JP7126069B2 - Electromagnetic pulse acoustic non-destructive inspection method - Google Patents

Description

The present invention relates to a non-destructive inspection method using electromagnetic pulses to detect internal defects in an object to be inspected and to measure the thickness of a highly conductive material constituting a part of the object to be inspected.

At present, reduction of CO ² emissions on a global scale is called for in order to cope with global warming. In such a trend, the realization of a hydrogen society is desired, and as one of them, attempts are being made to develop and popularize hydrogen fuel cell vehicles. For the spread of this hydrogen fuel cell vehicle, it is necessary to cover the installation of hydrogen stations nationwide. There are currently various types of pressure vessels installed in hydrogen stations. For example, there are low-alloy steel pressure vessels, low-alloy steel liner hoop-wrap vessels, aluminum alloy liner full-wrap vessels, and plastic liner full-wrap vessels. The transition to lightweight pressure vessels by combining plastic liners and FRP (fiber reinforced plastic) is progressing.

Defects in lightweight pressure vessels include boundary delamination at the interface between the metal or plastic liner and FRP due to manufacturing conditions and operation, internal delamination within the FRP layer, fatigue cracks in the metal liner due to hydrogen embrittlement, and long There is thinning of the metal liner due to the period of operation.
Damage to the pressure vessel can lead to serious accidents, requiring time and money for maintenance, which is one of the obstacles to the realization of a hydrogen-based society.
Pressure vessels are used not only in hydrogen stations but also in engineering fields such as oil refining industry, chemical industry, power industry, gas industry and nuclear power industry under severe high temperature/low temperature/high pressure environment and have similar problems. there is

In addition, as part of CO ² countermeasures, weight reduction and structural simplification are required for transportation equipment such as automobiles and aircraft. As one measure to meet this demand, heavy materials such as steel plates are replaced with lightweight materials such as aluminum and CFRP (Carbon Fiber Reinforced Plastic) for airframe and vehicle structures, and machine parts such as bolt joints and riveted joints are used. Attempts have been made to reduce the weight of joints, reduce the number of parts, and reduce maintenance costs by replacing the joints with adhesive joints.

In the trend of weight reduction and structural simplification of transportation equipment, and combination of pressure vessels, non-destructive inspection that can inspect the reliability of adhesive joints and internal defects with high accuracy and ensure safety. is increasing in importance.

Conventional non-destructive inspection methods include the following.
(a) X-ray imaging method in which an object to be inspected is placed between an X-ray generator and a film (Patent Document 1)
(b) An ultrasonic flaw detection method in which an ultrasonic generator is applied to the surface of an object to be inspected and the reflected or transmitted ultrasonic waves are detected and judged (Patent Document 2)
(c) A percussion method in which the surface of an object to be inspected is hit with a hammer and judged from the echo sound (Patent Document 3)
(d) Infrared imaging method for measuring infrared distribution on the surface of an inspection object (Patent Document 4)
(e) Microwave method for irradiating microwaves from the surface of an object to be inspected (Patent Document 5)
(f) Acoustic diagnostic method using pulsed electromagnetic force (Patent Document 6)

Japanese Patent No. 6321878 JP 2017-198663 A JP-A-52-86386 JP 2016-3959 A JP-A-2004-69507 Japanese Patent No. 3738424

In the X-ray imaging method described above, since the object to be inspected must be placed between the X-ray generator and the film, there are various restrictions such as the shape, size, and location of the object to be inspected, making it difficult to use easily. Met.
The ultrasonic flaw detection method irradiates the surface of the object to be inspected with ultrasonic waves and searches for internal defects from the ultrasonic waves reflected from the metal on the back side. Therefore, it is difficult to apply to structural materials using FRP, which has large vibration damping. In addition, since the high frequency is out of the audible range, the ultrasonic wave is easily attenuated and scattered by internal contaminants, making its analysis very difficult.
Although the percussion method has been widely used since ancient times, it requires a considerable amount of time to master because it requires experience and intuition, and it is not quantitative and has low reliability.
In the infrared imaging method and the microwave method, infrared rays and microwaves are rapidly attenuated by the object to be inspected, so only the surface of the object to be inspected can be measured.
In the acoustic diagnosis and measurement method using pulsed electromagnetic force, a pulsed magnetic field is generated by applying a large pulsed current to the transmission coil, and the elastic wave generated in the metal by the Lorentz force and magnetostrictive effect is received and analyzed to determine the object to be inspected. Although it is a method for detecting and evaluating defects in objects, the method disclosed in Prior Art Document 6 aims at non-destructive detection of the fixed state of reinforcing bars or anchor bolts embedded in concrete. It is not possible to evaluate the properties (thickness reduction) of the bonded portion, the inside of the bonded body, and the back side of the bonded body.

However, as a result of intensive research, the inventors have found that an acoustic diagnosis/measurement method using a pulsed electromagnetic force uses a sound source generated from a conductor existing inside or on the back of an object to be inspected, thereby making it possible to It is possible to receive and analyze signals with internal information, and a joint made by joining two dissimilar materials (highly conductive material/non-(low) conductive material or low conductive material/non-conductive material) Also, the present inventors have found that the method is effective for diagnosing laminates in which a large number of electrically conductive fibers, carbon particles, or metal particles exist continuously in the base material in an electrically conductive state.
Based on this finding, the inventors of the present invention aim to provide a non-destructive inspection method that can easily and accurately explore the presence or absence and position of internal defects in an inspection object and the properties of the back surface by a method using a pulse magnetic field. and

