Artificial bird Hugoniot relation parameter measuring device and method based on Hopkinson rod

Abstract

The invention provides an artificial bird Hugoniot relation parameter measuring device and method based on a Hopkinson rod, relates to the technical field of bird impact tests, and overcomes the defect that a certain physical quantity needs to be indirectly calculated through a Hugoniot pressure relation in a traditional method by directly measuring the impact wave velocity and the post-wave mass point velocity. And secondly, the device can realize effective decoupling of device deformation and dynamic behaviors of the bird body, so that the influence of the material size, rigidity characteristics and the like of the measurement device on the constitutive model of the bird body is reduced. According to the method, through test preparation, test, measurement data processing, measurement data correction, validity analysis and empirical index analysis, tests are carried out on artificial birds with different densities, Hugoniot curves of the artificial birds with different densities are fitted, and then a bird body constitutive model and parameters are obtained. According to the method for deducing the state equation and the parameters of the state equation in the forward direction based on the physical state theory, the constitutive model and the parameters of the bird body cannot change along with the change of working conditions, and the universality of test data is improved.

Description

Technical Field

[0001] This application relates to the technical field of bird strike tests. Specifically, it relates to a device and method for measuring the Hugoniot relationship parameters of an artificial bird based on a Hopkinson bar. Background Art

[0002] The identification of the load-bearing capacity of an aircraft structure is a basic requirement for aircraft design. Impact loads are one of the most common load types that an aircraft may encounter. During flight, the front structures such as the windshield, nose, and wings will inevitably be impacted by external objects such as birds, hailstones, and stones. Due to its high destructiveness and frequency, the International Aeronautical Federation has classified bird strikes as class "A" aviation disasters. Impact tests are the ultimate and most effective test method in the research on the anti-impact design of aircraft structures.

[0003] In the research on aircraft bird strike resistance, since the physical process of bird strike is usually accompanied by severe deformation or even local damage of the aircraft structure, involving highly complex non-linear mechanical problems, it is difficult to accurately describe it only relying on theoretical analysis. At the same time, due to the high cost and long cycle of bird strike tests, their practical applications are significantly restricted. Therefore, the anti-bird strike design of modern aircraft structures shows a high dependence on numerical simulation technology.

[0004] In current bird strike finite element simulation research, a coupling method is usually adopted, that is, the deformation of the bird body and the structure affects each other. For example, the bird body is numerically discretized by the Smoothed Particle Hydrodynamics (SPH) method, while the Lagrange method is used for numerical discretization of the target structure. Therefore, the material constitutive models and parameters of the bird body and the aircraft structure are important bases for finite element simulation research. For the determination of the bird body constitutive model and parameters, an inversion method is usually adopted. Specifically, according to the application conditions of the bird body numerical model, an equivalent and simplified structural response measurement test needs to be designed to obtain systematic basic test data, which is used as the benchmark for constitutive model determination and constitutive parameter inversion.

[0005] However, the above method belongs to the research category of dynamic inverse problems. The obtained bird body constitutive model and parameters will change with the working conditions and do not meet the need for universality. Therefore, the research on the bird body constitutive model and parameters can be based on the physical state theory to deduce the state equation and its parameters in the forward direction, so that the constitutive model and parameters return to the inherent properties of the material, and describe its dynamic mechanical behavior from a more physically meaningful perspective.

[0006] To deduce the bird body constitutive model and parameters applicable to the finite element simulation of aircraft structure bird strike resistance in the forward direction, it is first necessary to fit the Hugoniot relationship formula of the artificial bird (i.e., the shock wave velocity V sWith the particle velocity after the wave V p in the linear relationship), the sound speed in the medium C 0 and the linear Hugoniot relationship constant k . The existing experimental methods for the Hugoniot relationship of artificial birds are mainly based on bird impact on a rigid target plate or a flat plate impact test to obtain the Hugoniot relationship of artificial birds V s and V p .

[0007] However, in the bird impact on a rigid target plate method, V p is directly obtained through the impact test, while V s is indirectly calculated through the Hugoniot pressure relationship; similarly, in the flyer plate impact test method, V s is directly obtained through the impact test, while V p is indirectly calculated through the Hugoniot pressure relationship. Therefore, these methods cannot directly measure the V p and V s of the artificial bird decoupled from the structural deformation, thus affecting the accuracy and universality of the data. SUMMARY OF THE INVENTION

[0008] The purpose of this application is to provide a Hopkinson bar-based device and method for measuring the Hugoniot relationship parameters of artificial birds, aiming at the deficiency that the existing experimental methods for the Hugoniot relationship of artificial birds cannot directly measure the V p and V s of the artificial bird decoupled from the structural deformation.

[0009] To achieve the above purpose, the technical solution adopted in this application is as follows: On the one hand, this application provides a Hopkinson bar-based device for measuring the Hugoniot relationship parameters of artificial birds, including a bracket and a Hopkinson bar movably arranged on the bracket. The Hopkinson bar includes an impact bar, an incident bar, and a transmission bar arranged in sequence along the axial direction. There is a gap for clamping the artificial bird between the incident bar and the transmission bar. The impact bar is driven to impact the incident bar to generate a shock wave. The shock wave propagates through the incident bar to the artificial bird. Part of the shock wave is reflected by the artificial bird to the incident bar to form a reflected wave, and part of the shock wave is transmitted through the artificial bird to the transmission bar to form a transmitted wave; A first strain gauge group and a second strain gauge group are arranged at intervals along the axial direction on the outer periphery of the incident bar, and a third strain gauge group is arranged on the outer periphery of the transmission bar. The first strain gauge group, the second strain gauge group and the third strain gauge group generate voltage signals for measuring the strain of the shock wave, the reflected wave and the transmitted wave respectively, and calculate the particle velocity behind the wave of the artificial bird according to the strain of the shock wave, the reflected wave and the transmitted wave; A first piezoelectric film sensor and a second piezoelectric film sensor are respectively arranged on the clamping surfaces of the incident bar and the transmission bar. The first piezoelectric film sensor and the second piezoelectric film sensor generate voltage signals for measuring the normal forces on the two axial end faces of the artificial bird respectively, and calculate the shock wave velocity of the artificial bird according to the time difference between the voltage signals generated by the first piezoelectric film sensor and the second piezoelectric film sensor.

[0010] Furthermore, the device further includes an energy absorption device fixedly arranged on the bracket. The Hopkinson bar further includes an absorption bar which is arranged axially on the side of the transmission bar away from the incident bar, and one end of the absorption bar away from the transmission bar is inserted into the energy absorption device to absorb the shock wave that is not reflected and transmitted.

[0011] Furthermore, the impact bar, the incident bar, the transmission bar and the absorption bar are coaxially arranged.

[0012] Furthermore, the impact bar, the incident bar, the transmission bar and the absorption bar have the same diameter, which is 1.0 - 1.2 times the diameter of the circumcircle of the artificial bird with the largest mass in the test outline.

[0013] Furthermore, the device further includes a normal camera and an oblique camera arranged on the same side of the artificial bird. The optical axis of the normal camera is perpendicular to the axis of the Hopkinson bar, and the included angle between the optical axis of the oblique camera and the axis of the Hopkinson bar is an acute angle to photograph the deformation process of the artificial bird from different fields of view.

[0014] Furthermore, the distance between the first strain gauge group and the end of the incident bar close to the impact bar is 1 / 4 - 1 / 3 of the length of the incident bar, the distance between the second strain gauge group and the end of the incident bar close to the transmission bar is 1 / 4 - 1 / 3 of the length of the incident bar, and the distance between the third strain gauge group and the end of the transmission bar close to the incident bar is 1 / 4 - 1 / 3 of the length of the transmission bar.

[0015] Furthermore, the first strain gauge group includes at least two strain gauges symmetrically arranged along the axial direction on both sides of the incident bar, the second strain gauge group includes at least two strain gauges symmetrically arranged along the axial direction on both sides of the incident bar, and the third strain gauge group includes at least two strain gauges symmetrically arranged along the axial direction on both sides of the transmission bar.

