A nondestructive testing device and method for Young's modulus and Poisson's ratio of a thin rod

Abstract

The invention relates to a nondestructive detection device and method for Young's modulus and Poisson's ratio of a thin rod. The density of the thin rod is measured based on the Archimedean principle. A detection device is constructed by using a signal generator, an excitation probe, a receiving probe, a voltage amplifier, a thin rod bracket and an oscilloscope. A low frequency and a high frequency are respectively selected to emit a burst of 20 cycles of Hanning window sine waves in the thin rod, and the first wave packet of the received wave under low-frequency excitation is extracted, corresponding to the longitudinal guided wave velocity. Then, the second wave packet of the received wave under high-frequency excitation is extracted, corresponding to the bending guided wave velocity. The rod wave and the transverse wave are approximated according to the low-frequency longitudinal guided wave and the high-frequency bending guided wave, so that the Young's modulus and the Poisson's ratio of the thin rod can be inversely calculated. The invention relates to a method for measuring the Young's modulus and the Poisson's ratio of a millimeter-level diameter thin rod of a uniform isotropic linear elastic material.

Description

Technical Field

[0001] The invention relates to a nondestructive testing device and method for Young's modulus and Poisson's ratio of a thin rod, belonging to the technical field of nondestructive testing. Background Art

[0002] Thin rods are widely used in mechanical devices and composite materials. Elastic constants, such as Young's modulus and Poisson's ratio, are important indicators for evaluating the mechanical properties of thin rods. Traditional methods for measuring the elastic constants of rod-like structures are mainly based on destructive tests such as tension and torsion. However, these methods require that the specimens have a certain cross-sectional area. For thin rods with a diameter of millimeters, traditional testing methods are difficult to apply because the thin rods cannot be tightened on traditional mechanical testing machines.

[0003] Therefore, the ultrasonic vibration method provides a new way to determine the elastic constants of thin rods due to its excellent non-destructive testing characteristics. Summary of the invention

[0004] The present invention provides a nondestructive testing device and method for the Young's modulus and Poisson's ratio of a thin rod, which can realize the elastic modulus test of a millimeter-level thin rod.

[0005] The technical solution adopted by the present invention to solve the technical problem is:

[0006] A nondestructive testing device for Young's modulus and Poisson's ratio of a thin rod, comprising a signal generator, an excitation probe, a receiving probe, a voltage amplifier and an oscilloscope;

[0007] The output end of the signal generator for generating the incident wave is connected to the excitation probe, the excitation probe is connected to the receiving end of the thin rod to be measured, the transmission end of the thin rod to be measured is connected to the receiving probe, and the receiving probe is simultaneously connected to the input end of the voltage amplifier;

[0008] The output end of the signal generator and the output end of the voltage amplifier are both connected to the oscilloscope;

[0009] It also includes brackets, two brackets are arranged opposite to each other, and the thin rod to be measured is placed on the top of the brackets;

[0010] As a further preferred embodiment of the present invention, the bracket includes a base, a slanted plate is connected to the side of the base, an angle is formed between the bottom edge of the slanted plate and the base, the top edge of the slanted plate is connected to the support plate, and the support plate is arranged perpendicular to the base;

[0011] As a further preferred embodiment of the present invention, a circular arc groove is provided at the center position of the top side edge of the support plate, and the curvature of the circular arc groove matches the circumferential wall of the thin rod to be measured;

[0012] As a further preferred embodiment of the present invention, the angle formed between the bottom edge of the inclined plate and the base is 45°;

[0013] A nondestructive testing method based on Young's modulus and Poisson's ratio of a thin rod specifically comprises the following steps:

[0014] Step S1: using a balance cylinder method to measure the density of the thin rod to be measured;

[0015] Step S2: preparing equipment, including a signal generator, an excitation probe, a receiving probe, a voltage amplifier, an oscilloscope, and a bracket;

[0016] Step S3: construct a nondestructive testing device, connect the output end of the signal generator to the excitation probe, connect the receiving probe to the input end of the voltage amplifier, and connect the output end of the signal generator and the output end of the voltage amplifier to the oscilloscope; place the thin rod to be tested on a symmetrically arranged bracket, and apply a coupling agent to both ends of the thin rod to be tested;

