CN112881206A - Electromagnetic loading device capable of generating large displacement and test method thereof - Google Patents
Electromagnetic loading device capable of generating large displacement and test method thereof Download PDFInfo
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- 238000011068 loading method Methods 0.000 title claims abstract description 171
- 238000010998 test method Methods 0.000 title abstract description 7
- 238000011549 displacement method Methods 0.000 title description 2
- 238000006073 displacement reaction Methods 0.000 claims abstract description 73
- 238000012360 testing method Methods 0.000 claims abstract description 37
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- RYGMFSIKBFXOCR-UHFFFAOYSA-N Copper Chemical compound [Cu] RYGMFSIKBFXOCR-UHFFFAOYSA-N 0.000 claims description 7
- 239000010949 copper Substances 0.000 claims description 6
- 229910052802 copper Inorganic materials 0.000 claims description 6
- 230000035945 sensitivity Effects 0.000 claims description 6
- 238000004804 winding Methods 0.000 claims description 4
- 238000004088 simulation Methods 0.000 abstract description 5
- 238000007599 discharging Methods 0.000 abstract description 3
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- 238000007906 compression Methods 0.000 description 6
- 238000005516 engineering process Methods 0.000 description 6
- 230000006698 induction Effects 0.000 description 5
- 238000004880 explosion Methods 0.000 description 4
- 229910001069 Ti alloy Inorganic materials 0.000 description 3
- 230000001133 acceleration Effects 0.000 description 3
- 229910000831 Steel Inorganic materials 0.000 description 1
- 229910001080 W alloy Inorganic materials 0.000 description 1
- 230000009286 beneficial effect Effects 0.000 description 1
- 238000006243 chemical reaction Methods 0.000 description 1
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- 239000010959 steel Substances 0.000 description 1
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N3/00—Investigating strength properties of solid materials by application of mechanical stress
- G01N3/30—Investigating strength properties of solid materials by application of mechanical stress by applying a single impulsive force, e.g. by falling weight
- G01N3/317—Investigating strength properties of solid materials by application of mechanical stress by applying a single impulsive force, e.g. by falling weight generated by electromagnetic means
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N3/00—Investigating strength properties of solid materials by application of mechanical stress
- G01N3/02—Details
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N3/00—Investigating strength properties of solid materials by application of mechanical stress
- G01N3/32—Investigating strength properties of solid materials by application of mechanical stress by applying repeated or pulsating forces
- G01N3/38—Investigating strength properties of solid materials by application of mechanical stress by applying repeated or pulsating forces generated by electromagnetic means
Abstract
An electromagnetic loading device generating large displacement and a test method thereof.A driving coil and a sliding sleeve are sleeved on a central rod, and the inner circumferential surface of the sliding sleeve is in sliding fit with the outer circumferential surface of the central rod. The secondary coil is sleeved on the sliding sleeve, and the interference fit between the secondary coil and the sliding sleeve is realized. Magnetic yokes made of soft magnetic materials are designed outside the driving coil and the secondary coil, magnetic lines of force of a pulse magnetic field generated by the driving coil and the secondary coil under pulse excitation are restrained to be outwards dispersed, and the magnetic lines of force are concentrated around the coils, so that the electromagnetic force is increased under the condition that the capacitance size and the initial capacitance voltage of a charging and discharging circuit of the driving coil are not increased. Through numerical simulation, under the condition that the maximum voltage and the maximum capacitance are limited, the main stressed part of the loading device is always in the elastic stage of the secondary coil, the loading rod and the cushion block in the loading process, so that the whole loading device can be repeatedly used, and the test repeatability is good.
Description
Technical Field
The invention relates to the field of dynamic loading, in particular to a dynamic loading test device and a test method for generating large displacement based on electromagnetic force.
Background
The common loading modes for generating large displacement loading mainly comprise motor and hydraulic loading, air cannon loading, explosion drive loading and the like. However, these methods have limitations, and the motor and hydraulic driving method is to drive the loading device to load the test piece through the motor or the hydraulic device, but this method has limitations in the loading speed, and cannot realize a large displacement loading of several tens of millimeters in a microsecond millisecond time. The loading of the air cannon is realized by instantly releasing high-pressure gas to push a bullet in the launching tube to move and utilizing the impact of the bullet to load; the explosion driving loading is to load the test piece by the impact load generated by the explosion of the explosive. Although the two loading modes can realize large displacement loading within microsecond millisecond time, the loading time is reduced along with the increase of the displacement. In addition, the loading modes of air cannon loading and explosion drive loading are complex in device and test program; the repeatability of the test results is poor under the influence of the loading mode.
