A composite material structure health monitoring method and system

Abstract

The application discloses a composite material structure health monitoring method and system, and relates to the technical field of ultrasonic detection, aiming to solve the problem that the traditional nondestructive ultrasonic detection method does not consider the anisotropy of the wave velocity of heterogeneous materials, which easily leads to inaccurate monitoring results. The method comprises the following steps: obtaining the structural characteristic parameters of a composite material structure to be monitored and the array parameters of a PMUT transducer; determining target plane wave parameters according to the structural characteristic parameters and the array parameters; controlling the PMUT transducer to emit incident plane waves at multiple angles and collecting reflected plane waves; calculating the elastic wave propagation speed corresponding to each transmission angle and performing anisotropic delay time compensation on the incident plane waves and the reflected plane waves according to the elastic wave propagation speed to obtain a corrected signal; and constructing a B-mode ultrasonic image of a monitoring area of the composite material structure to be monitored based on the corrected signal. The composite material structure health monitoring method provided by the application is used for improving the defect monitoring accuracy by performing anisotropic compensation on echo signals.

Description

Technical Field

[0001] This invention relates to the field of ultrasonic testing technology, and in particular to a method and system for monitoring the health of composite material structures. Background Technology

[0002] Composite materials are multiphase materials formed by combining two or more materials with different properties through a composite process, combining the advantages of each component. Among them, carbon fiber reinforced polymers (CFRP) have become the preferred material for key load-bearing components in aerospace, high-end equipment and other fields due to their core characteristics of being lightweight, high-strength, fatigue-resistant, and corrosion-resistant. However, CFRP has problems such as significant anisotropy, weak interlaminar properties, hidden and rapid propagation of impact and fatigue damage, and strong sudden failure. Conducting structural health monitoring of CFRP can capture early micro-damage in real time, accurately assess the structural operating status and damage evolution, and effectively avoid safety accidents such as sudden fractures.

[0003] Non-destructive structural health monitoring (SHM) focuses on real-time, continuous monitoring of in-service conditions, providing early warning of defect propagation risks and preventing sudden failures. Traditional ultrasonic testing relies on large, bulky transducers, requires coupling media, and is complex to operate, unable to achieve in-situ continuous monitoring, making it difficult to meet the real-time and long-term stability requirements of SHM and unsuitable for direct application to monitoring carbon fiber reinforced composites. Furthermore, carbon fiber reinforced composites exhibit significant anisotropy and a layered structure in terms of sound propagation, with complex defect types such as delamination, porosity, and fiber breakage, leading to distortion of unidirectional sound wave propagation. Traditional coherent plane wave composite imaging algorithms achieve imaging through multi-angle plane wave excitation and coherent superposition of echoes, failing to consider the anisotropy of wave velocity in heterogeneous materials, thus easily resulting in inaccurate monitoring results. Summary of the Invention

[0004] The purpose of this invention is to provide a method and system for monitoring the health of composite material structures, which solves the problems that traditional monitoring methods cannot perform in-situ continuous monitoring and that the anisotropy of wave velocity in heterogeneous materials can easily lead to inaccurate monitoring results.

[0005] To achieve the above objectives, the present invention provides the following technical solution: In a first aspect, the present invention provides a method for monitoring the structural health of composite materials, comprising: Obtain the structural characteristic parameters of the composite material structure to be monitored and the array parameters of the PMUT transducer; The target plane wave parameters are determined based on the structural feature parameters and the array parameters; the target plane wave parameters include the plane wave scanning range, angular step size, and number of excitation angles. The PMUT transducer is controlled to emit incident plane waves at multiple angles to the composite material structure to be monitored according to the target plane wave parameters, and the reflected plane waves are collected; the reflected plane waves are signals formed by the reflection of the multi-angle plane waves after they are emitted to the composite material structure to be monitored. Based on the incident plane wave and the reflected plane wave, a multi-angle coherent plane wave composite algorithm is used to calculate the elastic wave propagation velocity corresponding to each emission angle, and anisotropic delay time compensation is performed on the incident plane wave and the reflected plane wave according to the elastic wave propagation velocity to obtain a corrected signal; the elastic wave propagation velocity includes the equivalent sound velocity of the incident plane wave and the equivalent sound velocity of the reflected plane wave. Based on the corrected signal, a B-mode ultrasound image of the monitoring area of ​​the composite material structure to be monitored is constructed, and the B-mode ultrasound image is used for defect assessment of the composite material structure to be monitored.

[0006] Optionally, the structural feature parameters include the sound velocity and height in the first dimension direction; the array parameters include the ultrasonic element spacing, fractional bandwidth, and the center frequency emitted by the PMUT transducer; determining the target plane wave parameters based on the structural feature parameters and the array parameters includes: The sound velocity in the first dimension direction is determined based on the anisotropic propagation model and density of the composite material structure to be monitored. According to the formula: ; Determine the extreme values ​​of the scanning angle for the plane wave scanning range, and determine the plane wave scanning range based on the extreme values ​​of the scanning angle; in, To scan the extreme values ​​of the deflection angle, This is the ratio of the speed of sound in the first dimension to the center frequency. The distance between ultrasonic array elements; According to the formula: ; Determine the angle step size; in, For the angle step size, For height; The number of excitation angles is determined based on the extreme values ​​of the scanning deflection angle and the angle step size.

[0007] Optionally, the step of calculating the elastic wave propagation velocity corresponding to each emission angle using a multi-angle coherent plane wave composite algorithm based on the incident plane wave and the reflected plane wave includes: According to the formula: ; Calculate the first deflection angle; the first deflection angle is the deflection angle of the incident plane wave; According to the formula: ; Calculate the second deflection angle; the second deflection angle is the deflection angle of the reflected plane wave; Based on the Christofer equation, determine the eigenvalues ​​corresponding to the first deflection angle and the eigenvalues ​​corresponding to the second deflection angle, respectively. According to the formula: ; Determine the equivalent speed of sound of the incident plane wave; According to the formula: ; Determine the equivalent speed of sound of the reflected plane wave; in, For the j-th first deflection angle, For the i-th second deflection angle, The eigenvalue corresponding to the first deflection angle. This is the eigenvalue corresponding to the second deflection angle. Let be the equivalent speed of sound of the incident plane wave. The equivalent speed of sound for reflected plane waves. The density of the composite material structure to be monitored is given by i, where both i and j are greater than 0.

