JP2000221167A - Method for diagnosing stress using barkhausen noise - Google Patents

Abstract

PROBLEM TO BE SOLVED: To measure not only the stress of an elastic area but the stress of a plastic area, exceeding a yield point by plastically deforming part of a Barkhausen noise detect part of a steel material, applying residual stress and detecting Barkhausen noises generated from the part. SOLUTION: When a compressive residual stress -σγ is applied in an in-plane direction of a Barkhausen noise measurement part of a steel material with a tensile yield stress σty, an external stress F in the range of 0<=F+σty can be diagnosed. When a tensile residual stress σγ(>0) is applied in the in-plane direction of a measurement face of the Barkhausen noise measurement part of a steel material with a compressive yield stress -σcy (σcy>0), the external force F in the range of -(σγ+σcy)<=F<=0 can be diagnosed. At this time, linear correlation range of a calibration curve increases as the residual stress σγbecomes larger, so that the external stress F can be diagnosed up to a larger value.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for non-destructively diagnosing external stress acting on a steel material using Barkhausen noise generated from a ferromagnetic material such as a steel material.

[0002]

2. Description of the Related Art Building members such as buildings and bridges,
The stress acting on components of equipment such as crane is usually
It is constantly changing, and it may be necessary to measure those stress changes for safety. Usually, since the above-mentioned member is a ferromagnetic steel material, a technique for diagnosing stress from the magnetic properties of the steel material has been conventionally proposed.

For example, a method of detecting magnetic permeability in a direction perpendicular to a measurement area as a voltage signal and converting it into a stress value (JP-A-48-33885, JP-A-49-25994), A method in which a circuit is devised to directly detect a difference between orthogonal magnetic permeability as a voltage signal and obtain a stress from the magnitude of the signal (Japanese Patent Application Laid-Open Nos. 60-17330 and 60-243526),
A method for detecting a change in coercive force when a stress is applied (Japanese Patent Application Laid-Open No. 50-159787) and a method for inspecting stress or fatigue deformation using both Barkhausen noise and acoustic emission Japanese Patent Laid-Open No. 59-112257), a method of forming two ferromagnetic layers of different types on an object to be measured, and detecting a time difference of occurrence of large Barkhausen noise generated in each layer to detect stress and temperature (Japanese Patent Laid-Open No. Showa 61-25816
No. 1), a method for measuring the two-dimensional distribution of stress and defects from eddy current (Japanese Patent Application Laid-Open No. 63-81262), and a method for simultaneously detecting coercive force and Barkhausen noise to detect hardness and stress (particularly, JP-A-63-279185), detecting a magnetic signal from a region where a rail is locally heat-treated to form a spheroidized cementite structure, or a region where a small piece having the same structure is adhered to the rail. To determine the stress by using
No. 0669), and the like.

All of these techniques utilize the fact that the magnetic properties of a steel material change in accordance with the structure such as the crystal grain size and precipitates and the stress. In terms of stress, the range of stress to be detected that is common to all is within the elastic region.
This means that although there is almost no limited description of "stress in the elastic region" in the above specification, the stress range of the embodiment is the elastic region, and the object of the embodiment is a laser.
It is clear from the fact that there is no specification that the measurement can be performed in the elastic region in the actual use state of the device or the like, and that the measurement can also be performed in the plastic region in the specification. In the fatigue diagnosis, the steel material is in the plastic region. In this case, the detection target is not the stress but the degree of damage to the structure.

[0005] Buildings and the like using steel materials are designed within the elastic range, except in special cases. Therefore, if a stress higher than the yield stress acts on those members and enters the plastic region, it is in a very dangerous state.
However, conventionally, there has been no method in the world for diagnosing a stress higher than the yield stress using a magnetic signal such as Barkhausen noise.

[0006]

As described above, conventionally,
When diagnosing the stress acting on steel or the like using a magnetic signal, there is no method capable of measuring a stress range equal to or higher than the yield stress.

