An ultrasonic measurement method and system for residual stress of a composite curved surface part

Abstract

The present application belongs to the technical field of air-coupled ultrasonic guided wave detection, and discloses an ultrasonic measurement method and system for residual stress of a composite curved part, comprising the following steps: determining the center frequency and incident angle of two groups of air-coupled ultrasonic transducers; determining the distance between the transmitting transducer and the receiving transducer of the two groups of different center frequencies, and the height of the measured curved surface; applying different known stresses, measuring the acoustic time difference of the two groups of different center frequency air-coupled ultrasonic transducers at different detection positions, establishing and calibrating the corresponding relationship formula of the acoustic time difference of the ultrasonic guided wave in the composite flat plate component and the applied stress; measuring the acoustic time difference of the target section of the composite curved component with unknown stress, and according to the relationship formula, inverting the residual stress of the target section of the composite component. The present application adopts the above method and system, and performs acoustic time difference measurement and stress inversion based on the air-coupled ultrasonic guided wave method, thereby accurately realizing the detection of the residual stress of the composite curved component.

Description

Technical Field

[0001] This invention relates to the field of air-coupled ultrasonic guided wave testing technology, and in particular to an ultrasonic measurement method and system for residual stress in composite curved surface parts. Background Technology

[0002] Due to their lightweight and high strength, composite materials have become indispensable key materials in aerospace, automotive manufacturing, and bridge construction. During the manufacturing process, residual stress inevitably occurs in composite materials. The distribution of this internal residual stress significantly affects the mechanical properties and service life of components, potentially leading to deformation, impacting stability and assembly accuracy, and reducing fatigue life. Therefore, accurate detection of residual stress in composite material components is crucial.

[0003] Compared to residual stress detection in planar components, composite curved surface components face greater challenges in residual stress detection due to their curved geometry, material anisotropy, and internal structural heterogeneity. Existing methods for residual stress detection in curved surface components mainly include blind hole methods, X-ray diffraction, and methods combined with machine learning prediction. Blind hole methods require drilling holes in the component, which damages the material; X-ray diffraction can only obtain surface stress information and cannot reflect the internal stress of the composite material; methods combined with machine learning prediction require large datasets for model training, and the trained model cannot predict the residual stress of curved surfaces with other manufacturing processes or ply structures. In contrast, ultrasonic guided wave testing has advantages such as low cost, full-field measurement, and no material damage, making it particularly suitable for stress assessment of large-size composite components. However, current mainstream ultrasonic testing research focuses on flat components, and there is an urgent need for an ultrasonic testing method for residual stress in curved surface components.

[0004] Existing contact ultrasonic testing methods require specialized ultrasonic probe wedges precisely matched to the radius of curvature of the component to effectively measure residual stress on curved surfaces. This significantly increases testing costs and makes it difficult to apply to curved surfaces with varying curvature. When testing complex curved surfaces, the probe wedge cannot maintain constant contact with the surface, leading to reduced signal stability and directly affecting ultrasonic signal acquisition, thus compromising measurement accuracy. Furthermore, contact ultrasonic probes require the application of coupling agent, causing surface contamination. Air-coupled ultrasonic guided wave technology achieves non-contact excitation and reception through the air medium, avoiding the contamination problems associated with coupling agents. However, existing air-coupled ultrasonic guided wave technology also faces numerous technical bottlenecks when testing curved components, such as the impact of varying air segment distance and surface curvature on measurement accuracy. The anisotropy of composite materials also affects the measurement results.

[0005] Therefore, there is an urgent need to develop a novel air-coupled ultrasonic guided wave stress detection technology to stably, efficiently, and accurately measure the residual stress of composite curved surface components, thereby overcoming the limitations of existing technologies for detecting residual stress in thin-walled composite curved surface components and providing a reliable detection method for engineering applications. Summary of the Invention

[0006] The purpose of this invention is to provide an ultrasonic measurement method and system for residual stress in composite curved surface components, which can accurately detect residual stress in composite curved surface components.

[0007] To achieve the above objectives, the present invention provides an ultrasonic measurement method for residual stress in composite curved surface parts, comprising the following steps: Step S1: Determine the center frequencies of the two sets of air-coupled ultrasonic transducers based on the dispersion curve of the composite material guided wave. Step S2: Based on Snell's law and experimental data, determine the incident angles of two sets of air-coupled ultrasonic transducers with different center frequencies; Step S3: Based on the test data, and taking the standard that the guided wave signal does not overlap with the air direct wave in the time domain, determine the distance between the transmitting transducer and the receiving transducer with two different center frequencies, and the distance from the measured surface height. Step S4: Measure the acoustic time difference of two groups of air-coupled ultrasonic transducers with different center frequencies at different detection positions; Step S5: Apply prestress to the composite plate component using a tensile machine, measure the corresponding acoustic time using an air-coupled ultrasonic guided wave detection system to obtain the acoustic time difference, and establish and calibrate the correspondence between the acoustic time difference of the ultrasonic guided wave in the composite plate component and the applied stress. Step S6: Following the process in step S4, perform acoustic time difference detection on the target segment of the composite material curved surface component with unknown stress, and invert the residual stress of the target segment of the composite material component according to the relationship in step S5.

