JPH05322829A - Nondestructive measurement method of lateral cracking fatigue crack in rail - Google Patents

Abstract

(57) [Abstract] [Purpose] The present invention is directed to a horizontal crack that is generated by branching or bending in a horizontal crack that occurs on the tread surface or inside the rail head that is in use using the potentiometric method and propagates by fatigue. A non-destructive measurement method for quantitatively evaluating the presence or absence of a crack, the position and size of a horizontal crack accompanying it, and the growth depth of a transverse crack. [Structure] Inside the rail head, the amount of potential change between a fatigue cracked part and a normal part with no cracks was measured on the rail tread, and the potential change amount, measurement interval and lateral cracking property were calculated in advance. Analysis is performed using the relationship with the crack growth depth. [Effect] Improved reliability of rails in use.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a horizontal crack that propagates under the surface of a rail head substantially parallel to the head surface when a fatigue crack is generated on or inside the rail head during use. The present invention relates to a non-destructive inspection method for lateral cracks that branch or bend to grow in the transverse direction of the rail and lead to lateral fracture of the rail.

[0002]

2. Description of the Related Art In recent years, the speed of passenger railways and mines
While the heavy load of resource transportation railways is being promoted, rails with excellent damage resistance are required.
No. 1, “Welding Low Alloy Heat Treatment Rail” and Japanese Patent Laid-Open No. 57-57
-1982216 gazette "high-strength rail", strength,
Rails with excellent wear resistance, damage resistance, and weldability have been developed. However, on the head surface (tread) where the wheels come into contact with the rails, sometimes dark spots (crown surface shelling) or TD (Transeverse Defe) are performed.
Fatigue cracks called cts) occur. Due to rolling contact fatigue with the wheels due to repeated running of the train, they grow into fatigue cracks just below the rail surface, almost parallel to the rail tread surface, and then they branch or bend and propagate downward to the rail cross section. However, the crack sometimes causes rail breakage.

The problem of lateral cracking has been particularly emphasized in recent years in high-speed operation sections of Shinkansen and conventional lines, and various nondestructive inspections such as visual inspection, ultrasonic inspection method, acoustic inspection method, etc. Although flaw detection has been attempted by the method, it has not been put into practical use due to various technical problems. For example, even in the most general-purpose ultrasonic inspection method, especially a branched crack that occurs under a horizontal crack below the rail surface cannot be detected because it is shielded by the horizontal crack from the tread surface of the rail head. In addition, there was a problem that rust and grease from the side of the head deteriorated the rail surface properties, and continuous measurement was not possible from this position, making it difficult to practically use this method. ..

From such a background, the person concerned with the present invention uses the potential difference method as a nondestructive inspection method for a structure such as a metal circular tube, as described in detail in JP-A-61-296253. Use to quantify the position of various defects existing in structural materials such as pressure vessels and piping in nuclear power, thermal power generation facilities, chemical plants, etc., the depth from the outer surface, the size of defects and the inclination angle of defects, etc. Developed an inspection method that does. That is, this method applies a current to the structural material from the current input / output terminal connected to the constant current generator, measures the potential difference between two points at a plurality of positions, obtains the surface potential distribution, and obtains an abnormal maximum value at that time. Assuming the presence of the buried defect from the position αm, the potential difference ΔΦmi between the respective positions centered on the position αm is stored in association with the position information yi, and then analyzed based on theoretical search calculation. However, it is a non-destructive inspection method by a potential difference method that quantitatively evaluates the accurate position, depth, inclination angle, size, etc. of the buried defect. Further, according to such an inspection method, the presence or absence of the buried defect, the position and the depth of the defect, etc. can be easily quantitatively determined by the online method even for the structure in the operating state where the stress is actually applied. It has usefulness that can be evaluated.

[0005]

However, such a nondestructive inspection method has no problem as it is a general and simple crack shape for structural materials such as containers and pipes. However, there are the following problems with rails that are repeatedly subjected to high loads due to running trains. That is, in the case of a rail, a crack is formed almost horizontally on the tread surface just below the road surface, and a crack that splits or bends midway and propagates in the transverse direction of the rail is secondarily formed, which breaks the rail. It is a problem that causes it. This lateral crack has a problem that it cannot be detected by the conventional magnetic flaw detection method, electromagnetic induction flaw detection method, penetration flaw detection method, ultrasonic flaw detection method, or the like.

That is, the magnetic flaw detection method and the electromagnetic induction flaw detection method can detect only defects existing on the surface or just under the surface. Further, it is difficult to distinguish between a horizontal crack and a lateral crack, and a horizontal crack with a large shape is detected. The penetrant inspection method can detect only the defect portion open on the surface. In the ultrasonic flaw detection method, horizontal cracks cause sound waves to be blocked by horizontal cracks, and the sound waves cannot be reflected from the cracks, which requires discontinuous measurement from the side of the rail head. It is necessary, and lacks reliability and is not practical. Further, the nondestructive inspection method described in Japanese Patent Laid-Open No. 61-296253 described above is also limited to the detection of simple cracks or defects that are not branched or bent.