According to the present invention, a residual stress state at a measurement site of a Barkhausen noise of a steel material is controlled in advance,
It is an object of the present invention to provide a method capable of measuring not only an elastic region but also a stress in a plastic region beyond a yield point.

[0008]

The gist of the present invention is as follows.

(1) A steel material is AC-excited using a magnetic head composed of an excitation head and a detection head, and a voltage signal induced in the detection head is frequency-separated to detect Barkhausen noise. A method of diagnosing external stress applied to a steel material from the voltage value of the steel material, wherein a part of the Barkhausen noise detection site of the steel material is plastically deformed to apply a residual stress, and the region where the residual stress is applied is provided. A stress diagnostic method characterized by increasing the range of diagnosable external stress by detecting Barkhausen noise generated from a site including the stress.

(2) A range of 0 ≦ F ≦ σr + σty by applying a compressive residual stress of −σr (σr> 0) to a measurement site of Barkhausen noise of a steel material having a tensile yield stress of σty in a measurement plane direction. 3. The stress diagnosis method according to the above 1, wherein the external stress F can be diagnosed.

(3) The compressive yield stress is -σcy (σcy> 0)
Σr (>) at the barkhausen noise measurement site of steel
2. The stress diagnosis method according to the above 1, wherein the external stress F in the range of-([sigma] r + [sigma] cy)?

(4) The stress diagnosis method according to any one of the above (1) to (3), wherein the residual stress is isotropically distributed in the measurement plane.

(5) When the detection depth of Barkhausen noise is d, compressive residual stress or tensile residual stress is applied to a depth of at least 0.5 d from the surface of the measurement site. The stress diagnosis method according to any one of the above items.

[0014]

DETAILED DESCRIPTION OF THE INVENTION Barkhausen noise of steel
Since the stress varies depending on the structure such as external stress and crystal grain size, precipitates and dislocations, it is essential that the structure is not changed in order to diagnose external stress. That is, even if external stress acts on the steel material, when it is within the elastic range,
Since there is no structural change, Barkhausen noise depends only on stress and changes reversibly with respect to stress. However, an external stress greater than the yield stress acts on the steel material, and when it enters the plastic region, dislocation multiplication and crystal rotation occur and the structure changes, so it is no longer possible to diagnose only the external stress. It will be possible.

By controlling the initial state of the residual stress at the measurement site, the present inventors have made it possible to hardly cause a structural change even when the magnitude of the external stress becomes larger than the yield stress. Further, in such a state, a detailed investigation of the relationship between stress and Barkhausen noise resulted in the present invention.

FIGS. 1 (a), 1 (b) and 1 (c) are stress (σ) vs. strain (ε) curves of a normal steel material. (A) shows the case where the external stress is in the elastic region where the external stress is equal to or lower than the yield stress, and changes almost reversibly on the stress versus strain curve. σ / ε is the Young's modulus E. (B), when an external tensile stress having a magnitude equal to or greater than the tensile yield stress σty is applied, (c)
Is a case where an external compressive stress having a magnitude equal to or greater than the compressive yield stress-σcy is applied. (B) and (c) are in the plastic region. Usually σty and σcy, and εty and εcy
Are almost the same value.

The present inventors have described in detail the relationship between the stress or strain and the magnitude of Barkhausen noise when plastic deformation is performed from the elastic region to the plastic region, and further to various strains in the plastic region. Was measured. As a result, when one end is subjected to plastic deformation to the compression side or the tension side and a tensile stress or a compressive stress is newly applied to the sample in a state where the residual stress is applied,
It has been found that the stress range in which the linear correlation between stress or strain and Barkhausen noise is established is significantly improved as compared with the case where there is no residual stress.