[0008] Preferably, in step S1, the guided wave dispersion curve is calculated using the anisotropic elastic matrix and density parameters of the composite material to obtain the A1 mode cutoff frequency, and the appropriate center frequencies of the two sets of air-coupled ultrasonic transducers are determined. Among them, air-coupled ultrasonic transducers appear in pairs, in conjunction with dedicated ultrasonic pulse transmitting and receiving equipment.

[0009] Preferably, in step S2, the phase velocity of mode A0 is obtained from the guided wave dispersion curve, and the incident angle applicable to both groups of air-coupled ultrasonic transducers with different center frequencies is determined based on Snell's law and the detection experimental data. Among them, Snell's law formula: (1); in, The angle of refraction; Angle of incidence; The phase velocity of the composite medium; denoted as the phase velocity in the air medium.

[0010] Preferably, in step S3, based on the test data, the distance between the transmitting transducer and the height of the measured surface are determined, with the standard that the guided wave signal does not overlap with the air direct wave in the time domain. This applies to both sets of transmitting transducers and receiving transducers with different center frequencies.

[0011] Preferably, in step S4, the acoustic time difference of two sets of air-coupled ultrasonic transducers with different center frequencies at different detection positions is measured. The specific process is as follows: Step S41: Move the first group of center frequencies to... f The transmitting and receiving transducers of unit 1 are positioned at the initial detection location, and the center frequency of the first group is fixed at [value missing]. f The transmitting transducer 1 collects ultrasonic signals and records the initial detection position. The frequency of the guided wave reaching the center of the first group is... f 1 receiving transducer time Maintain the center frequency of the first group as f The transmitting transducer of unit 1 remains unchanged, and the center frequency of the first group is moved to . f The receiving transducer of device 1 is moved to the second detection position to acquire ultrasonic signals, and the frequency of the guided wave at the second detection position reaching the center of the first group is recorded. f 1 receiving transducer time ; Step S42: Move the second group of center frequencies to... f The transmitting and receiving transducers of unit 2 are connected to the center frequency of the first group. f The transmitting and receiving transducers of unit 1 have the same initial detection positions, and the center frequency of the second group is fixed at 1. f The transmitting transducer of unit 2 collects ultrasonic signals and records the initial detection position. The frequency at which the guided wave reaches the center of the second group is... f 2. Time of receiving transducer Maintain the center frequency of the second group as f The transmitting transducer of group 2 remains unchanged, and the center frequency of the second group is moved to . f The receiving transducer of 2 is connected to the center frequency of the first group. f At the second detection position, where the transmitting and receiving transducers are identical, ultrasonic signals are acquired, and the frequency of the guided wave reaching the center of the second group at the second detection position is recorded. f 2. Time of receiving transducer .

[0012] Preferably, the propagation distance of the transmitted waveguide from the transmitting transducer to the shelf is denoted as the air section distance of the transmitting transducer. The propagation distances of the guided wave at the two detection positions in the composite skin layer are respectively and The propagation distances of the receiving transducer's receiving guided waves to the corresponding two detection positions between the transducer and the shelf are denoted as the air segments of the receiving transducer. and Guided waves of different frequencies propagate at the same speed in air, denoted as ; The propagation velocities of guided waves of different frequencies in the composite skin layer are respectively and ; Based on the parameter settings, the derivation is as follows: (2); (3); (4); (5); Subtracting formulas (4) from (2) and (5) from (3), we get: (6); (7); Let formulas (7) and (6) be used to obtain the sound time difference. As shown below: (8); make Then formula (8) simplifies to: (9); Further results were obtained: (10).

