Ultrasonic imaging method for complex-surface multilayer anisotropic composite material

Abstract

The invention discloses an ultrasonic imaging method for a complex-surface multilayer anisotropic composite material. The method comprises the steps that an acoustic propagation model is established according to profile characteristics of the composite material, acoustic anisotropy characteristics changing along with the appearance and a preset ultrasonic detection mode, and the acoustic propagation model comprises medium attribute information of all spatial positions of the composite material and position and geometric information of an ultrasonic excitation unit and an ultrasonic receiving unit; for the acoustic propagation model, performing excitation in the preset ultrasonic detection mode, and obtaining an excitation signal waveform and a received acquisition signal waveform; and on the basis of the excitation signal waveform and the acquisition signal waveform, positive wave field information and reverse wave field information are calculated, and then a self-defined target is used for reverse time migration imaging to obtain an imaging result. According to the invention, full-depth synchronous focusing imaging in an anisotropic and complex molded surface coupling scene can be realized, and the imaging effect is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of ultrasonic detection of composite materials, and more particularly to an ultrasonic imaging method for complex-surface multi-layer anisotropic composite materials. Background Art

[0002] In the aviation industry, the use of composite materials in new aircraft has increased significantly, with composites accounting for over 50% of the total aircraft weight. Examples include the Boeing B787's fuselage, center wing box, raked wingtips, tail cone, horizontal and vertical stabilizer, control surfaces, internal pressure bulkheads, floor structures, and certain engine components. Many aviation composite materials, exemplified by CFRP (carbon fiber composites), exhibit anisotropic properties. As the industry continues to evolve, traditional simple shapes are no longer sufficient to meet current product requirements. In practical engineering, professionals optimize mass distribution and design complex surfaces to achieve the desired combination of lightweight and high strength.

[0003] To ensure product quality and service safety, it is crucial to perform nondestructive testing on components during trial production, manufacturing, and service to identify damage locations and characterize defect types. However, current research on ultrasonic imaging of complex surface components is limited by the complexity of conformal scanning path planning and the difficulty of coordinating multiple systems. Mainstream imaging methods rely on calculating the acoustic propagation path. This becomes significantly more difficult when faced with factors such as complex surfaces and anisotropy. Furthermore, echo signals with complex acoustic propagation paths, such as multiple reflections in the echo data, cannot be utilized and are instead treated as imaging noise.

[0004] Currently, imaging inspection of complex surface structures remains a significant challenge for ultrasonic phased array technology. To overcome the failure of traditional phased array technology in complex surface structure inspection, researchers are focusing on two main areas: upgrading traditional phased arrays to flexible arrays and improving post-processing algorithms to enhance contour extraction and defect imaging.

[0005] The main purpose of improving the traditional phased array into a flexible array is to enable the array elements to effectively receive reflected wave signals. When the array element axis deviates from the normal line of the complex profile, the corresponding reflected signal is easily lost, thus the internal defects of the component cannot be detected. However, when the array element arrangement is parallel to the profile, this problem can be effectively solved. In 2010, Hunter et al. used a mechanical design method to attach an ultrasonic transducer array to the curved surface of a metal sample, determined the anchor point position of the transducer, and fitted the predicted sample surface profile. After automatic focusing post-processing by combining the algorithm, the internal imaging detection of the complex profile component was realized. Although the use of the predicted profile can achieve good focusing effect, the defect imaging position deviates from the actual position of the defect, and there is a relatively obvious error between the predicted profile and the actual profile. In 2016, Nakahata et al. used a commercial flexible ultrasonic array probe to collect ultrasonic data by attaching a flexible array to the surface of a complex profile component sample, and used a traditional focusing method for post-processing to realize the internal defect imaging detection of the complex profile component. However, the premise of defect imaging is to know the geometric position of all array elements, otherwise the defect cannot be effectively imaged.

