A method for evaluating the reliability of fatigue crack detection pieces

Abstract

The present invention proposes a method for evaluating the reliability of a fatigue crack detection sheet, which relates to the technical field of rail fatigue crack monitoring. The method involves installing a fatigue crack detection sheet at a predetermined position on a rail specimen to form a fatigue sample. A fatigue test is then performed on the fatigue sample while simultaneously monitoring the resistance change of the fatigue crack detection sheet. The fatigue test is terminated when the resistance of the fatigue crack detection sheet suddenly increases. The fatigue cracks generated on the rail specimen and the detection cracks generated on the fatigue crack detection sheet are compared, and the reliability of the fatigue crack detection sheet is determined based on the comparison results. The method for evaluating the reliability of a fatigue crack detection sheet proposed by the present invention can effectively evaluate the reliability of a fatigue crack detection sheet.

Description

Technical Field

[0001] The invention relates to the technical field of rail fatigue crack monitoring, and in particular to a method for evaluating the reliability of a fatigue crack detection piece. Background Art

[0002] Rails are a crucial component of railway tracks, guiding the wheels of rolling stock while also carrying and transmitting wheel forces to the sleepers. Rails are subject to complex and variable stresses and operate in a harsh environment, leading to numerous fatigue cracks on rails and switches. This not only impacts ride stability and comfort but, in severe cases, can also cause rail breakage, directly endangering train safety.

[0003] The railway industry primarily monitors fatigue cracks in rails and turnout components in service using nondestructive testing methods such as ultrasonic testing, magnetic particle testing, and eddy current testing. Currently, a new technological development involves attaching conductive test strips to the rail surface and monitoring fatigue cracks by measuring changes in the strip's resistance. However, this new monitoring technology still presents numerous drawbacks and challenges.

[0004] The detection sheet is directly attached to the surface of rails and turnout components to detect surface cracks. The crack detection sheet consists of a specific resistance wire that detects cracks by detecting the on / off state of the resistance. When the resistance of the crack detection sheet is very low, the component surface is considered intact and crack-free. When the resistance of the crack detection sheet changes significantly, the resistance wire is considered disconnected, indicating a crack has occurred on the component surface.

[0005] Therefore, the reliability of the test strips is crucial. Whether they can withstand field use in complex environments directly affects the accuracy of surface fatigue crack monitoring results for rail and switch components. Furthermore, since rail and switch components are subject to high summer temperatures, severe winter cold, rain immersion, and atmospheric corrosion during field use, whether the test strips will prematurely fail under these fatigue loads and complex environments, and whether they can properly monitor crack initiation, also poses a technical challenge.

[0006] In view of this, the inventors, based on their many years of experience in production design in this field and related fields, have designed a method for evaluating the reliability of fatigue crack detection pieces after repeated experiments, in order to solve the problems existing in the prior art. Summary of the Invention

[0007] The object of the present invention is to provide a method for evaluating the reliability of a fatigue crack detection piece, which can effectively evaluate the reliability of the fatigue crack detection piece.

[0008] To achieve the above-mentioned objectives, the present invention proposes a method for evaluating the reliability of a fatigue crack detection sheet, wherein a fatigue crack detection sheet is installed at a predetermined position on a rail specimen to form a fatigue sample, a fatigue test is performed on the fatigue sample while simultaneously monitoring the resistance change of the fatigue crack detection sheet. When the resistance of the fatigue crack detection sheet suddenly increases, the fatigue test is stopped, the fatigue crack generated on the rail specimen and the detection crack generated on the fatigue crack detection sheet are compared, and the reliability of the fatigue crack detection sheet is determined based on the comparison result.

[0009] Compared with the prior art, the present invention has the following characteristics and advantages:

[0010] The fatigue crack detection sheet reliability evaluation method proposed in the present invention installs the fatigue crack detection sheet on a rail sample so that it undergoes relevant fatigue tests and inspections together with the rail sample. This can more realistically simulate the wear of on-site components and the fatigue crack detection sheet, and thus more realistically reflect the performance of the fatigue crack detection sheet in on-site use.