[0008] Optionally, anisotropic time delay compensation is performed on the incident plane wave and the reflected plane wave based on the elastic wave propagation velocity to obtain a corrected signal, including: According to the formula: ; Calculate the delay time; in, To delay time, Let be the deflection angle of the j-th incident plane wave; Let the coordinates of the imaging point be in the first dimension. Let the coordinates of the imaging point be in the second dimension. Let be the coordinates of the i-th ultrasonic element in the second dimension. The incident plane wave and the reflected plane wave are compensated based on the delay time to obtain a corrected signal.

[0009] Optionally, the step of compensating the incident plane wave and the reflected plane wave according to the delay time to obtain the corrected signal includes: According to the formula: ; Determine the correction signal; in, Let be the composite pixel intensity of the corrected signal at the imaging point (x,z). The incident angle of the incident plane wave is Time-sonic array element The correction signal.

[0010] Optionally, constructing a B-mode ultrasound image of the monitoring area of ​​the composite material structure to be monitored based on the corrected signal includes: By mapping the composite pixel intensity of each imaging point to the target imaging region, a B-mode ultrasound image of the CFRP sample monitoring area is obtained.

[0011] Compared with the prior art, the present invention provides a method for monitoring the health of composite material structures, comprising: The invention involves acquiring structural characteristic parameters of the composite material structure to be monitored and array parameters of the PMUT transducer; determining target plane wave parameters based on the structural characteristic parameters and the array parameters; controlling the PMUT transducer to emit incident plane waves at multiple angles to the composite material structure according to the target plane wave parameters, and acquiring reflected plane waves; calculating the elastic wave propagation velocity corresponding to each emission angle using a multi-angle coherent plane wave composite algorithm based on the incident and reflected plane waves, and performing anisotropic delay time compensation on the incident and reflected plane waves according to the elastic wave propagation velocity to obtain a corrected signal; the elastic wave propagation velocity includes the equivalent sound velocity of the incident plane wave and the equivalent sound velocity of the reflected plane wave; and constructing a B-mode ultrasound image of the monitoring area of ​​the composite material structure to be monitored based on the corrected signal. This invention innovatively applies the PMUT transducer to defect monitoring of composite material structures, enabling in-situ continuous monitoring of composite material structures. Using PMUT transducers for ultrasonic signal transmission and reception can effectively compensate for the acoustic attenuation of anisotropic composite materials, improve the signal-to-noise ratio and resolution of defect detection. At the same time, by using a multi-angle coherent plane wave composite algorithm, combined with its anisotropic characteristics, the elastic wave propagation velocity at each transmission angle can be calculated. The time delay of the imaging point can be accurately calculated by the elastic wave propagation velocity at each transmission angle, effectively compensating for the anisotropic propagation effect, thereby improving the accuracy of imaging, that is, improving the accuracy of defect monitoring in composite material structures.

[0012] Secondly, the present invention also provides a composite material structure health monitoring system, applied to the aforementioned composite material structure health monitoring method. The system includes: a parameter acquisition module, a PMUT transducer, a multi-channel ultrasonic excitation circuit, a data processing module, and an imaging module; the PMUT transducer is connected to the multi-channel ultrasonic excitation circuit; the PMUT transducer is attached to the surface of the composite material structure to be monitored. The parameter acquisition module is used to acquire the structural characteristic parameters of the composite material structure to be monitored and the array parameters of the PMUT transducer; and to determine the target plane wave parameters based on the structural characteristic parameters and the array parameters; the target plane wave parameters include the plane wave scanning range, angular step size, and excitation angle number; The multi-channel ultrasonic excitation circuit is used to send excitation signals to the PMUT transducer according to the target plane wave parameters; The PMUT transducer is used to emit incident plane waves at multiple angles to the composite material structure to be monitored after receiving the excitation signal, and to collect the reflected plane waves and send the reflected plane waves to the data processing module; the reflected plane waves are signals formed by the reflection of the multi-angle plane waves after they are emitted to the surface of the sample to be monitored. The data processing module is used to calculate the elastic wave propagation velocity corresponding to each emission angle based on the incident plane wave and the reflected plane wave using a multi-angle coherent plane wave composite algorithm, and to perform anisotropic delay time compensation on the incident plane wave and the reflected plane wave based on the elastic wave propagation velocity to obtain a corrected signal. The imaging module is used to construct a B-mode ultrasound image of the monitoring area of ​​the composite material structure to be monitored based on the corrected signal. The B-mode ultrasound image is used for defect assessment of the composite material structure to be monitored.

[0013] Optionally, the PMUT transducer includes multiple transducer channels, which are arranged in one-dimensional or two-dimensional order; each transducer channel includes multiple ultrasonic array elements arranged in a matrix; the ultrasonic array elements in the same transducer channel have different radii along the column direction; each transducer channel is connected to one of the transmission channels of the multi-channel ultrasonic excitation circuit.

[0014] Optionally, the system further includes a signal amplifier, a filter, and a data storage device; the input terminal of the signal amplifier is connected to the output terminal of the PMUT transducer, the output terminal of the signal amplifier is connected to the input terminal of the filter, and the output terminal of the filter is connected to the data storage device and the data processing module.

[0015] Optionally, the radius of the ultrasonic array elements along the column direction within the same transducer channel can be gradually increased or gradually decreased.

