Evaluation method of wheel tread braking thermal fatigue damage based on thermal-mechanical coupling

Abstract

The present invention relates to a wheel tread braking thermal fatigue damage evaluation method based on thermal-mechanical coupling, which belongs to the field of wheel-rail damage detection, including building a small-scale brake shoe-wheel-rail coupling contact simulation test device and a temperature measurement device, continuously adjusting the braking parameters based on the temperature measurement results to meet the requirements of the wheel-rail friction coefficient and the braking temperature, and then performing a periodic tread braking test for a certain number of cycles, so that the wheel sample exhibits a typical thermal fatigue damage behavior under the thermal-mechanical coupling; obtaining the thermal fatigue damage parameters of the wheel sample after the test through microscopic analysis; calculating the thermal fatigue damage degree T according to the statistical thermal fatigue damage parameters, and evaluating the anti-tread braking thermal fatigue performance of different wheel materials according to the magnitude of the thermal fatigue damage degree T. The present invention can effectively and stably reproduce the wheel tread braking thermal fatigue damage, and can quantitatively describe the thermal fatigue damage degree of the wheel, and can realize the evaluation of the wheel material tread braking thermal fatigue performance.

Description

Technical Field

[0001] The invention relates to the field of wheel-rail damage detection, and in particular to a method for evaluating wheel tread braking thermal fatigue damage based on thermal-mechanical coupling. Background Art

[0002] With the development of economy, the volume of railway passenger and freight transportation has increased rapidly, and railway transportation has been developing in the direction of high speed and heavy load. As one of the core components of the wheel-rail system, the safety and reliability of wheels directly affect transportation safety. Subways and freight trains generally use tread braking to slow down or stop trains. Tread braking requires the wheels to bear not only the wheel-rail rolling contact load, but also the braking thermal load. Long-term thermal-mechanical coupling causes phase change in the microstructure of the wheel material and produces thermal fatigue damage, such as thermal cracks and thermal peeling. Among them, thermal cracks mostly extend along the radial direction of the wheel, and their continued extension will lead to the serious consequence of radial cracking of the wheel, posing a hidden danger to driving safety. Due to the particularity of the coupling effect of thermal load and mechanical load in the wheel tread braking thermal fatigue problem, the wheel tread braking thermal fatigue evaluation method itself has also become an important aspect of the research on wheel thermal fatigue performance.

[0003] Among the current evaluation methods for metal thermal fatigue performance, most of them only consider the effect of thermal load. Generally, the sample is placed in a set hot and cold environment for alternating cycles, and the thermal fatigue damage of the sample is observed after a certain number of times. However, the test results under the effect of thermal load alone cannot reflect the thermal fatigue damage behavior of the tread wheels on site. Therefore, how to evaluate thermal fatigue damage in combination with thermal-mechanical coupling is a problem that needs to be considered at present. Summary of the invention

[0004] The purpose of the present invention is to overcome the shortcomings of the prior art, provide a wheel tread brake thermal fatigue damage evaluation method based on thermal-mechanical coupling, and solve the deficiencies of the prior art.

[0005] The object of the present invention is achieved by the following technical solution: a wheel tread braking thermal fatigue damage evaluation method based on thermal-mechanical coupling, the evaluation method comprising:

[0006] S1. Build a small-scale brake shoe-wheel-rail coupling contact simulation test equipment and temperature measurement equipment to enable the coupling of sliding contact between the wheel sample and the brake shoe sample and rolling contact with the rail sample;

[0007] S2. Process the wheel material to be tested into a ring-shaped sample, and the brake shoe sample into a block-shaped sample. The width of the brake shoe sample is the same as that of the wheel sample, ensuring that the wheel and the rail sample are in line contact, and the wheel and the brake shoe sample are in surface contact;

[0008] S3, after setting the wheel-rail contact vertical force according to the Herzt simulation criterion and the wheel sample speed according to the angular velocity simulation criterion, select the initial braking parameters and conduct a tread braking test;

[0009] S4. Continuously adjust the braking parameters according to the temperature rise curve after one braking test, and perform a periodic tread braking test for a certain number of cycles according to the adjusted braking parameters;

[0010] S5. Take three small samples from the wheel specimen after the test, clean, dry, grind, polish and corrode the longitudinal sections, and then calculate the thermal fatigue damage parameters;

[0011] S6. Calculate the thermal fatigue damage degree of the wheel based on the statistical thermal fatigue damage parameters T , and according to the degree of thermal fatigue damage T The size of is used to evaluate the tread braking thermal fatigue resistance of different wheel materials.

