A long-stroke pressure pillow with a built-in deformation measuring device and a loading method thereof

Abstract

The present invention relates to a long-stroke pressure pillow with a built-in deformation measuring device. The pillow comprises an upper metal plate, a lower metal plate, an oil inlet, an oil outlet, several curved ends, a deformation measuring device, and a sensor plug-in plate. The curved ends are open inward and fixedly connected end to end to form a ring frame. The curved ends are designed to be wavy in height and include at least two curved surfaces. The edges of the upper and lower metal plates are respectively connected to the upper and lower ends of the curved ends and lie in the same plane. The curved ends, the upper and lower metal plates form a pressure chamber, with the oil inlet located at the center of the lower curved surface of one curved end and the oil outlet located at the center of the upper curved surface of the opposite curved end. The deformation measuring device is mounted on the upper and lower metal plates and located within the pressure chamber. It is connected to an external data acquisition device via a sensor plug-in plate. The sensor plug-in plate is located at the center of the upper or lower curved surface of the curved end. The present invention has the advantages of high loading capacity, large stroke, built-in high-precision deformation measuring device, and controllable deformation.

Description

Technical Field

[0001] The invention relates to the technical field of geotechnical engineering, and in particular to a long-stroke pressure pillow with a built-in deformation measuring device and a loading method thereof. Background Art

[0002] Large-scale geotechnical mechanics model tests are an indispensable means to ensure the safe construction and operation of deep geotechnical engineering projects. Unlike the hydrostatic pressure characteristics of the deep-sea environmental stress field, the deep-earth environmental stress field is characterized by unequal stress in three directions. Simulating the deep-earth environmental stress field requires a true triaxial loading tester. Current geotechnical mechanics physical model tests are developing towards larger tonnage and larger specimens. Large-tonnage jacks are extremely expensive and have extremely high technical risks. The idea of ​​using a group of jacks reduces the technical difficulty of loading, but increases the difficulty of control and also amplifies the uneven loading problem caused by rigid loading. In order to meet the needs of deep geotechnical engineering, it is necessary to develop a flexible loading device with strong loading capacity, small size, and low economic cost.

[0003] A pressure pillow is a small, simple, flexible loading device commonly used in on-site in-situ tests. Most existing pressure pillows on the market are made of two steel plates that are die-formed and then welded together. They have a very low loading capacity and are mostly used for mine stress monitoring. When pressurized, they tend to be cylindrical rather than flat, and do not have a loading function similar to a jack. For example, the pressure pillows disclosed in Chinese patent CN202073560U-Flexible Mine Pressure Stress Monitoring Pressure Pillow and Monitoring Device, and the 2020 Shandong University of Science and Technology Master's thesis "Research on the Pressure Resistance of Mine Drilling Pressure Pillows_Sun Jiangui" and other documents. Chinese patent document CN202693420U proposes an ultra-high pressure pressure pillow, but the loading capacity is only about 60MPa, which cannot meet further engineering needs (5000m burial depth related projects). Chinese patent document CN117686349A mentions a hydraulic bladder with a loading capacity of up to 150MPa, but the stroke is relatively short.

[0004] Furthermore, the aforementioned pressure pillow and similar pressure pillow-type flexible loading devices currently on the market lack inherent displacement measurement capabilities and require indirect measurement of their own travel using external displacement sensors. These indirect measurements are subject to environmental interference and lack the ability to isolate the installation gap. (In contrast, a jack displacement meter is directly connected to the piston to eliminate external interference and installation gaps, thus failing to meet laboratory control accuracy requirements (1 μm). Existing pressure pillows also have a short travel, making them suitable only for use on hard rock.

[0005] Existing pressure pillows are difficult to install displacement sensors on. The reasons are: 1) The pressure pillow is made of welded thin plates, which deforms the plates. High-strength metal plates cannot be machined after welding, resulting in a sloped mounting surface for the displacement meter, with a random inclination angle. 2) During pressure pillow loading, the thin metal plates deform under tension, causing lateral displacement at the displacement meter's measuring point. Displacement meters measure the vertical distance between two planes moving perpendicular to each other. Both conditions (1) and (2) result in the displacement meter measuring the length of a sloped line with an uncertain angle, which restricts the use of existing high-precision displacement meters.