[0016] On the other hand, the present application provides a method for measuring the Hugoniot relation parameters of an artificial bird based on a Hopkinson bar. The method is implemented by the device of any of the above, and the method includes: Test preparation: Determine the diameters of the impact bar, incident bar, and transmission bar according to the diameter of the artificial bird; determine the lengths of the impact bar, incident bar, and transmission bar according to the strain and stress requirements of the artificial bird. Test: Drive the impact bar to strike the incident bar to generate a shock wave. The shock wave propagates through the incident bar to the artificial bird. Part of the shock wave is reflected by the artificial bird to the incident bar to form a reflected wave, and part of the shock wave is transmitted through the artificial bird to the transmission bar to form a transmitted wave. Use the first strain gauge group, the second strain gauge group, and the third strain gauge group to measure the strains of the shock wave, reflected wave, and transmitted wave respectively. Use the first piezoelectric film sensor and the second piezoelectric film sensor to measure the normal forces on the two axial end faces of the artificial bird respectively. Measurement data processing: Calculate the particle velocity behind the wave of the artificial bird according to the strains of the shock wave, reflected wave, and transmitted wave. The calculation formula is: (6) Where, V p is the particle velocity behind the wave of the artificial bird, C 0 is the one-dimensional elastic wave velocity of the impact bar, , E is the elastic modulus of the impact bar, ρ 0 is the density of the impact bar, ε i is the strain of the shock wave, ε r is the strain of the reflected wave, ε t is the strain of the transmitted wave; Calculate the shock wave velocity of the artificial bird according to the time difference of the voltage signals generated when measuring the normal forces on the two axial end faces of the artificial bird. The calculation formula is: (7) Where, V s is the shock wave velocity of the artificial bird, L G is the length of the artificial bird, t input is the time when the first piezoelectric film sensor starts to generate a voltage signal, t output is the time when the second piezoelectric film sensor starts to generate a voltage signal; Measurement data correction and validity analysis: Correct the strains measured by the first strain gauge group, the second strain gauge group, and the third strain gauge group through Fourier transform. Calculate the corrected normal forces on the two axial end faces of the artificial bird according to the corrected strains, and compare the corrected normal forces on the two axial end faces of the artificial bird with the normal forces measured by the first piezoelectric film sensor and the second piezoelectric film sensor to determine the validity of the measurement data. Analysis of empirical indicators: For artificial birds with different densities, repeated experiments are prepared from measurement data correction to validity analysis. Hugoniot curves of artificial birds with different densities regarding the particle velocity behind the wave and shock wave velocity are fitted. The slopes and intercepts of the Hugoniot curves of artificial birds with different densities are compared to judge the influence of the density of artificial birds on their mechanical behavior.

[0017] Furthermore, during the experiment preparation, the lengths of the impact bar, incident bar, and transmission bar are determined according to the strain and stress requirements of the artificial bird, including: Determine the lengths of the incident bar and transmission bar: Assume that the preset lengths of the incident bar and transmission bar are equal, both being L’ , and the preset lengths of the incident bar and transmission bar L’ should be such that the strain of the artificial bird measured does not have waveform superposition of shock waves and reflected waves; If the time required from when the shock wave reaches the second strain gauge group to when the reflected wave propagates back to the second strain gauge group along the incident bar is greater than the width of the shock wave, then the preset lengths of the incident bar and transmission bar L’ are determined as the lengths of the incident bar and transmission bar L ; Determine the length of the impact bar: The preset length of the impact bar L B ’ should be such that the strain of the artificial bird measured does not have waveform superposition of shock waves and reflected waves. At the same time, the preset length of the impact bar L B ’ should be such that stress balance can be achieved during the loading process of the artificial bird; The calculation formula for the width of the shock wave is: (1) where ΔT is the width of the shock wave, C 0 is the one-dimensional elastic wave velocity of the impact bar, , E is the elastic modulus of the impact bar and incident bar, ρ 0 is the density of the impact bar and incident bar; The calculation formula for the number of round trips of the shock wave propagating in the artificial bird is: (2) where n is the number of round trips propagating in the artificial bird, C G is the one-dimensional elastic wave velocity of the artificial bird, L G is the length of the artificial bird; If the time required for the reflected wave to propagate back to the second strain gauge group along the incident bar after the shock wave reaches the second strain gauge group is greater than the width of the shock wave, and the number of round trips of the shock wave propagating in the artificial bird is greater than 3 to achieve stress balance during the loading process of the artificial bird, then the preset length of the impact bar L B ’ is determined as the length of the impact bar L B .

[0018] Furthermore, in the measurement data correction and validity analysis, the strains measured by the first strain gauge group, the second strain gauge group, and the third strain gauge group are corrected through Fourier transform, including: converting the strains measured by the first strain gauge group and the second strain gauge group from the time domain to the frequency domain through Fourier transform, then the one-dimensional wave equation of the Hopkinson bar becomes: (8) The general solution of this one-dimensional wave equation is: (9) where is the angular frequency, x is any length of the Hopkinson bar along the axial direction, is the strain under frequency domain analysis, and the functions and are the Fourier forms of the strain propagating along the axial direction at x of the Hopkinson bar. The modulus and phase of the complex exponential functions and reflect the attenuation and propagation of the shock wave, γ is the propagation coefficient, is related to the attenuation coefficient and the phase velocity , and the calculation formula is: (10) where i is the imaginary number in the complex variable function, the attenuation coefficient is an even function, and the wave number is an odd function; Thus, the Fourier transforms of the axial particle velocity and the normal force at any length of the Hopkinson bar are: (11) (12) where is the axial particle velocity at any length of the Hopkinson bar under frequency domain analysis, is the normal force at any length of the Hopkinson bar under frequency domain analysis,A is the cross-sectional area of the incident rod and the transmission rod; The attenuation coefficient is calculated from the strain of the shock wave measured by the first strain gauge group and the wave number , and the attenuation coefficient is calculated from the strain of the reflected wave measured by the second strain gauge group and the wave number ; Take and The average value of is used as the attenuation coefficient , Take and The average value of is used as the wave speed , Substitute and into the Fourier transform of the axial particle velocity and the normal force of the Hopkinson rod at any length, and the frequency-domain forms of the velocities and normal forces of the modified artificial bird at both axial ends are obtained. Then, through the inverse Fourier transform, the time-domain forms are obtained, and the strains measured by the first strain gauge group, the second strain gauge group, and the third strain gauge group are corrected.

[0019] Furthermore, in the measurement data correction and validity analysis, the corrected normal forces of the artificial bird at both axial ends are calculated according to the corrected strain, and the corrected normal forces of the artificial bird at both axial ends are compared with the normal forces measured by the first piezoelectric film sensor and the second piezoelectric film sensor to determine the validity of the measurement data, including: calculating the peak values of the corrected normal forces of the artificial bird at both axial ends according to the strains corrected by the first strain gauge group, the second strain gauge group, and the third strain gauge group and , and The occurrence times of are respectively and ; The peak values of the normal forces of the artificial bird at both axial ends are measured by the first piezoelectric film sensor and the second piezoelectric film sensor respectively and , and The occurrence times of are respectively and ; The validity judgment formula for the measurement data of the first piezoelectric film sensor is: (17) If it satisfies and The difference is < 5%, and and The difference is < 5%, then the measurement data of the first piezoelectric film sensor is determined to be valid; The validity judgment formula for the measurement data of the second piezoelectric thin film sensor is as follows: (18) If it satisfies and The difference < 5%, and and The difference < 5%, then it is determined that the measurement data of the second piezoelectric thin film sensor is valid.

[0020] The beneficial effects of this application include: This application provides a device for measuring the Hugoniot relationship parameters of an artificial bird based on a Hopkinson bar, including a bracket and a Hopkinson bar movably arranged on the bracket. The Hopkinson bar includes an impact bar, an incident bar, and a transmission bar arranged in sequence along the axial direction. There is a gap for clamping the artificial bird between the incident bar and the transmission bar. The impact bar is driven to impact the incident bar to generate a shock wave. The shock wave propagates through the incident bar to the artificial bird. Part of the shock wave is reflected by the artificial bird to the incident bar to form a reflected wave, and part of the shock wave is transmitted through the artificial bird to the transmission bar to form a transmitted wave. A first strain gauge group and a second strain gauge group are arranged at intervals along the axial direction on the outer periphery of the incident bar, and a third strain gauge group is arranged on the outer periphery of the transmission bar. The first strain gauge group, the second strain gauge group, and the third strain gauge group are respectively used to generate voltage signals to measure the strains of the shock wave, the reflected wave, and the transmitted wave, and calculate the particle velocity behind the wave of the artificial bird according to the strains of the shock wave, the reflected wave, and the transmitted wave. A first piezoelectric thin film sensor and a second piezoelectric thin film sensor are respectively arranged on the clamping surfaces of the incident bar and the transmission bar. The first piezoelectric thin film sensor and the second piezoelectric thin film sensor are respectively used to generate voltage signals to measure the normal forces on the two axial end faces of the artificial bird, and calculate the shock wave velocity of the artificial bird according to the time difference of the voltage signals generated by the first piezoelectric thin film sensor and the second piezoelectric thin film sensor. By directly measuring the shock wave velocity and the particle velocity behind the wave, the device provided by this application avoids the disadvantages of indirectly calculating a certain physical quantity through the Hugoniot pressure relationship formula in the traditional method. Through accurate real-time measurement, it can more accurately describe the dynamic response of the artificial bird when it is impacted, improving the accuracy and reliability of the data. Secondly, this device can effectively decouple the deformation of the device from the dynamic behavior of the bird body, thereby reducing the influence of the material size, stiffness characteristics, etc. of the measurement device on the constitutive model of the bird body. This advantage not only improves the universality of the test data but also provides a more scientific and credible basis for subsequent simulation research and aircraft structure design, and has a wide range of application prospects.

