JPH07167839A - Inspection coil for electromagnetic induction flaw detection and flaw detecting method - Google Patents

Abstract

PURPOSE:To provide an electromagnetic induction flaw detecting method of an anisotropic conductive material (for example, carbon fiber reinforced plastics), etc., by using a rectangular inspection coil for selectively allowing an induction current to flow in a specific direction on a surface of a specimen. CONSTITUTION:A rectangular inspection coil 1 put on a surface of carbon fiber reinforced plastics 4 is connected to an induction current detector 5, the detector 5 allows an alternating current to flow to the inspection coil 1 and therewith converts an impedance change of the coil 1 into a voltage to output, and a recorder 6 records a voltage change. Therefore, where a longitudinal direction of the inspection coil 1 is superposed on the fiber direction (X direction) of 0 deg. of the carbon fiber reinforced plastics 4, the flaw detection of a fiber rupture can be very accurately made, by selectively allowing an induction current to flow in the fiber direction (high conductance direction).

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an inspection coil for an electromagnetic induction test, an anisotropic conductive material (for example, carbon fiber reinforced plastics, hereinafter referred to as CFRP) and a long isotropic conductive material using electromagnetic induction. The present invention relates to a defect detection method for materials (for example, various metal pipes and wires).

[0002]

2. Description of the Related Art Electromagnetically induced flaw detection is widely used as a flaw detection method for running metallic materials because it can be inspected nondestructively and quickly. In recent years, its application has also been tried as a flaw detection method for carbon fiber reinforced plastics. ing.

For example, p47-52 of the previously published "Proceedings of the 4th Symposium on Nondestructive Evaluation of New Materials and Their Products (January 1993)" contains artificial fiber breaking scratches. An example of inspecting a unidirectionally reinforced CFRP laminate and a 0 ° and 90 ° bidirectionally reinforced CFRP laminate by an electromagnetic induction flaw detection method (also referred to as an eddy current method) has been reported. However, it is difficult to detect fiber breakage with a unidirectional reinforcing plate,
It is described that the reason is that the electrical resistance in the direction perpendicular to the fiber is higher by about 3 to 4 orders of magnitude as compared with that in the fiber direction, and therefore it is difficult for an induced current to flow. In addition, it is said that the bidirectional reinforced plate could be detected because the above-mentioned anisotropy of conductivity was relaxed, but fiber break scratches were put in both 0 ° layer and 90 ° layer, and only one layer It can be predicted from the results of the unidirectional strengthening plate that there is no detection sensitivity. The problem with this report is that since a vortex-shaped induced current is passed through the plate surface using a probe-type inspection coil, it is strongly affected by the anisotropy of electrical resistance, which should be improved as a practical technique. Kimono.

Regarding the shape of the electromagnetic induction flaw detection coil, p670-672 of the previously published "Non-destructive Inspection Handbook (edited by the Japan Non-Destructive Inspection Association, published in April 1978, first edition)".
The probe-type coil with a wire wound in a circular shape is used for flaw detection on the surface of a plate-like object, and the penetrating type that allows a rod or tube to pass through the inspection coil for flaw detection on long rods or tubes. Coils are commonly used.

When the probe type inspection coil is used for flaw detection of a plate-like object made of an isotropic conductive material, a circular induction current flows in the plane of the plate, so that flaw detection can be performed with the same sensitivity regardless of the defect direction. There is. However, when it is used for an anisotropic conductive material such as a CFRP laminated plate, the magnitude of the induced current is determined by the resistance value integrated with respect to the path through which the current flows. The problem of diminishing occurs. On the other hand, when a cylindrical through-type coil is used for a long isotropic conductive material such as a tube or a rod, an induced current flows in the circumferential direction of the material, which causes the following problems. In other words, the linear scratch extending in the length direction is orthogonal to the induced current, while the linear scratch in the circumferential direction is parallel, so the change in the induced current due to the latter defect is small compared to the former and detected. The problem is that the sensitivity is considerably reduced.

[0006]

DISCLOSURE OF THE INVENTION The present invention has been made in view of the above-mentioned problems of the prior art, and it is possible to detect defects in a fiber break of CFRP, which is an anisotropic conductive material, with high sensitivity regardless of the laminated structure. It is an object of the present invention to provide a method and a method capable of detecting linear scratches of a long isotropic conductive material with the same sensitivity regardless of the orientation.

[0007]

In order to solve the above-mentioned problems, the electromagnetic induction flaw inspection coil and flaw detection method of the present invention are designed to selectively flow an induction current in a specific direction on the surface of a test body during electromagnetic induction flaw detection. A test coil characterized by being wound in a rectangular shape, and using the test coil, an induced current is selectively passed in the direction of high conductivity of an anisotropic conductive material (for example, CFRP) for flaw detection (for example, fiber breakage). And an electromagnetic induction flaw detection method in which a flaw is detected by selectively flowing an induced current in a long isotropic conductive material in a direction orthogonal to the linear flaw.