[0017] Step S4: according to the estimated values ​​of Young's modulus and Poisson's ratio of similar materials, respectively calculate the speeds of the rod wave, the shear wave, the longitudinal guided wave, and the bending guided wave, determine the low-frequency range in which the speed of the rod wave is approximately equal to the longitudinal guided wave, and determine the high-frequency range in which the speed of the shear wave is approximately equal to the bending guided wave;

[0018] Step S5: Select a low frequency as the center frequency of the incident wave to carry out the first measurement, select a high frequency as the center frequency of the incident wave to carry out the second measurement; the incident wave propagates between the transmission end and the receiving end of the thin rod to be measured, and the first wave packet that appears under the low-frequency excitation is extracted as the longitudinal guided wave, and the second wave packet that appears under the high-frequency excitation is extracted as the bending guided wave;

[0019] Step S6: The rod wave velocity of the thin rod to be measured is approximately equal to the longitudinal guided wave, and the transverse wave velocity is approximately equal to the bending guided wave. Therefore, the longitudinal guided wave and the bending guided wave obtained in step S5 can be substituted into the calculation formula of the Young's modulus and Poisson's ratio of the thin rod to be measured to obtain the accurate values ​​of the Young's modulus and Poisson's ratio of the thin rod to be measured;

[0020] As a further preferred embodiment of the present invention, in step S1, the step of measuring the density of the thin rod to be measured using the balance cylinder method is:

[0021] Take a number of thin rods to be tested, first use a balance to measure the mass of the thin rods in the air, and then use a balance to measure the mass of the thin rods in water. The density of the thin rods is as shown in formula (1):

[0022]

[0023] Among them, ρ s is the density of the thin rod to be measured, m a is the mass of the thin rods to be measured in the air, m w is the mass of the thin rods to be measured in water, ρ ais the density of air, ρ w is the density of water;

[0024] As a further preferred embodiment of the present invention, in step S3, the incident wave generated by the signal generator is composed of a 20-cycle Hanning window sine wave, the maximum amplitude of the incident wave is set to a peak-to-peak mode of 10V, and the voltage wave follows the rule:

[0025]

[0026] Among them, f c is the center frequency, t is the time series;

[0027] As a further preferred embodiment of the present invention, in step S4, the Young's modulus and Poisson's ratio of a material similar to the thin rod to be measured are selected as the estimated values ​​of the Young's modulus and Poisson's ratio of the thin rod to be measured, respectively, and are recorded as: E0, μ0;

[0028] Estimate the rod wave velocity and shear wave velocity in the thin rod to be tested. The calculation formula for the rod wave velocity of the thin rod to be tested is:

[0029]

[0030] Where c0 is the rod wave velocity, E0 is the estimated value of the Young's modulus of the thin rod to be measured, and ρ s is the density of the thin rod to be measured, and the calculation formula for the shear wave velocity of the thin rod to be measured is:

[0031]

[0032] Among them, c T is the shear wave velocity, ρ s is the density of the thin rod to be tested, E0 is the estimated value of the Young's modulus of the thin rod to be tested, and μ0 is the estimated value of the Poisson's ratio of the thin rod to be tested;

[0033] The calculation formula of longitudinal guided wave velocity is:

[0034] c lg =ω / k lg (5)

[0035] Among them, c lg is the longitudinal guided wave velocity, ω is the incident wave angular frequency, k lg is the longitudinal guided wave number;

[0036] k lg The calculation formula is:

[0037]

[0038] Where a is the radius of the thin rod to be measured, J n is the value of the nth order first kind Bessel function, n is 0, 1, etc., the coefficient αlg The calculation formula is Coefficient β lg The calculation formula is ω is the angular frequency of the incident wave, and ω=2π×f c , f c is the center frequency;

[0039] The calculation formula for the bending guided wave velocity is:

[0040] c fg =ω / k fg (6)

