Ballastless track concrete mesoscopic fatigue damage prediction method and system

Abstract

The invention relates to a ballastless track concrete mesoscopic fatigue damage prediction method and system, and the method comprises the steps: processing a profile image of a concrete beam test piece, and obtaining a mesoscopic finite element model containing aggregate, slurry and an interface; replacing the key area of the model track slab with a mesoscopic finite element model to form a macro-mesoscopic coupling model; aggregate in the coupling model is set as an elastomer, slurry and an interface adopt a plastic damage constitutive structure, coupling stress is determined according to different train dynamic loads and environment temperatures under the condition of considering the fatigue accumulation effect, the fatigue damage increment of each grid unit in the macro-micro coupling model is further determined, and the total damage is accumulated according to the time scale, so that the coupling stress is determined; when the total damage of a certain unit exceeds a set value, the unit fails, and a corresponding crack propagation path and fatigue life are obtained. The method can accurately predict the crack propagation path and life of the track plate under train and temperature load, is suitable for false joint cracking risk assessment, and provides support for durability design of ballastless tracks.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of fatigue damage detection, in particular to a concrete mesoscopic fatigue damage prediction method and system for ballastless track. BACKGROUND

[0002] The statements in this section merely provide background information related to the present application and do not necessarily constitute the prior art.

[0003] The concrete of the ballastless track is a special concrete material used in the track transportation system of high-speed railway, subway, etc., which is used to replace the ballast bed in the traditional ballast track to directly support the steel rail and the sleeper, forming a flat and stable track structure.

[0004] The concrete structure of the ballastless track is prone to fatigue damage under the long-term train load and environmental temperature change, and its damage process begins with the micro-crack evolution at the mesoscopic scale (aggregate, paste and interface). The traditional macro model is difficult to accurately describe the non-uniformity and damage localization characteristics of the concrete inside, resulting in large deviation of the fatigue life prediction.

[0005] In the prior art, the fatigue analysis of the ballastless track is mostly based on the homogeneity assumption, regarding the concrete as a homogeneous material, ignoring the mesoscopic non-uniformity of the aggregate distribution, mortar matrix and interface transition zone (ITZ), which makes it impossible to accurately describe the damage localization and micro-crack initiation mechanism. At the same time, the preset false joint of the track slab as a stress concentration area, how the surrounding mesoscopic components (such as aggregate arrangement, ITZ strength) affect the crack initiation and propagation has not been systematically quantified, making the mesoscopic damage evolution mechanism unclear.

[0006] In order to solve the technical problems existing in the background art, the present application provides a concrete mesoscopic fatigue damage prediction method and system for ballastless track, which realizes the mesoscopic evolution simulation of the fatigue damage of the track slab by reconstructing the real aggregate distribution in three dimensions and establishing a nested macro-mesoscopic finite element model, and can accurately predict the crack path and fatigue life, providing a theoretical basis for the maintenance of the ballastless track. SUMMARY

[0007] In order to solve the technical problems existing in the background art, the present application provides a concrete mesoscopic fatigue damage prediction method and system for ballastless track, which realizes the mesoscopic evolution simulation of the fatigue damage of the track slab by reconstructing the real aggregate distribution in three dimensions and establishing a nested macro-mesoscopic finite element model, and can accurately predict the crack path and fatigue life, providing a theoretical basis for the maintenance of the ballastless track.

[0008] In order to achieve the above purpose, the present application adopts the following technical solutions: The first aspect of the present application provides a concrete mesoscopic fatigue damage prediction method for ballastless track, comprising the following steps: Obtain the cross-sectional image of the concrete beam specimen and preprocess, obtain the aggregate edge through edge detection, fit the three-dimensional profile of the aggregate through a plurality of cross-sectional images, and generate a mesoscopic finite element model containing aggregate, paste and interface; A macro finite element model of the ballastless track is constructed, a key area of a track slab of the model is replaced by a meso finite element model to form a macro-meso coupled model, and a grid unit is divided; The aggregate in the macro-meso coupled model is set as an elastic body, the paste and the interface adopt a plastic damage constitutive, under the condition of considering the fatigue cumulative effect, the coupled stress is determined according to different train dynamic loads and environmental temperatures; According to the obtained coupled stress, the fatigue damage increment of each grid unit in the macro-meso coupled model is determined, and the total damage is accumulated according to the time scale, when the total damage of a certain unit exceeds a set value, the unit fails, and the corresponding crack propagation path and fatigue life are obtained.

[0009] Further, the cross-sectional image of the concrete beam specimen is obtained, specifically: a plurality of concrete beam specimens are prepared, the specimens are cut along the neutral plane, and the surface of part of the cut specimens is polished and polished, the polished surface is scanned by using a three-dimensional structured light grating scanning device, and the cross-sectional image is obtained.

[0010] Further, the obtained cross-sectional image is preprocessed, edge detection is performed based on a threshold segmentation method, aggregate edge feature points are obtained, a three-dimensional profile of the aggregate is constructed based on a finite element software combined with a plurality of cross-sectional images, the surface of the solid aggregate is fitted, the solid between the cross sections is determined based on an interpolation method, the three-dimensional reconstruction of the aggregate is realized, and a meso finite element model containing the aggregate, the paste and the interface is generated.

[0011] Further, the macro finite element model of the ballastless track includes a lower foundation, a support layer, a mortar layer and a track slab arranged from bottom to top, a steel rail is arranged on the track slab, the steel rail is connected to the track slab through a fastener, and a fatigue load is transmitted to the track slab through the steel rail; a region where a false joint is located is selected on the track slab, and a region corresponding to the length of the specimen is selected in the region as a meso finite element section for replacing the meso finite element model.

[0012] Further, the fatigue damage variable D characterizes the damage accumulation degree of the ballastless track concrete in the fatigue loading process, and is as follows: ; In the formula, N i is the number of times of the current fatigue load; Nf ,i is the fatigue life value corresponding to the current stress level; i is the fatigue stress grade.

[0013] Further, the coupling stress is determined according to different train dynamic loads and environmental temperature changes, including: constructing vibration equations of the rail and the track slab under the high-speed moving excitation of the train load, determining the track critical speed and the wave number through Fourier transform and simultaneous processing, further determining the displacement distribution of the rail and the track slab under the high-speed moving excitation of the train; and obtaining the relationship between the track slab stress and the driving speed under different driving speeds according to the normal stress calculation method of the bending beam. corresponding relationship of the frequency , further determining the displacement distribution of the rail and the track slab under the high-speed moving excitation of the train; and obtaining the relationship between the track slab stress and the driving speed under different driving speeds according to the normal stress calculation method of the bending beam.