[0013] Preferably, in step S5, a prestress is applied to the composite material plate component using a tensile machine, and the corresponding acoustic time is measured using an air-coupled ultrasonic guided wave detection system to obtain the acoustic time difference. The corresponding relationship between the acoustic time difference of the ultrasonic guided wave in the composite material plate component and the applied stress is established and calibrated. The specific process is as follows: Step S51: Acquire the corresponding waveform signal using the air-coupled ultrasonic guided wave detection system, perform noise reduction processing on the signal, select the acoustic time corresponding to the guided wave segment of the waveform signal and record and save it; according to step S4, acquire and save the acoustic time at different positions of the air-coupled ultrasonic transducer at different frequencies to obtain the acoustic time difference. ; Step S52: Apply different known stresses to the composite plate specimen on a tensile machine. Changes in stress conditions will affect the propagation speed of ultrasonic guided waves in the composite skin, and thus affect... The values ​​are shown below: (11); Record A relationship is fitted to the stress, and measured. S 0 segments ,get S Stress conditions in segment 0.

[0014] A system for ultrasonic measurement of residual stress in composite curved surface parts includes an air-coupled ultrasonic guided wave testing fixture module, a stress presetting and loading module, an ultrasonic signal excitation and acquisition module, and a signal data processing module. The air-coupled ultrasonic guided wave testing fixture module is mounted on a robotic arm and moved by the robotic arm to the testing position above the curved component. Based on the determined parameters, the height of the two sets of air-coupled ultrasonic transducers from the test piece, the incident angle, and the testing distance between the transmitting transducer and the receiving transducer are adjusted, and the two sets of air-coupled ultrasonic transducers are moved to the corresponding testing positions.

[0015] Preferably, the air-coupled ultrasonic guided wave testing fixture module specifically includes: a dovetail groove displacement slide rail, a transducer clamping assembly, and a robotic arm connector; The robotic arm connector is fixed to the robotic arm flange with screws; the dovetail groove displacement slide rail is connected and fixed to the robotic arm connector with bolts and nuts; the transducer clamping assembly can slide along the dovetail groove displacement slide rail, and the distance between the transmitting transducer and the receiving transducer can be adjusted according to the scale line of the slide rail. The transducer clamping assembly includes: an x-axis adjusting slide, an R-axis rotary platform, a z-axis adjusting slide, a connector, an air-coupled ultrasonic transducer, and a transducer clamping assembly; The R-axis rotating platform is fixed to the X-axis adjusting slide with screws and is used to adjust the incident and receiving angles of the air-coupled ultrasonic transducer; the Z-axis adjusting slide is fixed to the R-axis rotating platform with screws and is used to adjust the height distance between the air-coupled ultrasonic transducer and the detection component; the connector is connected to the Z-axis adjusting slide with screws; the transducer clamp is connected to the connector with bolts and nuts; the transducer clamp uses M4×70 long bolts and nuts to clamp air-coupled ultrasonic transducers of different frequencies.

[0016] Preferably, the stress presetting and loading module includes an electronic universal testing machine, a controller, and a main control computer, used to apply different known stresses to the composite planar component; and to set the stress holding time to facilitate the acquisition and storage of ultrasonic guided wave data; The ultrasonic signal excitation and acquisition module excites the composite curved surface component with ultrasonic signals according to the determined detection process parameters. The air-coupled ultrasonic guided wave detection fixture module moves the air-coupled ultrasonic transducer to the determined detection position and acquires the ultrasonic echo data multiple times. The guided wave data of the air-coupled ultrasonic transducer on the detected component under the same conditions is saved to reduce random errors. The signal data processing module completes the import and noise reduction of ultrasonic guided wave signal data, collects the acoustic time of different frequencies of air-coupled ultrasonic transducers under different stress states at a determined detection position, and calculates the acoustic time difference to achieve the fitting calibration of acoustic time difference-stress; it performs acoustic time difference detection on composite curved surface components with unknown stress under different frequencies of air-coupled ultrasonic transducers and inverts to obtain its internal stress.

[0017] Therefore, the present invention employs the above-mentioned ultrasonic measurement method and system for residual stress in composite curved surface parts, and the beneficial effects are as follows: (1) This invention can solve the technical bottlenecks such as the influence of changes in air segment distance and surface curvature on measurement accuracy. For composite curved surface components, traditional detection techniques have problems such as damaging the material structure and being easily affected by curvature in practical applications. The air-coupled ultrasonic guided wave method for acoustic time difference measurement and stress inversion eliminates the influence of air segment distance and surface curvature, and improves the stability of the detection results.

[0018] (2) During operation, the detection component does not come into contact with the composite material curved surface component, thus avoiding damage to the surface of the composite material, and is suitable for detection in engineering practice.

[0019] (3) The present invention is simple and quick to operate, and can meet the requirements of laboratory measurement and engineering actual testing applications, and can meet the residual stress testing requirements of composite curved surface components.

