Ultrasonic phased array synthetic aperture focusing imaging method for delamination damage in CFRP composites

Abstract

The application discloses an ultrasonic phased array synthetic aperture focusing imaging method for CFRP composite material delamination damage, and aims at the problem that ultrasonic waves are complicated in the internal propagation of composite materials. The method comprises the following steps: moving an ultrasonic transducer in a one-dimensional direction transversely to collect a plurality of groups of synthetic aperture imaging amplitudes, wherein the imaging area corresponding to each aperture is a region with a predetermined width directly below the aperture; and superimposing the plurality of groups of synthetic aperture imaging amplitudes to obtain a CFRP laminate internal delamination damage imaging graph. Compared with a traditional synthetic aperture focusing imaging method, the imaging precision is improved.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of ultrasonic nondestructive testing, and particularly relates to an ultrasonic phased array synthetic aperture focusing imaging method for delamination damage of a composite material. BACKGROUND

[0002] Carbon fiber reinforced plastics (CFRP) are widely used in the fields of aerospace, automobile and construction due to their excellent properties such as light weight and high strength. CFRP laminates are prone to damage due to complex manufacturing processes. The inconsistency of the fiber orientation of each ply of the CFRP laminates can lead to significant differences in strength and stiffness in the thickness direction, making delamination damage one of the most common damages in CFRP laminates. During production and service, delamination damage will continue to expand due to stress, greatly reducing the strength and reliability of the structure. Ultrasonic testing technology is widely used in the nondestructive testing of CFRP laminates due to its high resolution and real-time imaging characteristics.

[0003] Conventional single-probe ultrasonic nondestructive testing has low detection accuracy and small coverage range. Ultrasonic phased array, as an advanced nondestructive testing technology, has been widely researched and applied in many fields at home and abroad. It realizes imaging and positioning of internal defects in materials through an array probe that can emit and receive ultrasonic signals. In the field of CFRP laminate damage detection, ultrasonic phased array technology has important application value. The accuracy of damage detection using full focusing imaging method and synthetic aperture focusing imaging method is related to the accurate calculation of ultrasonic ray path. Lin et al. used Dijkstra algorithm to invert the sound propagation path in CFRP material laminated flat plate and realized full focusing imaging of damage. However, due to the complex multilayer structure and anisotropic characteristics of CFRP laminates, especially for oblique incidence of ultrasonic waves, it is difficult to accurately predict the sound propagation path, resulting in high complexity of sound time calculation when applying full focusing method to CFRP laminates with complex shape structure. Moreover, due to the physical limitations of the size of the transducer, it is difficult to improve the lateral resolution of the imaging quality, and it is difficult to accurately image defects with small size and dense arrangement. SUMMARY

[0004] The purpose of the present application is to overcome the shortcomings of the prior art and provide a method for high-precision imaging of internal delamination damage of CFRP composite materials.

[0005] This invention provides an ultrasonic phased array synthetic aperture focusing imaging method for delamination damage in CFRP composite materials, comprising the steps of: providing the CFRP composite material with a thickness of D; the ultrasonic phased array being disposed on the surface of the CFRP composite material, including a plurality of transducers linearly arranged in a transverse direction along the surface of the CFRP composite material, the center-to-center distance between adjacent transducers being d, such that the width and depth directions of the CFRP composite material define the region to be detected; determining the number of transducers required to be excited for each aperture in the synthetic aperture, the focusing depth of the synthetic aperture being the plate thickness D; moving the ultrasonic phased array on the surface of the composite material along the transverse direction from a starting position to a termination position by a preset displacement; and performing the following steps at the starting position, the termination position, and a plurality of intermediate positions between the starting position and the termination position to obtain ultrasonic signals at each position. Where j represents the number of times the phased array moves: a set of transducers is determined as the transducers in the aperture; according to the calculated delay Simultaneously, the transducers in this group are excited to generate ultrasonic signals; the signals received by the transducers in this group are collected, among which the first... The signal received by the nth transducer in each aperture is The signals received by each transducer are delayed and superimposed; a Hilbert transform is then performed to obtain the ultrasonic signal received by that aperture. In the formula, h represents the Hilbert transform; and switching to another set of transducers to switch to another aperture, and repeating steps S31 to S34 until the ultrasonic signals of all apertures of the ultrasonic phased array at that position are obtained; the acquired ultrasonic signals at each position Synthetic aperture focusing imaging is performed, and the imaging results are superimposed to obtain a damage imaging map.

