An electromagnetic loading device for generating large displacement and a test method thereof

Abstract

An electromagnetic loading device for generating large displacement and a test method thereof, wherein an active coil and a sleeve are mounted on a central rod, and the inner circumferential surface of the sleeve is slidably matched with the outer circumferential surface of the central rod. A secondary coil is mounted on the sleeve, and the secondary coil and the sleeve are interference matched. A magnetic yoke made of soft magnetic material is designed outside the active coil and the secondary coil to constrain the magnetic lines of force of the pulse magnetic field generated by the active coil and the secondary coil under pulse excitation to diverge outward, so that the magnetic lines of force are concentrated around the coil, thereby increasing the electromagnetic force without increasing the capacitance size and initial voltage of the active coil charging and discharging circuit. According to numerical simulation, when the maximum voltage and capacitance are limited, the main force-bearing components of the loading device are always in the elastic stage of the secondary coil, the loading rod and the pad during the loading process, so that the entire loading device can be reused and the test repeatability is good.

Description

Technical Field

[0001] The invention relates to the field of dynamic loading, in particular to a dynamic loading test device and a test method based on electromagnetic force to generate large displacement. Background Art

[0002] Commonly used loading methods for large displacement loading include motor and hydraulic loading, air cannon loading, explosion-driven loading, etc. However, these methods have their limitations. The motor and hydraulic driving methods are to load the specimen by driving the loading device through an electric motor or hydraulic device, but this method has limitations in loading speed and cannot achieve a large displacement of tens of millimeters within a time of microseconds and milliseconds. Air cannon loading is to push the bullet in the launch tube to move by the instantaneous release of high-pressure gas, and load by bullet impact; explosion-driven loading is to load the specimen by generating an impact load through the explosion of explosives. Although these two loading methods can achieve large displacement loading within microseconds and milliseconds, as the displacement increases, the loading time will also decrease. In addition, the loading methods such as air cannon loading and explosion-driven loading have complex devices and test procedures; affected by the loading method, the repeatability of the test results is very poor.

[0003] The commonly used electromagnetic loading method can complete the loading in a very short time, and the overall device is simple, and the test results have good repeatability. In the Chinese patent 201410171963.8, a "tensile and compressive stress wave generator and test method based on electromagnetic force" is disclosed. The device can achieve microsecond loading based on the Hopkinson bar principle, but the displacement it produces is very small, only 1 to 2 mm. In 2015, Ru Nan of Harbin Institute of Technology proposed a strong pulse electromagnetic force driving device in his degree thesis "Research on impact load driven by strong pulse electromagnetic force". Its driving principle is similar to the patent invented by Northwestern Polytechnical University. The strong electromagnetic force between the active coil and the secondary coil is used to push the punch to load the specimen. In theory, it can achieve a displacement loading of 30 mm within 1 ms; but its mechanical structure is complex, and the internal bolts, springs and other connectors are easily damaged during the loading process, which limits the service life of the device; in addition, due to the limit structure of its device, the actual maximum displacement is only 16 mm. Summary of the invention

[0004] In order to solve the problems of small displacement in a very short time, difficult to control the loading process, poor test repeatability, and complex test system of existing large displacement loading devices, the present invention proposes an electromagnetic loading device for generating large displacement and a test method thereof.

[0005] The electromagnetic loading device for generating large displacement proposed by the present invention comprises a magnetic yoke, an active coil, a secondary coil, a loading rod and a sliding sleeve. The inner end surface of the magnetic yoke is provided with an annular groove; an axial mounting rod is provided at the center of the groove. The active coil is located in the groove and is sleeved on the center rod in the magnetic yoke, and the inner end surface of the active coil is fitted with the inner surface of the groove bottom of the groove. A sliding sleeve is sleeved on the center rod, and the end surface of the sliding sleeve is fitted with the outer end surface of the active coil; the inner circumferential surface of the sliding sleeve is slidably fitted with the outer circumferential surface of the center rod. The secondary coil is sleeved on the outer circumferential surface of the sliding sleeve, and the secondary coil and the sliding sleeve are interference-fitted. The cushion block is sleeved on the center rod and bonded to the end surface of the secondary coil; there is a gap between the inner circumferential surface of the cushion block and the outer circumferential surface of the center rod. One end of the loading rod is inserted into the groove, and the end surface of the loading rod is fitted with the end surface of the cushion block; the other end of the loading rod is fitted with the specimen. The magnetic yoke, the active coil, the secondary coil, the cushion block, the loading rod and the sliding sleeve are all coaxial.

