Earthquake low-frequency elastic parameter test system and test method

Abstract

The invention discloses an earthquake low-frequency elastic parameter test system and test method. The system comprises a signal generating and amplifying unit used for generating and amplifying a low-frequency sinusoidal signal; the testing unit is used for enabling the rock sample and the reference sample to generate low-frequency vibration based on the low-frequency sinusoidal signal, collecting deformation of the rock sample and the reference sample and converting the deformation into a voltage signal; the first signal amplification module is used for amplifying the voltage signal; and the control unit is used for converting the amplified voltage signal into a digital signal, calculating a low-frequency elastic parameter of the rock sample based on the digital signal, calculating a longitudinal wave speed and a transverse wave speed of the rock sample based on the elastic parameter, and controlling generation of a sinusoidal signal. According to the invention, the strain information of the specified area on the surface of the tested object is collected through the electrical measurement method, and the frequency elastic modulus under the seismic frequency can be efficiently and accurately obtained.

Description

Technical Field

[0001] The present invention belongs to the technical field of rock physics, and more specifically, relates to a seismic low-frequency elastic parameter testing system and a testing method. Background Art

[0002] At present, there are some main methods for measuring the acoustic parameters of rocks in the laboratory at home and abroad. The first category is the propagation time method: its representative method is the ultrasonic pulse method; the second category is the resonance rod method: the resonance rod method is a low-frequency test technology operating at the kilohertz level; the third category is the stress-strain method: the stress-strain method is another important low-frequency test technology. The stress-strain measurement technology obtains the acoustic properties of rock samples by directly recording the forced deformation applied to the rock sample. Under laboratory conditions, the size of the core is limited, which is on the order of centimeters. In order to ensure that this size is several times larger than the wavelength of the sound wave, the ultrasonic pulse method can only perform high-frequency measurements (MHz order of magnitude). However, it is well known that whether the test results of rock acoustic parameters under laboratory high-frequency (MHz) conditions are directly applied to data processing and data interpretation in the seismic exploration and logging frequency band (10Hz-10kHz) has always been an important problem that has plagued the geophysical community. The essence of this problem is the dispersion problem of wave propagation. In view of this, directly conducting routine tests of rock acoustic parameters at low frequencies (field seismic exploration and logging frequency bands) is a long-term goal pursued by petrophysicists. At present, there are several institutions that have developed and used low-frequency testing equipment, namely the Colorado School of Mines and Lawrence National Laboratory in the United States, Reading University in France, Australian National University, Curtin University and KARLE Institute in Denmark. The low-frequency testing equipment developed by the above institutions all adopts Spencer's stress-strain method in principle, but there are slight differences in the test frequency and temperature and pressure conditions. However, the only institution that has published the test results publicly is Michael Batzle Rock Physics Laboratory of Colorado School of Mines. In short, low-frequency elastic modulus testing still has problems such as long test cycle, cumbersome test steps, and high experimental difficulty.

[0003] The information disclosed in the background technology section of the present invention is only intended to deepen the understanding of the general background technology of the present invention, and should not be regarded as acknowledging or suggesting in any form that the information constitutes the prior art already known to those skilled in the art. Summary of the invention

[0004] The purpose of the present invention is to provide a seismic low-frequency elastic parameter testing system and a testing method to achieve efficient and accurate acquisition of seismic low-frequency elastic parameters.

[0005] To achieve the above object, the present invention proposes a seismic low-frequency elastic parameter testing system and testing method.

[0006] According to the first aspect of the present invention, a seismic low-frequency elastic parameter testing system is provided, including:

[0007] A signal generating and amplifying unit, configured to generate and amplify a low-frequency sine signal;

[0008] A testing unit, configured to cause the rock sample and the reference sample to generate low-frequency vibrations based on the low-frequency sine signal, collect the deformation amounts of the rock sample and the reference sample, and convert the deformation amounts into voltage signals;

[0009] A first signal amplifying module, configured to amplify the voltage signal;

[0010] A control unit, configured to convert the amplified voltage signal into a digital signal, calculate the low-frequency elastic parameters of the rock sample based on the digital signal, calculate the longitudinal wave velocity and the transverse wave velocity of the rock sample based on the elastic parameters, and control the generation of the sine signal;

[0011] The signal generating and amplifying unit, the testing unit, the first amplifying module, and the control unit are electrically connected in sequence, and the signal generating and amplifying unit is electrically connected to the control unit.

