A method for testing rail corrosion fatigue behavior based on corrosion-fatigue coupling and multi-scale characterization

Abstract

This invention discloses a method for testing the corrosion fatigue behavior of rails based on corrosion-fatigue coupling and multi-scale characterization. The method includes: extracting fatigue specimens from heat-treated rail materials, preferably from half the height of the rail head, and mechanically polishing the surface; constructing a locally sealed corrosion environment, the corrosion environment chamber being made of transparent acrylic material, equipped with a liquid level observation window and upper and lower through holes penetrating the specimen; installing the specimen in a high-frequency fatigue loading testing machine; starting the corrosion fatigue test, recording fatigue life data in real time and plotting the S-N curve; interrupting the test at a set stage before the specimen completely fractures, and extracting the crack initiation region; and using SEM, EBSD, and three-dimensional confocal microscopy to perform multi-scale characterization of the crack path and microstructure evolution. This method achieves synchronous coupling between corrosion and fatigue loading, and through staged interruption of the test combined with multi-scale characterization, dynamically tracks the entire process of crack initiation, propagation, and failure.

Description

Technical Field

[0001] This invention belongs to the field of service performance testing technology for metallic materials, and particularly relates to a method for testing the corrosion fatigue behavior of rails based on corrosion-fatigue coupling and multi-scale characterization. Background Technology

[0002] The large-scale construction of high-speed railways has made the service environment of rails increasingly complex. Long-term exposure to corrosive media such as Cl⁻ ions, SO₄²⁻ ions, and water vapor under conditions of coastal environments, high humidity, and water accumulation in tunnels leads to pitting and cracking on the rail surface. Combined with the frequent alternating loads of high-speed trains, corrosion fatigue has become one of the main failure modes of rails. Existing studies mostly employ simple static corrosion + fatigue loading methods, lacking the ability to reproduce the coupling effect of corrosion and load under real service conditions. Furthermore, traditional methods often only obtain fatigue life endpoint data and cannot dynamically track the initiation and propagation process of cracks, which limits the elucidation of the corrosion fatigue mechanism.

[0003] Existing research methods for studying the corrosion fatigue performance of rails mainly fall into two categories: One type employs a test method that simultaneously applies corrosion environment and fatigue loading, evaluating fatigue performance by obtaining the SN curve of the material in the corrosion environment. However, this type of method typically only focuses on the final fatigue life or fatigue limit, and the test cannot be interrupted, making it difficult to obtain key evolutionary information during crack initiation and propagation, and thus failing to reveal the formation mechanism of corrosion fatigue damage. The other type of method uses a stepwise testing approach, where corrosion precedes fatigue, for example, artificially creating pitting on the sample surface using electrochemical methods before fatigue performance testing. While this method can study the impact of corrosion on fatigue performance to some extent, the corrosion process and fatigue loading are independent, failing to truly reflect the dynamic coupling effect of corrosion and alternating loads in actual service, leading to insufficient understanding of the corrosion fatigue mechanism and consequently affecting the accuracy of life prediction models. Therefore, there is an urgent need to develop a testing method that can realistically simulate the service environment, achieve corrosion-fatigue coupled loading, and perform multi-scale dynamic characterization of the entire crack process, providing a scientific basis for rail design optimization, maintenance strategy formulation, and life prediction. Summary of the Invention

[0004] The purpose of this invention is to provide a method for testing the corrosion fatigue behavior of rails based on corrosion-fatigue coupling and multi-scale characterization. By simulating the actual service corrosion environment and coupling it with a high-frequency fatigue loading device, the synchronous coupling effect of corrosion and fatigue load is achieved. Through staged interruption tests combined with multi-scale characterization methods, the entire process of crack initiation, propagation, and failure is dynamically tracked. This method allows for multiple interruptions during the experiment, extracting samples from crack initiation zones at different stages, and characterizing them using techniques such as SEM, EBSD, and three-dimensional confocal microscopy to obtain systematic data on macroscopic morphology, microstructure, and crack propagation paths. This not only helps in establishing corrosion fatigue life prediction models but also provides experimental basis for material modification and protective design.

[0005] To solve the above-mentioned technical problems, the present invention adopts the following technical solution:

[0006] This invention discloses a method for testing the corrosion fatigue behavior of rails based on corrosion-fatigue coupling and multi-scale characterization, comprising the following steps:

[0007] (1) Sample preparation: Fatigue samples are cut from the heat-treated rail material, preferably from 1 / 2 height of the rail head, and the surface is mechanically polished to eliminate residual stress and surface defects.

