Load testing device and method for high strain rate tensile testing

Abstract

This invention discloses a load testing device and method for high strain rate tensile testing. The device includes an elastic rod (1), strain gauges (2), a tensile testing machine (3), a clamp connector (4), and a data acquisition unit (5). One end of the elastic rod is fixed to the lower crossbeam (31) of the tensile testing machine, and one end of the specimen (6) is connected to the other end of the elastic rod through the clamp connector. The other end of the specimen is fixed to the upper crossbeam (32) of the tensile testing machine. Several strain gauges are spaced apart on the elastic rod, and the output ends of the strain gauges are connected to the data acquisition unit. Each strain gauge independently transmits its stress signal to the data acquisition unit. This invention can obtain ideal and reliable dynamic mechanical property data by decomposing the transmission and superposition of stress waves during material tensile testing at high strain rates, reducing the oscillation effect of load signals, obtaining the true stress loaded on the sample, and improving the accuracy of test results.

Description

Technical Field

[0001] This invention relates to a material performance testing device and method, and more particularly to a load testing device and method for high strain rate tensile testing. Background Technology

[0002] In quasi-static tests for material load measurement, resistive load cells and other sensors are used to detect the load. Due to the low test speed, the acceleration of various components and the vibration of the system are small, and the sensors have sufficient response time, making it easy to measure the material load accurately. However, in dynamic tests, the measured load signal often exhibits significant fluctuations. Moreover, for the same material, the dynamic test curves measured by different testers vary significantly. Accurate stress-strain curve measurement is a key issue affecting the quality of dynamic tests, leading to large load measurement errors. Especially in dynamic tests with high strain rates (>500 / s), the load signal oscillates greatly, significantly affecting the accuracy and usability of subsequent measurement data.

[0003] Currently, single-bar, Hopkinson bar, and hydraulic servo testing machines are commonly used equipment for measuring material loads. Because the testing time of a Hopkinson bar is typically below 500µs, it is only suitable for testing processes with ultra-high strain rates (>1000 / s). At ultra-high strain rates, high-strength steel samples cannot reach the state of fracture failure, making it unsuitable for load measurement testing of high-strength steel materials such as those used in the automotive industry. Hydraulic servo testing machines can usually directly measure the tensile load of the specimen through a load sensor, but when the tensile speed is high, the measured load data exhibits significant oscillations. This is mainly due to the resonance at the clamping end caused by the propagation, reflection, and superposition of stress waves during the short time of dynamic loading, meaning the data obtained by the load sensor is no longer the true load during the specimen's tensile process.

[0004] Chinese invention patent application CN201811602413.1 discloses a Hopkinsonian band dynamic testing system, specifically comprising: a horizontal cross support platform, a central cubic box, bands, band fixation, and a support frame; the bands in the X and Y directions are horizontally placed, while the bands in the Z direction are vertically placed. The band fixation and support frame neatly and symmetrically bind the various small individual bands together to form a larger square band; a gap of 1mm to 2mm is reserved between each individual band; resistance strain gauges are attached to each individual band; the cross-sectional area and length of the bands in each direction are equal, and the dynamic stress wave propagation law and dynamic response signal monitoring method within each band are identical. The system uses loading hydraulic cylinders and loading actuators in three directions to apply static confining pressure loads to the test specimen, which differs from the unidirectional stress loading method required for sheet metal. Simultaneously, the dynamic stress pulse time provided by the annular electromagnetic pulse is too short, preventing the specimen from reaching a fracture failure state, thus making it unsuitable for testing the fracture of metal sheets. Summary of the Invention

[0005] One of the objectives of this invention is to provide a load testing device for high strain rate tensile testing, which can be used to measure the tensile load value of materials under high strain rates.

[0006] The second objective of this invention is to provide a load testing method for high strain rate tensile testing, which can reduce the oscillation effect of the load signal and improve the accuracy of the test results during material tensile testing at high strain rates.

[0007] This invention is implemented as follows:

[0008] A load testing device for high strain rate tensile testing includes an elastic rod, strain gauges, a tensile testing machine, a clamp connector, and a data acquisition unit. One end of the elastic rod is fixed to the lower crossbeam of the tensile testing machine, one end of the specimen is connected to the other end of the elastic rod through the clamp connector, and the other end of the specimen is fixed to the upper crossbeam of the tensile testing machine. Several strain gauges are respectively arranged at intervals on the elastic rod, and the output ends of the strain gauges are respectively connected to the data acquisition unit. Each strain gauge independently transmits its stress signal to the data acquisition unit.

