A Cellular Structure Detection Method Based on Negative Group Velocity Feature Analysis
The honeycomb structure detection method based on negative group velocity feature analysis solves the problems of low detection efficiency and difficulty in feature extraction, and achieves simple and clear defect detection results, which is suitable for on-site inspection of composite materials.
Patent Information
- Application Number
- CN202210142389.8
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- Filing Date
- 2022-02-16
- Publication Date
- 2025-11-14
- Estimated Expiration
- 2042-02-16
AI Technical Summary
Existing technologies are inefficient, difficult to extract features, and susceptible to interference when detecting defects in cellular structures, resulting in poor detection performance.
A detection method based on negative group velocity characteristic analysis is adopted. The negative group velocity frequency band is determined by calculating the dispersion curve of the cellular structure, the frequency is selected to emit acoustic signals, and the signals are collected along the acoustic wave propagation path to calculate the group velocity and determine the defect location.
It simplifies operation, makes signal characteristics easy to identify, and provides clear results, making it suitable for field applications and applicable to defect detection of composite materials.
Smart Images
Figure CN116642955B_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of acoustic testing, and in particular to a method for detecting cellular structures based on negative group velocity characteristic analysis. Background Technology
[0002] Honeycomb structures are layered composite structures made of upper and lower skins and a honeycomb core bonded together by welding or adhesive. Due to their lightweight, high specific strength, and high specific stiffness, they are widely used in construction, automotive, marine, and aerospace industries. However, various types of damage inevitably occur during manufacturing or use, with debonding of the skin and honeycomb core being a typical example. Because this damage occurs inside the structure, effective detection methods are needed.
[0003] Acoustic methods, as one of the non-destructive testing methods, are widely used in defect detection of composite materials. These methods mainly include acoustic emission, acoustic impedance, ultrasonic C-scan, and Lamb wave methods. Among them, acoustic emission can detect dynamic defects and is therefore mainly used for dynamic monitoring rather than static defect detection. Acoustic impedance is fast and simple to operate, but its detection effect is poor when the impedance difference between the defective and intact areas is small. Ultrasonic C-scan can obtain accurate images of honeycomb structures, but its detection efficiency is correspondingly low and it requires a coupling agent. The Lamb method has strong defect sensitivity when suitable modes are selected to excite relatively pure modes. However, due to the dispersion and multimodal characteristics of Lamb waves, and the presence of the honeycomb core further increases the complexity of Lamb wave propagation in the skin, the requirements for parameter selection are higher, making the identification and extraction of defect features more difficult.
[0004] Therefore, this invention proposes a cellular structure detection method based on negative group velocity feature analysis. This method is based on the negative group velocity feature commonly found in cellular structures. This feature is easy to obtain, exhibits significant differences in characteristics between defective and intact signals, is easy to observe, suitable for field application, and is easy to implement and promote. Summary of the Invention
[0005] The purpose of this invention is to overcome the problems of low detection efficiency, difficulty in feature extraction, and poor detection effect caused by interference in the existing technology for detecting defects in cellular structures. A cellular structure detection method based on negative group velocity feature analysis is proposed.
[0006] To address the aforementioned technical problems, this invention proposes a cellular structure detection method based on negative group velocity feature analysis, the method comprising the following steps:
[0007] (1) Calculate the dispersion curve of the cellular structure;
[0008] (2) Determine the frequency band where negative group velocity exists based on the dispersion curve calculated in step (1);
[0009] (3) Select a frequency within the frequency band where negative group velocity exists as determined in step (2), and transmit a pulse train acoustic signal of that frequency to the cell structure under test;
[0010] (4) Select two detection points on the propagation path of the sound wave signal and collect the sound wave signals at the two detection points;
[0011] (5) Calculate the group velocity of the signal propagating in the structure based on the two collected signals, and determine whether there is a defect at the detection position based on the positive or negative value of the calculated group velocity.
[0012] As an improvement to the above technical solution, the group velocity is the slope of the dispersion curve, and the method for determining the frequency band where negative group velocity exists in step (2) includes:
[0013] Calculate the slope of the dispersion curve; the frequency band corresponding to a negative slope is the frequency band where negative group velocity exists.
[0014] As another improvement to the above technical solution, when the detection method determines the frequency band where negative group velocity exists by calculating the slope of the dispersion curve, the specific formula for calculating the group velocity from the dispersion curve is as follows:
[0015]
[0016] Among them, C g Let ω be the group velocity, ω be the angular frequency, and k be the wave vector.
[0017] As another improvement to the above technical solution, in step (4) of the detection method, the two detection points selected on the propagation path of the sound wave signal are on the same straight line as the excitation point, and the excitation point is the position point where the sound wave signal is emitted.