[0006] In some embodiments, the acquired ultrasonic signals at each location are subjected to synthetic aperture focusing imaging, including discretizing the area to be measured, dividing it into grids with the layup interface as the lateral boundary, numbered k from top to bottom (k=1, 2, …, K), and with the thickness direction as the longitudinal boundary, numbered l from left to right (l=1, 2, …, L), and all imaging points within the imaging area. amplitude The expression is: In the formula, Let i be the centroid position of the i-th aperture in the j-th iteration. The round-trip sound propagation time is the distance from the center of the i-th aperture in the j-th iteration to the imaging point in the region with width x and height D directly below the aperture; and the synthetic aperture focusing imaging is performed based on the amplitude of the imaging point.

[0007] In some embodiments, the transducers in the synthetic aperture are switched sequentially.

[0008] In some embodiments, the step distance of the synthetic aperture is 1.

[0009] In some embodiments, the CFRP composite material is a quasi-isotropic CFRP laminate with 45° / 90° / -45° / 0° arrangement.

[0010] In some embodiments, the directivity patterns of different aperture numbers are drawn according to the directivity function of the phased linear array, and the number of excitation transducer chips included in the synthetic aperture is determined according to the directivity concentration effect and the delay deviation.

[0011] In some embodiments, the directivity function of the phased linear array is , wherein N is the number of excitation transducer chips required for the synthetic aperture, θ is the angle between the sound propagation direction and the z-axis, is the wavelength, c is the group velocity of the quasi-longitudinal wave in the vertical direction of the CFRP laminate, f is the center frequency of the transducer, and .

[0012] In some embodiments, the delay is calculated according to the propagation of the ultrasonic signal at a constant sound speed c , wherein, is the distance from the center of the nth transducer in each aperture to the center of the aperture.

[0013] In some embodiments, the distance x of movement is determined according to the spacing d between the centers of two adjacent transducers in the ultrasonic probe; x = d / J.

[0014] In some embodiments, the method further comprises the step of quantitatively characterizing the size of the damage using the descending method to evaluate the imaging quality of the damage.

[0015] Overall, the method proposed in the present application can accurately image multiple densely arranged delamination damages inside the CFRP laminate, and compared with the traditional synthetic aperture imaging technology, the imaging accuracy is improved. Specifically, compared with the existing technology, the present application has at least the following beneficial effects:

[0016] Firstly, some embodiments of the present application select a certain width of the area directly below the synthetic aperture as the imaging area corresponding to the aperture, fully utilize the feature that the sound speed of the CFRP laminate is consistent in the vertical direction, avoid using oblique incidence of ultrasonic waves, and simplify the imaging algorithm.

[0017] Secondly, some embodiments of the present application overcome the physical limitation of the size of the transducer itself, move the ultrasonic transducer transversely along the direction of the transducer arrangement, improve the imaging quality, and can accurately identify small-sized and close-together layered damage defects in the transverse direction. BRIEF DESCRIPTION OF DRAWINGS

[0018] Figure 1 A flowchart of the ultrasonic phased array synthetic aperture focusing imaging method for the layered damage of the CFRP composite material of an embodiment of the present application;

[0019] Figure 2 A schematic diagram of the model established by the present application;

[0020] Figure 3 A linear array acoustic beam pointing diagram of the synthetic aperture of different excitation transducer wafer quantities;

[0021] Figure 4 A delay comparison diagram of the synthetic aperture of the excitation transducer wafer quantity of 5 calculated based on the isotropic and anisotropic CFRP acoustic models;

[0022] Figure 5 A schematic diagram of the ultrasonic transducer array excitation mode of the present application;

[0023] Figure 6 A time-domain signal diagram received by the 9th synthetic aperture in the first position;

[0024] Figure 7 A result diagram of the synthetic aperture focusing imaging obtained by the method according to the embodiment of the present application;

[0025] Figure 8a A result diagram of the imaging in which the imaging region is the entire detection region;

