JP2023029151A - Electromagnetic material evaluation method and device using magnetism - Google Patents

Abstract

To provide a method and a device for evaluating local conductivity and permeability of metal regardless of a nonmagnetic body and a magnetic body.SOLUTION: In a method for inspecting electromagnetic characteristics of an inspected object, and in a nondestructive inspection device having a magnetic probe comprising an application coil for applying an AC magnetic field, and a magnetic sensor for detecting a magnetic field induced in an inspected object by the applied magnetic field, an AC constant current source for composing AC currents of at least two predetermined frequencies in the application coil or energizing them in time series, a detector for detecting signals of respective predetermined frequencies of output signals of the magnetic sensor, and an analyzer for analyzing output signals of the detector, two predetermined frequencies are determined on the basis of, plate thickness information of an inspected object, a phase component of a differential vector between a magnetic field vector with strength and a phase obtained by a first frequency by the detector as components and a second magnetic field vector obtained by a second frequency is detected, and conductivity and permeability of an inspected object are obtained from a relationship between the phase component and conductivity and permeability in each plate thickness.SELECTED DRAWING: Figure 1

Description

The present invention magnetically and non-destructively evaluates the electrical conductivity and magnetic permeability, which are the electromagnetic properties of non-magnetic and magnetic metal materials, and evaluates metal fatigue and metal transformation due to heat treatment. It relates to a method and apparatus.

When evaluating the electromagnetic properties of metal materials, one of the conventional methods for measuring electrical conductivity is to apply a current to the test object and measure the resulting voltage to obtain electrical conductivity. ing. However, in this method, the current distribution differs depending on the shape of the metal to be inspected, so it is necessary to estimate the current distribution by simulation and obtain the conductivity. For this reason, the most accurate method is the four-probe method, in which the test material is cut into a given shape and measured. In the conventional method, it was necessary to measure the current and voltage with contact electrodes, but some non-contact inspection methods have been developed. There is a method of measuring conductivity by measuring with a capacitance sensor (Patent Document 1).

When measuring magnetic permeability, which is another parameter of electromagnetic properties, it is not necessary to measure it because the magnetic permeability in a non-magnetic material is the same as the magnetic permeability in a vacuum. On the other hand, the magnetic permeability of a magnetic material is greater than that of a vacuum, and it is not constant and varies depending on the strength of the applied magnetic field. Therefore, the HB curve showing the relationship between the applied magnetic field H and the magnetization B of the metal material is nonlinear and draws a hysteresis curve. For this reason, a magnetization measuring apparatus is used that measures the magnetization by cutting out an object to be inspected into a certain shape, placing the object to be inspected between large electromagnets, and varying the applied magnetic field.

A basic method for evaluating the electromagnetic properties of metal materials is to cut them into a certain shape and inspect them, which is an important evaluation in material development. Infrastructure structures such as bridges and metal structures such as transport aircraft such as airplanes and railways need to be periodically inspected non-destructively so that deterioration due to fatigue does not lead to large fracture damage. These deteriorations are highly correlated with the electromagnetic properties and cause changes in electrical conductivity and magnetic permeability. Therefore, deterioration can be detected by nondestructively inspecting these electromagnetic characteristics. In addition, parts made of steel plates used in automobiles and the like are changed in hardness by quenching and annealing, which is a heat treatment of steel plates, in order to reduce the impact in the event of a collision. In particular, partial quenching, in which portions of a single steel sheet material are heat-treated to provide locations with different hardnesses, is widely practiced. As for hardness due to heat treatment, if the steel is tempered slowly, it becomes a structure of ferrite or pearlite, which is the crystal structure of the steel sheet, and has low hardness. In this way, the steel material becomes these structures and other structures by heat treatment, and it is important to inspect the transformation rate in order to guarantee the mechanical properties such as hardness of the steel material as a product.