[0041] Among them, c fg is the wave velocity of the bending guided wave, ω is the angular frequency of the incident wave, k fg is the wave number of the bending guided wave;

[0042] k fg The calculation formula is:

[0043]

[0044] in, B 12 =-(βa) 2 J1(βa), B 13 =-(β fg a) 2 J1(β fg a), B 21 =α fg aJ0(α fg a)-2J1(α fg a), B 22 =β fg aJ0(β fg a)-2J1(β fg a), B 23 =[4-(β fg a) 2 ]J1(β fg a)-2β fg aJ0(β fg a),B 31 =α fg aJ0(α fg a)-J1(α fg a), B 33 =J1(β fg a);

[0045] Where a is the radius of the thin rod to be measured, J n is the value of the nth order first kind Bessel function, n is 0, 1, etc., the coefficient α fg The calculation formula is Coefficient β fg The calculation formula is ω is the angular frequency of the incident wave, and ω=2π×f c , f c is the center frequency;

[0046] The calculation formula of longitudinal wave velocity is:

[0047]

[0048] Among them, c L is the velocity of the longitudinal wave, E0 is the estimated value of the Young's modulus of the thin rod to be tested, μ0 is the estimated value of the Poisson's ratio of the thin rod to be tested, ρ s is the density of the thin rod to be measured;

[0049] As a further preferred embodiment of the present invention, in step S5, the specific method for determining the high-frequency region and the low-frequency region is: changing the center frequency f c , get c fg , c lg , c T , c0 changes with f c When the longitudinal wave velocity c lg When the wave velocity c0 is less than 5%, it is marked as point A. fg and the shear wave velocity c T When they intersect, it is recorded as point B; when the product of the center frequency and the diameter of the thin rod to be measured is less than point A, it is considered to be a low-frequency area, and when the product of the center frequency and the diameter of the thin rod to be measured is greater than point B, it is considered to be a high-frequency area;

[0050] As a further preferred embodiment of the present invention, in step S6, a frequency is selected in the low frequency region as f c , test the wave speed, record the propagation speed of the first wave packet in the received signal as c1, and obtain the Young's modulus of the thin rod to be tested:

[0051] E=c1 2 ρ s (8);

[0052] Select a frequency in the high frequency region as f c , test the wave speed, record the propagation speed of the second wave packet in the received signal as c2, and the Poisson's ratio of the thin rod to be tested is

[0053]

[0054] Through the above technical solution, compared with the prior art, the present invention has the following beneficial effects:

[0055] The nondestructive testing device and method provided by the present invention are based on the analysis of the forward problem of waveguide propagation in a thin rod, and the relationship between the wave velocity and Young's modulus and Poisson's ratio is clarified; then based on the relationship of the forward problem, the Young's modulus and Poisson's ratio of the thin rod to be tested can be obtained in reverse, thereby achieving high-precision detection of the elastic modulus of millimeter-level thin rods. BRIEF DESCRIPTION OF THE DRAWINGS

[0056] The present invention is further described below in conjunction with the accompanying drawings and embodiments.

[0057] Figure 1 It is a schematic diagram of a nondestructive testing device for Young's modulus and Poisson's ratio of a thin rod provided by the present invention;

[0058] Figure 2a-2b It is a multi-angle schematic diagram of the support structure provided by the present invention;

[0059] Figure 3a is a time domain diagram of the tone burst formed by the incident wave of the present invention, Figure 3b is a frequency domain diagram of the burst tone formed by the incident wave of the present invention, in which f c Take 1MHz;

[0060] Figure 4 is a graph showing the variation of wave velocities of rod wave, transverse wave, longitudinal guided wave and bending guided wave with frequency in an embodiment of the present invention;

[0061] Figure 5 The center frequency f is set in the embodiment provided by the present invention. c Schematic diagram of the measurement signal with 0.2MHz as the low-frequency incident wave;

[0062] Figure 6 The center frequency f is set in the embodiment provided by the present invention. c Schematic diagram of the measurement signal with 0.45 MHz as the high-frequency incident wave. DETAILED DESCRIPTION

[0063] The present invention will now be described in further detail with reference to the accompanying drawings. In the description of the present application, it should be understood that the orientation or positional relationship indicated by the terms "left side", "right side", "upper part", "lower part", etc. is based on the orientation or positional relationship shown in the accompanying drawings, and is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and "first", "second", etc. do not indicate the importance of the components, and therefore cannot be understood as a limitation on the present invention. The specific dimensions used in this embodiment are only for illustrating the technical solution by example, and do not limit the scope of protection of the present invention.