[0011] The method for evaluating the reliability of a fatigue crack detection piece proposed in the present invention is not only applicable to the reliability evaluation of fatigue crack monitoring by the fatigue crack detection piece, but also applicable to the reliability evaluation of monitoring instantaneous fracture by the fatigue crack detection piece. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] The drawings described herein are for illustrative purposes only and are not intended to limit the scope of the present invention in any way. In addition, the shapes and proportional dimensions of the various components in the drawings are merely illustrative and are used to help understand the present invention, and are not intended to specifically limit the shapes and proportional dimensions of the various components of the present invention. Those skilled in the art can select various possible shapes and proportional dimensions to implement the present invention according to specific circumstances under the guidance of the present invention.

[0013] Figure 1 Schematic diagram of the method for evaluating the reliability of a fatigue crack detection sheet proposed in the present invention;

[0014] Figure 2 Schematic diagram of the structure of a rail sample according to an embodiment of the present invention;

[0015] Figure 3 A side view of an embodiment of a rail specimen of the present invention;

[0016] Figure 4 A schematic diagram of a method for installing the fatigue crack detection sheet of the present invention;

[0017] Figure 5 Schematic diagram of another installation method of the fatigue crack detection sheet in the present invention;

[0018] Figure 6Schematic diagram of fatigue testing in a temperature environment box according to the present invention;

[0019] Figure 7 Schematic diagram of the connection between the fatigue crack detection sheet and the resistance measuring device in the present invention;

[0020] Figure 8 Schematic diagram of the structure of another embodiment of the rail specimen of the present invention;

[0021] Figure 9 is a side view of another embodiment of a rail specimen of the present invention;

[0022] Figure 10 Schematic diagram of fatigue cracks generated in a rail specimen in the present invention;

[0023] Figure 11 Schematic diagram of a detection crack of the fatigue crack detection sheet of the present invention;

[0024] Figure 12 Schematic diagram of the overlap between the fatigue crack on the rail specimen and the crack on the test piece in the present invention;

[0025] Figure 13 Schematic diagram showing that the fatigue crack on the rail specimen and the crack on the test piece do not coincide (position deviation) in the present invention;

[0026] Figure 14 Schematic diagram showing that the fatigue crack on the rail specimen and the crack on the test piece do not coincide with each other (early fracture) in the present invention.

[0027] Description of reference numerals:

[0028] 10. Fatigue crack detection piece; 11. Sensing wire;

[0029] 20. Rail specimen; 22. Original surface;

[0030] 23. Cutting line; 25. Pin hole;

[0031] 30. Fatigue cracks; 40. Detection cracks;

[0032] 50. Resistance measuring device; 51. Connecting wires;

[0033] 52. Welding connection point 60. Temperature environment chamber;

[0034] 70. Fatigue testing machine. DETAILED DESCRIPTION

[0035] The details of the present invention can be more clearly understood by referring to the accompanying drawings and the description of the specific embodiments of the present invention. However, the specific embodiments of the present invention described herein are only for the purpose of explaining the present invention and are not to be construed as limiting the present invention in any way. Based on the teachings of the present invention, a skilled person can conceive of any possible variations based on the present invention, and such variations should be considered to fall within the scope of the present invention.

[0036] like Figures 1 to 11 As shown, the present invention proposes a method for evaluating the reliability of a fatigue crack detection sheet. A fatigue crack detection sheet 10 is installed at a predetermined position on a rail specimen 20 to produce a fatigue sample. A fatigue test is performed on the fatigue sample while simultaneously monitoring the resistance change of the fatigue crack detection sheet 10. The fatigue test is stopped when the resistance of the fatigue crack detection sheet 10 suddenly increases. A fatigue crack 30 generated on the rail specimen 20 is compared with a detection crack 40 generated on the fatigue crack detection sheet 10, and the reliability of the fatigue crack detection sheet 10 is determined based on the comparison result.

