CN113433060A - Method for evaluating rolling contact fatigue performance of railway locomotive wheel surface - Google Patents
Method for evaluating rolling contact fatigue performance of railway locomotive wheel surface Download PDFInfo
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Abstract
The invention discloses a method for evaluating rolling contact fatigue performance of a railway locomotive wheel surface, which comprises the following steps: taking a contact experiment sample which comprises a wheel sample and a steel rail sample, processing and cleaning the contact sample, weighing the cleaned wheel sample, and then installing the wheel sample and the steel rail sample on a contact fatigue test sample machine; sequentially carrying out a non-lubricated rolling contact experiment and a lubricating rolling contact experiment under a lubricating condition on a wheel sample by using a contact fatigue sample machine; carrying out ultrasonic cleaning and weighing on the tested wheel sample to obtain the mass m of the tested wheel sample and the weight loss delta m of the wheel processing sample which is m-m0(ii) a Dissecting a wheel sample, collecting surface crack pictures by a metallographic microscope along the outer arc of the sample field by field, and acquiring the crack density and the crack depth of the wheel sample based on the collected pictures; and evaluating the rolling contact fatigue performance of the wheel surface based on the crack density, the crack depth and the weight loss. A standardized evaluation method for rolling contact fatigue performance is provided.
Description
Technical Field
The invention belongs to the technical field of wheel-rail contact relation, and particularly relates to a method for evaluating rolling contact fatigue performance of a railway locomotive wheel surface.
Background
The wheel is a core component of a railway locomotive and bears complicated mechanical and thermal loads, and various fatigue damages can be generated, wherein wheel tread stripping caused by rolling contact fatigue cracks generated on a contact surface is the most common damage form. The tread is stripped to generate impact load on the contact surface of the wheel rail, and the caused vibration can cause early failure of train parts and directly influence the running safety and reliability of the train, so that the tread stripping defect can be continuously put into use after being turned and repaired. The contact fatigue performance of the wheel determines the tread stripping generation period, and is directly related to the turning frequency and the service life of the wheel, thereby having important influence on the railway transportation efficiency and the economy. Therefore, the wheel rolling contact fatigue performance evaluation method is a basic technology of the wheel rail transportation system.
In the YBT 5345-2014 rolling contact fatigue test method, the conditions of the rolling contact test are oil lubrication, the friction coefficient of the contact surface of the test sample is less than 0.1, the plastic deformation of the surface is extremely small, the rolling contact fatigue crack is very slow to initiate, the crack can not be initiated even in a low-stress state, and the contact fatigue resistance of the wheel material can not be objectively evaluated; AAR-M107 "carbon steel wheel code", wherein the friction wear test is performed in a dry state, wherein the contact pressure is about 2200MPa, the sliding friction is 0.75%, the number of continuous revolutions is 50 ten thousand revolutions, and the contact fatigue test is performed in an oil-lubricated state, wherein the contact pressure is 1100MPa, the sliding friction is 0.3%, and the duration is stripping to stop the vibration sensor. By adopting the 2 test methods, the contact fatigue test period is long, the test result dispersion is large, and the fatigue life of the material can not be compared even in a low-stress state.
Disclosure of Invention
The invention provides a method for evaluating rolling contact fatigue performance of a railway locomotive wheel surface, aiming at improving the problems.
The invention is realized in such a way that a method for evaluating rolling contact fatigue performance of the surface of a railway locomotive wheel specifically comprises the following steps:
s1, taking a contact experiment sample, wherein the contact experiment sample comprises a wheel sample and a steel rail sample, the contact mode of the wheel sample and the steel rail sample adopts line contact, the contact sample is sequentially processed, cleaned and weighed, and the initial mass of the wheel sample is m0Then, mounting the cleaned wheel sample and the cleaned steel rail sample on a contact fatigue test sample machine;
s2, sequentially carrying out a non-lubrication rolling contact experiment and a lubrication condition rolling contact experiment on the wheel sample through a contact fatigue test sample machine;
s3, carrying out ultrasonic cleaning and weighing on the tested wheel sample to obtain the mass m of the tested wheel sample, and obtaining the weight loss delta m of the wheel processing sample, which is m-m0；
S4, dissecting the wheel sample, collecting surface crack pictures along the outer arc of the sample by field by using a metallographic microscope, and acquiring the crack density and the crack depth of the wheel sample based on the collected pictures;
and S5, evaluating the rolling contact fatigue performance of the wheel surface based on the crack density, the crack depth and the weight loss.