[0006] In summary, for true triaxial loading testing machines, the rigid loading method is difficult to overcome the inherent defects, the flexible loading device has low loading capacity, cannot obtain stable displacement data, is difficult to perform servo control, and has a short loading stroke. Therefore, it is urgent to carry out technical innovation on the loading device of the true triaxial testing machine and develop an extended-range pressure pillow with a built-in deformation measurement device to meet the testing needs of deep geotechnical engineering (5000m underground). Summary of the Invention

[0007] The technical problem to be solved by the present invention is to provide a large-stroke pressure pillow with a built-in deformation measuring device in response to the deficiencies in the above-mentioned prior art, which has the advantages of strong loading capacity, large stroke, built-in high-precision deformation measuring device, and controllable deformation.

[0008] The technical solution adopted by the present invention to solve the above-mentioned technical problems is:

[0009] A large-stroke pressure pillow with a built-in deformation measuring device comprises an upper metal plate, a lower metal plate, an oil inlet and an oil outlet, and also comprises a plurality of curved ends, a deformation measuring device and a sensor plug-in plate; a plurality of the curved ends are opened inwards and fixedly connected after being assembled end to end to form an annular frame; the curved ends are designed to be wavy in the height direction and include at least two curved surfaces to increase the stroke of the pressure pillow; the edges of the upper metal plate and the lower metal plate are respectively assembled with the upper end and the lower end of the curved end and fixedly connected, and the upper metal plate and the upper end of the curved end are located on the same plane The inner surface, the lower metal plate and the lower end of the curved end are located in the same plane; the curved end and the upper metal plate and the lower metal plate form a pressure chamber of the pressure pillow, the oil inlet is located at the center position of the lower curved surface of one of the curved ends, and the oil outlet is located at the center position of the upper curved surface of the opposite curved end; the deformation measuring device is installed on the upper metal plate or the lower metal plate and is located inside the pressure chamber, and the deformation measuring device is connected to the external data acquisition equipment through the sensor plug-in board; the sensor plug-in board is located at the center position of the upper curved surface or the lower curved surface of one of the curved ends.

[0010] In the above scheme, the deformation measuring device includes a special-shaped LVDT, a threaded rod and a sensor plug; the special-shaped LVDT includes a tail base and a telescopic rod, and the three vertices of the tail base are provided with threaded holes adapted to the threaded rods, and the telescopic rod is installed on the tail base; the three threaded rods are respectively inserted into the three threaded holes of the tail base, and the tail base is kept level with the reference plane by adjusting the three threaded rods; after leveling, one end of the threaded rod is fixedly connected to the lower metal plate or the upper metal plate by cold welding, and the telescopic rod is connected to the upper metal plate or the lower metal plate for measuring the change in the distance between the upper metal plate and the lower metal plate; a ball is provided at the top of the telescopic rod for reducing friction between the telescopic rod and the upper metal plate or the lower metal plate; the lead of the special-shaped LVDT is fixed to the sensor plug, and the sensor plug is connected to the sensor plug board.

[0011] In the above solution, the upper metal plate has the same thickness as the upper end of the curved end; and the lower metal plate has the same thickness as the lower end of the curved end.

[0012] In the above solution, the curved end is formed by bending a whole piece of high-strength metal plate, and the tensile strength of the high-strength metal plate is not less than 700 MPa and the elongation at break is not less than 15%.

[0013] In the above solution, there are four curved ends, which are arranged in a one-to-one correspondence with the four sides of the metal plate.

[0014] In the above scheme, the fixed connection between adjacent curved ends, as well as between the curved ends and the upper and lower metal plates are all welded. The weld positions are determined according to the simulation results and are set in accordance with the principle of avoiding high stress areas.

[0015] In the above solution, the effective loading area of ​​the pressure pillow is (500-1000)×(500-1000) mm.

[0016] In the above solution, the curved end is provided with through holes at the installation positions of the oil inlet, the oil outlet and the sensor plug-in plate, and the oil inlet, the oil outlet and the sensor plug-in plate are all welded to the through holes.

