High-temperature uniaxial bidirectional electromagnetic Hopkinson rod experiment system and method

Abstract

The invention discloses a high-temperature uniaxial bidirectional electromagnetic Hopkinson rod experiment system and method. The system comprises an upper computer, a high-temperature furnace, a guide rail, a sample pushing device, a sample cold contact time measuring device, a stress loading power supply, two coaxial electromagnetic Hopkinson rods and two rod end pushing devices. And a strain gauge is arranged on each electromagnetic Hopkinson rod. According to the system, off-line heating is conducted on a sample through a high-temperature furnace, the sample is pushed into two coaxial electromagnetic Hopkinson rods through a sample pushing device after being heated, and the electromagnetic Hopkinson rods and the sample are tensioned through a rod end pushing device; in the whole process, the cold contact time point can be measured in advance through the strain gauge and the cold contact time measuring device, and the advanced working time of the sample pushing device relative to the rod end pushing device is calculated through the upper computer, so that the cold contact time of the sample and the electromagnetic Hopkinson rod is shortened to be within 1ms, and the high-temperature (not lower than 1200 DEG C) test on the sample (a connecting structure) can be realized.

Description

Technical Field

[0001] The invention relates to the field of dynamic mechanical performance testing of connection structures, and in particular to a high-temperature uniaxial bidirectional electromagnetic Hopkinson rod experimental system and method. Background Art

[0002] With the requirements for improving engine thrust and efficiency in aerospace technology, higher requirements are placed on the performance of advanced hypersonic aircraft and their corresponding engines. In order to obtain higher engine thrust and working efficiency, the engine turbine inlet temperature also increases. In order to meet the structural safety of aircraft structures under extreme high temperature conditions, various high-temperature resistant materials are widely used in corresponding engine components. However, such materials and structures in extreme high temperature environments are also threatened by various impact loads while bearing thermal loads. In this process, the coupling effect of high temperature and high strain rate significantly affects the mechanical properties of materials and structures. At the same time, high-temperature bolt fasteners are widely used for structural assembly in related areas such as aircraft thermal protection structures and engine components. As the node part of load transfer, under the action of external loads, the structure often fails at the bolt connection structure position, such as pull-off, breakage, shearing and other failure behaviors. Therefore, it is necessary to fully understand the dynamic mechanical behavior of bolted connection structures under high temperature service conditions, conduct mechanical property tests of bolted connection structures under high temperature and high rate coupling, and study the corresponding deformation and failure mechanisms.

[0003] In the prior art, the dynamic mechanical properties test of the connection structure can be performed using high-speed hydraulic servo testing machines and impact pendulums. The connection structure is directly loaded using a high-speed hydraulic servo testing machine, or a dynamic load is applied to the structure using an impact pendulum, and the mechanical properties of the structure and the structural deformation response under the impact load are measured. However, when the loading rate exceeds 1m / s, the load signal will show obvious fluctuations due to the inertia effect of the fixture and the superposition effect of stress waves. Even with the use of efficient load measurement modules and long loading fixtures, the improvement effect is not obvious.

[0004] In addition, the prior art also uses a mechanical Hopkinson tension rod or Hopkinson compression rod device to test the dynamic mechanical properties of the structure. The mechanical Hopkinson rod device includes a launch device, an impact rod (bullet), an incident rod, a transmission rod and corresponding clamping supports and buffer devices, etc., wherein the bullet, the incident rod, the sample and the transmission rod remain coaxial, and the sample is located between the incident rod and the transmission rod. The device generally uses high-pressure gas to launch the impact rod to impact the incident rod, thereby generating a series of stress waves. The stress wave propagates along the incident rod, and is reflected and transmitted at the connecting end faces of the incident rod, the transmission rod and the sample to form a reflected wave and a transmitted wave. At the same time, the stress wave completes multiple reflections in the sample so that the sample reaches stress equilibrium. Strain gauges are attached to the incident rod and the transmission rod to collect the incident wave, reflected wave and transmitted wave signals, and the mechanical performance response of the structure can be calculated with the help of one-dimensional stress wave theory.