[0009] The elastic rod has a length of 450-800mm and a diameter of 20-30mm.

[0010] The number of strain gauges shall not be less than three.

[0011] The strain gauge consists of three gauges, with two gauges located at the two ends of the elastic rod and the other gauge located in the middle of the elastic rod.

[0012] A load testing method for high strain rate tensile testing, the load testing method for high strain rate tensile testing is implemented based on a load testing device for high strain rate tensile testing; the load testing method for high strain rate tensile testing includes the following steps:

[0013] Step 1: Fix the specimen between the elastic rod and the upper crossbeam of the tensile testing machine, and attach no less than three strain gauges at intervals on the elastic rod;

[0014] Step 2: Turn on the tensile testing machine and stretch the upper crossbeam upwards until the specimen breaks;

[0015] Step 3: During the test time when the upper crossbeam is stretched upward, the stress signals of several strain gauges are collected in real time using a data acquisition device.

[0016] Step 4: Calculate the load value of the specimen based on the stress signals from several strain gauges.

[0017] In step 2, the upward stretching rate of the upper crossbeam is set to a high strain rate, which is in the range of 500-1200 / s.

[0018] In step 3, the stress signal of each strain gauge includes the strain value and stress value at the bonding position of the strain gauge.

[0019] Step 4 includes:

[0020] Step 4.1: Convert the stress signal of each strain gauge into a frequency domain signal using Fourier transform;

[0021] At any time t, the strain value at any position x away from the top of the elastic rod is ε(x,t), and the stress value is N(x,t). ε(x,t) is obtained through Fourier transform. The Fourier transform of N(x,t) yields...

[0022] Step 4.2: Obtain the frequency domain equation based on the frequency domain signal;

[0023] Based on the propagation and dispersion effect of one-dimensional stress waves, the following equations are obtained:

[0024]

[0025]

[0026] Where A is the cross-sectional area of ​​the elastic rod, E(ω) is Young's modulus, β(ω) is the dispersion coefficient, F(ω) is the one-dimensional stress wave forward transfer function, and D(ω) is the one-dimensional stress wave reverse transfer function.

[0027] Step 4.3: Calculate the maximum likelihood function of the frequency domain signals from several strain gauges. The calculation formula is as follows:

[0028]

[0029] Where N is the total number of strain gauges, i.e., N≥3;

[0030] ε(x j ,t) is the strain value including noise;

[0031] The strain value after noise removal;

[0032] By applying the principle of time-domain to frequency-domain transformation, equation (3) can be transformed into:

[0033]

[0034] Step 4.4: Substitute the positions x of several strain gauges and their stress signals into equation (1), and use the function values ​​of equation (4) The objective is to minimize the value of F(ω), and the solutions for F(ω) and D(ω) are calculated as follows:

[0035]

[0036]

[0037] in,

[0038]

[0039]

[0040]

[0041]

[0042]

[0043]

[0044]

[0045] and These are components of the one-dimensional stress wave forward transfer function F(ω) and the one-dimensional stress wave reverse transfer function D(ω). The average dispersion coefficient;

[0046] Step 4.5: Substitute the solutions of F(ω) and D(ω) into equation (2) to obtain the data of the loading force on the end of the specimen connected to the elastic rod in the frequency domain;

[0047] Step 4.6: Perform an inverse Fourier transform on the data of the applied force in the frequency domain to obtain the load-time curve.

[0048] Compared with the prior art, the present invention has the following beneficial effects:

[0049] 1. Because the present invention uses at least three strain gauges, it can obtain ideal and reliable dynamic mechanical performance data by decomposing the transmission and superposition of stress waves, while avoiding the influence of white noise on the test data, thereby reducing the load signal oscillation effect, obtaining the true stress loaded on the sample, and improving the accuracy of the test results.

[0050] 2. This invention, by combining a tensile testing machine and an elastic rod, overcomes the problem of the short testing time of the elastic rod, achieving a theoretically unlimited testing time until the specimen fractures and fails. Simultaneously, the application of the elastic rod avoids the large oscillations in the load signal measured by the hydraulic servo material testing machine, enabling reliable stress-strain curves to be obtained in high strain rate tensile tests. It is suitable for testing high-strength steel and other automotive industry materials.