The invention according to claim 1 (electromagnetic pulse acoustic nondestructive inspection method) provides a first nondestructive test method for a joined body 11 in which either a nonconductive material 11b or a low conductive material 11c is adhered to a high conductive material 11a. It is an inspection method (coil movement, sensor fixation).
A bonded body 11 in which either a non-conductive material 11b or a low-conductive material 11c is adhered to a highly conductive material 11a is used as an inspection object A. A pulsed magnetic field is applied to the inspection object A, and the pulsed magnetic field causes the above-mentioned An eddy current is induced in the highly conductive material 11a, and an interaction force between the eddy current and the pulse magnetic field excites the highly conductive material 11a to generate an elastic wave with the highly conductive material 11a as a sound source. , the elastic wave is detected on the side of the non-conductive material 11b or the side of the low-conductive material 11c, and then the waveform of the elastic wave and the waveform of the reference elastic wave in the previously obtained reference body B having no internal defects are detected. In the electromagnetic pulse acoustic non-destructive inspection method for estimating the presence or absence of defects inside the inspection object A by comparing
dividing the inspection object A into a plurality of inspection sections;
In the inspection section, a sensor 14 is provided at a fixed position on the surface of the object to be inspected A to be measured, and a transmission coil for generating a pulse magnetic field is arranged on the surface of the object to be inspected A to be measured. 12 is moved relative to the joint 11, which is the object A to be inspected, and the elastic waves are detected at a plurality of points by sensors 14 provided at fixed points. Select one or more items from the following (a) to (d) with the waveform of the reference elastic wave in the reference body B having no internal defects obtained in advance, compare the results of the selected items, and It is characterized by estimating the position of the defect inside the inspection object .
(a) difference between the intensity of the sound appearing in the waveform of the reference elastic wave and the intensity of the sound appearing in the waveform of the elastic wave of the object to be inspected; Time lag (c) Attenuation state of the waveform of the elastic wave of the inspection object with respect to the waveform of the reference elastic wave (d) Frequency of the waveform of the elastic wave of the inspection object with respect to the waveform of the reference elastic wave

The invention according to claim 2 (electromagnetic pulse acoustic non-destructive inspection method) is a first non- destructive inspection method (coil movement, sensor fixation) of a joined body 11 in which a non-conductive material 11b is adhered to a low-conductive material 11c. is.
A bonded body 11 in which a non-conductive material 11b is adhered to a low-conductive material 11c is used as an inspection object A. A pulsed magnetic field is applied to the inspection object A, and the low-conductive material 11c of the bonded body 11 is generated by the pulsed magnetic field. to induce an eddy current, and the interaction force between the eddy current and the pulse magnetic field excites the low-conductivity material 11c to generate an elastic wave with the low-conductivity material 11c as a sound source, and the elastic wave is detected on the non-conductive material 11b side,
After that, the waveform of the elastic wave is compared with the waveform of the reference elastic wave in the reference body B that has no internal defect obtained in advance, and the presence or absence of the defect inside the inspection object A is estimated. In the inspection method ,
dividing the inspection object A into a plurality of inspection sections;
In the inspection section, a sensor 14 is provided at a fixed position on the surface of the object to be inspected A to be measured, and a transmission coil for generating a pulse magnetic field is arranged on the surface of the object to be inspected A to be measured. 12 is moved relative to the bonded body 11, which is the object to be inspected, and the elastic waves are detected at a plurality of points by sensors 14 provided at fixed points. Select one or more items from the following (a) to (d) with the waveform of the reference elastic wave in the obtained reference body B having no internal defects, compare the results of the selected items, and perform the inspection It is characterized by estimating the position of the defect inside the object A.
(a) difference between the intensity of the sound appearing in the waveform of the reference elastic wave and the intensity of the sound appearing in the waveform of the elastic wave of the object to be inspected; Time lag (c) Attenuation state of the waveform of the elastic wave of the inspection object with respect to the waveform of the reference elastic wave (d) Frequency of the waveform of the elastic wave of the inspection object with respect to the waveform of the reference elastic wave

The invention according to claim 3 (electromagnetic pulse acoustic nondestructive inspection method) provides a second nondestructive test method for a joined body 11 in which either a nonconductive material 11b or a low conductive material 11c is adhered to a high conductive material 11a. Inspection method (coil and sensor movement).
A bonded body 11 in which either a non-conductive material 11b or a low-conductive material 11c is adhered to a highly conductive material 11a is used as an inspection object A. A pulsed magnetic field is applied to the inspection object A, and the pulsed magnetic field causes the above-mentioned An eddy current is induced in the highly conductive material 11a, and an interaction force between the eddy current and the pulse magnetic field excites the highly conductive material 11a to generate an elastic wave with the highly conductive material 11a as a sound source. , the elastic wave is detected on the side of the non-conductive material 11b or the side of the low-conductive material 11c, and then the waveform of the elastic wave and the waveform of the reference elastic wave in the previously obtained reference body B having no internal defects are detected. In the electromagnetic pulse acoustic non-destructive inspection method for estimating the presence or absence of defects inside the inspection object A by comparing
The transmitter coil 12 for generating a pulse magnetic field and the sensor 14 are moved relative to the bonded structure 11, which is the object to be inspected A, while maintaining a constant interval L, and the sensor 14 moving together with the transmitter coil 12 moves the The elastic wave is detected at a plurality of locations, and then the waveform of the elastic wave and the waveform of the reference elastic wave in the reference body B obtained in advance without internal defects are measured by one of the following (a) to (d): Alternatively, a plurality of items are selected, the results of the selected items are compared, and the position of the defect inside the inspection object A is estimated .
(a) difference between the intensity of the sound appearing in the waveform of the reference elastic wave and the intensity of the sound appearing in the waveform of the elastic wave of the object to be inspected; Time lag (c) Attenuation state of the waveform of the elastic wave of the inspection object with respect to the waveform of the reference elastic wave (d) Frequency of the waveform of the elastic wave of the inspection object with respect to the waveform of the reference elastic wave