[0006] On the other hand, researchers continue to explore the imaging capability of traditional phased array probes for complex profile structures by improving the acoustic coupling between phased array and profile, improving the post-processing algorithm, etc. In 2020, researchers proposed a multi-step angular spectrum method based on reverse time migration (RTM), which uses data collected by a linear array probe to attempt to extract the profile information of a small curvature component and image internal defects. RTM is a wave equation-based imaging method that converts multiple reflection signals from the so-called "imaging noise" in traditional imaging methods into "imaging effective data" by introducing RTM. The reconstructed profile of the imaging result is close to the actual profile but has a significant error, and based on the actual profile, internal defects can be effectively imaged, with a large number of wave-shaped noise and a small number of false defects. In addition, researchers have proposed an ultrasonic imaging method combining RTM imaging with point clouds. A camera is used to reconstruct the point cloud profile of a complex profile component with a vertical discontinuous interface, and then an imaging background is established based on the reconstructed profile. The data collected by the ultrasonic linear array is post-processed using the RTM method, and finally the imaging of the cut and hole defects is completed. The defect morphology feature provided by the result of this method is lost, and there is obvious wave-shaped background noise near the defect, and the imaging effect needs to be further improved. In addition, accurate coordinate coupling is required between the point cloud profile extraction system and the ultrasonic imaging system, and the calibration requirement is high.

[0007] Through analysis, the existing technology mainly has the following defects:

[0008] 1) When the acoustic properties of the material are complex, the acoustic calculation method based on the assumption of sound rays becomes difficult to use;

[0009] 2) In the propagation environment, when there are many possible sound propagation paths, the existing imaging method generally uses direct waves for imaging, without using multiple reflection-refraction waves;

[0010] 3) The existing reverse time migration imaging method is limited to imaging internal defects of simple materials and simple shape samples, and is not suitable for imaging internal defects of samples with large curvature complex surfaces, laminated anisotropy and other characteristics. At present, there is little research on ultrasonic imaging of structures with complex surfaces and complex acoustic characteristics such as large curvature and laminated anisotropy. SUMMARY

[0011] The purpose of the present application is to overcome the defects of the prior art, and to provide a complex surface multilayer anisotropic composite material ultrasonic imaging method. The method comprises the following steps:

[0012] According to the surface characteristics of the composite material, the acoustic anisotropy characteristics changing with the shape, and the predetermined ultrasonic detection mode, an acoustic propagation model is established, which contains the medium attribute information of each position in space of the composite material, the position and geometric information of the ultrasonic excitation unit and the ultrasonic receiving unit;

[0013] For the acoustic propagation model, excitation is carried out in the predetermined ultrasonic detection mode, and the excitation signal waveform and the received acquisition signal waveform are obtained;

[0014] Based on the excitation signal waveform and the acquisition signal waveform, the forward wave field information and the inverse wave field information are calculated, and then the self-defined target reverse time migration imaging is used to obtain the imaging result.

[0015] Compared with the prior art, the advantage of the present application is that the proposed ultrasonic imaging method is a full-depth synchronous focusing ultrasonic material internal defect imaging method, which can adapt to high-difficulty scenes coupled by complex surface and anisotropy two complex factors, and can efficiently utilize multiple types of ultrasonic echo data, without the need to calculate the sound propagation path. The present application can effectively perform ultrasonic imaging on the internal part of the complex surface, multilayer anisotropic composite material, and can realize self-defined target imaging.

[0016] Other features and advantages of the present application will become apparent from the following detailed description of exemplary embodiments thereof, with reference to the accompanying drawings. BRIEF DESCRIPTION OF DRAWINGS

[0017] The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate embodiments of the present application and, together with the description, serve to explain the principles of the present application.

[0018] Figure 1is a flow chart of a method for ultrasonic imaging of a complex-surface multilayer anisotropic composite material according to one embodiment of the present invention;

[0019] Figure 2 is a schematic diagram comparing different acoustic modeling methods according to an embodiment of the present invention;

[0020] Figure 3 is a schematic diagram of the cosine of the angle between the coordinate axes of the constitutive coordinate system and the coordinate axes of the observation coordinate system according to one embodiment of the present invention;

[0021] Figure 4 is a schematic diagram of the RTM imaging principle of a custom target according to an embodiment of the present invention;

[0022] Figure 5 is a schematic diagram of an ultrasonic testing model for an L-shaped CFRP component under water immersion conditions according to an embodiment of the present invention;

[0023] Figure 6 2. It is a schematic diagram of a self-transmitted and self-received data set and a data set corresponding to an excitation array element according to an embodiment of the present invention;

[0024] Figure 7 1 is a schematic diagram of RTM imaging results based on a full-transmit-full-receive dataset and a self-transmit-self-receive dataset according to an embodiment of the present invention. DETAILED DESCRIPTION

[0025] Various exemplary embodiments of the present invention will now be described in detail with reference to the accompanying drawings. It should be noted that unless otherwise specifically stated, the relative arrangement of components and steps, numerical expressions and numerical values ​​set forth in these embodiments do not limit the scope of the present invention.

