A Method for Establishing a Rolling Contact Fatigue Damage Function of Heavy Haul Railway Rails

Abstract

The present invention relates to the technical field of transportation, and specifically, to a method for establishing a rolling contact fatigue damage function of heavy-haul railway rails, which includes the following steps: Step 1, determine the critical initiation position of rolling contact fatigue; Step 2, determine the critical wear number for fatigue initiation; Step 3, estimate the rolling contact fatigue initiation rate; Step 4, determine the damage function through a linear relationship. The present invention can preferably establish a damage function model.

Description

Technical Field

[0001] The present invention relates to the technical field of transportation, and specifically, to a method for establishing a rolling contact fatigue damage function of heavy haul railway rails. Background Art

[0002] With the development of the national economy, heavy haul freight railways have become an important resource transportation mode in China. The axle load of heavy haul trains is large, and the line operation frequency is increased, which greatly improves the transportation efficiency. However, at the same time, the service conditions of the rails are deteriorated, and the rolling contact fatigue problem of the rails in small-radius curve sections is prominent. Rolling contact fatigue deteriorates the wheel-rail service state, reduces the driving safety, and greatly increases the operation and maintenance costs.

[0003] The best way to control rolling contact fatigue is to inhibit its initiation. Therefore, in engineering, a rolling contact fatigue initiation prediction model is necessary. The damage function model, as an engineering prediction tool for wheel-rail rolling contact fatigue, is widely accepted worldwide. Once the damage function of a certain material rail is determined and combined with the prediction results of a train dynamics model that fully considers various influencing factors, it can be judged whether rolling contact fatigue occurs in the rails of different sections and the severity of the rolling contact fatigue damage, that is, the applicability of the rail of this material is obtained, providing guidance for the formulation of maintenance strategies such as rail material selection and preventive turning for different sections. However, the establishment of the current damage function model is relatively complex and not accurate enough. Summary of the Invention

[0004] The content of the present invention is to provide a method for establishing a rolling contact fatigue damage function of heavy haul railway rails, which can preferably establish a damage function model.

[0005] According to a method for establishing a rolling contact fatigue damage function of heavy haul railway rails of the present invention, it includes the following steps:

[0006] Step 1: Determine the critical initiation position of rolling contact fatigue;

[0007] Step 2: Determine the critical wear number for fatigue initiation;

[0008] Step 3: Estimate the rolling contact fatigue initiation rate;

[0009] Step 4: Determine the damage function through a linear relationship.

[0010] Preferably, in Step 1, the method for determining the critical crack initiation position is:

[0011] Along the train running direction, there is a phenomenon that rolling contact fatigue appears from scratch on the entry transition curve, while on the exit transition curve, it changes from existing to disappearing. The critical position where the crack just occurs corresponds to the first threshold value A of rolling contact fatigue. First, determine the critical position where the crack just occurs, that is, as the superelevation increases in the transition curve section, the superelevation position where the crack-free state reaches a crack surface length of 2 mm is determined as the critical initiation position.

[0012] Preferably, in step 2, determine the wear number at the critical crack initiation position through train dynamics, that is, determine the abscissa of the threshold value A in the damage function, specifically as follows:

[0013] 1.1) Establish a train dynamics model;

[0014] Establish a train dynamics model including two locomotives and one freight car in the SIMPACK environment. Another 104 freight cars are applied to the coupler at the tail of the freight car model in the form of equivalent loads. Take the guiding wheel pair of the front bogie of the locomotive as axle 1 and so on. The last wheel pair of the rear steering knuckle of the second locomotive in internal reconnection is axle 8, and the same applies to the freight car. The locomotive sub-model includes 1 car body, 2 frames and 4 wheel pairs, with a total of 54 degrees of freedom, while the freight car sub-model includes 1 car body, 4 side frames, 4 wheel pairs, bolster carriers and bolster, with a total of 68 degrees of freedom. The couplers between the locomotive and the locomotive, and between the locomotive and the freight car are simulated by force elements. In the model, the car body and the bogie are connected by secondary suspension, and the bogie and the wheel pair are connected by primary suspension. The spring and shock absorber elements of the primary and secondary suspensions are simulated by force elements. The dynamic simulation speed is taken as the heavy-haul train speed of 67 km / h, and the time step is taken as 0.02 s, which corresponds to a moving distance of 0.37 m.

[0015] In the track sub-model of the train dynamics model, the relevant superelevation and transition curve length parameters are set according to the actual situation of the line. The simulated train passing speed is taken as the train speed measured on-site.