[0014] Further, the coupling stress is determined according to different train dynamic loads and environmental temperature changes, specifically: when the vehicle passes, the fatigue load spectrum acting on the rail is applied to the macro-micro coupling model to obtain the fatigue stress of the track slab under the action of the train load, and the stress amplitude of the track slab under the train load is determined; the track slab temperature load at the mth month t time is applied, the temperature stress is taken as a base value and the fatigue stress spectrum equivalent to the train load is superimposed to obtain the fatigue stress base value and amplitude of the track slab under the joint action of the train load and the environmental temperature change at the mth month t time; it is assumed that the stress spectrum of the track slab caused by the train is constant within a set period, and the change of the temperature stress in the track slab is the same, and the stress field is obtained.

[0015] Further, the fatigue damage increment of each grid element in the macro-micro coupling model is determined, specifically: the fatigue life of each element under the first i level loading mode is determined, and the fatigue damage increment of each element after the second i level loading action ΔN i times is determined, the corresponding damage increments are superimposed to determine the fatigue damage increment of each element after the train group passes at a certain time. ΔN i

[0016] Further, the total damage D is accumulated according to the time scale, specifically: the fatigue damage increments of each element at different times are superimposed respectively to obtain the fatigue damage increments of each element in each day and each month, and the annual fatigue damage variable of each element is further determined.

[0017] The second aspect of the present application provides a concrete meso fatigue damage prediction system for ballastless track, comprising: The meso modeling module is configured to: obtain the cross-sectional image of the concrete beam test piece and pre-process, obtain the aggregate edge through edge detection, fit the three-dimensional profile of the aggregate through a plurality of cross-sectional images, and generate a meso finite element model containing aggregate, paste and interface; ​The macro-micro coupling modeling module is configured to: construct a macro finite element model of the ballastless track, replace key areas of the model track slab with a micro finite element model to form a macro-micro coupling model, and divide grid units; The material constitutive and load module is configured to: set the aggregate in the macro-micro coupling model as an elastic body, use a plastic damage constitutive for the paste and the interface, determine the coupling stress according to different train dynamic loads and environmental temperatures under the condition of considering the fatigue cumulative effect; The fatigue damage calculation module is configured to: determine the fatigue damage increment of each grid unit in the macro-micro coupling model according to the obtained coupling stress, and accumulate the total damage according to the time scale, when the total damage of a certain unit exceeds a set value, the unit fails, and the corresponding crack propagation path and fatigue life are obtained.

[0018] Compared with the prior art, the above one or more technical solutions have the following beneficial effects: 1. The traditional model regards concrete as a homogeneous material, ignores the mechanical differences of aggregates, mortar and interface transition zones, cannot predict the real crack path, is prone to overestimate the fatigue life, and relies on the fatigue equation fitted by experiments, and cannot reflect the differences in microstructure and multi-field coupling effect. The scheme reveals the nature of concrete fatigue damage from the micro scale, and realizes efficient calculation of engineering by macro-micro coupling. The micro cracks of concrete fatigue damage are accurately modeled by using the micro scale, the real crack initiation position is captured, and the non-uniformity is quantified. The macro-micro nested model uses the micro model only in the key area (around the false joint), and uses the macro model in the remaining area, balancing the precision and the amount of calculation. The different thermal expansion coefficients of each component of the concrete will generate additional tensile stress at the interface, which will further accelerate the expansion of the micro cracks caused by temperature under the superposition of train cyclic load, realizing multi-physical field coupling. Finally, the fatigue damage is calculated by unit, reflecting the local stress concentration effect, which can dynamically update the material stiffness and simulate the feedback of stiffness degradation on the overall stress.

[0019] 2. By three-dimensionally reconstructing the real aggregate distribution, a nested macro-micro finite element model is established to accurately characterize the non-uniformity (aggregate, paste and interface transition zone) of the concrete, overcome the limitations of the traditional homogeneous assumption model, significantly improve the simulation accuracy of fatigue damage evolution, and realize accurate modeling at the micro scale.

[0020] 3. Combined with the plastic damage theory and the fatigue accumulation criterion, the gradual damage process of the mortar component is simulated, the crack initiation, propagation path and fatigue life are accurately predicted, which is especially suitable for fatigue risk assessment of key areas such as false joints, and realizes accurate prediction of fatigue damage evolution.

[0021] 4. Considering the coupling effect of train load and environmental temperature variation, the superimposed effect of fatigue stress and temperature stress is calculated through nested model to reflect the complex stress state of ballastless track in actual operation and realize multi-load coupling analysis.

[0022] 5. The local mesoscopic model is used to replace the key area (such as the vicinity of false joint) in macro model to significantly reduce the calculation scale while ensuring the calculation accuracy, and realize efficient and targeted fatigue damage analysis.

[0023] 6. The damage state (such as false joint expansion depth and plate cracking trend) of track slab under different operation years can be quickly predicted to provide scientific basis for the durability design and maintenance strategy of ballastless track, and it is especially suitable for long-term performance evaluation of high-speed railway. BRIEF DESCRIPTION OF DRAWINGS

[0024] The drawings constituting a part of the specification of the present application are used to provide further understanding of the present application, the illustrative embodiments of the present application and the description thereof serve to explain the present application, and do not constitute improper limitation on the present application.

