A method for a Hopkinson bar-based fixed-point controllable impact test

Abstract

The application relates to the technical field of impact test, in particular to a fixed-point controllable impact test method based on a Hopkinson bar. In the impact test method, a control error determination method based on peak impact force and impulse is established to more accurately determine the control error condition of each round of impact test, to provide accurate guidance for the next round of impact test, so that the accuracy of the control input of the next round of impact test is improved, the test efficiency is greatly improved, and the test cost is reduced. When the error value of one round of test is greater than the allowable error threshold, the control input is iteratively updated, so that a smooth transition from open-loop estimation to closed-loop correction is realized; in the control input update iteration process, a double-index closed-loop correction method based on the target peak impact force and the target impulse is adopted, so that the update iteration accuracy of the control input is greatly improved.

Description

Technical Field

[0001] This application relates to the field of impact testing technology, and in particular to a fixed-point controlled impact testing method based on a Hopkinson bar. Background Technology

[0002] With the rapid development of underground engineering, prefabricated buildings, traffic protection structures, and critical infrastructure, the dynamic performance of structures under impact, explosive shock, equipment collision, and explosive debris has attracted increasing attention. Conducting repeatable, controllable, and measurable physical tests on the impact resistance of structures is a crucial foundation for revealing the stress mechanisms, damage evolution laws, and optimizing protective designs.

[0003] Traditional impact tests based on Hopkinson bars often suffer from problems such as inaccurate adjustment of the impact position and difficulty in precisely controlling the impact input energy level when used for large-scale structural models. This results in low impact input control accuracy and consequently low test efficiency.

[0004] Therefore, there is a need to provide an improved technical solution that addresses the shortcomings of the existing technology. Summary of the Invention

[0005] The purpose of this application is to provide a fixed-point controlled impact test method based on a Hopkinson bar, so as to solve or alleviate the problems existing in the prior art.

[0006] To achieve the above objectives, this application provides the following technical solution: A fixed-point controlled impact test method based on a Hopkinson bar, the test method comprising the following steps: Step 1: Determine the parameters of the structural model, as well as the location of the impact point, impact energy level, and control parameters on the structural model, based on the experimental objective. Step 2: Install the reaction frame, structural model and Hopkinson bar impact system on the base in sequence; Step 3: According to the preset target impact position on the structural model, adjust the Hopkinson bar impact system to align the impact axis with the target impact position; Step 4: Arrange pressure sensors, force sensors, strain gauges, displacement gauges, and accelerometers at the monitoring locations on the reaction frame and structural model. Step 5, input the first [number] in the Hopkinson bar impact system. The target control parameters for this impact include the target peak impact force. Target momentum and allowable error threshold And determine the initial control input for this round of testing. ; The entire test setup was then subjected to a no-load inspection and alignment check. Step 6: Activate the Hopkinson bar impact system to apply impact loading to the target position in the impact force plane on the structural model, and record the control input, reaction force response, strain response, displacement response, acceleration response and damage development process. Step 7: After the impact loading is completed, the pressure time history during the impact process is collected using a pressure sensor. Based on pressure time history Determine the impact force time history Based on the impact time history Determine the peak impact force With impulse ; Then based on peak impact force With impulse Calculate the first Control error of secondary impact ,when At that time, the control input for the next round of impact Make corrections and conduct the next round of impact testing; when When the impact control parameters of this round are considered to have met the set control requirements, the impact test under this condition is stopped. Step 8: According to the research needs, repeatedly adjust the arrangement position, impact velocity and target impact energy level of the Hopkinson bar impact system, carry out multi-condition comparative tests, and complete the impact resistance performance evaluation of the structural model under different fixed-point impact conditions.