[0016] 1.2) Based on the wheel-rail rolling contact parameters of each axle at any moment output by the train dynamics model, determine the wear number when each axle passes through any position on the curve track.

[0017] Preferably, in step 3, first determine the damage caused by each train, specifically: calculate the number of trains passing through at the time of initiation from the number of days of crack initiation after the new rail is put into service on the corresponding radius curve observed on-site and the number of trains passing through each day. The reciprocal of the number of trains passing through at the time of initiation is the damage caused by each train.

[0018] Preferably, in step 3, determine the initiation rate of rail rolling contact fatigue, that is, the slope of the AB segment of the damage function; specifically:

[0019] The damages caused by locomotives and freight cars are calculated separately and linearly accumulated, and it is assumed that the corresponding data points of locomotives and freight cars are all on the AB segment; the ordinate of the damage function is the damage amount D, the abscissa is the wear number Tγ, and the intercept form function of the AB segment is Tγ = mD + a, where the reciprocal of m is the slope of the AB segment, and a represents the abscissa of point A in the first segment of the damage function. Considering the transverse dispersion of damage within the contact patch, the total fatigue damage amount D caused by the passage of a train is as follows:

[0020]

[0021] Among them, n L and n W represent the number of wheels of a train passing through the fatigue zone in the model. Since only single-section freight cars are considered in the model, the total damage of freight cars in the whole train is 105 times that of a single-section freight car. b L and b W represent the semi-major axis lengths of the wheel-rail contact patch, and the subscripts L and W represent locomotives and freight cars respectively;

[0022] Using the total damage amount caused by each train derived from the fatigue crack initiation days in the circular curve section and the corresponding Tγ values obtained from simulation calculations, the corresponding m values under different radius curves are determined through the above formula. Then, taking the reciprocal k of m is the corresponding slope, and further taking the average value of all the obtained k values is the slope of the AB segment of the damage function.

[0023] Preferably, in step 4, specifically:

[0024] 4.1) Determine the abscissa of point B:

[0025] First, calculate the average value of the wear numbers of each wheel passing through the fatigue zone in the circular curve section; considering the significant differences between locomotives and freight cars, then find the average value Tγ Lm of the average wear numbers of each locomotive wheel passing through the fatigue zone, and the average value Tγ Wm of the average wear numbers of each freight car wheel passing through the fatigue zone; the fatigue zone is the area with the largest predicted wear number; take the integer of the maximum value among the average value Tγ Lm and the average value Tγ Wm as the abscissa of point B of the damage function;

[0026] 4.2) Determine the abscissa of point C;

[0027] Based on the damage function development report of RSSB, derive the slope of the wear BC segment according to the slope of the AB segment of the damage function, and then obtain the coordinates of point C;

[0028] 4.3) According to the abscissa of the threshold value A in the damage function, the slope of the AB segment, the abscissa of point B, and the abscissa of point C, obtain the corresponding damage function model.

[0029] The beneficial effects of the present invention are as follows:

[0030] The original method for developing the damage function proposed by RSSB in the present invention has been improved by considering the critical positions where rolling contact fatigue (RCF) occurs on the transition curve, thereby more accurately and effectively determining the critical value at which rolling contact fatigue (RCF) begins.

[0031] Based on the actual observations of rolling contact fatigue of heavy-haul line rails and taking the simulation of the operating conditions of actual operating trains as the core means, the present invention is more applicable to the service conditions of heavy-haul rails and provides key support for more accurately predicting the damage of heavy-haul rails. The present invention can also be transplanted to other heavy-haul lines to establish damage function models for rails of more materials under different operating conditions, and ultimately realize the selection of rails of different materials based on quantitative damage prediction and personalized rail selection for any section of the road. Description of the Drawings

[0032] Figure 1 It is a flow chart of a method for establishing a rolling contact fatigue damage function of heavy-haul railway rails in an embodiment;

[0033] Figure 2 It is a schematic diagram of a train dynamics model in an embodiment;

[0034] Figure 3 It is a schematic diagram comparing the RCF and wear rate of U75V quenched rails in an embodiment;

[0035] Figure 4 It is a damage function model of U75V quenched rails in an embodiment;

[0036] Figure 5 It is a damage function model of U76CrRE (second-generation rare earth) heat-treated rails in an embodiment. Detailed Embodiments

[0037] To further understand the content of the present invention, the present invention will be described in detail with reference to the drawings and embodiments. It should be understood that the embodiments are only for explaining the present invention and not for limiting it.