The invention according to claim 4 (electromagnetic pulse acoustic nondestructive inspection method) is a second nondestructive inspection method (coil and sensor movement) of the joined body 11 in which the nonconductive material 11b is adhered to the low conductive material 11c. be.
A bonded body 11 in which a non-conductive material 11b is adhered to a low-conductive material 11c is used as an inspection object A. A pulsed magnetic field is applied to the inspection object A, and the low-conductive material 11c of the bonded body 11 is generated by the pulsed magnetic field. to induce an eddy current, and the interaction force between the eddy current and the pulse magnetic field excites the low-conductivity material 11c to generate an elastic wave with the low-conductivity material 11c as a sound source, and the elastic wave is detected on the non-conductive material 11b side,
After that, the waveform of the elastic wave is compared with the waveform of the reference elastic wave in the reference body B that has no internal defect obtained in advance, and the presence or absence of the defect inside the inspection object A is estimated. In the inspection method,
The transmitter coil 12 for generating a pulse magnetic field and the sensor 14 are moved relative to the bonded structure 11, which is the object to be inspected A, while maintaining a constant interval L, and the sensor 14 moving together with the transmitter coil 12 moves the The elastic wave is detected at a plurality of locations, and then the waveform of the elastic wave and the waveform of the reference elastic wave in the reference body B obtained in advance without internal defects are measured by one of the following (a) to (d): Alternatively, a plurality of items are selected, the results of the selected items are compared, and the position of the defect inside the inspection object A is estimated.
(b) The difference between the intensity of sound appearing in the waveform of the reference elastic wave and the intensity of sound appearing in the waveform of the elastic wave of the object to be inspected
(b) Time shift of the waveform of the elastic wave of the inspection object with respect to the waveform of the reference elastic wave
(c) Attenuation state of the waveform of the elastic wave of the inspection object with respect to the waveform of the reference elastic wave
(d) Frequency of the waveform of the elastic wave of the inspection object with respect to the waveform of the reference elastic wave

The invention according to claim 5 (electromagnetic pulse acoustic non-destructive inspection method) inspects the presence or absence of internal peeling N in the laminate 11' of the low conductive material 11b,
A pulsed magnetic field is applied to the layered body 11' of the low-conductivity material 11c, which is the inspection object A, to induce an eddy current in the layered body 11' by the pulsed magnetic field, and the interaction between the eddy current and the pulsed magnetic field. The entire laminate 11' is excited by a force to generate an elastic wave, and the elastic wave is detected on the surface of the laminate 11',
After that, one or more items from the following (a) to (d) are selected from the waveform of the elastic wave and the waveform of the reference elastic wave in the reference body B obtained in advance without internal defects, and selected. The presence or absence of a defect inside the inspection object A is estimated by comparing the results of the items selected.
(b) The difference between the intensity of sound appearing in the waveform of the reference elastic wave and the intensity of sound appearing in the waveform of the elastic wave of the object to be inspected
(b) Time shift of the waveform of the elastic wave of the inspection object with respect to the waveform of the reference elastic wave
(c) Attenuation state of the waveform of the elastic wave of the inspection object with respect to the waveform of the reference elastic wave
(d) Frequency of the waveform of the elastic wave of the inspection object with respect to the waveform of the reference elastic wave

The invention according to claim 6 relates to "detecting the position of internal peeling due to movement of the transmitting coil and fixing of the sensor, and in the electromagnetic pulse acoustic nondestructive inspection method according to claim 5,
A transmission coil 12 for generating a pulse magnetic field is moved relative to the laminate 11', which is the object to be inspected A, and the elastic waves are detected at a plurality of locations by sensors 14 provided at fixed locations. After that, one or more items from (a) to (d) are selected from the waveform of the elastic wave and the waveform of the reference elastic wave in the reference body B obtained in advance without internal defects, and the selected item are compared to estimate the position of the defect inside the object A to be inspected.

The invention according to claim 7 relates to "detecting the position of internal peeling by movement of the transmission coil and the sensor", and in the electromagnetic pulse acoustic nondestructive inspection method according to claim 5,
The transmission coil 12 for generating a pulse magnetic field and the sensor 14 are moved relative to the laminate 11', which is the object to be inspected A, while maintaining a constant distance L, and the sensor 14 moves together with the transmission coil 12. The elastic waves are detected at a plurality of points, and then the waveforms of the elastic waves and the waveforms of the reference elastic waves in the reference body B obtained in advance and having no internal defects are compared with the above (a) to (d). It is characterized by selecting one or a plurality of items, comparing the results of the selected items, and estimating the position of the defect inside the inspection object A. FIG .

According to the above, a pulsed magnetic field is applied to the inspection object A, the generated elastic wave is compared with the reference elastic wave, and the intensity, time shift, vibration mode, attenuation, and peak value interval of the waveform are used to determine the It is possible to estimate the presence or absence of an internal defect, its position, and the thickness of the inner layer material of the bonded body and the thickness of the laminate. Furthermore, if the elastic waves are subjected to FFT analysis, it is possible to improve the accuracy of these estimations more than in the case of comparing only the elastic waves.

1 is a conceptual diagram of a non-destructive inspection method using pulsed electromagnetic force according to the present invention; FIG. 1 is a conceptual diagram of a non-destructive inspection method for a joined body having internal defects; FIG. 1 is a cross-sectional view of a test pressure vessel used in the present invention; FIG. 1 is a conceptual diagram of a non-destructive inspection method for a laminate having internal defects; FIG. FIG. 2 shows acoustic waveforms and their FFT spectra of a non-defective reference body of a joint and an inspection object having boundary peeling; FIG. (a)-(f) are FFT spectra of acoustic waveforms at multiple locations of a defect-free reference body of a joint and a test object with boundary delamination. (g) is a line graph of maximum peak frequencies at multiple locations of a defect-free reference body of a joint and an inspection object with boundary delamination; (h) is an AE signal intensity line graph at multiple locations of a zygote defect-free reference and an inspection object with boundary delamination. (a) is a graph showing an interval interval between peak values of AE signals of a metal liner having a reference thickness and a metal liner with reduced thickness in a joined body, and (b) is a graph showing its FFT spectrum.

