JP3191726B2 - 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 stress acting on a steel structure or a machine component, particularly a periodic action, utilizing magnetic anisotropy caused by a magnetostrictive effect (in a narrow sense, an inverse magnetostrictive effect). The present invention relates to a method and a device for non-destructively measuring the maximum principal stress component of stress.

[0002]

2. Description of the Related Art As a method for measuring a stress acting on 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 change due to stress. Above all, the stress measurement method utilizing magnetic anisotropy generated by the magnetostriction effect is disclosed in Japanese Patent Application Laid-Open No. Sho 62 (1987) as a method for measuring stress acting on a steel structure or a mechanical part in a non-destructive and relatively simple manner. -121325,
JP-A-1-135338, JP-A-7-11027
No. 0 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)].

FIG. 5 shows an example of a stress measuring method utilizing magnetic anisotropy caused by the magnetostrictive effect.

In this method, a U-shaped yoke 11 wound with an exciting coil, a U-shaped yoke 12 wound with a detection coil, an AC power supply 13 for excitation, and a magnetic flux flowing through the DUT 20 are provided. The stress is measured by the following principle using a magnetostrictive sensor 1 which is composed of a voltmeter 14 for detecting the force, and in which the yokes 11 and 12 are arranged so as to be orthogonal to each other at the center of the yoke saddle portion.

[0005] When a tensile stress σ _X acts on the X-axis direction of the DUT 20, X, X,
The magnetic permeability μ _X and μ _Y in the Y-axis direction have a relationship represented by the following expression (2), that is, magnetic anisotropy, due to a magnetostrictive effect. μ _X > μ _Y (2)

[0006] 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 AC current is supplied from the AC power supply 13 to the exciting coil wound around the device 1 to excite the device under test 20, most of the magnetic flux emitted from the open end 11 a of the yoke 11 goes directly to the open end 11 b of the yoke 11. Since a magnetic anisotropy such as the equation (2) occurs in the device under test 20 due to the tensile stress σ _X , a part of the magnetic flux passes through the yoke 12 and the open end 1 of the yoke 11.
Flow to 1b. Therefore, an electromotive force V having an output waveform represented by the following equation (3) is induced in the voltmeter 14 attached to 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 the equation (4), the stress acting on the DUT 20 can be obtained by measuring V.

However, when the stress acts on the object to be measured periodically, the following problem occurs.

FIG. 6 shows the relationship between the electromotive force and the stress of the magnetostrictive sensor when a stress is applied and when the stress is removed.

As shown in the figure, the relationship between the stress and the electromotive force of the magnetostrictive sensor shows a so-called hysteresis in which the same electromotive force does not appear for the same stress when the stress is applied and when the stress is removed. It becomes impossible to obtain the stress uniquely from the electric power.

This is due to residual magnetization accumulated in the device under test during repeated measurements. Therefore, the actual fair 5-1033
No. 7 proposes a method of erasing the residual magnetization of an object to be measured by an AC demagnetization process and then performing a measurement.

[0013]

However, since the method described in Japanese Utility Model Publication No. 5-10337 requires several seconds for one demagnetization process, it is used, for example, for roads and bridges where vehicles frequently pass. It is not applicable when the period of the acting stress is short as seen in the steel structure being used.

The present invention has been made in order to solve such a problem, and it is intended to reduce the stress which acts periodically without performing the demagnetization treatment, particularly the maximum principal stress component which is important in the design of a steel structure. An object of the present invention is to provide a stress measuring method and a device using a magnetostrictive effect that can be measured accurately.

[0015]

The 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 as to be orthogonal to each other at the center of the yoke saddle. A magnetostrictive sensor is provided, which excites the device under test by passing an alternating current through the exciting coil and measures the electromotive force induced in the detection coil to determine the stress acting on the device under test. In the stress measurement method utilizing the magnetostrictive effect, (a) the output waveform of the electromotive force induced in the detection coil by rotating the magnetostrictive sensor in a non-contact manner on the object to be measured is represented by the following equation (1). ) Is obtained, and (b) of two parallel straight lines connecting the open end of the yoke around which the exciting coil is wound and the open end of the yoke around which the detection coil is wound. A set of straight lines and the The magnetostrictive sensor disposed and the maximum principal stress directions which is obtained from the meter C to become parallel,
(C) bringing the magnetostrictive sensor into contact with the object to be measured;
The problem is solved by a stress measurement method using the magnetostrictive effect, which is characterized by performing stress measurement.

