JP3048176B2 - Defect detection apparatus and method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a defect detecting apparatus for non-destructively detecting defects such as cracks in an object to be inspected, and particularly to aluminum and titanium used in trains, automobiles, space equipment, aircrafts, and the like. The present invention relates to a defect detection device suitable for detecting a defect or the like generated in a non-magnetic material such as a non-magnetic material with high accuracy.

[0002]

2. Description of the Related Art As a method for non-destructively detecting a defect in a test object, an eddy current is generated in the test object by changing a magnetic field applied to the test object, and the flow of the eddy current is obstructed by the defect. In some cases, the presence or absence of a defect is detected depending on whether or not there is a defect. Conventionally, as a flaw detection coil for this eddy current flaw detection, for example, Japanese Patent Application Laid-Open No. 50-129090, Non-Destructive Testing, Handbook: Leonardo, Press, Company (1963) No. 36-
Items 1 to 36-21 (NONDESTRUCTIVETESTING HAND
BOOK: THE RONALD PRESS COMPANY (1963) PP36-1 ~ 36
As described in -21), a structure in which only a detection coil is used in a self-induction coil and a structure in which only a detection coil and an excitation coil are used in a mutual induction coil are known.

[0003]

In the above prior art, an eddy current is generated in a test object by changing a magnetic field applied by an exciting coil, and when the eddy current is disturbed by a crack or the like, the eddy current is caused by the eddy current. The variation of the magnetic field is generated, and the variation is measured by a detection coil to determine the presence or absence of a crack or the like. In this type of apparatus, the crack cannot be detected and the sensitivity is low unless the excitation coil and the detection coil are brought into contact with or sufficiently close to the test object. For this reason, there is a problem that a defect or the like of the inspection object cannot be detected with high accuracy from a distant position. An object of the present invention is to detect a defect or the like of a test object from a distant position with high sensitivity, and furthermore, the detection result is not affected by the size of the distance (lift-off) or the material of the test object. An object of the present invention is to provide a defect detection device.

[0004]

The object of the present invention is to use a SQUID having a pickup coil capable of measuring up to a DC component of a magnetic field as a detection coil, and to be unaffected by a lift-off to a test object and a difference in material of the test object. By adopting a cancel type coil as the exciting coil,
Achieved.

[0005]

The pickup coil of the SQUID is arranged in the cancellation region where the magnetic field is zero near the two excitation coils of the cancellation type, so that the magnetic balance is maintained regardless of the lift-off. However, when a defect such as a crack exists in the inspection object, one of the two induced eddy currents is disturbed by the crack or the like, the two eddy currents become unbalanced, the zero point of the magnetic field moves, and the SQUID is Only when a crack exists, a unique signal is detected with high sensitivity. Further, by making the pickup coil of the SQUID of a differential type, it is possible to cancel the peripheral noise and enhance the directivity, and it is possible to detect the position of a defect or the like with high accuracy.

[0006]

An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a configuration diagram of a defect detection device according to one embodiment of the present invention. This defect detection device detects a crack 12 caused by fatigue or the like generated in a metal structural member which is an inspection object 10. The excitation coil 20 is composed of two excitation coils 20a and 20b.
b have opposite polarities. Exciting coil 20a,
20b is attached to the lower part of the cryostat 30 of the SQUID sensor, and a pickup coil 32 of the sensor is provided.
Are arranged in the zero point region of the magnetic field generated by the excitation coils 20a and 20b. Therefore, even if the magnitude of the magnetic field of the exciting coils 20a and 20b changes due to the exciting current, no signal is generated in the pickup coil 32 because the absolute values of the magnitudes of the two magnetic fields are the same and the polarities are reversed. The pickup coil 32 and the SQUID 31 are contained in the cryostat 30 and are cooled to the operating temperature by the refrigerant 33. The output of the SQUID 31 is sent to the SQ
It is connected to the UID controller 35. The current flowing through the excitation coils 20a and 20b is controlled by the excitation controller 21. The SQUID controller 35 and the excitation controller 21 are connected to the data processing device 50. The data processing device 50 is connected to the data processing device 50 by the magnitude of the signal detected by the SQUID 31 and the magnitude of the current flowing through the excitation coils 20a and 20b at that time. Calculate and calculate the position dimensions of The embodiment shown in FIG. 1 is an inspection apparatus for one channel and is a handy type embodiment.

