JPS59112257A - Method and device for nondestructive inspection of ferromagnetic material - Google Patents

Abstract

PURPOSE:To inspect the stress or fatigue deformation of ferromagnetic material by utilizing the relation between the high frequency component of an electromagnetic wave generated in the process of magnetizing the ferromagnetic material and the high frequency component of an elastic wave, and the correlation with its stress, etc. CONSTITUTION:The magnetic circuit device is composed of a laminated iron core 2, exciting coil 3, and AC power source 4 opposite to the material 1 to be inspected. An inspecting device consists of a BN (Barkhausen noise) coil sensor 7 installed near the surface of the material 1 without contacting and an AE (acoustic emission) sensor 8 installed in contact, with the material 1. The BN coil sensor 7 outputs a signal having a voltage proportional to the magnetic flux density of the section of a detection coil and the AE sensor 8 is a piezoelectric element which measures the elastic wave. The measurement result applied to the detection of uniaxial stress in case of external stress is varied to an iron steel material having positive magneto-striction shows that the simultaneous measurement of the BN and AE signals provides the accurate estimation of a stress state.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method and apparatus for non-destructively testing stress or fatigue deformation of ferromagnetic materials such as steel materials used in electrical machines, building structures, etc.

Conventionally, various methods have been used to inspect the stress state of this type of ferromagnetic material, such as the strain gauge method, % X-ray method, and magnetic property method. Reproducibility,
There were drawbacks such as limitations on measurement depth. In other words, the strain gauge method does not allow non-contact measurement, and furthermore, it is impossible to detect residual stress before gluing. The X-ray method has the disadvantage of simple dust in the equipment, but also has the disadvantage that the measurement depth is limited to several tens of microns (~10"-5 m) from the surface of the object to be measured.B
- Magnetic property methods such as H property measurement and coercive force measurement have problems with reproducibility because measurement errors occur due to minute gaps between the glove and the material to be measured. Although magnetic property methods are effective in detecting macroscopic defects in structures such as scratches and pinholes, they are not suitable for detecting local microscopic defects and changes such as damage caused by fatigue deformation.

Furthermore, Barkhausen noise C (hereinafter abbreviated as BN) is currently in the research and development stage as a non-destructive testing method for ferromagnetic materials.
is known to be effective in detecting stress and fatigue deformation. However, in addition to the above parameters, this method also requires
It also has the disadvantage of being sensitive to some microstructural changes in the material.

This method responds to, for example, changes in the chemical composition and metallographic structure of the material, so if these factors change in the object to be inspected, such as a machine or structure, it is difficult to uniquely determine the stress. I can't do it. Recently, attention has also begun to be paid to a method of utilizing elastic waves generated in conjunction with the BN signal for non-destructive testing.

However, this method has the disadvantage that it is difficult to distinguish between tensile stress and compressive stress when detecting stress.

The present invention was invented in view of the above situation, and it solves the shortcomings of conventional inspection methods and provides a method for inspecting ferromagnetic materials for stress or fatigue deformation. The present invention provides a non-destructive testing method and device.

First, the principle of the present invention will be explained. In the magnetization process of a ferromagnetic material, no matter how slowly and continuously the external magnetic field changes, the change in magnetic flux density of the material contains a discontinuous component, which is proven from the fact that the BN signal contains a high frequency component. ing. usually.

A ferromagnetic material is divided into regions called magnetic domains that have different spontaneous magnetization vectors, and the boundaries between the magnetic domains are called domain walls. In the process of growing a stable magnetic domain against an external magnetic field, that is, in the magnetization process, the domain wall moves irreversibly and discontinuously, and a high-frequency BN signal is generated. It is known that the stress state and fatigue deformation in the material affect the discontinuous movement of the domain wall. The principle of the present invention is to make use of the discontinuous movement of the domain wall and the correlation phenomenon between the parameters described above.

