Method for determining reference surface of high-temperature high-pressure cavity elastic element based on stiffness mutation

Abstract

The application discloses a high-temperature and high-pressure cavity elastic element reference surface determination method based on stiffness mutation and belongs to the field of elastic element test and measurement. The method comprises the following steps: S1, installing a force sensor at the connecting part of an upper pressing rod and an upper pressing plate and calibrating; S2, coaxially arranging a cleaned elastic element at the center of the working surface of a lower pressing plate, and then coaxially arranging a rigid ring at the inner side of the elastic element and abutting against the working surface of the lower pressing plate; and S3, driving the upper pressing rod to drive the upper pressing plate to move downward along the axial direction under the set target temperature and pressure, and synchronously drawing a system force-displacement curve, so as to determine the test reference surface. The high-temperature and high-pressure cavity elastic element reference surface determination method based on stiffness mutation solves the positioning problem of the test reference surface of the elastic element in the invisible environment of the high-temperature and high-pressure closed cavity, and simultaneously considers the positioning accuracy, the protection of the test piece and the controllable cost, and has a wide application prospect.

Description

Technical Field

[0001] This invention relates to the field of elastic element reference surface determination technology, and in particular to a method for determining the reference surface of elastic elements in high-temperature and high-pressure cavities based on stiffness abrupt changes. Background Technology

[0002] In extreme operating conditions such as petrochemicals and aerospace, the sealing performance of elastic elements directly affects the reliability of equipment operation. Performance testing under high temperature and high pressure conditions is a crucial step in ensuring product quality. Such tests require simulating extreme environments within a sealed cavity. However, the lack of visibility within the cavity makes accurately determining the critical contact point between the upper pressure plate and the elastic element a technical challenge. The working surface of the upper pressure plate corresponding to this critical point serves as the test reference surface, and its positioning accuracy directly determines the control accuracy of the elastic element's compression, thus affecting the validity of the sealing leakage measurement results.

[0003] The existing testing methods for determining this reference plane have the following main drawbacks:

[0004] Firstly, using a "quantitative force application" method to determine the contact state is one of the mainstream approaches. This method presets a fixed pressure value, and when the applied force reaches the preset value, it is determined that the upper pressure plate and the elastic element are in contact and form a reference surface. However, due to individual differences in the elastic element and changes in material properties under high temperature and high pressure, this method is difficult to accurately control the critical point of "upper pressure plate - elastic element compression": insufficient force will cause the elastic element to fail to reach the predetermined test compression amount, while excessive force will cause overpressure damage to the elastic element, and its deformation error will far exceed the allowable measurement range of ±0.01mm, directly leading to the distortion of subsequent sealing performance test results.

[0005] Secondly, some solutions employ a "fixed force threshold" criterion, using a force sensor mounted at the connection between the pressure rod and the upper pressure plate to determine the contact critical point based on force changes. However, system interference under high temperature and high pressure conditions renders this method unsuitable: on the one hand, the mechanical friction generated by the pressure rod's movement directly adds to the force sensor reading; on the other hand, in external opening test scenarios, a corrugated ring is needed to construct a sealed cavity, and the elastic force of the corrugated ring itself mixes into the measured value. The values ​​of these interfering forces are far greater than the effective force actually acting on the elastic element, resulting in severe distortion of the force sensor measurement results and failure of the contact critical point determination.

[0006] Thirdly, another approach utilizes displacement sensors for auxiliary judgment. These sensors are fixed to the upper pressure rod, and the reference surface is determined by monitoring whether the displacement of the upper pressure rod reaches a predetermined value. However, this method fails to consider the special effects of high-temperature and high-pressure conditions: the elastic element and the test fixture will undergo thermal deformation at high temperatures, and the high pressure difference will cause them to deform under load. Furthermore, the sealed cavity is closed and invisible, making it impossible to correct the deformation in real time. The resulting overall deformation error far exceeds the allowable range of ±0.01mm for measuring minute compression, thus failing to achieve accurate positioning of the reference surface.

