Method for evaluating allowable additional stress of seamless track on bridge based on fatigue performance

Abstract

The application discloses a kind of bridge seamless line rail allowable additional stress evaluation method based on fatigue performance, including steps as follows: selecting track traffic bridge seamless line rail specimen, the fatigue test of the rail specimen prepared is carried out using lifting method, the fatigue limit of rail under different average stress is measured.Reference lifting method test data processing mode, determine fatigue strength based on reliability theory.Based on test data, the Smith diagram of rail fatigue limit is constructed, and the allowable additional stress based on the actual service stress level of bridge seamless line is calculated.Meanwhile, through the strength checking formula in the specification of seamless line, the safety factor suitable for different line stress level can be deduced back.The application can quantitatively evaluate the fatigue performance of track traffic bridge seamless line rail under actual service stress, and determine the allowable additional stress limit that can meet the fatigue performance and material strength of rail at the same time.

Description

Technical Field

[0001] This invention belongs to the field of rail fatigue performance testing technology, and relates to a method for evaluating the allowable additional stress of seamless track rails on bridges based on fatigue performance. Specifically, it relates to an evaluation method for exploring the allowable additional stress of seamless track rails on rail transit bridges based on fatigue performance and material strength. Background Technology

[0002] With the rapid development of rail transit, seamless track, with its advantages such as smoothness, safety, and the ability to reduce the impact of vehicles on bridges, thereby reducing vibration and noise in the bridge structure and reducing the workload of track maintenance, is becoming a widely used track structure type in my country's urban rail transit and elevated railway lines. Compared with tunnel or roadbed tracks, which generally only need to avoid fatigue failure during long-term service, seamless track on bridges must bear additional stress and higher temperature stress. Therefore, it is also necessary to ensure that the total stress of the rails is within the allowable range to avoid accidents such as rail breakage or instability.

[0003] To address the aforementioned issues, it is necessary to establish a quantitative relationship between fatigue strength and total stress limit through experiments. However, current research on rail fatigue testing mainly focuses on fatigue life prediction and crack initiation mechanisms, lacking sufficient research on the fatigue performance of rails under different stress levels. Taking Chinese patent application number 202210357648.9 as an example, this patent discloses a method for predicting rail rolling contact fatigue. By extracting the Smith-Watson-Topper (SWT) parameter values ​​of all nodes near the wheel-rail contact area on any plane and selecting the maximum value of the SWT parameter, the fatigue crack initiation life at critical points can be obtained, thus predicting the location and life of rail crack initiation. However, this method cannot reflect the degradation mode of fatigue performance of seamless track rails on bridges with higher service stresses, and cannot accurately quantify the relationship model between fatigue limit and mean stress. Furthermore, current research rarely considers the combined effects of fatigue performance and material strength when assessing the safety of seamless track on bridges. Summary of the Invention

[0004] To address the shortcomings of existing technologies, the present invention aims to provide a method for evaluating the allowable additional stress of seamless track rails on bridges based on fatigue performance, thereby solving the aforementioned technical problems in the prior art.

[0005] The objective of this invention can be achieved through the following technical solutions:

[0006] 1. A method for evaluating the allowable additional stress of seamless track rails on bridges based on fatigue performance, characterized by comprising the following steps:

[0007] S1. Select seamless railway rails that have been manufactured for many years but have not yet been put into use, and obtain their material mechanical properties, including ultimate tensile strength σ. u Yield strength σ y The median and variance;

[0008] S2. The above-mentioned rails are made into standard-sized test pieces;

[0009] S3. The fatigue test of the specimen in S2 is carried out using the lifting method;

[0010] S4. Determine the allowable fatigue stress amplitude in S3, use the rise and fall method to process the test data, calculate the mean and variance of the test results, and determine the fatigue strength of the rail based on the reliability theory.

[0011] S5. Construct a fatigue limit line diagram (in the form of a Smith chart) to describe the fatigue performance of rails under different average stresses.

[0012] S6. Based on the geometric relationship, the expressions for the upper and lower limit stresses of the fatigue limit can be obtained from the Smith diagram in S5.

[0013]

[0014]

[0015] Where: σ max σ min The upper and lower limit stresses for rail fatigue; σ mean σ represents the average stress of the rail. limit y represents the maximum allowable stress value of the rail. A ~y F x represents the ordinate values ​​of nodes A through F in the Smith chart; A ~x G These are the x-coordinates of nodes A through G in the Smith graph.

[0016] S7. Based on the Smith chart in S5, determine the allowable stress value, and let the difference between the vertical coordinates of points D and E be Δσ. 临界 ,but:

[0017]

[0018] The allowable fatigue stress amplitude Δσ is obtained 容许 for:

[0019]

[0020] Where: Δσ 临界 The critical fatigue stress amplitude of the rail is based on the Smith chart from fatigue tests; Δσ p,tΔσ represents the allowable fatigue stress amplitude of the rail based on the test stress level. 容许 The allowable stress amplitude for rail fatigue under any service stress level.

