Defect detection method and system based on time-varying mechanism modal coupling point

Abstract

The invention relates to the technical field of nondestructive testing, and discloses a defect detection method and system based on a modal coupling point of a time-varying mechanism, and the method comprises the following steps: realizing periodic time-varying stiffness through time modulation so as to construct the modal coupling point, scanning modulation parameters, and degenerating the fundamental frequency and the first-order harmonic frequency of a medium under the two modulation parameters. The modal coupling points have high-sensitivity sensing ability to tiny disturbance, specifically, under the influence of defects, the degeneracy degree of the modal coupling points is degraded, frequency splitting occurs, and the splitting degree can reflect the sizes of the defects. Based on the principle, a piezoelectric plate is externally connected with a negative capacitance circuit to realize time modulation of equivalent stiffness so as to construct a modal coupling point, excitation and measurement response are applied to the surface of a medium, and split frequency response is obtained. And due to the square root relationship between the response and the defect, the detection of the tiny defect is more advantageous.

Description

Technical Field

[0001] The present invention relates to the technical field of nondestructive testing, and in particular to a defect detection method and system based on a time-varying mechanism modal coupling point. Background Art

[0002] With the development of industrialization, the safety and durability requirements of various industrial equipment and large-scale construction projects are becoming higher and higher. Timely and correct detection of structural defects is an important measure to ensure the safety and reliability of production and life. The main principle of defect detection technology is to feedback defect information based on the change of the dynamic characteristics of the defective structure itself, such as the natural frequency, vibration mode, strain energy, etc., which respond under the influence of defects. However, this method has poor accuracy and is affected by factors such as vibration.

[0003] The defect detection method based on modal coupling points also senses and identifies defects through frequency response. The modal coupling point is a degenerate point where the intrinsic frequency and intrinsic mode of a structure are simultaneously merged. When there are disturbances such as defects in the structure, its degeneracy is degraded, and the degenerate frequency is split. The information of the defect is judged by the degree of frequency splitting. In addition, this frequency splitting becomes a nonlinear change relationship as the defect expands, which is more advantageous for the detection of smaller defects.

[0004] A common method for constructing modal coupling points in elastic media is to use an electromechanically coupled piezoelectric scheme combined with a feedback control strategy to modulate the feedback coefficient to control the formation of modal coupling points. For example, the Journal of Mechanics and Physics of Solids (J.Mech.Phys.Solids, Vol. 149, 2021, p. 104325) reported that two pairs of feedback-controlled piezoelectric elements were set at symmetrical positions on the surface of an elastic medium. The modal coupling points were realized by modulating the feedback coefficients, and the surface cracks were detected. The frequency splitting caused by the cracks changes with the crack size in a square root-dependent relationship. This scheme that relies on feedback control is essentially a time-invariant system that requires multiple control elements. The structural design and modulation system are relatively complex, and feedback control is prone to stability problems.

[0005] The time control scheme that introduces time variables can break the limitation of the number of primitives, and the modal coupling point can be constructed using a single functional primitive. The core of this type of method is the design of the time modulation scheme. For example, Physical Review Applied (Physical Review Applied 2022 Vol. 18, No. 6, p. 064055) reported a mechanical device with time-modulated mass, which has constant stiffness and time-varying inertial mass, and can construct modal coupling points for disturbance perception. However, this scheme relies on mechanical structure design and is relatively complex. The design of a time modulation system using a more flexible and adjustable piezoelectric mechanism is the focus of future research. Summary of the invention

[0006] In view of the above existing problems, the present invention is proposed.

[0007] Therefore, the present invention provides a defect detection method based on time-varying mechanism modal coupling points. Traditional defect detection methods often rely on fixed excitation signals and analysis algorithms, and lack the ability to adapt to material properties and environmental changes. The present invention enhances the real-time monitoring capability of material defects by introducing a time-varying mechanism, dynamically adjusting the excitation signal, and constructing modal coupling points, while improving the reliability and applicability of detection under complex working conditions.

[0008] In order to solve the above technical problems, the present invention provides the following technical solutions, which are defect detection methods based on time-varying mechanism modal coupling points, including: constructing modal coupling points in a defect-free medium through a time modulation mechanism, and determining modulation parameters corresponding to the modal coupling points; applying the same time-varying mechanism to the elastic medium under test, inputting a sinusoidal excitation force, and measuring the output response spectrum; judging the existence and size of defects according to the frequency response splitting in the response spectrum.

