Sample for detecting near-tread fatigue crack growth rate of rail head of steel rail

Abstract

The invention discloses a sample for detecting the near-tread fatigue crack growth rate of a steel rail head, which is a C-shaped tensile sample and meets the following conditions: W / B = 2, X / W = 0.5, and r1 / r2 is not limited, W represents the width of the sample, B represents the thickness of the sample, X represents the offset size of a loading hole, the value of X 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, and the value of X represents the offset size of the loading hole. R1 represents the outer radius of the sample, and r2 represents the inner radius of the sample; an inverted-V-shaped notch is formed in the inner arc of the crack of the C-shaped tensile sample, the offset of the inverted-V-shaped notch is + / -2 degrees, and dovetail grooves are symmetrically formed in the outer side of the inverted-V-shaped notch and are 6mm away from the center line. The C-shaped tensile sample provided by the invention can be used for detecting the fatigue crack propagation rates of different depths of the hardened layer of the rail head of the quenched steel rail.

Description

Technical Field

[0001] The invention belongs to the field of railway transportation and metal material detection technology, and specifically relates to a test specimen for detecting the fatigue crack growth rate of a rail head near the tread surface, and in particular provides a C-shaped tensile test specimen for detecting the fatigue crack growth rate of a hardened layer of a rail head near the tread surface at different depths. Background Art

[0002] With the speed increase and heavy-duty railway transportation, rail damage is becoming more and more serious. The heat treatment method is low-cost and effective to improve the toughness of the rail head. However, the detection of fatigue crack growth rate of the quenched hardened layer (hat-shaped) of the rail has always troubled the inspectors, because the depth of the quenched rail tread hardened layer is about 10-15mm. According to the requirements of the iron standard TB / T2344-2020, if Figure 1 As shown, using a 45×20×180mm SEB specimen, only the fatigue crack growth rate of the ligament 10mm below the tread of the rail head can be detected. This position has left the main area of ​​the hardened layer of the quenched rail head, and it is impossible to detect the fatigue crack growth rate of different depths of the hardened layer of the quenched rail head. Summary of the invention

[0003] In view of one or more problems existing in the prior art, the present invention provides a specimen for detecting the fatigue crack growth rate of the tread surface near the rail head of a rail, which is a C-shaped tensile specimen, satisfying: W / B=2, X / W=0.5, and no restriction is imposed on r1 / r2, wherein W represents the width of the specimen, B represents the thickness of the specimen, X represents the offset size of the loading hole, and its value is equal to the difference between the vertical distance from the outer arc at 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 at the crack of the C-shaped tensile specimen, the offset of the inverted V-shaped notch is ±2°, and dovetail grooves are symmetrically provided at the outer side of the inverted V-shaped notch and 6 mm away from the center line.

[0004] In some embodiments, the C-shaped tensile test specimen selects a W value according to the depth of the hardened layer of the quenched rail tread to be tested, or selects a W value according to the needs of the test, thereby determining the thickness of the test ligament.

[0005] In some embodiments, the C-shaped tensile specimen is taken from the cross section of the rail head, and the operation is: grooving from the inside of the rail head toward the tread, and using a sawing machine, a lathe, a milling machine, a grinder and a wire cutting machine to process the C-shaped tensile specimen.

[0006] In some embodiments, the surface roughness of the C-shaped tensile specimen is ≤1.6 μm, 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 use of the C-shaped tensile test specimen provided by the present invention in detecting the fatigue crack growth rate of the near-tread surface of the rail head also belongs to the content of the present invention.

[0009] The C-shaped tensile specimen provided by the present invention can change the height of the ligament for detecting fatigue crack growth rate by changing the specimen width W, thereby solving the problem that the SEB specimen cannot detect fatigue crack growth rates of different depths of the hardened layer of the rail head of the quenched rail. The specimen for detecting fatigue crack growth rate of the tread surface of the rail head provided by the present invention has a simple use principle, is easy to operate, and has strong practicality. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] Figure 1 Schematic diagram of the sampling location of SEB specimens according to TB / T2344-2020 standard.

[0011] Figure 2 Schematic diagram of the C-shaped tensile specimen structure for fatigue crack growth rate specimen test.