[0038] Embodiment

[0039] As Figure 1 shown, this embodiment provides a method for establishing a rolling contact fatigue damage function of heavy-haul railway rails, which includes the following steps:

[0040] Step 1: Determine the critical initiation position of rolling contact fatigue.

[0041] Determination of the critical crack initiation position

[0042] Along the running direction of the train, there is a phenomenon of rolling contact fatigue from no to some on the entry relaxation curve, and from some to no on the exit relaxation curve. The critical position where the crack just occurs corresponds to the first threshold value A of rolling contact fatigue. First, the critical position where the crack just occurs is determined, that is, the position where the relaxation curve segment changes from no crack to a superelevation position of 2 mm long on the crack surface as the superelevation increases, which is determined as the critical initiation position.

[0043] Using the train dynamics model introduced above, the train passing behavior of curves with different radii is calculated respectively, and the wear number at the high / low fatigue decritical initiation position of concern on the relaxation curve is obtained, that is, the critical parameter A of the U75V quenched rail damage function is obtained.

[0044] The critical wear number A values ​​obtained from different curve transition curve segments are re-tabulated. Finally, the extracted wear numbers are averaged and rounded to 33N, which corresponds to point A in the damage function.

[0045] Step 2: Determine the critical wear number for fatigue initiation.

[0046] In step 2, the wear number at the critical position of crack initiation is determined by train dynamics, that is, the horizontal coordinate of the threshold value A in the damage function is determined as follows:

[0047] 1.1) Establish a train dynamics model;

[0048] A train dynamics model consisting of two locomotives and one freight car is established in the SIMPACK environment. The other 104 freight cars are applied to the rear coupler of the freight car model in the form of equivalent loads. Figure 2 As shown in the figure, the guide wheel pair of the front bogie of the locomotive is 1 axle, and the last wheel pair of the rear steering knuckle of the second locomotive in the inner coupling is 8 axles. The same is true for freight cars. Respectively represent the resistance of the engine and the truck, and 104 It represents the total resistance of the remaining 104 freight cars; the locomotive sub-model includes 1 car body, 2 frames and 4 wheelsets, with a total of 54 degrees of freedom, while the freight car sub-model includes 1 car body, 4 side frames, 4 wheelsets, load saddle and rocker, with a total of 68 degrees of freedom; the couplings between locomotives and locomotives, and between locomotives and freight cars are simulated by force elements; the secondary suspension is used to connect the car body and bogie, and the primary suspension is used to connect the bogie and wheelsets. The first and second suspension elements of springs and shock absorbers are simulated by force elements; the dynamic simulation speed is 67km / h for heavy-load trains (slightly higher for no-load trains), and the time step is 0.02s, corresponding to a moving distance of 0.37m.

[0049] In the track sub-model of the train dynamics model, the relevant superelevation and transition curve length parameters are set according to the actual situation of the line; the simulated train passing speed is taken as the train speed actually measured on site.

[0050] 1.2) Based on the wheel-rail rolling contact parameters (creep force / rate, contact point position, minor semi-axis length of the contact patch, etc.) of each axle at any moment output by the train dynamics model, determine the wear number when each axle passes through any position on the curved track. Develop a corresponding numerical program in MATLAB, and introduce the obtained wear number into the damage function model, then the rolling contact fatigue damage prediction at any position on the curved rail can be realized.

[0051] It should be noted that the rolling contact fatigue of the rail basically occurs continuously throughout the curve, indicating that its dominant factor is the quasi-steady state or low-frequency dynamic interaction between the wheel and rail, which has nothing to do with the medium- and high-frequency dynamic interaction between the wheel and rail. Therefore, the multi-layer complex structure of the track is ignored during modeling, and a rigid rail with a standard gauge is used instead, but the measured medium- and long-wave irregularities of the track are considered.

[0052] Step 3: Estimate the initiation rate of rail rolling contact fatigue based on the threshold value A and the damage caused by each train.

[0053] In Step 3, first determine the damage caused by each train, specifically: calculate the number of trains passing through at initiation from the number of days after the new rail is put into service on the curve with the corresponding radius observed on-site (on-site tracking test) and the number of trains passing through per day, and the reciprocal of the number of trains passing through at initiation is the damage caused by each train.