[0016] Compared with the prior art, the beneficial effects of the composite material structure health monitoring system provided by the present invention are the same as those of the composite material structure health monitoring method described in the above technical solution, and will not be repeated here. Attached Figure Description

[0017] The accompanying drawings, which are included to provide a further understanding of the invention and form part of this invention, illustrate exemplary embodiments of the invention and are used to explain the invention, but do not constitute an undue limitation of the invention. In the drawings: Figure 1 This is a schematic diagram of a composite material structure health monitoring system provided by the present invention; Figure 2 This is a schematic diagram of the PMUT transducer provided by the present invention; Figure 3 This is a schematic diagram of the structure of the composite material to be monitored provided by the present invention; Figure 4 A schematic diagram of the time delay of a multi-angle plane wave provided by the present invention; Figure 5 The present invention provides a flowchart of a composite material structure health monitoring method.

[0018] Figure label: 1-Parameter acquisition module, 2-Multi-channel ultrasonic excitation circuit, 3-PMUT transducer, 31-Transducer channel, 311-Ultrasonic array element, 4-Signal amplifier, 5-Filter, 6-Data storage, 7-Data processing module, 8-Imaging module. Detailed Implementation

[0019] To facilitate a clear description of the technical solutions in the embodiments of the present invention, the terms "first" and "second" are used to distinguish identical or similar items with essentially the same function and effect. For example, the first threshold and the second threshold are merely used to distinguish different thresholds and do not limit their order. Those skilled in the art will understand that the terms "first" and "second" do not limit the quantity or execution order, and that the terms "first" and "second" are not necessarily different.

[0020] It should be noted that in this invention, the terms "exemplary" or "for example" are used to indicate examples, illustrations, or descriptions. Any embodiment or design described as "exemplary" or "for example" in this invention should not be construed as being more preferred or advantageous than other embodiments or designs. Specifically, the use of terms such as "exemplary" or "for example" is intended to present the relevant concepts in a concrete manner.

[0021] In this invention, "at least one" refers to one or more, and "more than one" refers to two or more. "And / or" describes the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A alone, A and B simultaneously, or B alone, where A and B can be singular or plural. The character " / " generally indicates that the preceding and following related objects are in an "or" relationship. "At least one of the following" or similar expressions refer to any combination of these items, including any combination of single or plural items. For example, at least one of a, b, or c can represent: a, b, c, a combination of a and b, a combination of a and c, a combination of b and c, or a, b, and c, where a, b, and c can be single or multiple.

[0022] Traditional ultrasonic testing relies on large, bulk transducers, requires coupling media such as water immersion, and is complex to operate, unable to achieve continuous in-situ monitoring, thus failing to meet the real-time and long-term stability requirements of structural health monitoring (SHM) and cannot be directly applied to the monitoring of in-service components. Micro-Electro-Mechanical Systems (MEMS), on the other hand, are miniaturized electromechanical devices manufactured based on semiconductor micro-nano fabrication technology. They are characterized by small size, light weight, low cost, and ease of mass production. Piezoelectric micromachined ultrasonic transducers (PMUTs), as a product combining MEMS technology and piezoelectric materials, generate ultrasonic signals through the inverse piezoelectric effect of a piezoelectric thin film and receive echoes through the direct piezoelectric effect. With their miniaturization, CMOS process compatibility, and low power consumption, they are gradually replacing traditional bulk ultrasonic transducers and have become a research hotspot in the field of structural health monitoring (SHM). However, the application of PMUT technology is still in its early stages, and significant bottlenecks remain in non-destructive testing of composite materials, specifically: Poor device compatibility with composite materials: Existing PMUTs generally suffer from high quality factors, narrow fractional bandwidths, and fixed resonant frequencies, making them unsuitable for the multilayered anisotropy and high acoustic attenuation characteristics of CFRP, resulting in insufficient axial resolution and difficulty in distinguishing closely spaced internal defects; Insufficient targeting of imaging algorithms: Traditional coherent plane wave composite imaging (Coherent Plane Wave)... The Compound (CPWC) algorithm achieves imaging through multi-angle plane wave excitation and coherent superposition of echoes, but does not consider the anisotropy of wave velocity in heterogeneous materials. Synthetic Aperture (SA) expands the imaging field of view through virtual aperture synthesis, assuming uniform wave velocity distribution. Its core model is based on the assumption of "homogeneous medium and consistent wave velocity", and does not perform quantitative optimization for the acoustic parameters of composite materials (such as large differences in wave velocity between fibers and matrix, and complex interface reflections). In CFRP monitoring, it is prone to signal superposition interference, low signal-to-noise ratio, and poor defect location and quantification accuracy. The monitoring system has low integration: some traditional monitoring schemes rely on external transmitting devices and external signal processing systems, which cannot take advantage of the miniaturization of PMUT. Moreover, the multi-channel drive and signal processing circuits are complex and difficult to adapt to the narrow space monitoring needs of aerospace and other scenarios. The application scenarios are limited: existing PMUT research focuses on monitoring liquid media or homogeneous metal materials, and has not solved the problem of acoustic attenuation and complex interface reflection interference in the monitoring of internal defects in composite materials. It cannot be directly transferred to the monitoring of heterogeneous composite materials such as CFRP, and lacks a quantitative online characterization system.

[0023] To address the aforementioned problems, this invention provides a method and system for monitoring the health of composite material structures. It innovatively designs and fabricates a dedicated high-bandwidth, variable-frequency PMUT transducer, constructs a quantified multi-angle coherent plane wave composite imaging algorithm based on the anisotropic propagation characteristics of acoustic waves, integrates a low-power, multi-channel CMOS chip-level or board-level transmitting and receiving circuit system, and completes real-time, dynamic quantitative assessment of internal defects in CFRP. Through collaborative hardware and software innovation, it effectively compensates for anisotropic propagation effects, enabling long-term, dynamic, and intelligent high-precision non-destructive structural health monitoring of CFRP. The following description is in conjunction with the accompanying drawings.