[0017] In the above solution, the oil inlet, the oil outlet and the sensor plug-in plate are all arranged parallel to the upper metal plate and the lower metal plate.

[0018] Correspondingly, the present invention also proposes a loading method for the large-stroke pressure pillow of the above-mentioned built-in deformation measuring device, and the loading method is as follows: the data transmission line of the data acquisition equipment is connected to the built-in special-shaped LVDT through a sensor plug-in board, the oil inlet is connected to an external oil pump through a high-pressure oil pipe, the oil pump pumps oil to the pressure chamber through the oil inlet, and the air in the pressure chamber is discharged through the oil outlet. After the air is exhausted, the oil outlet is closed; the deformation control rate of the pressure pillow is set in the control software, and the difference between the rate and the actual deformation rate of the pressure pillow is used as a signal to control the deformation of the pressure pillow, and oil is continuously pumped into the pressure chamber to achieve loading of the target; the actual deformation rate of the pressure pillow is calculated based on the data collected by the built-in special-shaped LVDT.

[0019] The beneficial effects of the present invention are:

[0020] (1) The present invention welds the curved end to the upper and lower metal plates so that the upper and lower surfaces are all flat, thereby minimizing the stress concentration area during the loading process. It can withstand an internal pressure of up to 150 MPa. Combined with its own large loading area, it can meet the loading requirements of up to 8000 tons. At the same time, the stroke of the pressure pillow is increased by setting a multi-curved curved end. The increased stroke is caused by the increase in the opening angle of the curved surface, so it will not significantly increase the internal stress at the end, that is, the loading capacity of the pressure pillow will not be reduced while the stroke is increased. At present, model experiments are developing towards larger specimens. Large-volume specimens can include more information such as structural surfaces / tectonic zones that determine the properties of engineering rock masses, but a larger volume also means that the specimen will produce greater deformation under the same load. At the same time, specimens containing weak surfaces (structural surfaces, etc.) will deform more than complete specimens. The traditional pressure pillow loading plane advancement stroke is within 4mm (referring to the incremental distance between the upper and lower planes during loading). Beyond this stroke, the pressure pillow enters plastic deformation and cannot be reused. Therefore, as a loading device for model tests, the traditional pressure pillow is only suitable for hard rocks (such as granite, etc.), and is not suitable for softer rocks (such as some sandstones, shales, mudstones, etc.) or rock masses containing weak surfaces. In addition, there is currently little understanding of the properties of rock masses in deep rock engineering. The existing consensus is that under high ground stress environments, rocks are more likely to undergo rheology, and even harder rocks are prone to large deformations. In summary, in order to broaden the test scope and explore deep rock mechanics, it is necessary to increase the stroke of the pressure pillow.

[0021] (2) The present invention has a built-in deformation measuring device, which includes a special-shaped LVDT and a threaded rod. The special-shaped LVDT includes a tail base and a telescopic rod. The tail base is a triangular base, and the telescopic rod is installed on the tail base. There are three threaded rods, which respectively pass through the tail base of the special-shaped LVDT. The tail base is leveled by adjusting the height of the three threaded rods so that it remains horizontal with the reference plane (three points determine a plane); after leveling, the three threaded rods are welded to the lower metal plate or the upper metal plate by cold welding, and then the telescopic rod is connected to the upper metal plate to measure the change in the distance between the upper metal plate and the lower metal plate; the ball at the top of the telescopic rod can greatly reduce the friction between the telescopic rod and the upper metal plate, ensuring that the telescopic rod will not be deviated by the friction force and always moves along the vertical direction between the upper and lower metal plates. Therefore, the present invention solves the problem that the conventional displacement meter of the traditional pressure pillow cannot be used normally due to the deformation of the thin steel plate.

[0022] (3) The present invention has a built-in high-precision LVDT with a deformation control accuracy of up to 1μm. As a loading device of the model testing machine, in conjunction with a servo control system, the pressure pillow can be loaded and controlled according to the oil pressure or deformation rate, realizing a dual control mode of stress and deformation. The loading path can be freely designed by the test personnel to meet the simulation requirements of complex working conditions in deep geotechnical engineering. As a loading device for field experiments, the deformation measurement is stable and accurate and is not affected by the environment.