[0051] This invention can obtain ideal and reliable dynamic mechanical property data by decomposing the transmission and superposition of stress waves during tensile testing of materials at high strain rates, reducing the oscillation effect of load signals, obtaining the true stress loaded on the sample, and improving the accuracy of test results. Attached Figure Description

[0052] Figure 1 This is a front view of the load testing device for high strain rate tensile testing of the present invention. In the figure, the arrow indicates the tensile direction.

[0053] Figure 2 This is a flowchart of the load testing method for high strain rate tensile testing according to the present invention;

[0054] Figure 3 The figure shows the load-time curve of Example 1, which was measured using the load testing method of the high strain rate tensile test of the present invention. In the figure, the solid line is the load-time curve measured by the present invention, and the dashed line is the load-time curve measured by the conventional test method.

[0055] Figure 4 The stress signal graph is obtained by load testing using the high strain rate tensile test method of this invention. The dotted line represents the stress signal curve of the strain gauge located at the upper part of the elastic rod, the dashed line represents the stress signal curve of the strain gauge located at the middle part of the elastic rod, and the solid line represents the stress signal curve of the strain gauge located at the lower part of the elastic rod.

[0056] In the diagram, 1 is the elastic rod, 2 is the strain gauge, 3 is the tensile testing machine, 31 is the lower crossbeam, 32 is the upper crossbeam, 4 is the clamp connector, 5 is the data acquisition device, 51 is the aviation plug, 6 is the specimen, and 7 is the computer. Detailed Implementation

[0057] The present invention will be further described below with reference to the accompanying drawings and specific embodiments.

[0058] Please see the appendix Figure 1 A load testing device for high strain rate tensile testing includes an elastic rod 1, strain gauges 2, a tensile testing machine 3, a clamp connector 4, and a data acquisition device 5. One end of the elastic rod 1 is fixed to the lower crossbeam 31 of the tensile testing machine 3, and one end of the specimen 6 is connected to the other end of the elastic rod 1 through the clamp connector 4. The other end of the specimen 6 is fixed to the upper crossbeam 32 of the tensile testing machine 3. Several strain gauges 2 are respectively arranged at intervals on the elastic rod 1, and the output ends of the strain gauges 2 are respectively connected to the data acquisition device 5. The stress signal of each strain gauge 2 is independently transmitted to the data acquisition device 5, and the data acquisition device 5 can use several data channels to receive the data of several strain gauges 2.

[0059] Due to space limitations imposed by the tensile testing machine 3, the length of the elastic rod 1 is 450-800mm and the diameter is 20-30mm.

[0060] The number of strain gauges 2 is no less than three.

[0061] Preferably, there are three strain gauges 2, with two strain gauges 2 respectively located at the two ends of the elastic rod 1, and the third strain gauge 2 located in the middle of the elastic rod 1. To avoid interference between the strain gauges and other components, two of the strain gauges 2 can be positioned 100mm away from the two ends of the elastic rod 1. The farther the two strain gauges 2 are from the ends of the elastic rod 1, i.e., the smaller the distance between the two strain gauges 2, the higher the strain rate that can be measured. The strain gauges 2 can be positioned appropriately according to the required strain rate range to meet the application range of automotive engineering and make full use of the length of the elastic rod 1.

[0062] Please see the appendix Figure 2 A load testing method for high strain rate tensile testing is disclosed, which is implemented based on a load testing device for high strain rate tensile testing. The load testing method for high strain rate tensile testing includes the following steps:

[0063] Step 1: Fix the specimen 6 between the elastic rod 1 and the upper crossbeam 32 of the tensile testing machine 3, and attach no less than three strain gauges 2 at intervals on the elastic rod 1.

[0064] Step 2: Turn on the tensile testing machine 3 and stretch the upper crossbeam 32 upwards until the specimen 6 breaks.

[0065] Preferably, the upward stretching rate of the upper crossbeam 32 is set to a high strain rate, which is in the range of 500-1200 / s.

[0066] Because the elastic rod 1 is relatively short, the test time is determined by the upward stretching speed of the upper crossbeam 32 and the material fracture elongation of the specimen 6. The stress wave is reflected and superimposed multiple times in the elastic rod 1, and stress signals at several locations on the elastic rod 1 are collected by several strain gauges 2.

