Multi-thin-layer heterogeneous material elastic parameter in-situ nondestructive measurement method, medium and equipment

Abstract

The invention discloses an in-situ nondestructive measurement method, medium and equipment for elastic parameters of a multi-thin-layer heterogeneous material, and belongs to the technical field of ultrasonic measurement. The method comprises the steps that a multi-mode ultrasonic propagation multi-parameter model is established for a to-be-measured structure, a propagation time theoretical value corresponding to each ultrasonic mode is calculated, and the to-be-measured structure is a multi-thin-layer heterostructure; laser ultrasonic linear scanning is carried out on the to-be-detected structure, ultrasonic signals of all ultrasonic modes propagating in different directions are collected, and a line scanning ultrasonic data set is obtained; for a selected ultrasonic mode, extracting propagation time experimental values under different excitation-receiving point combinations from ultrasonic signals of the line scanning ultrasonic data set; and aiming at the selected ultrasonic mode, minimizing the difference between the propagation time theoretical value and the propagation time experimental value as a target function, and using a parameter optimization algorithm to invert the elastic parameter of the to-be-tested structure. According to the invention, long-distance and non-contact in-situ nondestructive measurement can be realized, and the operation is simple.

Description

Technical Field

[0001] The present invention relates to the technical field of ultrasonic measurement, and more specifically, to a method, medium and device for in-situ non-destructive measurement of elastic parameters of multi-thin-layer heterogeneous materials. Background Art

[0002] Multi-thin-layer heterogeneous structures are widely used in industrial fields such as electronic packaging and aerospace because they can simultaneously exhibit the properties of multiple materials. Since the materials of different layers in a multi-thin-layer heterogeneous structure usually have different mechanical properties such as elastic parameters and thermal expansion coefficients, and complex working conditions such as high and low temperature alternation and external corrosion may occur during service, the mechanical properties of the materials are prone to degradation, which may further lead to phenomena such as delamination and fracture, seriously affecting the structural performance. During the material research and development process, continuous non-destructive measurement of the dynamic evolution behavior of the elastic parameters of the materials in a multi-thin-layer heterogeneous structure can reveal the failure mechanism of the materials and structures, which is crucial for improving the reliability of multi-thin-layer heterogeneous structures. Therefore, there is an urgent need for methods for measuring and evaluating the evolution of the elastic parameters of multi-thin-layer heterogeneous structure materials. However, the materials of the internal interlayers in a multi-thin-layer heterogeneous structure cannot be exposed, making it difficult to directly measure them by traditional methods. Therefore, how to in-situ non-destructively measure the elastic parameters of the internal materials of a multi-thin-layer heterogeneous structure is crucial for material research and development and reliability evaluation.

[0003] Currently, a mainstream solution for characterizing the elastic parameters of multi-thin-layer heterogeneous structure materials is to rely on methods such as mechanical tensile tests and dynamic mechanical analysis (DMA) to test on bulk samples. However, the testing of bulk materials cannot accurately reflect the in-situ mechanical state of the internal materials in a multi-thin-layer heterogeneous structure under multi-thin-layer conditions during actual service. Therefore, it is impossible to accurately characterize the mechanical property evolution process of the internal materials during reliability tests or long-term service. Another method is to perform a shear test on a multi-thin-layer heterogeneous structure sample and measure the shear strength of the sample to indirectly characterize the elastic parameters of the internal materials. However, this method is a destructive experiment. Therefore, a large number of parallel samples need to be prepared in reliability analysis, which is costly, time-consuming, and cannot directly obtain the specific values and evolution process of the elastic parameters of the same sample. To meet the urgent need for a method for in-situ non-destructive measurement of elastic parameters during the research and development of the internal materials of multi-thin-layer heterogeneous structures, geometric and acoustic parameters such as the thin layer thickness, density, sound velocity, and attenuation coefficient in a multi-thin-layer heterogeneous structure can be obtained by establishing an ultrasonic propagation theory model and combining a multi-parameter inversion algorithm; and then elastic parameters such as Young's modulus and Poisson's ratio can be calculated.

[0004] In the current ultrasonic measurement methods for multi-thin-layer heterostructure material parameters, one type is the ultrasonic transmission / reflection coefficient spectrum method. This type of method uses the amplitude, phase, or complex spectral ratio of the transmission / reflection signal and the reference signal for material parameter inversion. Compared with other methods based on the time-domain signals of interface reflection peaks, the advantage of this type of method is that it can be free from the influence of the signal aliasing problem at the multi-thin-layer interface. On this basis, by changing the ultrasonic incident angle and measuring the angular-resolved transmission / reflection coefficient spectrum, the complete longitudinal and transverse wave sound velocities, densities, and thin layer thicknesses can be obtained simultaneously, thereby obtaining the complete material elastic parameters. The main disadvantages of this type of method are that an additional reference signal is required to calibrate the ultrasonic incident signal spectrum, the ultrasonic incident angle needs to be accurately adjusted and measured, and the signal amplitude spectrum may be affected by factors such as rough surface scattering that are difficult to quantify. In addition, the models of this type of method usually need to assume that each layer of material in the multi-thin-layer structure is isotropic, so it cannot handle structures containing anisotropic materials. Another type of method is the geometric acoustics method that regards ultrasonic waves as a series of rays. This type of method calculates the propagation times of ultrasonic signals of different modes that have undergone transmission, reflection, refraction, and mode conversion based on the geometric relationship between the ultrasonic excitation point and the detection point and Snell's law or the ray tracing method, and can be used to measure parameters such as thin layer thickness, sound velocity, and elastic constants in multi-thin-layer structures. In addition, by solving the Christoffel equation to calculate the mapping relationship between the sound velocity and propagation angle of anisotropic materials and substituting it into the above model, the measurement of multi-thin-layer anisotropic material parameters can be realized. In the above methods, ultrasonic waves are excited and received through contact or immersion piezoelectric ultrasonic transducers. The sample needs to be immersed in water or coated with a liquid couplant, and problems such as depolarization of the piezoelectric transducer and drying of the couplant will occur under harsh working conditions such as high temperature. Therefore, the above ultrasonic measurement methods cannot achieve in-situ non-destructive measurement of the elastic parameters of the materials inside the multi-thin-layer heterostructure. Laser ultrasonic technology uses lasers to achieve non-contact excitation and reception of ultrasonic waves, and is expected to realize the characterization of the elastic parameters of the materials inside the multi-thin-layer heterostructure under high temperature conditions. Currently, relevant research mainly uses two lasers placed on the same side or opposite sides of the measured sample to excite and receive ultrasonic field signals at different positions, extracts information such as the laser ultrasonic transmission coefficient spectrum, zero group velocity laser ultrasonic Lamb wave mode, and laser ultrasonic surface wave dispersion characteristics from them, and combines multi-parameter optimization algorithms for iterative calculation to perform material parameter inversion. However, the current research usually only inverses the thickness of the material or the sound velocity of a single mode, and cannot obtain the complete material elastic parameters; or requires the measured material to be located on the surface or near the surface of the multi-thin-layer heterostructure and cannot measure the materials inside the interlayer.

