Elastic constant measurement method, system, and ultrasound device

Abstract

The application belongs to the technical field of material analysis, and provides an elastic constant measurement method, a system and an ultrasonic device. The method combines a sandwich structure and places the sandwich structure in an acoustic coupling medium, collects ultrasonic data passing through the sandwich structure through a transmission omnidirectional ultrasonic mode, can construct a five-layer sound line tracking model, and uses a particle swarm optimization algorithm to calculate the optimal ultrasonic speed by comparing the actual propagation time of ultrasonic waves in the five-layer sound line tracking model with the predicted propagation time, and then obtains the elastic constant of the material to be measured. The scheme provided by the application solves the problem that the existing ultrasonic characterization thin layer material method is easily affected by the measurement error introduced by wrinkles, provides an ideal measurement environment state, and innovatively uses the transmission omnidirectional ultrasonic mode to reduce the complexity and measurement cost of the device, and realizes nondestructive, accurate and reliable measurement of the elastic constant of the material.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of material analysis, and particularly relates to an elastic constant measurement method, a system and an ultrasonic device. BACKGROUND

[0002] As one of the core parameters for characterizing the mechanical properties of materials, the elastic constant plays an important role in the research of engineering materials, product design and quality evaluation. Accurate measurement of the elastic constant of materials, especially for various non-standard shapes or small-sized samples, has always been a key issue in the field of industrial detection and material analysis.

[0003] At present, the methods for measuring the elastic constant of materials mainly include destructive testing and non-destructive testing. Although the traditional tensile test is intuitive, it has high requirements for sample preparation and is not suitable for some materials that are difficult to clamp or have a small size. Moreover, since the tensile method is usually destructive, it cannot be used for quality evaluation of finished products. Although the nanoindentation technique is suitable for micro-area measurement, it is often difficult to avoid the substrate effect when testing thin films or coatings, which easily affects the accuracy of the results.

[0004] Among the non-destructive testing methods, ultrasonic technology has attracted widespread attention due to its sensitivity to material elastic properties and relatively convenient operation. However, the results of common ultrasonic measurement methods are easily affected by the shape and boundary conditions of the sample. In particular, for materials with small thickness, the measurement accuracy is easily affected by the coupling conditions and the surface state of the sample, or the sample placement posture and the precision of the incident angle are extremely sensitive, which easily affects the propagation path and mode conversion efficiency of the sound wave, thereby reducing the accuracy of the modulus inversion. SUMMARY

[0005] In order to overcome the defects of the prior art, the application provides an elastic constant measurement method, which comprises the following steps:

[0006] Placing the material to be measured between two flat substrates to construct a sandwich structure comprising a first substrate, a material to be measured and a second substrate arranged in sequence;

[0007] Placing the sandwich structure in an acoustic coupling medium, collecting ultrasonic data passing through the sandwich structure by a transmission omnidirectional ultrasonic method, and constructing a five-layer acoustic ray tracing model comprising a first liquid layer, a first substrate layer, a material layer, a second substrate layer and a second liquid layer arranged in sequence based on the ultrasonic data;

[0008] Based on the ultrasonic data, an actual propagation time of an ultrasonic wave in the five-layer sound ray tracing model is obtained, a predicted propagation time of the ultrasonic wave in the five-layer sound ray tracing model is calculated through a semi-analytical sound ray tracing algorithm, and an optimal ultrasonic wave speed is calculated based on the actual propagation time and the predicted propagation time through a particle swarm optimization algorithm, so as to obtain the elastic constant of the material to be measured through the optimal ultrasonic wave speed.

[0009] Preferably, the ultrasonic data collected through the transmission omnidirectional ultrasonic mode and passing through the sandwich structure is realized through a first ultrasonic probe and a second ultrasonic probe arranged in the acoustic coupling medium in a hemispherical omnidirectional manner.

[0010] The first ultrasonic probe moves linearly along a preset scanning axis in a direction away from the second substrate relative to the first substrate to serve as an omnidirectional transmission source, the second ultrasonic probe is fixedly arranged in a direction away from the first substrate relative to the second substrate to serve as an omnidirectional receiver, the central axes of the first ultrasonic probe and the second ultrasonic probe coincide, and the sound wave transmission end of the first ultrasonic probe and the sound wave receiving end of the second ultrasonic probe are located in the same plane.

[0011] Specifically, the parameters for constructing the five-layer sound ray tracing model further include:

[0012] The thicknesses of the first liquid layer, the first substrate layer, the material layer, the second substrate layer, and the second liquid layer;

[0013] The longitudinal wave speeds of the ultrasonic wave in the first liquid layer, the first substrate layer, the second substrate layer, and the second liquid layer, and the transverse wave speeds in the first substrate layer and the second substrate layer;

[0014] The material density of the material layer.

[0015] Specifically, the actual propagation time of the ultrasonic wave in the five-layer sound ray tracing model based on the ultrasonic data includes a first actual propagation time of the ultrasonic wave propagating in a full longitudinal wave mode and a second actual propagation time of the ultrasonic wave propagating in a hybrid wave mode of longitudinal wave, transverse wave, transverse wave, transverse wave, and longitudinal wave in the five-layer sound ray tracing model based on the ultrasonic data.