[0025] Figure 1 is a schematic diagram of a ballastless track concrete mesoscopic fatigue damage calculation process provided by one or more embodiments of the present application; Figure 2 is a cross-sectional schematic diagram of a concrete beam specimen provided by one or more embodiments of the present application; Figure 3 is a schematic diagram of aggregate distribution of beam specimen sequence cross section provided by one or more embodiments of the present application; Figure 4 is a schematic diagram of nested mesoscopic finite element calculation model of ballastless track fatigue damage provided by one or more embodiments of the present application; Figure 5 is a schematic diagram of tensile in the plastic damage mechanics characteristics of concrete provided by one or more embodiments of the present application; Figure 6 is a schematic diagram of compression in the plastic damage mechanics characteristics of concrete provided by one or more embodiments of the present application; Figure 7 is a schematic diagram of vibration calculation model of ballastless track under train moving excitation provided by one or more embodiments of the present application; Figure 8 is a schematic diagram of dynamic stress distribution of track slab under train moving excitation provided by one or more embodiments of the present application; Figure 9 is a schematic diagram of the relationship between dynamic stress amplitude of track slab and vehicle speed under train moving excitation provided by one or more embodiments of the present application; Figure 10is a schematic diagram of a temperature change curve of a track slab provided by one or more embodiments of the present application; Figure 11 is a schematic diagram of a tensile stress distribution of a track slab false joint under train load provided by one or more embodiments of the present application; Figure 12 is a schematic diagram of a compressive stress distribution of a track slab false joint under train load provided by one or more embodiments of the present application; Figure 13 is a schematic diagram of a tensile stress distribution of a track slab false joint under the combined action of train and temperature provided by one or more embodiments of the present application; Figure 14 is a schematic diagram of a compressive stress distribution of a track slab false joint under the combined action of train and temperature provided by one or more embodiments of the present application; Figure 15 is a schematic diagram of a fatigue damage variable distribution of a track slab bridge section operated for 10 years provided by one or more embodiments of the present application; Figure 16 is a schematic diagram of a fatigue damage variable distribution of a track slab tunnel section operated for 10 years provided by one or more embodiments of the present application; Figure 17 is a schematic diagram of a fatigue damage variable micro-distribution of a track slab false joint under train load when operated for 10 years provided by one or more embodiments of the present application; Figure 18 is a schematic diagram of a fatigue damage variable micro-distribution of a track slab false joint under train load when operated for 30 years provided by one or more embodiments of the present application; Figure 19 is a schematic diagram of a fatigue damage variable micro-distribution of a track slab false joint under train load when operated for 60 years provided by one or more embodiments of the present application; Figure 20 is a schematic diagram of a fatigue damage variable micro-distribution of a track slab false joint under train load when operated for 120 years provided by one or more embodiments of the present application; Figure 21 is a schematic diagram of a fatigue damage variable micro-distribution of a track slab false joint under the combined action of train and temperature when operated for 10 years provided by one or more embodiments of the present application; Figure 22 is a schematic diagram of a fatigue damage variable micro-distribution of a track slab false joint under the combined action of train and temperature when operated for 20 years provided by one or more embodiments of the present application; Figure 23 is a schematic diagram of a fatigue damage variable micro-distribution of a track slab false joint under the combined action of train and temperature when operated for 30 years provided by one or more embodiments of the present application; Figure 24is a schematic diagram of the mesoscopic distribution of fatigue damage variables of the track slab under the joint action of train and temperature when the track is operated for 60 years, provided by one or more embodiments of the present application. Figure 25 is a schematic diagram of the mesoscopic fatigue damage calculation process, provided by one or more embodiments of the present application. DETAILED DESCRIPTION

[0026] The present application will be further described below in conjunction with the accompanying drawings and embodiments.

[0027] It should be noted that the following detailed description is exemplary and is intended to provide further explanation of the present application. Unless otherwise specified, all technical and scientific terms used in the present application have the same meaning as generally understood by those skilled in the art to which the present application belongs.

[0028] The related technical terms involved in the present application are as follows: The preset false joint refers to a weak section artificially designed in the track slab, which avoids random harmful cracks in the concrete structure due to shrinkage, temperature change or load stress by actively controlling the crack position and expansion path, and is also called an induced joint or a controlled joint. In terms of structure, the false joint is a shallow groove precast when the track slab is cut or poured, with part of the concrete at the bottom remaining uncut and connected, rather than completely disconnected.

[0029] As introduced in the background, the traditional macroscopic model has limitations: the existing fatigue analysis model regards concrete as a homogeneous material, ignoring the mesoscopic heterogeneity of aggregate distribution, mortar matrix and interface transition zone (ITZ), which leads to the inability to accurately describe damage localization and micro-crack initiation mechanism. At the same time, the macroscopic model is difficult to capture the real path of crack propagation along the aggregate-matrix interface (usually bypassing the aggregate or penetrating the weak interface), affecting the accuracy of fatigue life prediction.

[0030] At the same time, as a fatigue sensitive area, how the mesoscopic components around the preset false joint of the track slab (such as aggregate arrangement and ITZ strength) affect crack initiation and propagation has not been systematically quantified.

[0031] In addition, how the restraint stress caused by temperature gradient and the train dynamic load stress interact at the mesoscopic scale (such as interface debonding caused by the difference in thermal expansion coefficient) lacks accurate modeling. And how the mesoscopic damage (micro-cracks) gradually evolves into macroscopic visible cracks (such as false joint expansion to slab cracking) needs to establish a quantitative correlation model.

[0032] Therefore, the following embodiments present a method and system for predicting microscopic fatigue damage in ballastless track concrete. By scanning concrete specimen slices and reconstructing the actual aggregate distribution in three dimensions, a nested macroscopic-microscopic finite element model is established, and fatigue evolution is simulated using plastic damage theory. For the local structure near the dummy joints in the track slab, a microscopic model of the beam specimen is established by scanning concrete beam specimen slices and reconstructing it in three dimensions. Based on the beam specimen model, a nested microscopic finite element calculation model for track slab fatigue damage is assembled. Aggregates are considered as elastic bodies, and concrete mortar is considered as a damaged elastoplastic body. Based on the unique vibration loading mode and fatigue damage evolution characteristics of ballastless track during operation, fatigue damage accumulation criteria and fatigue life equations are used to predict the damage status of concrete mortar components. This model can accurately predict the crack propagation path and life of the track slab under train and temperature loads, and is particularly suitable for assessing the risk of dummy joint cracking, providing technical support for the durability design of ballastless track.

[0033] Example 1: like Figure 1 As shown, a method for predicting microscopic fatigue damage in ballastless track concrete includes the following steps: The cross-sectional images of the concrete beam specimens were acquired and preprocessed. The aggregate edges were obtained through edge detection. The three-dimensional contour of the aggregate was fitted by multiple sets of cross-sectional images to generate a mesoscopic finite element model containing aggregate, paste and interface. A macroscopic finite element model of the ballastless track was constructed, and the key areas of the track slab in the model were replaced with a mesoscopic finite element model to form a macro-mesoscopic coupled model, and then meshed. In the macro-micro coupled model, the aggregate is set as an elastic body, and the slurry and interface adopt plastic damage constitutive model. Under the condition of fatigue accumulation effect, the coupled stress is determined according to different train dynamic loads and ambient temperatures. Based on the obtained coupled stress, the fatigue damage increment of each mesh element in the macro-micro coupled model is determined, and the total damage is accumulated over time. D When the total damage of a certain unit D When the value is ≥1.0, the unit fails, and the corresponding crack propagation path and fatigue life are obtained.

[0034] This scheme establishes a nested macro-micro finite element model by reconstructing the real aggregate distribution in three dimensions. It can accurately reflect the influence of the non-homogeneity inside concrete (aggregate, paste and interface transition zone) on fatigue damage evolution, and overcome the limitations of the traditional homogeneous assumption model.

