Shield tunnel joint toughness test reciprocating loading method and system

Abstract

The application provides a kind of shield tunnel joint toughness test reciprocating loading method and system, it is related to tunnel engineering test field, comprising: based on initial axial force to test piece is carried out reciprocating loading, obtains displacement, load, acoustic emission impact number and strain data in loading process, calculates stiffness degradation index, residual deformation index, acoustic emission damage index, strain concentration index and comprehensive damage index;According to the stiffness degradation index, residual deformation index, acoustic emission damage index, strain concentration index and comprehensive damage index, judge damage stage, according to damage stage calculates displacement amplitude and loading rate of next loading.The application introduces variable axial force coupling mode and variable rate step control, solves the problem that traditional constant parameter loading is difficult to match joint nonlinear damage evolution and seismic P-Delta effect, significantly improves the simulation reality and damage capture accuracy of test, provides reliable data support for shield tunnel joint toughness evaluation.

Description

Technical Field

[0001] This invention belongs to the field of tunnel engineering testing technology, specifically relating to a reciprocating loading method and system for testing the toughness of shield tunnel joints. Background Technology

[0002] With the rapid development of urban rail transit and underground space development, shield tunnel design is moving towards larger cross-sections, new joints, and higher toughness. Tunnel toughness, as a key indicator for measuring a structure's ability to maintain function, resist damage, and recover after earthquakes under extreme loads such as earthquakes and fires, has become an important concept in the next generation of tunnel design. Large-section shield tunnels are widely used in deep-buried tunnels and cross-sea tunnels. High-strength concrete and new joint designs (such as flexible joints and composite joints) have significantly improved the tunnel's load-bearing capacity and seismic toughness. However, research on the hysteretic energy dissipation characteristics and damage evolution mechanisms of these high-toughness joints under seismic loads is increasingly urgent. Quasi-static tests have become a key means of evaluating their toughness performance. However, the ultimate working conditions of large-section tunnel joints place extremely high demands on the load, displacement, and strength of the loading device. In addition, real seismic responses are often accompanied by axial force fluctuations (P-Delta effect) and nonlinear evolution of stiffness and energy dissipation. Traditional constant parameter loading modes cannot accurately reproduce this complex process and cannot accurately evaluate the toughness level of the joint. Summary of the Invention

[0003] The purpose of this invention is to provide a reciprocating loading method and system for toughness testing of shield tunnel joints, in order to improve the aforementioned problems. To achieve the above objective, the technical solution adopted by this invention is as follows:

[0004] Firstly, this application provides a reciprocating loading method for testing the toughness of a shield tunnel joint, comprising:

[0005] The specimen is subjected to reciprocating loading based on the initial axial force. During the loading process, the longitudinal displacement is obtained, and the axial force is corrected based on the longitudinal displacement and the initial coupling coefficient.

[0006] The stiffness degradation index is calculated based on the peak load and peak displacement during the loading process;

[0007] The residual deformation index is calculated based on the peak displacement during loading and the residual displacement after unloading.

[0008] The acoustic emission damage index is calculated based on the number of acoustic emission impacts and the acoustic emission energy rate during the loading process;

[0009] Calculate the strain concentration index based on the material's yield strain and the maximum principal strain during the loading process;

[0010] The comprehensive damage index is calculated based on the stiffness degradation index, residual deformation index, acoustic emission damage index, and strain concentration index. The initial coupling coefficient is corrected and updated based on the stiffness degradation index;

[0011] Based on the stiffness degradation index, residual deformation index, acoustic emission damage index, strain concentration index, and comprehensive damage index, the damage stage is determined, and the displacement amplitude and loading rate of the next loading are calculated based on the damage stage.

[0012] Secondly, a reciprocating loading system for testing the toughness of a shield tunnel joint includes:

[0013] The first module is used to reciprocate load the specimen based on the initial axial force, obtain the longitudinal displacement during the loading process, and correct the axial force according to the longitudinal displacement and the initial coupling coefficient.

[0014] The second module is used to calculate the stiffness degradation index based on the peak load and peak displacement during the loading process;

[0015] The third module is used to calculate the residual deformation index based on the peak displacement during the loading process and the residual displacement after unloading.

[0016] The fourth module is used to calculate the acoustic emission damage index based on the number of acoustic emission impacts and the acoustic emission energy rate during the loading process;

[0017] The fifth module is used to calculate the strain concentration index based on the material's yield strain and the maximum principal strain during the loading process.

[0018] The sixth module is used to calculate the comprehensive damage index based on the stiffness degradation index, residual deformation index, acoustic emission damage index, and strain concentration index. The seventh module is used to correct the initial coupling coefficient based on the stiffness degradation index and update the coupling coefficient.