[0020] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Attached Figure Description

[0021] Figure 1 This is a flowchart of an ultrasonic measurement method for residual stress in curved composite material parts according to the present invention; Figure 2 This is a schematic diagram of the probe moving method of the present invention; Figure 3 The following are waveform diagrams of air-coupled ultrasonic transducers according to an embodiment of the present invention; wherein, (a) is a waveform diagram of a 100kHz air-coupled ultrasonic transducer; and (b) is a waveform diagram of a 200kHz air-coupled ultrasonic transducer. Figure 4 This is a schematic diagram of the air-coupled ultrasonic guided wave testing fixture module of the present invention; Figure 5 This is a diagram of the transducer clamping assembly of the present invention.

[0022] Figure Labels 1. Dovetail groove displacement slide rail; 2. Transducer clamping assembly; 3. Robotic arm flange; 4. Robotic arm connector; 21. X-axis adjusting slide; 22. R-axis rotary platform; 23. Z-axis adjusting slide; 24. Connector; 25. Air-coupled ultrasonic transducer; 26. Transducer clamping assembly. Detailed Implementation

[0023] The technical solution of the present invention will be further described below with reference to the accompanying drawings and embodiments.

[0024] like Figure 1 As shown, the present invention provides an ultrasonic measurement method for residual stress in curved composite material parts, comprising the following steps: Step S1: Determine the center frequencies of the two sets of air-coupled ultrasonic transducers based on the dispersion curve of the composite material guided wave. Step S2: Based on Snell's law and experimental data, determine the incident angles of two sets of air-coupled ultrasonic transducers with different center frequencies; Step S3: Based on the test data, and taking the standard that the guided wave signal does not overlap with the air direct wave in the time domain, determine the distance between the transmitting transducer and the receiving transducer with two different center frequencies, and the distance from the measured surface height. Step S4: Under different stress conditions, detect the acoustic time difference of two groups of air-coupled ultrasonic transducers with different center frequencies at different detection positions; Step S5: Apply prestress to the composite plate component using a tensile machine, measure the corresponding acoustic time using an air-coupled ultrasonic guided wave detection system to obtain the acoustic time difference, and establish and calibrate the correspondence between the acoustic time difference of the ultrasonic guided wave in the composite plate component and the applied stress. Step S6: Following the process in step S4, perform acoustic time difference detection on the target segment of the composite material curved surface component with unknown stress, and invert the residual stress of the target segment of the composite material component according to the relationship in step S5.

[0025] Example 1 This embodiment describes an air-coupled ultrasonic guided wave non-destructive testing method for curved carbon fiber composite components. The tested sample is a carbon fiber honeycomb sandwich curved structure. The upper and lower skins are M40J plain weave carbon fiber with a layup pattern of [(0 / 90) / (45 / -45)] and a thickness of 0.6 mm. The honeycomb sandwich is made of aluminum honeycomb with a thickness of approximately 15 mm. The maximum diameter of the curved surface is 850 mm. The transmitting transducer is a focusing transducer, and the receiving transducer is a planar transducer. This invention is an ultrasonic measurement method for residual stress in curved composite component parts, comprising the following steps: Step S1: Determine the appropriate center frequencies of the two sets of air-coupled ultrasonic transducers based on the dispersion curve of the composite material waveguide.

[0026] During the experiment, it should be ensured that the guided wave exists only in A0 and S0 modes. The dispersion curve of the guided wave is calculated using the anisotropic elastic matrix and density parameters of the composite material, yielding the cutoff frequency of the A1 mode. The center frequency of the selected air-coupled ultrasonic transducer should be lower than the frequency corresponding to the occurrence of the Lamb wave in the A1 mode. Simultaneously, to ensure that the guided wave does not alias with the direct air wave, the center frequency of the air-coupled ultrasonic transducer should also be higher than the frequency corresponding to the A0 mode under the airborne sound velocity.

[0027] Both 100kHz and 200kHz meet the requirements, and these two frequencies were selected as the center frequencies of the air-coupled ultrasonic transducers. The air-coupled ultrasonic transducers are used in pairs, in conjunction with dedicated ultrasonic pulse transmitting and receiving equipment.

[0028] Step S2: Based on Snell's law and experimental data, determine the incident angle that is applicable to both groups of air-coupled ultrasonic transducers with different center frequencies.

[0029] The phase velocity of mode A0 is obtained from the guided wave dispersion curve. Based on Snell's law and experimental data, the incident angle applicable to two sets of air-coupled ultrasonic transducers with different center frequencies is determined.

[0030] Among them, Snell's law formula: (1); in, The angle of refraction; Angle of incidence; The phase velocity of the composite medium; denoted as the phase velocity in the air medium.