[0007] Furthermore, the "Method for Controlling and Measuring the Axial Compression Displacement Deformation of a Sealing Ring" disclosed in Chinese Invention Patent No. CN105157975B uses a limiting pad to restrict the compression amount in order to indirectly determine the reference surface. However, in this scheme, the upper pressure plate completely presses the pad, resulting in excessive compression deformation of the elastic element, which cannot meet the high-precision testing requirements of 0.01mm. Moreover, the rigid contact design of the pad cannot adapt to the elastic deformation characteristics of the elastic element, further aggravating the testing error.

[0008] In summary, existing testing methods cannot effectively solve the problem of high-precision positioning of the reference surface for elastic element testing in the absence of visibility in high-temperature, high-pressure, sealed cavities, and thus cannot meet the technical requirements for testing the sealing performance of elastic elements under extreme working conditions. Summary of the Invention

[0009] The purpose of this invention is to provide a method for determining the reference surface of elastic elements in high-temperature and high-pressure cavities based on stiffness abrupt changes, thereby solving the aforementioned technical problems.

[0010] To achieve the above objectives, this invention provides a method for determining the reference surface of an elastic element in a high-temperature, high-pressure cavity based on a sudden change in stiffness, comprising the following steps:

[0011] S1. Install a force sensor at the connection between the upper pressure rod and the upper pressure plate. At the same time, evenly assemble multiple grating ruler displacement sensors along the circumference above the upper pressure plate. Connect the signals of the force sensor and the grating ruler displacement sensor to the test computer through the data acquisition module to complete the calibration of the force sensor and the grating ruler displacement sensor respectively.

[0012] S2. Use a level to adjust the flatness and relative parallelism of the upper and lower pressure plates. Then, place the cleaned elastic element coaxially in the center of the working surface of the lower pressure plate. Then, place the rigid ring coaxially inside the elastic element and fit it against the working surface of the lower pressure plate. Leave an anti-friction gap between the outer wall of the rigid ring and the inner wall of the elastic element. The height of the rigid ring is equal to the height of the elastic element itself minus the preset deformation amount.

[0013] S3. Under the set target temperature and pressure, start the servo motor to drive the upper pressure rod to move the upper pressure plate downward along the axial direction. The test computer collects the force value data of the force sensor and the displacement data of the grating ruler displacement sensor in real time through the data acquisition module, and simultaneously plots the system force-displacement curve. Based on the ratio of instantaneous force value to instantaneous displacement in the force-displacement curve, the slope of the force-displacement curve is obtained, and the stiffness and its rate of change are obtained. Finally, the test reference surface is determined according to whether the stiffness changes abruptly.

[0014] Preferably, the elastic element in step S2 is an inner opening structure or an outer opening structure. When the elastic element is an outer opening structure, a corrugated ring matching the outer diameter of the elastic element is selected, and the corrugated ring is coaxially sleeved on the outside of the elastic element and placed in the annular positioning groove of the working surface of the lower pressure plate.

[0015] Preferably, the rigid ring in step S2 is made of GH4169 high-temperature alloy, which has an elastic modulus of 200GPa-210GPa at room temperature, a stiffness greater than that of the elastic element at the target temperature, and a coefficient of thermal expansion less than that of the elastic element.

[0016] Preferably, in step S3, the upper pressure plate moves downward at a speed of 0.01 mm / s to 0.05 mm / s to find the reference.

[0017] Preferably, in step S3, when the elastic element has an internally open structure, the determination process includes the following three stages:

[0018] Initial displacement control stage: The upper pressure plate does not contact the elastic element and rigid ring, and only overcomes air resistance and mechanical friction of the upper pressure rod. At this time, the stiffness is... ;

[0019] Compression stage of the internally open elastic element: The upper pressure plate contacts the elastic element, the force value collected by the force sensor changes, and At this point, the control mode is switched to force control mode, and the upper pressure plate is moved downward at a rate of 1000 N / s. The elastic element undergoes elastic deformation, and the stiffness change at this time satisfies the following conditions:

[0020] ;

[0021] In the formula, and These represent the compression stage of an internally open elastic element. Time and Stiffness at any moment This represents the coefficient for determining abrupt changes in stiffness. ;

[0022] Rigid ring support stage: When the upper pressure plate is pressed down until the inner wall of the inner open elastic element is completely in contact with the outer wall of the rigid ring, the rigid ring provides rigid support, causing a sudden change in force value, until the stiffness change meets the following conditions:

[0023] ;

[0024] In the formula, and These represent the internally open elastic element under the rigid ring support stage. Time and Stiffness at any moment This represents the coefficient for determining abrupt changes in stiffness. ;

[0025] Stop the movement of the upper pressure plate. At this time, the displacement value of the upper pressure plate is the test zero point, and the plane where the working surface of the upper pressure plate is located is regarded as the test reference plane of the elastic element.

