Method for opening longitudinal and transverse crack type nuclear injury cracks of steel rail

Abstract

The invention provides a method for opening longitudinal and transverse crack type nuclear damage cracks of a steel rail, and belongs to the technical field of material failure analysis, the method for opening the longitudinal and transverse crack type nuclear damage cracks of the steel rail is used for opening fractures at longitudinal and transverse type nuclear damage positions of a rail head, and comprises the following steps: detecting a damaged steel rail by utilizing ultrasonic waves; obtaining an area and a boundary position of a longitudinal horizontal crack in the damaged steel rail; a three-point bending and breaking test is conducted on the damaged steel rail with the area where the longitudinal horizontal crack is located as the center; after the damaged steel rail is subjected to the three-point bending and breaking test, the damaged steel rail is transversely broken and forms two fracture samples, and a longitudinal horizontal crack is reserved in one fracture sample; and cutting the fracture sample with the longitudinal horizontal crack based on the boundary position, forming a cutting surface on the fracture sample along the longitudinal direction of the rail head, and exposing the longitudinal horizontal crack out of the cutting surface. According to the opening method for the longitudinal and transverse crack type nuclear flaw crack of the steel rail, the longitudinal and horizontal crack fracture in the longitudinal and transverse crack type nuclear flaw of the steel rail can be accurately and completely opened.

Description

Technical Field

[0001] The invention belongs to the technical field of material failure analysis, and in particular relates to a method for opening longitudinal and transverse core cracks in rails. Background Art

[0002] Rail head cracks are fatigue cracks or brittle cracks that form and develop at manufacturing defects (such as metallurgical defects and heat treatment defects) within the rail head under the action of operating loads. Based on the crack morphology, rail head cracks can be divided into two types: longitudinal and transverse cracks and transverse cracks. The longitudinal and transverse cracks are fatigue cracks that occur simultaneously in both longitudinal and transverse directions. Their damage morphology is unique and has a significant impact on on-site rail flaw detection and safe railway operation.

[0003] The damage characteristics of rail core damage of longitudinal and transverse cracks are as follows: a longitudinal fatigue crack parallel to the tread is first formed inside the rail head, and then expands into a transverse fatigue crack; in the early stage of core damage or the "white core" longitudinal fatigue crack fracture, strip crack sources and fatigue arcs originating from the strip crack sources can be observed; in the late stage of core damage or the "black core" longitudinal fatigue fracture, fatigue arcs and strip crack sources are usually not observed, and the longitudinal fatigue fracture at this time is mainly a rolling deformation morphology; the strip crack source is generally located at a depth of 5mm to 12mm from the tread and is parallel to the tread; the transverse fatigue crack originates from the longitudinal fatigue crack and expands toward the rail bottom and the side of the rail head.

[0004] In the failure analysis process of rail longitudinal and transverse crack core damage, the key to observing the original crack source morphology is to accurately detect the size and position of the longitudinal horizontal crack in the rail head, and then open the crack fracture.

[0005] Fracture analysis, a core technique for metal component failure analysis, is crucial for determining the crack source location and propagation direction. However, existing technologies for opening the fracture surface of longitudinal and transverse cracks in rails present significant limitations. Conventional pressure-breaking and tapping methods struggle to fully open the longitudinal horizontal cracks located within the rail head, 5 to 12 mm deep from the tread. While three-point bending and flattening methods can effectively open surface cracks, they are inadequate for locating and opening internal defects and damage. Furthermore, while ultrasonic testing can detect transverse fatigue cracks in rail heads, its equipment is expensive, complex, and requires specialized personnel, severely limiting the efficiency of failure analysis. Furthermore, existing technologies often only partially open the fracture surface of longitudinal horizontal cracks, failing to ensure that the fracture extends through the entire horizontal crack region. This makes it difficult to observe the original crack source within the longitudinal horizontal crack, significantly hindering in-depth analysis and determination of the damage cause. This not only complicates failure analysis but can also lead to misdiagnosis of the damage cause, threatening the safety and reliability of railway transportation.