[0031] The speed of sound propagation in air is 340 m / s. The phase velocities of 100 kHz and 200 kHz in the composite medium are 680 m / s and 800 m / s, respectively. The optimal incident angles are 30° and 25°, and the incident angle of the two sets of transducers is determined to be 29°.

[0032] Step S3: Based on the collected ultrasonic guided wave signal, and taking the standard that the guided wave signal does not cause time-domain aliasing with the air direct wave, determine the distance between the transmitting transducer and the receiving transducer, which are applicable to two sets of different center frequencies, and the height of the distance from the transducer to the surface under test. The detection distances are 240 mm and 244 mm, respectively, and the bottom of the transducer is about 30 mm away from the surface under test.

[0033] Step S4: At a position where the fiber direction is parallel to the line connecting the transducers, detect the acoustic time difference of two sets of air-coupled ultrasonic transducers with different center frequencies at different detection positions.

[0034] Step S41: Move the first group of center frequencies to... f The transmitting and receiving transducers of unit 1 are positioned at the initial detection location, with a detection distance of 240mm between them. The center frequency of the first group is fixed at [value missing]. f The transmitting transducer 1 collects ultrasonic signals and records the initial detection position. The frequency of the guided wave reaching the center of the first group is... f 1 receiving transducer time Maintain the center frequency of the first group as f The transmitting transducer of unit 1 remains unchanged, and the center frequency of the first group is moved to . f The receiving transducer of device 1 is moved to the second detection position. At this time, the detection distance between the two transducers is 244mm. Ultrasonic signals are acquired, and the frequency of the guided wave reaching the center of the first group at the second detection position is recorded. f 1 receiving transducer time ; Step S42: Move the second group of center frequencies to... f The transmitting and receiving transducers of unit 2 are connected to the center frequency of the first group. f The transmitting and receiving transducers of unit 1 are in the same initial detection position, with a detection distance of 240mm between them. The center frequency of the second group is fixed at [value missing]. f The transmitting transducer of unit 2 collects ultrasonic signals and records the initial detection position. The frequency at which the guided wave reaches the center of the second group is... f 2. Time of receiving transducer Maintain the center frequency of the second group as f The transmitting transducer of group 2 remains unchanged, and the center frequency of the second group is moved to . f The receiving transducer of 2 is connected to the center frequency of the first group. f At the second detection position, where the transmitting and receiving transducers are identical, the detection distance between the two transducers is 244 mm. Ultrasonic signals are acquired, and the frequency of the guided wave reaching the second group's center at the second detection position is recorded. f 2. Time of receiving transducer .

[0035] Step S43, as Figure 2 As shown, the propagation distance of the transmitted waveguide from the transmitting transducer to the layer plate is denoted as the air section distance of the transmitting transducer. The propagation distances of the guided wave at the two detection positions in the composite skin layer are respectively and The propagation distances of the receiving transducer's receiving guided waves to the corresponding two detection positions between the transducer and the shelf are denoted as the air segments of the receiving transducer. and Guided waves of different frequencies propagate at the same speed in air, denoted as ; The propagation velocities of guided waves of different frequencies in the composite skin layer are respectively and ; Based on the parameter settings, the derivation is as follows: (2); (3); (4); (5); Subtracting formulas (4) from (2) and (5) from (3), we get: (6); (7); Let formulas (7) and (6) be used to obtain the sound time difference. As shown below: (8); make Then formula (8) can be simplified to: (9); Further results were obtained: (10).

[0036] Step S5: Apply prestress to the composite plate component using a tensile machine, and measure the corresponding acoustic time using an air-coupled ultrasonic guided wave detection system to obtain the acoustic time difference. Establish and calibrate the correspondence between the acoustic time difference of the ultrasonic guided wave in the composite plate component and the applied stress.

[0037] Step S51: Acquire the corresponding waveform signals using an air-coupled ultrasonic guided wave detection system, such as... Figure 3 As shown, noise reduction processing is performed on the signal, and the acoustic time corresponding to the guided wave segment of the waveform signal is selected, recorded, and saved. Following step S4, acoustic times at different locations of the air-coupled ultrasonic transducer at different frequencies are acquired and saved to obtain the acoustic time difference. .

[0038] Step S52: Apply different known stresses to the composite plate specimen on a tensile machine. Changes in stress conditions will affect the propagation speed of ultrasonic guided waves in the composite skin, and thus affect... The values ​​are shown below: (11); Record Fitting a relationship with stress By measuring S 0 segments ,get SStress conditions in segment 0.

[0039] Step S6: Following the process in step S4, target the composite material curved surface component with unknown stress. S Segment 0 performs acoustic time difference detection, and based on the relationship in step S5, the target composite material component is inverted. S Residual stress in segment 0.