[0005] However, the specimens currently loaded by the mechanical Hopkinson bar device have complex structures and large geometric dimensions. This results in asymmetric deformation at both ends of the specimen, that is, unbalanced dynamic loads on both ends; in addition, the constant loading rate was not effectively achieved in the test, affecting the validity and accuracy of the test results. Even if a special matching design is used to eliminate the influence of the inertial effect of the connection structure between the test piece and the loading rod on the load measurement, since the traditional mechanical Hopkinson bar only relies on one end of the incident rod for loading, it takes a long time for both ends of the specimen to reach stress equilibrium, and it is difficult to ensure the validity of the test results.

[0006] The prior art also uses a uniaxial bidirectional electromagnetic Hopkinson rod device for bidirectional loading, and heats the sample by means of a local heating method, and adds a transition section and a cooling device between the sample and the loading rod to control the temperature of the loading rod. Compared with the mechanical Hopkinson rod device, the uniaxial bidirectional electromagnetic Hopkinson rod uses capacitor discharge to generate sinusoidal pulses, and uses the principle of electromagnetic induction to generate corresponding sinusoidal pulse electromagnetic repulsion in each pair of primary coils and secondary coils at both ends, thereby generating two columns of opposing stress waves in the rod, which propagate synchronously along the loading rod to the sample, completing dynamic loading of the sample. The sample can be kept on the loading rod for direct heating (online heating solution), thereby achieving high-temperature dynamic loading of the sample.

[0007] However, when the sample is heated using the online heating scheme, since the sample and the loading rod are always in contact, the maximum temperature that can be reached in the test is limited by the loading rod, and it is difficult to make further breakthroughs. So far, the dynamic tests of high-temperature connectors using online heating schemes have been difficult to reach a test temperature above 300°C while ensuring the accuracy of the measurement results, even if the above-mentioned methods of limiting the temperature rise at the sample end of the loading rod are combined. The main problem is that before the test, the sample needs to be firmly connected to the loading rod by manual operation using methods such as gluing or threading, and the sample cannot be clamped quickly and automatically. Summary of the invention

[0008] In view of the above-mentioned deficiencies in the prior art, the present invention provides a high-temperature uniaxial bidirectional electromagnetic Hopkinson bar experimental system and method, which solves the problem that the existing electromagnetic Hopkinson bar device adopts an online heating scheme and cannot achieve fast and automatic clamping of samples and testing.

[0009] In order to achieve the above-mentioned object of the invention, the technical solution adopted by the present invention is:

[0010] A high-temperature uniaxial bidirectional electromagnetic Hopkinson rod experimental system is provided, which includes a host computer, a high-temperature furnace, a guide rail, a sample pushing device, a sample cold contact time measuring device, a stress loading power supply, two coaxial electromagnetic Hopkinson rods and two rod end pushing devices; each electromagnetic Hopkinson rod is provided with a strain gauge;

[0011] A guide rail runs through the high temperature furnace and is used to place the sample and restrict the movement of the sample;

[0012] High temperature furnace, used to heat the sample;

[0013] A sample pushing device, used to push the sample into two coaxial electromagnetic Hopkinson rods on the guide rail;

[0014] The rod end pushing device is used to push the electromagnetic Hopkinson rod placed thereon to tighten the electromagnetic Hopkinson rod and the sample;

[0015] The strain gauge is used to record the midpoint of the incident stress wave and the reflected stress wave starting point, and use it as the time point when the stress wave starts and ends loading the specimen;

[0016] Cold contact time measuring device, used to measure the time point when the sample leaves the high temperature furnace and the time point when the sample starts to contact with the electromagnetic Hopkinson bar;

[0017] The upper computer is used to use the time from the time when the sample starts to contact the electromagnetic Hopkinson rod to the time when the stress wave starts to load the sample as the advance working time of the sample pushing device relative to the rod end pushing device; the time from the time when the sample leaves the high-temperature furnace to the time when the sample starts to contact the electromagnetic Hopkinson rod is used as the heat loss time, and the actual temperature of the sample during the test is determined through heat transfer analysis based on the heat loss time;

[0018] The stress loading power supply is electrically connected to the two electromagnetic Hopkinson rods and is used to provide the same power to the two electromagnetic Hopkinson rods at the same time, so that the two electromagnetic Hopkinson rods can load stress waves with the same amplitude and change trend at both ends of the sample at the same time.

