A bird-cutting load measuring device and method based on Hopkinson bar

Abstract

A bird-cutting load measurement device and method based on a Hopkinson bar, wherein the end of the Hopkinson bar adjacent to the air cannon muzzle is a wedge-shaped end. The leading edge of the wedge-shaped end is in the vertical direction. There are projectile-facing surfaces on the wedge surfaces of the wedge-shaped end. The leading edge of the wedge-shaped end is also the leading edge of each projectile-facing surface, and the trailing edge of each projectile-facing surface is a C-shaped curve formed by the edge of the wedge surface of the wedge end. The present invention solves the problem in existing engine fan blade bird strike research that the bird-cutting load history cannot be accurately measured due to the coupling of the dynamic deformation of the bird body and the deformation of the blade, and provides basic data for the study of the engine fan blade bird-cutting problem and especially the study of the bird body constitutive model and parameter optimization. The present invention simplifies the engine bird strike conditions of different heading speeds, blade rotation speeds, and blade leading edge angles into the basic problem of quasi-rigid target plate bird-cutting with different half-wedge angles θ, and measures the load history of the accurate bird-cutting process decoupled from the target plate deformation, which is conducive to obtaining a universal response law.

Description

Technical Field

[0001] The present invention relates to the technical field of bird strike test, in particular to a measuring device and a measuring method for decoupling measurement of bird-cutting load of an engine fan blade in the technical field of bird strike test. Background Art

[0002] In the study of bird strike resistance of aircraft and engine structures, impact testing is the final and most effective inspection method in the research of impact resistance design of structural parts. However, in order to improve efficiency and save costs, finite element simulation methods are often used at this stage to perform initial design and iterative optimization of the structure.

[0003] In current bird strike finite element simulation research, a coupling method is generally adopted, that is, the deformation of the bird and the structure are coupled. For example, the bird is numerically discretized using the smoothed particle hydrodynamics method (SPH), and the target structure to be studied is numerically discretized using the Lagrange method (see Bird-strike simulation for certification of the Boeing 787 composite moveable trailing edge, Composite Structures, 2008, Issue 86, Pages 258-268). Therefore, the material constitutive model and parameters of the bird, aircraft, and engine structure are an important foundation for finite element simulation research. For the bird's constitutive model and parameters, their determination generally adopts the inversion method. It is necessary to design equivalent and simplified structural response measurement tests based on the operating conditions of the bird's numerical model to obtain systematic basic test data as a benchmark reference for constitutive model determination and constitutive parameter inversion.

[0004] For example, bird strikes on components such as windshields, noses, and wings can be compared to combinations of bird strikes on flat plates at different angles. Corresponding methods for measuring equivalent flat plate bird strike parameters include: measuring bird strike loads using a Hopkinson bar with a flat or inclined end (see "Bird impact forces and pressures on rigid and compliant targets," AFFDL-TR-77-60, University of Dayton, 1978); measuring displacements, strains, and loads at specific points using an elastic-plastic plate (see "Inversion of Constitutive Parameters of Bird Bodies I and II," Acta Aeronautica Sinica, 2011, Vol. 32, No. 5, pp. 802-811 and 812-821); and measuring pressures and loads at specific points using a rigid plate (see "On the determination of the shock and steady state parameters of gelatine from cylinder impact experiments," International Journal of Impact Engineering, 2018, No. 116, pp. 22-33).

[0005] In order to study and verify the bird body constitutive model and parameters suitable for finite element simulation of bird strike on engine fan blades, it is necessary to establish research conditions with actual working condition characteristics, that is, to introduce the bird cutting state. At present, the published methods for measuring equivalent bird strike parameters include: measuring momentum based on a simulated blade ballistic pendulum (see Impact damage on titanium leading edges from small soft body objects, AFML-TR-79-4019, University of Dayton, 1979), measuring momentum based on a single-degree-of-freedom rigid wedge-shaped pulley (see Characterization of real and substitute birds through experimental and numerical analysis of momentum, average impact forces and residual energy in bird strike on three rigid targets: A flat plate, a wedge and asplitter, International Journal of Impact Engineering, 2017, 99, 1-13), and measuring multi-directional momentum based on a rigid simulated blade rotating frustum and optical methods (see Development and validation of a set-up to measure the transferred multi-axial impact momentum of a bird strike on a booster vane, International Journal of Impact Engineering, 2017, 99, 102-110). In the invention with publication number CN111579190A, a horizontal ejection-impact blade bird-cutting test device and test method are disclosed for measuring load.

[0006] However, the above-mentioned simulated blade ballistic pendulum method, single-degree-of-freedom rigid wedge pulley method, and simulated blade frustum optical measurement method all measured overall transferred momentum, that is, reflected the overall characteristics of the target plate after the entire bird-cutting process, and failed to accurately reflect the bird-cutting load history in stages; the above-mentioned method based on the horizontal ejection-impact blade bird-cutting test device can reflect the bird-cutting load history to a certain extent, but its measured quantity has obvious correlation with the target plate shape and target plate material properties, and the large deformation of the bird body is coupled with the large deformation of the target plate, which fails to meet the needs of universality. Therefore, providing a bird-cutting load measurement device and measurement method that can measure the load history of the blade in the bird-cutting state that is decoupled from the blade deformation has great engineering scientific significance for studying and verifying the applicability of the undetermined bird body constitutive model and parameters in the blade bird-cutting state. Summary of the Invention

[0007] In order to overcome the deficiency of the existing bird-cutting test technology that cannot accurately measure the bird-cutting load history decoupled from the target plate deformation, the present invention proposes a bird-cutting load measurement device and measurement method based on a Hopkinson bar.

[0008] The bird-cutting load measurement device based on a Hopkinson rod includes a Hopkinson rod, a strain gauge assembly, a bracket, and an energy absorption plate. The Hopkinson rod is mounted on the bracket, with the axis of the Hopkinson rod coinciding with the axis of the air cannon barrel. The first strain gauge group and the second strain gauge group in the strain gauge assembly are adhered to the circumferential surface of the Hopkinson rod. The energy absorption plate is fixed to the bracket and adjacent to the planar end of the Hopkinson rod, and is used to cushion the Hopkinson rod after impact and limit the movement of the Hopkinson rod. Each pair of strain gauges in the strain gauge assembly is respectively connected to a Wheatstone bridge box. The bird-cutting load measurement device is provided with a laser velocimeter and a high-speed camera. The device is characterized in that:

[0009] The end of the Hopkinson rod adjacent to the air cannon muzzle is a wedge-shaped end; the end of the Hopkinson rod adjacent to the energy absorbing plate is a flat end.

[0010] Two flat surfaces are symmetrically cut on the circumferential surface of the Hopkinson rod adjacent to the air cannon muzzle. One end of the two flat surfaces intersects at the end face of the Hopkinson rod, forming a wedge-shaped end. The front end of the wedge-shaped end is a straight line, which serves as the leading edge of the wedge-shaped end. When the Hopkinson rod is positioned, the leading edge is aligned vertically.

[0011] The two planes are the two wedge surfaces of the wedge-shaped end; each wedge surface has a groove for embedding the edging; the surface of each edging and each wedge surface together constitute the two projectile-facing surfaces of the Hopkinson rod; the leading edge of the wedge-shaped end is also the leading edge of each projectile-facing surface, and the trailing edge of each projectile-facing surface is a C-shaped curve formed by the edge of the wedge surface of the wedge end; each C-shaped curve has a vertex M, and each vertex M is located at the farthest end of the C-shaped curve from the front edge of the projectile-facing surface.

[0012] The included angles between the axis of the Hopkinson rod and each of the projectile-facing surfaces are all half-wedge angles θ; the diameter D of the Hopkinson rod is 1.2 to 1.3 times the diameter of the bird with the largest mass in the test outline.

[0013] The strain gauge assembly includes a first strain gauge group and a second strain gauge group. The first and second strain gauge groups are sequentially distributed along the axis on the outer circumferential surface between the vertex M of the trailing edge of the wedge end and the planar end of the Hopkinson rod and are located within the strain gauge bonding section. Each of the first and second strain gauge groups includes two pairs of strain gauges distributed axially along the Hopkinson rod, one pair of strain gauges bonded to the circumferential surface of the Hopkinson rod at the 3 o'clock and 9 o'clock directions, and the other pair of strain gauges bonded to the circumferential surface of the Hopkinson rod at the 6 o'clock and 12 o'clock directions. The strain gauge sensitive grids of each strain gauge are aligned along the axis of the Hopkinson rod.

[0014] A laser velocimeter, a first normal high-speed camera, a second normal high-speed camera and an oblique high-speed camera are arranged between the wedge-shaped end of the Hopkinson rod and the muzzle of the air cannon.

[0015] The half-pitch angle θ is 10° to 60°. Bird-cutting tests are carried out by using wedge-shaped ends with different half-pitch angles to simulate engine bird strike conditions at different heading speeds, blade rotation speeds and blade leading edge angles.

[0016] The groove extends from the front edge to the rear edge of the facing surface, has a depth of 3 mm, and a length of the groove along the facing surface is 0.5 to 0.6 times the length of the wedge surface.

[0017] The first strain gauge group is located near the wedge-shaped end, and the second strain gauge group is located near the planar end. The distance between the starting point of the strain gauge attachment section and the vertex M of the rear edge of the projectile surface is D; the distance between the ending point of the strain gauge attachment section and the vertex M of the rear edge of the projectile surface is 3D. D is the diameter of the Hopkinson bar.

[0018] The two laser beams of the laser velocimeter are perpendicular to and intersect the extended axis of the air cannon barrel. The lens of the first normal high-speed camera is positioned horizontally and perpendicular to the extended axis of the air cannon barrel, used to film the bird-cutting process in a horizontal field of view. The lens of the oblique high-speed camera is positioned horizontally and perpendicular to the projectile-facing surface of the wedge-shaped end of the Hopkinson rod, used to film the bird-cutting process in an oblique field of view. The second normal high-speed camera is located at the bottom of the wedge-shaped end of the Hopkinson rod, with its lens facing vertically upward and perpendicular to the extended axis of the air cannon barrel, used to film the bird-cutting process in a vertical upward field of view.

[0019] The specific process of using the device to measure bird cutting load proposed by the present invention is:

[0020] Step 1, test preparation:

[0021] The test preparation includes determining the diameter D and length L of the Hopkinson rod according to the test outline and placing the Hopkinson rod.