Further, the method for determining the test parameters of the lubrication-free rolling-sliding contact experiment is as follows:
taking the maximum contact stress of the wheel in service as the contact stress P for experiments0(ii) a Contact stress P for experiment0Determining the test load F of a contact fatigue test specimen machine0；
Taking the actual running rotating speed of the wheel as the wheel test rotating speed V0；
Setting the maximum slip ratio of the actual running of the wheel to be the slip delta of the experimental sample;
the experimental weekly value satisfies the following conditions: the method comprises the following steps of (1) enabling a wheel sample to generate surface cracks, but the cracks are not fully expanded to generate flake peeling on the surface of the wheel sample, wherein the flakes are metal peeling sheets with the area of about 1 square mm and the thickness of micron level;
further, the method for determining the experimental parameters of the rolling-sliding contact experiment under the lubricating condition specifically comprises the following steps:
taking the maximum contact stress of the wheel in service as the contact stress P for experiments0(ii) a Contact stress P for experiment0Determining the test load F of a contact fatigue test specimen machine0；
Taking the actual running rotating speed of the wheel as the wheel test rotating speed V0；
Taking the actual running slip ratio of the wheel under the linear working condition as the slip delta of the experimental sample, wherein the slip delta is smaller than the maximum actual running slip ratio of the wheel;
the experiment frequency meets the following requirements: the initiated cracks are expanded to the inside, the expansion depth of the cracks is tens of times or even hundreds of times of the original cracks, the cracks are fully expanded, so that large stripping blocks begin to appear on the surface of the wheel sample, and the large stripping blocks refer to metal stripping blocks with the area of about 3 square mm and the thickness of about 1 mm.
Further, the value range of the test parameters of the lubrication-free rolling-sliding contact experiment is as follows:
the contact stress is 1000-1500MPa, the rotating speed is 400-800 rpm, the slip is 0.5-1.0%, and when the friction coefficient reaches 0.25, the rotation is continued for 6000-15000 rpm.
Further, the test parameters of the lubrication-free rolling-sliding contact test are as follows:
the contact pressure stress is 1227MPa, the rotating speed is 500 r/min, the slip is 0.75%, and when the friction coefficient reaches 0.25, the rotating is continued for 9000 r.
Further, the range of the experimental parameters of the rolling-sliding contact experiment under the lubricating condition is as follows:
the contact stress is 1000-1500MPa, the rotating speed is 400-800 r/min, the slip is adjusted to 0.1-0.5%, the total experimental rotation number is 10000-30000 r, and the lubricating medium is water, oil or 10% glycol aqueous solution.
Further, the experimental parameters of the rolling-sliding contact experiment under the lubricating condition are as follows:
the contact pressure stress is 1227MPa, the rotating speed is 500 r/min, the slip is adjusted to 0.3 percent, the total experimental rotating speed is 20000 r, and the lubricating medium adopts 10 percent glycol aqueous solution.
The method can quantitatively evaluate the difference of the contact fatigue performance of the surface of the wheel material, and has good guiding effect on the optimization selection of the wheel material for the locomotive or the development of a novel wheel material; in addition, the method can be used for evaluating the surface contact fatigue performance of the wheel material for the railway locomotive and can be popularized and used for evaluating the surface contact fatigue performance of the wheel material for the rail transit.
Drawings
FIG. 1 is a schematic illustration of a wheel specimen sampling provided in accordance with an embodiment of the present invention;
FIG. 2 is a schematic diagram of a rail sample provided by an embodiment of the present invention;
FIG. 3 is a schematic illustration of a wheel specimen processing provided by an embodiment of the present invention;
FIG. 4 is a schematic view of a steel rail sample according to an embodiment of the present invention;
FIG. 5 is a schematic diagram of a rolling-sliding contact experiment provided by an embodiment of the present invention;
FIG. 6 is a view of a wheel specimen dissected and sampled after the rolling contact test provided by the embodiment of the present invention is completed;
FIG. 7 shows the wheel plastic deformation and crack morphology under actual conditions provided by an embodiment of the present invention;
FIG. 8 is a graph of the wheel plastic deformation and crack morphology of example 1, wherein (a) is wheel 1 and (b) is wheel 2;
fig. 9 shows the wheel plastic deformation and crack morphology of the wheel 1 in comparative example 1 according to an embodiment of the present invention.