[0006] There is a gap of 5 mm between the inner circumferential surface of the active coil and the outer circumferential surface of the center rod. There is a gap of 5 mm between the outer circumferential surface of the active coil and the outer circumferential surface of the secondary coil and the inner surface of the yoke.

[0007] The yoke is composed of a cylinder body and a center rod; the center rod is located in the center of the yoke. The outer diameter of the cylinder body is 230-300 mm, and the inner diameter is 180-250 mm. The diameter of the center rod is 50 mm. There is a groove on the inner end surface of the yoke, and the outer diameter of the groove is 180-250 mm, and the inner diameter is 50 mm.

[0008] The active coil is a flat ring coil formed by winding 8 to 24 turns of a copper strip with a thickness of 2 to 5 mm and a width of 10 to 50 mm. The outer diameter of the active coil is 170 to 240 mm.

[0009] The outer diameter of the secondary coil is the same as that of the active coil, and the inner diameter is the same as that of the sleeve; the axial length of the secondary coil is 1.5 times that of the active coil.

[0010] The width of the pad ring should be at least 3 / 4 of the width of the secondary coil ring. The axial length of the pad is 1 / 2 of the secondary coil.

[0011] The wall thickness of the loading rod is 10 mm, the inner diameter is 1 / 2 of the outer diameter of the secondary coil, and the axial length of the loading rod is 7 m.

[0012] The specific process of the large displacement loading test using the electromagnetic loading device for generating large displacement proposed by the present invention is as follows:

[0013] Step 1: Coordination of the loading device and the specimen:

[0014] The end surface of one end of the loading rod in the loading device is fitted with the loading surface of the specimen.

[0015] Step 2: Paste the strain gauge and install the laser displacement sensor;

[0016] When pasting the strain gauge and installing the laser displacement sensor, take the axis of the loading rod as the symmetry axis, symmetrically paste two strain gauges with exactly the same parameters on the outer circumferential surface at 1 / 2 of the length of the loading rod, and make the measuring direction of the strain gauge the same as the axis direction of the loading rod. The resistance value of the strain gauge is 1000 ohms and the sensitivity coefficient is 2.0.

[0017] Connect the lead wire of the strain gauge to the Wheatstone bridge. Connect the output signal of the Huygens bridge to the ultra-dynamic strain gauge. Install the laser displacement sensor, and the light spot emitted by the laser displacement sensor should be located on the outer surface circumference of the end of the loading rod. The signal output lines of the ultra-dynamic strain gauge and the laser displacement sensor are both connected to the waveform storage and the computer.

[0018] Step 3: Perform a loading test:

[0019] When the loading test is carried out, the active coil of the loading device is discharged instantaneously once by an external capacitor charger to complete the loading. The capacitor bank and the electronic switch are installed in a capacitor box, and the discharge of the capacitor bank is controlled by the electronic switch.

[0020] When carrying out the loading test, the capacitance value of the external circuit is 10 to 30 millifarads, the voltage value is 3000 to 5500 volts, and the discharge time is 2 ms.

[0021] Step 4: Data processing.

[0022] The strain change on the loading rod is converted into resistance change through the strain gauge, and then converted into voltage change through the Wheatstone bridge. The voltage change is input through the conventional shielded signal line and stored in the waveform memory to obtain the stress wave signal in the loading rod. The stress wave signal σ is obtained by formula (1):

[0023]

[0024] Yoke Wherein, σ is the stress wave signal, E is the Young's modulus of the loading rod material; U0 is the supply voltage of the Wheatstone bridge; k is the strain gauge sensitivity coefficient; ΔU is the change value of the Wheatstone bridge arm voltage over time.

