Non-destructive inspection method for railway wheels

Abstract

A method for non-destructive testing of residual stress changes in railway wheels using ultrasonic acoustoelasticity is provided. This non-destructive inspection method for railway wheels measures the difference in sound velocity by irradiating ultrasonic shear waves deflected in both the radial and circumferential directions of the wheel. The inspection is carried out by comparing the difference in sound velocity measured between the test wheel to be inspected and a comparison wheel of the same type, manufactured by the same process, and with the same diameter as the test wheel provided on the same vehicle or the same trainset.

Description

[Technical Field]

[0001] The present invention relates to a non-destructive inspection method for railway wheels, and more particularly to a method for non-destructive inspection of residual stress changes using an ultrasonic acoustoelastic method. [Background technology]

[0002] When the outer circumference of a railway wheel is overheated above the allowable temperature due to a tread brake failure or other reason, tensile residual stress is generated, which in the worst case scenario could lead to wheel fracture. Therefore, it is necessary to check the changes in such residual stress. Furthermore, when a brake failure occurs, it may be necessary to check the changes in the wheel's residual stress and determine whether it is safe to continue using the wheel. Residual stress in mechanical components is typically measured using strain gauges, and destructive methods, such as cutting and inspecting railway wheels, are also widely used.

[0003] On the other hand, non-destructive methods are desirable for such inspections, and known methods for measuring residual stress include measuring interatomic distances, such as a method using X-rays (see, for example, Patent Document 1) or a method using synchrotron radiation. However, both of these methods require large-scale equipment and are not suitable for measurements at railway sites. For this reason, simple empirical methods have traditionally been used, such as inferring the degree of heat input from the state of peeling paint on the wheel, or inferring changes in residual stress by measuring deformation in the axial direction of the wheel (changes in inner surface distance).

[0004] Non-Patent Document 1 describes a non-destructive method for measuring residual stress in railway wheels using an acoustoelastic method that uses an electromagnetic acoustic transducer (EMAT). When ultrasonic shear waves are injected into an elastic body that has become mechanically anisotropic due to stress, the elastic body exhibits birefringence with respect to the shear waves, and the difference in sound speed between two shear waves deflected in the principal stress direction is measured as being proportional to the difference in principal stress. This residual stress measurement device that uses the ultrasonic acoustoelastic method is compact and can direct ultrasonic shear waves into the wheel without using a highly viscous couplant, making it easy to handle and advantageous for measurements at railway operation sites. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Patent Publication No. 2021-189092 [Non-patent literature]

[0006] [Non-Patent Document 1] Murayama, Riichi, Fujisawa, Kazuo, Yonehara, Sadao; Development of a wheel residual stress measuring device; Journal of the Institute of Electrical Engineers of Japan 110-D (1990) 866 Summary of the Invention [Problem to be solved by the invention]

[0007] In direct measurement of residual stress using ultrasonic acoustoelasticity, acoustic anisotropy is calculated from the difference in sound velocities of shear waves in orthogonal directions, so the measured value is the sum of stress and anisotropy of the material structure. Therefore, blank materials (stress-free test specimens) are required for evaluations that eliminate the anisotropy of the material structure. Generally, it is rare to have blank materials prepared in advance for each wheel, so it is necessary to prepare blank materials by cutting out a part of the wheel to be inspected that has not been subjected to stress changes.

[0008] The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a method for non-destructively inspecting changes in residual stress in railway wheels using an ultrasonic acoustoelastic method. [Means for solving the problem]

[0009] The present invention is a non-destructive inspection method for railway wheels, which measures the difference in sound velocity by irradiating ultrasonic shear waves deflected in both the radial and circumferential directions of the railway wheel, and is characterized in that the inspection of the inspection wheel is carried out by comparing the difference in sound velocity measured between the inspection wheel to be inspected and a comparison wheel of the same type, manufactured by the same process, and with the same diameter as the inspection wheel, which is provided on the same vehicle or the same train set.

[0010] According to this feature, it is possible to know the degree of change in net residual stress excluding the anisotropy of the material structure of the wheel, without preparing a blank material.

[0011] In the above invention, the comparison wheel may be selected from a plurality of wheels having the same measured sound velocity difference, and the comparison wheel may have the same running history as the test wheel. With such a feature, it is possible to more accurately determine the degree of change in net residual stress, excluding anisotropy of the wheel material structure.

