JP3204073B2 - Stress measuring method and apparatus utilizing magnetostriction effect - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and an apparatus for non-destructively measuring a stress applied to a steel structure or a mechanical part by utilizing magnetic anisotropy caused by a magnetostrictive effect.

[0002]

2. Description of the Related Art As a method for measuring a stress applied to a ferromagnetic material such as a steel material, there is a stress measuring method utilizing a magnetostrictive effect, that is, a phenomenon in which magnetic properties are changed by the stress. Above all, a stress measurement method utilizing magnetic anisotropy caused by the magnetostriction effect is disclosed in Japanese Patent Laid-Open No. JP-A-121325, JP-A-1-135338, JP-A-7-110
No. 270 or Reference 1 [Sakai et al .: Proceedings of the 50th Annual Scientific Lecture Meeting of the Japan Society of Civil Engineers, P662-663 (1995.
9)].

[0003] This method is based on the following principle. FIG. 3 shows a principle diagram of a stress measurement method using magnetic anisotropy generated by the magnetostriction effect. In FIG. 3, 1 is a magnetostrictive sensor, 11 is a U-shaped yoke wound with an exciting coil, 11a and 11b are open ends of the yoke 11, 12 is a U-shaped yoke wound with a detection coil, 12a. , 12b are open ends of the yoke 12, 13 is an AC power supply, 14 is a voltmeter,
Reference numeral 20 denotes an object to be measured (magnetic material), and reference numeral 30 denotes a direction in which a magnetic flux flows. Here, the magnetostrictive sensor 1 indicates the whole of the yoke 11, the yoke 12, the AC power supply 13, and the voltmeter 14. The yoke 11 and the yoke 12 are orthogonal to each other at the center of the yoke saddle.

Now, when a tensile stress σ _X acts on the X-axis direction of the DUT 20, X, X,
The magnetic permeability μ _X , μ _Y in the Y-axis direction is related by the following equation (2) due to the magnetostrictive effect, that is, magnetic anisotropy occurs μ _X > μ _Y (2)

[0005] The magnetostrictive sensor 1 is brought close to the measured object 20 in such a state, and the yoke 1 of the magnetostrictive sensor 1 is moved.
When an object to be measured 20 is excited by passing an alternating current through the exciting coil wound around the coil 1, most of the magnetic flux coming out of the open end 11a of the yoke 11 goes directly to the open end 11b of the yoke 11, but Since a magnetic anisotropy as shown in the equation (2) is generated in 20 by the tensile stress σ _X , a part of the magnetic flux flows through the yoke 12 to the open end 11 b of the yoke 11. Therefore, an electromotive force V having an output waveform shown in the following equation (3) is induced in the detection coil wound around the yoke 12. V = M ₀ · (μ _X −μ _Y ) · COS [2 · (θ−π / 4)] (3) where V is a rectified value of an AC electromotive force induced in the detection coil, M ₀ is a constant determined by excitation conditions, coil conditions, magnetic characteristics of the device under test 20, etc., and COS [2 · (θ−π /
4)] is a cosine function, and θ is the open ends 12a and 12 of the yoke 12.
The angle between the straight line connecting b and the X axis.

The difference in magnetic permeability (μ _X −μ _Y ) is the difference in stress (σ
_X− σ _Y ), the equation (3) is calculated by the following equation (4)
Can be rewritten as V = M · (σ _X −σ _Y ) · COS [2 · (θ−π / 4)] (4) where M is an excitation condition, a coil condition, and a magnetic characteristic of the DUT 20. It is a constant determined by the above.

From equation (4), the stress applied to the object to be measured can be obtained by measuring V.

However, the sensitivity of this magnetostrictive sensor (hereinafter referred to as
Magnetostrictive sensitivity) greatly depends on the distance between the magnetostrictive sensor called "lift-off" and the object to be measured. Therefore, the correct stress cannot be measured unless the measurement is always performed with a constant lift-off during the measurement.

For this purpose, Japanese Patent Laying-Open No. 62-121325 proposes a method of providing a lift-off detecting coil, previously determining the relationship between the induced voltage generated in the coil and the lift-off, and correcting the magnetostriction sensitivity. ing.