[0035] This scheme combines plastic damage theory and fatigue damage accumulation criteria to simulate the fatigue damage process of concrete mortar components. It can accurately predict crack initiation, propagation path and fatigue life, and is especially suitable for assessing the risk of dummy cracks.

[0036] The scheme comprehensively considers the coupling effect of train load and environmental temperature variation, and calculates the superposition effect of fatigue stress and temperature stress through nested model, so as to more truly reflect the complex stress state of ballastless track in actual operation.

[0037] The scheme adopts local mesoscopic model to replace the key area (such as the vicinity of false joint) in macro model, significantly reduces the calculation scale while ensuring the calculation accuracy, and realizes efficient and targeted fatigue damage analysis.

[0038] The model of the scheme can quickly predict the damage state (such as false joint expansion depth and plate cracking trend) of the track slab under different operation years, and provides a scientific basis for the durability design and maintenance strategy of ballastless track, and is especially suitable for long-term performance evaluation of high-speed railway.

[0039] The scheme can be simplified as follows: S1: Constructing a fatigue damage mesoscopic model of a concrete beam specimen; S2: Constructing a fatigue damage nested mesoscopic finite element model of ballastless track; S3: Constitutive relation (plastic damage, fatigue constitutive relation); S4: Load source (train load, temperature); S5: Mesoscopic fatigue damage calculation method (considering damage of each element).

[0040] S1: Constructing a fatigue damage mesoscopic model of a concrete beam specimen.

[0041] Since the structure of ballastless track is huge, it is difficult to establish a complete mesoscopic finite element calculation model for the actual track, and it is not necessary, therefore, when the mesoscopic fatigue damage of ballastless track concrete is analyzed, the scheme is implemented in two steps.

[0042] First, a mesoscopic finite element model is established for a concrete beam specimen, and then the obtained beam specimen mesoscopic model is assembled and spliced to replace the local track slab in the macro calculation model of ballastless track, and a nested mesoscopic finite element calculation model for fatigue damage of the actual track slab is established.

[0043] In this embodiment, the size of the concrete beam specimen is 400mm×100mm×100mm, first cut along the neutral plane of the specimen to become two specimens with a size of 400mm×100mm×50mm, and then cut along the neutral plane of the two specimens to become four specimens with a size of 400mm×100mm×25mm. The four specimens have a total of eight 400mm×100mm planes, and five of them are polished (the repeated section corresponding to the cut is polished only one), and a non-contact three-dimensional structured light grating scanning device is used to scan the concrete surface.

[0044] Digital image processing was performed based on the aggregate distribution in the cross-section of the concrete beam. First, a high-resolution image of the concrete surface was acquired. Then, software (such as MATLAB) was used to perform edge detection on the aggregates in the model and smooth the aggregate edges to obtain the outer contour of the aggregates.

[0045] To reconstruct the three-dimensional model of the concrete specimen, five concrete cross-sectional images were obtained. Figure 3 Two-dimensional image features were extracted, and MATLAB software was used to perform preprocessing such as cropping, enhancement, and segmentation on the images. The commonly used threshold segmentation method was employed to separate regions with different concrete properties and to identify aggregate edge feature points.

[0046] Using finite element software (such as ANSYS) to perform 3D modeling of concrete, five sections are placed in the order of the cut positions. The 3D contour of the aggregate is constructed by parallel sections, and the smooth surface of the solid aggregate is fitted. The interpolation method is used to calculate and determine whether any given position between two 2D sections is aggregate or paste. The geometry of the aggregate can be expanded into a 3D solid, and the 3D reconstruction of the aggregate is completed. Finally, a 3D microscopic calculation model of the concrete beam specimen is generated.

[0047] In this embodiment, the thickness of the transition zone between the aggregate and the slurry interface in concrete is typically 0.01mm to 0.1mm. Considering the operability of the calculation in the model, the material interface thickness is set to 1mm. Tetrahedral elements are used for meshing the microscopic model. Generally, the fine aggregate particle size is less than 5mm, and the coarse aggregate particle size is greater than 5mm. To balance the accuracy of the model with computational efficiency, the size of the aggregate and slurry mesh elements is set to 1mm, and the size of the transition layer element is set to 0.5mm.

[0048] S2: Construct a nested micro-finite element model of fatigue damage in ballastless track.

[0049] In this embodiment, the ballastless track is selected as CRTS II type slab track. The dynamic fatigue stress calculation model of the ballastless track includes a lower foundation, a support layer, a mortar layer and a track slab arranged from bottom to top. The track slab is equipped with rails, which are connected to the track slab by fasteners. The fatigue load is transferred to the track slab through the rails.

[0050] By replacing a portion of the track slab in the model with the micro-finite element model established by S1, a micro-calculation model for fatigue damage of ballastless track can be constructed. The micro-model mainly considers the fatigue damage characteristics of cement-based materials, which can be used to calculate and analyze the micro-evolution of fatigue damage of track slabs under train load and environmental temperature change.

[0051] On the basis of the calculation and verification of the three-dimensional mesoscopic modeling of the concrete beam specimen, a three-dimensional ballastless track fatigue damage nested mesoscopic finite element analysis model is established considering the constitutive relationship of concrete plastic fatigue damage. In order to eliminate the boundary effect, the length of the model is 5 track slabs. A key analysis mesoscopic finite element section with a length of 400 mm (the length of the aforementioned concrete beam specimen), a width of 1275 mm (half the width of the track slab), and a thickness of 200 mm (the thickness of the track slab) is set on the track slab directly below the stress point of the center rail of the model. The center of the section contains a preset false joint on the upper surface of the track slab. For the sake of simplifying the calculation, the cross section of the false joint is regarded as an inverted triangle during modeling.

[0052] In this embodiment, the track slab mesoscopic analysis section 400 mm x 1275 mm x 200 m is spliced from the aforementioned three-dimensional mesoscopic reconstruction model of the 400 mm x 100 mm x 100 m concrete specimen. In the 400 mm long track slab section, 13 400 mm x 100 mm x 100 m specimens are placed in two rows, one above the other. It is noted that the contact surfaces of the two specimens in the upper and lower rows and the two adjacent specimens in the same row are the same surface to ensure the continuity of the concrete mesoscopic structure model. The width of 25 mm of the extra specimens on the edge is cut off, and thus a concrete three-dimensional mesoscopic structure that is symmetrical about the horizontal neutral plane of the track slab and circulates 6 times along the lateral direction of the track slab is formed in the track slab mesoscopic modeling section.

