An air-coupled composite ultrasonic testing method

Abstract

The application discloses an air coupling-based composite material ultrasonic detection method, which is applied to a workpiece to be detected, and the workpiece to be detected is composed of a composite material. The method comprises the following steps: a sound field reference model corresponding to the workpiece to be detected is constructed; a detection ultrasonic signal is sent to a detection area of the workpiece to be detected, and mixed sound field data corresponding to the detection area is received; based on the sound field reference model, signal separation processing is performed on the mixed sound field data, and internal reflection signals are obtained; spatial distribution analysis is performed on the internal reflection signals, and a defect detection result corresponding to the workpiece to be detected is obtained. Through the technical features of the application, the reflection signals interfering with the detection result can be separated in the process of ultrasonic detection of the workpiece to be detected, so that the reliability and accuracy of internal defect identification of the workpiece to be detected are improved.

Description

Technical Field

[0001] This application relates to the field of ultrasonic testing technology, and more specifically, to an ultrasonic testing method for composite materials based on air coupling. Background Technology

[0002] Air-coupled ultrasonic testing, as a non-contact testing method, is widely used in workpiece quality evaluation due to its advantages such as not requiring a coupling agent during the testing process and being suitable for rapid on-site screening. Its basic principle is to use air as the coupling medium. An ultrasonic signal is emitted from a transmitting probe towards the workpiece to be tested. The sound waves penetrate the workpiece or are reflected by the internal interface of the workpiece and picked up by a receiving probe. By analyzing the echo signal, the presence of defects inside the workpiece can be determined.

[0003] However, the workpieces to be inspected are often made of composite materials, and thick composite materials themselves exhibit significant anisotropy. Therefore, detection methods in related technologies, such as discrimination methods based on the non-reciprocity of sound wave propagation, may still show amplitude differences in the forward and reverse transmitted signals even when there are no internal defects in the workpiece, leading to inaccurate detection results. Furthermore, the surface of composite materials may have rough structures such as resin-rich layers, sprayed coatings, or slight wear textures. These rough structures will generate strong random reflections of the incident ultrasonic signal, forming a surface-reflected sound field. The superposition of the surface-reflected sound field and the internal-reflected sound field formed by internal defects in the workpiece will severely interfere with the detection results, making it difficult to effectively identify internal defects in the workpiece. Summary of the Invention

[0004] In view of the above-mentioned deficiencies in the related technologies, the technical problem to be solved by this application includes at least how to improve the accuracy and effectiveness of identifying internal defects in composite materials.

[0005] To address at least one of the aforementioned technical problems, this application proposes an ultrasonic testing method for composite materials based on air coupling.

[0006] According to one aspect of this application, an ultrasonic testing method for composite materials based on air coupling is provided, applied to a workpiece to be tested, the workpiece being tested being made of composite materials, the method comprising:

[0007] Construct a sound field reference model corresponding to the workpiece to be inspected;

[0008] It sends ultrasonic signals to the area to be inspected of the workpiece and receives mixed sound field data corresponding to the area to be inspected.

[0009] Based on the acoustic field reference model, signal separation processing is performed on the mixed acoustic field data to obtain the internal reflection signal;

[0010] Spatial distribution analysis of internal reflection signals yields defect detection results for the workpiece under test.

[0011] In one specific embodiment, the workpiece to be tested has a calibration reference area, which includes multiple calibration reference positions;

[0012] Constructing a sound field reference model corresponding to the workpiece to be inspected, including:

[0013] A preset number of calibration ultrasound signals are sent to each calibration reference position, and feedback ultrasound signals corresponding to each calibration reference position are received.

[0014] Multiple feedback ultrasound signals are time-aligned to obtain the average echo sequence corresponding to each calibration reference position;

[0015] Based on multiple feedback ultrasonic signals and multiple average echo sequences, a sound field reference model corresponding to the workpiece to be tested is generated.

[0016] In one specific embodiment, each feedback ultrasound signal includes a first surface reflection signal corresponding to a calibration reference position;

[0017] Based on multiple feedback ultrasonic signals and multiple average echo sequences, a sound field reference model corresponding to the workpiece to be tested is generated, including:

[0018] Calculate the first theoretical arrival time corresponding to the first surface reflection signal;

[0019] The average echo sequence is processed by envelope extraction, and the reflection envelope peak and the first measured arrival time corresponding to the reflection envelope peak are generated by combining the first theoretical arrival time.

[0020] The arrival time offset is determined based on the first theoretical arrival time and the first measured arrival time.

[0021] A sound field baseline model is constructed based on the arrival time offset, the peak value of the reflection envelope, and the first measured arrival time.

[0022] In some embodiments, an ultrasonic signal is sent to the area to be inspected of the workpiece, and mixed sound field data corresponding to the area to be inspected is received, including:

[0023] A detection scanning path is constructed based on the region to be detected, and the detection scanning path includes multiple locations to be detected.

[0024] Send detection ultrasonic signals to each location to be detected and receive the corresponding mixed sound field signals;

[0025] Envelope processing is performed on the mixed sound field signal to obtain mixed sound field data associated with multiple detection locations.

[0026] In one specific embodiment, based on a sound field reference model, signal separation processing is performed on the mixed sound field data to obtain internal reflection signals, including:

[0027] The second surface reflection signal is determined based on the acoustic field reference model and mixed acoustic field data;

[0028] The mixed sound field data is corrected based on the reflection signal from the second surface to obtain the internal reflection signal.

[0029] In one specific embodiment, the second surface reflection signal is obtained based on the acoustic field reference model and the mixed acoustic field data, including:

[0030] Based on the mixed sound field data, the second theoretical arrival time is calculated and a detection time window is constructed;

[0031] Based on the second theoretical arrival time and the detection time window, the candidate surface reflection peak value and the second measured arrival time corresponding to the candidate surface reflection peak value are determined.

[0032] The second surface reflection signal is determined based on the detection time window, the second measured arrival time, and the peak value of the candidate surface reflection.

[0033] In one specific embodiment, spatial distribution analysis of the internal reflection signal is performed to obtain the defect detection result corresponding to the workpiece to be inspected, including:

[0034] The internal reflection signal is standardized to obtain the reflection intensity data corresponding to the area to be detected; the reflection intensity data includes the reflection intensity parameter and the position coordinates corresponding to the reflection intensity parameter;

[0035] Spatial neighborhood analysis is performed based on reflection intensity parameters and location coordinates to obtain neighborhood analysis data.

[0036] Based on neighborhood analysis data, the defect detection results corresponding to the workpiece to be inspected are determined.

[0037] According to a second aspect of this application, an air-coupled ultrasonic testing device for composite materials is provided, applied to a workpiece to be tested, the workpiece being tested being made of composite material, the device comprising:

[0038] The model building module is used to build a sound field reference model corresponding to the workpiece to be inspected.

[0039] The workpiece inspection module is used to send ultrasonic signals to the inspection area of ​​the workpiece and receive mixed sound field data corresponding to the inspection area.

[0040] The signal processing module is used to perform signal separation processing on the mixed sound field data based on the sound field reference model to obtain the internal reflection signal;

[0041] The spatial analysis module is used to perform spatial distribution analysis on the internal reflection signals to obtain the defect detection results corresponding to the workpiece to be inspected.

[0042] According to a third aspect of this application, an electronic device is provided, comprising a processor and a memory, wherein the memory stores at least one instruction and at least one program, the at least one instruction and at least one program being loaded and executed by the processor to implement the air coupling-based ultrasonic testing method for composite materials as described above.

[0043] According to a fourth aspect of this application, a computer storage medium is provided, which stores at least one instruction and at least one program, wherein the at least one instruction and at least one program are loaded and executed by a processor to implement the air coupling-based ultrasonic testing method for composite materials as described above.

[0044] Implementing this application will have the following beneficial effects:

[0045] In this application, before performing ultrasonic testing on the workpiece, a sound field reference model corresponding to the workpiece is first constructed. Then, based on the sound field reference model, signal separation is performed on the mixed sound field data corresponding to the workpiece to obtain internal reflection signals. Establishing the sound field reference model enables accurate identification and separation of surface reflection noise from the mixed signals, thereby avoiding interference from reflection noise generated by the rough structure of the composite material surface on the test results. Furthermore, spatial distribution analysis based on the separated internal reflection signals accurately identifies internal defects in the workpiece, avoiding misjudgments caused by single-point signal fluctuations and significantly improving the reliability of detecting internal defects in composite materials. Attached Figure Description

[0046] To more clearly illustrate the technical solutions in the embodiments of this application or related technologies, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0047] Figure 1 A schematic flowchart of an ultrasonic testing method for composite materials based on air coupling, provided in an embodiment of this application;

[0048] Figure 2 A schematic diagram illustrating the process of constructing the acoustic field reference model provided in the embodiments of this application;

[0049] Figure 3 A schematic diagram illustrating the process for determining the mixed sound field data provided in the embodiments of this application;

[0050] Figure 4 This is a schematic diagram illustrating the process of determining the internal reflection signal provided in the embodiments of this application.