[0023] (4) Compared with the existing pressure pillows on the market, the present invention has the advantages of strong loading capacity, large stroke, and controllable deformation; compared with the jack, it has the advantages of low processing difficulty, small space requirement, and low economic cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] The present invention will be further described below with reference to the accompanying drawings and embodiments, in which:

[0025] Figure 1 This is a front view of a large-stroke pressure pillow with a built-in deformation measuring device according to the present invention;

[0026] Figure 2 yes Figure 1 AA cross-sectional view of the pressure pillow shown;

[0027] Figure 3 yes Figure 1 A schematic structural diagram of a deformation measuring device for a pressure pillow is shown;

[0028] Figure 4 yes Figure 3 A schematic structural diagram of the tail base of the deformation measuring device shown;

[0029] Figure 5 yes Figure 3 Schematic diagram of the installation of the threaded rod of the deformation measuring device shown;

[0030] Figure 6 This is a schematic diagram of the application of a large-stroke pressure pillow with a built-in deformation measuring device according to the present invention.

[0031] In the figure: 1. Curved end; 1-1. First curved end; 1-2. Second curved end; 1-3. Third curved end; 1-4. Fourth curved end; 2. Upper metal plate; 3. Lower metal plate; 4. Oil inlet; 5. Oil outlet; 6. Deformation measuring device; 6-1. Special-shaped LVDT; 6-1-1. Tail base; 6-1-2. Telescopic rod; 6-1-3. Ball bearing; 6-2. Threaded rod; 6-3. Sensor plug; 7. Grille; 8. Sensor plug board. DETAILED DESCRIPTION

[0032] In order to have a clearer understanding of the technical features, purposes and effects of the present invention, specific embodiments of the present invention are now described in detail with reference to the accompanying drawings.

[0033] like Figure 1-2 As shown, a long-stroke pressure pillow with a built-in deformation measuring device provided by a preferred embodiment of the present invention includes an upper metal plate 2, a lower metal plate 3, four curved ends 1, a deformation measuring device 6 and a sensor plug-in plate 8, an oil inlet 4, and an oil outlet 5. The four curved ends 1 are open inward and are fixedly connected end to end to form a ring frame, wherein the first curved end 1-1 and the second curved end 1-2 are arranged opposite each other, and the third curved end 1-3 and the fourth curved end 1-4 are arranged opposite each other. The four sides of the upper metal plate 2 and the lower metal plate 3 are respectively fixedly connected to the upper and lower ends of the four curved ends 1, and the upper metal plate 2 and the upper ends of the curved ends 1 are located in the same plane, and the lower metal plate 3 and the lower ends of the curved ends 1 are located in the same plane. The four curved ends 1 and the upper and lower metal plates 3 form the pressure chamber of the pressure pillow. The curved end 1 is designed to be wavy along the height direction and includes at least two curved surfaces to increase the stroke of the pressure pillow. Specifically, the cross-section of the curved surface along the height direction is an arc. The angle formed by the line connecting the upper / lower vertex and the side vertex of the arc and the horizontal direction is the curved surface opening angle. As the loading progresses, the curved surface opening angle gradually increases, and the distance between the upper and lower vertices of the arc increases accordingly. The sum of the increase in the vertex distances of all the curved surfaces is the stroke of the pressure pillow. The first curved end 1-1 is provided with a through hole at the center of the upper and lower curved surfaces respectively, and the second curved end 1-2 is provided with a through hole at the center of the upper curved surface at one end. The oil inlet 4 and the sensor plug-in plate 8 are respectively embedded in the two through holes of the first curved end 1-1, and the oil outlet 5 is embedded in the through hole of the second curved end 1-2, and are all welded and fixed. This design avoids the intersection of the curved surfaces (stress concentration area) and facilitates the discharge of gas from the top during oil filling. The deformation measuring device 6 is fixedly mounted on the lower metal plate 3 and is located inside the pressure chamber. The deformation measuring device 6 is connected to an external data acquisition device through a sensor plug-in board 8 .