[0037] The reliability evaluation method of the fatigue crack detection piece proposed in the present invention is as follows: Figure 1 As shown, the fatigue crack detection piece 10 is installed on the rail sample 20 so that it can undergo relevant fatigue tests and inspections together with the rail sample 20. This can more realistically simulate the wear of on-site components and the fatigue crack detection piece 10, and more realistically reflect the performance of the fatigue crack detection piece 10 in on-site use.

[0038] The fatigue crack detection piece reliability evaluation method proposed in the present invention is applicable not only to the reliability evaluation of the fatigue crack detection piece 10 for fatigue crack monitoring, but also to the reliability evaluation of the fatigue crack detection piece 10 for monitoring instantaneous fracture conditions.

[0039] In an optional embodiment of the present invention, Figure 2 、 Figure 3 As shown, the rail sample 20 has an original surface 22 , a cutting line 23 is opened on the original surface 22 , and the predetermined position is set on the original surface 22 and has a predetermined distance from the end of the cutting line 23 .

[0040] The original surface 22 of the rail specimen 20 is identical to the original surface of the field component, accurately reflecting the roughness of the original rail surface. This minimizes the impact of varying surface conditions on the reliability of the fatigue crack detection sheet 10 and more accurately reflects the performance of the fatigue crack detection sheet in field use. In an optional embodiment, during installation, the working surface of the fatigue crack detection sheet 10 is adhered to the original surface 22 of the rail specimen 20.

[0041] In an optional example of this embodiment, the predetermined distance is 3 mm to leave ample space for the pre-crack.

[0042] The predetermined distance is set because before the fatigue test begins, according to the requirements of standard GB / T 6398-2017, a large load is needed to pre-form the fatigue crack, and a fatigue crack of a certain size must be generated at the tip of the online cutting notch, so that a formal fatigue test with controlled fatigue rate can be carried out later.

[0043] In an optional example of this embodiment, the cutting line 23 is formed by machining.

[0044] In an optional embodiment of the present invention, the length of the cutting line 23 is 1 / 4 of the effective width W of the rail sample 20; of course, other lengths are also possible, and those skilled in the art can also determine it according to actual conditions.

[0045] In an optional example of this embodiment, the rail sample 20 is a rail normally used on site. The size of the rail sample 20 can be optimized according to the actual size of the rail. A cutting line 23 is machined inside the notch by wire-cutting electric discharge. One surface of the rail sample 20 is the original surface of the rail, and the other surface is the machined surface.

[0046] In the present invention, the sidewalls of the rail specimen 20 are notched. This notch is intentionally machined later to accommodate a COD gauge extensometer, which is used to measure crack propagation length during fatigue testing and thereby control the corresponding fatigue crack growth rate. For its operating principle and installation method, please refer to the compliance method in Appendix B of GB / T 6398-2017. Preferably, the preparation process for the rail specimen 20 can be designed and prepared based on the compact tensile specimen shape specified in GB / T 6398, "Metallic Materials - Fatigue Crack Growth Methods."

[0047] In an optional example of this embodiment, the fatigue crack detection sheet 10 is adhered to the rail specimen 20 .

[0048] In one optional example, the fatigue crack detection sheet 10 is attached as follows: 1. First, clean the surface (original surface) of the mounting location using a non-woven fabric soaked in acetone or alcohol. 2. Apply adhesive, such as 502 adhesive, to the cleaned original surface 22. 3. Immediately place the fatigue crack detection sheet 10 in the desired orientation at the desired location and apply pressure using your fingers or another rolling tool.

[0049] In an optional example of this embodiment, the fatigue crack detection plate 10 has at least one conductive sensing wire 11. The fatigue crack detection plate is installed in an orientation such that the sensing wire 11 forms an angle with the cutting line 23. The side of the fatigue crack detection plate 10 on which the sensing wire 11 is installed is its working surface.

[0050] In one optional example, the angle between the sensing wire 11 and the cutting line 23 ranges from 30 to 90 degrees. By setting different angles between the sensing wire 11 and the cutting line 23 (which also corresponds to the installation angle of the fatigue crack detection piece 10), it is possible to evaluate the situation in which the crack propagation direction may not be perpendicular to the installation direction of the fatigue crack detection piece 10 in actual applications.