[0005] Upon analysis, the existing technologies mainly have the following defects: 1) Mechanical measurement methods based on mechanical stretching, dynamic mechanical analysis, etc. of bulk materials are non-in-situ measurements and cannot accurately invert the evolution process of the elastic parameters of the materials in the multi-thin-layer heterostructure under actual working conditions.

[0006] 2) Methods such as shear tests based on multi-thin-layer heterostructures belong to destructive measurements, with high sample preparation and testing costs, long time cycles, and unable to directly obtain the specific numerical values and evolution processes of the material elastic parameters of the same sample.

[0007] 3) The method based on ultrasonic transmission / reflection coefficient spectra requires an additional standard bulk material to obtain a reference signal, needs to accurately adjust and measure the ultrasonic incident angle, and is easily affected by factors such as the surface roughness of the sample.

[0008] 4) Traditional ultrasonic measurement methods based on contact or immersion piezoelectric ultrasonic transducers require a liquid coupling medium and have the problem of transducer depolarization at high temperatures, and cannot achieve non-contact measurement and in-situ measurement under harsh conditions such as high temperatures; In summary, the existing laser ultrasonic measurement methods cannot measure the complete elastic parameters of the internal materials of the interlayers in multi-thin-layer heterostructures. Therefore, it is necessary to further provide an improved solution to achieve in-situ non-destructive measurement of the elastic parameters of the internal materials of multi-thin-layer heterostructures. Summary of the Invention

[0009] The object of the present invention is to overcome the defects of the above-mentioned prior art and provide a method, medium, and device for in-situ non-destructive measurement of the elastic parameters of multi-thin-layer heterogeneous materials.

[0010] According to the first aspect of the present invention, there is provided a method for in-situ non-destructive measurement of the elastic parameters of multi-thin-layer heterogeneous materials. The method includes the following steps: For the structure to be measured, establish a multi-parameter model of multi-mode ultrasonic propagation and calculate the theoretical values of the propagation time corresponding to each ultrasonic mode, where the structure to be measured is a multi-thin-layer heterostructure; Perform laser ultrasonic linear scanning on the structure to be measured, collect ultrasonic signals of each ultrasonic mode propagating in different directions, and obtain a line-scanned ultrasonic data set; For a selected ultrasonic mode, extract the experimental values of the propagation time under different excitation-reception point combinations from the ultrasonic signals in the line-scanned ultrasonic data set; For the selected ultrasonic mode, use a parameter optimization algorithm to invert the elastic parameters of the structure to be measured with the objective of minimizing the difference between its theoretical value of the propagation time and the experimental value of the propagation time.

[0011] According to the second aspect of the present invention, there is provided a computer-readable storage medium, on which a computer program is stored, where the computer program, when executed by a processor, implements the steps of the above-mentioned method for in-situ non-destructive measurement of the elastic parameters of multi-thin-layer heterogeneous materials.

[0012] According to a third aspect of the present invention, there is provided a computer device including a memory and a processor, and a computer program capable of running on the processor is stored on the memory. Wherein, when the processor executes the computer program, the steps of the above-mentioned in-situ non-destructive measurement method for elastic parameters of multi-thin-layer heterogeneous materials are implemented.

[0013] Compared with the prior art, the advantages of the present invention are as follows. The provided in-situ non-destructive measurement method for elastic parameters of multi-thin-layer heterogeneous materials based on non-contact laser ultrasonic technology first establishes a multi-parameter model for multi-mode ultrasonic propagation in a multi-thin-layer heterogeneous structure, and calculates the propagation time of each transmitted ultrasonic mode at different relative positions of the excitation / receiving points; then sets laser ultrasonic excitation and receiving points on both sides of the structure to be measured, linearly scans the excitation or receiving points, and collects ultrasonic signals under each pair of excitation / receiving point combinations; then selects a suitable transmitted ultrasonic mode, extracts the corresponding experimental value of the propagation time from the experimentally collected ultrasonic signals, and compares it with the theoretically calculated value, and iteratively inversely calculates the elastic parameters and thickness of the material to be measured with the help of a target optimization algorithm. The present invention can realize long-distance and non-contact measurement, realize in-situ non-destructive measurement under working conditions such as high temperature during material reliability evaluation and actual service process, and can realize the monitoring of the evolution of elastic parameters of the same sample.

