Flat plate damage detection method and system based on out-of-plane velocity field singular component analysis

Abstract

The present invention discloses a flat plate damage detection method and system based on the analysis of the singular components of the out-of-plane velocity field. The steps include: measuring the out-of-plane velocity field of the flat plate structure; selecting the time window to be analyzed according to the out-of-plane velocity field energy function; performing attenuation compensation on the out-of-plane velocity field within the selected time window; performing a TKEO (Teager-Kaiser energy operator) transform on the attenuated and compensated out-of-plane velocity field; calculating the energy map after the TKEO transform of the out-of-plane velocity field; and determining the damage location and size according to the singular peak positions in the energy map after the TKEO transform of the out-of-plane velocity field. The present invention can be used to analyze the out-of-plane velocity field of the flat plate structure, and then perform structural damage imaging. The present invention can be used in combination with advanced instruments such as a laser scanning vibrometer and is widely applied to the damage detection of flat plate structures.

Description

Technical Field

[0001] The present invention discloses a flat plate damage detection method based on the analysis of singular components of the out-of-plane velocity field, and specifically relates to the technical field of structural condition monitoring. Background Art

[0002] Flat plate structures are widely used as key components in buildings, automobiles, and aerospace vehicles. During their long-term service, due to the influence of manufacturing defects, environmental factors, and accidental accidents, etc., structural damage will inevitably occur. If these damages cannot be detected and repaired in time, it will affect the safe and reliable operation of the overall structure. Under this background, in recent years, some non-destructive testing technologies have developed rapidly and have been used to detect damages in structures. Non-destructive testing technologies such as eddy current, ultrasonic, and infrared detection have been widely applied to flat plate damage detection. However, these technologies generally require a rough prediction of the damage location, and the damage location must be easily accessible, which is difficult to meet in practical applications. Summary of the Invention

[0003] Aiming at the defects of the prior art, the present application aims to propose a flat plate damage detection method based on the analysis of singular components of the out-of-plane velocity field, which can cover a larger detection area, strengthen the information characteristics of the damage area, and accurately judge whether damage occurs and determine its location and size.

[0004] The present invention adopts the following technical solutions to solve the above technical problems:

[0005] A flat plate damage detection method based on the analysis of singular components of the out-of-plane velocity field, the specific steps include:

[0006] Step 1: Measure the out-of-plane velocity field of the flat plate structure;

[0007] Step 2: Select the time window to be analyzed according to the energy function of the out-of-plane velocity field;

[0008] Step 3: Perform attenuation compensation on the out-of-plane velocity field within the selected time window;

[0009] Step 4: Perform the TKEO transform on the attenuated and compensated out-of-plane velocity field;

[0010] Step 5: Calculate the energy after the TKEO transform of the out-of-plane velocity field;

[0011] Step 6: Determine the damage location and size according to the singular peak position in the energy diagram after the TKEO transform of the out-of-plane velocity field.

[0012] Further, the specific calculation method of Step 1 is as follows:

[0013] Measure the out-of-plane velocity field v(i, j, k) of the flat plate structure,

[0014] where \(i = 1, 2, \cdots, M\) and \(j = 1, 2, \cdots, N\) are the measuring point numbers in the \(x\) and \(y\) directions of the flat plate structure respectively; \(k = 1, 2, \cdots, T\) is the discrete time series.

[0015] Furthermore, the specific calculation method of Step 2 is as follows:

[0016] (1) Define the energy function of the out-of-plane velocity field with respect to time as the out-of-plane velocity field energy function:

[0017]

[0018] where \(E(k)\) is the out-of-plane velocity field energy function;

[0019] (2) Normalize the out-of-plane velocity field energy function:

[0020]

[0021] where is the normalized out-of-plane velocity field energy function;

[0022] (3) Determine the time window \([k a , k b :

[0023]

[0024] Furthermore, the specific calculation method of Step 3 is as follows:

[0025] (1) Define the out-of-plane velocity field attenuation compensation function:

[0026]

[0027] where \(C(k)\) is the out-of-plane velocity field attenuation compensation function;

[0028] (2) Apply the attenuation compensation function to the original out-of-plane velocity field:

[0029]

[0030] where is the out-of-plane velocity field after attenuation compensation.

[0031] Furthermore, the specific calculation method of Step 4 is as follows:

[0032]

[0033] where \(\Psi(i, j, k)\) is the TKEO transform of the out-of-plane velocity field after attenuation compensation.

[0034] As a further preferred embodiment of the present invention, the specific calculation method of Step 5 is as follows:

[0035]

[0036] In the formula, E(i,j) is the energy after the TKEO transformation of the out-of-plane velocity field of the flat plate structure.

[0037] Further, the specific method for obtaining the out-of-plane velocity field of the flat plate structure in step one is as follows:

[0038] Apply excitation at the geometric center position on the back of the flat plate structure with an excitation sensor, and simultaneously measure the out-of-plane velocity field on the front of the flat plate structure with a laser scanning vibrometer.

[0039] As a further preferred solution of the present invention, the laser sensor uses a PSV-400 laser scanning vibrometer, and the excitation sensor is a piezoelectric ceramic sensor.