[0051] Figure 5 This is a flowchart illustrating the internal reflection signal analysis provided in the embodiments of this application.

[0052] Figure 6 This is a schematic diagram of the structure of an ultrasonic testing device for composite materials based on air coupling, provided in an embodiment of this application. Detailed Implementation

[0053] The technical solutions in the embodiments of this specification will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this specification, and not all embodiments. Based on the embodiments in this specification, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0054] It should be noted that the terms "first," "second," etc., in this application specification, claims, and the accompanying drawings are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that such data can be interchanged where appropriate so that the embodiments of this application described herein can be implemented in orders other than those illustrated or described herein. Furthermore, the terms "comprising" and "having," and any variations thereof, are intended to cover non-exclusive inclusion; for example, a process, method, system, product, or server that includes a series of steps or units is not necessarily limited to those steps or units explicitly listed, but may include other steps or units not explicitly listed or inherent to these processes, methods, products, or devices.

[0055] Various exemplary embodiments, features, and aspects of this application will now be described in detail with reference to the accompanying drawings. The same reference numerals in the drawings denote elements that have the same or similar functions. Although various aspects of the embodiments are shown in the drawings, they are not necessarily drawn to scale unless specifically indicated otherwise.

[0056] The term “exemplary” as used herein means “serving as an example, embodiment, or illustration.” Any embodiment illustrated herein as “exemplary” is not necessarily to be construed as superior to or better than other embodiments.

[0057] In this document, the term "and / or" describes a relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent three cases: A exists alone, A and B exist simultaneously, and B exists alone. Additionally, the term "at least one" in this document means any combination of at least two of any one or more elements. For example, including at least one of A, B, and C can mean including any one or more elements selected from the set consisting of A, B, and C.

[0058] Furthermore, to better illustrate this application, numerous specific details are provided in the following detailed description. Those skilled in the art should understand that this application can be implemented without certain specific details. In some instances, methods, means, components, and circuits well-known to those skilled in the art have not been described in detail in order to highlight the main points of this application.

[0059] In related technologies, when performing ultrasonic testing on workpieces made of composite materials based on air coupling, the presence of rough structures such as resin-rich layers, sprayed coatings, or slight wear textures on the surface of the composite material causes strong random reflections of incident ultrasonic waves on the surface of the workpiece, which are then directly reflected into the air. This superposition with the sound field reflected from internal material defects interferes with the testing results. To address this issue, this application proposes an air coupling-based ultrasonic testing method for composite materials. By constructing a surface reflection sound field recognition and suppression mechanism, the surface reflection sound field is separated from the internal material reflection sound field in terms of propagation path and temporal structure, thereby restoring the effective identification capability of air coupling ultrasonic testing for internal defects in composite materials.

[0060] The method proposed in this application will be described below with reference to specific technical features and accompanying drawings.

[0061] Figure 1 This is a schematic flowchart illustrating an ultrasonic testing method for composite materials based on air coupling, provided in an embodiment of this application. Figure 1 As shown, the method includes:

[0062] Step S101: Construct a sound field reference model corresponding to the workpiece to be tested.

[0063] Step S102: Send an ultrasonic signal to the area to be inspected of the workpiece and receive mixed sound field data corresponding to the area to be inspected.

[0064] Step S103: Based on the sound field reference model, perform signal separation processing on the mixed sound field data to obtain the internal reflection signal.

[0065] Step S104: Perform spatial distribution analysis on the internal reflection signal to obtain the defect detection results corresponding to the workpiece to be inspected.

[0066] The ultrasonic testing method disclosed in this application can be executed by an ultrasonic testing system. The ultrasonic testing system may include a control module, a transceiver module, and an amplification module. The control module controls the transceiver module to send detection ultrasonic signals and calibration ultrasonic signals to the workpiece to be tested, receives mixed sound field data and feedback ultrasonic signals returned by the transceiver module, and processes the mixed sound field data and feedback ultrasonic signals in conjunction with the amplification module. The transceiver module is used to send detection ultrasonic signals and calibration ultrasonic signals to the workpiece to be tested and to receive mixed sound field data and feedback ultrasonic signals. The amplification module is used to amplify the mixed sound field data and feedback ultrasonic signals. Compared with traditional air-coupled ultrasonic testing, this ultrasonic testing system has a high signal-to-noise ratio, can filter out noise, and improves the quality of the detection signal.

[0067] Specifically, the control module can be a high-frequency ultrasonic transmitter and receiver JPR-600C, capable of transmitting frequency-modulated waves and featuring FFT, pulse compression processing, and digital-analog filtering functions. Its configuration parameters can be: pulse voltage between 10V and 600V, output bandwidth between 30kHz and 10MHz, receiving bandwidth between 300Hz and 30MHz, transmit wavenumber between 1 and 300, and amplification between 0dB and 80dB. The transceiver module can be a high-sensitivity air-coupled ultrasonic probe with a frequency between 30kHz and 5MHz. The amplification module can be a high signal-to-noise ratio bandpass preamplifier with an amplification of 60dB.

[0068] In one specific embodiment, before performing air-coupled ultrasonic testing on the workpiece, a sound field reference model matching the material properties of the workpiece is first constructed. See also... Figure 2 In a specific embodiment, step S101, which involves constructing a sound field reference model corresponding to the workpiece to be tested, may include:

[0069] Step S201: Send a preset number of calibration ultrasound signals to each calibration reference position, and receive the feedback ultrasound signal corresponding to each calibration reference position.

[0070] In one specific embodiment, before executing step S201, the ultrasonic testing system and the detection position of the workpiece to be tested are first configured. During the model construction process, the workpiece to be tested has a calibration reference area, which may include multiple calibration reference positions. Since the constructed acoustic field reference model is used to identify and separate the surface reflection signals formed by the rough structure during ultrasonic testing, and to avoid the inclusion of internal defect reflection components in the constructed acoustic field reference model, the calibration reference area can preferentially select areas confirmed by process records to have no obvious internal anomalies. By discretizing the calibration reference area according to a preset scanning step size, multiple calibration reference positions can be obtained.

[0071] Specifically, the transceiver module in the ultrasonic testing system can be positioned above the calibration reference area of ​​the workpiece to be tested. The transceiver module transmits calibration ultrasonic signals propagating through the air to the surface of the workpiece. In the transceiver module, the transmitting probe and the receiving probe can be arranged at intervals along the normal direction above the surface of the workpiece, ensuring that their main sound beams cover the same calibration reference area.

[0072] Each calibration reference position can correspond to a surface sampling point. For each calibration reference position, the propagation distance from the center of the transmitting probe to the surface sampling point and the propagation distance from the surface sampling point to the center of the receiving probe are recorded, forming the corresponding air propagation path length. At the same time, the transmission pulse width, center frequency, excitation period, and number of repeated transmissions of the calibration ultrasonic signal are set (i.e., the preset number mentioned in step S201), forming a unified set of reference excitation parameters.

[0073] In addition, to ensure comparability between different calibration reference positions, the peak transmitted sound pressure level should be kept constant, preferably ranging from 200 Pa to 2000 Pa; the center frequency of transmission is preferably ranging from 100 kHz to 800 kHz; and the scanning step size is preferably ranging from 1 mm to 20 mm. When the surface coating of the workpiece to be inspected is thick, the scanning step size can be reduced to improve the characterization ability of local roughness reflection differences.

[0074] The total path length of airborne propagation can be calculated using the following formula:

[0075] ;

[0076] in, It can represent the total air propagation path length at the j-th calibration reference position, and its unit is meters. It can represent the propagation distance from the transmitting probe to the j-th surface sampling point, in meters. This can represent the propagation distance from the j-th surface sampling point to the receiving probe, in meters. Essentially, this formula decomposes the propagation process of the first surface reflection signal formed in the calibration reference area into two parts: the "incident segment" and the "return segment," which are used for subsequent arrival time reference calculations.

[0077] After completing the above arrangements, a unified detection pose basis is obtained for subsequent repeated transmissions and receptions.

[0078] In some embodiments, in order to establish a reflected sound field reference corresponding to the surface rough structure and thus obtain a sound field reference model, each calibration reference position can be repeatedly emitted multiple times to reduce the adverse effects of accidental airflow disturbances and single-excitation micro-fluctuations on the reference modeling. The preferred number of repetitions is between eight and sixty-four. Specifically, step S201 can be implemented as follows:

[0079] At each calibration reference position, the control module controls the transmitting probe to repeatedly transmit calibration ultrasonic signals propagating through the air to the workpiece under test according to the reference excitation parameter set. The receiving probe synchronously acquires the echo signal. This echo signal is the feedback ultrasonic signal described in step S201.