[0007] As described above, in the fixed-point controlled impact test method based on the Hopkinson bar, preferably, in step 5, a prediction function g for the impact characteristics and impact velocity is established based on a one-dimensional elastic wave theoretical model or a historical test database, and the target peak impact force is... Target momentum The initial impact velocity is obtained by substituting it into the prediction function g. ; Then the initial impact velocity Introduce the control mapping relationship obtained from the pre-calibration of the Hopkinson bar impact system. In the process, the initial control input is obtained. .

[0008] In the Hopkinson bar-based fixed-point controlled impact testing method described above, preferably, in step 7, the impact force time history for a single pressure sensor can be expressed as: In the formula, is The measured pressure time history of a single pressure sensor. The force-converted area corresponding to a single pressure sensor; For the case of multiple pressure sensors arranged in combination, the impact force time history can be expressed as: In the formula, The measured pressure time history of the k-th pressure sensor is given. Let n be the force-converted area corresponding to the k-th pressure sensor, and n be the number of pressure sensors involved in the calculation.

[0009] The fixed-point controlled impact testing method based on the Hopkinson bar, as described above, preferably includes the impact force time history... The definite integral is obtained by performing a definite integral over the time threshold. The impulse of the second impact impulse The calculation formula is as follows: In the formula, The effective impact duration; And in the impact time course Extracting peak impact force from the curve .

[0010] The preferred method for fixed-point controlled impact testing based on the Hopkinson bar, as described above, is the first... Control error of secondary impact The calculation formula is: ; in, and These are the weighting coefficients, and ; For the target peak impact force, For the first The peak impact force of the second impact; To achieve the target volume; For the first The momentum of the second impact.

[0011] The fixed-point controlled impact test method based on the Hopkinson bar, as described above, preferably, when At that time, the control input for the next round of impact Iterative updates are performed according to the following formula: ; In the formula, For the first Control inputs for the wheel; For the first Control inputs for the wheel; For the target peak impact force, This represents the peak impact force of the r-th round; and This is a correction factor.

[0012] In the fixed-point controlled impact testing method based on the Hopkinson bar described above, preferably, in step 5, the input energy of the i-th impact... for: In the formula, For input energy; For the first Initial velocity of the impact; m is the equivalent mass of the impactor.

[0013] The fixed-point controlled impact testing method based on the Hopkinson bar described above, preferably, for the local intensity of the impact at different impact locations, can further employ the impact energy per unit contact area. Characterization: In the formula, Impact energy per unit contact area This represents the equivalent contact area at the corresponding impact location.

[0014] In the fixed-point controlled impact test method based on the Hopkinson bar described above, preferably, in step 3, a model plane coordinate system is established in the impact force surface of the structural model, and the target impact position is parameterized as follows: In the formula, For the first The target impact location and These are the coordinates of the target impact location in the model plane coordinate system.

[0015] As described above, the fixed-point controlled impact test method based on the Hopkinson bar preferably introduces a normalized position parameter to characterize the positional relationship of different impact points relative to the model reference center. : In the formula, The coordinates are the reference center coordinates of the model. This is a reference length.

[0016] Compared with the closest prior art, the technical solution of this application has the following beneficial effects: In this impact testing method, a control error determination method based on the dual indicators of peak impact force and impulse is established to more accurately determine the control error of each round of impact testing, providing precise guidance for the next round of impact testing. This is beneficial to improving the accuracy of the control input of the next round of impact testing, greatly improving testing efficiency, and reducing testing costs.

[0017] When the error value of a test exceeds the allowable error threshold, the control input is iteratively updated, thus achieving a smooth transition from open-loop prediction to closed-loop correction. During the update and iteration of the control input, a dual-index closed-loop correction method based on the target peak impact force and the target impulse is adopted, which can greatly improve the update and iteration accuracy of the control input. Attached Figure Description

[0018] The accompanying drawings, which form part of this application, are used to provide a further understanding of this application. The illustrative embodiments and descriptions of this application are used to explain this application and do not constitute an undue limitation of this application. Wherein: Figure 1 This is a schematic flowchart of a test method provided according to some embodiments of this application; Figure 2 This is a schematic diagram of an overall testing system provided according to some embodiments of this application.