[0040] Compared with the prior art, the present invention adopts the above technical solutions and has the following technical effects:

[0041] The detection method proposed by the present invention can realize damage location and quantification by analyzing the singular components of the out-of-plane velocity field of the flat plate structure. Compared with conventional local non-destructive testing techniques, this method does not require prior knowledge of the damage location, is easy to operate, and has an obvious effect on enhancing damage characteristics. This method can be used in conjunction with advanced sensors such as laser scanning vibrometers and is efficiently applied to flat plate damage detection. Brief Description of the Drawings

[0042] Figure 1 is a schematic flow chart of the method of the present invention;

[0043] Figure 2 is a schematic diagram of the out-of-plane velocity field of the flat plate structure in the present invention;

[0044] Figure 3 is a schematic diagram of the time window of the out-of-plane velocity field of the selected flat plate structure in the present invention;

[0045] Figure 4 is a schematic diagram of the decay compensation function of the out-of-plane velocity field within the selected time window in the present invention;

[0046] Figure 5 is a schematic diagram of the out-of-plane velocity field of the flat plate structure after decay compensation in the present invention;

[0047] Figure 6 is a schematic diagram of the TKEO transformation of the out-of-plane velocity field of the flat plate structure in the present invention;

[0048] Figure 7 is a schematic diagram of the energy after the TKEO transformation of the out-of-plane velocity field of the flat plate structure in the present invention. Detailed Description of the Invention

[0049] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings:

[0050] Those skilled in the art of this technology can understand that, unless otherwise defined, all terms (including technical terms and scientific terms) used herein have the same meaning as the general understanding of those of ordinary skill in the art to which the present invention belongs.

[0051] Embodiment 1

[0052] This embodiment is a flat plate damage detection system based on the analysis of the singular components of the out-of-plane velocity field. As Figure 1 shown, the system includes: an excitation sensor, a flat plate structure to be measured, and a laser scanning vibrometer. The excitation sensor is located at the geometric center position on the back of the flat plate structure to be measured, and the laser scanning vibrometer is located directly in front of the flat plate structure to be measured, at a set distance from the flat plate structure to be measured.

[0053] Embodiment 2

[0054] Based on the detection system provided in the above embodiment, this embodiment is a flat plate damage detection method based on the analysis of the singular components of the out-of-plane velocity field, including the following steps:

[0055] Step 1. Measure the out-of-plane velocity field v(i,j,k) of the flat plate structure,

[0056] where i = 1, 2,..., M and j = 1, 2,..., N are the measuring point numbers in the x and y directions respectively; k = 1, 2,..., T is the discrete time series.

[0057] Step 2. Select the time window to be analyzed according to the out-of-plane velocity field energy function:

[0058]

[0059]

[0060]

[0061] where E(k) is the out-of-plane velocity field energy function, is the normalized out-of-plane velocity field energy function, [k a ,k b is the selected time window.

[0062] Step 3. Perform attenuation compensation on the out-of-plane velocity field within the selected time window:

[0063]

[0064]

[0065] Among them, C(k) is the out-of-plane velocity field attenuation compensation function, which is the out-of-plane velocity field after attenuation compensation.

[0066] Step 4. Perform the TKEO transform on the out-of-plane velocity field after attenuation compensation:

[0067]

[0068] Among them, Ψ(i, j, k) is the TKEO transform of the out-of-plane velocity field after attenuation compensation.

[0069] Step 5. Calculate the energy diagram of the out-of-plane velocity field after TKEO transform:

[0070]

[0071] Among them, E(i, j) is the energy of the out-of-plane velocity field of the flat plate structure after TKEO transform.

[0072] Step 6. Determine whether there is damage to the flat plate structure according to whether there are singular peaks in E(i, j), and determine the damage position and size from the peak position.

[0073] The working principle of the present invention is as follows: Flat plate damage will cause singularities in the out-of-plane velocity field at the damage location. Accordingly, structural damage can be identified by analyzing the singular components in the out-of-plane velocity field. In order to fully reveal the singular components of the out-of-plane velocity field, the out-of-plane velocity field within the selected time window is attenuated and compensated, and the TKEO transform is performed on the out-of-plane velocity field after attenuation compensation, thereby amplifying the singular components at the damage location. Then, the energy of the out-of-plane velocity field after TKEO transform is further calculated. It is determined whether there is damage to the flat plate structure according to whether there are singular peaks in the energy diagram of the out-of-plane velocity field after TKEO transform, and the damage position and size are determined from the position of the singular peak.

[0074] As a vibration parameter of the flat plate structure, the out-of-plane velocity field can cover a larger detection area compared with conventional local non-destructive testing methods, and can also strengthen the information characteristics of the damage area, accurately judge the occurrence of damage and perform damage location and quantification.

