Closed-loop controlled constant amplitude impact loading device and method for electromagnetic shock fatigue testing

Abstract

This invention discloses a closed-loop controlled constant-amplitude impact loading device and method for electromagnetic impact fatigue testing, belonging to the field of materials testing technology. The device includes an impact loading module, a specimen clamping and carrier wave transmission module, and a closed-loop control circuit consisting of a data acquisition module and an automatic control module. The impact loading module uses a pulsed power supply to drive an electromagnetic coil to generate eddy current repulsion, pushing a punch to impact an incident rod, generating a high-strain-rate stress wave. The data acquisition module acquires the reflected or transmitted wave signal of the specimen under load through strain gauges on the incident or transmitted rod, and calculates the deviation from the preset value based on the signal. The automatic control module calculates the input parameters for the next loading in real time based on the deviation signal and adjusts the impact energy to achieve constant-amplitude loading throughout the entire life cycle. This invention solves the problem of existing impact fatigue tests failing to maintain a constant load after specimen cracking, achieving closed-loop adaptive control and providing reliable data for material performance evaluation.

Description

Technical Field

[0001] This invention belongs to the technical field of fatigue testing equipment, specifically relating to a closed-loop control constant amplitude impact loading device and method for electromagnetic shock fatigue testing. Background Technology

[0002] Impact fatigue refers to the type of load caused by repeated impact loading, and it is one of the main failure modes of critical components (such as landing gear and engine blades) in fields such as aviation and aerospace. In practical engineering, impact fatigue testing is often used to test the life and failure behavior of materials and structures under cyclic loading, and to obtain their impact load-life (SN) curves. This requires that the stress or strain amplitude of the impact applied to the specimen in each test be kept constant, so as to obtain high-cycle impact fatigue life in controlled stress tests and low-cycle impact fatigue life in controlled strain tests.

[0003] Currently, typical impact fatigue testing methods include pendulum, falling weight, and split Hopkinson bar (SHB) methods, all of which are modifications of traditional single-impact devices. Among these, energy-based testing machines, such as pendulum and falling weight models, struggle to directly obtain the loading waveform of the specimen. Furthermore, in a single impact, the specimen is subjected to multiple progressively decaying stress waves, making it difficult to obtain the material's impact fatigue SN curve, thus limiting their application in accurate SN curve testing. The SHB-type impact fatigue loading method, however, enables visualization of the loading waveform and achieves continuous constant-amplitude loading of the specimen through rod size design. Related technologies have been implemented in several patent documents, such as patent number 202110337545.1, which discloses a device for tensile / compressive impact fatigue testing based on a Hopkinson bar, and patent application number 202311630663.7, which discloses a pneumatic reciprocating rod-type oscilloscope impact fatigue testing device and method. However, these solutions all achieve continuous multiple impact loading by adding continuous reset and impact control modules. Essentially, they all adopt an open-loop control mode with a preset waveform. The loading waveform is fixed after being preset before the test, so it does not have the function of automatic adjustment during multiple impact loading processes.

[0004] This open-loop mode is applicable before fatigue crack initiation in the specimen, when the specimen's own wave impedance is essentially constant. By setting the same loading incident waveform for each impact, the reflected and transmitted waves can also remain constant. Since the strain and stress of the specimen in the SHB test are proportional to the amplitudes of the reflected and transmitted waves, respectively, this method can maintain constant stress and strain during each loading. However, after fatigue crack initiation in the specimen, the wave impedance will continuously decrease. Crack propagation caused by continuous repeated impact loading leads to a gradual decrease in the amplitude of the transmitted wave and a gradual increase in the amplitude of the reflected wave. During this stage, it is difficult to control the constant amplitude loading of stress or strain on the specimen. Traditional hydraulic / electronically controlled low-strain-rate loading fatigue testing machines are technically mature. Although they can achieve constant amplitude loading of the specimen throughout its entire loading life through closed-loop control of the load or displacement, their loading strain rate is far lower than the high strain rate required for impact loading, and they lack the ability to automatically adjust the loading waveform, thus failing to simulate impact conditions.

[0005] In summary, existing impact fatigue testing techniques, due to their extremely high loading rates and lack of real-time control mechanisms, cannot achieve adaptive waveform adjustment to maintain constant amplitude loading throughout the entire damage evolution process of the specimen, especially during the crack propagation stage. This limitation affects the integrity of impact fatigue SN curve testing and also restricts in-depth research on the failure mechanism of materials throughout the entire impact fatigue process. Summary of the Invention

[0006] The purpose of this invention is to address the limitations of existing impact fatigue testing techniques, which can only preset the impact waveform before the experiment and struggle to achieve constant amplitude loading control and stress-strain closed-loop control during the experiment. This invention provides a closed-loop controlled constant amplitude impact loading device and method for electromagnetic impact fatigue testing. The device uses a pulsed current to generate an induced magnetic field through a discharge coil. This induced magnetic field generates eddy currents within the magnetic field, which in turn generate an induced magnetic field around the coil. The two magnetic fields are in opposite directions, creating eddy current repulsion that pushes the punch to impact the incident rod, generating a high strain rate stress wave on the specimen. After each impact, the transmission rod returns to its initial position under the action of the push arm and damping deceleration. The incident rod also returns to its initial position under the action of a limiting device. The PLC controls the pulsed power supply to re-drive the punch to impact the incident rod, achieving automatic high-frequency loading cycle control. During the experiment, only adjustments to the impact loading system are needed through a data acquisition system and an automatic control system to achieve stress-strain closed-loop control, improve the stability of the incident wave amplitude, and automatically control high-frequency cyclic loading.

[0007] To achieve the above objectives, the technical solution provided by this invention is:

[0008] A closed-loop controlled constant amplitude impact loading device for electromagnetic shock fatigue testing includes an impact loading module, a specimen clamping and carrier transmission module, a data acquisition module, and an automatic control module.

[0009] The impact loading module is used to generate a controllable impact, including a pulse power supply, a return spring, an electromagnetic actuator, and a reciprocating punch connected to the electromagnetic actuator. The pulse power supply is electrically connected to the electromagnetic actuator to generate an electromagnetic pulse; the return spring is used to reset the punch after the impact.