[0021] The present application also provides a method for measuring the Hugoniot relationship parameters of artificial birds based on a Hopkinson bar, which is implemented by any of the above-mentioned devices. This method conducts experiments through experiment preparation, experimentation, measurement data processing, measurement data correction and validity analysis, and empirical index analysis. Experiments are carried out on artificial birds with different densities to fit the Hugoniot curves of artificial birds with different densities, and then the constitutive model and parameters of the bird body are obtained. This method of deriving the equation of state and its parameters from the positive direction based on the physical state theory will not cause the constitutive model and parameters of the bird body to change with the working conditions, improving the universality of the experimental data. Description of the Drawings

[0022] To more clearly illustrate the technical solutions of the present application, the drawings required for use in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present application and should not be regarded as limiting the scope. For those of ordinary skill in the art, other related drawings can be obtained based on these drawings without creative efforts.

[0023] Figure 1 Side view of a device for measuring the Hugoniot relationship parameters of artificial birds based on a Hopkinson bar provided by the present application; Figure 2 is Figure 1 front view of; Figure 3 Side view of the equivalent elastic modulus calibration test; Figure 4 Flowchart of a method for measuring the Hugoniot relationship parameters of artificial birds based on a Hopkinson bar provided by the present application; Figure 5 Comparison diagram of the experimental normal force and the simulated normal force for equivalent elastic modulus calibration; Figure 6 Comparison diagram of the normal force at the left and right end faces of the artificial bird before and after waveform correction; Figure 7 Schematic diagram of the original voltage signals of the first and second piezoelectric film sensors after calibration; Figure 8 For an artificial bird with a density of 1.050 g / cm 3 scatter plot of the particle velocity behind the wave and the shock wave velocity; Figure 9 For an artificial bird with a density of 0.990 g / cm 3 scatter plot of the particle velocity behind the wave and the shock wave velocity; Figure 10 For an artificial bird with a density of 0.950 g / cm 3Scatter plot of the particle velocity behind the wave and the shock wave velocity of the artificial bird; Figure 11 Comparison diagram of Hugoniot relationship curves fitted for artificial birds with different densities.

[0024] Icons: 1. Air cannon barrel; 2. Impact rod; 3. Wave shaper; 4. Incident rod; 5. Artificial bird; 6. Transmission rod; 7. Absorbing rod; 8. Bracket; 9. Energy absorption device; 10. First strain gauge group; 11. Second strain gauge group; 12. Third strain gauge group; 13. First Wheatstone bridge box; 14. Second Wheatstone bridge box; 15. Third Wheatstone bridge box; 16. First piezoelectric film sensor; 17. Second piezoelectric film sensor; 18. Data collector; 19. DC regulated power supply; 20. Normal camera; 21. Oblique camera; 22. Calibration projectile; 23. Experimental normal force at a strain rate of 2.70 / s; 24. Simulated normal force at a strain rate of 2.70 / s; 25. Experimental normal force at a strain rate of 5.09 / s; 26. Simulated normal force at a strain rate of 5.09 / s; 27. Diagram of the normal force on the left end face of the artificial bird without waveform correction during one test; 28. Diagram of the normal force on the right end face of the artificial bird without waveform correction during one test; 29. Diagram of the normal force on the left end face of the artificial bird with waveform correction during one test; 30. Diagram of the normal force on the right end face of the artificial bird with waveform correction during one test; 31. Diagram of the original voltage signal of the first piezoelectric film sensor during one test; 32. Diagram of the original voltage signal of the second piezoelectric film sensor during one test; 33. Artificial bird with a density of 1.050 g / cm 3 Hugoniot relationship curve fitted for the artificial bird; 34. Artificial bird with a density of 0.990 g / cm 3 Hugoniot relationship curve fitted for the artificial bird; 35. Artificial bird with a density of 0.950 g / cm 3 Hugoniot relationship curve fitted for the artificial bird. Detailed implementation manners To make the objectives, technical solutions, and advantages of this application clearer, the technical solutions in this application will be clearly and completely described below in conjunction with the accompanying drawings in this application. Obviously, the described embodiments are some, but not all, of the embodiments of this application. Usually, the components of this application described and illustrated in the drawings here can be arranged and designed in various different configurations.

[0025] Accordingly, the following detailed description of the embodiments of the present application provided in the drawings is not intended to limit the scope of the claimed present application, but merely represents selected embodiments of the present application. It should be noted that, without conflict, the various features in the embodiments of the present application may be combined with each other, and the combined embodiments are still within the protection scope of the present application.

[0026] It should be noted that like reference numerals and letters indicate like items in the following drawings. Therefore, once an item is defined in one drawing, it does not need to be further defined and explained in subsequent drawings.

[0027] In the description of the present application, it should be noted that the orientation or positional relationship indicated by the terms "center", "upper", "lower", "left", "right", "vertical", "horizontal", "inner", "outer", etc. is based on the orientation or positional relationship shown in the drawings, or the orientation or positional relationship in which the product of this application is customarily placed when in use. It is only for the convenience of describing the present application 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 therefore should not be construed as a limitation to the present application. In addition, the terms "first", "second", "third", etc. are only used for distinguishing descriptions and cannot be understood as indicating or implying relative importance.

[0028] In addition, terms such as "horizontal" and "vertical" do not mean that the components are required to be absolutely horizontal or hanging vertically, but may be slightly inclined. For example, "horizontal" only means that its direction is more horizontal relative to "vertical", and does not mean that the structure must be completely horizontal, but may be slightly inclined.

[0029] In the description of the present application, it should also be noted that unless otherwise clearly specified and limited, the terms "set", "installed", "connected", "connected" should be understood in a broad sense. For example, it may be a fixed connection, a detachable connection, or an integral connection; it may be a mechanical connection or an electrical connection; it may be directly connected, or indirectly connected through an intermediate medium, and may be the communication inside two elements. For those of ordinary skill in the art, the specific meanings of the above terms in the present application can be understood according to specific situations.

[0030] On one hand of the present application, there is provided a device for measuring the Hugoniot relation parameters of an artificial bird based on a Hopkinson bar, as Figure 1 and Figure 2As shown in the figure, it includes a bracket 8 fixed on the ground and a Hopkinson bar movably arranged on the bracket 8. On the upper surface of the bracket 8, eight groups of support bars are arranged at intervals. Each group of support bars contains two support bars, which are respectively located on the two side edges of the bracket 8. Roller shafts are respectively installed on each group of support bars, and two rollers are respectively installed on each roller shaft. The distance between the two rollers on each roller shaft meets the support requirements of the Hopkinson bar and has no interference with the roller shaft. The Hopkinson bar includes an impact bar 2, an incident bar 4, and a transmission bar 6 that are sequentially arranged in the axial direction from left to right and slide on the rollers. An artificial bird 5 is clamped between the right end face of the incident bar 4 and the left end face of the transmission bar 6. The impact bar 2 is placed in the barrel 1 of the air cannon. One end of the incident bar 4 adjacent to the barrel 1 of the air cannon (i.e., the left end of the incident bar 4) is the bullet-facing end. The impact bar 2 is driven by the air cannon to impact the bullet-facing end of the incident bar 4 in parallel to generate a shock wave. The shock wave is an approximate compression square wave. The shock wave propagates through the incident bar 4 to the artificial bird 5. Part of the shock wave is reflected by the artificial bird 5 to the incident bar 4 to form a reflected wave, and part of the shock wave is transmitted through the artificial bird 5 to the transmission bar 6 to form a transmitted wave. A waveform shaper 3 is pasted at the center of the bullet-facing end face of the incident bar 4. By adjusting the number of layers of the waveform shaper 3, the rise time of the loading wave can be precisely controlled, thereby optimizing the loading waveform. The waveform shaper 3 can be made of materials with negligible strength such as vacuum sealing mud.

[0031] A first strain gauge group 10 and a second strain gauge group 11 are pasted on the outer peripheral surface of the incident bar 4 at intervals in the axial direction. A third strain gauge group 12 is pasted on the outer peripheral surface of the transmission bar 6. The first strain gauge group 10, the second strain gauge group 11, and the third strain gauge group 12 generate voltage signals respectively for measuring the strains of the shock wave, the reflected wave, and the transmitted wave. The particle velocity behind the wave of the artificial bird 5 is calculated based on the strains of the shock wave, the reflected wave, and the transmitted wave.