Hereinafter, a specific description will be given with reference to the drawings. FIG.
(A) shows that the sample at the origin O is subjected to a compressive stress exceeding the yield point F and is unloaded after reaching the point G, and is in the state of the point H, that is, in the state of the compressive residual stress of -σr. Shows the case. FIGS. 3A and 3B show typical examples of the rate of change of Barkhausen noise in the case where a tensile stress is applied to this and the relationship between the stress and the strain passes from the point I to the point J.

Here, the magnitude of the Barkhausen noise was evaluated by the effective voltage, and the rate of change was based on the effective voltage of the Barkhausen noise at the point H. FIG.
As can be seen from (a), the Barkhausen noise is σr +
A linear correlation was shown in the range of σty '. In practice, σty '≒ σ
was ty. Therefore, by using this relationship as a calibration curve, the tensile stress F can be set to 0 ≦ F ≦ σr + σty
Can be diagnosed within the range. FIG. 3B shows a case where distortion is taken on the horizontal axis. From this relationship, strain ε is also 0 ≦ ε
The diagnosis can be made within the range of ≦ εIH + εty ′.

Here, εty ′ ≒ εty. Within this linear correlation range, Barkhausen noise reversibly changes with respect to stress or strain. This is because, even when the sample is in the plastic region, σ / ε = E is almost established between the points G and J as shown in FIG. FIG.
In (a), by controlling the residual stress so that the point H is in the state of the point G, that is, the residual stress −σr
Is controlled to approximately -σcy, it is possible to further widen the range of the linear correlation of the calibration curves shown in FIGS. 3 (a) and 3 (b).

FIG. 2B shows changes in stress and strain when a compressive stress is applied to the sample as in the case of FIG. The difference between the two is that the maximum compressive strain at the point G 'is smaller than that at the point G in (a), but the compressive residual stress at the point H' is controlled to be the same value as the point H. The rate of change of Barkhausen noise was measured when a tensile stress was applied from point H ′ to point I ′, and further beyond point J ′. In the case shown in FIGS. 3 (a) and 3 (b) Was similar to FIGS. 2 and 3 show that the same calibration curve can be obtained as long as the same amount of compressive residual stress is applied even if the amount of strain to be applied is different. This indicates that when the compressive residual stress is actually applied, there is a margin in the control range of the strain, and it can be seen that the control is easy.

The rate of change of Barkhausen noise when a normal sample whose residual stress was not controlled was subjected to a tensile stress was examined. The range in which the rate of change showed a linear correlation with stress or strain, and It was found that the sensitivity represented by the slope of the straight line was significantly lower than when there was a compressive residual stress. A typical example of this case is shown in FIG.
It was shown to.

FIG. 5A shows that the sample at the origin O has a yield point A
In this case, the load is unloaded after reaching the point B by applying a tensile stress exceeding the point B, and the state is at the point C, that is, the state is under the tensile residual stress of σr. FIGS. 6A and 6B show typical examples of the rate of change of Barkhausen noise in the case where a compressive stress is applied thereto and the relationship between stress and strain passes from point D to point E. Here, the magnitude of Barkhausen noise was evaluated as in the case of FIG. However, the effective value voltage of Barkhausen noise at the point C was used as a reference. As can be seen from FIG. 6A, Barkhausen noise showed a linear correlation in the range of-([sigma] r + [sigma] cy '). Actually, σcy ′ ≒ σcy. Therefore, by using this relationship as a calibration curve,
The compression stress F can be diagnosed in the range of-(σr + σcy) ≦ F ≦ 0.

FIG. 6B shows a case where distortion is taken on the horizontal axis. From this relationship, the strain ε is also − (εCD + εcy ′) ≦ ε ≦ 0
Can be diagnosed within the range. Where εcy '≒ εcy
It is. Within this linear correlation range, Barkhausen noise reversibly changes with respect to stress or strain. This is because σ / ε = E is substantially established between the point B and the point E as shown in FIG. 5A even when the sample is in the plastic region. In FIG. 5A, by controlling the residual stress so that the point C becomes the state of the point B,
By controlling the residual stress σr to approximately σty, FIG.
It is possible to further widen the range of the linear correlation of the calibration curves shown in (a) and (b).