The common electromagnetic loading mode can complete loading in a very short time, the whole device is simple, and the repeatability of the test result is good. The chinese patent 201410171963.8 discloses an electromagnetic force-based tensile and compressive stress wave generator and a test method, which can realize microsecond loading based on the hopkinson rod principle, but the displacement generated by the device is very small, and is only 1-2 mm. The Ru nan at the university of Harbin in 2015 provides a strong pulse electromagnetic force driving device in a academic paper 'impact load research driven by strong pulse electromagnetic force', the driving principle of the strong pulse electromagnetic force driving device is similar to that of the patent invented by the northwest industrial university, a punch is pushed to load a test piece by using strong electromagnetic force between a driving coil and a secondary coil, and theoretically, displacement loading of 30mm within 1ms can be realized; but the mechanical structure is complex, and the connecting pieces such as internal bolts, springs and the like are easy to damage in the loading process, so that the service life of the device is limited; in addition, the actual maximum displacement is only 16mm, limited by the limit structure of the device.
Disclosure of Invention
The invention provides an electromagnetic loading device generating large displacement and a test method thereof, aiming at solving the problems that the existing large displacement loading device has small displacement in a very short time, the loading process is difficult to control, the test repeatability is poor, the test system is complex and the like.
The electromagnetic loading device for generating large displacement comprises a magnetic yoke, a driving 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 bar is located in the center of the recess. The driving coil is positioned in the groove and sleeved on the central rod in the magnetic yoke, and the inner end surface of the driving coil is attached to the inner surface of the bottom of the groove. A sliding sleeve is sleeved on the central rod, and the end face of the sliding sleeve is attached to the outer end face of the driving coil; the inner circumferential surface of the sliding sleeve is in sliding fit with the outer circumferential surface of the central rod. The secondary coil is sleeved on the outer circumferential surface of the sliding sleeve, and the interference fit between the secondary coil and the sliding sleeve is realized. The cushion block is sleeved on the central rod and is bonded to the end face of the secondary coil; a gap is provided between the inner circumferential surface of the spacer and the outer circumferential surface of the center rod. One end of the loading rod is arranged in the groove, and the end face of the loading rod is attached to the end face of the cushion block; the other end of the loading rod is attached to the test piece. The magnet yoke, the driving coil, the secondary coil, the cushion block, the loading rod and the sliding sleeve are coaxial.
A gap of 5mm is provided between the inner circumferential surface of the active coil and the outer circumferential surface of the center rod. And 5mm gaps are reserved between the outer circumferential surface of the driving coil and the outer circumferential surface of the secondary coil and the inner surface of the magnetic yoke.
The magnetic yoke consists of a cylinder body and a central rod; the central rod is positioned in the inner center of the magnetic yoke. The outer diameter of the cylinder body is 230-300 mm, and the inner diameter is 180-250 mm. The diameter of the central rod is 50 mm. A groove is formed in the inner end face of the magnetic yoke, the outer diameter of the groove ranges from 180 mm to 250mm, and the inner diameter of the groove is 50 mm.
The driving coil is a flat ring coil formed by winding 8-24 turns of a copper strip with the thickness of 2-5 mm and the width of 10-50 mm. The outer diameter of the active coil is 170-240 mm.
The outer diameter of the secondary coil is the same as that of the driving coil, and the inner diameter of the secondary coil is the same as that of the sliding sleeve; the axial length of the secondary coil is 1.5 times that of the active coil.
The spacer ring width should be at least 3/4 times the secondary coil ring width. The axial length of the spacer is 1/2 of the secondary coil.
The wall thickness of the loading rod is 10mm, 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.
The specific process of the large displacement loading test by using the electromagnetic loading device generating large displacement provided by the invention is as follows:
step 1: matching of the loading device and the test piece:
and attaching the end face of one end of a loading rod in the loading device to the loading surface of the test piece.