[0010] The specimen clamping and carrier transmission module is used to transmit the impact output by the impact loading module to the specimen. It includes an incident rod, a transmission rod, and a rod system reset mechanism arranged coaxially. The specimen is coaxially fixed between the end faces of the incident rod and the transmission rod. The rod system reset mechanism is used to reset the incident rod and the transmission rod to their initial positions after each impact.

[0011] The data acquisition module is used to monitor the stress wave amplitude values ​​of the incident rod and the transmission rod in real time, calculate and output the deviation signal between the monitored stress wave amplitude value and the preset threshold.

[0012] The automatic control module includes a programmable controller; the programmable controller is connected to the impact loading module and the data acquisition module; the automatic control module and the data acquisition module form a closed-loop feedback control loop; the programmable controller is configured to receive the deviation signal between the stress wave amplitude and the target loading amplitude monitored in real time by the data acquisition module, and dynamically adjust the input parameters of the impact loading module according to the deviation signal to adjust the magnitude of the impact force during the next impact, thereby realizing closed-loop control and automatic compensation of the load amplitude on the specimen in continuous impact testing.

[0013] Furthermore, the data acquisition module includes strain gauges, a data acquisition unit, an amplifier, and a comparator mounted on the incident rod and / or the transmission rod;

[0014] The data acquisition unit is used to convert the stress wave acquired by the strain gauge into an electrical signal; the amplifier is used to condition the amplitude of the converted signal; and the comparator is used to compare the amplitude of the conditioned stress wave with the target loading amplitude and output a deviation signal.

[0015] Furthermore, the automatic control module also includes a calculator, which is connected in communication with the comparator and the programmable controller. The calculator has pre-stored control logic and a calibration model determined by pre-experimentation, which is used to calculate the input parameters of the impact loading module based on the deviation signal and send them to the programmable controller.

[0016] Furthermore, the comparator is configured to selectively compare based on the input control mode: in the first loading control mode, the comparator compares the transmitted wave amplitude value with a first preset threshold to obtain a transmitted wave amplitude deviation signal; in the second loading control mode, the comparator compares the reflected wave amplitude value with a second preset threshold to obtain a reflected wave amplitude deviation signal.

[0017] Meanwhile, the calculator is configured to perform selective calculations based on the input control mode: in the first load control mode, the calculator receives the transmitted wave amplitude deviation signal output by the comparator and calculates the adjustment amount of the input parameters; in the second load control mode, the calculator receives the reflected wave deviation signal output by the comparator and calculates the adjustment amount of the input parameters.

[0018] Furthermore, the electromagnetic actuator also includes a push rod, a discharge coil, and an induction coil;

[0019] The reset spring, discharge coil, induction coil, and punch are coaxially mounted on the push rod in sequence; the pulse power supply is connected to the discharge coil through an external pulse power supply connection line.

[0020] The discharge coil and the induction coil are arranged opposite to each other and fixed on a bracket. They can generate pulsed magnetic fields in opposite directions under the action of pulse power, thereby forming eddy current repulsion to drive the punch.

[0021] The end of the push rod is connected to the punch; the return spring is sleeved on the push rod, with its two ends abutting between a fixing member and a bracket to reset the punch after impact.

[0022] Furthermore, the electromagnetic actuator also includes a displacement sensor mounted on the punch or push rod;

[0023] The displacement sensor is used to detect the displacement of the punch or push rod and is electrically connected to the programmable controller to confirm the occurrence of the punch impact event and the completion of the reset event.

[0024] Furthermore, the specimen clamping and carrier transmission module also includes an incident rod limiting device, an incident rod limiting ring, and a transmission rod limiting ring;

[0025] The incident rod limiting ring is fixedly sleeved on the incident rod;

[0026] The incident rod limiting device is installed on the incident rod and corresponds to the position of the incident rod limiting ring, and is close to the impact end of the incident rod. It is fixedly connected to the test bench of the load-bearing closed-loop control constant amplitude impact loading device through the base, and is coaxially clearance-fitted with the incident rod. The incident rod limiting device is used to slow down the movement speed of the incident rod by damping during the impact and axial movement of the incident rod, and to contact the incident rod limiting ring when the incident rod returns to its original position, so as to achieve axial limiting of the incident rod.

[0027] The limiting ring of the transmission rod is fixedly sleeved on the transmission rod body and close to the end of the transmission rod. It is used to contact the pushing component of the rod system reset mechanism to transmit the reset thrust.

[0028] Furthermore, the linkage reset mechanism includes a servo motor, a damping reducer, a push arm, a slider-slide assembly, a first position sensor, and a second position sensor;

[0029] The damping reducer is coaxially positioned near the end of the transmission rod; the push arm is coaxially mounted on the transmission rod and located between the transmission rod limiting ring and the damping reducer.

[0030] The slider-slider assembly is fixed on the test bench, including a slide bar and a slider slidably connected to the slide bar. The slider is driven by a servo motor and is fixedly connected to the push arm.

[0031] The first and second position sensors are installed on the slider-slider assembly, with their installation positions corresponding to the initial positions of the incident rod and the transmission rod, as well as the initial position of the push arm, respectively, to collect the position information of the slider. When the push arm is in the initial position, the transmission rod limiting ring is set at a safe distance from the push arm, so that the transmission rod limiting ring does not contact the push arm when the incident rod and the transmission rod move under impact. The safe distance is obtained based on the pre-experiment calibration.

[0032] The programmable controller is electrically connected to the first position sensor, the second position sensor, and the servo motor, and is used to: after each impact, control the servo motor to start according to a preset delay time, drive the slider and the push arm, thereby pushing the transmission rod limiting ring to push the transmission rod, the specimen, and the incident rod back to the initial position as a whole until the incident rod limiting ring contacts and limits the incident rod limiting device; and monitor the reset status of the incident rod and the transmission rod in real time according to the position information of the first position sensor and the second position sensor.