[0019] The eighth module is used to determine the damage stage based on the stiffness degradation index, residual deformation index, acoustic emission damage index, strain concentration index and comprehensive damage index, and to calculate the displacement amplitude and loading rate for the next loading based on the damage stage.

[0020] The beneficial effects of this invention are as follows:

[0021] This invention provides a reciprocating loading test method based on multidimensional discrimination and closed-loop correction of joint status. By introducing a variable axial force coupling mode and variable rate graded control, it solves the problem that traditional constant parameter loading is difficult to match the nonlinear damage evolution of joints and the seismic P-Delta effect, significantly improving the simulation realism and damage capture accuracy of the test, and providing reliable data support for the toughness assessment of shield tunnel joints.

[0022] Other features and advantages of the invention will be set forth in the description which follows, and will be apparent in part from the description, or may be learned by practicing embodiments of the invention. Attached Figure Description

[0023] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0024] Figure 1 This is an elevation view of the reciprocating loading test device according to an embodiment of this application;

[0025] Figure 2 This is a flowchart of the reciprocating loading method for the toughness test of a shield tunnel joint according to an embodiment of this application;

[0026] Figure 3 This is a top view of the reciprocating loading test apparatus according to an embodiment of this application;

[0027] Figure 4 for Figure 1 BB cross-sectional view; Figure 5 for Figure 1 Enlarged view of point A in the middle;

[0028] Figure 6 This is a schematic diagram of the reciprocating loading device for the toughness test of a shield tunnel joint according to an embodiment of this application; Symbol Explanation: 1-Concrete segment joint; 2-Upper loading beam; 3-Upper hydraulic jack; 4-Left L-beam; 5-Right L-beam; 6-Left hinge support; 7-Right hinge support; 8-Lower loading beam; 9-Lower loading beam support; 10-Lower hydraulic jack; 11-Left anti-rotation device; 12-Right anti-rotation device; 13-Side hydraulic jack; 14-Steel plate; 15-Hole; 16-Slide rail device; 17-Reinforcing device; 18-Reinforcing rib; 19-Lower loading support; 800-Shield tunnel joint toughness test reciprocating loading equipment; 801-Processor; 802-Memory; 803-Multimedia component; 804-I / O interface; 805-Communication component. Detailed Implementation

[0029] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, 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, not all, of the embodiments of the present invention. The components of the embodiments of the present invention described and shown in the accompanying drawings can generally be arranged and designed in various different configurations. Therefore, the following detailed description of the embodiments of the present invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

[0030] It should be noted that similar labels and letters in the following figures indicate similar items. Therefore, once an item is defined in one figure, it does not need to be further defined and explained in subsequent figures.

[0031] The test method of the present invention includes the following preparatory steps:

[0032] Specimen arrangement: As follows Figure 1 The test apparatus shown has the segment joint specimen installed between the left hinge support 6 and the right hinge support 7, and positioned by the left L-beam 4 and the right L-beam 5; the upper loading beam 2 and the lower loading beam 8 are connected, and the sliding rail and limit connection status of the anti-overturning device are checked.

[0033] Sensor Deployment and Calibration: Displacement sensors, strain sensors, load sensors, and acoustic emission probes were deployed at key locations on the specimen, and a DIC camera was installed. Displacement sensors were vertically arranged along the top and sides of the segment joint to capture overall deformation and stiffness changes; strain sensors were placed on the concrete surface of the joint area to monitor local yielding and crack initiation; load sensors were installed at the output ends of the upper hydraulic jack 3 and lower hydraulic jack 10 to acquire loading force data; acoustic emission probes were evenly distributed in the high-stress area at the joint-segment connection to capture microcrack initiation and propagation signals; the DIC camera was aimed at the joint and adjacent segment areas to acquire full-field displacement and strain field data. Zero-point calibration and sensitivity calibration were performed on each sensor, and sampling channels and range configurations were established.

[0034] Based on the above configuration, a reciprocating loading test was conducted, and the loading parameters were adjusted using the method described in this application during the loading process.

[0035] Example 1:

[0036] See Figure 2This application provides a reciprocating loading method for testing the toughness of a shield tunnel joint, including steps S100, S200, S300, S400, S500, S600, S700 and S800.

[0037] S100. The specimen is subjected to reciprocating loading based on the initial axial force. During the loading process, the longitudinal displacement is obtained, and the axial force is corrected based on the longitudinal displacement and the initial coupling coefficient.