A Vickers hardness test is performed as a method for checking whether the mechanical properties obtained by heat treatment are obtained. This Vickers hardness test is a method in which a hard needle-like object is pressed against an object to be inspected, and the hardness is inspected based on the size of the generated dent. Since this method damages the surface, it cannot be applied to products, and a method of inspection by sampling is adopted. On the other hand, since it is known that there is a high correlation between mechanical properties and magnetic permeability and electrical conductivity, several methods have been developed for magnetically inspecting them non-destructively. For example, there is a method in which a U-shaped magnetizer is used to pass magnetic flux through a steel material to be inspected, and a magnetic sensor detects magnetic flux leaking from the opposite side of the steel material (Patent Document 2).

General magnetic non-destructive inspection methods include eddy current testing, in which an alternating magnetic field is applied to an object to generate eddy currents and the magnetic field generated by the eddy currents is detected; There is known a leakage magnetic flux testing method in which a magnetic field is applied using a device and a leaking magnetic field is detected. These are often used to detect cracks in metal structures. There is an extremely low frequency eddy current method for detecting plate thickness changes in steel materials due to corrosion (Patent Document 3).
The extremely low frequency eddy current method uses two frequencies, measures the magnetic field detected at each frequency with a magnetic sensor, analyzes the obtained signal as a magnetic field vector consisting of strength and phase, obtains the difference vector, The plate thickness is estimated from the phase. There are few methods for evaluating electromagnetic properties by these eddy current testing methods. For example, as a method of measuring conductivity and magnetic permeability by eddy current testing, the A method of estimating by comparison with a database has been reported (Patent Document 4).

JP 2002-156362 Japanese Patent Laid-Open No. 5-126798 Patent No. 6551885 Japanese Patent Laid-Open No. 9-113488

As a method of evaluating electromagnetic properties, it is necessary to stabilize the contact state of the electrodes and to analyze the current distribution in advance. It was difficult to estimate the conductivity accurately for In addition, when the leakage magnetic flux flaw detection method is used as the magnetic permeability, the inspection results differ depending on the shape and thickness of the object, so it is necessary to compensate for the fluctuations in these inspection results. In addition, since the probe for flaw detection is U-shaped and large, and the detection section is provided on the opposite side, it is difficult to inspect the local magnetic permeability. In addition, there is a problem that leakage magnetic flux testing cannot be applied to non-magnetic metals. In the eddy current flaw detection method, changes due to the frequency of the applied magnetic field and the plate thickness of the inspection target were not taken into consideration. In addition, the extremely low frequency eddy current used to measure the plate thickness is a method of measuring the plate thickness, not a method of analyzing the electromagnetic characteristics of the object, and furthermore, the variation due to the estimated plate thickness due to the electromagnetic characteristics is not considered. rice field.

In view of the current situation, the present inventor has developed a method that can evaluate the electrical conductivity and magnetic permeability, which are the electromagnetic properties of metals regardless of their types, such as non-magnetic materials and magnetic materials. The inventors have developed a method and an apparatus capable of evaluating characteristics, and have completed the present invention.

An electromagnetic material evaluation method and apparatus using magnetism according to the present invention is a method for inspecting the electromagnetic properties of an object to be inspected, comprising an applying coil for applying an alternating magnetic field to the object to be inspected, and a magnetic field applied by the applying coil A magnetic probe composed of a magnetic sensor that detects the magnetic field induced to the inspection object by is provided, and an alternating magnetic field of at least two predetermined frequencies is synthesized and applied to this application coil, or time-sequentially a constant alternating current source for supplying alternating current of each frequency to the magnetic sensor, a detector for detecting the signal of each predetermined frequency of the output signal of the magnetic sensor, and an analyzer for analyzing the output signal of the detector. In the inspection device, two predetermined frequencies are determined based on the thickness information of the inspection object obtained in advance, and the intensity and phase obtained by detecting the first frequency with the detector are used as components. Detecting the phase component of the difference vector obtained as the vector difference between the magnetic field vector obtained by the detection at the second frequency and the second magnetic field vector having the components of the intensity and phase obtained by detection at the second frequency, and detecting the phase component is used to inspect the electrical conductivity and magnetic permeability of the object to be inspected from the database of the relationship between electrical conductivity and magnetic permeability for each plate thickness and the phase.