[0019] Explanation of reference numerals in the attached figures: 1. Base; 2. Hopkinson bar impact system; 3. Structural model; 4. Reaction frame. Detailed Implementation

[0020] The present application will now be described in detail with reference to the accompanying drawings and embodiments. Various examples are provided by way of interpretation and not by way of limitation. In fact, those skilled in the art will recognize that modifications and variations can be made to the present application without departing from the scope or spirit thereof. For example, a feature represented or described as part of one embodiment may be used in another embodiment to produce yet another embodiment. Therefore, it is desirable that the present application encompass such modifications and variations that fall within the scope of the appended claims and their equivalents.

[0021] In the following description, the terms "first / second / third" are used merely to distinguish similar objects and do not represent a specific order of objects. It is understood that "first / second / third" may be interchanged in a specific order or sequence where permitted, so that the embodiments of this application described herein can be implemented in an order other than that illustrated or described herein.

[0022] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure belongs. The terminology used herein is for the purpose of describing embodiments of this disclosure only and is not intended to limit this disclosure.

[0023] In the description of this application, the terms "longitudinal," "lateral," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," and "bottom," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing this application and do not require that this application be constructed and operated in a specific orientation, and therefore should not be construed as limiting this application. The terms "connected," "linked," and "set up" used in this application should be interpreted broadly. For example, they can refer to fixed connections or detachable connections; direct connections or indirect connections through intermediate components; wired connections, radio connections, or wireless communication signal connections. Those skilled in the art can understand the specific meaning of the above terms according to the specific circumstances.

[0024] The present application will now be described in detail with reference to the accompanying drawings and embodiments. It should be noted that, unless otherwise specified, the embodiments and features described in the embodiments of the present application can be combined with each other.

[0025] According to specific embodiments of this application, such as Figure 1 As shown, this application provides a fixed-point controlled impact test method based on a Hopkinson bar, the test method including the following steps: Step 1: Determine the parameters of structural model 3, as well as the impact point location, impact energy level, and control parameters on structural model 3, according to the purpose of the experiment. In this embodiment, the parameters of structural model 3 include external shape, geometric dimensions, boundary conditions, and impact force plane.

[0026] Step 2: Sequentially install the reaction frame 4, structural model 3, and Hopkinson bar impact system 2 on the base 1; in this embodiment, as... Figure 2 As shown, structural model 3 is set between reaction frame 4 and Hopkinson rod impact system 2, and the side of structural model 3 facing Hopkinson rod impact system 2 is its impact force surface.

[0027] Step 3: According to the preset target impact position on the structural model 3, adjust the Hopkinson rod impact system 2 so that the impact axis is aligned with the target impact position; Step 4: Arrange pressure sensors, force sensors, strain gauges, displacement gauges, and accelerometers at the monitoring locations on the reaction frame 4 and structural model 3. In this embodiment, pressure sensors are preferentially arranged at key reaction force transmission locations on the reaction frame 4. Alternatively, a high-speed photography device can be set up on one side of the test device to achieve full-process and all-round monitoring of the test.

[0028] Step 5, input the first [unclear] into the Hopkinson bar impact system 2. The target control parameters for this impact include the target peak impact force. Target momentum and allowable error threshold And determine the initial control input for this round of testing. ; In this embodiment, in step 5, based on a one-dimensional elastic wave theoretical model or a historical test database, a prediction function g for impact characteristics and impact velocity is established, and the target peak impact force is... Target momentum The initial impact velocity is obtained by substituting it into the prediction function g. ; Then the initial impact velocity Incorporate the control mapping relationship obtained from the pre-calibration of the Hopkinson bar impact system 2. In the process, the initial control input is obtained. In this embodiment, In the formula, Let i be the control input for the i-th impact. Let be the initial velocity of the impactor corresponding to the i-th impact, and a2, a1, and a0 be calibration coefficients obtained through fitting the Hopkinson bar impact system calibration test. It is a monotonic function within the calibration interval. Initial control input quantity. To meet The control input quantities. Among them, the functions in the control mapping relationship... Specifically, a quadratic polynomial function is used, where the initial velocity of the impactor is equal to the product of the calibration coefficient a2 and the square of the control input, the product of the calibration coefficient a1 and the control input, and the sum of the calibration coefficient a0; the initial control input is the control input that makes the initial velocity of the impactor reach the initial impact velocity in this quadratic polynomial function.