[0024] See Figure 1 This invention provides a composite material structure health monitoring system, which includes a parameter acquisition module 1, a multi-channel ultrasonic excitation circuit 2, a PMUT transducer 3, a signal amplifier 4, a filter 5, a data storage device 6, a data processing module 7, and an imaging module 8. The PMUT transducer 3 is connected to the multi-channel ultrasonic excitation circuit 2. The PMUT transducer 3 is attached to the surface of the composite material structure to be monitored. The input terminal of the signal amplifier 4 is connected to the output terminal of the PMUT transducer, the output terminal of the signal amplifier 4 is connected to the input terminal of the filter 5, and the output terminal of the filter 5 is connected to the data storage device 6 and the data processing module 7.

[0025] The parameter acquisition module 1 is used to acquire the structural characteristic parameters of the composite material structure to be monitored and the array parameters of the PMUT transducer; and to determine the target plane wave parameters based on the structural characteristic parameters and the array parameters; the target plane wave parameters include the plane wave scanning range, angular step size and excitation angle number; The multi-channel ultrasonic excitation circuit 2 is connected to the parameter acquisition module and is used to receive parameter commands, i.e., target plane wave parameters. The multi-channel ultrasonic excitation circuit 2 is also used to send excitation signals to the PMUT transducer 3 according to the target plane wave parameters. The PMUT transducer 3 is a transmitting and receiving unit for ultrasonic signals. After receiving the excitation signal, it transmits incident plane waves at multiple angles to the composite material structure to be monitored, and collects reflected plane waves. The collected reflected plane waves are sent to the signal amplifier 4, which amplifies the reflected plane waves. The filter 5 filters the amplified signal to provide high-quality data for subsequent imaging. The amplified and filtered reflected plane waves are sent to the data processing module 7. The reflected plane waves are signals formed by the reflection of multi-angle plane waves after they are emitted to the surface of the sample to be monitored.

[0026] The data processing module 7 is used to calculate the elastic wave propagation speed corresponding to each emission angle based on the reflected plane wave using a multi-angle coherent plane wave composite algorithm, and to perform anisotropic delay time compensation on the reflected plane wave based on the elastic wave propagation speed to obtain the corrected signal.

[0027] Imaging module 8 is used to construct B-mode ultrasound images of the monitoring area of ​​the composite material structure to be monitored based on the corrected signal. The B-mode ultrasound images are used for defect assessment of the composite material structure to be monitored.

[0028] See Figure 2 The PMUT transducer 3 includes multiple transducer channels 31, arranged in one-dimensional or two-dimensional configurations. Each transducer channel includes multiple ultrasonic array elements 311 arranged in a matrix. The radii of the ultrasonic array elements 311 along the column direction within the same transducer channel are different, and the radii of the ultrasonic array elements vary regularly along the column direction. Specific variation rules can be set according to requirements; for example, the radii of the ultrasonic array elements along the column direction within the same transducer channel may gradually increase or decrease, or increase first and then decrease, etc. The ultrasonic array elements of each transducer channel are connected in parallel. Each transducer channel 31 is connected to one transmission channel of the multi-channel ultrasonic excitation circuit 2. For example, the transducer channels form a 1×32 channel linear array with a channel spacing of 520 μm. Each transducer channel consists of 24 ultrasonic array elements connected in parallel (3×8), with ultrasonic array element radii ranging from 45 μm to 62.5 μm. Figure 2 As shown, from top to bottom, the radius of the ultrasonic elements in the first row is 45 μm, the radius of the ultrasonic elements in the last row is 62.5 μm, and the radius of the ultrasonic elements in the middle rows increases by 2.5 μm with each row, for a total of 768 ultrasonic elements. This PMUT transducer has a fractional bandwidth greater than or equal to 80%, an operating frequency of 3~8MHz, a driving voltage of 10Vpp, and outputs a wide-bandwidth ultrasonic signal.

[0029] The aforementioned PMUT transducer 3, due to its ultrasonic array elements with different radii, can correspond to different resonant frequencies, thus possessing a large fractional bandwidth. Utilizing its wideband characteristics, it can cover reflected signals from defects at different depths in composite materials, while simultaneously improving acoustic energy output efficiency through a multi-channel parallel design.

[0030] Optionally, the multi-channel ultrasonic excitation circuit employs a parallel, programmable, high-voltage pulse drive architecture. Its core function is to provide each channel of the PMUT transducer with independently controllable, precisely timed, and amplitude-adjustable bipolar excitation pulses, enabling multi-angle plane wave transmission and beam control. In practical applications, the FPGA or MCU in the multi-channel ultrasonic excitation circuit generates a reference clock and outputs independently programmable delay and pulse parameters for each channel, such as frequency, number of cycles, and phase, ensuring multi-channel synchronization and deflection focusing. Each channel has one high-voltage pulse generator, producing bipolar square wave pulses with frequencies ranging from 0.1-50MHz and amplitudes from 0.5-40Vpp, adapting to the PMUT's driving requirements.

[0031] Optionally, based on the compatibility of MEMS and CMOS processes, the multi-channel ultrasonic excitation circuit and PMUT transducer can be integrated into a single design using chip integration technology, eliminating the need for additional adapter cables and independent PCB-level deployment, further reducing system size and power consumption, and adapting to application scenarios with higher integration.

[0032] See Figure 3 The composite material structure to be monitored is a three-dimensional structure. The green boxes represent carbon fiber layups in the x-direction, the red boxes represent the cross-sections of the carbon fibers in the x-direction, and the blue boxes represent the cross-sections of the carbon fibers in the y-direction. The z-direction is the direction of carbon fiber stacking; the z-direction is referred to as the first dimension, the x-direction as the second dimension, and the y-direction as the third dimension. The composite material structure to be monitored can be placed on the xy plane, with the transducer channels arranged along the x-direction.

[0033] Optionally, the structural characteristic parameters include the sound velocity and height in the first dimension direction, where the sound velocity in the first dimension direction is the sound velocity of the composite material structure to be monitored in the z-direction, and the height is the height of the composite material structure to be monitored in the z-direction; the array parameters include the ultrasonic element spacing, fractional bandwidth, and the center frequency emitted by the PMUT transducer; the parameter acquisition module may include: The first-dimensional direction sound velocity determination unit is used to determine the first-dimensional direction sound velocity based on the anisotropic propagation model and density of the composite material structure to be monitored.