[0019] Furthermore, each electromagnetic Hopkinson rod includes a loading rod. During testing, the two ends of the strain gauge are respectively embedded in the two loading rods. In the same electromagnetic Hopkinson rod, a primary coil is movably sleeved at the middle and rear part of each loading rod. The primary coil is installed on the sample pushing device. An impact flange is provided at the end of the loading rod. A secondary coil is sleeved on the loading rod and between the primary coil and the impact flange. The primary coil is electrically connected to a stress loading power supply. When the stress loading power supply provides power to the primary coil, the primary coil and the secondary coil generate corresponding sinusoidal pulse electromagnetic repulsion, thereby forming a stress wave. The stress wave propagates along the loading rod to the sample, thereby realizing high-temperature dynamic loading of the sample.

[0020] Furthermore, the rod end pushing device includes a first servo motor and a loading platform arranged on the base; a mobile base is arranged on the loading platform through the sliding of a screw rod; the primary coil is placed on the mobile base; the first servo motor drives the screw rod to rotate through gears, thereby realizing the pushing of the mobile base and the electromagnetic Hopkinson rod.

[0021] Furthermore, the sample pushing device includes a second servo motor and a pushing rod. The shaft of the second servo motor drives the pushing rod to move linearly through gears. Driven by the second servo motor, the pushing rod pushes the sample in the high-temperature furnace into two coaxial electromagnetic Hopkinson rods.

[0022] Further, the cold contact time measuring device comprises a first ring, a first laser transmitter, a first laser receiver, a second ring, a second laser transmitter and a second laser receiver; wherein:

[0023] The first ring is arranged on the push rod; when the push rod contacts the sample, the distance between the first ring and the optical path of the first laser emitter is equal to the distance between the sample and the exit of the high-temperature furnace, so that when the push rod pushes the sample to leave the high-temperature furnace, the first ring blocks the first laser receiver from receiving the optical signal of the first laser emitter, and records the current time point as the time point when the sample leaves the high-temperature furnace;

[0024] The second ring is set on any electromagnetic Hopkinson rod; the distance from the second ring to the optical path of the second laser emitter is equal to the horizontal distance from the electromagnetic Hopkinson rod to the sample, so that when the electromagnetic Hopkinson rod and the sample are tightened, the second ring blocks the second laser receiver from receiving the optical signal of the second laser emitter, and records the current time point as the time point when the sample and the electromagnetic Hopkinson rod begin to contact.

[0025] Furthermore, the stress loading power supply is an RLC circuit, which controls the capacitor in the RLC circuit to discharge the two electromagnetic Hopkinson rods simultaneously, so that the two electromagnetic Hopkinson rods generate two series of electromagnetic pulses with consistent amplitude and change trend, and then stress waves with consistent amplitude and change trend are loaded on both ends of the sample at the same time; the pulse width of the electromagnetic pulse waveform is controlled by adjusting the capacitor parameters; the amplitude of the electromagnetic pulse waveform is controlled by adjusting the discharge voltage.

[0026] Furthermore, a bracket for supporting the loading rod is provided on the base.

[0027] Furthermore, the secondary coil is a copper sheet.

[0028] An experimental method based on a high temperature uniaxial bidirectional electromagnetic Hopkinson bar experimental system is provided, which comprises the following steps:

[0029] S1. Place the sample on the guide rail and push the sample into a high temperature furnace for heating;

[0030] S2, pushing the heated sample into two coaxial electromagnetic Hopkinson rods through the sample pushing device;

[0031] S3, taking the time from the time when the sample starts to contact the electromagnetic Hopkinson rod to the time when the stress wave starts to load the sample as the advance working time of the sample pushing device relative to the rod end pushing device, and pushing the electromagnetic Hopkinson rod installed on it through the rod end pushing device, so that the electromagnetic Hopkinson rod and the sample are tightened;

[0032] S4. The stress loading power supply provides the same power to the two electromagnetic Hopkinson rods at the same time, so that the two electromagnetic Hopkinson rods load stress waves with the same amplitude and change trend at both ends of the sample at the same time to complete the experiment.