[0032] A first piezoelectric film sensor 16 and a second piezoelectric film sensor 17 are respectively and closely pasted at the centers of the clamping surfaces of the incident bar 4 and the transmission bar 6. That is, the first piezoelectric film sensor 16 is distributed at the center of the right end face of the incident bar 4, and the second piezoelectric film sensor 17 is distributed at the center of the left end face of the transmission bar 6. The first piezoelectric film sensor 16 and the second piezoelectric film sensor 17 generate voltage signals respectively for measuring the normal forces on the two axial end faces of the artificial bird 5. The shock wave velocity of the artificial bird 5 is calculated based on the time difference of the voltage signals generated by the first piezoelectric film sensor 16 and the second piezoelectric film sensor 17.

[0033] It should be understood that when the compression properties of the impact bar 2, the incident bar 4, and the transmission bar 6 meet the linear elasticity, the strain measured by the strain gauge group has a linear conversion relationship with the particle velocity and the normal force on the left and right end faces of the artificial bird 5.

[0034] It should be noted that the voltage signals generated by the first strain gauge group 10, the second strain gauge group 11, and the third strain gauge group 12 can be processed according to the bridge conversion formula of the Wheatstone bridge to obtain the strain. The specific implementation method is as follows: Connect the first strain gauge group 10 to the first Wheatstone bridge box 13 according to the conventional method in the prior art; connect the second strain gauge group 11 to the second Wheatstone bridge box 14; connect the third strain gauge group 12 to the third Wheatstone bridge box 15; the three Wheatstone bridges in the first Wheatstone bridge box 13, the second Wheatstone bridge box 14, and the third Wheatstone bridge box 15 all adopt the opposite-arm measurement method in the prior art. When the piezoelectric film sensor is measured, connect the output ports of the first Wheatstone bridge box 13, the second Wheatstone bridge box 14, and the third Wheatstone bridge box 15 to the input ports of the data collector 18 according to the conventional method in the prior art. The first Wheatstone bridge box 13, the second Wheatstone bridge box 14, and the third Wheatstone bridge box 15 are respectively connected to the DC regulated power supply 19, and the DC regulated power supply 19 supplies power to the three Wheatstone bridge boxes. Connect the output ports of the first piezoelectric film sensor 16 and the second piezoelectric film sensor 17 to the input ports of the data collector 18 according to the conventional method in the prior art. Ground the data collector 18 and the DC regulated power supply 19 according to the conventional method in the prior art.

[0035] Generally speaking, by directly measuring the shock wave velocity and the particle velocity after the wave, the device provided by the present application avoids the drawback of indirectly calculating a certain physical quantity through the Hugoniot pressure relation in the traditional method. Through accurate real-time measurement, the dynamic response of the artificial bird 5 when it is impacted can be described more accurately, improving the accuracy and reliability of the data. Secondly, the device of the present invention can effectively decouple the deformation of the device from the dynamic behavior of the bird body, thereby reducing the influence of the material size and stiffness characteristics of the measuring device on the constitutive model of the bird body. This advantage not only improves the universality of the test data, but also provides a more scientific and credible basis for subsequent simulation research and aircraft structure design, and has a wide application prospect.

[0036] Furthermore, the device further includes an energy absorption device 9 fixedly arranged on the bracket 8. The Hopkinson bar further includes an absorption bar 7 slidably arranged on the roller. The absorption bar 7 is axially arranged on the side of the transmission bar 6 away from the incident bar 4. The energy absorption device 9 is arranged on the side of the absorption bar 7 away from the transmission bar 6. One end of the absorption bar 7 adjacent to the energy absorption device 9 (i.e., the right end of the absorption bar 7) is the energy absorption end, and the energy absorption end is inserted into the energy absorption device 9. The inside of the energy absorption device 9 is filled with putty to effectively absorb the shock wave that is not reflected and transmitted (i.e., the remaining energy after the impact), and to limit the movement of the incident bar 4 and the transmission bar 6.

[0037] Furthermore, the impact bar 2, the incident bar 4, the transmission bar 6, and the absorption bar 7 are coaxially arranged and are all coaxial with the air cannon barrel 1. This coaxial arrangement design can effectively ensure the parallel impact between the impact bar 2 and the incident bar 4, thus ensuring that the propagation direction of the shock wave is accurate without error, avoiding possible angular deviations and irregular propagations during the impact process, and ensuring the high precision and reliability of the test measurement.

[0038] Furthermore, the impact bar 2, the incident bar 4, the transmission bar 6, and the absorption bar 7 are all made of nylon PA66. The impact bar 2, the incident bar 4, the transmission bar 6, and the absorption bar 7 have the same diameter, which is 1.0 - 1.2 times the diameter of the circumcircle of the largest artificial bird 5 in the test outline. The lengths of the impact bar 2, the incident bar 4, the transmission bar 6, and the absorption bar 7 are determined by the conventional method in the prior art. Among them, the incident bar 4 and the transmission bar 6 need to ensure that the strain of the artificial bird 5 measured does not have the waveform superposition of the shock wave and the reflected wave; the impact bar 2 should ensure that the strain of the artificial bird 5 measured does not have the waveform superposition of the shock wave and the reflected wave, and at the same time, it is necessary to achieve stress balance during the loading process of the artificial bird 5; the length of the absorption bar 7 depends on the length of the actual test bench, and it is necessary to ensure that the impact energy transmitted by the transmission bar 6 can be transmitted to the energy absorption device 9 as much as possible, preventing the transmission bar 6 from generating a large axial displacement during the impact, so that the artificial bird 5 cannot experience a uniform deformation process.

[0039] Further, the device further includes a normal camera 20 and an oblique camera 21 arranged on the same side of the artificial bird 5. Specifically, the normal camera 20 is arranged in the gap between the incident bar 4 and the transmission bar 6 by a conventional method, and the normal camera 20 is located on the side of the artificial bird 5 perpendicular to the axis of the Hopkinson bar. Moreover, the lens of the normal camera 20 is horizontally placed, and its optical axis is perpendicular to the axis of the Hopkinson bar to capture the deformation process of the artificial bird 5 in a horizontal field of view. Similarly, the oblique camera 21 is arranged in the gap between the incident bar 4 and the transmission bar 6 by a conventional method, and the oblique camera 21 and the normal camera 20 are arranged on the same side of the artificial bird 5. And, the lens of the oblique camera 21 is inclined, and the included angle between its optical axis and the axis of the Hopkinson bar is an acute angle to capture the deformation process of the artificial bird 5 in an oblique field of view. Preferably, both the normal camera 20 and the oblique camera 21 are high-speed cameras.

[0040] Further, the first strain gauge group 10 is located at the 1 / 4 - 1 / 3 length of the incident bar 4 near the impact bar 2 end, that is, the distance between the first strain gauge group 10 and the left end of the incident bar 4 is 1 / 4 - 1 / 3 of the length of the incident bar 4; the second strain gauge group 11 is located at the 1 / 4 - 1 / 3 length of the incident bar 4 near the transmission bar 6 end, that is, the distance between the second strain gauge group 11 and the right end of the incident bar 4 is 1 / 4 - 1 / 3 of the length of the incident bar 4; the third strain gauge group 12 is located at the 1 / 4 - 1 / 3 length of the transmission bar 6 near the incident bar 4 end, that is, the distance between the third strain gauge group 12 and the left end of the transmission bar 6 is 1 / 4 - 1 / 3 of the length of the transmission bar 6, so as to ensure that the distance between the first strain gauge group 10 and the second strain gauge group 11 is greater than 1 / 3 of the length of the incident bar 4, for correcting the stress wave dispersion and attenuation caused by the viscoelastic Hopkinson bar.

[0041] Further, the first strain gauge group 10 includes two strain gauges symmetrically arranged along the axis on both sides of the incident bar 4, the second strain gauge group 11 includes two strain gauges symmetrically arranged along the axis on both sides of the incident bar 4, and the third strain gauge group 12 includes two strain gauges symmetrically arranged along the axis on both sides of the transmission bar 6. The two strain gauges forming the same strain gauge group are pasted at the 3 o'clock direction and the 9 o'clock direction on the outer peripheral surface of the corresponding bar, or, the two strain gauges forming the same strain gauge group are pasted at the 6 o'clock direction and the 12 o'clock direction on the outer peripheral surface of the corresponding bar, and the strain gauge grids of each strain gauge are arranged along the axis direction of the corresponding bar.