[0034] Specifically, the anisotropic propagation model is shown in equation (1): (1); Where C is the stiffness matrix. For axial tensile or compressive stiffness in the x-direction, The coupling stiffness of the lateral deformation in the y-direction caused by normal stress in the x-direction. For the axial stiffness in the z-direction, For axial tensile or compressive stiffness in the y-direction, The coupling stiffness of the lateral deformation in the z direction caused by the normal stress in the y direction. The coupling stiffness of the transverse deformation in the z direction caused by normal stress in the x direction. The coupling stiffness of the lateral deformation in the z direction caused by the normal stress in the y direction. For axial tensile or compressive stiffness in the z-direction, For the out-of-plane shear modulus of the yz plane, In-plane shear modulus of the xz plane This is the in-plane shear modulus of the xy plane.

[0035] According to formula (2): (2); Determine the sound speed in the first dimension, i.e., the sound speed in the z-direction.

[0036] in, For the speed of sound in the first dimension, The density of the composite material structure to be monitored.

[0037] The plane wave scanning range determination unit is used to determine the range according to formula (3): (3); Determine the extreme values ​​of the scanning angle for the plane wave scanning range, and determine the plane wave scanning range based on the extreme values ​​of the scanning angle; in, To scan the extreme values ​​of the deflection angle, This is the ratio of the speed of sound in the first dimension to the center frequency. The distance between ultrasonic array elements; the plane wave scanning range is... .

[0038] Angle step size determination unit, used according to formula (4): (4); Determine the angle step size; in, For the angle step size, For height; The excitation angle number determination unit is used to determine the excitation angle number based on the extreme value of the scanning deflection angle and the angle step size.

[0039] Specifically, according to formula (5): (5); Determine the number of excitation angles.

[0040] in, The number of excitation angles.

[0041] Excitation signal parameter configuration: Combined with a high-bandwidth PMUT transducer, the number of excitation signal cycles and the center frequency are selected based on the height. For shallow defects <5mm, a high-frequency short pulse is used: center frequency 6~8MHz, 1~2 cycles; for deep defects >10mm, a low-frequency long pulse is used: center frequency 3~5MHz, 3~5 cycles, to improve penetration capability. The excitation voltage amplitude is adjustable within the range of 5~20Vpp to balance the signal-to-noise ratio and power consumption.

[0042] Before actual monitoring, a defect-free CFRP standard sample can be used to perform a complete acquisition and imaging using the above parameters to evaluate the image signal-to-noise ratio and resolution. If the signal-to-noise ratio is lower than the set threshold, the excitation angle number should be increased or the receiving gain adjusted until the imaging quality requirements are met.

[0043] Optionally, the multi-channel ultrasonic excitation circuit sets a programmed time delay based on the target plane wave parameters, and sequentially applies plane wave excitation signals at different angles to the multi-channel PMUT transducer. Specifically, to synthesize the incident angle relative to the normal direction is... For the approximate plane wave, a delayed scanning strategy is adopted, and the time delay applied to the i-th ultrasonic element of the PMUT transducer is as shown in Equation (6): (6); in, For time delay, Let be the position of the i-th ultrasonic element. The location of the array geometric center of the PMUT transducer. The speed of sound in the first dimension.

[0044] The excitation signal of the ultrasonic array element is shown in formula (7): (7); in, As an excitation signal, t represents the original stimulus source.

[0045] In practical applications, when excited at each angle, all N channels of the multi-channel ultrasonic excitation circuit synchronously receive the reflected plane wave from the surface of the defect and the data storage device to be monitored. The data storage device stores M×N sets of full matrix data.

[0046] Optionally, the data processing module communicates bidirectionally with the multi-channel ultrasonic excitation circuit, receiving pre-processed echo data (i.e., reflected plane waves) and issuing parameter configuration and control commands. Specifically, the data processing module may include: The preprocessing unit is used to perform median filtering and noise reduction and signal amplification on the reflected plane wave to suppress electrical noise and environmental interference.

[0047] The propagation speed calculation unit is used to calculate the elastic wave propagation speed in the corresponding propagation direction for any emission angle, based on the anisotropic propagation model; the propagation speed is related to the propagation direction.

[0048] Specifically, the propagation speed calculation unit includes a first deflection angle determination subunit, used to calculate the propagation speed according to formula (8): (8); Calculate the first deflection angle; the first deflection angle is the deflection angle of the incident plane wave; The second deflection angle determines the sub-unit, used according to formula (9): (9); Calculate the second deflection angle; the second deflection angle is the deflection angle of the reflected plane wave; The eigenvalue determination subunit is used to determine the eigenvalues ​​corresponding to the first deflection angle and the eigenvalues ​​corresponding to the second deflection angle, respectively, according to the Christofer equation. Specifically, the Christofel equation is shown in formula (10): (10); The eigenvalues ​​are calculated as shown in formula (11): (11); in, For equivalent stiffness, The equivalent stiffness when vibrating along the x-direction. The equivalent stiffness when vibrating along the z-direction. It is an asymmetric angular term. for eigenvalues, , .

[0049] Substituting the first deflection angle into formulas (10) and (11) will yield the characteristic value corresponding to the first deflection angle. Substituting the second deflection angle into formulas (10) and (11) will yield the characteristic value corresponding to the second deflection angle.

[0050] The equivalent sound velocity determination sub-unit is used to determine the equivalent sound velocity according to formula (12): (12); Determine the equivalent speed of sound of the incident plane wave; According to formula (13): (13); Determine the equivalent speed of sound of the reflected plane wave; in, For the j-th first deflection angle, For the i-th second deflection angle, The eigenvalue corresponding to the first deflection angle. This is the eigenvalue corresponding to the second deflection angle. Let be the equivalent speed of sound of the incident plane wave. The equivalent speed of sound for reflected plane waves. The density of the composite material structure to be monitored is given by i, where both i and j are greater than 0.