Detailed Description
The following detailed description of the embodiments of the present invention will be given in order to provide those skilled in the art with a more complete, accurate and thorough understanding of the inventive concept and technical solutions of the present invention.
The surface rolling contact fatigue damage consists of two processes of crack initiation and crack propagation, the maximum shear stress is positioned on a contact surface to cause the crack initiation condition is that a material generates plastic deformation and initiates cracks to a certain degree, the surface is easy to initiate cracks when the traction coefficient (friction coefficient) is more than 0.25 under the general condition, the propagation condition is the 'oil wedge effect' of a lubricant in the initiated cracks, and the method for evaluating the rolling contact fatigue performance of the surface of the railway locomotive wheel is designed on the basis of the method, and the method specifically comprises the following steps:
s1: taking experimental samples of a contact experiment, wherein the experimental samples comprise a wheel sample and a steel rail sample, the sampling positions and the shapes of the two samples are respectively shown in a figure 1 and a figure 2, the sampling positions of the steel rail sample are relatively loosely arranged, and the contact mode of the wheel sample and the steel rail sample adopts line contact;
s2: FIG. 3 is a diagram for processing a wheel sample, FIG. 4 is a diagram for processing a steel rail sample, the processed wheel sample and the steel rail sample are cleaned by ultrasonic cleaning, and then the cleaned wheel sample is weighed to obtain an initial mass m of the wheel sample0Mounting the cleaned wheel sample and the cleaned steel rail sample on a disc type friction wear and contact fatigue test machine, wherein the schematic diagram after mounting is shown in FIG. 5;
s3: a non-lubricated rolling contact test was conducted in order to initiate contact fatigue cracks on the surface of the wheel specimen. Calculating the maximum contact stress of the wheel in service according to the actual working condition of the wheel as the contact stress P for experiment0(ii) a According to Hertz's theory of elastic forcesTheoretical formula (equation 1) to calculate the experimental load F0Loading an experimental sample by a hydraulic loading system in the contact fatigue test prototype; determining the rotating speed V of the experimental sample according to the actual running speed of the locomotive0(ii) a Setting the slip delta of an experimental sample according to the maximum slip rate of the actual operation of the locomotive, so that the surface of a wheel sample generates a shear stress for driving contact fatigue crack initiation; starting a contact fatigue test sample machine, automatically stopping when the friction coefficient reaches 0.25, starting the machine to run at a set revolution, increasing the friction coefficient to a maximum value, and then rotating the machine at the maximum friction coefficient, wherein the surface of a sample has the mechanical condition of contact fatigue crack initiation; and air cooling is carried out on the sample in the experimental process.
Wherein: p0 — maximum contact stress (MPa); pi-constant, 3.146; f-load applied to the specimen, N; mu.s1-poisson's ratio of the main sample; mu.s2-poisson's ratio of the test sample; e1-modulus of elasticity of the main specimen, N/mm 2; e2-modulus of elasticity of the test specimen, N/mm 2; l is the contact length of the sample, mm; r11 — radius of curvature of the main specimen perpendicular to the rolling direction, mm; r12 — radius of curvature of the main specimen in the rolling direction, mm; r21-radius of curvature of the test specimen perpendicular to the rolling direction, mm; r22-radius of curvature of the test specimen in the rolling direction, mm.
In the dry contact test (i.e., the non-lubricated rolling contact test), the test parameters set the range: the contact stress is 1000-; wherein the optimal parameters of the dry contact experiment are as follows: the contact pressure stress is 1227MPa (the actual maximum load of the locomotive wheels), the rotating speed is 500 r/min, the slip is 0.75 percent, and the locomotive continuously rotates 9000 r after the friction coefficient reaches 0.25.
