Method and device for testing bending moment of pipe

Abstract

The invention discloses a pipe bending moment testing method and device, and relates to the technical field of pipe performance testing. The testing method comprises the following steps that two sealing clamping assemblies are used for conducting sealing clamping on the two axial ends of a pipe sample to form a pressure bearing cavity, the two sealing clamping assemblies are rotationally connected with corresponding supporting frames, and a hydraulic servo system communicates with an inner cavity of the pipe sample; controlling the hydraulic servo system to fill a pressure medium into the pipe sample; a load applying assembly is controlled to drive a pressing block to move at a constant speed, and loads are applied to the pipe sample in the radial direction through the pressing block, so that the pipe sample is bent and deformed under the combined action of internal pressure and bending moment; the data acquisition and analysis system is used for acquiring detection values of the strain gauge, the internal pressure sensor, the force sensor and the displacement sensor, and the bending moment applied to the pipe sample is calculated according to a mechanical model. According to the invention, the pipe can be tested under the bending moment and internal pressure combined load working condition.

Description

Technical Field

[0001] This invention relates to the field of pipe performance testing technology, and in particular to a method and apparatus for testing pipe bending moment. Background Technology

[0002] Metal tubing is a critical structural and functional component in modern industry, widely used in automobile chassis, aircraft hydraulic lines, spacecraft fuel delivery pipelines, and building structures. In these applications, tubing often needs to withstand complex bending loads while simultaneously bearing internal fluid pressure. Therefore, accurately evaluating its forming performance under the combined effects of bending moment and internal pressure is crucial.

[0003] It is well known that materials exhibit different forming properties when deformed under different stress states. Currently, the testing of pipe mechanical properties mainly relies on uniaxial tensile tests. This method can only provide basic parameters of the material under a single stress state and cannot reflect its true behavior under complex stress states. The free bulging test for pipes, which has emerged in recent years, can provide data on biaxial stress; however, this method can only characterize the deformation characteristics of pipes under tensile stress in both the axial and circumferential directions, and its stress state is still fundamentally different from that under bending conditions. Currently, the three-point bending test is a widely used method for evaluating bending loads. However, it is difficult to accurately measure the critical bending moment of the pipe under internal pressure using existing equipment in a three-point bending load test.

[0004] Therefore, existing technologies lack a dedicated device capable of effectively simulating and testing the deformation failure behavior of pipes under the combined effects of bending moment and internal pressure. This often leads to reliance on experience or overly conservative safety factors during design, potentially resulting in safety hazards, material waste, and excessive structural weight. Therefore, developing a testing device capable of accurately reproducing the "bending-internal pressure" combined load condition has significant engineering value and scientific importance for promoting lightweight design and improving structural safety and reliability.

[0005] In view of the problems existing in the above-mentioned prior art, those skilled in the art urgently need a method and device for testing the bending moment of pipes. Summary of the Invention

[0006] The purpose of this invention is to provide a method and apparatus for testing the bending moment of pipes, so as to solve the problems existing in the prior art and realize the testing of pipes under combined bending moment and internal pressure load conditions.

[0007] To achieve the above objectives, the present invention provides the following solution: This invention provides a method for testing the bending moment of a pipe, comprising the following steps: using two sealing clamping assemblies to seal and clamp both ends of a pipe sample along its axial direction to form a pressure-bearing cavity; rotatably connecting the two sealing clamping assemblies to corresponding support frames, and connecting a hydraulic servo system to the inner cavity of the pipe sample; setting strain gauges on the outer wall of the pipe sample, placing a pressure block at the middle position along the axial direction of the pipe sample, and abutting a load application assembly against the pressure block; connecting the strain gauges, the internal pressure sensor of the hydraulic servo system, the force sensor and displacement sensor of the load application assembly to a data acquisition and analysis system; controlling the hydraulic servo system to fill the interior of the pipe sample with a pressure medium; controlling the load application assembly to drive the pressure block to move at a uniform speed and apply a radial load to the pipe sample through the pressure block, causing the pipe sample to bend and deform under the combined action of internal pressure and bending moment; using the data acquisition and analysis system to collect the detection values ​​of the strain gauges, the internal pressure sensor, the force sensor and the displacement sensor, and calculating the bending moment applied to the pipe sample according to a mechanical model.

[0008] In some embodiments, the pressure block has an arc-shaped groove on the side near the tubular sample; at least a portion of the outer wall of the tubular sample is located within the arc-shaped groove, and the strain gauge is disposed between the outer wall of the tubular sample and the inner wall of the arc-shaped groove.