[0064] As explained in the background technology, the prior art is about thin rods with a diameter of millimeters, but it is impossible to measure their elastic constants because they cannot be tightened by traditional mechanical testing machines. This is because the existing elastic constant testing methods of rod structures are mostly based on destructive testing. For rods with larger diameters, they can be anchored by support, and for rods with small diameters (thin wires), they can be anchored by winding. However, for thin rods with a diameter of about 1 mm and a certain rigidity, they cannot be anchored in the above manner, and therefore the elastic constant cannot be determined by destructive loading. Therefore, a detection device and a detection method are needed to meet the measurement requirements of millimeter-level thin rods and achieve high-precision results.

[0065] like Figure 1 As shown in the figure, it is a preferred embodiment of the non-destructive testing device given by the present application. It can be seen from the figure that the whole includes the following components: a signal generator (Tektronix AFG31000), an excitation probe (M5W sensor), a receiving probe (M5W sensor), a voltage amplifier (PXPA3 amplifier) ​​and an oscilloscope (Tektronix MSO64); the connection relationship between the various components is: the output end of the signal generator for generating an incident wave is connected to the excitation probe, the excitation probe is connected to the receiving end of the thin rod to be tested, the transmission end of the thin rod to be tested is connected to the receiving probe, and the receiving probe is also connected to the input end of the voltage amplifier; the output end of the signal generator and the output end of the voltage amplifier are both connected to the oscilloscope. In this device, in order to better fix and support the thin rod to be tested, the applicant has developed the following: Figure 2a-2b The bracket shown, when in use, comprises two brackets arranged opposite to each other, and the thin rod to be measured is placed on the top of the bracket.

[0066] Here is a preferred embodiment of the bracket, including a base, an inclined plate connected to the side of the base, an angle formed between the bottom edge of the inclined plate and the base (an optimal angle of 45° is selected here), and the top edge of the inclined plate is connected to a support plate, and the support plate is arranged perpendicular to the base. The material used for the bracket is ABS plastic. When the thin rod to be measured is placed on the top of the bracket, in order to better fix the thin rod to be measured, an arc groove is opened at the center position of the top side edge of the support plate, and the curvature of the arc groove matches the circumferential wall of the thin rod to be measured.

[0067] Based on the above detection device, this application provides a related detection method, which specifically includes the following steps:

[0068] Step S1: Use the balance cylinder method to measure the density of the thin rod to be tested, in preparation for the subsequent derivation of the Young's modulus and Poisson's ratio of the thin rod to be tested.

[0069] Step S2: Prepare equipment, including a signal generator, an excitation probe, a receiving probe, a voltage amplifier, an oscilloscope, and a bracket.

[0070] Step S3: Build a nondestructive testing device, connect the output end of the signal generator with the excitation probe, the signal generator is used to generate an incident wave, and the maximum amplitude of the incident wave is set to 10Vpp; the excitation probe is used to transmit the incident wave to the thin rod; the receiving probe is connected to the input end of the voltage amplifier, the receiving probe is used to receive the vibration wave after the thin rod is transmitted, and the voltage amplifier is used to amplify the energy of the received wave; the output end of the signal generator and the output end of the voltage amplifier are both connected to the oscilloscope, and the oscilloscope is used to display the vibration wave generated by the signal generator and the received vibration wave amplified by the voltage amplifier; place the thin rod to be tested on a symmetrically arranged bracket, apply a coupling agent (used to remove the air between the excitation probe, the receiving probe and the thin rod) at both ends of the thin rod to be tested, and connect the thin rod to the excitation probe and the receiving probe.