[0026] The following description of at least one exemplary embodiment is merely illustrative in nature and is in no way intended to limit the invention, its application, or uses.

[0027] Technologies, methods, and equipment known to ordinary technicians in the relevant art may not be discussed in detail, but where appropriate, the technologies, methods, and equipment should be considered part of the specification.

[0028] In all examples shown and discussed herein, any specific values ​​should be interpreted as merely exemplary and not limiting. Therefore, other examples of the exemplary embodiments may have different values.

[0029] It should be noted that like reference numerals and letters refer to like items in the following figures, and therefore, once an item is defined in one figure, it need not be further discussed in subsequent figures.

[0030] The synchronous focused ultrasonic imaging method for complex-surface multi-layer anisotropic composite materials provided by the present invention can be used for various types of composite materials and adopts various ultrasound generation methods. For example, phased array probes, ultrasonic plane probes, ultrasonic focusing probes, flexible probes, air-coupled probes, etc. For the sake of clarity, the following uses the use of phased array probes to generate ultrasound and perform imaging and defect detection on carbon fiber reinforced plastic (CFRP) as an example. Carbon fiber composite materials are representatives of anisotropic composite materials, and L-shaped CFRP multi-directional plates are typical of complex-surface anisotropic composite material components. This article mainly takes the imaging of the corner area (R area) of the L-shaped CFRP multi-directional plate as an example to illustrate the technical solution of the present invention.

[0031] In general, the present invention relates to a phased array ultrasonic imaging method for complex-profile anisotropic composite multi-directional panels based on high-accuracy acoustic modeling. The method generally involves: using a linear array phased array ultrasonic probe to collect ultrasonic echo signals from a sample under water immersion conditions. For complex-profile composite component scenarios, a highly accurate acoustic propagation model is established, taking into account the acoustic anisotropy characteristics that vary with the shape. Subsequently, the ultrasonic excitation signal waveform and the acquired signal waveform are used as inputs to an RTM (reverse time migration) imaging algorithm to calculate the positive and reverse wave fields. Finally, the imaging conditions are used to output the final imaging results of internal defects and other features.

[0032] Specifically, see Figure 1 As shown, the provided method for ultrasonic imaging of complex-surface multilayer anisotropic composite materials includes the following steps:

[0033] Step S110 : establishing a laminated anisotropic sound propagation model for acoustic simulation for the target composite material.

[0034] Figure 2 This is a comparative diagram of three acoustic modeling methods, Figure 2 (a) is an isotropic model, where the interior of the component is an isotropic medium. Figure 2 (b) is a uniform anisotropic model, where the components are layered according to the order in which the CFRP is laid, and different anisotropic parameters are assigned to each layer, but the local coordinates are consistent everywhere; Figure 2 (c) is the laminated anisotropic model. Based on the uniform anisotropic model, the local coordinate system is optimized to be consistent with the actual laying situation, and the acoustic propagation characteristics of the model are more realistic.

[0035] In engineering, the anisotropic characteristics of CFRP are often ignored and the entire component is simplified into an isotropic medium with a fixed sound velocity. For CFRP laminates, the fixed sound velocity is taken as the sound velocity in the direction perpendicular to the carbon fiber. This model is an isotropic simplified model. Figure 2As shown in (a), the isotropic simplified model has the advantages of simple modeling and low computational complexity. However, in the aviation composite material scenario, the isotropic simplified model ignores the strong anisotropic characteristics of CFRP, resulting in the inability to accurately restore the sound propagation path, causing defect misjudgment or loss of focus.

[0036] In order to be closer to the real situation, the anisotropic characteristics of CFRP can be considered in the modeling process to improve the accuracy of the model. The acoustic model that describes the anisotropy of the material in a unified global coordinate system is called the anisotropic homogenization model. Figure 2 As shown in (b), the anisotropic homogenization model can distinguish the differences in the laying angles of different layers in the CFRP laminate structure. Its anisotropy is as follows: Figure 2 As shown in (b), the local coordinate system is the same. However, in the widely used L-shaped CFRP laminate, especially when modeling its R-zone, the tangent and depth directions of the laminate vary with its spatial position, with the left and right ends differing by as much as 90 degrees. The sound velocity of the CFRP medium varies significantly within this 90-degree range. Assuming that the anisotropic characteristics are uniform everywhere and do not vary with position will lead to distortion in the acoustic model's simulation of sound propagation, similarly resulting in inaccurate imaging of the R-zone.

