A damage identification method based on active regulation of mode lines

Abstract

The application provides a damage identification method based on active regulation of mode line, which comprises the following steps: firstly, using the piezoelectric sheet to obtain the response of a structure to be measured under the excitation of multiple selected frequencies of the healthy state; then obtaining the response of the structure to the excitation of multiple selected frequencies of the damage state; and finally obtaining the coefficient k fa The excitation response of the healthy state is modulated, so that the ODS of the structure to be measured is consistent when the structure is healthy and contains damage, damage is located on the mode line of each frequency, and thus the damage can be located. The detection time is short, real-time monitoring can be realized, the influence of the mode line on damage position identification is eliminated, and the detection result is accurate.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of structural health monitoring, in particular to a vibration-based structural health monitoring method. BACKGROUND

[0002] Vibration-based damage detection (VDD) and structural health monitoring (SHM) methods have been studied for a long time and widely applied in various engineering fields. Since the detection efficiency of this method for the global structure is high, and the excitation and measurement technology is relatively perfect, the traditional VDD is very suitable for the detection of large structures such as high-rise buildings, bridges, etc. In recent years, with the wide application of new materials and new structures, VDD has been further developed. VDD has been used for damage detection of lightweight materials such as carbon fiber reinforced plastics, honeycomb structures, lattice sandwich panel structures, etc. Traditional VDD usually uses low-frequency detection, which is difficult to detect small damage, and requires complex signal analysis and processing to accurately locate the damage. Therefore, people have proposed high-frequency VDD methods, including local defect resonance method, local wave number analysis method, etc. Experiments have proved that high-frequency VDD has the advantages of high resolution and sensitivity to small damage. However, high-frequency VDD requires high-resolution measurement points, and the measurement of vibration modes will consume a lot of time, which brings difficulties to real-time monitoring of SHM. On the other hand, when the structure is excited by a high-frequency signal, the vibration mode will contain many node lines. When the damage is located on these node lines, VDD cannot be used for damage detection. SUMMARY

[0003] In order to overcome the lack of precision of the existing low-frequency VDD technology, and in view of the high time-consuming of the current high-frequency VDD detection method, the present application proposes a damage identification method based on active regulation of mode nodal line, which modulates the nodal line of the structure response mode (Operational deflection shapes, abbreviated as ODS), so that the ODS of the structure to be tested remains the same when healthy and damaged, so that the damage is located on the nodal line of each frequency, thereby locating the damage. The detection time is short, and real-time monitoring can be realized; and the influence of the nodal line on damage location identification is eliminated, and the detection result is accurate.

[0004] The technical scheme of the present application is as follows:

[0005] A damage identification method based on active regulation of mode nodal line, characterized in that it comprises the following steps:

[0006] S1. Arrange a plurality of piezoelectric sheets in an array on the structure to be tested, wherein a part of the piezoelectric sheets are used as exciters, and the other piezoelectric sheets are used as sensors;

[0007] S2. Adopting multiple selected frequencies, generating each frequency by signal generator, and exciting piezoelectric sheet as exciter one by one after power amplifier; meanwhile, adopting oscilloscope to connect the rest of piezoelectric sheet as sensor, collecting the response of piezoelectric sheet as sensor under each selected frequency excitation Wherein subscript s represents the serial number of piezoelectric sheet as exciter, f represents excitation frequency, a represents the serial number of piezoelectric sheet as sensor, and superscript I represents healthy structure; adopting scanning laser vibration meter to automatically scan and test the measurement area, obtaining the vibration ODS response of healthy structure under each excitation frequency of each piezoelectric sheet as sensor, denoted as S xyfa , wherein x, y are the positions of the measurement points;

[0008] S3. When there is damage in the structure to be measured, repeating S2 to obtain Superscript D represents damaged structure;

[0009] S4. Using the obtained in S2 and S3 to determine the coefficient k fa , so that the coefficient k fa satisfies:

[0010]

[0011] Since there is damping in the actual structure to be measured, the measured is a complex number; and k fa is also a complex number, indicating the amplitude and phase of the excitation signal;

[0012] S5. Multiplying the obtained coefficient k fa with the vibration ODS response S xyfa of the healthy structure to be measured, that is, formula (2):

[0013]

[0014] A series of ODSs are obtained, and the damage is located on the nodal line thereof.