[0012] In the above-described invention, the ultrasonic shear waves may be incident on the rim surface or the back surface of the test wheel and the comparison wheel, respectively, or may be incident on the ultrasonic shear waves using an electromagnetic ultrasonic probe. With such features, it is possible to easily determine the degree of change in net residual stress, excluding anisotropy of the material structure of the wheel, even at a railway operation site. [Brief explanation of the drawings]

[0013] [Figure 1] FIG. 2 is a diagram showing the vibration direction of an incident transverse wave in the ultrasonic acoustoelastic method. [Figure 2]FIG. 2 is a cross-sectional perspective view of a rim portion of a railway wheel. [Figure 3] 1 is a graph showing the results of measuring the acoustic anisotropy of an unused railway wheel in terms of stress conversion values. [Figure 4] FIG. 1 is a side view of a railway wheel showing differences in the distribution of acoustic anisotropy. DETAILED DESCRIPTION OF THE INVENTION

[0014] A non-destructive inspection method for railway wheels according to the present invention will be described below with reference to FIGS.

[0015] As shown in Figure 1, a method for measuring residual stress using ultrasonic acoustoelasticity is known as a non-destructive testing method for railway wheels. Details are publicly known as described in Non-Patent Document 1, but the ultrasonic acoustoelasticity method uses the following principle. For example, an elastic body that has mechanical anisotropy due to residual stress or the like exhibits birefringence with respect to shear waves. This is because shear waves incident on this elastic body have different sound velocities depending on their polarization direction and the mechanical anisotropy of the elastic body. In particular, when two shear waves polarized in the principal stress direction are incident on this elastic body, the difference in sound velocities of the shear waves is proportional to the difference in principal stress. In this way, an elastic body that has mechanical anisotropy will also exhibit corresponding acoustic anisotropy.

[0016] Therefore, in the ultrasonic acoustoelastic method, if the principal stresses on the xy plane of the elastic member to be measured are σ1 in the x direction and σ2 in the y direction, two ultrasonic transverse waves (shear waves) W1 and W2 deflected in the x and y directions, respectively, which are the principal stress directions, are incident on the member from the xy plane. Then, by utilizing the fact that the difference in sound speed between the two ultrasonic transverse waves W1 and W2 is proportional to the difference in principal stresses σ1 and σ2, the difference in principal stresses σ1 and σ2 can be calculated. In other words, the sound velocities of the two ultrasonic transverse waves W1 and W2 are measured, and the difference in the principal stresses in the two directions is obtained from the difference in sound speeds.

[0017] This difference in sound velocity and the difference in principal stress are related by the equation that expresses the acoustic anisotropy Φ as follows: Φ=(V1-V2)V0=α+C A (σ1-σ2) Here, the sound velocities of ultrasonic shear waves W1 and W2 are V1 and V2, respectively. The average sound velocity of the two ultrasonic shear waves W1 and W2 in a stress-free state is V0. The tissue acoustic anisotropy that depends on the microstructure (material structure) in a stress-free state of a metal structure, etc. is α. The acoustoelastic constant is C. A In other words, the acoustic anisotropy Φ is expressed as the sum of the tissue acoustic anisotropy α, which is the acoustic anisotropy based on the material structure in a stress-free state, and the acoustic anisotropy based on the strains caused by the principal stresses σ1 and σ2.

[0018] On the other hand, in the rim portion 1 of a railway wheel as shown in Figure 2, it is known that the principal directions of residual stress are the circumferential direction θ and the radial direction r. This is because railway wheels generate residual stress in the circumferential direction due to hot rolling and heat treatment during manufacturing, as well as residual stress due to plastic deformation caused by radial stress caused by rolling contact of the tread surface 2 with the rail during use. Therefore, in nondestructive testing of railway wheels using the ultrasonic acoustoelastic method, ultrasonic shear waves polarized in the principal stress directions, the circumferential direction θ and the radial direction r, are incident, as described above. In other words, two ultrasonic shear waves W1 and W2, deflected so that their vibration directions are directed in the circumferential direction θ and the radial direction r, respectively, are incident on the rim portion 1 so that their vibration directions are perpendicular to each other. The surface on which such ultrasonic shear waves W1 and W2 are incident on the rim portion 1 is preferably the rim surface 11 or back surface 12, which is the side surface of the railway wheel and has a plane including both the circumferential direction θ and the radial direction r. Of the side surfaces of the rim portion 1 of the railway wheel, the side without the flange 3 is the rim surface 11, and the side with the flange 3 is the back surface 12.

[0019] The ultrasonic shear waves W1 and W2 are, for example, incident alternately so that the respective sound velocities can be measured. Here, the ultrasonic shear waves W1 and W2 are preferably incident using a probe that can incident ultrasonic shear waves on a metal material without contact, such as an electromagnetic acoustic wave (EMAT) probe. At railway operation sites, inspections must be performed with high workability. Since ultrasonic waves can be incident without contacting the transducer with the inspection surface, no maintenance of the inspection surface is required, and no contact medium is required, this eliminates the need for preparation and cleanup, including transportation of the entire inspection device.