[0014] Other features and advantages of the present invention will become clear through the following detailed description of exemplary embodiments of the present invention with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] The drawings incorporated in the specification and constituting a part of the specification illustrate embodiments of the present invention and, together with the description, are used to explain the principles of the present invention.

[0016] Figure 1 is a flowchart of an in-situ non-destructive measurement method for elastic parameters of multi-thin-layer heterogeneous materials based on non-contact laser ultrasonic technology according to an embodiment of the present invention; Figure 2 is a schematic diagram showing the variation law of the group velocity of ultrasonic body waves in single crystal silicon with the propagation direction angle according to an embodiment of the present invention; Figure 3 is a schematic diagram of the ultrasonic wave propagation path inside a "silicon-UF-silicon" multi-thin-layer heterogeneous structure according to an embodiment of the present invention; Figure 4 is a schematic diagram of an in-situ non-destructive measurement device for elastic parameters of multi-thin-layer heterogeneous materials based on non-contact laser ultrasonic technology according to an embodiment of the present invention; Figure 5 is a schematic diagram of the finite element simulation ultrasonic B-scan image and the propagation time distribution results of the first 12 ultrasonic transmission modes according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0017] 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 arrangements of components and steps, numerical expressions, and numerical values set forth in these embodiments do not limit the scope of the present invention.

[0018] The following description of at least one exemplary embodiment is merely illustrative in nature and is in no way a limitation on the present invention or its application or use.

[0019] Technologies, methods, and devices known to those of ordinary skill in the relevant art may not be discussed in detail, but where appropriate, such technologies, methods, and devices should be regarded as part of the specification.

[0020] In all the examples shown and discussed herein, any specific values should be construed as merely exemplary and not as a limitation. Thus, other examples of the exemplary embodiments may have different values.

[0021] It should be noted that: like reference numerals and letters denote like items in the following drawings, and thus, once an item is defined in one drawing, further discussion thereof is not required in subsequent drawings.

[0022] The in-situ non-destructive measurement method for elastic parameters of multi-thin-layer heterogeneous materials based on non-contact laser ultrasonic technology provided by the present invention generally includes: for a multi-thin-layer heterogeneous structure, establishing a multi-mode ultrasonic propagation multi-parameter model, where the parameters include the thickness of each layer of material, elastic parameters (such as Young's modulus, Poisson's ratio, independent elastic constants of anisotropic materials, etc.), and the orientation angle of anisotropic materials (if any), and calculating the propagation time of each transmitted ultrasonic mode signal at different relative distances between the excitation / reception points; using the established all-optical non-contact laser ultrasonic excitation and reception measurement device to perform multi-point line scanning on the structure to be measured, and collecting multi-mode ultrasonic signals propagating in different directions in an ultrasonic transmission manner; selecting a suitable ultrasonic mode, and extracting the propagation time under different excitation / reception point combinations from the experimentally collected ultrasonic signals; aiming at minimizing the error between the experimental value and the calculated value of the propagation time of the selected ultrasonic mode using the theoretical model, using a parameter optimization algorithm for iterative optimization to invert the material parameters to be measured.

[0023] Hereinafter, a multi-thin-layer heterogeneous structure "silicon-UF-silicon" commonly used in the research and development of underfill (UF) materials in the field of electronic packaging will be taken as an example for detailed description.

[0024] Specifically, referring to Figure 1 as shown, the in-situ non-destructive measurement method for elastic parameters of multi-thin-layer heterogeneous materials based on non-contact laser ultrasonic technology includes the following steps: Step S1: For a multi-thin-layer heterostructure, establish a multi-parameter model of multi-mode ultrasonic propagation and calculate the theoretical propagation time of each transmitted ultrasonic mode.

[0025] For example, the multi-parameters include the thickness of each layer of material, elastic parameters (such as Young's modulus, Poisson's ratio, independent elastic constants of anisotropic materials, etc.), and the orientation angle of anisotropic materials (if any).

[0026] In an isotropic linear elastic solid medium, body waves include longitudinal (L) and transverse (T) wave modes, and their corresponding sound velocities can be calculated by the following formulas: (1) (2) where and are the sound velocities of the longitudinal and transverse waves respectively, is Young's modulus, is Poisson's ratio, is the density. Similarly, Young's modulus and Poisson's ratio of the material can be calculated from the density and the longitudinal and transverse wave sound velocities: (3) (4) In an anisotropic solid, body waves include a quasi-longitudinal wave and two quasi-transverse wave modes with different polarization directions, and their sound velocities can be obtained by solving the Christoffel equation using the density and the complete independent elastic constants. Taking single-crystalline silicon (Si) in the cubic crystal system as an example, assuming that the <100> crystal direction family is parallel to the three coordinate axes of the Cartesian coordinate system, its anisotropic elastic parameters can be characterized by a 6×6 elastic stiffness matrix which contains 3 independent elastic constants , , and can be expressed as follows:

[0027] Figure 2 is the variation law of the group velocity of the 3 ultrasonic body wave modes propagating inside single-crystalline silicon with the propagation direction angle, including the quasi-longitudinal wave (Quasi Pressure, QP), the quasi-transverse wave with vertical polarization (Quasi Shear Vertical, QSV), and the quasi-transverse wave with horizontal polarization (Quasi Shear Horizontal). Among them, the 3 independent elastic constants and the density of silicon are respectively = 165.6 GPa, = 63.9 GPa, = 79.5 GPa, = 2330 kg / m 3 .