[0038] ;

[0039] In the formula, The axial force (kN) is corrected in real time. The initial axial force (kN) is determined based on the tunnel depth and geological conditions, and is generally taken as 0.8 to 1.2 times the design axial force. The coupling coefficient (kN / mm) characterizes the formation constraint stiffness. The initial coupling coefficient is calculated based on the formation elastic modulus and tunnel geometric parameters. This represents the real-time longitudinal displacement (mm) caused by the deformation of the specimen under axial force; the positive and negative signs correspond to the positive and negative loading stages, respectively. This formula is used to simulate the axial force fluctuation (P-Delta effect) caused by changes in the formation constraint stiffness under seismic loading, forming an initial control command sequence and issuing it.

[0040] S200. Calculate the stiffness degradation index based on the peak load and peak displacement during the loading process, as follows:

[0041] S210. Calculate the secant stiffness of the load based on the peak load and peak displacement during the loading process.

[0042] ;

[0043] In the formula, For the first i Secant stiffness under secondary loading (kN / mm); For the first i The peak load (kN) of the second loading was collected by the load sensor; For the first i The peak displacement (mm) of the second loading was collected by the displacement sensor.

[0044] S220. Obtain the initial stiffness of the specimen. , as a benchmark value;

[0045] S230. Based on the secant stiffness and initial stiffness of the specimen, the stiffness degradation index is calculated.

[0046] ;

[0047] In the formula, Initial stiffness (kN / mm); It is a dimensionless stiffness degradation index, with a value range of 0 to 1. The smaller the value, the more severe the stiffness degradation. For the first i Secant stiffness under secondary loading.

[0048] S300. Calculate the residual deformation index based on the peak displacement during the loading process and the residual displacement after unloading.

[0049] ;

[0050] In the formula: For the first i The residual displacement (mm) after each unloading cycle is collected by a displacement sensor. For the first i Peak displacement of the cycle (mm); It is a dimensionless residual deformation index, with a value range of 0 to 1. The larger the value, the more significant the accumulation of plastic deformation.

[0051] S400. Calculate the acoustic emission damage index based on the number of acoustic emission impacts and the acoustic emission energy rate during the loading process;

[0052] S410. Obtain the preset impact number threshold and the acoustic emission impact number during the loading process, and obtain the first factor by calculating the ratio of the acoustic emission impact number to the impact number threshold;

[0053] ;

[0054] In the formula, For the first i Number of acoustic emission impacts (hits) in each cycle; The preset impact number threshold (calibrated according to material properties, typically 5000-10000 for concrete); U1 is the first factor;

[0055] S420. The acoustic emission energy rate is calculated by dividing the acoustic emission energy by the loading duration of the current cycle.

[0056] S430. The second factor is obtained by calculating the ratio of acoustic emission energy rate to the historical maximum energy rate.

[0057] ;

[0058] In the formula, For the first i Acoustic emission energy rate under sub-load (aJ / s); The historical maximum energy rate is used to characterize the intensity of microcrack activity; U2 is the second factor.

[0059] S440. Calculate the product of the first factor and the second factor to obtain the acoustic emission damage index. ;

[0060]

[0061] In the formula, The acoustic emission damage index is defined as follows: U1 is the first factor, and U2 is the second factor. For the first i Acoustic emission energy rate under sub-load (aJ / s); This represents the highest energy rate in history. For the first i Number of acoustic emission impacts in each cycle; This is a preset threshold for the number of impacts;

[0062] S500. Calculate the strain concentration index based on the material's yield strain and the maximum principal strain during the loading process.

[0063] ;

[0064] In the formula, For the first i The maximum principal strain monitored by DIC during the second loading; The yield strain of the material is taken as 0.002 for concrete and 0.002 for steel reinforcement. For strain concentration index.

[0065] The maximum principal strain during the loading process was obtained by acquiring data using a DIC camera and then processing it, as detailed below:

[0066] Random speckle patterns were created on the surface of the specimen. The speckle image before deformation was divided into several sub-regions to obtain the speckle image before deformation.

[0067] During the specimen loading process, speckle images of specimen deformation were acquired;

[0068] Compare and analyze the speckle image before deformation and the speckle image during deformation, and calculate the displacement of each speckle.

[0069] Using the gray-level distribution of the sub-region as a feature, the normalized cross-correlation algorithm (NCC) is used to find the target sub-region in the deformed image that best matches the gray level of the reference sub-region, and the displacement vector of the sub-region center (feature point) is obtained.

[0070] Based on the displacement of the speckle, the strain distribution of the whole field is obtained by solving the strain tensor, and the maximum principal strain is extracted.

