A method for comprehensively controlling the loading force in fatigue tests of asymmetric hydraulic dampers

Abstract

This invention discloses a method for comprehensively controlling the loading force in fatigue testing of an asymmetric hydraulic damper, characterized by a short force control adjustment cycle and rapid loading force balancing. The invention is achieved through the following technical solution: a computer generates control command signals for the hydraulic damper testing system and controls the displacement and force output by the hydraulic vibrator; the displacement signal is processed into a velocity signal or the acceleration signal is converted into a velocity signal; the comprehensive control software establishes a force loading function based on the load, test frequency, and test time corresponding to the initial amplitude A0 controlled by the force servo system; during the test, the comprehensive control software collects data from sensors, controls the force of the vertical displacement amplitude of the asymmetric hydraulic damper, implements synchronous control of horizontal translational or torsional loading throughout the entire displacement range, controls the torsional effect of the specimen during the loading test, obtains the relationship between the total horizontal force and displacement, measures the difference in horizontal force at each horizontal loading point, and realizes the measurement of the force and displacement of the horizontal torsion of the structure.

Description

Technical Field

[0001] This invention relates to a method for controlling the loading force of an asymmetric hydraulic damper during fatigue testing using a comprehensive control method. Background Technology

[0002] Statistics show that the sudden fracture of machine parts operating normally under alternating loads is called fatigue. The same strain amplitude will lead to the same fatigue damage. Different tests are required for different stress concentration conditions, resulting in a large workload. Approximately 80% of machine parts fail due to fatigue. Fatigue damage has the following characteristics: 1. The stress level leading to fatigue failure is low; the fatigue limit is lower than the tensile strength, even lower than the yield strength, and it requires multiple stress cycles, generally thousands or even millions of cycles before failure. 2. Fatigue failure is highly sensitive to defects; fatigue cracks originate in areas of high stress concentration or surface defects, such as surface cracks, soft spots, inclusions, abrupt corners, and tool marks.

[0003] 2. After fatigue fracture, no macroscopic plastic deformation is observed. Typically, three parts can be observed on the fatigue fracture surface.

[0004] Most components operate under variable amplitude loads. Fatigue failure under variable amplitude loads is the result of accumulated damage caused by loads of different frequencies and amplitudes. The damage caused by each cycle can be considered as the reciprocal of the cycle life N under that load, 1 / N. This damage is cumulative; the damage caused by n cycles of variable amplitude load equals the sum of the cycle ratios. Internal friction of the damper is a significant factor causing oil leakage failure. Necessary slow-speed testing, controlling the maximum force on the damper to within 10% of the design maximum force, is a necessary test for assessing damper quality. To test the damper's performance under loads of different frequencies, dynamic tests of the maximum damping force at different frequencies are required.

[0005] Currently available dampers can be categorized into two types based on their damping force generation mechanism: velocity-dependent and displacement-dependent. Typical velocity-dependent dampers include oil dampers and viscoelastic dampers, characterized by a reaction force proportional to velocity or its power. Typical displacement-dependent dampers include various forms of lead and steel dampers, where the reaction force is proportional to deformation in the elastic stage and remains essentially constant in the yield stage. The energy dissipation performance parameters of commonly used dampers are generally determined through cyclic testing, using the area ratio of the force-displacement hysteresis curve to assess the damper's energy dissipation capacity. This method analyzes data from a single cycle waveform with fixed frequency, displacement amplitude, and loading waveform. For variations in these parameters, a separate graphical analysis is required. Because the energy dissipation (damping) mechanisms of different dampers vary, the parameters related to their energy dissipation capacity also differ. Changes in physical quantities such as displacement, frequency, and velocity will all cause changes in the energy dissipation performance of the damper. In monotonic loading tests, with a fixed displacement amplitude and frequency, different loading waveforms lead to varying damper velocities during loading, thus affecting the damper's energy dissipation capacity. In monotonic loading, maintaining a constant velocity requires simultaneously changing both the loading frequency and displacement amplitude, inevitably resulting in differences in the damper's energy dissipation time and power, i.e., differences in the absolute value of energy dissipation. Simply using monotonic loading is insufficient. Since the external excitation experienced by a real structure is a stochastic process, the resulting response is also a stochastic process. The damper attached to the structure undergoes a stochastic motion process with characteristics specific to the structural response frequency range. Therefore, to comprehensively evaluate the damper's energy dissipation performance, it is necessary to consider the actual motion process of the damper; simply evaluating it through monotonic loading tests with different frequency, displacement, and velocity combinations is inadequate.