[0053] In order to reduce the calculation scale, the macroscopic mechanical model is used to describe the remaining area of the ballastless track except the track slab mesoscopic modeling section. The model is composed of rails, fasteners, track slabs, wide-narrow joints, longitudinal reinforcement, mortar layers, supporting layers, and lower foundations. The rails are simulated by beam elements, the track slabs, wide-narrow joints, mortar, and supporting layers are simulated by solid elements, and the reinforcement is simulated by bar elements.

[0054] The rails are divided into 4 beam elements per span with fastener spacing as the unit, and the unit size is 0.1625 m. In order to make the macroscopic model and the mesoscopic model fit each other, all solid models are divided by tetrahedral elements, and the unit size of the track slab and the supporting layer is 50 mm, the unit size of the wide-narrow joint is 10 mm, the unit size of the mortar is 5 mm, and the unit size of the aggregate and the paste is 1 mm. At the macro-mesoscopic boundary of the model, i.e., the boundary of the macro-mesoscopic section on the track slab and the boundary between the track slab mesoscopic section and the lower mortar, the mutual correspondence of the nodes is considered to realize the reasonable and effective nesting of the mesoscopic model in the macroscopic model.

[0055] The fatigue damage nested mesoscopic finite element model of the ballastless track is used to calculate the concrete fatigue mesoscopic evolution. The original macroscopic model is replaced by the nested mesoscopic model established in this step, and the local material constitutive change process is considered.

[0056] Train load is the loading mode of track geometry irregularity excitation, 8 sets of 350 km / h speed of EMU, operation time 6:30~23:30 every 10 minutes a train. Environmental temperature change is the track slab temperature daily variation curve obtained by monthly average standardization processing according to the measured data of the high-speed rail temperature of a certain line throughout the year. The train load and environmental temperature change are applied to the nested mesoscopic model, the fatigue stress of the track slab can be calculated, and the fatigue damage mesoscopic evolution of the track slab can be calculated and analyzed by using the dynamic fatigue damage calculation method of ballastless track.

[0057] S3: Local concrete meso-constitutive of track slab.

[0058] 1. Plastic damage. In order to more effectively simulate the mesoscopic evolution of fatigue damage of ballastless track concrete, the concrete plastic damage theory is adopted to assign the plastic damage constitutive to the concrete. In the calculation model, the aggregate is simulated as an elastic body, and the paste and material interface are described by the plastic damage model. The detailed mechanical parameters of the concrete mesoscopic components are shown in Table 1.

[0059] Table 1 Mechanical parameter values of concrete beam specimen mesoscopic components

[0060] The concrete plastic damage model simulates the performance degradation of concrete by introducing a damage factor, and the fatigue damage variable is used to represent the damage degree of the material in the fatigue loading process. Due to the difference in mechanical behavior of concrete structure under tensile and compressive load, the material has two failure mechanisms of tensile cracking and compression crushing. The tensile and compressive properties of the material are defined as shown in Figure 5 and 6 .

[0061] When the material enters the unloading softening section, the damage variable D can be used to represent the stiffness degradation, and the constitutive relationship is: ; ; In the formula, , is the tensile and compressive stress of the material; , is the tensile and compressive strain of the material; , is the equivalent plastic strain of the material tensile and compressive; is the initial elastic modulus of the material.

[0062] In the concrete plastic damage constitutive, the parameter relationship of material damage variable D and nonlinear strain , needs to be input. The parameters are obtained by Figure 5 andFigure 6 It is known that, , and , The relationship can be expressed as: ; ; In the formula, D is expressed as a fatigue damage factor, which is determined by the fatigue constitutive equation.

[0063] 2. Fatigue constitutive equation. According to the concrete single-logarithmic fatigue equation: ; In the formula, S i is the fatigue stress level, i.e. the ratio of the maximum stress to the flexural strength: σ max,i / σ k,0 ; R i is the stress cycle ratio, i.e. the ratio of the maximum stress to the minimum stress, σ min,i / σ max,i ; N f,i is the number of cycles at the time of fatigue failure; a , b is a coefficient determined by fatigue tests, and is taken as a = 1.0, b = 0.06110112; σ k,0 is the flexural strength of the concrete under static load.

[0064] The damage accumulation degree of ballastless track concrete during fatigue loading is characterized by the fatigue damage variable D According to the P-M criterion, the damage degree under various amplitude fatigue loads is shown in the following formula: ; In the formula, N i is the number of times of the current fatigue load; Nf ,i is the fatigue life value corresponding to the current stress level; i is the fatigue stress level.

[0065] S4: Load source (train load, temperature).

[0066] 1. Train Load. Based on the fundamental principles of structural dynamics, a dynamic calculation method for ballastless track under moving excitation is established. The CRTS II type slab track is simplified as a double-layer composite beam on an elastic foundation, such as... Figure 7 As shown in the model, the rails and track slabs are simplified as homogeneous Euler beams with uniform cross-sections. The vibration effects of various parts of the track under the track slab are ignored, and the fasteners, mortar, and lower supports are simplified as uniformly distributed springs and dampers. The train load is simplified as a vibration load moving at high speed along the rails. Based on the principle of superposition of wheelset actions, the force characteristics of the track structure when multiple wheelsets pass can be obtained after calculating the action of a single wheelset.

[0067] Under the excitation of high-speed moving train load, the vibration equations of the rail and track slab can be expressed as: ; ; In the formula, , This refers to the vertical displacement of the rails and track slabs. , The bending stiffness of the two rails and the track slab; , The mass per unit length distributed between the two rails and the track slab; , Distributed damping for the fasteners and the under-plate support; , This refers to the distributed stiffness between the fastener and the lower support of the track slab. This is the Dirac function.

[0068] The load is based on speed Amplitude , frequency is The moving harmonic load. The stiffness of the support under the track slab is calculated by considering the equivalent stiffness of the mortar layer, support layer, and lower foundation.

[0069] The above equation is transformed by Fourier transform into: ; ; In the formula, is the wave number, which is the frequency domain abscissa corresponding to the spatial coordinate x; Frequency represents the time coordinate. t The frequency domain abscissa.

[0070] Solving the above equations simultaneously, we get: ; ; The function in the formula f(ξ, ω) It can be represented as: ; The above formula shows that when =0, the displacement tends to infinity, and the orbit is in a critical state of resonance, thus the critical speed and wave number of the orbit can be determined and the corresponding relationship of frequency ω .

[0071] The simultaneous equations are inverse Fourier transformed, and the time history of the displacement of the rail and the track slab under the excitation of the high-speed moving train is obtained, which is expressed as: ; .