[0034] The pressure pillow of the present invention features an upper metal plate 2 of equal thickness and coplanarity with the upper end of the curved end 1; a lower metal plate 3 of equal thickness and coplanarity with the lower end of the curved end 1. The pillow's upper and lower surfaces are both flat, minimizing stress concentration areas during loading and enabling it to withstand loads up to 150 MPa. Furthermore, the multi-curved curved end 1 increases the pillow's travel. This increased travel is achieved by increasing the angle of the curved surfaces, thus minimizing stress buildup. Therefore, it does not significantly increase the internal stress at the end, effectively increasing the travel without compromising the pillow's loading capacity.

[0035] like Figure 3-5 As shown, the deformation measurement device 6 includes a special-shaped LVDT 6-1, a threaded rod 6-2, and a sensor plug 6-3. The special-shaped LVDT 6-1 includes a tail base 6-1-1 and a telescopic rod 6-1-2. The tail base 6-1-1 is a triangular base with threaded holes at three vertices adapted for the threaded rod 6-2. The telescopic rod 6-1-2 is mounted on the tail base 6-1-1. Three threaded rods 6-2 extend through the tail base 6-1-1 of the shaped LVDT. The tail base 6-1-1 is leveled with the reference plane by adjusting the height of the three threaded rods 6-2 (three points define a plane). After leveling, the ends of the three threaded rods 6-2 are cold-welded (e.g., laser welding) to the lower metal plate 3. The telescopic rod 6-1-2 then connects to the upper metal plate 2 to measure the change in distance between the upper and lower metal plates 3. Ball bearings 6-1-3 are installed at the top of the telescopic rod 6-1-2 to significantly reduce friction between the telescopic rod 6-1-2 and the upper metal plate (converting sliding friction to rolling friction), ensuring that the telescopic rod 6-1-2 is not deflected by friction and always moves along the perpendicular line between the upper and lower metal plates. The leads of the shaped LVDT 6-1 are welded to the sensor plug 6-3, which is connected to the sensor board 8. The pressure pillow of the present invention measures the change of the vertical distance between the upper metal plate 2 and the lower metal plate 3 through the built-in special-shaped LVDT6-1, thereby obtaining the deformation of the pressure pillow, and the deformation control accuracy can reach 1μm.

[0036] The pressure pillow of the present invention serves as a loading device of the model testing machine. In conjunction with the servo control system, it can not only perform loading control according to the oil pressure, but also control the loading of the pressure pillow through the deformation rate (the difference between the deformation rate and the actual deformation rate of the pressure pillow is used as a signal to control the deformation of the pressure pillow, and the actual deformation rate of the pressure pillow is calculated based on the data collected by the built-in special-shaped LVDT), thereby realizing a dual control mode of stress and deformation. The loading path can be freely designed by the test personnel to meet the simulation requirements of complex working conditions in deep geotechnical engineering. As a loading device for field experiments, the deformation measurement is stable and accurate and is not affected by the environment.

[0037] Further optimized, the curved end 1 is formed by bending a single piece of high-strength metal plate. The high-strength metal plate has a tensile strength of no less than 700 MPa and an elongation at break of no less than 15%. In this embodiment, the curved end 1, upper metal plate 2, and lower metal plate 3 are all 15 mm thick. The high-strength metal plate is Q690E.

[0038] Further optimization is performed, and the fixed connection methods between the four curved ends 1, as well as between the curved end 1 and the upper metal plate 2 and the lower metal plate 3 are all welding. The positions of the welds are determined according to the simulation results and are set in accordance with the principle of avoiding high stress areas.

[0039] Further optimization, the effective loading area of ​​the pressure pillow (i.e., the plane area) is (500-1000)×(500-1000) mm. In this embodiment, the effective loading area of ​​the pressure pillow is 800×800 mm.

[0040] Further optimized, the pressure pillow of the present invention also includes a grid 7 component, which includes a series of rectangular steel bars. The height of the steel bars is slightly lower than the net height of the pressure chamber of the pressure pillow. The steel bars are fixed to the lower metal plate 3 by electric welding to support the upper metal plate 2.

[0041] Further optimized, the oil inlet 4 , the oil outlet 5 and the sensor plug-in plate 8 are all arranged parallel to the upper metal plate 2 and the lower metal plate 3 .

[0042] As a further optimization, the extended ends of the oil inlet 4 and the oil outlet 5 are processed with internal threads to facilitate connection with the ultra-high pressure oil pipe.