[0006] A hydraulic damper is a velocity-sensitive vibration absorption and attenuation device. It absorbs and attenuates the energy of vibrations and impacts, thereby reducing the dynamic response of components and protecting important facilities such as buildings, engineering structures, and mechanical structures from vibration and impact damage caused by gusts of wind. Hydraulic dampers are mainly used for seismic resistance in important large-scale buildings such as hospitals, power plants, bridges, aviation, railways, and skyscrapers, as well as pipelines and critical equipment in nuclear power plants, thermal power plants, and chemical plants. To test the technical performance indicators and manufacturing quality of hydraulic dampers, a hydraulic damper testing system must be built to conduct performance tests and quality inspections. The testing requirements for hydraulic dampers mainly include the following:

[0007] (1) The hydraulic damper is tested for motion resistance at low speed under a set speed. That is: at a set speed, the low-speed motion resistance time curve is plotted;

[0008] (2) Hydraulic damper release speed test. Under rated load, after the hydraulic damper control valve is in the closed state, the piston movement speed is measured. That is: set the load and plot the speed-time curve;

[0009] (3) Hydraulic damper lock-up speed test. In the frequency range of 1-33Hz, under different vibration loads, the hydraulic damper control valve automatically closes (locks up) at a certain speed within the range of 2-10mm / s. This speed is called the lock-up speed.

[0010] (4) Durability and fatigue test. Test whether there is oil leakage in the dynamic seal of the hydraulic damper piston rod after N reciprocating motions, and evaluate the sealing performance and performance stability of the product;

[0011] (5) Dynamic stiffness test of hydraulic damper. Select a frequency in the frequency range of 1 to 33 Hz, set the maximum load to the rated load, measure the relationship between load and displacement, and plot the curve.

[0012] Hydraulic asymmetric dampers differ from traditional viscoelastic dampers. Viscoelastic dampers primarily dissipate energy by utilizing the phase difference between shear stress and shear strain during shear deformation of viscoelastic materials, increasing the additional damping of the structure and reducing its dynamic response under wind or seismic loads. Current Chinese standards and regulations for the seismic fatigue performance testing of viscoelastic dampers fail to fully reflect their performance characteristics, causing many high-performance viscoelastic dampers to fail to meet the fatigue performance requirements of current standards. Furthermore, due to the unique properties of viscoelastic materials, viscoelastic dampers exhibit significant recovery of mechanical properties after a period of time if they have not been damaged. Therefore, this issue addresses the problem of the loading regime in the seismic fatigue performance testing of viscoelastic dampers underestimating their performance. Hydraulic asymmetric dampers feature pressure compensation and do not require system oil replenishment during use. Its main function is as follows: when the damping piston deviates slightly from its neutral position, the damper provides hydraulic damping through a small hole on the piston. Simultaneously, the internal valves work together to ensure effective damping. When the damping force is excessive, the safety valve opens to reduce damping, effectively controlling the maximum damping force. Without any compensation measures, the static force conflict is very large, and this conflict increases with the increase of external load and positional deviation. Without conflict compensation, the system has poor disturbance rejection performance and significant static force conflict, especially poor disturbance rejection stiffness. Although the system eventually reaches stability, the existence of significant dynamic and static force conflict will have adverse effects. The damper has an asymmetrical structure. Although the internal damping valve, safety valve, and replenishing valve are structurally identical, the inherent tolerances in each part during machining mean that the basic characteristics of the valves, such as internal leakage and opening force, cannot be completely identical. When a damper is under load, the damping force generated by it will not be completely uniform depending on the external load. Even with a uniform load, due to the damper's own structure, the center position of the product will undergo slight displacement, causing the center position to continuously shift to one side, ultimately leading to the interruption of the test. Therefore, we also call this type of damper an asymmetric hydraulic damper.

[0013] To evaluate the performance of damper products and provide a basis for product life determination, fatigue testing is required. The specific requirements for fatigue testing are: it must be conducted according to the product's fatigue test spectrum. That is, an initial test load F is applied at a frequency f, and the loading test is performed along the piston axis of the product. The number of cycles is 1×10⁻⁶. 6 One cycle consists of two tests. If the test specimen is still intact after one cycle, the load can be increased by 10% to 20% of the initial load to continue the test until the test specimen is damaged.

[0014] Existing technologies typically employ a double-column frame structure and a movable crossbeam. Internal friction within the damper is a significant factor causing oil leakage and damage. Necessary slow-speed testing, controlling the maximum force on the damper to within 10% of its design maximum, is a crucial test for assessing damper quality and is also a requirement of the ASSHTO standard. The hydraulic system drives the crossbeam's vertical movement. In contrast, the hydraulic damper fatigue testing bench uses a four-column frame structure, consisting of a base, actuator, columns, displacement sensors, high-precision load sensors, and hydraulic clamps for tooling. The upper crossbeam is hydraulically driven to move up and down, secured by a hydraulic clamping device to adjust the test space. The actuator is located on the upper crossbeam, and a spoke-type load sensor is mounted on the actuator piston head. Different types of fatigue clamps can be configured to accommodate various fatigue tests. This testing bench is primarily used for durability and life testing of hydraulic dampers. The testing process is fully automated, and the number of tests can be set; the bench automatically stops when the set number of tests is reached. This test bench features long lifespan and low noise, and also has overload and travel protection functions to protect force sensors and vibration dampers from damage.

[0015] The control system of the hydraulic damper fatigue testing bench is an electro-hydraulic control system. This electro-hydraulic servo system mainly consists of a servo amplifier, hydraulic cylinder, and force sensor. It is primarily suitable for performance testing of dampers, including fatigue life, endurance fatigue, reciprocating fatigue, tensile fatigue, and bending fatigue. It can collect displacement and force sensor data in real time during the experiment, record information such as product model, product code, test time, test personnel, damping coefficient, and test conclusions, plot the FS curve (power curve) and FV curve of the hydraulic damper, and automatically generate a "Hydraulic Damper Product Test Record Sheet".