[0037] In order to restore the position-varying anisotropy characteristics in the R region of the L-shaped CFRP component, a global coordinate system and a local coordinate system that changes with the surface normal direction are introduced in the anisotropic modeling process. That is, in the local coordinate system at each position, the depth direction coincides with the coordinate axis of the local coordinate system, which can restore the scene to a higher degree. This model is called a multi-layer anisotropic complex model, such as Figure 2 (c) shown.

[0038] Among the three modeling approaches mentioned above, the laminated anisotropic complex model can best fully describe the acoustic characteristics of the L-shaped CFRP component, so the laminated anisotropic model is preferred.

[0039] In step S120 , for the laminate anisotropic sound propagation model, the stiffness matrix of each ply is unified from the local coordinate system to the global coordinate system through the conformal transformation principle.

[0040] When establishing a multi-layer anisotropic complex model for the R zone of a CFRP component, it is necessary to convert the local coordinate system description of the properties of the CFRP at various locations into a global coordinate system description for unified computational expression. For imaging acoustic models, the key is to convert the stiffness matrix required for sound velocity calculation from a local coordinate system description that conforms to natural characteristics and corresponds to the constitutive coordinate system at various locations into a global coordinate system description with a unified computational formula. For example, the stiffness matrix rotation method involved is called the Bond transform.

[0041] For simplicity of formal expression, the material stiffness matrix can be expressed in a constitutive coordinate system based on the symmetry of the medium. From the perspective of material application, forces and displacements are typically measured and expressed in an observation coordinate system. Therefore, only the stiffness matrix expressed in the observation coordinate system can directly participate in data processing and calculations in the observation coordinate system. By establishing the transformation relationship between the stiffness matrices of the coordinate systems, the change of CFRP fiber orientation with the layup can be described at the level of the stiffness matrix, thus providing a foundation for establishing the complex ultrasonic propagation environment of multilayer structures.

[0042] Specifically, the material stiffness matrix is ​​a 6×6 matrix, and the rotation process is relatively complex. Bond transformation is usually used to transform the stiffness matrix between coordinate systems. The Bond transformation process is described as follows:

[0043] Let σ, ε, C be the stress tensor, strain tensor and stiffness matrix in the observation coordinate system (i.e., the global coordinate system), σ 0 , ε 0 , C 0 are the stress tensor, strain tensor, and stiffness matrix in the constitutive coordinate system (corresponding to the local coordinate system). The stress tensor and strain tensor in the constitutive coordinate system and the observation coordinate system have the following relationship:

[0044]

[0045] From the symmetry of the stress tensor and strain tensor, we can see that the M matrix is ​​a real orthogonal matrix. Substituting the above relationship into the constitutive equation in the constitutive coordinate system:

[0046] σ=MC 0 M T ε (2)

[0047] Comparing the constitutive equation in the observation coordinate system, we can see that:

[0048] C=MC 0 M T (3)

[0049] Among them, M is called the coordinate transformation matrix of the stiffness matrix. Use x, y, and z to represent the coordinate axes of the observation coordinate system. 0 、y 0 、z 0 Represents the coordinate axes of the constitutive coordinate system, and α ij Represents the cosine value of the angle between the constitutive coordinate system axis i and the observation coordinate system axis j, for example, α xy Represents the cosine of the angle between the x-axis of the constitutive coordinate system and the y-axis of the observation coordinate system. For the cosine of the angle between the two coordinate systems, see Figure 3 shown.

[0050] Depend on Figure 3The definition of , can directly write the transformation matrix M, expressed as:

[0051]

[0052] Using the transformation matrix M, we can transform Figure 2 The stiffness matrix of each ply in the anisotropic laminate model shown is unified from the local coordinate system to the global coordinate system.

[0053] Step S130 : Based on the established sound propagation model and known ultrasonic detection schemes, a custom target RTM imaging method is used to obtain imaging results.

[0054] This step S130 mainly includes: exciting the established acoustic propagation model in a predetermined ultrasonic detection manner, and obtaining the excitation signal waveform and the received acquisition signal waveform; calculating the positive wave field information and the inverse wave field information based on the excitation signal waveform and the acquisition signal waveform, and then using reverse time migration imaging to obtain the imaging result. Through this design, full-depth synchronous focused ultrasonic imaging of complex-surface multi-directional plates of anisotropic composite materials can be achieved. In the custom target RTM imaging calculation process of this article, imaging of different types of targets is achieved by selecting different ultrasonic data set inputs. The selected ultrasonic data sets include all-transmit and all-receive data types and self-transmit and self-receive data types.