[0016] The predicted propagation time of the ultrasonic wave in the five-layer sound ray tracing model includes a first predicted propagation time of the ultrasonic wave propagating in the full longitudinal wave mode and a second predicted propagation time of the ultrasonic wave propagating in the hybrid wave mode.

[0017] Further, the method for calculating the first predicted propagation time and the second predicted propagation time includes:

[0018] The coordinates of the incident point of the ultrasonic wave at the junction of the first liquid layer and the first substrate layer are determined by the coordinates of the first ultrasonic probe, the scanning speed of the first ultrasonic probe, and the coordinates of the second ultrasonic probe.

[0019] The coordinates of the exit point corresponding to each selectable ultrasonic ray are determined based on the coordinates of the incident point and the parameters of the five-layer acoustic ray tracking model.

[0020] The ultrasonic propagation ray that minimizes the lateral distance between the emission point and the second ultrasonic probe is determined as the first predicted propagation path corresponding to the first predicted propagation time and the second predicted propagation path corresponding to the second predicted propagation time, thereby determining the first predicted propagation time and the second predicted propagation time.

[0021] Specifically, the step of calculating the predicted propagation time of ultrasound in the five-layer acoustic ray tracking model using the particle swarm optimization algorithm includes:

[0022] Initialize a particle swarm, and define the position of each particle in the swarm by a candidate inversion vector representing the predicted longitudinal wave velocity and the predicted transverse wave velocity in the material layer.

[0023] The five-layer acoustic ray tracing model is used to calculate the first and second predicted propagation times of ultrasound for each candidate inversion vector.

[0024] Further, the calculation of the optimal ultrasonic velocity based on the actual propagation time and the predicted propagation time includes:

[0025] An objective function is constructed based on the first actual propagation time, the second actual propagation time, and the first predicted propagation time and the second predicted propagation time corresponding to each candidate inversion vector. The candidate inversion vector that minimizes the objective function is determined as the optimal inversion vector, and the predicted longitudinal wave velocity and the predicted transverse wave velocity corresponding to the optimal inversion vector are determined as the optimal ultrasonic velocity.

[0026] Specifically, the elastic constants of the material under test include Young's modulus and Poisson's ratio, which are determined by the material density of the material under test and the predicted longitudinal wave velocity and predicted transverse wave velocity corresponding to the optimal ultrasonic velocity.

[0027] The present invention also proposes an elastic constant measurement system, the system being used to implement the method described above, comprising:

[0028] The acquisition module is used to acquire ultrasonic data passing through the sandwich structure using a transmission omnidirectional ultrasonic method;

[0029] The constructing module is configured to construct a five-layer acoustic ray tracing model including a first liquid layer, a first substrate layer, a material layer, a second substrate layer and a second liquid layer arranged in sequence based on the ultrasonic data;

[0030] The calculating module is configured to obtain an actual propagation time of ultrasonic waves in the five-layer acoustic ray tracing model based on the ultrasonic data, calculate a predicted propagation time of the ultrasonic waves in the five-layer acoustic ray tracing model by a semi-analytical acoustic ray tracing algorithm, and calculate an optimal ultrasonic wave speed based on the actual propagation time and the predicted propagation time by a particle swarm optimization algorithm, so as to obtain the elastic constant of the material to be measured by the optimal ultrasonic wave speed.

[0031] The application further provides a transmission type omnidirectional ultrasonic device, which is applied to the method and includes two hemispherical omnidirectional first and second ultrasonic probes.

[0032] The central axes of the first and second ultrasonic probes coincide, and the sound wave emitting end of the first ultrasonic probe and the sound wave receiving end of the second ultrasonic probe are located in the same plane.

[0033] The application has at least the following beneficial effects:

[0034] The application can ingeniously include various forms of materials into a unified measurement body by placing the material to be measured between two flat substrates to construct a sandwich structure, eliminate the interference of material folds, bending or irregular shapes on measurement, provide stable boundary conditions for ultrasonic wave propagation, and accurately predict the real sound wave propagation path at low computational cost by combining the transmission type omnidirectional ultrasonic method with the five-layer acoustic ray tracing model and the semi-analytical acoustic ray tracing algorithm.

[0035] Further, the transmission type omnidirectional ultrasonic method uses two hemispherical omnidirectional ultrasonic probes capable of emitting and receiving wide-angle sound waves, and the setting of the fixed receiving probe and the moving transmitting probe constructs an accurate acoustic scanning coordinate system, provides a reliable data basis for the construction of the sound ray tracing model, and significantly reduces the complexity and manufacturing cost of the device.

[0036] The scheme can also realize intelligent screening of complex paths through the sound ray determination method of minimizing the lateral distance, and the particle swarm optimization algorithm and the calculation mode of minimizing the objective function can find a set of optimal longitudinal and transverse wave speeds, so that the predicted data and the actual data are best matched, the elastic constant calculation with high precision and low error is ensured, and one-stop nondestructive measurement from original data to final engineering application parameters is realized.

[0037] Therefore, the present application provides an elastic constant measurement method, system and ultrasonic device, which solves the problem that the existing ultrasonic characterization method of thin layer material is easily affected by the measurement error introduced by the wrinkle, provides an ideal measurement environment state, and innovatively uses the transmission type omnidirectional ultrasonic method to reduce the complexity and measurement cost of the device, and realizes nondestructive, accurate and reliable measurement of the elastic constant of the material. BRIEF DESCRIPTION OF DRAWINGS

[0038] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the drawings needed in the embodiment description will be briefly introduced. Obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can be obtained by those skilled in the art without creative labor.