S4: then, the rolling contact test under the lubricating condition is carried out, so that the 'oil wedge effect' of the lubricant is utilized to cause the contact fatigue crack initiated on the surface of the wheel sample to expand inwardsAnd the number and the shape of the cracks are easy to measure. The proper lubricant is adopted to lubricate the rolling contact fatigue test sample, the lubricating property of the lubricant is required to be similar to that of water, and the environmental conditions of rain, snow and the like under the actual working condition of the wheel can be simulated; experimental load F0Wheel sample rotation speed V0Consistent with the no-lubrication contact test; properly adjusting the slip ratio delta of the contact surface of the wheel and the rail sample, and selecting the actual running slip ratio of the straight line working condition of the wheel as the slip ratio delta of the experimental sample to be smaller than the maximum actual running slip ratio of the wheel; the contact fatigue crack initiated on the surface of the sample is ensured to be easy to propagate inwards while the shear stress of the contact surface is properly reduced; the upper sample in the graph 5 is a wheel sample, the lower sample is a steel rail sample, different servo motors are connected, and the slip ratio control of the samples is realized by adjusting the rotating speed of the motors; the shadow part is a wheel-rail contact spot, a nozzle sprays lubricating liquid to lubricate a sample for a rolling contact fatigue test, a contact fatigue sample testing machine is started, a certain experiment cycle is set, the experiment cycle is proper, the test cycle is not too short or too long, the crack propagation depth is small when the test cycle is too short, the number and the form of the cracks are not easy to measure, the cracks with smaller angles are fully propagated and peeled under the action of the oil wedge effect when the test cycle is too long, the measurement result of the number and the depth of the cracks is influenced, and the deviation is brought to the evaluation of the surface crack initiation resistance of the wheel material;
in the wet contact test (i.e., the rolling contact test under lubrication conditions), the test parameter setting range: the contact stress and the rotating speed are set to be consistent with those of a dry contact experiment, the slip is adjusted to be 0.1-0.5%, the total rotating speed of the experiment is 10000-30000 r, and the lubricating medium can adopt water, oil and 10% glycol aqueous solution. Wherein the optimal parameters of the wet contact experiment are as follows: the contact stress and the rotating speed are set to be consistent with those of a dry contact experiment, the slip is adjusted to be 0.3%, the total rotating speed of the experiment is 20000 revolutions, and a lubricating medium adopts 10% of glycol aqueous solution.
S5: carrying out ultrasonic cleaning on the wheel sample after the experiment, then weighing to obtain the mass m of the wheel sample after the experiment, and thus obtaining the weight loss delta m of the wheel sample0Δ m is the loss due to spalling from complete crack propagation at smaller angles and is one degree of the number of surface contact fatigue cracksThe amount can be used for measuring the surface contact fatigue crack initiation resistance of the wheel material;
s6: the wheel sample is weighed and then dissected, the boss part of the wheel sample is cut off along the circumferential direction in a linear cutting mode, and then a longitudinal section sample is cut along one half of the contact surface, as shown in figure 6, the analysis sample is the boss part of the sample, and the inspection surface is a longitudinal section along the central line of the contact surface; then decomposing the sample into small samples with proper arc length, and after inlaying, roughly grinding, finely grinding and polishing the longitudinal section;
s7: collecting surface crack pictures by field along the outer arc of the sample by 30-100 times by using a metallographic microscope, wherein the number of the fields is more than 20;
and (3) collecting surface crack pictures by field along the outer arc of the sample by 50 times by using a metallographic microscope, wherein the number of the fields is 30.
S8: counting cracks of the collected metallographic pictures to obtain the number Ai of the cracks of each field, and obtaining the density L of the cracks as sigma Ai/r n according to the number n of the fields and the diameter r of the fields; and length and depth measurement is carried out, the crack density can measure the surface contact fatigue crack initiation resistance of the wheel material, and the crack depth can measure the surface contact fatigue crack propagation resistance of the wheel material, so that the surface contact fatigue performance of the wheel material is evaluated.
And S9, evaluating the rolling contact fatigue performance of the wheel surface based on the crack density, the crack depth and the weight loss.
The importance of the crack density, the crack depth and the weightlessness in the comprehensive evaluation of the rolling contact fatigue performance of the wheel surface can be reflected by the weight value.