[0071] Strain is the spatial partial derivative of displacement. In DIC, based on the displacement difference between preceding and following characteristic points, the least squares method is used to perform a quadratic polynomial fitting on the displacement field to solve for the in-plane strain tensor. According to the principal strain formula in mechanics of materials, the maximum and minimum principal strains are directly solved from the in-plane strain tensor. The DIC software can automatically complete the above calculations and output information such as the maximum principal strain contour map of the entire field.

[0072] S600. Calculate the comprehensive damage index based on the stiffness degradation index, residual deformation index, acoustic emission damage index, and strain concentration index.

[0073] ;

[0074] In the formula, , , , For the weighting coefficients, satisfying + + + =1; the default value is 1. =0.4, =0.2, =0.2, =0.2, which can be adjusted according to the purpose of the experiment. The value ranges from 0 to 1, with a larger value indicating more severe damage. As a strain concentration index, The residual deformation index, As an indicator of acoustic emission damage, As an index of stiffness degradation;

[0075] S700. Correct the initial coupling coefficient according to the stiffness degradation index and update the coupling coefficient;

[0076] In the variable axial force coupling mode, the axial force-displacement coupling coefficient can be dynamically adjusted according to the damage state:

[0077] ;

[0078] In the formula, The initial coupling coefficient (kN / mm); Stiffness degradation index, which reflects the degradation of the stiffness of the formation-structure interaction after damage; For the updated coupling coefficients.

[0079] S800. Based on the stiffness degradation index, residual deformation index, acoustic emission damage index, strain concentration index and comprehensive damage index, determine the damage stage, and calculate the displacement amplitude and loading rate of the next loading based on the damage stage.

[0080] The first judgment result is obtained by judging whether the stiffness degradation index is greater than or equal to the first stiffness threshold, whether the residual deformation index is less than the deformation threshold, and whether the acoustic emission damage index is less than the acoustic emission threshold. If the first judgment result is yes for all of them, it is determined to be the stable response stage.

[0081] As an example, the first stiffness threshold is 0.95, the deformation threshold is 0.15, and the acoustic emission threshold is 0.3; that is, when and and This indicates that the specimen is in a stable response stage (elastic state).

[0082] If the first judgment result is negative, then determine whether the stiffness degradation index is greater than the second stiffness threshold and whether the comprehensive damage index is less than the comprehensive threshold to obtain the second judgment result. If both of the second judgment results are positive, then it is determined to be the cumulative damage stage.

[0083] As an example, the second stiffness threshold is 0.85, and the combined threshold is 0.7; that is, when or or ,and This indicates that the specimen has entered the cumulative damage stage (cumulative plastic state).

[0084] If the second judgment result is negative, or the strain concentration index is greater than the preset strain threshold, then it is determined to be in the critical failure stage.

[0085] As an example, the strain threshold is 3; that is... or or This indicates that the specimen is approaching its ultimate bearing capacity and has entered the critical failure stage.

[0086] The displacement correction factor and rate adjustment factor are determined based on the damage stage;

[0087] This is the displacement correction factor, during the steady-state response phase. 1.0, cumulative damage stage The value is 0.5, indicating the critical failure stage. It is 0.25;

[0088] Rate adjustment coefficient; steady response phase The cumulative damage stage is 1.0~1.5. The value is 0.5, indicating the critical failure stage. It is 0.1;

[0089] Based on the yield displacement of the specimen Calculate the increment of the base displacement amplitude ;

[0090] The basic displacement amplitude increment (mm) is generally taken as... to ,in The yield displacement of the specimen (mm) can be estimated through preloading tests or finite element analysis.

[0091] The displacement amplitude increment is corrected by using a displacement correction factor to obtain the corrected displacement amplitude increment;

[0092] ;

[0093] In the formula, To correct the displacement amplitude increment, This is the displacement correction factor; The increment of the basic displacement amplitude;

[0094] The displacement amplitude for the next loading cycle is calculated based on the corrected displacement amplitude increment; that is, the corrected displacement amplitude increment is added to the current displacement amplitude as the displacement amplitude for the next loading cycle.

[0095] The initial loading rate is adjusted according to the rate adjustment coefficient. Make corrections to obtain the corrected loading rate;

[0096] ;

[0097] In the formula, The initial loading rate, This is the rate adjustment coefficient. To correct the loading rate;

[0098] This method also includes determining the increment of the number of single-stage cycles based on the stage of damage:

[0099] Increment of loop count; steady response phase 0, cumulative damage stage 2, critical failure stage =0;

[0100] The number of single-stage cycles refers to the number of cycles under a single constant load level; the corrected number of single-stage cycles is:

[0101] ;

[0102] In the formula, This is the corrected number of single-level loops. The initial number of single-stage cycles is generally set to 2; the number of cycles is increased to 4 during the cumulative damage stage to fully capture the damage evolution characteristics.