[0026] Preferably, in step S3, when the elastic element has an externally open structure, the determination process includes the following four stages:

[0027] Initial displacement control stage: The upper pressure plate does not contact the elastic element, rigid ring, and corrugated ring, and only overcomes air resistance and mechanical friction of the upper pressure rod. At this time, the stiffness is... ;

[0028] During the bellows compression stage: the upper pressure plate contacts the bellows, and the force value collected by the force sensor changes. Switch the control mode to force control mode. At this time, the upper pressure plate is controlled to move downward at a rate of 5000 N / s. The stiffness change at this time meets the following conditions:

[0029] ;

[0030] In the formula, and These represent the compression stage of the corrugated ring, Time and Stiffness at any moment This represents the coefficient for determining abrupt changes in stiffness. ;

[0031] Compression stage of the externally open elastic element: As the upper pressure plate continues to move downwards, it contacts the elastic element and causes it to undergo elastic deformation. At this time, the stiffness change satisfies the following condition:

[0032] ;

[0033] In the formula, and These represent the compression stages of an externally open elastic element. Time and Stiffness at any moment This represents the coefficient for determining abrupt changes in stiffness. ;

[0034] Rigid ring support stage: When the upper pressure plate is pressed down until the inner wall of the outer open elastic element is completely in contact with the outer wall of the rigid ring, the rigid ring provides rigid support, causing a sudden change in force value, until the stiffness change meets the following conditions:

[0035] ;

[0036] In the formula, and These represent the externally open elastic element under the rigid ring support stage. Time and Stiffness at any moment This represents the coefficient for determining abrupt changes in stiffness. ;

[0037] Stop the movement of the upper pressure plate. At this time, the displacement value of the upper pressure plate is the test zero point, and the plane where the working surface of the upper pressure plate is located is regarded as the test reference plane of the elastic element.

[0038] Therefore, the present invention employs the above-mentioned method for determining the reference surface of the elastic element in a high-temperature and high-pressure cavity based on a sudden change in stiffness, which has the following beneficial effects:

[0039] 1. Positioning accuracy meets standards: It can achieve ±0.01mm level control of elastic element compression, accurately position the test reference surface, avoid problems such as leakage measurement distortion and misjudgment of test results caused by reference deviation, and ensure the scientific nature of sealing performance testing;

[0040] 2. Protect the integrity of the test specimen: By using a rigid ring for rigid support and a stop mechanism triggered by a sudden change in stiffness, the elastic element is prevented from being over-compressed and deformed or failing elastically, thus reducing the cost of test specimen wear and ensuring the effectiveness of subsequent repeated tests.

[0041] 3. Strong anti-interference ability: effectively avoids interference factors such as pressure bar friction, corrugated ring force, thermal deformation and load deformation under high temperature and high pressure environment, ensuring accurate acquisition of force and displacement data and improving the reliability of test data;

[0042] 4. Wide range of applicable scenarios: It can meet the testing needs of both internal and external opening elastic elements. In the external opening scenario, a sealed cavity is constructed with the assistance of a corrugated ring, which is suitable for the sealing performance testing of different types of elastic elements.

[0043] 5. Operation and cost controllable: No complex auxiliary equipment modification is required, the operation process is simple and efficient, reducing the dependence on special high temperature interference resistant equipment, and indirectly reducing the procurement and maintenance costs of test equipment.

[0044] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Attached Figure Description

[0045] Figure 1 This is a flowchart of the method for determining the reference surface of an elastic element in a high-temperature and high-pressure cavity based on a sudden change in stiffness, as described in this invention.