[0026] Figure 8b A result diagram of the imaging in which the imaging region is the aperture width directly below the aperture;

[0027] Figure 8c A result diagram of the imaging in which the imaging region is the region of the single transducer width directly below the aperture;

[0028] Figure 8d A result diagram of the imaging in which the imaging region is the 0.1mm width superposition directly below the aperture according to the embodiment of the present application;

[0029] Figure 9 A defect transverse direction amplitude curve obtained by using different imaging regions;

[0030] Figure 10 A schematic diagram of the specific process of the ultrasonic signal step of the imaging method according to the embodiment of the present application;

[0031] Figure 11 The specific process diagram of the step of synthesizing aperture focusing imaging of the collected multiple groups of signals according to the imaging method of the embodiment of the application. DETAILED DESCRIPTION

[0032] The technical solutions of the application are further described below with reference to the drawings.

[0033] In general, the application proposes an ultrasonic phased array synthetic aperture focusing imaging method for CFRP composite material delamination damage. In order to make the purpose, technical solutions and effects of the application more clear and explicit, the application is further described in detail below. It should be understood that the specific embodiments described herein are only used to explain the application and do not limit the application.

[0034] The specific structure and functional details disclosed herein are only representative and are for the purpose of describing the exemplary embodiments of the application. However, the application can be embodied in many alternative forms, and should not be interpreted as being limited only to the embodiments set forth herein.

[0035] It should be understood that although the terms "first", "second", etc. may be used herein to describe various elements, these elements should not be limited by these terms. These terms are only used to distinguish one element from another. For example, without departing from the scope of the exemplary embodiments, a first element can be called a second element, and similarly a second element can be called a first element. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0036] The terms used herein are only for the purpose of describing specific embodiments and are not intended to limit the exemplary embodiments. Unless the context clearly indicates otherwise, the singular form "a", "an", and "the" as used herein is also intended to include the plural. It should also be understood that the terms "comprise" and / or "include" specify the presence of stated features, integers, steps, operations, units and / or components, without excluding the presence or addition of one or more other features, integers, steps, operations, units, components and / or combinations thereof.

[0037] It should also be noted that in some alternative implementations, the mentioned functions / actions can occur in an order different from that indicated in the figures. For example, depending on the functions / actions involved, two figures shown successively can actually be performed substantially simultaneously or sometimes in reverse order.

[0038] The ultrasonic phased array synthetic aperture focusing imaging method for CFRP composite material delamination damage proposed by the application comprises the following steps:

[0039] Step S0, provide a 45° / 90° / -45° / 0° quasi-isotropic CFRP laminate with thickness D, use a phased array of transducer linear array for nondestructive testing, the center-to-center distance between adjacent transducers is d; the imaging method is synthetic aperture focusing imaging;

[0040] Step S1, determine the number of synthetic apertures, for example, according to the directivity function of the phased linear array shown in equation (1) Draw the directivity diagram of the synthetic aperture with different numbers of excitation transducer wafers, in equation (1), N is the number of excitation transducer wafers required for the synthetic aperture, θ is the angle between the sound propagation direction and the z-axis, is the wavelength, c is the vertical group velocity of the quasi-longitudinal wave in the CFRP laminate, and f is the center frequency of the transducer wafer.

[0041]

[0042] (2)

[0043] Select the number of synthetic apertures with good directivity concentration and small delay deviation, and the focusing depth of the synthetic aperture is the thickness D of the plate.

[0044] In order to make the synthetic aperture focus better, it is necessary to apply a delay to the transducer wafers in the aperture, according to the calculation formula (3) of the delay in an isotropic propagation medium :

[0045] Among them, is the distance from the center of the nth transducer wafer in each aperture to the center of the aperture;

[0046] Step S2, move the ultrasonic probe along a one-dimensional transverse direction several times, each time moving a distance x.

[0047] Step S3, each time moving to a new position, then exciting signals in turn with the same number of synthetic apertures and delays, and collecting the signals obtained after each aperture is excited. Repeat this step J times, and the signal of the nth transducer wafer in the ith aperture in the jth time is , and the signal obtained after each aperture is excited is obtained by delay stacking .

