CN113624590A - Single pulse separation type Hopkinson pressure bar experimental device based on electromagnetic force loading - Google Patents
Single pulse separation type Hopkinson pressure bar experimental device based on electromagnetic force loading Download PDFInfo
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Abstract
The application provides a single pulse disconnect-type hopkinson depression bar experimental apparatus based on electromagnetic force loading, it includes: the device comprises an incident rod, a flange, a circular tube, a mass block, a stress wave generator and a transmission rod; the near end of the incident rod is connected with a flange; the circular tube and the mass block are sleeved on the incident rod, the circular tube is attached to one end of the flange, and the mass block is attached to the circular tube; the stress wave generator generates a compression wave and is attached to the other end of the flange; a sample is clamped between the incident rod and the transmission rod; the compression waves form a first compression wave and a second compression wave after passing through the flange, and the first compression wave loads the sample; the second compression wave is reflected by the mass block and the flange in sequence to form a tensile wave, and the tensile wave is transmitted to the sample along the incident rod along with the first compression wave; wherein after a first compression wave loads the specimen, a subsequent tension wave drops the specimen so that a single compression load is applied to the specimen. Through this application, realized single tensile pulse unipolar one-way or unipolar bidirectional loading to the sample.
Description
Technical Field
The invention relates to a dynamic mechanical property testing technology of materials, in particular to a single pulse separation type Hopkinson pressure bar experimental device based on electromagnetic force loading.
Background
Currently, in the field of solid mechanics, the split hopkinson rod technology is the most widely adopted for measuring the mechanical properties of materials under high strain rates. The basic principle of the method is as follows: and placing the short sample between two pressure rods or pull rods, generating stress wave pulses through a loading device, and inputting the stress wave pulses into the rods to load the sample. And simultaneously, a strain gauge which is stuck on the pressure lever or the pull rod and has a certain distance from the end part of the pressure lever or the pull rod is used for recording pulse signals. In the process, the compression bar or the pull bar always keeps an elastic state, and stress waves can be ensured to propagate in the bar at the elastic wave speed without distortion.
In the process of loading a sample by using a split Hopkinson pressure bar experimental device based on electromagnetic force loading, incident waves generated by electromagnetic repulsion force are transmitted to an interface between the sample and an incident bar, reflected waves and transmitted waves are generated, wherein the reflected waves can be reversely transmitted along the incident bar, the transmitted waves can be transmitted along the transmitted bar through the sample, and the sample can be deformed due to the loading of stress waves in the process. However, the reflected wave reaches the other end of the incident rod and then is reflected secondarily, the stress wave after secondary reflection is transmitted back to the sample to be loaded again, a new reflected wave is generated, and the process is repeated, so that the sample is loaded for multiple times, the sample is deformed, the internal microstructure is completely different from that after primary loading, and the research on the relationship between the mechanical property of the material and the internal microstructure under the high strain rate is difficult.
Disclosure of Invention
The invention mainly aims to provide a single-pulse separated Hopkinson pressure bar experimental device based on electromagnetic force loading, and aims to solve the problem that a sample cannot be loaded by the separated Hopkinson pressure bar experimental device based on electromagnetic force loading in the prior art.
According to an aspect of the embodiments of the present invention, an electromagnetic force loading-based single pulse split hopkinson pressure bar experimental apparatus is provided, which includes: the device comprises an incident rod, a flange, a circular tube, a mass block, a stress wave generator and a transmission rod; the near end of the incident rod is connected with a flange; the circular tube and the mass block are sleeved on the incident rod, the circular tube is attached to one end of the flange, and the mass block is attached to the circular tube; the stress wave generator is used for generating compression waves and is attached to the other end of the flange; a sample is clamped between the incident rod and the transmission rod in a contact clamping mode; the compression wave generated by the stress wave generator forms a first compression wave and a second compression wave after passing through the flange, and the first compression wave is transmitted to the sample along the incident rod and loads the sample; the second compression wave propagates along the circular tube to the mass, the second compression wave is reflected by the mass and the flange in sequence to form a tensile wave, and the tensile wave follows the first compression wave to propagate along the incident rod to the sample; wherein after the first compression wave loads the specimen, the subsequent tension wave drops the specimen such that a single compression load is applied to the specimen.