[0016] Existing fatigue testing methods mainly employ two approaches: force servo control and displacement servo control. The force servo control method uses the damper output force as the control target, applies a displacement sine wave for loading, and calculates the increment for automatic fine-tuning. The displacement servo control method uses the damper displacement as the control target, applies a sine wave for loading, and calculates the increment for automatic fine-tuning. For specimens with symmetrical structures, these two methods are relatively mature. However, for hydraulic dampers, although structurally symmetrical, the inherent tolerances in machining processes result in inconsistent valve characteristics, such as internal leakage and opening force. This leads to inconsistent damping forces under different external loads during load testing. Even with consistent loads, slight displacements in the product's center position due to its structure cause continuous lateral shifts, ultimately interrupting the test. Therefore, a testing device and control method are needed for loading tests on asymmetrical hydraulic damper lateral force-resisting structures. The shortcomings of both methods are:

[0017] 1) Start loading from an initial displacement range, set the fine-tuning step size, adjust the peak and valley values, and then enable automatic peak and valley control once the adjustment is complete. This method stops adjusting the force control when the force control target deviation is within range, but the force control adjustment cycle is long, the loaded force cannot reach equilibrium quickly, and the peak force value is prone to exceeding the limit.

[0018] 2) The waveform adjustment is discontinuous, and the asymmetry of the force peak and valley values ​​cannot be adjusted;

[0019] 3) Due to the inherent asymmetry of the damper product, the upper and lower displacements of the product at the midpoint position are inconsistent each time, resulting in different error values, long adjustment cycles, and easy for the peak force to exceed the limit.

[0020] 4) Analysis of the on-site test bench debugging and product testing revealed that directly using either force control or displacement control resulted in long target value adjustment cycles and difficulty in achieving stability. Problems such as the test failing to proceed normally often arose due to target values ​​exceeding limits.

[0021] 5) The force values ​​in the test are only collected and displayed. However, due to the asymmetry of the damper product itself, the upper and lower displacements of the product at the center position are inconsistent each time, resulting in different error values, long adjustment cycles, and the peak force is prone to exceeding the limit. Summary of the Invention

[0022] The purpose of this invention is to address the shortcomings of existing loading test devices and control methods for asymmetric hydraulic dampers resisting lateral forces. By combining force servo control and displacement servo control, this invention provides a comprehensive method for controlling the loading force of asymmetric hydraulic dampers in fatigue tests. This method is easy to operate, allows for continuous waveform adjustment, has a short force control adjustment cycle, enables rapid loading force balancing, allows for adjustment of the asymmetry of force peak and valley values, and ensures that the peak force value is not easily exceeded.

[0023] The above-mentioned objective of this invention can be achieved through the following technical solution: a method for comprehensively controlling the loading force of an asymmetric hydraulic damper in fatigue testing, characterized in that: a computer generates control command signals for the hydraulic damper testing system, controls the displacement and force output by the hydraulic vibrator, processes the displacement signal into a velocity signal or converts the acceleration signal into a velocity signal, and the computer comprehensive control software combines force servo control and displacement servo control. Based on the load F0 corresponding to the initial amplitude A0 and A1-A2 of the loading test device force servo system control, the test frequency f and the test time t are used to establish the force loading function F = F0 * sin2πft. During the test, the comprehensive control software collects data from the sensors, controls the force on the symmetrical vertical displacement amplitude A1 = A2 of the asymmetric hydraulic damper, implements synchronous control of horizontal translational or torsional loading of the entire displacement, controls the torsional effect of the asymmetric hydraulic damper structural specimen during the loading test, obtains the relationship between the total horizontal force and displacement, measures the difference in horizontal force at each horizontal loading point, and realizes the measurement of the force and displacement of the horizontal torsion of the structure.

[0024] Furthermore, during the experiment, the computer-controlled software of the hydraulic damper test system, based on the testing requirements of the hydraulic damper and the specific technical specifications of the test system, collects data from the sensors connected to the cylinder extension end, transforms the detected information into electrical signals or other required forms of information, outputs force, displacement, and acceleration motion parameters, controls the force on the symmetrical vertical displacement amplitude A1 = A2 of the asymmetrical hydraulic damper, and adjusts the symmetry of the peak and valley values ​​of the vertical force; then, using two triangular half-waves to form a sine curve periodic function, it adjusts the force control calculation ratio, replacing the previous incremental fine-tuning method, and simultaneously adjusts the adjustment amount of each half-wave of the asymmetrical hydraulic damper; setting the target load Fm, the load F0 corresponding to the initial amplitude A0, the load Fx corresponding to the amplitude Ax, the initial amplitude A0, the amplitude Ax+1 after Ax, and the proportional gain C, constructs the force control formula model: A i =(F m -F0) / (Fx-F0)*(A x+1 -A x )*C+A0, Ax amplitude x=0,1,2…..N-1; The force control formula model uses positive and negative half-axis to calculate and monitor separately, and corrects the positive and negative half-axis of the amplitude curve respectively to achieve symmetrical load on the positive and negative half-axis;