[0054] In Step 3, determine the initiation rate of rail rolling contact fatigue, that is, the slope of the AB segment of the damage function; specifically:

[0055] The first segment of the damage function is a straight line with a positive slope, and the intersection point with the horizontal axis is the critical wear number A. Here, calculate and linearly accumulate the damage caused by locomotives and freight cars separately, and assume that the corresponding data points of locomotives and freight cars are all on the AB segment (i.e., on the same straight line); the ordinate of the damage function is the damage amount D, the abscissa is the wear number Tγ, and the intercept form function of the AB segment is Tγ = mD + a, where the reciprocal of m is the slope of the AB segment, and a represents the abscissa of point A in the first segment of the damage function. Considering the lateral dispersion of damage within the contact patch, the total fatigue damage amount D caused by the passing of one train is:

[0056]

[0057] where, n L and n W represent the number of wheels of one train passing through the fatigue area in the model. Only single-unit freight cars are considered in the model, so the total damage of freight cars in a whole train is 105 times the damage of a single-unit freight car. b L and b W represent the minor semi-axis lengths of the wheel-rail contact patch, and the subscripts L and W represent locomotives and freight cars.

[0058] Using the total damage caused by each train derived from the number of days of fatigue crack initiation in the circular curve section and the corresponding Tγ value obtained from simulation calculations, the corresponding m value under different radius curves is determined through the above formula. Then, taking the reciprocal k of m gives the corresponding slope. Further, taking the average of all the obtained k values gives the slope of the AB section of the damage function.

[0059] Step 4: Determine the damage function through a linear relationship.

[0060] In Step 4, specifically:

[0061] 4.1) Determine the abscissa of point B:

[0062] First, calculate the average value of the wear of each wheel passing through the fatigue area in the circular curve section; considering the significant differences between locomotives and freight cars, then find the average value Tγ of the average wear of each locomotive wheel passing through the fatigue area Lm , and the average value Tγ of the average wear of each freight car wheel passing through the fatigue area Wm ; the fatigue area is the area with the largest predicted wear; take the integer of the maximum value among the average value Tγ Lm and the average value Tγ Wm as the abscissa of point B of the damage function.

[0063] In the final damage function, the coordinates of point A are (33, 0), the slope of the AB section is taken as 2.0×10 -6 , the coordinates of point B are (142, 2.2×10 -4 ), and the equation of the AB section of the final damage function is as follows:

[0064] D = Tγ * 2×10 -6 - 6.6×10 -5 .

[0065] 4.2) Determine the abscissa of point C.

[0066] Based on the damage function development report of RSSB, the slope of the wear BC section is derived from the slope of the AB section of the damage function, and then the coordinates of point C are obtained. From Figure 3 , it can be seen that when the wear number reaches 384.2, the wear of the U75V quenched rail is in balance with rolling contact fatigue, that is, point C of the damage function.

[0067] 4.3) According to the abscissa of the threshold value A in the damage function, the slope of the AB section, the abscissa of point B, and the abscissa of point C, obtain the corresponding damage function model.

[0068] Figure 4 Shows the damage function model of the U75V quenched rail obtained above.

[0069] Using the same method, the damage function of the U76CrRE (second-generation rare earth) heat-treated rail can be obtained, as Figure 5 shown. The finally obtained damage functions are as follows: 1) U75V quenching: A(33,0), B(142, 2.18E-4), C(384,0); 1) Second-generation rare earth (U76CrRE): A(42,0), B(177, 9.99E-5), C(455,0).

[0070] This embodiment considers the critical position where rolling contact fatigue (RCF) occurs on the transition curve, thereby more accurately and effectively determining the critical value at which rolling contact fatigue (RCF) starts, and obtaining a better damage function model.

[0071] The above has schematically described the present invention and its implementation manners. This description is not restrictive. What is shown in the drawings is only one of the implementation manners of the present invention, and the actual structure is not limited thereto. Therefore, if those of ordinary skill in the art are inspired by it and, without departing from the purpose of the present invention's creation, design structurally similar ways and embodiments to this technical solution without creative efforts, they shall fall within the protection scope of the present invention.