[0012] Optionally, the signal generating and amplifying unit includes:

[0013] A signal generating module, configured to generate a sine signal;

[0014] A second signal amplifying module, configured to amplify the sine signal.

[0015] The signal generating module is electrically connected to the second signal amplifying module, and the signal generating module is electrically connected to the control unit.

[0016] Optionally, the testing unit includes:

[0017] A clamping module, configured to clamp the rock sample and the reference sample;

[0018] An exciting module, configured to vibrate the rock sample and the reference sample based on the sine signal;

[0019] A collecting module, configured to collect the deformation amounts of the rock sample and the reference sample;

[0020] A conversion module, configured to convert the deformation amounts into voltage signals.

[0021] Optionally, the reference sample is respectively placed at the upper and lower ends of the rock sample to form a test sample, and the test sample is fixed on the workbench at the top of the exciting module.

[0022] Optionally, the clamping module includes:

[0023] A bottom plate for supporting the test sample and the excitation module;

[0024] A top plate for clamping and fixing the excitation module and the test sample together with the bottom plate;

[0025] A plurality of clamping rods, one end of each clamping rod is fixedly connected to the bottom plate, and the other end of each clamping rod is connected to the top plate. The plurality of clamping rods, together with the bottom plate and the top plate, clamp and fix the excitation module and the test sample.

[0026] Optionally, the acquisition module includes:

[0027] A plurality of corresponding strain gauges. Some of the strain gauges are vertically fixed on the outer surface of the side of the rock sample for measuring the axial vibration of the rock sample, some of the strain gauges are horizontally fixed on the outer surface of the side of the rock sample for measuring the radial vibration of the rock sample, and the remaining strain gauges are vertically fixed on the outer surface of the side of the reference sample for measuring the axial vibration of the reference sample;

[0028] The excitation module generates vibrations to deform the test sample, and based on the deformation, the resistance of the strain gauge changes.

[0029] Optionally, the conversion module includes:

[0030] A Wheatstone bridge electrically connected to all the strain gauges, and the Wheatstone bridge is used to convert the change in resistance into a voltage signal.

[0031] Optionally, the control unit includes:

[0032] An analog-to-digital conversion module for converting the voltage signal into the digital signal;

[0033] A calculation module for calculating the elastic parameters, longitudinal wave velocity and transverse wave velocity of the rock sample based on the digital signal;

[0034] A control module for controlling the generation of the sine signal;

[0035] The analog-to-digital conversion module is electrically connected to the amplification module and the calculation module respectively, and the control module is electrically connected to the signal generation and amplification unit.

[0036] Optionally, the low-frequency elastic parameters include:

[0037] Young's modulus, and the expression for calculating Young's modulus is:

[0038]

[0039] Poisson's ratio, and the expression for calculating the Poisson's ratio is as follows:

[0040]

[0041] where ε al is the axial strain of the reference sample, and ε ax is the axial strain of the rock sample, E al is the Young's modulus of the reference sample, and ε rad is the radial strain of the rock sample.

[0042] According to the second aspect of the present invention, a method for testing seismic low-frequency elastic parameters is proposed, including:

[0043] Generating and amplifying a low-frequency sine signal;

[0044] Vibrating a rock sample and a reference sample based on the sine signal, collecting the deformation amounts of the rock sample and the reference sample, and converting the deformation amounts into voltage signals;

[0045] Amplifying the voltage signals;

[0046] Converting the amplified voltage signals into digital signals, and calculating the low-frequency elastic parameters of the rock sample based on the digital signals;

[0047] Calculating the longitudinal wave velocity and the transverse wave velocity of the rock sample based on the low-frequency elastic parameters, and controlling the generation of the sine signal.