[0021] S8. Through theoretical analysis or statistical analysis of measured data, the actual service stress level of the seamless track on the bridge is obtained, including the dynamic bending stress σ. D and temperature stress σ T Based on the above data and combined with the strength verification formula in the seamless circuit specification, the allowable additional stress [σ] is calculated. A,tension And the corresponding safety factor K;

[0022]

[0023] Where: [σ A,tension ] represents the allowable additional stress; σ y σ is the rail yield strength; K is the safety factor; T For rail temperature stress; σ D This refers to the dynamic bending stress of the rail.

[0024] Preferably, the method for evaluating the allowable additional stress of seamless track rails on bridges based on fatigue performance is characterized in that, in step S3, when the step method is used for testing, the minimum stress σ min,t It remains unchanged.

[0025] Preferably, the method for evaluating the allowable additional stress of seamless track rails on bridges based on fatigue performance is characterized in that, in step S4, under the premise of ensuring that the test sample size meets the minimum number of observations related to the coefficient of variation, confidence level, and error limit, an appropriate confidence level and error limit are selected to finally determine the experimentally based allowable fatigue stress amplitude Δσ. p,t .

[0026] Preferably, the method for evaluating the allowable additional stress of seamless track rails on bridges based on fatigue performance is characterized by using a confidence level of 75% and an error limit of 5%, with the corresponding 5% quantile fatigue strength being:

[0027] Δσ p,t =Δσ p,m -2.048s.

[0028] Preferably, the method for evaluating the allowable additional stress of seamless track rails on bridges based on fatigue performance is characterized in that, in step S8, when σ D >Δσ 临界 At that time, by:

[0029]

[0030] get:

[0031] When σ D ≤Δσ 临界 At that time, by:

[0032]

[0033] get:

[0034] Where: σ D For the dynamic bending stress of the rail; Δσ 临界 The critical fatigue stress amplitude of the rail obtained in S7; [σ A,tension ] represents the allowable additional stress of the rail based on the Smith chart from fatigue tests; σ T For rail temperature stress; σ R For residual stress in the rail; σ y σ is the rail yield strength; K is the safety factor; limit This represents the maximum allowable stress value for the rail.

[0035] Beneficial effects of the invention:

[0036] 1. Based on fatigue test data, this invention constructs a Smith chart showing the change of rail fatigue limit with average stress, realizing a quantitative evaluation of the fatigue performance of seamless rails on rail transit bridges with different service stresses under the influence of factors such as rail transit type, train speed, rail smelting and rolling technology, and bridge span, laying the foundation for establishing a theoretical system for fatigue design of seamless rails on bridges.

[0037] 2. This invention can determine the allowable additional stress limit [σ] that simultaneously satisfies the fatigue performance and material strength of the seamless track rails on bridges, based on the actual levels of dynamic bending stress, residual stress, temperature stress, and additional stress. A,tension ].

[0038] 3. This invention can determine the value of the safety factor K when verifying the total stress of the rail based on the Smith chart of the rail fatigue limit and combined with the actual service stress of the seamless track on the bridge. By comparing with the current standard limit, it clarifies the strength evaluation criteria applicable to the rails of seamless track on different types of rail transit bridges. Attached Figure Description

[0039] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the accompanying drawings used in the description of the embodiments or the prior art will be briefly introduced below.

[0040] Figure 1 This is a schematic diagram of the control flow according to an embodiment of the present invention;

[0041] Figure 2 This is a Smith chart used to determine the allowable stress according to an embodiment of the present invention;

[0042] Figure 3 This is a Smith chart of an embodiment of the present invention when the dynamic bending stress is greater than the critical stress;

[0043] Figure 4 This is a Smith chart of an embodiment of the present invention when the dynamic bending stress is less than the critical stress. Detailed Implementation

[0044] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0045] like Figure 1 As shown, this embodiment of the invention provides a method for evaluating the allowable additional stress of seamless track rails on bridges based on fatigue performance, including the following steps:

[0046] S1. First, select U75V steel rails, the most commonly used type for straight sections of existing urban rail transit lines, with a rail weight of 60 kg / m. It is advisable to select rails that have been in production for many years but have not yet been put into use. Obtain the mechanical property parameters of the rails, including the ultimate tensile strength σ, by consulting the manufacturer or through material property testing. u Yield strength σ y The median and variance.

[0047] S2. The rails in S1 are made into physical rail specimens with a length of 1.2m each.