[0048] Excite ultrasonic signals for all transducer wafers in each aperture according to the calculated delay , and collect the signal received by the nth transducer wafer in the ith aperture .

[0049] ​​The signals received by the transducer wafers are delay-stacked, and then Hilbert transformed to obtain the ultrasonic signal received by the aperture according to formula (4) , wherein h represents the Hilbert transform.

[0050]

[0051] It is worth noting that the distance x of movement needs to be determined according to the center distance d between two adjacent transducer wafers in the ultrasonic probe, for example, to improve the imaging accuracy and realize full coverage of the imaging area by the aperture center.

[0052] Step S4: The acquired multiple groups of signals are subjected to synthetic aperture focusing imaging. The imaging area in the plane xoz with a width of X and a height of Z is discretized, and the grid is divided with the bedding interface as the transverse boundary, the serial number being k (k=1, 2, …, K, from top to bottom), and the thickness direction as the longitudinal boundary, the serial number being l (l=1, 2, …, L, from left to right), and all imaging points in the imaging area ) amplitude The expression is shown in formula (5):

[0053]

[0054] In the formula, is the centroid position of the i aperture in the j time, is the round-trip sound propagation time from the center of the i aperture in the j time to the imaging point in the detection area with a width of x and a height of the plate thickness D directly below the aperture.

[0055] Step S5, in order to quantitatively characterize the size of the damage, the descent method is used as shown in formula (6):

[0056]

[0057] The synthetic aperture focusing imaging in step S4 can specifically include the following steps:

[0058] Step S41: The imaging area of the CFRP laminate is discretized;

[0059] Step S42: The distances from all aperture centers to each point in the imaging area are calculated, and then the round-trip propagation time of all aperture centers to the imaging point with a width of x directly below the aperture is calculated according to the speed c of the ultrasonic wave vertically incident in the CFRP laminate.

[0060] Step S43, the acquired synthetic aperture signal is delay-stacked according to the delay of each transducer wafer in the aperture as the signal received at the center of the aperture , the signal is subjected to Hilbert transform;

[0061] Step S44, the imaging points in the detection area with a width of x and a height of the plate thickness D directly below each aperture are selected, and the imaging amplitude of the imaging point is obtained by interpolating the synthetic aperture signal according to the calculated acoustic propagation time ;

[0062] Step S45, the imaging amplitudes of the imaging points of the start position and the end position and each of the plurality of intermediate positions are sequentially calculated; and

[0063] Step S46, the obtained imaging amplitudes are superimposed to obtain the ultrasonic imaging image of the delamination damage of the CFRP laminate plate.

[0064] Embodiment 1:

[0065] The present example provides an ultrasonic phased array synthetic aperture focusing imaging method, which is simulated by the solid mechanics module of COMSOL Multiphysics 5.6 finite element simulation software (COMSOL Group, Stockholm, Sweden).

[0066] The specific steps of the synthetic aperture focusing imaging based on COMSOL finite element simulation are as follows:

[0067] Modeling of ultrasonic phased array detection of the CFRP laminate plate 10;

[0068] Since the ultrasonic phased array 20 used in the present application is a one-dimensional phased array arranged along the X direction, i.e., all transducer wafers are linearly arranged at equal intervals, at this time it can be approximately considered that the ultrasonic wave only interacts with the region of the member located in the ultrasonic probe detection plane; and the CFRP single-layer plate has transverse isotropy, so a two-dimensional plane strain model can accurately simulate the spatial distribution of the ultrasonic wave in the CFRP laminate plate. The solid mechanics field in COMSOL Multiphysics 5.6 is used for transient study, such as Figure 2As shown, first, a two-dimensional model in the thickness direction of the CFRP laminate is established in the geometric module, the model width is 16 mm, the thickness of the CFRP single-layer plate is 0.2 mm, a total of 32 layers, and the total thickness is 6.4 mm, 32 transducer chips with a width of 0.25 mm are arranged on the upper surface of the CFRP laminate 10 model in a one-dimensional equidistant linear arrangement, and the spacing between adjacent transducer chips is 0.05 mm. The material of each layer is assigned in the laying sequence of [45°, 90°, -45°, 0°]4[0°, -45°, 90°, 45°]4. Three delamination damage defects with a height of 0.2 mm and a width of 2 mm are arranged equidistantly in the composite plate.

