In-situ non-destructive measurement method, medium and device for elastic parameters of multi-thin-layer heterogeneous materials

Abstract

The application discloses a kind of multi-thin-layer heterogeneous material elastic parameter in-situ nondestructive measurement method, medium and equipment, belong to ultrasonic measurement technical field.The method includes: for the structure to be measured, establish multi-mode ultrasonic propagation multi-parameter model, and calculate the propagation time theoretical value corresponding to each ultrasonic mode, the structure to be measured is multi-thin-layer heterogeneous structure;For the structure to be measured, laser ultrasonic linear scanning is carried out, and the ultrasonic signals of each ultrasonic mode propagating along different directions are collected to obtain linear scanning ultrasonic data set;For selected ultrasonic mode, the propagation time experimental value under different excitation-receiving point combinations is extracted in the ultrasonic signal of the linear scanning ultrasonic data set;For the selected ultrasonic mode, the difference between the propagation time theoretical value and the propagation time experimental value is used as the objective function to minimize, and the elastic parameters of the structure to be measured are inverted using parameter optimization algorithm.The application can realize long-distance, non-contact in-situ nondestructive measurement, and simple operation.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of ultrasonic measurement, and more particularly to a method, medium and device for in-situ non-destructive measurement of elastic parameters of a multi-layered heterogeneous material. BACKGROUND

[0002] Multi-layered heterogeneous structures are widely used in the industries of electronic packaging, aerospace, etc. due to their ability to simultaneously exhibit the properties of multiple materials. However, the materials in different layers of the multi-layered heterogeneous structure usually have different mechanical properties such as elastic parameters and thermal expansion coefficients, and may be subjected to complex working conditions such as high-low temperature alternation and external corrosion during service, which can easily lead to degradation of the mechanical properties of the materials and thus cause phenomena such as delamination and fracture, seriously affecting the structural performance. In the process of material research and development, continuous non-destructive measurement of the dynamic evolution behavior of the elastic parameters of the materials in the multi-layered heterogeneous structure can reveal the failure mechanism of the materials and structure, which is crucial for improving the reliability of the multi-layered heterogeneous structure. Therefore, there is an urgent need for a method for measuring and evaluating the evolution of the elastic parameters of the materials in the multi-layered heterogeneous structure. However, the materials in the internal layers of the multi-layered heterogeneous structure cannot be exposed to the outside, making it difficult to directly measure them by traditional methods. Therefore, how to in-situ non-destructively measure the elastic parameters of the materials in the multi-layered heterogeneous structure is of great importance for material research and development and reliability evaluation.

[0003] Currently, a mainstream scheme for characterizing the elastic parameters of the materials in the multi-layered heterogeneous structure is to rely on mechanical tensile testing, dynamic mechanical analysis (DMA) and other methods to test on bulk samples. However, bulk material testing cannot accurately reflect the in-situ mechanical state of the materials in the multi-layered heterogeneous structure under multi-layered conditions during actual service, and thus cannot accurately characterize the mechanical performance evolution process of the internal materials during reliability testing or long-term service. Another method is to perform a shear test on the multi-layered heterogeneous structure sample to measure the shear strength of the sample, thereby indirectly characterizing the elastic parameters of the internal materials. However, this method is a destructive experiment, and thus requires the preparation of a large number of parallel samples in reliability analysis, which is costly and time-consuming, and cannot directly obtain the specific values and evolution process of the elastic parameters of the same sample. In order to meet the urgent need for in-situ non-destructive measurement of the elastic parameters of the materials in the multi-layered heterogeneous structure during the research and development process, a theoretical model of ultrasonic propagation can be established and combined with a multi-parameter inversion algorithm to obtain geometric and acoustic parameters such as the thickness, density, sound speed and attenuation coefficient of the thin layers in the multi-layered heterogeneous structure; and then calculate the elastic parameters such as Young's modulus and Poisson's ratio.