[0048] S3. Fatigue tests were conducted on the specimens from S2 using the lifting method. The specific procedure was as follows: the rail was simply supported on two supports with a support distance of 1m, rail head upwards, and a concentrated load was applied at the midpoint of the span, with 2 million loading cycles. The additional stress (σ) of the seamless track rail on the bridge was selected. A ) and temperature stress (σ T The sum of these values ​​is used as the minimum stress (σ) in the actual bending fatigue test. min,t The fatigue stress amplitude was continuously changed, and the fatigue resistance of the rail was measured using the lifting method.

[0049] Among them: when using the step method for testing, the minimum stress σ min,t The stress amplitude remains constant. A specific initial fatigue stress amplitude is selected to test the first specimen in the series. If the specimen fails within 2 million loading cycles, the stress amplitude of the next specimen is reduced by 10 MPa; if it does not fail after 2 million loading cycles, the stress amplitude of the next specimen is increased by 10 MPa. The test continues until all specimens in the series have been tested.

[0050] S4. Determine the allowable fatigue stress amplitude in S3. Referring to the data processing method of the rise and fall method, calculate the mean value Δσ of the test results. p,m The variance s was calculated, and the fatigue strength of the rail was determined based on the reliability theory.

[0051] To ensure that the test half-sample size meets the coefficient of variation (s / Δσ) p,m Given the minimum number of observations related to confidence level and error limit, select appropriate confidence level and error limit to ultimately determine the experimentally based allowable fatigue stress amplitude Δσ. p,t Taking a 75% confidence level and a 5% error limit as an example, the corresponding 5% quantile fatigue strength is:

[0052] Δσ p,t =Δσ p,m -2.048s.

[0053] S5, such as Figure 2 As shown, a Smith chart is constructed based on the data from S4; the horizontal axis of the chart represents the mean stress (σ). mean The vertical axis represents the maximum and minimum stress (σ). max σ min Points B and C, corresponding to the test results, can be connected to the material ultimate strength point A (σ) of the rail by two straight lines. u ,σ u (Connected). Considering the residual stress σ that always exists in the rail. R The origin is moved from O' to point O. Therefore, the actual coordinates of point B and point C are (σ... min,t +0.5Δσ p,t +σ R , σ min,t +Δσ p,t +σ R ) and (σ min,t +0.5Δσ p,t +σ R , σ min,t +σ R Construct a rod with a height equal to the maximum allowable stress (σ) of the steel. limit The horizontal line is set as the upper limit to ensure that all stresses are within the elastic range, σ limit Take 95% of the yield strength. This horizontal line intersects lines AB and AO at points D and F, respectively. A perpendicular line is drawn from point D to intersect line AC at point E. Furthermore, line AC intersects the x-coordinate at point G, and a perpendicular line is drawn from point G to intersect line AB at point H. At this point, the Smith chart of the tensioned rail consists of HDFEG. Based on the known coordinates of points A, B, and C, the coordinates of other key points are calculated as follows:

[0054] Table 1. Coordinates of key points in the Smith chart.

[0055]

[0056] Where: σ limit y represents the maximum allowable stress value of the rail. A ~y G x represents the ordinate values ​​of nodes A through G in the Smith chart; A ~x G These are the x-coordinates of nodes A through G in the Smith graph.

[0057] Compared to rails in tunnels or roadbed sections, seamless track rails on bridges bear additional stresses and higher temperature stresses on top of dynamic bending stress, leading to a decline in fatigue performance due to the increased average service stress. This method, by plotting Smith charts, comprehensively describes the fatigue performance variations of seamless track rails on bridges under different service stresses for various rail transit types (urban rail, conventional railways, high-speed rail, etc.) and bridge spans, providing necessary data support for the fatigue design theory of seamless track rails on bridges. Furthermore, this method, through coordinate axis transformation based on measured residual stress, enables the Smith charts to more accurately reflect the influence of residual stress on the fatigue performance of existing seamless track rails on bridges.

[0058] S6. Based on geometric relationships, the upper and lower limit stresses (σ) of the fatigue limit can be obtained from the Smith diagram in step 5. max σ min The expression;

[0059]

[0060]

[0061] S7. Referring to the rail strength calculation criteria in the seamless rail specifications, and based on the Smith chart in step 5, the allowable stress value can be determined by calculating the total rail stress. Let the difference between the vertical coordinates of points D and E be Δσ. 临界 ,but:

[0062]

[0063] The allowable fatigue stress amplitude Δσ is obtained 容许 for:

[0064]

[0065] S8. The allowable total tensile stress of the rail depends on the upper limit of the fatigue limit. Considering the significant differences in rail fatigue performance requirements among different types of rail transit, the remaining space for additional stress varies. Through theoretical analysis or statistical analysis of measured data, the actual service stress level of seamless track on the bridge, including dynamic bending stress σ, is obtained. Dand temperature stress σ T According to the dynamic bending stress σ D It should not exceed the allowable fatigue stress amplitude Δσ under operating stress. 容许 The allowable additional stress [σ] based on the Smith chart from fatigue tests was calculated. A,tension ]. Meanwhile, based on the above data, [σ] A,tension Substituting the values ​​into the strength verification formula, the corresponding safety factor K can be calculated.