[0048] The beneficial effects of the present invention are as follows: The present invention collects the deformation amounts of a rock sample and a reference sample through strain gauges fixed to the rock sample and the reference sample, represents the deformation amounts by the change in the resistance of the strain gauges, converts the resistance change into a voltage signal through a Wheatstone bridge, and converts the voltage signal into a digital signal through analog-to-digital conversion, and calculates the low-frequency elastic parameters of the rock sample based on the digital signal; in laboratory tests, elastic parameters are usually obtained in the ultrasonic frequency band (about 1 MHz), and the dispersion or attenuation mechanism that plays a major role in this frequency band may be different from that in the seismic frequency band. Therefore, direct measurement in the seismic frequency band is very beneficial for clarifying the seismic wave dispersion and attenuation mechanisms. The present invention can efficiently and accurately obtain the frequency elastic modulus at seismic frequencies by collecting the strain information of a specified area on the surface of the test object through an electrical measurement method.

[0049] The system of the present invention has other characteristics and advantages, which will be obvious from the accompanying drawings incorporated herein and the subsequent specific embodiments, or will be described in detail in the accompanying drawings incorporated herein and the subsequent specific embodiments. These accompanying drawings and specific embodiments are used together to explain the specific principles of the present invention. Description of the Drawings

[0050] The above and other objects, features, and advantages of the present invention will become more apparent by describing the exemplary embodiments of the present invention in more detail with reference to the accompanying drawings. In the exemplary embodiments of the present invention, the same reference numerals generally represent the same components.

[0051] Figure 1 A schematic diagram of a seismic low-frequency elastic parameter testing system according to the present invention is shown.

[0052] Figure 2 A schematic diagram of a seismic low-frequency elastic parameter testing system according to Embodiment 2 of the present invention is shown.

[0053] Figure 3 A physical diagram of a fast seismic low-frequency elastic modulus testing component module according to Embodiment 2 of the present invention is shown.

[0054] Figure 4 A schematic diagram of the horizontal and vertical deformation of a rock sample under the axial force provided by a vibration exciter according to Embodiment 2 of the present invention is shown.

[0055] Figure 5 A test result diagram of a standard aluminum sample in a fast seismic low-frequency elastic modulus according to Embodiment 3 of the present invention is shown.

[0056] Figure 6 A test result diagram of plexiglass in a fast seismic low-frequency elastic modulus according to Embodiment 4 of the present invention is shown.

[0057] Figure 7 A schematic diagram of the change of the Young's modulus of plexiglass with frequency according to Embodiment 4 of the present invention is shown. Detailed implementation manners

[0058] The present invention will be described in more detail below with reference to the accompanying drawings. Although the preferred embodiments of the present invention are shown in the drawings, it should be understood that the present invention can be implemented in various forms and should not be limited by the embodiments set forth herein. On the contrary, these embodiments are provided to make the present invention more thorough and complete, and to fully convey the scope of the present invention to those skilled in the art.

[0059] As Figure 1 shown, a seismic low-frequency elastic parameter testing system according to the present invention includes:

[0060] A signal generating and amplifying unit for generating and amplifying a low-frequency sine signal;

[0061] A testing unit for causing a rock sample and a reference sample to generate low-frequency vibrations based on the low-frequency sine signal, collecting the deformation amounts of the rock sample and the reference sample, and converting the deformation amounts into voltage signals;

[0062] The first signal amplification module is used to amplify the voltage signal;

[0063] The control unit is used to convert the amplified voltage signal into a digital signal, calculate the low-frequency elastic parameters of the rock sample based on the digital signal, calculate the longitudinal wave velocity and transverse wave velocity of the rock sample based on the elastic parameters, and control the generation of the sine signal;

[0064] The signal generation and amplification unit, the test unit, the first amplification module and the control unit are electrically connected in sequence, and the signal generation and amplification unit is electrically connected to the control unit.

[0065] Specifically, in the present invention, the control unit controls the signal generation and amplification unit to generate a low-frequency sine signal, amplifies this low-frequency sine signal and outputs it to the test unit. After receiving this low-frequency sine signal, the test unit generates a sine vibration of the same frequency, causing the rock sample and the reference sample to perform sine vibration. Furthermore, the deformation amounts of the rock sample and the reference sample are collected, and these deformation amounts are converted into voltage signals and sent to the first signal amplification module for amplification. The amplified voltage signal is input into the control unit for analog-to-digital conversion to obtain a digital signal containing deformation amount information. The control unit calculates the elastic parameters of the rock sample according to the deformation amount information in this digital signal, and then calculates the longitudinal wave velocity and transverse wave velocity of the rock sample according to the elastic parameters.

