A specimen for detecting the fatigue crack propagation rate of a rail head near the tread surface

Abstract

The application discloses a sample for detecting fatigue crack propagation rate of a rail head near a tread surface, which is a C-shaped tensile sample and satisfies the conditions of W / B=2, X / W=0.5, and no limitation on r1 / r2, wherein W represents the width of the sample, B represents the thickness of the sample, X represents a loading hole offset size, the value of which is equal to the difference between the vertical distance from the outer circular arc at the crack to the center line of the loading hole and W, r1 represents the outer radius of the sample, and r2 represents the inner radius of the sample; and a reverse V-shaped notch is arranged at the inner circular arc at the crack of the C-shaped tensile sample, the offset amount of the reverse V-shaped notch is within the range of plus or minus 2 degrees, and dovetail grooves are symmetrically arranged outside the reverse V-shaped notch and 6 mm away from the center line. The C-shaped tensile sample can be used for detecting the fatigue crack propagation rate of a hardened layer at different depths of a quenched rail head.

Description

Technical Field

[0001] This invention belongs to the field of railway transportation and metal material testing technology, specifically relating to a specimen for testing the fatigue crack propagation rate of the rail head near the tread surface, and more particularly to a C-shaped tensile specimen for testing the fatigue crack propagation rate of different depths of the hardened layer near the rail head near the tread surface. Background Technology

[0002] With the increasing speed and weight of railway transportation, rail damage is becoming increasingly severe. Heat treatment is a cost-effective and efficient method to improve the strength and toughness of rail heads. However, the detection of fatigue crack propagation rate in the hardened layer (cap-shaped) of the rail has been a persistent challenge for inspectors. This is because the depth of the hardened layer on the tread of the hardened rail is approximately 10-15 mm. According to the requirements of the railway standard TB / T2344-2020, if... Figure 1 As shown, using a 45×20×180mm SEB sample, only the fatigue crack propagation rate of the ligament 10mm below the rail head tread can be detected. This position is outside the main area of ​​the hardened layer of the quenched rail head, and it is impossible to detect the fatigue crack propagation rate at different depths of the hardened layer of the quenched rail head. Summary of the Invention

[0003] To address one or more problems existing in the prior art, the present invention provides a specimen for detecting the fatigue crack propagation rate near the tread surface of a rail head. This specimen is a C-shaped tensile specimen satisfying: W / B = 2, X / W = 0.5, and without limitation on r1 / r2. Here, W represents the width of the specimen, B represents the thickness of the specimen, X represents the offset dimension of the loading hole, which is equal to the difference between the vertical distance from the outer arc of the crack to the center line of the loading hole and W, r1 represents the outer radius of the specimen, and r2 represents the inner radius of the specimen. Furthermore, an inverted V-shaped notch is provided at the inner arc of the crack in the C-shaped tensile specimen, with an offset of ±2°. A dovetail groove is symmetrically provided on the outer side of the inverted V-shaped notch, 6 mm from the center line.

[0004] In some embodiments, the W value of the C-shaped tensile specimen is selected based on the depth of the hardened layer of the quenched rail tread to be tested, or the W value is selected according to the testing requirements, thereby determining the thickness of the ligament to be tested.

[0005] In some embodiments, the C-shaped tensile specimen is taken from the cross section of the rail head, and the operation is as follows: a groove is cut from the inside of the rail head towards the tread surface, and the C-shaped tensile specimen is processed using a saw, lathe, milling machine, grinding machine and wire cutting machine.

[0006] In some embodiments, the surface roughness of the C-shaped tensile specimen is ≤1.6μm, and the parallelism and perpendicularity of the specimen are not less than 0.2%W.

[0007] In some embodiments, the width of the inverted V-shaped notch of the C-shaped tensile specimen is within 0.1 mm but not less than 1.6 mm, and the root radius of the inverted V-shaped notch of the C-shaped tensile specimen is not greater than 0.1 mm.

[0008] The application of the C-shaped tensile specimen provided by this invention in detecting the fatigue crack propagation rate near the tread of the rail head is also within the scope of this invention.

[0009] The C-shaped tensile specimen provided by this invention can change the ligament height for detecting fatigue crack propagation rate by altering the specimen width W, thus solving the problem that SEB specimens cannot detect fatigue crack propagation rates at different depths of the hardened layer in quenched rail heads. The specimen provided by this invention for detecting fatigue crack propagation rate near the tread surface of rail heads is simple in principle, easy to operate, and highly practical. Attached Figure Description

[0010] Figure 1 This is a schematic diagram of the sampling location for SEB samples according to the TB / T2344-2020 standard.

[0011] Figure 2 This is a schematic diagram of a C-shaped tensile specimen used in fatigue crack propagation rate testing.

[0012] Figure 3 A schematic diagram of the structure of a C-shaped tensile specimen with different ligament heights and near-tread fatigue crack propagation rates, selected for different W values. Detailed Implementation

[0013] The present invention will be further described in detail below with reference to specific embodiments. The embodiments are merely descriptions of the best implementation of the present invention and do not limit the scope of the present invention in any way.