[0009] In some embodiments, the sealing clamping assembly includes a sealing mandrel and clamps. The sealing mandrel includes a connecting section and a sealing section. The sealing sections of the two sealing mandrels are respectively inserted into the interior of both axial ends of the pipe sample, and a sealing element is provided between the outer wall of the sealing section and the inner wall of the pipe sample. The two clamps are respectively sleeved on the outer sides of both axial ends of the pipe sample, and the clamps and the sealing sections are used to clamp the ends of the pipe sample. The connecting sections of the two sealing mandrels are each provided with a rotating shaft perpendicular to the axial direction of the pipe sample, and the rotating shaft is rotatably connected to the corresponding support frame through a bearing.

[0010] In some embodiments, the hydraulic servo system further includes an inlet pipe, an outlet pipe, a booster, an overflow valve, and a pressure medium tank; the sealing mandrel is provided with a medium channel communicating with the inner cavity of the tubular sample; one end of the inlet pipe is connected to the medium channel of one of the sealing mandrels, and the other end is connected to the pressure medium tank, and the booster is provided on the inlet pipe; one end of the outlet pipe is connected to the medium channel of another of the sealing mandrels, and the other end is connected to the pressure medium tank, and the internal pressure sensor and the overflow valve are provided on the outlet pipe.

[0011] In some embodiments, in the step of "controlling the hydraulic servo system to fill the interior of the pipe sample with a pressure medium": the hydraulic servo system is controlled to fill the interior of the pipe sample with a pressure medium and maintain a set internal pressure; or, the hydraulic servo system is controlled to fill the interior of the pipe sample with a pressure medium and the internal pressure is controlled to change according to a preset program; in the step of "controlling the load application component to drive the pressure block to move at a constant speed and apply a radial load to the pipe sample through the pressure block, so that the pipe sample undergoes bending deformation under the combined action of internal pressure and bending moment": the pipe sample undergoes bending deformation under the combined action of internal pressure and increasing bending moment until it buckles or ruptures.

[0012] In some embodiments, the bending radius R of the tubular sample is calculated using the following formula: ; The formula for calculating the bending angle θ of the tubular sample is: ; The formula for calculating the bending moment M of the tubular sample is: ; Wherein, L is the axial length of the bent portion of the pipe sample, l is the axial distance from the rotation center of the sealing mandrel to the end face of the sealing section, δ is the detection value of the displacement sensor, F is the detection value of the force sensor, p is the detection value of the internal pressure sensor, and r is the radius of the outer wall of the pipe sample.

[0013] In some embodiments, the method further includes: controlling the load application component to stop loading when the load applied by the load application component to the pipe specimen has passed its maximum value and is decreasing; and obtaining the ultimate bending moment value and bending moment-strain curve of the pipe specimen based on the test data.

[0014] In some embodiments, the step of “obtaining the ultimate bending moment value of the pipe specimen based on test data” includes: plotting the bending moment-bending curvature relationship curve of the pipe specimen based on the calculation results, and obtaining the ultimate bending moment value of the pipe specimen under a set internal pressure based on the peak value of the bending moment-bending curvature relationship curve; wherein, the relationship between the bending curvature k of the pipe specimen and the bending radius R is: k=1 / R.

[0015] In some embodiments, the load application assembly further includes a movable crossbeam, an upper plate, a lower plate, a guide post, and a connecting rod; the upper plate is arranged parallel to the lower plate and is located above the lower plate, and the support frame is disposed on the lower plate; the bottom surface of the upper plate abuts against the top of the pressure block, the force sensor is disposed below the movable crossbeam, and both ends of the connecting rod are respectively connected to the force sensor and the top surface of the upper plate; the upper plate is provided with a guide hole for the guide post to pass through, one end of the guide post is connected to the lower plate, and the other end passes upward through the guide hole.

[0016] The present invention also provides an apparatus for implementing the above-mentioned method for testing the bending moment of a pipe, comprising a sealing clamping assembly, a support frame, a strain gauge, a pressure block, a hydraulic servo system, a load loading assembly, and a data acquisition and analysis system; two of the sealing clamping assemblies are used to seal and clamp the two ends of the pipe sample along the axial direction to form a pressure-bearing cavity, and the two sealing clamping assemblies are rotatably connected to the corresponding support frame; the strain gauge is disposed on the outer wall surface of the pipe sample, and the pressure block is disposed at the middle position along the axial direction of the pipe sample; the hydraulic servo system is in communication with the interior of the pipe sample for filling the pipe sample with a pressure medium, and the hydraulic servo system includes an internal pressure sensor; the load loading assembly abuts against the pressure block for applying a radial load to the pipe sample, and the load loading assembly includes a force sensor and a displacement sensor; the strain gauge, the internal pressure sensor, the force sensor, and the displacement sensor are respectively connected to the data acquisition and analysis system.