[0051] Preferably, Figure 4 、 Figure 5 As shown, the included angle between the sensing wire 11 and the cutting line 23 is 45 degrees or 90 degrees. When the included angle between the sensing wire 11 and the cutting line 23 is 45 degrees, as shown in FIG. Figure 5 As shown, the fatigue crack detection sheet 10 can simulate its monitoring reliability for cracks that propagate in a direction not perpendicular to the fatigue crack detection sheet 10. The case where the sensing wire 11 and the cutting line 23 are at an angle of 45 degrees is representative. For rails, considering the attachment direction and location of the fatigue crack detection sheet 10, cracks that actually develop at the attachment location are almost always at right angles to the attachment direction. This means that fatigue cracks 30 propagate at an angle driven by shear stress, and the resulting fatigue cracks are generally larger than 45 degrees.

[0052] In an optional embodiment of the present invention, a fatigue tester 70 is used to perform a fatigue test on the fatigue sample.

[0053] In an optional embodiment of the present invention, the rail specimen 20 is a compact tensile specimen. Using the rail specimen 20 in a compact tensile specimen form for fatigue testing (where the fatigue testing employs the same fatigue loading method as for compact tensile specimens) effectively controls the fatigue crack growth rate, facilitates the reliability evaluation of the crack detection piece under different fatigue crack growth rates, and accurately evaluates the reliability of the crack detection piece under other variables under the same crack growth rate.

[0054] In an optional example of this embodiment, a pin hole 25 is opened on the rail sample 20 , and the rail sample 20 is installed on the fatigue testing machine through the pin hole 25 .

[0055] Preferably, two pin holes 25 of the same shape are provided on the rail sample 20 , and the distances between the cutting line 23 and the two pin holes 25 are the same.

[0056] In another optional embodiment of the present invention, the rail specimen 20 is a three-point bending fatigue specimen, and accordingly, the fatigue test is a three-point bending fatigue test. This three-point bending fatigue specimen can also effectively control the fatigue crack growth rate. For the preparation of the three-point bending fatigue specimen and the specific process of the three-point bending fatigue test, please refer to the relevant provisions of GB / T6398-2017 "Metallic Materials Fatigue Test - Fatigue Crack Growth Method".

[0057] In an optional example of this embodiment, test parameters are set for a fatigue testing machine. These test parameters include at least the cyclic loading frequency, minimum cyclic load, maximum cyclic load, fatigue crack growth length, and stress intensity factor. By setting the test parameters of the fatigue testing machine to different values, different fatigue crack growth rates can be established to simulate the initiation and growth of actual fatigue cracks on the rail surface and evaluate the reliability of the fatigue crack detection sheet 10 at different fatigue crack growth rates.

[0058] In an optional example, the fatigue crack growth rate requirements in TB / T 2344.1 "Rail Part 1 43kgm to 75kgm Rails" can be referred to set the various test parameters of the fatigue testing machine.

[0059] Preferably, the cyclic loading frequency is 15-40 Hz, the minimum cyclic load / maximum cyclic load R=0.5, the fatigue crack extension length is 5-10 mm, and the stress intensity factor is 10 MPa·m 1 / 2 (Low stress intensity factor amplitude △K condition, the test under this condition is a fatigue test with low fatigue crack growth rate) or 13.5MPa·m 1 / 2 (High stress intensity factor amplitude △K condition, the test under this condition is a fatigue test with high fatigue crack growth rate).

[0060] In an optional embodiment of the present invention, the sudden increase in resistance refers to the resistance value of the fatigue crack detection piece 10 increasing by more than or equal to 10 6 ohm.

[0061] During the fatigue test, a fatigue crack 30 is generated on the surface of the rail sample 20. The fatigue crack 30 extends from the notch tip of the cutting line 23 along the extension line. When the fatigue crack 30 extends to the area covered by the fatigue crack detection sheet 10, the sensing wire 11 in the fatigue crack detection sheet 10 will break along with the fatigue crack 30 and form a detection crack 40. At this time, the resistance of the fatigue crack detection sheet 10 will change. When the resistance value of the fatigue crack detection sheet 10 increases by 10 or more, the fatigue crack 40 will be formed. 6 When the value is greater than ohm, it means that a detection crack 40 has also occurred on the fatigue crack detection piece 10, and the fatigue test should be stopped at this time.