[0039] Figure 1 The method flowchart of the elastic constant measurement method provided for embodiment 1 is shown in the figure.

[0040] Fig. 2(a) and Fig. 2(b) are example diagrams of sandwich structures.

[0041] Figure 3 The example diagram of the transmission type omnidirectional ultrasonic device constructed for the two hemispherical omnidirectional ultrasonic probes is shown in the figure.

[0042] Figure 4 The method flowchart for calculating the predicted propagation time is shown in the figure.

[0043] Figure 5 The formula flowchart for PI film Young's modulus and Poisson's ratio inversion is shown in the figure.

[0044] Figure 6A general flow chart for the experiment in Example 2;

[0045] Figure 7 A schematic diagram of the semi-analytical ray tracing for the five-layer ray tracing model;

[0046] Figure 8 A diagram of the ultrasound travel time extraction for B-scan imaging results and mode sequences;

[0047] Figure 9 A statistical distribution diagram of the inversion parameters obtained by 200 independent runs of the particle swarm optimization algorithm;

[0048] Figure 10 A comparison diagram of the theoretically predicted and experimentally measured ultrasound travel times;

[0049] Figure 11 A schematic diagram of the module structure of the elastic constant measurement system provided in Example 1. DETAILED DESCRIPTION

[0050] The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative work fall within the scope of protection of the present application.

[0051] In the following, various embodiments of the present application will be described more fully. The present application can have various embodiments, and adjustments and changes can be made therein. However, it should be understood that there is no intention to limit various embodiments of the present application to the specific embodiments disclosed herein, but the present application should be understood to encompass all adjustments, equivalents and / or alternatives falling within the spirit and scope of various embodiments of the present application.

[0052] In the following, the term "include" or "may include" used in various embodiments of the present application indicates the presence of the disclosed functions, operations or elements, and does not limit the addition of one or more functions, operations or elements. In addition, as used in various embodiments of the present application, the terms "include", "have" and their cognates merely mean to indicate the presence of a specific feature, number, step, operation, element, component or combination of the foregoing, and should not be understood as first excluding the presence or addition of one or more other features, numbers, steps, operations, elements, components or combinations of the foregoing or the possibility of one or more features, numbers, steps, operations, elements, components or combinations of the foregoing.

[0053] In various embodiments of the present application, the expression "or" or "at least one of A or / and B" includes any and all combinations of one or more of the listed items. For example, the expression "A or B" or "at least one of A or / and B" can include A, can include B, or can include both A and B.

[0054] The expressions used in various embodiments of the present application, such as "first", "second", and the like, can modify various constituent elements in various embodiments, but can not limit the corresponding constituent elements. For example, the above expressions do not limit the order and / or importance of the elements. The above expressions are used only for the purpose of distinguishing one element from other elements. For example, the first user device and the second user device indicate different user devices, although both are user devices. For example, a first element can be called a second element, and likewise, a second element can be called a first element, without departing from the scope of various embodiments of the present application.

[0055] It should be noted that, in the present application, unless otherwise explicitly specified and defined, the terms "mounting", "connecting", "fixing", and the like should be understood in a broad sense, for example, can be fixed connection, can be detachable connection, or integral connection; can be mechanical connection, or can be electrical connection; can be direct connection, or can be indirect connection through an intermediate medium; can be internal communication of two elements. For those of ordinary skill in the art, the specific meaning of the above terms in the present application can be understood according to the specific circumstances.

[0056] In the present application, it is understood by those of ordinary skill in the art that the terms indicating the orientation or positional relationship herein are based on the orientation or positional relationship shown in the drawings, which is only for the convenience of describing the present application and simplifying the description, and is not intended to indicate or imply that the device or element referred to must have a particular orientation, be constructed and operated in a particular orientation, and therefore cannot be understood as a limitation on the present application.

[0057] The terms used in various embodiments of the present application are used only for the purpose of describing specific embodiments and are not intended to limit various embodiments of the present application. As used herein, the singular form is intended to include the plural form as well, unless the context clearly indicates otherwise. Unless otherwise defined, all terms used herein, including technical terms and scientific terms, have the same meaning as commonly understood by one of ordinary skill in the art to which various embodiments of the present application belong. The terms such as those defined in a generally used dictionary will be interpreted as having the same meaning as the contextual meaning in the relevant technical field and will not be interpreted as having an idealized or overly formal meaning, unless clearly defined in various embodiments of the present application.

[0058] Example 1

[0059] Please refer toFigure 1 The embodiment provides a method for measuring an elastic constant. The method provided by the embodiment can construct a stable coupling scene, can eliminate interference on measurement caused by material surface wrinkles and local warping, greatly simplifies a way of collecting ultrasonic data, and does not need to rotate a material sample or accurately adjust an angle. The method specifically comprises the following steps.

[0060] S100: placing a material to be measured between two flat substrates to construct a sandwich structure comprising a first substrate, the material to be measured and a second substrate arranged in sequence.