Furthermore, in order to inspect changes in local electromagnetic properties, the electromagnetic material evaluation apparatus is provided with an encoder that determines the measured position by combining two frequencies as the magnetic field applied by the applying coil and applying it. It is characterized by inspecting the distribution of electrical conductivity and magnetic permeability of the object to be inspected based on the positional information obtained from the differential vector and the phase information of the difference vector.

According to the present invention, it is possible to nondestructively evaluate the electrical conductivity and magnetic permeability of nonmagnetic and magnetic metals. This makes it possible to evaluate aging deterioration of metal structures and transformation of steel materials due to heat treatment.

1 is a configuration diagram of an electromagnetic material evaluation apparatus according to the present invention; FIG. FIG. 4 is a diagram showing a method of obtaining a phase from a difference vector between a first magnetic field vector and a second magnetic field vector; FIG. 10 is a diagram comparing combinations of frequencies when obtaining the relationship between the conductivity and the phase of the difference vector in a non-magnetic material with a plate thickness of 8 mm. FIG. 10 is a diagram showing the relationship between the phase and electrical conductivity of a non-magnetic material with a plate thickness of 8 mm using a difference vector between frequencies of 200 Hz and 100 Hz. Here, the result of judging the electrical conductivity of aluminum and copper having a plate thickness of 8 mm as specimens is also shown in the figure. FIG. 4 is a diagram comparing combinations of frequencies when obtaining the relationship between the product σμ of conductivity and permeability and the phase of the difference vector in a magnetic material having a thickness of 8 mm. FIG. 4 is a diagram comparing combinations of frequencies when obtaining the relationship between the product σμ of conductivity and permeability and the phase of the difference vector in a magnetic material with a plate thickness of 16 mm. FIG. 4 is a diagram showing the relationship between the phase of a steel plate with a thickness of 1.4 mm and the product σμ of electrical conductivity and magnetic permeability based on a difference vector between frequencies of 200 Hz and 100 Hz. FIG. 8 is a diagram showing changes in the product σμ of electrical conductivity and magnetic permeability of steel sheets heat-treated at each temperature using the relational expression shown in FIG. 7 ; Using the relational expression shown in FIG. 7, the phase of a partially quenched steel plate with a thickness of 1.4 mm was determined by line scanning, and local changes in the product σμ of the conductivity and permeability of the steel plate were examined. It is a diagram.

In the following, embodiments of the present invention will be described in detail with reference to the accompanying drawings. Members having similar uses and functions are denoted by the same reference numerals, and descriptions thereof are omitted.

In the first embodiment, as shown in FIG. 1, a magnetic probe 4 comprising an application coil 2 and a magnetic sensor 3 is brought close to or brought into contact with a metallic specimen 1 for measurement. A magnetic field is applied to the specimen by the application coil 2 to generate an eddy current, and the magnetic field generated by the eddy current is measured by a magnetoresistive element (MR) as a magnetic sensor 3 . As a magnetic sensor, not only MR but also tunnel type resistance element (TMR), magnetoimpedance element (MI), superconducting quantum interference device (SQUID), etc. can be used as long as they are sensitive from low frequencies. In a general eddy current flaw detector, the applied coil is driven by an alternating current constant voltage source, but in the electromagnetic material evaluation apparatus of the present invention shown in FIG. , a constant magnetic field is applied to the object. Here, in order to apply a predetermined frequency, two AC frequencies are synthesized or switched over time to be generated by the frequency oscillator 6, and current is passed through the application coil by a constant current source. Here, as the predetermined frequency, an optimum frequency is selected based on plate thickness information obtained by measuring the plate thickness with a microgauge or ultrasonic waves in advance. The frequencies to be applied are not limited to the selected two frequencies, but may be a plurality of frequencies including other frequencies, and the two optimum frequencies may be selected at the time of analysis. Also, since a waveform containing a very large number of frequencies is a pulse wave, it is also possible to select two optimal frequency signals at the time of analysis after using this pulse wave. The applied current value at each synthesized frequency must be a constant alternating current amplitude value in order to apply a magnetic field of the same strength to the specimen 1 at each frequency. A canceling coil may be provided at the magnetic sensor 3 so that the magnetic field generated by the applying coil does not enter directly. A signal is output through the measurement circuit 7 of the magnetic sensor, and the signal of the real component that is in phase with the reference signal is shifted by 90° from the detectors 8-1 and 8-2 at the same frequencies as the frequency of the applied magnetic field. It detects imaginary component signals. Upon detection, the signal can be analyzed into magnetic field vectors consisting of magnitude and phase, or in another notation, each real and imaginary component. Since two frequencies were used here, two detectors were used. The outputs of the detectors 8-1 and 8-2 are switched by the multiplexer 9, and the data is taken into the data recording/analyzing device 10, recorded, analyzed, and displayed. Here, even without using a detector, it is possible to AD-convert the output time waveform of the sensor circuit, record the data, and digitally analyze the in-phase component and the 90° phase component using a personal computer. In this case, a lock-in detector is not required, so the size of the device can be reduced.

