A true triaxial tensile method of concrete test specimen

Abstract

The application discloses a true triaxial tensile method for a concrete test piece and belongs to the technical field of concrete mechanical property testing, and specifically comprises the following steps: S1, concrete test piece preparation and installation; S2, self-adaptive configuration of a true triaxial tensile testing machine hydraulic power system; S3, true triaxial tensile loading; and S4, data synchronous acquisition and processing.The true triaxial tensile method for a concrete test piece is adopted, an independent loading system and a high-precision clamping technology are integrated, and the technical difficulty of applying accurate and controllable true triaxial tensile load to the concrete test piece is solved.

Description

Technical Field

[0001] This invention relates to the field of concrete mechanical property testing technology, and in particular to a true triaxial tensile method for concrete specimens. Background Technology

[0002] Concrete is typically subjected to complex multiaxial stress states in practical engineering structures, such as the internal constraints of large-volume concrete structures, the prestressed state of nuclear power plant containment structures, and the confining pressure of underground structures. Among these, tensile stress is a key factor leading to concrete cracking and failure. Therefore, accurately determining the tensile properties of concrete under true triaxial stress is crucial for a deeper understanding of its failure mechanisms, the establishment of accurate constitutive models, and the assessment of structural safety.

[0003] Existing methods for testing the multiaxial properties of concrete have many limitations. Traditional uniaxial tests cannot reflect the interactions between multiaxial stresses. Furthermore, existing multiaxial testing equipment often suffers from strong mechanical or hydraulic coupling between the axes of the loading system, leading to mutual interference of applied loads and making truly independent and precise control difficult. In addition, regarding specimen clamping, general-purpose clamps are prone to stress concentration, end slippage, and eccentric loading when transferring multiaxial loads, especially tensile loads. This causes the specimen's stress state to deviate from the preset path, resulting in distorted test data that fails to accurately reflect the material's tensile strength and multiaxial strength envelope.

[0004] Therefore, a systematic testing method is urgently needed. This method should be able to overcome the two major bottlenecks of coupling interference in the loading system and force transmission distortion in the clamping system, and achieve accurate and reliable loading and data acquisition of concrete specimens under complex true triaxial stress paths, especially those including tensile principal stress paths. Summary of the Invention

[0005] The purpose of this invention is to provide a true triaxial tensile method for concrete specimens, which solves the technical problem of applying precise and controllable true triaxial tensile loads to concrete specimens by integrating a completely decoupled independent loading system with high-precision clamping technology.

[0006] To achieve the above objectives, the present invention provides a true triaxial tensile method for concrete specimens, specifically including the following steps: S1. Preparation and installation of concrete specimens; S2, True Triaxial Tensile Testing Machine Hydraulic Power System Adaptive Configuration; S3, True Triaxial Tensile Loading; S4. Data synchronous acquisition and processing.

[0007] Preferably, S1 specifically includes the following operations: S1.1 Prepare concrete specimens of a predetermined shape, and align and rigidly connect the three orthogonal stress-bearing end faces of the specimens with the corresponding connecting surfaces of the triaxial tension-compression clamps with high precision. S1.2. The other three connecting surfaces of the triaxial tension / compression clamp are rigidly connected to the loading output ends of the true triaxial tensile testing machine in the X, Y, and Z directions respectively through the loading end connectors.

[0008] Preferably, the hydraulic power system of the true triaxial tensile testing machine in S2 includes a hydraulic oil tank, which is connected to the hydraulic subsystems in the X, Y, and Z directions. Each of the three hydraulic subsystems in the X, Y, and Z directions includes a hydraulic pump group, a servo control valve group, and an actuator. An oil cooler is installed on the return oil pipeline between the hydraulic subcontrol system in the X, Y, and Z directions and the oil tank. The hydraulic subsystems in the X, Y, and Z directions are connected to the central controller.

[0009] Preferably, S3 specifically includes the following operations: S3.1 The central controller generates and sends control commands to the hydraulic sub-control systems in the X, Y, and Z directions respectively, based on the preset triaxial stress or strain path. The hydraulic sub-control system in the S3.2, X, Y, and Z directions drives its respective actuators to independently and synchronously transfer the load to the three corresponding end faces of the concrete specimen through the loading end connector and the three-way tension-compression clamp, thereby realizing a complex three-dimensional stress state including tensile principal stress inside the concrete specimen.