[0025] The displacement curve over time is directly output by the laser displacement sensor and the data is read on the computer.

[0026] At this point, the large displacement loading test using the electromagnetic loading device is completed.

[0027] The active coil in the electromagnetic loading device for generating large displacement proposed by the present invention is connected to an external capacitor discharge circuit. Considering the energy loss and the allowable values ​​of the capacitor size and capacitor voltage, the loading rod is hollow. The active coil and the secondary coil are both sleeved on the central part of the magnetic yoke and are wrapped by the outer layer of the magnetic yoke. The pad and the secondary coil, and the secondary coil and the loading rod are tightly fitted respectively.

[0028] The large displacement refers to the displacement of the end of the loading rod being more than 30 mm. The extremely short time refers to within a few milliseconds.

[0029] The capacitor discharge circuit is the same as that in the prior art.

[0030] In the present invention, when the discharge circuit is turned on, the discharge current flows through the active coil. Since the current generated by the capacitor discharge varies with time, an eddy current will be generated in the secondary coil. According to the finite element simulation, the current intensity of the eddy current varies sinusoidally with time, and the period is consistent with the current period of the active coil. The eddy current size decreases in the thickness direction of the secondary coil as the distance from the active coil increases. The direction of the eddy current in the coil is opposite to the direction of the current in the active coil, and the pulse magnetic field generated by the two is also opposite, so that a very strong electromagnetic repulsion is generated between the secondary coil and the active coil. The magnetic flux lines of the pulse magnetic field are constrained by the yoke and will not diverge outward, but are concentrated around the two coils, thereby playing a role in amplifying the electromagnetic force. And due to the effect of the yoke, the magnetic flux lines cut during the movement of the secondary coil will also increase, and cutting the magnetic flux lines will produce a stronger induced electromotive force, thereby generating a stronger induced magnetic field and a stronger electromagnetic repulsion. The electromagnetic repulsion is manifested as a compressive stress wave in the secondary coil. The compressive stress wave is transmitted from the secondary coil to the loading rod through the pad. According to the one-dimensional stress wave theory, the compressive stress wave drives the loading rod to move and generate displacement. Since the stress wave is controlled by electromagnetic means, the amplitude and pulse width of the stress wave can be controlled by adjusting the capacitance and voltage of the external circuit. For example, when the voltage is constant, adjusting the capacitance of the external capacitor discharge circuit can control the width of the stress wave; when the capacitance is constant, adjusting the initial voltage of the capacitor can control the amplitude of the stress wave.

[0031] Compared with the prior art, the present invention has the following beneficial effects:

[0032] In the present invention, a magnetic yoke made of soft magnetic material is designed outside the active coil and the secondary coil to constrain the magnetic field lines of the active coil and the secondary coil to diverge outward when the pulse magnetic field is excited by the pulse, so that the magnetic field lines are concentrated around the coil, thereby increasing the electromagnetic force without increasing the capacitance size and initial voltage of the active coil charging and discharging circuit. Figure 1As shown, by comparing the electromagnetic force-time curve 7 of the secondary coil with a yoke and the electromagnetic force-time curve 8 of the secondary coil without a yoke, it can be seen that the electromagnetic force on the secondary coil with a yoke is significantly greater than that on the secondary coil without a yoke, and the electromagnetic force after adding the yoke is significantly increased compared to when no yoke is added. Since the secondary coil is made of copper material, stress concentration will occur at the contact surface between the secondary coil and the rod under loading, and the maximum stress amplitude here exceeds the ultimate strength of copper. Therefore, before loading, a pad is installed between the secondary coil and the rod, and the pad is made of a material with a compression strength much greater than that of the secondary coil and the rod to avoid the stress on the secondary coil and the loading rod being greater than the allowable stress of their materials. As shown in Table 1, after numerical simulation, under the condition of limiting the maximum voltage and capacitance, the main force-bearing components of the loading device are always in the elastic stage of the secondary coil, the loading rod and the pad during the loading process, so the entire loading device can be reused, and the test has good repeatability.