FIG. 5B shows changes in stress and strain when a tensile stress is applied to the sample as in the case of FIG. 5A. The difference between the two is that the maximum tensile strain at the point B 'is smaller than that at the point B in (a). However, the residual tensile stress at the point C' is controlled to have the same value as the point C. The rate of change of Barkhausen noise when a compressive stress was applied from point C ′ to point D ′ and further beyond point E ′ was measured. The case shown in FIGS. 6A and 6B was used. Was similar to 5 and 6
Indicates that it is easy to control the strain when the tensile residual stress is applied, as in the case of FIGS. 2 and 3.

The rate of change of Barkhausen noise when compressive stress was applied to a normal sample whose residual stress was not controlled was examined. The range in which the rate of change showed a linear correlation with stress or strain, and It was found that the sensitivity represented by the slope of the straight line was significantly lower than that in the case where there was a tensile residual stress. A typical example in this case is shown in FIG.
It was shown to.

Normally, a magnetic head composed of an excitation head and a detection head is applied to a measurement site on a sample surface to detect Barkhausen noise at that site. It suffices if it is within the detection area of the Hausen noise. In the vicinity of the sample surface where Barkhausen noise is measured, since the external stress of tension or compression applied to the sample is almost in the in-plane direction of the sample surface, the controlled residual stress is applied in the in-plane direction of the sample surface. Is preferred. Further, it is more preferable that the residual stress is isotropically distributed in the plane so that the diagnostic accuracy of the stress does not decrease even if the external stress is applied from any direction.

From the above results, the tensile yield stress is σty
-Σr at the measurement site of Barkhausen noise of steel
By applying the compressive residual stress of (σr> 0) in the in-plane direction of the measurement, it is possible to diagnose the external stress F in the range of 0 ≦ F ≦ σr + σty, and the compressive yield stress becomes −σcy.
By applying a tensile residual stress of σr (> 0) in the in-plane direction to the measurement site of the Barkhausen noise of a steel material with (σcy> 0), − (σr + σcy) ≦ F ≦ 0
It is possible to diagnose the external stress F in the range of The larger σr is, the wider the linear correlation range of the calibration curve is, and the diagnosis up to a larger external stress becomes possible. Normally, the upper limit of σr is the size corresponding to the yield stress, but control of residual stress larger than the yield stress becomes possible by performing the method in which dislocation slip is suppressed.

Since the attenuation increases as Barkhausen noise generated from a deeper part of the sample, the voltage generated in the detection coil decreases. The depth d at which the Barkhausen noise attenuates to 1 / e with respect to the sample surface is called skin depth, and d = (ρ / πfμ) ^1/2 ,
ρ is an electric resistance, f is a detection frequency of Barkhausen noise, and μ is a magnetic permeability. The depth at which the residual stress is applied must be at least 0.5d or more, where the detected depth is d. If it is shallower than 0.5 d, the range in which the linear correlation between them is satisfied in the relationship between Barkhausen noise and stress or strain is reduced.

Methods for applying residual stress to a Barkhausen noise measurement site include, for example, a method in which small steel balls such as air blast and shot blast and ceramic particles collide with the sample surface at high speed, skin pass rolling, and sander. Polishing, local heating and cooling methods, etc. are available, but in order to impart isotropic residual stress to the sample surface,
Air blast, shot blast and local heating and cooling are suitable. Even in the case of using a sander, the residual stress can be isotropically applied by isotropic polishing.

It is desirable to apply the residual stress using these methods before the object to be measured is actually installed, that is, at a stage where no external stress is applied. If the treatment is performed at this stage, the absolute value of the external stress after installation can be measured. If a residual stress is applied in a state where the external stress is already applied and the external stress applied thereto is unknown, the relative change of the external stress from that point can be known. It is preferable that the residual stress to be applied has a size corresponding to the yield stress, since uniform residual stress is easily applied.