Japanese Utility Model Laid-Open Publication No. 1-135338 discloses a method of inserting a spacer having a known thickness between a sensor and an object to be measured to ensure a constant lift-off.

[0011]

However, in the method of providing a lift-off detecting coil described in Japanese Patent Application Laid-Open No. 62-121325, it is necessary to newly provide a lift-off detecting coil in the sensor. Not only will this become a major obstacle in implementing the technology, but the signal processing device will also be complicated.

In the method disclosed in Japanese Utility Model Laid-Open Publication No. 1-135338, in which a spacer is inserted between a sensor and an object to be measured, a surface treatment layer such as an anticorrosive layer whose thickness is unknown on the surface of the object to be measured. When the measurement is performed, it is troublesome that the measurement must be performed after removing the surface treatment layer.

SUMMARY OF THE INVENTION The present invention has been made to solve such a problem, and does not require a special lift-off detection mechanism. Even if there is a surface treatment layer of unknown thickness on the surface of the object to be measured, there is no problem. It is another object of the present invention to provide a method and apparatus for measuring stress using a magnetostrictive effect capable of measuring stress with high accuracy.

[0014]

An object of the present invention is to provide a U-shaped yoke around which an exciting coil is wound and a U-shaped yoke around which a detection coil is wound, so that they are orthogonal to each other at the center of the yoke saddle. In this case, the open end side of the U-shaped yoke is brought close to the object to be measured, an alternating current is applied to the exciting coil to excite the object to be measured, and an electromotive force induced in the detecting coil. In the stress measuring method using a magnetostrictive effect using a magnetostrictive sensor capable of measuring the stress applied to the object to be measured, the magnetostrictive sensor is induced in the detection coil by rotating the magnetostrictive sensor. The parameter A when the output waveform of the electromotive force is represented by the following equation (1) is obtained, and the magnetostriction is calculated using the previously obtained relation between the parameter A and the lift-off and the relation between the lift-off and the magnetostriction sensitivity. It is solved by the stress measurement method using magnetostrictive effect, characterized in that to correct the degree. V = A + B · COS [2 · (θ−C)] (1) where V is a rectified value of the AC electromotive force induced in the detection coil, and θ is a coil around the detection coil. Angle between the straight line connecting the open ends of the U-shaped yoke and the direction of the maximum principal stress, CO
S [2 · (θ-C)] is a cosine function, and B is changed by the principal stress difference.
Parameter (amplitude component), C indicates the principal stress direction
Parameter .

FIG. 4 shows an example of the output waveform of the electromotive force actually obtained when the magnetostrictive sensor is rotated on a steel plate in a certain stress state.

It can be seen that the output waveform of the electromotive force that fluctuates with the period π represented by the above equation (4) is actually measured.

Equation (4) can be generally expressed as in equation (1) above. FIG. 4 also shows the values of the parameters A, B, and C when the output waveform of the electromotive force is regressed to the equation (1).

Hereinafter, parameter A is referred to as a bias component, and parameter B is referred to as an amplitude component. The parameter B, which is an amplitude component, is a parameter that changes depending on the stress state of the DUT, that is, the principal stress difference, and the parameter C is a parameter that indicates the phase component, that is, the principal stress direction.

FIG. 5 shows an example in which a workpiece to which a stress of 0, 5, and 10 kgf / mm ² is applied is used.
FIG. 9 is a diagram illustrating a relationship between a bias component, a load stress, and a lift-off when a bias component is obtained by regressing an output waveform of an electromotive force obtained when the length is changed to 3 or 4 mm according to Expression (1).

It can be seen that the bias component is hardly affected by the load stress and changes only by lift-off.

FIG. 6 is a diagram showing the relationship between the bias component and the lift-off obtained from the results of FIG. If the bias component is known, the lift-off can be determined.

If the following method is used by utilizing the above-described relationship, the magnetostrictive sensitivity of the magnetostrictive sensor can be corrected, and highly accurate stress measurement can be performed.