[0061] Exemplarily, referring to FIGS. 2(a)-2(b), the step S100 can use two isotropic flat acrylic plates to clamp the PI film to form a flat sandwich structure.

[0062] S200: placing the sandwich structure in an acoustic coupling medium, collecting ultrasonic data passing through the sandwich structure by using a transmission omnidirectional ultrasonic method, and constructing a five-layer acoustic ray tracing model comprising a first liquid layer, a first substrate layer, a material layer, a second substrate layer and a second liquid layer based on the ultrasonic data.

[0063] In the embodiment, the sandwich structure can be placed in the acoustic coupling medium in a flat manner or an approximately flat manner, so as to be collected by using the transmission omnidirectional ultrasonic method.

[0064] Preferably, the step S200 is implemented by using a first ultrasonic probe and a second ultrasonic probe arranged in the acoustic coupling medium in a hemispherical omnidirectional manner. The first ultrasonic probe is used as an omnidirectional emission source and is linearly moved along a preset scanning axis in a direction away from the second substrate relative to the first substrate. The second ultrasonic probe is used as an omnidirectional receiver and is fixedly arranged in a direction away from the first substrate relative to the second substrate. The center axes of the first ultrasonic probe and the second ultrasonic probe coincide, and the sound wave emission end of the first ultrasonic probe and the sound wave receiving end of the second ultrasonic probe are located in the same plane.

[0065] Referring to FIGS. 3(a)-3(b), the step S200 can be implemented by using a first ultrasonic probe and a second ultrasonic probe arranged in the acoustic coupling medium in a hemispherical omnidirectional manner. Figure 3In the embodiment, the step S200 uses two hemispherical omnidirectional ultrasonic probes with consistent or approximately consistent sensitivity in a wide angle range of emission and reception to realize signal acquisition in a transmission omnidirectional ultrasonic mode. Specifically, one hemispherical omnidirectional ultrasonic probe is arranged on the upper side of the sandwich structure and one hemispherical omnidirectional ultrasonic probe is arranged on the lower side of the sandwich structure. The two hemispherical omnidirectional ultrasonic probes are coaxial and coplanar and avoid longitudinal bias. The omnidirectional ultrasonic probe arranged on the lower side of the sandwich structure is fixed as an omnidirectional receiver, and the omnidirectional ultrasonic probe arranged on the upper side of the sandwich structure is linearly stepped along the scanning axis as an omnidirectional transmitter. By using the large-angle coverage characteristics of the omnidirectional acoustic field, the propagation time of the longitudinal wave and the transverse wave through the entire sandwich structure can be recorded synchronously by the A-scan signal acquired at each step without rotating the sample and fine adjusting the incident angle.

[0066] It should be noted that "A" in the A-scan signal represents amplitude, and the waveform, position and amplitude of the A-scan signal can help analyze the material condition and are a direct tool for positioning and quantitative analysis in ultrasonic testing.

[0067] Specifically, the parameters for constructing the five-layer acoustic line tracking model further include the thicknesses of the first liquid layer, the first substrate layer, the material layer, the second substrate layer and the second liquid layer, the longitudinal wave velocities of the ultrasonic waves in the first liquid layer, the first substrate layer, the second substrate layer and the second liquid layer, the transverse wave velocities in the first substrate layer and the second substrate layer, and the material density of the material layer.

[0068] It should be noted that when the acoustic beam of the ultrasonic wave is incident on the interface between the first liquid layer and the first substrate layer and the interface between the first substrate layer and the material layer in an oblique incidence manner, reflection, refraction and mode conversion occur;

[0069] At the interface between the first water layer and the first substrate layer, the ultrasonic propagation in the near-field region is still dominated by the longitudinal wave, and after the mode conversion from the longitudinal wave (L wave) to the transverse wave (T wave) occurs, the far-field energy is dominated by the T wave. Similar mode conversion also occurs at the interface between the first substrate layer and the material layer, the interface between the material layer and the second substrate layer, and the interface between the second substrate layer and the second liquid layer. Therefore, the ultrasonic propagation through the sandwich structure will form several different mode sequences, and the mode of ultrasonic propagation in each layer of medium is dominated by the L wave or the T wave.

[0070] Exemplarily, when water is used as the acoustic coupling medium in step S200, the first liquid layer comprises a first water layer, and the second liquid layer comprises a second water layer, since only L waves exist in the water layer and no T waves exist, L waves and T waves coexist in the substrate layer and the material layer as different media, and the L wave speed is faster than the T wave, therefore, in the five-layer acoustic ray tracing model constructed in step S200, the propagation speed of the full longitudinal wave mode (L-L-L-L-L wave mode) is the fastest, and it appears first in the time domain signal; and the propagation speed of the mixed wave mode (L-T-T-T-L wave mode) of the longitudinal wave, the transverse wave, the transverse wave, the transverse wave and the longitudinal wave in turn is the slowest, and it appears last in the time domain signal. By using this characteristic, the method proposed in this embodiment can distinguish different propagation paths according to the difference between the arrival times of different propagation modes.