[0066] In one example, the signal generation and amplification unit includes:

[0067] The signal generation module is used to generate a sine signal;

[0068] The second signal amplification module is used to amplify the sine signal.

[0069] The signal generation module is electrically connected to the second signal amplification module, and the signal generation module is electrically connected to the control unit.

[0070] In one example, the test unit includes:

[0071] The clamping module is used to clamp the rock sample and the reference sample;

[0072] The excitation module is used to vibrate the rock sample and the reference sample based on the sine signal;

[0073] The acquisition module is used to acquire the deformation amounts of the rock sample and the reference sample;

[0074] The conversion module is used to convert the deformation amount into a voltage signal.

[0075] In one example, the reference sample is respectively placed at the upper and lower ends of the rock sample to form a test sample, and the test sample is fixed on the workbench at the top of the excitation module.

[0076] In one example, the clamping module includes:

[0077] A bottom plate for supporting a test sample and a vibration excitation module;

[0078] A top plate for clamping and fixing the vibration excitation module and the test sample with the bottom plate;

[0079] A plurality of clamping rods, one end of each clamping rod is fixedly connected to the bottom plate, and the other end of each clamping rod is connected to the top plate. The plurality of clamping rods, together with the bottom plate and the top plate, clamp and fix the vibration excitation module and the test sample.

[0080] In one example, the acquisition module includes:

[0081] A plurality of corresponding strain gauges. Some strain gauges are vertically fixed on the outer surface of the side of the rock sample for measuring the axial vibration of the rock sample, some strain gauges are horizontally fixed on the outer surface of the side of the rock sample for measuring the radial vibration of the rock sample, and the remaining strain gauges are vertically fixed on the outer surface of the side of the reference sample for measuring the axial vibration of the reference sample;

[0082] The vibration excitation module generates vibrations to deform the test sample, and based on the deformation, the resistance of the strain gauges changes.

[0083] Specifically, a resistance strain gauge is a resistive sensor and a key component of the electrical measurement method. It reflects the strain of the measured sample by the change in its own electrical resistance. The strain felt by the pasted strain gauge due to mechanical vibration maintains a proportional relationship with the electrical resistance change rate. The proportional coefficient is the strain gauge sensitivity coefficient, which is determined by the resistance strain gauge itself. To enhance the manual operability of the experiment, a semiconductor strain gauge with an insulating substrate and a large sensitivity coefficient is selected.

[0084] In one example, the conversion module includes:

[0085] A Wheatstone bridge electrically connected to all strain gauges, and the Wheatstone bridge is used to convert the change in resistance into a voltage signal.

[0086] Specifically, the characteristic of the Wheatstone bridge is that the resistance change rate and the output voltage value maintain a high linear relationship.

[0087] In one example, the control unit includes:

[0088] An analog-to-digital conversion module for converting the voltage signal into a digital signal;

[0089] A calculation module for calculating the elastic parameters, longitudinal wave velocity, and transverse wave velocity of the rock sample based on the digital signal;

[0090] A control module for controlling the generation of a sine signal;

[0091] The analog-to-digital conversion module is electrically connected to the amplification module and the calculation module respectively, and the control module is electrically connected to the signal generation and amplification unit.

[0092] In one example, the low-frequency elastic parameters include:

[0093] Young's modulus, and the expression for calculating Young's modulus is:

[0094]

[0095] Poisson's ratio, and the expression for calculating Poisson's ratio is:

[0096]

[0097] where ε al is the axial strain of the reference sample, ε ax is the axial strain of the rock sample, E al is the Young's modulus of the reference sample, and ε rad is the radial strain of the rock sample.

[0098] The present invention will be further described below in conjunction with the accompanying drawings and specific embodiments, but it is not a limitation of the present invention. It should be noted that, without conflict, the embodiments and features in the embodiments of the present invention can be combined with each other.