[0040] Example 2 The present invention also provides an ultrasonic measurement system for residual stress of composite curved surface parts, for implementing the above-described method. The system includes: an air-coupled ultrasonic guided wave testing fixture module, a stress presetting and loading module, an ultrasonic signal excitation and acquisition module, and a signal data processing module.

[0041] The air-coupled ultrasonic guided wave testing fixture module is mounted on a robotic arm and moved by the robotic arm to the testing position above the curved component. Based on the determined parameters, the height of the two sets of air-coupled ultrasonic transducers from the test piece, the incident angle, and the testing distance between the transmitting transducer and the receiving transducer are adjusted, and the two sets of air-coupled ultrasonic transducers are moved to the corresponding testing positions.

[0042] like Figure 4 As shown, the air-coupled ultrasonic guided wave testing fixture module specifically includes: a dovetail groove displacement slide rail 1, a transducer clamping assembly 2, and a robotic arm connector 4. The robotic arm connector 4 is fixed to the robotic arm flange 3 with screws; the dovetail groove displacement slide rail 1 is connected and fixed to the robotic arm connector 4 with bolts and nuts; the transducer clamping assembly 2 can slide along the dovetail groove displacement slide rail 1, and the distance between the transmitting transducer and the receiving transducer can be adjusted according to the scale lines of the slide rail.

[0043] like Figure 5 As shown, the transducer clamping assembly 2 includes: an x-axis adjusting slide 21, an R-axis rotating platform 22, a z-axis adjusting slide 23, a connector 24, an air-coupled ultrasonic transducer 25, and a transducer clamping component 26. The R-axis rotating platform 22 is fixed to the x-axis adjusting slide 21 by screws and is used to adjust the incident and receiving angles of the air-coupled ultrasonic transducer; the z-axis adjusting slide 23 is fixed to the R-axis rotating platform 22 by screws and is used to adjust the height distance between the air-coupled ultrasonic transducer and the detection component; the connector 24 is connected to the z-axis adjusting slide 23 by screws; the transducer clamping component 26 is connected to the connector 24 by bolts and nuts; the transducer clamping component 26 clamps the air-coupled ultrasonic transducer 25 with M4x70 long bolts and nuts, and can clamp air-coupled ultrasonic transducers of different frequencies.

[0044] For the air-coupled ultrasonic guided wave testing fixture module, operators can replace the manually adjustable components with electric or hydraulic control components to improve the accuracy of movement or rotation and reduce the impact of manual operation on the test results.

[0045] The stress presetting and loading module, including an electronic universal testing machine, a controller, and a main control computer, is used to apply different known stresses to planar composite material components; it also allows setting the stress holding time to facilitate the acquisition and storage of ultrasonic guided wave data.

[0046] The ultrasonic signal excitation and acquisition module excites the composite curved surface component with ultrasonic signals according to the determined detection process parameters. The air-coupled ultrasonic guided wave detection fixture module moves the air-coupled ultrasonic transducer to the determined detection position and acquires the ultrasonic echo data multiple times. The guided wave data of the air-coupled ultrasonic transducer on the detected component under the same conditions is saved to reduce random errors.

[0047] The signal data processing module completes the import and noise reduction of ultrasonic guided wave signal data, collects the acoustic time of different frequencies of air-coupled ultrasonic transducers under different stress states at a determined detection position, and calculates the acoustic time difference to achieve the fitting calibration of acoustic time difference-stress; it performs acoustic time difference detection on composite curved surface components with unknown stress under different frequencies of air-coupled ultrasonic transducers and inverts to obtain its internal stress.

[0048] Based on the measured residual stress at the target detection location, and combined with the finite element simulation model of the curved ultrasonic guided wave, the residual stress of the entire composite curved surface component is obtained.

[0049] Therefore, the present invention employs the aforementioned ultrasonic measurement method and system for residual stress in curved composite material components, which overcomes technical bottlenecks such as the impact of changes in air segment distance and surface curvature on measurement accuracy. Based on the air-coupled ultrasonic guided wave method for acoustic time difference measurement and stress inversion, the influence of air segment distance and surface curvature is eliminated, improving the stability of the detection results. During operation, the detection component does not come into contact with the curved composite material component, avoiding damage to the composite material surface, making it suitable for practical engineering applications.

[0050] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the technical solutions of the present invention, and these modifications or equivalent substitutions cannot cause the modified technical solutions to deviate from the spirit and scope of the technical solutions of the present invention.