Furthermore, if the external magnetic field strength is sufficiently high, a discontinuous component of the magnetic flux density may occur due to the rotation of the spontaneous magnetization vector, which is another magnetization mechanism. In this way, there is a magnetization cycle that generates a discontinuous component in the change in magnetic flux density other than the discontinuous movement of the domain wall, and the present invention can easily prevent the generation of any discontinuous component in the change in magnetic flux density of a ferromagnetic material. It uses measurements of high-frequency electromagnetic waves and elastic waves.

Detection of discontinuous movement of domain walls, discontinuous rotation of spontaneous magnetization vectors, etc. can be measured by the following two physical conversion methods. The first method is to detect high frequency components of electromagnetic waves using electromagnetic induction by a coil. This is the same as the normal BN signal measurement method. The second method is to measure the high frequency components of elastic waves generated through the presence of magnetostriction (also called magnetostriction) using a piezoelectric element sensor or the like. The movement of domain walls accompanies the generation and cancellation of local magnetostriction, generating elastic waves. This method is suitable for acoustic take.
It is called emission (hereinafter abbreviated as AE).

The present invention utilizes the above principle, that is, the relationship between the high frequency component of electromagnetic waves and the high frequency component of elastic waves generated during the magnetization process of a ferromagnetic material has a correlation with its stress or fatigue deformation. , Therefore, the present invention is configured as follows.

The nondestructive testing method for ferromagnetic materials according to the present invention detects high frequency components of electromagnetic waves and elastic waves generated during the magnetization process of ferromagnetic materials, and analyzes these high frequency components.
It is characterized by inspecting stress or fatigue deformation of ferromagnetic materials.

Furthermore, the non-destructive inspection apparatus for ferromagnetic materials according to the present invention is an apparatus for carrying out the above method, and further includes: a magnetic circuit device that applies an alternating magnetic field to a part of the ferromagnetic material of the inspected material; A detection device that detects electromagnetic waves and elastic waves generated during the magnetization process of a magnetic material; and a signal processing device that extracts a high frequency component from the output of the detection device and analyzes the component characteristics; It is characterized by testing fatigue type I.

Next, embodiments of the present invention will be described based on the drawings.

FIG. 1 is an explanatory diagram of a magnetic circuit device and a detection device according to an embodiment of the present invention. In this embodiment, the material to be inspected 1 is a thick plate.
This applies to wide ferromagnetic structures such as sheets.

The magnetic circuit device includes a U-shaped laminated iron core 2 installed facing the material to be inspected 1, and an excitation coil 6 wound around this iron core.
and an AC power supply 4 that supplies an excitation current l to this excitation coil.
Together with the material to be inspected 1, it forms a magnetic circuit shown at 5 in the figure. The external magnetic field strength at this time is approximately determined by the number of turns of the excitation coil and loop 6, the excitation current i supplied from a certain power source 4, and the gap d between the material to be inspected 1 and the iron core 2, and its value is determined by the gap. It is detected and measured by the attached Gaussmeter probe 6.

The detection device includes a BN coil sensor 7 that is placed in the vicinity of the surface of the material to be inspected 1 in a non-contact manner, and an AE sensor 8 that is placed in contact with the material to be inspected 1 . The BN coil sensor 7 is
It is a sensor that measures electromagnetic waves, and a voltage proportional to the magnetic flux density in the cross section of the detection coil is extracted as a signal from the sensor. Eight AE sensors measure elastic waves and use piezoelectric elements. When the elastic waves generated in the magnetic circuit portion of the inspected material 1 propagate through the inspected material 1 and reach the AE sensor 8, this sensor extracts a voltage proportional to the displacement or speed as a signal.

FIG. 2 is an explanatory diagram of a magnetic circuit device and a detection device according to another embodiment of the present invention. This example is.

The object is a case where the material to be inspected 1 is a ferromagnetic structure such as a wire or a sheet material with a narrow rod 1 width, and in particular, in this figure, a wire material is illustrated as the material to be inspected.