[0055] In one embodiment, the acoustic propagation model corresponding to the stacked multi-layer anisotropic model includes medium property information of each spatial position of the composite material, and position and geometric information of the ultrasonic excitation unit and the ultrasonic receiving unit.

[0056] In one embodiment, reverse time migration (RTM) imaging is used. RTM imaging is based on wave field simulation calculation and can achieve synchronous focusing imaging of targets at full depth.

[0057] In this invention, a custom target RTM imaging method is proposed based on different data set selection methods. Figure 4 is the RTM imaging principle diagram of the custom target, where Figure 4 (a) Schematic diagram of collecting ultrasound experimental data; Figure 4 (b) Schematic diagram of the establishment of a corresponding acoustic propagation model based on experimental conditions (such as ultrasonic detection method, distribution of ultrasonic excitation units and ultrasonic receiving units, etc.), actual component surface and internal structure characteristics, for forward and reverse wave field calculations and RTM imaging.

[0058] Combine Figure 4 As shown, the custom target RTM imaging designed by the present invention includes the following steps:

[0059] Step S1: Based on the experimental conditions and the structural characteristics of the complex surface component, a corresponding acoustic propagation simulation model is established. The model includes the medium property information at each position in the space, and the position and geometric information of the excitation unit and the receiving unit.

[0060] Step S2: Calculate the positive wave field corresponding to the excitation unit using the excitation signal. During the sound propagation calculation process, retain the positive wave field information S(x, z, t) at each moment (frame), where x and z are spatial coordinates and t represents time.

[0061] Step S3: Calculate the inverse wave field corresponding to the receiving unit using the received signal. The input signal can selectively use a self-transmitting and self-receiving signal or a full-transmitting and full-receiving signal according to the characteristics of the imaging required. The inverse wave field information R(x, z, t) at each moment (frame) is retained during the sound propagation calculation process.

[0062] Step S4, applying the imaging conditions to the corresponding frames of the positive wave field and the inverse wave field and superimposing them, which is expressed as:

[0063]

[0064] Where T is the total duration of wavefield simulation, f is the functional expression of imaging conditions, and I represents the final imaging result.

[0065] During the custom target RTM imaging calculation process, imaging of different target types is achieved by selecting different ultrasound dataset inputs. In addition to dataset selection, key factors influencing the final imaging results are the accuracy of the acoustic propagation simulation model and the choice of imaging conditions. In one embodiment, the present invention uses a stacked anisotropic model for acoustic propagation simulation calculations, adopts cross-correlation imaging conditions, and introduces positive wavefield energy distribution to compensate for the imaging results. The imaging condition formula is expressed as:

[0066]

[0067] In summary, the present invention targets the imaging scenario of internal features of complex-surface anisotropic composite materials, considers the acoustic anisotropy characteristics that change with the external shape, establishes a high-accuracy acoustic propagation model, then uses the ultrasonic excitation signal waveform and acquisition signal waveform as input to the RTM imaging algorithm, calculates the positive wave field and the reverse wave field, and uses the imaging conditions to achieve imaging results of internal defects and internal laminate interface features.

[0068] It should be understood that the above embodiments can be appropriately changed or modified by those skilled in the art without departing from the spirit and scope of the present application. For example, the phased array probe can be replaced by other types of ultrasonic transducers, such as a conventional ultrasonic planar probe, an ultrasonic focused probe, a flexible probe, an air-coupled probe, etc. For another example, the reverse-time migration imaging method can be replaced by a full-waveform inversion method or other imaging methods of the same wave field type. For still another example, the self-defined target RTM imaging can be replaced by other imaging conditions. In addition, in addition to imaging the interior of a composite material, the present application can also be used for profile imaging of a complex profile object.

[0069] Further, in order to verify the feasibility of the present application, the ultrasonic detection of an L-shaped CFRP laminated multidirectional plate with a defect in the R region under water immersion conditions using a phased array probe is simulated numerically, and the RTM imaging results and corresponding analysis are given based on the numerical simulation data.