Claims

1. An ultrasonic measurement method for residual stress in curved composite material parts, characterized in that, Includes the following steps: Step S1: Determine the center frequencies of the two sets of air-coupled ultrasonic transducers based on the dispersion curve of the composite material guided wave. Step S2: Based on Snell's law and experimental data, determine the incident angles of two sets of air-coupled ultrasonic transducers with different center frequencies; Step S3: Based on the test data, and taking the standard that the guided wave signal does not overlap with the air direct wave in the time domain, determine the distance between the transmitting transducer and the receiving transducer with two different center frequencies, and the distance from the measured surface height. Step S4: Measure the acoustic time difference of two groups of air-coupled ultrasonic transducers with different center frequencies at different detection positions; Step S5: Apply prestress to the composite plate component using a tensile machine, measure the corresponding acoustic time using an air-coupled ultrasonic guided wave detection system to obtain the acoustic time difference, and establish and calibrate the correspondence between the acoustic time difference of the ultrasonic guided wave in the composite plate component and the applied stress. Step S6: Following the process in step S4, perform acoustic time difference detection on the target segment of the composite material curved surface component with unknown stress, and invert the residual stress of the target segment of the composite material component according to the relationship in step S5.

2. The ultrasonic measurement method for residual stress in composite curved surface parts according to claim 1, characterized in that, In step S1, the guided wave dispersion curve is calculated using the anisotropic elastic matrix and density parameters of the composite material to obtain the A1 mode cutoff frequency and determine the appropriate center frequencies of the two sets of air-coupled ultrasonic transducers. Among them, air-coupled ultrasonic transducers appear in pairs, in conjunction with dedicated ultrasonic pulse transmitting and receiving equipment.

3. The ultrasonic measurement method for residual stress in composite curved surface parts according to claim 2, characterized in that, In step S2, the phase velocity of mode A0 is obtained from the waveguide dispersion curve. Based on Snell's law and the detection experimental data, the incident angle applicable to both groups of air-coupled ultrasonic transducers with different center frequencies is determined. Among them, Snell's law formula: （1）； in, The angle of refraction; Angle of incidence; The phase velocity of the composite medium; denoted as the phase velocity in the air medium.

4. The ultrasonic measurement method for residual stress in composite curved surface parts according to claim 3, characterized in that, In step S3, based on the test data, and taking the time-domain aliasing of the guided wave signal with the direct air wave as the standard, the distance between the transmitting transducer and the receiving transducer, which are applicable to two sets of different center frequencies, and the height of the distance from the measured surface are determined.

5. The ultrasonic measurement method for residual stress in composite curved surface parts according to claim 4, characterized in that, In step S4, the acoustic time difference of two sets of air-coupled ultrasonic transducers with different center frequencies at different detection positions is measured. The specific process is as follows: Step S41: Move the first group of center frequencies to... f The transmitting and receiving transducers of unit 1 are positioned at the initial detection location, and the center frequency of the first group is fixed at [value missing]. f The transmitting transducer 1 collects ultrasonic signals and records the initial detection position. The frequency of the guided wave reaching the center of the first group is... f 1 receiving transducer time Maintain the center frequency of the first group as f The transmitting transducer of unit 1 remains unchanged, and the center frequency of the first group is moved to . f The receiving transducer of device 1 is moved to the second detection position to acquire ultrasonic signals, and the frequency of the guided wave at the second detection position reaching the center of the first group is recorded. f 1 receiving transducer time ; Step S42: Move the second group's center frequency to... f The transmitting and receiving transducers of unit 2 are connected to the center frequency of the first group. f The transmitting and receiving transducers of unit 1 have the same initial detection positions, and the center frequency of the second group is fixed at 1. f The transmitting transducer of unit 2 collects ultrasonic signals and records the initial detection position. The frequency at which the guided wave reaches the center of the second group is... f 2. Time of receiving transducer Maintain the center frequency of the second group as f The transmitting transducer of group 2 remains unchanged, and the center frequency of the second group is moved to . f The receiving transducer of 2 is connected to the center frequency of the first group. f At the second detection position, where the transmitting and receiving transducers are identical, ultrasonic signals are acquired, and the frequency of the guided wave reaching the center of the second group at the second detection position is recorded. f 2. Time of receiving transducer .