[0103] When the test termination conditions or safety thresholds are reached, the system will be unloaded and shut down, and complete test data, discrimination logs, and path correction records will be output.

[0104] This embodiment provides a test apparatus for use in conjunction with the above method, such as... Figure 1 The diagram shows the elevation of the device, where the cast-in-place concrete segment joint 1 is the test object of this invention. It is fixed to the left L-beam 4 and right L-beam 5 via a left hinge support 6 and a right hinge support 7. The right L-beam can apply axial force to the right hinge support 7 via a side hydraulic jack 13, the force of which comes from the reaction force provided by four steel columns. The right L-beam 5 can slide left and right along a slide rail via a right anti-rotation device 12. The slide rail restricts the vertical and rotational freedom of the right L-beam 5, while allowing it to move freely axially to accommodate axial deformation. The right anti-rotation device 12 is welded to the main structure through multiple reinforcing ribs, forming a stable reaction force transmission path. The left L-beam 4 is also a sliding support, fixed to the main structure via a left anti-rotation device 11. The slide rail of the left anti-rotation device 11 also restricts the vertical and rotational freedom of the left L-beam 4. The concrete segment joint 1 is provided with positive and negative bending moments by the upper hydraulic jack 3 and the lower hydraulic jack 10. The upper hydraulic jack 3 acts on the joint through the upper loading beam 2, and the lower hydraulic jack 10 acts on the joint through the lower loading beam 8. When a positive bending moment is applied, the lower loading beam 8 can be supported on the lower loading beam bracket 9.

[0105] Figure 3 The top view of the device shows that the slide rail of the left anti-rotation device 11 is parallel to the axis of the L-beam, allowing the left L-beam 4 to slide along the slide rail to accommodate deformation. Simultaneously, the constraint between the slide rail and the left L-beam 4 transmits the vertical reaction force and the torque resisting rotation. The structure of the right anti-rotation device 12 is symmetrical to that of the left anti-rotation device 11. Through the slide rail and reinforcing ribs, it restricts the vertical displacement and rotational freedom of the right L-beam 5, forming a bidirectional symmetrical load transfer and anti-rollover system.

[0106] Figure 4 for Figure 1 BB sectional view, Figure 1 The lower hydraulic jack 10 is mounted on the lower loading support 19 to meet the jack's stroke requirements. The lower loading support 19 is fixed to the main structure with high-strength bolts, forming a stable reaction force transmission path. Simultaneously, displacement sensors are arranged on the lower loading support 19 to monitor the vertical displacement of the tunnel segment. The displacement signals are input into a data acquisition and discrimination module to generate control signals and update the loading path. The lower loading beam 8 and the upper loading beam 2 are connected to the corresponding jacks via high-strength bolts, forming a complete load transmission link.

[0107] Figure 5 for Figure 1The enlarged view at point A shows a detail of the left anti-rotation device 11. During reverse loading, to prevent the left L-beam 4 from being lifted and rotated, a π-shaped steel plate 14 is welded onto the left L-beam 4. The steel plate 14 has two holes 15 into which high-strength bolts can be inserted to fix it to the slide rail device 16. The slide rail device 16 has a slide rail, allowing the left L-beam 4 and the steel plate 14 to slide left and right within it, but restricting their vertical and rotational freedom. To ensure the strength of the slide rail, a reinforcing device 17 is provided, which is movable and detachable. The slide rail device 16 is fixed to the main structure by an I-beam and high-strength bolts. A reinforcing rib 18 is provided below the slide rail device 16. The entire left anti-rotation device 11 forms a stable load transfer path through the slide rail, steel plate 14, high-strength bolts, and reinforcing rib 18, transferring the vertical torque and rotational constraint reaction force of the L-beam to the main structure.

[0108] Existing loading devices include:

[0109] Vertical quasi-static loading device: It applies unidirectional load through reaction frame and hydraulic cylinder. It is suitable for small cross-section segments, but requires large reaction frame or reaction wall. It has insufficient loading capacity and no anti-overturning structure. The segments are prone to displacement during reciprocating loading. It is especially unsatisfactory for large cross-section segments and cannot meet the testing requirements of large cross-section and new joints.

[0110] Horizontal unidirectional loading device: It adopts a horizontal frame and its loading capacity can meet the test requirements of large cross-section joints, but it can only load in one direction and cannot cope with the reciprocating loading of large cross-section joints.