[0009] As a preferred solution of the defect detection method based on the time-varying mechanism modal coupling point described in the present invention, the construction of the modal coupling point includes pasting a piezoelectric sheet on the lower surface of a defect-free elastic medium, and realizing the periodic time variation of the equivalent stiffness of the piezoelectric sheet by connecting a negative capacitance circuit controlled by a switch, thereby forming a modal coupling point in the medium.

[0010] As a preferred solution of the defect detection method based on the time-varying mechanism modal coupling point of the present invention, wherein: the periodic time variation of the equivalent stiffness of the piezoelectric sheet includes the modulation amplitude α and the stiffness modulation frequency ωω m Determine together, where ω m is the key modulation parameter, which is determined experimentally to achieve the best modal coupling effect.

[0011] As a preferred solution of the defect detection method based on the time-varying mechanism modal coupling point of the present invention, wherein: the modulation parameter corresponding to the modal coupling point is determined by continuously increasing the modulation parameter ω m , observe the response peaks at the fundamental frequency and the first-order harmonic frequency in the response spectrum, where the modulation parameter ω m Starting from the fundamental frequency, the response peak of the first-order harmonic frequency increases with ω m The modulation parameter at this time is determined as ω ma , note that there should be two modal coupling points near 2 times the fundamental frequency, that is, the modulation parameter ω ma There are two options, either of which you can use as a next step.

[0012] As a preferred solution of the defect detection method based on the time-varying mechanism modal coupling point of the present invention, the time-varying mechanism includes selecting a set of sinusoidal signals of frequency and phase,

[0013] U(t)=Asin(ω c t)

[0014] Where A is the excitation amplitude, ω c is the excitation frequency, t is the time, the excitation frequency is set within the range of 0.5 to 1.5 times the fundamental frequency, the measurement position of the output response is consistent with the excitation position, the measurement data is the z-direction component of the medium acceleration, and the output data is processed to obtain the response spectrum;

[0015] A time-varying factor T(t) is set, the frequency and phase of the signal are considered, and time delay and nonlinear characteristics are introduced. After improvement, the excitation signal is defined as:

[0016] F(t)=Asin(ω c t+φ)·T(t)

[0017] T(t)=1+αcos(βt+γ)

[0018] Among them, α, β, and γ are modulation amplitude, modulation frequency, and modulation phase, respectively. This form allows the signal to have dynamic changes in the time domain and enhances the adaptability to medium characteristics.

[0019] As a preferred solution of the defect detection method based on time-varying mechanism modal coupling point of the present invention, wherein: the measured output response spectrum includes a frequency resolution determined by the sampling frequency f s and the number of sampling points N(t), and introduce the time-varying sampling frequency f s (t), so that the local adaptation signal characteristic changes, the calculation formula is:

[0020]

[0021] Where Δf(t) represents the frequency resolution;

[0022] In the generation of the output response spectrum, it is necessary to ensure that the response spectrum reflects the modal coupling characteristics, and the influence of modal coupling is reflected by the fast Fourier transform and the modulation factor:

[0023] S output (f)=|S(f)|·G(f)

[0024] G(f)=1+k·e -bf

[0025] Among them, S output(f) is the final output response spectrum, S(f) is the response spectrum after fast Fourier transform, G(f) is the modulation factor, k is the adjustment parameter, and b is the frequency attenuation parameter.

[0026] As a preferred solution of the defect detection method based on the time-varying mechanism modal coupling point of the present invention, wherein: the determination of the existence and size of the defect includes arranging a time-modulated piezoelectric sheet on the lower surface of the elastic medium to be tested, and the time modulation mechanism of the piezoelectric sheet is the same as the modulation mechanism of the piezoelectric sheet arranged on the lower surface of the defect-free medium;

[0027] Set the modulation parameter to the modulation parameter ω corresponding to the selected modal coupling point in the defect-free medium ma ;

[0028] An excitation device and a measuring device are arranged on the upper surface of the elastic medium to be tested. The excitation parameters are set the same as those of the defect-free medium. The frequency response spectrum is measured. If there are defects in the medium to be tested, two resonance peaks will appear in the frequency response under the influence of the defects. The size of the defect can be quantitatively judged by analyzing the degree of splitting of the two resonance peaks in the response spectrum. The greater the degree of splitting, the larger the size of the defect.

