Method for testing mechanical state of concrete bonding interface of ballastless track

Abstract

The invention discloses a ballastless track concrete bonding interface mechanical state testing method, belongs to the technical field of track traffic engineering, and realizes a multi-field coupling loading test on a ballastless track interlayer test piece by constructing an interlayer mechanical testing device comprising a servo loading mechanism, a DIC technology and finite element mechanical analysis. A high-speed camera is adopted to synchronously record the whole process of interlayer interface damage, an interface stress distribution cloud picture is obtained in combination with a distributed strain patch, and a load-displacement curve and interlayer slippage data are synchronously collected. A refined finite element model containing a cohesion unit is established based on measured data, and iterative fitting of a simulation result and test data is achieved by dynamically adjusting interface damage parameters. According to the method, the limitation of a traditional single-point stress test is broken through, space-time multi-scale analysis of interlayer mechanical behaviors is achieved, the technical problems that an interlayer interface failure mechanism is not clear and simulation model parameters are difficult to calibrate are solved, and a novel test is provided for durability evaluation of a ballastless track structure.

Description

Technical Field

[0001] The present invention relates to the technical field of rail transportation engineering, and in particular to a method for testing the mechanical state of a ballastless track concrete bonding interface. Background Art

[0002] The mechanical properties of the interlaminar interface of ballastless track are key indicators for ensuring the safe service of high-speed railways. Traditional interlaminar mechanical property testing methods have the following significant drawbacks: the use of circular or rectangular cross-section specimens results in uneven interface stress analysis, failing to truly simulate the trapezoidal stress analysis characteristics of actual track structures. Furthermore, there is a lack of visual observation of the entire process of interlaminar microcrack initiation (less than 0.1mm) and propagation. Model parameters rely on empirical values, resulting in a low degree of agreement with measured data (correlation coefficient R < 0.8), making it difficult to support engineering reliability assessments.

[0003] To address these issues, this invention achieves precise, multi-scale, temporal and spatial characterization of interlaminar mechanical behavior through the collaborative innovation of trapezoidal stress specimen design, an ultra-high-speed dynamic testing system, a data-driven finite element model, and the use of L-shaped brackets. The trapezoidal cross-section design reduces the stress concentration factor to below 1.2. Ultra-high-speed cameras (frame rate ≥ 50,000 fps) and nanosensors (response time ≤ 1μs) simultaneously capture interfacial microcrack propagation and dynamic stress field changes. Combined with finite element parameter inversion technology (error ≤ ±5%), this method overcomes the technical bottlenecks of traditional methods in stress uniformity, dynamic response analysis, and model reliability, providing a scientific basis for ballastless track structural optimization and lifecycle maintenance. Summary of the Invention

[0004] In view of the deficiencies in the prior art, the present invention provides a method for testing the mechanical state of the concrete bonding interface of ballastless track, which solves the problems raised in the above-mentioned background technology.

[0005] Technical solution: To solve the above technical problems, according to one aspect of the present invention, more specifically, a method for testing the mechanical state of the ballastless track concrete bonding interface includes the following steps:

[0006] S1. Preparation of Trapezoidal Stress Test Specimens: Prepare interlaminar composite specimens with a trapezoidal cross-section. The specimens consist of upper and lower track structural layers and an intermediate interface layer. The upper base width of the trapezoidal cross-section is 100-150 mm, the lower base width is 200-300 mm, the height is 80-120 mm, and the included angle between the two sides is 120°-150°. Controllable adjustment of the interlaminar stress concentration area is achieved by changing the cross-sectional dimension gradient.

[0007] The upper and lower structural layers are made of C60 grade RPC reactive powder concrete with a compressive strength of ≥150MPa and an elastic modulus of ≥45GPa; the interface layer is made of epoxy resin-based composite material with a thickness of 0.5-2mm and a shear modulus of 1.2-2.5GPa.

[0008] S2. Ultra-high-speed dynamic testing system construction: Build a multi-parameter synchronous testing system including an ultra-high-speed camera (frame rate ≥ 50,000 fps), high-precision strain sensors (accuracy ≤ ±0.1 με), and a servo hydraulic loading device. The strain sensors are arranged in an array with a density of ≥ 10 pieces / cm at the interlayer interface. 2 ;

[0009] An ultra-high-speed camera equipped with a microscope lens assembly enables magnified observation of localized areas of interlayer interfaces (magnification ≥ 500x), and achieves microsecond-level time alignment through a synchronized trigger device and servo loading system. The high-precision strain sensor is a nano-piezoresistive sensor with a sensitive gate made of a graphene / metal composite film. Its response time is ≤ 1μs and it can measure dynamic strains in the range of 0-20,000με.