[0051] The aforementioned calculation unit incorporates an angle-dependent equivalent sound velocity, which reduces phase errors caused by anisotropy, thereby minimizing the impact of waveform distortion and attenuation in composite materials.

[0052] Optionally, the data processing module may also include: The delay time calculation unit is used to calculate the delay time according to formula (14): (14); Calculate the delay time; in, To delay time, Let be the deflection angle of the j-th incident plane wave; Let the coordinates of the imaging point be in the first dimension. Let the coordinates of the imaging point be in the second dimension. Let be the coordinates of the i-th ultrasonic element in the second dimension.

[0053] See Figure 4 , Figure 4 (a) is a coordinate axis diagram of the imaging area. Figure 4 The black dots in (a) are the imaging points. The time delay of the normally incident plane wave is as follows: Figure 4 (b) shows the path indicated by the arrow. The angle of incidence is... The time delay of the incident plane wave is as follows Figure 4 The path with arrows is shown in (c).

[0054] The correction unit is used to compensate the reflected plane wave according to the delay time to obtain a correction signal.

[0055] Specifically, the correction unit can be used according to formula (15): (15); Determine the correction signal; in, Let be the composite pixel intensity of the corrected signal at the imaging point (x,z). The incident angle of the incident plane wave is Time-sonic array element The correction signal.

[0056] Optionally, the imaging module can be used to map the composite pixel intensity of each imaging point to the target imaging region to obtain a B-mode ultrasound image of the CFRP sample monitoring area.

[0057] Optionally, the imaging module can also be used to enhance the image and extract edges of the imaging structure, measure the geometric parameters such as the width and depth of the defect, compare them with the actual defect parameters, and output a quantitative evaluation report.

[0058] Figure 1The aforementioned system employs a high-bandwidth PMUT transducer. Through multi-angle plane wave excitation and wideband signal reception, it can compensate for the acoustic attenuation of anisotropic composite materials, improve the signal-to-noise ratio and resolution of defect detection, and thus enhance monitoring accuracy. Specifically, the digital processing module, through the performance of the anisotropic elastic wave propagation film, can accurately calculate the elastic wave propagation velocity at each emission angle. The multi-angle elastic wave propagation velocity calculation takes into account the anisotropic propagation effect of the composite material structure. Therefore, based on the calculated elastic wave propagation velocity, the time delay of each imaging point can be accurately calculated, effectively compensating for the anisotropic propagation effect, thereby improving imaging accuracy and achieving effective monitoring of defects in composite material structures.

[0059] See Figure 5 The present invention also provides a method for monitoring the health of composite material structures, applied to the aforementioned composite material structure health monitoring system, such as... Figure 5 As shown, the method includes the following steps: Step 501: Obtain the structural characteristic parameters of the composite material structure to be monitored and the array parameters of the PMUT transducer; Step 502: Determine the target plane wave parameters based on the structural feature parameters and the array parameters; the target plane wave parameters include the plane wave scanning range, angular step size, and number of excitation angles; Step 503: Control the PMUT transducer to emit incident plane waves at multiple angles to the composite material structure to be monitored according to the target plane wave parameters, and collect the reflected plane waves; the reflected plane waves are signals formed by the reflection of the multi-angle plane waves after they are emitted to the composite material structure to be monitored. In practical applications, the target plane wave parameters are sent to the multi-channel ultrasonic excitation circuit, which generates an excitation signal and sends it to the PMUT transducer, so that the PMUT transducer emits the incident plane wave according to the target plane wave parameters.

[0060] Step 504: Based on the incident plane wave and the reflected plane wave, the elastic wave propagation velocity corresponding to each emission angle is calculated using a multi-angle coherent plane wave composite algorithm, and anisotropic delay time compensation is performed on the incident plane wave and the reflected plane wave based on the elastic wave propagation velocity to obtain a corrected signal; the elastic wave propagation velocity includes the equivalent sound velocity of the incident plane wave and the equivalent sound velocity of the reflected plane wave. Step 505: Construct a B-mode ultrasound image of the monitoring area of ​​the composite material structure to be monitored based on the corrected signal. The B-mode ultrasound image is used for defect assessment of the composite material structure to be monitored.

[0061] As an optional approach, the structural characteristic parameters include the sound velocity in the first dimension direction and the height; the array parameters include the ultrasonic element spacing, fractional bandwidth, and the center frequency emitted by the PMUT transducer; step 502 can be based on implementing: S1: Determine the sound velocity in the first dimension direction based on the anisotropic propagation model and density of the composite material structure to be monitored; S2: According to the formula: ; Determine the extreme values ​​of the scanning angle for the plane wave scanning range, and determine the plane wave scanning range based on the extreme values ​​of the scanning angle; in, To scan the extreme values ​​of the deflection angle, This is the ratio of the speed of sound in the first dimension to the center frequency. The distance between ultrasonic array elements; S3: According to the formula: ; Determine the angle step size; in, The angle step size is... For height; S4: Determine the number of excitation angles based on the extreme values ​​of the scanning deflection angle and the angle step size.

[0062] Optionally, the calculation of the elastic wave propagation velocity corresponding to each emission angle using a multi-angle coherent plane wave composite algorithm based on the reflected plane wave in step 504 can be specifically implemented based on S41-S45: S41: According to the formula: ; Calculate the first deflection angle; the first deflection angle is the deflection angle of the incident plane wave; S42: According to the formula: ; Calculate the second deflection angle; the second deflection angle is the deflection angle of the reflected plane wave; S43: Determine the eigenvalues ​​corresponding to the first deflection angle and the second deflection angle respectively according to the Christofer equation; S44: According to the formula: ; Determine the equivalent speed of sound of the incident plane wave; S45: According to the formula: ; Determine the equivalent speed of sound of the reflected plane wave; in, For the j-th first deflection angle, For the i-th second deflection angle, The eigenvalue corresponding to the first deflection angle. This is the eigenvalue corresponding to the second deflection angle. Let be the equivalent speed of sound of the incident plane wave. The equivalent speed of sound for reflected plane waves. The density of the composite material structure to be monitored is given by i, where both i and j are greater than 0.