[0071] S300: obtaining actual propagation times of the ultrasonic waves in the five-layer acoustic ray tracing model based on the ultrasonic data, calculating predicted propagation times of the ultrasonic waves in the five-layer acoustic ray tracing model by a semi-analytical acoustic ray tracing algorithm, and calculating an optimal ultrasonic wave speed based on the actual propagation times and the predicted propagation times by a particle swarm optimization algorithm, and then obtaining the elastic constant of the material to be measured by the optimal ultrasonic wave speed.

[0072] It should be noted that the L-L-L-L-L wave mode and the L-T-T-T-L wave mode each correspond to a predicted propagation time and an actual propagation time. In step S300, the obtained actual propagation times include a first actual propagation time of the ultrasonic waves propagating in the L-L-L-L-L wave mode and a second actual propagation time of the ultrasonic waves propagating in the L-T-T-T-L wave mode in the five-layer acoustic ray tracing model based on the ultrasonic data; and the calculated predicted propagation times include a first predicted propagation time of the ultrasonic waves propagating in the L-L-L-L-L wave mode and a second predicted propagation time of the ultrasonic waves propagating in the L-T-T-T-L wave mode in the five-layer acoustic ray tracing model.

[0073] In this embodiment, the Young's modulus and the Poisson's ratio as parameters representing the elastic constant of the material to be measured, can be determined by the density of the material to be measured and the speed of the longitudinal wave and the speed of the transverse wave corresponding to the optimal ultrasonic wave speed.

[0074] Specifically, referring to Figures 4-5 , the method for calculating the first predicted propagation time and the second predicted propagation time in step S300 comprises:

[0075] S310: determining the coordinates of the incident point of the ultrasonic waves at the junction of the first liquid layer and the first substrate layer by the coordinates of the first ultrasonic probe, the scanning speed of the first ultrasonic probe and the coordinates of the second ultrasonic probe.

[0076] Exemplarily, the embodiment can employ a semi-analytical ray tracing scheme to determine the real L-L-L-L-L wave mode propagation path and L-T-T-T-L wave mode propagation path with low computational cost, specifically:

[0077] Let the longitudinal wave speed in the first water layer and the longitudinal wave speed in the second water layer be denoted as Let the longitudinal wave speed in the first substrate layer be denoted as and the transverse wave speed be denoted as Let the longitudinal wave speed in the material layer be denoted as and the transverse wave speed be denoted as Let the longitudinal wave speed in the second substrate layer be denoted as and the transverse wave speed be denoted as Let the thicknesses of the first water layer, the first substrate layer, the material layer, the second substrate layer, and the second water layer be denoted as ;

[0078] Except for the elastic constant of the material layer, the rest of the parameters in the five-layer ray tracing model can be provided by experiments or material manufacturers, for example The thicknesses of the first water layer and the second water layer can be measured by a vernier caliper or other measuring tools The sound speeds in the first substrate layer and the second substrate layer can be calculated by the time of flight of the pulse echo signal of the surface of the substrate layer adjacent thereto The density of the material layer can be measured by the density gradient technique according to the ASTM D-1505-90 standard, and the above measurement methods are all disclosed in the prior art, which will not be described herein

[0079] The omnidirectional ultrasonic probe arranged on the upper side of the sandwich structure performs linear scanning along the x-axis with a uniform step size of At the first scanning step, the coordinates of the ultrasonic probe arranged on the upper side of the sandwich structure can be represented as , and the ultrasonic probe arranged on the lower side of the sandwich structure is fixed at the coordinates The search range of all possible surface incident points is limited to a certain interval on the interface between the first water layer and the first substrate layer, and the starting point of the certain interval can be defined as having the same lateral coordinates as the omnidirectional ultrasonic probe arranged on the upper side of the sandwich structure, and the ending point of the certain interval can be defined as having the same lateral coordinates as the omnidirectional ultrasonic probe arranged on the lower side of the sandwich structure, between the starting point and the ending point, the incident interface is uniformly divided into intervals, thereby being able to generate possible surface incident points, wherein the lateral coordinates of the incident points in the first interval may be expressed as:

[0080]

[0081] S320: determining the coordinates of the exit points corresponding to each of the optional ultrasound propagation sound lines based on the coordinates of the incident point and the parameters of the five-layer sound line tracing model.

[0082] For each possible surface incident point, the corresponding incident ultrasound angle may be expressed as:

[0083]

[0084] According to Snell's law, the refraction angle at the interface between the first water layer and the first substrate layer may be expressed as:

[0085]

[0086] Correspondingly, the refraction angle at the interface between the first substrate layer and the material layer , the refraction angle at the interface between the material layer and the second substrate layer , and the refraction angle at the interface between the second substrate layer and the second water layer may be expressed as:

[0087]

[0088] wherein the refraction angles corresponding to the L-L-L-L-L wave mode , , , are in turn , and the refraction angles corresponding to the L-T-T-T-L wave mode , , , are in turn .

[0089] And the transverse exit coordinates of the exit points of each of the optional potential propagation sound lines may be determined by the accumulated total transverse offset , and the formula is:

[0090]

[0091] S330: determining the ultrasound propagation sound line that minimizes the transverse distance between the exit point and the second ultrasound probe as the predicted propagation path, and further determining the first predicted propagation time and the second predicted propagation time through the predicted propagation path.