[0012] Figure 3 Schematic diagram of the structure of C-shaped tensile specimens with different ligament heights for testing the near-tread fatigue crack growth rate for different selections of W. DETAILED DESCRIPTION

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

[0014] The present invention provides a test specimen for detecting the fatigue crack growth rate of the tread surface near the rail head, such as Figure 2 As shown, the shape, size and notch of the specimen are shown. Specifically, the specimen is a C-shaped tensile specimen, satisfying: W / B=2, X / W=0.5, and there is no restriction on r1 / r2, wherein W represents the width of the specimen, B represents the thickness of the specimen, X represents the offset size of the loading hole, and its value is equal to the difference between the vertical distance from the outer arc at 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 at the crack of the C-shaped tensile specimen, the offset of the inverted V-shaped notch is ±2°, and dovetail grooves are symmetrically provided on the outside of the inverted V-shaped notch and 6 mm away from the center line for clamping the extensometer.

[0015] Specifically, the C-shaped tensile specimen provided by the present invention is taken from the cross section of the rail head. The specimen is processed by sawing the specimen blank from the rail head using a sawing machine, and then processed by a lathe and a milling machine, and finally processed by an internal grinder, an external grinder and a surface grinder. After the C-shaped tensile specimen is processed by the grinder, the size requirements are as follows: Figure 2 As shown, the surface roughness of the sample is ≤1.6μm, and the parallelism and verticality of the sample 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, and molybdenum wire cutting can be used.

[0016] Furthermore, the C-shaped tensile specimen provided by the present invention can select the W value according to the depth of the hardened layer of the quenched rail tread to be tested, or select the W value according to the needs of the test, so as to determine the thickness of the test ligament, such as Figure 3 As shown in h1, h2 and h3, it is convenient to detect the fatigue crack growth rate of different depths of the hardened layer of the rail head of the quenched rail.

[0017] When using the C-shaped tensile specimen provided by the present invention to detect the fatigue crack growth rate of the rail head near the tread surface, the C-shaped tensile specimen can be clamped on the U-shaped clamp, and the C-shaped tensile specimen should be located in the middle of the U-shaped hook, with a deviation within 0.76mm, and the center line deviation of the upper and lower force rods is within 0.76mm. Then, the fatigue crack growth rate test is performed using the MTS810 material testing machine imported from the United States (for example, the TB / T2344-2020 standard can be referred to). During the test, the prefabricated fatigue crack growth amount is at least 0.025W, or 1.3mm, whichever is greater, and the sum of the notch and the prefabricated fatigue crack length is 0.3W.

[0018] Finally, it should be noted that the above is only a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art can still modify the technical solutions described in the aforementioned embodiments or replace some of the technical features therein by equivalents. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A test specimen for detecting the fatigue crack growth rate of the tread surface near the 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, wherein W represents the width of the specimen, B represents the thickness of the specimen, X represents the offset size of the loading hole, and its value is equal to the difference between the vertical distance from the outer arc at 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 arranged at the inner arc at the crack of the C-shaped tensile specimen, the offset of the inverted V-shaped notch is ±2°, and dovetail grooves are symmetrically arranged on the outside of the inverted V-shaped notch and 6 mm away from the center line.

2. The sample according to claim 1, characterized in that The W value of the C-shaped tensile test specimen is selected according to the depth of the hardened layer of the quenched rail tread to be tested, or the W value is selected according to the needs of the test, so as to determine the thickness of the test ligament.

3. The sample according to claim 1 or 2, characterized in that The C-shaped tensile specimen is taken from the cross section of the rail head, and the operation is: grooving from the inside of the rail head toward the tread, and using a sawing machine, a lathe, a milling machine, a grinder and a wire cutting machine to process the C-shaped tensile specimen.

4. The sample according to any one of claims 1 to 3, characterized in that The surface roughness of the C-shaped tensile specimen is ≤1.6 μm, and the parallelism and verticality of the specimen are not less than 0.2%W.

5. The sample according to any one of claims 1 to 4, characterized in that The width of the inverted V-shaped notch of 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 of the C-shaped tensile specimen is not greater than 0.1mm.

6. Use of the test specimen according to any one of claims 1 to 5 in detecting the fatigue crack growth rate of the tread surface near the rail head of a rail.

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