[0042] On the other hand, the present application provides a method for measuring the Hugoniot relation parameters of an artificial bird based on a Hopkinson bar, and the method is implemented by the device of any of the above, as Figure 4 shown, the method includes: S1. Test preparation: Determine the diameters of the impact rod 2, incident rod 4, transmission rod 6, and absorption rod 7 according to the diameter of the artificial bird 5; determine the lengths of the impact rod 2, incident rod 4, and transmission rod 6 according to the strain and stress requirements of the artificial bird 5; determine the length of the absorption rod 7 according to the length of the actual test bench. S11. Determine the diameters of the impact rod 2, incident rod 4, transmission rod 6, and absorption rod 7 according to the diameter of the artificial bird 5: Determine the diameters of the four rods according to the artificial bird 5 with the largest mass in the current test specified in the test outline. The diameters of the four rods are equal, and are 1.0 - 1.2 times the circumscribed circle diameter of the artificial bird 5 with the largest mass.

[0043] In this embodiment, the artificial bird body with the largest mass specified in the test outline is 247.4 g. The shape of the artificial bird 5 is a cylindrical shape with a major - axis - to - minor - axis ratio of 3:10, and the maximum density of the artificial bird 5 is 1.050 g / cm3. The length of the 247.4 - g artificial bird 5 is 30 mm, and the diameter is 100 mm; the diameters of the four rods are 1 times the diameter of the 247.4 - g artificial bird 5, and the diameters of the four rods are determined to be 100 mm.

[0044] S12. Determine the lengths of the impact rod 2, incident rod 4, and transmission rod 6 according to the strain and stress requirements of the artificial bird 5: S121. Determine the lengths of the incident rod 4 and transmission rod 6: Assume that the preset lengths of the incident rod 4 and transmission rod 6 are equal, both being L’ , and the preset lengths of the incident rod 4 and transmission rod 6 L’ should be such that the strain of the measured artificial bird 5 does not have waveform superposition of shock waves and reflected waves; If the time required for the shock wave generated by the impact of the impact rod 2 on the incident rod 4 to reach the second strain gauge group 11, propagate along the incident rod 4 to the artificial bird 5, be reflected as a reflected wave by the artificial bird 5 and then propagate back to the second strain gauge group 11 along the incident rod 4 is greater than the width of the shock wave, then determine the preset lengths of the incident rod 4 and transmission rod 6 L’ as the lengths of the incident rod 4 and transmission rod 6 L ; S122. Determine the length of the impact rod 2: The preset length of the impact rod 2 L B ’ should be such that the strain of the measured artificial bird 5 does not have waveform superposition of shock waves and reflected waves. At the same time, the preset length of the impact rod 2 L B ’ should be such that stress balance can be achieved during the loading process of the artificial bird 5.

[0045] The impact rod 2 moves at a speed VWhen the impact rod 2 impacts the incident rod 4, a shock wave is generated in the incident rod 4. The shock wave is an approximate compressive square-wave strain signal. The calculation formula for the width of the shock wave is: (1) Where, ΔT is the width of the shock wave, C 0 is the one-dimensional elastic wave velocity of the impact rod 2, , E is the elastic modulus of the impact rod 2 and the incident rod 4, ρ 0 is the density of the impact rod 2, the incident rod 4, the transmission rod 6 and the absorption rod 7.

[0046] The calculation formula for the number of round trips of the shock wave propagating in the artificial bird 5 is: (2) Where, n is the number of round trips of propagation in the artificial bird 5, C G is the one-dimensional elastic wave velocity of the artificial bird 5, approximately 1500 m / s, L G is the length of the artificial bird 5.

[0047] If the time required for the shock wave generated by the impact of the impact rod 2 on the incident rod 4 to reach the second strain gauge group 11, propagate along the incident rod 4 to the artificial bird 5, be reflected by the artificial bird 5 as a reflected wave and then propagate back to the second strain gauge group 11 along the incident rod 4 is greater than the width of the shock wave, and the number of round trips of the shock wave propagating in the artificial bird 5 is greater than 3, so as to achieve stress balance during the loading process of the artificial bird 5, then the preset length L B ’ is determined as the length L B .

[0048] S13. Determine the length of the absorption rod 7: The length of the absorption rod 7 L A depends on the length of the actual test bench. The absorption rod 7 is used as a carrier to transfer the impact energy to the energy absorption device 9. The length L A needs to ensure that the impact energy transmitted by the transmission rod 6 can be transferred to the energy absorption device 9 as much as possible, preventing the transmission rod 6 from generating a large axial displacement during impact, so that the artificial bird 5 cannot experience a uniform deformation process.

[0049] In this embodiment, the preset L’ = 3000 mm, L B ’= 400 mm. The impact rod 2, incident rod 4, transmission rod 6, and absorption rod 7 are all made of nylon PA66, and their one-dimensional elastic wave velocity is 1800 m / s. When L B ’ = 400 mm, it is calculated through formula (1) that ΔT = 0.44 ms. When the shock wave reaches the second strain gauge group 11 and propagates along the axial direction of the incident rod 4 to the right end face of the incident rod 4, and is reflected by the artificial bird 5 as a reflected wave (where the reflected wave is a tensile wave) and propagates back to the second strain gauge group 11, the total propagation distance of the wave is 2000 mm, and the propagation duration is 1.11 ms, which is greater than the width of the shock wave. The shock wave will not be superimposed with the reflected tensile wave, causing difficulties in experimental data analysis. And it is calculated through formula (2) that n = 11, which is greater than 3, indicating that the stress in the artificial bird 5 can be balanced. Therefore, setting the lengths of the incident rod 4 and the transmission rod 6 L to be 3000 mm and the length of the impact rod 2 L B to be 400 mm is reasonable.

[0050] After determining the diameter and parameters, the impact rod 2 is arranged in the air cannon barrel 1, and the incident rod 4, transmission rod 6, and absorption rod 7 are successively arranged on the bracket 8, so that the impact rod 2, incident rod 4, transmission rod 6, and absorption rod 7 are all coaxial with the air cannon barrel 1, and the projectile-facing end face of the incident rod 4 is located at one end close to the air cannon barrel 1, and the energy-absorbing end of the absorption rod 7 is closely attached to the energy-absorbing device 9.

[0051] S2. Calibration of measuring devices: Calibrate the first piezoelectric film sensor 16 and the second piezoelectric film sensor 17; determine the relationship between the pixel coordinates and the world coordinates in the fields of view of the normal camera 20 and the oblique camera 21; based on the calibration projectile 22 impact test, calibrate the equivalent elastic moduli of the impact rod 2, incident rod 4, transmission rod 6, and absorption rod 7 E’ .

[0052] S21. Calibrate the first piezoelectric film sensor 16 and the second piezoelectric film sensor 17: When the artificial bird 5 is not clamped between the incident rod 4 and the transmission rod 6 and the right end face of the incident rod 4 is in close contact with the left end face of the transmission rod 6, the impact rod 2 impacts the incident rod 4 in parallel. By converting the voltage signals collected by the first strain gauge group 10, the second strain gauge group 11, and the third strain gauge group 12 into stress signals, the relationships between the stress signals and the voltage signals of the first piezoelectric film sensor 16 and the second piezoelectric film sensor 17 are respectively obtained, and the calibration curve is determined by the fitting relationship. As Figure 7As shown, the original voltage signal of the calibrated piezoelectric film sensor assembly is presented. The peak value of the voltage signal of the first piezoelectric film sensor 16 is greater than that of the second piezoelectric film sensor 17, indicating that the forces on the left and right end faces of the artificial bird 5 are not equal.

[0053] S22. Determine the relationship between the pixel coordinates and the world coordinates in the fields of view of the normal camera 20 and the oblique camera 21: Place a calibration ruler at the clamping position of the incident rod 4 and the transmission rod 6 on the artificial bird 5, and make the calibration ruler be located in both the horizontal field of view captured by the normal camera 20 and the oblique field of view captured by the oblique camera 21. Measure the pixel coordinate differences at both ends of the calibration ruler along the axis of the artificial bird 5 in the horizontal field of view and the oblique field of view respectively, so as to obtain the relationship between the pixel coordinates and the world coordinates in the axis direction of the artificial bird 5 in the horizontal field of view captured by the normal camera 20 and the relationship between the pixel coordinates and the world coordinates in the axis direction of the artificial bird 5 in the oblique field of view captured by the oblique camera 21.

[0054] S23. Based on the calibration bullet 22 impact test, calibrate the equivalent elastic moduli of the impact rod 2, the incident rod 4, the transmission rod 6, and the absorption rod 7 E’ : Since the impact rod 2, the incident rod 4, the transmission rod 6, and the absorption rod 7 are all made of nylon PA66, the equivalent elastic modulus calibrated with the incident rod 4 E’ shall be taken as the standard. As Figure 3 shown, remove the impact rod 2, the transmission rod 6, and the absorption rod 7 in S1 from the bracket 8, and use a cylindrical nylon PA66 calibration bullet 22 to impact the bullet-facing end face of the incident rod 4 at different speeds respectively.