[0046] Figure 2 This is a cross-sectional view of the experimental arrangement of the externally open elastic element described in this invention;

[0047] Figure 3 This is a cross-sectional view of the experimental arrangement of the internally open elastic element described in this invention;

[0048] Figure 4 This is a graph showing the real-time stiffness change of the internally open elastic element during compression, as described in the experimental example.

[0049] Figure 5 This is a graph showing the real-time stiffness change of the externally open elastic element during compression, as described in the experimental example.

[0050] 1. Upper pressure plate; 2. Corrugated ring; 3. Elastic element; 4. Rigid ring; 5. Lower pressure plate. Detailed Implementation

[0051] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the embodiments of the present invention will be further described in detail below with reference to the accompanying drawings and examples. It should be understood that the specific embodiments described herein are merely illustrative of the embodiments of the present invention and are not intended to limit the embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of this application. Examples of the embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout.

[0052] It should be noted that the terms "comprising" and "having," and any variations thereof, are intended to cover non-exclusive inclusion, such as a process, method, system, product, or server that includes a series of steps or units, not necessarily limited to those steps or units explicitly listed, but may include other steps or units not explicitly listed or inherent to such process, method, product, or device.

[0053] The embodiments of the present invention will now be described in detail with reference to the accompanying drawings.

[0054] like Figures 1-3 As shown, the method for determining the reference surface of an elastic element in a high-temperature, high-pressure cavity based on a sudden change in stiffness includes the following steps:

[0055] S1. Install a force sensor at the connection between the upper pressure rod and the upper pressure plate 1. At the same time, evenly assemble multiple grating ruler displacement sensors along the circumference above the upper pressure plate 1. Connect the signals of the force sensor and the grating ruler displacement sensor to the test computer through the data acquisition module to complete the calibration of the force sensor and the grating ruler displacement sensor respectively.

[0056] S2. Using a level, adjust the flatness and relative parallelism of the upper pressure plate 1 and the lower pressure plate 5. Then, coaxially place the cleaned elastic element 3 at the center of the working surface of the lower pressure plate 5. Next, coaxially place the rigid ring 4 inside the elastic element 3 and make it fit against the working surface of the lower pressure plate 5. A friction-resistant gap is left between the outer wall of the rigid ring 4 and the inner wall of the elastic element 3, and the height of the rigid ring 4 is equal to the height of the elastic element 3 itself minus the preset deformation amount; that is, the rigid ring is the height of the elastic element after being compressed according to the test requirements. For example, if the height of the elastic element itself is 5mm and the required deformation amount for the elastic element test is 0.8mm, then the elastic element needs to be compressed to 4.2mm, that is, the rigid ring is selected to be 4.2mm.

[0057] The elastic element 3 mentioned in step S2 is an inner opening structure or an outer opening structure. When the elastic element 3 is an outer opening structure, a corrugated ring 2 that matches the outer diameter of the elastic element 3 is selected, and the corrugated ring 2 is coaxially sleeved on the outside of the elastic element 3 and placed in the annular positioning groove on the working surface of the lower pressure plate 5.

[0058] The rigid ring 4 mentioned in step S2 is made of GH4169 high-temperature alloy, which has an elastic modulus of 200GPa-210GPa at room temperature. Its stiffness at the target temperature is greater than that of the elastic element 3, and its coefficient of thermal expansion is less than that of the elastic element 3.

[0059] S3. Under the set target temperature and pressure, start the servo motor to drive the upper pressure rod to move the upper pressure plate 1 downward along the axial direction. The test computer collects the force value data of the force sensor and the displacement data of the grating ruler displacement sensor in real time through the data acquisition module, and simultaneously plots the system force-displacement curve. Based on the ratio of instantaneous force value to instantaneous displacement in the force-displacement curve, the slope of the force-displacement curve is obtained, and the stiffness and its rate of change are obtained (i.e., the slope of the force-displacement curve is equal to the stiffness). Finally, the test reference surface is determined according to whether the stiffness changes abruptly.

[0060] In step S3, the upper pressure plate 1 moves downward at a speed of 0.01 mm / s to 0.05 mm / s to find the reference.