[0033] The beneficial effects of the present invention are:

[0034] 1. This system heats the sample offline through a high-temperature furnace. After heating, the sample is pushed into two coaxial electromagnetic Hopkinson rods by a sample pushing device, and the electromagnetic Hopkinson rods and the sample are tightened by a rod end pushing device. The cold contact time point can be measured in advance by a strain gauge and a cold contact time measuring device during the whole process, and the advance working time of the sample pushing device relative to the rod end pushing device can be calculated by the host computer, so that the time (cold contact time) from the sample being tightened by the electromagnetic Hopkinson rod to the stress wave being loaded is shortened to less than 1ms, and the sample (connection structure) can be tested at high temperature (not less than 1200℃).

[0035] 2. This system can run automatically, automatically realize high-temperature synchronous assembly and testing of samples, and accurately control the cold contact time of samples.

[0036] 3. This system measures the time from when the sample leaves the high-temperature furnace to when the sample begins to contact the electromagnetic Hopkinson rod as the heat loss duration. Based on the heat loss duration, the actual temperature of the sample during the test is determined through heat transfer analysis, which can improve the accuracy of the test.

[0037] 4. This system uses RLC circuit as the stress loading power supply, which can effectively control the pulse width and amplitude of the stress wave, and the maximum allowable discharge voltage is 2000V. Using high voltage for discharge, the system can reach a maximum loading speed of 40m / s. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Figure 1 This is a schematic diagram of the structure of this system;

[0039] Figure 2 It is a structural schematic diagram of the guide rail part;

[0040] Figure 3 It is a structural schematic diagram of the rod end pushing device;

[0041] Figure 4 Schematic diagram of pushing the sample into two coaxial electromagnetic Hopkinson rods;

[0042] Figure 5 is the electrical signal recorded in the high temperature experiment;

[0043] Figure 6It is a schematic diagram of load balance and constant loading rate realization of bolt connection test piece;

[0044] Wherein: 1. base; 2. loading platform; 3. moving base; 4. screw; 5. first servo motor; 6. primary coil; 7. loading rod; 8. secondary coil; 9. impact flange; 10. strain gauge; 11. guide rail; 12. specimen; 13. first laser receiver; 14. push rod; 15. second servo motor; 16. first ring; 17. first laser transmitter; 18. high temperature furnace; 19. bracket; 20. second ring; 21. second laser transmitter; 22. second laser receiver; 23. stress loading power supply. DETAILED DESCRIPTION

[0045] The specific implementation modes of the present invention are described below so that those skilled in the art can understand the present invention. However, it should be clear that the present invention is not limited to the scope of the specific implementation modes. For those of ordinary skill in the art, as long as various changes are within the spirit and scope of the present invention as defined and determined by the attached claims, these changes are obvious, and all inventions and creations utilizing the concept of the present invention are protected.

[0046] like Figure 1 , Figure 2 , Figure 3 and Figure 4 As shown, the high-temperature uniaxial bidirectional electromagnetic Hopkinson rod experimental system includes a host computer, a high-temperature furnace 18, a guide rail 11, a sample pushing device, a sample cold contact time measuring device, a stress loading power supply 23, two coaxial electromagnetic Hopkinson rods and two rod end pushing devices; each electromagnetic Hopkinson rod is provided with a strain gauge 10;

[0047] The guide rail 11 passes through the high temperature furnace 18 and is used to place the sample 12 and restrict the movement of the sample 12;

[0048] A high temperature furnace 18, used to heat the sample 12;

[0049] A sample pushing device, used for pushing the sample 12 on the guide rail 11 into two coaxial electromagnetic Hopkinson rods;

[0050] A rod end pushing device, used for pushing the electromagnetic Hopkinson rod mounted thereon, so that the electromagnetic Hopkinson rod and the sample 12 are tightened;

[0051] The strain gauge 10 is used to record the midpoint of the incident stress wave and the starting point of the reflected stress wave, and use it as the time point when the stress wave starts loading the sample and ends (recorded as C);

[0052] A cold contact time measuring device, used to measure the time point when the sample 12 leaves the high temperature furnace 18 (denoted as A) and the time point when the sample 12 begins to contact the electromagnetic Hopkinson bar (denoted as B);

[0053] The upper computer is used to take the time from the time when the sample 12 starts to contact the electromagnetic Hopkinson rod to the time when the stress wave starts to load the sample as the advance working time of the sample pushing device relative to the rod end pushing device; the time from the time when the sample 12 leaves the high-temperature furnace 18 to the time when the sample 12 starts to contact the electromagnetic Hopkinson rod is measured as the heat loss time. Based on the heat loss time, the commercial finite element software Abaqus is used to perform heat transfer analysis to simulate the temperature change of the sample and the end of the loading rod within two cold contact times (A to B, B to C), determine the actual temperature of the sample 12 during the test, verify the effectiveness of the high-temperature dynamic torsion experiment, and ensure that the experimental results can accurately reflect the dynamic shear mechanical behavior of the material at a specific temperature.