[0029] The overall test apparatus is then subjected to a no-load check and alignment verification. In this embodiment, the formal test can only proceed after the Hopkinson bar impact path, sensor working status, data acquisition status, and boundary conditions of structural model 3 have been checked and confirmed to meet the test requirements. Step 6: Activate the Hopkinson bar impact system 2 to apply impact loading to the target position in the impact force plane on the structural model 3, and record the control input, reaction force response, strain response, displacement response, acceleration response and damage development process. Step 7: After the impact loading is completed, the pressure time history during the impact process is collected using a pressure sensor. Based on pressure time history Determine the impact force time history Based on the impact time history Determine the peak impact force With impulse ; Then based on peak impact force With impulse Calculate the first Control error of secondary impact ,when At that time, the control input for the next round of impact Make corrections and conduct the next round of impact testing; when When the impact control parameters of this round are considered to have met the set control requirements, the impact test under this condition is stopped. In this embodiment, after the test under a certain condition is completed, key parameters such as pressure time history, impact force time history, peak impact force and impulse are extracted, and the structural dynamic response and failure mode under different target impact positions and different impact energy levels are compared and analyzed to provide a reliable basis for exploring the force mechanism and damage evolution law of structural model 3.

[0030] Step 8: According to the research needs, repeatedly adjust the arrangement position, impact velocity and target impact energy level of the Hopkinson bar impact system, carry out multi-condition comparative tests, and complete the impact resistance performance evaluation of structural model 3 under different fixed-point impact conditions.

[0031] In this impact testing method, a control error determination method based on the dual indicators of peak impact force and impulse is established to more accurately determine the control error of each round of impact testing, providing precise guidance for the next round of impact testing. This is beneficial to improving the accuracy of the control input of the next round of impact testing, greatly improving testing efficiency, and reducing testing costs.

[0032] In step 7, for a single pressure sensor, the impact force time history can be expressed as: In the formula, is The measured pressure time history of a single pressure sensor. The force-converted area corresponding to a single pressure sensor; For the case of multiple pressure sensors arranged in combination, the impact force time history can be expressed as: In the formula, The measured pressure time history of the k-th pressure sensor is given. Let n be the force-converted area corresponding to the k-th pressure sensor, and n be the number of pressure sensors involved in the calculation, where n is a natural number greater than 1, specifically n = 1, 2, 3, 4, 5, 6...

[0033] Impact time history The definite integral is obtained by performing a definite integral over the time threshold. The impulse of the second impact impulse The calculation formula is as follows: In the formula, The effective impact duration; And in the impact time course Extracting peak impact force from the curve .

[0034] No. Control error of secondary impact The calculation formula is: ; in, and These are the weighting coefficients, and ; For the target peak impact force, For the first The peak impact force of the second impact; To achieve the target volume; For the first The momentum of the second impact.

[0035] In this embodiment, the formula in and These are the weighting coefficients for peak impact force error and impact impulse error, respectively. To ensure the rationality of the evaluation function, they satisfy mathematical constraints: and .

[0036] In practical engineering applications, weighting coefficients and The specific value is determined based on the damage sensitivity characteristics of the test object: (1) When the test object is a brittle structure or a high yield strength material that is highly sensitive to stress amplitude, a greater weight should be given to the peak force error, and the value should be set accordingly. (Preferred, (2) When the test object is a plastic, porous or composite energy-absorbing material that is sensitive to cumulative energy absorption, the impulse error should be given a greater weight and set... (Preferred, ).