[0004] In the current ultrasonic measurement methods of multi-layered heterogeneous structure material parameters, one of them is the ultrasonic transmission / reflection coefficient spectrum method. This method uses the amplitude, phase or complex frequency spectrum ratio of the transmission / reflection signal and the reference signal to perform material parameter inversion. Compared with other methods based on the time domain signal of the interface reflection peak, the advantage of this method is that it can be not affected by the aliasing problem of the multi-layer interface signal. On this basis, by changing the ultrasonic incident angle, the angle-resolved transmission / reflection coefficient spectrum can be measured, and the complete longitudinal and transverse wave speeds, density and thin layer thickness can be obtained, so that the complete material elastic parameters can be obtained. The main disadvantage of this method is that an additional reference signal is needed to calibrate the incident ultrasonic 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 model of this method usually needs to assume that each layer of material in the multi-layer structure is isotropic, so it cannot handle structures containing anisotropic materials. Another method is the geometric acoustics method that regards the ultrasonic wave as a series of rays. This method is based on the geometric relationship between the ultrasonic excitation point and the detection point and the Snell law or the sound ray tracing method to calculate the propagation time of the ultrasonic signal in different modes after transmission, reflection, refraction and mode conversion, which can be used to measure the thin layer thickness, sound speed, elastic constant and other parameters in the multi-layer structure. In addition, by solving the Christoffel equation to calculate the mapping relationship between the anisotropic material sound speed and the propagation angle and substituting it into the above model, the measurement of the multi-layer anisotropic material parameters can be realized. In the above method, the ultrasonic wave is excited and received by a contact or water-immersed piezoelectric ultrasonic transducer, and the sample needs to be immersed in water or coated with a liquid coupling agent. In harsh conditions such as high temperature, problems such as depolarization of the piezoelectric transducer and drying of the coupling agent may occur. Therefore, the above ultrasonic measurement method cannot realize the in-situ non-destructive measurement of the internal material elastic parameters of the multi-layer heterogeneous structure. Laser ultrasonic technology uses laser to realize non-contact excitation and reception of ultrasonic waves, and is expected to realize the characterization of the internal material elastic parameters of the multi-layer heterogeneous structure under high temperature conditions. Current research mainly uses two lasers placed on the same side or opposite side of the sample to be measured to excite and receive ultrasonic wave field signals at different positions, extracts information such as laser ultrasonic transmission coefficient spectrum, zero group velocity laser ultrasonic Lamb wave mode and laser ultrasonic surface wave dispersion characteristics, and combines a multi-parameter optimization algorithm to iteratively calculate the material parameters. However, the current research usually only inverts the thickness or single-mode sound speed of the material, and cannot obtain the complete material elastic parameters; or requires the measured material to be on the surface or near the surface of the multi-layer heterogeneous structure, and cannot measure the material inside the interlayer.

[0005] Through analysis, the prior art mainly has the following defects:

[0006] 1) Mechanical measurement methods based on bulk materials, such as mechanical tension and dynamic mechanical analysis, are non-in-situ measurements and cannot accurately invert the evolution of elastic parameters of materials in multi-thin-layer heterostructures under actual working conditions.

[0007] 2) Methods such as shear tests based on multi-thin-layer heterostructures are destructive measurements, with high sample preparation and testing costs and long time cycles. Furthermore, they cannot directly obtain the specific values ​​and evolution process of the material elastic parameters of the same sample.

[0008] 3) The method based on ultrasonic transmission / reflection coefficient spectrum requires additional standard bulk material to obtain reference signal, and requires accurate adjustment and measurement of ultrasonic incident angle. It is also susceptible to factors such as sample surface roughness.

[0009] 4) Traditional ultrasonic measurement methods based on contact or water-immersion piezoelectric ultrasonic transducers require liquid coupling media and suffer from transducer depolarization at high temperatures, making it impossible to achieve non-contact measurement and in-situ measurement under harsh conditions such as high temperatures.

[0010] In summary, existing laser ultrasonic measurement methods cannot measure the complete elastic parameters of the internal materials of multi-layered heterostructures. Therefore, further improvements are needed to achieve in-situ non-destructive measurement of the elastic parameters of the internal materials of multi-layered heterostructures. Summary of the Invention

[0011] The purpose of this invention is to overcome the shortcomings of the prior art and provide a method, medium, and device for in-situ non-destructive measurement of elastic parameters of multi-thin-layer heterogeneous materials.

[0012] According to a first aspect of the present invention, an in-situ non-destructive measurement method for elastic parameters of multi-thin-layer heterogeneous materials is provided. The method includes the following steps:

[0013] For the structure under test, a multi-mode ultrasound propagation multi-parameter model is established, and the theoretical propagation time corresponding to each ultrasound mode is calculated. The structure under test is a multi-thin-layer heterostructure.

[0014] A laser ultrasonic linear scan is performed on the structure under test to collect ultrasonic signals of various ultrasonic modes propagating in different directions, thereby obtaining a linear scan ultrasonic dataset.

[0015] For a selected ultrasound mode, experimental propagation time values ​​under different excitation-receiver combinations are extracted from the ultrasound signals of the line scan ultrasound dataset.

[0016] For the selected ultrasound mode, the elastic parameters of the structure under test are derived using a parameter optimization algorithm with the objective function of minimizing the difference between the theoretical and experimental propagation times.

[0017] According to a second aspect of the present application, a computer readable storage medium is provided, having stored thereon a computer program, wherein the computer program, when executed by a processor, implements the steps of the above-mentioned in-situ non-destructive measurement method of elastic parameters of multi-thin-layer heterogeneous materials.

[0018] According to a third aspect of the present application, a computer device is provided, comprising a memory and a processor, and having stored on the memory a computer program capable of running on the processor, wherein the processor implements the steps of the above-mentioned in-situ non-destructive measurement method of elastic parameters of multi-thin-layer heterogeneous materials when executing the computer program.

