A device and method for ultrasonically detecting elastic modulus of small-size thin plate samples

Abstract

The present invention discloses an ultrasonic device and method for detecting the elastic modulus of a small-sized thin plate sample, which belongs to the technical field of ultrasonic measurement. The ultrasonic device for detecting the elastic modulus of a small-sized thin plate sample comprises a measuring tool (1), a signal generator (2), a first low-pass filter (3), a second low-pass filter (4) and a high-speed sampling oscilloscope (5). The device and method proposed by the present invention can measure hard, small-sized, thin samples that are difficult to measure with existing solutions. The method has the advantages of convenient measurement, high reliability, high success rate, good test repeatability, etc. The method is of great significance for the rapid and accurate detection of the physical properties of small-sized, thin, hard samples synthesized in the laboratory.

Description

Technical Field

[0001] The invention belongs to the technical field of ultrasonic measurement, and mainly relates to a device and method for ultrasonically measuring elastic modulus. Background Art

[0002] Elastic modulus is one of the most important and characteristic mechanical properties of materials. It is a representation of the ease of elastic deformation of an object and an important measurement indicator in the field of materials science. From a macroscopic perspective, the elastic modulus is a measure of the ability of an object to resist elastic deformation. From a microscopic perspective, it is a reflection of the bond strength between atoms, ions or molecules. All factors that affect the bond strength can be reflected in the elastic modulus of the material, such as bonding method, crystal structure, chemical composition, microstructure, etc. Therefore, the elastic modulus is of great significance for evaluating the physical properties of a substance.

[0003] The superhard ceramic materials synthesized in the laboratory have the characteristics of large elastic modulus, high synthesis cost, rare quantity, and small size, which makes it difficult to collect stress-strain data within its elastic range and cannot be measured by direct method. At present, the two main methods used are indentation method and ultrasonic measurement: indentation method is a destructive testing method that will destroy the sample being tested and can only reflect the local properties of the sample; ultrasonic measurement of elastic modulus is a non-destructive testing method. By measuring the wave velocity of ultrasonic transverse waves and longitudinal waves in the sample being tested, the elastic modulus of the sample being tested can be calculated, which can reflect the overall properties of the sample block.

[0004] In ultrasonic measurement, the ultrasonic frequency will directly affect the measurement accuracy. The higher the frequency, the higher the time resolution of the received signal. The current common high-frequency industrial ultrasonic probe has a frequency of about 1MHz~15MHz. The probe is large in size and can only transmit and receive longitudinal waves or transverse waves, which makes it difficult to meet the needs of measuring the elastic modulus of small-sized samples.

[0005] On the other hand, the current common ultrasonic measurement of elastic modulus of small-sized samples is to directly bond or press the sample onto a single ultrasonic transceiver. The bonding scheme requires a lot of time to bond the sample each time, and the bonding layer will also affect the measurement results; the pressing scheme needs to adjust the pressing backing material according to different samples to reduce the energy of the transmitted signal to strengthen the reflection signal of the second interface of the sample. The more cycles of the ultrasonic excitation signal, the greater the ultrasonic energy generated, and the easier it is to identify the echo signal. The single ultrasonic transceiver scheme generally excites the ultrasonic wave with a 3-5 cycle sine wave signal, and calculates the wave velocity by dividing the time difference between the reflection signal of the first interface of the sample and the reflection signal of the second interface of the sample by twice the thickness of the sample. Due to energy attenuation, the amplitude of the reflection signal of the second interface of the sample is significantly smaller than the reflection signal of the first interface. When the sample thickness is very small, the ultrasonic propagation time in the sample will also decrease, and the arrival time of the reflection signals of the two interfaces is very close. The reflection signal of the second interface of the sample will be confused by the tail of the reflection signal of the first interface of the sample, making it difficult to observe the starting position of the reflection signal of the second interface, and the benchmark for time difference measurement is difficult to determine, so the wave velocity cannot be accurately calculated. Summary of the invention

[0006] The technical problem to be solved by the present invention is to overcome the deficiencies of the prior art and provide a device and method for ultrasonically detecting the elastic modulus of a small-sized thin plate sample.