Particular embodiments may include one or more of the following. The first compressional wave is a compressional incident wave. And the second compression wave generates a compression reflection wave on the end face of the mass block, which is attached to the circular tube, and the compression reflection wave is transmitted to the flange along the circular tube and is reflected by the flange to form a tension wave. The inner diameter of the flange is larger than the diameter of the incident rod, and the outer diameter of the flange is the same as that of the circular tube. The inner diameter of the circular tube is the same as the diameter of the incident rod. The length of pipe is greater than the length of quality piece, the internal diameter of pipe with the internal diameter of quality piece is the same and the external diameter of pipe is less than the external diameter of quality piece. A round hole is formed in the center of the mass block, and the incident rod penetrates through the round hole of the mass block. One side of the flange is provided with a threaded hole, and the incident rod is in threaded connection with the flange through the threaded hole. The incident rod and the transmission rod are made of the same material, length and diameter.
According to another aspect of the embodiments of the present invention, there is also provided an electromagnetic force loading-based single pulse split hopkinson pressure bar experimental apparatus, including: a first load platform module, comprising: the device comprises a first incident rod, a first flange, a first circular tube, a first mass block and a first stress wave generator; the near end of the first incident rod is connected with a first flange; the first round pipe and the first mass block are sleeved on the first incident rod, the first round pipe is attached to one end of the first flange, and the first mass block is attached to the first round pipe; the first stress wave generator is used for generating compression waves and is attached to the other end of the first flange; a second load platform module comprising: the second incident rod, the second flange, the second circular tube, the second mass block and the second stress wave generator; the near end of the second incident rod is connected with a second flange; the second round pipe and the second mass block are sleeved on the second incident rod, the second round pipe is attached to one end of the second flange, and the second mass block is attached to the second round pipe; the second stress wave generator is used for generating compression waves and is attached to the other end of the second flange; a sample is clamped between the far end of the first incident rod and the far end of the second incident rod in a contact clamping mode; the compression wave generated by the first stress wave generator passes through the first flange to form a first compression wave and a second compression wave, and the first compression wave is transmitted to the sample along the first incident rod and loads the sample; the second compression wave propagates along the first circular tube to the first mass, the second compression wave is reflected by the first mass and the first flange in sequence to form a first tensile wave, and the first tensile wave propagates along the first incident rod to the sample along with the first compression wave; the compression wave generated by the second stress wave generator passes through the second flange to form a third compression wave and a fourth compression wave, and the third compression wave is transmitted to the sample along the second incident rod and loads the sample; the fourth compression wave propagates along the second circular tube to the second mass, the fourth compression wave is reflected by the second mass and the second flange in sequence to form a second tensile wave, and the second tensile wave propagates along the second incident rod to the sample along with the third compression wave; wherein the first and third compression waves load the specimen simultaneously, and the subsequent first and second tension waves drop the specimen such that a single compression load is applied to the specimen.
According to the technical scheme, the compression wave is divided into two parts after passing through the flange, one part is used as a compression incident wave and is transmitted to the sample along the incident rod, the other part is transmitted along the circular tube and is secondarily reflected by the mass block and the flange in sequence, finally, a column of tensile wave is formed at the flange and is transmitted to the sample along the incident rod along with the compression incident wave, after the compression incident wave loads the sample, the sample cannot be clamped continuously due to the fact that the sample is only in a contact state with the incident rod, and the sample can fall off, so that single-time stretching pulse uniaxial unidirectional or uniaxial bidirectional loading of the sample is achieved.
Drawings
The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this application, illustrate embodiment(s) of the invention and together with the description serve to explain the invention without limiting the invention. In the drawings:
FIG. 1 is a schematic diagram of a single pulse uniaxial unidirectional split Hopkinson pressure bar experimental apparatus based on electromagnetic force loading according to an embodiment of the invention;
FIG. 2 is a schematic diagram of a single pulse uniaxial unidirectional split Hopkinson pressure bar experimental apparatus based on electromagnetic force loading according to another embodiment of the invention;
FIG. 3 is a schematic diagram of a single pulse uniaxial bidirectional split Hopkinson pressure bar experimental apparatus based on electromagnetic force loading according to an embodiment of the invention;
fig. 4 is a schematic diagram of a single pulse uniaxial bidirectional split hopkinson pressure bar experimental device based on electromagnetic force loading according to another embodiment of the invention.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the technical solutions of the present invention will be clearly and completely described below with reference to the specific embodiments of the present invention and the accompanying drawings. It is to be understood that the described embodiments are merely exemplary of the invention, and not restrictive of the full scope of the invention. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
The technical solutions provided by the embodiments of the present invention are described in detail below with reference to the accompanying drawings.