[0022] Ⅰ Determine the diameter D of the Hopkinson bar

[0023] The diameter D and length L of the Hopkinson bar are determined based on the bird with the largest mass in the current test and the minimum initial impact velocity specified in each test outline. The diameter D of the Hopkinson bar is 1.2 to 1.3 times the diameter of the bird with the largest mass.

[0024] Ⅱ Determine the length L of the Hopkinson bar

[0025] ⅰDetermine the theoretical impact stroke l ref and theoretical impact time t ref

[0026] Theoretical impact stroke l ref The theoretical impact time t is the distance from the moment the front end of the bird body contacts the leading edge of the wedge end to the moment the tail end of the bird body moves to the wedge end's bullet-facing surface; ref The bird body passes through the theoretical impact stroke l at the initial impact speed v ref time.

[0027] The theoretical impact stroke l is obtained by formula (1): ref :

[0028]

[0029] Where l is the length of the bird and d is the diameter of the bird.

[0030] The theoretical impact time t is obtained by formula (2): ref:

[0031]

[0032] Where v is the initial impact velocity of the bird.

[0033] ⅱDetermine the length L of the Hopkinson bar

[0034] The length L of the Hopkinson bar is determined by the preset length L' of the Hopkinson bar.

[0035] The preset length L' of the Hopkinson rod should be such that the measured bird-cutting load history does not cause the superposition of compression waves and reflected tensile waves.

[0036] If the time required for the compression wave generated by the impact of the wedge-shaped end of the bird body to reach the second strain gauge group, propagate along the axis of the Hopkinson rod to the flat end of the Hopkinson rod, be reflected as a tensile wave, and propagate back along the axis of the Hopkinson rod to the second strain gauge group is greater than the theoretical impact time t ref , the preset length L' of the Hopkinson rod is determined as the length L of the Hopkinson rod.

[0037] III. Placement of Hopkinson rod:

[0038] The Hopkinson rod is placed so that it is coaxial with the air cannon barrel, and the wedge-shaped end of the Hopkinson rod is located at one end of the Hopkinson rod close to the air cannon muzzle, and the distance between the leading edge of the wedge-shaped end and the air cannon muzzle is 1 to 31; where l is the length of the bird body.

[0039] Step 2: Calibration of measuring device:

[0040] The measurement device calibration includes measuring the laser beam spacing; determining the relationship between the pixel coordinates in the field of view of the high-speed camera and the world coordinates; and calibrating the equivalent elastic modulus E of the Hopkinson rod material based on a calibration bullet impact test.

[0041] ⅠMeasure the distance between laser beams

[0042] Measure the horizontal distance l1 between the two intersection points of the two laser beams of the laser velocimeter and the extended line of the air cannon barrel axis.

[0043] Ⅱ Determine the relationship between pixel coordinates in the field of view of a high-speed camera and world coordinates

[0044] A calibration ruler is placed on the extension line of the air cannon barrel axis and located in the horizontal field of view captured by the first normal high-speed camera. The pixel coordinate difference between the two ends of the calibration ruler along the extension line of the air cannon barrel axis is measured in the horizontal field of view to obtain the relationship between the pixel coordinates in the direction of the extension line of the air cannon barrel axis in the horizontal field of view captured by the first normal high-speed camera and the world coordinates.

[0045] Ⅲ Calibration of the equivalent elastic modulus E of the Hopkinson bar material

[0046] The Hopkinson rod in step 1 was horizontally rotated 180 degrees, so that the flat end of the Hopkinson rod was adjacent to the air cannon muzzle and the wedge-shaped end of the Hopkinson rod was adjacent to the energy absorbing plate. A cylindrical nylon PA66 calibration projectile was used to impact the flat end of the Hopkinson rod at different speeds.

[0047] A finite element simulation model of a calibration bullet made of nylon PA66 impacting the flat end of a Hopkinson rod was established. The nylon PA66 used in the Hopkinson rod and the calibration bullet was set as a linear elastic material with an elastic modulus of E'. The peak deviation between the simulated load history and the experimental load history was minimized through iteration, and the elastic modulus E' after iterative optimization was determined as the equivalent elastic modulus E of the Hopkinson rod.

[0048] Step 3, test:

[0049] The test includes launching a bird to impact the wedge-shaped end of the Hopkinson bar and collecting a voltage signal.

[0050] Based on the test preparation described in Step 1, a bird strike test was conducted. A bird was launched through an air cannon. The high-pressure air accelerated the bird along the axial direction of the air cannon barrel. After exiting the air cannon muzzle, the bird passed through two laser beams from a laser velocimeter and struck the wedge-shaped end of a Hopkinson bar. As the bird passed through the two laser beams, two pulse signals with a time difference of Δt1 were generated. The bird struck the wedge-shaped end of the Hopkinson bar and slid along the projectile-facing surface. The impact of the bird generated a shock wave, which initially manifested as a compression wave that propagated along the Hopkinson bar axis toward the planar end of the bar.

[0051] When this compression wave passes through the first and second strain gauge groups, the four pairs of strain gauges are compressed, and the first and second Wheatstone bridge box groups each generate voltage signals that are recorded by the data logger, reflecting the load history of the bird impacting the wedge end. When the compression wave propagates along the axis of the Hopkinson bar to the planar end of the Hopkinson bar and is reflected as a tensile wave that propagates back to the second and first strain gauge groups, the four pairs of strain gauges are stretched, and the second and first Wheatstone bridge box groups each generate voltage signals that are recorded by the data logger.

[0052] Under the impact of the bird body, the Hopkinson rod slides on the bracket until it hits the energy absorbing plate and stops.

[0053] Step 4: Measurement data processing:

[0054] The measurement data processing includes calculating the initial impact velocity of the bird body based on the measurement results of the laser velocimeter and the high-speed camera; processing the voltage signal measured by the strain gauge to obtain the load history and momentum transfer history of the bird cutting process.

[0055] Ⅰ Calculation of the bird's initial impact velocity based on the measurement results of the laser velocimeter

[0056] The initial impact velocity v1 of the bird measured by the laser velocimeter is calculated based on the time difference Δt1 between the two pulse signals generated after the bird passes through the two laser beams of the laser velocimeter, where v1 = l1 / Δt1.

[0057] Ⅱ Calculation of the bird's initial impact velocity based on the measurement results of a high-speed camera

[0058] An image taken by the first normal high-speed camera at the moment when the front end of the bird enters the field of view of the high-speed camera is selected, and an image taken by the first normal high-speed camera at the moment before the front end of the bird leaves the field of view of the high-speed camera is selected. The flight distance l2 of the bird is calculated based on the relationship between pixel coordinates and world coordinates. The time difference Δt2 is obtained based on the frame number difference between the images at the two moments, and the speed v2 of the bird measured by the first normal high-speed camera is calculated, v2=l2 / Δt2.

[0059] III Processing the voltage signal measured by the strain gauge

[0060] The voltage signals measured by the first and second strain gauge groups are processed according to the Wheatstone bridge conversion formula to obtain the strain history ε. In this strain history, the shock wave is a compression wave and a reflected tensile wave. Only the compression wave is extracted for analysis, and this compression wave reflects the load history of the bird cutting process. The product of the strain history ε, the equivalent elastic modulus E of the Hopkinson bar, and the cross-sectional area A of the Hopkinson bar is the load history F of the bird cutting process, which is calculated as follows:

[0061] F=A·E·ε (3)

[0062] The peak value of the load history F is the load peak F peak .

[0063] The integral of the load history F over time t is the momentum transfer history I of the bird cutting process, which reflects the momentum I along the axial direction of the Hopkinson rod transferred from the bird body to the Hopkinson rod during the bird cutting process. The calculation formula is:

[0064] I=∫F·dt (4)

[0065] The peak value of the momentum transfer process I is the momentum I transferred from the bird body to the Hopkinson rod along the axis of the Hopkinson rod during the bird cutting process. T .

[0066] Step 5: Validity analysis of measurement data:

[0067] The measurement data validity analysis includes comparing the initial impact velocity of the bird measured by a high-speed camera and a laser velocimeter to determine the validity of the velocity measurement; and comparing the load history measured by four pairs of strain gauges, namely the first strain gauge group and the second strain gauge group, to determine the validity of the load measurement.

[0068] I. Determining the validity of speed measurement

[0069] Compare the initial impact velocity v1 of the bird measured by the laser velocimeter with the initial impact velocity v2 of the bird measured by the first normal high-speed camera. If the difference between v1 and v2 is less than 5%, the criterion is calculated as follows:

[0070]

[0071] If the criterion is met, the measurement of the bird's initial impact velocity is determined to be valid, and the average value of v1 and v2 is taken as the bird's initial impact velocity v.

[0072] II. Determining the validity of load measurement

[0073] The first strain gauge group includes two pairs of strain gauges, one pair of which is bonded at the 3 o'clock and 9 o'clock directions on the circumferential surface of the Hopkinson bar. The load history F at the 3 o'clock and 9 o'clock directions of the first strain gauge group is measured. (3,9) , another pair of strain gauges are bonded at 6 o'clock and 12 o'clock on the circumferential surface of the Hopkinson bar, and the load history F at 6 o'clock and 12 o'clock of the first strain gauge group is measured. (6,12) , the load peak value F measured by the two pairs of strain gauges is obtained by the method described in step 4 peak,(3,9) , F peak,(6,12) and transfer momentum I T,(3,9) , I T,(6,12) The subscript (3,9) indicates the 3 o'clock and 9 o'clock directions, and the subscript (6,12) indicates the 6 o'clock and 12 o'clock directions. Compare the load peaks and transferred momentum measured by the two pairs of strain gauges. If the measured load peak F peak,(3,9) and F peak,(6,12) The difference is less than 5%, and the momentum I T,(3,9) and I T,(6,12) The difference is less than 5%, and the criterion is calculated as follows:

[0074]

[0075] If the criterion is met, it is determined that the compression wave has formed a plane wave at the position of the first strain gauge group, and the bird-cutting load measurement is valid. Take the load history F (3,9) and the load history F (6,12) The average value of the load history F of the first strain gauge group is taken as SG1 , accordingly, the load peak value F of the first strain gauge group is obtained by the method described in step 4 peak,SG1 and the transferred momentum I of the first strain gauge group T,SG1 , and the impact time T of the first strain gauge group is obtained. The impact time T is the load history F of the first strain gauge group SG1 The duration of the compression wave.