[0007] The technical solution of the present invention is as follows:

[0008] A device for ultrasonically detecting elastic modulus of a small-sized thin plate sample, comprising a measuring tool 1, a signal generator 2, a first low-pass filter 3, a second low-pass filter 4 and a high-speed sampling oscilloscope 5;

[0009] It is characterized in that the structure of the measuring tool 1 is as follows: the first high-frequency ultrasonic transceiver 11 and the second high-frequency ultrasonic transceiver 12 are fixed on the guide rail 13 to ensure that the two high-frequency ultrasonic transceivers are centered, the first high-frequency ultrasonic transceiver 11 is fixed, and the second high-frequency ultrasonic transceiver 12 can be moved along the guide rail 13 to clamp the sample, and elastic clamping is adopted so that the clamping force can be adjusted to ensure reliable contact with the sample surface. The signal of the first high-frequency ultrasonic transceiver 11 is divided into two lines through a splitter, the first one is connected to the signal generator 2 through a coaxial cable, and the second one is connected to channel 1 of the high-speed sampling oscilloscope 5 through a coaxial cable through a first low-pass filter 3, and the second high-frequency ultrasonic transceiver 12 is connected to channel 2 of the high-speed sampling oscilloscope 5 through a coaxial cable through a second low-pass filter 4, and the first low-pass filter 3 and the second low-pass filter 4 are exactly the same.

[0010] Furthermore, the first high-frequency ultrasonic transceiver 11 is composed of a lithium niobate transducer 111, a tungsten carbide rod 112, a steel frame 113, and a printed circuit board 116 with a pin spring terminal 114 and a coaxial cable connector 115; the two end faces of the tungsten carbide rod 112 are polished, the surface of the lithium niobate transducer 111 is gold-plated, and is bonded to one end of the tungsten carbide rod 112 by hot-melt resin, the tungsten carbide rod 112 is fixed by the steel frame 113, and one side of the lithium niobate transducer 111 is connected to the contact of the pin spring terminal 114, and the contact Reliable, small contact surface, avoiding the clutter signal generated on the back of the transducer, the pin spring terminal 114 is welded on the printed circuit board 116, and is connected to the positive pole of the coaxial cable connector 115, the steel frame 113 is connected to the other side of the lithium niobate transducer 111 through the tungsten carbide rod 112, and is connected to the negative pole of the coaxial cable connector 115, and can apply an excitation signal or receive a signal through the coaxial cable connector 115; the structure of the second high-frequency ultrasonic transceiver 12 is exactly the same as that of the first high-frequency ultrasonic transceiver 11.

[0011] Preferably, the shear wave excitation frequency of the lithium niobate transducer 111 is 30 MHz, and the longitudinal wave excitation frequency is 50 MHz, and longitudinal waves and shear waves can be generated simultaneously within the excitation signal range of 20 MHz to 50 MHz.

[0012] Preferably, the cut-off frequency of the first low-pass filter 3 and the second low-pass filter 4 is 200 MHz.

[0013] Preferably, the sampling rate of the high-speed sampling oscilloscope 5 is 6.25 GS / s.

[0014] Preferably, the length of the tungsten carbide rod 112 is 18 mm.

[0015] A method for ultrasonically detecting the elastic modulus of a small-sized thin plate sample, wherein the frequency of a signal generator 2 is adjusted to a frequency at which a lithium niobate transducer 111 can simultaneously excite longitudinal waves and transverse waves, a signal is generated by the signal generator 2 and converted into an ultrasonic wave by a first high-frequency ultrasonic transceiver 11 and emitted, the first high-frequency ultrasonic transceiver 11 receives a reflection signal of a first interface of the sample, a second high-frequency ultrasonic transceiver 12 receives a transmission signal passing through two tungsten carbide rods and a sample thickness, and the two high-frequency ultrasonic transceivers receive the received reflected or transmitted ultrasonic signals through their respective niobium After the lithium acid transducer converts the electric signal into an electrical signal, it is transmitted to the two channels of the high-speed sampling oscilloscope 5 respectively. The time difference of the two signals is directly measured by comparing the two corresponding waveforms of the high-speed sampling oscilloscope 5 at the same time base, and the wave velocity is calculated by dividing the sample thickness by the time difference. Since the ultrasonic shear wave velocity is significantly smaller than the longitudinal wave velocity, after a certain length of tungsten carbide rod path, the shear wave signal will lag significantly in time compared with the longitudinal wave signal, and the two are clearly distinguished. Using one excitation signal frequency, the shear wave and the longitudinal wave can be measured simultaneously. The wave velocity of the ultrasonic longitudinal wave passing through the measured sample is measured by the above method as follows: , the shear wave velocity of ultrasonic shear wave passing through the sample is ;

[0016] Then the elastic modulus of the sample being tested is:

[0017] The shear modulus is:

[0018] in, is the density of the sample being tested.