[0071] Step S4: According to the estimated values ​​of Young's modulus and Poisson's ratio of similar materials, the velocities of the rod wave, transverse wave, longitudinal guided wave and bending guided wave are calculated respectively, and the low-frequency range in which the rod wave velocity is approximately equal to the longitudinal guided wave velocity is determined, and the high-frequency range in which the transverse wave velocity is approximately equal to the bending guided wave velocity is determined.

[0072] Step S5: Select a low frequency as the center frequency of the incident wave and carry out the first measurement, select a high frequency as the center frequency of the incident wave and carry out the second measurement; the incident wave propagates between the transmission end and the receiving end of the thin rod to be measured, and the first wave packet that appears under low-frequency excitation is extracted as the longitudinal guided wave, and the second wave packet that appears under high-frequency excitation is extracted as the bending guided wave.

[0073] Step S6: The rod wave velocity of the thin rod to be tested is approximately equal to the longitudinal guided wave, and the transverse wave velocity is approximately equal to the bending guided wave. Therefore, the longitudinal guided wave and bending guided wave obtained in step S5 can be substituted into the calculation formula of the Young's modulus and Poisson's ratio of the thin rod to be tested to obtain the accurate values ​​of the Young's modulus and Poisson's ratio of the thin rod to be tested.

[0074] In step S1, the steps of measuring the density of the thin rod to be measured using the balance cylinder method are as follows:

[0075] Take a number of thin rods to be tested, first use a balance to measure the mass of the thin rods in the air, and then use a balance to measure the mass of the thin rods in water. The density of the thin rods is as shown in formula (1):

[0076]

[0077] Among them, ρ s is the density of the thin rod to be measured, m a is the mass of the thin rods to be measured in the air, m w is the mass of the thin rods to be measured in water, ρ a is the density of air, ρ w is the density of water.

[0078] In step S3, the incident wave generated by the signal generator is composed of a 20-cycle Hanning window sine wave, and its voltage wave follows the rule:

[0079]

[0080] Among them, f c is the center frequency, t is the time; for example, when fc = 1MHz, the incident wave has Figure 3a The time domain diagram shown and Figure 3b The frequency domain diagram is shown.

[0081] In step S4, the Young's modulus and Poisson's ratio of a material similar to the thin rod to be measured are selected as the estimated values ​​of the Young's modulus and Poisson's ratio of the thin rod to be measured, respectively, and are recorded as: E0, μ0;

[0082] Estimate the rod wave velocity and shear wave velocity in the thin rod to be tested. The calculation formula for the rod wave velocity of the thin rod to be tested is:

[0083]

[0084] Where c0 is the rod wave velocity, E0 is the estimated value of the Young's modulus of the thin rod to be measured, and ρ s is the density of the thin rod to be measured, and the calculation formula for the shear wave velocity of the thin rod to be measured is:

[0085]

[0086] Among them, c T is the shear wave velocity, ρ s is the density of the thin rod to be tested, E0 is the estimated value of the Young's modulus of the thin rod to be tested, and μ0 is the estimated value of the Poisson's ratio of the thin rod to be tested;

[0087] The calculation formula of longitudinal guided wave velocity is:

[0088] c lg =ω / k lg (5)

[0089] Among them, c lg is the longitudinal guided wave velocity, ω is the incident wave angular frequency, k lg is the longitudinal guided wave number;

[0090] k lg The calculation formula is:

[0091]

[0092] Where a is the radius of the thin rod to be measured, J n is the value of the nth order first kind Bessel function, n is 0, 1, etc., the coefficient α lgThe calculation formula is Coefficient β lg The calculation formula is ω is the angular frequency of the incident wave, and ω=2π×f c , f c is the center frequency;

[0093] The calculation formula for the bending guided wave velocity is:

[0094] c fg =ω / k fg (6)

[0095] Among them, c fg is the wave velocity of the bending guided wave, ω is the angular frequency of the incident wave, k fg is the wave number of the bending guided wave;

[0096] k fg The calculation formula is:

[0097]