The magnetic circuit arrangement differs from the embodiment of FIG.

It is composed of an annular solenoid 9 and an AC power source 4.

A material to be inspected 1 is disposed passing through the center of this annular solenoid. And magnetic field strength measurement.

υ is detected and measured by a Gaussmeter flow pro placed at the center of the solenoid 9 in its length direction.

The detection device is composed of a BN coil sensor 10 and an AE sensor 8, each having a winding shape capable of narrowing the volume horizontally. The AE sensor 8 is installed on the inspected material 1 via a web guide 11 because the surface of the inspected material 1 has four radii. As in the embodiment shown in FIG. 1, electromagnetic waves and elastic waves are extracted from the detection device configured in this manner.

FIG. 6 is a block diagram of a signal processing device according to an embodiment of the present invention.

The electric signals corresponding to electromagnetic waves and elastic waves obtained by the detection device 12 (corresponding to the symbols 7.8.10 in FIGS. 1 and 2) are transmitted to the front amplifier and the main amplifier 16 at
It is amplified by about 00 dB. The frequency of the signal is determined by the filter 14.
is narrowed down to a predetermined frequency range. The lower limit of frequency is several tens of kilohartz (~104H2) and the upper limit is several megahartz (~'
IO'Hz). At the beginning of signal analysis, the bandpass filter 14 is used in this high frequency band to set the signal to a predetermined frequency. Six types of methods are illustrated as subsequent signal recording processing methods. The first method is to measure the signal output from the filter 14 using an effective value voltmeter 15, and the second method is to frequency-analyze the signal output from the filter 14 using a spectrum analyzer 16. It is. A sixth method is to pass the output signal of the filter 14 through an envelope detector 17 and read the peak value of the envelope signal using an oscilloscope or waveform storage device 18.

Fig. 4 is a diagram showing the results of measurement by applying the present invention to detect uniaxial stress when changing external stress on a steel material with positive magnetostriction, and the output of the BN signal is With the dashed line,
The AE multiplied signal output is shown as a solid line. The external magnetic field is 50
A Hz sinusoidal alternating magnetic field (parallel to the stress axis, 200 oersteds rms) is used and the variation of the rms voltage value of each signal with respect to stress is illustrated. The stress dependence of the f3N signal becomes extremely small when the tensile stress is 6 Kp/2 or more. On the other hand, the AE multiplied signal monotonically decreases in both tensile and compressive stress states compared to the non-stress state.

Obviously, the stress state cannot be uniquely determined by measuring the BN signal or the AE multiplied signal alone. The simultaneous measurement of the BN signal and the AE multiplied signal according to the present invention makes it possible to accurately evaluate such a stress state.

In the above-mentioned example, the shortcomings of the non-destructive inspection method based on the single measurement of the BN signal or the AE multiplied signal are sufficiently compensated for by the simultaneous measurement of both signals, making it possible to accurately evaluate stress in ferromagnetic structures. I have to.

It is a matter of course that the reliability of data obtained by simultaneous measurements is higher than that obtained by individual measurements, but an additional advantage is the large measurement depth of the present invention.

The measurement depth of the present invention can be controlled by the frequency of the external alternating magnetic field.
It is several millimeters (~10=m) that intersect more than twice.

Further, damage caused by fatigue deformation can be detected by the method according to the present invention by observing the waveforms of the BN signal and the AE multiplied signal. If a magnetic circuit device is set at a location where fatigue deformation has occurred in the signal waveform of an object in a healthy state, drooping will be observed in the envelope waveform of the generated signal. Furthermore, the non-destructive inspection according to the present invention is also effective in detecting metallurgical factors such as the chemical structure of a material, the metal structure, and the distribution of non-metallic inclusions.

For testing stress, fatigue deformation, etc. of structures made of ferromagnetic materials, an appropriate one of the following analysis methods is adopted. The following plurality of measurement operations are performed under the conditions of a predetermined AC external magnetic field strength and a predetermined signal frequency range.