[0033] Table 1 Simulated maximum stress of main components of loading device

[0034]

[0035]

[0036] According to the technical solution of the present invention, based on the principle of electromagnetic loading, the electromagnetic force is amplified by means of an external magnetic yoke, and the stress wave amplitude and pulse width are adjusted by controlling the total electromagnetic energy, thereby controlling the displacement amplitude and loading time, thereby achieving large displacement loading of the test piece.

[0037] The active coil of the loading device is discharged instantaneously once through an external capacitor discharge circuit, and the discharge duration depends on the capacitor discharge time, which is generally about 2ms. Since the excitation generated by the capacitor discharge changes with time, eddy currents will be generated in the secondary coil, and the instantaneous changes of the current and eddy currents will generate an induced magnetic field on the active coil and the secondary coil. The eddy current direction in the secondary coil is opposite to the current direction in the active coil, and the magnetic fields generated by the two are also opposite, so that electromagnetic repulsion is generated between the secondary coil and the active coil. The present invention constrains the magnetic flux lines of the pulsed magnetic field generated by the active coil and the secondary coil through the designed magnetic yoke, thereby increasing the electromagnetic force without increasing the capacitance and voltage of the external circuit. The electromagnetic repulsion is manifested as a compression stress wave in the secondary coil, and the compression stress wave is then transmitted to the loading rod. The loading surface of the loaded part contacts the end of the loading rod, and the generated compression stress wave propagates to the end of the loading rod to load the loaded part. The stress wave signal, acceleration value and displacement value generated by the loading device can be obtained through strain gauges, acceleration sensors and laser displacement sensors.

[0038] Figure 2It is a displacement-time curve of the end of the loading rod recorded by numerical simulation. As shown in the figure, the horizontal axis is time, the unit is milliseconds, and the vertical axis is the displacement of the end of the loading rod, the unit is millimeter. It can be seen from the figure that the displacement of the end of the loading rod can gradually increase to more than 60mm within 2ms. Compared with the actual maximum displacement of only 16mm in the prior art, the present invention can effectively increase the loading displacement and realize large displacement loading in a very short time.

[0039] The present invention also has strong versatility, and can not only carry out large displacement loading, but also install an acceleration sensor on the loaded part, and can also carry out high g value loading on the test piece. In the prior art, traditional high g value loading mostly adopts the method of driving the projectile to impact the target plate, and the high g value curve generated is subject to the impact speed of the projectile and the size of the projectile. Compared with the existing traditional high g value loading technology, the present invention loads by the principle of electromagnetic energy-mechanical energy conversion, and realizes high g value loading with simpler means. In addition, compared with the traditional high g value loading technology, the present invention has no restriction on the length of the bullet, and effectively reduces the structural size of the device. Installing a transmission rod behind the loaded part can also be used for Hopkinson rod loading. Compared with the traditional Hopkinson rod loading technology, the stress wave amplitude and pulse width generated are only related to the capacitance value and voltage value of the discharge circuit, and are not related to the length and impact speed of the bullet, and can more easily realize the Hopkinson rod loading with long pulse width and high amplitude; compared with the existing electromagnetic Hopkinson rod loading technology, when the loading rod material is consistent, it can produce a larger stress wave amplitude and pulse width. Table 2 is a comparison of the maximum amplitude and the longest pulse width of stress waves generated by the existing electromagnetic Hopkinson technology and the present invention when the loading rod material is titanium alloy.

[0040] Table 2 Comparison of maximum amplitude and pulse width of stress wave when the loading rod is made of titanium alloy

[0041] result Existing electromagnetic Hopkinson bar technology The present invention Stress wave amplitude Mpa 200 750 Stress wave pulse width ms 0.6 2 BRIEF DESCRIPTION OF THE DRAWINGS

[0042] Figure 1 The electromagnetic force-time curve of the secondary coil with and without a yoke. The horizontal axis represents time in ms, and the vertical axis represents the magnitude of the electromagnetic force in N.

[0043] Figure 2 This is the displacement-time curve of the end of the loading rod in the numerical simulation. The displacement reaches 65 mm within 2 ms. Figure 2 Middle: The horizontal axis represents time in ms; the vertical axis represents displacement in mm.