[0080] Step S202: Perform time alignment processing on multiple feedback ultrasound signals to obtain the average echo sequence corresponding to each calibration reference position.

[0081] In some embodiments, each feedback ultrasound signal may include at least a first surface reflection signal corresponding to a calibration reference position and a first time-domain signal corresponding to the first surface reflection signal. For multiple feedback ultrasound signals corresponding to each calibration reference position, time alignment processing is performed based on the included time-domain signals, and the average is calculated to obtain a repetitive emission average echo sequence corresponding to each calibration reference position, i.e., an average echo sequence.

[0082] Step S203: Based on multiple feedback ultrasonic signals and multiple average echo sequences, generate a sound field reference model corresponding to the workpiece to be tested.

[0083] In some embodiments, a sound field reference model corresponding to the workpiece to be tested is generated based on multiple feedback ultrasonic signals and multiple average echo sequences, including:

[0084] Step a: Calculate the first theoretical arrival time corresponding to the first surface reflection signal.

[0085] Step b: Perform envelope extraction processing on the average echo sequence, and combine it with the first theoretical arrival time to generate the reflection envelope peak value and the first measured arrival time corresponding to the reflection envelope peak value.

[0086] Step c: Determine the arrival time offset based on the first theoretical arrival time and the first measured arrival time.

[0087] Step d: Construct a sound field baseline model based on the arrival time offset, reflection envelope peak value, and the first measured arrival time.

[0088] Specifically, for step a, the first theoretical arrival time corresponding to the reflected signal from the first surface can be calculated by combining the air velocity. The air velocity is significantly affected by ambient temperature; therefore, the ambient temperature needs to be recorded simultaneously during model construction. Furthermore, for the detection environment, if humidity monitoring is available at the engineering site, the air velocity can be further corrected using humidity monitoring data. For ordinary factory buildings or blade maintenance warehouses, the air velocity can be obtained using a temperature correction method.

[0089] The first theoretical time of arrival, which is the theoretical propagation time of the calibrated ultrasonic signal from the transmitting probe to the surface of the workpiece under test and back to the receiving probe, can be calculated using the following formula:

[0090] ;

[0091] in, This represents the first theoretical arrival time of the j-th calibration reference position, in seconds. The total airborne path length at the j-th calibration reference position is expressed in meters. This represents the air speed constant at zero degrees Celsius, with a value of 331.3 meters per second. This represents the ambient temperature, expressed in degrees Celsius. Essentially, this formula uses the air propagation path and the environmentally corrected air speed of sound to predict the time and location at which the reflected echo from a rough surface structure should appear, providing a theoretical basis for subsequent envelope extraction and time window constraints.

[0092] In addition, if the span of multiple calibration reference areas is large, the theoretical arrival time can be calculated separately by dividing the area into blocks to reduce the propagation distance deviation caused by the large curvature surface.

[0093] In some embodiments, in step b, envelope extraction processing is performed on the average echo sequence corresponding to each calibration reference position, preferably using Hilbert envelope processing, to obtain a smooth reflection energy profile. Subsequently, a calibration time window is constructed centered on the first theoretical arrival time. The calibration time window can be a local time search window, within which the reflection envelope peak value and the first measured arrival time corresponding to that peak value are extracted. The first measured arrival time is the time when the actually measured first surface reflection signal arrives at the receiving probe. The half-width of the calibration time window is preferably in the range of five microseconds to fifty microseconds; when the installation height of the transceiver module is high or the surface roughness of the workpiece to be tested is large, the calibration time window can be appropriately enlarged.

[0094] The peak value of the reflection envelope can be extracted using the following formula:

[0095] ;

[0096] in, This represents the peak value of the reflection envelope at the j-th calibration reference position, in Pascals. The instantaneous sound pressure of the average echo sequence at the j-th calibration reference position is expressed in Pascals. Indicates to The orthogonal components after Hilbert transform are expressed in Pascals (Pa). The essence of this formula is to transform the original oscillating echo into a monotonic energy envelope, thereby stably extracting the peak amplitude that truly reflects the strength of the reflection.

[0097] For step c, the arrival time offset relative to the first theoretical arrival time is calculated by combining the first theoretical arrival time and the first measured arrival time. The arrival time offset reflects the influence of the surface micro-roughness on the local elongation or shortening of the reflection path. If the arrival time offset corresponding to a certain calibration reference position continuously deviates from the adjacent points, it can be preliminarily determined that there is a significant change in the surface roughness state of that calibration reference position.

[0098] For step d, a sound field reference model is constructed based on the peak reflection envelope and time characteristics (including at least the first measured arrival time and arrival time offset) extracted from each calibration reference position. In modeling, instead of directly using single-point amplitudes, the amplitude attenuation relationship, time offset relationship, and spatial continuity of adjacent calibration reference positions are incorporated to enhance the sound field reference model's ability to characterize local surface roughness and texture changes of the workpiece under test.

[0099] In one specific embodiment, the normalized reflection intensity is first calculated to eliminate the influence of small fluctuations in the excitation sound pressure. Further, the reflection gradient between adjacent calibration reference positions is calculated to reflect the spatial rate of change in surface roughness. Finally, the position coordinates, reflection intensity, first measured arrival time, and arrival time offset corresponding to each calibration reference position are associated and stored to form a set of surface reflection sound field features, which is the sound field reference model.

[0100] In the subsequent formal inspection stage of the workpiece, once the echo signal received by the receiving probe contains a component that is highly consistent with the sound field reference model, it can be preferentially determined that it belongs to the surface reflection noise of the workpiece, rather than the reflection noise formed by internal defects of the workpiece.

[0101] The reflection intensity can be normalized using the following formula:

[0102] ;

[0103] in, It can represent the normalized reflection intensity at the j-th calibration reference position. The value represents the peak reflection envelope at the j-th calibration reference position, expressed in Pascals (Pa). n can represent the total number of calibration reference positions within the calibration reference region. This represents the sum of the peak reflection envelopes corresponding to all calibration reference locations, expressed in Pascals (Pa). Essentially, this formula uses the average reflection level of the calibration reference area as a reference to evaluate whether the reflection intensity at a particular calibration reference location is too high or too low.

[0104] The reflection gradient can be calculated using the following formula:

[0105] ;

[0106] in, It can represent the reflection gradient of the j-th calibration reference position relative to the previous calibration reference position, with the unit being / meter. and These represent the normalized reflection intensities at two adjacent calibration reference positions, respectively. and These represent the spatial coordinates of two adjacent calibration reference positions, in meters. Essentially, this formula makes the spatial undulations of surface roughness reflection explicit, used to distinguish between uniformly rough areas and locally anomalously rough areas.

[0107] In step S203, steps b and c are the core steps in constructing the acoustic field reference model. By converting the original oscillation signal into measurable and comparable reflection characteristics, the subsequent monitoring process no longer relies on visual observation of the waveform, but is determined based on unified amplitude and time characteristics. This provides a stable foundation for surface reflection acoustic field modeling and improves the uniformity, effectiveness, and reliability of the acoustic field reference model.

[0108] In a specific embodiment, during the execution of step S102, the configuration of the ultrasonic testing system and the workpiece to be tested at their testing positions can be performed under the testing arrangement conditions established in step S101. Specifically, the workpiece to be tested has a testing area, which can be the entire area of ​​the workpiece or determined according to different testing requirements. Each testing area can include multiple testing positions. Under the testing arrangement conditions established in step S101, the transmitting probe is moved along the testing area, causing it to sequentially emit ultrasonic signals coupled via air at multiple testing positions. The receiving probe synchronously records the mixed sound field signal after each excitation and extracts the corresponding signal peak value and signal arrival time; these parameters together constitute the mixed sound field data. Since the workpiece to be tested exhibits two types of sound fields during ultrasonic testing—surface rough structure reflection and internal material defect reflection—the mixed sound field signal simultaneously contains both the second surface reflection signal and the internal reflection signal.

[0109] Please see Figure 3 Step S102, which involves sending an ultrasonic signal to the area to be inspected of the workpiece and receiving mixed sound field data corresponding to the area to be inspected, may include:

[0110] Step S301: Construct a detection scanning path based on the area to be detected. The detection scanning path includes multiple locations to be detected.

[0111] In a specific embodiment, based on the detection arrangement conditions established in step S101, a detection scanning path is constructed along the area to be detected. Preferably, the detection scanning path can be deployed along the main detection direction of the workpiece. For curved structures such as wind turbine blade webs, aerospace composite skins, and composite material tank shells, the area to be detected can be further discretized into several parallel scanning bands, and each band can be detected sequentially.

[0112] In the detection scanning path, each position to be detected inherits the configuration information in step S101, such as probe installation height, probe angle, transmission center frequency and receiving gain settings, so as to ensure that the mixed sound field data and the sound field reference model are in the same detection system.