[0019] The present invention adopts a lithium niobate transducer bonded with a tungsten carbide rod combined with a needle spring contact to form a high-frequency ultrasonic transceiver, which avoids the interference of clutter generated on the back of the transducer. The high strength and high uniformity of the tungsten carbide material can meet the requirements of measuring superhard materials, and the tungsten carbide rod path can separate the longitudinal wave signal and the transverse wave signal in time; two high-frequency ultrasonic transceivers form a top-to-top structure, and a high-speed sampling oscilloscope is used to simultaneously collect the signals received by the two high-frequency ultrasonic transceivers, and the first interface reflection signal and the transmission signal of the sample are used to calculate the ultrasonic propagation time in the sample. The transmission signal will not be affected by the tailing of the first interface reflection signal at all, and the time difference measurement reference object is clear. Compared with the single reflection measurement scheme, the signal confusion problem when measuring thin thickness samples is fundamentally avoided. Even if a multi-cycle ultrasonic excitation signal is used, it will not affect the signal recognition, and the wave velocity can be measured more accurately to calculate the elastic modulus.

[0020] In summary, the present invention has the following beneficial effects:

[0021] 1. A symmetrical high-frequency ultrasonic transceiver is designed to measure the ultrasonic wave velocity by combining the reflected signal and the transmitted signal, thus avoiding the problem of signal confusion.

[0022] 2. A high-frequency ultrasonic transceiver based on a lithium niobate transducer and tungsten carbide material that can simultaneously excite transverse and longitudinal ultrasonic waves was designed. While reliably loading high-frequency signals, it also reduced clutter. The tungsten carbide rod path can separate longitudinal and transverse wave signals in time, and achieve simultaneous measurement of longitudinal and transverse waves at the same frequency. The structural strength of the device also meets the requirements for clamping and measuring small-sized hard materials.

[0023] 3. The present invention aims to perform ultrasonic nondestructive elastic modulus testing on small-sized and thin samples. The device and method proposed by the present invention can measure hard small-sized and thin samples that are difficult to measure with existing solutions. From the relevant experimental details and test results, this method has the advantages of convenient measurement, high reliability, high success rate, and good test repeatability. This method is of great significance for the rapid and accurate detection of the physical properties of small-sized and thin hard samples synthesized in the laboratory. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 It is a block diagram of the system composition of the present invention.

[0025] Figure 2 It is a structural schematic diagram of the testing tool 1 of the present invention.

[0026] Figure 3 It is a structural diagram of the high-frequency ultrasonic transceiver of the present invention.

[0027] Figure 4 In Example 2, under a 30 MHz excitation signal, without clamping the sample, the time-consistent image of the longitudinal wave transmission signal and the reflection signal is obtained when two tungsten carbide rods are directly facing each other.

[0028] Figure 5 In Example 2, under a 30 MHz excitation signal, without clamping the sample, the time-consistent image of the shear wave transmission signal and the reflection signal when two tungsten carbide rods are directly facing each other.

[0029] Figure 6 It is a schematic diagram of the ultrasonic signal propagation path of the present invention.

[0030] Figure 7 This is the waveform collected by the two transceiver devices under the 30 MHz excitation signal in Example 4 (generating clearly distinguishable longitudinal and transverse wave signals).

[0031] Figure 8 In Example 4, under a 30 MHz excitation signal, the oscilloscope measures the longitudinal wave time difference.

[0032] Fig. 9 In Example 4, under a 30 MHz excitation signal, the oscilloscope measures the shear wave time difference. DETAILED DESCRIPTION

[0033] Embodiment 1 Hardware structure of the present invention

[0034] The system block diagram of the device for ultrasonically detecting elastic modulus of small-sized thin plate samples of the present invention is as follows: Figure 1 Given, the measurement tooling composition diagram is given by Figure 2 Given, the high-frequency ultrasonic transceiver device is composed of Figure 3 Given, the propagation path of high-frequency ultrasonic signal is given by Figure 6 Given.