[0029] As a preferred solution of the defect detection system based on the time-varying mechanism modal coupling point of the present invention, it includes: a modulation parameter determination module corresponding to the modal coupling point, a defect detection module, a defect detection module, and a judgment module;

[0030] The module for determining the modulation parameters corresponding to the modal coupling point is used to determine the modulation parameters ω corresponding to the modal coupling point in a defect-free medium. ma size;

[0031] The module also includes an excitation unit for exciting the elastic medium to vibrate and generating a resonance peak in the response spectrum;

[0032] A measuring unit, used for measuring the output response and obtaining a response spectrum;

[0033] The defect detection module is used to set the modulation parameter ω selected in the defect-free medium to the medium under test. ma , and input the excitation and measure the output response. If two resonance peaks appear in the frequency response, it is judged that there is a defect, and the degree of splitting reflects the size of the defect;

[0034] The module also includes:

[0035] An excitation unit, used to excite the elastic medium to vibrate and generate a resonance peak in the response spectrum;

[0036] A measuring unit, used for measuring the output response and obtaining a response spectrum;

[0037] The piezoelectric patch with an external negative capacitance circuit is used to achieve the time variation of the equivalent stiffness of the piezoelectric patch through time modulation. The modulation parameter ω m Select the parameter ω selected in the modulation parameter determination module corresponding to the modal coupling point ma ;

[0038] The judging module judges that the measured medium has defects if two split resonance peaks appear in the frequency response.

[0039] A computer device includes a memory and a processor, wherein the memory stores a computer program, and is characterized in that when the processor executes the computer program, the steps of a defect detection method based on a time-varying mechanism modal coupling point are implemented.

[0040] A computer-readable storage medium stores a computer program thereon, wherein when the computer program is executed by a processor, the steps of a defect detection method based on a time-varying mechanism modal coupling point are implemented.

[0041] Beneficial effects of the present invention: This method can achieve two modal coupling points and respond to defects by adjusting the time modulation parameters. The modal coupling point is easy to obtain and determine, and can generally be found by performing parameter modulation near 2 times the fundamental frequency. The response of the second-order modal coupling point is in a square root relationship with the defect, which is more advantageous than the traditional linear response. The modal coupling point can be constructed and detected by time modulation of a single piezoelectric element. The external circuit of the piezoelectric piece is relatively simple, and the periodic opening and closing control of the switch is relatively easy to achieve. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the drawings required for describing the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work. Among them:

[0043] Figure 1 A schematic flow chart of a defect detection method based on a time-varying mechanism modal coupling point provided by an embodiment of the present invention.

[0044] Figure 2 A schematic diagram of a cylindrical elastic medium and a piezoelectric piece with an external negative capacitance circuit for a defect detection method based on a time-varying mechanism modal coupling point provided by an embodiment of the present invention.

[0045] Figure 3 The left figure in the defect detection method based on time-varying mechanism modal coupling point provided by an embodiment of the present invention is the evolution spectrum of the eigenfrequency ω with the modulation parameter ωm obtained by theoretical calculation, and the right figure is the frequency response evolution spectrum obtained by using the piezoelectric piece as the excitation and sensing measurement unit.

[0046] Figure 4 According to a defect detection method based on a time-varying mechanism modal coupling point provided by an embodiment of the present invention, at a second-order modal coupling point, the frequency splitting value changes in a square root relationship with an increase in the additional mass disturbance.

[0047] Figure 5 An embodiment of the present invention provides a method for defect detection based on a time-varying mechanism modal coupling point, including a modulation parameter determination module and a defect detection module corresponding to a modal coupling point arranged in an elastic medium.

[0048] Figure 6 A schematic diagram of frequency splitting of a modal coupling point under the influence of a defect in a defect detection method based on a time-varying mechanism modal coupling point provided by an embodiment of the present invention.

[0049] Figure 7 A schematic diagram of the working modules of a defect detection system based on a time-varying mechanism modal coupling point provided by an embodiment of the present invention. DETAILED DESCRIPTION

[0050] In order to make the above-mentioned purposes, features and advantages of the present invention more obvious and easy to understand, the specific implementation methods of the present invention are described in detail below in conjunction with the drawings of the specification. Obviously, the described embodiments are part of the embodiments of the present invention, but not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary persons in the art without creative work should fall within the scope of protection of the present invention.