Using a flat test piece made of the same material as the material constituting the steel structure or the mechanical part for which the stress measurement is to be performed, a predetermined stress is applied, and the magnetostrictive sensor is rotated at a certain lift-off, as shown in FIG. Such an output waveform is obtained. A similar output waveform is obtained by changing the stress applied to the test piece. This is repeated for the range of stress that is presumed to be actually applied to the steel structure or the mechanical part.

FIG. 7 is a diagram showing the relationship between the stress and the amplitude component at a certain lift-off (1 mm in this case) obtained in this manner.

From the results shown in FIG. 7, the amplitude component can be approximated by a straight line as shown in equation (5). B = α + β · (σ _X −σ _Y ) (5) Here, α is an amplitude component in a state where the load stress is zero, and β is a slope of a straight line in FIG. 7, which is the definition of the magnetostriction sensitivity described above. . In this way, the magnetostriction sensitivity at a certain lift-off is determined.

Next, a similar test is performed by changing the lift-off, and the magnetostriction sensitivity at each lift-off is obtained.

FIG. 8 is a diagram showing the relationship between lift-off and magnetostriction sensitivity obtained in this way.

FIG. 9 is a diagram showing the relationship between the lift-off and the ratio of the magnetostriction sensitivity based on the case of the standard lift-off (3 mm in the figure).

This relation can be regressed to a polynomial such as equation (6). ^{R = C1 · X 2 + C2} · X + C3 ··· (6) wherein, R represents the ratio of the magnetostriction sensitivity relative to the case of a standard lift-off, C1, C2, C3 are coefficients of approximation curves, X is is liftoff . In this way, the magnetostriction sensitivity can be obtained from the lift-off.

Therefore, if the relations shown in FIGS. 6 and 9 are determined in advance for the material constituting the steel structure or the mechanical part as the object to be measured, the bias component obtained by the actual measurement by the magnetostrictive sensor can be obtained. From FIG. 6, the lift-off is obtained by using FIG. 6. From this lift-off, the ratio of the magnetostrictive sensitivity is obtained by the equation (6), and the magnetostrictive sensitivity can be corrected. Then, by using the measured amplitude component and the corrected magnetostriction sensitivity, the stress applied to the object to be measured can be calculated by equation (5).

The method of measuring stress using the magnetostriction effect is as follows.
The magnetostrictive sensor, a power supply that supplies an alternating current to the magnetostrictive sensor, a detector that detects an electromotive force induced in the magnetostrictive sensor, a motor that rotates the magnetostrictive sensor, and an encoder that can measure a rotation angle of the motor. The present invention can be realized by a stress measuring device utilizing the magnetostrictive effect, comprising a calculating means for calculating a stress according to the stress measuring method.

[0032]

FIG. 1 shows a flowchart of a series of algorithms for calculating stress from the output of a magnetostrictive sensor according to the present invention.

First, the magnetostriction sensitivity at the standard lift-off is input, and the magnetostriction sensor is set to an arbitrary lift-off. Next, the output waveform is obtained by rotating the magnetostrictive sensor, and V
= A + B · COS [2 · (θ−C)]. Then, the lift-off of the bias component measured from the relationship between the bias component and the lift-off obtained in advance is obtained. Further, the magnetostriction sensitivity at this lift-off is obtained from the relationship between the ratio of the magnetostriction sensitivity based on the lift-off obtained in advance and the standard lift-off case. The stress is calculated based on the magnetostriction sensitivity and the amplitude component.

FIG. 2 shows an embodiment of a portion provided with a magnetostrictive sensor and its rotating mechanism in a stress measuring device utilizing the magnetostrictive effect of the present invention. In FIG. 2, 1 is a magnetostrictive sensor, 2
Is a DC servo motor with an encoder, 3 is a pinion gear, 4 is a ring gear, 5 is a ball bearing, 6
Is a C-ring, 7 is a ring spacer, and 8 is a housing.