[0113] In other embodiments, to enable point-by-point comparison of subsequently acquired mixed sound field data, a detection path sequence and a synchronous acquisition timing table can be established. The detection path sequence defines the spatial coordinates of the k-th detection location, and the synchronous acquisition timing table defines the sampling start time, sampling duration, and repetition period for each transmission. The sampling duration should cover surface reflection echoes (i.e., the second surface reflection signal), internal defect reflection echoes (i.e., the internal reflection signal), and a certain margin of trailing attenuation. The preferred range for the sampling duration is fifty microseconds to one thousand microseconds. The repetition period should be greater than the time required for the mixed sound field signal to completely attenuate, preferably ranging from 0.5 milliseconds to twenty milliseconds.

[0114] The spatial coordinates of the location to be detected can be updated according to the following formula:

[0115] ;

[0116] in, This represents the coordinates of the k-th position to be detected in the scanning direction, in meters. This indicates the starting coordinates of the first location to be detected, in meters. The step size represents the distance between two adjacent detection positions, in meters, with a preferred value ranging from 0.1 mm to 10 mm. k represents the detection position number, a positive integer. Essentially, this formula discretizes the continuous detection area into a sampling sequence that can be executed and recorded point-by-point, providing a unified spatial index for subsequently constructing the mixed sound field sequence corresponding to the mixed sound field data.

[0117] In other embodiments, if the area to be detected is a two-dimensional surface scan, then band numbering and cross-band displacement parameters can be added to the above one-dimensional coordinates. The core is still to ensure that each detection position has a unique spatial identifier and a unified sampling timing. By transforming "continuous area detection" into "discrete position detection," each mixed sound field signal received by the subsequent receiving probe can correspond one-to-one with a specific spatial position, which facilitates the reliable separation of the second surface reflection signal from the internal reflection signal.

[0118] Step S302: Send a detection ultrasonic signal to each location to be detected and receive the corresponding mixed sound field signal.

[0119] In some embodiments, according to the detection scanning path, at each location to be detected, the transmitting probe emits a detection ultrasonic signal according to a synchronous acquisition timing table, and the receiving probe synchronously acquires the echo signal (i.e., the mixed sound field signal). Because the effective ultrasonic energy of a single emitted detection ultrasonic signal incident on the workpiece is low under air coupling conditions, and there may be weak airflow disturbances, structural curvature changes, and slight probe posture fluctuations at the detection site, each location to be detected can be repeatedly excited multiple times. The multiple initial mixed sound field signals received from these multiple acquisitions are then averaged to obtain the final mixed sound field signal, thereby improving the stability of the received mixed sound field signal. The preferred number of repeated excitations is between four and thirty-two.

[0120] The average signal from multiple repeated excitations can be calculated using the following formula:

[0121] ;

[0122] in, It can represent the first The average signal of repeated excitation at each detection location, i.e., the mixed sound field signal, is measured in Pascals. Indicates the number of times. This indicates the number of repeated excitations at the location to be detected, with a preferred value range of four to thirty-two. Indicates the first The first location to be detected The first received original time-domain echo signal, i.e. the initial mixed sound field signal, is measured in Pascals. The value represents the sampling time in seconds. The essence of this formula is to average multiple excitations to retain stable mixed sound field signals that repeatedly appear at the same location, thus reducing random transient disturbances and making the mixed characteristics of surface and internal reflections clearer.

[0123] The mixed acoustic field signal contains two types of components. The first type is the air-side surface reflection component caused by the surface roughness of the workpiece under test, i.e., the second surface reflection signal, which usually arrives earlier. The second type is the internal reflection component, i.e., the internal reflection signal, which is the signal that has been detected after entering the workpiece and interacting with internal defects, interlayer interfaces, or local structural discontinuities before coupling back into the air, and which usually arrives later. Therefore, the raw signal acquired in this sub-step is essentially a mixed acoustic field signal, rather than a single type of reflection signal.

[0124] In other embodiments, to facilitate subsequent processing, time reference unification and amplitude normalization preparation can be performed on each received mixed sound field signal. Time reference unification typically uses the transmission trigger moment as time zero; amplitude normalization preparation involves recording the current transmission voltage, probe gain, and ambient temperature to prevent incomparability between signals from different detection locations.

[0125] Step S303: Perform envelope processing on the mixed sound field signal to obtain mixed sound field data associated with multiple detection locations.

[0126] In some embodiments, before performing envelope processing on the mixed sound field signal, the average time-domain echo sequence corresponding to each detection location can be bound to its spatial coordinates to form a set of time-domain echo sequences with location marking.

[0127] Specifically, step S303 may be implemented in the following ways:

[0128] Envelope extraction is performed on the mixed sound field signal at each detection location. The Hilbert envelope method is preferred, as it converts high-frequency oscillation waveforms into positive continuous envelopes, facilitating the uniform extraction of peak values ​​and arrival times. Furthermore, to avoid the envelope peaks being affected by extremely short-period oscillations, a short-window smoothing process can be superimposed after envelope extraction. The preferred smoothing window length is between two and twenty sampling points.

[0129] The envelope of the mixed sound field signal can be calculated using the following formula:

[0130] ;

[0131] in, It can represent the envelope of the mixed sound field at the k-th position to be detected, in Pascals. This represents the mixed sound field signal at the k-th detection position, expressed in Pascals. Indicates to The orthogonal components obtained after Hilbert transform are expressed in Pascals (Pa). The essence of this formula is to transform the original alternating sound pressure waveform into an envelope curve reflecting the local sound energy intensity, giving subsequent peak extraction a clear physical meaning.

[0132] Furthermore, a preset reception time window is obtained, and the maximum value of the mixed sound field envelope is searched within the preset reception time window, and defined as the peak value of the mixed sound field at this detection location. At this stage, surface reflection and internal reflection have not yet been separated, so the peak value of the mixed sound field may be dominated by reflections from surface rough structures, or by reflections from internal defects, or by a combination of both.

[0133] Within the preset reception time window, the peak value of the mixed sound field can be extracted using the following formula:

[0134] ;

[0135] in, This represents the peak value of the mixed sound field at the k-th detection location, expressed in Pascals. This represents the envelope of the mixed sound field at the k-th position to be detected, in Pascals. This represents the first theoretical arrival time corresponding to the k-th calibration reference position established in step S101, in seconds. This can represent the time-weighting coefficient, with the unit being seconds, and the preferred value range being one microsecond to fifty microseconds. The essence of this formula is to introduce time weighting during peak search, prioritizing effective echoes related to the known reflection propagation range and suppressing weak stray oscillations far from the main propagation range.

[0136] After obtaining the peak value of the mixed sound field, it is also necessary to extract the measured arrival time corresponding to the peak value. The measured arrival time can usually be taken as the moment when the envelope of the mixed sound field first reaches a certain proportion of the peak value or the moment when the envelope reaches its maximum value. If the fixed proportion method is used, the proportion coefficient is preferably in the range of 0.2 to 0.6; if the peak moment method is used, appropriate smoothing should be used to avoid multi-peak interference. Finally, the peak value and measured arrival time of the mixed sound field at each detection location are obtained.

[0137] The peak values ​​of the mixed sound field corresponding to each detection location and the measured arrival time are arranged sequentially according to the detection scanning path, and then bound one by one with the spatial coordinates corresponding to the detection location to form mixed sound field data. Furthermore, to improve the usability of the mixed sound field data in the subsequent signal separation process, local envelope energy can also be recorded in the mixed sound field data.

[0138] Specifically, local envelope energy is used to describe the overall intensity of the mixed sound field signal corresponding to a certain detection location within a certain time window, and can be used to distinguish between two different echo patterns: "peak-shaped surface reflection" and "tail-shaped internal reflection".

[0139] The local envelope energy can be calculated using the following formula:

[0140] ;

[0141] in, This represents the local envelope energy of the k-th detection location within the receiving time window, expressed in Pascals per second. This represents the envelope of the mixed sound field at the k-th position to be detected, in Pascals. These represent the start and end times of the integration, respectively, in seconds, and their values ​​are given by the synchronous acquisition timing table in the preceding steps. The essence of this formula is to incorporate echo persistence information beyond the instantaneous peak value into the description, thereby avoiding insufficient characterization caused by relying solely on single-point peak values ​​in subsequent steps.

[0142] In other embodiments, if the workpiece to be tested has at least a portion of its surface as a large curvature surface, the surface normal angle or the local incident angle of the probe corresponding to the location of the large curvature surface can be included in the mixed sound field data to enhance subsequent interpretation capabilities.

[0143] In this embodiment, the mixed sound field signal corresponding to each detection location is compressed into a unified feature expression to obtain mixed sound field data, which facilitates subsequent batch identification and separation of the mixed sound field data to obtain the internal reflection signal. After the above processing, the mixed sound field data can at least include: the spatial coordinates of the detection location, the peak value of the mixed sound field, the measured arrival time, the local envelope energy, and the time-domain echo sequence after location marking.