[0061] In step S3, when the elastic element 3 has an internal opening structure, the determination process includes the following three stages:

[0062] Initial displacement control stage: The upper pressure plate does not contact the elastic element and rigid ring, and only overcomes air resistance and mechanical friction of the upper pressure rod. At this time, the stiffness is... ;

[0063] Compression stage of the internally open elastic element: The upper pressure plate contacts the elastic element, the force value collected by the force sensor changes, and At this point, the control mode is switched to force control mode, and the upper pressure plate is moved downward at a rate of 1000 N / s. The elastic element undergoes elastic deformation, and the stiffness change at this time satisfies the following conditions:

[0064] ;

[0065] In the formula, and These represent the compression stage of an internally open elastic element. Time and Stiffness at any moment This represents the coefficient for determining abrupt changes in stiffness. At this point, it can be determined that the rigid ring has not yet been pressed down;

[0066] Rigid ring support stage: When the upper pressure plate is pressed down until the inner wall of the inner open elastic element is completely in contact with the outer wall of the rigid ring, the rigid ring provides rigid support, causing a sudden change in force value, until the stiffness change meets the following conditions:

[0067] ;

[0068] In the formula, and These represent the internally open elastic element under the rigid ring support stage. Time and Stiffness at any moment This represents the coefficient for determining abrupt changes in stiffness. At this point, it can be determined that the rigid ring has been pressed down;

[0069] Stop the movement of the upper pressure plate. At this time, the displacement value of the upper pressure plate is the test zero point, and the plane where the working surface of the upper pressure plate is located is regarded as the test reference plane of the elastic element.

[0070] In step S3, when the elastic element has an externally open structure, the determination process includes the following four stages:

[0071] Initial displacement control stage: The upper pressure plate does not contact the elastic element, rigid ring, and corrugated ring, and only overcomes air resistance and mechanical friction of the upper pressure rod. At this time, the stiffness is... ;

[0072] During the bellows compression stage: the upper pressure plate contacts the bellows, and the force value collected by the force sensor changes. Switch the control mode to force control mode. At this time, the upper pressure plate is controlled to move downward at a rate of 5000 N / s. The stiffness change at this time meets the following conditions:

[0073] ;

[0074] In the formula, and These represent the compression stage of the corrugated ring, Time and Stiffness at any moment This represents the coefficient for determining abrupt changes in stiffness. At this point, it can be determined that the rigid ring was not pressed down;

[0075] Compression stage of the externally open elastic element: As the upper pressure plate continues to move downwards, it contacts the elastic element and causes it to undergo elastic deformation. At this time, the stiffness change satisfies the following condition:

[0076] ;

[0077] In the formula, and These represent the compression stages of an externally open elastic element. Time and Stiffness at any moment This represents the coefficient for determining abrupt changes in stiffness. At this point, it can be determined that the rigid ring was not pressed down;

[0078] Rigid ring support stage: When the upper pressure plate is pressed down until the inner wall of the outer open elastic element is completely in contact with the outer wall of the rigid ring, the rigid ring provides rigid support, causing a sudden change in force value, until the stiffness change meets the following conditions:

[0079] ;

[0080] In the formula, and These represent the externally open elastic element under the rigid ring support stage. Time and Stiffness at any moment This represents the coefficient for determining abrupt changes in stiffness. At this point, it can be determined that the rigid ring is being pressed.

[0081] Stop the movement of the upper pressure plate. At this time, the displacement value of the upper pressure plate is the test zero point, and the plane where the working surface of the upper pressure plate is located is regarded as the test reference plane of the elastic element.

[0082] In this embodiment, the subsequent compression deformation of the elastic element 3 can be precisely controlled based on a determined reference plane, providing an initial reference for sealing performance testing and avoiding test errors caused by overpressure damage or insufficient compression of the elastic element 3.

[0083] Experimental Example

[0084] Experimental objective: To verify the accurate positioning capability of the test reference surface of elastic elements with different opening types under the high temperature, high pressure, closed cavity and invisible environment of the present invention, to verify the effectiveness of the stiffness change judgment rule, and to compare with the pad block scheme of the prior patent (CN105157975B) to highlight the high precision and specimen protection advantages of the present invention.