[0099] Embodiment 1

[0100] This embodiment provides a seismic low-frequency elastic parameter testing system, including:

[0101] A signal generation and amplification unit for generating and amplifying a low-frequency sine signal; the signal generation and amplification unit includes a signal generation module and a second signal amplification module. The signal generation module is used for generating a sine signal; the second signal amplification module is used for amplifying the sine signal; the signal generation module is electrically connected to the second signal amplification module, and the signal generation module is electrically connected to the control unit;

[0102] A test unit is used to generate low-frequency vibrations of a rock sample and a reference sample based on a low-frequency sine signal, collect the deformation amounts of the rock sample and the reference sample, and convert the deformation amounts into voltage signals. The test unit includes a clamping module, an exciting module, a collection module, and a conversion module. The clamping module is used to clamp the rock sample and the reference sample. The exciting module is used to vibrate the rock sample and the reference sample based on the sine signal. The collection module is used to collect the deformation amounts of the rock sample and the reference sample. The conversion module is used to convert the deformation amounts into voltage signals. The reference samples are respectively placed at the upper and lower ends of the rock sample to form a test sample, and the test sample is fixed on the workbench at the top of the exciting module. The clamping module includes a bottom plate, a top plate, and a plurality of clamping rods. The bottom plate is used to support the test sample and the exciting module. The top plate is used to clamp and fix the exciting module and the test sample with the bottom plate. One end of each of the plurality of clamping rods is fixedly connected to the bottom plate, and the other end of the clamping rod is connected to the top plate. The plurality of clamping rods, together with the bottom plate and the top plate, clamp and fix the exciting module and the test sample. The collection module includes a plurality of corresponding strain gauges. Some of the strain gauges are vertically fixed on the outer surface of the side of the rock sample to measure the axial vibration of the rock sample, some of the strain gauges are horizontally fixed on the outer surface of the side of the rock sample to measure the radial vibration of the rock sample, and the remaining strain gauges are vertically fixed on the outer surface of the side of the reference sample to measure the axial vibration of the reference sample. The exciting module generates vibrations to deform the test sample, and based on the deformation, the resistance of the strain gauge changes. The resistance strain gauge is a resistive sensor and is a key component of the electrical measurement method. It reflects the strain of the measured sample by the change in its own electrical resistance. The strain felt by the pasted strain gauge due to mechanical vibration maintains a proportional relationship with the rate of change of the electrical resistance. The proportionality coefficient is the sensitivity coefficient of the strain gauge, and this sensitivity coefficient is determined by the resistance strain gauge itself. To enhance the manual operability of the experiment, a semiconductor strain gauge with an insulating substrate and a large sensitivity coefficient is selected. The conversion module is a Wheatstone bridge, which is electrically connected to all the strain gauges. The Wheatstone bridge is used to convert the change in resistance into a voltage signal. The characteristic of the Wheatstone bridge is that the rate of change of resistance maintains a high linear relationship with the output voltage value.

[0103] A control unit is used to convert the amplified voltage signal into a digital signal, calculate the low-frequency elastic parameters of the rock sample based on the digital signal, calculate the longitudinal wave velocity and the transverse wave velocity of the rock sample based on the elastic parameters, and control the generation of the sine signal. The control unit includes a control module, an analog-to-digital conversion module, and a calculation module. The analog-to-digital conversion module is used to convert the voltage signal into a digital signal. The calculation module is used to calculate the elastic parameters, the longitudinal wave velocity, and the transverse wave velocity of the rock sample based on the digital signal. The control module is used to control the generation of the sine signal. The analog-to-digital conversion module is electrically connected to the amplification module and the calculation module respectively, and the control module is electrically connected to the signal generation and amplification unit.

[0104] The low-frequency elastic parameters include Young's modulus and Poisson's ratio;

[0105] The expression for calculating Young's modulus is as follows:

[0106]

[0107] The expression for calculating Poisson's ratio is as follows:

[0108]

[0109] where ε al is the axial strain of the reference sample, ε ax is the axial strain of the rock sample, E al is the Young's modulus of the reference sample, and ε rad is the radial strain of the rock sample.