[0144] For step S103, the obtained mixed sound field data is processed for propagation path identification using the sound field reference model. A second theoretical arrival time is calculated, and a surface reflection time window is constructed. The second theoretical arrival time is the theoretical propagation time of the detected ultrasonic signal from the transmitting probe back to the receiving probe, which can be calculated based on the air propagation distance and the speed of sound in air. The mixed sound field signal appearing within the detection time window is identified as the second surface reflection signal. For the identified second surface reflection signal, amplitude subtraction can be used to suppress it from the original received signal, thereby reducing the reflection noise generated by the surface rough structure. After the above processing, the weakened internal reflection signal corresponding to the second surface reflection signal is obtained.

[0145] For details, please refer to Figure 4In some embodiments, step S103, which involves performing signal separation processing on the mixed sound field data based on the sound field reference model to obtain the internal reflection signal, may include:

[0146] Step S401: Determine the second surface reflection signal based on the sound field reference model and the mixed sound field data.

[0147] In a specific embodiment, since the purpose of step 103 is to perform signal separation, a propagation time reference must first be established for each location to be detected, so that the time of appearance of surface reflection can be quantified, so as to accurately identify and separate the second surface reflection signal in the mixed sound field signal.

[0148] Specifically, based on the acoustic field reference model and mixed acoustic field data, the reflection signal from the second surface is obtained, including:

[0149] Step 1: Based on the mixed sound field data, calculate the second theoretical arrival time and construct the detection time window.

[0150] Step II: Based on the second theoretical arrival time and the detection time window, determine the candidate surface reflection peak value and the second measured arrival time corresponding to the candidate surface reflection peak value.

[0151] Step III: Determine the second surface reflection signal based on the detection time window, the second measured arrival time, and the candidate surface reflection peak value.

[0152] Under air-coupled ultrasonic testing conditions, the propagation path of the surface reflection signal is the shortest. Its propagation process mainly includes: an air propagation segment from the transmitting probe to the surface of the workpiece under test, and an air propagation segment from the surface of the workpiece to the receiving probe. Therefore, without considering internal propagation, the theoretical arrival time of the surface reflection echo should be determined by both the total air propagation path and the air velocity. Since slight fluctuations can occur due to factors such as ambient temperature, airflow, and probe height, a time window with a tolerance width can be constructed to improve data accuracy.

[0153] For step I, the second theoretical arrival time corresponding to the second surface reflection signal can be calculated according to the following formula:

[0154] ;

[0155] in, It can represent the second theoretical arrival time corresponding to the k-th position to be detected, in seconds. This represents the total airborne path length at the k-th location to be detected, in meters. This value can be inherited from the geometric arrangement result of step S101. This represents the effective air velocity at the k-th detection location, in meters per second. It can also be corrected based on the on-site temperature, with a commonly used value range of 330 to 350 meters per second.

[0156] In some embodiments, a detection time window can be constructed to accommodate minor surface roughness variations of the workpiece, slight probe orientation deviations, and local air disturbances. The half-width of the detection time window can be determined by the reference reflection peak width, the second theoretical arrival time, and the local roughness.

[0157] The half-width of the time window can be calculated using the following formula:

[0158] ;

[0159] in, It can represent the half-width of the time window corresponding to the detection time window of the k-th position to be detected, in seconds. The value represents the width of the surface reflection reference peak obtained in step S101 at the k-th detection position, in seconds. This represents the relative expansion coefficient, which is a dimensionless quantity, and its preferred value range is 0.01 to 0.1. This represents the absolute extension compensation amount, in seconds, with a preferred value range of 0.5 microseconds to 20 microseconds. This can represent the second theoretical arrival time of the k-th position to be detected, in seconds. The essence of this formula is to incorporate the influence of "the width of the reference waveform itself", "the longer the propagation time, the easier it is to drift" and "the minimum tolerance at the system level" into the time window design at the same time, so that subsequent identification will not miss detections due to being too narrow, nor will it falsely detect detections due to being too wide.

[0160] Based on the above, the detection time window for the k-th position to be detected can be defined as the interval from the second theoretical arrival time minus half the time window width to the second theoretical arrival time plus half the time window width, i.e. After completing the above calculations, we can obtain the propagation time reference set, the detection time window set, and the time gating parameter set.

[0161] For step II, a time-gated search is performed on the mixed sound field time-domain echo sequence for each location to be detected. Specifically, within the corresponding detection time window, the local main peak of the envelope curve is searched, and this main peak is regarded as a candidate echo for surface reflection. Since the mixed sound field envelope sequence and the corresponding peak information have already been extracted in step S102, the envelope processing of the time-domain echo after the location marking can continue in this process, or the envelope sequence saved in step S102 can be directly called.

[0162] In one specific embodiment, to prevent local clutter or extremely weak noise peaks from being misidentified as the main surface reflection peaks, a candidate peak intensity threshold can be set. This threshold can be set based on the reflection envelope peak value in step S101. Typically, a certain proportion of the reflection envelope peak value can be used as the minimum threshold, and the proportion coefficient is preferably in the range of 0.2 to 0.8. If the surface roughness of the workpiece to be tested is strong, the proportion coefficient should be appropriately reduced to avoid missing the true surface reflection peaks. If the ambient noise at the testing site is high, the proportion coefficient should be appropriately increased to suppress false peaks from entering the candidate set.

[0163] The candidate surface reflection peak at the k-th detection location can be extracted using the following formula:

[0164] ;

[0165] in, This represents the peak value of the candidate surface reflection at the k-th detection location, in Pascals. This represents the envelope of the mixed sound field at the k-th position to be detected, in Pascals. This represents the second theoretical arrival time of the k-th position to be detected, in seconds. This represents the half-width of the time window corresponding to the detection time window at the k-th position to be detected, in seconds. The essence of this formula is to use Gaussian time weighting to enhance the echo components adjacent to the arrival time of the theoretical surface reflection, so that the extraction of candidate peaks prioritizes following the propagation physical path, rather than simply relying on absolute amplitude.

[0166] In other embodiments, for complex curved surfaces or thick coating areas, there may be two similar peak values ​​within the detection time window. In such cases, it is advisable to prioritize the peak value that is "closer to the reference reflection level in step S101 and has a sharper peak shape" as the candidate main peak, while reserving the other peak as a secondary candidate for further discrimination.

[0167] After obtaining the candidate peak, it is also necessary to record the second measured arrival time corresponding to the peak. At this time, the second measured arrival time may not be the true surface reflection arrival time, but a candidate time.

[0168] Furthermore, in certain special scenarios, such as thick-coated composite materials or curved surfaces with small local bending radii, the shallow internal reflected echoes may arrive earlier and partially fall within the surface reflection time window. Therefore, for step III, relying solely on time gating is insufficient; it is also necessary to combine a sound field reference model to match and determine the amplitude, arrival time deviation, and local energy pattern of the candidate echoes. This will further narrow down the "candidate echoes appearing within the time window" to "echoes that truly belong to surface reflection," thus distinguishing the second surface reflection signal from the internal reflection signal.

[0169] Specifically, the reference reflection amplitude at the k-th detection position can be set to be... The second theoretical arrival time is The reference normalized reflection intensity is The peak value of the candidate surface reflection is The second measured arrival time is The candidate local envelope energy is Then, surface reflection matching coefficients can be constructed.

[0170] The surface reflection matching coefficient is calculated using the following formula:

[0171] ;

[0172] in, It can represent the surface reflection matching coefficient at the k-th detection position, and is a dimensionless quantity. This represents the peak reflectance of the candidate surface, measured in Pascals (Pa). This represents the peak value of the reflection envelope corresponding to the detection location established in step S101, in Pascals. This represents the relative amplitude tolerance coefficient, which is a dimensionless quantity, and its preferred value range is 0.1 to 1. This represents the absolute compensation term for amplitude, in Pascals (Pa), with a preferred value range of 0.01 Pa to 1 Pa. This indicates the second measured arrival time, in seconds. This indicates the arrival time of the second theory, in seconds. This indicates the half-width of the time window, in seconds. This represents the envelope energy of the candidate echo within the local window, expressed in Pascals per second. This represents the energy balance coefficient, measured in Pascals per second (Pa), with a preferred value range of 10⁻¹² to 10⁻⁶ Pascals per second. Essentially, this formula combines three conditions—"amplitude close to the reference," "time close to the reference," and "energy form satisfying surface reflection characteristics"—for evaluation, thereby improving the reliability of surface reflection identification.

[0173] Furthermore, a surface reflection confirmation threshold is set. This threshold is preferably in the range of 0.3 to 0.8. When If the value is greater than or equal to the confirmation threshold, the candidate mixed sound field signal is determined to be a confirmed second surface reflection signal. Otherwise, it is included in the internal reflection candidate signal set.