[0033] This invention also provides a closed-loop controlled constant amplitude impact loading method for electromagnetic shock fatigue testing, which is implemented using a designed closed-loop controlled constant amplitude impact loading device; the closed-loop controlled constant amplitude impact loading method includes the following steps:

[0034] Step 1: Clamp the specimen between the incident rod and the transmission rod, and set the target loading amplitude and control mode;

[0035] Step 2: Control the impact loading module to strike the incident rod, generating an incident stress wave to load the specimen;

[0036] Step 3: Perform reset operations on the impact loading module and the specimen clamping and carrier transmission module in sequence;

[0037] Step 3.1: Control the cut-off of the pulse power supply, the electromagnetic pulse disappears, and the return spring forces the punch to reset;

[0038] Step 3.2: The control lever reset mechanism is activated, causing the transmission rod, the incident rod, and the specimen as a whole to return to their corresponding initial positions;

[0039] Step 4: Acquire wave signals reflecting the loading state of the specimen through the data acquisition module, and compare them with the target loading amplitude to generate a deviation signal;

[0040] Step 5: The automatic control module calculates and adjusts the input parameters of the impact loading module based on the deviation signal;

[0041] Step 6: Return to step 2 for the next impact loading, wherein the impact loading in step 2 is performed using the input parameters adjusted in step 5; repeat steps 2 to 6 until the test ends.

[0042] Furthermore, when the control mode is the first loading control mode, the target loading amplitude is the first preset threshold; in step 3, the wave signal is the transmitted wave signal; in step 4, when the transmitted wave amplitude is lower than the first preset threshold, the adjustment operation is to increase the input parameter of the next impact; when the transmitted wave amplitude is greater than the first preset threshold, the adjustment operation is to decrease the input parameter of the next impact.

[0043] When the control mode is the second loading control mode, the target loading amplitude is the second preset threshold; in step 3, the wave signal is the reflected wave signal; in step 4, when the reflected wave amplitude is lower than the second preset threshold, the adjustment operation is to increase the input parameter of the next impact; when the reflected wave amplitude is greater than the second preset threshold, the adjustment operation is to decrease the input parameter of the next impact.

[0044] The advantages of this invention are:

[0045] 1. The closed-loop control constant amplitude impact loading device of the present invention, on the one hand, through a closed-loop feedback loop composed of a data acquisition module and an automatic control module, monitors the reflected wave signal and transmitted wave signal in real time during the loading impact process, and automatically compensates and feeds back to adjust the electromagnetic impact force to the set value. On the other hand, by resetting the impact loading module, the incident rod and the transmission rod, it realizes automated constant amplitude high-frequency loading cycle, improves the stability of the loading amplitude, reduces the relative error of the incident wave strain amplitude, and thus accurately obtains the complete SN curve of the material under high-frequency impact load.

[0046] 2. Addressing the issue in the field of impact fatigue where the focus is primarily on the impact frequency and strain rate effects, and there is currently no unified standard for the boundary between high-cycle and low-cycle fatigue, this invention employs two modes—short-life fatigue under high-stress amplitude impact and long-life fatigue under low-stress amplitude impact—to automatically classify and adjust impact fatigue life. Different control and adjustment strategies are designed for different control modes. Specifically, for the long-life fatigue mode under low-stress amplitude impact, considering that the strain amplitude is relatively small, the stress level is below the material's yield strength, and the deformation is mainly elastic strain, the control strategy adopts a transmission wave signal-based control method, i.e., control is achieved by monitoring the strain gauge signals on the transmission rod. When cracks begin to initiate in the specimen with increasing impact frequency during the test, the specimen's wave impedance decreases. At this point, to ensure constant stress and transmission wave amplitude on the specimen, the incident wave amplitude is increased through an automatic control module. For short-life fatigue modes under high-stress amplitude impact, considering the large strain amplitude and stress level approaching or exceeding the yield strength, with plastic strain dominating, a control strategy based on reflected wave signals is adopted. This involves monitoring the results using strain gauges on the incident rod. As the number of impacts increases during the test, crack initiation and propagation occur, leading to a decrease in the specimen's wave impedance. To ensure constant specimen strain, the reflected wave amplitude must be kept constant, which is achieved by automatically reducing the incident wave amplitude through a control module. A single device can simultaneously meet the impact fatigue test requirements of two different modes by switching control modes. This system has a wide range of applications and can be used for long-term stable observation of specimen fatigue life behavior, reducing observation costs.

[0047] 3. In this invention, the impact loading module uses a pulse power supply and an electromagnetic driver. The electromagnetic drive method has a fast response speed and high control accuracy. Combined with the closed-loop feedback control of the data acquisition module and the automatic control module, it improves the stability and repeatability of the incident wave amplitude, thus ensuring the acquisition of accurate impact fatigue SN curves.

[0048] Additional aspects and advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. Attached Figure Description

[0049] The above and / or additional aspects and advantages of the present invention will become apparent and readily understood from the description of the embodiments taken in conjunction with the following drawings, in which:

[0050] Figure 1 This is a connection block diagram of the closed-loop control constant amplitude impact loading device of the present invention;

[0051] Figure 2 This is a schematic diagram of the control circuit of the closed-loop control constant amplitude impact loading device of the present invention;

[0052] Figure 3This is a front view of the impact loading module in this invention;

[0053] Figure 4 This is a schematic diagram of the automatic compensation control process of the automatic control module and the data acquisition module in this invention.

[0054] Explanation of reference numerals in the attached drawings: 1-Fasting nut, 2-Reset spring, 3-Push rod, 4-Discharge coil, 5-Induction coil, 6-Variable cross-section amplifier, 7-Punch, 8-Pressure sensor, 9-Displacement sensor, 10-Pulse power supply connection line, 11-Bracket, 12-Incident rod limiting device, 13-Incident rod, 14-Specimen, 15-Transmission rod, 16-Transmission rod strain gauge, 1701-Incident rod limiting ring, 1702-Transmission rod limiting ring, 18-Push arm, 19-Damping reducer, 20-Programmable controller, 21-Calculator, 22-Incident rod strain gauge, 23-Data acquisition unit, 24-First position sensor, 2501-Sliding rod, 2502-Sliding block, 26-Second position sensor, 27-Pulse power supply, 28-Amplifier, 29-Comparator, 30-Servo motor. Detailed Implementation

[0055] The embodiments of the present invention are described in detail below. These embodiments are exemplary and intended to explain the present invention, and should not be construed as limiting the present invention.