[0110] Example 2

[0111] As Figure 2 shown, this example provides a seismic low-frequency elastic parameter testing system, including:

[0112] Computer control unit, signal generator, power amplifier, shaker, gripper, strain gauge, Wheatstone bridge, signal amplifier; the computer control unit controls the signal generator to output a signal, which is a sine signal with a specific frequency. First, it passes through the power amplifier and then is transmitted to a small vibration shaker. The shaker converts the vibration into an electrical signal. The sine vibration measures the deformation of the rock and the deformation of the reference aluminum block along the axial direction. The strain gauges pasted on the surfaces of the core and the reference aluminum block will sense this deformation amount, causing a change in their resistance. The electrical measurement method can be used to test the strain in a specified area on the surface of an object. The measurement method is to convert the measured strain change into a resistance change through certain strain sensing components, and then through related equipment, convert it into a voltage (or current) change and amplify it with an amplifier. Finally, the display and processing results are given. The sensing component is a sensitive resistance strain gauge. The resistance strain gauge is a resistive sensor and is a key component of the electrical measurement method. It reflects the strain of the measured sample through the change in its own electrical resistance. The strain generated by mechanical vibration felt by the pasted strain gauge maintains a proportional relationship with the rate of change of electrical resistance. The proportionality coefficient is the sensitivity coefficient of the strain gauge, and this sensitivity coefficient is determined by the resistance strain gauge itself. The instrument is a resistance strain gauge based on the Wheatstone bridge. The characteristic of the Wheatstone bridge is that the rate of change of resistance maintains a highly linear relationship with the output voltage value. Four pairs of semiconductor type strain gauges with insulating substrates are pasted on the surface of the rock sample, with two pairs arranged vertically and two pairs arranged horizontally. Two pairs of semiconductor type strain gauges arranged vertically are pasted on the surface of the reference aluminum sample. When the shaker emits a sine signal vibration, both the rock sample and the reference aluminum sample will undergo varying degrees of deformation. The resistance of the semiconductor type strain gauges arranged vertically and horizontally on the surface of the rock sample and the semiconductor type strain gauges arranged vertically on the surface of the reference aluminum sample will change with the sine signal. The relative change value of the resistance will be converted into a voltage signal through the Wheatstone bridge circuit, and finally, after amplification and acquisition processing, the strain information can be obtained. Semiconductor type strain gauges with a large sensitivity coefficient are used. At the same time, to reduce the technical difficulty of preparing samples and enhance the manual operability of the experiment, large sensitivity coefficient semiconductor strain gauges with insulating substrates are selected. During the process of selecting the strain gauges, a large number of basic experiments were carried out (including strain gauges of foil material types, semiconductor type strain gauges without substrates and semiconductor type strain gauges with substrates, as well as semiconductor strain gauges of different shapes such as rod-shaped and columnar), and finally, large sensitivity coefficient semiconductor strain gauges with insulating substrates were selected. The changing resistance change amount is converted into a voltage signal through a group of Wheatstone bridges. This signal passes through a signal amplifier and an analog-to-digital converter and is finally collected by the acquisition system, and finally, the strain information of the core to be measured and the reference aluminum block is obtained. To enable the small vibration shaker to play its role, the entire test system is equipped with corresponding mechanical structures, such as Figure 3As shown in the figure, the sample to be tested is bonded to the aluminum workbench of the exciter with epoxy resin glue, and then the whole sample to be tested bonded with the exciter is placed in the middle of the gripper; the aluminum workbench has three functions: First, it provides a horizontal reference plane for the rock sample to be tested, ensuring that when the exciter undergoes periodic sinusoidal mechanical vibration in the axial direction, the rock is stressed along the axial direction and the stress is uniform, and this function is jointly completed by the aluminum workbench and the bearing; Second, it provides a medium for the output of the mechanical vibration of the exciter; Third, the weight of aluminum itself can make the exciter perform better in the low-frequency working range. When measuring and installing the sample, the length of the sample is different each time, and the length of the support rod needs to be adjusted by adding or reducing shims to keep the vibration table of the exciter in natural balance, that is, no external force can be applied to the aluminum workbench of the exciter.

[0113] Figure 4 It is a schematic diagram of the vertical and horizontal deformations of the rock sample under the axial sinusoidal force provided by the vibration exciter. When loading and unloading the axial sinusoidal force, there is a phase change of about 180℃ in the deformations in the horizontal and vertical directions. According to the strain information of the test sample and the reference aluminum sample, under the assumption that the rock sample is homogeneous and isotropic, and under the same stress, the Young's modulus of the rock sample can be obtained by the following formula:

[0114]

[0115] ε al is the axial strain of the reference aluminum, ε ax is the axial strain of the sample to be tested, E al is the Young's modulus (known) of the reference aluminum. The Poisson's ratio of the rock sample can be obtained by the following formula:

[0116]

[0117] ε rad is the radial strain of the sample to be tested.