[0010] L-shaped multi-directional constraint bracket system: In order to solve the problems of single-degree-of-freedom constraint, insufficient rigidity and poor interface adaptability of traditional fixtures, an L-shaped multi-directional constraint bracket system is designed. The L-shaped multi-directional constraint bracket is integrally cast from high-strength alloy steel (40CrNiMoA, yield strength ≥785MPa). The main body consists of three modules: a vertical clamping arm, a horizontal support platform and a bidirectional actuator. The clamping arm and the support platform form a 90° rigid angle through a precision hinge (fit clearance <5μm). The internal preload force reaches 50kN, and the angle stiffness is increased to 3 times that of the traditional fixture (measured deformation <0.05mm). The inner side of the clamping arm is inlaid with a replaceable ceramic liner (Al2O3-TiC composite material, hardness HV1800), and the surface is laser-etched with a micron-scale groove array (depth 10-50μm, density 20-100 lines / cm 2 ), by adjusting the groove parameters to achieve customized engagement with the rough interface of the specimen, the friction coefficient can be controlled in the range of 0.15-0.35. The horizontal support platform is integrated with a hydraulic servo leveling module (resolution 0.001°), which drives 12 sets of micro-cylinders to compensate for the inclination deviation through real-time feedback of the specimen deformation data (DIC strain field analysis), ensuring that the loading axis is always perpendicular to the contact interface (angle deviation <0.01°). The brackets are arranged symmetrically on both sides of the specimen, and a bidirectional actuator (MaxonEC-4pole200W) is used to apply lateral restraint forces of equal amplitude and opposite direction (0-20kN continuously adjustable), forming a closed mechanical loop to effectively offset the lateral friction component.

[0011] S3. Multi-field coupled loading test: A trapezoidal wave dynamic load (rising edge ≤ 5ms, falling edge ≤ 10ms) is applied to the trapezoidal specimen. Synchronous data acquisition includes: images of the entire process of microcrack initiation and growth at the interlayer interface captured by an ultra-high-speed camera (resolution ≤ 0.1mm / pixel); real-time three-dimensional stress field data output by a strain sensor array (sampling frequency ≥ 1MHz); and load-displacement curves recorded by a servo loading device (accuracy ≤ ±0.01%FS).

[0012] The loading parameters of the trapezoidal wave load are: peak load range 50-500kN (corresponding to contact stress 10-100MPa); loading frequency 10-100Hz (covering the characteristic frequency of high-speed train wheel-rail load); number of cycles ≥10 6 times (simulating a 30-year service cycle);

[0013] S4. Micromechanical model construction: A micromechanical model of the interlayer interface is established based on digital image correlation (DIC) technology. DIC technology is used to process ultra-high-speed images to obtain the full-field displacement vector field; based on the theory of continuum mechanics, the interface shear strain rate distribution is calculated:

[0014]

[0015] Where u and v are displacement components, and x and y are coordinate directions. The three-dimensional strain field inside the interface layer is reconstructed using digital volume correlation (DVC) technology.

[0016] S5. Damage evolution inversion analysis: Combining the measured stress field data with the microscopic model, a damage constitutive equation considering the strain rate effect is established:

[0017]

[0018] Among them, σ0 is the initial shear strength, γ is the shear strain, and γ c is the critical damage strain, is the strain rate, is the reference strain rate, and n is the strain rate sensitivity index. The constitutive model parameters are updated by the Bayesian inference method, and the objective function is defined as:

[0019]

[0020] Among them, θ is the model parameter vector, D is the measured data set, σ i is the standard deviation of the measurement noise;

[0021] S6. Establishment of full life prediction model: Based on the trapezoidal test data, the fatigue life curve is fitted and the two-parameter Weibull distribution is used to describe the failure probability of the interlayer interface:

[0022]

[0023] Where N is the number of cycles, N0 is the characteristic life, and k is the shape parameter. The validation method of the full life prediction model includes comparing the damage growth rate of the trapezoidal specimen with the actual track structure (error ≤ 5%).

[0024] Furthermore, the preparation materials and dimensional parameters of the trapezoidal specimens must be strictly implemented in accordance with the design requirements to ensure the consistency of the specimen quality and performance.

[0025] Furthermore, the parameters and connection methods of each device in the ultra-high-speed dynamic test system must comply with regulations to ensure the accuracy and synchronization of data collection.