[0174] It should be noted that the specific implementation steps of step S401 do not directly give the internal reflection signal corresponding to the final internal defect. Instead, the second surface reflection signal that can be determined is separated from the mixed reflection signal, and the part that is "not like the second surface reflection signal" is temporarily retained and processed in step S402 to determine the real internal reflection signal.

[0175] In the above steps, by combining the three types of features—time, amplitude, and energy—it is possible to avoid mistakenly deleting internal shallow abnormal signals, thereby ensuring the effectiveness of subsequent internal defect identification.

[0176] Step S402: Correct the mixed sound field data based on the second surface reflection signal to obtain the internal reflection signal.

[0177] In one specific embodiment, after confirming the second surface reflection signal, surface reflection suppression is performed on the original mixed sound field echo sequence in the mixed sound field data. The core of the suppression method is amplitude subtraction, but a simple direct deletion of the entire segment is not feasible because surface reflections and internal reflections may have local temporal overlap. Specifically, a surface reflection estimation envelope is constructed based on the surface reflection peak value, peak width, and peak time corresponding to the second surface reflection signal, and then this estimated envelope is proportionally subtracted from the original mixed sound field envelope sequence.

[0178] Let the envelope of the mixed sound field at the k-th position to be detected be... The unit is Pascal. The peak surface reflection value corresponding to the second surface reflection signal is The unit is Pascals (Pa). The second measured arrival time is... The unit is seconds. The equivalent width of surface reflection is... The unit is seconds. The surface reflection estimation envelope can be constructed using either a local Gaussian shape or a local biexponential shape. For ease of engineering implementation, Gaussian shape estimation should be preferred.

[0179] The corrected envelope after surface reflection suppression is calculated using the following formula:

[0180] ;

[0181] in, This represents the internal reflection correction envelope after surface reflection suppression corresponding to the k-th detection position, in Pascals. This represents the surface reflection deduction factor, which is a dimensionless quantity, and its preferred value range is 0.5 to 1.2. Typically, the peak width can be determined by combining the baseline peak width from step S101 and the candidate peak full width at half maximum (FWHM) from step S102. The essence of this formula is to approximate the surface reflection component with a local estimated envelope that matches the surface reflection shape, and then subtract it from the mixed sound field data, thereby preserving as much of the remaining component related to internal propagation as possible.

[0182] Furthermore, after subtraction, a non-negative truncation is employed to ensure that no negative envelope values ​​are found. The main peak is re-searched and the local envelope energy is recalculated within the corrected envelope to extract the internal reflection enhancement envelope sequence and the internal reflection signal. After completing the above steps, the corrected echo sequence after reflection suppression, the internal reflection enhancement envelope sequence, and the internal reflection signal can be obtained.

[0183] In other embodiments, if the surface reflection matching coefficient at a certain detection location is significantly high and the peak surface reflection is much larger than the other echoes, the subtraction factor should be appropriately high. If there is some overlap between surface reflection and internal reflection, the subtraction factor should be low to prevent excessive erasure of internal reflections.

[0184] In other embodiments, to facilitate subsequent spatial distribution analysis, the intensity of the internal reflection residual signal can be additionally recorded. The residual signal intensity reflects the difference in envelope energy before and after subtracting surface reflection, and can be used to determine whether a certain detection location still retains sufficiently strong internal reflection information. The residual signal intensity is calculated using the following formula:

[0185] ;

[0186] in, It represents the ratio of the residual signal intensity at the k-th detection position, and is a dimensionless quantity. This represents the internal reflection correction envelope after surface reflection suppression at the k-th detection location, in Pascals. This represents the envelope of the original mixed sound field at the k-th position to be detected, in Pascals. and Indicates the start and end times of the integration time window, in seconds; This represents a tiny positive number to prevent the denominator from being zero, and its preferred value range is 10 to the power of -15 to 10 to the power of -9 Pa²s / second. Essentially, this formula measures "how much effective energy remains after deducting surface reflections," thus providing an auxiliary reliability indicator for subsequently determining the location of internal anomalies.

[0187] In other embodiments, the internal reflection enhancement envelope sequence can be standardized to generate an internal reflection signal feature set that can be directly used in subsequent steps. That is, in some embodiments, the internal reflection signal used for spatial distribution analysis can also be an internal reflection signal feature set. This set may include at least: the spatial coordinates of the location to be detected, the internal reflection peak value after surface reflection suppression, the measured arrival time of the internal reflection, and the ratio of the local envelope energy of the internal reflection to the residual signal intensity.

[0188] Step S104 is executed to perform spatial distribution analysis of the amplitude of the internal reflection signal corresponding to different detection locations. When the amplitude of the internal reflection signal corresponding to a certain detection location is significantly higher than that of the surrounding area, it is determined that there may be internal defects in the composite material at that location, such as pore defects or fiber corrugation structures. By continuously scanning along the detection scanning path and recording the signal change trend, a structural internal defect distribution map corresponding to the workpiece under test is established. Finally, the defect location and defect distribution information of the detection area are output, completing the air-coupled ultrasonic testing.

[0189] Please see Figure 5 In some embodiments, step S104, which involves spatial distribution analysis of the internal reflection signal to obtain the defect detection result corresponding to the workpiece to be inspected, may include:

[0190] Step S501: Standardize the internal reflection signal to obtain the reflection intensity data corresponding to the area to be detected; the reflection intensity data includes the reflection intensity parameter and the position coordinates corresponding to the reflection intensity parameter.

[0191] In one specific embodiment, the set of internal reflection signal features is first rearranged according to the detection path order to form a sequence of internal reflection features with one-to-one correspondence between positions. Since the coupling state, local curvature, and residual attenuation may still differ at different detection locations, the original internal reflection peak value cannot be directly used as the basis for defect judgment; instead, standardization processing should be performed first. During standardization, the internal reflection peak value, local envelope energy, and residual signal intensity ratio are jointly normalized to obtain more stable internal reflection intensity data.

[0192] The reflection intensity parameter can be calculated using the following formula:

[0193] ;

[0194] in, This represents the reflection intensity parameter corresponding to the k-th detection position, which is a dimensionless quantity. This represents the internal reflection peak value at the k-th detection location, in Pascals. This represents the average value of the peak reflection within the entire area to be detected, expressed in Pascals (Pa). This represents the peak stabilization constant, with values ​​ranging from 10⁻⁶ Pa to 10⁻³ Pa. This represents the local envelope energy of the internal reflection at the k-th position to be detected, expressed in Pascals per second. This represents the average local envelope energy of the entire area to be detected, expressed in Pascals per second. This represents the energy stabilization constant, with values ​​ranging from 10 to 10 to 10 to 15 Pascals squared to 10 to 10 to 9 Pascals squared. It represents the ratio of the residual signal intensity at the k-th detection position, and is a dimensionless quantity. This represents the residual stabilization constant, with values ​​ranging from 10 to 10 to the power of -6 to 10 to the power of -3. This represents the residual enhancement index, with a value ranging from 0.3 to 1.

[0195] The essence of this formula is to couple three factors—the strength of the peak, the energy level, and the sufficiency of the remaining components after deducting surface reflection—into a unified intensity quantity, thereby avoiding misjudgment based solely on a single peak value.

[0196] After standardization, the reflection intensity parameters are obtained, and together with the position coordinates (i.e., the aforementioned spatial coordinates) corresponding to each position to be detected, they form a position-related feature sequence.

[0197] Step S502: Perform spatial neighborhood analysis based on reflection intensity parameters and location coordinates to obtain neighborhood analysis data.

[0198] In one specific embodiment, spatial neighborhood analysis is performed on the reflection intensity parameters corresponding to each detection location and the location-related feature sequence formed based on the location coordinates. The principle is that true internal defects usually cause the internal reflection intensity of the corresponding detection location to be significantly higher than that of the preceding and following neighbors, while the signal change corresponding to a homogeneous material region or a region without internal defects is usually more gradual.

[0199] Specifically, for each location to be detected, several neighboring points before and after it are selected as local background, and the degree of abnormal enhancement of that location relative to the neighboring background is calculated. The neighborhood half-width is usually set by the scanning step size and the expected minimum defect size, and the preferred value range is two to ten sampling points; if the object to be detected is a large-sized pore agglomeration area, the neighborhood half-width can be appropriately increased.

[0200] The background intensity of the neighborhood of the k-th detection location can be calculated using the following formula:

[0201] ;

[0202] in, This represents the background intensity in the neighborhood of the k-th detection location, and is a dimensionless quantity. This represents the number of valid points in the neighborhood of the k-th location to be detected that participated in the calculation. This represents the reflection intensity parameter at the j-th location to be detected. and represents the spatial coordinates of the j-th and k-th positions to be detected, in meters. r can represent the number of points corresponding to the neighborhood half-width, with a value ranging from two to ten. This represents the background attenuation length, in meters, with a preferred value range of one to twenty scan steps.

[0203] The essence of this formula is to construct a local normal background using a distance-weighted approach, so that neighboring points closer to the current point have a greater influence, while points further away have a smaller influence.