The present invention will be described in detail below with reference to the drawings. In the present invention, the acoustic wave generated in the inspection object A is detected by the transducer 14 (acoustic emission sensor (hereinafter referred to as an AE sensor)) installed on the surface of the inspection object A, and signal processing is performed. The presence or absence of internal defects in the inspection object A, its thickness (plate thickness), defect positions, or cracks (cracks) generated in the liner R of the joint body, which is one of the inspection objects A, are evaluated non-destructively. The method.

In FIG. 1, a non-destructive inspection apparatus 10 using pulsed electromagnetic force of the present invention includes a transmission coil 12 provided on the surface of a reference body B free of internal defects with a predetermined gap H, and this transmission coil 12 through a power cable. It is composed of a power supply unit 13 for applying a pulse current to the coil 12, a sensor 14 attached to the surface of the inspection object A, and a measurement unit 15 connected to the sensor 14 by a signal cable. The measurement unit 15 is provided with an arithmetic function and a display function. The inspection object A in FIGS. 2 and 4 is the same.

The transmitting coil 12 is composed of a single coil composed of a spirally wound electric wire. A core may be used in the coil. The circuit of the present invention is well-known, and although not shown, a capacitor is charged from a DC high-voltage power supply, and the charge of the charged capacitor is applied to the transmission coil 12 as a pulse current by turning on a mechanical switch or a semiconductor switch. is configured to The transmission coil 12 is attached to the surface of the inspection object A with a gap H provided therebetween. The gap H is kept constant at the time of inspection.

The sensor 14 is a known sensor, and is a device that is installed on the measurement surface of the inspection object A, detects an elastic wave (acoustic signal) generated in the inspection object A, and converts it into an electric signal. The sensor 14 may be an AE sensor, an acceleration sensor, an optical measurement sensor, or a microphone that converts acoustic signals into electrical signals. An AE sensor is employed here.

The power supply unit 13 applies a pulse current to the transmitting coil 12 through a power cable.

The measurement unit 15 samples the output waveform of the AE sensor 14, amplifies it with an amplifier, removes unnecessary signals with a filter or the like, A/D converts it, and outputs the A/D converted digital data. Digital data is stored in a memory, and digital data is subjected to a predetermined calculation according to a program having a predetermined signal processing procedure via a CPU, and the result is stored in the memory or displayed via a display device.

The measurement unit 15 has a known configuration commercially available as, for example, an acoustic analysis device, and performs acoustic analysis. Furthermore, it has a Fourier transform function such as FFT (Fast Fourier Transform).
Note that the measurement unit 15 is not limited to this, and if only the waveform of the detection signal of the elastic wave from the sensor 14 needs to be measured, for example, an oscilloscope or the like may be used.

The first test object A is a bonded body in which a non-conductive material 11b is adhered to a highly conductive material 11a, and the second is a bonded body in which a low conductive material 11c is adhered to a highly conductive material 11a. The above is shown in FIG. For the sake of simplification, these combinations are represented in one drawing.
In FIG. 1, when the highly conductive material 11a is provided on the liner R side and the non-conductive material 11b is provided on the outer shell G side, the highly conductive material 11a is provided on the liner R side and the outer shell G side is provided with the non-conductive material 11b. When the low-conductivity material 11c is provided, the low-conductivity material 11c may be provided on the liner R side and the non-conductive material 11b may be provided on the outer shell G side.
The third is a laminate 11' of low-conductivity material 11c (Fig. 4).
The highly conductive material 11a is a material having an electric conductivity exceeding 10 ⁶ S/m, and is generally a metallic material such as alloy steel or aluminum.
The non-conductive material 11b is a material having an electrical conductivity of less than 10 ⁻⁴ S/m, and typical examples thereof include ceramics, GFRP (glass fiber reinforced plastic), and plastics.
The low-conductivity material 11c is a material whose electric conductivity is within the range of 10 ^-4 to 10 ⁴ S/m, and includes CFRP (carbon fiber reinforced plastic), CFRC (carbon fiber reinforced concrete), CNF composite material (carbon nano Typical examples of fiber composite materials include composites in which carbon nanofibers are dispersed in polymer materials such as polyethylene and polypropylene, CNT composite materials (carbon nanotube composite materials), and solid polymer electrolyte membranes.

The joined body 11 is a material in which two or more materials with different properties are strongly bonded at the interface while maintaining their respective phases to improve characteristics such as strength, rigidity, and weight reduction. . Here, the liner R as shown in FIG. A material to which GFRP is adhered, for example, there is a pressure vessel as a representative example. In addition, bodies of automobiles and aircraft are examples of structures formed by bonding two or more materials having different properties.

Internal defects of such a pressure vessel or body include the adhesive joint portion S between the liner R, which is the inner layer material, and the outer shell G, or the partial boundary peeling P of the adhesive joint portion S of the dissimilar material structure, There are delamination/internal delamination N inside the shell G, thinning and fatigue crack W of the liner R which is the inner layer material.

The laminate 11' is formed by stacking and bonding several sheets, films, veneers, or the like. A typical example is CFRP, which is obtained by stacking carbon fiber woven fabric prepregs in different fiber directions and curing them. The defects of the laminate 11' include delamination N and transverse cracks. A practical example of use would be the giant turbine blades in wind farms.
Although bonding using an adhesive has been described as a typical example of bonding of the bonded body 11 and the laminated body 11', fusion bonding may also be used. The delamination N is, for example, a portion where the joint between the layers is separated due to an impact or the like after joining, but here also includes a defective fusion portion where the joint is incomplete due to the presence of air bubbles or foreign matter.