[0019] Compared with the prior art, the in-situ non-destructive measurement method of elastic parameters of multi-thin-layer heterogeneous materials based on non-contact laser ultrasonic technology has the following advantages. First, a multi-parameter model of multi-mode ultrasonic propagation in a multi-thin-layer heterogeneous structure is established, and the propagation time of each transmitted ultrasonic mode under different relative positions of excitation / receiving points is calculated. Then, laser ultrasonic excitation and receiving points are arranged on both sides of the structure to be measured, and linear scanning is performed on the excitation or receiving points to collect ultrasonic signals under each pair of excitation / receiving point combination. Then, a suitable transmitted ultrasonic mode is selected, the corresponding propagation time experimental value is extracted from the collected ultrasonic signals, and compared with the theoretical calculation value. Finally, the elastic parameters and thickness of the material to be measured are iteratively inverted by means of a target optimization algorithm. The present application can realize remote and non-contact measurement, in-situ non-destructive measurement under high temperature and other working conditions during material reliability evaluation and actual service, and can realize the evolution monitoring of the material elastic parameters of the same sample.

[0020] Other features and advantages of the present application will become apparent from the following detailed description of exemplary embodiments thereof, taken in conjunction with the accompanying drawings. BRIEF DESCRIPTION OF DRAWINGS

[0021] The accompanying drawings incorporated in and forming a part of the specification, illustrate embodiments of the present application and, together with the description, serve to explain the principles of the application.

[0022] Figure 1 is a flowchart of the in-situ non-destructive measurement method of elastic parameters of multi-thin-layer heterogeneous materials based on non-contact laser ultrasonic technology according to an embodiment of the present application;

[0023] Figure 2 is a schematic diagram of the variation of the group velocity of ultrasonic bulk waves in a single crystal silicon with the propagation direction angle according to an embodiment of the present application;

[0024] Figure 3 is a schematic diagram of the ultrasonic wave propagation path in a "silicon-UF-silicon" multi-thin-layer heterogeneous structure according to an embodiment of the present application;

[0025] Figure 4Fig. 1 is a schematic diagram of a non-contact laser-ultrasound based multi-layered heterogeneous material elastic parameter in-situ non-destructive measurement device according to an embodiment of the present application;

[0026] Figure 5 Fig. 4 is a schematic diagram of finite element simulation ultrasound B-scan image and the first 12 ultrasound transmission mode propagation time distribution results according to an embodiment of the present application. DETAILED DESCRIPTION

[0027] Various exemplary embodiments of the present application will now be described in detail with reference to the accompanying drawings. It should be noted that the relative arrangement of components and steps, numerical expressions, and numerical values set forth in these embodiments are not limiting to the scope of the present application unless otherwise specifically stated.

[0028] The following description of at least one exemplary embodiment is merely exemplary in nature and is in no way intended to limit the scope of the application, its application, or uses.

[0029] Techniques, methods, and apparatus known to those of ordinary skill in the relevant art can not be discussed in detail herein. However, where appropriate, such techniques, methods, and apparatus should be considered as being part of the specification.

[0030] In all of the examples shown and discussed herein, any specific values should be interpreted as merely exemplary, and not as a limitation. Thus, other examples of exemplary embodiments can have different values.

[0031] It should be noted that like reference numerals and letters in the various figures indicate similar items, and thus, once any term is defined in one figure, it is not necessary to discuss it further in connection with other figures.

[0032] The non-contact laser-ultrasound based multi-layered heterogeneous material elastic parameter in-situ non-destructive measurement method provided by the present application generally includes: for a multi-layered heterogeneous structure, establishing a multi-mode ultrasound propagation multi-parameter model, wherein the parameters include the thickness of each layer of material, the elastic parameters (such as Young's modulus, Poisson's ratio, independent elastic constants of anisotropic material, etc.), the orientation angle of the anisotropic material (if any), and the propagation time of each transmission ultrasound mode signal at different excitation / receiving point relative distances; using the established full-optical non-contact laser-ultrasound excitation and receiving measurement device, performing multi-point line scanning on the structure to be measured, and collecting multi-mode ultrasound signals propagating in different directions in an ultrasound transmission mode; selecting a suitable ultrasound mode, extracting the propagation time under different excitation / receiving point combinations from the collected ultrasound signals; and using a parameter optimization algorithm to iteratively optimize the error minimization of the selected ultrasound mode propagation time experimental value and the theoretical model calculation value, and inverting the material parameters to be measured.

[0033] In the following, a multi-layered heterostructure "Si-UF-Si" commonly used in the development of underfill (UF) materials in the field of electronic packaging is taken as an example for detailed description.

[0034] Specifically, referring to Figure 1 As shown, the provided in-situ non-destructive measurement method of elastic parameters of multi-layered heterostructure materials based on non-contact laser ultrasonic technology includes the following steps:

[0035] Step S1, for a multi-layered heterostructure, a multi-mode ultrasonic propagation multi-parameter model is established, and the theoretical propagation time of each transmitted ultrasonic mode is calculated.

[0036] For example, the multi-parameters include the thickness of each layer of material, the elastic parameters (such as Young's modulus, Poisson's ratio, independent elastic constants of anisotropic material, etc.), the orientation angle of anisotropic material (if any), etc.