[0015] 2. The damage identification method based on active control mode line according to claim 1, further comprising the following steps:

[0016] S6. First, normalize the ODS xyf , and then set a threshold TH (0 < TH < 1), defined as:

[0017]

[0018] S7. Define the damage index as the product of the amplitude of the nodal line at each frequency, ​Damage identification imaging can then be obtained.

[0019] Furthermore, the number of piezoelectric elements is nine.

[0020] Furthermore, three of the piezoelectric elements serve as exciters, while the other six serve as sensors.

[0021] Furthermore, the excitation process in S2 is a linear combination of excitation methods, including modulation of phase and amplitude.

[0022] Furthermore, the multiple selected frequencies mentioned in S2 are 1kHz-9kHz, with one selected at 1kHz intervals, for a total of 9 frequencies.

[0023] This invention provides a damage identification method based on nodal line active modulation (NLAM). Based on the principle that damage located at the nodal line of a mode shape does not alter the original mode shape, the method modulates the amplitude and phase of the excitation signals from each excitation piezoelectric element using nodal line active modulation (NLAM). This ensures that the signals measured by the piezoelectric elements acting as sensors remain consistent regardless of whether the structure is damaged, thus guaranteeing that the overall ODS of the structure remains consistent, indicating that the damage is located at the nodal line of the mode shape. In this case, the location of the damage can be calculated using only the ODS measured under healthy conditions as a reference. This invention offers advantages such as high efficiency, independence from structural material properties, and applicability to the location of various types of damage. Based on the reference signal measured when the structure under test is healthy, this invention requires only a few voltage signals detected by sensors to achieve real-time monitoring of damaged structures, enabling rapid monitoring and location of various types of damage in complex structures. Attached Figure Description

[0024] Figure 1 For mounting aluminum plates and piezoelectric sheets with crack damage.

[0025] Figure 2 The diagram shows the nodal lines obtained by superimposing the results at various frequencies calculated in step six under specific combined excitations; the red dot in the diagram represents the location of the damage center.

[0026] Figure 3 The image shown is the damage detection image obtained in step eight. The right side is a magnified view of the damage area, where the dashed lines indicate the location of the crack damage. Detailed Implementation

[0027] To more clearly illustrate the technical solution of the present invention, specific embodiments are described below.

[0028] by Figure 1 The aluminum plate with a side length of 300mm shown is the structural component to be tested, to verify and illustrate the damage identification method of the present invention.

[0029] Step one: nine piezoelectric pieces are evenly arranged on the aluminum plate, in this embodiment, nine piezoelectric pieces are arranged in the form of an array with one at the center of the circle and the rest evenly arranged on the circumference, but in actual measurement, other arrangement modes such as rectangular array can also be selected. In this embodiment, three piezoelectric pieces numbered ①, ② and ③ are used as actuators, and the other six piezoelectric pieces numbered ④-⑨ are used as sensors.

[0030] The linear combination excitation mode is adopted, including modulation of phase and amplitude.

[0031] Step two: select nine frequencies every 1 kHz in the range of 1 kHz-9 kHz, generate each frequency by a signal generator, and excite the piezoelectric pieces as actuators one by one after power amplification; at the same time, connect the rest of the piezoelectric pieces as sensors to an oscilloscope to collect the responses of the piezoelectric pieces as sensors under excitation at each selected frequency wherein subscript s represents the serial number of the piezoelectric piece as an actuator, f represents the excitation frequency, a represents the serial number of the piezoelectric piece as a sensor, and superscript I represents a healthy structure; a scanning laser vibration tester is used to automatically scan and test the measurement area to obtain the vibration ODS responses of the healthy structure at each excitation frequency of each piezoelectric piece as a sensor, denoted as S xyfa wherein x and y are the positions of the measurement points. In the excitation process, the linear combination excitation mode is adopted, including modulation of phase and amplitude.

[0032] Step three: set a rectangular crack at the position (75, 50) of the aluminum plate, and the crack is at an angle of 60° with the bottom edge of the aluminum plate. Repeat step two using the same frequencies in step two to obtain superscript D represents a damaged structure.

[0033] Step four: compare the output signals obtained in steps two and three to make the coefficient k fa satisfy

[0034] Since there is damping in the actual structure to be measured, each vibration signal measured is a complex number. k fa is also a complex number, which represents the amplitude and phase of the regulated excitation signal.