[0018] As an improvement to the above technical solution, the formula for calculating the group velocity of the signal propagating in the structure based on the acoustic signals collected at the two detection points in step (5) of the detection method is as follows:
[0019]
[0020] Among them, C g ' is the measured group velocity of the acoustic signal propagating in the cellular structure, L is the distance between the two detection points, and t is the distance between the two detection points. f t represents the peak time of the acoustic wave packet at a detection point far from the excitation point. n This refers to the peak moment of the acoustic wave packet at the detection point closest to the excitation point.
[0021] As a further improvement to the above technical solution, the specific method for judging whether there is a defect at the detection position in step (5) of the detection method based on the positive or negative value of the calculated group velocity is as follows: when C g When C > 0, and the measured group velocity of the acoustic signal propagating in the cellular structure is positive, a defect exists at the detection location; when C g When the measured group velocity of the acoustic signal propagating in the cellular structure is negative (<0), the detection location is an intact area.
[0022] As another improvement to the above technical solution, the detection position determined by the detection method refers to the area where the line connecting the excitation point and the distant detection point is located.
[0023] As a further improvement to the above technical solution, when there is a debonding defect at the detection location, the measured group velocity of the acoustic signal propagating in the honeycomb structure is positive.
[0024] Compared with existing technologies, the advantages of the cellular structure detection method based on negative group velocity feature analysis described in this invention are as follows:
[0025] 1. The method described in this invention directly calculates the group velocity of signals collected from two points along the sound wave propagation path, thereby completing defect detection and judging the quality of the honeycomb structure at the measured location. The operation is simple.
[0026] 2. The method described in this invention does not require signal processing, the signal characteristics are easy to identify, the results are clear, it is suitable for field application, and it is easy to promote.
[0027] 3. The frequency band used in the method described in this invention is relatively low compared to conventional ultrasonic testing, with small attenuation, making it suitable for the detection of honeycomb structures composed of materials with large acoustic attenuation, such as composite materials. Attached Figure Description
[0028] Figure 1 This is a graph showing the dispersion curves calculated based on typical honeycomb and flat panel structures; among them, Figure 1 (a) is a graph showing the sound propagation characteristics of a honeycomb structure. Figure 1 (b) is a graph showing the acoustic propagation characteristics of a flat plate structure;
[0029] Figure 2 This is a flowchart of the method for cellular structure detection described in this invention;
[0030] Figure 3 This is a schematic diagram of a typical cellular structure detection and measurement site;
[0031] Figure 4 This is a signal waveform diagram obtained by actual measurement of the intact and defective areas of a typical honeycomb structure using the method described in this invention. Figure 4(a) is a waveform diagram of the signal collected at points A and B in the intact area. Figure 4 (b) is a waveform diagram of the signal collected at points C and D in the defect area. Detailed Implementation
[0032] The technical solution of the present invention will be described in detail below with reference to the accompanying drawings and embodiments.
[0033] This invention proposes a method for detecting cellular structure defects based on negative group velocity characteristic analysis to solve the problem of cellular structure defect detection.
[0034] like Figure 2 The diagram illustrates the specific implementation steps of the cellular structure detection method based on negative group velocity feature analysis according to the present invention, including the following steps:
[0035] Calculate the dispersion curve of the cellular structure;
[0036] Identify the frequency bands where negative group velocities exist;
[0037] Within a defined frequency band where negative group velocities exist, select a frequency as the excitation frequency for transmitting the acoustic signal.
[0038] After determining the excitation frequency, a series of acoustic signals are emitted.
[0039] Signals are collected at two points along the sound wave propagation path, and the group velocity of the signal propagating in the structure is calculated based on the collected signals at the two points.
[0040] The presence of debonding at the detection location is determined by whether the calculated group velocity is positive or negative (to determine if there is a negative group velocity): if there is a negative group velocity, it means that there is no debonding on the line connecting the excitation point and the detection point, and the honeycomb structure is intact; if there is no negative group velocity, that is, the group velocity is positive, it means that there is debonding on the line connecting the excitation point and the detection point.
[0041] After completing one test, proceed to the next location for testing, until all tests are completed.
[0042] The experimental object selected in this embodiment is a nickel-based high-temperature alloy honeycomb structure commonly used in the aerospace industry. Its panel thickness d1 is 0.2mm, honeycomb core height h is 4.1mm, honeycomb core cell side length a is 4mm, and core cell thickness d2 is 0.1mm (non-Y direction) and 0.2mm (Y direction). The honeycomb core and the panel are connected by brazing. If the two are not connected due to improper manufacturing process or service process, it is a defect of non-welding (equivalent to debonding).
[0043] like Figure 1 As shown in (a), the calculated acoustic propagation characteristics curve of the honeycomb structure is obtained. Figure 1(a) It can be seen that for this cellular structure, a negative group velocity exists in the frequency band around 50kHz; since the debonding region can be compared to a flat plate, the acoustic propagation characteristics of the debonding region can be analyzed using the acoustic propagation characteristic curve of a flat plate structure, i.e., Figure 1 As shown in (b), the plate thickness and material are the same as those of the honeycomb structure panel. Figure 1 (b) It can be seen that there is no negative group velocity in the debonding region below 60kHz. Therefore, 50kHz is selected as the frequency of the excitation signal.