[0098] in, B 12 =-(βa) 2 J1(βa), B 13 =-(β fg a) 2 J1(β fg a), B 21 =α fg aJ0(α fg a)-2J1(α fg a), B 22 =β fg aJ0(β fg a)-2J1(β fg a), B 23 =[4-(β fg a) 2 ]J1(β fg a)-2β fg aJ0(β fg a),B 31 =α fg aJ0(α fg a)-J1(α fg a), B 33 =J1(β fg a);

[0099] Where a is the radius of the thin rod to be measured, J n is the value of the nth order first kind Bessel function, n is 0, 1, etc., the coefficient α fg The calculation formula is Coefficient βfg The calculation formula is ω is the angular frequency of the incident wave, and ω=2π×f c , f c is the center frequency;

[0100] The calculation formula of longitudinal wave velocity is:

[0101]

[0102] Among them, c L is the velocity of the longitudinal wave, E0 is the estimated value of the Young's modulus of the thin rod to be tested, μ0 is the estimated value of the Poisson's ratio of the thin rod to be tested, ρ s is the density of the thin rod to be measured.

[0103] What needs to be specifically explained here is that step S4 mentions the need to calculate the speeds of the rod wave, transverse wave, longitudinal waveguide, and bending waveguide, determine the low-frequency range where the rod wave speed is approximately equal to the longitudinal waveguide, and determine the high-frequency range where the transverse wave speed is approximately equal to the bending waveguide. Then here is how to determine the so-called low-frequency range and high-frequency range. For ease of understanding, this application provides the following Figure 4 As shown in the judgment diagram, change the center frequency f c , get c fg , c lg , c T , c0 changes with f c When the longitudinal wave velocity c lg When the wave velocity c0 is less than 5%, it is marked as point A. fg and the shear wave velocity c T When they intersect, it is recorded as point B; when the product of the center frequency and the diameter of the thin rod to be measured is less than point A, it is considered to be a low-frequency area, and when the product of the center frequency and the diameter of the thin rod to be measured is greater than point B, it is considered to be a high-frequency area.

[0104] Finally, combining step S5 and step S6, a frequency is selected in the low frequency region as f c , test the wave speed, record the propagation speed of the first wave packet in the received signal as c1, and obtain the Young's modulus of the thin rod to be tested:

[0105] E=c 12 ρ s (8);

[0106] Select a frequency in the high frequency region as f c , test the wave speed, record the propagation speed of the second wave packet in the received signal as c2, and the Poisson's ratio of the thin rod to be tested is

[0107]

[0108] A special case needs to be explained here. When the Young's modulus and Poisson's ratio of the thin rod to be tested cannot be estimated, there is no need to use the calculation method of steps S4-S6. 50kHz can be directly used as the low-frequency incident wave and 1MHz can be directly used as the high-frequency incident wave.

[0109] Example:

[0110] In order to verify the effectiveness of the nondestructive testing device and method given above, an aluminum rod with a diameter of 2 mm is selected as the thin rod to be tested in the embodiment. The density ρ of the thin rod to be tested is obtained by the water displacement method. s 2797kg / m 3 The Young's modulus E0 and Poisson's ratio μ0 are estimated to be 68 GPa and 0.3 respectively. fg , c lg , c T , c0 changes with f c The change curve of Figure 4 As shown, the frequency-diameter product corresponding to point A is 0.4MHz mm, and the frequency corresponding to point B is 0.9MHz mm, so the center frequency f is set c The low frequency incident wave is 0.2MHz, and the measured signal is Figure 5 As shown, set the center frequency f c The high frequency incident wave is 0.45MHz, and the measured signal is Figure 6 As shown. The length of the thin rod to be measured is 1m. The calculation results show that Figure 5 The propagation speed of the first wave crest is c1=4969m / s, Figure 6 The propagation velocity of the second wave peak in the equation is c2 = 3049 m / s. The calculated Young's modulus and Poisson's ratio are shown in Table 1.