[0026] Furthermore, the load parameters, data acquisition accuracy and frequency of the multi-field coupled loading test must meet the requirements of simulating actual working conditions.

[0027] Furthermore, in the process of constructing the micromechanical model, the application of DIC technology and DVC technology must follow relevant principles and methods to ensure the accuracy of the model.

[0028] Furthermore, in the damage evolution inversion analysis, the establishment of the constitutive equation and the parameter updating method must be reasonable and effective to reflect the actual damage evolution law.

[0029] Furthermore, the establishment and verification process of the full life prediction model needs to be scientific and rigorous to provide a reliable basis for the durability assessment of the ballastless track structure.

[0030] The beneficial effects of the ballastless track concrete bonding interface mechanical state testing method of the present invention are:

[0031] (1) The present invention breaks through the limitations of traditional single-point stress testing and realizes spatiotemporal multi-scale analysis of interlayer mechanical behavior, which can accurately obtain the dynamic failure process of the interlayer interface and refined stress distribution data.

[0032] (2) The present invention solves the technical problems of unclear interlayer interface failure mechanism and difficult calibration of simulation model parameters, and provides a reliable new test method for the durability evaluation of ballastless track structure. Through innovative specimen design, test system construction and data analysis methods, the accuracy and reliability of test data are improved, and the test results are more consistent with the actual track structure, providing strong support for engineering practice. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] The present invention will be further described in detail below with reference to the accompanying drawings and specific implementation methods.

[0034] Figure 1 It is a structural schematic diagram of the present invention;

[0035] Figure 2 It is the trapezoidal dynamic load loading diagram of the present invention. DETAILED DESCRIPTION

[0036] The present invention will be described in detail below with reference to the accompanying drawings and in combination with embodiments. It should be noted that, unless there is a conflict, the embodiments and features in the embodiments of the present application can be combined with each other.

[0037] In order to make the technical solution of the present invention clearer, the present invention is further described in detail below with reference to the accompanying drawings and specific embodiments.

[0038] Reference Figure 1-Figure 2 , the test method for the mechanical state of the ballastless track concrete bonding interface is implemented as follows:

[0039] Specimen Preparation: Trapezoidal stress test specimens and rectangular specimens were prepared in strict accordance with design requirements. For the trapezoidal specimens, the pouring quality of the upper and lower structural layers of C60-grade RPC reactive powder concrete was precisely controlled to ensure that the compressive strength and elastic modulus met the standards. The thickness of the epoxy resin-based composite material in the intermediate interface layer was controlled within the specified range. For the rectangular specimens, the aspect ratio was precisely calibrated, and a layered pouring process was used to preset a controllable roughness of 0.1-0.3mm (Ra = 0.18 ± 0.03mm measured by a laser profilometer). The specimen height was ensured to meet the design requirements.

[0040] Test system setup and commissioning: Install an ultra-high-speed camera, high-precision strain sensors, a servo-hydraulic loading device, and an L-shaped multi-directional restraint bracket system. Carefully adjust the ultra-high-speed camera's frame rate, resolution, and magnification to ensure microsecond-level time alignment with the servo loading system. Check the layout and accuracy of the strain sensors. Debug various parameters of the L-shaped multi-directional restraint bracket system, including angular stiffness, friction interface parameters, and the hydraulic servo leveling module, to ensure proper operation of the entire test system.

[0041] Loading test: The prepared specimen is mounted on an L-shaped multi-directional restraint support system and loaded using a servo-hydraulic loading device according to the set trapezoidal wave dynamic load parameters. During the loading process, an ultra-high-speed camera, strain sensors, and servo loading device synchronously collect data.

[0042] Data Processing and Model Building: Systematically organize and deeply analyze the vast amount of collected data. Use DIC technology to process ultra-high-speed images to obtain the full-field displacement vector field, calculate the interface shear strain rate distribution, reconstruct the three-dimensional strain field, and establish a micromechanical model. Based on the measured stress field data, use Bayesian inference to update the parameters of the damage constitutive equation, fit the fatigue life curve, and establish a full life prediction model.

[0043] Model Verification and Optimization: The damage growth rate of the trapezoidal specimen is compared with the actual track structure. If the error is within 5%, the accuracy of the full-life prediction model is verified. If the error exceeds the range, the cause is analyzed in depth and the model is optimized and adjusted to ensure that the model accurately reflects the mechanical state of the ballastless track concrete bond interface.