[0069] The number of synthetic apertures is determined. Figure 3 The directivity pattern of the one-dimensional phased array when the number of excited transducer chips required for the synthetic aperture is 2, 3, 4, 5, 6, 7, 8 is shown in FIG. 5. Figure 3 As can be seen, when the number of excited transducer chips is 2, 3, and 4, the main lobe width of the acoustic beam is relatively large, and when the number of excited transducer chips is greater than or equal to 5, the main lobe width of the acoustic beam is relatively small, indicating that it has good spatial resolution. And with the increase of the number of excited transducer chips, the main lobe width decreases, and the amplitude of the acoustic energy decreases. With the increase of the number of excited transducer chips, the sound ray deflection angle increases, and due to the anisotropy of the material, the larger the deflection angle, the easier it is to produce deflection error, so the number of excited transducer chips required for the synthetic aperture used in the present application is 5, and the focusing depth of the synthetic aperture is 6.4 mm.

[0070] The CFRP laminate is an anisotropic material and has a multi-layer structure. The delay of each transducer chip in the aperture propagating in the CFRP laminate is calculated based on the spatial distribution of the quasi-longitudinal wave group velocity of the anisotropic CFRP acoustic model . The comparison between the delay calculated based on the constant sound speed and the delay calculated based on the anisotropic CFRP acoustic model is shown in FIG. 6. Figure 4 Since the size of the transducer chip used in the present application is small, when the number of apertures is 5, and are almost the same. Therefore, each aperture can excite the transducer chip to generate a piezoelectric signal according to the delay calculated based on the constant sound speed acoustic model .

[0071] The synthetic aperture data is collected.

[0072] As shown in FIG. 7, the synthetic aperture data is collected by exciting the transducer chip according to the delay calculated based on the constant sound speed acoustic model Figure 5As shown, the number of the selected excitation apertures is 5, the first, second, third, fourth and fifth transducer chips of the ultrasonic probe are simultaneously excited as the first aperture excitation signal of the starting position, the displacement amplitude signals of the center positions of each transducer in the aperture are output, the displacement amplitude signals of the center positions of the five transducer chips are superimposed according to the calculated delay as the displacement amplitude signal received by the first aperture of the starting position, which is shown as Figure 6 which includes the defect echo component and the composite component of the bottom echo and the defect echo.

[0073] Then, the second, third, fourth, fifth and sixth transducer chips are simultaneously excited as the second aperture excitation signal of the starting position, and the displacement amplitude signal received by the second aperture of the starting position is obtained according to the obtaining step of the displacement amplitude signal received by the first aperture. By analogy, until the last transducer chip of the starting position is excited, and the last received displacement amplitude signal of the starting position is obtained. Thus, the synthetic aperture data of the starting position is obtained. As shown in Table 1.

[0074] Table 1 Relationship between transducer chip and synthetic aperture:

[0075] Simultaneous excitation transducer wafer number Aperture number Aperture data for first position 1, 2, 3, 4, 5 1 A 1.1 (t) 2, 3, 4, 5, 6 2 A 2.1 (t) 6, 7, 8, 9, 10 3 A 31 (t)] … … … 28, 29, 20, 31, 32 28 A 28.1 (t)]

[0076] The starting position can be set according to the detection needs. Generally, the ultrasonic probe is located at the position of the first transverse boundary of the detected region, for example, the ultrasonic probe is located at the leftmost position in the x direction. Figure 2

[0077] Thus, the ultrasonic probe is moved 0.1 mm in the one-dimensional direction to the second position, the above steps are repeated to obtain the synthetic aperture data of the second position, the ultrasonic probe is moved 0.1 mm in the one-dimensional direction to obtain the synthetic aperture data of the third position, and the ultrasonic probe is moved J times until it moves to the terminal position, i.e. the Jth position, which is away from the first transverse boundary to the second transverse boundary (for example, the rightmost position) of the detected region. The number of movements J, i.e. the number of positions of the synthetic aperture data to be collected, can be determined according to the distance moved each time by the ultrasonic probe and the size of the transducer chip in the ultrasonic probe, i.e. x = d / J. The starting position, the second position, the third position and the terminal position are the center positions of the synthetic aperture.