[0056] Furthermore, the terms "first," "second," etc., used in this disclosure are for distinguishing one element from another and do not imply any order or importance. In the following description, when referring to the accompanying drawings, unless otherwise explained, the same reference numerals in different drawings denote the same or similar elements.

[0057] like Figures 1-3 This embodiment provides a complete closed-loop controlled constant amplitude impact loading device for electromagnetic shock fatigue testing, with the entire device mounted on a stable test platform. This closed-loop controlled constant amplitude impact loading device for electromagnetic shock fatigue testing includes an impact loading module, a specimen clamping and carrier wave transmission module, a data acquisition module, and an automatic control module.

[0058] The impact loading module includes a pulse power supply 27 and an electromagnetic driver. The pulse power supply 27 is electrically connected to the electromagnetic driver via an external pulse power connection line 10, and generates an electromagnetic pulse by supplying power to the electromagnetic driver. In a preferred embodiment of the present invention, the electromagnetic driver includes a push rod 3 and a return spring 2, a discharge coil 4, an induction coil 5, and a punch 7 arranged coaxially on the push rod 3 in sequence. The pulse power supply 27 is connected to the discharge coil 4 via the external pulse power connection line 10. The discharge coil 4 and the induction coil 5 are arranged in close contact with each other, and are fixedly and insulatedly mounted on a bracket 11. Specifically, they are supported and fixed by a base plate on the bracket and a vertical support frame for the coils. The end of the push rod 3 is connected to the reciprocating punch 7. The return spring 2 is sleeved on the push rod 3, and its two ends abut against a fixing member (which may be the fastening nut 1 shown in the figure) and the bracket 11, so that the punch is reset by the spring compression force stored in it after impact. When the discharge coil 4 is energized, a pulsed magnetic field is formed around it. Due to electromagnetic induction, this magnetic field passes through the induction coil 5, thereby generating extremely strong induced eddy currents and a reverse pulsed magnetic field within the induction coil. Since the pulsed magnetic fields generated by the two coils are in opposite directions, a strong eddy current repulsion force is formed between them, thus driving the push rod 3 and the punch 7 to move, achieving the impact on the specimen clamping and carrier transmission module. To optimize energy transfer, a variable cross-section amplifier 6 is installed between the end of the support and the end face of the punch, near the induction coil 5, to concentrate all the eddy current repulsion force to the punch 7, thereby improving the impact test effect. Simultaneously, this structural design simplifies the energy transfer process, enabling more precise control of the punch's impact frequency. Furthermore, it also includes a pressure sensor 8 and / or a displacement sensor 9 fixed on the punch or push rod 3. The pressure sensor 8 is connected to the automatic control module (specifically the programmable controller 20) to detect the impact intensity of the punch and transmit the detection result to the automatic control module. The displacement sensor 9 is also electrically connected to the automatic control module (specifically the programmable controller 20) to detect the real-time position of the punch 7 or push rod 3, especially to confirm the occurrence of the impact event (punch impacting the incident rod) and the completion of the reset event (impact loading module reset).

[0059] The specimen clamping and carrier wave transmission module is used to transmit the mechanical impact output by the impact loading module to the specimen 14. It includes an incident rod 13, a transmission rod 15, and a rod reset mechanism, all coaxially arranged. The specimen 14 is coaxially fixed between the end faces of the incident rod 13 and the transmission rod 15. The fixing method can be threaded connection, adhesive bonding, or clamping and fixing with a special fixture designed according to experimental requirements. The left end face of the incident rod 13 (the end face near the punch) is the impact surface, which bears the impact force of the punch 7. The specimen clamping and carrier wave transmission module also includes an incident rod limiting device 12, an incident rod limiting ring 1701, and a transmission rod limiting ring 1702. The incident rod limiting device 12 and the incident rod limiting ring 1701 are both coaxially arranged at one end of the incident rod (the impacted end), and the incident rod limiting ring 1701 is fixedly sleeved on the rod body of the incident rod. The incident rod limiting device 1 is positioned close to the punch 7. It is fixedly connected to the test bench of the bearing closed-loop control constant amplitude impact loading device (not shown in the figure) via a base and is coaxially clearance-fitted with the incident rod. The incident rod limiting device 12 can dampen the movement speed of the incident rod 13 during its axial movement (moving to the right as shown in the figure) after receiving the impact. It can also contact the incident rod limiting ring 1701 when the incident rod 13 resets, thus limiting the axial position of the incident rod. The incident rod limiting device 12 can buffer the movement of the incident rod by connecting the incident rod to the base using elastic elements such as springs or rubber bands. The transmission rod limiting ring 1702 is fixedly sleeved on the transmission rod body and close to the end of the transmission rod, and is used to contact the pushing component of the rod reset mechanism to transmit the reset thrust.

[0060] The rod system reset mechanism, under the control of the automatic control module, automatically resets the incident rod and the transmission rod to their initial positions after each impact. This mechanism includes a servo motor 30, a damping reducer 19, a push arm 18, a slider assembly, a first position sensor 24, and a second position sensor 26. Specifically, the damping reducer 19 is coaxially positioned near the end of the transmission rod to absorb / reduce impact energy when it contacts the transmission rod; the push arm 18 is coaxially mounted on the transmission rod body and near its end, located between the transmission rod limiting ring 1702 and the damping reducer 19; and when the push arm 18 is in its initial position, the transmission rod limiting ring is spaced at a safe distance from the push arm, ensuring that the transmission rod limiting ring does not contact the push arm during the impact, thus preventing contact from affecting experimental accuracy. This safe distance is obtained through pre-experiment calibration, which can be achieved using known and mature technologies; that is, those skilled in the art know how to perform pre-experiment calibration to obtain this safe distance. In this embodiment, the safe distance between the transmission rod limiting ring 1702 and the push arm 18 is preferably designed to be 10cm. Combined with the buffering effect of the incident rod limiting device 12 and the damping reducer 19, it can be ensured that the transmission rod limiting ring 1702 does not contact the push arm 18 during impact motion, which is sufficient to meet the impact fatigue test of various specimens.