A first magnetic field vector and a second magnetic field vector obtained by applying and detecting two magnetic fields of frequencies _f1 and _f2 can be shown as in FIG. θ is obtained as the phase of the difference vector, which is the difference between the first magnetic field vector and the second magnetic field vector. Electrical conductivity σ and magnetic permeability μ are the electromagnetic properties of metals. In the present invention, the value of the product σμ of the conductivity σ and the magnetic permeability μ is obtained from θ. Since the magnetic permeability of a non-magnetic material such as aluminum or copper is the same as the magnetic permeability of a vacuum, the conductivity σ can be obtained from the value of σμ. Also, in the case of magnetic materials such as iron and steel materials, conductivity and permeability cannot be separated, but if either parameter is known in advance, the other parameter can naturally be determined. In addition, since changes in mechanical properties such as transformation due to heat treatment and deterioration over time are correlated with both conductivity and magnetic permeability, that is, σμ, σμ, which is the product of the two, is important.

FIG. 3 shows the optimization of two frequencies for a metal plate thickness of 8 mm, which is a non-magnetic material. Since it is a non-magnetic material, its magnetic permeability is the same as 4π×10 ⁻⁷ H/m, which is the magnetic permeability of a vacuum, and is constant. Therefore, σμ can be expressed as a graph of conductivity σ. It shows the relationship between conductivity σ and phase when the combination of two frequencies is changed. The graph of the phase of the difference vector obtained by setting the first frequency to 30 Hz and the second frequency to 50 Hz has no linearity, and it can be seen that the conductivity cannot be estimated from the phase. On the other hand, it can be seen that the graph of the phase θ of the difference vector obtained by increasing the frequency and setting the first frequency to 100 Hz and the second frequency to 200 Hz has the best linearity. Therefore, it can be seen that the electrical conductivity of the specimen can be evaluated by using the relational expression between the phase θ and the electrical conductivity σ in the case of a non-magnetic material having a plate thickness of 8 mm.

As a test piece, a copper and aluminum plate that was 8 mm measured with a microgauge was measured with a first frequency of 100 Hz and a second frequency of 200 Hz. Inputting into the calibration equation for σ yields a conductivity of 5.9×10 ⁷ S/m for copper and 3.7×10 ⁷ S/m for aluminum, which values are comparable to those of metallic materials. It matched the value known as the physical property value.

Next, FIG. 5 shows the optimization of two frequencies of steel material which is a magnetic material. It shows the relationship between the product σμ of conductivity and permeability and the phase θ when the combination of two frequencies at 8 mm is changed. The graph of the phase of the difference vector obtained by setting the first frequency to 1 Hz and the second frequency to 3 Hz has poor linearity. On the other hand, it can be seen that the graph of the phase θ of the difference vector obtained when the first frequency is 5 Hz and the second frequency is 20 Hz has the best linearity and the highest sensitivity. As the plate thickness increases, the frequency to be selected becomes lower. For example, the combination of frequencies of 5 Hz and 20 Hz, which had good linearity when the plate thickness was 8 mm, has slightly poor linearity when the plate thickness is 16 mm, as shown in FIG. On the other hand, when the frequencies are combined to 1 Hz and 3 Hz, the linearity is improved. In this way, the thicker the plate, the lower the frequency, and the thinner the plate, the higher the frequency.