The technical solutions provided by the embodiments of the present invention are described in detail below with reference to the accompanying drawings.
According to the embodiment of the invention, the single pulse separation type Hopkinson pressure bar experimental device based on electromagnetic force loading is provided, and single loading of unidirectional compression of a sample under high strain rate can be realized through the embodiment.
With reference to fig. 1, the device mainly comprises: the device comprises an incident rod 1, a flange 2, a circular tube 3, a mass block 4, a stress wave generator 5 and a transmission rod 6.
Wherein, the pole 1 of inciting includes near-end and distal end, is connected with flange 2 at the near-end of pole 1 of inciting, and flange 2 can be round platform type flange, and the diameter of flange 2 is greater than the diameter of pole 1 of inciting. The near end of the incident rod 1 is respectively sleeved with a round tube 3 and a mass block 4, the round tube 3 is made of the same material as the incident rod 1, the outer diameter of the round tube 3 is consistent with the outer diameter of the flange 2, and the inner diameter of the round tube 3 is slightly larger than the diameter of the incident rod 1. The mass block 3 is a metal mass block, and the sectional area of the metal mass block is far larger than that of the circular tube 3. The mass block 3 can be fixed by a bracket, and a round hole with a diameter slightly larger than that of the incident rod is formed at the central position of the mass block 3, so that the incident rod 1 can pass through the round hole. When loading, the two ends of the circular tube 3 are respectively attached to the flange 2 and the mass block 4. The near end direction of the incident rod 1 is also provided with a stress wave generator 5 attached to the flange 2, the stress wave generator 5 is used for generating compression stress waves, and the stress wave generator 5 can be a loading gun comprising a main coil, a secondary coil, a stress wave amplifier and other components. At the distal end of the incident rod 1, a transmission rod 6 is disposed opposite to the incident rod 1, and the material, length and diameter of the transmission rod 6 are the same as those of the incident rod 1. The sample 7 is clamped between the incident rod 1 and the transmission rod 6 in a contact clamping manner or a fitting clamping manner. The sample is stuck, for example, by means of vaseline.
When the stress wave generator 5 generates a compression stress wave, the compression wave enters the incident rod 1 through the flange 2 and is divided into two parts at the contact part of the flange 2 and the circular tube 3 and the incident rod 1, namely, the compression stress wave is formed into a first compression wave and a second compression wave. The first compression wave is transmitted to the sample 7 along the incident rod 1 and carries out compression loading on the sample 7, and the first compression wave is also a compression incident wave; the second compression wave propagates along the circular tube 3 and generates a compression reflection wave at the end face attached to the mass 4, and the compression reflection wave propagates along the circular tube 3 to the flange 2 and is reflected at the free end of the flange to form a row of tensile waves, and then the first compression wave propagates along the incident rod 1 to the sample 7. After the sample 7 is loaded by the compressed incident wave, the sample 7 is only in contact with the incident rod 1, and the subsequent tensile wave makes the sample not be clamped continuously, i.e. the sample falls. Repeated loading is avoided in the process, and single compression loading of the sample under high strain rate is realized.
Referring to fig. 2, the apparatus further includes, on the basis of fig. 1: capacitor bank module 9, main circuit charge-discharge module 10, control module 11 and data collection station 12, specifically:
the capacitor bank module 9 is composed of a capacitor bank and a discharge thyristor, and mainly functions to store high-voltage current and discharge the main coil of the loading gun when needed. The capacitor bank module 9 can adopt a gradient capacitor bank for changing the pulse width of the stress wave generated in the discharging and loading process, the capacitance of each gear is fixed, and the capacitance is directly selected through the control module, so that the situation that the capacitance is changed by repeatedly replacing the connection mode of the capacitor in the experiment process is avoided. The capacitor bank controls the capacitor to discharge through the discharging controllable silicon, the capacitor bank and the discharging controllable silicon are installed in the capacitor cabinet, and the generated discharging current is output to the main coil of the loading gun.
The main circuit charge-discharge module 10 mainly comprises a charge circuit and a discharge circuit, and comprises a transformer, a current-limiting resistor, a filter inductor, a leakage resistor, a vacuum contactor, a current/voltage sensor and the like. The main circuit charging and discharging module 11 mainly functions to charge and discharge the capacitor bank. In the charging circuit, a transformer can boost the voltage of 380V to the maximum 3000V, the capacitor bank is charged through rectification, and the charging circuit stops charging when the voltage of the capacitor bank reaches a set voltage value. In the discharging circuit, the vacuum contactor is triggered to be conducted through delayed signal pulses, and the capacitor group instantly discharges to the discharging coil to generate electromagnetic force. The circuit can effectively control the amplitude of the stress wave by setting the charging voltage value.