The method for evaluating the rolling contact fatigue performance of the surface of the wheel of the railway locomotive is designed based on the contact fatigue damage mechanism of the surface of the wheel rail, and the mechanism of the contact fatigue damage of the rail is known relatively uniformly, namely: when the friction coefficient mu of the wheel rail exceeds 0.25, the contact surface of the wheel rail generates plastic deformation, contact fatigue cracks are generated due to the ratchet effect, and after the cracks are generated, the cracks are expanded inwards to cause surface peeling due to the oil wedge effect generated by entering water into the cracks in a wet environment or a rain and snow environment. Based on the principle, the invention adopts the lubrication-free rolling-sliding contact experiment, and controls the test cycle after the friction coefficient mu reaches 0.25, so that not only the surface cracks of the wheel sample are initiated, but also the cracks are not fully expanded to generate flake peeling on the surface of the wheel sample, thereby completely keeping the surface cracks initiated on the surface of the wheel sample for the first time as far as possible and controlling the measurement deviation of the number of the surface cracks. In view of the high surface shear stress of the wheel sample in the lubrication-free rolling contact process, shallow depth and small angle of the generated surface crack, and difficulty in measuring the quantity, the depth and the length, the lubrication rolling contact experiment is carried out after the lubrication-free rolling contact experiment based on the mechanical condition of the wheel rail surface contact fatigue crack propagation, the oil wedge effect generated when the lubricant enters the initiated crack is utilized to rapidly expand the crack, and in order to ensure the oil wedge effect, a certain slip ratio is required to be set to provide enough tangential force. By controlling the experiment frequency, the initiated cracks are properly expanded to the inside, so that the measurement of the number, the depth and the length of the surface contact fatigue cracks is easy, the possibility that the cracks with smaller angles are fully expanded and peeled off under the action of an oil wedge effect is reduced, the integrity of the contact surface is ensured, the measurement precision of the number, the depth and the length of the cracks is improved, and the sample weight loss generated in the process is caused by the full expansion of the cracks with smaller angles and is also a measure of the number of the surface contact fatigue cracks. Therefore, the method can quantitatively evaluate the difference of the contact fatigue performance of the surface of the wheel material, and has good guiding function on the optimization selection of the wheel material for the locomotive or the development of a novel wheel material; in addition, the method can be used for evaluating the surface contact fatigue performance of the wheel material for the railway locomotive and can be popularized and used for evaluating the surface contact fatigue performance of the wheel material for the rail transit.
The present invention will be described in detail with reference to examples 1, 2 and 3.
Example 1
Based on the mechanical condition that the contact fatigue crack on the surface of the wheel rail can be initiated, namely the friction coefficient mu exceeds 0.25, the contact fatigue crack on the surface of the wheel sample can be initiated, a lubrication-free rolling contact experiment (namely a dry contact experiment) is adopted, and the test cycle after the friction coefficient mu reaches 0.25 is controlled, so that the surface crack of the wheel sample is initiated, the crack is not fully expanded, and the flaky peeling is generated on the surface of the wheel sample, thereby completely keeping the surface crack initiated on the surface of the wheel sample for the first time as far as possible, and controlling the measurement deviation of the number of the surface crack; in view of high surface shear stress of a wheel sample in the lubrication-free rolling contact process, shallow depth and small angle of generated surface cracks and difficulty in measuring quantity, depth and length, based on the mechanical condition of the wheel rail surface contact fatigue crack propagation, a rolling contact experiment (namely a wet contact experiment) under the lubrication condition is carried out after the lubrication-free rolling contact experiment, cracks are propagated by utilizing an oil wedge effect generated when a lubricant enters the initiated cracks, and the initiated cracks are moderately propagated to the inside by controlling the experiment cycle, so that the quantity, the depth and the length of the surface contact fatigue cracks are easily measured, and the weight loss of the sample generated in the process is caused by the full propagation of the cracks with smaller angles and is also a measure of the quantity of the surface contact fatigue cracks.
In the embodiment, two types of wheel steel with different strength levels are adopted, the chemical components and the yield strength of the steel rail are shown in table 1, and the contact fatigue damage incidence rate of the surface of the low-strength wheel is obviously higher than that of the high-strength wheel in the actual service process.