[0028] Figure 3 This is a schematic diagram of the ultrasonic propagation path inside the "Silicon-UF-Silicon" multi-thin layer heterostructure, where is the location of the ultrasonic excitation point, is the position of the ultrasound receiving point, It is The thickness of the layer material, Ultrasound is the first In this model, the upper and lower layers of the structure to be tested are both single crystal silicon with (001) orientation, and <100> The crystal orientation family is parallel to the three coordinate axes of the Cartesian coordinate system. A series of equally spaced laser ultrasonic excitation points are set in the direction parallel to the silicon

[100] direction to generate multi-mode ultrasonic signals; a laser ultrasonic receiving point is set on the surface of the structure to be tested on the opposite side of the center of the ultrasonic excitation point array to detect the out-of-plane components of the multi-mode ultrasonic transmission signal propagating in different directions. When the excitation point array direction is parallel to the main symmetry axis direction of silicon, and the excitation point array and the receiving point are located on the symmetry plane of silicon, all received ultrasonic modes propagate in the incident plane, so the model can be simplified to a two-dimensional model, and at this time the vibration direction of the QSH mode of silicon is in the in-plane direction and is not included in the received ultrasonic signal.

[0029] When ultrasound is incident obliquely on two solid interfaces with different acoustic impedances, reflection, refraction and mode conversion phenomena will occur. When the ultrasound propagation medium is uniform relative to the ultrasound wavelength, the propagation of ultrasound can be approximated as a series of rays passing through the excitation point and the receiving point. For the selected transmission ultrasound mode , its propagation time It can be calculated by the following formula: (6) in, and The ultrasonic wave of this mode is The group velocity and propagation angle in the layer, For the The thickness of the layer, is the number of layers. According to the relative position relationship between the excitation point and the receiving point, the propagation angle of the ultrasonic wave in each layer satisfies the following constraints: (7) For example, for a three-layer structure with N=3, in addition to the above constraints, two additional propagation angle constraints are still required to fully describe the propagation path of the transmission ultrasound mode. The following provides corresponding propagation angle constraint calculation methods for each possible situation: 1) For the case where both sides of the interface are isotropic media, the relationship between the ultrasonic propagation angles on both sides of the interface can be described by Snell's law: (8) where and are the phase velocities of this mode in the materials on both sides of the interface.

[0030] 2) For the case where anisotropic materials are included on both sides of the interface, since the phase velocity (determining the refraction angle) and the group velocity (determining the propagation time) of the anisotropic material are not equal, and the variation law of the sound velocity with the propagation angle is difficult to express by an analytical formula, it is extremely difficult to use Snell's law to calculate the propagation path. At this time, ray tracing methods such as the Dijkstra algorithm can be used to calculate the constraint conditions of the remaining propagation angles.

[0031] 3) For the structure in this embodiment, since the materials and orientations of the upper and lower silicon layers are the same, when the selected propagation modes of the transmitted ultrasonic waves in the two silicon layers are the same (such as QP→L→QP, QSV→T→QSV, etc.), the group velocity and propagation direction of this mode in the two silicon layers are the same: (9) (10) At this time, the propagation angle of this mode in the second layer can be calculated by the following formula: (11) Substituting the above constraint conditions into formula (4), the propagation time of the ultrasonic transmission mode can be expressed as a function of : (12) Formula (12) gives all possible propagation times of the ultrasonic transmission mode under the conditions of passing through the excitation point and the receiving point . According to Fermat's theorem, the propagation time of this mode is the minimum value of the above possible propagation times: (13) Based on formula (13), only one propagation angle needs to be searched to solve the propagation path and time of the selected ultrasonic transmission mode in the structure to be measured.

[0032] Step S2, construct a measurement device, perform a linear scan of laser ultrasound, collect multi-mode ultrasonic signals propagating in different directions, and obtain a line-scan ultrasound data set.

[0033] Figure 4 It is a schematic diagram of an in-situ non-destructive measurement device for elastic parameters of multi-thin-layer heterogeneous materials based on non-contact laser ultrasonic technology. The device mainly includes a pulsed laser 10, a laser attenuator 20, a laser focusing component 30, a moving platform 40, a sample to be measured 50, an ultrasonic receiving unit 60, a signal acquisition and control unit 70, and a calculation unit 80. Among them, the ultrasonic receiving unit 60 is a device that can realize non-contact detection of ultrasonic signals, including but not limited to a laser Doppler vibrometer, a two-wave mixing laser interferometer, a confocal Fabry-Perot interferometer, etc. The signal acquisition and control unit 70 can realize the acquisition and storage of ultrasonic signals, and can send control instructions to other components based on synchronous signals, software control, etc., to coordinate and complete laser ultrasonic excitation, detection, acquisition, and scanning operations. When acquiring signals, an internal filter can be used to improve the signal-to-noise ratio of ultrasonic signals. The components that can be included include but are not limited to a computer, an acquisition card, an oscilloscope, a signal generator, etc.

[0034] Regarding the linear scanning function of laser ultrasound, the goals to be achieved are to locate the ultrasonic excitation point and the receiving point and to controllably adjust their relative positions. There are various specific implementation methods, including but not limited to: using a moving platform to load the ultrasonic receiving unit for translation or loading the pulsed laser and laser attenuation and focusing components for simultaneous translation; using a galvanometer to deflect the laser beam of the pulsed laser or the ultrasonic receiving unit; performing array splitting of the laser beam of the pulsed laser or the ultrasonic receiving unit in space and using devices such as an optical switch for switching, etc.