[0072] The displacement distribution of the rail and the track slab under the excitation of the moving train load is obtained by solving the above formula. According to the normal stress calculation method of the flexural beam, the relationship between the stress of the track slab and the train speed under different train speeds is obtained. According to the stress equivalence criterion, the track load spectrum when a vehicle passes at a speed of 350 km / h under the excitation of the moving train load is calculated based on the stress at a certain position on the rail.

[0073] To determine the influence of the high-speed moving excitation of the train on the dynamic characteristics of the ballastless track, the dynamic stress on the track slab is taken as an example for calculation and analysis. The common train speed is taken. Since this scheme only considers the high-speed moving effect of the train load, the influence of the train vibration will be considered in the following track irregularity excitation, and the wheel load action frequency =0 is taken, and the variation of the dynamic stress of the track slab is shown in Figure 8 .

[0074] The results show that under the high-speed moving action of the train load, the influence range of one bogie on the track slab has a linear relationship with the train speed.

[0075] The high-speed moving excitation of the train has a certain influence on the dynamic stress amplitude of the track slab. The relationship between the dynamic stress amplitude of the track slab and the train speed under the high-speed moving excitation of the train is shown in Figure 9 .

[0076] As can be seen from Figure 9 , the dynamic stress of the track slab has a positive growth relationship with the train speed. When the train speed is low, the dynamic stress grows slowly, and when the train speed approaches the critical speed, the dynamic stress of the track slab rises rapidly.

[0077] Therefore, under the current operating train speed conditions, the influence of the moving excitation effect of the train on the dynamic amplitude of the ballastless track is small, and it can usually be ignored.

[0078] 2. Temperature. Statistical analysis was performed using measured temperature data from the track slab over a full year. The analysis focused on the upper, middle, and lower surfaces of the track slab. The annual temperature distribution of the track slab was obtained as follows: Figure 10 As shown, the track slab temperature exhibits a variation pattern with a base value on an annual cycle and an amplitude on a daily cycle. The results indicate that the temperature variation amplitude of each layer of the track slab gradually decreases with depth, and the extreme values ​​appear with a lag. Therefore, with increasing depth, the time of occurrence of the track slab temperature extreme values ​​gradually lags.

[0079] In a temperature monitoring test of the ballastless track of a high-speed railway, the daily average temperature variation of the track slab showed a similar amplitude pattern each month. The monthly temperature differences were mainly due to changes in the overall baseline value. The monthly temperature curves could all be fitted as periodic functions. ; In the formula, T The temperature of the track slab is expressed in °C. t Time is measured in hours (h). T m This represents the average plate temperature for each month.

[0080] The monthly average plate temperature variation is mainly affected by changes in the monthly average air temperature. The plate temperature is determined by the difference between the monthly average air temperature and the plate temperature. T m The relationship with air temperature is used to construct the daily average temperature variation curve of the track slab, as shown in the following formula.

[0081] ; In the formula, T e Ambient temperature, in °C; T o The average difference between the track slab temperature and the air temperature for each month is used as the basis. Based on the daily average air temperature variation curve, the pattern of track slab temperature variation is predicted, and a comparative analysis is performed with the daily average track temperature variation curve. The results show that the track slab temperature predicted based on meteorological data has a good agreement with the daily average track temperature variation curve divided by month. Therefore, given the local monthly average air temperature, rapidly predicting the track slab temperature variation curve provides a convenient way to analyze the stress pattern and fatigue characteristics of track slabs under the influence of environmental temperature changes.

[0082] S5: Calculation method for fine-grained fatigue damage (the calculation process considers damage assessment of each individual unit), such as... Figure 25 As shown, it includes the following steps: (1) Apply loads and determine the stress field in the mesoscopic part; (2) Substitute the stress corresponding to each element into the fatigue life equation and fatigue damage accumulation criterion, define the damage for each element, and calculate the fatigue damage variable for each element. (3) Determine the impact of damage evolution on the track slab material parameters, and modify the material properties of each unit according to the damage situation of each unit; (4) Iterative calculation is performed to determine the change process of fatigue damage variable with the number of times it is applied.

[0083] (1) Apply load and determine the stress field of the mesoscopic part.

[0084] The fatigue load spectrum acting on the rails when the vehicle passes is applied to... Figure 4 In the calculation model, the fatigue stress of the track slab under train load is obtained, and the stress amplitude of the track slab under train load is determined; the first... n Year m moon t Temperature load on track slab at any given time (i.e., daily temperature variation curve of track slab) t =6:30~23:30, and assuming the plate temperature is constant within 1 hour), the temperature stress is used as the base value and superimposed with the equivalent fatigue stress spectrum under train load to obtain the first n Year m moon t The fatigue stress baseline and amplitude of the track slab under the combined effects of train load and ambient temperature changes are determined. Assuming a constant stress spectrum caused by trains over a year and uniform daily temperature stress variations within the track slab over a month, the stress field (tensile and compressive stress) is obtained. Figures 11-24 As shown in the figure, the horizontal and vertical axes represent the 400×200mm analysis area taken from the side of the track slab. The track slab dimensions are 6500×2550×200mm, and the side dimension is 2550×200mm. The analysis area of ​​400×200mm was taken from the side.

[0085] (2) Substitute the stress corresponding to each element into the fatigue life equation and fatigue damage accumulation criterion, define the damage for each element, and calculate the fatigue damage variable for each element.

[0086] Determine the first i Fatigue life of each unit under level loading mode N f,i Then determine the first i Level loading effect ΔN i Each subsequent unit ΔD i (Each unit in the first) i (damage increment during loading), and superimposed. ΔD i Determine the load effects at each level when a vehicle passes by at time t in month m of year n. ΔN i Each subsequent unit ΔD The increment of fatigue damage variable for each unit when a train passes by.ΔDl =8 ΔD , the damage variable increment of each unit in one hour is ΔD h =6 ΔD l , respectively superimposed t = 6:30-7:30, 7:30-8:30… 22:30-23:30 each unit of ΔD h (total 17 periods), the damage variable increment of each unit in a day is ΔD d , the damage variable increment of each unit in a month is ΔD m =30 ΔD d , respectively superimposed 1~12 months each unit of ΔD m (total 12 months), the damage variable increment of each unit in a year is ΔD n , the damage variable of each unit in the calculation year is finally determined D=ΣΔD n .

[0087] (3) Determine the influence of damage evolution on the material parameters of the track slab. Modify the material properties for each unit according to its damage condition.

[0088] Determine the stiffness and strength of each unit of the track slab micro part according to the D , change the material properties of the track slab in the calculation model at an interval of one year, simulate the material degradation in the fatigue loading process, and recalculate the fatigue load spectrum of a vehicle acting on the rail.