Next, a method of installing the transmitting coil 12 and the sensor 14 in the main inspection will be described. FIG. 1 schematically shows the case of using a reference body B having no internal defect of the joined body 11, and FIG. In this case, a boundary separation P with a width K was provided in the adhesive joint portion S as an internal defect. Of course, the internal defect is not limited to boundary peeling P, and there are other defects as described above. Here, boundary separation P is taken as a representative example.
The method of installing the transmitting coil 12 and the sensor 14 in this inspection is the same for the laminate 11 ′ as for the joined body 11 . In this case, although not shown, a reference body B having the same structure as the inspection object A and having no internal defects and an inspection object A having an internal defect shown in FIG. 4 are used.
In any case, when the inspection object A is a joined body 11, the transmission coil 12 is placed away from the upper surfaces of the non- or low-conductive materials 11b and 11c, which are the measurement surfaces, and in the case of the laminate 11' be installed away from one side. Let H be the separation height.

When the object A to be inspected is the joined body 11, the sensor 14 is placed in contact with the surface of the non- or low-conductivity materials 11b and 11c (that is, the pulse magnetic field irradiation surface). When the inspection object A is a laminate 11', it is placed in contact with its surface (pulse magnetic field irradiation surface).
In relation to the transmitting coil 12 , the sensor 14 is installed at a position separated by a distance L from the transmitting coil 12 .

The non-destructive inspection apparatus 10 using pulsed electromagnetic force of the present invention is installed with respect to the inspection object A or the reference body B as described above. The reference body B has the same structure as the inspection object A and is a member without defects.
In this inspection, when a pulse current is applied to the transmission coil 12, a pulse magnetic field is generated from the transmission coil 12 side toward the inside of the inspection object A (or the reference body B).
When the inspection object A (or the reference body B) is provided with (a) a highly conductive material 11a on the liner R side and a non-conductive material 11b or a low conductive material 11c on the outer shell G side, this pulse The magnetic field induces eddy currents in the highly conductive material 11a.
When the inspection object A is (a) provided with the low-conductivity material 11c on the liner R side and the non-conductivity material 11b on the outer shell G side, the pulse magnetic field is weaker than the high-conductivity material 11a, but the pulse magnetic field is low. An eddy current is induced in the conductive material 11c. In either case, the depth of the eddy currents depends on the strength of the pulsed magnetic field, but for the same strength of the pulsed magnetic field, naturally the eddy currents of the low-conductivity material 11c are smaller than those of the high-conductivity material 11a.
When the inspection object A (or the reference body B) is the laminated body 11′, the entire inspection object A (or the reference body B) (in particular, the depth corresponding to the intensity of the pulse magnetic field from the pulse magnetic field irradiation surface) within range) induces eddy currents. In the joined body 11, as a target value, a signal of the conductive material 11a, which is the liner R, is obtained at a maximum depth of 30 mm from the irradiated surface.
Then, the interaction force between the magnetic field accompanying this eddy current and the magnetic field of the pulse magnetic field excites the high-conductivity material 11a (or the low-conductivity material 11c). An elastic wave (acoustic emission) is emitted from a certain high-conductivity material 11a (or low-conductivity material 11c) or, in the case of the laminate 11', the entirety (in particular, within the range where eddy currents are generated).

This elastic wave has a frequency component of several kHz to several tens of kHz. Metal materials mainly emit many signals having frequency components of 100 kHz to 300 kHz. Acoustic emissions (AE) mainly propagate in materials because high frequency signals are attenuated significantly in air. In this case, if the highly conductive material 11a is a magnetic material, the force associated with the magnetic energy is added to the excitation force and strengthened.

The elastic wave is a deformation wave that propagates through an elastic body, and is also called an elastic stress wave or an elastic strain wave. It is roughly divided into a "volume wave" that causes a change in volume and an "equal volume wave" that causes a change in shape but not a change in volume. Compression waves and tension waves in a one-dimensional object correspond to the former, and shear waves or torsion waves correspond to the latter. The propagation velocity of elastic waves depends on the elastic modulus, Poisson's ratio and density of the elastic body.

Next, a non-destructive inspection method using this device 10 will be described. FIG. 1 shows an inspection of a defect-free reference body B to obtain reference data. On the other hand, FIG. 2 shows an inspection of an inspection object A to be inspected, in which an adhesive joint portion S has boundary peeling P. FIG. T denotes the thickness of the high-conductivity material 11a or the low-conductivity material 11c that forms the liner R. As shown in FIG.
As already described, the inspection object A is irradiated with a pulsed magnetic field. The irradiated surface is the side of the non- or low-conductivity material (outer shell G) 11b and 11c. A gap H is provided between the irradiation surface and the transmitting coil 12 .
The sensor 14 is placed in contact with the non- or low-conductivity material (shell G) 11b, 11c.
The inspection object A is irradiated with a pulsed magnetic field to induce an eddy current in the high-conductivity material 11a or the low-conductivity material 11c on the liner R side by the pulsed magnetic field, and the eddy current and the pulsed magnetic field are generated. The interaction force excites the high-conductivity material 11a or the low-conductivity material 11c. This excitation generates an elastic wave whose sound source is the high-conductivity material 11a or the low-conductivity material 11c, and propagates through the non- or low-conductivity materials (outer shells G) 11b and 11c. The sensor 14 installed on the surface of the non- or low-conductivity materials 11b and 11c, which is the outer shell G, detects the transmitted elastic wave, and the measurement unit 15 connected to the sensor 14 performs a predetermined calculation (the elastic wave , FFT analysis of the elastic wave, and acquisition of the FFT spectrum) are performed, and the waveform is displayed on a display device as required.
For the reference body B having no internal defects, the data is obtained in advance by the same procedure as described above and stored in the storage device.
After that, the reference data (reference elastic wave waveform and its reference FFT spectrum) and the inspection data (inspection elastic wave waveform and its inspection FFT spectrum) are compared, and the following inspection data for the data of the reference body B are obtained. One or a plurality of items shown in (a) to (d) are selected, the results of the selected items are compared, the characteristic portions are extracted, and the presence or absence of internal defects in the inspection object A is estimated. This is done in the same way for both the joined body 11 and the laminated body 11'.
(a) the difference between the intensity of the sound appearing in the waveform of the reference elastic wave and the intensity of the sound appearing in the waveform of the elastic wave of the inspection object A; Waveform time shift (c) Attenuation state of the waveform of the elastic wave of the inspection object A with respect to the waveform of the reference elastic wave (d) Frequency of the waveform of the elastic wave of the inspection object A with respect to the waveform of the reference elastic wave