[0008] (2) Constructing a localized controllable corrosion environment: A localized sealed corrosion environment box is set up outside the working section of the sample. A corrosion solution containing chloride ions, preferably 3.5 wt.% NaCl solution, with a pH of 6.9-7.1, is added to the environment box to make the sample in a controllable corrosion environment. The corrosion environment box is made of transparent acrylic material and has a liquid level observation window and upper and lower through holes that penetrate the sample.

[0009] (3) Corrosion-fatigue synchronous coupling loading: The specimen is installed in a high-frequency fatigue loading test machine and an alternating load is applied under the action of a corrosive environment so that the corrosion process and fatigue loading are carried out synchronously. The loading waveform is a sine wave, the stress ratio R=0.1, and the loading frequency is 50~150 Hz.

[0010] (4) Real-time recording of test data: Start the corrosion fatigue test, record fatigue life data in real time and plot the SN curve;

[0011] (5) Staged interruption test: Before the specimen is completely broken, the test is interrupted multiple times according to the preset number of cycles or crack propagation stage to obtain specimens at different damage stages.

[0012] (6) Multiscale characterization analysis: Multiscale analysis of the interrupted sample, including SEM, EBSD and three-dimensional confocal microscopy.

[0013] Furthermore, the pH is 7.

[0014] Furthermore, the bottom of the corrosive environment chamber is sealed with waterproof tape to prevent solution leakage, and the solution temperature and flow state can be adjusted according to the test requirements.

[0015] Furthermore, the fatigue loading system has a maximum load of not less than 50 kN and is equipped with automatic shutdown and data backup functions.

[0016] Furthermore, after fatigue interruption, the location of crack initiation was reconstructed in three dimensions to obtain the crack initiation angle, pit morphology, and distribution characteristics.

[0017] Furthermore, a graded loading method was used to gradually reduce the stress level to obtain the corrosion fatigue limit under different stress conditions.

[0018] Furthermore, this method achieves synchronous coupling between corrosion and fatigue load, and dynamically tracks the entire process of crack initiation, propagation, and failure through staged interruption tests combined with multi-scale characterization methods.

[0019] Compared with the prior art, the beneficial technical effects of the present invention are as follows:

[0020] This invention provides a controllable and repeatable multi-scale testing method for rail corrosion fatigue. By simulating the actual service corrosion environment and coupling it with a high-frequency fatigue loading device, the method achieves synchronous coupling between corrosion and fatigue load. Through staged interruption tests combined with multi-scale characterization techniques, it dynamically tracks the entire process of crack initiation, propagation, and failure. The method allows for multiple interruptions during the test, extracting samples from crack initiation zones at different stages, and characterizing them using techniques such as SEM, EBSD, and three-dimensional confocal microscopy to obtain systematic data on macroscopic morphology, microstructure, and crack propagation paths. This not only helps in establishing corrosion fatigue life prediction models but also provides experimental basis for material modification and protective design. Attached Figure Description

[0021] The present invention will be further described below with reference to the accompanying drawings.

[0022] Figure 1 This is a schematic diagram illustrating the specific implementation process of the present invention. Detailed Implementation

[0023] In recent years, the construction and operation scale of China's high-speed railways has continued to expand, with train speeds generally increasing to 300 km / h or even higher. As the core load-bearing component of the track structure, the service safety and lifespan of the rails directly affect operational safety and maintenance costs. U75V rails, commonly used in high-speed railway lines, possess high strength, high toughness, and excellent wear resistance. However, when serving in complex environments such as coastal high-salt spray, humid and hot atmospheres, tunnel water seepage, and cold and snowy conditions, they are exposed to various corrosive media for extended periods, especially in environments containing chloride ions (Cl⁻), making them highly susceptible to the nucleation and expansion of localized corrosion pits.