The control module 11 adopts a digital signal delay pulse transmitter to control the charging and discharging of the capacitor bank by sending a pulse signal to the silicon controlled switch. The control module 11 mainly includes a circuit board, a Programmable Logic Controller (PLC), a synchronous transformer, a pulse transformer, an electromagnetic relay, a delay signal generator, etc., and is a weak current part of the circuit system. Siemens S7-200SMART series PLC and Siemens SMART1000IE touch screen are used as the core of a loading control module and are used for realizing the control of the whole electromagnetic loading working flow.
The data acquisition unit 12 is used for calculating a strain signal through strain change acquired by the strain gauge 8 arranged on the waveguide rod. The strain gauges on the waveguide rods can convert the strain changes on the two rods into resistance changes respectively, and further into output voltage changes of two bridge arms of the Wheatstone half bridge, and the voltage changes are input into the data acquisition unit 12 through two conventional shielding signal lines. Data acquisition unit 12 may calculate the waveguide rod strain signal based on the Wheatstone bridge equation. Wherein, the data collector adopts GEN3i manufactured by Germany HBM company.
The experimental method for the single-pulse uniaxial unidirectional separation type hopkinson pressure bar based on electromagnetic force loading of the embodiment is described in detail below, and specifically comprises the following steps:
and step 1, installing equipment.
The loading gun, the waveguide rod, the circular tube and the mass block are mounted on the experiment table through the same shaft, so that two ends of the circular tube are respectively attached to the flange and the mass block, and the waveguide rods can freely move in the axis direction. The incident rod is tightly attached to the amplifier end of the loading gun, and a main coil, a secondary coil and a stress wave amplifier in the loading gun are arranged according to experimental requirements. A sample is placed between the two waveguide rods such that the sample axis remains coaxial with the waveguide rods. Two strain gauges with identical parameters are symmetrically adhered to the surface of the waveguide rod along the axial line at the length of the two waveguide rods 1/2 and are connected into a Wheatstone bridge of a data acquisition system through a lead wire.
A stress wave generator 5, a flange 2, an incident rod 1, a circular tube 3, a mass block 4 and a transmission rod 6 are coaxially arranged on an experiment table in sequence, and the incident rod 1 and the transmission rod 6 can freely move in the axial direction. In addition, the two ends of the round pipe 3 are respectively attached to the flange 2 and the mass block 4. The sample 7 is held between two waveguide rods so that the axis of the sample is coaxial with the waveguide rods. Two strain gauges 8 with identical parameters are symmetrically adhered to the surface of the waveguide rod along the axial line at the length of the two waveguide rods 1/2 and are connected to a Wheatstone bridge of the data acquisition unit 12 through lead wires.
The waveguide rod (incident rod and transmission rod) used in the method is a titanium alloy rod with the diameter of 15mm and the length of 2500mm, wherein one end, far away from a sample, of the incident rod is provided with a flange with the outer diameter of 22mm and the length of 9mm, the flange can be a circular truncated cone-shaped flange, one side of the flange is provided with a threaded hole with the diameter basically consistent with the size of the incident rod, and the incident rod is in threaded connection with the flange. The round tube is a titanium alloy round tube with the outer diameter of 22mm, the inner diameter of 15.3mm and the length of 700 mm. The mass block is a titanium alloy energy absorption device with the diameter of 70mm, the length of 150mm and the diameter of a central through hole of 16 mm. The end surfaces of the two waveguide rods are smooth planes perpendicular to the waveguide rods, and the sample is clamped between the two waveguide rods. The sample is a cylindrical aluminum alloy sample with the diameter of 8mm and the length of 8 mm.
And 2, setting experiment parameters.
And starting the experimental system control module, and setting experimental parameters including the capacitance and the charging voltage value of the pulse capacitor bank. Selecting a required capacitance value and a required voltage value according to the corresponding relation between the pulse width and amplitude of the loading wave and the parameters of the capacitance and the voltage required by the experiment;
and step 3, charging the pulse capacitor bank.