[0017] The present invention achieves the following technical effects compared to the prior art: The present invention discloses a method and apparatus for testing the bending moment of pipes. An internal pressure is applied to the inside of a pipe sample using a hydraulic servo system, and the applied internal pressure value is detected by an internal pressure sensor. A load application component applies a load to the pipe sample, causing it to bend under the support of a support frame and a sealing clamping component. Strain gauges detect the strain value of the pipe sample, a force sensor measures the magnitude of the force applied to the pipe sample by the load application component, and a displacement sensor detects the displacement values ​​of the load application component and the pipe sample. Finally, a data acquisition and analysis component calculates the bending moment applied to the pipe sample based on all the acquired measurements and the mechanical model of the pipe sample. In other words, the present invention can test and calculate the bending moment value of pipes under combined bending moment and internal pressure load conditions. Attached Figure Description

[0018] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0019] Figure 1 This is a schematic diagram showing the connection between the pipe sample and the sealing mandrel, clamp, and pressure block in some embodiments of the present invention; Figure 2 This is a schematic diagram showing the connection between the sealing mandrel and the support frame in some embodiments of the present invention; Figure 3 for Figure 1 Longitudinal section view in the middle; Figure 4 for Figure 1 The transverse section view in the middle; Figure 5 This is a schematic diagram of the overall structure of the pipe bending moment testing device in some embodiments of the present invention; Figure 6 This is a force-displacement relationship curve of the tubular sample of the present invention; Figure 7 This is a stress analysis diagram of the tubular sample of the present invention; Figure 8 This is a curve showing the bending moment-bending curvature relationship of the tubular sample of the present invention. In the diagram: 1-Support frame; 2-Bearing; 3-Sealing mandrel; 4-Clamp; 5-Pressure block; 6-Pipe sample; 7-Seal; 8-Guide post; 9-Upper plate; 10-Connecting rod; 11-Force sensor; 12-Modible crossbeam; 13-Screw rod; 14-Upper fixed beam; 15-Data acquisition and analysis system; 16-Relief valve; 17-Pressure medium tank; 18-Pressure booster; 19-Internal pressure sensor; 20-Pressure medium pipeline; 21-Strain gauge; 22-Base; 23-Lower plate. Detailed Implementation

[0020] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0021] The purpose of this invention is to provide a method and apparatus for testing the bending moment of pipes, so as to solve the problems existing in the prior art and realize the testing of pipes under combined bending moment and internal pressure load conditions.

[0022] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0023] This invention provides a method for testing the bending moment of pipes, such as... Figures 1 to 8 As shown, it includes the following steps: Step S1: Use two sealing clamping assemblies to seal and clamp the two ends of the pipe sample 6 in the axial direction to form a pressure-bearing cavity. Rotately connect the two sealing clamping assemblies to the corresponding support frame 1, and connect the hydraulic servo system to the inner cavity of the pipe sample 6. Step S2: Strain gauge 21 is installed on the outer wall of the tube sample 6, and pressure block 5 is placed at the middle position of the tube sample 6 in the axial direction, and the load application component is brought into contact with pressure block 5. Step S3: Connect the strain gauge 21, the internal pressure sensor 19 of the hydraulic servo system, the force sensor 11 of the load application component, and the displacement sensor to the data acquisition and analysis system 15 respectively; Step S4: Control the hydraulic servo system to fill the interior of the tubular sample 6 with pressure medium; Step S5: Control the load application component to drive the pressure block 5 to move at a constant speed and apply a load to the pipe sample 6 radially through the pressure block 5, so that the pipe sample 6 undergoes bending deformation under the combined action of internal pressure and bending moment. Step S6: Use the data acquisition and analysis system 15 to collect the detection values ​​of strain gauge 21, internal pressure sensor 19, force sensor 11 and displacement sensor, and calculate the bending moment applied to the pipe sample 6 according to the mechanical model.

[0024] It should be noted that the mechanical model of this invention refers to the mechanical model of the testing device, such as... Figure 7 As shown, the mechanical model includes the parameters of the pipe sample 6, the parameters of the sealing clamping assembly, and the measured values ​​of each sensor.

[0025] In some embodiments, the pressure block 5 is provided with an arc-shaped groove on the side near the tubular sample 6; at least a portion of the outer wall of the tubular sample 6 is located in the arc-shaped groove, and the strain gauge 21 is disposed between the outer wall of the tubular sample 6 and the inner wall of the arc-shaped groove.

[0026] In some embodiments, the sealing clamping assembly includes a sealing mandrel 3 and a clamp 4. The sealing mandrel 3 includes a connecting section and a sealing section. The sealing sections of the two sealing mandrels 3 are respectively inserted into the interior of the two axial ends of the pipe sample 6, and a sealing element 7 is provided between the outer wall of the sealing section and the inner wall of the pipe sample 6. The two clamps 4 are respectively sleeved on the outer sides of the two axial ends of the pipe sample 6, and the clamps 4 and the sealing sections are used to clamp the ends of the pipe sample 6. The connecting sections of the two sealing mandrels 3 are each provided with a rotating shaft perpendicular to the axial direction of the pipe sample 6, and the rotating shaft is rotatably connected to the corresponding support frame 1 through a bearing 2.