[0063] Optionally, before step 504, the transmitted plane wave may be preprocessed, including median filtering for noise reduction, baseline correction, etc., to improve signal purity.

[0064] Optionally, the anisotropic delay time compensation for the incident plane wave and the reflected plane wave based on the elastic wave propagation velocity in step 504 to obtain the corrected signal can be specifically implemented based on S46-S47: S46: According to the formula: ; Calculate the delay time; in, To delay time, Let be the deflection angle of the j-th incident plane wave; Let the coordinates of the imaging point be in the first dimension. Let the coordinates of the imaging point be in the second dimension. Let be the coordinates of the i-th ultrasonic element in the second dimension. S47: Compensate for the incident plane wave and the reflected plane wave according to the delay time to obtain a corrected signal.

[0065] As an optional approach, S47 can be implemented based on the following steps: According to the formula: ; Determine the correction signal; in, Let be the composite pixel intensity of the corrected signal at the imaging point (x,z). The incident angle of the incident plane wave is Time-sonic array element The correction signal.

[0066] As an optional approach, step 505 can specifically be used for: By mapping the composite pixel intensity of each imaging point to the target imaging region, a B-mode ultrasound image of the CFRP sample monitoring area is obtained.

[0067] Figure 5The aforementioned method employs a high-bandwidth PMUT transducer and a multi-angle CPWC algorithm for coordinated adaptation. Through multi-angle plane wave excitation and wideband signal reception, it compensates for the acoustic attenuation of anisotropic composite materials, thereby improving the signal-to-noise ratio and resolution of defect detection. Simultaneously, based on the anisotropic parameter model of the composite material and considering its anisotropic characteristics, the time delay of the virtual focus is accurately calculated, effectively compensating for anisotropic propagation effects. A high-bandwidth PMUT transducer is formed by coupling ultrasonic array elements of multiple frequencies, enabling variable-frequency and variable-period excitation and reception according to the defect. Furthermore, through end-to-end algorithm optimization including preprocessing, delay time calculation, delay compensation, and signal correction via coherent superposition, accurate measurement of defect width and depth can be achieved, with a relative error of less than 0.1 nm for depth measurement and less than 0.6 mm for width measurement. Moreover, this invention can adjust model parameters according to composite materials of different thicknesses and defect types, adapting to various defect types such as delamination, grooves, and fiber pull-out, making it widely applicable.

[0068] In the above embodiments, implementation can be achieved entirely or partially through software, hardware, firmware, or any combination thereof. When implemented using software, it can be implemented entirely or partially in the form of a computer program product. The computer program product includes one or more computer programs or instructions. When the computer program or instructions are loaded and executed on a computer, the processes or functions described in the embodiments of the present invention are performed entirely or partially. The computer can be a general-purpose computer, a special-purpose computer, a computer network, a terminal, a user equipment, or other programmable device. The computer program or instructions can be stored in a computer-readable storage medium or transferred from one computer-readable storage medium to another. For example, the computer program or instructions can be transferred from one website, computer, server, or data center to another website, computer, server, or data center via wired or wireless means. The computer-readable storage medium can be any available medium that a computer can access or a data storage device such as a server or data center that integrates one or more available media. The available medium can be a magnetic medium, such as a floppy disk, hard disk, or magnetic tape; it can also be an optical medium, such as a digital video disc (DVD); or it can be a semiconductor medium, such as a solid-state drive (SSD).

[0069] Although the invention has been described herein in conjunction with various embodiments, those skilled in the art will understand and implement other variations of the disclosed embodiments by reviewing the accompanying drawings, the disclosure, and the appended claims in carrying out the claimed invention. In the claims, the word "comprising" does not exclude other components or steps, and "a" or "an" does not exclude a plurality. A single processor or other unit can implement several functions listed in the claims. While different dependent claims may recite certain measures, this does not mean that these measures cannot be combined to produce good results.

[0070] Although the invention has been described in conjunction with specific features and embodiments, it is obvious that various modifications and combinations can be made therein without departing from the spirit and scope of the invention. Accordingly, this specification and drawings are merely exemplary descriptions of the invention as defined by the appended claims, and are considered to cover any and all modifications, variations, combinations, or equivalents within the scope of the invention. Clearly, those skilled in the art can make various alterations and modifications to the invention without departing from its spirit and scope. Thus, if such modifications and modifications of the invention fall within the scope of the claims and their equivalents, the invention is also intended to include such modifications and modifications.

Claims

1. A method for monitoring the structural health of composite materials, characterized in that, include: Obtain the structural characteristic parameters of the composite material structure to be monitored and the array parameters of the PMUT transducer; The target plane wave parameters are determined based on the structural feature parameters and the array parameters; the target plane wave parameters include the plane wave scanning range, angular step size, and number of excitation angles. The PMUT transducer is controlled to emit incident plane waves at multiple angles to the composite material structure to be monitored according to the target plane wave parameters, and the reflected plane waves are collected; the reflected plane waves are signals formed by the reflection of the multi-angle plane waves after they are emitted to the composite material structure to be monitored. Based on the incident plane wave and the reflected plane wave, a multi-angle coherent plane wave composite algorithm is used to calculate the elastic wave propagation velocity corresponding to each emission angle, and anisotropic delay time compensation is performed on the incident plane wave and the reflected plane wave according to the elastic wave propagation velocity to obtain a corrected signal; the elastic wave propagation velocity includes the equivalent sound velocity of the incident plane wave and the equivalent sound velocity of the reflected plane wave. Based on the corrected signal, a B-mode ultrasound image of the monitoring area of ​​the composite material structure to be monitored is constructed, and the B-mode ultrasound image is used for defect assessment of the composite material structure to be monitored.