[0070] First, an L-shaped CFRP laminated multidirectional plate model is established to simulate the actual experimental environment. Figure 5 is an ultrasonic detection model of an L-shaped CFRP component under water immersion conditions, i.e. the model used in the simulation, wherein the CFRP multidirectional plate contains 48 carbon fiber layers, and like the actual CFRP component, the layers have four different angles, the laying sequence used in the simulation is [[90 / -45 / 90 / 45][90 / 90 / -45 / 90 / 0 / 90 / 45 / 0 / 45 / -45]2]2, the mechanical properties of each layer are the same, and the values of the independent elastic constants are all set to C 11 = 13.60, C 13 = 6.97, C 33 = 131.29, C 44 = 5.26, C 66 = 3.31 (unit: GPa), the parameters of each layer are changed according to the laying angle setting, the overall thickness of the plate is 9.6 mm, the outer contour radius is 17.6 mm, and the inner contour radius is 8.0 mm; the density of water in the propagation environment is p = 1000.0 kg / m3, and the sound speed is c water = 1496.6 m / s; the top of the model is placed with various transceiving elements, the total number of elements is 32, the element width is 0.5 mm, the element center distance is 0.6 mm, and the signal sampling frequency is 100 MHz. Figure 5 The size and position of the circular hole defect are also shown, the diameter of the circular hole is 1.5 mm, and the circular hole is placed in the middle of the R region closer to the bottom. In the model, the bending part of the CFRP is modeled in detail, and the z-axis of the local coordinate system at each point of the bending part is established along the thickness direction, i.e. the surface normal coincides with the z-axis of the coordinate system corresponding to each point of the bending part.

[0071] In terms of signal excitation and reception, the excitation signal adopts a Gaussian sinusoidal waveform, the functional form of which is shown in Equation 7. The 32 array elements in the phased array are all excited by the signal, and all the array elements receive the signal, i.e., the complete data set is collected in the full-transmit full-receive mode.

[0072]

[0073] where A represents the amplitude, D represents the pulse width, f represents the main frequency, and t is the time

[0074] The signal data obtained in the simulation experiment on the model with defects is shown in Figure 6 The left graph is the self-transmit self-receive data set of each array element, and the right graph is the data set in which array element 16 transmits and all array elements receive (i.e., the data set corresponding to the excitation of array element 16). In the same set of phased array ultrasonic signal data, the results obtained by using the full-transmit full-receive data and the self-transmit self-receive data for RTM imaging are shown in Figure 7 The imaging information of the water coupling layer is not shown, and only the imaging results of the CFRP part are retained, Figure 7 The white dashed line in the middle is the contour mark of the hole-type defect.

[0075] Figure 7 (a) is the RTM imaging result based on the full-transmit full-receive data. It can be seen that the bright spot at a relatively deep position corresponds to the top of the hole-type defect, and the center of the bright spot falls on the top of the white line. In addition, there are many arc-shaped bright strips near the surface. The arc-shaped bright strips correspond to the internal lamination interfaces of the CFRP. When the laying angles of adjacent layers are significantly different, the difference in acoustic impedance also becomes significant, resulting in strong interlayer reflection signals. These signals account for a major part of the full-transmit full-receive data set, and finally correspond to the presentation in the RTM imaging result. Figure 7 (b) is the RTM imaging result based on the self-transmit self-receive data. It can be seen that when only the self-transmit self-receive data of each array element is retained and all self-transmit other-receive data is excluded for RTM imaging, the imaging of the internal lamination interfaces of the CFRP becomes weak and invisible, and the defect contour becomes more prominent, showing different imaging functions.

[0076] Figure 7 The imaging results based on different use modes of a set of data are shown, verifying that for anisotropic composite multi-directional plate complex profile composites, the present application changes the use mode of a set of data and has effectiveness in imaging different internal features by the RTM imaging method. At the same time, it is illustrated that when imaging a small range of defects, it is not true that the larger the amount of input data, the better the imaging effect. By excluding data with weak defect echoes, the signal-to-noise ratio of defect imaging can be improved, and using the complete phased array signal data set can image the lamination interfaces.

[0077] In summary, compared with the prior art, the present invention has the following advantages:

[0078] 1) This paper proposes a phased array ultrasonic imaging method for complex surface components made of anisotropic composite multi-directional plates. By establishing an accurate acoustic model of the anisotropic and complex surface characteristics and using it for RTM imaging calculations, it is possible to obtain high-quality internal defect imaging results in scenarios where anisotropy and complex surfaces are coupled.