[0076] The second strain gauge group includes two pairs of strain gauges, one pair of which is bonded at the 3 o'clock and 9 o'clock directions on the circumferential surface of the Hopkinson bar. The load history F at the 3 o'clock and 9 o'clock directions of the second strain gauge group is measured. (3,9) ', another pair of strain gauges are bonded at 6 o'clock and 12 o'clock on the circumferential surface of the Hopkinson bar, and the load history F of the second strain gauge group at 6 o'clock and 12 o'clock is measured (6,12) ', accordingly, the load peak value F measured by the two pairs of strain gauges is obtained by the method described in step 4 peak,(3,9) ', F peak,(6,12) ' and transfer momentum I T,(3,9) ', I T,(6,12)'; The subscript (3,9) indicates the 3 o'clock and 9 o'clock directions, and the subscript (6,12) indicates the 6 o'clock and 12 o'clock directions. Compare the load peaks and transferred momentum measured by the two pairs of strain gauges. If the measured load peak F peak,(3,9) ' and F peak,(6,12) 'The difference is less than 5%, and the momentum I T,(3,9) 'and I T,(6,12) 'The difference is less than 5%, the criterion is calculated as follows:

[0077]

[0078] If the criterion is met, it is determined that the compression wave remains a plane wave at the position of the second strain gauge group, and the bird-cutting load measurement is valid. Take the load history F (3,9) ' and the load history F (6,12) The average value of ' is used as the load history F of the second strain gauge group SG2 , accordingly, the load peak value F of the second strain gauge group is obtained by the method described in step 4 peak,SG2 and the transferred momentum I of the second strain gauge group T,SG2 , and the impact time T' of the second strain gauge group is obtained. The impact time T' is the load history F of the second strain gauge group. SG2 The duration of the compression wave.

[0079] Compare the load peak and transfer momentum of the first strain gauge group and the second strain gauge group. If the load peak F of the first strain gauge group peak,SG1 and the peak load F of the second strain gauge group peak,SG2 The difference is less than 5%, and the transferred momentum of the first strain gauge group I T,SG1 and the transferred momentum I of the second strain gauge group T,SG2 The difference is less than 5%, and the criterion is calculated as follows:

[0080]

[0081] If the criterion is met, it is determined that the influence of the diffusion effect on the compression wave during the process of propagating from the position of the first strain gauge group to the position of the second strain gauge group meets the requirements of the test outline, and the bird-cutting load measurement is valid; take the load history F of the first strain gauge group SG1 and the peak load F of the first strain gauge group peak,SG1 , the transferred momentum of the first strain gauge group I T,SG1 , the impact time T of the first strain gauge group is used as the basis for empirical index analysis.

[0082] Step 6, empirical indicator analysis:

[0083] The empirical index analysis includes dimensionless processing of the measured response characteristics to form empirical indicators of the bird cutting load. The response characteristics include load peak, transferred momentum, and momentum center of mass time.

[0084] The specific process of empirical indicator analysis is:

[0085] Ⅰ Obtaining the Theoretical Transfer Momentum I ref and the theoretical average force F ref

[0086] The theoretical transfer momentum I is obtained by formula (9): ref

[0087] I ref =m·(vsinθ)·sinθ=mvsin 2 θ (9)

[0088] In formula (9), m is the mass of the bird.

[0089] The theoretical force F is obtained by formula (10): ref

[0090]

[0091] The theoretical average force F ref Theoretical impact time t ref Theoretical transfer momentum I ref .

[0092] Ⅱ Obtain the dimensionless load peak value F peak,N , momentum transfer rate MT and dimensionless momentum center of mass time T cen,N

[0093] The dimensionless load peak F peak,N is the peak load F of the first strain gauge group peak,SG1 and the theoretical average force F ref ratio.

[0094] The dimensionless transferred momentum is characterized by the momentum transfer rate MT; the momentum transfer rate MT is the transferred momentum I of the first strain gauge group T,SG1 With the initial momentum I initial The ratio of the initial momentum I initial I is the product of the bird's mass m and the initial impact velocity v; initial =mv.

[0095] Dimensionless momentum center of mass time T cen,N The time T required for the first strain gauge group to transfer half of its momentum cen The ratio of the impact time T of the first strain gauge group. The time T required for the first strain gauge group to transfer 1 / 2 of the momentum cen Refers to the load history F based on the first strain gauge group SG1In the momentum transfer process obtained by the method described in step 4, the transferred momentum is I T,SG1 / 2 hours required.

[0096] Thus, the process of measuring the bird cutting load using the bird cutting load measuring device based on the Hopkinson bar is completed.

[0097] The present invention solves the problem in existing engine fan blade bird strike research that the bird-cutting load history cannot be accurately measured due to the coupling of the dynamic deformation of the bird body and the deformation of the blade, and provides basic data for the study of the engine fan blade bird-cutting problem and especially the study of the bird body constitutive model and parameter optimization.

[0098] Compared with the prior art, the present invention has the following beneficial effects:

[0099] Focusing on the engineering science problem of bird strike on engine fan blades and conducting basic research on the problem of bird cutting on blades, the present invention proposes a bird cutting load measurement device and measurement method based on a Hopkinson bar.

[0100] The bird-cutting load measurement device based on a Hopkinson bar proposed in the present invention processes one end of a Hopkinson bar made of nylon PA66 into a wedge-shaped end with a groove, and adheres a rim made of titanium alloy TC4 with the same shape as the groove into the groove, so that the wedge-shaped end with the rim forms a quasi-rigid target plate, and the target plate providing bird-cutting load and the Hopkinson bar providing measurement are integrated. The engine bird strike conditions with different heading speeds, blade rotation speeds, and blade leading edge angles are equivalently simplified to the basic problem of bird-cutting with a quasi-rigid target plate with different half-wedge angles θ. The load history of the bird-cutting process is accurately measured and decoupled from the deformation of the target plate, which is conducive to obtaining a universal response law.

[0101] Compared with the Hopkinson rod made of metal materials, the Hopkinson rod made of nylon PA66 effectively reduces the footprint of the device and improves the convenience of the test due to its low wave velocity.

[0102] The present invention proposes that the distance between the starting point of the strain gauge attachment section and the vertex of the trailing edge of the wedge end is D, and the distance between the ending point of the strain gauge attachment section and the vertex of the trailing edge of the wedge end is 3D. This enables: when the shock wave reaches the first strain gauge group, because the distance between the position of the first strain gauge group and the said trailing edge vertex is greater than D, according to the Saint-Venant principle, the specific distribution of the load only affects the stress distribution near the load application area, where the shock wave has formed a plane wave; when the shock wave reaches the second strain gauge group, because the distance between the position of the second strain gauge group and the said trailing edge vertex is less than 3D, the shock wave propagation distance is shorter, and the dispersion effect has no significant impact on the shock wave. In the present invention, at the same axial position of the Hopkinson rod, a pair of strain gauges are attached to the 3 o'clock and 9 o'clock directions of the circumferential surface of the Hopkinson rod, and a pair of strain gauges are attached to the 6 o'clock and 12 o'clock directions of the circumferential surface of the Hopkinson rod. This is used to determine the impact of the Saint-Venant principle and generalized wave impedance mismatch on the shock wave within the cross section of the Hopkinson rod, and further determine whether the shock wave has formed a plane wave at the position of the strain gauge group.

[0103] Compared with the currently proposed simulated blade ballistic pendulum method, single-degree-of-freedom rigid wedge pulley method, and simulated blade frustum optical measurement method for blade bird cutting research, the present invention can obtain the full-process load history of target plate bird cutting, rather than just the overall momentum transfer after the bird cutting process. When the momentum transfer history of two bird cutting tests is similar, there will be a large difference in the load history of the two tests. The precise load history is measured and the momentum transfer history is obtained by integrating the load history over time. Compared with the existing test technology that directly uses the transferred momentum as the measurement target, the technical solution of the present invention is conducive to a more comprehensive study of the characteristics of the bird cutting process; compared with the currently proposed method based on the horizontal ejection-impact blade bird cutting test device for blade bird cutting research, the present invention can decouple blade deformation from the dynamic behavior of the bird body, and weaken the influence of the target plate size and stiffness characteristics.

[0104] The present invention obtains the effective full-process load history of a real bird and integrates it to obtain the momentum transfer history through test preparation, measurement device calibration, test, measurement data processing, measurement data validity analysis, and empirical index analysis. The bird cutting test is carried out on birds of different masses at different initial impact velocities to obtain several groups of dimensionless load peak values ​​F peak,N , momentum transfer rate MT and dimensionless momentum center of mass time T cen,NThe experimental data characterizes the response characteristics and distribution laws of the bird cutting process from multiple angles. The response characteristics and distribution laws of the bird cutting process are used as the basis for determining the equivalence between the bird model and constitutive parameters used in the finite element simulation and the real bird. When the response characteristics and distribution laws in the finite element simulation are consistent with the response characteristics and distribution laws of the real bird, it is considered that the bird model and constitutive parameters used in the finite element simulation are equivalent to the real bird under the bird cutting conditions, and then the bird model and constitutive parameters are generalized. The present invention can also be used to characterize the response characteristics and distribution laws of artificial birds, and serve as the basis for determining the equivalence between artificial birds and real birds.

[0105] In order to verify the effect of the present invention, two repeatability tests were conducted based on the bird-cutting load measurement device of the present invention with a half-wedge angle θ=30°, the two tests being Test No. 1 and Test No. 2. Figure 8 、 Figure 9 When the momentum transfer history 29 of test No. 1 and the momentum transfer history 30 of test No. 2 are similar, there will be a large difference between the load history 27 of test No. 1 and the load history 28 of test No. 2. According to the present invention, the load history of the bird cutting process is accurately measured and the momentum transfer history of the bird cutting process is obtained by integrating the load history with time. Compared with the existing test technology that directly uses the transferred momentum as the measurement quantity, the technical solution of the present invention is conducive to a more comprehensive study of the characteristics of the bird cutting process.