[0075] The following is a specific embodiment to illustrate the detection method of the present invention:

[0076] The CFRP flat plate used in the embodiment is 500 mm long, 500 mm wide and 3 mm thick. There is a prefabricated delamination damage with a size of 15 mm × 15 mm at a distance of 125 mm from each of the two adjacent sides of the plate. A piezoelectric sensor is used as an exciter to apply a five-cycle sine excitation modulated by a Hanning window with a center frequency of 50 kHz at the geometric center position on the back of the plate. At the same time, a laser scanning vibrometer is used to measure the out-of-plane velocity field on the front of the plate. The measurement area of the out-of-plane velocity field is a 375×375 square measurement point grid covering the entire front of the plate. At each measurement point, a velocity response signal of 1 millisecond is collected at a sampling frequency of 512 kHz, and an out-of-plane velocity field composed of 512 time series is obtained.

[0077] The out-of-plane velocity fields of the measured flat plate structure at the 105th, 305th, 420th and 500th time series are as Figure 2 shown, where the horizontal axis x represents the coordinate along the length of the plate, and the vertical axis y represents the coordinate along the width of the plate. According to formulas (1), (2) and (3), the time window of the out-of-plane velocity field of the selected flat plate structure is [43, 512], as Figure 3 shown. According to formula (4), the attenuation compensation function of the out-of-plane velocity field of the flat plate structure within the selected time window is obtained, as Figure 4 shown. According to formula (5), the out-of-plane velocity fields of the 105th, 305th, 420th and 500th time series after attenuation compensation are obtained, as Figure 5 shown. According to formula (6), the TKEO transform of the out-of-plane velocity fields of the 105th, 305th, 420th and 500th time series is obtained, as Figure 6 shown. According to formula (7), the energy of the out-of-plane velocity field of the flat plate structure after TKEO transform is obtained, as Figure 7 shown. It can be found from Figure 7 that there is a singular peak at a distance of 125 mm from each of the two adjacent sides of the plate, indicating the presence of damage. The peak corresponding position coincides with the damage position, and the size of the peak region coincides with the damage size, realizing the damage detection of the flat plate.

[0078] In summary, the present invention proposes a flat plate damage detection method based on the analysis of singular components of the out-of-plane velocity field. Compared with conventional local non-destructive testing techniques, this method does not require prior knowledge of the damage position, is simple to operate, and can accurately achieve damage detection.

[0079] The above embodiments are only used to illustrate the technical idea of the present invention, and the protection scope of the present invention cannot be limited thereby. Any changes made on the basis of the technical solution according to the technical idea proposed by the present invention shall fall within the protection scope of the present invention.

Claims

1. A flat plate damage detection method based on singular component analysis of off-plane velocity field, characterized in that: The method comprises: Step 1: Measure the velocity field of the flat plate structure. The specific calculation method of step 1 is as follows: The off-plane velocity field of the flat plate structure is denoted as v(i,j,k), Wherein, i = 1, 2, ..., M and j = 1, 2, ..., N are the measurement point numbers in the x and y directions of the flat plate structure respectively; k = 1, 2, ..., T is a discrete time series; Step 2: Select the time window to be analyzed according to the energy function of the off-surface velocity field; the specific calculation method of step 2 is as follows: S2.1 defines the change of the off-surface velocity field energy with time as the off-surface velocity field energy function: Where, E(k) is the energy function of the off-surface velocity field; S2.2 Normalize the off-surface velocity field energy function: in, is the normalized off-surface velocity field energy function; S2.3 Determine the time window [k a ,k b ]: Step 3: Perform attenuation compensation on the velocity field off the surface within the selected time window; the specific calculation method of step 3 is as follows: S3.1 defines the off-surface velocity field attenuation compensation function: Where C(k) is the off-surface velocity field attenuation compensation function; S3.2 applies the attenuation compensation function to the original off-surface velocity field: in, is the off-surface velocity field after attenuation compensation; Step 4: Perform TKEO transformation on the off-surface velocity field after attenuation compensation; Step 5: Calculate the energy diagram of the off-surface velocity field after TKEO transformation; Step 6: Determine the damage location and size based on the singular peak position in the energy diagram after TKEO transformation of the off-surface velocity field.

2. A flat plate damage detection method based on off-surface velocity field singular component analysis as claimed in claim 1, characterized in that: The specific calculation method of step 4 is as follows: Among them, Ψ(i,j,k) is the TKEO transformation of the off-surface velocity field after attenuation compensation.

3. A flat plate damage detection method based on off-plane velocity field singular component analysis as claimed in claim 2, characterized in that: The specific calculation method of step 5 is as follows: Among them, E(i,j) is the energy of the flat plate structure off-surface velocity field after TKEO transformation.

4. A flat plate damage detection method based on off-plane velocity field singular component analysis as claimed in claim 1, characterized in that: The specific method for obtaining the off-surface velocity field of the flat plate structure in step 1 is: An excitation sensor is used to apply excitation at the geometric center of the back side of the plate structure, and a laser scanning vibrometer is used to measure the off-plane velocity field on the front side of the plate structure.

5. A flat plate damage detection method based on off-surface velocity field singular component analysis as claimed in claim 4, characterized in that: The laser scanning vibrometer is a PSV-400 laser scanning vibrometer, and the excitation sensor is a piezoelectric ceramic sensor.

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