Sampling according to a wheel rim and a steel rail head shown in figures 1 and 2, processing wheel and steel rail samples according to figures 3 and 4, sequentially performing a lubrication-free rolling contact experiment and a lubrication condition rolling contact experiment according to a friction wear and contact fatigue testing machine and a table 2, and performing three tests on the wheel 1 and the wheel 2 by using test parameters of an example 1 in the table 2 to obtain a sample contact fatigue cycle average value.
The weight loss of the wheel sample is obtained by measuring the mass of the wheel sample before and after the experiment, see table 3, and it can be seen that the weight loss of the wheel 1 sample in the embodiment 1 is obviously larger than that of the wheel 2 sample, and the difference of the occurrence rates of the surface contact fatigue damage in the actual service process of the two wheels is consistent, that is, the surface contact fatigue performance of the wheel 2 is obviously better than that of the wheel 1.
Cutting off the boss part of the wheel sample along the circumferential direction in a linear cutting mode, cutting off a longitudinal section sample along one half of the contact surface, decomposing the longitudinal section sample into small samples with proper arc length as shown in figure 6, and after embedding, roughly grinding, finely grinding and polishing the longitudinal section; collecting surface crack pictures by field along the outer arc of the sample by 50 times by adopting a metallographic microscope, wherein the number of the fields is 30; the crack density and depth were obtained from the metallographic pictures of the crack morphology, see table 3. It can be seen that the crack density and depth of the wheel 1 sample in the example 1 are obviously greater than those of the wheel 2 sample, and the difference between the occurrence rates of the surface contact fatigue damage in the actual service process of the two wheels is consistent, that is, the surface contact fatigue performance of the wheel 2 is obviously better than that of the wheel 1.
As shown in fig. 8, the metallographic pictures of the longitudinal section test corrosion after the inlaying, the rough grinding, the fine grinding and the polishing are compared and analyzed with the wheel plastic deformation morphology (fig. 7) under the actual working condition, so that the consistency of the sample surface plastic deformation and the crack initiation expansion morphology obtained by the method in the embodiment and the actual wheel plastic deformation and the crack initiation expansion morphology is better, and the test evaluation result is objective and effective by adopting the test method in the embodiment.
Comparative example 1
The wheel and rail materials adopted in the comparative example are the same as those in example 1, wheel rims and rail heads of the wheels and the rails shown in figures 1 and 2 are sampled, wheel and rail samples are processed according to figures 3 and 4, fatigue tests are carried out according to the test parameters of the comparative example 1 in the table 2 and the test mode of figure 5, 3 times of tests are carried out, and the average value of the contact fatigue cycles of the samples is obtained, and the fact that the surface contact fatigue performance of the wheel 2 is better than that of the wheel 1 is shown in the table 3. Comparing the experimental period of the comparative examples and examples, it is clear that the experimental period using the experimental method of the examples is significantly shorter than that of the comparative example, as shown in table 4.
The metallographic morphology picture of the comparative example 1 is obtained by dissecting, inlaying, roughly grinding, finely grinding, polishing and corroding the longitudinal section of the wheel sample of the comparative example 1 by the same method as that of the example 1, as shown in fig. 9, the metallographic morphology picture of the comparative example 1 is analyzed by comparing with the plastic deformation morphology (fig. 7) of the wheel under the actual working condition, and the wheel sample of the comparative example 1 has no obvious plastic deformation, which indicates that the surface plastic deformation morphology of the comparative example sample is greatly different from the plastic deformation morphology of the actual wheel.
TABLE 1 chemical composition and yield Strength of wheel steels, Rail steels
Table 2 experimental parameters of example 1 and comparative example 1
Table 3 weight loss and crack density, depth for the examples
TABLE 4 number of trials and period conditions
| Categories | Experiment period/day | Categories | Experiment period/day |
| Example 1 | 11 | Comparative example 1 | 77 |
| Example 2 | 12 | Comparative example 2 | 93 |
| Example 3 | 9 | Comparative example 3 | 62 |
Example 2
The chemical compositions and yield strengths of the wheels and rails used in this example are shown in Table 1, which is the same as example 1. Test samples were prepared according to the sampling method and processing method of example 1, and dry + wet rolling contact fatigue tests were performed in a frictional wear and contact fatigue testing machine using the test parameters of example 2 in table 2, with the same test frequency as in example 1.