[0067] Step 3: During the test time when the upper crossbeam 32 is stretched upward, the stress signals of several strain gauges 2 are collected in real time by the data acquisition device 5. The stress signal of each strain gauge 2 includes the strain value and stress value at its bonding position.

[0068] Step 4: Calculate the load value of specimen 6 based on the stress signals of several strain gauges 2.

[0069] Step 4.1: Convert the stress signal of each strain gauge 2 into a frequency domain signal using Fourier transform.

[0070] Taking strain gauge 2 as an example, the method for converting its stress signal into a frequency domain signal is as follows:

[0071] Assume that at any time t, the strain value of strain gauge 2 at any position x away from the top of elastic rod 1 is ε(x,t), and the stress value is N(x,t). ε(x,t) is obtained through Fourier transform. The Fourier transform of N(x,t) yields...

[0072] Step 4.2: Obtain the frequency domain equation based on the frequency domain signal.

[0073] Based on the theory of one-dimensional stress waves, considering the propagation and dispersion effect of one-dimensional stress waves, the following equation is obtained:

[0074]

[0075]

[0076] Where A is the cross-sectional area of ​​elastic rod 1.

[0077] E(ω) is Young's modulus, which is the ratio of stress to strain and is a physical quantity used to describe the ability of a solid material to resist deformation.

[0078] β(ω) is the dispersion coefficient, which is a physical quantity that describes the characteristic dispersion of stress waves. It is calculated by fitting the stress signal.

[0079] F(ω) is the forward transmission function of a one-dimensional stress wave, and D(ω) is the reverse transmission function of a one-dimensional stress wave. The one-dimensional stress wave is transmitted multiple times on the elastic rod 1, and the signal at each position is the superposition of the forward and reverse transmitted one-dimensional stress waves.

[0080] The one-dimensional stress wave forward transfer function F(ω) and the one-dimensional stress wave backward transfer function D(ω) are unknowns and require stress signals from at least two locations on the elastic rod 1 to solve. By setting up no fewer than three strain gauges 2, the one-dimensional stress wave forward transfer function F(ω) and the one-dimensional stress wave backward transfer function D(ω) can be solved using their stress signals, and the influence of white noise on the calculation results can be eliminated.

[0081] The method for converting the stress signals of several strain gauges 2 into frequency domain signals is the same, and will not be repeated here.

[0082] Step 4.3: Calculate the maximum likelihood function of the frequency domain signal from several strain gauges. The calculation formula is as follows:

[0083]

[0084] Where N is the total number of strain gauges 2, i.e., N≥3.

[0085] ε(x j ε(x,t) represents the strain value containing noise. All strain values ​​ε(x,t) contain noise (white noise). The greater the noise, the greater the error in the test results.

[0086] The strain value after noise removal is obtained by taking the same noise contained in all strain values ​​ε(x,t) as the noise floor, and subtracting the noise floor from each strain value ε(x,t).

[0087] By applying the principle of time-domain to frequency-domain transformation, equation (3) can be transformed into:

[0088]

[0089] Step 4.4: Substitute the positions x of several strain gauges 2 and their stress signals into equation (1), and use the function values ​​of equation (4) The objective is to minimize the value of F(ω), and the solutions for F(ω) and D(ω) are calculated as follows:

[0090]

[0091]

[0092] in,

[0093]

[0094]

[0095]

[0096]

[0097]

[0098] h1(ω), h2(ω), g1(ω), g2(ω), E1(ω), and E2(ω) are all components of the one-dimensional stress wave forward transfer function F(ω) and the one-dimensional stress wave reverse transfer function D(ω). The average dispersion coefficient is obtained by averaging the dispersion coefficients β(ω).

[0099] Step 4.5: Substitute the solutions of F(ω) and D(ω) into equation (2) to obtain the data of the loading force on the end of the specimen 6 connected to the elastic rod 1 in the frequency domain.

[0100] Step 4.6: Perform an inverse Fourier transform on the data of the applied force in the frequency domain to obtain the load-time curve.