[0025] In displacement servo control, the median value of the force-time, displacement-time, and force-displacement curves is used as the zero point. The allowable deviation of the displacement of the damper under test is set, and peak-valley adjustment is performed. After the adjustment is in place, automatic peak-valley control is activated, and the required data is continuously collected. Loading begins with an initial displacement range value. Based on the displacement of each loading point, synchronous control of horizontal translational or torsional loading of the entire displacement is implemented. The torsional effect of the asymmetric hydraulic damper structure during the loading test is controlled to obtain data such as horizontal force and displacement at each loading point of the structure, and the relationship between the total horizontal force and displacement is obtained. Alternatively, the force and displacement of the horizontal torsion of the structure can be measured by the measured difference of horizontal force at each horizontal loading point and the distance between the horizontal loading systems.

[0026] Compared with the prior art, the present invention has the following advantages:

[0027] This invention combines force servo control and displacement servo control. Based on the load F0 corresponding to the initial amplitude A0 controlled by the force servo system, the test frequency f, and the test time t, a force loading function F = F0 * sin2πft is established. The integrated control software collects and controls the force on the symmetrical upper and lower displacement amplitudes A1 = A2 of the asymmetrical hydraulic damper, adjusting the symmetry of the upper and lower force peak and valley values. This allows for continuous waveform adjustment, adjustable force peak and valley asymmetry, and convenient operation. Test force indication accuracy: ±1.0% at each point within the 2%-FS range; test signal measurement resolution: ≥1 / 100,000, indication accuracy 0.005FS.

[0028] This invention uses two triangular half-waves to form a sine curve, a periodic function, to adjust the force control calculation ratio, replacing the previous incremental fine-tuning method. It also adjusts the amount of each half-wave of the asymmetric hydraulic damper, avoiding the defects of discontinuous waveform adjustment and unadjustable force peak and valley asymmetry in existing technologies.

[0029] This invention employs a force control formula model: A i =(F m -F0) / (Fx-F0)*(A x+1 -A x )*C+A0, Ax amplitude x=0,1,2…..N-1; The force control formula model uses positive and negative half-axis to calculate and monitor separately, and corrects the positive and negative half-axis separately to achieve symmetrical load on the positive and negative half-axis; It solves the problem of the asymmetry of the damper product itself, which causes the product to have inconsistent upper and lower displacements at the product's center position each time, resulting in different error values, long adjustment cycles, and easy over-limit force peaks.

[0030] This invention, in displacement servo control, uses the median value of the force-time, displacement-time, and force-displacement curves as the zero point, sets the allowable deviation of the damper's displacement, and performs peak-valley adjustments. After adjustment, automatic peak-valley control is activated, and loading begins with an initial displacement range value. This overcomes the problems of existing technologies that directly use force control and displacement control, resulting in long target value adjustment cycles, difficulty in achieving stability, and test failures due to target value exceeding limits. Experimental verification shows that this invention has a short adjustment cycle, uninterrupted adjustment waveform, and no displacement deviation from the zero point. It can achieve any of the following methods: load control, displacement control, or strain control. Its accuracy, sensitivity, and reliability are higher than other types of testing machines, and it is practical and effective.

[0031] This invention utilizes an electro-hydraulic servo fatigue testing machine for anchorage steel strand fatigue testing. Simultaneously, by changing the fixtures, other fatigue tests can be performed, such as fastener fatigue testing, rail bending fatigue testing, and component bending fatigue testing. Due to the electro-hydraulic servo loading method, the frequency can be increased, thus significantly shortening the test time. With the addition of a computer, complex program-controlled loading, data processing and analysis, as well as printing, display, and plotting can be achieved. Various configurations of servo valves and actuators, along with appropriate pump sources, can form systems with frequencies ranging from 0.0001 to 300 Hz. The servo controller sends control signals to the servo valve, which in turn controls the high-pressure oil from the high-pressure hydraulic source to drive the actuator, transforming it into mechanical motion acting on the specimen. Simultaneously, load sensors, strain sensors, and displacement sensors convert stress, strain, and displacement into electrical signals. One signal is fed back to the servo controller for comparison with a given signal; the difference signal is sent to the servo valve to adjust the actuator position. This process is repeated continuously until the force on the specimen reaches the required accuracy. The other signal of force, displacement, and strain is fed into the readout unit for display and recording. Attached Figure Description

[0032] Figure 1 This is a flowchart of the fatigue test loading force of the asymmetric hydraulic damper under the integrated control of the present invention;

[0033] Figure 2 This is a schematic diagram of the continuously adjustable waveform curve of the integrated control method software test interface;

[0034] Figure 3 This is a schematic diagram of the time t-displacement time-force curve of the present invention;

[0035] Figure 4 This is a schematic diagram of the force-displacement curve of the present invention.

[0036] Figure 5 This is a schematic diagram of the hydraulic damper loading system of the present invention.

