Electromagnetic Stress Wave Generator Capable of Generating Trapezoidal Stress Waves and Experimental Method

Abstract

An electromagnetic stress wave generator capable of generating trapezoidal stress waves and an experimental method. Four groups of circuits discharge the same discharge coil in sequence, and the discharge time of each group of circuits to the same discharge coil is reasonably controlled, realizing the sequential superposition of sine-shaped stress waves to generate trapezoidal stress waves. The four groups of compressive stress waves are orderly and reasonably superposed to form trapezoidal stress waves. Since the current pulse excitation connected to the discharge coil is a sine wave that changes with time generated by capacitor discharge, eddy currents are generated in the secondary coil. The instantaneous changes of the current and eddy currents generate induced magnetic fields on the discharge coil and the secondary coil. The direction of the eddy current in the secondary coil is opposite to the direction of the current in the discharge coil, and the two generate opposite magnetic fields, generating an electromagnetic repulsive force between the secondary coil and the discharge coil. This electromagnetic repulsive force appears as a compressive stress wave in the secondary coil. The present invention realizes the loading of different stress waveforms on materials in Hopkinson bar experiments and is also applicable to other stress wave loading experiments.

Description

Technical Field

[0001] The present invention relates to the technical field of material impact dynamics experiments, and particularly to a device and method for generating a trapezoidal stress wave by an electromagnetic stress wave generator that designs multiple groups of circuits to discharge in sequence. Background Technique

[0002] In dynamic loading experiments of various types of materials or structures, trapezoidal waves with different pulse widths and amplitudes are often used to load specimens to more accurately obtain various mechanical parameters of the materials and simulate the real loading environment. Currently, for stress waveform loading corresponding to different waveforms, Lu Fangyun et al. mentioned in the book "Hopkinson Bar Experimental Techniques" that taking the Hopkinson bar experiment as an example, in the traditional Hopkinson bar experiment technique, the stress wave is generated by a compressed gas driving a bullet to impact the incident bar. The disadvantages of this method are as follows: Since the installation position of the impact bar in the air gun is not the same each time it is launched, and it is difficult to determine the corresponding relationship between the impact speed and the air pressure, it is impossible to accurately control the amplitude of the incident wave. Therefore, multiple experiments need to be tried to obtain the required strain rate. Secondly, for experiments with too large a strain rate span, due to the limitation of the air gun air pressure, the length of the impact bar needs to be changed to obtain different strain rates. The higher the strain rate, the shorter the impact bar used, and the shorter the stress wave width generated in the experiment, which limits the strain range obtained in the experiment, and the operation of replacing the bullet is cumbersome. More importantly, since there is a lower limit to the launch speed of the impact bar, some lower strain rates cannot be obtained by the traditional Hopkinson pressure bar in actual tests, such as a strain rate of 10 s-1. Due to different experimental system parameters, the standardization of the split Hopkinson pressure bar experimental technique has always been an international problem.

[0003] The electromagnetic Hopkinson bar experimental technique is a new dynamic loading technique developed by combining the traditional Hopkinson bar experimental technique with electromagnetic drive technology. Compared with the traditional Hopkinson bar, the stress wave generation method in the electromagnetic Hopkinson bar has an essential difference. In the traditional Hopkinson bar, the stress wave is generated by a bullet impacting the incident bar, while in the electromagnetic Hopkinson bar, the stress wave is generated by electromagnetic induction between the discharge coil and the secondary coil in the electromagnetic loading gun.

[0004] Due to the limitations of the structural form, even when different waveforms of current pulses are applied, the stress pulses generated by the electromagnetic loading coils in the prior art are mostly still sinusoidal stress pulses. The electromagnetic stress wave generator disclosed in the invention with the application number 201410171963.8 can generate sinusoidal stress pulses based on the principle of electromagnetic induction, but it cannot generate trapezoidal stress pulses with good repeatability and a plateau section like the traditional Hopkinson bar system. Although the superposition method is used in the invention with the application number 201510051071.9 and the invention name "Main coil of electromagnetic stress wave generator and charging / discharging method", its effect is limited to changing the pulse width and amplitude of the sinusoidal stress pulse and cannot generate trapezoidal stress waves. In the article titled "A versatile split Hopkinson pressure bar using electromagnetic loading" published by Nie and Suo et al. in the International Journal of Impact Engineering in 2018, a shaping method was proposed to convert the sinusoidal stress wave generated by the electromagnetic Hopkinson bar into an approximate square wave using a shaping piece. However, this method is complex to operate. Stress waves with different pulse widths and amplitudes require shaping pieces with different thicknesses and sizes. And because the good plasticity of the shaping piece material is utilized to achieve the shaping effect, the rising and falling edges of the shaped stress wave are both very long, resulting in a narrow pulse width of the stress wave plateau section and cannot be applied to various loading situations.