[0111] Table 1 Comparison of measured and actual values ​​of Young's modulus and Poisson's ratio of aluminum rod

[0112] E measurement value (GPa) E actual value (GPa) E Error rate 69.1 68.9 0.29％ μMeasurement value μactual value μError rate 0.3279 0.33 0.64％

[0113] As can be seen from Table 1, the Young's modulus and Poisson's ratio calculated by the nondestructive testing device and testing method provided by the present application are compared with the actual data provided by the aluminum rod production factory, and the errors are less than 0.64%.

[0114] Therefore, this application can be widely promoted in related fields.

[0115] It will be understood by those skilled in the art that, unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as those generally understood by those skilled in the art to which this application belongs. It should also be understood that terms such as those defined in common dictionaries should be understood to have meanings consistent with the meanings in the context of the prior art, and will not be interpreted with idealized or overly formal meanings unless defined as herein.

[0116] The meaning of "and / or" described in this application means that the situations where each exists alone or both exist at the same time are included.

[0117] The term “connection” as used in this application may mean a direct connection between components or an indirect connection between components via other components.

[0118] Based on the above ideal embodiments of the present invention, the relevant staff can make various changes and modifications without departing from the technical concept of the present invention through the above description. The technical scope of the present invention is not limited to the contents of the specification, and its technical scope must be determined according to the scope of the claims.

Claims

1. A nondestructive testing method based on Young's modulus and Poisson's ratio of a thin rod, characterized in that: The specific steps include: Step S1: using a balance cylinder method to measure the density of the thin rod to be measured; Step S2: preparing equipment, including a signal generator, an excitation probe, a receiving probe, a voltage amplifier, an oscilloscope, and a bracket; Step S3: construct a nondestructive testing device, connect the output end of the signal generator to the excitation probe, connect the excitation probe to one end of the thin rod to be tested, connect the other end of the thin rod to be tested to the receiving probe, connect the receiving probe to the input end of the voltage amplifier, and connect the output end of the signal generator and the output end of the voltage amplifier to an oscilloscope; place the thin rod to be tested on a symmetrically arranged bracket, and apply a coupling agent to both ends of the thin rod to be tested; Step S4: according to the estimated values ​​of Young's modulus and Poisson's ratio of similar materials, respectively calculate the estimated values ​​of the rod wave, shear wave, longitudinal guided wave and bending guided wave velocities, determine the low-frequency range in which the rod wave velocity is approximately equal to the longitudinal guided wave velocity, and determine the high-frequency range in which the shear wave velocity is approximately equal to the bending guided wave velocity; Step S5: The specific method for determining the high-frequency region and the low-frequency region is: changing the center frequency f c , and obtain the bending guided wave velocity c fg , longitudinal guided wave velocity c lg , shear wave velocity c T , c lg Follow c When the longitudinal wave velocity c lg When the wave velocity c0 is less than 5%, it is marked as point A. fg and the shear wave velocity c T When they intersect, it is recorded as point B; when the product of the center frequency and the diameter of the thin rod to be measured is less than point A, it is considered to be a low-frequency area, and when the product of the center frequency and the diameter of the thin rod to be measured is greater than point B, it is considered to be a high-frequency area; a low frequency is selected as the center frequency of the incident wave to carry out the first measurement, and a high frequency is selected as the center frequency of the incident wave to carry out the second measurement; the incident wave propagates between the transmission end and the receiving end of the thin rod to be measured, and the first wave packet that appears under low-frequency excitation is extracted as a longitudinal guided wave, and the second wave packet that appears under high-frequency excitation is extracted as a bending guided wave; Step S6: The rod wave velocity of the thin rod to be tested is approximately equal to the longitudinal guided wave, and the transverse wave velocity is approximately equal to the bending guided wave. Therefore, the longitudinal guided wave and bending guided wave obtained in step S5 can be substituted into the calculation formula of the Young's modulus and Poisson's ratio of the thin rod to be tested to obtain the accurate values ​​of the Young's modulus and Poisson's ratio of the thin rod to be tested.