The wheel sample weight loss was obtained by measuring the mass of the wheel sample before and after the experiment, see table 3. It can be seen that the weight loss of the example 2 wheel 1 sample is significantly greater than the wheel 2 sample. The wheel specimens were statistically analyzed for crack-shaped crack density and depth by the same method as in example 1, and are shown in Table 3. It can be seen that the crack density, depth of the example 2 wheel 1 sample is significantly greater than that of the wheel 2 sample.
The consistency of the surface plastic deformation and crack initiation and propagation morphology of the sample in the embodiment and the actual wheel plastic deformation and crack initiation and propagation morphology are better according to the comparative analysis of the method in the embodiment 1.
Comparative example 2
The wheel and rail materials adopted by the comparative example are the same as those of the example 2, test samples are prepared according to the sampling method and the processing method of the comparative example 1, the test parameters of the comparative example 2 in the table 2 are adopted to carry out rolling contact fatigue test in a friction wear and contact fatigue testing machine, the test is carried out for 3 times, the average value of the contact fatigue cycles of the samples is obtained, and from the test result (table 3), the fatigue life of the wheel 1 and wheel 2 samples reaches 1 multiplied by 107In this case, the fatigue life of wheel 1 and wheel 2 cannot be compared, whereas the fatigue life of 2 materials can be compared using the method of the example, and the test period is significantly shorter than that of the comparative method, as shown in table 4.
And (3) dissecting, inlaying, roughly grinding, finely grinding, polishing and corroding the longitudinal section of the wheel sample of the comparative example 1 by the same method as the embodiment 1 to obtain a metallographic morphology picture of the comparative example 1, and comparing and analyzing the metallographic morphology picture with the wheel plastic deformation morphology of the actual working condition, namely, the wheel sample of the comparative example 2 has no obvious plastic deformation, and the fact that the surface plastic deformation morphology of the comparative example 2 is greatly different from the actual wheel plastic deformation morphology is shown.
Example 3
The chemical compositions and yield strengths of the wheels and rails used in this example are shown in Table 1, which is the same as example 1. Test samples were prepared according to the sampling method and processing method of example 1, and dry-state + wet-state rolling contact fatigue tests were performed in a frictional wear and contact fatigue testing machine using the test parameters of the examples in table 2, with the same test frequency as in example 1.
The wheel sample weight loss was obtained by measuring the mass of the wheel sample before and after the experiment, see table 3. It can be seen that the weight loss of the example 3 wheel 1 sample is significantly greater than the wheel 2 sample. The wheel specimens were statistically analyzed for crack density and depth using the same methods as in example 1, see table 3. It can be seen that the crack density, depth of the example 3 wheel 1 sample is significantly greater than that of the wheel 2 sample. It can be seen that the surface contact fatigue performance of the wheel 2 is significantly better than that of the wheel 1.
The wheel sample deformation morphology in the example 3 is dissected and analyzed by the same method as the example 1, and compared with the wheel plastic deformation morphology under the actual working condition, and the obtained conclusion is the same as the example 1, namely the surface plastic deformation and crack initiation and propagation morphology of the sample obtained in the example 3 has better consistency with the actual wheel plastic deformation and crack initiation and propagation morphology.
Comparative example 3
The wheel and rail materials adopted in the comparative example are the same as those in example 3, test samples are prepared according to the sampling method and the processing method of the comparative example 1, the rolling contact fatigue test is carried out on a friction wear and contact fatigue testing machine by adopting the test parameters of the table 2, the test is carried out for 3 times, the contact fatigue cycle average value of the samples is obtained, and from the test result (table 3), the surface contact fatigue life of the wheel 2 is longer than that of the wheel 1, but the test period of the example is obviously shorter than that of the comparative example, and the test period is specifically shown in table 4.
And (3) analyzing the metallographic morphology of the longitudinal section of the wheel sample of the comparative example 3 by the same method as the comparative example 1, and comparing and analyzing the metallographic morphology with the morphology of the plastic deformation of the wheel under the actual working condition to obtain the conclusion that the wheel sample of the comparative example 1, namely the wheel sample of the comparative example 3 has no obvious plastic deformation.
The invention has been described above with reference to the accompanying drawings, it is obvious that the invention is not limited to the specific implementation in the above-described manner, and it is within the scope of the invention to apply the inventive concept and solution to other applications without substantial modification.