[0092] In step S330, the transverse distance between the exit point of the propagating sound ray and the omnidirectional ultrasonic probe arranged on the lower side of the sandwich structure searched in step S320 The specific sound ray that is minimized is considered to be the real ultrasonic propagation path, and the corresponding calculation predicts the theoretical flight propagation time of the five-layer sound ray tracing model The formula is:

[0093]

[0094] Wherein, represents the radius of the hemispherical omnidirectional ultrasonic probe, is the first predicted propagation time corresponding to the L-L-L-L-L wave mode, is the second predicted propagation time corresponding to the L-T-T-T-L wave mode.

[0095] In step S300, the particle swarm optimization (PSO) based inversion algorithm first initializes a particle swarm, and the position of each particle is defined by a candidate inversion vector , which can represent the predicted longitudinal wave speed and the predicted transverse wave speed in the material layer, and then the algorithm enters the iterative evaluation stage. The five-layer sound ray tracing model calculates the first predicted propagation time of the L-L-L-L-L wave mode sequence and the second predicted propagation time of the L-T-T-T-L wave mode sequence for each candidate inversion vector, and compares them with the experimental time obtained by the transmission omnidirectional ultrasonic acquisition, i.e., compares the first predicted propagation time with the first actual propagation time , compares the second predicted propagation time with the second actual propagation time , and continues the iterative search process until the optimal inversion vector that minimizes the objective function is searched, and the formula for calculating the objective function includes:

[0096]

[0097] Wherein, represents the number of scanning steps used.

[0098] After obtaining the optimal inversion vector , the predicted longitudinal wave speed and the predicted transverse wave speed corresponding to the optimal inversion vector can be determined as the optimal ultrasonic wave speed, i.e., the predicted longitudinal wave speed and the predicted transverse wave speed in the corresponding material layer are determined;

[0099] Taking a polyimide (PI) film material with a thickness of 0.12 mm as an example, in the ultrasonic material characterization, the mechanical response of the PI film can be regarded as a linear elastic response due to the small strain induced by high-frequency ultrasound, and the formula for calculating the Young's modulus and Poisson's ratio The formula can include:

[0100]

[0101] wherein, represents the material density of the material to be measured.

[0102] It should be noted that the embodiment enumerates the example of measuring the PI film material, but does not represent the limitation of the material to be measured for the method proposed in the embodiment. In actual application, the method proposed in the embodiment can be applied to flexible materials such as film materials, and can also be used to measure the elastic constant of rigid materials.

[0103] Embodiment 2

[0104] Please refer to Figures 6-7 To verify the feasibility of the method proposed in embodiment 1, this embodiment uses a smooth surface acrylic plate as a way to support the PI film on both sides to construct the sandwich structure proposed in step S100 as a sample and performs an experiment, wherein the thickness of the acrylic plate is 4.70 mm, the size is 90x70 mm, the longitudinal wave speed in the acrylic plate is 2680 m / s and the transverse wave speed is 1330 m / s, the thickness of the PI film is 0.12 mm, and the size is also 90x70 mm. The PI film exhibits isotropic mechanical properties, and the mass density is measured to be 1.42 g / cm³.

[0105] To avoid wrinkles in the PI film and ensure perfect fit between the layers, the PI film is clamped in a clamp to apply uniform pressure and eliminate possible air gaps between the layers. Two identical hemispherical omnidirectional ultrasonic probes are used in the experiment, each made of 1-3 type piezoelectric composite material, with a diameter of 15 mm, a center frequency of 2.91 MHz, and a -6 dB bandwidth range of 0.93 to 4.92 MHz. It has achieved omnidirectional sensitivity within an angle range of 5° to 175°, and can emit and receive ultrasonic waves from almost all directions. One omnidirectional ultrasonic probe is installed above the sample as a transmitting ultrasonic probe to perform linear scanning, and the other omnidirectional ultrasonic probe is fixed below the sample to receive ultrasonic signals;

[0106] Both of the two ultrasonic probes work in transmission mode, the sampling frequency is 2000MHz and the sampling time is 80μs when collecting the ultrasonic transmission A-scan signal, in order to improve the signal-to-noise ratio, each A-scan signal is averaged by 150 repeated sampling, and then band-pass filtering is implemented in the frequency band of 1-7.5MHz, the upper ultrasonic probe is driven by a three-axis displacement platform, and moves along the x-axis relative to the lower ultrasonic probe from about -102mm to +7mm position, the total scanning stroke is 110mm, and the scanning step is 1mm, an ultrasonic transmission A-scan signal is collected at each position;

[0107] Through the above scanning method, 110 ultrasonic A-scan signals are collected in a single scan, the distance from the upper ultrasonic probe to the upper surface of the sample is the thickness of the first water layer , and the distance from the lower ultrasonic probe to the lower surface of the sample is the thickness of the second water layer , which is measured by switching the corresponding ultrasonic probe to the pulse-echo mode, recording the ultrasonic echo and extracting the flight propagation time, and the thickness of the first water layer is 18.78mm, and the thickness of the second water layer is 24.28mm.