[0204] After obtaining the neighborhood background intensity, the spatial anomaly enhancement value is calculated using the following formula:

[0205] ;

[0206] in, This represents the spatial anomaly enhancement value at the k-th location to be detected, and is a dimensionless quantity. This represents the reflection intensity parameter at the k-th position to be detected. This represents the background intensity in the neighborhood of the k-th detection location. This represents the background stabilization constant, with values ​​ranging from 10 to the power of -6 to 10 to the power of -3.

[0207] when When the initial anomaly threshold is exceeded, the location to be detected can be recorded as an initial defect candidate point. The preferred value range for the initial anomaly threshold is 0.2 to 2. When the material of the workpiece to be detected is relatively uniform, a lower initial anomaly threshold can be used; when the surface of the workpiece to be detected is complex or the local structure changes significantly, a higher initial anomaly threshold can be used.

[0208] Through the above steps, the neighborhood analysis data can include at least the neighborhood background intensity, spatial anomaly enhancement value, and initial defect candidate points. Identifying anomaly detection locations that significantly stand out from the surrounding material background from multiple detection locations improves the reliability of subsequent defect localization and analysis.

[0209] Step S503: Based on neighborhood analysis data, determine the defect detection results corresponding to the workpiece to be inspected.

[0210] In some embodiments, since the composite material forming the workpiece to be inspected typically does not correspond to a single isolated sampling point, but forms an abnormal region on a continuous inspection scan path, the initial defect candidate points can be continuously merged.

[0211] Specifically, the distance between adjacent candidate points is checked along the detection scanning path. If the distance between adjacent candidate points is less than the continuity determination distance, they are merged into the same continuous defect segment; otherwise, they are considered different defect segments. The preferred value range for the continuity determination distance is one to five scanning steps.

[0212] After forming continuous defect segments, the comprehensive defect indication value for each segment is calculated. The comprehensive defect indication value considers not only the maximum anomaly within the segment, but also the segment length and energy accumulation to prevent extremely narrow isolated spikes from being misjudged as real defects.

[0213] The overall defect indication value can be calculated using the following formula:

[0214] ;

[0215] in, It can represent the comprehensive defect indication value of the u-th defect continuous segment, and is a dimensionless quantity. This indicates the maximum value of spatial anomaly enhancement within this section. This represents the spatial length of the u-th consecutive defect segment, in meters. This represents the length normalization constant, with the unit being meters. The preferred value range is from one scan step to ten scan steps. This represents the number of sampling points contained in the u-th consecutive defect segment. This represents the sum of the reflection intensity parameters corresponding to all areas to be detected within this section.

[0216] The essence of this formula is to combine the abnormal peak value, the continuous distribution length, and the overall intensity of the section, so that the output is more in line with the spatial unfolding characteristics of defects in actual engineering.

[0217] Furthermore, for each continuous defect segment, its start position, end position, peak position, and comprehensive defect indication value are recorded to form a set of defect characteristic parameters. A final judgment and result output are then performed for each continuous defect segment.

[0218] Specifically, a comprehensive defect judgment threshold is first set, preferably ranging from one to five. When the comprehensive defect indication value of a certain segment is greater than or equal to the threshold, the area to be detected corresponding to that segment is determined to be an internal defect area. If the comprehensive defect indication value is lower than the threshold, it is retained as a general structural fluctuation area or a weak anomaly area but is not included in the final defect result.

[0219] For the finally confirmed defective sections, the peak position of the section is taken as the main defect location, and the start and end positions of the section are taken as the defect influence range. Each section is then mapped along the detection scanning path to the coordinates of the composite material detection area to form an internal defect distribution map. For two-dimensional scanning scenarios, defective sections on different scanning bands can be further stitched together to form a two-dimensional defect heat map.

[0220] In some embodiments, to ensure a uniform output of defect detection results, a defect confidence score can be calculated for each confirmed defect segment. The defect confidence score can be calculated using the following formula:

[0221] ;

[0222] in, Let represent the defect confidence level of the u-th confirmed defect segment, which is a dimensionless quantity. This represents the comprehensive defect indication value for the u-th defect continuous segment. This represents the defect confidence scaling constant, with a preferred value range of 0.5 to 5. Essentially, this formula maps the overall defect indication value to a range of zero to one, facilitating engineers' rapid assessment of defect confidence levels.

[0223] The final output of the defect detection results may include at least one or more of the following: a defect distribution map inside the composite material, defect location information, and defect confidence level.

[0224] As can be seen from the embodiments provided in this application above, the technical solutions disclosed in this application can achieve the following technical effects:

[0225] (1) Through systematic modeling, the reflection phenomenon caused by the surface rough structure is quantified into a callable acoustic field reference model, providing a basis for subsequent separation of surface reflections. In the model construction process, normalized reflection intensity and adjacent point gradient calculation are used to eliminate the influence of excitation fluctuations and environmental disturbances, making the reflection characteristics at different locations comparable. At the same time, by repeating emission averaging and envelope extraction, random disturbances are reduced, thereby improving the reliability and repeatability of the acoustic field reference model in subsequent application processes.

[0226] (2) In the process of ultrasonic testing of the workpiece, the spatial coordinates are first correlated with the mixed sound field signal to provide accurate positional information for subsequent defect localization and separation of surface reflection signals. At the same time, by repeatedly averaging the excitation, random disturbances are suppressed, which can improve the stability of surface reflection signals and internal reflection signals.

[0227] (3) In the process of separating surface reflection signals from internal reflection signals, by matching theoretical propagation time with measured time and combining multiple features such as amplitude and energy for joint judgment, the accuracy of determining the type of reflection signal can be improved, avoiding misjudgment or omission. At the same time, the introduction of indicators such as matching coefficient and residual energy ratio enhances the adaptability to complex surface structures (such as coatings and curved surfaces).

[0228] (4) In the spatial distribution analysis process, firstly, standardization is used to eliminate coupling differences and avoid misleading defect judgment by single-point peaks. Secondly, spatial anomaly enhancement analysis is used to identify anomaly points that stand out significantly relative to the background, avoiding misjudgment caused by uniform structural fluctuations. In addition, by merging continuous segments and calculating comprehensive defect indicator values, the defect location, range and confidence level are output, which facilitates quick interpretation by engineers.

[0229] This application also provides an ultrasonic testing device for composite materials based on air coupling, such as... Figure 6 As shown, the device includes:

[0230] Model building module 610 is used to build a sound field reference model corresponding to the workpiece to be inspected;

[0231] The workpiece inspection module 620 is used to send an ultrasonic signal to the area to be inspected of the workpiece and to receive mixed sound field data corresponding to the area to be inspected.

[0232] The signal processing module 630 is used to perform signal separation processing on the mixed sound field data based on the sound field reference model to obtain the internal reflection signal;

[0233] The spatial analysis module 640 is used to perform spatial distribution analysis on the internal reflection signal to obtain the defect detection results corresponding to the workpiece to be inspected.

[0234] In other embodiments, the model building module 610 may include:

[0235] The first signal interaction module is used to send a preset number of calibration ultrasound signals to each calibration reference position and to receive feedback ultrasound signals corresponding to each calibration reference position.

[0236] The time alignment module is used to perform time alignment processing on multiple feedback ultrasound signals to obtain the average echo sequence corresponding to each calibration reference position;

[0237] The first model generation module is used to generate a sound field reference model corresponding to the workpiece to be tested based on multiple feedback ultrasonic signals and multiple average echo sequences.

[0238] In other embodiments, the first model generation module may include:

[0239] The first calculation module is used to calculate the first theoretical arrival time corresponding to the first surface reflection signal;

[0240] The first envelope processing module is used to perform envelope extraction processing on the average echo sequence, and generate the reflection envelope peak value and the first measured arrival time corresponding to the reflection envelope peak value by combining the first theoretical arrival time.

[0241] The offset determination module is used to determine the arrival time offset based on the first theoretical arrival time and the first measured arrival time.

[0242] The second model generation module is used to construct a sound field reference model based on the arrival time offset, the peak value of the reflection envelope, and the first measured arrival time.

[0243] In other embodiments, the workpiece inspection module 620 may include:

[0244] The path building module is used to build a detection scanning path based on the region to be detected. The detection scanning path includes multiple locations to be detected.

[0245] The second signal interaction module is used to send detection ultrasound signals to each location to be detected and to receive the corresponding mixed sound field signals.

[0246] The second envelope processing module is used to perform envelope processing on the mixed sound field signal to obtain mixed sound field data associated with multiple detection locations.

[0247] In other embodiments, the signal processing module 630 may include:

[0248] The first signal determination module is used to determine the second surface reflection signal based on the sound field reference model and the mixed sound field data;

[0249] The correction module is used to correct the mixed sound field data based on the reflection signal from the second surface to obtain the internal reflection signal.