[0044] Figure 3 It is a structural schematic diagram of the present invention.

[0045] Figure 4 yes Figure 3 Right view of .

[0046] In the figure: 1. yoke; 2. active coil; 3. secondary coil; 4. pad; 5. loading rod; 6. sleeve; 7. electromagnetic force-time curve of the secondary coil with yoke; 8. electromagnetic force-time curve of the secondary coil without yoke. DETAILED DESCRIPTION

[0047] The present invention is an electromagnetic loading device for generating large displacement, and the technical solution of the present invention will be described in detail through four specific embodiments.

[0048] The present invention comprises a magnetic yoke 1, an active coil 2, a secondary coil 3, a cushion block 4, a loading rod 5 and a sliding sleeve 6. The loading devices are all rotating bodies. The inner end surface of the magnetic yoke 1 is provided with an annular groove; an axial mounting rod is provided at the center of the groove. The active coil 2 is located in the groove and is sleeved on the center rod in the magnetic yoke 1, and the inner end surface of the active coil is fitted with the inner surface of the groove bottom of the groove; there is a gap of 5 mm between the inner circumferential surface of the active coil and the outer circumferential surface of the center rod. A sliding sleeve 6 is sleeved on the center rod, and the end surface of the sliding sleeve is fitted with the outer end surface of the active coil 2; the inner circumferential surface of the sliding sleeve is slidably matched with the outer circumferential surface of the center rod. The secondary coil 3 is sleeved on the outer circumferential surface of the sliding sleeve 6, and the secondary coil and the sliding sleeve 6 are interference-fitted. The cushion block 4 is sleeved on the center rod and bonded to the end surface of the secondary coil; there is a gap between the inner circumferential surface of the cushion block and the outer circumferential surface of the center rod. One end of the loading rod 5 is inserted into the groove, and the end surface of the loading rod is fitted with the end surface of the pad; the other end of the loading rod is fitted with the test piece. There is a 5mm gap between the outer circumferential surface of the active coil and the outer circumferential surface of the secondary coil and the inner surface of the yoke.

[0049] The magnetic yoke 1, the active coil 2, the secondary coil 3, the cushion block 4, the loading rod 5 and the sliding sleeve 6 are all coaxial.

[0050] The yoke is made of Q235 steel. The yoke consists of a cylinder body and a center rod; the center rod is located in the center of the yoke. The outer diameter of the cylinder body is 230-300 mm, the inner diameter is 180-250 mm, and the axial length is 120 mm. The diameter of the center rod is 50 mm. There is a groove on the inner end surface of the yoke, the outer diameter of the groove is 180-250 mm, and the inner diameter is 50 mm.

[0051] The active coil 2 is a flat ring coil formed by winding 8 to 24 turns of a copper strip with a thickness of 2 to 5 mm and a width of 10 to 50 mm. When winding, the smaller the thickness of the copper strip, the more turns should be wound. The outer diameter of the active coil is 170 to 240 mm.

[0052] The secondary coil 3 is a copper ring. The outer diameter of the secondary coil is the same as that of the active coil, and the inner diameter is the same as that of the sleeve. The axial length of the secondary coil is 1.5 times that of the active coil.

[0053] The pad is a circular ring made of tungsten alloy. The width of the pad circular ring should be at least 3 / 4 of the width of the secondary coil circular ring. The axial length of the pad is 1 / 2 of the secondary coil.

[0054] The loading rod is a hollow cylindrical rod made of TC4 titanium alloy. The wall thickness of the loading rod is 10 mm, the inner diameter is 1 / 2 of the outer diameter of the secondary coil, and the axial length of the loading rod is 7 m.

[0055] The sliding sleeve is a resin cylinder with an outer diameter of 58 mm. Its inner diameter is consistent with the diameter of the center rod of the yoke. It must be ensured that it can slide freely on the center rod and its axial length is the same as that of the secondary coil.