Next, the operation of each part of the embodiment shown in FIG. 1 will be described with reference to FIGS. FIG. 2 shows the excitation coils 20a and 20a when the inspection object 10 having no defects such as cracks is inspected.
It is a figure which shows the magnetic field distribution by 20b. As shown in FIG. 2, when there is no defect, the magnetic fields applied by the exciting coils 20a and 20b to the device under test 10 are the same and opposite magnetic fields. Have the same magnitude. For this reason, the pickup coil 32 arranged between the excitation coils 20a and 20b is in the zero magnetic field region, and the distance (lift-off) between the excitation coils 20a and 20b and the device under test 10 is increased.
Does not produce an output at the sensor 3.

FIG. 3 is a diagram showing a magnetic field distribution by the exciting coils 20a and 20b when the inspection object 10 has a crack 12. As shown in FIG. As shown in FIG. 3, when the crack 12 is present in front of the exciting coil 20b, unlike the case of FIG. 2, an overcurrent i caused by a change in the applied magnetic field of the exciting coil 20b is generated.
The flow of e 'is disturbed, and is different from the eddy current ie caused by the change in the applied magnetic field of the exciting coil 20a. That is, ie ≠ ie '. Thereby, the excitation coil 20
a and 20b are different, and the sensor 3 has a crack 12
Signal is obtained.

FIG. 4 is a diagram showing an example of signal output of the SQUID sensor when scanning and measuring the inspection object 10 having the crack 12. FIG. 4A shows a signal output waveform obtained by one scan, that is, one-dimensional scanning. Positive and negative signal waveforms are obtained only when the signal passes over the crack 12. FIG. 4 (b)
It is a signal output waveform obtained when two-dimensional scanning is performed in the x and y directions. The data processing device 50 determines the length and the depth of the crack 12 from the data of the signal output waveform.

FIG. 5 is a graph showing the relationship between the depth of the crack 12 and the output of the SQUID sensor. As shown in FIG.
The crack 12 of the inspection object 10 is determined in advance by the same measurement as described above.
The relationship between the depth 1 of the SQUID sensor and the signal output of the SQUID sensor is obtained in advance, and the length and the depth of the crack 12 can be determined from the measurement data of FIGS. 4A and 4B using this relationship.

According to the above-described embodiment, since the SQUID can be used to detect even the DC component of the exciting magnetic field, the frequency of the exciting current is made lower to increase the depth of penetration of the magnetic field into the test object. This makes it possible to detect even deep cracks.