[0037] In isotropic linear elastic solid medium, body waves contain longitudinal (L) and transverse (T) modes, and the corresponding sound speeds can be calculated by the following formula:

[0038] (1)

[0039] (2)

[0040] wherein, and are the sound speeds of longitudinal and transverse waves respectively, is Young's modulus, is Poisson's ratio, is density. Similarly, the Young's modulus and Poisson's ratio of the material can be calculated from the density and the longitudinal and transverse wave speeds:

[0041] (3)

[0042] (4)

[0043] And in anisotropic solid, body waves contain a quasi-longitudinal wave and two quasi-transverse wave modes with different polarization directions, and the sound speeds can be obtained by solving the Christoffel equation using density and complete independent elastic constants. Taking cubic crystal system single crystal silicon (Si) as an example, assuming that its <100> crystal direction family is parallel to the three coordinate axes of the Cartesian coordinate system, the anisotropic elastic parameters can be represented by a 6x6 elastic stiffness matrix , which contains 3 independent elastic constants , , , which can be expressed as follows:

[0044]

[0045] Figure 2 are the variations of group velocities of three ultrasonic bulk wave modes propagating inside a single crystal silicon with the propagation direction angle, including quasi pressure (QP), quasi shear vertical (QSV) and quasi shear horizontal (QSH) modes, respectively. The three independent elastic constants and the density of silicon are = 165.6 GPa, = 63.9 GPa, = 79.5 GPa, = 2330 kg / m 3 .

[0046] Figure 3 is a schematic diagram of ultrasonic wave propagation path inside a "silicon-UF-silicon" multi-thin-layer heterostructure, where is the position of the ultrasonic excitation point, is the position of the ultrasonic receiving point, is the thickness of the layer material, is the propagation angle of the ultrasonic wave inside the layer. In this model, the upper and lower layers of the structure to be measured are both (001) oriented single crystal silicon, and the <100> crystal direction family is parallel to the three coordinate axes of the Cartesian coordinate system. A series of equal-interval laser ultrasonic excitation points are arranged in parallel to the silicon

[100] direction to generate multi-mode ultrasonic signals; an ultrasonic receiving point is arranged on the surface of the structure to be measured opposite the center of the excitation point array to detect the out-of-plane components of the multi-mode ultrasonic transmission signals propagating in different directions. When the excitation point array direction is parallel to the main symmetry axis direction of the silicon, and the excitation point array and the receiving point are located on the symmetry plane of the silicon, all the 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 the silicon is in-plane and is not included in the received ultrasonic signals.

[0047] When ultrasonic waves obliquely incident on the interface between two solids with different acoustic impedances, reflection, refraction and mode conversion phenomena occur. When the ultrasonic propagation medium has uniformity relative to the ultrasonic wavelength, the propagation of ultrasonic waves can be approximated as a series of rays passing through the excitation point and the receiving point. For the selected transmitted ultrasonic mode , the propagation time can be calculated by the following formula:

[0048] (6)

[0049] where, and are the group velocity and propagation angle of the mode in the i-th layer, respectively, is the thickness of the i-th 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 constraint condition:

[0050] (7)

[0051] For example, for a three-layer structure with N = 3, in addition to the above constraint conditions, two additional propagation angle constraint conditions are required to completely describe the propagation path of the transmitted ultrasonic mode. The corresponding propagation angle constraint condition calculation methods are provided below for each possible case:

[0052] 1) For the case where the materials on both sides of the interface are isotropic, the ultrasonic propagation angle relationship on both sides of the interface can be described by Snell's law:

[0053] (8)

[0054] where and are the phase velocities of the mode in the materials on both sides of the interface.

[0055] 2) For the case where the materials on both sides of the interface contain anisotropic materials, since the phase velocity (determining the refraction angle) and the group velocity (determining the propagation time) of anisotropic materials are not equal, and the sound speed varies with the propagation angle, it is difficult to use an analytical formula to represent the variation law. Therefore, it is extremely difficult to use Snell's law to calculate the propagation path. At this time, the Dijkstra algorithm and other ray tracing methods can be used to calculate the constraint condition of the remaining propagation angle.

[0056] 3) For the structure in the present embodiment, since the materials and orientations of the upper and lower silicon layers are the same, when the propagation mode of the transmitted ultrasonic mode in the two silicon layers is selected to be the same (for example, QP→L→QP, QSV→T→QSV, etc.), the group velocity and propagation direction of the mode in the two silicon layers are the same:

[0057] (9)

[0058] (10)

[0059] At this time, the propagation angle of the mode in the second layer can be calculated by the following formula:

[0060] (11)​​

[0061] Substituting the above constraints into equation (4), the propagation time of the ultrasonic transmission mode can be expressed as a function of :

[0062] (12)

[0063] Equation (12) gives all possible propagation times of the ultrasonic transmission mode under the condition that the excitation point and the receiving point According to Fermat's principle, the propagation time of this mode is the minimum value of the above possible propagation times:

[0064] (13)

[0065] Based on equation (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.

[0066] Step S2, construct a measurement device, perform a linear laser-ultrasonic scan, collect multi-mode ultrasonic signals propagating in different directions, and obtain a linear scan ultrasonic data set.