[0051] In the following description, many specific details are set forth to facilitate a full understanding of the present invention, but the present invention may also be implemented in other ways different from those described herein, and those skilled in the art may make similar generalizations without violating the connotation of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed below.

[0052] Secondly, the term "one embodiment" or "embodiment" as used herein refers to a specific feature, structure, or characteristic that may be included in at least one implementation of the present invention. The term "in one embodiment" that appears in different places in this specification does not necessarily refer to the same embodiment, nor is it a separate or selective embodiment that is mutually exclusive with other embodiments.

[0053] The present invention is described in detail with reference to schematic diagrams. When describing the embodiments of the present invention, for the sake of convenience, the cross-sectional diagrams showing the device structure will not be partially enlarged according to the general scale, and the schematic diagrams are only examples, which should not limit the scope of protection of the present invention. In addition, in actual production, the three-dimensional dimensions of length, width and depth should be included.

[0054] At the same time, in the description of the present invention, it should be noted that the directions or positional relationships indicated by the terms "upper, lower, inner and outer" are based on the directions or positional relationships shown in the drawings, which are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific direction, be constructed and operated in a specific direction, and therefore cannot be understood as limiting the present invention. In addition, the terms "first, second or third" are only used for descriptive purposes and cannot be understood as indicating or implying relative importance.

[0055] In the present invention, unless otherwise clearly specified and limited, the terms "install, connect, connect" should be understood in a broad sense, for example: it can be a fixed connection, a detachable connection or an integral connection; it can also be a mechanical connection, an electrical connection or a direct connection, or it can be indirectly connected through an intermediate medium, or it can be the internal communication of two components. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0056] Example 1, reference Figure 1 - Figure 4 , which is the first embodiment of the present invention, provides a defect detection method based on a time-varying mechanism modal coupling point, comprising:

[0057] S1: Realize the modal coupling point and determine the modulation parameters through the time modulation mechanism in the defect-free medium.

[0058] Furthermore, a piezoelectric sheet is attached to the lower surface of a defect-free elastic medium, and a negative capacitance circuit controlled by a switch is connected to realize the periodic time variation of the equivalent stiffness of the piezoelectric sheet, forming a modal coupling point in the medium. m Determine together, where ω m is the key modulation parameter, which is determined experimentally to achieve the best modal coupling effect.

[0059] It should be noted that the modulation parameters corresponding to the modal coupling point are determined by continuously increasing the modulation parameter ω m , observe the response peaks at the fundamental frequency and the first-order harmonic frequency in the response spectrum, where the modulation parameter ω m Starting from the fundamental frequency, the response peak of the first-order harmonic frequency increases with ω m The modulation parameter at this time is determined as ω ma , note that there should be two modal coupling points near 2 times the fundamental frequency, that is, the modulation parameter ω ma There are two options, either of which you can use as a next step.

[0060] It should also be noted that Figure 2Taking the cylindrical elastic medium shown in the figure as an example, the modal coupling points are constructed in the defect-free cylindrical medium and the corresponding modulation parameters are determined. First, a piezoelectric sheet ( Figure 2 The light-colored cylinder at the bottom), the polarization direction of the piezoelectric film is in the z direction. The upper and lower surfaces of the piezoelectric film are connected as follows Figure 2 The switch-controlled negative capacitance circuit shown in the figure can realize the regulation of the equivalent stiffness of the piezoelectric film by opening and closing the circuit. The time-varying equivalent stiffness of the piezoelectric film is shown in the following formula:

[0061]

[0062] The modulation law expressed by the above formula is: when the switch is off, the modulus of the piezoelectric film is E p ; When the switch is closed, the negative capacitance circuit is connected, and the equivalent modulus of the piezoelectric film is The square wave modulation of the modulus leads to the square wave modulation of the stiffness. α is the modulation amplitude, which is determined by the circuit element parameters, and in this embodiment, α=0.42; ωm is the stiffness modulation frequency, that is, the modulation parameter to be determined.

[0063] S2: Perform time modulation in the measured medium using the selected modulation parameters.

[0064] Furthermore, we select a set of sinusoidal signals with different frequencies and phases.