[0079] 2) By leveraging a single, all-transmitter, all-receiver dataset in different ways, this method enables imaging of various targets within the material (such as defects and laminate interfaces), known as custom-targeted RTM imaging. This imaging method eliminates the need to address multipath issues and leverages the characteristics of reverse time migration imaging to restore the wavefield propagation process.

[0080] 3) In the same imaging process, the present invention achieves full-depth synchronous focus imaging of different material characteristics and different targets by changing the way the same set of experimental data is used;

[0081] 4) Compared with existing imaging methods, the present invention has a better signal-to-noise ratio and improves the utilization rate of multiple reflection waves and other types of signals in the signal.

[0082] In summary, based on solving the acoustic modeling of complex structures, the present invention realizes full-depth focused synchronous imaging in the coupling scenario of anisotropy and complex surfaces, providing an imaging detection method for defects and delamination of composite materials, which is of great significance to improving the manufacturing quality and service safety of composite components with complex surface characteristics.

[0083] The present invention may be a system, a method and / or a computer program product. The computer program product may include a computer-readable storage medium carrying computer-readable program instructions for causing a processor to implement various aspects of the present invention.

[0084] Computer-readable storage medium can be a tangible device that can keep and store the instructions used by the instruction execution device.Computer-readable storage medium can be, for example, but not limited to, an electrical storage device, a magnetic storage device, an optical storage device, an electromagnetic storage device, a semiconductor storage device or any suitable combination thereof.More specific examples (non-exhaustive list) of computer-readable storage medium include: a portable computer disk, a hard disk, a random access memory (RAM), a read-only memory (ROM), an erasable programmable read-only memory (EPROM or flash memory), a static random access memory (SRAM), a portable compact disc read-only memory (CD-ROM), a digital versatile disk (DVD), a memory stick, a floppy disk, a mechanical encoding device, for example, a punch card or a convex structure in a groove having instructions stored thereon, and any suitable combination thereof.Computer-readable storage medium used herein is not interpreted as a transient signal itself, such as radio waves or other freely propagating electromagnetic waves, electromagnetic waves propagated by waveguides or other transmission media (for example, light pulses by fiber optic cables), or electrical signals transmitted by wires.

[0085] The computer-readable program instructions described herein can be downloaded from a computer-readable storage medium to each computing / processing device, or downloaded to an external computer or external storage device via a network, such as the Internet, a local area network, a wide area network, and / or a wireless network. The network can include copper transmission cables, fiber optic transmission, wireless transmission, routers, firewalls, switches, gateway computers, and / or edge servers. The network adapter card or network interface in each computing / processing device receives the computer-readable program instructions from the network and forwards the computer-readable program instructions to be stored in the computer-readable storage medium in each computing / processing device.

[0086] The computer program instructions for performing the operation of the present invention can be assembly instructions, instruction set architecture (ISA) instructions, machine instructions, machine-dependent instructions, microcode, firmware instructions, state setting data, or source code or object code written in any combination of one or more programming languages, including object-oriented programming languages ​​such as Smalltalk, C++, Python, and conventional procedural programming languages ​​such as "C" language or similar programming languages. The computer readable program instructions can be executed entirely on the user's computer, partially on the user's computer, as an independent software package, partially on the user's computer, partially on a remote computer, or completely on a remote computer or server. In the case of a remote computer, the remote computer can be connected to the user's computer via any type of network, including a local area network (LAN) or a wide area network (WAN), or can be connected to an external computer (e.g., using an Internet service provider to connect via the Internet). In some embodiments, an electronic circuit, such as a programmable logic circuit, a field programmable gate array (FPGA), or a programmable logic array (PLA), is personalized by utilizing the state information of the computer readable program instructions, and the electronic circuit can execute the computer readable program instructions, thereby realizing various aspects of the present invention.

[0087] Various aspects of the present invention are described herein with reference to flowcharts and / or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of the present invention. It should be understood that each block of the flowcharts and / or block diagrams, and combinations of blocks in the flowcharts and / or block diagrams, can be implemented by computer-readable program instructions.

[0088] These computer-readable program instructions can be provided to a processor of a general-purpose computer, a special-purpose computer, or other programmable data processing device, thereby producing a machine, so that when these instructions are executed by the processor of the computer or other programmable data processing device, a device is generated that implements the functions / actions specified in one or more blocks in the flowchart and / or block diagram. These computer-readable program instructions can also be stored in a computer-readable storage medium, where these instructions cause the computer, programmable data processing device, and / or other device to operate in a specific manner. Thus, the computer-readable medium storing the instructions comprises an article of manufacture that includes instructions for implementing various aspects of the functions / actions specified in one or more blocks in the flowchart and / or block diagram.