[0005] An electromagnetic loading coil disclosed in the invention with the application number 202110536839.7, which can generate a square wave with a high amplitude and a long pulse width, slows down the attenuation degree of the electromagnetic force through the magnetic concentration and magnetic saturation effects of the soft magnetic material, making the generated square stress wave have a longer plateau section. However, the amplitude of its stress wave is also limited by the magnetic saturation effect. Although the electromagnetic loading coil disclosed in the invention with the application number 202110536462.5 can theoretically generate any stress waveform, the generated stress waveform depends on the shape of the current applied in the main coil. Currently, it is difficult to find a pulse current generator on the market that can generate a pulse current with both the pulse width and amplitude meeting the experimental requirements.

[0006] A method for generating trapezoidal stress waves disclosed in the invention with the application number 202210525286.X uses four groups of circuits to discharge four groups of coils in sequence, and superimposes four groups of sinusoidal stress waves into trapezoidal stress waves through the superposition principle. However, the electromagnetic loading gun designed by this method has four groups of coils, with a complex structure. Moreover, when one of the four groups of circuits discharges the coil, it will be affected by other groups of coils, resulting in a decrease in the amplitude of the generated stress wave. Summary of the Invention

[0007] To overcome the deficiencies in the existing electromagnetic Hopkinson bar experimental technology, such as the inability to generate trapezoidal stress waves, insufficient stress wave amplitude, and randomness in stress wave shaping, the present invention proposes an electromagnetic stress wave generator and experimental method capable of generating trapezoidal stress waves.

[0008] The electromagnetic stress wave generator capable of generating trapezoidal stress waves proposed by the present invention includes a charging / discharging circuit, an electromagnetic loading gun, a secondary coil, and an incident bar. The inner end face of the electromagnetic loading gun has a secondary coil, and the end face of the cantilever end of the incident bar is attached to the surface of the secondary coil. The four circuits in the charging / discharging circuit are connected in parallel and then connected to the two terminals of the discharging coil in the electromagnetic loading gun. A strain gauge is pasted on the outer surface of the incident bar; the strain gauge is connected to a data collector.

[0009] The electromagnetic loading gun includes an electromagnetic loading gun housing, a discharging coil, an insulating layer, and two discharging coil terminals. The discharging coil is wound in a spiral manner with a copper strip inside the housing; the total number of turns of the discharging coil is 10 turns. An insulating layer is filled between each layer of the wound discharging coils, and the thickness of the insulating layer between the inner surface of the electromagnetic loading gun and the outermost discharging coil is 2 mm, and the thickness of the insulating layer between each turn of the discharging coils is 1 mm. The two discharging coil terminals extend out from the bottom plate of the electromagnetic loading gun and are connected to the four parallel discharging circuits. The terminal of the discharging coil is connected in series with a discharging coil switch.

[0010] The secondary coil is connected to the electromagnetic loading gun through a secondary coil connection bolt, and the secondary coil is coaxial with the center of the electromagnetic loading gun.

[0011] The outer diameter of the discharging coil is 44.7 mm, and the inner diameter is 8 mm. The cross-section of the discharging coil wire is rectangular, with a length of 6 mm and a width of 2 mm, and the radial spacing of the coils is 1 mm.

[0012] The charging / discharging circuit includes four circuits and a discharging circuit. Each circuit has a discharging circuit and a charging circuit; the four circuits are the first circuit 14, the second circuit 15, the third circuit 16, and the fourth circuit 17; the four circuits are all the same. The discharging circuit includes a discharging resistance switch and a discharging resistance.