[0037] when At that time, the control input for the next round of impact Iterative updates are performed according to the following formula: ; In the formula, For the first In the second trial Control inputs for the wheel; For the first In the second trial Control inputs for the wheel; For the target peak impact force, For the first The peak impact force in the r-th round of the test; and This is a correction factor.

[0038] In this embodiment, subscript The anchor is a macroscopic experimental sequence, representing the current system executing the [number]th [test]. The impact test; the superscript 'r' indicates the micro-control dimension, representing the control measures taken to achieve this. The impact test achieved the set target accuracy, and the system is currently in the r-th round of closed-loop correction iteration.

[0039] In this embodiment, when In this process, the control input is iteratively updated, thus achieving a smooth transition from open-loop prediction to closed-loop correction. During the update and iteration of the control input, a dual-index closed-loop correction method based on the target peak impact force and the target impulse is adopted, which can greatly improve the update and iteration accuracy of the control input.

[0040] In this embodiment, the formula in and These are the peak force feedback gain coefficient and the impulse feedback gain coefficient, respectively, used to control the step size and stability of the closed-loop iterative correction.

[0041] In actual engineering implementation, the above-mentioned gain coefficient can be tuned by pre-test trial and error method or step response analysis method. Its selection follows the following physical constraint principles: (1) Peak force feedback gain coefficient The value of is negatively correlated with the overall dynamic stiffness of the test system. When the stiffness of the loading system or the specimen is large, even a small change in the driving input can easily cause a drastic change in the contact force. In this case, a smaller value should be selected. Value (preferred) (1) To suppress overshoot and divergence; (2) Impulse feedback gain coefficient The value of is mainly related to the inertial characteristics of the system, and is usually within . The selection is made within the specified interval. Combined with the aforementioned physical constraints, the system can guarantee smooth convergence to the target impact characteristic parameters within a finite number of iterations.

[0042] In step 5, the input energy of the i-th impact for: In the formula, For input energy; For the first Initial velocity of the impact; m is the equivalent mass of the impactor.

[0043] For the local impact intensity at different impact locations, the impact energy per unit contact area can be further used. Characterization: In the formula, Impact energy per unit contact area This represents the equivalent contact area at the corresponding impact location.

[0044] In step 3, a model plane coordinate system is established in the impact force surface of structural model 3, and the target impact position is parameterized as follows: In the formula, For the first The target impact location and These are the coordinates of the target impact location in the model plane coordinate system.

[0045] To characterize the positional relationship of different impact points relative to the model reference center, a normalized position parameter is introduced. : In the formula, The coordinates are the reference center coordinates of the model. This is a reference length.

[0046] The above description is merely a preferred embodiment of this application and is not intended to limit this application. Various modifications and variations can be made to this application by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A method for fixed-point controlled impact testing based on a Hopkinson bar, characterized in that, The experimental method includes the following steps: Step 1: Determine the parameters of the structural model, as well as the location of the impact point, impact energy level, and control parameters on the structural model, based on the experimental objective. Step 2: Install the reaction frame, structural model and Hopkinson bar impact system on the base in sequence; Step 3: According to the preset target impact position on the structural model, adjust the Hopkinson bar impact system to align the impact axis with the target impact position; Step 4: Arrange pressure sensors, force sensors, strain gauges, displacement gauges, and accelerometers at the monitoring locations on the reaction frame and structural model. Step 5, input the first [number] in the Hopkinson bar impact system. The target control parameters for this impact include the target peak impact force. Target momentum and allowable error threshold And determine the initial control input for this round of testing. ; The entire test setup was then subjected to a no-load inspection and alignment check. Step 6: Activate the Hopkinson bar impact system to apply impact loading to the target position in the impact force plane on the structural model, and record the control input, reaction force response, strain response, displacement response, acceleration response and damage development process. Step 7: After the impact loading is completed, the pressure time history during the impact process is collected using a pressure sensor. Based on pressure time history Determine the impact force time history Based on the impact time history Determine the peak impact force With impulse ; Then based on peak impact force With impulse Calculate the first Control error of secondary impact ,when At that time, the control input for the next round of impact Make corrections and conduct the next round of impact testing; when When the impact control parameters of this round are considered to have met the set control requirements, the impact test under this condition is stopped. Step 8: According to the research needs, repeatedly adjust the arrangement position, impact velocity and target impact energy level of the Hopkinson bar impact system, carry out multi-condition comparative tests, and complete the impact resistance performance evaluation of the structural model under different fixed-point impact conditions.

