that: When the computer program or instruction is executed by a processor, the steps of the method according to any one of claims 1 to 7 are implemented.

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