[0006] The invention patent "A method for opening cracks in metal workpieces without damaging the fracture", application number: 202110298098.3, publication (announcement) number: CN113155560 A, relates to the technical field of material failure analysis. The invention uses the three-point bending principle to non-destructively open the cracks in the workpiece, mainly solving the problem of non-destructive opening of surface cracks in metal parts for fracture analysis. The technical defects of the technical solution of this patent are mainly reflected in the fact that its method is mainly aimed at surface cracks. It cannot locate and open internal defects such as longitudinal and horizontal cracks inside the rails, and cannot meet the specific needs of opening longitudinal and transverse cracks in the rails. The invention patent "A Method for Sampling and Fracture Analysis of Vertical and Horizontal Nucleation Flaws" (Application Number: 201310131831.8, Publication (Announcement) Number: CN201310131831.8) relates to the field of metal failure analysis. This invention utilizes ultrasonic testing to detect the location of transverse fatigue cracks within the rail head. The transverse fatigue cracks are pressed open by wire cutting to expose the fracture surface. The macroscopic morphology is observed to determine the type of nucleation flaw. A sample is then cut to reveal the longitudinal fatigue crack. Finally, a scanning electron microscope and micro-area energy spectrometer are used for observation and analysis. This technical solution aims to address the sampling and fracture analysis issues of vertical and horizontal nucleation flaws in rail heads, particularly the detection and analysis of transverse fatigue cracks. This patent's technical solution has technical flaws, primarily in that while it involves the analysis of vertical and horizontal nucleation flaws, it fails to detect the size and location of longitudinal horizontal cracks, making it impossible to ensure the complete opening of longitudinal horizontal cracks. Furthermore, ultrasonic testing equipment is expensive and complex to operate, requiring specialized personnel to operate, impacting work efficiency.

[0007] In summary, the existing technology has many shortcomings in opening the fracture surface of longitudinal and transverse cracks in rails. There is an urgent need for a method that can accurately and completely open the fracture surface of longitudinal and horizontal cracks to improve the accuracy and efficiency of failure analysis and ensure the safety and reliability of railway transportation. Summary of the Invention

[0008] The purpose of the present invention is to propose a method for opening cracks in longitudinal and transverse crack type core damage of rails, which can accurately and completely open the longitudinal horizontal crack fractures in longitudinal and transverse crack type core damage of rails, so as to solve the problem that the longitudinal horizontal crack fractures cannot be effectively located and completely opened in the prior art.

[0009] In order to achieve the above-mentioned object of the invention, the present invention proposes a method for opening a longitudinal and transverse crack of a rail, which is used to open the fracture at the longitudinal and transverse crack position of the rail head, wherein the opening method comprises:

[0010] Using ultrasound to detect the damaged rail to obtain the area and boundary position of the longitudinal horizontal crack in the damaged rail;

[0011] A three-point bending and crushing test is performed on the damaged rail with the area where the longitudinal horizontal crack is located as the center; after the three-point bending and crushing test, the damaged rail is transversely fractured and formed into two fracture specimens, and the longitudinal horizontal crack is retained in one of the fracture specimens;

[0012] The fracture specimen retaining the longitudinal horizontal crack is cut based on the boundary position of the longitudinal horizontal crack, and a cutting surface is formed on the fracture specimen along the longitudinal direction of the rail head, and the longitudinal horizontal crack is exposed on the cutting surface.

[0013] Compared with the prior art, the present invention has the following characteristics and advantages:

[0014] The present invention proposes a method for opening longitudinal and transverse cracks in rails. Ultrasonic waves are used to detect the damaged rails, thereby accurately determining the location of the longitudinal horizontal cracks within the rails. Based on the precise location of the longitudinal horizontal cracks, a three-point bending and compression test is first performed. The fracture path is precisely controlled through the three-point bending and compression test, ensuring that the longitudinal horizontal cracks are completely retained within a single fracture specimen. The fracture specimen is then cut to expose the longitudinal horizontal cracks on the cut surface. This method ensures that the longitudinal horizontal cracks within the damaged rails are completely opened, effectively locating the original crack source and enabling microscopic analysis. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] 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.