V = A + B · COS [2 · (θ−C)] (1) where V is a rectified value of an AC electromotive force induced in the detection coil, and θ is a value of the detection coil. Angle between the straight line connecting the open ends of the U-shaped yoke and the maximum principal stress direction, CO
S [2 · (θ−C)] is a cosine function, and A, B, and C are parameters.

First, in order to measure the maximum principal stress component, it is necessary to know the direction of the maximum principal stress. However, in a complicated steel structure,
It is not easy to estimate the maximum principal stress direction before stress measurement. Then, the maximum principal stress direction can be obtained by using the magnetostrictive sensor as follows.

Since the above equation (4) can be rewritten into the equation (1), the maximum principal stress direction can be known by obtaining the parameter C. In practice, the magnetostrictive sensor is rotated at a fixed distance (referred to as lift-off) from the object to be measured, that is, by changing θ, the output waveform of the electromotive force induced in the detection coil of the magnetostrictive sensor is obtained. The output waveform is regressed to equation (1) to find parameter C.

FIG. 3 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 stressed state with a periodically acting stress. The figure 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).

In this manner, the maximum principal stress direction of the periodically acting stress is determined. At the same time, the maximum principal stress component is also obtained from the parameter B representing the stress state. However, as described above, if the measured object has remanent magnetization due to repeated measurements, the relationship between the stress and the electromotive force of the magnetostrictive sensor is determined by a hysteresis. Therefore, accurate stress cannot be obtained.

Then, when the relationship between the lift-off and the stress-electromotive force hysteresis curve was examined, it was found that the lift-off should be reduced as shown below.

FIG. 4 shows the effect of lift-off on the stress-electromotive force hysteresis curve. Lift off 1.0
It can be seen that when the distance is reduced from 0.1 mm to 0.1 mm, the spread of the hysteresis becomes smaller, and the difference between the electromotive forces at the same stress when the stress is applied and when the stress is removed becomes smaller.

Therefore, after arranging the magnetostrictive sensor under the condition that the maximum principal stress component can be determined, that is, two parallel lines connecting the open end of the yoke around which the exciting coil is wound and the open end of the yoke around which the detection coil is wound. If one set of straight lines is made parallel to the maximum principal stress direction obtained from the parameter C and the stress is measured by bringing the magnetostrictive sensor into contact with the object to be measured, a more accurate maximum principal stress can be obtained. The stress component is determined.

As can be seen from FIG. 4 , when the lift-off is reduced, the output itself increases (the magnetostriction sensitivity increases), so that the error in converting the output into stress can be reduced, and more accurate stress measurement is possible. Becomes

According to such a method, the maximum principal stress component of the periodically acting stress can be accurately measured without performing the demagnetization treatment.

The stress measurement is performed by using the magnetostrictive effect, comprising the magnetostrictive sensor, a rotating mechanism for rotating the magnetostrictive sensor, and a spring mechanism for attaching and detaching the magnetostrictive sensor to and from the object to be measured. Can be realized by: Also,
Since the magnetostrictive sensor is attached to and detached from the object to be measured by the spring mechanism, the magnetostrictive sensor can be brought into contact with the object to be measured with a constant force or separated at a constant interval, and high-precision measurement with good reproducibility can be performed.

[0027]

FIG. 1 is a flowchart showing an embodiment of the method of the present invention.

First, a magnetostrictive sensor is set on an object to be measured with a standard, for example, a lift-off of 1 mm (S1). Next, the output is measured by rotating the magnetostrictive sensor (S2), the output waveform is obtained, and the regression is made to the equation of V = A + B · COS [2 · (θ−C)], and the parameter C which is the maximum principal stress direction is obtained. It is determined (S3). Then, the magnetostrictive sensor is rotated so that one set of two parallel straight lines obtained by connecting the open ends of both yokes of the magnetostrictive sensor is parallel to the maximum principal stress direction (S4). Thereafter, the magnetostrictive sensor is brought into contact with the object to be measured (S5), and the stress is measured (S6).
The obtained stress is the maximum principal stress.

FIG. 2 shows a magnetostrictive sensor of a stress measuring device according to the present invention and its peripheral portion. In the drawings, (a) shows a front view and (b) shows a side view.