[0061] The slider-slider assembly is fixed to the test bench by a connecting frame. It includes a slide rod 2501 and a slider 2502 slidably connected to the slide rod. The slider 2502 is driven by a servo motor 30, and the slider is fixedly connected to one end of the push arm. The other end of the push arm is nested on the rod body of the transmission rod. Under the drive of the slider, the swing arm 18 can slide along the transmission rod 15. When it contacts the transmission rod limiting ring 1702, it drives the transmission rod, the specimen and the incident rod to reset to the left (in the direction shown in the figure) until the incident rod limiting ring 1701 contacts the incident rod limiting device 12, indicating that the reset is in place. Servo motor 30, first position sensor 24 and second position sensor 26 are all connected to automatic control module (specifically programmable controller in automatic control module). After each impact, programmable controller controls servo motor 30 to start according to preset delay time, drive slider and push arm. After push arm 18 contacts transmission rod limit ring 1702, it drives transmission rod 15, specimen 14 and incident rod 13 to move together and push them back to the initial position until incident rod limit ring contacts incident rod limit device and resets to the position.

[0062] To facilitate reset control, this embodiment of the invention fixes two position sensors on the support of the sliding rod, including a first position sensor 24 and a second position sensor 26, for collecting the position information of the slider during the reset process. The installation position of the first position sensor 24 (defined as position A) corresponds to the initial position of the incident rod and the transmission rod, and the installation position of the second position sensor (defined as position B) corresponds to the initial position of the swing arm 18. When the push arm is in its initial position (corresponding to position B), the transmission rod limiting ring 1702 maintains a safe distance between itself and the push arm 18. A damping reducer 19 is used to smooth the reset action. During the reset process, the reset status of the incident rod and the transmission rod is monitored in real time based on the position information of the first position sensor 24 and the second position sensor 26 to determine whether the incident rod and the transmission rod have been reset to the correct position.

[0063] In this embodiment of the invention, the data acquisition module includes a transmission rod strain gauge 16 mounted on the transmission rod and an incident rod strain gauge 22 mounted on the incident rod. It also includes a data acquisition unit 23, an amplifier 28, and a comparator 29. After the punch impacts the end face of the incident rod, a compression wave propagates along the incident rod. When the compression wave reaches the contact surface between the specimen and the incident rod, part of the compression wave forms a reflected wave, while the other part propagates through the specimen on the transmission rod, generating a transmitted wave. Both the transmitted and reflected waves reflect the loading state of the specimen. Specifically, for long-life behavior under low-stress amplitude impact, elastic strain dominates, and transmitted wave control can be used, i.e., the transmitted wave is monitored based on the transmission rod strain gauge 16. For short-life behavior under high-stress amplitude impact, the stress level is close to or exceeds the yield strength, and plastic deformation dominates, and reflected wave control can be used, i.e., the reflected wave is monitored based on the incident rod strain gauge 22. Therefore, the data acquisition unit 23 converts the transmitted wave signal and / or incident wave signal acquired by the strain gauges into corresponding electrical signals, uses the amplifier 28 to condition and amplify the converted signal, and then sends it to the comparator 29. The comparator 29 is internally preset with the target loading amplitude (including the incident wave amplitude and the transmitted wave amplitude). The comparator is used to compare the conditioned stress wave amplitude with the target loading amplitude and output a deviation signal, which is then input to the automatic control module.

[0064] The automatic control module includes a programmable logic controller (PLC) 20 and a calculator 21. The PLC is electrically connected to the pulse power supply 27 of the impact loading module, and the calculator 21 is communicatively connected to the comparator 29 of the data acquisition module. The automatic control module and the data acquisition module form a closed-loop feedback loop. The PLC is configured to receive the deviation signal between the stress wave amplitude and the target loading amplitude monitored in real time by the data acquisition module, and dynamically adjust the input parameters (voltage and / or current) of the pulse power supply based on this deviation signal to adjust the impact force during the next impact. This achieves closed-loop control and automatic compensation of the load amplitude on the specimen during continuous impact testing. Specifically, for both long-life behavior under low-stress amplitude impact and short-life behavior under high-stress amplitude impact, the designed closed-loop control loop can effectively control both material fatigue failure modes. For long-life behavior, the strain amplitude is small, the stress level is below the yield strength, and elastic strain dominates, requiring transmission wave signal control. When the wave impedance decreases due to crack initiation during the impact test, the incident wave amplitude needs to be automatically increased to compensate for and maintain the stability of the transmission wave amplitude in order to maintain the constant stress on the specimen, thereby achieving closed-loop control of the specimen's stress state. In the experiment, the transmission wave amplitude is compared with a preset threshold by comparator 29, and the impact force is adjusted by feedback from programmable controller 20. For short-life behavior under high-stress amplitude impact, the strain amplitude is large, the stress level is close to or exceeds the yield strength, and plastic strain is significant, requiring reflected wave signal control. When the wave impedance decreases due to crack initiation and propagation during the impact test, the incident wave amplitude can be automatically reduced to maintain the stability of the reflected wave amplitude in order to maintain the constant strain on the specimen, thereby achieving closed-loop control of the specimen's strain state. During the closed-loop control process, the calculator 21 receives the deviation signal output by the comparator 29 and, using its internally stored control logic and a calibration model determined through pre-experiments, calculates the input parameters of the pulse power supply and sends them to the programmable logic controller (PLC). The calibration model can be an impact force-current-voltage data mapping table, which is established through multiple pre-experiment calibrations as follows:

[0065] Step S1: Using a standard specimen of the same type of material, with the specimen intact, fix a set of pulse power supply parameters, including voltage and corresponding current.

[0066] Step S2: Perform an impact test and record the impact force, standard transmitted wave amplitude, and standard reflected wave amplitude generated at this time on the intact sample using strain gauges and a data acquisition device.

[0067] Step S3: Repeat steps S1-S2, changing the pulse power supply parameters to obtain a series of corresponding impact forces, standard transmitted wave amplitude values, and standard reflected wave amplitude values, thereby establishing a data mapping table of impact force-current-voltage data. The standard transmitted wave amplitude value and the standard reflected wave amplitude value serve as preset thresholds for the comparator's judgment operation.