Step 2: pasting a strain gauge and installing a laser displacement sensor;
when the strain gauge is adhered and the laser displacement sensor is installed, two strain gauges with the same parameters are symmetrically adhered to the outer circumferential surface of the position 1/2 of the loading rod by taking the axis of the loading rod as a symmetry axis, and the measuring direction of the strain gauge is 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.
And connecting the lead of the strain gauge into a Wheatstone bridge. And the output signal of the Wheatstone bridge is connected to the ultra-dynamic strain gauge. And installing a laser displacement sensor, wherein light spots emitted by the laser displacement sensor are positioned on the circumference of the outer surface of the tail end of the loading rod. The signal output lines of the ultra-dynamic strain gauge and the laser displacement sensor are connected into a waveform memory and a computer.
And step 3: carrying out a loading test:
when a loading test is carried out, the driving coil of the loading device is instantaneously discharged once through the external capacitor charger, and loading is completed. And the capacitor bank and the electronic switch are arranged in the capacitor box, and the discharge of the capacitor bank is controlled through the electronic switch.
When a loading test is carried out, the capacitance value of the external circuit is 10-30 millifarads, and the voltage value is 3000-5500 volts; the discharge time was 2 ms.
And 4, step 4: and (6) 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, and the voltage change is input through a conventional shielding signal wire and stored in the waveform memory to obtain a stress wave signal in the loading rod. The stress wave signal sigma is obtained through a formula (1):
wherein, the sigma is a stress wave signal, and E is the Young modulus of the material of the loading rod; u shape0A supply voltage for the wheatstone bridge; k is the sensitivity coefficient of the strain gauge; Δ U is a change value of the wheatstone bridge arm voltage with time.
The change curve of the displacement along with the time is directly output through a laser displacement sensor, and data is read on a computer.
And completing the large displacement loading test by using the electromagnetic loading device.
The driving coil in the electromagnetic loading device for generating large displacement is connected with an external capacitance discharge circuit. The loading rod is hollow in consideration of energy loss, capacitance and allowable value of capacitance voltage. The driving coil and the secondary coil are sleeved on the magnetic yoke at the central part and are wrapped by the outer layer part of the magnetic yoke. The cushion block and the secondary coil, and the secondary coil and the loading rod are tightly attached to each other respectively.
The large displacement means that the displacement of the tail end of the loading rod is more than 30 mm. Said very short time is within a few milliseconds.
The capacitor discharge circuit is the same as the prior art.
In the invention, after the discharge circuit is conducted, the discharge current flows through the active coil, and the current generated by the capacitor discharge is changed along with time, so that current eddy current is generated in the secondary coil. The direction of the eddy current in the coil is opposite to the direction of the current in the driving coil, and the pulse magnetic fields generated by the eddy current and the driving coil are also opposite, so that extremely strong electromagnetic repulsion is generated between the secondary coil and the driving coil. The magnetic induction lines of the pulse magnetic field are restrained by the magnetic yokes, do not diverge outwards, but are concentrated around the two coils, so that the electromagnetic force is amplified. And because the effect of yoke, the magnetic induction line that cuts also can become many in the motion process of secondary coil, cuts the magnetic induction line and can produce stronger induced electromotive force, and then produces stronger induction magnetic field and stronger electromagnetic repulsion. The electromagnetic repulsion is expressed as a compression stress wave in the secondary coil, the compression stress wave is transmitted into the loading rod from the secondary coil through the cushion block, and the compression stress wave drives the loading rod to move to generate displacement according to the one-dimensional stress wave theory. Because the stress wave is controlled in an electromagnetic mode, the amplitude and the pulse width of the stress wave can be controlled by adjusting the capacitance and the voltage of an external circuit, for example, when the voltage is constant, the width of the stress wave can be controlled by adjusting the capacitance of an external capacitance discharge circuit; when the capacitance is fixed, the amplitude of the stress wave can be controlled by adjusting the initial voltage of the capacitance.