[0054] The stress loading power supply 23 is electrically connected to the two electromagnetic Hopkinson rods and is used to provide the same power to the two electromagnetic Hopkinson rods at the same time, so that the two electromagnetic Hopkinson rods load stress waves with the same amplitude and change trend at both ends of the sample 12 at the same time.

[0055] Each electromagnetic Hopkinson rod includes a loading rod 7. During testing, the two ends of the strain gauge 10 are respectively embedded in the two loading rods 7. In the same electromagnetic Hopkinson rod, a primary coil 6 is movably sleeved on the middle and rear part of each loading rod 7. The primary coil 6 is installed on the sample pushing device. An impact flange 9 is provided at the end of the loading rod 7. A secondary coil 8 is sleeved on the loading rod 7 and between the primary coil 6 and the impact flange 9. The primary coil 6 is electrically connected to a stress loading power supply. When the stress loading power supply provides power to the primary coil 6, the primary coil 6 and the secondary coil 8 generate corresponding sinusoidal pulse electromagnetic repulsion, thereby forming a stress wave. The stress wave propagates along the loading rod 7 to the sample 12, thereby realizing high-temperature dynamic loading of the sample 12.

[0056] The rod end pushing device includes a first servo motor 5 and a loading platform 2 arranged on a base 1; a mobile base 3 is slidably arranged on the loading platform 2 through a screw rod 4; a primary coil 6 is placed on the mobile base 3; the first servo motor 5 drives the screw rod 4 to rotate through a gear, thereby pushing the mobile base 3 and the primary coil 6. The primary coil 6 pushes the secondary coil 6 toward the impact flange 9 during the movement, and pushes the loading rod 7 through the extrusion of the secondary coil 6 and the impact flange 9. A bracket 19 for supporting the loading rod 7 is arranged on the base 1.

[0057] The sample pushing device includes a second servo motor 15 and a pushing rod 14. The shaft of the second servo motor 15 drives the pushing rod 14 to move linearly through gears. Driven by the second servo motor 15, the pushing rod 14 pushes the sample 12 in the high-temperature furnace 18 into two coaxial electromagnetic Hopkinson rods.

[0058] The cold contact time measuring device comprises a first ring 16, a first laser transmitter 17, a first laser receiver 13, a second ring 20, a second laser transmitter 21 and a second laser receiver 22; wherein:

[0059] The first ring 16 is arranged on the push rod 14; when the push rod 14 contacts the sample 12, the distance between the optical path of the first ring 16 and the first laser emitter 17 is equal to the distance between the sample 12 and the exit of the high-temperature furnace 18, so that when the push rod 14 pushes the sample 12 to leave the high-temperature furnace 18, the first ring 16 blocks the first laser receiver 13 from receiving the optical signal of the first laser emitter 17, and records the current time point as the time point when the sample 12 leaves the high-temperature furnace 18;

[0060] The second ring 20 is set on any electromagnetic Hopkinson rod; the distance of the optical path from the second ring 20 to the second laser emitter 21 is equal to the horizontal distance from the electromagnetic Hopkinson rod to the sample 12, so that when the electromagnetic Hopkinson rod and the sample 12 are tightened, the second ring 20 blocks the second laser receiver 22 from receiving the optical signal of the second laser emitter 21, and records the current time point as the time point when the sample 12 starts to contact with the electromagnetic Hopkinson rod.