[0118] Then, according to the elastic wave theory, the longitudinal and transverse wave velocities Vs LF can be obtained by the following formula:

[0119]

[0120]

[0121] E and v are the Young's modulus and Poisson's ratio calculated above respectively, ρ is the density of the sample, and LF represents low frequency.

[0122] Example 3

[0123] In this embodiment, an elastic material, namely a standard aluminum sample, is selected and experiments are conducted using the seismic low-frequency elastic parameter testing system of Embodiment 2. Tests are carried out in the frequency range of 2 - 2000 Hz, and the dispersion curves of Young's modulus and Poisson's ratio of the standard aluminum sample in the frequency band from 2 Hz to 2000 Hz are obtained. As Figure 5 shown. From seismic to ultrasonic frequencies, Young's modulus and Poisson's ratio basically remain unchanged, being 71 GPa and 0.33 respectively. That is, neither Young's modulus nor Poisson's ratio shows dispersion in the low-frequency band, and it is consistent with the measurement results at ultrasonic frequencies. Generally, aluminum can be regarded as a completely elastic medium under weak stress, and the experimental results fully conform to this understanding. This is sufficient to confirm the reliability of this rapid seismic low-frequency elastic modulus testing system for measuring non-dispersive samples.

[0124] Embodiment 4

[0125] In this embodiment, a viscoelastic material, namely plexiglass, is selected and experiments are conducted using the seismic low-frequency elastic parameter testing system of Embodiment 2. As Figure 6 shown, in the low-frequency measurement section of 2 - 2000 Hz, the Young's modulus of plexiglass increases from 4.25 GPa to 5.4 GPa, an increase of 27%, showing a strong dispersion phenomenon. The highest value of Young's modulus that can be measured in the low-frequency band still has a difference of 0.2 GPa compared with the Young's modulus of 5.6 GPa in the ultrasonic frequency band. If the measurement frequency band is wide enough, it should be possible to observe that Young's modulus continues to increase with frequency until it approaches the measurement results in the ultrasonic frequency band. In the low-frequency measurement band, the Poisson's ratio of plexiglass has no obvious change trend, with a floating change of about 4%, and the value is basically consistent with the ultrasonic test results. Batzle M. also reported similar experimental phenomena, as Figure 7 shown. The plexiglass samples they selected are different from those we tested, but the change law of Young's modulus is the same. This is also sufficient to confirm the reliability of this rapid seismic low-frequency elastic modulus testing system for measuring dispersive samples.

[0126] Embodiment 5

[0127] This embodiment provides a method for testing seismic low-frequency elastic parameters, including:

[0128] Generating and amplifying a low-frequency sine signal;

[0129] Based on the low-frequency sine signal, causing a rock sample and a reference sample to generate low-frequency vibrations, collecting the deformation amounts of the rock sample and the reference sample, and converting the deformation amounts into voltage signals;

[0130] Amplifying the voltage signal;

[0131] Converting the amplified voltage signal into a digital signal, and calculating the low-frequency elastic parameters of the rock sample based on the digital signal;

[0132] Based on the low-frequency elastic parameters, the longitudinal wave velocity and the shear wave velocity of the rock sample are calculated to control the generation of the sine signal.

[0133] The embodiments of the present invention have been described above. The above description is exemplary and not exhaustive, and is also not limited to the disclosed embodiments. Many modifications and variations are obvious to those of ordinary skill in the art without departing from the scope and spirit of the described embodiments.