[0008]

The present invention will be described in detail with reference to the drawings. Figure 1
Is a schematic diagram showing a situation in which an induced current flows in a material by the inspection coil of the present invention. When an alternating current is supplied from a power supply 2 to the inspection coil 1 wound in a rectangular shape, a coil is formed in the test body 3. The induced current I flows in the direction of canceling the fluctuating magnetic field H. The shape of the path through which the induced current flows is substantially similar to the shape of the inspection coil 1, and it becomes possible to selectively flow the induced current in the test body in the direction coinciding with the longitudinal direction of the coil 1. The induced current is a magnetic field H that opposes the magnetic field H.
Since r is generated, the impedance of the inspection coil 1 changes, and the change in induced current can be detected from this impedance change.

When the rectangular inspection coil is applied to an anisotropic conductive material, the induced current is selectively directed in the same direction by matching the longitudinal (long side) direction of the coil with the high conductivity direction of the material. Can be flowed for flaw detection. When a rectangular inspection coil is applied to a long isotropic conductive material such as a tube or rod, the longitudinal direction of the coil is made to coincide with the longitudinal direction of the material so that the induced current can selectively flow in the same direction. Thus, it is possible to detect a linear flaw in a direction orthogonal to the induced current.

Next, the requirements for the rectangular inspection coil will be described. Generally, the larger the size of the inspection coil, the larger the lift-off (distance between the inspection coil and the test body), and the advantage that it is less susceptible to changes in lift-off.
There is a drawback that the detection sensitivity of defects and the position resolution are lowered.
The rectangular inspection coil can more selectively pass the induced current as it becomes longer, but the size of the coil in the lateral (short side) direction is limited by the size of the lift-off, and the size equal to or greater than the lift-off. Required. On the other hand, the dimension in the vertical direction affects the defect detection sensitivity and the position resolution, but it is desirable that the dimension is set to be twice or more the width in the horizontal direction from the viewpoint of selectively flowing the induced current.

[0011]

EXAMPLE FIG. 2 is an embodiment of the present invention and shows an example of detecting a fiber break of a CFRP laminated plate by using the above rectangular inspection coil. The inspection coil 1 placed on the surface of the CFRP laminated plate 4 is connected to the induced current detector 5,
The detector 5 applies an alternating current to the inspection coil 1 and converts the impedance change of the coil into a voltage and outputs the voltage.
The recorder 6 records the voltage change. The figure shows the case where the longitudinal direction of the inspection coil 1 is aligned with the fiber direction (X direction) of 0 ° of the CFRP laminated plate 4, and the induced current I is selectively flown in the fiber direction (high conductivity direction). As a result, fiber breakage can be detected with high sensitivity. Specifically, either the inspection coil 1 or the CFRP laminated plate 4 is relatively scanned in the x direction, and this scanning is repeated at arbitrary intervals in the y direction, whereby flaw detection on the entire surface can be performed. Further, in the case of detecting the breakage of the fiber in different directions, either the inspection coil 1 or the CFRP laminated plate 4 may be rotated so that the longitudinal direction of the inspection coil coincides with the fiber direction, and then the above operation is performed.

According to the apparatus configuration of FIG. 2, the laminated configuration is (0 /
90 / ± 45) s, plate thickness 1.2mm, length 300mm,
A CFRP laminate having a width of 200 mm was used as a test piece for flaw detection. The test piece was artificially inserted into the prepreg of 0 ° layer, 90 ° layer, and + 45 ° layer on the front side with a fiber breakage scratch having a length of 3 mm at right angles to the fiber direction. These scratches are staggered in position so that they do not overlap. The inspection coil used has a length of 30 mm, a width of 10 mm, and a diameter of 0.2 mm.
The conductor wire is wound 30 times and the same frequency is applied to the same coil.
A current of 0 KHz and 0.1 A was applied. The results of flaw detection are shown in FIG. (A), (b) and (c) of FIG. 3 are the results of flaw detection by the method of the present invention, in which the longitudinal direction of the rectangular inspection coil 1 is made to coincide with the fiber direction of each of the above prepregs having artificial defects, and It was obtained by scanning one direction. On the other hand, (d), (e), and (f) in the same figure show the results of flaw detection by applying the same current as above to a conventional pancake type inspection coil having a diameter of 10 mm. It can be seen from FIG. 3 that the conventional method, which had almost no flaw detection, can be detected with substantially the same sensitivity regardless of the fiber direction by the present invention.