[0085] Experimental equipment and materials: High-temperature and high-pressure test furnace (capable of simulating working conditions of temperature ≤800℃ and pressure ≤10MPa); Servo motor drive system (displacement control accuracy ±0.001mm, force control accuracy ±1N); High-precision force sensor (range 0-±200kN, accuracy 0.1%FS); Grating ruler displacement sensor (3 units, installed at 60° intervals around the circumference, range 0-50mm, accuracy ±0.001mm); Data acquisition module (sampling frequency 1000Hz) and test computer (including software for real-time plotting of force-displacement curves and stiffness calculation); Precision level (accuracy 0.02mm / m).

[0086] Table 1 Experimental Materials

[0087]

[0088] Table 2 Experimental parameters

[0089]

[0090] Experimental steps

[0091] (a) General preparation steps:

[0092] Sensor calibration: The force sensor and three grating rulers are calibrated using a standard force source and a laser interferometer to ensure that the force measurement error is ≤0.1%FS and the displacement measurement error is ≤±0.001mm.

[0093] Pressure plate adjustment: Use a level to adjust the flatness (≤0.01mm / m) and relative parallelism (≤0.02mm / m) of the upper and lower pressure plates to ensure that the elastic elements are subjected to uniform force;

[0094] Specimen installation: Clean the surface of the elastic element of oil and oxide scale, and place the cleaned elastic element coaxially at the center of the working surface of the lower pressure plate (axial deviation ≤ 0.1mm); then smoothly insert the rigid ring into the inner hole of the elastic element, ensuring that the bottom surface of the rigid ring is completely in contact with the working surface of the lower pressure plate, and the gap between the outer wall and the inner wall of the elastic element is 0.2mm (no friction).

[0095] Meanwhile, if the elastic element has an externally open structure, an additional corrugated ring is fitted on the outside of the elastic element and placed in the annular positioning groove of the lower pressure plate to ensure that the corrugated ring is coaxial with the elastic element.

[0096] Test procedure for internally open elastic elements:

[0097] Environmental settings: Close the furnace door, set the temperature to 300℃ and the pressure to 2MPa, start the heating and pressurization system, and maintain the temperature and pressure for 30 minutes after they stabilize (fluctuation ≤ ±5℃, ±0.1MPa).

[0098] Initial displacement control: Start the servo motor and move the upper pressure plate downward at a rate of 0.03 mm / s. The data acquisition module collects force and displacement data in real time and plots the force-displacement curve (in the initial stage, the force value is stable within ±5N and the slope (stiffness) is 0).

[0099] During the compression phase of the elastic element: When the slope first changes significantly (stiffness not equal to 0), record the displacement value as 0.171mm ± 0.01mm. Switch to force control mode (1000N / s rate), continue to compress, and calculate the slope of the force-displacement curve. ;

[0100] Rigid ring support stage: Continue to press down, until the slope of the force-displacement curve abruptly changes to... (It is 6 times the previous stiffness value (277.77 kN / mm before the abrupt change), and satisfies) Immediately stop the movement of the upper pressure plate and record the displacement value at this time as 0.571mm. The working surface of the upper pressure plate corresponding to this displacement is the test reference surface.

[0101] Repeat the verification: Replace with 3 internally open elastic elements of the same specification, repeat the above steps, and record the displacement value of the reference plane each time.

[0102] Test steps for externally open elastic elements:

[0103] Environmental setup and sensor calibration are the same as for internal opening testing;

[0104] Initial displacement control: The upper pressure plate moves downward at a rate of 0.03 mm / s, and the force value is stable within ±8N in the initial stage, with a slope (stiffness) of 0.

[0105] Corrugated ring compression stage: After the upper pressure plate contacts the corrugated ring, the slope first shows a significant change (the slope is not equal to 0). Record the displacement value at this time as 0.143mm ± 0.01mm. Switch to force control mode (5000N / s rate), continue to press down and calculate the rate. ;

[0106] Compression phase of elastic element: Continue pressing down until the elastic element contacts;

[0107] Rigid ring support stage: Continue downward pressure until the curve slope abruptly changes to (It is 7.14 times the slope of the previous stiffness value (201.33 kN / mm before the abrupt change). Stop the movement of the upper pressure plate, record the displacement value of 0.943mm, and determine it as the test reference surface;

[0108] Comparative experiment: The limiting pad of the prior patent was used to replace the rigid ring, and the external opening test was repeated to record the deformation and surface condition of the elastic element after compression.