[0089] The computer readable program instructions can also be loaded onto a computer, other programmable data processing apparatus, or other device to cause a series of operational steps to be performed on the computer, other programmable data processing apparatus or other device to produce a computer implemented process such that the instructions which execute on the computer, other programmable data processing apparatus, or other device implement the functions / acts specified in the flowchart and / or block diagram block or blocks.

[0090] The computer readable program instructions can also be loaded onto a computer, other programmable data processing apparatus, or other device to cause a series of operational steps to be performed on the computer, other programmable data processing apparatus or other device to produce a computer implemented process such that the instructions which execute on the computer, other programmable data processing apparatus, or other device implement the functions / acts specified in the flowchart and / or block diagram block or blocks.

[0091] Embodiments of the present application have been described above, and the description is intended to be illustrative, and not restrictive, of the various embodiments of the present application. Many modifications and variations of the described embodiments of the present application are possible, given the benefit of the present disclosure, without departing from the scope and spirit of the described embodiments of the present application. The scope of the present application is defined by the appended claims.

Claims

1. A method for ultrasonic imaging of complex-surface multilayer anisotropic composite materials, comprising the following steps: An acoustic propagation model is established based on the surface characteristics of the composite material, the acoustic anisotropy characteristics that change with the shape, and the predetermined ultrasonic detection method. The acoustic propagation model includes medium property information at various spatial locations of the composite material, and the position and geometric information of the ultrasonic excitation unit and the ultrasonic receiving unit. For the acoustic propagation model, excitation is performed in the predetermined ultrasonic detection manner, and an excitation signal waveform and a received signal waveform are obtained; Based on the excitation signal waveform and the acquisition signal waveform, the positive wave field information and the reverse wave field information are calculated, and then the self-defined target reverse time migration imaging is used to obtain the imaging result.

2. The method according to claim 1, characterized in that The imaging results are obtained according to the following steps: Based on the acoustic propagation model, the positive wave field corresponding to the excitation unit is calculated using the excitation signal to obtain the positive wave field information; Based on the acoustic propagation model, selectively using the received signal to calculate the inverse wave field corresponding to the receiving unit to obtain inverse wave field information; The imaging conditions are applied to the corresponding moments of the positive wave field and the reverse wave field and superimposed to obtain the imaging results, which are expressed as: Where S(x, z, t) is the positive wavefield information, R(x, z, Tt) is the reverse wavefield information, t represents the time, T represents the total duration of the wavefield simulation, f represents the functional expression of the imaging condition, I represents the imaging result, and x and z represent the spatial coordinates.

3. The method according to claim 2, characterized in that The cross-correlation imaging condition is adopted, and the positive wave field energy distribution is introduced to compensate the imaging result, which is expressed as:

4. The method according to claim 1, wherein The predetermined ultrasonic detection method is to use a phased array ultrasonic probe for ultrasonic excitation, and to realize composite material imaging by selecting different ultrasonic data sets during the excitation process. The selected ultrasonic data sets include an all-transmit and all-receive data type and a self-transmit and self-receive data type.

5. The method according to claim 1, wherein The predetermined ultrasonic detection method includes a phased array ultrasonic probe, an ultrasonic plane probe, an ultrasonic focusing probe, a flexible probe, and an air-coupled probe.

6. The method according to claim 1, characterized in that The acoustic propagation model is a laminate anisotropic model, and the stiffness matrix of each ply is unified from the local coordinate system to the global coordinate system.

7. The method according to claim 1, characterized in that The acoustic propagation model is established for a complex-profile fiber-reinforced resin-based composite laminate multidirectional plate. The z-axis of the local coordinate system of each bending part of the complex-profile carbon fiber composite laminate multidirectional plate model is established along the thickness direction.

8. The method according to claim 1, characterized in that The imaging results include internal imaging and contour imaging of the composite material.

9. A computer-readable storage medium having a computer program stored thereon, wherein: When the computer program is executed by a processor, the steps of the method according to any one of claims 1 to 8 are implemented.

10. A computer device comprising a memory and a processor, wherein a computer program capable of being run on the processor is stored in the memory, characterized in that: When the processor executes the computer program, the steps of the method according to any one of claims 1 to 8 are implemented.

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