[0035] like Figure 1 As shown, the entire measuring device consists of a measuring fixture 1, a signal generator 2, a first low-pass filter 3, a second low-pass filter 4 and a high-speed sampling oscilloscope 5. Figure 2 As shown, the measuring fixture 1 is two identical high-frequency ultrasonic transceivers installed on a guide rail. The two high-frequency ultrasonic transceivers elastically clamp the sample, which can be achieved by using a spring device, and the clamping force can be adjusted by adjusting the spring compression. Figure 3 As shown, the two high-frequency ultrasonic transceiver devices have exactly the same structure, and are composed of a lithium niobate transducer 111, a tungsten carbide rod 112, a steel frame 113, and a printed circuit board 116 with a pin spring terminal 114 and a coaxial cable connector 115; the two end faces of the tungsten carbide rod 112 are polished, and the lithium niobate transducer 111 is bonded to the bottom surface and fixed on the steel frame 113; finally, the printed circuit board 116 is used to lead the positive and negative electrodes on both sides of the lithium niobate transducer 111 to the positive and negative electrodes of the coaxial cable connector 115 through the pin spring terminal 114 and the steel frame 113.

[0036] Example 2 Device Calibration

[0037] After the device is assembled, the experimental device is calibrated. Without clamping the sample, the tungsten carbide columns of the two high-frequency ultrasonic transceiver devices are in top contact. The signal generator 2 is adjusted to generate a sine wave with a frequency of 30MHz, a phase of 180°, and 5 cycles, and is continuously triggered at intervals of 1ms. At this time, the longitudinal wave signals of channel 1 and channel 2 of the high-speed sampling oscilloscope 5 should be at the same position in time. If they are different, the time offset of channel 2 of the oscilloscope is fine-tuned until the time position of the longitudinal wave transmission signal of channel 2 is consistent with the time position of the longitudinal wave reflection signal of channel 1 (such as Figure 4 As shown in the figure, since the lengths of the two tungsten carbide rods are consistent, the time positions of the shear wave reflection signal of channel 1 and the shear wave transmission signal of channel 2 are also consistent. This correction is used to eliminate the errors caused by the signal transmission path and the oscilloscope channel delay. When the frequency of the ultrasonic excitation signal remains unchanged, there is no need to repeat the calibration.

[0038] The tungsten carbide rod 112 of the second high-frequency ultrasonic transceiver 12 is rotated and adjusted (actually the angle of the lithium niobate transducer is adjusted) so that the tungsten carbide rods of the two high-frequency ultrasonic transceivers are in contact with each other, the shear wave signals of channel 1 and channel 2 are in phase, and the shear wave transmission signal amplitude of channel 2 is the largest (such as Figure 5 As shown), the tungsten carbide rod 112 is fixed after the adjustment is completed. This correction is used to match the shear wave vibration direction of the two ultrasonic transceiver devices.

[0039] Example 3 Measurement principle of the present invention

[0040] The entire ultrasonic propagation path is as follows Figure 6 As shown, the lengths of the two tungsten carbide rods are exactly the same. The lithium niobate transducer of the first high-frequency ultrasonic transceiver 11 transmits ultrasonic waves and can receive the first interface reflection signal of the sample. This echo is a clear and non-aliased signal, which can characterize the time it takes for the ultrasonic wave to pass through the length of the tungsten carbide rod twice. The transmission signal received by the lithium niobate transducer of the second high-frequency ultrasonic transceiver 12 is the time it takes for the ultrasonic wave to pass through two tungsten carbide rods and the thickness of a sample. The two signals are received by two channels of the high-speed sampling oscilloscope 5, and do not affect each other. The time difference measurement reference is clear. Under the same time base, the time difference of the two signals can be easily measured by comparing the two waveforms directly. The wave velocity can be calculated by dividing the sample thickness by the time difference. The selected lithium niobate transducer can simultaneously generate longitudinal waves and transverse waves within the excitation signal range of 20MHz to 50MHz. Since the transverse wave velocity is significantly smaller than the longitudinal wave velocity, the transverse wave signal has a significant time lag compared to the longitudinal wave signal through a certain length of tungsten carbide path, so that the device can simultaneously measure the longitudinal wave velocity and transverse wave velocity of the measured sample under the same excitation signal frequency.