[0067] Figure 4 is a schematic diagram of a multi-thin-layer heterogeneous material elastic parameter in-situ non-destructive measurement device based on non-contact laser-ultrasonic technology. The device mainly includes a pulsed laser 10, a laser attenuator 20, a laser focusing assembly 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 computing unit 80. 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 hybrid 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 synchronization signals, software control, etc. to coordinate the completion of laser-ultrasonic excitation, detection, acquisition, scanning operations. When signal acquisition, built-in filters can be used to improve the signal-to-noise ratio of ultrasonic signals. Components that can be included include but are not limited to computers, acquisition cards, oscilloscopes, signal generators, etc.

[0068] For the laser-ultrasonic linear scanning function, the goal to be achieved is to locate and controllably adjust the relative positions of the ultrasonic excitation point and the receiving point, and there are various specific implementation methods, including but not limited to: using a mobile platform to load the ultrasonic receiving unit for translation or loading the pulsed laser and the laser attenuation and focusing assembly for simultaneous translation; using a galvanometer to deflect the laser beam of the pulsed laser or the ultrasonic receiving unit; arraying the laser beams of the pulsed laser or the ultrasonic receiving unit in space and switching using a light switch or the like.

[0069] In combination Figure 4 As shown in the figure, the working process of the provided measurement device mainly includes:

[0070] The pulsed laser 10 outputs excitation laser, which is irradiated to the surface of the sample to be measured 50 through the laser attenuator 20 and the laser focusing assembly 30 in turn, forming a focused 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;

[0071] The ultrasonic receiving unit 60 is used to detect the ultrasonic signals on the opposite surface of the sample to be measured 50, and the signal acquisition and control unit 70 is used to collect and store the signals;

[0072] The mobile platform 40 is controlled to perform a series of translations to change the relative positions of the ultrasonic excitation point and the receiving point, and the ultrasonic signal acquisition and storage are performed respectively;

[0073] The calculation unit 80 reads a series of ultrasonic signal data collected, and performs subsequent multi-mode ultrasonic propagation time calculation and sample material parameter inversion calculation.

[0074] In summary, the ultrasonic signal excitation unit focuses the energy-controllable pulsed laser beam to the surface of the sample 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 sample to be measured. The scanning unit performs multi-point linear scanning on the ultrasonic excitation / receiving point to obtain multi-mode ultrasonic signals propagating in different directions. The signal acquisition and control unit coordinates and controls each excitation, detection, acquisition, and scanning unit based on software synchronization and signal synchronization. The calculation unit calculates the theoretical value of the propagation time of each mode of ultrasonic signal using the established theoretical model, extracts the experimental value 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 a parameter optimization algorithm to invert the material parameters of the sample to be measured.

[0075] Step S3, selecting a suitable ultrasonic mode, extracting the propagation time under different excitation / receiving point combinations from the experimentally collected ultrasonic signals, and obtaining the experimental value of the propagation time under different excitation-receiving point combinations.

[0076] In this step, first need to select the appropriate ultrasonic mode, for subsequent material parameter inversion.

[0077] First, according to the approximate value of the thickness and acoustic velocity of each layer of the structure to be measured, based on the theoretical model in step S1, the propagation time of the possible ultrasonic transmission mode under different ultrasonic excitation / receiving point relative positions is calculated, a pseudo-ultrasonic B-scan image is generated, and compared with the B-scan image generated by the experimental data, which facilitates the identification of the order of appearance of each mode and the shape in the B-scan image.

[0078] In one embodiment, for the selection of ultrasonic modes, the following conditions need to be met:

[0079] 1) Among the selected ultrasonic modes, all possible body wave modes in the layer to be measured must be included. For example, in a "silicon-UF-silicon" structure, the UF material is isotropic, and the selected ultrasonic modes must include at least one of the longitudinal wave and transverse wave modes propagating in the UF (e.g., QP→L→QP and QSV→T→QSV).

[0080] 2) When selecting ultrasonic modes, modes with a 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, propagate at a slower speed in the layer to be measured, and propagate at a faster speed outside the layer to be measured.

[0081] 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 accurate extraction of propagation time.

[0082] After identifying and selecting the appropriate ultrasonic mode, under the premise of ensuring that no waveform aliasing occurs, the signal extreme value is extracted by sliding window, autocorrelation method, and other image processing methods, and the peak time of the selected mode in each ultrasonic time domain waveform and the corresponding ultrasonic excitation / receiving point relative distance are extracted and recorded.

[0083] Step S4, using a parameter optimization algorithm to invert the elastic parameters and thickness of the material to be measured.

[0084] Specifically, the acoustic velocities (group velocities for anisotropic materials) of all longitudinal and transverse wave modes of the layer to be measured and the thickness are selected as variables , which are input into the theoretical model provided in step S1 to calculate the theoretical propagation time of the selected ultrasonic mode under different excitation / receiving point relative positions . Using an optimization algorithm to iteratively update the variables so that the difference between the theoretical propagation time calculated based on the current parameters and the experimental propagation time extracted in step S3 is minimized (i.e., the objective function of the inversion problem ), then the variables at this time is the optimal value.