[0016] Figure 1 Schematic diagram of longitudinal and transverse core cracks of the rail in the present invention;

[0017] Figure 2 is a schematic diagram of ultrasonic testing of a damaged rail in the present invention;

[0018] Figure 3 Schematic diagram for determining the boundary position of a longitudinal horizontal crack in the present invention;

[0019] Figure 4 Schematic diagram of the three-point bending fracture test in the present invention (1);

[0020] Figure 5 Schematic diagram of the three-point bending fracture test in the present invention (2);

[0021] Figure 6It is a schematic diagram of cutting the fracture specimen in the present invention.

[0022] Description of reference numerals:

[0023] 10. Damaged rail; 20. Longitudinal and transverse cracks; 21. Non-metallic inclusions; 22. Longitudinal and horizontal cracks; 23. Transverse fatigue extension; 31. Support base; 32. Indenter; 40. Ultrasonic thickness gauge; 50. Vertical projection boundary; h. Reflection depth. DETAILED DESCRIPTION

[0024] 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.

[0025] The present invention proposes a method for opening longitudinal and transverse core cracks of rails, such as Figures 2 to 6 As shown, the method for opening the longitudinal horizontal crack 22 in the rail head includes:

[0026] Using ultrasonic waves to detect the damaged rail 10, the area where the longitudinal horizontal crack 22 in the damaged rail 10 is located and the boundary position of the longitudinal horizontal crack 22 are obtained;

[0027] A three-point bending fracture test is performed on the damaged rail 10 with the longitudinal horizontal crack 22 as the center. After the three-point bending fracture test, the damaged rail 10 is transversely fractured along the rail head into two fracture specimens, with the longitudinal horizontal crack 22 remaining in the fracture specimen on one side.

[0028] The fracture specimen retaining the longitudinal horizontal crack 22 is cut based on the boundary position of the longitudinal horizontal crack 22 and a cutting surface along the longitudinal direction of the rail head is formed on the fracture specimen, and the longitudinal horizontal crack 22 is exposed on the cutting surface.

[0029] The present invention proposes a method for opening longitudinal and transverse cracks in rails. Ultrasonic testing is used to detect the damaged rail 10, thereby accurately determining the location of the longitudinal horizontal crack 22 within the rail's longitudinal and transverse crack core. Based on the precise location of the longitudinal horizontal crack 22, a three-point bending and compression test is first performed. This test precisely controls the fracture path, ensuring that the longitudinal horizontal crack 22 is completely retained within a single fracture specimen. The fracture specimen is then cut to expose the longitudinal horizontal crack 22 on the cut surface. This method ensures that the longitudinal horizontal crack 22 within the damaged rail 10 is completely opened, effectively locating the original crack source and enabling microscopic analysis.

[0030] The causes of rail longitudinal and transverse core damage are: Figure 1 As shown in the figure, when there are large non-metallic inclusions 21 distributed along the rolling direction of the rail in the distribution area of wheel-rail contact shear stress 3mm to 10mm below the tread, the wheel-rail contact shear stress in the inclusion area will increase significantly due to the stress concentration effect, thereby triggering crack initiation. The crack first fatigue propagates along the direction of the inclusion to form a longitudinal horizontal crack 22. When the longitudinal horizontal crack extension length exceeds the inclusion, it will turn into transverse fatigue extension 23, thus forming a longitudinal and transverse crack core flaw 20.

[0031] In the present invention, the transverse fatigue fracture formed after three-point bending fracture generally forms an angle of 0° to 45° with the vertical direction of the rail.

[0032] In an optional embodiment of the present invention, ultrasonic waves are used to detect the damaged rail head 10 to obtain the location and boundary position of the longitudinal horizontal crack 22 in the damaged rail 10, including:

[0033] The ultrasonic thickness gauge 40 is used to measure the thickness of the tread 11 of the damaged rail 10. The location where the ultrasonic wave is obviously reflected is the area where the longitudinal horizontal crack 22 is located. The depth value and boundary position of the longitudinal horizontal crack 22 are recorded.