[0035] Step five: multiply the obtained coefficient k fa with the response S xyfa of the healthy structure, a series of ODSs can be obtained, and the damage is located on the nodal lines of the ODSs; multiplying the coefficient k fa with the response S xyfa of the healthy structure can ensure that the ODS modes of the structure to be measured are consistent whether there is damage or not, which implies that the damage is located on the nodal lines of these ODSs.

[0036] Step six: In order to highlight these nodal lines, the ODSs xyf Normalization Then, a threshold TH (0 < TH < 1) is set to define

[0037] The superimposed nodal line diagram obtained under the specific combination excitation at each frequency is shown in Fig. 4, wherein the red origin represents the damage center position. Figure 2

[0038] Step seven: Defining the damage index as the product of the nodal line amplitudes at each frequency, The damage identification imaging is obtained, as shown in Fig. 5, wherein the right side is a local enlarged view of the damage, and the dashed line represents the crack damage position. Figure 3

[0039] The damage identification method shown in the present application can make the ODSs of the structure to be measured consistent between the healthy and the damage-containing states by modulating the nodal lines of the ODSs, so that the damage is located on the nodal lines at each frequency, thereby locating the damage. The method can realize the rapid monitoring and positioning of various damages in complex structures.

[0040] The embodiments are preferred embodiments of the present application, but the present application is not limited to the above embodiments, and any obvious improvement, replacement or modification made by those skilled in the art without departing from the essential content of the present application shall fall within the protection scope of the present application.​​

Claims

1. A damage identification method based on active regulation of mode shape nodal lines, characterized in that, The method comprises the following steps: S1. arranging a plurality of piezoelectric pieces in an array on a structure to be measured, wherein a part of the piezoelectric pieces are used as actuators and the other piezoelectric pieces are used as sensors; S2. Adopting multiple selected frequencies, generating each frequency by signal generator, and exciting each piezoelectric sheet as exciter after power amplifier; meanwhile, adopting oscilloscope to connect the rest of piezoelectric sheets as sensor, collecting the response of piezoelectric sheet as sensor under each selected frequency excitation Wherein subscript s represents the serial number of piezoelectric sheet as exciter, f represents excitation frequency, a represents the serial number of piezoelectric sheet as sensor, and superscript I represents healthy structure; adopting scanning laser vibration meter to automatically scan and test the measurement area, obtaining the vibration ODS response of healthy structure under each excitation frequency of each piezoelectric sheet as sensor, denoted as S xyfa Wherein x, y are the positions of measurement points; S3. When there is a damage in the structure to be tested, repeat S2 to obtain The superscript D indicates the damaged structure. S4. Using the results from S2 and S3 Determining the coefficient k using equation (1) fa such that the coefficient k fa satisfies: Since there is damping in the actual structure under test, the measured are complex numbers; and k fa is also a complex number, representing the amplitude and phase of the control excitation signal; S5. The resulting coefficient k is multiplied by the measured vibration ODS response S fa xyfa S5. The resulting coefficient k is multiplied by the measured vibration ODS response S​ A series of ODS are obtained, and the damage is located on the nodal line thereof.

2. The damage identification method based on active regulation of mode shape nodal lines according to claim 1, characterized in that, The method further comprises the following steps: S6. First, ODS xyf Normalization A threshold TH (0 < TH < 1) is set, defined as: S7. Define the damage indicator as the product of the amplitudes of the branch lines at each frequency, Damage identification imaging is obtained.

3. The damage identification method based on active regulation of mode shape nodal lines according to claim 1, characterized in that, The number of the piezoelectric pieces is 9.

4. The damage identification method based on actively regulated mode shape nodal line according to claim 3, characterized in that, Three of the piezoelectric pieces are used as actuators and the other six piezoelectric pieces are used as sensors.

5. The damage identification method based on active regulation of mode shape nodal lines according to claim 3, characterized in that, The excitation process in S2 is through a linear combination excitation mode, including modulation of phase and amplitude.

6. The damage identification method based on actively regulated mode line according to claim 3, wherein, The plurality of selected frequencies in S2 are 1 kHz-9 kHz, one selected every 1 kHz, and a total of 9.

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