[0035] Combined with Figure 4 As shown, the working process of the provided measurement device mainly includes: Using the pulsed laser 10 to output excitation laser, which successively passes through the laser attenuator 20 and the laser focusing component 30 and irradiates the surface of the sample to be measured 50, forming a focused light spot with energy less than the laser damage threshold of the sample to be measured, and generating ultrasonic signals on the surface and inside of the sample; Using the ultrasonic receiving unit 60 to detect the ultrasonic signals on the opposite surface of the sample to be measured 50, and collecting and storing them by the signal acquisition and control unit 70; Controlling the moving platform 40 to perform a series of translations, changing the relative positions of the ultrasonic excitation point and the receiving point, and respectively collecting and storing ultrasonic signals; The calculation unit 80 reads a series of collected ultrasonic signal data, and performs subsequent multi-mode ultrasonic propagation time calculation and inversion calculation of the parameters of the material to be measured.

[0036] In summary, the ultrasonic signal excitation unit focuses a pulsed laser beam with controllable energy onto the surface of the structure to be measured, and generates multi-mode ultrasonic signals based on the laser ultrasonic thermoelastic effect. The ultrasonic signal detection unit uses a non-contact laser ultrasonic signal detection device to receive the ultrasonic signals on the opposite side of the structure to be measured. The scanning unit performs multi-point linear scanning on the ultrasonic excitation / reception points to obtain multi-mode ultrasonic signals propagating in different directions. The signal acquisition and control unit coordinately controls each excitation, detection, acquisition, and scanning unit based on software synchronization and signal synchronization. The calculation unit uses the established theoretical model to calculate the theoretical values of the propagation time of each mode of ultrasonic signal; extracts the experimental values of the propagation time of the selected ultrasonic mode from the collected ultrasonic signals; and minimizes the difference between the theoretical value and the experimental value of the propagation time of the selected ultrasonic mode based on the parameter optimization algorithm to invert the material parameters to be measured.

[0037] Step S3: Select a suitable ultrasonic mode, extract the propagation time under different excitation / reception point combinations from the experimentally collected ultrasonic signals, and obtain the experimental values of the propagation time under different excitation-reception point combinations.

[0038] In this step, it is first necessary to select a suitable ultrasonic mode for subsequent inversion of material parameters.

[0039] First, based on the approximate values of the thickness and sound velocity of each layer of material in the structure to be measured, and using the theoretical model in Step S1, calculate the propagation time of possible ultrasonic transmission modes at different relative positions of ultrasonic excitation / reception points, generate a pseudo ultrasonic B-scan image, and compare it with the B-scan image generated from experimental data to facilitate the identification of the appearance order of each mode and its shape in the B-scan image.

[0040] In one embodiment, for the selection of ultrasonic modes, the following conditions need to be met: 1) Among the selected multiple ultrasonic modes, all possible body wave modes in the material layer to be measured must be included. Taking the "silicon-UF-silicon" structure as an example, if the layer to be measured is an isotropic UF material, then the selected ultrasonic modes must include at least one mode propagating in the UF layer in the longitudinal wave and transverse wave modes respectively (such as: QP→L→QP and QSV→T→QSV).

[0041] 2) When selecting ultrasonic modes, modes with a relatively high proportion of propagation time in the total propagation time in the layer to be measured should be selected as much as possible. For example, multiple reflections occur in the layer to be measured, the wave propagates at a slower speed in the layer to be measured, and at a faster speed outside the layer to be measured.

[0042] 3) When selecting ultrasonic modes, signals with high signal-to-noise ratio and no aliasing with other modes should be selected as much as possible to facilitate the accurate extraction of the propagation time.

[0043] After identifying and selecting the appropriate ultrasonic mode, and on the premise of ensuring no waveform aliasing, the signal extreme values are extracted through a sliding window, the autocorrelation method, and other image processing methods, and the peak time within each ultrasonic time-domain waveform of the selected mode and the relative distance between the corresponding ultrasonic excitation / reception points are extracted and recorded.

[0044] Step S4, use a parameter optimization algorithm to invert the elastic parameters and thickness of the material to be measured.

[0045] Specifically, select the sound velocities of all longitudinal and transverse wave modes (group velocity for anisotropic materials) of the material layer to be measured and the thickness as variables , input them into the theoretical model provided in step S1, and calculate the theoretical propagation time of the selected ultrasonic mode at different relative positions of the excitation / reception points. . Use an optimization algorithm to iteratively update the variables so that the theoretical value of the propagation time calculated based on the current parameters and the experimental value of the propagation time extracted in step S3 The difference (i.e., the objective function of the inversion problem ) is minimized, and then the variables are the optimal values.

[0046] In one embodiment, the objective function of the inversion problem can be defined as the sum of the two-norms of the differences between the experimental values and the theoretical values of the propagation time for each selected ultrasonic mode, expressed as follows: (14) As can be seen from the above formula, the closer the variable is to the actual value, the smaller the value of the function . Therefore, parameter optimization algorithms such as particle swarm optimization algorithm, genetic algorithm, simulated annealing algorithm, ant colony algorithm, etc. can be used to minimize the objective function, thereby determining the parameters to be measured.

[0047] Finally, based on the density of the material to be measured and the longitudinal and transverse wave sound velocities obtained by inversion, the Young's modulus and Poisson's ratio of the isotropic material to be measured can be calculated through formulas (3) and (4) in step S1, or the elastic constants of the anisotropic material to be measured can be calculated by solving the Christoffel equation. Among them, the density of the material to be measured can be measured by methods such as a density balance or the Archimedes drainage method.

[0048] In order to further verify the effect of the present invention, a specific scenario was selected for finite element simulation and experimental verification to measure the thickness, Young's modulus, Poisson's ratio, etc. of the UF material in the "silicon-UF-silicon" structure.