[0085] In one embodiment, the objective function of the inversion problem can be defined as the sum of the squared norm of the difference between the experimental and theoretical values of the propagation time of each selected ultrasonic mode, as follows:

[0086] (14)

[0087] As can be seen from the above formula, the variable is closer to the actual value, the value of the function is smaller. Therefore, a parameter optimization algorithm such as a particle swarm algorithm, a genetic algorithm, a simulated annealing algorithm, an ant colony algorithm, etc. can be used to minimize the objective function, thereby determining the to-be-measured parameters.

[0088] Finally, based on the density of the to-be-measured material and the inversion-obtained longitudinal and transverse wave speeds, the Young's modulus and Poisson's ratio of the to-be-measured isotropic material can be calculated through formulas (3) and (4) in step S1, or the elastic constants of the to-be-measured anisotropic material can be calculated by solving the Christoffel equation. The density of the to-be-measured material can be measured by using a density balance or the Archimedes drainage method, etc.

[0089] In order to further verify the effect of the present application, a specific scenario is 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.

[0090] First, the COMSOL software or other software is used to perform finite element simulation on the laser ultrasonic transmission line scanning experiment of silicon-UF-silicon, and the simulation data is used for multi-parameter inversion. The ultrasonic B-scan image obtained by simulation and the propagation time distribution of the first 12 transmission ultrasonic modes with the shortest propagation time are as shown in Figure 5 The transmission ultrasonic modes are named by three groups of letters representing their propagation modes in the three layers. Among them, P and V represent QP and QSV modes in silicon respectively, L and T represent longitudinal (L) and transverse (T) modes in UF respectively, and three consecutive letters represent that the ultrasonic wave of the mode has undergone two intralayer reflections in one layer of material, corresponding to a propagation time of 3 times the single-layer propagation time. For example, "P-L-V" represents the propagation form of the mode in the three-layer structure as "QP → L → QSV" or "QSV → L → QP"; "P-LLL-P" corresponds to the case of "QP → (L → L → L) → QP". From Figure 5It can be seen that the lines corresponding to the calculated transmission ultrasonic mode propagation time are highly consistent with the corresponding patterns of the B-scan image, reflecting the accuracy of the given theoretical model. According to the mode selection basis given above, three modes of “P-L-P”, “P-T-P” and “V-LLL-V” are selected for parameter inversion. In the simulated ultrasonic transmission data set, the propagation time of these three modes under different relative positions of ultrasonic excitation / reception points is extracted, the particle swarm algorithm is used for iterative inversion of the thickness and longitudinal and transverse wave speeds of the UF material, and the Young's modulus and Poisson's ratio are calculated 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, and the parameter inversion error is less than 0.548%, indicating that the method can realize accurate measurement of material thickness and elastic parameters in a multi-thin-layer heterogeneous structure.

[0091] Table 1: Finite element simulation set values and inversion results of each material parameter

[0092]

[0093] 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 turn, and the corresponding density, sound speed and Young's modulus also increase in turn. The Archimedes drainage method is used to measure the density of the block sample with the same batch and the same preparation process, which is used for the conversion of sound speed and elastic parameters; the ultrasonic reflection test is carried out using an ultrasonic probe with a center frequency of 125 MHz at a sampling rate of 5 GHz, and the longitudinal wave speed of the material is calculated based on the sample thickness and the time of appearance of multiple surface reflection echoes as a reference value. The thickness of UF in the “silicon-UF-silicon” multi-thin-layer heterogeneous structure sample is calculated by measuring the total thickness of the sample and subtracting the thickness of the silicon wafer. Similar to the finite element simulation process, laser ultrasonic transmission experiments and material parameter inversion are carried out on the three samples to be tested, and the corresponding results are shown in Table 2. In the three experimental results, the material thickness and longitudinal wave speed inversion results are also close to the reference values, with a relative error of less than 3.722%, and the variation trend of the sound speed and elastic parameters of the three UF materials conforms to the change of the filler ratio, indicating that the method can realize accurate measurement of material thickness and elastic parameters in a multi-thin-layer heterogeneous structure, and can distinguish the difference in elastic parameters caused by the difference in material components. The results also show that the measurement method given in the present application can accurately measure the material elastic parameters in a certain range of material elastic parameters, and is expected to be applied to continuous in-situ non-destructive measurement in material reliability analysis process.

[0094] Table 2: Reference values and experimental inversion results of each material parameter

[0095]

[0096] It should be noted 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 ultrasonic receiving unit in the measuring device is a device capable of 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 scanning unit in the measuring device can realize positioning and controllable adjustment of the relative positions of the ultrasonic excitation point and the receiving point, and the specific implementation modes include but are not limited to: using a mobile platform to load the ultrasonic receiving unit for translation or loading a pulsed laser and a laser attenuation and focusing assembly for simultaneous translation; using a galvanometer to deflect the laser beam of the pulsed laser or the ultrasonic receiving unit; arraying the laser beam of the pulsed laser or the ultrasonic receiving unit in space and switching using a light switch or the like. For another example, the objective function used for the inversion of the material parameters to be measured is the sum of the two norms of the difference between the experimental values and the theoretical values of each selected ultrasonic mode propagation time, and the objective is to minimize the difference (or maximize the similarity) between the theoretical values and the experimental values of the selected transmitted ultrasonic mode propagation time, and any function that can achieve the above objective can be used as the objective function. For another example, the inversion algorithm used by the present application for measuring the elastic parameters of the material to be measured is used to solve the global maximum value of the objective function in the search range of the measured variables, which can be a particle swarm algorithm, a genetic algorithm, a simulated annealing algorithm, an ant colony algorithm or other parameter optimization algorithms.