Claims

1. An earthquake low-frequency elastic parameter testing system, characterized in that, it includes: A signal generating and amplifying unit for generating and amplifying a low-frequency sine signal; A testing unit for causing the rock sample and the reference sample to generate low-frequency vibrations based on the low-frequency sine signal, collecting the deformation amounts of the rock sample and the reference sample, and converting the deformation amounts into voltage signals; A first signal amplification module for amplifying the voltage signal; A control unit for converting the amplified voltage signal into a digital signal, calculating the low-frequency elastic parameters of the rock sample based on the digital signal, calculating the longitudinal wave velocity and the transverse wave velocity of the rock sample based on the low-frequency elastic parameters, and controlling the generation of the sine signal; The signal generating and amplifying unit, the testing unit, the first amplification module and the control unit are electrically connected in sequence, and the signal generating and amplifying unit is electrically connected to the control unit.

2. The earthquake low-frequency elastic parameter testing system according to claim 1, characterized in that, The signal generating and amplifying unit includes: A signal generating module for generating a sine signal; A second signal amplification module for amplifying the sine signal. The signal generating module is electrically connected to the second signal amplification module, and the signal generating module is electrically connected to the control unit.

3. The earthquake low-frequency elastic parameter testing system according to claim 1, characterized in that, The testing unit includes: A clamping module for clamping the rock sample and the reference sample; An exciting module for vibrating the rock sample and the reference sample based on the sine signal; A collecting module for collecting the deformation amounts of the rock sample and the reference sample; A conversion module for converting the deformation amounts into voltage signals.

4. The earthquake low-frequency elastic parameter testing system according to claim 3, characterized in that, The reference samples are respectively placed at the upper and lower ends of the rock sample to form a test sample, and the test sample is fixed on the workbench at the top of the exciting module.

5. The earthquake low-frequency elastic parameter testing system according to claim 4, characterized in that, The clamping module includes: A bottom plate for supporting the test sample and the exciting module; A top plate for clamping and fixing the exciting module and the test sample together with the bottom plate; A plurality of clamping rods, one end of the clamping rod is fixedly connected to the bottom plate, the other end of the clamping rod is connected to the top plate, and the plurality of clamping rods together with the bottom plate and the top clamp and fix the exciting module and the test sample.

6. The earthquake low-frequency elastic parameter testing system according to claim 5, characterized in that, The collecting module includes: A plurality of corresponding strain gauges, some of the strain gauges are vertically fixed on the outer surface of the side of the rock sample for measuring the axial vibration of the rock sample, some of the strain gauges are horizontally fixed on the outer surface of the side of the rock sample for measuring the radial vibration of the rock sample, and the remaining part of the strain gauges are vertically fixed on the outer surface of the side of the reference sample for measuring the axial vibration of the reference sample; The excitation module generates vibrations to deform the test sample, and based on the deformation, the resistance of the strain gauge changes.

7. The seismic low-frequency elastic parameter test system according to claim 6, wherein, the conversion module includes: a Wheatstone bridge electrically connected to all the strain gauges, and the Wheatstone bridge is used to convert the change in the resistance into a voltage signal.

8. The seismic low-frequency elastic parameter test system according to claim 1, wherein, the control unit includes: an analog-to-digital conversion module for converting the voltage signal into the digital signal; a calculation module for calculating the low-frequency elastic parameters, longitudinal wave velocity, and transverse wave velocity of the rock sample based on the digital signal; a control module for controlling the generation of the sine signal; the analog-to-digital conversion module is electrically connected to the amplification module and the calculation module respectively, and the control module is electrically connected to the signal generation and amplification unit.

9. The seismic low-frequency elastic parameter test system according to claim 1, the low-frequency elastic parameters include: Young's modulus, and the expression for calculating Young's modulus is: Poisson's ratio, and the expression for calculating Poisson's ratio is: Among them, ε al is the axial strain of the reference sample, ε ax is the axial strain of the rock sample, E al is the Young's modulus of the reference sample, ε rad is the radial strain of the rock sample.

10. The seismic low-frequency elastic parameter test method according to claim 1, wherein, it includes: generating and amplifying a low-frequency sine signal; using the low-frequency sine signal to cause the rock sample and the reference sample to generate low-frequency vibrations, collecting the deformation amounts of the rock sample and the reference sample, and converting the deformation amounts into voltage signals; amplifying the voltage signal; converting the amplified voltage signal into a digital signal, and calculating the low-frequency elastic parameters of the rock sample based on the digital signal; calculating the longitudinal wave velocity and transverse wave velocity of the rock sample based on the low-frequency elastic parameters, and controlling the generation of the sine signal.

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