[0013] Each of the four groups of circuits includes a capacitor charger, a capacitor charging switch, a capacitor, a current-limiting resistor, a diode, and a discharge switch. The capacitor chargers in the four groups of circuits are each connected to any terminal of the capacitor charging switch through a wire. The other terminal of the capacitor charging switch is connected to the negative terminal of the capacitor. The other output terminal of the capacitor charger is connected to any terminal of the current-limiting resistor. The other terminal of the current-limiting resistor is connected to the positive terminal of the capacitor. The positive terminals of the capacitors in the four groups of circuits are each connected to the current inflow end of the diode through a wire. The negative terminals of the capacitors are each connected to any one of the terminals of the discharge switch.

[0014] Connect the other terminals of the discharge switches in the four groups of circuits together and connect them to the negative terminal of the discharge coil. Connect the current outflow ends of the diodes in each group of circuits together and connect them to the positive terminal of the discharge coil switch. The negative terminal of the discharge coil switch is connected to the positive terminal of the discharge coil.

[0015] Connect the negative terminal of the discharge resistance switch to the negative terminal of the discharge coil switch. Connect the positive terminal of the discharge resistance switch to any terminal of the discharge resistance. The other terminal of the discharge resistance is connected to the negative terminal of the discharge coil.

[0016] The experimental process of the electromagnetic stress wave generator proposed by the present invention is as follows:

[0017] Step 1, connect the circuit;

[0018] Step 2, arrange the equipment:

[0019] Coaxially install the electromagnetic loading gun, the secondary coil, and the incident rod on the experimental bench in sequence. The centers of the electromagnetic loading gun, the secondary coil, and the incident rod are coaxial, and the secondary coil and the incident rod can only move freely in the axial direction.

[0020] Step 3, paste strain gauges:

[0021] Symmetrically paste two identical strain gauges on the circumferential surface at the midpoint of the length of the incident rod, and connect each strain gauge to a Wheatstone bridge respectively.

[0022] Step 4, load:

[0023] Close the capacitor charging switch, and charge the capacitors to 600V respectively through the capacitor chargers in each group of circuits. The discharge switches of the four groups of discharge circuits enter the waiting-to-be-triggered state.

[0024] Set the digital delay generator 24 to control the delay times of the discharge switches of the four groups of discharge circuits to be 0ms, 0.13ms, 0.26ms, and 0.39ms respectively.

[0025] The trigger delay generator closes the discharge switch of the first group of circuits to discharge the discharge coil; the discharge switch of the second group of circuits closes 0.13 ms after the discharge switch of the first group of circuits closes to discharge the discharge coil; the discharge switch of the third group of circuits closes 0.26 ms after the discharge switch of the first group of circuits closes to discharge the discharge coil; the discharge switch of the fourth group of circuits closes 0.39 ms after the discharge switch of the first group of circuits closes to discharge the discharge coil. The discharge switches of the four groups of discharge circuits all disconnect 0.2 ms after closing to reduce the influence between the discharge circuits of each group. After the discharge coil is energized, it will generate an electromagnetic repulsive force on the secondary coil, and the electromagnetic repulsive force acts on the incident rod to generate a trapezoidal stress wave.

[0026] In the present invention, an external excitation current is connected to the discharge coil, and the excitation current flows through the discharge coil. Since the excitation current is generated by the discharge of a capacitor and changes with time, an induced magnetic field will be generated in the discharge coil. The changing induced magnetic field generates an eddy current in the secondary coil. The direction of the eddy current in the secondary coil is opposite to the direction of the current in the discharge coil, and the pulse magnetic fields generated by the two are also opposite, so that a very strong electromagnetic repulsive force is generated between the secondary coil and the discharge coil. The electromagnetic repulsive force appears as a stress wave in the secondary coil. By controlling the superposition of several stress waves, a trapezoidal stress wave is obtained.

[0027] Compared with the prior art, the beneficial effects achieved by the present invention are:

[0028] In the present invention, four groups of circuits are used to discharge the same discharge coil in sequence, and the on-off times of the discharge switches of different discharge circuits are controlled by a DG645 digital delay generator. Although the control of the coil group discharge by different circuits has been used in the inventions with application numbers 201510051071.9 and 202210525286.X, in the invention with application number 201510051071.9, its effect is limited to changing the pulse width and amplitude of the sine-type stress pulse and cannot generate a trapezoidal stress wave. However, for ductile materials, such as metal materials, in order to achieve constant strain rate loading, experimenters need trapezoidal stress waves more. In addition, in the inventions with application numbers 201510051071.9 and 202210525286.X, multiple groups of circuits are used to discharge multiple groups of coils. When one group of circuits discharges one group of coils, it will be affected by other groups of coils. Mutual inductance is generated between the discharge coils, reducing the amplitude of the stress wave.