[0027] It should be noted that each sealing mandrel 3 has two symmetrically arranged rotating shafts in its connecting section, and the two rotating shafts are rotatably connected to the corresponding support frame 1 through bearings.

[0028] In some embodiments, such as Figure 5 As shown, the hydraulic servo system also includes an inlet pipe, an outlet pipe, a booster 18, an overflow valve 16, and a pressure medium tank 17; the sealing mandrel 3 is provided with a medium channel communicating with the inner cavity of the pipe sample 6; one end of the inlet pipe is connected to the medium channel of one sealing mandrel 3, and the other end is connected to the pressure medium tank 17, and a booster 18 is provided on the inlet pipe; one end of the outlet pipe is connected to the medium channel of another sealing mandrel 3, and the other end is connected to the pressure medium tank 17, and an internal pressure sensor 19 and an overflow valve 16 are provided on the outlet pipe.

[0029] In some embodiments, the step of “controlling the hydraulic servo system to fill the interior of the tubular sample 6 with a pressure medium” involves: controlling the hydraulic servo system to fill the interior of the tubular sample 6 with a pressure medium and maintaining a set internal pressure; or, controlling the hydraulic servo system to fill the interior of the tubular sample 6 with a pressure medium and controlling the internal pressure to change according to a preset program.

[0030] In some embodiments, in step S5 above: the tubular sample 6 undergoes bending deformation under the combined action of internal pressure and increasing bending moment until it buckles or ruptures.

[0031] In some embodiments, the bending radius R of the tubular sample 6 is calculated using the following formula: ; The formula for calculating the bending angle θ of pipe sample 6 is: ; The formula for calculating the bending moment M of pipe specimen 6 is: ; Where L is the axial length of the bent portion of the pipe sample 6, l is the axial distance from the rotation center of the sealing mandrel 3 to the end face of the sealing section, δ is the detection value of the displacement sensor, F is the detection value of the force sensor 11, p is the detection value of the internal pressure sensor 19, and r is the radius of the outer wall of the pipe sample 6.

[0032] It should be noted that, as Figure 7 As shown, L in this invention is the axial length of the pipe sample 6 located between the end faces of the sealing sections of the two sealing mandrels 3. It can also be understood as L being the total length of the pipe sample 6 minus the length of the clamped portion; l is the axial distance between the central axis of the rotating shaft and the end face of the sealing section.

[0033] In some embodiments, the test method further includes: when the load applied by the load application component to the tubular specimen 6 passes its maximum value and decreases, controlling the load application component to stop loading; The ultimate bending moment and bending moment-strain curve of pipe specimen 6 were obtained based on the test data.

[0034] In some embodiments, the step of “obtaining the ultimate bending moment value of the pipe specimen 6 based on the test data” includes: plotting the bending moment-bending curvature relationship curve of the pipe specimen 6 based on the calculation results, and obtaining the ultimate bending moment value of the pipe specimen 6 under the set internal pressure based on the peak value of the bending moment-bending curvature relationship curve; wherein, the relationship between the bending curvature k of the pipe specimen 6 and the bending radius R is: k=1 / R.

[0035] In some embodiments, such as Figure 5 As shown, the load application assembly also includes a movable crossbeam 12, an upper plate 9, a lower plate 23, a guide post 8, and a connecting rod 10; the upper plate 9 is arranged parallel to the lower plate 23, and the upper plate 9 is located above the lower plate 23, and the support frame 1 is set on the lower plate 23; the bottom surface of the upper plate 9 abuts against the top of the pressure block 5, a force sensor 11 is set below the movable crossbeam 12, and the two ends of the connecting rod 10 are respectively connected to the force sensor 11 and the top surface of the upper plate 9; the upper plate 9 is provided with a guide hole for the guide post 8 to pass through, one end of the guide post 8 is connected to the lower plate 23, and the other end passes upward through the guide hole.

[0036] It should be noted that the load application assembly of the present invention also includes a lead screw 13, an upper fixed beam 14, and a base 22. The lower plate 23 is disposed on the base 22. The two ends of the lead screw 13 are respectively connected to the upper fixed beam 14 and the base 22. The movable crossbeam 12 is threadedly connected to the lead screw 13, and the lead screw 13 is connected to the drive motor. The drive motor drives the lead screw 13 to rotate, thereby driving the movable crossbeam 12 to move up and down in the vertical direction. Furthermore, the displacement sensor of the present invention can be disposed on the movable crossbeam 12.