6. The ultrasonic measurement method for residual stress in curved composite material parts according to claim 5, characterized in that, The propagation distance of the transmitted waveguide from the transmitting transducer to the shelf is denoted as the air section distance of the transmitting transducer. The propagation distances of the guided wave at the two detection positions in the composite skin layer are respectively and The propagation distances of the receiving transducer's receiving guided waves to the corresponding two detection positions between the transducer and the shelf are denoted as the air segments of the receiving transducer. and Guided waves of different frequencies propagate at the same speed in air, denoted as ; The propagation velocities of guided waves of different frequencies in the composite skin layer are respectively and ; Based on the parameter settings, the derivation is as follows: （2）； （3）； （4）； （5）； Subtracting formulas (4) from (2) and (5) from (3), we get: （6）； （7）； Let formulas (7) and (6) be used to obtain the sound time difference. As shown below: （8）； make Then formula (8) simplifies to: （9）； Further results were obtained: （10）。 7. The ultrasonic measurement method for residual stress in curved composite material parts according to claim 6, characterized in that, In step S5, a prestress is applied to the composite material plate component using a tensile machine, and the corresponding acoustic time is measured using an air-coupled ultrasonic guided wave detection system to obtain the acoustic time difference. The correspondence between the acoustic time difference of the ultrasonic guided wave in the composite material plate component and the applied stress is then established and calibrated. The specific process is as follows: Step S51: Acquire the corresponding waveform signal using the air-coupled ultrasonic guided wave detection system, perform noise reduction processing on the signal, select the acoustic time corresponding to the guided wave segment of the waveform signal and record and save it; according to step S4, acquire and save the acoustic time at different positions of the air-coupled ultrasonic transducer at different frequencies to obtain the acoustic time difference. ; Step S52: Apply different known stresses to the composite plate specimen on a tensile machine. Changes in stress conditions will affect the propagation speed of ultrasonic guided waves in the composite skin, and thus affect... The values ​​are shown below: （11）； Record Fitting a relationship with stress By measuring S 0 segments ,get S Stress conditions in segment 0.

8. A system for ultrasonic measurement of residual stress in composite curved surface parts according to any one of claims 1-7, characterized in that, It includes an air-coupled ultrasonic guided wave testing fixture module, a stress preset and loading module, an ultrasonic signal excitation and acquisition module, and a signal data processing module; The air-coupled ultrasonic guided wave testing fixture module is mounted on a robotic arm and moved by the robotic arm to the testing position above the curved component. Based on the determined parameters, the height of the two sets of air-coupled ultrasonic transducers from the test piece, the incident angle, and the testing distance between the transmitting transducer and the receiving transducer are adjusted, and the two sets of air-coupled ultrasonic transducers are moved to the corresponding testing positions.

9. The system for ultrasonic measurement of residual stress in composite curved surface parts according to claim 8, characterized in that, The air-coupled ultrasonic guided wave testing fixture module specifically includes: a dovetail groove displacement slide rail, a transducer clamping assembly, and a robotic arm connector; The robotic arm connector is fixed to the robotic arm flange with screws; the dovetail groove displacement slide rail is connected and fixed to the robotic arm connector with bolts and nuts; the transducer clamping assembly can slide along the dovetail groove displacement slide rail, and the distance between the transmitting transducer and the receiving transducer can be adjusted according to the scale line of the slide rail. The transducer clamping assembly includes: an x-axis adjusting slide, an R-axis rotary platform, a z-axis adjusting slide, a connector, an air-coupled ultrasonic transducer, and a transducer clamping assembly; The R-axis rotating platform is fixed to the X-axis adjusting slide with screws and is used to adjust the incident and receiving angles of the air-coupled ultrasonic transducer; the Z-axis adjusting slide is fixed to the R-axis rotating platform with screws and is used to adjust the height distance between the air-coupled ultrasonic transducer and the detection component; the connector is connected to the Z-axis adjusting slide with screws; the transducer clamp is connected to the connector with bolts and nuts; the transducer clamp uses M4×70 long bolts and nuts to clamp air-coupled ultrasonic transducers of different frequencies.

10. The system for ultrasonic measurement of residual stress in composite curved surface parts according to claim 9, characterized in that, The stress presetting and loading module, including an electronic universal testing machine, a controller, and a main control computer, is used to apply different known stresses to planar composite material components; it also allows setting the stress holding time to facilitate the acquisition and storage of ultrasonic guided wave data. The ultrasonic signal excitation and acquisition module excites the composite curved surface component with ultrasonic signals according to the determined detection process parameters. The air-coupled ultrasonic guided wave detection fixture module moves the air-coupled ultrasonic transducer to the determined detection position and acquires the ultrasonic echo data multiple times. The guided wave data of the air-coupled ultrasonic transducer on the detected component under the same conditions is saved to reduce random errors. The signal data processing module completes the import and noise reduction of ultrasonic guided wave signal data, collects the acoustic time of air-coupled ultrasonic transducers at different frequencies under different stress states at a determined detection position, calculates the acoustic time difference, and realizes the fitting calibration of acoustic time difference-stress. The internal stress of a composite curved surface component with unknown stress was obtained by inverting the acoustic time difference under different frequency air-coupled ultrasonic transducers.

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