When the present invention is actually used, a calibration curve indicating the relationship between the external stress in the member to be measured and the RMS voltage of Barkhausen noise is measured in advance, and the actually measured RMS voltage is used as the stress. This calibration curve may be used when converting to.

[0033]

The present invention will be specifically described below with reference to examples.

(Example 1) The yield stress σty is 24 kgf /
The relationship between Barkhausen noise and external stress was investigated using a steel type of mm ² . The measurement sample is a steel pipe having an outer diameter of 318 mm, a thickness of 6.9 mm, and a length of 6 m. However, those with and without compressive residual stress applied to the steel pipe surface by shot blasting were used. Barkhausen noise was measured while applying bending stress to each steel pipe, and the relationship between the two was examined. The measurement of Barkhausen noise on the steel pipe was performed at a portion where the maximum tensile stress occurs in the axial direction. The stress applied to the measurement site was determined from a strain gauge attached adjacent to the Barkhausen noise measurement site.

The measurement of Barkhausen noise was performed as follows. An excitation head in which a 1000-turn enamel wire is wound on a U-shaped excitation core in which silicon steel sheets are laminated, and an acrylic bobbin having a cross-sectional area of 2 mm × 8 mm are 500
A magnetic head comprising a detection head wound with a turn enameled wire was applied to the surface of the sample under each bending stress, and the effective voltage of Barkhausen noise was measured. The excitation direction is the longitudinal direction of the steel pipe. Excitation frequency is 100H
z, the detection frequency is 10 kHz to 100 kHz.

The distribution in the depth direction of the magnitude of the residual stress on the surface of the steel pipe after the shot blast treatment was determined by X-ray residual stress measurement after etching a predetermined thickness from the surface in the thickness direction. As a result, the compressive residual stress (−σr = −) having the same magnitude as the yield stress up to a depth of about 200 μm from the surface.
24 kgf / mm ² ) was confirmed to enter isotropically in the plane. Formula for calculating skin depth d =
The detection depth of Barkhausen noise obtained from (ρ / πfμ) ^1/2 is about 160 μm.

FIG. 8 shows the relationship between the external tensile stress in the longitudinal direction at the measurement site and the rate of change of the effective voltage of Barkhausen noise. However, since σ / ε = E is established between the points G and J as shown in FIG. 2, the stress can be calculated from the strain, but in the stress range larger than the point J, σ / ε is obtained.
Since = E does not hold, stress cannot be determined from strain. In FIG. 8, for convenience, the values calculated using the relationship of σ / ε = E are used on the horizontal axis, but the stress range in which stress cannot be calculated from the strain is shown in parentheses. As can be seen from FIG. 8, the range where the linear correlation is established is 47 kgf / mm ² , as indicated by the arrow in the figure, and approximately σr + σty = 2.
It can be seen that the stress and the effective voltage of Barkhausen noise show a linear correlation up to the range of 4 + 24 = 48 kgf / mm ² . By using this relationship as a calibration curve, it is possible to diagnose external stress from the effective value voltage of Barkhausen noise.

FIG. 9 shows the case without the shot blast processing, in which the stress dependence of Barkhausen noise is small.
It can be seen that there is almost no linear correlation between the two.

As described above, by applying the compressive residual stress in the in-plane direction of the measurement, the external stress in the elastic region is not reduced.
It is possible to diagnose even external stresses equal to or higher than the yield stress.