[0010] Preferably, S4 specifically includes the following operations: S4.1 During the loading process, high-precision force sensors and displacement sensors integrated in the X, Y, and Z directions are used to collect the triaxial load and deformation data of the concrete specimen in real time. S4.2 The collected data is transmitted to the data processing unit for analysis of the strength, deformation and constitutive relationship of the concrete specimen under true triaxial tensile stress.

[0011] Preferably, the concrete specimen in S1 is a three-dimensional dumbbell shape, and the three-dimensional tension-compression clamp is integrally formed from high-strength alloy material, with the three-dimensional tension-compression clamp being embedded and interlocked with the concrete specimen.

[0012] Preferably, during the loading process of S3, it is necessary to control the ambient temperature of the concrete specimen and to use an oil cooler to cool the hydraulic oil temperature in real time.

[0013] Preferably, the triaxial stress paths preset in S3 include uniaxial tension-biaxial compression, biaxial tension-uniaxial compression, triaxial proportional tension, and non-proportional loading paths simulating complex stress states.

[0014] Therefore, the true triaxial tensile method for concrete specimens described above has the following beneficial effects: 1) By setting up a hydraulic subsystem in the X, Y, and Z directions and a shared oil tank, the coupling interference problem in multi-axis loading is solved, and precise, stable and completely independent X, Y, and Z three-axis loads can be applied to the specimen, especially ensuring the loading accuracy of the tensile principal stress. 2) By adopting an integrated high-precision three-dimensional tension-compression clamp and an embedded interlocking connection with the concrete specimen, the slippage, eccentricity and stress concentration problems commonly found in traditional clamps in multiaxial tensile testing are eliminated, making the stress state of the specimen highly consistent with the theoretical preset and significantly improving the reliability of the data. 3) The integrated tension and compression clamping method eliminates the need to change clamps between tension and compression tests, improving testing efficiency and providing a key technical means for in-depth research on the failure mechanism of concrete under multiaxial loads and the establishment of accurate constitutive models.

[0015] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Attached Figure Description

[0016] Figure 1 This is a schematic diagram of the structure of a true triaxial tensile testing machine for a concrete specimen according to the present invention. Figure 2 This is a schematic diagram of the structure of the testing machine frame in the true triaxial tensile testing machine for a true triaxial tensile testing method for concrete specimens according to the present invention. Figure 3 This is a schematic diagram of the triaxial tension-compression clamp in a true triaxial tension testing machine for a true triaxial tension method for concrete specimens according to the present invention. Figure 4 This is a schematic diagram of the structure of a concrete specimen in the true triaxial tensile method for concrete specimens according to the present invention; Figure 5 This is a schematic diagram of the internal structure of a concrete specimen in a true triaxial tensile method for concrete specimens according to the present invention; wherein, Figure 5 (a) in the figure is a schematic diagram of the internal structure of the concrete specimen in the X direction. Figure 5 (b) in the figure is a schematic diagram of the internal structure of the concrete specimen in the Y direction. Figure 5 (c) in the figure is a schematic diagram of the structure inside the concrete specimen in the Z direction.

[0017] Figure Labels 1. Testing machine frame; 2. X-direction actuator; 3. Y-direction actuator; 4. Z-direction actuator; 5. Hydraulic power unit; 6. Three-way tension / compression clamp; 7. Concrete specimen; 71. Specimen tensile working zone; 72. Specimen end loading zone; 8. Loading end connector; 9. Central controller and data acquisition system; 10. Specimen internal reinforcement. Detailed Implementation

[0018] The technical solution of the present invention will be further described below with reference to the accompanying drawings and embodiments.

[0019] Unless otherwise defined, the technical or scientific terms used in this invention shall have the ordinary meaning understood by one of ordinary skill in the art to which this invention pertains. The terms "first," "second," and similar terms used in this invention do not indicate any order, quantity, or importance, but are merely used to distinguish different components. Terms such as "comprising" or "including" mean that the element or object preceding the word encompasses the elements or objects listed following the word and their equivalents, without excluding other elements or objects. Terms such as "connected" or "linked" are not limited to physical or mechanical connections, but can include electrical connections, whether direct or indirect. Terms such as "upper," "lower," "left," and "right" are used only to indicate relative positional relationships; when the absolute position of the described object changes, the relative positional relationship may also change accordingly.