2. The fixed-point controlled impact test method based on the Hopkinson bar according to claim 1, characterized in that, In step 5, based on a one-dimensional elastic wave theoretical model or historical test database, a prediction function g for impact characteristics and impact velocity is established, and the target peak impact force is calculated. Target momentum The initial impact velocity is obtained by substituting it into the prediction function g. ; Then the initial impact velocity Introduce the control mapping relationship obtained from the pre-calibration of the Hopkinson bar impact system. In the process, the initial control input is obtained. .

3. The fixed-point controlled impact test method based on the Hopkinson bar according to claim 2, characterized in that, In step 7, for a single pressure sensor, the impact force time history can be expressed as: In the formula, is The measured pressure time history for a single pressure sensor. The force-converted area corresponding to a single pressure sensor; For the case of multiple pressure sensors arranged in combination, the impact force time history can be expressed as: In the formula, The measured pressure time history of the k-th pressure sensor is given. Let n be the force-converted area corresponding to the k-th pressure sensor, and n be the number of pressure sensors involved in the calculation.

4. The fixed-point controlled impact test method based on the Hopkinson bar according to claim 3, characterized in that, Impact time history The definite integral is obtained by performing a definite integral over the time threshold. The impulse of the second impact impulse The calculation formula is as follows: In the formula, The effective impact duration; And in the impact time course Extracting peak impact force from the curve .

5. The fixed-point controlled impact test method based on the Hopkinson bar according to claim 4, characterized in that, No. Control error of secondary impact The calculation formula is: ； in, and These are the weighting coefficients, and ; For the target peak impact force, For the first The peak impact force of the second impact; To achieve the target volume; For the first The momentum of the second impact.

6. The fixed-point controlled impact test method based on the Hopkinson bar according to claim 5, characterized in that, when At that time, the control input for the next round of impact Iterative updates are performed according to the following formula: ； In the formula, For the first Control inputs for the wheel; For the first Control inputs for the wheel; For the target peak impact force, This represents the peak impact force of the r-th round; and This is a correction factor.

7. The fixed-point controlled impact test method based on the Hopkinson bar according to claim 1, characterized in that, In step 5, the input energy of the i-th impact for: In the formula, For input energy; For the first Initial velocity of the impact; m is the equivalent mass of the impactor.

8. The fixed-point controlled impact test method based on the Hopkinson bar according to claim 7, characterized in that, For the local impact intensity at different impact locations, the impact energy per unit contact area can be further used. Characterization: In the formula, Impact energy per unit contact area This represents the equivalent contact area at the corresponding impact location.

9. The fixed-point controlled impact test method based on the Hopkinson bar according to claim 1, characterized in that, In step 3, a model plane coordinate system is established in the impact force surface of the structural model, and the target impact position is parameterized as follows: In the formula, For the first The target impact location and These are the coordinates of the target impact location in the model plane coordinate system.

10. The fixed-point controlled impact test method based on the Hopkinson bar according to claim 9, characterized in that, To characterize the positional relationship of different impact points relative to the model reference center, a normalized position parameter is introduced. : In the formula, The coordinates are the reference center coordinates of the model. This is a reference length.

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