Due to these problems, the present inventors have aimed to increase the speed of railways and increase the axial load of railways, so that the horizontal cracks generated inside the laid rail head may branch or fall below the cross section of the rail. The present invention provides a nondestructive measurement method that accurately detects the presence of a lateral crack that progresses while bending and contributes to safe running of a train.

[0008]

SUMMARY OF THE INVENTION The gist of the present invention is to dispose current input / output terminals connected to a constant current source on a tread surface of a rail head via a crack search position of the rail and to provide a potential difference between them. The potential difference measurement terminal connected to the measuring device is placed or moved in the rail longitudinal direction at any fixed interval to measure the potential difference or potential difference distribution near the transverse crack, and the value of the abnormal potential change obtained in advance , For its detection interval,
The following equation relating the vertical length component of the lateral crack, ΔV · t / ρ · I−ΔX / h = α (b · sin θ / h) ² (1) ΔV: potential difference t: Rail head width ρ: Resistivity
I: current value ΔX: measurement interval h: rail effective height α: shape factor
b: Transverse crack length θ: Based on the inclination angle of the transverse crack, the value of ΔV · t / ρ · I-ΔX / h is specifically determined and compared to determine the rail head. The propagation depth of a lateral crack that occurs in a crack, that is, the vertical component of the crack length, and the position and size of a horizontal crack that has a lateral crack from the abnormal potential change position are determined nondestructively. It is something to measure.

The present invention will be described in detail below with reference to the drawings. FIG. 1 shows an embodiment of the method of the present invention. In the figure, 1 is a rail of the non-destructive measurement object. Reference numeral 2 denotes a current input / output terminal, which is arranged with its lower end in contact with the head tread surface of the rail 1 at a spaced position sufficiently including a crack position in the rail longitudinal direction, and one of which is connected to the constant current source 3. There is. That is, the current supplied from the constant current source 3 is connected to the path from the current terminal 2 on the input side to the constant current source 3 through the crack search position on the rail 1. There is. Reference numeral 4 denotes a potential difference measuring terminal, one end of which is spacedly arranged between the current input / output terminals 2-2 which are separately arranged on the rail head surface, so that the potential difference can be measured.
The other end is connected to the potential difference measuring device 5. That is, the potential difference detection terminal 4-4 detects an abnormal potential change due to a lateral crack inside the rail 1, and the detected value is recorded by the potential difference measuring device 5. Reference numeral 6 denotes a data analysis device, which is connected to the potential difference measuring device 5.

The data analysis device 6 uses the potential difference recorded by the potential difference measurement device 5 or the abnormal potential change amount obtained from the potential difference distribution curve and its position based on the above calculation formula (1) to determine the rail 1 as shown in FIG. Is configured to measure the depth of a horizontal crack 7 that is branched or bent from the horizontal crack 7 that has occurred in the head of the human head, and the position and the length in the longitudinal direction of the horizontal crack 7 that has generated 8 Has been done.

According to the method of the present invention as described above, a constant current of at least several amperes is applied from the current input / output terminal 2 connected to the constant current source 3 on the tread surface of the rail head of the rail 1 of the non-destructive object. Meanwhile, the potential difference detection terminal 4 is fixed or moved in the longitudinal direction on the rail tread surface, the potential difference between the potential difference detection terminals 4 is measured, the measurement result is recorded by the potential difference measurement device 5, and further transmitted to the data analysis device 6. It
The data analysis device 6 performs the analysis based on the following newly found analysis principle.

The change in electric potential of a conductor in which a constant current flows is
When it is considered that the cross section and the electric resistivity are practically constant like a rail, there is a proportional relationship with the measurement interval from Ohm's law. Therefore, when a constant current is applied in the longitudinal direction of the rail, the potential change is hardly affected when only a horizontal crack is present, and conversely, an abnormal potential change occurs only when a lateral crack is present. Is found theoretically,
And because it was confirmed experimentally.

The basics of the theoretical analysis will be shown below. Figure 3
Shows a potential change in the V · t / ρ · I to X / h relationship diagram with and without lateral cracking.
That is, the potential curve measured at a constant interval af is ac in the sound part and abde in the horizontal crack part having a lateral crack.
And there is a horizontal crack between bd. In a specific measurement, ΔX is the distance between the measuring terminals, ΔV is the potential difference on a rail with a crack, and ΔV _o is the potential difference on a rail without a crack, according to Ohm's law, ΔV · t / ρ · I−ΔX / h = (ΔV / ΔV _o −1) · ΔX / h (2) is the amount of change in potential difference between ce.

On the other hand, as a result of studying horizontal cracks including many lateral cracks with varying length, inclination angle, etc., the value of ΔV · t / ρ · I-ΔX / h is It has been found that there is a good relationship as shown in FIG. 4 with the ratio of the vertical component of the lateral crack and the effective rail height b · sin θ / h without being affected by the horizontal crack. Therefore, this curve is represented by the formula (1), and the vertical component of the lateral crack can be separated from the horizontal crack by measuring the potential difference change amount. Here, α is a shape factor, and changes a little depending on the depth of existence of the horizontal crack, but the amount of change is small and can be regarded as a constant value for practical use.