[0106] The technical solution of the present invention is used to conduct tests on birds with different masses at different initial impact velocities. Figure 10 、 Figure 11 and Figure 12 The non-dimensionalized peak load F of 18 groups of real birds weighing 280g, 680g and 1000g at initial impact speeds of 120m / s to 200m / s were obtained based on the bird cutting load measurement device with a half-wedge angle θ = 30° of the present invention. peak,N , momentum transfer rate MT and dimensionless momentum center of mass time T cen,N .exist Figure 10 、 Figure 11 and Figure 12 In the figure, the circle represents a 280g bird, the triangle represents a 680g bird, and the square represents a 1000g bird. Figure 10 , as the initial impact velocity increases, the dimensionless load peak F peak,N The distribution of remains constant; see Figure 11 , with the increase of initial impact velocity, the distribution of momentum transfer rate MT shows a decreasing trend, and the momentum transfer rate MT of the smaller mass bird is higher than that of the larger mass bird; see Figure 12 , as the initial impact velocity increases, the dimensionless momentum center of mass time T cen,NThe distribution remains constant.

[0107] When referring to the dimensionless load peak value F obtained in the finite element simulation established by the measuring device and measuring method of the present invention, peak,N , transfer momentum MT, momentum center of mass time T cen,N and Figure 10 、 Figure 11 、 Figure 12 When the distribution pattern of the real bird is consistent, it is believed that the bird body model and constitutive parameters used in the finite element simulation can be applied to the bird cutting conditions of the present invention, and then the bird body model and constitutive parameters can be promoted. BRIEF DESCRIPTION OF THE DRAWINGS

[0108] Figure 1 A top view of the bird-cutting load measurement device based on a Hopkinson bar.

[0109] Figure 2 for Figure 1 side view.

[0110] Figure 3 for Figure 1 Front view of .

[0111] Figure 4 Top view of the equivalent elastic modulus calibration test.

[0112] Figure 5 Flowchart of the present invention.

[0113] Figure 6 Schematic diagram of the simulated load history when the wedge end has and does not have a hemming.

[0114] Figure 7 Comparison chart of the experimental load history and simulation load history for equivalent elastic modulus calibration.

[0115] Figure 8 Schematic diagram of the load history measured during the test.

[0116] Figure 9 Schematic diagram of the momentum transfer process measured during the experiment.

[0117] Figure 10 Schematic diagram of dimensionless load peak.

[0118] Figure 11 Schematic diagram of momentum transfer rate.

[0119] Figure 12 This is a dimensionless momentum center-of-mass time diagram.

[0120] Figure: 1. Air cannon barrel; 2. Air cannon muzzle; 3. Bird body; 4. Laser velocimeter; 5. First normal high-speed camera; 6. Oblique high-speed camera; 7. Edge wrapping; 8. Wedge-shaped end; 9. Hopkinson bar; 10. First strain gauge group; 11. Second strain gauge group; 12. First Wheatstone bridge box group; 13. Second Wheatstone bridge box group; 14. DC regulated power supply; 15. Data logger; 16. Energy absorption plate; 17. Bracket; 18. Second normal high-speed camera; 19. Calibration projectile; 20. Plane end; 21. Wedge-shaped end without edge wrapping 1. Simulated load history of the wedge-shaped end; 22. Simulated load history of the wedge-shaped end with an edge; 23. Test load history of a nylon bullet impacting a flat end at a speed of 3 m / s; 24. Simulated load history of a nylon bullet impacting a flat end at a speed of 3 m / s; 25. Test load history of a nylon bullet impacting a flat end at a speed of 6 m / s; 26. Simulated load history of a nylon bullet impacting a flat end at a speed of 6 m / s; 27. Load history of test No. 1; 28. Load history of test No. 2; 29. ​​Momentum transfer history of test No. 1; 30. Momentum transfer history of test No. 2; M. Apex of the C-shaped trailing edge of the wedge surface at the wedge end. DETAILED DESCRIPTION

[0121] This embodiment is a bird-cutting load measurement device based on a Hopkinson bar, comprising a Hopkinson bar 9, a strain gauge assembly, a bracket, and an energy-absorbing plate. The Hopkinson bar is mounted on the bracket 17; the first strain gauge group 10 and the second strain gauge group 11 of the strain gauge assembly are adhered to the circumferential surface of the Hopkinson bar; the end of the Hopkinson bar adjacent to the air cannon muzzle 2 is a wedge-shaped end 8, and the other end is a flat end 20. The energy-absorbing plate 16 is adjacent to the flat end. During the test, the launched bird 3 is accelerated in the air cannon barrel 1 and flies out of the air cannon muzzle 2, striking the wedge-shaped end 8 of the Hopkinson bar, generating a shock wave that propagates axially along the Hopkinson bar.

[0122] The Hopkinson rod is placed on the bracket 17, and the axis of the Hopkinson rod coincides with the axis of the air cannon barrel 1; the end of the Hopkinson rod adjacent to the air cannon muzzle 2 is a wedge-shaped end 8, and the end of the Hopkinson rod adjacent to the energy absorbing plate 16 is a flat end 20.

[0123] The Hopkinson rod 9 is made of nylon PA66, and the length L and diameter D of the Hopkinson rod are determined according to the mass of the bird and the initial impact velocity in the test outline: wherein, the diameter D of the Hopkinson rod 9 is greater than the diameter of the circumscribed circle of the cross-section of the bird with the largest mass in the test outline; at the same time, the diameter D of the Hopkinson rod 9 is set with an allowance considering the shape, flight posture, and impact position error of the bird during the test, and the diameter D of the Hopkinson rod 9 is 1.2 to 1.3 times the diameter of the circumscribed circle of the cross-section of the bird with the largest mass in the test outline; the length L of the Hopkinson rod 9 is determined according to the conventional method in the prior art, and must satisfy the condition that the measured bird-cutting load history does not contain the superposition of compression wave and reflected tensile wave waveforms.

[0124] Two planes are symmetrically cut on the circumferential surface of the Hopkinson rod 9 adjacent to the air cannon muzzle 2, and one end of the two planes intersects at the end face of the Hopkinson rod, forming the wedge-shaped end 8 of the Hopkinson rod. The front end of the wedge-shaped end is a straight line, which is the leading edge of the wedge-shaped end 8. When the Hopkinson rod is placed, the leading edge is in the vertical direction.

[0125] The two planes are the two wedge surfaces of the wedge-shaped end; each wedge surface has a groove for embedding the edging 7; the surface of each edging and each wedge surface together constitute the two projectile-facing surfaces of the Hopkinson rod; the leading edge of the wedge-shaped end is also the leading edge of each projectile-facing surface, and the trailing edge of each projectile-facing surface is a C-shaped curve formed by the edge of the wedge surface of the wedge-shaped end 8; each C-shaped curve has a vertex M, and each vertex M is located at the farthest end of the C-shaped curve from the front edge of the projectile-facing surface.

[0126] The included angles between the axis of the Hopkinson rod 9 and each of the impact surfaces are all half-wedge angles θ, θ=10°~60°; bird-cutting tests are carried out by using wedge-shaped ends 8 with different half-wedge angles to simulate engine bird strike conditions at different heading speeds, blade rotation speeds and blade leading edge angles.

[0127] The groove on the wedge surface extends from the front edge of the projectile-facing surface to the rear edge. The groove is 3 mm deep, and its length along the projectile-facing surface is 0.5 to 0.6 times the length of the wedge surface. A rim 7 made of titanium alloy TC4, identical in shape, is embedded and fixed in the groove, forming a rimmed projectile-facing surface. This rimming improves the rigidity, strength, and hardness of the wedge-shaped end, making the rimmed wedge end 8 a quasi-rigid bird-cutting target.

[0128] The edge 7 is made of titanium alloy TC4 material, and the wedge-shaped end 8 is made of nylon PA66 material. The wave impedances of the two materials are not matched; however, since the thickness of the edge 7 is only 3 mm, stress balance can be achieved immediately after loading. Figure 6 For a Hopkinson bar with a diameter of D = 110 mm, a half-wedge angle θ = 30°, a 60 mm length along the impact surface, a bird weight of 280 g, and an initial impact velocity of 130 m / s, a simulated load history 22 for the wedge-shaped end 8 with the edging and a simulated load history 21 for the wedge-shaped end 8 without the edging were obtained. Comparing the simulated load histories with and without the edging reveals that the edging 7 not only improves the stiffness, strength, and hardness of the wedge-shaped end, but also helps filter out high-frequency components in the bird-cutting load. It also has no effect on the load history measurement, preventing waveform distortion in the measured load history.

[0129] The strain gauge assembly includes a first strain gauge group 10 and a second strain gauge group 11. The first and second strain gauge groups are sequentially distributed along the axis of the Hopkinson rod on the outer circumferential surface between the rear edge vertex M of the projectile surface and the planar end 20 of the Hopkinson rod and are located within the strain gauge attachment section; the first strain gauge group 10 is located near the wedge-shaped end 8, and the second strain gauge group 11 is located near the planar end 20. The distance between the starting point of the strain gauge attachment section and the rear edge vertex M of the projectile surface is D, and the distance between the end point of the strain gauge attachment section and the rear edge vertex M is 3D, where D is the diameter of the Hopkinson rod.

[0130] The first strain gauge group and the second strain gauge group each include two pairs of strain gauges distributed along the axial direction of the Hopkinson rod, wherein one pair of strain gauges is bonded to the Figure 3 The Hopkinson rod is shown in the 3 o'clock and 9 o'clock directions. Another pair of strain gauges are bonded to the Figure 3 The 6 o'clock direction and 12 o'clock direction of the circumferential surface of the Hopkinson rod are shown. The strain gauge sensitive grid of each strain gauge is along the axis direction of the Hopkinson rod.

[0131] When the compression performance of the Hopkinson rod 9 satisfies linear elasticity, the strain history measured by the strain gauge group and the bird-cutting load history are in a linear conversion relationship, so that the Hopkinson rod can accurately measure the bird-cutting load history.

[0132] According to conventional methods, the two pairs of strain gauges in the first strain gauge group 10 are respectively connected to the two Wheatstone bridge boxes in the first Wheatstone bridge box group 12; the two pairs of strain gauges in the second strain gauge group 11 are respectively connected to the two Wheatstone bridge boxes in the second Wheatstone bridge box group 13; the four Wheatstone bridges in the first Wheatstone bridge box group 12 and the second Wheatstone bridge box group 13 all use the arm measurement method in the prior art. According to conventional methods in the prior art, the output ports of the four Wheatstone bridge boxes in the first Wheatstone bridge box group 12 and the second Wheatstone bridge box group 13 are connected to the input ports of the data acquisition device 15; the first Wheatstone bridge box group 12 and the second Wheatstone bridge box group 13 are respectively connected to the DC regulated power supply 14, and the DC regulated power supply 14 supplies power to the four Wheatstone bridge boxes. According to conventional methods in the prior art, the DC regulated power supply 14 and the data acquisition device 15 are grounded.