[0037] In the diagram: 1. Horizontal force sensor, 2. Horizontal force jack, 3. Horizontal force adjustment device, 4. Reaction beam, 5. Portal column horizontal loading beam, 6. Screw nut hinge connector, 7. Hydraulic damper structural specimen, 8. Tension and compression sensor, 9. Vertical force jack. Detailed Implementation

[0038] According to the present invention, the computer generates control command signals for the hydraulic damper test system and controls the displacement and force output by the hydraulic vibrator, processes the displacement signal into a velocity signal or converts the acceleration signal into a velocity signal. The integrated control software establishes a force loading function based on the load, test frequency, and test time t corresponding to the initial amplitude A0 and A1-A2 controlled by the force servo system. During the test, the integrated control software collects data from the sensors, controls the force on the symmetrical vertical displacement amplitude A1=A2 of the asymmetric hydraulic damper, implements synchronous control of horizontal translational or torsional loading of the entire displacement, controls the torsional effect of the asymmetric hydraulic damper structural specimen during the loading test, obtains the relationship between the total horizontal force and displacement, measures the difference in horizontal force at each horizontal loading point, and realizes the measurement of the force and displacement of the horizontal torsion of the structure.

[0039] The specific steps are as follows:

[0040] The computer combines force servo control and displacement servo control. The loading test device establishes the force loading function F = F0 * sin2πft based on the load F0 corresponding to the initial amplitude A0 controlled by the force servo system, the test frequency f and the test time t.

[0041] During the test, the computer-controlled software of the hydraulic damper test system, based on the testing requirements of the hydraulic damper and the specific technical specifications of the test system, collects data from the sensors connected to the cylinder extension end, converts the detected information into electrical signals or other required forms of information, and outputs force, displacement, and acceleration motion parameters. It controls the force on the symmetrical vertical displacement amplitude A1 = A2 of the asymmetrical hydraulic damper, adjusting the symmetry of the peak and valley values ​​of the vertical force. Then, it uses a periodic function of a sine curve composed of two triangular half-waves to adjust the force control calculation ratio, replacing the previous incremental fine-tuning method, and simultaneously adjusts the adjustment amount for each half-wave of the asymmetrical hydraulic damper. It sets the target load Fm, the load F0 corresponding to the initial amplitude A0, the load Fx corresponding to the amplitude Ax, the initial amplitude A0, the amplitude Ax+1 after Ax, and the proportional gain C, constructing the force control formula model: A i =(F m -F0) / (Fx-F0)*(A x+1 -A x )*C+A0, Ax amplitude x=0,1,2…..N-1; The force control formula model uses positive and negative half-axis to calculate and monitor separately, and corrects the positive and negative half-axis of the amplitude curve respectively to achieve symmetrical load on the positive and negative half-axis;

[0042] In displacement servo control, the median value of the force-time, displacement-time, and force-displacement curves is used as the zero point. The allowable deviation of the displacement of the damper under test is set, and peak-valley adjustment is performed. After the adjustment is in place, automatic peak-valley control is activated, and the required data is continuously collected. Loading begins with an initial displacement range value. Based on the displacement of each loading point, synchronous control of horizontal translational or torsional loading of the entire displacement is implemented. The torsional effect of the asymmetric hydraulic damper structure during the loading test is controlled to obtain data such as horizontal force and displacement at each loading point of the structure, and the relationship between the total horizontal force and displacement is obtained. Alternatively, the force and displacement of the horizontal torsion of the structure can be measured by the measured difference of horizontal force at each horizontal loading point and the distance between the horizontal loading systems.

[0043] The computer generates control command signals for the hydraulic damper testing system and controls the displacement and force output by the hydraulic vibrator. It processes the displacement signal into a velocity signal or converts the acceleration signal into a velocity signal. The integrated control software establishes a force loading function based on the load corresponding to the initial amplitude A0 and A1-A2 controlled by the force servo system, the test frequency, and the test time t. During the test, the integrated control software collects data from the sensors and controls the force on the symmetrical vertical displacement amplitude A1=A2 of the asymmetric hydraulic damper. It implements synchronous control of horizontal translational or torsional loading throughout the entire displacement range, controls the torsional effect of the asymmetric hydraulic damper structural specimen during the loading test, obtains the relationship between the total horizontal force and displacement, and measures the difference in horizontal force at each horizontal loading point, thus realizing the measurement of the force and displacement of the horizontal torsion of the structure.

[0044] The hydraulic damper testing system includes a hydraulic vibrator with displacement and force sensors, a test bench, a high-flow electro-hydraulic servo valve for dynamic testing, a low-flow electro-hydraulic servo valve for static testing, a hydraulic oil source with an accumulator, oil source control, tension / compression force sensors, displacement sensors, analog control, CNC, data acquisition, and a power supply. The hydraulic oil in the accumulator is drained back to the tank, preventing high-pressure oil from the accumulator from directly impacting the return oil lines and connected low-pressure components. The accumulator provides instantaneous oil replenishment; when the hydraulic vibrator moves at low speed, the hydraulic pump supplies oil to the accumulator; when the vibrator moves at high speed, the hydraulic pump and accumulator work together to supply oil to the vibrator. This provides a large flow output in a short time, eliminating pressure pulsations generated by the hydraulic pump and stabilizing the system pressure.