[0044] This invention overcomes the bottleneck of mismatch between specimen shape and actual working conditions in traditional interlaminar mechanical testing through the collaborative design of "geometric optimization, mechanical balance, and dynamic perception." The geometric optimization of rectangular specimens is a key driver for the implementation of this technology. Its design logic and advantages can be systematically explained as follows:

[0045] 1. Geometry optimization: High-precision mapping of rectangular specimens to real contact interfaces

[0046] Traditional interlayer shear tests mostly use circular or rectangular specimens with an unbalanced aspect ratio. Their geometric characteristics are significantly different from the actual contact surface between ballastless track layers (a multi-layer rectangular composite structure of track slab, mortar layer, and base plate), resulting in distortion of the stress transfer path.

[0047] The rectangular specimen design of the present invention achieves geometric matching through the following innovations:

[0048] Strict calibration of the aspect ratio: Based on the actual dimensions of the contact surface between track layers (e.g., the typical dimensions between layers of CRTS III slab track are 645mm×2850mm), the aspect ratio of the specimen is optimized to 2:1 (300mm×150mm). The long side is aligned with the longitudinal extension direction of the track, while the short side corresponds to the lateral constraint dimension, achieving isomorphic mapping between the loading direction and the service stress.

[0049] Mechanical advantages of right-angled edges: Finite element simulation comparison (ABAQUS 2022 version, mesh accuracy 0.5mm) shows that the traditional circular specimens induce a stress diffusion effect (edge ​​stress attenuation rate >35%) due to the edge curvature during shear loading, while the rectangular right-angle design makes the contact pressure symmetrically distributed along the central axis (maximum pressure fluctuation <5%), significantly suppressing the measurement distortion caused by local stress concentration during sliding ( Figure 1 ).

[0050] Size-load compatibility: The specimen height (50 mm) was optimized through orthogonal testing (L9(3^4)). This allows for the interface roughness gradient resulting from the layered casting process while also avoiding the additional bending moment due to the specimen's own weight (simulation results show a bending moment interference of <0.1 kN·m).

[0051] 2. Material-process synergy: Reproduction of service status of interface micromorphology

[0052] The geometric advantages of rectangular specimens must be combined with material processing to accurately reproduce the actual mechanical behavior of the track interlayer interface:

[0053] Gradient material matching: The specimen uses a C40-C20 concrete composite material consistent with the interlayer structure of the ballastless track (the upper layer C40 simulates the track slab, and the lower layer C20 simulates the mortar layer). The interlayer stiffness gradient is restored through the difference in elastic modulus (C40: 32.5GPa, C20: 25.5GPa).

[0054] Controllable prefabrication of interface roughness: Using layered casting process, preset 0.1-0.3mm controllable roughness at the interface (laser profiler measured Ra = 0.18 ± 0.03mm), accurately simulating the microscopic morphology characteristics formed by the construction process (such as roughening treatment) under service conditions ( Figure 2 ).

[0055] Dynamic sensing compatibility: The planar characteristics of the rectangular specimen facilitate the integration of fiber Bragg grating sensor (FBG, accuracy 1με) arrays. The long side layout allows the arrangement of sensing nodes along the principal stress direction, enabling simultaneous monitoring of multiple parameters such as shear displacement, interface delamination, and crack propagation.

[0056] 3. Engineering Verification: Comprehensive Performance Advantages of Rectangular Specimens

[0057] Through comparative tests and engineering data verification, rectangular specimens show significant advantages over traditional designs:

[0058] Maximized contact area: Specimen size 300mm×150mm×50mm achieves contact area ≥450cm within the standard testing machine stroke 2 (42% improvement compared to round specimens), ensuring statistical uniformity of shear force distribution.

[0059] Boundary effect suppression: The right-angle edge design increases the effective shear area from 68% of the circular specimen to 92%, and reduces boundary interference to less than 5% (DIC full-field strain analysis results).

[0060] Data repeatability: 30 sets of repeated tests showed that the shear strength coefficient of variation of the rectangular specimen (CV = 3.2%) was significantly lower than that of the traditional specimen (CV = 8.7%), proving the contribution of its geometric stability to test consistency.

[0061] The above-described embodiments merely illustrate several implementations of the present invention, and while their descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that a person skilled in the art would be able to make numerous variations and improvements without departing from the spirit of the present invention, all of which fall within the scope of protection of the present invention. Therefore, the scope of protection of the present invention shall be determined by the appended claims.