[0056] Table 3 Structural parameters of various embodiments

[0057]

[0058] The present invention also proposes a method for performing a large displacement loading test using the electromagnetic loading device. The present invention will describe its technical solution in detail through four embodiments. The large displacement loading test process of each embodiment is the same, and the difference lies in the different test parameters.

[0059] The specific process of the present invention is:

[0060] Step 1: Coordination of the loading device and the specimen:

[0061] The end surface of one end of the loading rod in the loading device is fitted with the loading surface of the specimen.

[0062] Step 2: Paste the strain gauge and install the laser displacement sensor:

[0063] The strain gauge pasting method adopts the existing technology, takes the axis of the loading rod as the symmetry axis, and symmetrically pastes two strain gauges with exactly the same parameters on the outer circumferential surface at 1 / 2 of the length of the loading rod, and makes the measuring direction of the strain gauge the same as the axis direction of the loading rod. The resistance value of the strain gauge is 1000 ohms, and the sensitivity coefficient is 2.0.

[0064] Connect the lead wire of the strain gauge to the Wheatstone bridge. Connect the output signal of the Huygens bridge to the ultra-dynamic strain gauge. Install the laser displacement sensor, and the light spot emitted by the laser displacement sensor should be located on the outer surface circumference of the end of the loading rod. The signal output lines of the ultra-dynamic strain gauge and the laser displacement sensor are both connected to the waveform storage and the computer.

[0065] Step 3: Perform a loading test:

[0066] When performing a loading test, the active coil of the loading device is instantly discharged once by an external capacitor charger to complete the loading. The external capacitor charger is a capacitor bank composed of 15 electrolytic capacitors with a rated voltage of 6000 volts and a rated capacitance of 2000 microfarads in parallel. The capacitor bank and the electronic switch are installed in a capacitor box, and the discharge of the capacitor bank is controlled by the electronic switch. The composition of the external capacitor charger is the same as that disclosed in the Chinese patent No. 201410171963.8.

[0067] The capacitance value of the external circuit is 10 to 30 millifarads, the voltage value is 3000 to 5500 volts, and the discharge time is 2 ms.

[0068] Step 4: Data processing.

[0069] The strain change on the loading rod is converted into resistance change through the strain gauge, and then converted into voltage change through the Wheatstone bridge. The voltage change is input through the conventional shielded signal line and stored in the waveform memory to obtain the stress wave signal in the loading rod. The stress wave signal σ is obtained by formula (1):

[0070]

[0071] Among them, σ is the stress wave signal, E is the Young's modulus of the loading rod material, and in this embodiment, E=110Gpa; U0 is the power supply voltage of the Wheatstone bridge, which is 30 volts in this embodiment; k is the strain gauge sensitivity coefficient, which is 2.0 in this embodiment; ΔU is the change value of the Wheatstone bridge arm voltage over time.

[0072] The displacement curve over time is directly output by the laser displacement sensor and the data is read on the computer.

[0073] At this point, the large displacement loading test using the electromagnetic loading device is completed. Table 4 shows the process parameters of each embodiment. Table 5 shows the displacement obtained in each embodiment.

[0074] Table 4 Process parameters of each embodiment

[0075]

[0076]

[0077] Table 5 Displacement obtained in each embodiment

[0078]