[0037] The present invention also provides an apparatus for implementing the above-mentioned method for testing the bending moment of pipes, comprising a sealing clamping assembly, a support frame 1, a strain gauge 21, a pressure block 5, a hydraulic servo system, a load loading assembly, and a data acquisition and analysis system 15; two sealing clamping assemblies are used to seal and clamp the two ends of the pipe sample 6 in the axial direction to form a pressure-bearing cavity, and the two sealing clamping assemblies are rotatably connected to the corresponding support frame 1; the strain gauge 21 is disposed on the outer wall surface of the pipe sample 6, and the pressure block 5 is disposed at the middle position in the axial direction of the pipe sample 6; the hydraulic servo system is in communication with the interior of the pipe sample 6 for filling the pipe sample 6 with a pressure medium, and the hydraulic servo system includes an internal pressure sensor 19; the load loading assembly abuts against the pressure block for applying a radial load to the pipe sample 6, and the load loading assembly includes a force sensor 11 and a displacement sensor; the strain gauge 21, the internal pressure sensor 19, the force sensor 11, and the displacement sensor are respectively connected to the data acquisition and analysis system 15.

[0038] This invention provides a method and apparatus for testing the bending moment of pipes, addressing the problem that traditional uniaxial stress testing or recently developed free bulging methods cannot induce bending moment deformation in pipes, thus failing to effectively evaluate their forming performance under combined bending and internal pressure loads. The testing apparatus of this invention includes: a support and loading frame, a hydraulic servo system, a sealing clamping assembly, and a data acquisition and analysis system. The support and loading frame provides the bending load; the hydraulic servo system provides controllable liquid pressure into the pipe; the sealing clamping assembly seals the pipe blank ends; and the data acquisition and analysis system simultaneously records the bending load, internal pressure, displacement, and pipe wall strain. The testing method of this invention mainly includes the following steps: preparing a pipe sample 6 and installing the sealing clamping assembly; attaching strain gauges 21 to specific locations on the sample; filling the sealed pipe blank cavity with a fluid medium at a set pressure; applying a bending load to the pipe blank using a pressure block 5, causing it to bend under the combined action of internal pressure and bending moment until failure; and acquiring and recording data in real time for analysis.

[0039] The method for testing the bending moment of pipes according to the present invention mainly includes the following steps: Step 1: Sample Preparation and Installation: Cut a metal tube sample 6 to the required length and clean its surface; install the sealing clamping assembly at both ends of the tube sample 6 to achieve a seal, and connect the sealing mandrel 3 to the support frame 1 through the bearing 2, so that the tube sample 6 forms a closed pressure-bearing cavity. Fix the support frame 1 to the base 22 with bolts; place the pressure block 5 in the middle of the tube; place the upper plate 9 on the pressure block 5 through the guide post 8.

[0040] Step 2, Sensor system setup: Strain gauge 21 is attached to the expected maximum bending moment area on the outer surface of the tubular sample 6, i.e., the middle position, to measure the surface strain at that position.

[0041] Step 3, System Connection: Connect the strain gauge 21 to the data acquisition and analysis system 15; connect the sealing clamping assembly to the hydraulic servo system through the pressure medium pipeline 20. The hydraulic servo system includes a booster 18, an internal pressure sensor 19 for monitoring internal pressure, and an overflow valve 16 to ensure stable internal pressure.

[0042] Step 4, Composite Load Test: The hydraulic servo system fills the inner cavity of the pipe sample 6 with and maintains the set internal pressure p; then, the movable crossbeam 12 controls the pressure block 5 to apply a uniform vertical downward displacement to the middle position of the pipe sample 6, thereby applying a bending load, so that the pipe sample undergoes bending deformation under the combined action of constant internal pressure p and increasing bending moment, until it buckles or breaks.

[0043] Step 5, Data Acquisition and Analysis: Throughout the test, the data acquisition and analysis system 15 collects and records in real time the downward load F measured by the force sensor 11, the internal pressure p measured by the internal pressure sensor 19, the indenter displacement δ measured by the displacement sensor, and the strain ε measured by the strain gauge 21. Based on the downward load F and the mechanical model of the device, the bending moment M applied to the pipe specimen 6 is calculated. The experimental data is processed to obtain the ultimate bending moment value of the pipe specimen 6 under the combined action of "bending moment-internal pressure" and the bending moment-strain relationship curve.

[0044] A sealing element 7 is provided between the sealing mandrel 3 and the tubular sample 6 of the present invention. The sealing element 7 is a rubber ring or a polymer sealing element. The axial sealing with the end of the tubular sample 6 is achieved by the clamping force of the end clamp 4. Furthermore, the sealing mandrel 3 at both ends is connected to the support frame 1 through the bearing bearing to achieve hinged support. While achieving sealing, it allows the tubular sample 6 to generate necessary end displacement and end deflection when bending and deforming.

[0045] The hydraulic servo system of this invention has a pressure closed-loop control function, which can accurately maintain the internal pressure p at a constant value according to instructions during the test, or change it according to a preset program. The pressure medium filled into the inner cavity of the pipe sample 6 is an emulsion or hydraulic oil.