Claims (7)
1. A method for evaluating rolling contact fatigue performance of a railway locomotive wheel surface is characterized by comprising the following steps:
s1, taking a contact experiment sample, wherein the contact experiment sample comprises a wheel sample and a steel rail sample, the wheel sample and the steel rail sample are in line contact, the contact sample is sequentially processed, cleaned and weighed, and the initial mass of the wheel sample is m0Then, mounting the cleaned wheel sample and the cleaned steel rail sample on a contact fatigue test sample machine;
s2, sequentially carrying out a non-lubrication rolling contact experiment and a lubrication condition rolling contact experiment on the wheel sample through a contact fatigue test sample machine;
s3, carrying out ultrasonic cleaning and weighing on the tested wheel sample to obtain the mass m of the tested wheel sample, and obtaining the weight loss delta m of the wheel processing sample, which is m-m0；
S4, dissecting the wheel sample, collecting surface crack pictures along the outer arc of the sample by field by using a metallographic microscope, and acquiring the crack density and the crack depth of the wheel sample based on the collected pictures;
and S5, evaluating the rolling contact fatigue performance of the wheel surface based on the crack density, the crack depth and the weight loss.
2. The method for evaluating rolling contact fatigue performance of a railroad locomotive wheel surface according to claim 1, wherein the method for determining test parameters of a lubrication-free rolling contact test is as follows:
taking the maximum contact stress of the wheel in service as the contact stress P for experiments0Based on experimental contact stress P0Determining the test load F of a contact fatigue test specimen machine0；
Taking the actual running rotating speed of the wheel as the wheel test rotating speed V0；
Setting the maximum slip ratio of the actual running of the wheel to be the slip delta of the experimental sample;
the experimental weekly value satisfies the following conditions: the surface cracks were initiated in the wheel samples, but the cracks did not sufficiently spread and flake-like flaking occurred on the surface of the wheel samples.
3. The method for evaluating rolling contact fatigue performance of a railroad locomotive wheel surface according to claim 1, wherein the experimental parameter determination method of the rolling contact experiment of the lubrication condition is as follows:
taking the maximum contact stress of the wheel in service as the contact stress P for experiments0Based on experimental contact stress P0Determining the test load F of a contact fatigue test specimen machine0；
Taking the actual running rotating speed of the wheel as the wheel test rotating speed V0；
Taking the actual running slip ratio of the wheel under the linear working condition as the slip delta of the experimental sample, wherein the slip delta is smaller than the maximum actual running slip ratio of the wheel;
the experiment frequency meets the following requirements: the initiated cracks are expanded to the inside, and the lines are fully expanded, so that the surface of the wheel sample begins to have large stripping blocks.
4. The method for evaluating rolling contact fatigue performance of a railroad locomotive wheel surface according to claim 2, wherein the test parameters of the unlubricated rolling contact test have values in the ranges:
the contact stress is 1000-1500MPa, the rotating speed is 400-800 rpm, the slip is 0.5-1.0%, and when the friction coefficient reaches 0.25, the rotation is continued for 6000-15000 rpm.
5. The method of evaluating rolling contact fatigue performance of a railroad locomotive wheel surface according to claim 4, wherein the test parameters of the unlubricated rolling contact test are:
the contact pressure stress is 1227MPa, the rotating speed is 500 r/min, the slip is 0.75%, and when the friction coefficient reaches 0.25, the rotating is continued for 9000 r.
6. The method for evaluating rolling contact fatigue performance of a railroad locomotive wheel surface according to claim 3, wherein the range of experimental parameters of the rolling contact experiment under the lubricating condition is as follows:
the contact stress is 1000-1500MPa, the rotating speed is 400-800 r/min, the slip is adjusted to 0.1-0.5%, the total experimental rotation number is 10000-30000 r, and the lubricating medium is water, oil or 10% glycol aqueous solution.
7. The method of evaluating rolling contact fatigue performance of a railroad locomotive wheel surface according to claim 6, wherein the experimental parameters of the rolling contact experiment of the lubrication condition are:
the contact pressure stress is 1227MPa, the rotating speed is 500 r/min, the slip is adjusted to 0.3 percent, the total experimental rotating speed is 20000 r, and the lubricating medium adopts 10 percent glycol aqueous solution.
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