2. The method for monitoring the health of composite material structures according to claim 1, characterized in that, The structural feature parameters include the sound velocity and height in the first dimension direction; the array parameters include the ultrasonic element spacing, fractional bandwidth, and the center frequency emitted by the PMUT transducer; the target plane wave parameters are determined based on the structural feature parameters and the array parameters, including: The sound velocity in the first dimension direction is determined based on the anisotropic propagation model and density of the composite material structure to be monitored. According to the formula: ； Determine the extreme values ​​of the scanning angle for the plane wave scanning range, and determine the plane wave scanning range based on the extreme values ​​of the scanning angle; in, To scan the extreme values ​​of the deflection angle, This is the ratio of the speed of sound in the first dimension to the center frequency. The distance between ultrasonic array elements; According to the formula: ； Determine the angle step size; in, For the angle step size, For height; The number of excitation angles is determined based on the extreme values ​​of the scanning deflection angle and the angle step size.

3. The method for monitoring the health of composite material structures according to claim 2, characterized in that, Based on the incident plane wave and the reflected plane wave, the elastic wave propagation velocity corresponding to each emission angle is calculated using a multi-angle coherent plane wave composite algorithm, including: According to the formula: ； Calculate the first deflection angle; the first deflection angle is the deflection angle of the incident plane wave; According to the formula: ； Calculate the second deflection angle; the second deflection angle is the deflection angle of the reflected plane wave; Based on the Christofer equation, determine the eigenvalues ​​corresponding to the first deflection angle and the eigenvalues ​​corresponding to the second deflection angle, respectively. According to the formula: ； Determine the equivalent speed of sound of the incident plane wave; According to the formula: ； Determine the equivalent speed of sound of the reflected plane wave; in, For the j-th first deflection angle, For the i-th second deflection angle, The eigenvalue corresponding to the first deflection angle. This is the eigenvalue corresponding to the second deflection angle. Let be the equivalent speed of sound of the incident plane wave. The equivalent speed of sound for reflected plane waves. The density of the composite material structure to be monitored is given by i, where both i and j are greater than 0.

4. The method for monitoring the health of composite material structures according to claim 3, characterized in that, Anisotropic time delay compensation is performed on the incident plane wave and the reflected plane wave based on the elastic wave propagation velocity to obtain the corrected signal, including: According to the formula: ； Calculate the delay time; in, To delay time, Let be the deflection angle of the j-th incident plane wave; Let the coordinates of the imaging point be in the first dimension. Let the coordinates of the imaging point be in the second dimension. Let be the coordinates of the i-th ultrasonic element in the second dimension. The incident plane wave and the reflected plane wave are compensated based on the delay time to obtain a corrected signal.

5. The method for monitoring the health of composite material structures according to claim 4, characterized in that, The step of compensating the incident plane wave and the reflected plane wave according to the delay time to obtain the corrected signal includes: According to the formula: ； Determine the correction signal; in, Let be the composite pixel intensity of the corrected signal at the imaging point (x,z). The incident angle of the incident plane wave is Time-sonic array element The correction signal.

6. The method for monitoring the health of composite material structures according to claim 1, characterized in that, The B-mode ultrasound image of the monitoring region of the composite material structure to be monitored, constructed based on the corrected signal, includes: By mapping the composite pixel intensity of each imaging point to the target imaging region, a B-mode ultrasound image of the CFRP sample monitoring area is obtained.

7. A composite material structure health monitoring system, characterized in that, The composite material structure health monitoring method according to any one of claims 1-6 includes: a parameter acquisition module, a PMUT transducer, a multi-channel ultrasonic excitation circuit, a data processing module, and an imaging module; the PMUT transducer is connected to the multi-channel ultrasonic excitation circuit; the PMUT transducer is attached to the surface of the composite material structure to be monitored; The parameter acquisition module is used to acquire the structural characteristic parameters of the composite material structure to be monitored and the array parameters of the PMUT transducer; and to determine the target plane wave parameters based on the structural characteristic parameters and the array parameters; the target plane wave parameters include the plane wave scanning range, angular step size, and excitation angle number; The multi-channel ultrasonic excitation circuit is used to send excitation signals to the PMUT transducer according to the target plane wave parameters; The PMUT transducer is used to emit incident plane waves at multiple angles to the composite material structure to be monitored after receiving the excitation signal, and to collect the reflected plane waves and send the reflected plane waves to the data processing module; the reflected plane waves are signals formed by the reflection of the multi-angle plane waves after they are emitted to the surface of the sample to be monitored. The data processing module is used to calculate the elastic wave propagation velocity corresponding to each emission angle based on the incident plane wave and the reflected plane wave using a multi-angle coherent plane wave composite algorithm, and to perform anisotropic delay time compensation on the incident plane wave and the reflected plane wave based on the elastic wave propagation velocity to obtain a corrected signal. The imaging module is used to construct a B-mode ultrasound image of the monitoring area of ​​the composite material structure to be monitored based on the corrected signal. The B-mode ultrasound image is used for defect assessment of the composite material structure to be monitored.

8. The composite material structure health monitoring system according to claim 7, characterized in that, The PMUT transducer includes multiple transducer channels, which are arranged in one-dimensional or two-dimensional order. Each transducer channel includes multiple ultrasonic array elements arranged in a matrix. The ultrasonic array elements in the same transducer channel have different radii along the column direction. Each transducer channel is connected to one of the transmission channels of the multi-channel ultrasonic excitation circuit.

9. The composite material structure health monitoring system according to claim 7, characterized in that, The system also includes a signal amplifier, a filter, and a data storage device; the input of the signal amplifier is connected to the output of the PMUT transducer, the output of the signal amplifier is connected to the input of the filter, and the output of the filter is connected to the data storage device and the data processing module.

10. The composite material structure health monitoring system according to claim 8, characterized in that, The radius of the ultrasonic array elements along the column direction within the same transducer channel gradually increases or decreases.

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