And after the parameter setting is finished, starting a charging option of the control module to charge the pulse capacitor bank. After the set charging voltage is reached, the charging process is automatically stopped, and the charging voltage of the pulse capacitor bank is not increased.
And 4, discharging and loading the capacitor bank.
And after the capacitor is charged, starting a discharge switch to discharge the capacitor group to the main coil of the loading gun. When the discharge current flows through the primary coil, due to electromagnetic induction, a strong electromagnetic repulsion force is generated to act on the secondary coil and is amplified in the amplifier, and finally, a compression wave pulse is formed and transmitted into the incident rod. The compression wave is split into two at the pipe: one part of the compressed incident wave is transmitted to the sample along the incident rod, namely the compressed incident wave; the other part of the compression wave can be transmitted along the circular tube, compression reflection waves are generated on the end face attached to the metal mass block and are transmitted to the free end of the flange along the circular tube, a row of tensile waves are formed by reflection at the free end of the flange, and then the compression incident waves are transmitted to the sample direction along the incident rod. After the compression incident wave loads the sample, the reflected wave reversely propagates along the incident rod, and the transmitted wave propagates along the transmission rod. Because the sample and the incident rod are only in a contact state, the sample cannot be clamped continuously due to the tensile wave after the compression incident wave, and the sample can fall off. Repeated loading is avoided in the whole process, and single compression loading under high strain rate of the sample is realized. In the whole process, incident waves, reflected waves and transmitted waves can be collected by the strain gauge adhered to the waveguide rod.
And 5, acquiring and processing experimental data.
The strain gauges on the waveguide rods can respectively convert strain changes on the two rods into resistance changes, and further convert the resistance changes into output voltage changes of two bridge arms of a Wheatstone half bridge, and the voltage changes are input into a data acquisition unit through two conventional shielding signal wires. According to the Wheatstone bridge formula, the strain signal of the waveguide rod can be calculated as follows:
wherein ε is the strain signal, U0The input voltage of the Wheatstone bridge is K, the sensitivity coefficient of the strain gauge is K, and the delta U is the change value of the bridge arm voltage of the Wheatstone half bridge.
In the experiment loading process, a loading gun emits compression stress waves, an incident wave is collected by a strain gauge adhered to an incident rod firstly, the incident wave is reflected on the end face of a sample, and the returned reflected wave is collected by the strain gauge at the same position. On the other hand, after passing through the sample, the transmitted wave continues to propagate along the transmission rod and is collected by the strain gauge on the transmission rod. The internal stress of the sample can be solved by using a one-dimensional stress wave theory as follows:
wherein σsFor the internal stress of the sample, E is the modulus of elasticity of the waveguide rod, A is the cross-sectional area of the waveguide rod, AsThe cross-sectional area of the sample corresponding to the direction of loading,. epsiloniFor an incident wave signal on a certain waveguide rod, epsilonrFor reflected wave signals obtained on the waveguide rod,. epsilontIs the transmitted wave signal on the waveguide rod.
For the strain of the sample, directly measuring by sticking a strain gage on the surface of the sample; or determining the deformation of the object by using a high-speed camera and adopting a Digital Image Correlation (Digital Image Correlation) technology according to the statistical Correlation of speckle fields randomly distributed on the surface of the object before and after the deformation, and calculating the strain field of the sample.
The stress-strain curve of the sample can be obtained through conventional data processing: and (3) according to the stress of the sample calculated by the formula (2) and the strain of the sample obtained by measurement, drawing the strain of the sample as an x axis and the stress as a y axis to obtain a stress-strain curve of the sample.
The embodiment of the invention also provides a single-pulse uniaxial bidirectional separation type Hopkinson pressure bar experimental device based on electromagnetic force loading, and the single loading of the bidirectional stretching of the sample under the high strain rate can be realized through the embodiment.
Referring to fig. 3, the apparatus includes: the device comprises a first loading platform module and a second loading platform module, wherein the first loading platform module and the second loading platform module are identical modules, and both the first loading platform module and the second loading platform module generate compression stress waves.
Specifically, the first loading platform module includes: the device comprises a first incident rod 21, a first flange 22, a first round tube 23, a first mass block 24 and a first stress wave generator 25; the proximal end of the first incident rod 21 is connected with a first flange 22; the first mass block 24 is sleeved on the first incident rod 21 at a position near the proximal end of the first incident rod 21; the first round pipe sleeve 23 is arranged on the first incident rod 21 and is respectively attached to the first flange 22 and the first mass block 24; the first stress wave generator 25 is for generating a compression wave and is attached to the first flange 22.