[0111] The loading device provided by this invention adopts a horizontal, ship-shaped self-reaction structure, eliminating dependence on reaction walls and reducing site requirements. It is suitable for reciprocating loading of large-section, high-strength concrete, and high-toughness joints, achieving ±1000kN loads and ±100mm displacements, simulating quasi-static stress characteristics under seismic loads, and meeting toughness evaluation requirements. An innovative anti-tilting device is added to prevent large-section segments from flipping or shifting during loading, improving test accuracy and safety.

[0112] Example 2:

[0113] This embodiment provides a reciprocating loading system for testing the toughness of a shield tunnel joint, including:

[0114] The first module is used to reciprocate load the specimen based on the initial axial force, obtain the longitudinal displacement during the loading process, and correct the axial force according to the longitudinal displacement and the initial coupling coefficient.

[0115] The second module is used to calculate the stiffness degradation index based on the peak load and peak displacement during the loading process;

[0116] The third module is used to calculate the residual deformation index based on the peak displacement during the loading process and the residual displacement after unloading.

[0117] The fourth module is used to calculate the acoustic emission damage index based on the number of acoustic emission impacts and the acoustic emission energy rate during the loading process;

[0118] The fifth module is used to calculate the strain concentration index based on the material's yield strain and the maximum principal strain during the loading process.

[0119] The sixth module is used to calculate the comprehensive damage index based on the stiffness degradation index, residual deformation index, acoustic emission damage index, and strain concentration index. The seventh module is used to correct the initial coupling coefficient based on the stiffness degradation index and update the coupling coefficient.

[0120] The eighth module is used to determine the damage stage based on the stiffness degradation index, residual deformation index, acoustic emission damage index, strain concentration index and comprehensive damage index, and to calculate the displacement amplitude and loading rate for the next loading based on the damage stage.

[0121] As an optional implementation, the second module includes:

[0122] The first unit is used to calculate the secant stiffness of the load based on the peak load and peak displacement during the loading process.

[0123] The second unit is used to obtain the initial stiffness of the specimen;

[0124] The third unit is used to calculate the stiffness degradation index based on the secant stiffness and initial stiffness of the specimen.

[0125] As an optional implementation, the fourth module includes:

[0126] The fourth unit is used to obtain the preset impact number threshold and the acoustic emission impact number during the loading process, and obtains the first factor by calculating the ratio of the acoustic emission impact number to the impact number threshold;

[0127] The fifth unit is used to calculate the acoustic emission energy rate by dividing the acoustic emission energy by the loading time;

[0128] The sixth unit is used to obtain the second factor by calculating the ratio of the acoustic emission energy rate to the historical maximum energy rate;

[0129] The seventh unit is used to calculate the product of the first and second factors to obtain the acoustic emission damage index.

[0130] As an optional implementation, the eighth module includes:

[0131] The eighth unit is used to determine whether the stiffness degradation index is greater than or equal to the first stiffness threshold, whether the residual deformation index is less than the deformation threshold, and whether the acoustic emission damage index is less than the acoustic emission threshold, and to obtain the first judgment result. If the first judgment result is yes, it is determined to be the stable response stage.

[0132] The ninth unit is used to determine whether the stiffness degradation index is greater than the second stiffness threshold and whether the comprehensive damage index is less than the comprehensive threshold if the first judgment result is not present, and to obtain the second judgment result. If the second judgment result is both present, it is determined to be in the cumulative damage stage.

[0133] The tenth unit is used to determine the critical failure stage if the second judgment result exists or the strain concentration index is greater than the preset strain threshold.

[0134] Example 3:

[0135] Corresponding to the above method embodiments, this embodiment also provides a reciprocating loading device for testing the toughness of a shield tunnel joint. The reciprocating loading device for testing the toughness of a shield tunnel joint described below can be referred to in correspondence with the reciprocating loading method for testing the toughness of a shield tunnel joint described above.

[0136] Figure 6 This is a block diagram illustrating a reciprocating loading device 800 for testing the toughness of a shield tunnel joint, according to an exemplary embodiment. Figure 6As shown, the reciprocating loading device 800 for testing the toughness of a tunnel joint includes a processor 801 and a memory 802. The device may also include one or more of the following: a multimedia component 803, an input / output (I / O) interface 804, and a communication component 805. The processor 801 controls the overall operation of the reciprocating loading device 800 to complete all or part of the steps in the aforementioned reciprocating loading method for testing the toughness of a tunnel joint. The memory 802 stores various types of data to support the operation of the device 800. This data may include, for example, commands for any application or method operating on the device 800, and application-related data such as contact data, sent and received messages, images, audio, video, etc. The memory 802 can be implemented by any type of volatile or non-volatile storage device or a combination thereof, such as static random access memory (SRAM), electrically erasable programmable read-only memory (EEPROM), erasable programmable read-only memory (EPROM), programmable read-only memory (PROM), read-only memory (ROM), magnetic storage, flash memory, magnetic disk or optical disk.