[0097] In summary, compared with the prior art, the present application mainly has the following advantages:

[0098] 1) The present application is based on laser ultrasonic technology, which can realize remote and non-contact measurement, in-situ non-destructive measurement under high temperature and other working conditions during material reliability evaluation and actual service, and can realize the evolution monitoring of the material elastic parameters of the same sample.

[0099] 2) The present application uses a pulsed laser to simultaneously generate multiple mode ultrasonic signals propagating in different directions in a multi-layer heterostructure, without using multiple ultrasonic transducers or adjusting the sample angle, thereby avoiding the signal consistency problem caused by multiple adjustments.

[0100] 3) The present application can obtain ultrasonic signals propagating in different directions by linearly scanning the laser ultrasonic excitation / receiving point, and only needs to set the relative distance between the scanning points, without the need for accurate measurement of the sample angle, and the operation is simpler.

[0101] 4) The present application can realize in-situ measurement of the elastic parameters of the interlayer material in a multi-layer heterostructure without exposing the sample to the outside, and has high measurement accuracy.

[0102] The present application can be a system, a method, and / or a computer program product. The computer program product can include a computer readable storage medium (or media) having computer readable program instructions thereon for causing a processor to carry out aspects of the present application.

[0103] The computer readable storage medium can be a tangible device that can retain and store instructions for use by an instruction execution device. The computer readable storage medium can be, for example, but is not limited to, an electronic 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 the following: a portable computer diskette, 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 mechanically encoded device such as punch-cards or raised structures in a groove having instructions recorded thereon, and any suitable combination of the foregoing. A computer readable storage medium, as used herein, is not to be construed as being transitory signals per se, such as radio waves or other freely propagating electromagnetic waves, electromagnetic waves propagating through a waveguide or other transmission media (e.g., light pulses passing through a fiber-optic cable), or electrical signals transmitted through a wire.

[0104] Computer readable program instructions described herein can be downloaded to respective computing / processing devices from a computer readable storage medium or to an external computer or external storage device via a network, for example, the Internet, a local area network, a wide area network and / or a wireless network. The network can comprise copper transmission cables, optical transmission fibers, wireless transmission, routers, firewalls, switches, gateway computers and / or edge servers. A network adapter card or network interface in each computing / processing device receives computer readable program instructions from the network and forwards the computer readable program instructions for storage in a computer readable storage medium within the respective computing / processing device.

[0105] Computer readable program instructions for carrying out operations of the present application can be assembler instructions, instruction-set-architecture (ISA) instructions, machine instructions, machine dependent instructions, microcode, firmware instructions, state-setting data, or either source code or object code written in any combination of one or more programming languages, including an object oriented programming language such as Smalltalk, C++ or the like and conventional procedural programming languages, such as the "C" programming language or similar programming languages. The computer readable program instructions can execute entirely on the user's computer, partly on the user's computer, as a stand-alone software package, partly on the user's computer and partly on a remote computer or entirely on the remote computer or server. In the latter scenario, the remote computer can 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 the connection can be made to an external computer (for example, through the Internet using an Internet Service Provider). In some embodiments, electronic circuitry including, for example, programmable logic circuitry, field-programmable gate array (FPGA), or programmable logic array (PLA) can execute the computer readable program instructions by utilizing state information of the computer readable program instructions to personalize the electronic circuitry, in order to perform aspects of the present application.

[0106] 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 apparatus or other device to produce a computer implemented process such that the instructions which execute on the computer or other programmable apparatus provide processes for implementing the functions / acts specified in the flowchart and / or block diagram block or blocks.

[0107] 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 apparatus or other device to produce a computer implemented process such that the instructions which execute on the computer or other programmable apparatus provide processes for implementing the functions / acts specified in the flowchart and / or block diagram block or blocks.

[0108] 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.

[0109] 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.