Compared with the prior art, the invention has the following beneficial effects:
in the invention, magnetic yokes made of soft magnetic materials are designed outside the driving coil and the secondary coil, magnetic lines of force of a pulse magnetic field generated by the driving coil and the secondary coil under pulse excitation are restrained to be outwards dispersed, and the magnetic lines of force are concentrated around the coils, so that the electromagnetic force is increased under the condition that the capacitance size and the capacitance initial voltage of a charging and discharging circuit of the driving coil are not increased, as shown in fig. 1, compared with an electromagnetic force-time curve 7 of the secondary coil under the condition of a magnetic yoke and an electromagnetic force-time curve 8 of the secondary coil under the condition of no magnetic yoke, the electromagnetic force of the secondary coil under the condition of the magnetic yoke is obviously greater than that of the secondary coil under the condition of no magnetic yoke, and the electromagnetic force after the. Because the secondary coil is made of copper materials, the contact surface of the secondary coil and the rod can generate a stress concentration phenomenon under the loading state, and the maximum stress amplitude value exceeds the ultimate strength of copper, a cushion block is additionally arranged between the secondary coil and the rod before loading, and the cushion block is made of materials with compression strength far greater than that of the secondary coil and the rod, so that the stress borne by the secondary coil and the loading rod is prevented from being greater than the allowable stress of the materials. As shown in table 1, through numerical simulation, under the condition that the maximum voltage and the capacitance are limited, the main stressed components of the loading device are always in the elastic stage of the secondary coil, the loading rod and the cushion block in the loading process, so that the whole loading device can be repeatedly used, and the test repeatability is good.
Table 1 loading device main parts simulation maximum stress
According to the technical scheme of the invention, based on the principle of electromagnetic loading, the electromagnetic force is amplified by adding the magnetic yoke, and the amplitude and the pulse width of the stress wave are adjusted by controlling the total electromagnetic energy, so that the displacement amplitude and the loading time are controlled, and the large displacement loading of the test piece is realized.
The external capacitor discharge circuit is used for instantaneously discharging the active coil of the loading device once, and the discharge time depends on the capacitor discharge time, which is generally about 2 ms. Because the excitation generated by the capacitance discharge is changed along with time, eddy current can be generated in the secondary coil, the current and the transient change of the eddy current can generate induced magnetic fields on the active coil and the secondary coil, the direction of the eddy current in the secondary coil is opposite to that of the current in the active coil, and the magnetic fields generated by the eddy current and the current in the secondary coil are also opposite, so that electromagnetic repulsion force is generated between the secondary coil and the active coil. The magnetic yoke is designed to restrain the magnetic induction lines of the pulse magnetic field generated by the driving coil and the secondary coil, so that the electromagnetic force is increased under the condition that the capacitance and the voltage of an external circuit are not increased. The electromagnetic repulsion force appears as a compression stress wave in the secondary coil, which is then transmitted into the load bar. The loading surface of the loaded part is contacted with the tail end of the loading rod, and the generated compression stress wave is propagated to the tail end of the loading rod to load the loaded part. Stress wave signals, acceleration values and displacement values generated by the loading device can be obtained through the strain gauge, the acceleration sensor and the laser displacement sensor.
Fig. 2 is a plot of load bar end displacement versus time recorded using numerical simulations. As shown, the abscissa is time in milliseconds and the ordinate is the loading bar tip displacement in millimeters, it can be seen that the loading bar tip displacement can gradually increase to over 60mm over 2 ms. Compared with the actual maximum displacement of only 16mm in the prior art, the invention can effectively increase the loading displacement and realize large displacement loading in a very short time.
The invention also has stronger universality, not only can carry out large-displacement loading, but also can carry out high-g value loading on the test piece by installing the acceleration sensor on the loaded piece. In the prior art, the traditional high-g-value loading mode mostly adopts a mode of driving a projectile to impact a target plate, and a generated high-g-value curve is limited by the impact speed of the projectile and the size of the projectile. Compared with the traditional high-g-value loading technology, the loading method has the advantages that the loading is carried out by the principle of electromagnetic energy-mechanical energy conversion, and the high-g-value loading is realized by a simpler means. In addition, compared with the traditional high-g-value loading technology, the invention has no limitation on the length of the bullets, and effectively reduces the structural size of the device. Compared with the traditional Hopkinson rod loading technology, the amplitude and the pulse width of the generated stress wave are only related to the capacitance value and the voltage value of a discharge circuit and are unrelated to the length and the impact speed of a bullet, and the Hopkinson rod loading with a long pulse width and a high amplitude can be realized more easily; compared with the existing electromagnetic Hopkinson rod loading technology, under the condition that the materials of the loading rods are consistent, larger stress wave amplitude and pulse width can be generated. Table 2 shows the comparison between the maximum amplitude and the maximum pulse width of the stress wave generated by the present invention and the existing electromagnetic Hopkinson technology when the materials of the loading rod are all titanium alloys.