[0109] Post-experiment processing: such as Figure 4 and 5 As shown, the displacement value of the upper pressure plate reference surface, the stiffness data of each stage, and the state of the elastic element are recorded for each test; then, the force-displacement curve and stiffness change curve are plotted to verify the characteristics of the sudden change; and the residual deformation of the elastic element after the test is measured to assess whether there is overpressure damage.

[0110] Table 3 Stiffness Variation Results

[0111]

[0112] Table 4. Positioning accuracy results of the datum plane

[0113]

[0114] It can be seen that the positioning accuracy of the reference surface of the two types of open elastic elements in this invention reaches ±0.01mm, which meets the technical requirements, and the deviation of repeated tests is extremely small, which reflects good stability.

[0115] Table 5 Comparison results between this invention and prior patents

[0116]

[0117] As can be seen, the present invention avoids overpressure damage to elastic elements by using rigid ring rigid support and stiffness change stop mechanism, and the positioning accuracy is improved by an order of magnitude compared with the prior patent, which fully meets the requirements of micro compression test.

[0118] Meanwhile, the mutation point precisely corresponds to the contact moment of the rigid ring, verifying the core logic of the technical solution.

[0119] In summary, this experiment, through high-temperature and high-pressure testing of internally / externally open elastic elements, verified the feasibility of the technical solution of "rigid ring construction stiffness difference + sensor collaborative acquisition + stiffness mutation judgment": the datum plane positioning accuracy reached ±0.01mm, meeting the high-precision requirements for elastic element sealing performance testing; it effectively avoided interference factors under high-temperature and high-pressure environments, preventing overpressure damage to the elastic element; compared with the prior patented pad solution, it has significant advantages in accuracy, specimen protection, and repeatability, and can be widely used in determining the datum plane of elastic elements under extreme working conditions, thus verifying the effectiveness of the invention.

[0120] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the technical solutions of the present invention, and these modifications or equivalent substitutions cannot cause the modified technical solutions to deviate from the spirit and scope of the technical solutions of the present invention.

Claims

1. A method for determining the reference surface of an elastic element in a high-temperature, high-pressure cavity based on a sudden change in stiffness, characterized in that: Includes the following steps: S1. Install a force sensor at the connection between the upper pressure rod and the upper pressure plate. At the same time, evenly assemble multiple grating ruler displacement sensors along the circumference above the upper pressure plate. Connect the signals of the force sensor and the grating ruler displacement sensor to the test computer through the data acquisition module to complete the calibration of the force sensor and the grating ruler displacement sensor respectively. S2. Use a level to adjust the flatness and relative parallelism of the upper and lower pressure plates. Then, place the cleaned elastic element coaxially in the center of the working surface of the lower pressure plate. Then, place the rigid ring coaxially inside the elastic element and fit it against the working surface of the lower pressure plate. Leave an anti-friction gap between the outer wall of the rigid ring and the inner wall of the elastic element. The height of the rigid ring is equal to the height of the elastic element itself minus the preset deformation amount. S3. Under the set target temperature and pressure, start the servo motor to drive the upper pressure rod to move the upper pressure plate downward along the axis. The test computer collects the force value data of the force sensor and the displacement data of the grating ruler displacement sensor in real time through the data acquisition module, and simultaneously plots the system force-displacement curve. Based on the ratio of instantaneous force value to instantaneous displacement in the force-displacement curve, the slope of the force-displacement curve is obtained, and the stiffness and its rate of change are obtained. Finally, the test reference surface is determined according to whether the stiffness changes abruptly. The elastic element mentioned in step S2 is an internally open structure or an externally open structure; In step S3, when the elastic element is an internally open structure, the determination process includes the initial displacement control stage, the internally open elastic element compression stage, and the rigid ring support stage. Furthermore, the rigid ring support stage specifically includes the following steps: when the upper pressure plate is pressed down until the inner wall of the inner opening elastic element is completely in contact with the outer wall of the rigid ring, the rigid ring provides rigid support, causing a sudden change in the force value, until the stiffness change meets the following conditions: ； In the formula, and These represent the internally open elastic element under the rigid ring support stage. Time and Stiffness at any moment This represents the coefficient for determining abrupt changes in stiffness. ; Stop the movement of the upper pressure plate. At this time, the displacement value of the upper pressure plate is the test zero point, and the plane where the working surface of the upper pressure plate is located is regarded as the test reference plane of the elastic element. When the elastic element is an externally open structure, the determination process includes the initial displacement control stage, the corrugated ring compression stage, the externally open elastic element compression stage, and the rigid ring support stage. Furthermore, the rigid ring support stage specifically includes the following steps: when the upper pressure plate is pressed down until the inner wall of the outer open elastic element is completely in contact with the outer wall of the rigid ring, the rigid ring provides rigid support, causing a sudden change in the force value, until the stiffness change meets the following conditions: ； In the formula, and These represent the externally open elastic element under the rigid ring support stage. Time and Stiffness at any moment This represents the coefficient for determining abrupt changes in stiffness. ; Stop the movement of the upper pressure plate. At this time, the displacement value of the upper pressure plate is the test zero point, and the plane where the working surface of the upper pressure plate is located is regarded as the test reference plane of the elastic element.