[0061] In the specific implementation process, before the assembly begins, the light emitted by the laser tube emission module is in an unblocked state, and the laser receiver continuously outputs a low level after detecting the light. During the synchronous assembly process, when the sample 12 leaves the heating chamber of the high-temperature furnace 18, the first ring 16 on the push rod 14 just blocks the laser light path, causing the output signal of the first laser receiver 13 to become a high level, thereby recording the starting point of the 1st CCT, which is recorded as time A; when the sample 12 contacts the loading rod 7, the second ring 20 on the loading rod 7 just blocks the laser light path there, and causes the second laser receiver 22 to output a high level. The moment recorded at this time is both the end point of the 1st CCT and the starting point of the 2nd CCT, which is recorded as time B; then the stress wave reaches the sample 12 and starts dynamic loading. The midpoint of the incident wave and the reflected wave starting point recorded by the strain gauge 10 on the loading rod 7 is the moment when the incident wave propagates to the connection surface between the sample 12 and the loading rod 7, that is, the end point of the 2nd CCT, which is recorded as time C. Figure 5As shown, the output signals of the two sets of laser sensors and the strain gauge 10 on the loading rod 7 are recorded by the data acquisition device, and the 1st CCT of the experiment - time interval AB, and the 2nd CCT - time interval BC can be measured. Combined with the two measured cold contact times, the commercial finite element software Abaqus is used to perform heat transfer analysis on the cold contact process of the experiment, simulating the temperature changes of the sample 12 and the end of the loading rod 7 during the two cold contact times. Verify the effectiveness of the high-temperature dynamic torsion experiment and ensure that the experimental results can accurately reflect the dynamic shear mechanical behavior of the material at a specific temperature.

[0062] The stress loading power supply 23 is an RLC circuit, which controls the capacitor in the RLC circuit to discharge the two electromagnetic Hopkinson rods simultaneously, so that the two electromagnetic Hopkinson rods generate two series of electromagnetic pulses with consistent amplitude and change trend, and then simultaneously load stress waves with consistent amplitude and change trend at both ends of the sample 12; the pulse width of the electromagnetic pulse waveform is controlled by adjusting the capacitor parameters; the amplitude of the electromagnetic pulse waveform is controlled by adjusting the discharge voltage.

[0063] In one embodiment of the present invention, the load balance and constant loading rate of the bolt connection test piece are analyzed, such as Figure 6 As shown, the stress wave reaches both ends of the bolt connection test piece at the same time, and the stress wave amplitude and pulse width are almost completely consistent. In addition, this embodiment reasonably adjusts the waveform and pulse width of the loading stress wave according to the dynamic mechanical response of the bolt connection test piece, matches the sine stress wave for the bolt connection test piece, and makes the test piece failure located at the highest point of the sine stress wave, which well solves the problem of unbalanced dynamic load and non-constant loading rate at both ends of the bolt connection test piece. Through the matching design of the bolt connection test piece and making full use of the synchronization advantage of two coaxial electromagnetic Hopkinson bars in the application of impact loads, the waveform and pulse width of the loading stress wave are reasonably matched according to the dynamic response of the connection structure under different loading angles, and finally a method can be developed that can eliminate the inertia effect caused by the connection between the bolt connection and the loading device and the two-dimensional effect caused by the mismatch of wave impedance, and can apply high-rate impact loads to the bolt connection under different tensile-shear coupling load states.

[0064] In the specific implementation process, the experimental method corresponding to the high temperature uniaxial bidirectional electromagnetic Hopkinson bar experimental system includes the following steps:

[0065] S1, placing the sample 12 on the guide rail 11 and pushing the sample 12 into the high temperature furnace 18 for heating;

[0066] S2, pushing the heated sample 12 into two coaxial electromagnetic Hopkinson rods through a sample pushing device;

[0067] S3, taking the time from the time when the sample 12 starts to contact with the electromagnetic Hopkinson rod to the time when the stress wave starts to load the sample 12 as the advance working time of the sample pushing device relative to the rod end pushing device, and pushing the electromagnetic Hopkinson rod mounted thereon by the rod end pushing device to tighten the electromagnetic Hopkinson rod and the sample 12;

[0068] S4. The stress loading power supply 23 provides the same power to the two electromagnetic Hopkinson rods at the same time, so that the two electromagnetic Hopkinson rods load stress waves with the same amplitude and change trend at both ends of the sample 12 at the same time, and the experiment is completed.