Next, the above (a) to (d) will be described with reference to the results (graphs) of the non-destructive inspection using the apparatus 10. FIG.
In the graphs of FIG. 5 and subsequent figures, there is no defect in the reference body B on one side, and there is a defect on the inspection object A on the other side. A solid line indicates no defect, and a dashed line indicates a defect.
FIG. 5(a) shows the detection result of the AE signal when boundary delamination P exists between the outer shell G and the inner layer (liner) R of the inspection object A. The vertical axis represents the amplitude of the AE signal (unit: V), the horizontal axis is time (ms). Then, a pulsed magnetic field was applied to the object A to be inspected from the outer shell G side. In this case, the AE signal is the waveform (amplitude) of the elastic wave without internal separation indicated by the solid line and the waveform (amplitude) of the elastic wave with internal separation indicated by the dashed line. appears slightly large, the existence of internal defects can be inferred from the difference in AE signal intensity. Also, the attenuation of the elastic wave is slightly faster in the case of no internal separation indicated by the solid line than in the case of the case with internal separation indicated by the dashed line, and converges to zero. This is because the vibration mode (the manner of vibration) changes depending on the presence or absence of internal peeling, and this appears as a difference in the waveform of AE (elastic wave).

Furthermore, as can be seen from the figure (b) (the horizontal axis is the frequency and the vertical axis is the FFT spectrum intensity), the FFT analysis of the AE signal (elastic wave waveform) in the figure (a) shows that the broken line side (inspection object A) is shifted to a higher frequency side than the peak frequency on the solid line side (reference body B). This is thought to be caused by a change in the vibration mode of the boundary separation portion. That is, with respect to boundary separation, the difference can be determined to some extent by comparing the waveforms of elastic waves (amplitude, time lag, attenuation, and frequency), but the presence or absence of boundary separation can be detected more clearly by comparing the peak values of FFT frequencies. .
This inspection can deal with not only boundary peeling P between the outer shell G and the liner R of the joined body 11 but also internal peeling N of the joined body 11 . Moreover, it can be applied not only to the joined body 11 but also to the laminated body 11'. That is, when the internal delamination N exists inside the laminate 11', the same phenomenon results in the same measurement result.
Here, an example of the bonded body 11 in which the non-conductive material 11b is bonded to the highly conductive material 11a used as the metal liner R is shown, but the high conductive material having internal defects (boundary peeling P, internal peeling N) A similar tendency is exhibited in the joined body 11 of the conductive material 11a and the low conductive material 11c, the joined body 11 of the low conductive material 11c and the non-conductive material 11b, and the laminated body 11' of the low conductive material 11c.

6A to 6H show a method for detecting the "position" of an internal defect in FIGS. Body 11 was used.
As a first measurement method, the sensor 14 is fixed at a fixed position (a position 100 mm away from the internal defect), the transmission coil 12 is moved along the inspection surfaces of the inspection object A and the standard body B, and each movement At a point (the position of the sensor 14 being zero and the distance away from the transmission coil 12), the elastic wave was recorded and FFT-analyzed in the same manner as described above.
Using the AE sensor 14 as the origin, the transmission coil 12 was moved in the direction of the internal defect at intervals of 20 mm. At a point of 100 mm, the internal defect is provided, and when the distance exceeds 100 mm, the transmission coil 12 moves to a position on the opposite side of the AE sensor 14 beyond the internal defect.
6 (a) to (f) are graphs of AE signal intensity, FIGS. 6 (g) and 6 (h) are graphs connecting the maximum peak frequencies of FFT spectra at each measurement point, and graphs connecting AE signal intensities is.
(a) is a position 60 mm away from the AE sensor 14, (b) is a position 80 mm away, (c) corresponds to the center position of the internal defect and is 100 mm away from the AE sensor 14, (d) is an internal Beyond the defect, the position 120 mm away from the AE sensor 14, (e) the position 140 mm away, and (f) the position 160 mm away.
The AE signal intensity (Fig. 6(h)) gradually decreases as the transmission coil moves away from the AE sensor in the polygonal line connecting the square points with a solid line (no internal peeling), but the polygonal line connecting the circle points with a solid line ( With internal peeling), a decrease in signal intensity is observed up to a point beyond the internal peeling by 20 mm (a position of 120 mm from the AE sensor), and then there is an increase in signal intensity. It sharply decreases after 160mm. It is presumed that the defect position is near the lowest signal intensity position (120 mm). The position of the internal defect can be found from the increase and decrease of the maximum peak frequency.
In addition, the maximum peak frequency (FIG. 6(g)) is as low as 1 to 1.5 kHz in the case of the polygonal line connecting the square points with a solid line (no internal peeling), but the polygonal line connecting the circle points with a solid line ( In the case of internal peeling), it is as high as 6.6 to 7.5 kHz. From this, the presence or absence of peeling can be determined.
However, in the first method, the set position of the sensor 14 is fixed at a certain position, whereas the position of the internal defect in the actual inspection object A is unknown. The AE signal gradually weakens as the set position of the sensor 14 moves away from the position of the internal defect. (For example, when the set position of the sensor 14 is separated from the position of the internal defect by 180 mm or more, the AE signal result of the reference body B is approximated.) Therefore, in this method, the inspection object A is finely inspected (for example, A square of 180 mm or less is defined as one inspection section), and inspection is performed in each section.
Here, the joined body 11 in which the non-conductive material 11b is adhered to the highly conductive material 11a is used. A similar tendency is obtained in the joined body 11 to which the non-conductive material 11b is adhered and the laminated body 11' of the low-conductive material 11c.
As a second measurement method, the sensor 14 and the transmission coil 12 are moved along the test surface over the test object A and the standard body B while maintaining a constant distance between the sensor 14 and the transmission coil 12. The same analysis as in Method 1 was performed.
In the second method, since the distance between the sensor 14 and the transmission coil 12 is constant, if both are moved on the measurement surface while maintaining the distance, the AE signal intensity is almost constant in the case of the reference object B. is maintained, but in the case of the measurement object A, the AE signal intensity changes in the vicinity of the internal defect.
This is the same for the detection of internal defect positions in the laminate 11'.