[0046] After the test, the data acquisition and analysis system 15 of the present invention automatically plots and analyzes the "bending moment-internal pressure-strain" relationship curve, and determines the ultimate bending moment of the pipe specimen 6 according to the maximum bending load point or the specified strain offset criterion.

[0047] The testing method of this invention, through a specific sealing and loading design, allows the tubular sample 6 to withstand both controlled internal pressure and bending load simultaneously, thereby realistically reproducing its stress state under actual working conditions. By simultaneously acquiring load, pressure, displacement, and strain data, this method can construct a complete constitutive relationship of the material under this composite path.

[0048] This invention also provides an apparatus for implementing the above method. This apparatus provides loading force through a support and loading frame; provides precise internal pressure through a hydraulic servo system; and cleverly solves the coupling problem between pressurization and bending rotation through an innovative combination of a sealing clamping assembly and a load-bearing bearing, ensuring both the reliability of the seal and avoiding the impact of additional bending moment on test accuracy. It also achieves simultaneous measurement of multiple physical quantities through a data acquisition and analysis system. The testing apparatus includes four support frames 1, four load-bearing bearings, two sealing mandrels 3, two clamps 4, rubber rings, strain gauges 21, guide pillars 8, an upper plate 9, a lower plate 23, a base 22, a pressure block 5, a connecting rod 10, a force sensor 11, a movable crossbeam 12, a lead screw 13, an upper fixed beam 14, a data acquisition and analysis system 15, an overflow valve 16, a pressure medium tank 17, a booster 18, an internal pressure sensor 19, and a pressure medium pipeline 20. The sealing mandrel 3 is directly inserted into the pipe and sealed by a rubber ring. The sealing mandrel 3 balances the horizontal force caused by the liquid pressure through the support frame 1. Force sensor 11 is mounted on the lower surface of movable crossbeam 12. Force sensor 11 applies load to upper plate 9 through connecting rod 10. Upper plate 9 applies load to pressure head through hard contact. Guide post 8 ensures the direction of force applied by upper plate 9. Strain gauges 21 are attached to the middle position of the thin-walled tube along the axial and circumferential directions respectively. One side of the tube is connected to the outlet of pressure booster 18, and the inlet of pressure booster 18 is connected to pressure medium tank 17. The other side of the tube is connected to internal pressure sensor 19, which is connected to the inlet of relief valve 16. The outlet of relief valve 16 is connected to pressure medium tank 17. The strain signal output terminal of strain gauge 21 is connected to the strain signal input terminal of control system, and the pressure signal output terminal of internal pressure sensor 19 is connected to the pressure signal input terminal of control system.

[0049] The device of this invention provides realistic simulation of operating conditions, and for the first time, it achieves accurate simulation of the typical composite load path of "bending moment-internal pressure" in pipes under laboratory conditions, filling the gap in existing testing technologies.

[0050] The method of this invention provides rich and accurate data, and can simultaneously obtain a series of key parameters such as ultimate bending moment, critical buckling pressure, and bending strain field evolution, providing reliable experimental data support for theoretical research and high-precision simulation.

[0051] The method of this invention has significant application value and can directly serve the design and safety assessment of high-pressure pipelines and pressure-bearing structural pipe fittings in fields such as aerospace and automobile manufacturing. It helps to realize the transformation from "experience-based design" to "precision design" and promotes the development of lightweight technology.

[0052] The device of this invention has an ingenious structural design. The combination of the sealing component and the load-bearing bearing solves the contradiction between the constraint of the sample end and the bending rotation under pressure, thus ensuring the feasibility and accuracy of the test.

[0053] Example 1 Step 1, Sample Preparation and Installation: A 200mm long sample was cut from a 304 stainless steel pipe with a radius r=60mm and a wall thickness t=0.8mm. The end face was made flat using a lathe and the surface was cleaned with alcohol.

[0054] The sealing mandrel 3, clamp 4, and pressure block 5 are manufactured according to the diameter and wall thickness of the pipe.

[0055] Combination Figure 1-5 Optionally, rubber rings are fitted onto the sealing mandrel 3, and the pipe sample is inserted from both ends and secured with clamps 4. The two protruding parts of the sealing mandrel 3, i.e., the rotating shaft, are passed through the load-bearing bearing, and the load-bearing bearing is assembled with the support frame 1. The support frame 1 is fixed to the base 22 with bolts; the pressure block 5 is placed in the middle of the pipe; and the upper plate 9 is placed on the pressure block 5 through the guide post 8.

[0056] Step 2, Sensor System Layout: A resistance strain gauge is attached directly above the mid-span of the tubular specimen, either on the compression side or at the central axis of the tubular specimen.

[0057] Step 3: System Connection Combination Figure 5 Instructions: Connect strain gauge 21 to data acquisition and analysis system 15.