[0133] Conventionally, a laser velocimeter 4, a first normal high-speed camera 5, a second normal high-speed camera 18, and an oblique high-speed camera 6 are installed between the wedge-shaped end 8 of the Hopkinson rod 9 and the air cannon muzzle 2. Conventionally, the two laser beams of the laser velocimeter 4 are perpendicular to and intersect the extended axis of the air cannon barrel 1, and the laser velocimeter is connected to a data collector 15. According to the conventional method, the first normal high-speed camera 5 is set on one side of the Hopkinson rod, so that the lens of the first normal high-speed camera is placed horizontally and perpendicular to the extension line of the air cannon barrel, so as to shoot the bird cutting process in the horizontal field of view; the oblique high-speed camera 6 is set on the other side of the Hopkinson rod, so that the lens of the oblique high-speed camera is placed horizontally and perpendicular to the bullet-facing surface of the wedge-shaped end of the Hopkinson rod, so as to shoot the bird cutting process in the oblique field of view; the second normal high-speed camera 18 is set at the bottom of the wedge-shaped end 8 of the Hopkinson rod, so that the lens of the second normal high-speed camera is vertically upward and perpendicular to the extension line of the axis of the air cannon barrel 1, so as to shoot the bird cutting process in the vertical upward field of view.

[0134] The bracket 17 is fixed to the ground. A set of support rods is fixed to each end of the bracket's upper surface. Each set of support rods contains two support rods, one located on each side of the bracket. Each set of support rods is mounted on a roller shaft, each of which is equipped with two rollers. The spacing between the two rollers on each roller shaft satisfies the support of the Hopkinson bar and does not interfere with the roller shaft. The Hopkinson bar 9 is mounted on the rollers of the bracket 17, allowing it to slide on the bracket.

[0135] The energy absorbing plate 16 is fixed on the bracket 17 and is adjacent to the flat end of the Hopkinson rod. It is used to cushion the Hopkinson rod after impact and to limit the movement of the Hopkinson rod. The energy absorbing plate 16 adopts existing technology.

[0136] The method for measuring the bird-cutting load using the Hopkinson bar-based bird-cutting load measuring device proposed in this embodiment includes six steps: test preparation, measurement device calibration, testing, measurement data processing, measurement data validity analysis, and empirical index analysis. The specific process is as follows:

[0137] Step 1, test preparation:

[0138] The test preparation includes determining the diameter D and length L of the Hopkinson rod according to the test outline and placing the Hopkinson rod.

[0139] Ⅰ Determine the diameter D of the Hopkinson bar

[0140] According to the maximum mass bird in the current test and the minimum initial impact velocity specified in the test outline, the diameter D and length L of the Hopkinson rod 9 are determined. The diameter D of the Hopkinson rod 9 is 1.2 to 1.3 times the diameter of the maximum mass bird.

[0141] Ⅱ Determine the length L of the Hopkinson bar

[0142] ⅰDetermine the theoretical impact stroke l ref and theoretical impact time t ref

[0143] Theoretical impact stroke l ref The theoretical impact time t is the distance from the moment the front end of the bird body contacts the leading edge of the wedge end to the distance from the tail end of the bird body to the impact surface of the wedge end 8; ref The bird body passes through the theoretical impact stroke l at the initial impact speed v ref time.

[0144] The theoretical impact stroke l is obtained by formula (1): ref:

[0145]

[0146] Where l is the length of the bird and d is the diameter of the bird.

[0147] The theoretical impact time t is obtained by formula (2): ref :

[0148]

[0149] Where v is the initial impact velocity of the bird.

[0150] In this embodiment, the half-wedge angle θ of the wedge-shaped end 8 is 30°, the maximum mass of the bird specified in the test outline is 1000g, the minimum initial impact velocity of the bird specified is 120m / s, the shape of the bird is a cylinder with a length-to-diameter ratio of 2:1, and the density of the bird is 950kg / m 3 The length of a 1000g bird is 176mm, and its diameter d is 88mm. The diameter D of the Hopkinson rod 9 is 1.2 to 1.3 times the diameter of the 1000g bird, and the diameter D of the Hopkinson rod is determined to be 110mm. The second strain gauge group 11 is located within the strain gauge bonding section, and is 400mm away from the front edge of the impact surface. The theoretical impact stroke l of the 1000g bird is ref The theoretical impact time t is 252.2 mm at an initial impact velocity of 120 m / s. ref It is 2.1ms.

[0151] ⅱDetermine the length L of the Hopkinson bar

[0152] By presetting the length L' of the Hopkinson bar, the length L of the Hopkinson bar is determined.

[0153] The preset length L' of the Hopkinson rod should be able to prevent the compression wave and the reflected tensile wave from being superimposed on each other in the measured bird-cutting load history. To ensure that the compression wave and the reflected tensile wave are not superimposed on each other in the bird-cutting load history, it is necessary to ensure that the time required for the compression wave generated by the bird body 3 impacting the impact surface of the wedge-shaped end 8 to reach the second strain gauge group 11, propagate along the axis of the Hopkinson rod 9 to the flat end 20 of the Hopkinson rod, be reflected as a tensile wave, and propagate back along the axis of the Hopkinson rod to the second strain gauge group, is greater than the theoretical impact time t ref If this condition is met, the preset Hopkinson rod length L' is determined as the length L of the Hopkinson rod used.

[0154] In this embodiment, L' is preset to 3000 mm. From the time the compression wave reaches the second strain gauge group 11, propagates along the Hopkinson bar axially to the planar end 20, is reflected as a tensile wave, and propagates back to the second strain gauge group 11, the total propagation distance is 5200 mm. The wave velocity of nylon PA66 is 1800 m / s, and the propagation time is 2.9 ms, which is longer than the theoretical impact time of 2.1 ms. This prevents the compression wave from superimposing on the reflected tensile wave, which would complicate experimental data analysis. This allows for a margin in the Hopkinson bar length, so setting the Hopkinson bar length L to 3000 mm is reasonable.

[0155] Ⅲ Place the Hopkinson rod

[0156] The Hopkinson rod is placed so that the Hopkinson rod 9 is coaxial with the air cannon tube 1, and the wedge-shaped end 8 of the Hopkinson rod is located at one end of the Hopkinson rod close to the air cannon muzzle 2, and the distance between the leading edge of the wedge-shaped end and the air cannon muzzle 2 is 1 to 3l, where l is the length of the bird body, which is conducive to the placement of a laser velocimeter and a high-speed camera, and is conducive to measuring the initial impact velocity of the bird body.

[0157] Step 2: Calibration of measuring device:

[0158] The measurement device calibration includes measuring the laser beam spacing; determining the relationship between the pixel coordinates in the field of view of the high-speed camera and the world coordinates; and calibrating the equivalent elastic modulus E of the Hopkinson rod material based on a calibration bullet impact test.

[0159] ⅠMeasure the distance between laser beams

[0160] The horizontal distance l1 between the two intersection points of the two laser beams of the laser velocimeter 4 and the extended line of the axis of the air cannon barrel 1 is measured in a conventional manner.

[0161] Ⅱ Determine the relationship between pixel coordinates in the field of view of a high-speed camera and world coordinates

[0162] According to conventional methods, a calibration ruler is placed on the extension line of the axis of the air cannon barrel 1 and is located in the horizontal field of view captured by the first normal high-speed camera 5. The pixel coordinate difference between the two ends of the calibration ruler along the extension line of the axis of the air cannon barrel 1 is measured in the field of view to obtain the relationship between the pixel coordinates in the direction of the extension line of the axis of the air cannon barrel 1 in the horizontal field of view captured by the first normal high-speed camera 5 and the world coordinates.

[0163] Ⅲ Calibration of the equivalent elastic modulus E of the Hopkinson bar material

[0164] like Figure 4As shown, the Hopkinson rod 9 in step 1 is horizontally rotated 180 degrees so that the flat end 20 of the Hopkinson rod is adjacent to the air cannon muzzle 2, and the wedge-shaped end 8 of the Hopkinson rod is adjacent to the energy absorbing plate 16. A cylindrical nylon PA66 calibration bullet 19 is used to impact the flat end of the Hopkinson rod at different speeds.

[0165] A finite element simulation model was established for a calibration projectile 19 made of nylon PA66 impacting the flat end 20 of a Hopkinson rod. The nylon PA66 used in the Hopkinson rod and the calibration projectile was set to a linear elastic material with an elastic modulus E'. The elastic modulus E' of the nylon PA66 was iteratively optimized using conventional methods to minimize the peak deviation between the simulated and experimental load histories. The optimized elastic modulus E' of the nylon PA66 material was used as the equivalent elastic modulus E of the Hopkinson rod material and served as the basis for measurement data processing.

[0166] In this embodiment, the nylon PA66 calibration projectile has a length of 400 mm and a diameter of 100 mm. The calibration projectile 19 impacts the flat end 20 of the Hopkinson rod 9 at speeds of 3 m / s and 6 m / s, respectively. The load amplitudes generated by the calibration projectile impacting the flat end of the Hopkinson rod at 3 m / s and 6 m / s range from 0 to 60 kN, which covers the load amplitudes generated when impacting the wedge-shaped end 8 of the Hopkinson rod at the bird mass and initial impact velocity planned in the test outline. Based on the elastic modulus E' of nylon PA66 after iterative optimization, the simulated load history of the calibration bullet impacting the planar end of the Hopkinson rod at 3m / s and 6m / s is obtained; when the calibration bullet impacts the planar end of the Hopkinson rod at 3m / s, the peak error between the simulated load history 24 and the test load history 23 is less than 10%, which meets the requirements of the test outline; when the calibration bullet impacts the planar end of the Hopkinson rod at 6m / s, the peak error between the simulated load history 26 and the test load history 25 is less than 10%, which meets the requirements of the test outline; the elastic modulus E' of the nylon PA66 material used in the Hopkinson rod in the finite element simulation is used as the equivalent elastic modulus E of the Hopkinson rod material.