[0012] The small-scale brake shoe-wheel-rail coupling contact simulation test equipment and temperature measurement equipment in S1 include:

[0013] A small-scale brake shoe automatic loading system is designed based on a double-wheel rolling test machine, so that the brake shoe sample can be loaded and unloaded according to the specified time and pressure on the wheel sample to be tested, ensuring that the friction torque between the wheel shoes can be converted into the tangential force between the wheel and rail;

[0014] A brake temperature measurement system is designed based on K-type thermocouple; the hot end metal wire of the thermocouple is embedded in the surface of the brake shoe sample to ensure the measurement of the wheel shoe contact interface temperature during braking.

[0015] The adjustment of the braking parameters in S4 includes:

[0016] The brake shoe action time, brake shoe interval time and brake shoe pressure are adjusted. The brake shoe pressure is adjusted to ensure that the friction coefficient between the wheel and rail is greater than 0.2 when the brake shoe is in action. The brake shoe action time and interval time are adjusted to ensure that the temperature difference of the wheel shoe contact interface before and after the brake shoe is applied is greater than 250°C.

[0017] The periodic tread braking test of a certain number of cycles in S4 includes:

[0018] The rail sample is driven by a DC motor as the driving wheel and always maintains a set speed. The wheel sample to be tested is the driven wheel and always contacts the rail sample with a certain vertical force.

[0019] The brake shoe sample is periodically loaded on the wheel tread for the specified number of times according to the specified brake shoe pressure, action time and intermittent time.

[0020] The wheel thermal fatigue damage parameter statistics in S5 include:

[0021] White layer thickness : The thickness of the white layer at the jth position;

[0022] White layer density : The sum of the lengths of all white layer areas in the sample section / total sampling length;

[0023] Ash layer thickness : The thickness of the ash layer at the jth position;

[0024] Ash layer density : The sum of the lengths of all ash layers in the sample section / total sampling length;

[0025] Thermal crack opening angle : The angle between the opening of the jth thermal crack and the surface of the specimen;

[0026] Thermal crack depth : The distance from the deepest point of the jth thermal crack to the surface of the specimen.

[0027] Calculating the thermal fatigue damage degree T according to the statistical thermal fatigue damage parameters in S6 includes:

[0028] Find the maximum value of the white layer thickness for each wheel sample , , calculate the average value of the maximum white layer thickness , and the wheel specimen white layer damage index is obtained ,in is the density of the white layer;

[0029] Find the maximum value of the ash layer thickness on each wheel sample , , calculate the average value of the maximum ash layer thickness , and the wheel sample ash layer damage index is obtained ,in is the density of the ash layer;

[0030] Count the thermal fatigue cracks in each wheel sample. If the crack opening angle is greater than the set angle and the microstructure at the opening undergoes phase change, it is a thermal crack. Calculate the damage value of each thermal crack. , ,in, is the thermal crack opening angle, is the thermal crack depth;

[0031] Find the maximum thermal crack damage value on each wheel sample , calculate the average value of the maximum thermal crack damage , and the thermal crack damage index is obtained ,in, is the number of thermal cracks;

[0032] Finally, the thermal fatigue damage degree value is obtained ,in, is 1, is 10.

[0033] According to the degree of thermal fatigue damage T The evaluation of the anti-tread braking thermal fatigue performance of different wheel materials includes:

[0034] when T =0, the wheel has no thermal damage; when 0< T When ≤100, the wheel microstructure undergoes phase change, but no thermal cracks are generated, and the thermal damage is relatively mild. T When it is greater than 100, thermal fatigue cracks will appear on the wheel, and the thermal damage will be serious.