[0020] As shown in Figure 3, when the acoustic anisotropy of unused railway wheels was measured using this inspection method, the values ​​obtained by converting acoustic anisotropy into residual stress varied considerably. The section labeled "Cut" (the section with the smallest gradient of stress values ​​relative to radial position in the figure) is a cut piece of unused wheel. Even excluding the data for this cut wheel, it was found that unused railway wheels have a variation of approximately 100 MPa in residual stress at each measurement position depending on the distance from the wheel tread. It was also confirmed that all measurement results show a tendency consistent with the general theory that acoustic anisotropy decreases the closer to the wheel tread.

[0021] As described above, acoustic anisotropy Φ is the sum of the tissue acoustic anisotropy α and the acoustic anisotropy due to the principal stresses σ1 and σ2. As described above, railway wheels are manufactured through hot rolling, which results in anisotropy of the material structure. In other words, the acoustic anisotropy Φ of an unused railway wheel includes not only the acoustic anisotropy due to the residual stress immediately after manufacturing, but also the tissue acoustic anisotropy α due to the material structure. The variation in acoustic anisotropy Φ described above is thought to be influenced by the tissue acoustic anisotropy α, and if a stress value is calculated directly from the sound velocity difference of ultrasonic shear waves, the influence of the tissue acoustic anisotropy α will result in inaccuracies. If the tissue acoustic anisotropy α could be measured using a railway wheel blank that is also unused and has no residual stress, it would be possible to determine the residual stress from the acoustic anisotropy due to the residual stress, with the tissue acoustic anisotropy α removed from the measurement results of the inspection wheel to be inspected. However, it is not practical to prepare a blank for each inspection.

[0022] As described above, even unused railway wheels have variations in acoustic anisotropy, and it is unknown whether this variation is due to residual stress during manufacturing or to the material structure. Therefore, the inventors of the present application considered determining the degree of change in residual stress of the test wheel by comparing it with other wheels, rather than determining the residual stress of the test wheel to be inspected.

[0023] As shown in FIG. 4(a), assume that in a certain railway wheel 10a, regions of strong acoustic anisotropy due to residual stress and material structure immediately after manufacture are distributed in the gray area. The measurement position m of acoustic anisotropy is set at a predetermined distance from the outer periphery (tread) of the side surface of the rim portion 1, and is located near the outer periphery of the region of strong acoustic anisotropy in the railway wheel 10a. In this case, as shown in FIG. 4(b), in a railway wheel 10b, the distribution of residual stress and material structure immediately after manufacture may differ due to a different manufacturing process, and the distribution of the region of strong acoustic anisotropy may also differ. In this example, the measurement position m is located outside the region of strong acoustic anisotropy. Furthermore, as shown in FIG. 4(c), in a railway wheel 10c, the diameter of the tread may be different, and therefore the position of the region of strong acoustic anisotropy at the measurement position m, which is a predetermined distance from the tread, may differ significantly. In this example railway wheel 10c, measurement position m is located toward the inner periphery of an area with strong acoustic anisotropy. In this way, if the manufacturing process, materials, dimensions, etc. of the inspection wheel and the comparison railway wheel differ, even if the inspection wheel and the comparison railway wheel are compared by measuring acoustic anisotropy Φ as described above, the acoustic anisotropy immediately after manufacture will be different, making it impossible to determine the degree of change in residual stress in the inspection wheel.

[0024] Therefore, the present inventors proposed using a comparison wheel of the same type and diameter manufactured by the same manufacturing process as the test wheel, which is used on the same vehicle or the same trainset as the test wheel to be inspected. Here, the terms "same type," "same manufacturing process," and "same diameter" refer to wheels that have the same influence on acoustic anisotropy. Specifically, "same type" refers to wheels that use the same materials and wheel types, particularly wheels that have the same stress state in the rim during operation, such as the tread shape. The term "same manufacturing method" refers to wheels that use the same manufacturing processes, such as rolling and heat treatment, to ensure that the material structure, residual stress, and their distribution immediately after manufacturing are the same. Furthermore, the term "same diameter" refers to wheels that have the same diameter immediately after manufacturing. Furthermore, "railway wheels used on the same vehicle or trainset" refers to wheels that have the same running history. In other words, this refers to wheels that are used on the same vehicle or the same trainset of multiple vehicles in railway vehicle operation. This means that the wheels are considered to have the same history of events that affect acoustic anisotropy.