[0167] Step 3, test:

[0168] The test includes launching a bird to impact the wedge-shaped end of the Hopkinson bar and collecting a voltage signal.

[0169] Based on the test preparation described in step 1, a bird strike test is conducted. A bird 3 is launched through an air cannon. The high-pressure air accelerates the bird 3 axially along the air cannon barrel 1. After exiting the air cannon muzzle 2, the bird 3 passes through two laser beams from a laser velocimeter 4 and strikes the wedge-shaped end 8 of a Hopkinson bar 9. As the bird passes through the two laser beams, two pulse signals are generated, with a time difference of Δt1 between the two pulse signals. The bird strikes the wedge-shaped end 8 of the Hopkinson bar 9 and slides along the projectile-facing surface. The impact of the bird generates a shock wave, which initially manifests as a compression wave that propagates along the axis of the Hopkinson bar 9 toward the planar end 20 of the Hopkinson bar.

[0170] When the compression wave passes through the first strain gauge group 10 and the second strain gauge group 11, the four pairs of strain gauges are compressed, and the first Wheatstone bridge box group 12 and the second Wheatstone bridge box group 13 each generate a voltage signal, which is recorded by the data collector 15, reflecting the load history of the bird body 3 impacting the wedge-shaped end 8. When the compression wave propagates along the axis of the Hopkinson bar to the planar end 20 of the Hopkinson bar and is reflected as a tensile wave and propagates back to the second strain gauge group 11 and the first strain gauge group 10, the four pairs of strain gauges are stretched, and the second Wheatstone bridge box group 13 and the first Wheatstone bridge box group 12 each generate a voltage signal, which is recorded by the data collector 15.

[0171] Under the impact of the bird, the Hopkinson bar slides on the bracket 17 until it hits the energy absorbing plate 16 and stops.

[0172] Step 4: Measurement data processing:

[0173] The measurement data processing includes calculating the initial impact velocity of the bird body based on the measurement results of the laser velocimeter and the high-speed camera; processing the voltage signal measured by the strain gauge to obtain the load history and momentum transfer history of the bird cutting process.

[0174] Ⅰ Calculation of the bird's initial impact velocity based on the measurement results of the laser velocimeter

[0175] The conventional method in the prior art is used to calculate the initial impact velocity v1 of the bird 3 measured by the laser velocimeter 4 based on the time difference Δt1 between the two pulse signals generated after the bird 3 passes through the two laser beams of the laser velocimeter 4, where v1 = l1 / Δt1.

[0176] Ⅱ Calculation of the bird's initial impact velocity based on the measurement results of a high-speed camera

[0177] Using conventional methods in the prior art, an image taken by the first normal high-speed camera 5 at the moment when the front end of the bird enters the field of view of the high-speed camera is selected, and an image taken by the first normal high-speed camera 5 at the moment before the front end of the bird leaves the field of view of the high-speed camera is selected. Based on the relationship between the pixel coordinates and the world coordinates, the flight distance l2 of the bird 3 is calculated. Based on the frame number difference between the two images at the two moments, the time difference Δt2 between the two images at the two moments is obtained, and the initial impact velocity v2 of the bird 3 measured by the first normal high-speed camera 5 is calculated, where v2 = l2 / Δt2.

[0178] III Processing the voltage signal measured by the strain gauge

[0179] Conventionally, the voltage signals measured by the first strain gauge group 10 and the second strain gauge group 11 are processed according to the bridge conversion formula of the Wheatstone bridge to obtain the strain history ε. In this strain history, the shock wave is sequentially a compression wave and a reflected tensile wave. Only the compression wave is extracted for analysis, and the compression wave reflects the load history of the bird cutting process. The product of the strain history ε, the equivalent elastic modulus E of the Hopkinson bar, and the cross-sectional area A of the Hopkinson bar is the load history F of the bird cutting process, which is calculated as follows:

[0180] F=A·E·ε (3)

[0181] The peak value of the load history F is the load peak F peak .

[0182] The integral of the load history F over time t is the momentum transfer history I of the bird cutting process, which reflects the momentum along the axial direction of the Hopkinson rod 9 transferred from the bird body 3 to the Hopkinson rod 9 during the bird cutting process. The calculation formula is:

[0183] I=∫F·dt (4)

[0184] The peak value of the momentum transfer process I is the momentum I transferred from the bird body 3 to the Hopkinson rod 9 along the axial direction of the Hopkinson rod during the bird cutting process. T .

[0185] Step 5: Validity analysis of measurement data:

[0186] The measurement data validity analysis includes comparing the initial impact velocity of the bird measured by a high-speed camera and a laser velocimeter to determine the validity of the velocity measurement; and comparing the load history measured by four pairs of strain gauges, namely the first strain gauge group and the second strain gauge group, to determine the validity of the load measurement.

[0187] I. Determining the validity of speed measurement

[0188] Compare the initial impact velocity v1 of the bird measured by the laser velocimeter 4 with the initial impact velocity v2 of the bird measured by the first normal high-speed camera 5. If the difference between v1 and v2 is less than 5%, the criterion is calculated as follows:

[0189]

[0190] If the criterion is met, the measurement of the bird's initial impact velocity is determined to be valid, and the average value of v1 and v2 is taken as the bird's initial impact velocity v.

[0191] II. Determining the validity of load measurement

[0192] The first strain gauge group 10 includes two pairs of strain gauges, one pair of which is bonded at the 3 o'clock and 9 o'clock directions on the circumferential surface of the Hopkinson rod 9. The load history F at the 3 o'clock and 9 o'clock directions of the first strain gauge group is measured. (3,9) , another pair of strain gauges are bonded at 6 o'clock and 12 o'clock on the circumferential surface of Hopkinson bar 9, and the load history F at 6 o'clock and 12 o'clock of the first strain gauge group is measured. (6,12) , accordingly, the load peak value F measured by the two pairs of strain gauges is obtained by the method described in step 4 peak,(3,9) , F peak,(6,12) and transfer momentum I T,(3,9) , I T,(6,12) Here, the subscript (3,9) indicates the 3 o'clock and 9 o'clock directions, and the subscript (6,12) indicates the 6 o'clock and 12 o'clock directions. Comparing the load peaks and transferred momentum measured by the two pairs of strain gauges, if the measured load peak F peak,(3,9) and F peak,(6,12) The difference is less than 5%, and the momentum I T,(3,9) and I T,(6,12) The difference is less than 5%, and the criterion is calculated as follows:

[0193]

[0194] If the criterion is met, it is determined that the compression wave has formed a plane wave at the position of the first strain gauge group 10, and the bird-cutting load measurement is valid. The load history F is taken. (3,9) and load history F (6,12) The average value of the load history F of the first strain gauge group is taken as SG1 , accordingly, the load peak value F of the first strain gauge group 10 is obtained by the method described in step 4 peak,SG1 and the transferred momentum I of the first strain gauge group 10 T,SG1 , and the impact time T of the first strain gauge group 10 is obtained. The impact time T is the load history F of the first strain gauge group SG1 The duration of the compression wave.

[0195] The second strain gauge group 11 includes two pairs of strain gauges, one pair of which is bonded at the 3 o'clock and 9 o'clock directions on the circumferential surface of the Hopkinson rod 9. The load history F at the 3 o'clock and 9 o'clock directions of the second strain gauge group is measured. (3,9) ', another pair of strain gauges are bonded to the 6 o'clock and 12 o'clock directions on the circumferential surface of the Hopkinson rod 9, and the load history F of the second strain gauge group at 6 o'clock and 12 o'clock directions is measured (6,12) ', accordingly, the load peak value F measured by the two pairs of strain gauges is obtained by the method described in step 4 peak,(3,9) ', F peak,(6,12) ' and transfer momentum I T,(3,9) ', I T,(6,12) ';Here, the subscript (3,9) indicates the 3 o'clock and 9 o'clock directions, and the subscript (6,12) indicates the 6 o'clock and 12 o'clock directions. Comparing the load peaks and transferred momentum measured by the two pairs of strain gauges, if the measured load peak F peak,(3,9) ' and F peak,(6,12) 'The difference is less than 5%, and the momentum I T,(3,9) 'and I T,(6,12) 'The difference is less than 5%, the criterion is calculated as follows:

[0196]

[0197] If the criterion is met, it is determined that the compression wave remains a plane wave at the position of the second strain gauge group 11, and the bird-cutting load measurement is valid. The load history F is taken. (3,9) ' and the load history F (6,12) The average value of ' is used as the load history F of the second strain gauge group SG2 , accordingly, the load peak value F of the second strain gauge group 11 is obtained by the method described in step 4 peak,SG2 and the transferred momentum I of the second strain gauge group 11 T,SG2 , and the impact time T' of the second strain gauge group 11 is obtained. The impact time T' is the load history F of the second strain gauge group SG2 The duration of the compression wave.

[0198] Comparing the load peak and transfer momentum of the first strain gauge group 10 and the second strain gauge group 11, if the load peak F peak,SG1 and the peak load F of the second strain gauge group peak,SG2 The difference is less than 5%, and the transferred momentum of the first strain gauge group I T,SG1 and the transferred momentum I of the second strain gauge group T,SG2 The difference is less than 5%, and the criterion is calculated as follows:

[0199]

[0200] If the criterion is met, it is determined that the influence of the diffusion effect on the compression wave during the process of propagating from the position of the first strain gauge group 10 to the position of the second strain gauge group 11 meets the requirements of the test outline, and the bird-cutting load measurement is valid; take the load history F of the first strain gauge group SG1 and the peak load F of the first strain gauge group peak,SG1 , the transferred momentum of the first strain gauge group I T,SG1 , the impact time T of the first strain gauge group is used as the basis for empirical index analysis.

[0201] Step 6, empirical indicator analysis:

[0202] The empirical index analysis includes dimensionless processing of the measured response characteristics to form empirical indicators of the bird cutting load. The response characteristics include load peak, transferred momentum, and momentum center of mass time.

[0203] The specific process of empirical indicator analysis is:

[0204] Ⅰ Obtaining the Theoretical Transfer Momentum I ref and the theoretical average force F ref

[0205] The theoretical transfer momentum I is obtained by formula (9): ref

[0206] I ref =m·(vsinθ)·sinθ=mvsin 2 θ (9)

[0207] In formula (9), m is the mass of the bird.