A DC servo motor 2 having a magnetostrictive sensor 1 and an encoder is provided in the housing 6, and the rotation of the DC servo motor 2 is transmitted to the magnetostrictive sensor 1 via a pinion gear 3 and a ring gear 4. Can be At this time, the rotation is smoothly performed by the ball bearing 5. The magnetostrictive sensor 1 is fixed to a holder 7 that supports the magnetostrictive sensor by screws 8. The holder 7 for supporting the magnetostrictive sensor has a mechanism capable of being pushed down inside the housing 6 by a spring (omitted in the drawing).
The leading end of the pin 10 is pushed by the notch 16 and is pushed downward by the difference in diameter of the leading end of the pin 10. Push button 9
When the movement of the pin 10 is adjusted via the spring 15 and the pressing of the push button 9 is stopped, the holder 7 supporting the magnetostrictive sensor returns to the original position.

The magnetostrictive sensor 1 is rotated by a DC servomotor 2 having an encoder to determine a parameter C and determine the direction of the maximum principal stress. Next, the magnetostrictive sensor 1
The magnetostrictive sensor 1 is rotated by the DC servomotor 2 so that one of two parallel straight lines obtained by connecting the open ends of the two yokes is parallel to the maximum principal stress direction. Then, by pushing the push button 9 and pushing the pin 10, the tip of the pin 10 is cut out.
6 and the holder 7 supporting the magnetostrictive sensor is lowered downward by the diameter difference of the tip of the pin 10. At this time, the magnetostrictive sensor 1 fixed to the holder 7 supporting the magnetostrictive sensor is brought into contact with the measured object with a constant force. Also,
When the push button 9 is released, the magnetostrictive sensor 1 is accurately returned to the original position together with the holder 7. Therefore, highly accurate measurement with good reproducibility can be performed.

[0032]

Since the present invention is constructed as described above, it is possible to accurately determine the stress that acts periodically without performing demagnetization processing, especially the maximum principal stress component that is important in the design of steel structures. A method and apparatus for measuring stress using the magnetostrictive effect, which can be easily measured, can be provided.

[Brief description of the drawings]

FIG. 1 is a flowchart showing an embodiment of the method of the present invention.

FIG. 2 is a diagram showing a magnetostrictive sensor of a stress measuring device according to the present invention and a peripheral portion thereof.

FIG. 3 is a diagram showing an example of an output waveform of an electromotive force actually obtained when a magnetostrictive sensor is rotated on a steel plate in a certain stress state.

FIG. 4 is a diagram showing the effect of lift-off on a stress-electromotive force hysteresis curve.

FIG. 5 is a diagram showing an example of a stress measurement method using magnetic anisotropy generated by the magnetostriction effect.

FIG. 6 is a diagram illustrating a relationship between an electromotive force and a stress of a magnetostrictive sensor when a stress is applied and when a stress is removed.

[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 Housing 7 Holder supporting magnetostrictive sensor 8 Screw 9 Push button 10 Pin 11 U-shaped yoke 11a around which exciting coil is wound 11a Open end of yoke 11 11b Open end of yoke 11 12 U-shaped yoke around which detection coil is wound 12a Open end of yoke 12 12b Open end of yoke 12 AC power supply 14 Voltmeter 15 Spring 16 Notch 20 Cover Object 30 Direction of magnetic flux flow

Claims (2)

(57) [Claims] A U-shaped yoke wound with an exciting coil and a U-shaped yoke wound with a detection coil are arranged so as to be orthogonal to each other at the center of a yoke saddle. Stress measurement using a magnetostrictive effect using a magnetostrictive sensor for exciting an object to be measured by passing an alternating current and measuring an electromotive force induced in the detection coil to obtain a stress acting on the object to be measured. In the method, (A) a parameter C when an output waveform of an electromotive force induced in the detection coil by rotating the magnetostrictive sensor in a non-contact manner on the object to be measured is represented by the following equation (1): (B) one of two sets of parallel straight lines connecting the open end of the yoke around which the exciting coil is wound and the open end of the yoke around which the detection coil is wound, and the parameter The maximum lord found from C The magnetostrictive sensor disposed so that the force directions are parallel, by contacting the (c) said magnetostrictive sensor to the object to be measured,
A stress measurement method utilizing a magnetostrictive effect, wherein a stress measurement is performed. 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 A, B, and C are parameters. 2. A U-shaped yoke wound with an exciting coil and a U-shaped yoke wound with a detecting coil are arranged so as to be orthogonal to each other at the center of the yoke saddle portion. A magnetostrictive sensor for exciting an object to be measured by passing an alternating current thereto, measuring an electromotive force induced in the detection coil to obtain a stress acting on the object to be measured, and rotating the magnetostrictive sensor. A stress measuring device using a magnetostrictive effect, comprising a rotating mechanism and a spring mechanism for attaching and detaching the magnetostrictive sensor to and from the object to be measured.