TABLE 2 comparison of maximum amplitude and pulse width of stress wave when the loading rod is made of titanium alloy
| Results | Existing electromagnetic Hopkinson rod technology | The invention |
| Amplitude of stress wave Mpa | 200 | 750 |
| Stress wave pulse width ms | 0.6 | 2 |
Drawings
Fig. 1 is a graph of electromagnetic force exerted on a secondary coil with and without a yoke versus time, where the abscissa represents time in ms and the ordinate represents the magnitude of the electromagnetic force. The unit is N.
Fig. 2 is a displacement-time curve of the end of the loading rod in a numerical simulation, with a displacement of 65mm in 2 ms. In fig. 2: the abscissa represents time in ms; the ordinate represents the displacement in mm.
Fig. 3 is a schematic structural diagram of the present invention.
Fig. 4 is a right side view of fig. 3.
In the figure: 1. a magnetic yoke; 2. an active coil; 3. a secondary coil; 4. cushion blocks; 5. a loading rod; 6. a sliding sleeve; 7. the electromagnetic force-time curve of the secondary coil when the magnetic yoke exists; 8. the electromagnetic force-time curve of the secondary coil without the magnetic yoke.
Detailed Description
The invention relates to an electromagnetic loading device for generating large displacement, and the technical scheme of the invention is explained in detail through 4 specific embodiments.
The invention comprises a magnetic yoke 1, a driving coil 2, a secondary coil 3, a cushion block 4, a loading rod 5 and a sliding sleeve 6. The loading devices are all revolving bodies. An annular groove is formed in the inner end face of the magnetic yoke 1; an axial mounting bar is located in the center of the recess. The driving coil 2 is positioned in the groove and sleeved on the central rod in the magnetic yoke 1, and the inner end surface of the driving coil is attached to the inner surface of the bottom of the groove; there is a gap of 5mm 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 central rod, and the end face of the sliding sleeve is attached to the outer end face of the driving coil 2; the inner circumferential surface of the sliding sleeve is in sliding fit with the outer circumferential surface of the central 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 in interference fit. The cushion block 4 is sleeved on the central rod and is bonded to the end face of the secondary coil; a gap is provided between the inner circumferential surface of the spacer and the outer circumferential surface of the center rod. One end of the loading rod 5 is arranged in the groove, and the end face of the loading rod is attached to the end face of the cushion block; the other end of the loading rod is attached to the test piece. And 5mm gaps are reserved between the outer circumferential surface of the driving coil and the outer circumferential surface of the secondary coil and the inner surface of the magnetic yoke.
The magnetic yoke 1, the driving coil 2, the secondary coil 3, the cushion block 4, the loading rod 5 and the sliding sleeve 6 are all coaxial.
The magnetic yoke is made of Q235 steel. The magnetic yoke consists of a cylinder body and a central rod; the central rod is positioned in the inner center of the magnetic 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 central rod is 50 mm. A groove is formed in the inner end face of the magnetic yoke, the outer diameter of the groove ranges from 180 mm to 250mm, and the inner diameter of the groove is 50 mm.
The driving coil 2 is a flat ring coil formed by winding 8-24 turns of a copper strip with the thickness of 2-5 mm and the width of 10-50 mm; when winding, the thickness of the copper strip is smaller, and the number of turns should be larger. The outer diameter of the active coil is 170-240 mm.
The secondary coil 3 is a copper ring. The outer diameter of the secondary coil is the same as that of the driving coil, and the inner diameter of the secondary coil is the same as that of the sliding sleeve; the axial length of the secondary coil is 1.5 times that of the active coil.
The cushion block is a circular ring made of tungsten alloy. The spacer annular width should be at least 3/4 times the secondary coil annular width. The axial length of the spacer is 1/2 of the secondary coil.