[0062] In an optional example of the present invention, Figure 6 As shown, the resistance change of the fatigue crack detection piece 10 is measured using a resistance measuring device 50 .

[0063] Preferably, the resistance measuring device 50 is connected to the fatigue crack detection piece 10 via a connecting wire 51. The connection between the connecting wire 51 and the sensing wire 11 on the fatigue crack detection piece 10 can be connected via a welding connection point 52. Specifically, the welding connection point 52 is formed by manual soldering.

[0064] It should be noted that the connecting wire 51 only needs to be connected to one wire in the fatigue crack detection sheet 10 and connected to the resistance measuring device 50 to form a loop, rather than multiple loops in parallel. After the crack detection sheet 10 is attached to the rail sample 20, when the fatigue crack 30 on the rail sample 20 extends to the sensing wire 11 (copper foil wire) in the fatigue crack detection sheet 10, the sensing wire 11 will also crack along with the crack. At this time, the loop is disconnected. Therefore, through the resistance mutation (resistance increase of more than 10 6 Ohm) can monitor the cracks on the sample.

[0065] In an optional embodiment of the present invention, if the comparison result shows that the fatigue crack 30 and the detection crack 40 coincide with each other, the fatigue crack detection piece 10 is judged to be qualified; otherwise, the crack detection piece is judged to be unqualified.

[0066] In the embodiment, "coincidence" means that the detection crack 40 of the sensing wire in the fatigue crack detection piece 10 coincides with the expansion direction and position of the fatigue crack 30 on the surface of the rail sample 20 below it. If the detection crack 40 on the sensing wire 11 of the fatigue crack detection piece 10 coincides with the expansion direction and position of the fatigue crack 30 on the rail sample 20 below it, Figure 12 As shown, the fatigue crack detection piece 10 is considered to have a qualified crack monitoring capability; otherwise, the fatigue crack detection piece 10 is considered to have an unqualified crack monitoring capability. Figures 13 and 14 It should be noted that, Figure 13 As shown, when the detection crack 40 and the fatigue crack 30 have a relative displacement difference, or as Figure 14 As shown, the fatigue crack detection piece 10 breaks prematurely (as shown in FIG. Figure 14 ) are considered unqualified.

[0067] In the present invention, since the sensing wire 11 is bonded to the surface of the rail sample 20 (for example, by 502 glue), cracks on the surface of the rail sample 20 will cause the sensing wire 11 on the fatigue crack detection sheet 10 to crack. In an actual fatigue test, the relative position relationship between the fatigue crack 30 and the detection crack 40 is shown in the following photo. Figure 10 、 Figure 11 shown.

[0068] In an alternative embodiment of this embodiment, the fatigue crack 30 and the test crack 40 are respectively observed through an optical microscope to compare the fatigue crack 30 and the test crack 40 .

[0069] In another alternative embodiment of this embodiment, the fatigue crack 30 and the detection crack 40 are measured respectively by an optical image measuring instrument. Of course, other crack magnification devices can also be used to observe and magnify the fatigue crack 30 and the detection crack 40.

[0070] In an optional embodiment of the present invention, Figure 7 As shown, a fatigue test is performed on a fatigue sample in a temperature environment box 60 .

[0071] In an optional example of this embodiment, the temperature in the temperature environment box 60 is -40°C (simulating a low temperature environment) or +60°C (simulating a high temperature environment).

[0072] In an optional example, the fatigue test is started after the temperature in the temperature environment box 60 reaches the set temperature and is maintained for 5 minutes. Other loading parameters are consistent with room temperature fatigue, so as to analyze the ability of the fatigue crack detection piece 10 to monitor cracks in low and high temperature environments.