[0034] In this embodiment, an ultrasonic thickness gauge 40 is used to locate the boundary of the longitudinal horizontal crack 22 on the rail head tread, and the detailed position and size of the longitudinal horizontal crack 22 are found.

[0035] Because the longitudinal horizontal crack 22 in a rail crack is substantially parallel to the tread of the rail head, an ultrasonic thickness gauge 40 is used to measure the thickness of the rail head surface in the region of the longitudinal horizontal crack 22, based on the principle of ultrasonic measurement of metal thickness. Since the longitudinal horizontal crack 22 causes significant ultrasonic reflection, the ultrasonic thickness gauge 40 will display the depth of the longitudinal horizontal crack 22. The ultrasonic measurement results of the longitudinal horizontal crack 22 will differ significantly from those of the crack-free region of the rail head. By measuring multiple locations on the tread of the damaged rail 10 and observing the significant numerical differences during the ultrasonic thickness gauge measurement process, the boundary location of the region where the longitudinal horizontal crack 22 in the longitudinal and transverse crack is located can be determined.

[0036] Specifically, an ultrasonic coupling agent is applied to the rail head tread, and the operator moves the straight probe of the ultrasonic thickness gauge 40. When the depth value (reflection depth h) displayed on the thickness gauge screen is less than 20 mm, it is considered that a longitudinal horizontal crack 22 exists at that location. Figure 3At this time, if you slowly move the probe in one direction, the screen value will fluctuate slightly. As long as the value is less than 20mm, it is considered to be still in the horizontal crack area. Until the depth value displayed on the screen suddenly increases during the movement and is greater than 20mm (generally the value will be greater than 30mm, such as Figure 3 Position B is considered the boundary of the horizontal crack. Mark the center of the probe with a marker. Repeat the same method by moving the probe several times and observing the location where the depth displayed by the thickness gauge shows a significant change. Mark the vertical projection boundary 50 of the longitudinal horizontal crack 22 on the rail head surface.

[0037] In an optional example of this embodiment, the specification of the rail is 50kg / m-75kg / m, the rail head height of the rail is greater than 30mm, and the depth of the longitudinal horizontal crack 22 is basically in the range of 0mm to 15mm.

[0038] Preferably, the probe specification of the ultrasonic thickness gauge 40 is a small-sized microcrystalline probe with a probe diameter of 4 mm to 6 mm.

[0039] In an optional example of this embodiment, based on the measurement data of the ultrasonic thickness gauge 40, the vertical projection boundary 50 of the longitudinal horizontal crack 22 on the tread of the damaged rail head is marked to facilitate the precise positioning of the subsequent three-point bending fracture test and wire cutting.

[0040] In an optional embodiment of the present invention, a three-point bending fracture test is performed on the damaged rail 10 with the area where the longitudinal horizontal crack 22 is located as the center, including:

[0041] A three-point bending specimen 11 is taken along the lower jaw of the damaged rail 10, with the longitudinal horizontal crack 22 as the center.

[0042] The cut three-point bending specimen 11 is placed on the support base 31 of the bending tester, with the rail head tread of the three-point bending specimen 11 facing downward. The pressure head 32 of the bending tester is located directly above the area where the longitudinal horizontal crack 22 is located. The bending test is performed until the three-point bending specimen 11 breaks.

[0043] In an optional example of this embodiment, the length of the three-point bending specimen 11 is 300 mm-500 mm.

[0044] In an optional example of this embodiment, the displacement rate of the bending tester is set to 1 mm / min-3 mm / min, and the bending test is performed until the rail head bending specimen breaks.

[0045] In this embodiment, since the transverse fatigue crack in the damaged rail 10 is substantially perpendicular to the maximum tensile stress of bending, the fracture of the transverse fatigue crack in the damaged rail 10 can be completely opened through the three-point bending fracture test. At the same time, there is a certain probability that part of the longitudinal horizontal crack 22 in the rail head can be opened, but it cannot be guaranteed that the horizontal crack is completely opened.

[0046] The transverse fracture of three-point bending crushing should be able to completely include the entire transverse fatigue crack area. At the same time, the transition area between the transverse fatigue crack and the longitudinal fatigue crack can also be partially revealed.