[0049] First, perform finite element simulations on the laser ultrasonic transmission line scanning experiment of silicon-UF-silicon using COMSOL software or other software, and perform multi-parameter inversion using the simulation data. The ultrasonic B-scan image obtained from the simulation and the propagation time distribution of the first 12 transmission ultrasonic modes with the shortest propagation time are as Figure 5 shown. Each transmission ultrasonic mode is named with three groups of letters representing its propagation mode in the three layers. Among them, P and V represent the QP and QSV modes in silicon, respectively, and L and T represent the longitudinal wave (L) and transverse wave (T) modes in UF, respectively. Three consecutive letters indicate that the ultrasonic wave of this mode has undergone two in-layer reflections continuously in one layer of material, and the corresponding propagation time is three times the single-layer propagation time. For example, "P-L-V" indicates that the propagation form of this mode in the three-layer structure is "QP → L → QSV" or "QSV → L → QP"; "P-LLL-P" corresponds to the case of "QP → (L → L → L) → QP". From Figure 5 it can be seen that the lines corresponding to the propagation times of the calculated transmission ultrasonic modes are highly consistent with the corresponding patterns in the B-scan image, reflecting the accuracy of the given theoretical model. According to the ultrasonic mode selection criteria given above, three modes, namely "P-L-P", "P-T-P", and "V-LLL-V", were selected for parameter inversion. In the ultrasonic transmission dataset obtained from the simulation, extract the propagation times of these three modes at different relative positions of the ultrasonic excitation / receiving points, use the particle swarm algorithm to iteratively invert the thickness and longitudinal and transverse wave velocities of the UF material, and calculate the Young's modulus and Poisson's ratio based on the set density value. The finite element simulation set values, inversion values, and relative errors of each material parameter are shown in Table 1. The inversion error of each parameter is less than 0.548%, indicating that this method can accurately measure the material thickness and elastic parameters in a multi-thin-layer heterogeneous structure.

[0050] Table 1: Finite element simulation set values and inversion results of each material parameter

[0051] In the experimental verification, three UF materials with different filler ratios were selected for experimental verification. Among them, the filler ratios of UF-1, UF-2, and UF-3 increase in sequence, and the corresponding density, sound velocity, and Young's modulus are also theoretically increased in sequence. For the bulk samples of the same batch and the same preparation process, the Archimedes drainage method was used to measure the material density for the subsequent conversion of sound velocity and elastic parameters; an ultrasonic probe with a center frequency of 125 MHz was used to conduct ultrasonic reflection tests at a sampling rate of 5 GHz, and the longitudinal wave sound velocity of the material was calculated based on the sample thickness and the occurrence times of multiple surface reflection echoes as the reference value. The thickness of UF in the "silicon-UF-silicon" multi-thin-layer heterostructure sample was obtained by measuring the total thickness of the sample using a micrometer and subtracting the thickness of the silicon wafer. Similar to the finite element simulation process, laser ultrasonic transmission experiments and material parameter inversion were carried out on the three samples to be measured, and the corresponding results are shown in Table 2. Among the three groups of experimental results, the inversion results of the material thickness and longitudinal wave sound velocity are also relatively close to the reference values, with a relative error less than 3.722%. Moreover, the variation laws of the sound velocity and elastic parameters of the three UF materials conform to the trend of the change in the filler ratio, indicating that this method can accurately measure the material thickness and elastic parameters in the multi-thin-layer heterostructure and can distinguish the elastic parameter differences caused by material component differences. This result also shows that the measurement method given by the present invention can accurately measure the material elastic parameters within a certain range of material elastic parameter changes and is expected to be applied to continuous in-situ non-destructive measurement in the process of material reliability analysis.

[0052] Table 2: Reference values and experimental inversion results of each material parameter

[0053] It should be noted that, without departing from the spirit and scope of the present invention, those skilled in the art can make appropriate changes or modifications to the above embodiments. For example, the ultrasonic receiving unit in the measuring device is a device capable of realizing non-contact detection of ultrasonic signals, including but not limited to laser Doppler vibrometers, dual-wave mixing laser interferometers, confocal Fabry-Perot interferometers, etc. The scanning unit in the measuring device can realize the positioning of ultrasonic excitation points and receiving points and the controllable adjustment of the relative positions. The specific implementation methods include but are not limited to: using a moving platform to load the ultrasonic receiving unit for translation or loading a pulsed laser and laser attenuation and focusing components for simultaneous translation; using a galvanometer to deflect the laser beam of the pulsed laser or the ultrasonic receiving unit; performing array splitting of the laser beam of the pulsed laser or the ultrasonic receiving unit in space and using devices such as optical switches for switching, etc. Another example is that the objective function for the inversion of the parameters of the material to be measured is the sum of the two-norms of the differences between the experimental values and the theoretical values of the propagation times of each selected ultrasonic mode. Its goal is to minimize the difference (or maximize the similarity) between the theoretical value and the experimental value of the propagation time of the selected transmitted ultrasonic mode, and any function that can achieve the above goal can be used as the objective function. Another example is that the inversion algorithm used in the present invention for measuring the elastic parameters of the material to be measured is used to solve the global maximum value of the objective function within the search range of the variables to be measured, and it can be a parameter optimization algorithm such as a particle swarm algorithm, a genetic algorithm, a simulated annealing algorithm, an ant colony algorithm, or other inversion algorithms.

[0054] In summary, compared with the prior art, the present invention mainly has the following advantages: 1) Based on laser ultrasonic technology, the present invention can achieve long-distance and non-contact measurement, can realize in-situ non-destructive measurement under high-temperature and other working conditions during material reliability assessment and actual service process, and can monitor the evolution of the elastic parameters of the same sample.

[0055] 2) The present invention uses a pulsed laser to simultaneously generate multiple-mode ultrasonic signals propagating in different directions in a multi-thin-layer heterogeneous structure, without the need to use multiple ultrasonic transducers or adjust the sample angle, avoiding the signal consistency problem caused by multiple adjustments.