[0035] The present invention has the following advantages: the wheel tread braking thermal fatigue damage evaluation method based on thermal-mechanical coupling can fully reproduce the thermal fatigue damage behavior of the wheel under on-site tread braking, can quantitatively describe the thermal and mechanical loads to which the wheel is subjected during tread braking, can quantitatively describe the degree of thermal fatigue damage of the wheel under thermal-mechanical coupling, and can evaluate the thermal fatigue performance of the wheel material. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 It is a schematic diagram of the process of the present invention. DETAILED DESCRIPTION

[0037] In order to make the purpose, technical scheme and advantages of the embodiments of the present application clearer, the technical scheme in the embodiments of the present application will be clearly and completely described below in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. The components of the embodiments of the present application described and shown in the drawings here can be arranged and designed in various different configurations. Therefore, the detailed description of the embodiments of the present application provided below in conjunction with the drawings is not intended to limit the scope of protection of the application claimed for protection, but merely represents the selected embodiments of the present application. Based on the embodiments of the present application, all other embodiments obtained by those skilled in the art without making creative work belong to the scope of protection of the present application. The present invention is further described below in conjunction with the drawings.

[0038] like Figure 1 As shown, the present invention specifically relates to a wheel tread brake thermal fatigue damage evaluation method based on thermal-mechanical coupling, which can stably and comprehensively reproduce the thermal fatigue damage behavior of the on-site tread brake wheel, including damage such as thermal debonding and thermal cracking; specifically includes the following contents.

[0039] S1. Build a small-scale brake shoe-wheel-rail coupling contact simulation test equipment and temperature measurement equipment to enable the coupling of sliding contact between the wheel sample and the brake shoe sample and rolling contact with the rail sample;

[0040] Among them, a small-scale brake shoe automatic loading system is designed based on the double-wheel rolling test machine, so that the brake shoe sample can be loaded and unloaded on the wheel sample to be tested according to the specified time and pressure, ensuring that the friction torque between the wheel shoes can be converted into the tangential force between the wheel and rail; a brake temperature measurement system is designed based on a K-type thermocouple; the hot end metal wire of the thermocouple is embedded in the surface of the brake shoe sample to ensure the measurement of the wheel shoe contact interface temperature during braking.

[0041] S2. Process the wheel material to be tested into a ring-shaped sample, and the brake shoe sample into a block-shaped sample. The width of the brake shoe sample is the same as that of the wheel sample, ensuring that the wheel and the rail sample are in line contact, and the wheel and the brake shoe sample are in surface contact;

[0042] S3, after setting the wheel-rail contact vertical force according to the Herzt simulation criterion and the wheel sample speed according to the angular velocity simulation criterion, select the initial braking parameters and conduct a tread braking test;

[0043] S4. Continuously adjust the braking parameters according to the temperature rise curve after one braking test, and perform a periodic tread braking test for a certain number of cycles according to the adjusted braking parameters;

[0044] Among them, adjusting the braking parameters includes: adjusting the brake shoe action time, brake shoe interval time and brake shoe pressure; adjusting the brake shoe pressure to ensure that the friction coefficient between the wheel and rail is greater than 0.2 when the brake shoe is in action, and adjusting the brake shoe action time and interval time to ensure that the temperature difference of the wheel shoe contact interface before and after the brake shoe is applied is greater than 250°C.

[0045] The periodic tread braking test with a certain number of cycles includes:

[0046] The rail sample is driven by a DC motor as the driving wheel and always maintains a set speed. The wheel sample to be tested is the driven wheel and always contacts the rail sample with a certain vertical force. The brake shoe sample is periodically loaded on the wheel tread to the specified number of times according to the specified brake shoe pressure, action time and intermittent time.

[0047] S5. Clean the wheel specimen after the test, and take samples every 120° along the circumferential direction, taking a total of 3 samples. Clean, dry, grind, polish and corrode the longitudinal section, and then calculate the thermal fatigue damage parameters;

[0048] Among them, wheel thermal fatigue damage parameter statistics include: white layer thickness : thickness of the white layer at the jth position (μm); density of the white layer : The sum of the lengths of all white layer areas in the sample section / total sampling length (%); the thickness of the gray layer : The thickness of the ash layer at the jth position (μm); the density of the ash layer The sum of the lengths of all ash layers in the section / total sampling length (%); thermal crack opening angle : The angle between the opening of the jth thermal crack and the surface of the specimen (°); The depth of the thermal crack : The distance from the deepest point of the jth thermal crack to the surface of the specimen (μm).