According to the above-described measurement principle, regarding a horizontal crack generated on the rail head by the following procedure, whether the crack has a lateral crack which is branched or bent, and If there is a lateral crack, the position of the horizontal crack,
Detect size and vertical component length of transverse cracks.

(1) A constant current is applied to the rail portion having a crack to be measured and the portion before and after the rail, which has no crack. (2) The potential difference ΔV, ΔV _o between the portion having a crack and the portion having no crack is measured at the same measurement terminal interval ΔX. At that time, ΔV measures the amount of change sufficiently including the change in potential due to cracking. (3) Obtain the rail effective height h. h can be calculated as h = _So / t from the rail cross-sectional area _So and the rail head width t. (4) Substitute the parameters ΔX, ΔV, ΔV _o , and h into the equation (2) to obtain ΔV · t / ρ · I−ΔX / h. (5) ΔV · t / ρ · I-ΔX that was obtained in advance
/ H and b · s in θ / h
Calculate inθ / h. (6) Also, the presence or absence of a transverse crack and the size of the horizontal crack are known by taking the points at which the change in the potential gradient starts and ends.

[0017]

According to the method of the present invention as described above, it is possible to easily and highly reliably measure the position and depth of a laterally crackable crack that branches or bends from a horizontal crack generated in the rail head. There are features.

[0018]

EXAMPLES Next, examples of the method of the present invention will be described. The measurement is
In order to evaluate the detection of a lateral crack that is branched from a horizontal crack that cannot be measured by the method other than the method of the present invention, a rail test piece was prepared in which a crack was artificially included in advance in a practical rail head. A JIS-50N rail was used as the rail, and a horizontal crack and a lateral crack were prepared by the procedure as shown in FIG. That is, a part of the rail head is grooved and slitted to create a slit of about 0.3 mm thickness that simulates a horizontal crack and a lateral crack, and then the remaining part is made by the same high carbon component welding rod as the rail. Was made to have the same structure and hardness as the base metal rail by overlay welding, finishing, and normalizing. At that time, referring to the actual crack size, rail test pieces A, B and C having cracks shown in the following table were used. The measurement interval ΔX is 160 mm,
The current was 12A.

[0019]

[Table 1]

FIG. 4 shows ΔV · t / ρ · I−ΔX / h and b
・ On the curve (solid line) obtained by theoretical analysis of sin θ / h,
By plotting actual measurement results A, B and C, it was proved that transverse cracks existing under cracks that could not be measured nondestructively in the past can be detected with sufficient reliability. ..

[Brief description of drawings]

FIG. 1 shows the structure of an apparatus of the method of the present invention.

FIG. 2 shows model diagrams of horizontal and lateral cracks inside the rail head.

FIG. 3 shows how the potential difference changes depending on the presence or absence of a crack.

4] ΔV · t / ρ · I−ΔX / h and b · sin θ /
The theoretical analysis curve with h and an example are shown.

FIG. 5 shows a procedure for preparing a rail standard test piece having a lateral crack and a test piece example.

[Explanation of symbols]

 1 Rail 2 Current input / output terminal 3 Constant current source 4 Potential difference measuring terminal 5 Potential difference measuring device 6 Data analysis device 7 Horizontal crack 8 Horizontal crack

Front page continuation (72) Inventor Kazuo Sugino 1-1 Hibahata-cho, Tobata-ku, Kitakyushu, Fukuoka Prefecture (72) Inside the Yawata Works, Nippon Steel Co., Ltd. (72) Masumi Saka, Yoshinariyama, Yoshizawa, Aoba-ku, Sendai-shi, Miyagi 27-2 Minami Yoshinari 15-9 (72) Inventor Daijiro Yuasa 2-2-7 Yagiyama Honcho, Taihaku-ku, Sendai City, Miyagi Prefecture 208 Yagiyama Avenue 208 (72) Hiroyuki Abe 1-chome, Yagiyama Minami, Taihaku-ku, Sendai City, Miyagi Prefecture 5-6

Claims (1)

[Claims] 1. A current difference input / output terminal connected to a constant current source is spaced apart via a crack search position on a tread surface of a rail head, and a potential difference measuring terminal connected to a potential difference measuring device is provided between the terminals. Aligned or moved in the direction, measuring the potential difference or potential difference distribution in the vicinity of a lateral crack that is branched or bent from a horizontal crack, and the following formula from the abnormal potential change amount and its detection interval obtained as a result, △ V · t / ρ · I-ΔX / h = α (b · sin θ / h) ² ΔV: potential difference t: rail head width ρ: resistivity
I: current value ΔX: measurement interval h: rail effective height α: shape factor
b: Transverse crack length θ: Transverse crack depth based on the inclination angle of the transverse crack, and lateral crack that occurred in the rail head from the abnormal potential change position. A non-destructive inspection method for lateral cracks in a rail that is characterized by measuring the position and size of a horizontal crack.