[0069] In conclusion, the present invention solves the problems of waveform oscillation, unbalanced dynamic loads at both ends of the specimen and non-constant loading rate caused by the inertia effect of the fixture, and adopts an offline heating scheme to solve the problem of high-temperature dynamic loading of the connector, which can increase the maximum experimental temperature to 1200°C, expand the experimental capabilities and testing methods, and can apply high-rate impact loads to the bolted connection structure under high temperature conditions, providing a reliable experimental basis for studying the dynamic mechanical behavior of thermal structural connectors such as high-temperature alloys under high temperature and high strain rate coupling. The present invention makes full use of the synchronization advantage of two coaxial electromagnetic Hopkinson rods (uniaxial bidirectional electromagnetic Hopkinson pull rod system) to apply bidirectional tensile impact loads, and conducts mechanical property tests on bolted connectors at different temperatures (room temperature to 1200°C), loading rates (5 to 40m / s) and loading angles. Combined with quasi-static high-temperature mechanical property tests, the dependence of the mechanical properties of bolted connectors on loading rate, temperature and load state is quantitatively analyzed, and the ability to quickly predict the ultimate strength and yield strength of the connection structure at different temperatures and loading angles and within a wide range of loading rates can be achieved.

Claims

1. A high temperature uniaxial bidirectional electromagnetic Hopkinson bar experimental system, characterized in that: It comprises a host computer, a high temperature furnace (18), a guide rail (11), a sample pushing device, a sample cold contact time measuring device, a stress loading power supply (23), two coaxial electromagnetic Hopkinson rods and two rod end pushing devices; each electromagnetic Hopkinson rod is provided with a strain gauge (10); A guide rail (11) passes through the high temperature furnace (18) and is used to place the sample (12) and restrict the movement of the sample (12); A high temperature furnace (18) for heating the sample (12); A sample pushing device, used for pushing the sample (12) on the guide rail (11) into two coaxial electromagnetic Hopkinson rods; A rod end pushing device, used for pushing the electromagnetic Hopkinson rod mounted thereon, so that the electromagnetic Hopkinson rod and the sample (12) are tightened; The strain gauge (10) is used to record the midpoint of the incident stress wave and the starting point of the reflected stress wave, and use it as the time point when the stress wave starts and ends loading the sample; A cold contact time measuring device, used to measure the time point when the sample (12) leaves the high temperature furnace (18) and the time point when the sample (12) starts to contact with the electromagnetic Hopkinson bar; The host computer is used to use the time from the time when the sample (12) starts to contact the electromagnetic Hopkinson rod to the time when the stress wave starts to load the sample (12) as the advance working time of the sample pushing device relative to the rod end pushing device; the time from the time when the sample (12) leaves the high-temperature furnace (18) to the time when the sample (12) starts to contact the electromagnetic Hopkinson rod as the heat loss time, and determine the actual temperature of the sample (12) during the test through heat transfer analysis based on the heat loss time; The stress loading power supply (23) is electrically connected to the two electromagnetic Hopkinson rods and is used to simultaneously provide the same power to the two electromagnetic Hopkinson rods, so that the two electromagnetic Hopkinson rods simultaneously load stress waves with the same amplitude and change trend at both ends of the sample (12).

2. The high temperature uniaxial bidirectional electromagnetic Hopkinson bar experimental system according to claim 1, characterized in that: Each electromagnetic Hopkinson rod comprises a loading rod (7). During testing, two ends of a strain gauge (10) are respectively embedded in the two loading rods (7). In the same electromagnetic Hopkinson rod, a primary coil (6) is movably sleeved at the middle and rear part of each loading rod (7). The primary coil (6) is mounted on a sample pushing device. An impact flange (9) is provided at the end of the loading rod (7). A secondary coil (8) is sleeved on the loading rod (7) and between the primary coil (6) and the impact flange (9). The primary coil (6) is electrically connected to a stress loading power supply. When the stress loading power supply supplies power to the primary coil (6), the primary coil (6) and the secondary coil (8) generate corresponding sinusoidal pulse electromagnetic repulsion forces, thereby forming a stress wave, which propagates along the loading rod (7) to the sample (12), thereby achieving high-temperature dynamic loading of the sample (12).