[0049] S6. Calculate the thermal fatigue damage degree of the wheel based on the statistical thermal fatigue damage parameters T , and according to the degree of thermal fatigue damage T The size of is used to evaluate the tread braking thermal fatigue resistance of different wheel materials.

[0050] Among them, the parameters during the test include: the maximum contact stress between the wheel and rail samples should be ≥1200MPa, the friction coefficient between the wheel and rail is 0.2~0.3, the wheel sample rotation speed is 400~430r / min, the brake shoe action time is 5s~10s, the brake shoe interval time is 60~80s, the brake shoe action times is 800~1200 times, and the maximum braking temperature of a single action should be ≥250℃.

[0051] Furthermore, the degree of thermal fatigue damage is calculated based on the statistical thermal fatigue damage parameters. T include:

[0052] Find the maximum value of the white layer thickness for each wheel sample , , calculate the average value of the maximum white layer thickness , and the wheel specimen white layer damage index is obtained ,in is the density of the white layer; find the maximum value of the gray layer thickness on each wheel sample , , calculate the average value of the maximum ash layer thickness , and the wheel sample ash layer damage index is obtained ,in is the density of the ash layer;

[0053] Count the thermal fatigue cracks in each wheel sample. If the crack opening angle is greater than or equal to 40° and the microstructure at the opening undergoes a phase change, the crack is a thermal fatigue crack. Calculate the damage value of each thermal crack ,in, is the thermal crack opening angle, is the thermal crack depth, in μm, ; Find the maximum value of wheel thermal crack damage in each wheel sample , calculate the average value of the maximum damage of thermal cracks , and the thermal crack damage index is obtained ,in, is the number of thermal cracks;

[0054] Finally, the thermal fatigue damage degree value is obtained , Take 1, Take 10.

[0055] when T =0, the wheel has no thermal damage; when 0< T When ≤100, the wheel microstructure undergoes phase change, but no thermal cracks are generated, and the thermal damage is relatively mild. T When it is greater than 100, thermal fatigue cracks will appear on the wheel, and the thermal damage will be serious.

[0056] The above is only a preferred embodiment of the present invention. It should be understood that the present invention is not limited to the form disclosed herein, and should not be regarded as excluding other embodiments, but can be used for various other combinations, modifications and improvements, and can be modified within the scope of the concept described herein through the above teachings or the technology or knowledge of the relevant field. The changes and modifications made by those skilled in the art do not deviate from the spirit and scope of the present invention, and should be within the scope of protection of the claims attached to the present invention.