FIG. 4 is an explanatory view showing another embodiment of the present invention, showing an example of flaw detection of a steel pipe. A rectangular inspection coil 1 arranged on the outer peripheral surface of the steel pipe 7 so that the longitudinal direction of the coil coincides with the axial direction of the steel pipe 7, and a penetrating inspection coil 8 are connected to a two-channel induced current detector 5. Therefore, a voltage output proportional to the impedance change of each coil is recorded by the recorder 6.
A case will be described as an example in which the linear defect 9 in the circumferential direction and the linear defect 10 in the axial direction of the steel pipe as shown in the figure are detected by such a configuration. When the steel pipe 7 travels and the defect 9 comes under the rectangular inspection coil 1, the induced current flowing in the axial direction of the pipe is interrupted by the linear defect 9 in the circumferential direction orthogonal thereto, and the induced current decreases. Therefore, the impedance of the coil 1 changes and a defect can be detected. However, since the reduction of the induced current due to the linear defect 10 parallel to the direction of the induced current is slight, the defect detection sensitivity is greatly reduced. On the other hand, when the defects 9 and 10 arrive below the conventional through-type inspection coil 8, the relationship between the induced current and the direction of the defect is opposite to that described above, so that the defect 10 can be detected, but the defect 9 is difficult to detect. Becomes

As an actual flaw detection example, a steel pipe having a diameter of 30 mm and a wall thickness of 2 mm has a length of 5 mm and an opening width of 0.1 mm.
The results of flaw detection as a test piece in which a linear flaw having a depth of 0.3 mm is artificially inserted in the axial direction and the circumferential direction will be described. FIG. 5A shows the flaw detection result of the method of the present invention in which the rectangular coil and the feedthrough coil are used in combination, and FIG. 5B shows the flaw detection result when only the feedthrough coil of the conventional method is used. The rectangular inspection coil has the same structure as described above, and the through-type inspection coil has a diameter of 40 mm and a length of 10 mm.
A conductor wire having a thickness of 3 mm wound 30 times was used. In the figure, the peak 11 of the output voltage corresponds to the linear scratch 9 in the circumferential direction, and the peak 12 is the output corresponding to the linear scratch 10 in the axial direction. These results show that the conventional method can detect only defects in the axial direction, whereas the method of the present invention can detect defects in the axial direction and the circumferential direction with substantially the same sensitivity. As described above, according to the present invention, the linear defect extending in the axial direction and the circumferential direction of the steel pipe can be detected with high sensitivity by combining both the rectangular inspection coil and the through coil for flaw detection. By arranging a plurality of rectangular inspection coils on the outer peripheral surface of the steel pipe at a predetermined angle, it is possible to perform flaw detection on the entire outer surface of the pipe.

In the above embodiments, the case where a so-called self-induction type inspection coil in which the exciting coil and the coil for detecting the change in the induced current are the same is used.
A mutual induction type inspection coil in which both coils are separated may be used, or the inspection coil may be a differential type inspection coil divided in the scanning direction.

[0016]

As described above, according to the present invention, the rectangular inspection coil is used, and in the anisotropic conductive material, the induced current is selectively passed in the direction of high conductivity to detect flaws. Fiber breakage of reinforced plastics products can be detected with high sensitivity, and in long isotropic conductive materials, an induced current is sent in the direction orthogonal to the linear flaw to detect flaws, so regardless of the flaw direction. It has the effect of detecting linear scratches.

[Brief description of drawings]

FIG. 1 is a schematic view showing the function of a rectangular inspection coil of the present invention.

FIG. 2 is an embodiment diagram of the present invention, and is an explanatory diagram for detecting a fiber breakage of a CFRP laminated plate.

FIG. 3 is a diagram showing an example of a flaw detection result of fiber breakage of a CFRP laminated plate according to the present invention in comparison with that by a conventional method.

FIG. 4 shows another embodiment of the present invention and is an explanatory diagram for detecting a linear flaw in a steel pipe.

FIG. 5 is a diagram showing an example of a flaw detection result of a linear flaw of a steel pipe according to the present invention in comparison with that of a conventional method.

[Explanation of symbols]

 1 rectangular inspection coil 2 power supply 3 test body 4 CFRP laminated plate 5 induced current detector 6 recorder 7 steel pipe 8 through-type inspection coil 9 circumferential linear scratches 10 axial linear scratches 11 circumferential linear scratches Output peak corresponding to scratches 12 Output peak corresponding to linear scratches in the axial direction

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Yasuhiro Aikawa 5-10-1 Fuchinobe, Sagamihara-shi, Kanagawa Electronics Research Laboratory, Nippon Steel Corporation

Claims (3)

[Claims] 1. An electromagnetic induction flaw detector inspection coil, which is wound in a rectangular shape in order to selectively flow an induced current in a specific direction on the surface of a test body. 2. In the electromagnetic induction flaw detection of anisotropic conductive material, the rectangular inspection coil according to claim 1 is used,
A flaw detection method for an anisotropic conductive material, which comprises selectively inducing an induced current in a high conductivity direction to perform flaw detection. 3. In the electromagnetic induction flaw detection of a long isotropic conductive material, the rectangular inspection coil according to claim 1 is used, and an induced current is selectively passed in the longitudinal direction of the material to make it longitudinal. Characterized by detecting linear scratches in a right angle direction,
Testing method for long isotropic conductive materials.