[0068] During the closed-loop control process of the formal test, the calculator 21 receives the current stress wave amplitude deviation signal from the comparator 29, and then, based on the current control mode and the target loading amplitude (target incident wave amplitude or target transmitted wave amplitude), it searches and calculates the adjusted input parameters (voltage and / or current) of the pulse power supply in conjunction with the obtained data mapping table.

[0069] This invention configures two types of control modes according to experimental requirements. The first loading control mode is a long-life fatigue control mode under low-stress amplitude impact, and the second loading control mode is a short-life fatigue control mode under high-stress amplitude impact. The type of control mode can be input according to experimental requirements. The comparator in the data acquisition module is configured to selectively compare based on the input control mode. Specifically: in the first loading control mode, the comparator compares the transmitted wave amplitude with a first preset threshold (the target amplitude of the transmitted wave) to obtain a transmitted wave amplitude deviation signal; in the second loading control mode, the comparator compares the reflected wave amplitude with a second preset threshold (the target amplitude of the reflected wave) to obtain a reflected wave amplitude deviation signal. Correspondingly, the calculator and programmable controller are configured as follows: in the first loading control mode, the calculator receives the transmitted wave amplitude deviation signal output by the comparator and searches for the adjustment amount of the input parameters (voltage and / or current) of the pulse power supply; in the second loading control mode, the calculator receives the reflected wave deviation signal output by the comparator and searches for the adjustment amount of the input parameters of the pulse power supply. The programmable controller adjusts the input parameters of the pulse power supply during the next impact based on the calculation results from the calculator, thereby regulating the electromagnetic impact force.

[0070] A pressure sensor 8 and a displacement sensor 9 are also installed on the punch or push rod, both electrically connected to the programmable controller (PLC). These sensors are used to collect the intensity of the impact force on the punch and the displacement of the punch 7 (or push rod 4), respectively. The displacement sensors work in conjunction with the PLC to determine the completion of punch impact and reset events. Specifically, after the PLC detects that the punch has contacted the end face of the injection rod, it confirms that the impact event has been completed and controls the punch to return to its initial position. The specific retraction process is as follows: During the impact, the electromagnetic force propels the induction coil, push rod, and punch forward. Simultaneously, this compresses the return spring 2 on the push rod 3, storing its elastic potential energy. After the impact, the displacement sensor 9 monitors the punch displacement in real time. When the displacement sensor 9 detects that the punch has moved to the impact surface of the incident rod (the left end of the incident rod in the diagram), it sends the obtained signal to the PLC. The PLC confirms the impact is complete, cuts off or stops sending the power supply sustaining signal to the pulse power supply, de-energizing the discharge coil and eliminating the electromagnetic force. After the electromagnetic force disappears, the elastic restoring force of the return spring acting on the punch and push rod drives the induction coil, push rod, and punch as a whole to move away from the incident rod until they return to their initial stationary position. As the punch retracts under the action of the return spring, the displacement sensor continuously monitors its position. When the displacement sensor detects that the punch has returned to the preset "initial position," it sends a "punch reset complete" signal to the PLC. At this point, the punch reset cycle ends, preparing for the next impact.

[0071] As the core controller of the closed-loop control circuit, the programmable logic controller (PLC) receives adjustment signals of pulse power input parameters from the calculator, impact pressure signals from pressure sensor 8, position signals from displacement sensor 9, and position signals from position sensors (first position sensor 24 and second position sensor 26) at its input ports. Its output ports control the triggering and electrical parameters (such as charging voltage and charging current) of the pulse power supply 27, and the start, stop, and direction of the servo motor 30. The functions of the calculator 21 can be integrated into the internal processor of the PLC.

[0072] Reference Figure 4 The present invention also provides a method for conducting electromagnetic shock fatigue tests using the aforementioned closed-loop control constant amplitude impact loading device, comprising the following steps:

[0073] Step 1: Fabricate the test fixture according to the test requirements. Clamp the specimen between the end faces of the incident rod and the transmission rod using the fixture, ensuring tight contact. Then, the target loading amplitude and test fatigue life control mode (long-life fatigue mode under low-stress amplitude impact or short-life fatigue mode under high-stress amplitude impact) can be set through the programmable controller's human-machine interface. This embodiment describes the process using the long-life fatigue mode under low-stress amplitude impact as an example.

[0074] In step 2, the programmable controller 20 issues a command, and the pulse power supply 27 discharges to the discharge coil 4 with initial preset parameters (voltage and current parameters) to generate a pulsed magnetic field. This magnetic field passes through the induction coil 5 to generate a reverse induced magnetic field. Eddy current repulsion is formed between the two magnetic fields, pushing the push rod 3 and the punch 7 to move. The punch 7 accelerates and impacts the end face of the incident rod 13, generating a compression wave (incident wave) that propagates along the incident rod. When the compression wave reaches the contact surface between the specimen and the incident rod, part of the compression wave forms a reflected wave, and the other part passes through the specimen and propagates on the transmission rod to generate a transmitted wave. The strain gauge 13 on the incident rod and the strain gauge 16 on the transmission rod measure the amplitude of the reflected wave signal and the amplitude of the transmitted wave signal generated by the first impact, respectively, and transmit the collected wave signals to the data acquisition unit 23.

[0075] Step 3: During the impact, the pressure sensor 8 and displacement sensor 9 monitor the impact pressure and the displacement of the punch and feed it back to the programmable controller 20. The programmable controller 20 determines whether the punch has hit the incident rod based on the feedback displacement data. After confirming that the impact event has been completed, the control pulse power supply 27 is turned off and the reset spring 2 causes the punch 7 to return to the initial position.

[0076] To ensure the stress wave transmission is complete, the programmable controller 20 activates the servo motor 30 based on a preset delay time (calculated according to the wave velocity, the length of the incident rod, and the transmission rod). This causes the slider 25 to move towards position A. When the slider and the push arm move together and contact the transmission rod 15, they jointly push the transmission rod 15 forward, causing the specimen 14 and the incident rod 13 to return to their initial positions. When the slider reaches position A, indicating that it has returned to its correct position, the programmable controller controls the servo motor to reverse, and the slider drives the push arm back to position B. At this point, the first impact process ends, and all components are reset to their initial states.