[0047] In an optional embodiment of the present invention, the fracture specimen is cut using a wire cutting device.

[0048] Specifically, the fracture specimen (rail head) with the vertical projection boundary 50 of the longitudinal horizontal crack 22 on the tread after three-point bending fracture is placed in the wire cutting equipment. The cutting molybdenum wire of the wire cutting equipment is aligned with the edge of the longitudinal horizontal crack 22 of the fracture, and vertical cutting is performed along the vertical projection boundary 50 of the rail head tread.

[0049] In an optional example of this embodiment, a corresponding graphic of the longitudinal horizontal crack 22 is drawn in a drawing software according to the boundary position, and the data of the graphic is imported into a wire cutting device, which cuts the fracture specimen according to the data of the graphic.

[0050] In an optional example, any drawing software that can draw or export DXF or DWG graphic formats meets the requirements, such as AutoCAD, ZWCAD, HaochenCAD and SolidWorks.

[0051] Furthermore, an ultrasonic thickness gauge 40 is used to mark the vertical projection boundary 50 of the longitudinal horizontal crack 22 on the rail head tread of the damaged rail 10. The boundary position diagram is drawn in DXF or DWG format using drawing software. The DXF or DWG format is then imported into the wire cutting machine. The wire cutting machine can then perform cutting according to the imported DXF or DWG diagram.

[0052] In an alternative example, the main steps of the software drawing method are as follows:

[0053] (1) Take a graphic photo with a camera just above the vertical projection boundary 50 of the rail head tread;

[0054] (2) Two reference points are manually selected on the boundary map of the tread surface and the distance between the two reference points is measured for the calibration of the photo graphics size in the subsequent software;

[0055] (3) Import the graphic photo into the CAD software and adjust the scale of the image by scaling so that the distance between the reference points of the image is consistent with the actual size;

[0056] (4) Using the software's stroke function, draw the outline of the vertical projection boundary 50 in the photo to form a contour map;

[0057] (5) Save the drawn outline drawing in DXF or DWG graphic format.

[0058] In an optional embodiment of the present invention, the fracture specimen is sawn before cutting to reduce the height of the fracture specimen.

[0059] In an optional example of this embodiment, the sawing position is located at a depth of about 20 mm to 40 mm below the longitudinal horizontal crack 22, and the sawing direction is along the length direction of the damaged rail.

[0060] In an optional embodiment of the present invention, after the wire cutting process is completed, the sample below the longitudinal horizontal crack 22 is clamped using a vise, and the sample above the longitudinal horizontal crack 22 can be manually opened using a vise or a hammer, and finally the complete fracture of the longitudinal horizontal crack 22 of the rail head is opened to facilitate the subsequent analysis of the original crack source.

[0061] Now, in conjunction with an embodiment, the method for opening the longitudinal and transverse core cracks of the rail proposed by the present invention is described in detail. Specifically:

[0062] Using an ultrasonic thickness gauge 40, the boundary of the longitudinal horizontal crack 22 on the rail head tread of the damaged rail 10 is located, the detailed position and size of the horizontal crack are determined, and the boundary of the longitudinal horizontal crack 22 is marked on the rail head tread to form a vertical projection boundary 50. The damaged rail 10 corresponds to a 50kg / m-75kg / m rail. The height of the damaged rail 10 is greater than 30mm, and the depth of the longitudinal horizontal crack 22 in the damaged rail 10 is generally within the range of 0mm-15mm. The vertical projection boundary 50 of the longitudinal horizontal crack 22 in the rail head 22 is marked by the obvious numerical difference displayed during the measurement by the ultrasonic thickness gauge 40.

[0063] The ultrasonic thickness gauge 40 has a probe specification of a small-sized microcrystalline probe with a probe diameter of 4 mm to 6 mm.