Measurement of the thickness of the metal liner R of the joined body 11 and detection of cracks in the same metal liner R are described below. A joined body 11 in which a non-(or low) conductive material 11b (11c) is adhered to a metal liner R having a reference plate thickness, and a non-(or low) conductive material 11b ( 11c) are adhered to each other, and a pulsed magnetic field is applied as described above to detect the elastic wave.
FIG. 7(a) shows waveforms of AE signals, and FIG. 7(b) shows waveforms in the frequency domain obtained by Fourier transforming them and comparing the waveforms in the frequency domain.
From FIG. 7(a), the smaller the plate thickness, the shorter the interval between the peak values of the AE signal due to the reflection of the elastic wave. The degree of sheet thickness (thickness reduction) can be found from this peak value interval.
From FIG. 7(b), it is observed that the FFT spectrum of the maximum peak changes, and in some cases the half-value width widens, suggesting the presence of cracks.
The same tendency as described above also appears in the joined body 11 in which the low-conductivity material 11c is used as the liner R and the non-conductivity material 11b is joined as the shell material G.

A: inspection object, B: reference body, G: outer shell body, H: gap, L: distance, N: internal peeling, P: boundary peeling, R: inner layer body (liner) S: adhesive joint portion, W: Fatigue crack, 10: non-destructive inspection device, 11: joined body, 11': laminate, 11a: highly conductive material, 11b: non-conductive material, 11c: low conductive material, 12: transmission coil, 13: power supply part, 14: sensor, 15: measuring part

Claims (7)