[0089] (4) Determine the change process of fatigue damage variable with loading times by iterative calculation.

[0090] Repeat steps (1)~(3) to iteratively calculate the fatigue damage variable of each unit of the track slab under subsequent loading, and determine the change process of the fatigue damage variable with loading times. When a certain unit D =1.0, it means that damage has occurred in that unit.

[0091] The part of each unit D =1.0 indicates the damage area.

[0092] Verify the accuracy of the scheme by investigating the actual engineering conditions.

[0093] The investigation of a section of Ⅱ type slab track in a certain area which has been in operation for 10 years shows that the damage modes of the track slab mainly include false joint cracking, vertical cracks on the bottom of the slab, interface cracks at wide-narrow joints, etc. The proportion of false joint cracking is as high as 53.7%, which mainly concentrates in the bridge section and the roadbed section. The track slab in the tunnel is less affected by environmental temperature variation and has no obvious damage. It can be preliminarily judged that the crack damage of the track slab is mainly caused by temperature load and less affected by train load.

[0094] Therefore, the mesoscopic model considers the effects of train load and environmental temperature variation in the bridge section, and only considers the effect of train load in the tunnel section. Through the simulation calculation of the mesoscopic model, the distribution of the fatigue damage variable D of the track slab in the bridge section and the tunnel section after 10 years of operation is shown in Figure 15 and Figure 16 .

[0095] Figure 15 and Figure 16 The "yellow" area in the mesoscopic calculation result cloud map represents the case where the fatigue damage variable is 1.0, indicating that the concrete at this position has reached the fatigue failure state. Figure 15 It is shown that, at the time of 10 years of operation, there is a local area with a damage variable of 1.0 and a depth of 2 cm at the surface false joint of the track slab in the bridge section, indicating that the false joint has expanded by about 2 cm. The fatigue damage variable of the lower surface of the track slab has also reached 1.0 at multiple positions in the aggregate gap, indicating that the local damage of the lower surface of the track slab has begun to develop and multiple potential cracking paths have appeared, extending from the lower surface of the track slab to the inside, with an expansion depth of about 2 cm.

[0096] Figure 16 It is shown that, at the time of 10 years of operation, there is no obvious area with a fatigue damage variable of 1.0 at the surface false joint of the track slab in the tunnel section, indicating that there is no obvious crack expansion. The maximum fatigue damage variable value of the lower surface of the track slab is only 0.3, indicating that the track slab in the tunnel section has no obvious fatigue damage.

[0097] Under the action of train load considering only track irregularity excitation, the fatigue damage variable D near the false joint of the track slab is calculated, and the distribution after 10 years, 30 years, 60 years, and 120 years of operation is shown in Figures 17-19 .

[0098] Figure 17 and Figure 18 It is shown that, under the action of train load, the false joint can accelerate the development of fatigue damage in the lower part of the track slab, and the final failure mode of the track slab is cracking in the lower part and cracking in the upper false joint.

[0099] After 10 years of operation, the track slab has almost no fatigue damage, and the false joint tip D has a small value, indicating that the false joint will not crack at this time.

[0100] Within 30 years of operation, except for the false joint tip D , the rest of the distribution has a small value of 1.0 D , and the distribution is similar to the case where the false joint is ignored.

[0101] When the operation reaches the design life of 60 years, the false joint has shown obvious cracking, and the false joint has expanded about 2cm; due to the cracking of the false joint, the stress on the lower surface of the track slab has increased locally, and the value of the lower part of the track slab D has increased to a large extent.

[0102] When the operation life reaches 120 years, the track slab has obvious fatigue damage, the false joint has expanded about 4cm, and the part of the track slab D with a value of 1.0 has occupied the majority, D The distribution is significantly different from the case where the false joint is ignored, and the lower part D with a value of 1.0 has developed to a position of 1 / 3 of the thickness of the slab, which can be determined as the final fatigue damage mode.

[0103] Under the combined action of train load and temperature, the distribution of damage variables D of the track slab with false joints after 10 years, 20 years, 30 years, and 60 years of operation is shown in Figures 20-23 .

[0104] The results show that under the combined action of train and temperature, the expansion rate of the false joint increases, and the final damage mode of the track slab with false joints is the through cracking of the false joint and the cracking of the upper and lower parts of the slab.

[0105] After 10 years of operation, the false joint has expanded about 2cm, and after 20 and 30 years of operation, the false joint will expand 4cm and 5cm respectively. When the operation life reaches the design life of 60 years of ballastless track, the false joint has expanded to the lower surface of the track slab to form a through crack, and due to the through of the false joint, the stress on the slab is partially released, D the value of which decreases to a certain extent.

[0106] Example Two A ballastless track concrete mesoscopic fatigue damage system, comprising: A mesoscopic modeling module configured to: acquire a cross-sectional image of a concrete beam specimen and preprocess, acquire aggregate edges through edge detection, fit aggregate three-dimensional contours through multiple groups of cross-sectional images, and generate a mesoscopic finite element model containing aggregate, paste, and interfaces; The macro-micro coupled modeling module is configured to: construct a macro-finite element model of the ballastless track, replace the key areas of the track slab with a micro-finite element model to form a macro-micro coupled model, and divide the model into mesh elements; The material constitutive and load module is configured to: treat the aggregate in the macro-micro coupled model as an elastic body, and adopt plastic damage constitutive model for the slurry and interface. Under the condition of fatigue accumulation effect, the coupled stress is determined according to different train dynamic loads and ambient temperature. The fatigue damage calculation module is configured to: determine the fatigue damage increment of each mesh element in the macro-micro coupled model based on the obtained coupled stress, and accumulate the total damage over time. D When the total damage of a certain unit D When the value is ≥1.0, the unit fails, and the corresponding crack propagation path and fatigue life are obtained.

[0107] By reconstructing the real aggregate distribution in three dimensions and establishing a nested macro-micro finite element model, the influence of internal non-homogeneity (aggregate, paste and interface transition zone) of concrete on fatigue damage evolution can be accurately reflected, overcoming the limitations of the traditional homogeneous assumption model.

[0108] Combining plastic damage theory and fatigue damage accumulation criteria, the fatigue damage process of concrete mortar components is simulated, which can accurately predict crack initiation, propagation path and fatigue life, and is especially suitable for risk assessment of dummy cracks.

[0109] Taking into account the coupling effect of train load and environmental temperature change, the superposition effect of fatigue stress and temperature stress is calculated by nested model, which more realistically reflects the complex stress state of ballastless track in actual operation.

[0110] By replacing key areas in the macroscopic model (such as near the dummy joint) with a local microscopic model, the computational scale is significantly reduced while maintaining computational accuracy, thus enabling efficient and targeted fatigue damage analysis.