The second loading platform module comprises: a second incident rod 31, a second flange 32, a second round tube 33, a second mass block 34 and a second stress wave generator 35; the proximal end of the second incident rod 31 is connected with a second flange 32; the second mass block 34 is sleeved on the second incident rod 31 at a position near the proximal end of the second incident rod 31; the second round tube 33 is sleeved on the second incident rod 31 and is respectively attached to the second flange 32 and the second mass block 34; the second stress wave generator 35 is for generating a compression wave and is attached to the second flange 32.
The first incident rod 21 and the second incident rod 31 are disposed opposite to each other, and the sample 40 is held between the first incident rod 21 and the second incident rod 31 in a contact (bonding) manner.
The compression wave generated by the first stress wave generator 21 passes through the first flange 22 to form a first compression wave and a second compression wave, and the first compression wave propagates to the sample 40 along the first incident rod 21 and loads the sample 40; the second compression wave propagates to the first mass block 24 along the first circular tube 23, the second compression wave is reflected by the first mass block 24 and the first flange 22 in sequence to form a first tensile wave, and the first tensile wave propagates to the sample 40 along the first incident rod 21 along with the first compression wave; the compression wave generated by the second stress wave generator 31 passes through the second flange 32 to form a third compression wave and a fourth compression wave, and the third compression wave propagates to the sample 40 along the second incident rod 31 and loads the sample 40; the fourth compression wave propagates along the second tubular 32 towards the second mass 34, is reflected by the second mass 34 and the second flange 32 in sequence and forms a second tensile wave, which propagates along the second incident rod 31 towards the sample 40 following the third compression wave. With the above embodiment, after the two compressed incident waves load the sample, the two reflected waves are propagated backward along the incident rod. Because the sample is only in a contact state with the two incident rods, the two tensile waves following the compression incident wave can prevent the sample from being clamped continuously, and the sample can fall off. Repeated loading is avoided in the process, and single compression loading of the sample under high strain rate is realized.
Referring to fig. 4, the apparatus further includes, on the basis of fig. 3: the specific functions of the capacitor bank module 50, the main circuit charging and discharging module 60, the control module 70 and the data collector 80 may refer to the description herein before, and are not described herein again.
The experimental method for the single-pulse uniaxial bidirectional separation type hopkinson pressure bar based on electromagnetic force loading of the embodiment is described in detail below, and specifically comprises the following steps:
and step 1, installing equipment.
A stress wave generator 25, a flange 22, a round tube 23, a mass block 24, an incident rod 21, an incident rod 31, a mass block 34, a round tube 33, a flange 32 and a stress wave generator 35 are coaxially arranged on a laboratory bench in sequence, and the two incident rods can freely move in the axial direction. In addition, two ends of each round pipe are respectively attached to the flange and the mass block. The sample is clamped between two waveguide rods, and the axis of the sample is coaxial with the waveguide rods. The method for adhering the strain gauge 85 adopts the prior art, namely, a pair of strain gauges with the same parameters are symmetrically adhered to the surface of the waveguide rod along the axial line at the length of the waveguide rod 1/2, and the strain gauge with the resistance value of 1000 ohms and the sensitivity coefficient of 2.0 is adopted in the embodiment; and welding lead wires of the strain gauge on pins of the strain gauge, and respectively connecting the strain gauge into two opposite bridge arms of the Wheatstone half bridge through the lead wires. The fixed resistors on the other two legs of the wheatstone half bridge are both 1000 ohms. The supply voltage of the wheatstone half bridge is 30 volts dc. The two diagonal voltages of the wheatstone half bridge are input to the data collector 80 through two conventional single core shielded signal lines.
And 2, setting experiment parameters.
And starting the control module of the experiment system, and setting experiment parameters through the touch screen. Selecting the capacitance of the capacitor bank in the loading circuit using the loading pulse width according to the experiment; the amplitude of the applied carrier wave is used according to the experiment, the required charging voltage value is input, and the required charging voltage value is within the rated voltage of the pulse capacitor.
And step 3, charging the pulse capacitor bank.
After the parameter setting is finished, the charging option of the control module is started, and the main circuit charging and discharging module works to charge the pulse capacitor bank. And the charging is automatically stopped after the set charging voltage is reached, and the charging voltage of the pulse capacitor bank is not increased.
And 4, discharging and loading the capacitor bank.