[0065] U(t)=Asin(ω c t)

[0066] Where A is the excitation amplitude, ω c is the excitation frequency, t is the time, the excitation frequency is generally set in the range of 0.5 to 1.5 times the fundamental frequency, the measurement position of the output response is consistent with the excitation position, the measurement data is the z-direction component of the medium acceleration, and the output data is processed to obtain the response spectrum;

[0067] A time-varying factor T(t) is set, the frequency and phase of the signal are considered, and time delay and nonlinear characteristics are introduced. After improvement, the excitation signal is defined as:

[0068] F(t)=Asin(ω c t+φ)·T(t)

[0069] T(t)=1+αcos(βt+γ)

[0070] Among them, α, β, and γ are modulation amplitude, modulation frequency, and modulation phase, respectively. This form allows the signal to have dynamic changes in the time domain and enhances the adaptability to medium characteristics.

[0071] It should be noted that the frequency resolution is determined by the sampling frequency f s and the number of sampling points N(t), and introduce the time-varying sampling frequency fs (t), so that the local adaptation signal characteristic changes, the calculation formula is:

[0072]

[0073] Where Δf(t) represents the frequency resolution;

[0074] In the generation of the output response spectrum, it is necessary to ensure that the response spectrum reflects the modal coupling characteristics, and the influence of modal coupling is reflected by the fast Fourier transform and the modulation factor:

[0075] S output (f)=|S(f)|·G(f)

[0076] G(f(=1+k·e -bf

[0077] Among them, S output (f) is the final output response spectrum, S(f) is the response spectrum after fast Fourier transform, G(f) is the modulation factor, k is the adjustment parameter, and b is the frequency attenuation parameter.

[0078] Furthermore, if Figure 3 As shown in the right figure, the coordinate ω0 is the fundamental frequency. In this embodiment, ω0 = 66200 rad / s. m , the two resonance peaks keep approaching and finally merge at one point; continue to increase the modulation parameter ω m , after a period of merging, two resonance peaks appear again. The resonance peak merging point and the point where they separate again are two modal coupling points, and the corresponding two modulation parameters can be obtained, namely ω ma In this embodiment, ω ma =1.914 and 2.006 times the fundamental frequency. In this embodiment, the modulation parameter ω corresponding to the second modal coupling point is selected. ma , used for subsequent defect detection.

[0079] The same time-modulated piezoelectric piece is arranged on the lower surface of the measured medium, with the polarization direction in the z direction and the stiffness modulation frequency ω m Set to the ω selected in S1 ma =2.006ω0. The piezoelectric film parameters and circuit parameters are the same as those set in S1.

[0080] S3: Apply excitation to a defect-free medium and measure the response. If two split resonance peaks appear in the response spectrum, it is judged that there is a defect.

[0081] Furthermore, a time-modulated piezoelectric sheet is arranged on the lower surface of the elastic medium to be measured, and the time modulation mechanism of the piezoelectric sheet is the same as the modulation mechanism of the piezoelectric sheet arranged on the lower surface of the defect-free medium;

[0082] Set the modulation parameter to the modulation parameter ωma corresponding to the selected modal coupling point in the defect-free medium;

[0083] An excitation device and a measuring device are arranged on the upper surface of the elastic medium to be tested. The excitation parameters are set the same as those of the defect-free medium. The frequency response spectrum is measured. If there are defects in the medium to be tested, two resonance peaks will appear in the frequency response under the influence of the defects. The size of the defect can be quantitatively judged by analyzing the degree of splitting of the two resonance peaks in the response spectrum. The greater the degree of splitting, the larger the size of the defect.

[0084] It should be noted that the excitation is input on the surface of the measured medium and the output response is measured. The sinusoidal excitation force is the same as in S1, and the measured data is the z-direction component of the surface acceleration of the medium. Figure 4 As shown in the left sub-figure of , additional mass disturbance is applied to the surface of the measured medium, and the degenerate frequency at the modal coupling point is split. Figure 4 As shown in the right sub-figure of , the frequency splitting value increases with the increase of the added mass, showing a square root response trend. This shows that when the disturbance is extremely small, the detection sensitivity based on the modal coupling point is greater than the linear response method.

[0085] Example 2, reference Figure 2 , Figure 5 , Figure 6 , which is an embodiment of the present invention, provides a defect detection method based on a time-varying mechanism modal coupling point. In order to verify the beneficial effects of the present invention, scientific demonstration is carried out through experiments.