Figures 7 and 8 show the results of evaluation of the electromagnetic properties of the heat-treated steel sheets. Changing the hardness by heat treatment is performed in automobiles, machine parts, and the like. This example shows the difference in the treatment temperature of the electromagnetic properties when a steel plate with a thickness of 1.4 mm is heat-treated. When the plate thickness is 1.4 mm, the plate thickness becomes thin, so the frequency becomes high. As shown in FIG. 7, σμ, which is the electromagnetic characteristic with respect to the phase, has good linearity. FIG. 8 shows σμ of the steel sheets processed at each temperature using the calibration formula of this graph. The σμ of the steel sheet treated at a temperature of 700°C was large, decreased as the temperature increased, and was saturated at 900°C or higher. The structure of the steel sheet was a structure of ferrite and pearlite at 700°C, and changed to a structure of ferrite and martensite at 900°C or higher. Martensite is known to have a smaller magnetic permeability than pearlite, and it was found that the transformation rate at which the structure changed can be evaluated from the phase θ of the present invention.

Partial quenching is applied to partially change the hardness of a single part in automobiles and the like. In the present invention, an encoder is attached to the magnetic probe, and positional information is taken in as data at the same time as the phase is measured, in order to inspect whether the target portion has achieved the required hardness. In addition, the applied magnetic field was applied simultaneously and continuously by synthesizing two frequencies so that measurement could be performed while line-scanning the magnetic probe. FIG. 9 shows the phase of a partially quenched steel plate with a thickness of 1.4 mm obtained by line scanning, and a local change in the product σμ of the electrical conductivity and magnetic permeability of the steel plate. In this way, it was possible to evaluate to what extent local hardening was performed and whether sufficient hardening was achieved.

As another use, it has been found that mechanical properties, which are the deterioration of metal structures, are correlated with electromagnetic properties. Therefore, after measuring the thickness of the evaluation point of the metal structure with a microgauge or an ultrasonic plate thickness gauge, deterioration can also be diagnosed by electromagnetic characteristic evaluation.

1 Specimen 2 Applied Coil 3 Magnetic Sensor 4 Magnetic Probe 5 Constant Current Source 6 Frequency Oscillator 7 Measurement Circuit 8-1 Detector 8-1 Detector 9 Multiplexer 10 Data Recording/Analyzing Device

Claims (2)

A method for inspecting electromagnetic characteristics of an object to be inspected, comprising: an applying coil for applying an alternating magnetic field to the object to be inspected; and a magnetic sensor for detecting a magnetic field induced to the object by the magnetic field applied by the applying coil. Provide a magnetic probe consisting of
an alternating current constant current source for synthesizing at least two or more predetermined alternating magnetic fields to the applying coil, or applying an alternating current of each frequency in time series; In a non-destructive inspection device having a detector that detects signals of each predetermined frequency and an analyzer that analyzes the output signal of the detector,
Two predetermined frequencies are determined based on plate thickness information of the object to be inspected, and the magnetic field vector having the strength and phase components obtained by detecting at the first frequency and the second Detecting the phase component of the difference vector obtained as the difference between the second magnetic field vector whose components are the intensity and phase obtained by detection at the frequency of , and using this phase component to determine the conductivity and An electromagnetic material evaluation method, comprising inspecting the electrical conductivity and magnetic permeability of the inspection object from a database of the relationship between magnetic permeability and phase. In the non-destructive inspection apparatus, position information obtained by combining two frequencies as a magnetic field applied by the applying coil and applying an encoder for determining the measured position and phase information of the difference vector are used for the inspection. An electromagnetic material evaluation method characterized by inspecting the distribution of electrical conductivity and magnetic permeability of an object.

Images