After the capacitor is charged, a discharge switch is started to discharge the capacitor group to the main coils of the loading guns at the two ends. When a discharge current flows through the primary coil, a strong electromagnetic repulsion force is generated due to electromagnetic induction and acts on the secondary coil. Because the capacitor bank has short discharge time and strong discharge current, the electromagnetic repulsion generated at the moment forms a compression wave with short duration and large amplitude at the input end of the stress amplifier. The compression waves at the two ends are divided into two parts at the round pipe: one part of the compressed incident wave is transmitted to the sample along the incident rod, namely the compressed incident wave; the other part of the compression wave can be transmitted along the circular tube, compression reflection waves are generated on the end face attached to the metal mass block and are transmitted to the free end of the flange along the circular tube, a row of tensile waves are formed by reflection at the free end of the flange, and then the compression incident waves are transmitted to the sample direction along the incident rod. After the two compressed incident waves load the sample, the two reflected waves are propagated in the opposite direction along the incident rod. Because the sample is only in a contact state with the two incident rods, the two tensile waves following the compression incident wave can prevent the sample from being clamped continuously, and the sample can fall off. In the whole process, incident waves and reflected waves are collected by a strain gauge attached to an incident rod, and the shape and amplitude of the reflected waves are determined by the properties of the sample material.
And 5, acquiring and processing experimental data.
The strain gauges on the waveguide rods can respectively convert strain changes on the two rods into resistance changes, and further convert the resistance changes into output voltage changes of two bridge arms of a Wheatstone half bridge, and the voltage changes are input into a data acquisition unit through two conventional shielding signal wires. According to the Wheatstone bridge formula, the strain signal of the waveguide rod can be calculated as follows:
wherein ε is the strain signal, U0The input voltage of the Wheatstone bridge is K, the sensitivity coefficient of the strain gauge is K, and the delta U is the change value of the bridge arm voltage of the Wheatstone half bridge.
In the experiment loading process, a loading gun emits compression stress waves, and strain gauges adhered to two incident rods respectively collect incident waves epsiloni1And εi2After the incident wave reaches the sample, a reflected wave epsilon is generatedr1And εr2Counter-propagating along the incident rod and picked up by the strain gauge at the same location. The internal stress of the sample can be solved by using a one-dimensional stress wave theory as follows:
wherein σsFor the internal stress of the sample, E is the modulus of elasticity of the waveguide rod, A is the cross-sectional area of the waveguide rod, AsThe cross-sectional area of the sample corresponding to the direction of loading,. epsiloni1Is an incident wave signal on an incident rod, epsilonr1Is the reflected wave signal obtained on the incident rod; epsiloni2For incident wave signal on another incident rod, ∈r2Is the reflected wave signal obtained on the incident rod.
For the strain of the sample, directly measuring by sticking a strain gage on the surface of the sample; or determining the deformation of the object by using a high-speed camera and adopting DIC (Digital Image Correlation) technology according to the statistical Correlation of speckle fields randomly distributed on the surface of the object before and after the deformation, and calculating the strain field of the sample.
The stress-strain curve of the sample can be obtained through conventional data processing: and (3) drawing a graph by taking the strain of the sample as an x axis and the stress as a y axis according to the stress of the sample calculated by the formula (4) and the strain of the sample obtained by measurement, so as to obtain a stress-strain curve of the sample.
The invention adopts an electromagnetic loading technology, reasonably designs an incident rod, a flange, a circular tube and a mass block to process reflected waves, adopts a stress wave generator, designs a single pulse separated Hopkinson pressure bar experimental device based on electromagnetic force loading and a single pulse uniaxial two-way separated Hopkinson pressure bar experimental device based on electromagnetic force loading, and realizes single compression pulse loading of a sample under high strain rate. The experimental device is simple to operate and strong in controllability, and stress waves with preset pulse amplitudes and preset pulse widths can be obtained in different loading directions through selection of experimental parameters. The method and the device are beneficial to the promotion of relevant researches such as the research on the relation between the mechanical properties of the material and the internal microstructure under the high strain rate.
As will be appreciated by one skilled in the art, embodiments of the present invention may be provided as a method, system, or computer program product. Accordingly, the present invention may take the form of an entirely hardware embodiment, an entirely software embodiment or an embodiment combining software and hardware aspects. Furthermore, the present invention may take the form of a computer program product embodied on one or more computer-usable storage media (including, but not limited to, disk storage, CD-ROM, optical storage, and the like) having computer-usable program code embodied therein.