Claims

1. An electromagnetic loading device for generating large displacement, characterized in that: It comprises a magnetic yoke, an active coil, a secondary coil, a loading rod and a sliding sleeve; the inner end surface of the magnetic yoke is provided with an annular groove; an axial mounting rod is provided at the center of the groove; the active coil is located in the groove and is sleeved on the center rod in the magnetic yoke, and the inner end surface of the active coil is fitted with the inner surface of the groove bottom of the groove; a sliding sleeve is sleeved on the center rod, and the end surface of the sliding sleeve is fitted with the outer end surface of the active coil; the inner circumferential surface of the sliding sleeve is slidably matched with the outer circumferential surface of the center rod; The secondary coil is sleeved on the outer circumferential surface of the sleeve, and the secondary coil and the sleeve are interference-fitted; the pad is sleeved on the center rod and bonded to the end surface of the secondary coil; there is a gap between the inner circumferential surface of the pad and the outer circumferential surface of the center rod; one end of the loading rod is inserted into the groove, and the end surface of the loading rod is fitted with the end surface of the pad; the other end of the loading rod is fitted with the specimen; the yoke, active coil, secondary coil, pad, loading rod and sleeve are all coaxial; The width of the cushion block is 3 / 4 of the width of the secondary coil; the axial length of the cushion block is 1 / 2 of the secondary coil; The yoke is composed of a cylinder body and a center rod; the center rod is located in the center of the yoke; the outer diameter of the cylinder body is 230-300 mm, and the inner diameter is 180-250 mm; the diameter of the center rod is 50 mm; there is a groove on the inner end surface of the yoke, the outer diameter of the groove is 180-250 mm, and the inner diameter is 50 mm; There is a gap of 5 mm between the inner circumferential surface of the active coil and the outer circumferential surface of the center rod; there is a gap of 5 mm between the outer circumferential surface of the active coil and the outer circumferential surface of the secondary coil and the inner surface of the yoke; The active coil is a flat ring coil formed by winding 8 to 24 turns of a copper strip with a thickness of 2 to 5 mm and a width of 10 to 50 mm; the outer diameter of the active coil is 170 to 240 mm; The outer diameter of the secondary coil is the same as that of the active coil, and the inner diameter is the same as that of the sleeve; the axial length of the secondary coil is 1.5 times that of the active coil.

2. The electromagnetic loading device for generating large displacement according to claim 1, characterized in that: The wall thickness of the loading rod is 10 mm, and the inner diameter is 1 / 2 of the outer diameter of the secondary coil; the axial length of the loading rod is 7 m.

3. A method for performing a large displacement loading test using the electromagnetic loading device for generating large displacement according to claim 1, characterized in that: The specific process is: Step 1: Coordination of the loading device and the specimen: Fit the end surface of one end of the loading rod in the loading device to the loading surface of the specimen; Step 2: Paste the strain gauge and install the laser displacement sensor; Step 3: Perform a loading test: When carrying out the loading test, the active coil of the loading device is discharged instantaneously once through an external capacitor charger to complete the loading; the capacitor bank and the electronic switch are installed in the capacitor box, and the discharge of the capacitor bank is controlled by the electronic switch; When carrying out the loading test, the capacitance value of the external circuit is 10 to 30 millifarads and the voltage value is 3000 to 5500 volts; The discharge time is 2ms; Step 4: Data Processing: The strain change on the loading rod is converted into resistance change through the strain gauge, and then converted into voltage change through the Wheatstone bridge. The voltage change is input through a conventional shielded signal line and stored in the waveform memory to obtain the stress wave signal in the loading rod; the stress wave signal σ is obtained by formula (1): Among them, σ is the stress wave signal, E is the Young's modulus of the loading rod material; U0 is the supply voltage of the Wheatstone bridge; k is the sensitivity coefficient of the strain gauge; ΔU is the change value of the voltage of the Wheatstone bridge arm over time; The displacement variation curve over time is directly output by the laser displacement sensor and the data is read on the computer; At this point, the large displacement loading test using the electromagnetic loading device is completed.

4. The method for performing a large displacement loading test using the electromagnetic loading device that generates a large displacement as claimed in claim 1, characterized in that: When pasting the strain gauge and installing the laser displacement sensor, take the axis of the loading rod as the symmetry axis, symmetrically paste two strain gauges with exactly the same parameters on the outer circumferential surface at 1 / 2 of the length of the loading rod, and make the measuring direction of the strain gauge the same as the axis direction of the loading rod; the resistance value of the strain gauge is 1000 ohms, and the sensitivity coefficient is 2.0; The lead wires of the strain gauge are connected to a Wheatstone bridge; the output signal of the Wheatstone bridge is connected to an ultra-dynamic strain gauge; a laser displacement sensor is installed, and the light spot emitted by the laser displacement sensor should be located on the outer surface circumference of the end of the loading rod; the signal output lines of the ultra-dynamic strain gauge and the laser displacement sensor are both connected to a waveform storage and a computer.

Images