[0014] This invention provides a specimen for detecting the fatigue crack propagation rate near the tread surface of a rail head, such as... Figure 2 As shown, the shape, size, and notch of the specimen are illustrated. Specifically, the specimen is a C-shaped tensile specimen that satisfies: W / B = 2, X / W = 0.5, and there are no restrictions on r1 / r2. Here, W represents the width of the specimen, B represents the thickness of the specimen, X represents the offset dimension of the loading hole, which is equal to the difference between the vertical distance from the outer arc of the crack to the center line of the loading hole and W, r1 represents the outer radius of the specimen, and r2 represents the inner radius of the specimen. Furthermore, an inverted V-shaped notch is provided at the inner arc of the crack of the C-shaped tensile specimen. The offset of the inverted V-shaped notch is ±2°, and a dovetail groove is symmetrically provided on the outside of the inverted V-shaped notch at a distance of 6 mm from the center line for mounting the extensometer.

[0015] Specifically, the C-shaped tensile specimen provided by this invention is taken from the cross-section of the rail head. The specimen is processed by sawing a rough specimen from the rail head using a saw, followed by machining on a lathe and milling machine, and finally finished by an internal grinding machine, an external grinding machine, and a surface grinding machine. After grinding, the C-shaped tensile specimen meets the dimensional requirements as follows: Figure 2 As shown, the surface roughness of the specimen is ≤1.6μm, and the parallelism and perpendicularity of the specimen are not less than 0.2%W. The width of the inverted V-shaped notch set on the C-shaped tensile specimen is within 0.1W but not less than 1.6mm, and the root radius of the inverted V-shaped notch is not greater than 0.1mm. It can be processed by molybdenum wire cutting.

[0016] Furthermore, the C-shaped tensile specimen provided by this invention allows for the selection of the W value based on the depth of the hardened layer on the quenched rail tread as needed, or the selection of the W value according to the testing requirements, thereby determining the thickness of the ligament to be tested. Figure 3 The values ​​h1, h2, and h3 shown here make it easy to detect the fatigue crack propagation rate at different depths of the hardened layer on the rail head of a quenched steel rail.

[0017] When using the C-shaped tensile specimen provided by this invention to test the fatigue crack propagation rate near the tread surface of the rail head, the C-shaped tensile specimen should be positioned in the center of the U-shaped hook with a deviation within 0.76 mm, and the deviation between the center lines of the upper and lower force bars should be within 0.76 mm. Then, the fatigue crack propagation rate is tested using an MTS810 material testing machine imported from the United States (for example, referring to the TB / T2344-2020 standard). During testing, the pre-existing fatigue crack propagation amount should be at least 0.025W, or 1.3 mm, whichever is greater, and the sum of the notch length and the pre-existing fatigue crack length should be 0.3W.

[0018] Finally, it should be noted that the above descriptions are merely preferred embodiments of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. The use of a specimen for detecting the fatigue crack propagation rate near the tread surface of a rail head in detecting the fatigue crack propagation rate near the tread surface of a rail head, characterized in that, The specimen is a C-shaped tensile specimen, which satisfies: W / B = 2, X / W = 0.5, and there is no restriction on r1 / r2, where W represents the width of the specimen, B represents the thickness of the specimen, X represents the offset dimension of the loading hole, which is equal to the difference between the vertical distance from the outer arc of the crack to the center line of the loading hole and W, r1 represents the outer radius of the specimen, and r2 represents the inner radius of the specimen; and an inverted V-shaped notch is provided at the inner arc of the crack of the C-shaped tensile specimen, the offset of the inverted V-shaped notch is ±2º, and a dovetail groove is symmetrically provided on the outside of the inverted V-shaped notch at a distance of 6 mm from the center line.

2. The use according to claim 1, characterized in that, The W value of the C-shaped tensile specimen is selected according to the depth of the hardened layer of the quenched rail tread to be tested, or according to the testing requirements, thereby determining the thickness of the ligament to be tested.

3. The use according to claim 1 or 2, characterized in that, The C-shaped tensile specimen is taken from the cross section of the rail head. The operation is as follows: a groove is cut from the inside of the rail head towards the tread surface, and the C-shaped tensile specimen is processed using a saw, lathe, milling machine, grinding machine and wire cutting machine.

4. The use according to claim 1 or 2, characterized in that, The surface roughness of the C-shaped tensile specimen is ≤1.6μm, and the parallelism and perpendicularity of the specimen are not less than 0.2%W.

5. The use according to claim 1 or 2, characterized in that, The width of the inverted V-shaped notch of the C-shaped tensile specimen is within 0.1 mm but not less than 1.6 mm, and the root radius of the inverted V-shaped notch of the C-shaped tensile specimen is not greater than 0.1 mm.

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