The above description is only an example of the present invention, and is not intended to limit the present invention, and it is obvious to those skilled in the art that various modifications and variations can be made in the present invention. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the scope of the claims of the present invention.
Claims (10)
1. The utility model provides a single pulse disconnect-type hopkinson depression bar experimental apparatus based on electromagnetic force loading which characterized in that includes: the device comprises an incident rod, a flange, a circular tube, a mass block, a stress wave generator and a transmission rod;
the near end of the incident rod is connected with a flange; the circular tube and the mass block are sleeved on the incident rod, the circular tube is attached to one end of the flange, and the mass block is attached to the circular tube; the stress wave generator is used for generating compression waves and is attached to the other end of the flange; a sample is clamped between the incident rod and the transmission rod in a contact clamping mode;
the compression wave generated by the stress wave generator forms a first compression wave and a second compression wave after passing through the flange, and the first compression wave is transmitted to the sample along the incident rod and loads the sample; the second compression wave propagates along the circular tube to the mass, the second compression wave is reflected by the mass and the flange in sequence to form a tensile wave, and the tensile wave follows the first compression wave to propagate along the incident rod to the sample;
wherein after the first compression wave loads the specimen, the subsequent tension wave drops the specimen such that a single compression load is applied to the specimen.
2. The device of claim 1, wherein the first compressional wave is a compressional incident wave.
3. The apparatus of claim 1, wherein the second compression wave generates a compression reflection wave at an end surface of the proof mass that abuts the tubular, the compression reflection wave propagating along the tubular toward the flange and being reflected by the flange to form a tension wave.
4. The apparatus of claim 1, wherein the flange has an inner diameter greater than the diameter of the entrance rod, and an outer diameter equal to the outer diameter of the circular tube.
5. The apparatus of claim 1, wherein the inner diameter of the circular tube is the same as the diameter of the entrance rod.
6. The apparatus of claim 1, wherein the length of the tube is greater than the length of the mass, the inner diameter of the tube is the same as the inner diameter of the mass and the outer diameter of the tube is less than the outer diameter of the mass.
7. The device of claim 1, wherein a circular hole is formed at a central position of the mass, and the incident rod passes through the circular hole of the mass.
8. The apparatus according to claim 1, wherein one side of the flange has a screw hole, and the incident rod is screw-coupled to the flange through the screw hole.
9. The device of claim 1, wherein the incident rod and the transmission rod are the same in material, length, and diameter.
10. The utility model provides a single pulse disconnect-type hopkinson depression bar experimental apparatus based on electromagnetic force loading which characterized in that includes:
a first load platform module, comprising: the device comprises a first incident rod, a first flange, a first circular tube, a first mass block and a first stress wave generator; the near end of the first incident rod is connected with a first flange; the first round pipe and the first mass block are sleeved on the first incident rod, the first round pipe is attached to one end of the first flange, and the first mass block is attached to the first round pipe; the first stress wave generator is used for generating compression waves and is attached to the other end of the first flange;
a second load platform module comprising: the second incident rod, the second flange, the second circular tube, the second mass block and the second stress wave generator; the near end of the second incident rod is connected with a second flange; the second round pipe and the second mass block are sleeved on the second incident rod, the second round pipe is attached to one end of the second flange, and the second mass block is attached to the second round pipe; the second stress wave generator is used for generating compression waves and is attached to the other end of the second flange;
a sample is clamped between the far end of the first incident rod and the far end of the second incident rod in a contact clamping mode;
the compression wave generated by the first stress wave generator passes through the first flange to form a first compression wave and a second compression wave, and the first compression wave is transmitted to the sample along the first incident rod and loads the sample; the second compression wave propagates along the first circular tube to the first mass, the second compression wave is reflected by the first mass and the first flange in sequence to form a first tensile wave, and the first tensile wave propagates along the first incident rod to the sample along with the first compression wave;
the compression wave generated by the second stress wave generator passes through the second flange to form a third compression wave and a fourth compression wave, and the third compression wave is transmitted to the sample along the second incident rod and loads the sample; the fourth compression wave propagates along the second circular tube to the second mass, the fourth compression wave is reflected by the second mass and the second flange in sequence to form a second tensile wave, and the second tensile wave propagates along the second incident rod to the sample along with the third compression wave;
wherein the first and third compression waves load the specimen simultaneously, and the subsequent first and second tension waves drop the specimen such that a single compression load is applied to the specimen.
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