[0029] The key and difficulty of the present invention lie in reasonably designing the discharge circuit to reasonably control the sequential discharge of each group of circuits to the same discharge coil in terms of time, thereby realizing the sequential superposition of sine-shaped stress waves to generate a trapezoidal stress wave. Since the current pulse excitation connected to the discharge coil is a sine wave varying with time generated by capacitor discharge, eddy currents will be generated in the secondary coil. The instantaneous changes in the current and eddy currents will generate induced magnetic fields on the discharge coil and the secondary coil. The direction of the eddy current in the secondary coil is opposite to the direction of the current in the discharge coil, and the magnetic fields generated by the two are also opposite, thereby generating an electromagnetic repulsive force between the secondary coil and the discharge coil. The electromagnetic repulsive force is manifested as a compressive stress wave in the secondary coil. The present invention controls the sequential discharge of four circuits controlled by a DG645 digital delay generator. According to the superposition principle of stress waves, the four groups of compressive stress waves generated in the secondary coil are orderly and reasonably superposed together to form a trapezoidal stress wave.

[0030] Figure 5 The time interval between the discharges of each group of circuits is 0.13 ms, the charging voltage of the capacitor is 600 v. The waveform diagram of the stress wave generated in the incident bar after the sequential discharge of the four groups of circuits is shown. The abscissa is time, with the unit of ms, and the ordinate is stress, with the unit of Mpa. It can be seen from the figure that a trapezoidal stress wave that can be used for dynamic loading tests is obtained by this method. Due to the above advantages, the present invention can achieve the loading of different stress waveforms on materials in Hopkinson bar experiments and can also be applied to other experiments of stress wave loading. Description of the Drawings

[0031] Figure 1 It is a schematic diagram of the power supply and the charge / discharge circuit.

[0032] Figure 2 It is the top view and front view of the electromagnetic loading gun.

[0033] Figure 3 It is a schematic diagram of the structure of the electromagnetic loading gun.

[0034] Figure 4 It is a schematic diagram of the structure of the present invention.

[0035] Figure 5 It is the stress wave signal collected at the position where the incident bar is 1 m away from the electromagnetic loading gun in the embodiment.

[0036] In the figure: 1. Power supply; 2. Capacitor charger; 3. Capacitor; 4. Diode; 5. Bleeder resistor; 6. Discharge coil; 7. Current-limiting resistor; 8. Secondary coil; 9. Insulating layer; 10. Electromagnetic loading gun housing; 11. Incident rod; 12. Discharge circuit; 13. Discharge coil terminal; 14. First group of circuits; 15. Second group of circuits; 16. Third group of circuits; 17. Fourth group of circuits; 18. Capacitor charging switch; 19. Discharge switch; 20. Discharge coil switch; 21. Bleeder resistor switch; 22. Strain gauge; 23. Data collector; 24. Digital delay generator. Specific implementation mode

[0037] This embodiment is an electromagnetic stress wave generator and experimental method capable of generating trapezoidal stress waves, and its technical solution will be specifically described through the following embodiments.

[0038] The electromagnetic stress wave generator proposed in this embodiment includes a charge / discharge circuit 12, an electromagnetic loading gun, a discharge coil 6, a secondary coil 8, and an incident rod 11, where the secondary coil 8 and the incident rod 11 both adopt existing technologies.

[0039] The charge / discharge circuit 12 includes four groups of circuits and a group of bleeder circuits. Each group of circuits has a discharge circuit and a charging circuit respectively; the four groups of circuits are the first group of circuits 14, the second group of circuits 15, the third group of circuits 16, and the fourth group of circuits 17 respectively; the bleeder circuit includes a bleeder resistor switch 21 and a bleeder resistor 5.