[0045] Because the control flow rates differ significantly between static and dynamic tests of hydraulic dampers, two electro-hydraulic servo valves with different flow rates are designed in the hydraulic damper testing system for static and dynamic tests respectively. This improves the control accuracy of the system during static tests. Therefore, a control directional valve is used to select one of the electro-hydraulic servo valves for control; a high-flow-rate electro-hydraulic servo valve is selected for dynamic tests, and a low-flow-rate electro-hydraulic servo valve is selected for static tests. The electro-hydraulic servo valve converts the received current control signal into an electromechanical signal, outputting a flow rate and pressure proportional to the current control signal to drive the piston shaft in the hydraulic vibrator. The hydraulic vibrator then produces the same motion or force output as the command signal.

[0046] See Figure 1 During the initial loading process, the integrated control software sets parameters for frequency, target force value, target number of cycles, and control accuracy according to the loading force flow of the fatigue test of the asymmetric hydraulic damper. It compares the target load value with the target load value to determine if they match. If they do, a control output signal is generated, and loading force detection is performed. Otherwise, a feedback signal is sent for re-evaluation, and loading force detection continues. Based on the loading force detection, a voltage command signal generated by a signal source or computer is compared with the feedback signal in an adder to determine if the target number of cycles has been reached. If so, an error signal is obtained, which is then amplified by a power amplifier and converted into a drive current signal applied to the electro-hydraulic servo valve to complete the experiment. Otherwise, the loading process continues until the experiment is completed.

[0047] The integrated control software test interface features an automatic fine-tuning function. The fine-tuning step size can be set from 0.001 to 0.005 mm, and the fine-tuning cycle is 2 to 100 cycles. After entering automatic fine-tuning control, it can re-enter manual fine-tuning mode. During this time, the fatigue failure detection function is simultaneously disabled. If the user wants to adjust the automatic fine-tuning parameters again after entering automatic fine-tuning control, such as step size, fine-tuning cycle, and allowable deviation, they can simply modify the parameters on the peak-valley fine-tuning interface and then click to enable automatic fine-tuning again.

[0048] See Figure 2 In the test interface and parameter settings, the integrated control software collects the control of the upper force as follows: the amplitude of the upper and lower displacements, and adjusts the amplitude of the continuously adjusted waveform A1 = A2 to ensure the symmetry of the upper and lower force peak and valley values. Based on the fact that the rising period T1 = falling period T2, T2 = T3 + T4 + T5, and that the displacement adjustment amounts on both sides of the asymmetrical hydraulic damper are different, resulting in different error values, and the displacement variable is 0.1 mm, the force error value X coefficient μ = displacement adjustment amount is calculated, where T3 and T5 are the rate adjustment ranges, and T4 is the effective loading range.

[0049] See Figure 3 , Figure 4According to the experimental requirements, two or more horizontal force jacks and vertical force jacks, each independently controllable, are set at the same horizontal height in the horizontal loading system of the asymmetrical hydraulic damper. Horizontal force is applied to the corresponding positions of the asymmetrical hydraulic damper structural specimen by the horizontal force jacks, and constant or non-constant vertical pressure is applied to the asymmetrical hydraulic damper structural specimen by the vertical force jacks. This controls the torsional effect of the asymmetrical structural specimen during the loading test, achieving full-range displacement control loading.

[0050] The integrated control software collects data during the test according to the test plan and at a predetermined horizontal height, obtains the horizontal force and displacement data at each loading point of the asymmetric hydraulic damper structural specimen, and derives the force-displacement curve showing the relationship between the total horizontal force and displacement; it also measures the difference in horizontal force at each horizontal loading point and the distance between the horizontal loading systems, thus enabling the measurement of the horizontal torsional force and displacement of the structure.

[0051] See Figure 5 The hydraulic damper loading system includes: a servo loading cylinder fixedly connected to the seat space below the portal-shaped horizontal loading beam 5; a tension / compression sensor 8 connected to the main shaft of the servo loading cylinder via the horizontal loading beam; a vertical force jack 9 connected to a horizontal sliding support on the reaction beam 4; a screw-nut hinge connector 6 on the T-shaped column shaft below the portal horizontal loading beam; a horizontal force adjustment device 3 connected and fixed to the horizontal force sensor 1 via a reaction wall on one side of the portal column; horizontal force jacks 2 are all fixed at one end to the reaction wall, and the other end is connected to the horizontal force sensor 1 and the horizontal force adjustment device 3 via a hinge connector; the vertical force jack 9 is connected to the horizontal force sensor 1; the horizontal force jacks 2 and 9 connect to the asymmetric hydraulic damper structure. Specimen 7 is clamped between the telescopic rod of the horizontal force jack and the vertical force jack, fixing the asymmetric hydraulic damper structure specimen by clamping. The horizontal force jack, utilizing its feature of being set at the same horizontal height and capable of independent loading control, applies horizontal force to the corresponding position of the asymmetric hydraulic damper structure specimen, transmitting the reciprocating horizontal force to the specimen. It can independently apply horizontal force to the asymmetric hydraulic damper structure specimen. The vertical force jack applies constant or non-constant vertical pressure to the asymmetric hydraulic damper structure specimen. Horizontal force jack 2 and vertical force jack 9 control the torsional effect of the asymmetric structure during the loading test, implementing full-process displacement control loading to achieve control and measurement.