[0025] In other words, it was thought that if the test wheel and the comparison wheel, which have not had any abnormalities, are equivalent in terms of acoustic anisotropy as unused railway wheels immediately after manufacture and have the same history of events that affect the acoustic anisotropy during use, then they should have equivalent acoustic anisotropy. This acoustic anisotropy may depend on the material structure or on residual stress.

[0026] For example, if a wheel equipped with tread brakes experiences a brake release failure, the tread may overheat, causing the outer periphery to expand and undergo compressive deformation, and then, as it cools, the outer periphery may contract, resulting in tensile residual stress near the tread. Consider the case where a wheel continues to be used after the brake release failure, and it is necessary to determine whether this residual stress is appropriate from a safety perspective. In this case, a comparison wheel from the same rolling stock or trainset that has not experienced a brake release failure is selected. In other words, a wheel (comparison wheel) that is believed to have had the same acoustic anisotropy as the wheel (test wheel) immediately before the brake release failure is selected. Then, acoustic anisotropy is measured at a predetermined radial depth from the tread using the ultrasonic acoustoelastic method described above.

[0027] The acoustic anisotropy obtained, i.e., the difference in the sound velocities of the ultrasonic shear waves W1 and W2, includes the effects of both the acoustic anisotropy dependent on the material structure and the acoustic anisotropy dependent on residual stress. To calculate residual stress, the effect of the acoustic anisotropy dependent on the material structure must be calculated. However, when the measurement results of the test wheel are compared with those of the comparison wheel, the difference can be considered to be due to changes in residual stress resulting from the occurrence of an abnormality such as brake release. This allows the change in residual stress before and after the occurrence of an abnormality such as brake release on the test wheel to be calculated using the above-mentioned acoustic anisotropy Φ formula without knowing the tissue acoustic anisotropy α. In other words, the change in residual stress due to the abnormality can be understood, and it is possible to determine whether the continued use of the test wheel is safe. A similar judgment can also be made without calculating residual stress by comparing the sound speed difference between the test wheel and the comparison wheel and examining the change in the sound speed difference.

[0028] This makes it possible to extract only the change in residual stress before and after the occurrence of an abnormality in the test wheel, or the difference in sound speed due to that change, and therefore it is possible to determine the degree of net change in residual stress excluding the influence of the tissue acoustic anisotropy α based on the material structure of the test wheel, without having to prepare a blank material for determining the tissue acoustic anisotropy α.

[0029] The comparative wheel is preferably selected from a plurality of wheels having the same sound speed difference as the test wheel, measured by measuring the sound speeds of ultrasonic shear waves W1 and W2 for a plurality of railway wheels of the same vehicle or the same trainset as the test wheel. Here, "same sound speed difference" refers to a sound speed difference that is comparable to the test wheel that would lead to the same judgment result when compared with the test wheel for which continued use is deemed unsafe from a safety perspective; the numerical value does not need to be the same. Alternatively, from among such a plurality of wheels having the same sound speed difference, the wheel that exhibits a sound speed difference closest to the average value may be selected as the comparative wheel. Furthermore, this average value may be used as the measurement result for the comparative wheel.

[0030] While the exemplary embodiments of the present invention and the accompanying modifications have been described above, the present invention is not necessarily limited thereto and can be modified as appropriate by those skilled in the art. In other words, those skilled in the art will be able to find various alternative embodiments and modifications without departing from the scope of the appended claims.

Claims

1. A non-destructive inspection method for railway wheels, which measures the difference in sound speed by irradiating ultrasonic shear waves deflected in both the radial and circumferential directions of the railway wheel, A non-destructive inspection method for railway wheels, characterized in that the inspection wheel is inspected by comparing the sound speed difference measured between the inspection wheel to be inspected and a comparison wheel of the same type, manufactured by the same process, and with the same diameter as the inspection wheel, which is attached to the same vehicle or the same train set.

2. 2. The non-destructive inspection method for railway wheels according to claim 1, wherein the comparison wheel is selected from a plurality of wheels having the same measured sound velocity difference.

3. 2. The method for non-destructively inspecting railway wheels according to claim 1, wherein the comparison wheel has the same running history as the inspection wheel.

4. 4. A non-destructive inspection method for railway wheels according to claim 1, wherein the ultrasonic transverse waves are incident on the rim surface or the back surface of the inspection wheel and the comparison wheel, respectively.

5. 5. A non-destructive inspection method for railway wheels according to claim 4, wherein the ultrasonic transverse waves are applied by using an electromagnetic ultrasonic probe.

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