[0137] Multimedia component 803 may include a screen and an audio component. The screen may be, for example, a touchscreen, and the audio component is used to output and / or input audio signals. For example, the audio component may include a microphone for receiving external audio signals.

[0138] The received audio signal can be further stored in memory 802 or transmitted via communication component 805. The audio component also includes at least one speaker for outputting audio signals. I / O interface 804 provides an interface between processor 801 and other interface modules, such as a keyboard, mouse, buttons, etc. These buttons can be virtual or physical. Communication component 805 is used for wired or wireless communication between the shield tunnel joint toughness testing reciprocating loading device 800 and other devices. Wireless communication, such as Wi-Fi, Bluetooth, Near Field Communication (NFC), 2G, 3G, or 4G, or a combination thereof, is used. Therefore, the corresponding communication component 805 may include a Wi-Fi module, a Bluetooth module, or an NFC module.

[0139] Example 4:

[0140] Corresponding to the above embodiment of the reciprocating loading method for the toughness test of shield tunnel joints, this embodiment also provides a readable storage medium. The readable storage medium described below can be referred to in correspondence with the reciprocating loading method for the toughness test of shield tunnel joints described above.

[0141] A readable storage medium storing a computer program, which, when executed by a processor, implements the steps of the above-described embodiment of the reciprocating loading method for the toughness test of a shield tunnel joint.

[0142] The readable storage medium can specifically be a USB flash drive, external hard drive, read-only memory (ROM), random access memory (RAM), magnetic disk, or optical disk, or any other readable storage medium capable of storing program code.

[0143] It should be noted that, in this document, relational terms such as "first" and "second" are used merely to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0144] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A reciprocating loading method for testing the toughness of a shield tunnel joint, characterized in that, include: The specimen is subjected to reciprocating loading based on the initial axial force. During the loading process, the longitudinal displacement is obtained, and the axial force is corrected based on the longitudinal displacement and the initial coupling coefficient. The stiffness degradation index is calculated based on the peak load and peak displacement during the loading process; The residual deformation index is calculated based on the peak displacement during loading and the residual displacement after unloading. The acoustic emission damage index is calculated based on the number of acoustic emission impacts and the acoustic emission energy rate during the loading process; Calculate the strain concentration index based on the material's yield strain and the maximum principal strain during the loading process; The comprehensive damage index is calculated based on the stiffness degradation index, residual deformation index, acoustic emission damage index, and strain concentration index. The initial coupling coefficient is corrected and updated based on the stiffness degradation index; Based on the stiffness degradation index, residual deformation index, acoustic emission damage index, strain concentration index, and comprehensive damage index, the damage stage is determined, and the displacement amplitude and loading rate for the next loading are calculated based on the damage stage, including: The displacement correction factor and rate adjustment factor are determined based on the damage stage; The increment of the base displacement amplitude is calculated based on the yield displacement of the specimen. The increment of the base displacement amplitude is then corrected using a displacement correction factor to obtain the corrected displacement amplitude increment. The displacement amplitude for the next loading cycle is calculated based on the corrected displacement amplitude increment; The preset initial loading rate is corrected based on the rate adjustment coefficient to obtain the corrected loading rate.

2. The reciprocating loading method for the toughness test of a shield tunnel joint according to claim 1, characterized in that, The stiffness degradation index is calculated based on the peak load and peak displacement during the loading process, including: The secant stiffness of the load is calculated based on the peak load and peak displacement during the loading process. Obtain the initial stiffness of the specimen; The stiffness degradation index is calculated based on the secant stiffness and initial stiffness of the specimen.

3. The reciprocating loading method for the toughness test of a shield tunnel joint according to claim 1, characterized in that, Based on the number of acoustic emission impacts and the acoustic emission energy rate during the loading process, acoustic emission damage indices are calculated, including: Obtain the preset impact number threshold and the acoustic emission impact number during the loading process, and obtain the first factor by calculating the ratio of the acoustic emission impact number to the impact number threshold; The acoustic emission energy rate is calculated by dividing the acoustic emission energy by the loading time. The second factor is obtained by calculating the ratio of acoustic emission energy rate to the historical maximum energy rate; The acoustic emission damage index is obtained by calculating the product of the first factor and the second factor.