3. The high temperature uniaxial bidirectional electromagnetic Hopkinson bar experimental system according to claim 2 is characterized in that: The rod end pushing device comprises a first servo motor (5) and a loading platform (2) arranged on a base (1); a movable base (3) is slidably arranged on the loading platform (2) via a screw rod (4); a primary coil (6) is placed on the movable base (3); the first servo motor (5) drives the screw rod (4) to rotate via a gear, thereby pushing the movable base (3) and the electromagnetic Hopkinson rod.

4. The high temperature uniaxial bidirectional electromagnetic Hopkinson bar experimental system according to claim 1, characterized in that: The sample pushing device comprises a second servo motor (15) and a pushing rod (14); the rotating shaft of the second servo motor (15) drives the pushing rod (14) to move linearly through gears; the pushing rod (14) pushes the sample (12) in the high-temperature furnace (18) into two coaxial electromagnetic Hopkinson rods under the drive of the second servo motor (15).

5. The high temperature uniaxial bidirectional electromagnetic Hopkinson bar experimental system according to claim 4, characterized in that: The cold contact time measuring device comprises a first ring (16), a first laser transmitter (17), a first laser receiver (13), a second ring (20), a second laser transmitter (21) and a second laser receiver (22); wherein: The first ring (16) is arranged on the push rod (14); when the push rod (14) contacts the sample (12), the distance between the optical path from the first ring (16) to the first laser emitter (17) is equal to the distance from the sample (12) to the exit of the high-temperature furnace (18), so that when the push rod (14) pushes the sample (12) to leave the high-temperature furnace (18), the first ring (16) blocks the first laser receiver (13) from receiving the optical signal of the first laser emitter (17), and records the current time point as the time point when the sample (12) leaves the high-temperature furnace (18); The second ring (20) is arranged on any electromagnetic Hopkinson rod; the distance of the optical path from the second ring (20) to the second laser emitter (21) is equal to the horizontal distance from the electromagnetic Hopkinson rod to the sample (12), so that when the electromagnetic Hopkinson rod and the sample (12) are stretched tight, the second ring (20) blocks the second laser receiver (22) from receiving the optical signal of the second laser emitter (21), and records the current time point as the time point when the sample (12) and the electromagnetic Hopkinson rod begin to contact.

6. The high temperature uniaxial bidirectional electromagnetic Hopkinson bar experimental system according to claim 1, characterized in that: The stress loading power supply (23) is an RLC circuit, which controls the capacitor in the RLC circuit to discharge the two electromagnetic Hopkinson rods simultaneously, so that the two electromagnetic Hopkinson rods generate two series of electromagnetic pulses with the same amplitude and change trend, and then simultaneously load stress waves with the same amplitude and change trend at both ends of the sample (12); The pulse width of the electromagnetic pulse waveform is controlled by adjusting the capacitance parameter; the amplitude of the electromagnetic pulse waveform is controlled by adjusting the discharge voltage.

7. The high temperature uniaxial bidirectional electromagnetic Hopkinson bar experimental system according to claim 3, characterized in that: A bracket (19) for supporting the loading rod (7) is arranged on the base (1).

8. The high temperature uniaxial bidirectional electromagnetic Hopkinson bar experimental system according to claim 1, characterized in that: The secondary coil (8) is a copper sheet.

9. An experimental method based on the high temperature uniaxial bidirectional electromagnetic Hopkinson bar experimental system according to any one of claims 1 to 8, characterized in that: The following steps are involved: S1, placing the sample (12) on the guide rail (11) and pushing the sample (12) into a high temperature furnace (18) for heating; S2, pushing the heated sample (12) into two coaxial electromagnetic Hopkinson rods through a sample pushing device; S3, taking the time from the time when the sample (12) starts to contact the electromagnetic Hopkinson rod to the time when the stress wave starts to load the sample (12) as the advance working time of the sample pushing device relative to the rod end pushing device, and pushing the electromagnetic Hopkinson rod mounted thereon by the rod end pushing device, so that the electromagnetic Hopkinson rod and the sample (12) are tightened; S4. The stress loading power supply (23) provides the same power to the two electromagnetic Hopkinson rods at the same time, so that the two electromagnetic Hopkinson rods simultaneously load stress waves with the same amplitude and change trend at both ends of the sample (12), thereby completing the experiment.

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