Example 2 Yield stress σty is 45 kg / m
The relationship between Barkhausen noise and external stress was examined in the same manner as in Example 1 using a steel grade of m ² . However, the sample is a gutter-shaped test material cut out from a steel pipe having an outer diameter of 318 mm and a wall thickness of 7.9 mm to a length of 500 mm in the pipe axis direction and a width of 100 mm in the pipe circumferential direction. The steel tube surface was subjected to a shot blast treatment to which a compressive residual stress was applied and the steel tube surface was not applied. Compressive residual stress of shot blasted material (-σ
r) was −34 kgf / mm ² , and was isotropically in the measurement plane to a depth of about 120 μm from the surface.

FIG. 10 shows the relationship between the external stress and the effective voltage of Barkhausen noise when a bending stress was applied so that the outside of the gutter-shaped test material protruded. The excitation is in the longitudinal direction of the gutter-shaped test material. As indicated by the arrow in the figure,
The range in which the linear correlation holds is 77 kgf / mm ² ,
It can be seen that the external stress and the effective voltage of Barkhausen noise show a linear correlation up to a range of approximately σr + σty = 34 + 45 = 79 kgf / mm ² . By using this relationship as a calibration curve, it is possible to diagnose external stress from the effective value voltage of Barkhausen noise.

FIG. 11 shows the case without the shot blast processing, in which the stress dependence of Barkhausen noise is small and there is almost no linear correlation between the two.

As described above, by applying the compressive residual stress in the in-plane direction of the measurement, the external stress in the elastic region can be prevented.
It is possible to diagnose even external stresses equal to or higher than the yield stress.

Example 3 Medium carbon steel with a cross section of 10 mm × 10 mm (compression yield stress σcy = −30 kgf / mm ² )
Was decarburized to a depth of about 300 μm from the surface, and then quenched in water at 800 ° C. By this treatment, the inside of the square bar is transformed into martensite and the volume is expanded, but the decarburized surface is close to the α-Fe single phase state, so that no transformation occurs. Therefore, tensile residual stress is generated in the decarburized layer. As a result of the actual measurement, a tensile residual stress of 15 kgf / mm ² was generated over the entire decarburized layer in the axial direction of the square bar test material. The same measurement as in Example 1 was performed by applying an external compressive stress in the axial direction.

As a result, approximately-(σr + σcy) =-(1
5 + 30) = 45 kgf / mm ² The external stress and the effective voltage of Barkhausen noise show a linear correlation up to the range of 45 kgf / mm ^{2. By} using this relationship as a calibration curve, the external stress can be calculated from the effective voltage of Barkhausen noise. Diagnosis becomes possible.

As a comparative example, in the test material subjected to only the decarburization treatment, that is, in the case where almost no residual stress is generated, the stress range in which the linear correlation between the external stress and the Barkhausen noise is satisfied is determined when the tensile residual stress is present. Was less than half.

(Embodiment 4) When the depth of detection of Barkhausen noise is d and the depth of existence of residual stress is D, D / d
The range in which the linear correlation between the external stress and the effective value voltage of Barkhausen noise is established when is changed. actually,
D was changed by changing the shot blast condition while keeping the detection depth d of Barkhausen noise constant.
The method of measuring Barkhausen noise and the method of measuring residual stress are the same as in Example 1. When the shot blast conditions are changed, the residual stress magnitude σr is also changed together with the residual stress existence depth D. Therefore, the stress range in which the linear correlation is established is evaluated by using the actually measured linear correlation range as σline
When r was used, the evaluation was performed by σliner / (σr + σty). This is because the stress range in which the linear correlation holds is maximum (σr + σt
y), and the larger the σliner / (σr + σty), the wider the range in which the linear correlation is established. The results are shown in Table 1 below.

[0048]

[Table 1]

As can be seen from the above, when the detection depth of Barkhausen noise is d, the residual stress is applied at least to a depth of 0.5 d from the surface of the measurement site, so that the external stress and the Barkhausen noise can be effectively reduced. It can be seen that the linear correlation of the value voltage holds over a wider stress range.