[0101] Example 1:

[0102] In this embodiment, please refer to the appendix. Figure 1 The load testing device for high strain rate tensile testing includes an elastic rod 1, strain gauges 2, a hydraulically driven tensile testing machine 3, a clamp connector 4, and a data acquisition unit 5. In this embodiment, the strain gauge 2 is a resistance strain gauge, and the elastic rod 1 is a Hopkinson rod. One end of the cylindrical elastic rod 1, which is 500 mm long and 30 mm in diameter, is fixed to the lower crossbeam 31 of the tensile testing machine 3. One end of the specimen 6 is connected to the other end of the elastic rod 1 through the clamp connector 4, and the other end of the specimen 6 is fixed to the upper crossbeam 32 of the tensile testing machine 3. Three strain gauges 2 are respectively set at both ends (100 mm from the end) and the middle of the elastic rod 1. The output ends of the three strain gauges 2 are all connected to the data acquisition unit 5 through aviation plugs 51.

[0103] Please see the appendix Figure 2 This embodiment is used to test HC820 / 1180QP ultra-high strength steel sheet for automobiles. The test steps are as follows:

[0104] Step 1: Fix the specimen 6 between the elastic rod 1 and the upper crossbeam 32 of the tensile testing machine 3, and attach strain gauges 2 to both ends and the middle part of the elastic rod 1 respectively.

[0105] Step 2: Turn on the tensile testing machine 3, stretch the upper crossbeam 32 upwards at a stretching rate of 20 m / s, corresponding to a high strain rate of 1000 / s. The specimen 6 breaks within 1 ms.

[0106] Step 3: Acquire the stress signals of the three strain gauges 2 using the data acquisition device 5, as shown in the attached figure. Figure 4 As shown, the dotted line represents the stress signal curve of strain gauge 2 located at the upper part of elastic rod 1, the dashed line represents the stress signal curve of strain gauge 2 located at the middle part of elastic rod 1, and the solid line represents the stress signal curve of strain gauge 2 located at the lower part of elastic rod 1.

[0107] Data from data acquisition device 5 can be imported into computer 7 and then processed by a pre-set program within the computer.

[0108] Step 4: Calculate the load value of specimen 6 based on the stress signals from the three strain gauges 2.

[0109] Step 4.1: Convert the three stress signals into frequency domain signals using Fourier transform.

[0110] The three strain gauges are labeled from top to bottom as strain gauge 1#, strain gauge 2#, and strain gauge 3#. The position x1 of strain gauge 1# is 100mm, the position x2 of strain gauge 2# is 250mm, and the position x3 of strain gauge 3# is 400mm.

[0111] Assuming at any time t, the strain value of strain gauge #1 is ε1(x1,t), and the stress value is N1(x1,t). Perform a Fourier transform on ε1(x1,t) and N1(x1,t). The strain value of strain gauge #2 is ε2(x2,t), and the stress value is N2(x2,t). Perform a Fourier transform on ε2(x2,t) and N2(x2,t). The strain value of strain gauge #3 is ε3(x3,t), and the stress value is N3(x3,t). Perform a Fourier transform on ε3(x3,t) and N3(x3,t).

[0112] Step 4.2: Obtain the frequency domain equation based on the frequency domain signal.

[0113]

[0114]

[0115] Where A is the cross-sectional area of ​​elastic rod 1, E(ω) is Young's modulus, β(ω) is the dispersion coefficient, F(ω) is the one-dimensional stress wave forward transfer function, and D(ω) is the one-dimensional stress wave reverse transfer function.

[0116] Step 4.3: Calculate the maximum likelihood function of the three strain gauges 2.

[0117] The maximum likelihood function of the three strain gauges 2 is:

[0118] Where N = 3, ε(x) j ,t) is the strain value including noise. This represents the strain value after noise removal.

[0119] By applying the principle of time-domain to frequency-domain transformation, equation (3) can be transformed into:

[0120]

[0121] Step 4.4: Substitute the positions x of the three strain gauges 2 and their stress signals into equation (1), and use the function values ​​of equation (4) The objective is to minimize the value of F(ω), and the solutions for F(ω) and D(ω) are calculated as follows:

[0122]

[0123]

[0124] in,

[0125]

[0126]

[0127]

[0128]

[0129]

[0130] The average dispersion coefficient.

[0131] Step 4.5: Substitute the solutions of F(ω) and D(ω) into equation (2) to obtain the data of the loading force on the end of the specimen 6 connected to the elastic rod 1 in the frequency domain.

[0132] Step 4.6: Perform an inverse Fourier transform on the data of the applied force in the frequency domain to obtain the load-time curve, as shown in the attached figure. Figure 3 As shown in the figure, the solid line represents the load-time curve measured by this invention, and the dashed line represents the load-time curve measured by conventional testing methods. (From the attached figure...) Figure 3 It can be seen that the testing device and method of the present invention eliminate the influence of white noise by decomposing the transmission and superposition of stress waves, and eliminate the generation of load value oscillation in the test, which is beneficial to the subsequent data processing.