[0208] The theoretical average force F is obtained by formula (10): ref

[0209]

[0210] The theoretical average force F ref Theoretical impact time t ref Theoretical transfer momentum I ref .

[0211] Ⅱ Obtain the dimensionless load peak value F peak,N , momentum transfer rate MT and dimensionless momentum center of mass time T cen,N

[0212] The dimensionless load peak F peak,N is the peak load F of the first strain gauge group peak,SG1 and the theoretical average force F ref ratio.

[0213] The dimensionless transferred momentum is characterized by the momentum transfer rate MT; the momentum transfer rate MT is the transferred momentum I of the first strain gauge group T,SG1 With the initial momentum I initial The ratio of the initial momentum I initial I is the product of the bird's mass m and the initial impact velocity v; initial =mv.

[0214] Dimensionless momentum center of mass time T cen,N The time T required for the first strain gauge group to transfer half of its momentum cen The ratio of the impact time T of the first strain gauge group. The time T required for the first strain gauge group to transfer 1 / 2 of the momentum cen Refers to the load history F based on the first strain gauge group SG1 In the momentum transfer process obtained by the method described in step 4, the transferred momentum is I T,SG1 / 2 hours required.

[0215] Thus, the process of measuring the bird cutting load using the bird cutting load measuring device based on the Hopkinson bar is completed.

Claims

1. A bird-cutting load measuring device based on a Hopkinson rod, comprising a Hopkinson rod, a strain gauge assembly, a bracket and an energy absorbing plate; the Hopkinson rod (9) is placed on the bracket (17) so that the axis of the Hopkinson rod coincides with the axis of an air cannon barrel (1); a first strain gauge group (10) and a second strain gauge group (11) in the strain gauge assembly are adhered to the circumferential surface of the Hopkinson rod; the energy absorbing plate (16) is fixed on the bracket (17) and is adjacent to the plane end of the Hopkinson rod, and is used to cushion the Hopkinson rod after impact and to limit the movement of the Hopkinson rod; each pair of strain gauges in the strain gauge assembly is respectively connected to a Wheatstone bridge box; a laser velocimeter and a high-speed camera are provided in the bird-cutting load measuring device; It is characterized in that The end of the Hopkinson rod adjacent to the air cannon muzzle (2) is a wedge-shaped end; the end of the Hopkinson rod adjacent to the energy absorbing plate (16) is a flat end (20); Two planes are symmetrically cut on the circumferential surface of the Hopkinson rod adjacent to the air cannon muzzle, and one end of the two planes intersects with the end face of the Hopkinson rod, forming a wedge (8) of the Hopkinson rod; the front end of the wedge end is a straight line, and the straight line is the leading edge of the wedge end; when the Hopkinson rod is placed, the leading edge is along the vertical direction; The two planes are two wedge surfaces of the wedge-shaped end; each wedge surface has a groove for embedding the edge (7); the surface of each edge and each wedge surface together constitute the two projectile-facing surfaces of the Hopkinson rod; the leading edge of the wedge-shaped end is also the leading edge of each projectile-facing surface, and the trailing edge of each projectile-facing surface is a C-shaped curve formed by the edge of the wedge surface of the wedge-shaped end (8); each C-shaped curve has a vertex M, and each vertex M is located at the farthest end of the C-shaped curve from the front edge of the projectile-facing surface; The angles between the axis of the Hopkinson rod and each of the projectile-facing surfaces are all half-wedge angles θ, and the diameter D of the Hopkinson rod is 1.2 to 1.3 times the diameter of the bird with the largest mass in the test outline; The strain gauge assembly comprises a first strain gauge group (10) and a second strain gauge group (11); the first strain gauge group and the second strain gauge group are sequentially distributed along the axis on the outer circumferential surface between the trailing edge vertex M of the wedge end (8) and the plane end (20) of the Hopkinson rod and are located in the strain gauge pasting section; the first strain gauge group and the second strain gauge group each comprise two pairs of strain gauges distributed along the axial direction of the Hopkinson rod, one pair of strain gauges being adhered to the circumferential surface of the Hopkinson rod at the 3 o'clock direction and the 9 o'clock direction, and the other pair of strain gauges being adhered to the circumferential surface of the Hopkinson rod at the 6 o'clock direction and the 12 o'clock direction; the strain gauge sensitive grids of the strain gauges are all along the axial direction of the Hopkinson rod; A laser velocimeter (4), a first normal high-speed camera (5), a second normal high-speed camera (18) and an oblique high-speed camera (6) are arranged between the wedge-shaped end of the Hopkinson rod and the air cannon muzzle (2).

2. The bird-cutting load measuring device based on the Hopkinson bar according to claim 1, characterized in that: The half-wedge angle θ is 10° to 60°; bird-cutting tests are carried out by using wedge-shaped ends (8) with different half-wedge angles to simulate engine bird strike conditions at different heading speeds, blade rotation speeds, and blade leading edge angles.

3. The bird-cutting load measuring device based on the Hopkinson bar according to claim 1, characterized in that: The groove extends from the front edge to the rear edge of the facing surface; the depth of the groove is 3 mm, and the length of the groove along the facing surface is 0.5 to 0.6 times the length of the wedge surface.

4. The bird-cutting load measuring device based on the Hopkinson bar according to claim 1, characterized in that: The first strain gauge group (10) is close to the wedge-shaped end, and the second strain gauge group (11) is close to the plane end (20); the distance between the starting point of the strain gauge pasting section and the vertex M of the rear edge of the bullet-facing surface is D; the distance between the ending point of the strain gauge pasting section and the vertex M of the rear edge of the bullet-facing surface is 3D, and D is the diameter of the Hopkinson rod.

5. The bird-cutting load measuring device based on the Hopkinson bar according to claim 1, characterized in that: The two laser beams of the laser velocimeter (4) are perpendicular to and intersect with the extension line of the axis of the air cannon barrel (1); the lens of the first normal high-speed camera is placed horizontally and perpendicular to the extension line of the axis of the air cannon barrel, so as to shoot the bird cutting process in the horizontal field of view; the lens of the oblique high-speed camera is placed horizontally and perpendicular to the projectile-facing surface of the wedge-shaped end of the Hopkinson rod, so as to shoot the bird cutting process in the oblique field of view; the second normal high-speed camera (18) is located at the bottom of the wedge-shaped end of the Hopkinson rod, so that the lens of the second normal high-speed camera is vertically upward and perpendicular to the extension line of the axis of the air cannon barrel (1), so as to shoot the bird cutting process in the vertical upward field of view.