[0064] Taking the area where the longitudinal horizontal crack 22 is located as the center, cut a three-point bending specimen along the lower jaw of the rail head. The length of the bending specimen is 300mm to 500mm. Place the cut three-point bending specimen on the support base 31 of the bending tester, with the rail head tread facing downward. The bending span is selected to be as large as possible to reduce the bending load. Slowly move the bending tester pressure head 32 manually until it contacts the surface of the bending specimen. Set the displacement rate of the bending tester to 1mm / min-3mm / min, and perform the bending test until the rail head bending specimen breaks.

[0065] The vertical projection boundary 50 marked with the longitudinal horizontal crack 22 is measured and a corresponding graphic is drawn using CAD software. The drawn CAD graphic data is imported into the wire cutting equipment, and the rail head fracture surface retaining the longitudinal horizontal crack 22 is sampled. To improve the efficiency of the wire cutting process, the height of the rail head fracture sample can be further reduced using a sawing machine before the wire cutting process begins. The sawing position can be approximately 20mm to 40mm below the longitudinal horizontal crack 22.

[0066] After the wire cutting process is completed, the sample below the longitudinal horizontal crack 22 is clamped with a vise, and the sample above the longitudinal horizontal crack 22 is manually opened using a vise or a hammer, and finally a complete longitudinal horizontal crack fracture of the rail head is opened.

[0067] 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 opening longitudinal and transverse core cracks in rails, characterized in that: The opening method is used to open the fracture at the longitudinal and transverse core damage position of the rail head, and the opening method includes: Using ultrasound to detect the damaged rail to obtain the area and boundary position of the longitudinal horizontal crack in the damaged rail; performing a three-point bending and crushing test on the damaged rail with the region where the longitudinal horizontal crack is located as the center; after the three-point bending and crushing test, the damaged rail is transversely fractured and formed into two fracture specimens, with the longitudinal horizontal crack remaining in one of the fracture specimens; The fracture specimen retaining the longitudinal horizontal crack is cut based on the boundary position of the longitudinal horizontal crack, and a cutting surface is formed on the fracture specimen along the longitudinal direction of the rail head, and the longitudinal horizontal crack is exposed on the cutting surface.

2. The method for opening longitudinal and transverse core cracks in rails according to claim 1, characterized in that: The damaged rail head is detected by ultrasonic wave to obtain the location and boundary position of the longitudinal horizontal crack in the damaged rail, including: The thickness of the damaged rail tread is measured using an ultrasonic thickness gauge. The location where the ultrasonic wave is clearly reflected is the location of the longitudinal horizontal crack. The depth value and boundary location of the longitudinal horizontal crack are recorded.

3. The method for opening longitudinal and transverse core cracks in rails according to claim 2, characterized in that: Mark the projection of the longitudinal horizontal crack on the tread surface of the damaged rail head.

4. The method for opening longitudinal and transverse core cracks in rails according to claim 1, characterized in that: A three-point bending fracture test is performed on the damaged rail centered at the area where the longitudinal horizontal crack is located, including: Taking the area where the longitudinal horizontal crack is located as the center, a three-point bending specimen is taken along the lower jaw position of the damaged rail in the longitudinal direction of the rail head; The cut three-point bending specimen is placed on the support base of the bending tester with the rail head tread of the three-point bending specimen facing downward, and a bending test is performed until the three-point bending specimen breaks.

5. The method for opening longitudinal and transverse core cracks in rails according to claim 1, characterized in that: The fracture specimen is cut using a wire cutting device.

6. The method for opening longitudinal and transverse core cracks in rails according to claim 5, characterized in that: A corresponding graphic of the longitudinal horizontal crack is drawn in drawing software according to the boundary position, and the data of the graphic is imported into the wire cutting device, and the wire cutting device performs cutting on the fracture test according to the data of the graphic.

7. The method for opening longitudinal and transverse core cracks in rails according to claim 6, characterized in that: The graphics drawn or exported by the drawing software adopts DXF or DWG graphic format.

8. The method for opening longitudinal and transverse core cracks in rails according to claim 5, characterized in that: The fracture specimen before cutting is sawed to reduce the height of the fracture specimen.

9. The method for opening longitudinal and transverse core cracks in rails according to claim 5, characterized in that: The sawing position is located at a depth of 20mm-40mm below the longitudinal horizontal crack.

Images