[0066] like Figure 3 As shown, when σ D >Δσ 临界 At that time, by:

[0067]

[0068] get:

[0069] like Figure 4 As shown, when σ D ≤Δσ 临界 At that time, by:

[0070]

[0071] get:

[0072] The allowable additional fatigue stress [σ] can be determined based on the actual levels of dynamic bending stress and residual stress in the rail transit vehicle. A,tension The value of the safety factor K when verifying the total stress of the rail is determined and compared with the current standard limit, thus clarifying the evaluation criteria for the strength of rails in seamless tracks on rail transit bridges.

[0073] This invention establishes a curve relating the rail fatigue limit to the mean stress, enabling a realistic evaluation of the fatigue performance of seamless track rails on bridges under actual service stress levels. It also determines the allowable additional stress limit that simultaneously satisfies both rail fatigue performance and material strength requirements. This invention lays a theoretical foundation for the fatigue design of seamless track on bridges and the design of components related to the interaction between rail and bridge.

[0074] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the claimed invention.

Claims

1. A method for evaluating the allowable additional stress of seamless track rails on bridges based on fatigue performance, characterized in that, Includes the following steps: S1. Select seamless railway rails and obtain their material mechanical properties, including ultimate tensile strength σ. u Yield strength σ y The median and variance; S2. The above-mentioned rails are made into standard-sized test pieces; S3. The fatigue test of the specimen in S2 is carried out using the lifting method; S4. Determine the allowable fatigue stress amplitude in S3, use the rise and fall method to process the test data, calculate the mean and variance of the test results, and determine the fatigue strength of the rail based on the reliability theory. S5. Construct a fatigue limit curve to describe the fatigue performance of rails under different average stresses, and represent it in the form of a Smith chart. S6. Based on the geometric relationship, obtain the expressions for the upper and lower limit stresses of the fatigue limit from the Smith diagram in S5. Where: σ max σ min The upper and lower limit stresses for rail fatigue; σ mean σ represents the average stress of the rail. limit y represents the maximum allowable stress value of the rail. A ~y F x represents the ordinate values ​​of nodes A through F in the Smith chart; A ~x G These are the x-coordinate values ​​of nodes A through G in the Smith chart; S7. Based on the Smith chart in S5, determine the allowable stress value, and let the difference between the vertical coordinates of points D and E be Δσ. 临界 ,but: The allowable fatigue stress amplitude Δσ is obtained 容许 for: Where: Δσ 临界 The critical fatigue stress amplitude of the rail; Δσ 容许 Δσ represents the allowable fatigue stress amplitude of the rail. p,t This is the allowable fatigue stress amplitude of the rail based on experiments; S8. Through theoretical analysis or statistical analysis of measured data, the actual service stress level of the seamless track on the bridge is obtained, including the dynamic bending stress σ. D and temperature stress σ T Based on the above data and combined with the strength verification formula in the seamless circuit specification, the allowable additional stress [σ] is calculated. A,tension And the corresponding safety factor K; Where: [σ A,tension ] represents the allowable additional stress; σ y σ is the rail yield strength; K is the safety factor; T For rail temperature stress; σ D This refers to the dynamic bending stress of the rail.

2. The method for evaluating the allowable additional stress of seamless track rails on bridges based on fatigue performance according to claim 1, characterized in that, In S3, when the step method is used for testing, the minimum stress σ min,t It remains unchanged.

3. The method for evaluating the allowable additional stress of seamless track rails on bridges based on fatigue performance according to claim 1, characterized in that, In step S4, while ensuring that the test sample size meets the minimum number of observations related to the coefficient of variation, confidence level, and error limit, an appropriate confidence level and error limit are selected to finally determine the experimentally based allowable fatigue stress amplitude Δσ. p,t .

4. The method for evaluating the allowable additional stress of seamless track rails on bridges based on fatigue performance according to claim 3, characterized in that, Using a confidence level of 75% and an error limit of 5%, the corresponding 5% quantile fatigue strength is: Board p,t =Ds p,m -2.048s.

5. The method for evaluating the allowable additional stress of seamless track rails on bridges based on fatigue performance according to claim 1, characterized in that, In S8, when σ D >Δσ 临界 At that time, by: get: When σ D ≤Δσ 临界 At that time, by: get: Where: σ D For the dynamic bending stress of the rail; Δσ 临界 The critical fatigue stress amplitude of the rail obtained in S7; [σ A,tension ] represents the allowable additional stress of the rail based on the Smith chart from fatigue tests; σ T For rail temperature stress; σ R For residual stress in the rail; σ y σ is the rail yield strength; K is the safety factor; limit This represents the maximum allowable stress value for the rail.

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