Claims

1. The ballastless track concrete bonding interface mechanical state test method is characterized by: The steps include: S1. Preparation of Trapezoidal Stress Test Specimens: Prepare interlaminar composite specimens with a trapezoidal cross-section. The specimens consist of upper and lower track structural layers and an intermediate interface layer. The upper base width of the trapezoidal cross-section is 100-150 mm, the lower base width is 200-300 mm, the height is 80-120 mm, and the included angle between the two sides is 120°-150°. Controllable adjustment of the interlaminar stress concentration area is achieved by changing the cross-sectional dimension gradient. The upper and lower structural layers are made of C60 grade RPC reactive powder concrete with a compressive strength of ≥150MPa and an elastic modulus of ≥45GPa; the interface layer is made of epoxy resin-based composite material with a thickness of 0.5-2mm and a shear modulus of 1.2-2.5GPa. S2. Construction of ultra-high-speed dynamic testing system: Build a multi-parameter synchronous testing system including an ultra-high-speed camera, high-precision strain sensors, and a servo hydraulic loading device. The strain sensors are arranged in an array, with a density of ≥10 pieces / cm at the interlayer interface. 2 ; The ultra-high-speed camera is equipped with a microscope lens group to achieve magnified observation of local areas of the interlayer interface, and microsecond-level time alignment is achieved through a synchronous trigger device and servo loading system; The high-precision strain sensor is a nano-piezoresistive sensor with a sensitive gate material of graphene / metal composite film. The response time is ≤1μs and it can measure dynamic strain in the range of 0-20,000με. S3, Multi-field coupled loading test: Trapezoidal wave dynamic load is applied to the trapezoidal specimen, and the following data are collected simultaneously: the image of the entire process of microcrack initiation and growth at the interlayer interface acquired by the ultra-high-speed camera; the real-time data of the three-dimensional stress field output by the strain sensor array; and the load-displacement curve recorded by the servo loading device; The loading parameters of the trapezoidal wave load are: peak load range 50-500kN; loading frequency 10-100Hz; number of cycles ≥10 6 Second-rate; S4. Micromechanical model construction: A micromechanical model of the interlayer interface is established based on digital image correlation technology. Ultra-high-speed images are processed using DIC technology to obtain the full-field displacement vector field; based on the theory of continuum mechanics, the interface shear strain rate distribution is calculated: Where u and v are displacement components, and x and y are coordinate directions. The three-dimensional strain field inside the interface layer is reconstructed using digital volume correlation (DVC) technology. S5. Damage evolution inversion analysis: Combining the measured stress field data with the microscopic model, a damage constitutive equation considering the strain rate effect is established: Among them, σ0 is the initial shear strength, γ is the shear strain, and γ c is the critical damage strain, γ is the strain rate, γ0 is the reference strain rate, and n is the strain rate sensitivity index. The constitutive model parameters are updated by the Bayesian inference method, and the objective function is defined as: Among them, θ is the model parameter vector, D is the measured data set, σ i is the standard deviation of the measurement noise; S6. Establishment of full life prediction model: Based on the trapezoidal test data, the fatigue life curve is fitted and the two-parameter Weibull distribution is used to describe the failure probability of the interlayer interface: Where N is the number of cycles, N0 is the characteristic life, and k is the shape parameter. The validation method for the full life prediction model involves comparing the damage growth rate of the trapezoidal specimen with the actual track structure.

2. The method for testing the mechanical state of the ballastless track concrete bonding interface according to claim 1 is characterized in that: The preparation materials and dimensional parameters of the trapezoidal specimens must be strictly implemented in accordance with the design requirements to ensure the consistency of the specimen quality and performance.

3. The method for testing the mechanical state of the ballastless track concrete bonding interface according to claim 1 is characterized in that: The parameters and connection methods of each device in the ultra-high-speed dynamic test system must comply with regulations to ensure the accuracy and synchronization of data collection.

4. The method for testing the mechanical state of the ballastless track concrete bonding interface according to claim 1 is characterized in that: The load parameters, data acquisition accuracy and frequency of the multi-field coupled loading test must meet the requirements of simulating actual working conditions.

5. The method for testing the mechanical state of the ballastless track concrete bonding interface according to claim 1 is characterized in that: During the construction of the micromechanical model, the application of DIC technology and DVC technology must follow relevant principles and methods to ensure the accuracy of the model.

6. The method for testing the mechanical state of the ballastless track concrete bonding interface according to claim 1, characterized in that: In the damage evolution inversion analysis, the establishment of the constitutive equation and the parameter updating method must be reasonable and effective to reflect the actual damage evolution law.

7. The method for testing the mechanical state of the ballastless track concrete bonding interface according to claim 1, characterized in that: The establishment and verification process of the full life prediction model must be scientific and rigorous to provide a reliable basis for the durability assessment of ballastless track structures.

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