(1) Read the effective voltage value of the output of the BN sensor.

(2) Read the effective voltage value of the AE sensor output.

(3) Different frequency ranges (for example, at 100 km)
200 km Ruth I and 200 km Ruth ~ 300
Kilohartz 1) Take the ratio of the effective value of the output of the BN sensor.

(4) Take the ratio of the effective voltage values of the outputs of the AE sensors in different frequency ranges.

(5) Take the ratio of the effective voltage values of the outputs of the BN sensor and the AE sensor in the same frequency range.

(6) Find the ratio of the effective voltage values of the outputs of the BN sensor and AFj sensor in different frequency ranges.

(7) Measure the frequency distribution of the BN sensor signal.

(8) Measure the frequency distribution of the AE sensor signal.

(9) Observe the waveform of the envelope signal of the BN sensor.

Observe the waveform of the envelope signal of the αIAE sensor.

(b) Read the peak value of the envelope signal of the BN sensor.

2) Read the peak value of the envelope signal of the AE sensor.

(To) Take the ratio of the peak values of envelope signals of BN sensors in different frequency ranges.

α◆Take the ratio of the peak values of envelope signals of AE sensors in different frequency ranges.

(2) Take the ratio of the peak values of the envelope signals of the BN sensor and AE sensor in the same frequency range.

09 Take the ratio of the peak values of the envelope signals of the BN sensor and AE sensor in different frequency ranges.

αη The ratio of the peak values of the two peaks of the envelope signal of the BN sensor under high magnetic field is taken.

(f) Take the ratio of the two peak values of the envelope signal of the AE sensor observed under high field conditions.

As is clear from the above description, the present invention utilizes the relationship between the high frequency components of electromagnetic waves and the high frequency components of elastic waves generated during the magnetization process of ferromagnetic materials, and the correlation between the stress, etc. , which made it possible to test stress, etc. of ferromagnetic materials, eliminating the drawbacks of the prior art, and can be said to be an extremely useful explanation. Moreover, since the present invention is based on such a technical idea, its scope is not limited to the above-mentioned embodiments, but substantially the relationship between the high frequency components of electromagnetic waves and the high frequency components of elastic waves. It goes without saying that any method that utilizes the correlation with stress etc. is included.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram of a magnetic circuit device and a detection device according to one embodiment of the present invention, FIG. 2 is an explanatory diagram of a magnetic circuit device and a detection device according to another embodiment of the present invention, and FIG. FIG. 4 is a block diagram of a signal processing device according to an embodiment of the invention, and is a diagram showing an example of measurement results according to the invention. 1; Tested roofing material 6 ferromagnetic material) 1. 2. ; Laminated core, 3
; Excitation coil; 4; AC power supply; 7, 10; BN coil sensor; 8; AE sensor%; 9: Fi-shaped solenoid. Agent Patent Attorney Sanro Kimura Figure 1 Figure 4 Figure 2 Figure 3 5 Japanese Patent Application No. 57-221756 20 Name of Invention 'It I'l' Patent Name of Applicant Title
Hata Giken Co., Ltd. (name) 4. Agent 5. / 7. 11. 1. "Detailed description of the invention" column of the description. -Yotoi

Claims (2)

[Claims] (1) It is characterized by detecting high frequency components of electromagnetic waves and elastic waves generated in the magnetization process of ferromagnetic materials and analyzing these high frequency components to inspect stress or fatigue deformation of ferromagnetic materials. A non-destructive testing method for ferromagnetic materials. (2) A magnetic circuit device that applies an alternating magnetic field to a part of the ferromagnetic material to be inspected; a detection device that detects electromagnetic waves and elastic waves generated during the magnetization process of the ferromagnetic material; and an output of the detection device 1. A non-destructive testing device for magnetic materials, comprising: a signal processing device for extracting a high frequency component from a ferromagnetic material and analyzing its component characteristics.