[0040] In the electromagnetic stress wave generator, the inner end face of the electromagnetic loading gun housing 10 has a secondary coil 8, and the end face of the cantilever end of the incident rod 11 is attached to the surface of the secondary coil. The four groups of circuits in the charge / discharge circuit 12 are connected in parallel and then connected to the two terminals of the discharge coil in the electromagnetic loading gun. A strain gauge 22 is pasted on the outer surface of the incident rod; the strain gauge is connected to a data collector 23.

[0041] The secondary coil is made of copper sheet, with a radius of 45 mm and a thickness of 8 mm.

[0042] The incident rod has a radius of 7 mm and is made of TC4 titanium alloy.

[0043] The electromagnetic loading gun includes an electromagnetic loading gun housing 10, a discharge coil 6, an insulating layer 9, and two discharge coil terminals 13. The discharge coil therein is wound in a spiral manner with a copper strip inside the housing; the total number of turns of the discharge coil is 10. An insulating layer 9 is filled between each layer of the wound discharge coils, and the thickness of the insulating layer between the inner surface of the electromagnetic loading gun and the outermost discharge coil is 2 mm, and the thickness of the insulating layer between each turn of the discharge coils is 1 mm. The two discharge coil terminals extend out from 2 holes on the electromagnetic loading gun bottom plate and are connected to four groups of discharge circuits connected in parallel. The terminal 13 of the discharge coil 6 is connected in series with a discharge coil switch 20.

[0044] There is a through hole with a diameter of 6 mm at the center of the electromagnetic loading gun for placing a secondary coil connection bolt to support the secondary coil and make the secondary coil coaxial with the center of the electromagnetic loading gun.

[0045] The outer diameter of the discharge coil is 44.7 mm, and the inner diameter is 8 mm. The cross-section of the discharge coil wire is rectangular, with a length of 6 mm and a width of 2 mm, and the radial spacing between the coils is 1 mm.

[0046] The connection method of each component in the charge / discharge circuit 12 is as follows:

[0047] The first group of circuits 14 includes a capacitor charger 2, a capacitor charging switch 18, a capacitor 3, a current-limiting resistor 7, a diode 4, and a discharge switch 19. Among them: One terminal of the capacitor charger 2 is connected to any terminal of the capacitor charging switch 18 through a wire, the other terminal of the capacitor charging switch 18 is connected to the negative terminal of the capacitor 3, the other output terminal of the capacitor charger 2 is connected to any terminal of the current-limiting resistor 7, and the other terminal of the current-limiting resistor 7 is connected to the positive terminal of the capacitor 3. The positive terminal of the capacitor 3 in the first group of circuits 14 is connected to the current inflow end of the diode 4 through a wire, and the negative terminal of the capacitor 3 is connected to any one of the terminals of the discharge switch 19.

[0048] The composition and connection of the second group of circuits 15, the third group of circuits 16, and the fourth group of circuits 17 are the same as those of the first group of circuits 14. According to the connection method of the first group of circuits, the connection of the remaining groups of circuits is completed in turn. Each group of circuits is a discharge circuit.

[0049] Connect the other terminals of the discharge switches in each group of circuits together and connect them to the negative terminal of the discharge coil 6.

[0050] Connect the current outflow ends of the diodes in each group of circuits together and connect them to the positive terminal of the discharge coil switch 20; the negative terminal of the discharge coil switch 20 is connected to the positive terminal of the discharge coil 6.

[0051] Connect the negative terminal of the discharge resistance switch 21 to the negative terminal of the discharge coil switch 20, connect the positive terminal of the discharge resistance switch 21 to any terminal of the discharge resistance 5, and connect the other terminal of the discharge resistance 5 to the negative terminal of the discharge coil 6.

[0052] The digital delay generator 24 controls the delay time for the four discharge switches in the four groups of circuits to turn on through signal lines.

[0053] The resistance values of the current-limiting resistance and the discharge resistance are both 400Ω.

[0054] The specification of the capacitor is 2mf.

[0055] The power supply is a three-phase AC power supply of 220V. The capacitor charger adopts the power supply part of the existing electromagnetic riveting equipment.

[0056] The closing and opening times of the switches in each group of circuits are controlled by the digital delay generator. The channel delay times from the discharge switch of the first group of circuits to the discharge switch of the fourth group of circuits are set to be 0ms, 0.13ms, 0.26ms, and 0.39ms respectively.