[0108] Please refer to Figure 8 , by constructing an ultrasonic B-scan image from 110 A-scan time domain signals, and extracting the ultrasonic travel time of the L-L-L-L-L and L-T-T-T-L wave mode sequence, the extracted flight propagation time is used as the input of the particle swarm optimization algorithm together with the obtained experimental device parameters, and the search range of the longitudinal wave velocity is constrained in a reasonable interval [1000m / s, 2000m / s], and the search range of the transverse wave velocity is constrained in a reasonable interval [400m / s, 1000m / s], the selected parameter space covers a wide range of PI film sound velocity values, so as to test the robustness of the objective function;

[0109] The optimization process of this experiment adopts a particle swarm consisting of 100 particles, and the termination condition is set to reach the upper limit of 600 iterations or the optimal solution cannot be further improved in continuous 40 iterations, in order to ensure that the final solution can resist the inherent randomness interference of the PSO algorithm and guarantee its robustness and stability, the optimization program is independently executed for 200 times.

[0110] Please refer to Figure 9 , the statistical result diagram of 200 independent inversion runs for experimental data can show that the longitudinal wave velocity and the transverse wave velocity obtained by inversion present a clear and narrow unimodal distribution, the mean value of the longitudinal wave velocity is concentrated at 1654m / s, and the mean value of the transverse wave velocity is concentrated at 789m / s, and the standard deviations are 1.7m / s and 7.4m / s respectively, the data is substituted into the formula provided in embodiment 1​

[0111]

[0112] The Young's modulus can be calculated as 2.3915 GPa, and the Poisson's ratio 0.3527.

[0113] According to the data provided by the manufacturer of the PI film as the material of this experiment, the Young's modulus of the PI film is 2.50 GPa, the relative error is 4.34%, the Poisson's ratio is 0.34, the relative error is 3.74%, and Figure 10 The theoretical prediction and experimental measurement of the ultrasonic travel time comparison results shown in the figure show a high consistency, which shows that the method proposed in embodiment 1 has high feasibility.

[0114] Embodiment 3

[0115] Please refer to Figure 11 The system proposed in this embodiment is used to implement the elastic constant measurement method proposed in embodiment 1, and the system can include a terminal control system such as a computer system, and specifically includes:

[0116] The acquisition module 10 is configured to acquire ultrasonic data passing through the sandwich structure by a transmission omnidirectional ultrasonic method.

[0117] The construction module 20 is configured to construct a five-layer acoustic ray tracing model including a first liquid layer, a first substrate layer, a material layer, a second substrate layer and a second liquid layer arranged in sequence based on the ultrasonic data.

[0118] The calculation module 30 is configured to obtain an actual propagation time of the ultrasonic wave in the five-layer acoustic ray tracing model based on the ultrasonic data, calculate a predicted propagation time of the ultrasonic wave in the five-layer acoustic ray tracing model by a semi-analytical acoustic ray tracing algorithm, and calculate an optimal ultrasonic wave speed based on the actual propagation time and the predicted propagation time by a particle swarm optimization algorithm, and then obtain the elastic constant of the material to be measured by the optimal ultrasonic wave speed.

[0119] The calculation module 30 specifically includes:

[0120] The first coordinate unit 31 is configured to determine the coordinates of the incident point of the ultrasonic wave at the junction of the first liquid layer and the first substrate layer based on the coordinates of the first ultrasonic probe, the scanning speed of the first ultrasonic probe and the coordinates of the second ultrasonic probe.

[0121] The second coordinate unit 32 is configured to determine the coordinates of the exit point corresponding to each selectable ultrasonic propagation acoustic ray based on the coordinates of the incident point and the parameters of the five-layer acoustic ray tracing model.

[0122] The computing unit 33 is configured to determine the ultrasonic propagation path corresponding to the first predicted propagation time as the path that minimizes the transverse distance between the exit point and the second ultrasonic probe, and further determine the first predicted propagation time and the second predicted propagation time through the predicted propagation path.

[0123] Embodiment 4

[0124] Please refer to Figure 3 The embodiment provides a transmission type omnidirectional ultrasonic device, and the device can be applied to the elastic constant measurement method provided in Embodiment 1 and the elastic constant measurement system provided in Embodiment 3. The device specifically comprises two hemispherical omnidirectional first and second ultrasonic probes. The first ultrasonic probe is movably arranged on a first side of a sandwich structure, and the second ultrasonic probe is fixedly arranged on a second side of the sandwich structure. The first side and the second side are opposite sides.

[0125] The central axes of the first and second ultrasonic probes coincide, and the sound wave emitting end of the first ultrasonic probe and the sound wave receiving end of the second ultrasonic probe are located in the same plane.

[0126] In conclusion, the embodiment provides an elastic constant measurement method, system and ultrasonic device. The embodiment solves the problem that the ultrasonic characterization method for a thin layer material in the prior art is easily affected by measurement errors caused by wrinkles, provides an ideal measurement environment state, and innovatively uses a transmission type omnidirectional ultrasonic method to reduce the complexity of equipment and measurement cost, and realizes nondestructive, accurate and reliable measurement of the elastic constant of a material.