[0055] Establish a finite element simulation model for the nylon PA66 calibration bullet 22 to impact the bullet-facing end face of the incident rod 4, and set the nylon PA66 used for both the incident rod 4 and the calibration bullet 22 as a linear elastic material with an elastic modulus of E ; and make the peak deviation between the simulated normal force and the test normal force the smallest through iteration, and the elastic modulus after iterative optimization is determined as the equivalent elastic moduli of the impact rod 2, the incident rod 4, the transmission rod 6, and the absorption rod 7 E’ to be used as the basis for measurement data processing.

[0056] In this embodiment, the length of the calibration bullet 22 is 400 mm and the diameter is 100 mm. The calibration bullet 22 impacts the bullet-facing end face of the incident rod 4, and the strain rates are 2.70 / s and 3.09 / s respectively, and the generated normal force amplitudes are 0 - 85 kN. Based on the elastic modulus of the nylon PA66 after iterative optimization, the simulated normal forces on the bullet-facing end face of the incident rod 4 at the strain rates of 2.70 / s and 3.09 / s are obtained. As Figure 5As shown, when the strain rate is 2.70 / s, the peak error between the simulated normal force 24 and the test normal force 23 is less than 10%, meeting the requirements of the test outline; when the strain rate is 3.09 / s, the peak error between the simulated normal force 26 and the test normal force 25 is less than 10%, meeting the requirements of the test outline; the elastic modulus of the nylon PA66 material used for the incident bar 4 in this finite element simulation is used as the equivalent elastic modulus of the impact bar 2, incident bar 4, transmission bar 6, and absorber bar 7 E’ .

[0057] S3. Test: Drive the impact bar 2 to impact the incident bar 4 to generate a shock wave. The shock wave propagates through the incident bar 4 to the artificial bird 5. Part of the shock wave is reflected by the artificial bird 5 back to the incident bar 4 to form a reflected wave, and part of the shock wave is transmitted through the artificial bird 5 to the transmission bar 6 to form a transmitted wave; use the first strain gauge group 10, the second strain gauge group 11, and the third strain gauge group 12 to measure the strains of the shock wave, reflected wave, and transmitted wave respectively; use the first piezoelectric film sensor 16 and the second piezoelectric film sensor 17 to measure the normal forces on the two axial end faces of the artificial bird 5 respectively.

[0058] Based on the test preparation in S1, an impact test is carried out. The impact bar 2 is launched by an air cannon. The high-pressure air pushes the impact bar 2 to accelerate along the axis of the air cannon barrel 1. The impact bar 2 impacts the projectile-facing end, generating an approximate compressive square-wave strain signal (i.e., a shock wave) in the incident bar 4. This elastic compression wave reaches the interface between the incident bar 4 and the artificial bird 5. Part of the wave is transmitted to the artificial bird 5 and then continues to be transmitted from the artificial bird 5 to the transmission bar 6 to obtain the transmitted wave, and part of the wave is reflected back to the incident bar 4 in the form of a tensile wave as the reflected wave.

[0059] When the shock wave passes through the first strain gauge group 10 and the second strain gauge group 11, the two pairs of strain gauges are compressed, and the first Wheatstone bridge box 13 and the second Wheatstone bridge box 14 generate voltage signals respectively, which are recorded by the data collector 18. Part of the shock wave is reflected back to the incident bar 4 in the form of a tensile wave. When it propagates back through the second strain gauge group 11 and the first strain gauge group 10, the two pairs of strain gauges are stretched, and the second Wheatstone bridge box 14 and the first Wheatstone bridge box 13 generate voltage signals respectively, which are recorded by the data collector 18. Another part of the shock wave continues to be transmitted from the artificial bird 5 to the transmission bar 6. When it passes through the third strain gauge group 12, a pair of strain gauges is compressed, and the third Wheatstone bridge box 15 generates a voltage signal, which is recorded by the data collector 18. The voltage signals measured by the first strain gauge group 10, the second strain gauge group 11, and the third strain gauge group 12 are processed according to the bridge conversion formula of the Wheatstone bridge to obtain the strain.

[0060] When the shock wave reaches the interface between the incident bar 4 and the artificial bird 5, the first piezoelectric thin film sensor 16 generates a voltage signal, which is recorded by the data collector 18. A part of the shock wave reaches the artificial bird 5, and then continues to reach the interface between the artificial bird 5 and the transmission bar 6 from the artificial bird 5. At this time, the second piezoelectric thin film sensor 17 generates a voltage signal, which is recorded by the data collector 18.

[0061] S4. Measurement data processing: Calculate the particle velocity behind the wave of the artificial bird 5 according to the strains of the shock wave, reflected wave and transmitted wave; Calculate the shock wave velocity of the artificial bird 5 according to the time difference of the voltage signals generated when measuring the normal forces on the two axial end faces of the artificial bird 5.

[0062] S41. Calculate the particle velocity behind the wave of the artificial bird 5 according to the strains of the shock wave, reflected wave and transmitted wave: The calculation formula for the velocities of the two axial end faces (i.e., the left and right end faces) of the artificial bird 5 is: (3) (4) Where, V input and V output are the velocities of the two axial end faces of the artificial bird 5 respectively, C 0 is the one-dimensional elastic wave velocity of the impact bar 2, , E is the elastic modulus of the impact bar 2. Here, the elastic modulus E can also be replaced by the equivalent elastic modulus E’ , ρ 0 is the density of the impact bar 2, ε i is the strain of the shock wave, ε r is the strain of the reflected wave, ε t is the strain of the transmitted wave.

[0063] Since the velocity of the left end face of the artificial bird 5 > the velocity of the right end face of the artificial bird 5, the length of the artificial bird 5 will become shorter with time during the loading process. The calculation formula for the strain rate of the artificial bird 5 is: (5) Where, is the strain rate of the artificial bird 5.

[0064] Therefore, the calculation formula for the particle velocity behind the wave of the artificial bird 5 is: (6) Where, V p is the particle velocity behind the wave of the artificial bird 5.

[0065] S42. Calculate the shock wave velocity of the artificial bird 5 based on the time difference of the voltage signals generated when measuring the normal forces on the two axial end faces of the artificial bird 5: When the shock wave reaches the left and right ends of the artificial bird 5 successively, the first piezoelectric film sensor 16 and the second piezoelectric film sensor 17 start to generate voltage signals in sequence. Record the time when the two piezoelectric film sensors start to generate voltage signals. Then, the calculation formula for the shock wave velocity of the artificial bird 5 is: (7) Where, V s is the shock wave velocity of the artificial bird 5, t input is the time when the first piezoelectric film sensor 16 starts to generate a voltage signal, t output is the time when the second piezoelectric film sensor 17 starts to generate a voltage signal.

[0066] S5. Measurement data correction and validity analysis: Correct the strain measured by the first strain gauge group 10, the second strain gauge group 11, and the third strain gauge group 12 through Fourier transform; Calculate the corrected normal forces on the two axial end faces of the artificial bird 5 based on the corrected strain, and compare the corrected normal forces on the two axial end faces of the artificial bird 5 with the normal forces measured by the first piezoelectric film sensor 16 and the second piezoelectric film sensor 17 to determine the validity of the measurement data; S51. Correct the strain measured by the first strain gauge group 10, the second strain gauge group 11, and the third strain gauge group 12 through Fourier transform: Since the materials of the impact rod 2, the incident rod 4, the transmission rod 6, and the absorption rod 7 are all nylon PA66, and nylon is a polymer, showing viscoelasticity. For viscoelastic rods, the wave propagation is dispersive. In addition, due to material damping, wave attenuation will occur, so waveform correction is required.

[0067] The specific method of waveform correction is the same as that of S23. Obtain the strain measured by the first strain gauge group 10 and the second strain gauge group 11 through the test method of S23. Convert the strain measured by the first strain gauge group 10 and the second strain gauge group 11 from the time domain to the frequency domain through Fourier transform. Then, the one-dimensional wave equation of the Hopkinson bar becomes: (8) The general solution of formula (8) is: (9) Where, is the angular frequency, x is any length along the axis of the Hopkinson bar, is the strain under frequency domain analysis, and the function and is the Fourier form of the strain propagating axially at the x of the Hopkinson bar. The modulus and phase of the complex exponential functions and reflect the attenuation and propagation of the shock wave. γ is the propagation coefficient, is related to the attenuation coefficient and the phase velocity and the calculation formula is: (10) where, i is the imaginary number in the complex function. The attenuation coefficient is an even function, and the wave number is an odd function.