[0020] Example 1 This invention provides a true triaxial tensile method for concrete specimens, specifically including the following steps: S1. Concrete specimen preparation and installation; specifically including the following operations: S1.1 Prepare concrete specimens of a predetermined shape, and align and rigidly connect the three orthogonal load-bearing end faces of the specimen with the corresponding connecting surfaces of the three-way tension-compression clamp with high precision. The concrete specimen is a three-way dumbbell shape, and the three-way tension-compression clamp is integrally formed from high-strength alloy material. The shape of the connecting surface of the three-way tension-compression clamp matches the shape of the end face of the concrete specimen to achieve an embedded interlocking connection. The parallelism, symmetry, and perpendicularity errors of each connecting surface of the three-way tension-compression clamp are precisely controlled within the preset tolerance range to ensure that the load transfer is eccentric.

[0021] S1.2. The other three connecting surfaces of the triaxial tension / compression clamp are rigidly connected to the loading output ends of the true triaxial tensile testing machine in the X, Y, and Z directions respectively through the loading end connectors.

[0022] S2, True Triaxial Tensile Testing Machine Hydraulic Power System Adaptive Configuration; The hydraulic power system of the true triaxial tensile testing machine includes a hydraulic oil tank, which is connected to the hydraulic subsystems in the X, Y, and Z directions. This simplifies the system structure and ensures the consistency of the hydraulic fluid. Each of the X, Y, and Z direction hydraulic subsystems includes a hydraulic pump group, a servo control valve group, and an actuator. This achieves physical decoupling at the power source level, ensuring absolute independence of loading in each direction, thus realizing complete decoupling and independent precise control of the three-dimensional loading. An oil cooler is installed on the return oil line between the X, Y, and Z direction hydraulic subsystems and the oil tank. The X, Y, and Z direction hydraulic subsystems are connected to a central controller, which can independently and precisely set and control the parameters of each subsystem.

[0023] S3, True Triaxial Tensile Loading; specifically includes the following operations: S3.1 The central controller synchronously generates and sends control commands to the hydraulic sub-control systems in the X, Y, and Z directions according to the preset triaxial stress path or strain path. The preset triaxial stress path includes, but is not limited to: uniaxial tension-biaxial compression, biaxial tension-uniaxial compression, triaxial proportional tension, and non-proportional loading path simulating complex stress states, which is suitable for true triaxial mechanical performance testing under static and quasi-static loading rates.

[0024] The hydraulic sub-control system in the S3.2, X, Y, and Z directions drives its respective actuators to independently and synchronously transfer the load to the three corresponding end faces of the concrete specimen through the loading end connector and the three-way tension-compression clamp, thereby realizing a complex three-dimensional stress state, including tensile principal stress, inside the concrete specimen. During the loading process, it is necessary to control the ambient temperature of the concrete specimen and to use an oil cooler to cool the hydraulic oil temperature in real time to maintain the thermal stability of the system.

[0025] S4. Data Synchronization Acquisition and Processing; specifically including the following operations: S4.1 During the loading process, high-precision force sensors and displacement sensors integrated in the X, Y, and Z directions are used to collect the triaxial load and deformation data of the concrete specimen in real time. S4.2 The collected data is transmitted to the data processing unit, which can obtain the peak strength, stress-strain curve, failure mode, and key parameters for constitutive model verification of concrete under the specific true triaxial tensile path. This data is used to analyze the strength, deformation, and constitutive relationship of concrete specimens under true triaxial tensile stress.

[0026] Example 2 The method of this invention is used to conduct a true triaxial test on a C40 concrete triaxial dumbbell-shaped specimen, involving uniaxial tension and biaxial static compression.