[0078] Synthetic aperture focused imaging.

[0079] ​This step includes discretizing the imaging area into a 320x128 grid area, each grid being 0.05 mm wide, calculating the sound wave propagation time from the center of the transducer wafer in the ultrasonic probe to each grid node and reflected to the center of the transducer wafer, and linearly interpolating the acquired synthetic aperture data to obtain the imaging amplitude of the imaging point. It is worth noting that the imaging area corresponding to each aperture is a region directly below the center of the aperture with a width of 0.1 mm and a height of 6.4 mm.

[0080] It should be understood that the size of the above grid division is related to the resolution of imaging, and finer grid division can obtain higher resolution, but should be less than the transverse movement distance of the transducer wafer in the above, for example, 0.1 mm.

[0081] As shown in Figure 7 , the synthetic aperture focusing imaging is performed on the synthetic aperture data of the first position, the synthetic aperture data of the second position, and the synthetic aperture data of the third position respectively, and the imaging results are superimposed to obtain a synthetic aperture focusing image.

[0082] Figure 8a When using synthetic aperture focusing imaging, the imaging area corresponding to each aperture is a composite material delamination damage imaging image obtained by the entire ultrasonic probe covering the detection area, and Figure 8a It can be seen that this method is difficult to accurately image the delamination damage in the composite material. Figure 8b is a composite material delamination damage imaging image obtained by the imaging area corresponding to each aperture being a region directly below the aperture with a width of the aperture size and a height of the plate thickness; Figure 8c is a composite material delamination damage imaging image obtained by the imaging area corresponding to each aperture being a region directly below the aperture with a width of the size of a single transducer wafer and a height of the plate thickness; and Figure 8c It can be seen that reducing the imaging area corresponding to each aperture can enhance the imaging accuracy. Figure 8d is a composite material delamination damage imaging image obtained by using the present application, and it can be seen that the damage imaging image obtained by using the composite material delamination damage synthetic aperture ultrasonic imaging method proposed in the present application has higher accuracy.

[0083] The amplitude of the above imaging image is extracted as the position of the center of each defect, and the amplitude curve graph in the lateral direction of the amplitude value point is drawn, as shown in Figure 9 . Figure 9 In Figure 8a , curve 1 is the amplitude curve graph of Figure 8b , curve 2 is the amplitude curve graph of Figure 8c , curve 3 is the amplitude curve graph of Figure 8dthe amplitude curve graph in the lateral direction, the full width at half maximum (FWHM) thereof is calculated, which is equivalent to the lateral width at the point where the amplitude curve drops by about -6dB from the highest point, as the width of the defect imaging graph. It is obtained that Figure 8a The single defect width is 21.2 mm, Figure 8b The single defect width is 2.8 mm, Figure 8c The single defect width is 2.2 mm, Figure 8d The single defect width is 1.95 mm

[0084] According to The conventional synthetic aperture focusing method is difficult to accurately image the delamination damage in the CFRP laminates by the descending method, Figure 8a The size error in the lateral direction is as high as 900%, Figure 8b The size error in the lateral direction is 40%, Figure 8c The size error in the lateral direction is 10%, Figure 8d The size error in the lateral direction is only 2.5% for the delamination damage imaging graph obtained by using the synthetic aperture ultrasonic imaging method of the present application.

[0085] In the present application, the transducer can be a transducer wafer as described above, or a transducer of other structure.

[0086] It should be understood that the embodiments described herein are only for illustration and explanation of the present application, and are not intended to limit the present application. Some non-essential improvements and adjustments made by those skilled in the art based on the content of the present application are within the protection scope of the present application.