A bonded body in which either a non-conductive material or a low-conductivity material is adhered to a high-conductivity material is used as an inspection object, and a pulsed magnetic field is applied to the inspection object, and the high-conductivity material is vortexed by the pulsed magnetic field. An electric current is induced, the highly conductive material is excited by an interaction force between the eddy current and the pulsed magnetic field to generate an elastic wave with the highly conductive material as a sound source, and the elastic wave is transmitted to the non-conductive material. Detecting defects on the material side or on the low-conductivity material side, and then comparing the waveform of the elastic wave with the waveform of the reference elastic wave of a previously obtained reference body having no internal defects to detect defects inside the inspection object. In the electromagnetic pulse acoustic non-destructive inspection method for estimating the presence or absence of
dividing the inspection object into a plurality of inspection zones;
In the inspection section, a sensor is provided at a fixed position on the surface which is the measurement surface of the inspection object, and a transmission coil for generating a pulse magnetic field arranged on the surface which is the measurement surface of the inspection object is connected to the inspection section. It is moved relative to the joint body, which is an object, and the elastic waves are detected at a plurality of points by the sensors provided at the fixed points. Select one or more items from the following (a) to (d) for the waveform of the reference elastic wave in the reference body, compare the results of the selected items, and determine the position of the defect inside the inspection object An electromagnetic pulse acoustic non-destructive inspection method characterized by estimating
(a) difference between the intensity of the sound appearing in the waveform of the reference elastic wave and the intensity of the sound appearing in the waveform of the elastic wave of the object to be inspected; Time lag (c) Attenuation state of the waveform of the elastic wave of the inspection object with respect to the waveform of the reference elastic wave (d) Frequency of the waveform of the elastic wave of the inspection object with respect to the waveform of the reference elastic wave
A bonded body in which a non-conductive material is adhered to a low-conductive material is used as an object to be inspected, and a pulsed magnetic field is applied to the object to be inspected to induce an eddy current in the low-conductive material of the bonded body by the pulsed magnetic field, An interaction force between the eddy current and the pulse magnetic field excites the low-conductivity material to generate an elastic wave with the low-conductivity material as a sound source, and the elastic wave is detected on the non-conducting material side. ,
After that, an electromagnetic pulse acoustic non-destructive inspection method for estimating the presence or absence of defects inside the inspection object by comparing the waveform of the elastic wave with the waveform of the reference elastic wave of a reference body having no internal defects obtained in advance. in
dividing the inspection object into a plurality of inspection zones;
In the inspection section, a sensor is provided at a fixed position on the surface which is the measurement surface of the inspection object, and a transmission coil for generating a pulse magnetic field arranged on the surface which is the measurement surface of the inspection object is connected to the inspection section. It is moved relative to the joint body, which is an object, and the elastic waves are detected at a plurality of points by the sensors provided at the fixed points. Select one or more items from the following (a) to (d) for the waveform of the reference elastic wave in the reference body, compare the results of the selected items, and determine the position of the defect inside the inspection object An electromagnetic pulse acoustic non-destructive inspection method characterized by estimating
(a) difference between the intensity of the sound appearing in the waveform of the reference elastic wave and the intensity of the sound appearing in the waveform of the elastic wave of the object to be inspected; Time lag (c) Attenuation state of the waveform of the elastic wave of the inspection object with respect to the waveform of the reference elastic wave (d) Frequency of the waveform of the elastic wave of the inspection object with respect to the waveform of the reference elastic wave
A bonded body in which either a non-conductive material or a low-conductivity material is adhered to a high-conductivity material is used as an inspection object, and a pulsed magnetic field is applied to the inspection object, and the high-conductivity material is vortexed by the pulsed magnetic field. An electric current is induced, the highly conductive material is excited by an interaction force between the eddy current and the pulsed magnetic field to generate an elastic wave with the highly conductive material as a sound source, and the elastic wave is transmitted to the non-conductive material. Detecting defects on the material side or on the low-conductivity material side, and then comparing the waveform of the elastic wave with the waveform of the reference elastic wave of a previously obtained reference body having no internal defects to detect defects inside the inspection object. In the electromagnetic pulse acoustic non-destructive inspection method for estimating the presence or absence of
A transmission coil for generating a pulsed magnetic field and a sensor are moved relative to the bonded body, which is the object to be inspected, while maintaining a constant interval, and the sensor moving together with the transmission coil emits the elastic waves at a plurality of locations. After that, select one or more items from the following (a) to (d) for the waveform of the elastic wave and the waveform of the reference elastic wave in a previously obtained reference body without internal defects, An electromagnetic pulse acoustic non-destructive inspection method characterized by comparing results of selected items to estimate the position of a defect inside the inspection object .
(a) difference between the intensity of the sound appearing in the waveform of the reference elastic wave and the intensity of the sound appearing in the waveform of the elastic wave of the object to be inspected; Time lag (c) Attenuation state of the waveform of the elastic wave of the inspection object with respect to the waveform of the reference elastic wave (d) Frequency of the waveform of the elastic wave of the inspection object with respect to the waveform of the reference elastic wave
A bonded body in which a non-conductive material is adhered to a low-conductive material is used as an object to be inspected, and a pulsed magnetic field is applied to the object to be inspected to induce an eddy current in the low-conductive material of the bonded body by the pulsed magnetic field, An interaction force between the eddy current and the pulse magnetic field excites the low-conductivity material to generate an elastic wave with the low-conductivity material as a sound source, and the elastic wave is detected on the non-conducting material side. ,
After that, an electromagnetic pulse acoustic non-destructive inspection method for estimating the presence or absence of defects inside the inspection object by comparing the waveform of the elastic wave with the waveform of the reference elastic wave of a reference body having no internal defects obtained in advance. in
A transmission coil for generating a pulsed magnetic field and a sensor are moved relative to the bonded body, which is the object to be inspected, while maintaining a constant interval, and the sensor moving together with the transmission coil emits the elastic waves at a plurality of locations. After that, select one or more items from the following (a) to (d) for the waveform of the elastic wave and the waveform of the reference elastic wave in a previously obtained reference body without internal defects, An electromagnetic pulse acoustic non-destructive inspection method characterized by comparing results of selected items and estimating the position of a defect inside the inspection object A.
(b) The difference between the intensity of sound appearing in the waveform of the reference elastic wave and the intensity of sound appearing in the waveform of the elastic wave of the object to be inspected
(b) Time shift of the waveform of the elastic wave of the inspection object with respect to the waveform of the reference elastic wave
(c) Attenuation state of the waveform of the elastic wave of the inspection object with respect to the waveform of the reference elastic wave
(d) Frequency of the waveform of the elastic wave of the inspection object with respect to the waveform of the reference elastic wave
A pulsed magnetic field is applied to a laminate of a low-conductivity material, which is an object to be inspected, and an eddy current is induced in the laminate by the pulsed magnetic field. Exciting the whole to generate an elastic wave, detecting the elastic wave on the surface of the laminate,
After that, the waveform of the elastic wave and the waveform of the reference elastic wave in the previously obtained reference body without internal defects are selected by selecting one or more items from the following (a) to (d) An electromagnetic pulse acoustic non-destructive inspection method, characterized by comparing the results of items and estimating the presence or absence of defects inside the inspection object.
(b) The difference between the intensity of sound appearing in the waveform of the reference elastic wave and the intensity of sound appearing in the waveform of the elastic wave of the object to be inspected
(b) Time shift of the waveform of the elastic wave of the inspection object with respect to the waveform of the reference elastic wave
(c) Attenuation state of the waveform of the elastic wave of the inspection object with respect to the waveform of the reference elastic wave
(d) Frequency of the waveform of the elastic wave of the inspection object with respect to the waveform of the reference elastic wave
A transmission coil for generating a pulsed magnetic field is moved relative to the laminate, which is the object to be inspected, and the elastic waves are detected at a plurality of locations by sensors provided at fixed locations. Select one or more items from the above (a) to (d) from the waveform of and the waveform of the reference elastic wave in the reference body without internal defects obtained in advance, and compare the results of the selected items. 6. The electromagnetic pulse acoustic non-destructive inspection method according to claim 5, wherein the position of the defect inside the inspection object is estimated.
A transmission coil for generating a pulse magnetic field and a sensor are moved relative to the laminate as the object to be inspected while maintaining a constant interval, and the sensor moving together with the transmission coil emits the elastic waves at a plurality of locations. and then selecting one or more of the items (a) to (d) for the waveform of the elastic wave and the waveform of the reference elastic wave in a previously obtained reference body having no internal defects, 6. The electromagnetic pulse acoustic non-destructive inspection method according to claim 5, wherein the results of the selected items are compared to estimate the position of the defect inside the inspection object .

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