[0043] When the pressure pillow of the present invention is in operation, the data transmission line of the data acquisition device is connected to the built-in special-shaped LVDT 6-1 via the sensor plug-in board 8. An external oil pump is connected via the oil inlet 4 through a high-pressure oil pipe. The oil pump pumps oil through the oil inlet 4 into the pressure chamber composed of the curved end 1, the upper metal plate 2, and the lower metal plate 3. The air in the pressure chamber is discharged through the oil outlet 5. After the air is completely discharged, the oil outlet 5 is closed. The deformation control rate of the pressure pillow is set in the control software. The difference between this rate and the actual deformation rate of the pressure pillow (calculated based on the data collected by the built-in special-shaped LVDT 6-1) is used as a signal to control the deformation of the pressure pillow, continuously pumping oil into the pressure chamber to achieve target loading.

[0044] Figure 6This is an application scenario of the pressure pillow of the present invention as a loading tool. The loading control method of the pressure pillow of the present invention is described in conjunction with this scenario. A rock 12 is placed in the middle of the pressure chamber 9, and pads 11-1 to 11-4 are attached to the four sides of the rock 12. Displacement meters 13-1 and 13-2 are respectively installed on the pads 11-1 and 11-2 to measure rock deformation. Pressure pillows 10-1 to 10-4 are installed in the gap between the pads 11-1 to 11-4 and the pressure chamber 9. In order to reduce the influence of end friction, a pair of pressure pillows should be started first for loading. After reaching the target stress value, the other pair of pressure pillows should be started for loading. In this embodiment, the pressure pillows 10-1 and 10-3 are first started to load the sample 12, and oil is pumped into the pressure pillows 10-1 and 10-3 at the same rate. The data collected by the built-in displacement sensors 10-1-1, 10-3-1 and the displacement meters 13-1, 13-2 are always monitored. In the initial stage, the data collected by the built-in displacement sensors 10-1-1, 10-3-1 increase while the data collected by the displacement meters 13-1, 13-2 remain unchanged, which indicates that the gap between the pressure pillows 10-1, 10-3 and the pads 11-1, 11-3 (as well as the inner wall of the pressure chamber 9) is decreasing. When the data collected by displacement meters 13-1 and 13-2 begins to increase, stop pumping oil to pressure pillows 10-1 and 10-3, reset the data collected by built-in displacement sensors 10-1-1 and 10-3-1, and set the deformation control rate for pressure pillows 10-1 and 10-3 in the control software. The difference between this rate and the actual deformation rate of the pressure pillows (calculated based on data collected by built-in special-shaped LVDT 6-1) is then used as a signal to control the deformation of pressure pillows 10-1 and 10-3. Load is then applied to specimen 12 until the smaller of the internal pressures of pressure pillows 10-1 and 10-3 reaches the design pressure. At this point, although the internal pressures of pressure pillows 10-1 and 10-3 differ slightly, since the loading strokes are the same, specimen 12 remains at the center. According to the principle of force balance, the loads exerted on specimen 12 by pressure pillows 10-1 and 10-3 are equal. The same operation is performed on pressure pillows 10-2 and 10-4. It should be noted that the built-in displacement sensors 10-1-1 and 10-3-1 are the above-mentioned special-shaped LVDTs (linear displacement sensors).

[0045] The embodiments of the present invention are described above in conjunction with the accompanying drawings, but the present invention is not limited to the above-mentioned specific implementation methods. The above-mentioned specific implementation methods are merely illustrative and not restrictive. Under the guidance of the present invention, ordinary technicians in this field can also make many forms without departing from the scope of protection of the present invention and the claims, all of which are protected by the present invention.