4. The reciprocating loading method for the toughness test of a shield tunnel joint according to claim 1, characterized in that, Based on the stiffness degradation index, comprehensive damage index, acoustic emission damage index, and strain concentration index, the damage stage is determined, including: The first judgment result is obtained by judging whether the stiffness degradation index is greater than or equal to the first stiffness threshold, whether the residual deformation index is less than the deformation threshold, and whether the acoustic emission damage index is less than the acoustic emission threshold. If the first judgment result is yes for all of them, it is determined to be the stable response stage. If the first judgment result is negative, then determine whether the stiffness degradation index is greater than the second stiffness threshold and whether the comprehensive damage index is less than the comprehensive threshold to obtain the second judgment result. If both of the second judgment results are positive, then it is determined to be the cumulative damage stage. If the second judgment result is negative, or the strain concentration index is greater than the preset strain threshold, then it is determined to be in the critical failure stage.

5. The reciprocating loading method for the toughness test of a shield tunnel joint according to claim 1, characterized in that, The method includes: Random speckle patterns were created on the surface of the specimen to obtain speckle images before deformation. During the specimen loading process, speckle images of specimen deformation were acquired; Compare and analyze the speckle image before deformation and the speckle image during deformation, and calculate the displacement of each speckle. Based on the displacement of the speckle, the strain distribution across the entire field is obtained by solving the strain tensor, and the maximum principal strain is extracted.

6. A reciprocating loading system for testing the toughness of a shield tunnel joint, characterized in that, include: The first module is used to reciprocate load the specimen based on the initial axial force, obtain the longitudinal displacement during the loading process, and correct the axial force according to the longitudinal displacement and the initial coupling coefficient. The second module is used to calculate the stiffness degradation index based on the peak load and peak displacement during the loading process; The third module is used to calculate the residual deformation index based on the peak displacement during the loading process and the residual displacement after unloading. The fourth module is used to calculate the acoustic emission damage index based on the number of acoustic emission impacts and the acoustic emission energy rate during the loading process; The fifth module is used to calculate the strain concentration index based on the material's yield strain and the maximum principal strain during the loading process. The sixth module is used to calculate the comprehensive damage index based on the stiffness degradation index, residual deformation index, acoustic emission damage index, and strain concentration index. The seventh module is used to correct the initial coupling coefficient based on the stiffness degradation index and update the coupling coefficient. The eighth module is used to determine the damage stage based on the stiffness degradation index, residual deformation index, acoustic emission damage index, strain concentration index, and comprehensive damage index, and to calculate the displacement amplitude and loading rate of the next loading based on the damage stage, including: The displacement correction factor and rate adjustment factor are determined based on the damage stage; The increment of the base displacement amplitude is calculated based on the yield displacement of the specimen. The increment of the base displacement amplitude is then corrected using a displacement correction factor to obtain the corrected displacement amplitude increment. The displacement amplitude for the next loading cycle is calculated based on the corrected displacement amplitude increment; The preset initial loading rate is corrected based on the rate adjustment coefficient to obtain the corrected loading rate.

7. The reciprocating loading system for testing the toughness of shield tunnel joints according to claim 6, characterized in that, The second module includes: The first unit is used to calculate the secant stiffness of the load based on the peak load and peak displacement during the loading process. The second unit is used to obtain the initial stiffness of the specimen; The third unit is used to calculate the stiffness degradation index based on the secant stiffness and initial stiffness of the specimen.

8. The reciprocating loading system for testing the toughness of shield tunnel joints according to claim 6, characterized in that, The fourth module includes: The fourth unit is used to obtain the preset impact number threshold and the acoustic emission impact number during the loading process, and obtains the first factor by calculating the ratio of the acoustic emission impact number to the impact number threshold; The fifth unit is used to calculate the acoustic emission energy rate by dividing the acoustic emission energy by the loading time; The sixth unit is used to obtain the second factor by calculating the ratio of the acoustic emission energy rate to the historical maximum energy rate; The seventh unit is used to calculate the product of the first and second factors to obtain the acoustic emission damage index.

9. The reciprocating loading system for testing the toughness of a shield tunnel joint according to claim 6, characterized in that, The eighth module includes: The eighth unit is used to determine whether the stiffness degradation index is greater than or equal to the first stiffness threshold, whether the residual deformation index is less than the deformation threshold, and whether the acoustic emission damage index is less than the acoustic emission threshold, and to obtain the first judgment result. If the first judgment result is yes, it is determined to be the stable response stage. The ninth unit is used to determine whether the stiffness degradation index is greater than the second stiffness threshold and whether the comprehensive damage index is less than the comprehensive threshold if the first judgment result is not present, and to obtain the second judgment result. If the second judgment result is both present, it is determined to be in the cumulative damage stage. The tenth unit is used to determine the critical failure stage if the second judgment result exists or the strain concentration index is greater than the preset strain threshold.

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