[0056] 3) By linearly scanning the laser ultrasonic excitation / receiving points, the present invention can obtain ultrasonic signals propagating in different directions. Only the relative distance between the scanning points needs to be set, without the need to accurately measure the sample angle, and the operation is simpler.

[0057] 4) The present invention can realize the in-situ measurement of the elastic parameters of the interlayer material inside the multi-thin-layer heterogeneous structure, without the sample being exposed, and the measurement accuracy is high.

[0058] 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 having computer-readable program instructions thereon for causing a processor to implement aspects of the present invention.

[0059] A computer-readable storage medium may be a tangible device that can retain and store instructions for use by an instruction execution device. A computer-readable storage medium may be, for example, but is 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 of the foregoing. More specific examples (a non-exhaustive list) of the 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 disc (DVD), a memory stick, a floppy disk, a mechanically encoded device such as a punch card or raised structures in grooves having instructions stored thereon, and any suitable combination of the foregoing. The computer-readable storage medium as used herein is not to be construed as a transitory signal per se, such as a radio wave or other freely propagating electromagnetic wave, an electromagnetic wave propagating through a waveguide or other transmission medium (e.g., a light pulse through an optical fiber cable), or an electrical signal transmitted through a wire.

[0060] The computer-readable program instructions described herein may be downloaded to each computing / processing device from a computer-readable storage medium or may be downloaded to an external computer or external storage device through a network, such as the Internet, a local area network, a wide area network, and / or a wireless network. The network may include copper transmission cables, optical fiber transmission, wireless transmission, routers, firewalls, switches, gateway computers, and / or edge servers. A 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 for storage in a computer-readable storage medium in each computing / processing device.

[0061] The computer program instructions for performing the operations of the present invention may be assembly instructions, instruction set architecture (ISA) instructions, machine instructions, machine - related 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, etc., and conventional procedural programming languages such as the "C" language or similar programming languages. The computer - readable program instructions may be executed entirely on the user's computer, partially on the user's computer, executed as a stand - alone software package, partially on the user's computer and partially on a remote computer, or entirely on a remote computer or server. In the case of a remote computer, the remote computer may be connected to the user's computer through any type of network, including a local area network (LAN) or a wide area network (WAN), or, alternatively, may be connected to an external computer (e.g., via an Internet service provider through the Internet). In some embodiments, by using the state information of the computer - readable program instructions to customize an electronic circuit, such as a programmable logic circuit, a field - programmable gate array (FPGA), or a programmable logic array (PLA), the electronic circuit can execute the computer - readable program instructions to implement various aspects of the present invention.

[0062] Aspects of the present invention are described herein with reference to the flowchart and / or block diagram of a method, apparatus (system), and computer program product according to embodiments of the present invention. It should be understood that each block of the flowchart and / or block diagram, and combinations of blocks in the flowchart and / or block diagram, can be implemented by computer - readable program instructions.

[0063] 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 apparatus to produce a machine such that the instructions, when executed by the processor of the computer or other programmable data - processing apparatus, create a means for implementing the functions / actions specified in one or more blocks of the flowchart and / or block diagram. These computer - readable program instructions can also be stored in a computer - readable storage medium, which causes a computer, a programmable data - processing apparatus, and / or other devices to operate in a particular manner, so that the computer - readable medium storing the instructions includes a manufacture, which includes instructions for implementing various aspects of the functions / actions specified in one or more blocks of the flowchart and / or block diagram.

[0064] Computer-readable program instructions may also be loaded onto a computer, other programmable data processing apparatus, or other devices, causing a series of operational steps to be performed on the computer, other programmable data processing apparatus, or other devices to produce a computer-implemented process such that the instructions executed on the computer, other programmable data processing apparatus, or other devices implement the functions / acts specified in one or more boxes of the flowchart and / or block diagram.

[0065] The flowcharts and block diagrams in the figures illustrate the architecture, functionality, and operation of possible implementations of systems, methods, and computer program products according to various embodiments of the present invention. In this regard, each block in the flowchart or block diagram may represent a module, a segment of a program, or a portion of an instruction, which contains one or more executable instructions for implementing the specified logical function. In some alternative implementations, the functions noted in the blocks may occur out of the order noted in the figures. For example, two consecutive blocks may in fact be executed substantially in parallel, or they may sometimes be executed in the reverse order, depending on the functionality involved. It should also be noted that each block of the block diagrams and / or flowcharts, and combinations of blocks in the block diagrams and / or flowcharts, can be implemented by a dedicated hardware-based system that performs the specified functions or acts, or by a combination of dedicated hardware and computer instructions. As is well known to those skilled in the art, implementation by hardware, implementation by software, and implementation by a combination of software and hardware are equivalent.

[0066] The embodiments of the present invention have been described above. The above description is exemplary, not exhaustive, and is not limited to the disclosed embodiments. Many modifications and variations will be apparent to those of ordinary skill in the art in the technical field without departing from the scope and spirit of the described embodiments. The selection of the terms used herein is intended to best explain the principles of the embodiments, the practical application, or the improvement of the technology in the market, or to enable other ordinary skilled persons in the technical field to understand the embodiments disclosed herein. The scope of the present invention is defined by the appended claims.