[0058] One sealing mandrel 3 is connected to a pressure booster 18 via a pressure medium pipeline 20, and the pressure booster 18 is connected to a pressure medium tank 17; the other sealing mandrel 3 is connected to an internal pressure sensor 19 and an overflow valve 16 that ensures stable internal pressure via a pressure medium pipeline 20. The overflow valve 16 is connected to the pressure medium tank 17; the internal pressure sensor 19 is connected to the data acquisition and analysis system 15.

[0059] Connect the force sensor 11 to the data acquisition and analysis system 15.

[0060] Step 4: Composite Load Test Start the hydraulic servo system, control the booster 18 to fill the pipe sample 6 with pressure medium and remove air, and then adjust the internal pressure p through the overflow valve 16 and stabilize the internal pressure p at the preset value, such as 5MPa.

[0061] Start the data acquisition and analysis system 15 to record the indenter load force F measured by the force sensor 11, the internal pressure p measured by the internal pressure sensor 19, the indenter displacement δ measured by the displacement sensor, and the strain ε at point M measured by the strain gauge 21.

[0062] Start the drive motor, causing the movable crossbeam 12 to drive the pressure block 5 downwards at a uniform speed of 2 mm / min via the connecting rod 10. The pressure block 5 contacts the pipe and continuously applies load. Due to the height of the pipe ends being constrained by the sealing mandrel, bending deformation occurs.

[0063] During the deformation process, the two sealed mandrels 3 can rotate freely around the corresponding load-bearing bearings.

[0064] When the pressure head load F reaches its maximum value and decreases significantly, it indicates that the pipe has become unstable and buckled, and loading should be stopped.

[0065] Step 5: Data Collection and Analysis Combination Figure 6 The loading curve can be plotted by collecting the indenter load F and displacement δ during the experiment. The deformation process can be divided into three stages: elastic stage, plastic stage and post-buckling stage. The elastic stage is the linear stage, the plastic stage is from the point where the line leaves the line to the highest point, and the post-buckling stage is the part after the highest point.

[0066] Combination Figure 7 The system software calculates the pipe's bending radius R, bending curvature k, and bending angle θ based on the recorded displacement δ and the span of the device. It then calculates the bending moment experienced by the pipe during bending using the recorded load F and internal pressure p, based on the bending moment calculation formula.

[0067] Combination Figure 8 The bending moment-bending curvature relationship curve of the pipe was plotted based on the calculation results. The peak point Mmax on the curve is the ultimate bending moment of the pipe under the internal pressure of 5MPa. Simultaneously, the variation of strain ε with bending moment M can be analyzed to obtain the bending deformation capacity of the material.

[0068] Specific examples have been used to illustrate the principles and implementation methods of this invention. The descriptions of the above embodiments are only for the purpose of helping to understand the method and core ideas of this invention. Furthermore, those skilled in the art will recognize that, based on the ideas of this invention, there will be changes in the specific implementation methods and application scope. Therefore, the content of this specification should not be construed as a limitation of this invention.

Claims

1. A method for testing the bending moment of a pipe, characterized in that, Includes the following steps: Two sealing clamping assemblies are used to seal and clamp the two ends of the pipe sample in the axial direction to form a pressure-bearing cavity. The two sealing clamping assemblies are rotatably connected to the corresponding support frame, and the hydraulic servo system is connected to the inner cavity of the pipe sample. Strain gauges are installed on the outer wall of the tubular specimen, a pressure block is placed at the middle position of the tubular specimen in the axial direction, and the load application component abuts against the pressure block. The strain gauge, the internal pressure sensor of the hydraulic servo system, the force sensor and displacement sensor of the load application component are respectively connected to the data acquisition and analysis system; The hydraulic servo system is controlled to inject a pressure medium into the interior of the tubular sample. The load application component is controlled to drive the pressure block to move at a constant speed and apply a radial load to the pipe sample through the pressure block, so that the pipe sample undergoes bending deformation under the combined action of internal pressure and bending moment; The data acquisition and analysis system is used to collect the detection values ​​of the strain gauge, the internal pressure sensor, the force sensor and the displacement sensor, and the bending moment applied to the pipe sample is calculated according to the mechanical model.

2. The method for testing the bending moment of pipes according to claim 1, characterized in that, The pressure block has an arc-shaped groove on the side near the pipe sample; At least a portion of the outer wall surface of the tubular sample is located within the arc-shaped groove, and the strain gauge is disposed between the outer wall surface of the tubular sample and the inner wall surface of the arc-shaped groove.