The loading rod is hollow and cylindrical and is made of TC4 titanium alloy. The loading rod has a wall thickness of 10mm and an inner diameter of 1/2 which is the outer diameter of the secondary coil. The axial length of the loading rod is 7 m.
The sliding sleeve is a resin material cylinder, the outer diameter of the sliding sleeve is 58mm, the inner diameter of the sliding sleeve is consistent with the diameter of the central rod of the magnetic yoke, the sliding sleeve can freely slide on the central rod, and the axial length of the sliding sleeve is the same as that of the secondary coil.
TABLE 3 structural parameters of the examples
The invention also provides a method for carrying out a large displacement loading test by using the electromagnetic loading device. The present invention will be described in detail by 4 embodiments. The large displacement loading test procedure is the same for each example, except for the test parameters.
The specific process of the invention is as follows:
step 1: matching of the loading device and the test piece:
and attaching the end face of one end of a loading rod in the loading device to the loading surface of the test piece.
Step 2: pasting a strain gauge and installing a laser displacement sensor:
the strain gauge pasting method adopts the prior art, takes the axis of a loading rod as a symmetry axis, symmetrically pastes two strain gauges with completely the same parameters on the outer circumferential surface of the length 1/2 of the loading rod, and leads the measuring direction of the strain gauges to be 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.
And connecting the lead of the strain gauge into a Wheatstone bridge. And the output signal of the Wheatstone bridge is connected to the ultra-dynamic strain gauge. And installing a laser displacement sensor, wherein light spots emitted by the laser displacement sensor are positioned on the circumference of the outer surface of the tail end of the loading rod. The signal output lines of the ultra-dynamic strain gauge and the laser displacement sensor are connected into a waveform memory and a computer.
And step 3: carrying out a loading test:
when a loading test is carried out, the driving coil of the loading device is instantaneously discharged once through the external capacitor charger, and loading is completed. The external capacitor charger is characterized in that 15 electrolytic capacitors with rated voltage of 6000V and rated capacitance of 2000 microfarads are connected in parallel to form a capacitor bank, the capacitor bank and an electronic switch are installed in a capacitor box, and the electronic switch is used for controlling the discharge of the capacitor bank. The external capacitor charger is composed in the same manner as that disclosed in chinese patent No. 201410171963.8.
The capacitance value of the external circuit is 10-30 millifarads, and the voltage value is 3000-5500 volts; the discharge time was 2 ms.
And 4, step 4: and (6) 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, and the voltage change is input through a conventional shielding signal wire and stored in the waveform memory to obtain a stress wave signal in the loading rod. The stress wave signal sigma is obtained through a formula (1):
wherein, σ is a stress wave signal, E is a young modulus of the material of the loading rod, and in this embodiment, E is 110 Gpa; u shape0The supply voltage for the wheatstone bridge, in this example 30 volts; k is the sensitivity coefficient of the strain gauge, which is 2.0 in the embodiment;Δ U is a change value of the wheatstone bridge arm voltage with time.
The change curve of the displacement along with the time is directly output through a laser displacement sensor, and data is read on a computer.
And completing the large displacement loading test by using the electromagnetic loading device. Table 4 shows the process parameters of the examples. Table 5 shows the displacements obtained in the examples.
TABLE 4 Process parameters for the examples
TABLE 5 Displacement obtained in the examples
Claims (10)
1. An electromagnetic loading device for generating large displacement is characterized by comprising a magnetic yoke, a driving 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 bar is located in the center of the recess. The driving coil is positioned in the groove and sleeved on the central rod in the magnetic yoke, and the inner end surface of the driving coil is attached to the inner surface of the bottom of the groove. A sliding sleeve is sleeved on the central rod, and the end face of the sliding sleeve is attached to the outer end face of the driving coil; the inner circumferential surface of the sliding sleeve is in sliding fit with the outer circumferential surface of the central rod. The secondary coil is sleeved on the outer circumferential surface of the sliding sleeve, and the interference fit between the secondary coil and the sliding sleeve is realized. The cushion block is sleeved on the central rod and is bonded to the end face of the secondary coil; a gap is provided between the inner circumferential surface of the spacer and the outer circumferential surface of the center rod. One end of the loading rod is arranged in the groove, and the end face of the loading rod is attached to the end face of the cushion block; the other end of the loading rod is attached to the test piece. The magnet yoke, the driving coil, the secondary coil, the cushion block, the loading rod and the sliding sleeve are coaxial.