Claims

1. A method for establishing a rolling contact fatigue damage function of heavy haul railway rails, characterized in that: It includes the following steps: Step 1: Determine the critical initiation position of rolling contact fatigue; In Step 1, the method for determining the critical crack initiation position is as follows: Along the train running direction, there is a phenomenon of rolling contact fatigue from non - existence to existence on the entry transition curve, and a change from existence to non - existence on the exit transition curve. The critical position where the crack just occurs corresponds to the first threshold value A of rolling contact fatigue occurrence. First, determine the critical position where the crack just occurs, that is, on the transition curve section, as the superelevation increases, the superelevation position where the crack length on the crack surface reaches 2 mm from non - crack is determined as the critical initiation position; Step 2: Determine the critical wear number for fatigue initiation; Determine the wear number at the critical crack initiation position through train dynamics, that is, determine the abscissa of the threshold value A in the damage function; Step 3: Estimate the rolling contact fatigue initiation rate; Determine the rolling contact fatigue initiation rate of the rail, that is, the slope of the AB section of the damage function; Step 4: Determine the damage function through a linear relationship; In Step 4, specifically: 4.1) Determine the abscissa of point B: First, calculate the average value of the wear numbers of each wheel passing through the fatigue area in the circular curve section; considering the significant differences between locomotives and freight cars, then find the average value Tγ of the average wear numbers of each locomotive wheel passing through the fatigue area Lm , and the average value Tγ of the average wear numbers of each freight car wheel passing through the fatigue area Wm ; the fatigue area is the area with the largest wear number predicted by simulation; take the integer part of the larger number between the average value Tγ Lm and the average value Tγ Wm as the abscissa of point B of the damage function; 4.2) Determine the abscissa of point C; Based on the damage function development report of RSSB, deduce the slope of the wear BC section according to the slope of the AB section of the damage function, and then obtain the coordinates of point C; 4.3) According to the abscissa of the threshold value A in the damage function, the slope of the AB section, the abscissa of point B, and the abscissa of point C, obtain the corresponding damage function model.

2. The method for establishing a rolling contact fatigue damage function of heavy-haul railway rails according to claim 1, characterized in that: In Step 2, specifically as follows: 1.1) Establish a train dynamics model; Establish a train dynamics model including two locomotives and one freight car in the SIMPACK environment. Another 104 freight cars are applied at the coupler at the tail of the freight car model in the form of equivalent loads. Take the leading bogie's guiding wheel pair of the locomotive as axis 1, and so on. The last wheel pair of the rear steering knuckle of the second locomotive in internal - coupled connection is axis 8, and the same for the freight car. The locomotive sub - model includes 1 car body, 2 frames, and 4 wheel pairs, with a total of 54 degrees of freedom, while the freight car sub - model includes 1 car body, 4 side frames, 4 wheel pairs, bolster bearings, and bolster, with a total of 68 degrees of freedom. The couplers between locomotives and between locomotives and freight cars are simulated by force elements. In the model, the car body and the bogie are connected by secondary suspensions, and the bogie and the wheel pair are connected by primary suspensions. The spring and shock absorber elements of the primary and secondary suspensions are both simulated by force elements. The dynamic simulation speed is taken as the heavy - haul train speed of 67 km / h, and the time step is taken as 0.02 s, that is, the corresponding moving distance is 0.37 m; In the track sub - model of the train dynamics model, the relevant superelevation and transition curve length parameters are set according to the actual situation of the line. The simulated train passing speed is taken as the train speed measured on - site; 1.2) Based on the wheel - rail rolling contact parameters of each axis at any moment output by the train dynamics model, determine the wear number when each axis passes through any position on the curve track.

3. The method for establishing a rolling contact fatigue damage function of heavy-haul railway rails according to claim 2, characterized in that: In Step 3, first determine the damage caused by each train, specifically: Calculate the number of trains passing through at the time of initiation from the number of days after the new rail is put into operation on the curve with the corresponding radius observed on - site and the number of trains passing through per day. The reciprocal of the number of trains passing through at the time of initiation is the damage caused by each train.

4. The method for establishing a rolling contact fatigue damage function of heavy haul railway rails according to claim 3, wherein: In Step 3, specifically: The damages caused by locomotives and freight cars are calculated separately and linearly accumulated, and it is assumed that the corresponding data points of locomotives and freight cars are all on the AB segment; the ordinate of the damage function is the damage amount D, the abscissa is the wear number Tγ, and the intercept form function of the AB segment is Tγ = mD + a, where the reciprocal of m is the slope of the AB segment, and a represents the abscissa of point A in the first segment of the damage function. Considering the transverse dispersion of damage within the contact patch, the total fatigue damage amount D caused by a train passing through is: where n L and n W represent the number of wheels of a train passing through the fatigue area in the model. Only single-unit freight cars are considered in the model, so the total damage of freight cars in the whole train is 105 times that of a single-unit freight car. b L and b W represent the length of the semi-major axis of the wheel-rail contact patch. The subscripts L and W represent the locomotive and the freight car respectively; Using the total damage amount caused by each train derived from the fatigue crack initiation days in the circular curve segment and the corresponding Tγ values obtained from simulation calculations, the corresponding m values under different radius curves are determined through the above formula. Then, taking the reciprocal k of m gives the corresponding slope. Furthermore, taking the average value of all the obtained k values gives the slope of the AB segment of the damage function.

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