3. The method for testing the bending moment of pipes according to claim 1, characterized in that, The sealing clamping assembly includes a sealing mandrel and a clamp, and the sealing mandrel includes a connecting section and a sealing section; The sealing sections of the two sealing mandrels are respectively inserted into the interior of the two axial ends of the pipe sample, and a sealing element is provided between the outer wall of the sealing section and the inner wall of the pipe sample; The two clamps are respectively sleeved on the outer sides of both axial ends of the pipe sample, and the clamps and the sealing section are used to clamp the ends of the pipe sample; The connecting sections of the two sealing mandrels are each provided with a rotating shaft perpendicular to the axial direction of the tubular sample, and the rotating shaft is rotatably connected to the corresponding support frame through a bearing.

4. The method for testing the bending moment of pipes according to claim 3, characterized in that, The hydraulic servo system also includes an inlet pipe, an outlet pipe, a booster, an overflow valve, and a pressure medium tank; The sealing mandrel is provided with a medium channel communicating with the inner cavity of the tubular sample; One end of the liquid inlet pipe is connected to the medium channel of one of the sealing mandrels, and the other end is connected to the pressure medium tank, and the pressure booster is provided on the liquid inlet pipe; One end of the liquid outlet pipeline is connected to the medium channel of another sealing mandrel, and the other end is connected to the pressure medium tank. The liquid outlet pipeline is equipped with the internal pressure sensor and the overflow valve.

5. The method for testing the bending moment of pipes according to claim 1, characterized in that, In the step of "controlling the hydraulic servo system to fill the interior of the tubular sample with a pressure medium": The hydraulic servo system is controlled to fill the interior of the tubular sample with a pressure medium and maintain a set internal pressure; or, the hydraulic servo system is controlled to fill the interior of the tubular sample with a pressure medium and control the internal pressure to change according to a preset program. In the step of "controlling the load application component to drive the pressure block to move at a constant speed and applying a radial load to the pipe sample through the pressure block, so that the pipe sample undergoes bending deformation under the combined action of internal pressure and bending moment": The tubular sample undergoes bending deformation under the combined action of internal pressure and increasing bending moment until it buckles or ruptures.

6. The method for testing the bending moment of pipes according to claim 3, characterized in that, The formula for calculating the bending radius R of the tubular sample is as follows: ； The formula for calculating the bending angle θ of the tubular sample is: ； The formula for calculating the bending moment M of the tubular sample is: ； Wherein, L is the axial length of the bent portion of the pipe sample, l is the axial distance from the rotation center of the sealing mandrel to the end face of the sealing section, δ is the detection value of the displacement sensor, F is the detection value of the force sensor, p is the detection value of the internal pressure sensor, and r is the radius of the outer wall of the pipe sample.

7. The method for testing the bending moment of a pipe according to claim 6, characterized in that, The method further includes: When the load applied by the load application component to the tubular sample reaches its maximum value and decreases, the load application component is controlled to stop loading. The ultimate bending moment and bending moment-strain curve of the pipe specimen were obtained based on the test data.

8. The method for testing the bending moment of a pipe according to claim 7, characterized in that, The steps of "obtaining the ultimate bending moment value of the pipe specimen based on the test data" include: Based on the calculation results, the bending moment-bending curvature relationship curve of the pipe sample is plotted, and the ultimate bending moment value of the pipe sample under the set internal pressure is obtained based on the peak value of the bending moment-bending curvature relationship curve. The relationship between the bending curvature k and the bending radius R of the pipe sample is: k = 1 / R.

9. The method for testing the bending moment of a pipe according to claim 1, characterized in that, The load application assembly also includes a movable crossbeam, an upper plate, a lower plate, guide posts, and connecting rods; The upper plate and the lower plate are arranged parallel to each other, with the upper plate located above the lower plate, and the support frame is disposed on the lower plate; The bottom surface of the upper plate abuts against the top of the pressure block, the force sensor is provided below the movable crossbeam, and the two ends of the connecting rod are respectively connected to the force sensor and the top surface of the upper plate. The upper plate is provided with a guide hole for the guide post to pass through. One end of the guide post is connected to the lower plate, and the other end passes upward through the guide hole.

10. An apparatus for implementing the test method for pipe bending moment according to any one of claims 1-9, characterized in that, It includes a sealing clamping assembly, a support frame, strain gauges, pressure blocks, a hydraulic servo system, a load loading assembly, and a data acquisition and analysis system; The two sealing clamping assemblies are used to seal and clamp the two ends of the pipe sample in the axial direction to form a pressure-bearing cavity, and the two sealing clamping assemblies are respectively rotatably connected to the corresponding support frame; The strain gauge is disposed on the outer wall surface of the tubular sample, and the pressure block is disposed at the middle position of the tubular sample in the axial direction. The hydraulic servo system is internally connected to the pipe sample for filling the pipe sample with a pressure medium, and the hydraulic servo system includes an internal pressure sensor; the load loading assembly abuts against the pressure block for applying a radial load to the pipe sample, and the load loading assembly includes a force sensor and a displacement sensor; The strain gauge, the internal pressure sensor, the force sensor, and the displacement sensor are respectively connected to the data acquisition and analysis system.

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