[0133] The above are merely preferred embodiments of the present invention and are not intended to limit the scope of protection of the present invention. Therefore, any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A load testing method for high strain rate tensile testing, characterized by: The method is realized based on a load testing device of high strain rate tensile test; the load testing device of high strain rate tensile test comprises an elastic rod (1), strain gauges (2), a tensile testing machine (3), a clamp connector (4) and a data collector (5); one end of the elastic rod (1) is fixed on a lower crossbeam (31) of the tensile testing machine (3), one end of a sample (6) is connected with the other end of the elastic rod (1) through the clamp connector (4), and the other end of the sample (6) is fixed on an upper crossbeam (32) of the tensile testing machine (3); a plurality of strain gauges (2) are arranged on the elastic rod (1) at intervals, and output ends of the plurality of strain gauges (2) are connected to the data collector (5); each strain gauge (2) independently transmits its stress signal to the data collector (5); The load testing method of high strain rate tensile test comprises the following steps: Step 1: fixing the sample (6) between the elastic rod (1) and the upper crossbeam (32) of the tensile testing machine (3), and sticking not less than three strain gauges (2) on the elastic rod (1) at intervals; Step 2: turning on the tensile testing machine (3) to stretch the upper crossbeam (32) upward until the sample (6) is broken; Step 3: collecting stress signals of the plurality of strain gauges (2) in real time through the data collector (5) within the test time of the upward stretching of the upper crossbeam (32); Step 4: calculating the load value of the sample (6) according to the stress signals of the plurality of strain gauges (2); The step 4 comprises: Step 4.1: converting the stress signal of each strain gauge (2) into a frequency domain signal through Fourier transform; The strain value of the strain gauge (2) at any position x from the top of the elastic rod (1) at any time t is ε(x, t), and the stress value is N(x, t). The ε(x, t) is obtained by Fourier transform The N(x, t) is obtained by Fourier transform ; Step 4.2: obtaining a frequency domain equation according to the frequency domain signal; According to one-dimensional stress wave transmission and its dispersion effect, the following equation is obtained: Equation (1) Equation (2); Wherein, A is the cross-sectional area of the elastic rod (1), E(ω) is the Young's modulus, β(ω) is the dispersion coefficient, F(ω) is the one-dimensional stress wave forward transfer function; D(ω) is the one-dimensional stress wave reverse transfer function; Step 4.3: calculating the maximum likelihood function of the frequency domain signals of the plurality of strain gauges (2), and the calculation formula is: Equation (3); Wherein, N is the total number of strain gauges (2), that is, N≥3; strain values including noise; Strain value after noise removal; Through the time domain frequency domain conversion principle, equation (3) is converted into: Equation (4) Step 4.4: Substitute the position x of each strain gauge (2) and its stress signal into equation (1) and calculate the solution for F(ω) and D(ω) with the goal of minimizing the function value of equation (4) F(ω) = D(ω) = 0 Equation (5) Equation (6); Wherein, ； ； ； ； ； ； , , , , and are components of the one-dimensional stress wave forward transfer function F(ω) and the one-dimensional stress wave reverse transfer function D(ω), is the average diffusion coefficient; Step 4.5: substituting the solutions of F(ω) and D(ω) into equation (2) to obtain the data of the loading force on the end of the sample (6) connected with the elastic rod (1) in the frequency domain; Step 4.6: obtaining the load time curve through inverse Fourier transform of the data of the loading force in the frequency domain.

2. The method of claim 1, wherein: In the step 2, the stretching rate of the upper crossbeam (32) is set as a high strain rate, and the range of the high strain rate is 500-1200 / s.

3. The method of claim 1, wherein: In the step 3, the stress signal of each strain gauge (2) comprises a strain value and a stress value of the strain gauge (2) at the sticking position thereof.

4. The method of claim 1, wherein: The length of the elastic rod (1) is 450-800mm, and the diameter is 20-30mm.

5. The method of claim 1, wherein: The plurality of strain gauges (2) are three, two of which are arranged at two ends of the elastic rod (1) respectively, and the other one is arranged at the middle of the elastic rod (1).

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