[0073] In one optional example, a fan, a resistance wire, and a liquid nitrogen refrigeration system are provided within the temperature environment box 60. The temperature environment box 60 regulates the temperature within the temperature environment box 60 through resistance wire heating and liquid nitrogen refrigeration. Specifically, the low temperature of -40°C within the temperature environment box 60 is achieved by the device automatically adjusting the amount of liquid nitrogen sprayed into the environment box to achieve the set temperature, and the circulating fan within the box ensures a uniform temperature distribution within the box. The high temperature of 60°C within the temperature environment box 60 is achieved through the combined effect of resistance wire heating within the box and liquid nitrogen refrigeration, achieving precise temperature control within the box.

[0074] In an optional embodiment of the present invention, the fatigue test is performed on the fatigue sample at room temperature.

[0075] In an optional embodiment of the present invention, a salt spray test is performed on the fatigue specimen, and then a fatigue test is performed on the fatigue specimen after the salt spray test to examine the performance of the fatigue crack detection sheet 10 in an atmospheric corrosion environment. Specifically, a neutral salt spray test simulating atmospheric corrosion is performed on the fatigue specimen with the fatigue crack detection sheet 10 already installed, with reference to GB / T 10125 "Salt spray test for corrosion in artificial atmospheres." After the corrosion test, the fatigue specimen is mounted on a fatigue testing machine and subjected to a room temperature fatigue test. The fatigue crack detection sheet 10's ability to monitor cracks after corrosion is then analyzed to evaluate the waterproof performance and corrosion resistance of the fatigue crack detection sheet 10.

[0076] In an optional example of this embodiment, the test period of the salt spray test may be set to 120 hours.

[0077] In an optional example of this embodiment, the salt spray test is a neutral salt spray test.

[0078] In another optional embodiment of the present invention, after the fatigue specimen is subjected to other corrosion tests such as a periodic cyclic corrosion test, the fatigue specimen is then subjected to a fatigue test.

[0079] In an optional embodiment of the present invention, a wind tunnel test is performed on the fatigue specimen, and then a fatigue test is performed on the fatigue specimen after the wind tunnel test to simulate the application reliability of the fatigue crack detection piece 10 under high wind force.

[0080] In an optional embodiment of the present invention, an aging test is performed on the fatigue sample, and then a fatigue test is performed on the fatigue sample after the aging test to examine the application reliability of the fatigue crack detection piece 10 exposed to the natural environment for a long time.

[0081] In an optional embodiment of the present invention, Figure 8 、 Figure 9 As shown, a raw surface 22 with a variable cross section is prepared at the variable cross section of the rail sample 20 to examine the reliability of the fatigue crack detection piece 10 in detecting cracks on the variable cross section. A fatigue sample with a raw surface 22 with a variable cross section is prepared at the variable cross section of the rail sample 20. The fatigue crack detection piece 10 is installed on the curved surface just in front of the cutting line 23. Other experimental conditions are consistent with room temperature fatigue. The installation position of the rail sample 20 with a variable cross section and the fatigue crack detection piece 10 is shown in FIG. Figure 9 shown.

[0082] In an optional example of this embodiment, the corner where stress concentration occurs on the variable cross-section should be located right in front of the cutting line 23 , that is, in a collinear relationship with the cutting line 23 .

[0083] In an optional example, the distance between the original variable cross-section retained on the rail sample 20 and the tip of the cutting line 23 is a fixed value, such as 3 mm.

[0084] Preferably, the original surface 22 of the rail sample 20 may be the original cross-sectional surface of the actual component to be tested.

[0085] In the present invention, the selection position of the original surface 22 can be selected differently (i.e., the detection point is changed) according to the actual service conditions of the component to be detected (rail) to comprehensively evaluate the reliability of the fatigue crack detection piece 10 in monitoring cracks under field use conditions.

[0086] It should be noted that in the present invention, the original surface of the rail specimen 20 can be selected not only from the bottom surface of the rail but also from other locations where the rail or turnout has varying cross-sections. Stress concentration often occurs at the corners of rails and turnouts, making it more important to evaluate the reliability of the fatigue crack detection sheet 10 at these locations.