[0077] Step 4: Since the selected control mode is the long-life fatigue mode under low-stress amplitude impact, the data acquisition unit 23 converts the received reflected wave signal and transmitted wave signal into electrical signals, and only uses the converted reflected wave signal as monitoring data without participating in the subsequent processing. At this time, the data acquisition unit sends the converted transmitted wave signal (electrical signal) to the amplifier for amplification and conditioning processing. The comparator compares the processed transmitted wave signal with the first preset threshold (target amplitude of the transmitted wave) and sends the obtained deviation signal to the calculator 21. When the transmitted wave amplitude is lower than the first preset threshold, it indicates that the wave impedance of the specimen has decreased due to crack initiation. In order to maintain the constant stress on the specimen, it is necessary to increase the incident wave amplitude to compensate and maintain the stability of the transmitted wave amplitude, that is, it is necessary to increase the input parameter of the next impact. Therefore, the deviation signal is negative at this time. When the transmitted wave amplitude is greater than the first preset threshold, it is necessary to decrease the input parameter of the next impact. The deviation signal is positive at this time. When the transmitted wave amplitude is equal to the first preset threshold, the input parameter of the pulse power supply is not adjusted, and the PLC controls the pulse power supply to work according to the current input parameter.

[0078] Comparator 21 receives the transmitted wave amplitude deviation signal and calls the pre-stored calibration model to calculate the adjustment amount of the charging voltage (or charging current) of the pulse power supply 27 to compensate for this deviation (the adjustment amount is positive if it needs to be increased, and negative if it needs to be decreased), and sends the adjustment amount to the programmable controller 20. The programmable controller 20 issues new input parameters (original output parameters + adjustment amount) to the pulse power supply 27 according to the obtained adjustment amount.

[0079] Step 5: Return to Step 2 for the next impact loading, where the impact loading in Step 2 is performed using the new input parameters adjusted in Step 3. Repeat the above process to perform closed-loop controlled constant amplitude cyclic loading on the sample.

[0080] During subsequent cyclic loading, the pulse power supply 27 successively drives the electromagnetic coil with higher energy, generating greater eddy current repulsion, causing the punch 7 to impact at higher speeds and producing stronger incident waves. This process repeats, and as the crack continues to propagate, the wave impedance of the specimen continues to decrease. The control mode is then switched to a short-life control mode under high-stress amplitude impact (second loading control mode) to enhance the incident wave and maintain constant strain on the specimen.

[0081] The control process of the second loading control mode is similar to that of the first loading control mode, but the feedback signal is a reflected wave signal. Through closed-loop feedback control between the automatic control module and the data acquisition module, the amplitude of the incident wave is automatically reduced to maintain a stable reflected wave amplitude, thereby achieving closed-loop control of the specimen's strain state. When the incident wave intensity reaches the system's upper limit and cannot be compensated, or when the specimen completely breaks, causing the transmitted wave signal to disappear, the programmable control pre-determines the end of the test and stops the machine.

[0082] In practical applications, fatigue testing of the specimen can be carried out on a full life cycle according to the above test procedure, or the first loading control mode or the second loading control mode can be selected according to the test requirements.

[0083] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any person skilled in the art can easily conceive of various equivalent modifications or substitutions within the scope of the technology disclosed in the present invention, and such modifications or substitutions should all be covered within the scope of protection of the present invention.

Claims

1. A closed-loop controlled constant amplitude impact loading device for electromagnetic impact fatigue testing, characterized in that, It includes an impact loading module, a specimen clamping and carrier transmission module, a data acquisition module, and an automatic control module; The impact loading module is used to generate a controllable impact, including a pulse power supply, a return spring, an electromagnetic actuator, and a reciprocating punch connected to the electromagnetic actuator. The pulse power supply is electrically connected to the electromagnetic actuator to generate an electromagnetic pulse. The return spring is used to reset the punch after the impact. The specimen clamping and carrier transmission module is used to transmit the impact output by the impact loading module to the specimen. It includes an incident rod, a transmission rod, and a rod system reset mechanism arranged coaxially. The specimen is coaxially fixed between the end faces of the incident rod and the transmission rod. The rod system reset mechanism is used to reset the incident rod and the transmission rod to their initial positions after each impact. The data acquisition module is used to monitor the stress wave amplitude values ​​of the incident rod and the transmission rod in real time, calculate and output the deviation signal between the monitored stress wave amplitude value and the preset threshold. The automatic control module includes a programmable controller; the programmable controller is connected to the impact loading module and the data acquisition module; wherein the automatic control module and the data acquisition module form a closed-loop feedback control loop; the programmable controller is configured to: receive the deviation signal between the stress wave amplitude and the target loading amplitude monitored in real time by the data acquisition module, and dynamically adjust the input parameters of the impact loading module according to the deviation signal to adjust the magnitude of the impact force during the next impact, thereby realizing closed-loop control and automatic compensation of the load amplitude on the specimen in continuous impact testing.

2. The closed-loop controlled constant amplitude impact loading device for electromagnetic shock fatigue testing according to claim 1, characterized in that, The data acquisition module includes strain gauges, a data acquisition unit, an amplifier, and a comparator mounted on the incident rod and / or the transmission rod. The data acquisition unit is used to convert the stress wave acquired by the strain gauge into an electrical signal; the amplifier is used to perform amplitude conditioning on the converted signal; the comparator is used to compare the conditioned stress wave amplitude with the target loading amplitude and output a deviation signal.

3. The closed-loop controlled constant amplitude impact loading device for electromagnetic shock fatigue testing according to claim 2, characterized in that, The automatic control module also includes a calculator, which is communicatively connected to the comparator and the programmable controller. The calculator has pre-stored control logic and a calibration model determined through pre-experimentation, which is used to calculate the input parameters of the impact loading module based on the deviation signal and send them to the programmable controller.

4. The closed-loop controlled constant amplitude impact loading device for electromagnetic shock fatigue testing according to claim 3, characterized in that, The comparator is configured to make selective comparisons based on the input control mode: in a first loading control mode, the comparator compares the transmitted wave amplitude with a first preset threshold to obtain a transmitted wave amplitude deviation signal; in a second loading control mode, the comparator compares the reflected wave amplitude with a second preset threshold to obtain a reflected wave amplitude deviation signal. Meanwhile, the calculator is configured to perform selective calculations based on the input control mode: in the first loading control mode, the calculator receives the transmitted wave amplitude deviation signal output by the comparator and calculates the adjustment amount of the input parameter; In the second loading control mode, the calculator receives the reflected wave deviation signal output by the comparator and calculates the adjustment amount of the input parameter.