[0110] 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 in-situ non-destructive measurement of elastic parameters of multi-thin-layer heterogeneous materials, characterized in that, The method comprises the following steps: For a to-be-tested structure, a multi-mode ultrasonic propagation multi-parameter model is established, and theoretical values of propagation time corresponding to each ultrasonic mode are calculated, the to-be-tested structure being a multi-thin-layer heterogeneous structure; A linear scanning of laser ultrasonic is performed on the to-be-tested structure, ultrasonic signals of each ultrasonic mode propagating in different directions are collected, and a linear scanning ultrasonic data set is obtained; For a selected ultrasonic mode, experimental values of propagation time under different excitation-receiving point combinations are extracted from the ultrasonic signals in the linear scanning ultrasonic data set, wherein for each selected ultrasonic mode, the experimental value of propagation time is obtained according to the following steps: under the premise that waveform aliasing does not occur, the peak time of the selected ultrasonic mode in each ultrasonic time domain waveform and the corresponding relative distance of the ultrasonic excitation-receiving point are extracted through image processing, and then the corresponding experimental value of propagation time is calculated; For the selected ultrasonic mode, an elastic parameter of the to-be-tested structure is inversed by using a parameter optimization algorithm with the difference between the theoretical value of propagation time and the experimental value of propagation time as an objective function; Wherein, the theoretical values of propagation time corresponding to each ultrasonic mode are calculated according to the following steps: Based on the isotropic elastic wave speed calculation formula and the Christoffel equation of anisotropic elastic wave, the elastic parameters of each layer of material of the to-be-tested structure are converted into the sound speeds of longitudinal and transverse elastic wave modes, wherein for the sound speed of anisotropic material, the group velocity is taken, which is represented as a discrete mapping with respect to the propagation angle; Based on the sound speed and thickness of each layer of material, an ultrasonic transmission propagation model is established, and then for the selected ultrasonic mode , the propagation time thereof is calculated according to the following formula when the coordinate of the ultrasonic excitation point is , and the coordinate of the receiving point is :​ wherein, and are the group velocity and the propagation angle of the ultrasound wave of the ultrasound mode in the first layer, respectively, is the thickness of the first layer, is the number of layers of the structure to be measured; According to the relative position relationship between the excitation point and the receiving point, the constraint condition between the propagation angles of the ultrasonic wave of the selected ultrasonic mode in each layer is given, which is represented as: According to the isotropic and anisotropic characteristics of the materials on both sides of the interfaces of each layer, the constraint conditions of the remaining propagation angles are solved, wherein the number of constraint conditions to be calculated is the number of layers of the to-be-tested structure minus 1; The constraint conditions for all propagation angles are substituted into the calculation formula of and the propagation time theoretical value of the selected ultrasonic mode is obtained.

2. The method of claim 1, wherein, The objective function is set as: wherein, is the objective function, is a multi-parameter variable, including the sound velocities of all the longitudinal and transverse wave modes of the structure under test and the thickness ， is the selected ultrasonic mode theoretical values of the propagation times at different excitation-reception point relative positions, is the selected ultrasonic mode experimental values of the propagation times, denotes the two-norm, is the position of the ultrasonic excitation point.

3. The method of claim 1, wherein, The linear scanning of laser ultrasonic on the to-be-tested structure is realized by a measurement device, the measurement device comprising 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 comprises a pulsed laser, a laser attenuation assembly and a laser focusing assembly, which is used to focus pulsed laser to the surface of the to-be-tested structure and adjust the laser energy to form a focused spot with energy less than the laser damage threshold of the to-be-tested structure, and generate ultrasonic signals on the surface and inside of the to-be-tested structure based on the laser ultrasonic thermoelastic mechanism; The ultrasonic signal detection unit realizes non-contact detection of ultrasonic signals by using laser beams focused to the surface of the to-be-tested structure; The scanning unit is used to realize the scanning of the relative positions of ultrasonic excitation points and receiving points 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, and to coordinate the completion of laser ultrasonic excitation, detection, acquisition and scanning operations, and to use an internal filter to improve the signal-to-noise ratio of ultrasonic signals during signal acquisition; The computing unit is responsible for the post-processing of the ultrasonic signal dataset and uses a parameter optimization algorithm to invert the elastic parameters and thickness of the structure under test.

4. The method of claim 1, wherein, During the linear scanning process of the laser-ultrasonic for the structure under test, one end of the ultrasonic excitation point or receiving point is fixed, and the other end is linearly scanned at a fixed interval, and ultrasonic signals are collected at each scanning point to form the linear scanning ultrasonic dataset.

5. The method of claim 1, wherein, The ultrasonic modes are selected according to the following steps: Among the selected ultrasonic modes, all possible body wave modes in the material of the structure under test are included; Select the ultrasonic mode whose propagation time in the total propagation time accounts for more than a set threshold in the layer under test; Select the ultrasonic mode whose signal-to-noise ratio is higher than a set threshold and does not alias with other modes.

6. The method of claim 1, wherein, The use of a parameter optimization algorithm to invert the elastic parameters of the structure under test includes: For the structure under test of isotropic material, the Young's modulus and Poisson's ratio are calculated based on the following formula: wherein, is the speed of sound for the longitudinal mode of the isotropic material, is the speed of sound for the transverse mode of the isotropic material, is the Poisson's ratio, and are respectively: wherein, E is the Young's modulus, ν is the Poisson's ratio, ρ is the density; For the structure under test of anisotropic material, the elastic constants of the structure under test are calculated by solving the Christoffel equation.

7. A computer-readable storage medium having stored thereon a computer program, characterized in that, The computer program, when executed by a processor, implements the steps of the method according to any one of claims 1 to 6.

8. A computer device comprising a memory and a processor, having stored on the memory a computer program capable of running on the processor, characterized in that, The processor executes the computer program to implement the steps of the method according to any one of claims 1 to 6.

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