[0087] The fatigue crack detection piece reliability evaluation method proposed in the present invention can be applied not only to rails and switches, but also to bridges, wind power equipment, railway locomotive and vehicle components and other components that are subjected to fatigue loads and are prone to fatigue fracture and instantaneous fracture failure.

[0088] Please refer to Figures 1 to 11 The specific implementation process of the fatigue crack detection piece reliability evaluation method proposed by the present invention is now described in detail with reference to an embodiment:

[0089] A rail specimen 20 (compact tensile specimen) is prepared using on-site rails, with one side of the rail specimen 20 being the original surface 22 of the rail. A fatigue crack detection piece 10 is installed at a certain position in front of the notch of the cutting line 23 of the original surface 22. The rail specimen 20 is installed on a fatigue testing machine 70, and the loading frequency, load ratio R, crack extension length, and fatigue loading rate are set to perform a fatigue test. A resistance measuring device 50 is used to monitor the resistance change of the fatigue crack detection piece 10. When a sudden change in resistance occurs, the fatigue crack detection piece 10 is considered to be disconnected, and the fatigue test is stopped.

[0090] like Figure 10 、 Figure 11 Observe the rail sample 20 and the fatigue crack detection piece 10 thereon, and determine whether the fatigue crack detection piece 10 is qualified based on the relative position of the fatigue crack 30 on the rail sample 20 and the detection crack 40 in the sensing wire of the fatigue crack detection piece 10.

[0091] During the fatigue test, by setting different fatigue crack growth rates, the reliability of the fatigue crack detection piece 10 at different crack growth rates was investigated; by adding a temperature environment box 60, different fatigue environment temperatures were controlled to investigate the high / low temperature resistance of the fatigue crack detection piece 10; after the fatigue sample with the fatigue crack detection piece 10 installed was subjected to a salt spray corrosion test, a fatigue test was performed to investigate the waterproof and corrosion resistance of the fatigue crack detection piece 10; by installing the fatigue crack detection piece 10 at different angles to the cutting line 23, the monitoring ability of the fatigue crack detection piece 10 for cracks that do not grow in a direction perpendicular to the fatigue crack detection piece 10 was investigated; by preparing a fatigue sample rail specimen 20 containing the original variable cross-section at the variable cross-section of the rail, the detection ability of the fatigue crack detection piece 10 for cracks on the variable cross-section was investigated.

[0092] In this embodiment, the above five test items are mainly designed to evaluate the reliability of the fatigue crack detection piece 10. The test items are fatigue tests at high and low fatigue crack growth rates, fatigue tests at room temperature, low temperature (-40°C), and high temperature (+60°C), fatigue tests after salt spray corrosion, fatigue tests with the fatigue crack detection piece 10 installed at a 45° angle to the cutting line 23, and fatigue tests with the surface of the rail specimen 20 in its original variable cross-section shape. Any conditions not specified in the above items are assumed to be conducted at a high fatigue crack growth rate and room temperature to improve test efficiency.

[0093] Only fatigue crack detection sheets 10 that pass all five test items are considered reliable and effective, and can be used for online surface crack detection on rails and turnout components. Otherwise, if even one item fails, the fatigue crack detection sheet 10 is deemed unreliable.

[0094] The detailed explanations of the above-mentioned embodiments are intended only to explain the present invention so as to facilitate a better understanding of the present invention. However, these descriptions cannot be interpreted as limiting the present invention for any reason. In particular, the various features described in different embodiments may also be arbitrarily combined with each other to form other embodiments. Unless otherwise clearly described, these features should be understood to be applicable to any embodiment and are not limited to the described embodiments.