[0052] The above description is only a preferred embodiment of the present invention, but does not limit the present invention to the scope of the described embodiments. Various modifications and variations can be made by those skilled in the art. Any modifications, equivalent substitutions, or improvements made using the present invention should be included within the protection scope of the present invention.

Claims

1. A method for comprehensively controlling the loading force in fatigue tests of asymmetric hydraulic dampers, characterized in that: The computer generates control command signals for the hydraulic damper testing system and controls the displacement and force output by the hydraulic vibrator. It processes the displacement signal into a velocity signal or converts the acceleration signal into a velocity signal. The computer integrated control software combines force servo control and displacement servo control. Based on the load F0 corresponding to the initial amplitude A0 of the loading test device, the test frequency f, and the test time t, it establishes the force loading function F=F0×sin2πft. During the test, the integrated control software collects data from the sensors and controls the force on the symmetrical vertical displacement amplitude A1=A2 of the asymmetric hydraulic damper. It implements synchronous control of horizontal translational or torsional loading of the entire displacement, controls the torsional effect of the asymmetric hydraulic damper structural specimen during the loading test, obtains the relationship between the total horizontal force and displacement, and measures the difference in horizontal force at each horizontal loading point, thus realizing the measurement of the force and displacement of the horizontal torsion of the structure. Specifically, during the test, the computer-controlled software of the hydraulic damper test system collects data from the sensors connected to the cylinder extension end according to the testing requirements of the hydraulic damper and the specific technical indicators of the test system. It converts the detected information into electrical signals: output force and displacement, acceleration motion parameters, controls the force on the symmetrical upper and lower displacement amplitudes A1=A2 of the asymmetric hydraulic damper, and adjusts the symmetry of the upper and lower force peak and valley values. Then, it uses two triangular half-waves to form a sine curve periodic function to adjust the force control calculation ratio, replacing the previous incremental fine adjustment method. At the same time, for each half-wave adjustment of the asymmetric hydraulic damper, it sets the target load Fm, the load F0 corresponding to the initial amplitude A0, the load Fx corresponding to the amplitude Ax, the initial amplitude A0, the amplitude Ax+1 after Ax, and the proportional gain C, and constructs the force control formula model: Ai=(Fm-F0) / (Fx-F0)×(Ax+1-Ax)×C+A0, where Ax amplitude x=0,1,2……N-1. The force control formula model uses positive and negative half-axis to calculate and monitor separately, and corrects the positive and negative half-axis of the amplitude curve respectively to achieve symmetrical load on the positive and negative half-axis; In displacement servo control, the median value of the force-time, displacement-time, and force-displacement curves is used as the zero point. The allowable deviation of the displacement of the damper under test is set, and peak-valley adjustment is performed. After the adjustment is in place, automatic peak-valley control is activated, and the required data is continuously collected. Loading begins with an initial displacement range value. Based on the displacement of each loading point, synchronous control of horizontal translational or torsional loading of the entire displacement is implemented. The torsional effect of the asymmetric hydraulic damper structure during the loading test is controlled to obtain the horizontal force and displacement data at each loading point of the structure, and the relationship between the total horizontal force and displacement is obtained. Alternatively, the force and displacement of the horizontal torsion of the structure can be measured by the measured difference of the horizontal force at each horizontal loading point and the distance between the horizontal loading systems.

2. The method for comprehensively controlling the loading force of an asymmetric hydraulic damper in fatigue testing as described in claim 1, characterized in that: The hydraulic damper testing system includes a hydraulic vibrator with displacement and force sensors, a test bench, a high-flow electro-hydraulic servo valve for dynamic testing, a low-flow electro-hydraulic servo valve for static testing, a hydraulic oil source with an accumulator, oil source control, tension and compression force sensors, displacement sensors, analog control, numerical control, data acquisition, and power supply. An accumulator is used for instantaneous oil replenishment. When the hydraulic vibrator moves at low speed, the hydraulic pump supplies oil to the accumulator. When the vibrator moves at high speed, the hydraulic pump and the accumulator work together to supply oil to the vibrator. The hydraulic oil in the accumulator is drained back into the tank.

3. The method for comprehensively controlling the loading force in fatigue tests of an asymmetric hydraulic damper as described in claim 1, characterized in that: In the hydraulic damper testing system, two electro-hydraulic servo valves with different flow rates are designed for static and dynamic tests respectively. One of the electro-hydraulic servo valves is selected for control using a control directional valve. The large-flow electro-hydraulic servo valve is selected for dynamic testing, and the small-flow electro-hydraulic servo valve is selected for static testing. The electro-hydraulic servo valve converts the obtained current control signal into an electromechanical signal and outputs a flow rate and pressure proportional to the current control signal to drive the piston shaft in the hydraulic vibrator. The hydraulic vibrator generates the same motion or force output as the command signal.