[0027] like Figures 1 to 3As shown, the true triaxial tensile testing machine includes a testing machine frame 1. A hydraulic power system 5 and a central controller and data acquisition system 9 are respectively installed on both sides of the testing machine frame 1. The hydraulic power system 5 includes a hydraulic oil tank and hydraulic subsystems in the X, Y, and Z directions, respectively connected to the hydraulic oil tank. Each of the X, Y, and Z direction hydraulic subsystems includes a hydraulic pump group, a servo control valve group, and an actuator. An X-direction actuator 2, a Y-direction actuator 3, and a Z-direction actuator 4 are respectively installed on the testing machine frame 1. The X, Y, and Z-direction outward connecting surfaces of the triaxial tension / compression clamp 6 are connected to the piston rods of the X-direction actuator 2, Y-direction actuator 3, and Z-direction actuator 4 of the true triaxial testing machine through loading end connectors 8. The triaxial tension / compression clamp 6 is embedded and engaged with the concrete specimen 7. Figure 4 and Figure 5 As shown, the concrete specimen 7 is divided into a tensile working zone 71 and an end loading zone 72. The concrete specimen 7 contains internal reinforcement 10. Figure 5 (a) in the figure is a schematic diagram of the internal structure of the concrete specimen in the X direction. Figure 5 (b) in the figure is a schematic diagram of the internal structure of the concrete specimen in the Y direction. Figure 5 (c) in the diagram is a schematic diagram of the internal structure of the concrete specimen in the Z direction. The internal reinforcement 10 of the specimen is arranged along the non-working area or the loading area 72 at the end of the concrete specimen 7 to avoid significant interference with the stress field in the tensile working area 71 of the specimen. The internal reinforcement 10 of the specimen is mainly used to prevent the concrete specimen 7 from undergoing overall brittle fracture or local instability in the clamping area during multiaxial loading, and its presence does not change the principal tensile stress state in the tensile working area 71 of the specimen.

[0028] First, proceed to step S1: Prepare a 3D dumbbell-shaped concrete specimen 7 of C50 concrete. Clean the six end faces of the concrete specimen 7. Align the three concave connecting surfaces of the integrated triaxial tension-compression clamp 6 with the three protruding ends of the concrete specimen 7 in the X, Y, and Z directions, and apply high-strength epoxy resin adhesive to the contact surfaces for bonding and fixation. After the adhesive has cured, use a rigid loading end connector 8 (such as a flanged tie rod) to connect the X and Y outward connecting surfaces of the triaxial tension-compression clamp 6 to the actuator piston rods of the X-axis actuator 2 and Y-axis actuator 3 of the true triaxial testing machine, respectively, and connect the Z-axis outward connecting surface to the actuator piston rod of the Z-axis actuator 4. Ensure all connections are secure and without looseness.

[0029] Step S2: Set the test parameters in the central controller. The objective of this test is to apply displacement-controlled tensile loading in the Z-axis direction, while simultaneously applying compressive loads of 15 MPa in the X and Y axes. The central controller independently configures the hydraulic subsystem parameters in the X, Y, and Z directions.

[0030] Proceed to step S3: Start the test. The central controller synchronously issues commands: sending force control signals to the X and Y servo control valve groups, controlling X-direction actuator 2 and Y-direction actuator 3 to output constant force, so that the specimen quickly reaches and maintains a compressive stress of 15MPa in the X and Y directions. Simultaneously, a low-speed displacement control signal is sent to the Z-direction servo control valve group, driving Z-direction actuator 4 to stretch the specimen at a constant rate. Throughout the process, the three-axis loading system operates independently without interference.

[0031] Step S4: The data acquisition system synchronously records data from force and displacement sensors in the X, Y, and Z directions. As the Z-direction tension progresses, the tensile stress in the concrete specimen 7 gradually increases, while the compressive stresses in the X and Y directions are kept constant through closed-loop control. When the concrete specimen 7 fails under tensile stress in the Z direction, the system records the triaxial stress and strain values ​​at the moment of failure, as well as the complete stress-strain curve.

[0032] After the experiment, the data can be processed to obtain the tensile strength, stress-strain relationship and failure mode of the concrete in the Z direction under constant lateral pressure (X direction: -15MPa, Y direction: -15MPa), providing key experimental data for the theoretical study of multiaxial strength of concrete.