Claims

1. A wheel tread brake thermal fatigue damage evaluation method based on thermal-mechanical coupling, characterized in that: The evaluation method includes: S1. Build a small-scale brake shoe-wheel-rail coupling contact simulation test equipment and temperature measurement equipment to enable the coupling of sliding contact between the wheel sample and the brake shoe sample and rolling contact with the rail sample; S2. Process the wheel material to be tested into a ring-shaped sample, and the brake shoe sample into a block-shaped sample. The width of the brake shoe sample is the same as that of the wheel sample, ensuring that the wheel and the rail sample are in line contact, and the wheel and the brake shoe sample are in surface contact; S3, after setting the wheel-rail contact vertical force according to the Herzt simulation criterion and setting the wheel sample speed according to the angular velocity simulation criterion, select the initial braking parameters and conduct a tread braking test; S4. Continuously adjust the braking parameters according to the temperature rise curve after one braking test, and perform a periodic tread braking test for a certain number of cycles according to the adjusted braking parameters; S5. Take three small samples from the wheel specimen after the test, clean, dry, grind, polish and corrode the longitudinal section, and then calculate the thermal fatigue damage parameters; S6. Calculate the thermal fatigue damage degree T of the wheel according to the statistical thermal fatigue damage parameters, and evaluate the anti-tread braking thermal fatigue performance of different wheel materials according to the magnitude of the thermal fatigue damage degree T; The calculation of thermal fatigue damage degree T based on statistical thermal fatigue damage parameters includes: Find the maximum value e of the white layer thickness of each wheel sample max-i , i=1,2,3, calculate the average value of the maximum white layer thickness Get the wheel sample white layer damage index where ρ e is the density of the white layer; Find the maximum value b of the ash layer thickness on each wheel sample max-i , i=1,2,3, calculate the average value of the maximum ash layer thickness Get the wheel sample ash layer damage index where ρ b is the density of the ash layer; Count the thermal fatigue cracks in each wheel sample. If the crack opening angle is greater than the set angle and the microstructure at the opening undergoes phase change, it is a thermal crack. Calculate the damage value p of each thermal crack. j =r j d j , j = 1, 2, 3 ... n, where r j is the thermal crack opening angle, d j is the thermal crack depth; Find the maximum thermal crack damage value q on each wheel sample max-i , calculate the average value of the maximum thermal crack damage Get the thermal crack damage index Among them, ρ c is the number of thermal cracks; Finally, the thermal fatigue damage degree value is obtained as T = a1(T1+T2)+a2T3, where a1 is 1 and a2 is 10; Wheel thermal fatigue damage parameter statistics in S5 include: White layer thickness e j : The thickness of the white layer at the jth position; White layer density p e : The sum of the lengths of all white layer areas in the sample section divided by the total sampling length; Ash layer thickness b j : The thickness of the ash layer at the jth position; Ash layer density p b : The sum of the lengths of all ash layers in the sample section divided by the total sampling length; Thermal crack opening angle r j : The angle between the opening of the jth thermal crack and the surface of the specimen; Thermal crack depth d j : The distance from the deepest point of the jth thermal crack to the surface of the specimen.

2. The wheel tread braking thermal fatigue damage evaluation method based on thermal-mechanical coupling according to claim 1 is characterized in that: The small-scale brake shoe-wheel-rail coupling contact simulation test equipment and temperature measurement equipment in S1 include: A small-scale brake shoe automatic loading system is designed based on a double-wheel rolling test machine, so that the brake shoe sample can be loaded and unloaded according to the specified time and pressure on the wheel sample to be tested, ensuring that the friction torque between the wheel shoes can be converted into the tangential force between the wheel and rail; A brake temperature measurement system is designed based on K-type thermocouple; the hot end metal wire of the thermocouple is embedded in the surface of the brake shoe sample to ensure the measurement of the wheel shoe contact interface temperature during braking.

3. The wheel tread braking thermal fatigue damage evaluation method based on thermal-mechanical coupling according to claim 1 is characterized in that: The adjustment of the braking parameters in S4 includes: The brake shoe action time, brake shoe interval time and brake shoe pressure are adjusted. The brake shoe pressure is adjusted to ensure that the friction coefficient between the wheel and rail is greater than 0.2 when the brake shoe is in action. The brake shoe action time and interval time are adjusted to ensure that the temperature difference of the wheel shoe contact interface before and after the brake shoe is applied is greater than 250°C.

4. The wheel tread braking thermal fatigue damage evaluation method based on thermal-mechanical coupling according to claim 1 is characterized in that: The periodic tread braking test of a certain number of cycles in S4 includes: The rail sample is driven by a DC motor as the driving wheel and always maintains a set speed. The wheel sample to be tested is the driven wheel and always contacts the rail sample with a certain vertical force. The brake shoe sample is periodically loaded on the wheel tread for the specified number of times according to the specified brake shoe pressure, action time and intermittent time.

5. The wheel tread braking thermal fatigue damage evaluation method based on thermal-mechanical coupling according to claim 1 is characterized in that: The evaluation of the anti-tread braking thermal fatigue performance of different wheel materials according to the thermal fatigue damage degree T comprises: When T=0, the wheel has no thermal damage; when 0<T≤100, the wheel microstructure undergoes phase change, but no thermal cracks initiate, and the thermal damage is relatively mild at this time; when T>100, thermal fatigue cracks initiate in the wheel, and the thermal damage is severe at this time.

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