[0050]

According to the present invention, not only the stress in the elastic range but also the stress in the plastic range exceeding the yield stress can be diagnosed by controlling the residual stress state at the measurement site of Barkhausen noise of steel in advance. Even it becomes possible. By performing stress diagnosis on buildings, bridges, steel pipes, and the like using the present invention, diagnosis can be performed up to a high stress range that could not be diagnosed conventionally, and management accuracy is improved.

[0051]

[Brief description of the drawings]

FIG. 1 is a characteristic diagram showing a relationship between stress and strain of a general steel material.

FIG. 2 is a characteristic diagram showing a relationship between stress and strain at a Barkhausen noise measurement site according to the present invention.

FIG. 3 is a characteristic diagram showing the rate of change of the effective value voltage of stress or strain and Barkhausen noise when a compressive residual stress is applied.

FIG. 4 is a characteristic diagram showing a change rate of the effective value voltage of the stress and Barkhausen noise when no residual stress is applied (Comparative Example).

FIG. 5 is a characteristic diagram showing a relationship between stress and strain at a Barkhausen noise measurement site according to the present invention.

FIG. 6 is a characteristic diagram showing the rate of change of the effective value voltage of stress or strain and Barkhausen noise when a tensile residual stress is applied.

FIG. 7 is a characteristic diagram showing a rate of change of an effective value voltage of stress and Barkhausen noise when no residual stress is applied (Comparative Example).

FIG. 8 is a characteristic diagram showing a relationship between an external tensile stress and an effective value voltage of Barkhausen noise.

FIG. 9 is a characteristic diagram illustrating a relationship between an external tensile stress and an effective value voltage of Barkhausen noise (Comparative Example).

FIG. 10 is a characteristic diagram showing a relationship between an external tensile stress and an effective value voltage of Barkhausen noise.

FIG. 11 is a characteristic diagram illustrating a relationship between an external tensile stress and an effective value voltage of Barkhausen noise (Comparative Example).

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Shigehiko Yamana 2-6-3 Otemachi, Chiyoda-ku, Tokyo Inside Nippon Steel Corporation (72) Inventor Takao Sasaki 2-6-3, Otemachi, Chiyoda-ku, Tokyo Within Nippon Steel Corporation (72) Inventor Jun Tsujimoto 2-6-3 Otemachi, Chiyoda-ku, Tokyo F-term within Nippon Steel Corporation (reference) 2G053 AA19 AB20 BA15 BC02 CA03 CB24

Claims (5)

[Claims] 1. A steel material is AC-excited using a magnetic head including an excitation head and a detection head, and a voltage signal induced in the detection head is frequency-separated to detect Barkhausen noise. A method of diagnosing external stress applied to a steel material from a voltage value, wherein a part of a Barkhausen noise detection site of the steel material is plastically deformed to apply a residual stress, and the region where the residual stress is applied is provided. A stress diagnostic method characterized by increasing the range of diagnosable external stress by detecting Barkhausen noise generated from a site including the stress. 2. Applying a compressive residual stress of -σr (σr> 0) to a Barkhausen noise measurement site of a steel material having a tensile yield stress of σty in the in-plane direction of the steel, thereby reducing
The stress diagnosis method according to claim 1, wherein diagnosis of an external stress F in a range of ≤ F ≤ σr + σty is enabled. 3. A steel material having a compressive yield stress of −σcy (σcy> 0) has a σr (> 0) at a Barkhausen noise measurement site.
Is applied in the measurement plane direction to obtain an external stress F in a range of − (σr + σcy) ≦ F ≦ 0.
2. The stress diagnosis method according to claim 1, wherein diagnosis of stress is enabled. 4. The method according to claim 1, wherein the residual stress is isotropically distributed in the measurement plane.
The stress diagnosis method according to the item. 5. When the depth of detection of Barkhausen noise is d, compressive residual stress or tensile residual stress is applied to a depth of at least 0.5d from the surface of the measurement site. The stress diagnosis method according to any one of the above items.