5. The closed-loop controlled constant amplitude impact loading device for electromagnetic shock fatigue testing according to claim 1, characterized in that, The electromagnetic driver also includes a push rod, a discharge coil, and an induction coil; The reset spring, discharge coil, induction coil, and punch are coaxially arranged on the push rod in sequence; the pulse power supply is connected to the discharge coil through an external pulse power supply connection line. The discharge coil and the induction coil are arranged opposite to each other and fixedly installed on a bracket. Under the action of the pulse power supply, they can generate pulse magnetic fields in opposite directions, thereby forming eddy current repulsion to push the punch. The end of the push rod is connected to the punch; the return spring is sleeved on the push rod, with its two ends abutting between a fixing member and the bracket, so as to reset the punch after impact.

6. The closed-loop controlled constant amplitude impact loading device for electromagnetic shock fatigue testing according to claim 5, characterized in that, The electromagnetic actuator also includes a displacement sensor disposed on the punch or the push rod; The displacement sensor is used to detect the displacement of the punch or the push rod, and is electrically connected to the programmable controller to confirm the occurrence of the punch impact event and the completion of the reset event.

7. The closed-loop controlled constant amplitude impact loading device for electromagnetic shock fatigue testing according to claim 1, characterized in that, The specimen clamping and carrier transmission module also includes an incident rod limiting device, an incident rod limiting ring, and a transmission rod limiting ring; The incident rod limiting ring is fixedly sleeved on the incident rod; The incident rod limiting device is installed on the incident rod and corresponds to the position of the incident rod limiting ring, and is close to the impact end of the incident rod. It is fixedly connected to the test bench that carries the closed-loop controlled constant amplitude impact loading device through a base, and is coaxially clearance-fitted with the incident rod. The incident rod limiting device is used to slow down the movement speed of the incident rod by damping during the impact and axial movement of the incident rod, and to contact the incident rod limiting ring when the incident rod returns to its original position, thereby achieving axial limiting of the incident rod. The limiting ring of the transmission rod is fixedly sleeved on the transmission rod body and close to the end of the transmission rod, and is used to contact the pushing component of the rod system reset mechanism to transmit the reset thrust.

8. The closed-loop controlled constant amplitude impact loading device for electromagnetic shock fatigue testing according to claim 7, characterized in that, The linkage reset mechanism includes a servo motor, a damping reducer, a push arm, a slider assembly, a first position sensor, and a second position sensor; The damping reducer is coaxially positioned near the end of the transmission rod; the push arm is coaxially mounted on the transmission rod and located between the transmission rod limiting ring and the damping reducer. The slider-slider assembly is fixed on the test bench, including a slide bar and a slider slidably connected to the slide bar. The slider is driven by the servo motor and is fixedly connected to the push arm. The first position sensor and the second position sensor are mounted on the slider-slider assembly, with their mounting positions corresponding to the initial positions of the incident rod and the transmission rod, as well as the initial position of the push arm, respectively, for collecting the position information of the slider; and when the push arm is in the initial position, the transmission rod limiting ring is set at a safe distance from the push arm, so that the transmission rod limiting ring does not contact the push arm when the incident rod and the transmission rod move under impact, and the safe distance is obtained according to the pre-experiment calibration; The programmable controller is electrically connected to the first position sensor, the second position sensor, and the servo motor, and is used to: control the servo motor to start after each impact according to a preset delay time, drive the slider and the push arm, thereby pushing the transmission rod limiting ring to push the transmission rod, the specimen, and the incident rod back to the initial position as a whole until the incident rod limiting ring contacts and limits the incident rod limiting device; and monitor the reset status of the incident rod and the transmission rod in real time according to the position information of the first position sensor and the second position sensor.

9. A closed-loop controlled constant amplitude impact loading method for electromagnetic shock fatigue testing, characterized in that, The closed-loop control constant amplitude impact loading method is implemented based on any one of the closed-loop control constant amplitude impact loading devices described in 1-8; the closed-loop control constant amplitude impact loading method includes the following steps: Step 1: Clamp the specimen between the incident rod and the transmission rod, and set the target loading amplitude and control mode; Step 2: Control the impact loading module to strike the incident rod, generating an incident stress wave to load the specimen; Step 3: Perform reset operations on the impact loading module and the specimen clamping and carrier transmission module in sequence; Step 3.1: Control the cutting off of the pulse power supply, the electromagnetic pulse disappears, and the return spring forces the punch to reset; Step 3.2: Control the rod system reset mechanism to return the transmission rod, incident rod, and specimen as a whole to their corresponding initial positions; Step 4: Acquire wave signals reflecting the loading state of the specimen through the data acquisition module, and compare them with the target loading amplitude to generate a deviation signal; Step 5: The automatic control module calculates and adjusts the input parameters of the impact loading module based on the deviation signal; Step 6: Return to step 2 for the next impact loading, wherein the impact loading in step 2 is performed using the input parameters adjusted in step 5; repeat steps 2 to 6 until the test ends.

10. The closed-loop controlled constant amplitude impact loading method for electromagnetic shock fatigue testing according to claim 10, characterized in that, When the control mode is the first loading control mode, the target loading amplitude is the first preset threshold; in step 3, the wave signal is a transmitted wave signal; in step 4, when the transmitted wave amplitude is lower than the first preset threshold, the adjustment operation is to increase the input parameter of the next impact; when the transmitted wave amplitude is greater than the first preset threshold, the adjustment operation is to decrease the input parameter of the next impact. When the control mode is the second loading control mode, the target loading amplitude is the second preset threshold; in step 3, the wave signal is the reflected wave signal; in step 4, when the reflected wave amplitude is lower than the second preset threshold, the adjustment operation is to increase the input parameter of the next impact; when the reflected wave amplitude is greater than the second preset threshold, the adjustment operation is to decrease the input parameter of the next impact.

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