[0086] This embodiment uses a modal coupling point to detect the additional mass disturbance in a cylindrical elastic medium. Figure 5 As shown in the figure, the defect disturbance in the medium is equivalent to the additional mass disturbance, and the modal coupling point can also respond to it. In the modulation parameter determination module on the left, the time-modulated piezoelectric sheet is attached to the lower surface of the defect-free medium, and the polarization direction of the piezoelectric sheet is in the z direction. The upper and lower surfaces of the piezoelectric sheet are connected as shown in the figure. Figure 2 The switch-controlled negative capacitance circuit shown in FIG. The excitation and measurement devices are arranged on the upper surface of the defect-free medium. In this embodiment, the same piezoelectric sheet is used for excitation and sensing. The polarization direction and potential difference direction of the piezoelectric sheet are both in the z direction. The piezoelectric sheet is driven to produce a deformation in the z direction so that the medium vibrates in the z direction. The piezoelectric sensor measures the acceleration component in the z direction of the medium surface, and the output data is processed to obtain the response spectrum. The modulation parameter ω is continuously increased. m Get the modal coupling point and determine its corresponding modulation parameter ω ma .

[0087] Keep the settings of the time modulation piezoelectric sheet and the excitation measurement piezoelectric sheet of the modulation parameter determination module unchanged, and use the same time modulation piezoelectric sheet and the excitation measurement piezoelectric sheet in the defect detection module of the measured medium, where the modulation parameter is set to ω ma After excitation and response measurement, the response spectrum is obtained, such as Figure 6 As shown in the figure, the defects in the medium cause the degenerate single resonance peak to split and form two resonance peaks. Therefore, the presence or absence of defects in the medium can be determined by whether the two resonance peaks appear in the response spectrum, and the frequency splitting degree reflects the size information of the defect. The defect detection module can move and scan on the surface of the medium until all the media under test are fully detected.

[0088] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the present invention may be modified or replaced by equivalents without departing from the spirit and scope of the technical solutions of the present invention, which should all be included in the scope of the claims of the present invention.

[0089] Embodiment 3, the third embodiment of the present invention, is different from the first two embodiments in that:

[0090] If the functions are implemented in the form of software functional units and sold or used as independent products, they can be stored in a computer-readable storage medium. Based on this understanding, the technical solution of the present invention, or the part that contributes to the prior art or the part of the technical solution, can be embodied in the form of a software product. The computer software product is stored in a storage medium, including several instructions for a computer device (which can be a personal computer, a server, or a network device, etc.) to perform all or part of the steps of the methods described in each embodiment of the present invention. The aforementioned storage medium includes: U disk, mobile hard disk, read-only memory (ROM, Read-Only Memory), random access memory (RAM, Random Access Memory), disk or optical disk, etc., which can store program codes.

[0091] The logic and / or steps represented in the flowchart or otherwise described herein, for example, can be considered as an ordered list of executable instructions for implementing logical functions, and can be embodied in any computer-readable medium for use by an instruction execution system, device or apparatus (such as a computer-based system, a system including a processor, or other system that can fetch instructions from an instruction execution system, device or apparatus and execute instructions), or in conjunction with such instruction execution systems, devices or apparatuses. For the purposes of this specification, "computer-readable medium" can be any device that can contain, store, communicate, propagate or transmit a program for use by an instruction execution system, device or apparatus, or in conjunction with such instruction execution systems, devices or apparatuses.

[0092] More specific examples of computer-readable media (a non-exhaustive list) include the following: an electrical connection with one or more wires (electronic device), a portable computer disk case (magnetic device), a random access memory (RAM), a read-only memory (ROM), an erasable and programmable read-only memory (EPROM or flash memory), an optical fiber device, and a portable compact disk read-only memory (CDROM). In addition, the computer-readable medium may even be a paper or other suitable medium on which the program is printed, since the program may be obtained electronically, for example, by optically scanning the paper or other medium, followed by editing, deciphering or, if necessary, processing in another suitable manner, and then stored in a computer memory.

[0093] It should be understood that the various parts of the present invention can be implemented by hardware, software, firmware or a combination thereof. In the above-mentioned embodiments, a plurality of steps or methods can be implemented by software or firmware stored in a memory and executed by a suitable instruction execution system. For example, if implemented by hardware, as in another embodiment, it can be implemented by any one of the following technologies known in the art or their combination: a discrete logic circuit having a logic gate circuit for implementing a logic function for a data signal, a dedicated integrated circuit having a suitable combination of logic gate circuits, a programmable gate array (PGA), a field programmable gate array (FPGA), etc.