[0111] It can quickly predict the damage status of track slabs under different operating years (such as the depth of dummy joint expansion and the cracking trend of the slab), providing a scientific basis for the durability design and maintenance strategy of ballastless track, and is especially suitable for the long-term performance evaluation of high-speed railways.

[0112] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for predicting microscopic fatigue damage in ballastless track concrete, characterized in that, Includes the following steps: The cross-sectional images of the concrete beam specimens were acquired and preprocessed. The aggregate edges were obtained through edge detection. The three-dimensional contour of the aggregate was fitted by multiple sets of cross-sectional images to generate a mesoscopic finite element model containing aggregate, paste and interface. A macroscopic finite element model of the ballastless track was constructed, and the key areas of the track slab in the model were replaced with a mesoscopic finite element model to form a macro-mesoscopic coupled model, and then meshed. In the macro-micro coupled model, the aggregate is set as an elastic body, and the slurry and interface adopt plastic damage constitutive model. Under the condition of fatigue accumulation effect, the coupled stress is determined according to different train dynamic loads and ambient temperatures. Based on the obtained coupled stress, the fatigue damage increment of each mesh element in the macro-micro coupled model is determined, and the total damage is accumulated over time. When the total damage of a certain element exceeds a set value, the element fails, and the corresponding crack propagation path and fatigue life are obtained.

2. The method for predicting microscopic fatigue damage of ballastless track concrete as described in claim 1, characterized in that, To obtain cross-sectional images of concrete beam specimens, the following steps are taken: a number of concrete beam specimens are prepared, and cross-sections are performed along the neutral plane of the specimens. The resulting planes are then ground and polished. The polished surfaces are then scanned using a three-dimensional structured light grating scanning device to obtain cross-sectional images.

3. The method for predicting microscopic fatigue damage of ballastless track concrete as described in claim 1, characterized in that, The obtained cross-sectional images are preprocessed, and edge detection is performed based on the threshold segmentation method to obtain aggregate edge feature points. Based on finite element software, multiple sets of cross-sectional images are combined to construct the three-dimensional contour of the aggregate, fit the surface of the solid aggregate, and determine the solid between the cross-sections based on the interpolation method to realize the three-dimensional reconstruction of the aggregate and generate a mesoscopic finite element model containing aggregate, slurry and interface.

4. The method for predicting microscopic fatigue damage of ballastless track concrete as described in claim 1, characterized in that, The macroscopic finite element model of ballastless track includes a lower foundation, a support layer, a mortar layer, and a track slab arranged from bottom to top. The track slab is equipped with rails, which are connected to the track slab by fasteners. Fatigue loads are transferred to the track slab through the rails. The area where the dummy joint is located is selected on the track slab, and the area corresponding to the specimen length in this area is selected as the mesoscopic finite element section to replace the mesoscopic finite element model.

5. The method for predicting microscopic fatigue damage of ballastless track concrete as described in claim 1, characterized in that, fatigue damage variables D The degree of damage accumulation in ballastless track concrete during fatigue loading is characterized by the following formula: ； In the formula, N i This represents the number of times the current fatigue load has been applied. Nf ,i This represents the fatigue life value corresponding to the current stress level. i This represents the fatigue stress level.

6. The method for predicting microscopic fatigue damage of ballastless track concrete as described in claim 1, characterized in that, The coupled stress is determined based on different train dynamic loads and environmental temperature changes. This includes constructing the vibration equations of the rails and track slabs under high-speed train load excitation, and determining the critical track speed and wave number through Fourier transform and simultaneous processing. With frequency The corresponding relationship was further determined to determine the displacement distribution of the rails and track slabs under the excitation of high-speed train movement; based on the normal stress calculation method of the bending beam, the relationship between the stress of the track slab and the train speed under different train speeds was obtained.

7. The method for predicting microscopic fatigue damage of ballastless track concrete as described in claim 1, characterized in that, The coupling stress is determined based on different train dynamic loads and environmental temperature changes. Specifically, the fatigue load spectrum acting on the rail when the vehicle passes is applied to the macro-micro coupling model to obtain the fatigue stress of the track slab under the train load and determine the stress amplitude of the track slab under the train load. Apply the first m moon t The temperature load on the track slab at any given time is used as a baseline value. This temperature stress is then superimposed on the equivalent fatigue stress spectrum under train load to obtain the first... m moon t The fatigue stress baseline and amplitude of the track slab under the combined action of train load and environmental temperature change at any time are determined; assuming that the stress spectrum of the track slab caused by the train is constant within a set period and the temperature stress change within the track slab is the same, the stress field is obtained.

8. The method for predicting microscopic fatigue damage of ballastless track concrete as described in claim 1, characterized in that, Determine the fatigue damage increment of each mesh element in the macro-micro coupling model, specifically: determine the... i The fatigue life of each unit under the first loading mode, and the fatigue life of the second loading mode. i Level loading effect ΔN i The fatigue damage increment of each unit is then superimposed to determine the load levels at a given moment when the train passes by, by summing the corresponding damage increments. ΔN i The increase in fatigue damage per unit after a certain number of cycles.

9. The method for predicting microscopic fatigue damage of ballastless track concrete as described in claim 1, characterized in that, Cumulative total damage over time D Specifically, the fatigue damage increment of each unit at different times is superimposed to obtain the fatigue damage increment of each unit in daily and monthly data, and then the annual fatigue damage variable of each unit is determined.

10. A system for predicting microscopic fatigue damage in ballastless track concrete, characterized in that, include: The micro-modeling module is configured to: acquire and preprocess cross-sectional images of concrete beam specimens, obtain aggregate edges through edge detection, fit the three-dimensional contour of aggregates through multiple sets of cross-sectional images, and generate a micro-finite element model containing aggregates, paste and interfaces. The macro-micro coupled modeling module is configured to: construct a macro-finite element model of the ballastless track, replace the key areas of the track slab with a micro-finite element model to form a macro-micro coupled model, and divide the model into mesh elements; The material constitutive and load module is configured to: treat the aggregate in the macro-micro coupled model as an elastic body, and adopt plastic damage constitutive model for the slurry and interface. Under the condition of fatigue accumulation effect, the coupled stress is determined according to different train dynamic loads and ambient temperature. The fatigue damage calculation module is configured to: determine the fatigue damage increment of each mesh element in the macro-micro coupled model based on the obtained coupled stress, and accumulate the total damage over time. When the total damage of a certain element exceeds a set value, the element fails, and the corresponding crack propagation path and fatigue life are obtained.

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