[0250] In other embodiments, the first signal determination module may include:

[0251] The second calculation module is used to calculate the second theoretical arrival time and construct the detection time window based on the mixed sound field data;

[0252] The time determination module is used to determine the candidate surface reflection peak value and the second measured arrival time corresponding to the candidate surface reflection peak value based on the second theoretical arrival time and the detection time window.

[0253] The second signal determination module is used to determine the second surface reflection signal based on the detection time window, the second measured arrival time, and the candidate surface reflection peak value.

[0254] In other embodiments, the spatial analysis module 640 may include:

[0255] The standardization processing module is used to standardize the internal reflection signal to obtain the reflection intensity data corresponding to the area to be detected; the reflection intensity data includes the reflection intensity parameter and the position coordinates corresponding to the reflection intensity parameter;

[0256] The neighborhood analysis module is used to perform spatial neighborhood analysis based on reflection intensity parameters and location coordinates to obtain neighborhood analysis data.

[0257] The defect determination module is used to determine the defect detection results of the workpiece to be inspected based on neighborhood analysis data.

[0258] The apparatus and method embodiments described above are based on the same inventive concept and are used to implement the above-mentioned ultrasonic testing method for composite materials based on air coupling.

[0259] This application also provides an electronic device. The electronic device includes a processor and a memory, the memory storing at least one instruction, at least one program, code set, or instruction set. The processor loads and executes the at least one instruction, at least one program, code set, or instruction set to implement any of the air-coupling-based ultrasonic testing methods for composite materials as described in the method embodiments.

[0260] This application also provides a computer storage medium. This computer storage medium can be located in a server to store at least one instruction, at least one program, code set, or instruction set for implementing at least one instruction, at least one program, code set, or instruction set in the method embodiments. The at least one instruction, at least one program, code set, or instruction set is loaded and executed by a processor to implement any of the air-coupling-based ultrasonic testing methods for composite materials as described in the method embodiments.

[0261] Optionally, in this embodiment of the application, the storage medium may be located in at least one of multiple network servers in a computer network. Optionally, in this embodiment of the application, the storage medium may include, but is not limited to, various media capable of storing program code, such as USB flash drives, read-only memory (ROM), random access memory (RAM), portable hard drives, magnetic disks, or optical disks.

[0262] It should be noted that the above embodiments only illustrate several implementation methods of this application, and their descriptions are relatively specific and detailed, but they should not be construed as limiting the scope of this application's patent. The above description is exemplary and not exhaustive, nor is it limited to the disclosed embodiments. The technical features of the above embodiments can be combined arbitrarily. For the sake of brevity, not all possible combinations of the technical features in the above embodiments have been described. However, as long as the combination of these technical features does not contradict each other, it should be considered within the scope of this specification. It should be pointed out that for those skilled in the art, several modifications and improvements can be made without departing from the concept of this application, and these all fall within the protection scope of this application. Therefore, the protection scope of this patent application should be determined by the appended claims. The terminology used herein is chosen to best explain the principles, practical applications, or technical improvements in the market of the various embodiments, or to enable other those skilled in the art to understand the various embodiments disclosed herein.

Claims

1. An ultrasonic testing method for composite materials based on air coupling, applied to a workpiece to be tested, the workpiece being tested being made of composite materials, characterized in that, The method includes: Constructing a sound field reference model corresponding to the workpiece to be tested specifically includes: A preset number of calibration ultrasound signals are sent to each calibration reference position, and a feedback ultrasound signal corresponding to each calibration reference position is received. Multiple feedback ultrasound signals are time-aligned to obtain an average echo sequence corresponding to each calibration reference position; Based on the multiple feedback ultrasonic signals and multiple average echo sequences, a sound field reference model corresponding to the workpiece to be tested is generated. The workpiece to be tested has a calibration reference area, which includes multiple calibration reference positions. Sending an ultrasonic signal to the area to be inspected of the workpiece and receiving mixed acoustic field data corresponding to the area to be inspected; specifically including: A detection scanning path is constructed based on the region to be detected, and the detection scanning path includes multiple locations to be detected. The detection ultrasonic signal is sent to each of the locations to be detected, and the corresponding mixed sound field signal is received; Envelope processing is performed on the mixed sound field signal to obtain the mixed sound field data associated with the plurality of detection locations; Based on the aforementioned sound field reference model, the mixed sound field data undergoes signal separation processing to obtain the internal reflection signal; specifically including: Based on the sound field reference model and the mixed sound field data, the second surface reflection signal is determined; The mixed sound field data is corrected based on the second surface reflection signal to obtain the internal reflection signal; Spatial distribution analysis of the internal reflection signal is performed to obtain the defect detection result corresponding to the workpiece to be inspected; specifically including: The internal reflection signal is standardized to obtain reflection intensity data corresponding to the area to be detected; the reflection intensity data includes reflection intensity parameters and position coordinates corresponding to the reflection intensity parameters; Spatial neighborhood analysis is performed based on the reflection intensity parameters and the location coordinates to obtain neighborhood analysis data. Based on the neighborhood analysis data, the defect detection result corresponding to the workpiece to be inspected is determined.

2. The ultrasonic testing method for composite materials based on air coupling according to claim 1, characterized in that, Each of the feedback ultrasound signals includes a first surface reflection signal corresponding to the calibration reference position; The step of generating the acoustic field reference model corresponding to the workpiece to be tested based on the multiple feedback ultrasonic signals and multiple average echo sequences includes: Calculate the first theoretical arrival time corresponding to the first surface reflection signal; The average echo sequence is subjected to envelope extraction processing, and the reflection envelope peak value and the first measured arrival time corresponding to the reflection envelope peak value are generated by combining the first theoretical arrival time. Based on the first theoretical arrival time and the first measured arrival time, the arrival time offset is determined; The sound field reference model is constructed based on the arrival time offset, the reflection envelope peak value, and the first measured arrival time.

3. The ultrasonic testing method for composite materials based on air coupling according to claim 1, characterized in that, The process of obtaining the second surface reflection signal based on the sound field reference model and the mixed sound field data includes: Based on the hybrid sound field data, the second theoretical arrival time is calculated and a detection time window is constructed; Based on the second theoretical arrival time and the detection time window, the candidate surface reflection peak value and the second measured arrival time corresponding to the candidate surface reflection peak value are determined. The second surface reflection signal is determined based on the detection time window, the second measured arrival time, and the candidate surface reflection peak value.

4. An ultrasonic testing device for composite materials based on air coupling, characterized in that, The device includes: The model building module is used to construct a sound field reference model corresponding to the workpiece to be inspected; specifically, it includes: A preset number of calibration ultrasound signals are sent to each calibration reference position, and a feedback ultrasound signal corresponding to each calibration reference position is received. Multiple feedback ultrasound signals are time-aligned to obtain an average echo sequence corresponding to each calibration reference position; Based on the multiple feedback ultrasonic signals and multiple average echo sequences, a sound field reference model corresponding to the workpiece to be tested is generated. The workpiece to be tested has a calibration reference area, which includes multiple calibration reference positions. The workpiece inspection module is used to send ultrasonic signals to the inspection area of ​​the workpiece to be inspected, and to receive mixed sound field data corresponding to the inspection area; specifically, it includes: A detection scanning path is constructed based on the region to be detected, and the detection scanning path includes multiple locations to be detected. The detection ultrasonic signal is sent to each of the locations to be detected, and the corresponding mixed sound field signal is received; Envelope processing is performed on the mixed sound field signal to obtain the mixed sound field data associated with the plurality of detection locations; The signal processing module is used to perform signal separation processing on the mixed sound field data based on the sound field reference model to obtain the internal reflection signal; specifically, it includes: Based on the sound field reference model and the mixed sound field data, the second surface reflection signal is determined; The mixed sound field data is corrected based on the second surface reflection signal to obtain the internal reflection signal; The spatial analysis module is used to perform spatial distribution analysis on the internal reflection signal to obtain the defect detection result corresponding to the workpiece to be inspected, specifically including: The internal reflection signal is standardized to obtain reflection intensity data corresponding to the area to be detected; the reflection intensity data includes reflection intensity parameters and position coordinates corresponding to the reflection intensity parameters; Spatial neighborhood analysis is performed based on the reflection intensity parameters and the location coordinates to obtain neighborhood analysis data. Based on the neighborhood analysis data, the defect detection result corresponding to the workpiece to be inspected is determined.

5. An electronic device, characterized in that, The electronic device includes a processor and a memory, the memory storing at least one instruction and at least one program, the at least one instruction and the at least one program being loaded and executed by the processor to implement the air coupling-based ultrasonic testing method for composite materials as described in any one of claims 1 to 3.

6. A computer storage medium, characterized in that, The computer storage medium stores at least one instruction and at least one program, which are loaded and executed by a processor to implement the ultrasonic testing method for composite materials based on air coupling as described in any one of claims 1 to 3.

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