[0094] Example 4, reference Figure 7 , is an embodiment of the present invention, providing a defect detection system based on a time-varying mechanism modal coupling point, characterized in that: it includes a modal coupling point corresponding modulation parameter determination module 1, which is used to determine the modal coupling point corresponding modulation parameter ω in a defect-free medium. ma Size, including:

[0095] The excitation unit 11 is used to excite the elastic medium to vibrate and generate a resonance peak in the response spectrum;

[0096] The measuring unit 12 is used to measure the output response and obtain the response spectrum;

[0097] The piezoelectric patch with an external negative capacitance circuit is used to achieve the time variation of the equivalent stiffness of the piezoelectric patch through time modulation. The circuit is opened and closed by switching to perform time periodic modulation, and the modal coupling point is constructed based on the time-varying stiffness. The modulation parameter ω is continuously increased. m , until the two resonance peaks in the measured response spectrum merge, and determine the parameter ω at this time ma size;

[0098] Defect detection module 2 is used to set the modulation parameter ωma selected in the defect-free medium for the medium under test, input the excitation and measure the output response. If two resonance peaks appear in the frequency response, it is judged that there is a defect, and the degree of splitting reflects the size of the defect. It includes:

[0099] The excitation unit 21 is used to excite the elastic medium to vibrate and generate a resonance peak in the response spectrum;

[0100] The measuring unit 22 is used to measure the output response and obtain the response spectrum;

[0101] The piezoelectric patch with an external negative capacitance circuit is used to achieve the time variation of the equivalent stiffness of the piezoelectric patch through time modulation. The modulation parameter ω m Select the parameter ω selected in the modulation parameter determination module corresponding to the modal coupling point ma ;

[0102] Judgment module 3: If two split resonance peaks appear in the frequency response, it is judged that the measured medium has defects.

[0103] The invention requires simple equipment, can detect defects in elastic media using a single functional primitive (including time modulation and excitation measurement functions), and has a simple structure. The location of the modal coupling point of this method is basically known, and the modulation parameters can be determined near 2 times the base frequency using fewer parameter scanning steps. It can adapt to different structures and working conditions, and the modal coupling point responds more significantly to tiny defects, which is more advantageous for detecting subtle defects.

[0104] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the present invention may be modified or replaced by equivalents without departing from the spirit and scope of the technical solutions of the present invention, which should all be included in the scope of the claims of the present invention.

Claims

1. A defect detection method based on a time-varying mechanism modal coupling point, characterized in that: include, In a defect-free medium, a modal coupling point is constructed through a time modulation mechanism, and the modulation parameters corresponding to the modal coupling point are determined; Apply the same time-varying mechanism to the elastic medium under test, input a sinusoidal excitation force, and measure the output response spectrum; The existence and size of defects can be judged based on the frequency response splitting in the response spectrum.

2. The defect detection method based on time-varying mechanism modal coupling point according to claim 1, characterized in that: The construction of the modal coupling point includes pasting a piezoelectric sheet on the lower surface of a defect-free elastic medium, and realizing the periodic time variation of the equivalent stiffness of the piezoelectric sheet by connecting a negative capacitance circuit controlled by a switch, thereby forming a modal coupling point in the medium.

3. The defect detection method based on time-varying mechanism modal coupling point according to claim 2, characterized in that: The periodic time variation of the equivalent stiffness of the piezoelectric patch includes the modulation amplitude α and the stiffness modulation frequency ωω m Determine together, where ω m is the key modulation parameter, which is determined experimentally to achieve the best modal coupling effect.

4. The defect detection method based on time-varying mechanism modal coupling points according to claim 3 is characterized in that: The determining of the modulation parameter corresponding to the modal coupling point includes continuously increasing the modulation parameter ω m , observe the response peaks at the fundamental frequency and the first-order harmonic frequency in the response spectrum, where the modulation parameter ω m Starting from the fundamental frequency, the response peak of the first-order harmonic frequency increases with ω m The modulation parameter at this time is determined as ω ma , note that there should be two modal coupling points near 2 times the fundamental frequency, that is, the modulation parameter ω ma There are two options, either of which you can use as a next step.