[0044] The formula for calculating group velocity based on the acoustic signals collected at two detection points is as follows:
[0045]
[0046] It can be seen that if the peak time t of the signal packet collected by the detection point closer to the excitation point is... n The peak time t of the wave packet at a more distant point is less than f If t > 0, then the group velocity of the signal propagation is positive, and a defect exists in the region along the line connecting the excitation point and the detection point. Otherwise, if t > 0, then... f <t n If the group velocity is negative, then the region along the line connecting the excitation point to the detection point is the intact region.
[0047] like Figure 3 The diagram shows a typical cellular structure detection and measurement site in this embodiment. The excitation point and detection points A and B are marked, with point A being closer to the excitation point. The excitation probe emits a 50kHz pulse train signal, and the acoustic signals at the two points are collected respectively. The detection results for the intact and defective areas are shown below. Figure 4 As shown.
[0048] The time-domain signal obtained from measurements in the intact region is as follows: Figure 4 As shown in (a), it can be observed that the time corresponding to the peak value of the signal wave packet at point B, which is farther from the excitation point, is shorter than the time corresponding to the peak value of the signal wave packet at point A. This result indicates that a negative group velocity exists in this region. Figure 4 (b) shows the test results for an unwelded defect with a diameter of 35 mm. It can be observed that the peak time of the signal packet at point D, which is farther from the excitation point, is greater than the peak time of the signal packet at point C. This indicates that there is no negative group velocity in this region. This is because when a defect occurs in the cellular structure, the defect location can be equivalent to a single-layer plate, at which point the negative group velocity characteristic disappears.
[0049] In summary, the method proposed in this invention can accurately determine debonding defects within a honeycomb structure.
[0050] Finally, 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 it. Although the present invention has been described in detail with reference to the embodiments, those skilled in the art should understand that modifications or equivalent substitutions to the technical solutions of the present invention do not depart from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.
Claims
1. A method for detecting cellular structures based on negative group velocity feature analysis, the method comprising the following steps: (1) Calculate the dispersion curve of the cellular structure; (2) Determine the frequency band where negative group velocity exists based on the dispersion curve calculated in step (1); (3) Select a frequency within the frequency band where negative group velocity exists as determined in step (2), and transmit a pulse train acoustic signal of that frequency to the cell structure under test; (4) Select two detection points on the propagation path of the sound wave signal and collect the sound wave signals at the two detection points; (5) Calculate the group velocity of the signal propagating in the structure based on the two collected signals, and determine whether there is a defect at the detection position based on the positive or negative value of the calculated group velocity; In step (4) of the detection method, the two detection points selected on the propagation path of the acoustic signal are on the same straight line as the excitation point, and the excitation point is the position point where the acoustic signal is emitted; The formula for calculating the group velocity of the signal propagating in the structure based on the acoustic signals collected from the two detection points in step (5) of the detection method is as follows: Among them, C g ' is the measured group velocity of the acoustic signal propagating in the cellular structure, L is the distance between the two detection points, and t is the distance between the two detection points. f t represents the peak time of the acoustic wave packet at a detection point far from the excitation point. n This refers to the peak moment of the acoustic wave packet at the detection point closest to the excitation point.
2. The cellular structure detection method based on negative group velocity feature analysis according to claim 1, characterized in that, The group velocity is the slope of the dispersion curve. The method for determining the frequency band where negative group velocities exist in step (2) includes: Calculate the slope of the dispersion curve; the frequency band corresponding to a negative slope is the frequency band where negative group velocity exists.
3. The cellular structure detection method based on negative group velocity feature analysis according to claim 2, characterized in that, When the detection method determines the frequency band where negative group velocity exists by calculating the slope of the dispersion curve, the specific formula for calculating the group velocity from the dispersion curve is as follows: Among them, C g Let ω be the group velocity, ω be the angular frequency, and k be the wave vector.
4. The cellular structure detection method based on negative group velocity feature analysis according to claim 1, characterized in that, In step (5) of the detection method, the specific method for determining whether a defect exists at the detection location based on the positive or negative value of the calculated group velocity is as follows: when C g When '>0, and the measured group velocity of the acoustic signal propagating in the cellular structure is positive, a defect exists at the detection location; when C g When the measured group velocity of the acoustic signal propagating in the cellular structure is negative (<0), the detection location is an intact area.
5. The cellular structure detection method based on negative group velocity feature analysis according to claim 4, characterized in that, The detection location determined by the detection method refers to the area where the line connecting the excitation point and a more distant detection point is located.
6. The cellular structure detection method based on negative group velocity feature analysis according to claim 4, characterized in that, When a debonding defect exists at the detection location, the measured group velocity of the acoustic signal propagating in the honeycomb structure is positive.