[0041] During the experiment, the two sides of the thin slice sample are first polished in parallel, and then clamped on the measuring fixture 1 in the center. The elastic clamping force is adjusted so that the two sides of the sample are fully fitted to the two tungsten carbide rods and clamped on the fixture.

[0042] Turn on the signal generator 2 and the high-speed sampling oscilloscope 5. Adjust the signal generator 2 to generate a sine wave with a frequency of 30MHz, a phase of 180°, and 5 cycles, and trigger it continuously at an interval of 1ms. At this time, the first high-frequency ultrasonic transceiver 11 will generate significant longitudinal and transverse waves. Adjust the trigger voltage of channel 1 of the high-speed sampling oscilloscope 5 until the waveform is stable, and measure the time difference between the longitudinal wave first interface reflection signal of channel 1 of the high-speed sampling oscilloscope 5 and the longitudinal wave transmission signal of channel 2 (which can be obtained by measuring the time difference between any corresponding peaks of the two waveforms), which is the time it takes for the longitudinal wave to pass through the sample once. Divide this time by the sample thickness to obtain the longitudinal wave velocity. The time difference between the shear wave first interface reflection signal of channel 1 and the shear wave transmission signal of channel 2 of the high-speed sampling oscilloscope 5 is measured (which can be obtained by measuring the time difference between any corresponding peaks of the two waveforms). This is the time it takes for the shear wave to pass through the sample once. This time is divided by the sample thickness to obtain the shear wave velocity. .

[0043] The elastic modulus is calculated according to the elastic modulus E formula:

[0044] The shear modulus is calculated according to the shear modulus G formula:

[0045] Example 4 Test Case

[0046] Measure the elastic modulus of the aluminum oxide sample, which is a polished cylindrical thin slice with a sample thickness of 1.035 mm, a diameter of 3.008 mm, and a sample density of 4.02 g / cm3. After calibrating the equipment, clamp the sample on the measuring fixture 1, adjust the signal generator 2 to generate a 30 MHz, 5-cycle, 180° phase sine wave, and a trigger interval of 1 ms. Adjust the trigger voltage of channel 1 of the high-speed sampling oscilloscope 5 until the waveform is stable (such as Figure 7 The clamping force of the measuring fixture 1 is adjusted until the 2nd channel of the high-speed sampling oscilloscope 5 shows obvious longitudinal and transverse wave transmission signals. The time difference between the longitudinal wave reflection signal of the first interface of channel 1 and the longitudinal wave transmission signal of channel 2 measured by the high-speed sampling oscilloscope 5 is 95.20ns (as shown in Figure 8 As shown, the time difference of the third wave peak was measured in the experiment), and the longitudinal wave velocity was calculated to be 10871.85 m / s; the time difference between the shear wave reflection signal of the first interface of channel 1 and the shear wave transmission signal of channel 2 was measured by high-speed sampling oscilloscope 5 and was 162.72 ns (as shown Fig. 9 As shown in the figure, the time difference of the third wave peak is measured in the experiment), and the shear wave velocity is calculated to be 6360.62 m / s. Finally, the elastic modulus calculation formula is used to calculate the elastic modulus to be 403.28 GPa and the shear modulus to be 162.64 GPa.