2. The method for determining the reference surface of a high-temperature, high-pressure cavity elastic element based on a sudden change in stiffness according to claim 1, characterized in that: When the elastic element has an externally open structure, a corrugated ring matching the outer diameter of the elastic element is selected, and the corrugated ring is coaxially sleeved on the outside of the elastic element and placed in the annular positioning groove on the working surface of the lower pressure plate.

3. The method for determining the reference surface of a high-temperature, high-pressure cavity elastic element based on a sudden change in stiffness according to claim 2, characterized in that: The rigid ring mentioned in step S2 is made of GH4169 high-temperature alloy, which has an elastic modulus of 200GPa-210GPa at room temperature. Its stiffness at the target temperature is greater than that of the elastic element, and its coefficient of thermal expansion is less than that of the elastic element.

4. The method for determining the reference surface of a high-temperature, high-pressure cavity elastic element based on a sudden change in stiffness according to claim 2, characterized in that: In step S3, the upper pressure plate moves downward at a speed of 0.01 mm / s to 0.05 mm / s to find the reference.

5. The method for determining the reference surface of a high-temperature, high-pressure cavity elastic element based on a sudden change in stiffness, as described in claim 3 or 4, is characterized in that: When the elastic element has an internally open structure, in the initial displacement control stage: the upper pressure plate does not contact the elastic element and the rigid ring, and only overcomes air resistance and the mechanical friction of the upper pressure rod. At this time, the stiffness is... ; Compression stage of the internally open elastic element: The upper pressure plate contacts the elastic element, the force value collected by the force sensor changes, and At this point, the control mode is switched to force control mode, and the upper pressure plate is moved downward at a rate of 1000 N / s. The elastic element undergoes elastic deformation, and the stiffness change at this time satisfies the following conditions: ； In the formula, and These represent the compression stage of an internally open elastic element. Time and Stiffness at any moment This represents the coefficient for determining abrupt changes in stiffness. .

6. The method for determining the reference surface of a high-temperature, high-pressure cavity elastic element based on a sudden change in stiffness, as described in claim 3 or 4, is characterized in that: When the elastic element has an externally open structure, in the initial displacement control stage: the upper pressure plate does not contact the elastic element, rigid ring, and corrugated ring, and only overcomes air resistance and mechanical friction with the upper pressure rod. At this time, the stiffness is... ; During the bellows compression stage: the upper pressure plate contacts the bellows, and the force value collected by the force sensor changes. Switch the control mode to force control mode. At this time, the upper pressure plate is controlled to move downward at a rate of 5000 N / s. The stiffness change at this time meets the following conditions: ； In the formula, and These represent the compression stage of the corrugated ring, Time and Stiffness at any moment This represents the coefficient for determining abrupt changes in stiffness. ; Compression stage of the externally open elastic element: As the upper pressure plate continues to move downwards, it contacts the elastic element and causes it to undergo elastic deformation. At this time, the stiffness change satisfies the following condition: ； In the formula, and These represent the compression stages of an externally open elastic element. Time and Stiffness at any moment This represents the coefficient for determining abrupt changes in stiffness. .

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