[0127] The above description is only the preferred embodiment of the present application, and is not intended to limit the present application. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A method for measuring elastic constants, characterized in that, The method includes: The material to be tested is placed between two flat substrates to construct a sandwich structure comprising a first substrate, the material to be tested, and a second substrate arranged in sequence. The sandwich structure is placed in an acoustic coupling medium, and ultrasonic data passing through the sandwich structure is acquired by transmission omnidirectional ultrasound. Based on the ultrasonic data, a five-layer acoustic ray tracking model is constructed, including a first liquid layer, a first substrate layer, a material layer, a second substrate layer, and a second liquid layer arranged in sequence. Based on the ultrasonic data, the actual propagation time of the ultrasonic wave in the five-layer ray tracing model is obtained. The predicted propagation time of the ultrasonic wave in the five-layer ray tracing model is calculated by a semi-analytical ray tracing algorithm. The optimal ultrasonic velocity is calculated based on the actual propagation time and the predicted propagation time by a particle swarm optimization algorithm. The elastic constant of the material under test is then obtained by the optimal ultrasonic velocity. The step of obtaining the actual propagation time of ultrasound in the five-layer acoustic ray tracing model based on the ultrasound data includes: obtaining the first actual propagation time of ultrasound in the five-layer acoustic ray tracing model in a full longitudinal wave mode and the second actual propagation time in a mixed wave mode of longitudinal wave, transverse wave, transverse wave, transverse wave and longitudinal wave in sequence based on the ultrasound data. The calculation of the predicted propagation time of ultrasound in the five-layer acoustic ray tracing model includes: calculating the first predicted propagation time of ultrasound in the full longitudinal wave mode and the second predicted propagation time in the mixed wave mode in the five-layer acoustic ray tracing model.

2. The method according to claim 1, characterized in that, The acquisition of ultrasonic data through the sandwich structure via a transmission-type omnidirectional ultrasonic method is achieved by using a hemispherical omnidirectional first ultrasonic probe and a second ultrasonic probe disposed in the acoustic coupling medium. The first ultrasonic probe moves linearly along a preset scanning axis in a direction away from the second substrate relative to the first substrate to serve as an omnidirectional emission source. The second ultrasonic probe is fixedly disposed in a direction away from the first substrate relative to the second substrate to serve as an omnidirectional receiver. The central axes of the first ultrasonic probe and the second ultrasonic probe coincide. The sound wave emitting end of the first ultrasonic probe and the sound wave receiving end of the second ultrasonic probe are located in the same plane.

3. The method according to claim 2, characterized in that, The parameters for constructing the five-layer acoustic ray tracking model also include: The thicknesses of the first liquid layer, the first substrate layer, the material layer, the second substrate layer, and the second liquid layer; The longitudinal wave velocity of the ultrasound in the first liquid layer, the first substrate layer, the second substrate layer and the second liquid layer, and the transverse wave velocity in the first substrate layer and the second substrate layer; The material density of the material layer.

4. The method according to claim 2 or 3, characterized in that, The methods for calculating the first predicted propagation time and the second predicted propagation time include: The coordinates of the incident point of the ultrasonic wave at the junction of the first liquid layer and the first substrate layer are determined by the coordinates of the first ultrasonic probe, the scanning speed of the first ultrasonic probe, and the coordinates of the second ultrasonic probe. The coordinates of the exit point corresponding to each selectable ultrasonic ray are determined based on the coordinates of the incident point and the parameters of the five-layer acoustic ray tracking model. The ultrasonic propagation ray that minimizes the lateral distance between the emission point and the second ultrasonic probe is determined as the predicted propagation path, and then the first predicted propagation time and the second predicted propagation time are determined through the predicted propagation path.

5. The method according to claim 4, characterized in that, The step of calculating the optimal ultrasonic velocity based on the actual propagation time and the predicted propagation time using a particle swarm optimization algorithm includes: Initialize a particle swarm, and define the position of each particle in the swarm by a candidate inversion vector representing the predicted longitudinal wave velocity and the predicted transverse wave velocity in the material layer. The first and second predicted propagation times of ultrasound are calculated for each of the candidate inversion vectors using the five-layer acoustic ray tracing model. An objective function is constructed based on the first actual propagation time, the second actual propagation time, and the first predicted propagation time and the second predicted propagation time corresponding to each candidate inversion vector. The candidate inversion vector that minimizes the objective function is determined as the optimal inversion vector, and the predicted longitudinal wave velocity and the predicted transverse wave velocity corresponding to the optimal inversion vector are determined as the optimal ultrasonic velocity.

6. The method according to claim 5, characterized in that, The elastic constants of the material under test include Young's modulus and Poisson's ratio, which are determined by the material density of the material under test and the predicted longitudinal wave velocity and predicted transverse wave velocity corresponding to the optimal ultrasonic velocity.

7. A system for measuring elastic constants, characterized in that, For implementing the method as described in any one of claims 1-6, comprising: The acquisition module is used to acquire ultrasonic data passing through the sandwich structure using a transmission omnidirectional ultrasonic method; The construction module is used to construct a five-layer acoustic ray tracking model based on the ultrasound data, comprising a first liquid layer, a first substrate layer, a material layer, a second substrate layer, and a second liquid layer arranged in sequence. The calculation module is used to obtain the actual propagation time of the ultrasonic wave in the five-layer ray tracing model based on the ultrasonic data, calculate the predicted propagation time of the ultrasonic wave in the five-layer ray tracing model using a semi-analytical ray tracing algorithm, and calculate the optimal ultrasonic velocity based on the actual propagation time and the predicted propagation time using a particle swarm optimization algorithm, and then obtain the elastic constant of the material under test using the optimal ultrasonic velocity.

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