[0068] Thus, the Fourier transforms of the axial particle velocity and the normal force at any length of the Hopkinson bar are: (11) (12) where, is the axial particle velocity of the Hopkinson bar at any length under frequency domain analysis, is the normal force of the Hopkinson bar at any length under frequency domain analysis, A are the cross-sectional areas of the incident bar 4 and the transmitted bar 6.

[0069] Since the right end of the incident bar 4 is a free end face, the normal force is equal to zero. Therefore, the calculation formula for the normal force at the right end face is: (13) where, assuming that x =0 at the bullet-facing end of the incident bar 4, then x =L at the right end face of the incident bar 4.

[0070] Therefore, the calculation formula for the transfer function is: (14) where, is the transfer function.

[0071] It can be seen from formula (14) that the attenuation coefficient can be calculated from the amplitude of the transfer function, and the wave number can be calculated from the phase of the transfer function.

[0072] The attenuation coefficient and the wave number are calculated from the strain of the shock wave measured by the first strain gauge group 10., the attenuation coefficient is calculated from the strain of the reflected wave measured by the second strain gauge group 11 and the wave number ; Take and The average value of is used as the attenuation coefficient , take and The average value of is used as the wave speed , substitute and into the Fourier transforms of the axial particle velocity and normal force of the Hopkinson bar at any length to obtain the frequency-domain forms of the velocities and normal forces at the two axial end faces of the modified artificial bird 5, and then through the inverse Fourier transform, obtain the time-domain forms to complete the correction of the strains measured by the first strain gauge group 10, the second strain gauge group 11, and the third strain gauge group 12.

[0073] The normal forces at the two axial end faces of the artificial bird 5 are obtained from the strains measured by the first strain gauge group 10, the second strain gauge group 11, and the third strain gauge group 12. The calculation formula for the normal force at the left end face of the artificial bird 5 is: (15) The calculation formula for the normal force at the right end face of the artificial bird 5 is: (16) where F input and F output are the normal forces at the left and right end faces of the artificial bird 5 respectively. Here, the elastic modulus E can also be replaced by the equivalent elastic modulus E’ .

[0074] As Figure 6 shown, when the normal forces at the left and right end faces of the artificial bird 5 are not corrected for the waveform, the difference between the two is large. After the waveform correction, the difference between the two decreases, indicating that the waveform correction is a non-negligible step.

[0075] S52. According to the corrected strain, calculate the corrected normal forces at the two axial end faces of the artificial bird 5, and compare the corrected normal forces at the two axial end faces of the artificial bird 5 with the normal forces at the two axial end faces of the artificial bird 5 measured by the first piezoelectric film sensor 16 and the second piezoelectric film sensor 17 to determine the validity of the measurement data: Obtain the corrected strains of the first strain gauge group 10, the second strain gauge group 11, and the third strain gauge group 12 through S51, and calculate the peak values of the corrected normal forces at the two axial end faces of the artificial bird 5 and , and The times at which they occur are respectively and ; Based on the first piezoelectric thin film sensor 16 and the second piezoelectric thin film sensor 17, the peak values of the normal forces on the two axial end faces of the artificial bird 5 are measured respectively and , and The times when they occur are respectively and ; The validity judgment formula for the measurement data of the first piezoelectric thin film sensor 16 is: (17) If the formula (17) is satisfied, it is determined that the measurement data of the first piezoelectric thin film sensor 16 is valid; The validity judgment formula for the measurement data of the second piezoelectric thin film sensor 17 is: (18) If the formula (18) is satisfied, it is determined that the measurement data of the second piezoelectric thin film sensor 17 is valid.

[0076] S6. Empirical index analysis: Repeat the experiment preparation from measurement data correction to validity analysis for artificial birds 5 with different densities, fit the Hugoniot curves of artificial birds 5 with different densities regarding the particle velocity behind the wave and the shock wave velocity, compare the slopes and intercepts of the Hugoniot curves of artificial birds 5 with different densities, and judge the influence of the density of artificial birds 5 on the mechanical behavior of artificial birds 5.

[0077] According to the test outline, the particle velocity behind the wave and the shock wave velocity of 12 groups of artificial birds 5 with densities of 1.050 g / cm 3 , 0.990 g / cm 3 and 0.950 g / cm 3 are obtained at the strain rate of 666.7 / s - 2000.0 / s. As Figures 8 to 10 shown, as the particle velocity behind the wave increases, the shock wave velocity basically shows a linear increase. Figure 11 is the Hugoniot curve fitted based on artificial birds 5 with densities of 1.050 g / cm 3 , 0.990 g / cm 3 and 0.950 g / cm 3 . As Figure 11 shown, as the density of artificial birds 5 decreases, the intercept of the Hugoniot curve of artificial birds 5 decreases, and the slope basically remains constant, indicating that the mechanical behaviors of artificial birds 5 with different densities are different.

[0078] So far, the measurement process of the particle velocity and shock wave velocity after 5 waves of the artificial bird using the measurement device for Hugoniot relation parameters of the artificial bird based on the Hopkinson bar is completed. This method conducts experiments for artificial birds 5 with different densities through experimental preparation, experiments, measurement data processing, measurement data correction and validity analysis, and empirical index analysis, fits the Hugoniot curves of artificial birds 5 with different densities, and then obtains the constitutive model and parameters of the bird body. This method of deducing the equation of state and its parameters from the positive direction based on the theory of matter state will not cause the constitutive model and parameters of the bird body to change with the working conditions, and improves the universality of the experimental data.

[0079] The above are only the preferred embodiments of the present application and are not used to limit the present application. For those skilled in the art, various changes and modifications can be made to the present application. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. An apparatus for measuring the Hugoniot relation parameters of an artificial bird based on a Hopkinson bar, characterized in that, Comprising a bracket (8) and a Hopkinson bar movably arranged on the bracket (8), the Hopkinson bar includes an impact bar (2), an incident bar (4) and a transmission bar (6) arranged axially in sequence. There is a gap for clamping an artificial bird (5) between the incident bar (4) and the transmission bar (6). The impact bar (2) is driven to impact the incident bar (4) to generate a shock wave. The shock wave propagates through the incident bar (4) to the artificial bird (5). Part of the shock wave is reflected by the artificial bird (5) to the incident bar (4) to form a reflected wave, and part of the shock wave is transmitted through the artificial bird (5) to the transmission bar (6) to form a transmitted wave; A first strain gauge group (10) and a second strain gauge group (11) are arranged at intervals along the axis on the outer periphery of the incident bar (4). A third strain gauge group (12) is arranged on the outer periphery of the transmission bar (6). The first strain gauge group (10), the second strain gauge group (11) and the third strain gauge group (12) generate voltage signals for measuring the strain of the shock wave, the reflected wave and the transmitted wave respectively. The particle velocity behind the wave of the artificial bird (5) is calculated according to the strain of the shock wave, the reflected wave and the transmitted wave; A first piezoelectric film sensor (16) and a second piezoelectric film sensor (17) are respectively arranged on the clamping surfaces of the incident bar (4) and the transmission bar (6). The first piezoelectric film sensor (16) and the second piezoelectric film sensor (17) generate voltage signals for measuring the normal forces on the two axial end faces of the artificial bird (5) respectively. The shock wave velocity of the artificial bird (5) is calculated according to the time difference of the voltage signals generated by the first piezoelectric film sensor (16) and the second piezoelectric film sensor (17).

2. The device according to claim 1, characterized in that The device further includes an energy absorption device (9) fixedly arranged on the bracket (8). The Hopkinson bar further includes an absorption bar (7). The absorption bar (7) is arranged axially on the side of the transmission bar (6) away from the incident bar (4). One end of the absorption bar (7) away from the transmission bar (6) is inserted into the energy absorption device (9) to absorb the shock wave that is not reflected and transmitted.

3. The device according to claim 1 or 2, characterized in that, The impact bar (2), the incident bar (4) and the transmission bar (6) are coaxially arranged.

4. The device according to claim 1 or 2, characterized in that, The device further includes a normal camera (20) and an oblique camera (21) arranged on the same side of the artificial bird (5). The optical axis of the normal camera (20) is perpendicular to the axis of the Hopkinson bar. The included angle between the optical axis of the oblique camera (21) and the axis of the Hopkinson bar is an acute angle to photograph the deformation process of the artificial bird (5) from different fields of view.

5. The device according to claim 1 or 2, characterized in that, The distance between the first strain gauge group (10) and the end of the incident rod (4) close to the impact rod (2) is 1 / 4 to 1 / 3 of the length of the incident rod (4). The distance between the second strain gauge group (11) and the end of the incident rod (4) close to the transmission rod (6) is 1 / 4 to 1 / 3 of the length of the incident rod (4). The distance between the third strain gauge group (12) and the end of the transmission rod (6) close to the incident rod (4) is 1 / 4 to 1 / 3 of the length of the transmission rod (6).