Claims

1. An in-situ non-destructive measurement method for elastic parameters of a multi-thin-layer heterogeneous material, characterized in that The method comprises the following steps: For a structure to be measured, a multi-parameter model of multi-mode ultrasonic propagation is established, and theoretical values of propagation times corresponding to each ultrasonic mode are calculated, wherein the structure to be measured is a multi-thin-layer heterogeneous structure; Perform laser ultrasonic linear scanning on the structure to be measured, collect ultrasonic signals of each ultrasonic mode propagating in different directions, and obtain a line-scan ultrasonic data set; For a selected ultrasonic mode, extract experimental values of propagation times under different excitation-reception point combinations from the ultrasonic signals in the line-scan ultrasonic data set; For the selected ultrasonic mode, with minimizing the difference between its theoretical value of propagation time and the experimental value of propagation time as the objective function, use a parameter optimization algorithm to inversely calculate the elastic parameters of the structure to be measured.

2. The method according to claim 1, characterized in that, The objective function is set as: Among them, is the objective function, is a multi-parameter variable, including the sound velocities and thickness of all longitudinal and transverse wave modes of the structure to be measured ， is the selected ultrasonic mode is the theoretical value of the propagation time at different relative positions of the excitation-reception points, is the selected ultrasonic mode is the experimental value of the propagation time corresponding thereto, represents the two-norm, is the position of the ultrasonic excitation point.

3. The method according to claim 1, wherein Performing laser ultrasonic linear scanning on the structure to be measured is realized through a constructed measuring device, and the measuring device includes an ultrasonic signal excitation unit, an ultrasonic signal detection unit, a scanning unit, a signal acquisition and control unit, and a calculation unit, wherein: The ultrasonic signal excitation unit includes a pulsed laser, a laser attenuation component, and a laser focusing component, and is used to focus the pulsed laser onto the surface of the structure to be measured, adjust the laser energy, form a focused light spot with energy less than the laser damage threshold of the structure to be measured, and generate ultrasonic signals on and inside the surface of the structure to be measured based on the laser ultrasonic thermoelastic mechanism; The ultrasonic signal detection unit uses a laser beam focused on the surface of the structure to be measured to realize non-contact detection of ultrasonic signals; The scanning unit is used to realize the scanning of the relative positions of the ultrasonic excitation point and the reception point to obtain a multi-mode ultrasonic signal data set propagating in different directions; The signal acquisition and control unit is used to realize the acquisition and storage of ultrasonic signals, coordinate and complete laser ultrasonic excitation, detection, acquisition, and scanning operations, and use a built-in filter to improve the signal-to-noise ratio of ultrasonic signals during signal acquisition; The calculation unit is responsible for the post-processing of the ultrasonic signal data set, and uses a parameter optimization algorithm to inversely calculate the elastic parameters and thickness of the structure to be measured.

4. The method according to claim 1, wherein The theoretical values of propagation times corresponding to each ultrasonic mode are calculated according to the following steps: Based on the isotropic elastic wave sound speed calculation formula and the Christoffel equation of anisotropic elastic waves, convert the elastic parameters of each layer of material of the structure to be measured into the sound speeds of longitudinal and transverse elastic wave modes, wherein for the sound speed of anisotropic materials, the group velocity is taken, which is expressed as a discrete mapping with respect to the propagation angle; Based on the sound velocity and thickness of each layer of material, an ultrasonic transmission propagation model is established, and then for the selected ultrasonic mode , according to the following formula, calculate its propagation time when the ultrasonic excitation point coordinates are , and the receiving point coordinates are : Among them, and are respectively the group velocity and propagation angle of the ultrasonic wave in the ultrasonic mode in the layer, is the thickness of the layer, is the number of layers of the structure to be measured; According to the relative position relationship between the excitation point and the reception point, give the constraint conditions between the propagation angles of the ultrasonic waves of the selected ultrasonic mode in each layer, which are expressed as: According to the isotropic and anisotropic characteristics of the materials on both sides of each layer interface, solve the constraint conditions of the remaining propagation angles, wherein the number of constraint conditions to be calculated is the number of layers of the structure to be measured minus 1; Substitute all the constraint conditions of the propagation angle into 's calculation formula to obtain the theoretical value of the propagation time of the selected ultrasonic mode.

5. The method according to claim 1, wherein During the process of performing laser ultrasonic linear scanning on the structure to be measured, fix one end of the ultrasonic excitation point or the reception point, linearly scan the other end at a fixed interval, and collect ultrasonic signals at each scanning point, and finally form the line-scan ultrasonic data set.

6. The method according to claim 4, wherein The ultrasonic mode is selected according to the following steps: Among the selected multiple ultrasonic modes, all possible body wave modes in the material containing the structure to be measured are included; Select the ultrasonic modes in the layer to be measured whose proportion of the propagation time in the total propagation time is higher than the set threshold; Select the ultrasonic modes with a signal-to-noise ratio higher than the set threshold and not aliased with other modes.

7. The method according to claim 1, characterized in that For each ultrasonic mode, the experimental value of the propagation time is obtained according to the following steps: On the premise of no waveform aliasing, through image processing, extract the peak time of the selected ultrasonic mode in each ultrasonic time-domain waveform and the relative distance between the corresponding ultrasonic excitation-receiving points, and then calculate the corresponding experimental value of the propagation time.

8. The method according to claim 4, characterized in that The use of the parameter optimization algorithm to invert the elastic parameters of the structure to be measured includes: For the structure to be measured of isotropic material, calculate the Young's modulus and Poisson's ratio based on the following formula: wherein, is the sound velocity of the longitudinal wave mode of the isotropic material, the sound velocity of the transverse wave of the isotropic material, is the Poisson's ratio, and are respectively expressed as: wherein, is the Young's modulus, is the Poisson's ratio, is the density; For the structure to be measured of anisotropic material, calculate the elastic constants of the structure to be measured by solving the Christoffel equation.

9. A computer-readable storage medium having a computer program stored thereon, characterized in that, When the computer program is executed by a processor, it implements the steps of the method according to any one of claims 1 to 8.

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

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