2. The nondestructive testing method for Young's modulus and Poisson's ratio of a thin rod according to claim 1, characterized in that: In step S1, the steps of measuring the density of the thin rod to be measured using the balance cylinder method are as follows: Take a number of thin rods to be tested, first use a balance to measure the mass of the thin rods in the air, and then use a balance to measure the mass of the thin rods in water. The density of the thin rods is as shown in formula (1): Among them, ρ s is the density of the thin rod to be measured, m a is the mass of the thin rods to be measured in the air, m w is the mass of the thin rods to be measured in water, ρ a is the density of air, ρ w is the density of water.

3. The nondestructive testing method for Young's modulus and Poisson's ratio of a thin rod according to claim 1, characterized in that: In step S3, the incident wave generated by the signal generator is composed of a 20-cycle Hanning window sine wave, the maximum amplitude of the incident wave is set to 10 Vpp, and the ultrasonic waveform excited is Among them, f c is the center frequency, and t is the time series.

4. The nondestructive testing method for Young's modulus and Poisson's ratio of a thin rod according to claim 3, characterized in that: In step S4, the Young's modulus and Poisson's ratio of a material similar to the thin rod to be measured are selected as the estimated values ​​of the Young's modulus and Poisson's ratio of the thin rod to be measured, respectively, and are recorded as: E0, μ0; Estimate the rod wave velocity and shear wave velocity in the thin rod to be tested. The calculation formula for the rod wave velocity of the thin rod to be tested is: Where c0 is the rod wave velocity, E0 is the estimated value of the Young's modulus of the thin rod to be measured, and ρ s is the density of the thin rod to be measured according to formula (1), The calculation formula for the shear wave velocity of the thin rod to be measured is: Among them, c T is the shear wave velocity, ρ s is the density of the thin rod to be tested, E0 is the estimated value of the Young's modulus of the thin rod to be tested, and μ0 is the estimated value of the Poisson's ratio of the thin rod to be tested; The calculation formula of longitudinal guided wave velocity is: c lg =ω / k lg (5) Among them, c lg is the longitudinal guided wave velocity, ω is the incident wave angular frequency, k lg is the longitudinal guided wave number; k lg The calculation formula is: Where a is the radius of the thin rod to be measured, J n is the value of the nth order first kind Bessel function, n is 0, 1, etc., the coefficient α lg The calculation formula is Coefficient β lg The calculation formula is ω is the angular frequency of the incident wave, and ω=2π×f c , f c is the center frequency; The calculation formula for the bending guided wave velocity is: c fg =ω / k fg (6) Among them, c fg is the wave velocity of the bending guided wave, ω is the angular frequency of the incident wave, k fg is the wave number of the bending guided wave; k fg The calculation formula is: Among them, B 12 =-(βa) 2 J1(βa), B 13 =-(β fg a) 2 J1(b fg a),B 21 =a fg aJ0(a fg a)-2J1(a fg a),B 22 =b fg aJ0(β fg a)-2J1(b fg a),B 23 =[4-(β fg a) 2 ]J1(b fg a)-2b fg aJ0(β fg a),B 31 =a fg aJ0(a fg a)-J1(a fg a), B 33 =J1(β fg a); Where a is the radius of the thin rod to be measured, J n is the value of the nth order first kind Bessel function, n is 0, 1, etc., the coefficient α fg The calculation formula is Coefficient β fg The calculation formula is ω is the angular frequency of the incident wave, and ω=2π×f c , f c is the center frequency; The calculation formula of longitudinal wave velocity is: Among them, c L is the velocity of the longitudinal wave, E0 is the estimated value of the Young's modulus of the thin rod to be tested, μ0 is the estimated value of the Poisson's ratio of the thin rod to be tested, ρ s is the density of the thin rod to be measured.

5. The nondestructive testing method for Young's modulus and Poisson's ratio of a thin rod according to claim 4, characterized in that: In step S6, a frequency is selected in the low frequency region as f c , test the wave speed, record the propagation speed of the first wave packet in the received signal as c1, and obtain the Young's modulus of the thin rod to be tested: E=c 12 r s (8); Select a frequency in the high frequency region as f c , test the wave speed, record the propagation speed of the second wave packet in the received signal as c2, and obtain the Poisson's ratio of the thin rod to be tested:

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