4. The method for comprehensively controlling the loading force in fatigue tests of an asymmetric hydraulic damper as described in claim 1, characterized in that: The computer generates control command signals for the hydraulic damper test system and controls the displacement and force output by the hydraulic vibrator, processing the displacement signal into a velocity signal or converting the acceleration signal into a velocity signal.

5. The method for comprehensively controlling the loading force of an asymmetric hydraulic damper in fatigue testing as described in claim 1, characterized in that: During the initial loading process, the integrated control software sets parameters for frequency, target force value, target number of cycles, and control accuracy according to the loading force process of the fatigue test of the asymmetric hydraulic damper. It compares the target load value with the target load value and determines whether the target load value matches the comparison value. If they match, the control output signal is activated and the loading force is detected. Otherwise, the feedback signal is re-evaluated, and the loading force detection continues. Based on the loading force detection, the voltage command signal generated by the signal source or computer is compared with the feedback signal in the adder to determine whether the target number of cycles has been reached. If they do, an error signal is obtained. The error signal is then amplified by a power amplifier and converted into a drive current signal, which is applied to the electro-hydraulic servo valve to complete the experiment. Otherwise, the loading process continues until the experiment is completed.

6. The method for comprehensively controlling the loading force in fatigue tests of an asymmetric hydraulic damper as described in claim 1, characterized in that: The integrated control method software test interface is set with an automatic control fine-tuning function. The fine-tuning step size is set to 0.001-0.005 mm, and the fine-tuning cycle is 2-100 cycles. After entering automatic fine-tuning control, it will re-enter manual fine-tuning mode. At this time, the fatigue failure detection function will be turned off. If the user wants to adjust the automatic fine-tuning parameters again after entering automatic fine-tuning control, he / she only needs to modify the parameters on the peak-valley fine-tuning interface and click to enable automatic fine-tuning again.

7. The method for comprehensively controlling the loading force in fatigue tests of an asymmetric hydraulic damper as described in claim 1, characterized in that: In the test interface and parameter settings, the integrated control software collects the control of the upper force as follows: the amplitude of the upper and lower displacements, and adjusts the amplitude of the continuously adjusted waveform A1=A2 to adjust the symmetry of the upper and lower force peak and valley values. Based on the rising period T1=falling period T2, T2=T3+T4+T5 and the different displacement adjustment amounts on both sides of the asymmetrical hydraulic damper, the error values ​​are different. In the case of a displacement variable of 0.1mm, the force error value X coefficient μ=displacement adjustment amount is calculated, where T3 and T5 are the rate adjustment ranges, and T4 is the effective loading range.

8. The method for comprehensively controlling the loading force of an asymmetric hydraulic damper in fatigue testing as described in claim 1, characterized in that: According to the experimental requirements, two or more horizontal force jacks and vertical force jacks, each independently controllable, are set at the same horizontal height in the horizontal loading system of the asymmetrical hydraulic damper. Horizontal force is applied to the corresponding positions of the asymmetrical hydraulic damper structural specimen by the horizontal force jacks, and constant or non-constant vertical pressure is applied to the asymmetrical hydraulic damper structural specimen by the vertical force jacks to control the torsional effect of the asymmetrical structural specimen during the loading test, thus implementing full-range displacement control loading.

9. The method for comprehensively controlling the loading force of an asymmetric hydraulic damper in fatigue testing as described in claim 1, characterized in that: The hydraulic damper loading system includes: a servo loading cylinder fixed in the space below the horizontal loading beam (5) of the portal frame; a tension and compression sensor connected to the main shaft of the servo loading cylinder through the horizontal loading beam; a vertical force jack (9) connected to the horizontal sliding support on the reaction beam (4); a screw nut hinge connector (6) on the T-shaped column shaft below the portal frame horizontal loading beam; a horizontal force adjustment device (3) that connects and fixes the horizontal force sensor (1) through the reaction wall of one side of the portal frame; the horizontal force jacks (2) are all fixed to the reaction wall at one end, and the other end is connected to the horizontal force sensor (1) and the horizontal force adjustment device (3) through the hinge connector; the vertical force jack (9) is connected to the horizontal force sensor; the horizontal force jacks (2) and the vertical force jack (9) will not... The hydraulic damper structure specimen (7) is clamped between the horizontal force jack telescopic rod and the vertical force jack vertical force telescopic rod. The asymmetric hydraulic damper structure specimen is fixed by clamping. The horizontal force jack, taking advantage of the characteristic that it can be independently controlled by being set at the same horizontal height, applies a horizontal force to the corresponding position of the asymmetric hydraulic damper structure specimen, and transmits the reciprocating horizontal force to the specimen. It can independently apply a horizontal force to the asymmetric hydraulic damper structure specimen. The vertical force jack applies a constant or non-constant vertical pressure to the asymmetric hydraulic damper structure specimen. The horizontal force jack (2) and the vertical force jack (9) control the torsional effect of the asymmetric structure during the loading test, implement full displacement control loading, and realize control and measurement.

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