Claims

1. A device for ultrasonically detecting the elastic modulus of a small-sized thin plate sample, comprising a measuring tool (1), a signal generator (2), a first low-pass filter (3), a second low-pass filter (4) and a high-speed sampling oscilloscope (5); It is characterized in that The structure of the measuring tool (1) is as follows: a first high-frequency ultrasonic transceiver (11) and a second high-frequency ultrasonic transceiver (12) are fixed on a guide rail (13) to ensure that the two high-frequency ultrasonic transceivers are aligned; the first high-frequency ultrasonic transceiver (11) is fixed, and the second high-frequency ultrasonic transceiver (12) can be moved along the guide rail (13) to clamp the sample; elastic clamping is adopted so that the clamping force can be adjusted to ensure reliable contact with the sample surface; the signal of the first high-frequency ultrasonic transceiver (11) is divided into two lines through a splitter, the first line is connected to the signal generator (2) through a coaxial cable, and the second line is connected to channel 1 of a high-speed sampling oscilloscope (5) through a coaxial cable via a first low-pass filter (3); the second high-frequency ultrasonic transceiver (12) is connected to channel 2 of the high-speed sampling oscilloscope (5) through a coaxial cable via a second low-pass filter (4); the first low-pass filter (3) and the second low-pass filter (4) are exactly the same; The first high-frequency ultrasonic transceiver (11) is composed of a lithium niobate transducer (111), a tungsten carbide rod (112), a steel frame (113), and a printed circuit board (116) with a pin spring terminal (114) and a coaxial cable connector (115); the two end faces of the tungsten carbide rod (112) are polished, the surface of the lithium niobate transducer (111) is gold-plated, and is bonded to one end of the tungsten carbide rod (112) by hot-melt resin, the tungsten carbide rod (112) is fixed by the steel frame (113), and one side of the lithium niobate transducer (111) is connected to the contact of the pin spring terminal (114). The contact is reliable and the contact surface is small, thereby avoiding the generation of clutter signals on the back of the transducer. The pin spring terminal (114) is welded on the printed circuit board (116) and connected to the positive electrode of the coaxial cable connector (115). The steel frame (113) is connected to the other side of the lithium niobate transducer (111) through the tungsten carbide rod (112) and is connected to the negative electrode of the coaxial cable connector (115). An excitation signal can be applied or a signal can be received through the coaxial cable connector (115). The second high-frequency ultrasonic transceiver (12) has the same structure as the first high-frequency ultrasonic transceiver (11).

2. The device for ultrasonically detecting elastic modulus of small-sized thin plate samples according to claim 1, characterized in that: The lithium niobate transducer (111) has a transverse wave excitation frequency of 30 MHz and a longitudinal wave excitation frequency of 50 MHz, and can simultaneously generate longitudinal waves and transverse waves within an excitation signal range of 20 MHz to 50 MHz.

3. The device for ultrasonically detecting elastic modulus of small-sized thin plate samples according to claim 1, characterized in that: The cut-off frequencies of the first low-pass filter (3) and the second low-pass filter (4) are 200 MHz.

4. The device for ultrasonically detecting elastic modulus of small-sized thin plate samples according to claim 1, characterized in that: The sampling rate of the high-speed sampling oscilloscope (5) is 6.25 GS / s.

5. The device for ultrasonically detecting elastic modulus of small-sized thin plate samples according to claim 1, characterized in that: The length of the tungsten carbide rod (112) is 18 mm.

6. A method for ultrasonically detecting the elastic modulus of a small-sized thin plate sample, characterized in that: The device of claim 1 is used, the steps are as follows: adjusting the frequency of the signal generator (2) to a frequency at which the lithium niobate transducer (111) can simultaneously excite longitudinal waves and transverse waves, the signal generator (2) generates a signal and the first high-frequency ultrasonic transceiver (11) converts the signal into an ultrasonic wave and transmits it, the first high-frequency ultrasonic transceiver (11) receives a reflected signal from a first interface of the sample, the second high-frequency ultrasonic transceiver (12) receives a transmitted signal passing through two tungsten carbide rods and a sample thickness, the two high-frequency ultrasonic transceivers transmit the received reflected or transmitted ultrasonic signals through their respective The lithium niobate transducer converts the electrical signal into an electrical signal and transmits it to two channels of a high-speed sampling oscilloscope (5) respectively. The time difference between the two signals is directly measured by comparing the two corresponding waveforms of the high-speed sampling oscilloscope (5) at the same time base. The wave velocity is calculated by dividing the sample thickness by the time difference. Since the ultrasonic shear wave velocity is significantly smaller than the longitudinal wave velocity, the shear wave signal will significantly lag behind the longitudinal wave signal in time after passing through a certain length of tungsten carbide rod path. The two are clearly distinguished. Using one excitation signal frequency, the shear wave and longitudinal wave can be measured simultaneously. The above method is used to measure the wave velocity of the ultrasonic longitudinal wave passing through the measured sample: , the shear wave velocity of ultrasonic shear wave passing through the sample is ; Then the elastic modulus of the sample being tested is: ； The shear modulus is: , in, is the density of the sample being tested.

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