FIG. 6 is a diagram showing the application of the defect detection apparatus according to the present invention to inspection of trains, automobiles, aircraft bodies, and the like. In FIG. 6, a large number of rivet holes 11 are formed on the surface of an Al plate of a vehicle or a body, and cracks 12 may be generated in the rivet holes 11 due to fatigue.
Therefore, in order to measure this crack 12 with high speed and high accuracy,
Non-contact inspection is performed by a defect detection device using SQUID. Now, there are a number of rivet holes 11 on the surface of the measuring object 10 in FIG. 6, and a crack 12 is present in one of the rivet holes 11. In order to detect the crack 12, a plurality of exciting coil pairs 20 for generating an eddy current in the measuring body 10 by an AC magnetic field are provided on the surface of the cryostat 30. A pickup coil 32 is provided inside the cryostat 30 so as to correspond to the excitation coil pair 20. The plurality of pickup coils 32 are connected to a multi-type SQUID 31, and the SQUID 31 is a multi-channel amplifier 3
4 is connected to the SQUID controller 35. A drive gear box 4 composed of a commercially available motor gear is mounted on a scanning bar 42 fixed to the surface of the measurement body 10 with a suction cup 40.
3, which is controlled by the drive control device 44,
The entire defect detection device is moved by scanning.
The suction cup 40 can be attached to and detached from the measuring body 10 by a suction cup attachment / detachment lever 41, and can be freely moved to a range to be measured. The excitation coil pair 20 is controlled by an excitation controller 21, and the excitation controller 21, the SQUID controller 35, and the drive control device 44 are connected to a data processing device 50. With such a configuration, when inspecting the body of a train, a car, or the body of an aircraft, the defect detection device is scanned within a specific range by the drive control device 44 of the drive mechanism fixed to the surface of the measurement object by the suction cup 40, and the measurement is performed. Crack 1 in rivet hole 11 on body surface
2 and the like are determined in the same manner as in the above-described embodiment. According to the present embodiment, even in the case of a non-magnetic material such as an Al-based alloy material in a vehicle or a body, a defect such as a crack can be detected in a non-contact manner at high speed and with high sensitivity.

[0013]

According to the present invention, it is possible to detect a defect such as a crack in a test object with high sensitivity without being influenced by the distance even from a remote position and without depending on the material of the test object. Will be possible. In addition, since it is possible to detect even the DC component of the exciting current, it is possible to detect even a defect deep in the inspection object with high sensitivity.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of a defect detection device according to an embodiment of the present invention.

FIG. 2 is a diagram showing a magnetic field distribution of a test object having no defect.

FIG. 3 is a diagram showing a magnetic field distribution of a test object having a defect.

4A and 4B are a signal output waveform diagram at the time of one-dimensional scanning of a defect and a signal output waveform diagram at the time of two-dimensional scanning.

FIG. 5 is a graph showing a relationship between a defect depth and SQUID output.

FIG. 6 is a configuration diagram of a defect detection apparatus used for inspection of a train, an automobile, an airframe, and the like.

[Explanation of symbols]

3 ... sensor, 10 ... test object, 11 ... rivet hole, 12 ...
Crack, 20: excitation coil pair, 20a, 20b: excitation coil, 21: excitation controller, 30: cryostat, 31: SQUID, 32: pickup coil, 3
3. Refrigerant.

──────────────────────────────────────────────────続 き Continuing from the front page (72) Inventor Sadao Nemoto 502 Kandachi-cho, Tsuchiura-shi, Ibaraki Machinery Research Laboratory, Hitachi, Ltd. (56) References JP-A-2-78918 (JP, A) JP-A-60- 82850 (JP, A) JP-A-60-21445 (JP, A) JP-A-63-293461 (JP, A) JP-A-63-141449 (JP, U) JP-A-60-11493 (JP, Y2) (58) Field surveyed (Int. Cl. ⁷ , DB name) G01N 27/72-27/90

Claims (3)

(57) [Claims] 1. A defect detecting apparatus for non-destructively detecting a defect in an object to be inspected, comprising two air-core exciting coils arranged in parallel, wherein the magnitude of a magnetic field applied to the object to be inspected is the same and the polarity is A defect detection device comprising: two exciting coils opposite to each other; and a SQUID in which a differential pickup coil is arranged in a magnetic balance region formed by the two exciting coils. 2. A method for detecting the presence or absence of a defect in an object to be inspected by using the defect detection device according to claim 1, wherein a current is supplied to two air-core excitation coils to generate magnetic fields in the respective excitation coils. A defect detection method in which a pickup coil detects whether or not there is a difference between eddy currents corresponding to an excitation coil generated in an object to be inspected by changing a magnetic field over time, and determines that there is a defect when the difference occurs. 3. The defect according to claim 2, wherein a length and a depth of the defect are determined from a change in a signal waveform detected by the pickup coil by two-dimensionally scanning the exciting coil with respect to the inspection object. Detection method.