Claims

1. A method for evaluating the reliability of a fatigue crack detection piece, characterized in that: installing a fatigue crack detection sheet at a predetermined position on a rail sample to form a fatigue sample, performing a fatigue test on the fatigue sample while simultaneously monitoring a change in resistance of the fatigue crack detection sheet, stopping the fatigue test when the resistance of the fatigue crack detection sheet suddenly increases, comparing a fatigue crack generated on the rail sample with a detection crack generated on the fatigue crack detection sheet, and determining the reliability of the fatigue crack detection sheet based on the comparison result; The rail sample has an original surface, a cutting line is provided on the original surface, and the predetermined position is located on the original surface and has a predetermined distance from the end of the cutting line; The fatigue crack detection sheet is provided with at least one induction wire for conducting electricity, and the fatigue crack detection sheet is installed in a direction such that an angle is formed between the induction wire and the cutting line; If the comparison result shows that the fatigue crack coincides with the detection crack, the fatigue crack detection piece is judged to be qualified; otherwise, the fatigue crack detection piece is judged to be unqualified.

2. The method for evaluating the reliability of a fatigue crack detection piece according to claim 1, wherein: The predetermined distance is 3 mm.

3. The method for evaluating the reliability of a fatigue crack detection piece according to claim 1, wherein: The included angle between the sensing wire and the cutting line ranges from 30 to 90 degrees.

4. The method for evaluating the reliability of a fatigue crack detection piece according to claim 3, wherein: The included angle between the sensing wire and the cutting line is 45 degrees or 90 degrees.

5. The method for evaluating the reliability of a fatigue crack detection piece according to claim 1, wherein: The cutting line is formed by machining.

6. The method for evaluating the reliability of a fatigue crack detection piece according to claim 1, wherein: A fatigue test is performed on the fatigue sample using a fatigue testing machine.

7. The method for evaluating the reliability of a fatigue crack detection piece according to claim 6, wherein: A pin hole is provided on the rail sample, and the rail sample is mounted on the fatigue testing machine through the pin hole.

8. The method for evaluating the reliability of a fatigue crack detection piece according to claim 6, wherein: The test parameters of the fatigue testing machine are set, and the test parameters at least include cyclic loading frequency, minimum cyclic load, maximum cyclic load, fatigue crack extension length and stress intensity factor.

9. The method for evaluating the reliability of a fatigue crack detection piece according to claim 8, wherein: The cyclic loading frequency is 15-40 Hz, the minimum cyclic load / maximum cyclic load R=0.5, the fatigue crack extension length is 5-10 mm, and the stress intensity factor is 10 MPa·m 1 / 2 or 13.5 MPa·m 1 / 2 .

10. The method for evaluating the reliability of a fatigue crack detection piece according to claim 1, wherein: The sudden increase in resistance means that the resistance value of the fatigue crack detection piece increases by more than or equal to 10 6 ohm.

11. The method for evaluating the reliability of a fatigue crack detection piece according to claim 1, wherein: The fatigue crack and the test crack are respectively observed through an optical microscope to compare the fatigue crack and the test crack.

12. The method for evaluating the reliability of a fatigue crack detection piece according to claim 1, wherein: A fatigue test is performed on the fatigue sample in a temperature environment box.

13. The method for evaluating the reliability of a fatigue crack detection piece according to claim 12, wherein: The temperature in the temperature environment box is -40°C or +60°C.

14. The method for evaluating the reliability of a fatigue crack detection piece according to claim 1, wherein: The fatigue test was performed at room temperature.

15. The method for evaluating the reliability of a fatigue crack detection piece according to claim 1, wherein: A salt spray test is performed on the fatigue sample, and a fatigue test is performed on the fatigue sample after the salt spray test.

16. The method for evaluating the reliability of a fatigue crack detection piece according to claim 15, wherein: The time of the salt spray test is 120 hours.

17. The method for evaluating the reliability of a fatigue crack detection piece according to claim 1, wherein: A wind tunnel test is performed on the fatigue sample, and a fatigue test is performed on the fatigue sample after the wind tunnel test.

18. The method for evaluating the reliability of a fatigue crack detection piece according to claim 1, wherein: An aging test is performed on the fatigue sample, and a fatigue test is performed on the fatigue sample after the aging test.

19. The method for evaluating the reliability of a fatigue crack detection piece according to claim 1, wherein: The original surface including the variable cross-section is prepared at the variable cross-section of the rail sample.

20. The method for evaluating the reliability of a fatigue crack detection piece according to claim 1, wherein: The rail specimen is a compact tensile specimen.

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