[0024] The presence of corrosion pits creates stress concentration sources on the metal surface. Under alternating dynamic loads, this accelerates crack initiation and propagation, leading to corrosion fatigue failure. This failure mechanism is the result of the synergistic effect of corrosion chemical reaction and cyclic stress, and has the following characteristics: (1) High environmental sensitivity: Chloride ions destroy the passivation film on the metal surface, exposing fresh metal and accelerating anodic dissolution; (2) Significant stress concentration effect: Corrosion pits and changes in surface roughness cause local stress increase; (3) Shortened crack initiation cycle: Stress and corrosion reaction promote each other, significantly advancing the early crack initiation stage; (4) High propagation rate: Corrosion products accumulate along the crack tip, changing the local electrochemical environment and further accelerating crack propagation.

[0025] U75V steel rail material was selected, and the test was conducted according to the above method. The corrosive environment used was a 3.5 wt.% NaCl solution, the temperature was controlled at 25℃, and the loading frequency was set to 100 Hz. During the test, the temperature was increased to 10℃. 4 10 5 10 6 The cycle count was interrupted periodically to obtain samples at different stages. SEM observation revealed that cracks preferentially initiate at the corrosion pits, and with increasing cycles, the cracks gradually propagate and form the main crack. EBSD analysis showed that the crack propagation path is closely related to grain orientation, and corrosion accelerates grain boundary weakening. Compared to traditional continuous testing methods, this method can clearly reveal the entire process of crack initiation and propagation.

[0026] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made by those skilled in the art to the technical solutions of the present invention without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.

Claims

1. A method for testing the corrosion fatigue behavior of rails based on corrosion-fatigue coupling and multi-scale characterization, characterized in that, Includes the following steps: (1) Sample preparation: Fatigue samples are cut from the heat-treated rail material, preferably from 1 / 2 height of the rail head, and the surface is mechanically polished to eliminate residual stress and surface defects. (2) Constructing a localized controllable corrosion environment: A localized sealed corrosion environment box is set up outside the working section of the sample. A corrosion solution containing chloride ions, preferably 3.5 wt.% NaCl solution, with a pH of 6.9-7.1, is added to the environment box to make the sample in a controllable corrosion environment. The corrosion environment box is made of transparent acrylic material and has a liquid level observation window and upper and lower through holes that penetrate the sample. (3) Corrosion-fatigue synchronous coupling loading: The specimen is installed in a high-frequency fatigue loading test machine and an alternating load is applied under the action of a corrosive environment so that the corrosion process and fatigue loading are carried out synchronously. The loading waveform is a sine wave, the stress ratio R=0.1, and the loading frequency is 50~150 Hz. (4) Real-time recording of test data: Start the corrosion fatigue test, record fatigue life data in real time and plot the SN curve; (5) Staged interruption test: Before the specimen is completely broken, the test is interrupted multiple times according to the preset number of cycles or crack propagation stage to obtain specimens at different damage stages. (6) Multiscale characterization analysis: Multiscale analysis of the interrupted sample, including SEM, EBSD and three-dimensional confocal microscopy.

2. The method for testing the corrosion fatigue behavior of rails based on corrosion-fatigue coupling and multi-scale characterization according to claim 1, characterized in that, The pH is 7.

3. The method for testing the corrosion fatigue behavior of rails based on corrosion-fatigue coupling and multi-scale characterization according to claim 1, characterized in that, The bottom of the corrosive environment chamber is sealed with waterproof tape to prevent solution leakage, and the solution temperature and flow state can be adjusted according to the test requirements.

4. The method for testing the corrosion fatigue behavior of rails based on corrosion-fatigue coupling and multi-scale characterization according to claim 1, characterized in that, The fatigue loading system has a maximum load of not less than 50 kN and is equipped with automatic shutdown and data backup functions.

5. The method for testing the corrosion fatigue behavior of rails based on corrosion-fatigue coupling and multi-scale characterization according to claim 1, characterized in that, After fatigue interruption, the location of crack initiation was reconstructed in three dimensions to obtain the crack initiation angle, pit morphology and distribution characteristics.

6. The method for testing the corrosion fatigue behavior of rails based on corrosion-fatigue coupling and multi-scale characterization according to claim 1, characterized in that, The corrosion fatigue limit under different stress conditions was obtained by gradually reducing the stress level using a graded loading method.

7. The method for testing the corrosion fatigue behavior of rails based on corrosion-fatigue coupling and multi-scale characterization according to claim 1, characterized in that, This method achieves synchronous coupling of corrosion and fatigue load, and dynamically tracks the entire process of crack initiation, propagation, and failure through staged interruption tests combined with multi-scale characterization methods.

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