6. A method for measuring bird cutting load using the device according to claim 1, characterized in that: The specific process is: Step 1, test preparation: The test preparation includes determining the diameter D and length L of the Hopkinson rod according to the test outline and placing the Hopkinson rod; Ⅰ Determine the diameter D of the Hopkinson bar: Determine the diameter D of the Hopkinson rod based on the bird with the largest mass in the current test and the specified minimum initial impact velocity specified in the test outline; II Determine the length L of the Hopkinson bar: ⅰDetermine the theoretical impact stroke l ref and theoretical impact time t ref ; ⅱDetermine the length L of the Hopkinson bar; III. Placement of Hopkinson rod: The Hopkinson rod is placed so that the Hopkinson rod is coaxial with the air cannon barrel (1), and the wedge-shaped end of the Hopkinson rod is located at one end of the Hopkinson rod close to the air cannon muzzle, and the distance between the leading edge of the wedge-shaped end and the air cannon muzzle is 1 to 31; wherein l is the length of the bird body; Step 2: Calibration of measuring device: The measurement device calibration includes measuring the laser beam spacing; determining the relationship between the pixel coordinates in the field of view of the high-speed camera and the world coordinates; calibrating the equivalent elastic modulus E of the Hopkinson rod material based on the calibration bullet impact test; I measuring the laser beam spacing; II. Determine the relationship between pixel coordinates in the field of view of a high-speed camera and world coordinates; Ⅲ Calibrate the equivalent elastic modulus E of the Hopkinson rod material; Step 3, test: The test includes launching a bird body, impacting the wedge-shaped end of the Hopkinson bar, and collecting a voltage signal; Step 4: Measurement data processing: The measurement data processing includes calculating the initial impact velocity of the bird based on the measurement results of the laser velocimeter and the high-speed camera; processing the voltage signal measured by the strain gauge to obtain the load history and momentum transfer history of the bird cutting process; I. calculating the initial impact velocity of the bird based on the measurement results of the laser velocimeter; Ⅱ Calculate the initial impact velocity of the bird based on the measurement results of the high-speed camera; Ⅲ Processing the voltage signal measured by the strain gauge; The voltage signals measured by the first and second strain gauge groups are processed according to the Wheatstone bridge conversion formula to obtain the strain history ε. In this strain history, the shock wave is a compression wave and a reflected tensile wave. Only the compression wave is extracted for analysis, and this compression wave reflects the load history of the bird cutting process. The product of the strain history ε, the equivalent elastic modulus E of the Hopkinson bar, and the cross-sectional area A of the Hopkinson bar is the load history F of the bird cutting process, which is calculated as follows: F=A·E·ε (3) The peak value of the load history F is the load peak F peak ; The integral of the load history F over time t is the momentum transfer history I of the bird cutting process, which reflects the momentum I along the axial direction of the Hopkinson rod transferred from the bird body to the Hopkinson rod during the bird cutting process. The calculation formula is: I=∫F·dt (4) The peak value of the momentum transfer process I is the momentum I transferred from the bird body to the Hopkinson rod along the axis of the Hopkinson rod during the bird cutting process. T ; Step 5: Validity analysis of measurement data: The validity analysis of the measurement data includes comparing the initial impact velocity of the bird measured by a high-speed camera and a laser velocimeter to determine the validity of the velocity measurement; and comparing the load processes measured by four pairs of strain gauges, namely the first strain gauge group and the second strain gauge group, to determine the validity of the load measurement. I. Determining the validity of speed measurement: Compare the initial impact velocity v1 of the bird measured by the laser velocimeter with the initial impact velocity v2 of the bird measured by the first normal high-speed camera. If the difference between v1 and v2 is less than 5%, the criterion is calculated as follows: If the criterion is met, the measurement of the bird's initial impact velocity is determined to be valid, and the average of v1 and v2 is taken as the bird's initial impact velocity v; II. Determining the validity of load measurement: The load history F at the 3-point and 9-point directions of the first strain gauge group is measured. (3,9) ; Measure the load history F at 6 and 12 o'clock of the first strain gauge group (6,12) ; Get the peak load F measured by the two pairs of strain gauges peak,(3,9) , F peak,(6,12) and transfer momentum I T,(3,9) , I T,(6,12) ; The subscript (3,9) indicates the 3 o'clock and 9 o'clock directions, and the subscript (6,12) indicates the 6 o'clock and 12 o'clock directions; compare the load peaks and transferred momentum measured by the two pairs of strain gauges. If the measured load peak F peak,(3,9) and F peak,(6,12) The difference is less than 5%, and the momentum I T,(3,9) and I T,(6,12) The difference is less than 5%, and the criterion is calculated as follows: If the criterion is satisfied, it is determined that at the position of the first strain gauge group (10), the compression wave has formed a plane wave, and the bird-cutting load measurement is valid. The load history F is taken. (3,9) and the load history F (6,12) The average value of the load history F of the first strain gauge group is taken as SG1 , accordingly, the load peak value F of the first strain gauge group (10) is obtained by the method described in step 4 peak,SG1 and the transferred momentum I of the first strain gauge group (10) T,SG1 , and obtain the impact time T of the first strain gauge group (10), the impact time T is the load history F of the first strain gauge group SG1 The duration of the compression wave; the load history F at the 3 and 9 o'clock directions of the second strain gauge group is measured (3,9) 'The load history F of the second strain gauge group at 6 and 12 o'clock (6,12) ', get the load peak value F measured by the two pairs of strain gauges peak,(3,9) ', F peak,(6,12) ' and transfer momentum I T,(3,9) ', I T,(6,12) '; Compare the load peaks and transferred momentum measured by the two pairs of strain gauges. If the measured load peak F peak,(3,9) ' and F peak,(6,12) 'The difference is less than 5%, and the momentum I T,(3,9) 'and I T,(6,12) 'The difference is less than 5%, the criterion is calculated as follows: If the criterion is satisfied, it is determined that at the position of the second strain gauge group (11), the compression wave remains a plane wave, the bird-cutting load measurement is valid, and the load history F is taken. (3,9) ' and the load history F (6,12) The average value of ' is used as the load history F of the second strain gauge group SG2 , accordingly, the load peak value F of the second strain gauge group is obtained by the method described in step 4 peak,SG2 and the transferred momentum I of the second strain gauge group T,SG2 , and the impact time T' of the second strain gauge group is obtained. The impact time T' is the load history F of the second strain gauge group. SG2 duration of the mid-compression wave; Comparing the load peak and transfer momentum of the first strain gauge group (10) and the second strain gauge group (11), if the load peak F of the first strain gauge group peak,SG1 and the peak load F of the second strain gauge group peak,SG2 The difference is less than 5%, and the transferred momentum of the first strain gauge group I T,SG1 and the transferred momentum I of the second strain gauge group T,SG2 The difference is less than 5%, and the criterion is calculated as follows: If the criterion is met, it is determined that the influence of the diffusion effect on the compression wave during the propagation from the position of the first strain gauge group to the position of the second strain gauge group meets the requirements of the test outline, and the bird-cutting load measurement is valid; take the load history F of the first strain gauge group SG1 and the peak load F of the first strain gauge group peak,SG1 , the transferred momentum of the first strain gauge group I T,SG1 , the impact time T of the first strain gauge group is used as the basis for empirical index analysis; Step 6, empirical indicator analysis: The empirical index analysis includes dimensionless processing of the measured response characteristics to form empirical indicators of the bird cutting load, wherein the response characteristics include load peak, transferred momentum, and momentum center of mass time; The specific process of empirical indicator analysis is: Ⅰ Obtaining the Theoretical Transfer Momentum I ref and the theoretical average force F ref The theoretical transfer momentum I is obtained by formula (9): ref I ref =m·(vsinθ)·sinθ=mvsin 2 i(9) In formula (9), m is the mass of the bird; The theoretical force F is obtained by formula (10): ref The theoretical average force F ref Theoretical impact time t ref Theoretical transfer momentum I ref ; Ⅱ Obtain the dimensionless load peak value F peak,N , momentum transfer rate MT and dimensionless momentum center of mass time T cen,N The dimensionless load peak F peak,N is the peak load F of the first strain gauge group peak,SG1 and the theoretical average force F ref The ratio of The dimensionless transferred momentum is characterized by the momentum transfer rate MT; the momentum transfer rate MT is the transferred momentum I of the first strain gauge group T,SG1 With the initial momentum I initial The ratio of the initial momentum I initial I is the product of the bird's mass m and the initial impact velocity v; initial =mv; Dimensionless momentum center of mass time T cen,N The time T required for the first strain gauge group to transfer half of its momentum cen The ratio of the impact time T of the first strain gauge group; the time T required for the first strain gauge group to transfer 1 / 2 of the momentum cen Refers to the load history F based on the first strain gauge group SG1 In the momentum transfer process obtained by the method described in step 4, the transferred momentum is I T,SG1 / 2 hours required; Thus, the process of measuring the bird cutting load using the bird cutting load measuring device based on the Hopkinson bar is completed.

7. The method for measuring bird cutting load using the device according to claim 6, characterized in that: In step 1, determine the theoretical impact stroke l ref and theoretical impact time t ref The specific process is: Theoretical impact stroke l ref The theoretical impact time t is the distance from the moment the front end of the bird body contacts the leading edge of the wedge end to the moment the tail end of the bird body moves to the wedge end's bullet-facing surface; ref The bird body passes through the theoretical impact stroke l at the initial impact speed v ref time; The theoretical impact stroke l is obtained by formula (1): ref : Among them, l is the length of the bird body, d is the diameter of the bird body; The theoretical impact time t is obtained by formula (2): ref : Where v is the initial impact velocity of the bird; The specific process of determining the length L of the Hopkinson bar is: Determine the length L of the Hopkinson bar by the preset length L' of the Hopkinson bar; The preset length L' of the Hopkinson rod should be such that the measured bird-cutting load history does not cause the superposition of compression waves and reflected tensile waves; If the time required for the compression wave generated by the bird body 3 impacting the wedge-shaped end (8) and reaching the second strain gauge group (11), propagating along the axis of the Hopkinson rod (9) to the flat end (20) of the Hopkinson rod, being reflected as a tensile wave and propagating back along the axis of the Hopkinson rod to the second strain gauge group, is greater than the theoretical impact time t ref , the preset length L' of the Hopkinson rod is determined as the length L of the Hopkinson rod.

8. The method for measuring bird cutting load using the device according to claim 6, characterized in that: In step 2, the laser beam spacing is measured by measuring the horizontal distance l1 between the two intersection points of the two laser beams of the laser velocimeter and the extended lines of the air cannon barrel axis; The specific process of determining the relationship between the pixel coordinates in the field of view of the high-speed camera and the world coordinates is to place a calibration ruler on the extension line of the air cannon barrel axis and place the calibration ruler in the horizontal field of view captured by the first normal high-speed camera. The pixel coordinate difference between the two ends of the calibration ruler along the extension line of the air cannon barrel axis is measured in the horizontal field of view to obtain the relationship between the pixel coordinates in the direction of the extension line of the air cannon barrel axis in the horizontal field of view captured by the first normal high-speed camera and the world coordinates. The specific process of calibrating the equivalent elastic modulus E of the Hopkinson rod material is as follows: the Hopkinson rod in step 1 is horizontally rotated 180 degrees, so that the flat end of the Hopkinson rod is adjacent to the muzzle of the air cannon, and the wedge-shaped end of the Hopkinson rod is adjacent to the energy absorption plate; a cylindrical nylon PA66 calibration bullet is used to impact the flat end of the Hopkinson rod at different speeds; A finite element simulation model of a calibration bullet made of nylon PA66 impacting the flat end of a Hopkinson rod was established. The nylon PA66 used in the Hopkinson rod and the calibration bullet was set as a linear elastic material with an elastic modulus of E'. The peak deviation between the simulated load history and the experimental load history was minimized through iteration, and the elastic modulus E' after iterative optimization was determined as the equivalent elastic modulus E of the Hopkinson rod.

9. The method for measuring bird cutting load using the device according to claim 6, characterized in that: In step 3, when the launched bird impacts the wedge-shaped end of the Hopkinson bar, the bird flies out of the muzzle of the air cannon, passes through two laser beams of the laser velocimeter, and then impacts the wedge-shaped end of the Hopkinson bar. When the bird passes through the two laser beams, two pulse signals with a time difference of Δt1 are generated. The bird impacts the wedge-shaped end of the Hopkinson bar and slides along the projectile-facing surface. The impact of the bird generates a shock wave, which first manifests as a compression wave and propagates along the axis of the Hopkinson bar toward the planar end of the Hopkinson bar. When the compression wave passes through the first and second strain gauge groups, the four pairs of strain gauges are compressed, and the first and second Wheatstone bridge box groups each generate voltage signals that are recorded by the data collector, reflecting the load history of the bird impacting the wedge-shaped end. When the compression wave propagates along the axis of the Hopkinson bar to the planar end of the Hopkinson bar and is reflected as a tensile wave that propagates back to the second and first strain gauge groups, the four pairs of strain gauges are stretched, and the second and first Wheatstone bridge box groups each generate voltage signals that are recorded by the data collector. Under the impact of the bird body, the Hopkinson rod slides on the bracket until it hits the energy absorbing plate and stops.

10. The method for measuring bird cutting load using the device according to claim 6, characterized in that: In step 4, when calculating the initial impact velocity of the bird based on the measurement results of the laser velocimeter, the initial impact velocity v1 of the bird measured by the laser velocimeter is calculated based on the time difference Δt1 between the two pulse signals generated after the bird passes through the two laser beams of the laser velocimeter, where v1 = l1 / Δt1; When calculating the initial impact velocity of the bird based on the measurement results of the high-speed camera, an image taken by the first normal high-speed camera at the moment when the front end of the bird enters the field of view of the high-speed camera is selected, and an image taken by the first normal high-speed camera at the moment before the front end of the bird leaves the field of view of the high-speed camera is selected. The flight distance l2 of the bird is calculated based on the relationship between pixel coordinates and world coordinates. The time difference Δt2 is obtained based on the frame number difference between the images at the two moments, and the velocity v2 of the bird measured by the first normal high-speed camera is calculated, where v2=l2 / Δt2.

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