5. The defect detection method based on time-varying mechanism modal coupling point according to claim 4, characterized in that: The time-varying mechanism includes selecting a set of sinusoidal signals of frequency and phase, U(t)=Salin(ω c t) Where A is the excitation amplitude, ω c is the excitation frequency, t is the time, the excitation frequency is set within the range of 0.5 to 1.5 times the fundamental frequency, the measurement position of the output response is consistent with the excitation position, the measurement data is the z-direction component of the medium acceleration, and the output data is processed to obtain the response spectrum; A time-varying factor T(t) is set, the frequency and phase of the signal are considered, and time delay and nonlinear characteristics are introduced. After improvement, the excitation signal is defined as: F(t)=Asin(ω c t+φ)·T(t) T(t)=1+αcos(βt+γ) Among them, α, β, and γ are modulation amplitude, modulation frequency, and modulation phase, respectively. This form allows the signal to have dynamic changes in the time domain and enhances the adaptability to medium characteristics.

6. The defect detection method based on time-varying mechanism modal coupling points according to claim 5, characterized in that: The measured output response spectrum includes the frequency resolution determined by the sampling frequency f s and the number of sampling points N(t), and introduce the time-varying sampling frequency f s (t), so that the local adaptation signal characteristic changes, the calculation formula is: Where Δf(t) represents the frequency resolution; In the generation of the output response spectrum, it is necessary to ensure that the response spectrum reflects the modal coupling characteristics, and the influence of modal coupling is reflected by the fast Fourier transform and the modulation factor: S output (f)=|S(f)|·G(f) G(f)=1+k·e -bf Among them, S output (f) is the final output response spectrum, S(f) is the response spectrum after fast Fourier transform, G(f) is the modulation factor, k is the adjustment parameter, and b is the frequency attenuation parameter.

7. The defect detection method based on time-varying mechanism modal coupling points according to claim 6, characterized in that: The determination of the existence and size of the defect includes arranging a time-modulated piezoelectric sheet on the lower surface of the elastic medium to be tested, wherein the time modulation mechanism of the piezoelectric sheet is the same as the modulation mechanism of the piezoelectric sheet arranged on the lower surface of the defect-free medium; Set the modulation parameter to the modulation parameter ω corresponding to the selected modal coupling point in the defect-free medium ma ; An excitation device and a measuring device are arranged on the upper surface of the elastic medium to be tested. The excitation parameters are set the same as those of the defect-free medium. The frequency response spectrum is measured. If there are defects in the medium to be tested, two resonance peaks will appear in the frequency response under the influence of the defects. The size of the defect can be quantitatively judged by analyzing the degree of splitting of the two resonance peaks in the response spectrum. The greater the degree of splitting, the larger the size of the defect.

8. A system using the defect detection method based on time-varying mechanism modal coupling points as claimed in any one of claims 1 to 7, characterized in that: It includes a modulation parameter determination module corresponding to a modal coupling point, a defect detection module, a defect detection module, and a judgment module; The module for determining the modulation parameters corresponding to the modal coupling point is used to determine the modulation parameters ω corresponding to the modal coupling point in a defect-free medium. ma size; The module also includes an excitation unit for exciting the elastic medium to vibrate and generating a resonance peak in the response spectrum; A measuring unit, used for measuring the output response and obtaining a response spectrum; The defect detection module is used to set the modulation parameter ω selected in the defect-free medium to the medium under test. ma , and input the excitation and measure the output response. If two resonance peaks appear in the frequency response, it is judged that there is a defect, and the degree of splitting reflects the size of the defect; The module also includes: An excitation unit, used to excite the elastic medium to vibrate and generate a resonance peak in the response spectrum; A measuring unit, used for measuring the output response and obtaining a response spectrum; The piezoelectric patch with an external negative capacitance circuit is used to achieve the time variation of the equivalent stiffness of the piezoelectric patch through time modulation. The modulation parameter ω m Select the parameter ω selected in the modulation parameter determination module corresponding to the modal coupling point ma ; The judging module judges that the measured medium has defects if two split resonance peaks appear in the frequency response.

9. A computer device comprising a memory and a processor, wherein the memory stores a computer program, wherein: When the processor executes the computer program, the steps of the method according to any one of claims 1 to 7 are implemented.

10. A computer-readable storage medium having a computer program stored thereon, characterized in that: When the computer program 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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