[0057] After the delay generator is triggered, the switch of the first group of circuits closes to discharge the discharge coil. 0.13ms after the switch of the first group of circuits closes, the switch of the second group of circuits closes to discharge the discharge coil. 0.26ms after the switch of the first group of circuits closes, the switch of the third group of circuits closes to discharge the discharge coil. 0.39ms after the switch of the first group of circuits closes, the switch of the fourth group of circuits closes to discharge the discharge coil. The switches of the four groups of circuits all close for 0.2ms and then open to reduce the influence between the discharge circuits of each group.

[0058] The digital delay generator adopts the DG645 type.

[0059] The specific process of generating a trapezoidal stress wave in this embodiment is as follows:

[0060] Step 1, connect the circuit:

[0061] According to Figure 1 , connect the components in the circuit in sequence.

[0062] Step 2, arrange the equipment:

[0063] The electromagnetic loading gun, secondary coil and incident rod are coaxially installed on the experimental bench in sequence. After the secondary coil is connected to the secondary coil connection bolt through the central hole, the secondary coil connection bolt is inserted into the central hole of the electromagnetic loading gun, so that the end face of the secondary coil is closely attached to the electromagnetic loading gun, and the other end face of the secondary coil is closely attached to the incident rod; the centers of the electromagnetic loading gun, secondary coil and incident rod are coaxial, and the secondary coil and the incident rod can only move freely in the axial direction.

[0064] Step 3, paste strain gauges:

[0065] The method of pasting strain gauges adopts the existing technology, that is, on the circumference at half of the length of the incident rod, with the axis of the incident rod as the symmetry axis, two identical strain gauges are symmetrically pasted on the surface of the incident rod, strain gauge leads are welded on the leads of the strain gauges, and the strain gauge leads are connected to the Wheatstone bridge in the data acquisition system.

[0066] Step 4, loading:

[0067] Close the capacitor charging switch 18, and charge the capacitors of the four groups of circuits to 600V through the capacitor charger with a 220V three-phase AC power supply; the discharge switches 19 of the four groups of discharge circuits enter the waiting trigger state.

[0068] Set the DG645 digital delay generator 24 to control the delay times of the discharge switches of the four groups of discharge circuits to be 0ms, 0.13ms, 0.26ms and 0.39ms respectively.

[0069] Trigger the delay generator. After the delay generator is triggered, the discharge switch of the first group of circuits closes to discharge the discharge coil; 0.13ms after the discharge switch of the first group of circuits closes, the discharge switch of the second group of circuits closes to discharge the discharge coil; 0.26ms after the discharge switch of the first group of circuits closes, the discharge switch of the third group of circuits closes to discharge the discharge coil; 0.39ms after the discharge switch of the first group of circuits closes, the discharge switch of the fourth group of circuits closes to discharge the discharge coil. The discharge switches of the fourth group of discharge circuits are all disconnected 0.2ms after closing to reduce the influence between the discharge circuits of each group.

[0070] The electromagnetic repulsive force generated by the discharge coil on the secondary coil acts on the incident rod to generate a trapezoidal stress wave.

[0071] A pulsed current flows through the discharge coil to generate a high-intensity pulsed magnetic field. The secondary coil is in close contact with the discharge coil, and electromagnetic induction occurs to generate an extremely strong eddy current. The eddy current in the secondary coil interacts with the magnetic field generated by the discharge coil. The particles on the end face of the secondary coil close to the discharge coil will be affected by the Lorentz force, and a magnetic force is formed in the secondary coil. The magnetic force is manifested as a compressive stress pulse in the secondary coil. After the stress pulse is transmitted to the incident rod in close contact with the secondary coil, it propagates in the incident rod in the form of an elastic wave to conduct a dynamic loading test on the specimen. The strain gauge 22 pasted on the incident rod converts the strain signal when the stress wave passes by into a voltage signal, which is recorded by the data acquisition device 23.

[0072] After the four groups of discharge circuits discharge with a time delay of 0 ms, 0.13 ms, 0.26 ms, and 0.39 ms respectively, a trapezoidal stress wave as shown in Figure 5 is generated in the incident rod.