[0033] Therefore, this invention employs the aforementioned true triaxial tensile method for concrete specimens. By setting up a device architecture with hydraulic subsystems in the X, Y, and Z directions and a shared oil tank, it solves the coupling interference problem in multiaxial loading. This allows for the application of precise, stable, and completely independent X, Y, and Z-axis loads to the specimen, particularly ensuring the loading accuracy of the tensile principal stress. By using an integrated high-precision triaxial tension-compression clamp and an embedded interlocking connection with the concrete specimen, it eliminates the slippage, eccentricity, and stress concentration problems commonly encountered in traditional clamps during multiaxial tensile testing. This ensures that the stress state of the specimen is highly consistent with the theoretical preset, significantly improving data reliability. The integrated tension-compression clamping method eliminates the need to change clamps between tensile and compression tests, improving testing efficiency. This provides a key technical means for in-depth research on the failure mechanism of concrete under multiaxial loads and the establishment of accurate constitutive models.

[0034] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the technical solutions of the present invention, and these modifications or equivalent substitutions cannot cause the modified technical solutions to deviate from the spirit and scope of the technical solutions of the present invention.

Claims

1. A true triaxial tensile method for concrete specimens, characterized in that: Specifically, the following steps are included: S1. Preparation and installation of concrete specimens; S2, True Triaxial Tensile Testing Machine Hydraulic Power System Adaptive Configuration; S3, True Triaxial Tensile Loading; S4. Data synchronous acquisition and processing.

2. The true triaxial tensile method for concrete specimens according to claim 1, characterized in that: Specific in S1 Includes the following operations: S1.1 Prepare concrete specimens of a predetermined shape, and align and rigidly connect the three orthogonal stress-bearing end faces of the specimens with the corresponding connecting surfaces of the triaxial tension-compression clamps with high precision. S1.

2. The other three connecting surfaces of the triaxial tension / compression clamp are rigidly connected to the loading output ends of the true triaxial tensile testing machine in the X, Y, and Z directions respectively through the loading end connectors.

3. The true triaxial tensile method for concrete specimens according to claim 2, characterized in that: The hydraulic power system of the S2 true triaxial tensile testing machine includes a hydraulic oil tank, which is connected to the hydraulic subsystems in the X, Y, and Z directions. Each of the three hydraulic subsystems in the X, Y, and Z directions includes a hydraulic pump group, a servo control valve group, and an actuator. An oil cooler is installed on the return oil pipeline between the hydraulic subcontrol system in the X, Y, and Z directions and the oil tank. The hydraulic subsystems in the X, Y, and Z directions are connected to the central controller.

4. The true triaxial tensile method for concrete specimens according to claim 3, characterized in that: S3 specifically includes the following operations: S3.1 The central controller generates and sends control commands to the hydraulic sub-control systems in the X, Y, and Z directions respectively, based on the preset triaxial stress or strain path. The hydraulic sub-control system in the S3.2, X, Y, and Z directions drives its respective actuators to independently and synchronously transfer the load to the three corresponding end faces of the concrete specimen through the loading end connector and the three-way tension-compression clamp, thereby realizing a complex three-dimensional stress state including tensile principal stress inside the concrete specimen.

5. The true triaxial tensile method for concrete specimens according to claim 4, characterized in that: S4 specifically includes the following operations: S4.1 During the loading process, high-precision force sensors and displacement sensors integrated in the X, Y, and Z directions are used to collect the triaxial load and deformation data of the concrete specimen in real time. S4.2 The collected data is transmitted to the data processing unit for analysis of the strength, deformation and constitutive relationship of the concrete specimen under true triaxial tensile stress.

6. The true triaxial tensile method for concrete specimens according to claim 5, characterized in that: The concrete specimen in S1 is a three-dimensional dumbbell shape. The three-dimensional tension-compression clamp is integrally formed from high-strength alloy material and is embedded and interlocked with the concrete specimen.

7. The true triaxial tensile method for concrete specimens according to claim 6, characterized in that: During the loading process of S3, it is necessary to control the ambient temperature of the concrete specimen and the oil cooler to cool the hydraulic oil temperature in real time.

8. The true triaxial tensile method for concrete specimens according to claim 7, characterized in that: The preset triaxial stress paths in S3 include uniaxial tension-biaxial compression, biaxial tension-uniaxial compression, triaxial proportional tension, and non-proportional loading paths that simulate complex stress states.

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