2. The large displacement electromagnetic loading device of claim 1 wherein there is a 5mm gap between the inner circumferential surface of the active coil and the outer circumferential surface of the center rod. And 5mm gaps are reserved between the outer circumferential surface of the driving coil and the outer circumferential surface of the secondary coil and the inner surface of the magnetic yoke.
3. The large displacement electromagnetic loading device according to claim 1 wherein said yoke comprises a cylinder and a center rod; the central rod is positioned in the inner center of the magnetic yoke. The outer diameter of the cylinder body is 230-300 mm, and the inner diameter is 180-250 mm. The diameter of the central rod is 50 mm. A groove is formed in the inner end face of the magnetic yoke, the outer diameter of the groove ranges from 180 mm to 250mm, and the inner diameter of the groove is 50 mm.
4. The electromagnetic loading device for generating large displacement according to claim 1, wherein the driving coil is a flat-plate circular coil formed by winding 8-24 turns of a copper strip with the thickness of 2-5 mm and the width of 10-50 mm. The outer diameter of the active coil is 170-240 mm.
5. The electromagnetic loading device for generating large displacement according to claim 1, wherein the secondary coil has an outer diameter the same as that of the driving coil and an inner diameter the same as that of the sliding sleeve; the axial length of the secondary coil is 1.5 times that of the active coil.
6. The electromagnetic loading unit for generating large displacements of claim 1 wherein said spacer ring width is at least 3/4 times the ring width of said secondary coil. The axial length of the spacer is 1/2 of the secondary coil.
7. The electromagnetic loading device for generating large displacement according to claim 1, wherein the wall thickness of the loading rod is 10mm, 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.
8. A method for carrying out a large displacement loading test by using the electromagnetic loading device generating large displacement according to claim 1 is characterized by comprising the following specific processes:
step 1: matching of the loading device and the test piece:
and attaching the end face of one end of a loading rod in the loading device to the loading surface of the test piece.
Step 2: pasting a strain gauge and installing a laser displacement sensor;
and step 3: carrying out a loading test:
when a loading test is carried out, the driving coil of the loading device is instantaneously discharged once through the external capacitor charger, and loading is completed. And the capacitor bank and the electronic switch are arranged in the capacitor box, and the discharge of the capacitor bank is controlled through the electronic switch.
And 4, step 4: and (6) 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, and the voltage change is input through a conventional shielding signal wire and stored in the waveform memory to obtain a stress wave signal in the loading rod. The stress wave signal sigma is obtained through a formula (1):
wherein, sigma is a stress wave signal, and E is the Young modulus of the material of the loading rod; u shape0A supply voltage for the wheatstone bridge; k is the sensitivity coefficient of the strain gauge; Δ U is a change value of the wheatstone bridge arm voltage with time.
The change curve of the displacement along with the time is directly output through a laser displacement sensor, and data is read on a computer.
And completing the large displacement loading test by using the electromagnetic loading device.
9. The method for performing the large displacement loading test by using the electromagnetic loading device generating the large displacement according to claim 1, wherein when the strain gauge is attached and the laser displacement sensor is installed, two strain gauges with identical parameters are symmetrically attached to the outer circumferential surface of the loading rod at the position 1/2 with the axis of the loading rod as a symmetry axis, and the measuring direction of the strain gauge is the same as the axial direction of the loading rod. The resistance value of the strain gauge is 1000 ohms, and the sensitivity coefficient is 2.0.
And connecting the lead of the strain gauge into a Wheatstone bridge. And the output signal of the Wheatstone bridge is connected to the ultra-dynamic strain gauge. And installing a laser displacement sensor, wherein light spots emitted by the laser displacement sensor are positioned on the circumference of the outer surface of the tail end of the loading rod. The signal output lines of the ultra-dynamic strain gauge and the laser displacement sensor are connected into a waveform memory and a computer.
10. The method for performing a large displacement loading test by using the electromagnetic loading device generating large displacement according to claim 1, wherein the external circuit has a capacitance of 10-30 millifarads and a voltage of 3000-5500 volts; the discharge time was 2 ms.
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