Claims

1. An ultrasonic phased array synthetic aperture focusing imaging method for delamination damage in CFRP composites, characterized in that: The method comprises the steps of: Step S0, providing the CFRP composite material with a thickness of D; the ultrasonic phased array is arranged on the surface of the CFRP composite material, comprising a plurality of transducers arranged linearly in the transverse direction of the surface, and the center-to-center distance of adjacent transducers is d, so that the width direction and the depth direction of the CFRP composite material define a region to be detected; Step S1: determining the number of transducers required to be excited in each aperture of the synthetic aperture, and the focusing depth of the synthetic aperture is the plate thickness D; Step S2: moving the ultrasonic phased array on the surface from the starting position to the terminal position in the transverse direction by a preset displacement amount; Step S3, performing the following steps at the start position, the end position and a plurality of intermediate positions between the start position and the end position to obtain an ultrasound signal for each position where j denotes the number of times the phased array is moved; Step S30, determining a group of transducers in the plurality of transducers as the required transducers to be excited in the aperture; Step S31, in accordance with the calculated delay exciting the set of transducers to generate an ultrasound signal; Step S32, collect the signals received by the group of transducers, wherein the signal received by the nth transducer in the mth aperture is ; and the signal received by the nth transducer in the nth aperture is . Step S33, performing delay-and-sum on the signals received by the transducers; Step S34, a Hilbert transform is performed to obtain the ultrasonic signal received by the aperture where h represents the Hilbert transform. Step S35, switching to another group of transducers to switch to another aperture, and repeating steps S31 to S34 until the ultrasonic signals of all apertures of the ultrasonic phased array at the position are obtained; Step S4, the acquired ultrasonic signals of the positions Synthetic aperture focusing imaging is performed, and the imaging results are superimposed to obtain an injury imaging diagram.

2. The method for ultrasonic phased array synthetic aperture focusing imaging of delamination damage in CFRP composites according to claim 1, characterized in that: Wherein, The acquired ultrasonic signals from each location are used for synthetic aperture focusing imaging, including discretizing the area to be detected by dividing it into a grid with the layup interface as the lateral boundary, numbered k from top to bottom (k=1,2,…,K), and with the thickness direction as the longitudinal boundary, numbered l from left to right (l=1,2,…,L). All imaging points within the imaging area are then analyzed. amplitude The expression is: In the formula, Let i be the centroid position of the i-th aperture in the j-th iteration. The round-trip sound propagation time is the distance from the center of the i-th aperture in the j-th iteration to the imaging point in the region with width x and height D directly below the aperture; and the synthetic aperture focusing imaging is performed based on the amplitude of the imaging point.

3. The ultrasonic phased array synthetic aperture focusing imaging method for delamination damage in CFRP composites as claimed in claim 1, wherein: The excited transducers in the synthetic aperture are sequentially switched.

4. The method for ultrasonic phased array synthetic aperture focusing imaging of delamination damage in CFRP composites according to claim 1, characterized in that: The step distance of the synthetic aperture is 1.

5. The method for ultrasonic phased array synthetic aperture focusing imaging of delamination damage in CFRP composites according to claim 1, characterized in that: The CFRP composite material is a quasi-isotropic CFRP laminate arranged in 45° / 90° / -45° / 0°.

6. The method for ultrasonic phased array synthetic aperture focusing imaging of delamination damage in CFRP composites as claimed in claim 1, wherein: The directivity pattern of different transducer numbers is calculated according to the directivity function of the ultrasonic phased array, and the number of excited transducers included in the synthetic aperture is determined according to the directivity concentration effect and the delay deviation.

7. The method of claim 6, wherein the method further comprises: Comprise: Directivity function of the phased linear array where N is the number of transducers required to excite the synthetic aperture, θ is the angle between the acoustic propagation direction and the z-axis, is the wavelength, c is the group velocity of the quasi-longitudinal wave in the normal direction of the CFRP laminate, f is the center frequency of the transducer, and .

8. The method for ultrasonic phased array synthetic aperture focusing imaging of delamination damage in CFRP composites as claimed in claim 1, wherein: The delay is calculated from the ultrasound signals propagating with a constant sound speed c wherein is the distance from the center of the n-th transducer in each aperture to the center of the aperture.

9. The ultrasonic phased array synthetic aperture focusing imaging method for delamination damage in CFRP composites as claimed in claim 1, wherein: According to the center-to-center distance d of two adjacent transducers in the ultrasonic probe, the moving distance x is determined; x=d / J.

10. The method for ultrasonic phased array synthetic aperture focusing imaging of delamination damage in CFRP composites as claimed in claim 1, wherein: Also included is a step S5 of employing The size of the lesion is quantified using a descending method to assess the quality of the lesion imaging.

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