The magnetostrictive sensor 1 provided in the housing 8 is rotated via a pinion gear 3 and a ring gear 4 by a DC servomotor 2 provided with an encoder provided in the same housing 8. At this time, the center of rotation is kept constant by the C ring 6, and smooth rotation can be performed by the ball bearing 5.

If the lift-off is very small,
Since the output of the magnetostrictive sensor 1 is saturated, a certain amount of lift-off can be ensured by using the ring spacer 7.

[0037]

Since the present invention is configured as described above, there is no problem even if there is a surface treatment layer of unknown thickness on the surface of the measured object without providing a special lift-off detecting mechanism. It is possible to provide a stress measurement method and device using a magnetostriction effect capable of measuring stress with high accuracy. Further, according to the method of the present invention, the maximum principal stress direction can also be automatically measured.

[Brief description of the drawings]

FIG. 1 is a flowchart showing a series of algorithms for calculating stress from the output of a magnetostrictive sensor according to the present invention.

FIG. 2 is a diagram showing one embodiment of a portion provided with a magnetostrictive sensor and a rotation mechanism thereof in the stress measuring device utilizing the magnetostrictive effect of the present invention.

FIG. 3 is a principle diagram of a stress measurement method using magnetic anisotropy generated by a magnetostriction effect.

FIG. 4 is a diagram illustrating an example of an output waveform of an electromotive force that is actually obtained.

FIG. 5 is a diagram showing a relationship among a bias component, a load stress, and a lift-off.

FIG. 6 is a diagram illustrating a relationship between a bias component and a lift-off.

FIG. 7 is a diagram showing a relationship between stress and an amplitude component.

FIG. 8 is a diagram showing a relationship between lift-off and magnetostriction sensitivity.

FIG. 9 is a diagram showing the relationship between the ratio of magnetostriction sensitivity based on the case of lift-off and standard lift-off.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Magnetostrictive sensor 2 DC servomotor provided with encoder 3 Pinion gear 4 Ring gear 5 Ball bearing 6 C ring 7 Ring spacer 8 Housing 11 U-shaped yoke wound with exciting coil 11a Open end of yoke 11 11b Yoke 11 12 Open end of U-shape 12a Open end of yoke 12 12b Open end of yoke 12 AC power supply 14 Voltmeter 20 DUT 30 Direction of magnetic flux

Claims (2)

(57) [Claims] 1. A U-shaped yoke around which an exciting coil is wound and a U-shaped yoke around which a detection coil is wound are arranged so as to be orthogonal to each other at the center of a yoke saddle. The yoke's open end side is brought close to the DUT, an alternating current is applied to the excitation coil to excite the DUT, and the electromotive force induced in the detection coil is measured to measure the DUT. In a stress measurement method using a magnetostrictive effect using a magnetostrictive sensor that can determine the stress applied to the, the output waveform of the electromotive force induced in the detection coil by rotating the magnetostrictive sensor is as follows: The parameter A when expressed by the equation (1) is obtained, and the relationship between the previously obtained parameter A and the distance “lift-off” between the magnetostrictive sensor and the object to be measured, and the relationship between the lift-off and the magnetostrictive sensor. Sensitivity (hereinafter referred to as magnetostriction sensitivity)
A stress measurement method using the magnetostrictive effect, wherein the magnetostriction sensitivity is corrected using the relationship. V = A + B · COS [2 · (θ−C)] (1) where V is a rectified value of the AC electromotive force induced in the detection coil, and θ is a coil around the detection coil. Angle between the straight line connecting the open ends of the U-shaped yoke and the direction of the maximum principal stress, CO
S [2 · (θ-C)] is a cosine function, and B is changed by the principal stress difference.
Parameter (amplitude component), C indicates the principal stress direction
Parameter . 2. The magnetostrictive sensor according to claim 1, a power supply for supplying an alternating current to the magnetostrictive sensor, a detector for detecting an electromotive force induced in the magnetostrictive sensor, and a motor for rotating the magnetostrictive sensor. A stress measuring device utilizing the magnetostrictive effect, comprising: an encoder capable of measuring the rotation angle thereof; and an arithmetic means for calculating a stress according to the stress measuring method according to claim 1.