[0073] In this embodiment, by changing the capacitance value, the charging voltage of the capacitor, the shape, the number of turns of the discharge coil, and the delay time of the digital delay pulse generator, trapezoidal stress waves with different amplitudes and pulse widths can be generated. Increasing / decreasing the charging voltage of the capacitor can increase / decrease the amplitude of the stress wave; increasing the number of coil groups axially / radially can also increase the amplitude; increasing / decreasing the capacitance value of the capacitor can increase / decrease the pulse width of the stress wave. The incident rod with different sizes and materials can also be replaced according to needs.

Claims

1. An electromagnetic stress wave generator capable of generating a trapezoidal stress wave, characterized in that, It includes a charge / discharge circuit (12), an electromagnetic loading gun (10), a discharge coil (6), a secondary coil (8), and an incident rod (11). The inner end face of the electromagnetic loading gun has a secondary coil (8), and the end face of the cantilever end of the incident rod is in contact with the surface of the secondary coil. The four circuits in the charge / discharge circuit (12) are connected in parallel and then connected to the two terminals of the discharge coil in the electromagnetic loading gun. A strain gauge (22) is pasted on the outer surface of the incident rod, and the strain gauge is connected to a data collector (23). The charge / discharge circuit (12) includes four circuits and a current discharge circuit. Each circuit has a discharge circuit and a charge circuit. The four circuits are the first circuit (14), the second circuit (15), the third circuit (16), and the fourth circuit (17). The four circuits are all discharge circuits. The current discharge circuit includes a current discharge resistor switch (21) and a current discharge resistor (5). Connect the other terminals of the discharge switches in the four circuits together and connect them to the negative terminal of the discharge coil (6). Connect the current outflow ends of the diodes in each circuit together and connect them to the positive terminal of the discharge coil switch (20). The negative terminal of the discharge coil switch is connected to the positive terminal of the discharge coil. Connect the negative terminal of the current discharge resistor switch (21) to the negative terminal of the discharge coil switch, connect the positive terminal of the current discharge resistor switch to any terminal of the current discharge resistor (5), and connect the other terminal of the current discharge resistor to the negative terminal of the discharge coil (6). The electromagnetic loading gun (10) includes a housing, a discharge coil (6), an insulating layer (9), and two discharge coil terminals (13). The discharge coil is wound in a spiral manner with a copper strip inside the housing. The total number of turns of the discharge coil is 10. Insulating layers are filled between the wound layers of the discharge coil, and the thickness of the insulating layer between the inner surface of the electromagnetic loading gun and the outermost layer of the discharge coil is 2 mm, and the thickness of the insulating layer between each turn of the discharge coil is 1 mm. The two discharge coil terminals extend out from 2 holes on the bottom plate of the electromagnetic loading gun and are connected to the four parallel discharge circuits. The terminal (13) of the discharge coil (6) is connected in series with the discharge coil switch (20).

2. The electromagnetic stress wave generator capable of generating trapezoidal stress waves as described in claim 1, characterized in that, The secondary coil is connected to the electromagnetic loading gun through a secondary coil connection bolt, and the secondary coil is coaxial with the center of the electromagnetic loading gun.

3. The electromagnetic stress wave generator capable of generating trapezoidal stress waves as described in claim 1, wherein The outer diameter of the discharge coil is 44.7 mm, and the inner diameter is 8 mm. The cross-section of the discharge coil wire is rectangular, with a length of 6 mm and a width of 2 mm, and the radial spacing of the coil is 1 mm.

4. The electromagnetic stress wave generator capable of generating a trapezoidal stress wave according to claim 1, characterized in that, Each of the four sets of circuits includes a capacitor charger (2), a capacitor charging switch (18), a capacitor (3), a current-limiting resistor (7), a diode (4), and a discharge switch (19); among them: the capacitor chargers in the four sets of circuits are all connected to any terminal of the capacitor charging switch through wires, the other terminal of the capacitor charging switch is connected to the negative terminal of the capacitor, the other output terminal of the capacitor charger is connected to any terminal of the current-limiting resistor, and the other terminal of the current-limiting resistor is connected to the positive terminal of the capacitor; the positive terminals of the capacitors in the four sets of circuits are all connected to the current inflow end of the diode through wires, and the negative terminals of the capacitors are all connected to any one of the terminals of the discharge switch.

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