Claims

1. A long-stroke pressure pillow with a built-in deformation measuring device, comprising an upper metal plate, a lower metal plate, an oil inlet and an oil outlet, characterized in that: It also includes several curved ends, deformation measuring devices and sensor plug-in plates; several of the curved ends are opened inward and fixedly connected after being assembled end to end to form an annular frame, and the curved end is designed to be wavy in the height direction, including at least two curved surfaces to increase the stroke of the pressure pillow; the edges of the upper metal plate and the lower metal plate are respectively assembled with the upper end and the lower end of the curved end and fixedly connected, and the upper metal plate and the upper end of the curved end are located in the same plane, and the lower metal plate and the lower end of the curved end are located in the same plane; the curved end and the upper metal plate and the lower metal plate form a pressure chamber of the pressure pillow, the oil inlet is located at the center position of the lower curved surface of one of the curved ends, and the oil outlet is located at the center position of the upper curved surface of the opposite curved end; the deformation measuring device is installed on the upper metal plate or the lower metal plate and is located inside the pressure chamber, and the deformation measuring device is connected to the external data acquisition equipment through the sensor plug-in plate; the sensor plug-in plate is located at the center position of the upper curved surface or the lower curved surface of one of the curved ends; The deformation measuring device includes a special-shaped LVDT, a threaded rod and a sensor plug; the special-shaped LVDT includes a tail base and a telescopic rod, and the three vertices of the tail base are provided with threaded holes adapted to the threaded rods, and the telescopic rod is installed on the tail base; the three threaded rods are respectively inserted into the three threaded holes of the tail base, and the tail base is kept level with the reference plane by adjusting the three threaded rods; after leveling, one end of the threaded rod is fixedly connected to the lower metal plate or the upper metal plate by cold welding, and the telescopic rod is connected to the upper metal plate or the lower metal plate for measuring the change in the distance between the upper metal plate and the lower metal plate; a ball is provided at the top of the telescopic rod for reducing friction between the telescopic rod and the upper metal plate or the lower metal plate; the lead of the special-shaped LVDT is fixed to the sensor plug, and the sensor plug is connected to the sensor plug board.

2. The long-stroke pressure pillow with a built-in deformation measuring device according to claim 1, characterized in that: The upper metal plate has the same thickness as the upper end of the curved end; the lower metal plate has the same thickness as the lower end of the curved end.

3. The long-stroke pressure pillow with a built-in deformation measuring device according to claim 1, characterized in that: The curved end is formed by bending a whole piece of high-strength metal plate, and the tensile strength of the high-strength metal plate is not less than 700 MPa and the elongation at break is not less than 15%.

4. The long-stroke pressure pillow with a built-in deformation measuring device according to claim 1, characterized in that: There are four curved ends, which are arranged in one-to-one correspondence with the four sides of the metal plate.

5. The long-stroke pressure pillow with a built-in deformation measuring device according to claim 1, characterized in that: The fixed connection between adjacent curved ends, as well as between the curved ends and the upper and lower metal plates, is welded. The weld positions are determined based on the simulation results and are set to avoid high stress areas.

6. The long-stroke pressure pillow with a built-in deformation measuring device according to claim 1, characterized in that: The effective loading area of ​​the pressure pillow is (500-1000)×(500-1000) mm.

7. The long-stroke pressure pillow with a built-in deformation measuring device according to claim 1, characterized in that: The curved end is provided with through holes at the installation positions of the oil inlet, the oil outlet and the sensor plug-in plate, and the oil inlet, the oil outlet and the sensor plug-in plate are all welded to the through holes.

8. The long-stroke pressure pillow with a built-in deformation measuring device according to claim 1 or 7, characterized in that: The oil inlet, the oil outlet and the sensor plug-in plate are all arranged parallel to the upper metal plate and the lower metal plate.

9. The method for loading a long-stroke pressure pillow with a built-in deformation measuring device according to any one of claims 1 to 8, characterized in that: The loading method comprises the following steps: a data transmission line of a data acquisition device is connected to a built-in special-shaped LVDT via a sensor plug-in board; an oil inlet is connected to an external oil pump via a high-pressure oil pipe; the oil pump pumps oil into the pressure chamber through the oil inlet; air in the pressure chamber is discharged through the oil outlet; and after the air is completely discharged, the oil outlet is closed; a deformation control rate of the pressure pillow is set in the control software; the difference between the rate and the actual deformation rate of the pressure pillow is used as a signal to control the deformation of the pressure pillow, and oil is continuously pumped into the pressure chamber to achieve target loading; The true deformation rate of the pressure pillow is calculated based on the data collected by the built-in special-shaped LVDT.

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