6. The device according to claim 1 or 2, characterized in that, The first strain gauge group (10) includes at least two strain gauges symmetrically arranged along the axis on both sides of the incident rod (4). The second strain gauge group (11) includes at least two strain gauges symmetrically arranged along the axis on both sides of the incident rod (4). The third strain gauge group (12) includes at least two strain gauges symmetrically arranged along the axis on both sides of the transmission rod (6).

7. A method for measuring the Hugoniot relation parameters of an artificial bird based on a Hopkinson bar, characterized in that, The method is implemented by the device according to any one of claims 1 to 6, and the method includes: Test preparation: Determine the diameters of the impact rod (2), the incident rod (4), and the transmission rod (6) according to the diameter of the artificial bird (5); Determine the lengths of the impact rod (2), the incident rod (4), and the transmission rod (6) according to the strain and stress requirements of the artificial bird (5); Test: Drive the impact rod (2) to impact the incident rod (4) to generate a shock wave. Part of the shock wave is reflected by the artificial bird (5) to form a reflected wave, and part of the shock wave is transmitted by the artificial bird (5) to form a transmitted wave; Measure the strains of the shock wave, the reflected wave, and the transmitted wave respectively; Measure the normal forces on both axial end faces of the artificial bird (5) respectively; Measurement data processing: Calculate the particle velocity behind the wave of the artificial bird (5) according to the strains of the shock wave, the reflected wave, and the transmitted wave. The calculation formula is: Among them, V p is the particle velocity behind the wave of the artificial bird (5), C 0 is the one-dimensional elastic wave velocity of the impact rod (2), , E is the elastic modulus of the impact rod (2), ρ 0 is the density of the impact rod (2), ε i is the strain of the shock wave, ε r is the strain of the reflected wave, ε t is the strain of the transmitted wave; Calculate the shock wave velocity of the artificial bird (5) according to the time difference of the voltage signals generated when measuring the normal forces on both axial end faces of the artificial bird (5). The calculation formula is: Wherein, V s is the shock wave velocity of the artificial bird (5), L G is the length of the artificial bird (5), t input is the time when the first piezoelectric film sensor (16) starts to generate a voltage signal, t output is the time when the second piezoelectric film sensor (17) starts to generate a voltage signal; Measurement data correction and validity analysis: Correct the strains measured by the first strain gauge group (10), the second strain gauge group (11), and the third strain gauge group (12) through Fourier transform; Calculate the corrected normal forces on both axial end faces of the artificial bird (5) according to the corrected strains, and compare the corrected normal forces on both axial end faces of the artificial bird (5) with the normal forces measured by the first piezoelectric film sensor (16) and the second piezoelectric film sensor (17) to determine the validity of the measurement data; Empirical index analysis: Repeat the test preparation to the measurement data correction and validity analysis for the artificial bird (5) with different densities, fit the Hugoniot curves of the artificial bird (5) with different densities regarding the particle velocity behind the wave and the shock wave velocity, compare the slopes and intercepts of the Hugoniot curves of the artificial bird (5) with different densities, and judge the influence of the density of the artificial bird (5) on the mechanical behavior of the artificial bird (5).

8. The method according to claim 7, wherein In the test preparation, determining the lengths of the impact bar (2), the incident bar (4), and the transmission bar (6) according to the strain and stress requirements of the artificial bird (5) includes: Determining the lengths of the incident bar (4) and the transmission bar (6): Assume that the preset lengths of the incident rod (4) and the transmission rod (6) are equal, both being L’ , and the preset lengths of the incident rod (4) and the transmission rod (6) L’ should be able to prevent the waveforms of the shock wave and the reflected wave from being superimposed on the strain of the artificial bird (5) measured; If the time required for the reflected wave to propagate back to the second strain gauge group (11) along the incident bar (4) after the shock wave reaches the second strain gauge group (11) is greater than the width of the shock wave, then the preset lengths of the incident bar (4) and the transmission bar (6) L’ are determined as the lengths of the incident bar (4) and the transmission bar (6) L ; Determining the length of the impact bar (2): The preset length of the impact rod (2) L B ’ should be able to prevent the waveform superposition of shock waves and reflected waves in the strain of the artificial bird (5) measured. At the same time, the preset length of the impact rod (2) L B ’ should be able to achieve stress balance during the loading process of the artificial bird (5); The calculation formula for the width of the shock wave is: Among them, ΔT is the width of the shock wave, C 0 is the one-dimensional elastic wave velocity of the impact rod (2), , E are the elastic moduli of the impact rod (2) and the incident rod (4), ρ 0 are the densities of the impact rod (2) and the incident rod (4); The calculation formula for the number of round trips of the shock wave propagating in the artificial bird (5) is: Among them, n is the number of back-and-forth transmissions in the artificial bird (5), C G is the one-dimensional elastic wave velocity of the artificial bird (5), L G is the length of the artificial bird (5); If the time required for the reflected wave to propagate back to the second strain gauge group (11) along the incident bar (4) since the shock wave reaches the second strain gauge group (11) is greater than the width of the shock wave, and the number of round trips of the shock wave propagating in the artificial bird (5) is greater than 3 to achieve stress balance during the loading process of the artificial bird (5), then the preset length of the impact bar (2) L B ’ is determined as the length of the impact bar (2) L B .

9. The method according to claim 7 or 8, characterized in that, In the measurement data correction and validity analysis, correcting the strain measured by the first strain gauge group (10), the second strain gauge group (11), and the third strain gauge group (12) through Fourier transform includes: converting the strain measured by the first strain gauge group (10) and the second strain gauge group (11) from the time domain to the frequency domain through Fourier transform, then the one-dimensional wave equation of the Hopkinson bar becomes: The general solution of this one-dimensional wave equation is: Among them, is the angular frequency, x is any length of the Hopkinson bar along the axial direction, is the strain under frequency domain analysis, and the function and are the Fourier forms of the strain propagating along the axial direction at the x of the Hopkinson bar. The modulus and phase of the complex exponential functions and reflect the attenuation and propagation of the shock wave. γ is the propagation coefficient, is related to the attenuation coefficient and the phase velocity ; , i is the imaginary number in complex functions, and the attenuation coefficient is an even function, and the wave number is an odd function. Thus, the Fourier transforms of the axial particle velocity and the normal force at any length of the Hopkinson bar are: wherein, is the axial particle velocity of the Hopkinson bar at any length under frequency domain analysis, is the normal force of the Hopkinson bar at any length under frequency domain analysis, A is the cross-sectional area of the incident bar (4) and the transmission bar (6); Calculate the attenuation coefficient from the strain of the shock wave measured by the first strain gauge group (10). and the wave number ; calculate the attenuation coefficient from the strain of the reflected wave measured by the second strain gauge group (11). and the wave number ; take and The average value of is used as the attenuation coefficient ; take and The average value of is used as the wave speed ; substitute and into the Fourier transform of the axial particle velocity and the normal force at any length of the Hopkinson bar, obtain the frequency-domain forms of the velocities and normal forces at the two axial ends of the artificial bird (5) after correction, and then through the inverse Fourier transform, obtain the time-domain forms, thus completing the correction of the strains measured by the first strain gauge group (10), the second strain gauge group (11), and the third strain gauge group (12).

10. The method according to claim 9, wherein In the measurement data correction and validity analysis, calculating the corrected normal forces on the two end faces of the artificial bird (5) along the axial direction according to the corrected strain, and comparing the corrected normal forces on the two end faces of the artificial bird (5) along the axial direction with the normal forces measured by the first piezoelectric film sensor (16) and the second piezoelectric film sensor (17) to determine the validity of the measurement data includes: calculating the peak values of the corrected normal forces on the two end faces of the artificial bird (5) along the axial direction according to the strains corrected by the first strain gauge group (10), the second strain gauge group (11) and the third strain gauge group (12). and , and The times when they occur are respectively and ; According to the first piezoelectric film sensor (16) and the second piezoelectric film sensor (17), the peak values of the normal forces on the two axial end faces of the artificial bird (5) are measured respectively and , and The times when they occur are respectively and ; The validity judgment formula for the measurement data of the first piezoelectric film sensor (16) is: If the following conditions are met and the difference is less than 5%, and and the difference is less than 5%, then it is determined that the measurement data of the first piezoelectric film sensor (16) is valid; The validity judgment formula for the measurement data of the second piezoelectric film sensor (17) is: If and the difference is < 5%, and and the difference is < 5%, then it is determined that the measurement data of the second piezoelectric film sensor (17) is valid.

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