JP7090262B2 - Delamination detector and method - Google Patents

Description

The present invention relates to a delamination detection device and a method for carbon fiber reinforced plastic.

Carbon fiber reinforced plastic (CFRP) is a lightweight, high-strength, high-rigidity material. Therefore, CFRP is widely used as a structural material for automobiles, aerospace equipment, and the like.
However, in CFRP, delamination occurs due to impact or the like. Delamination between layers is difficult to distinguish visually and must be detected by non-destructive inspection.

As a non-destructive inspection means for CFRP, the vertical flaw detection method, which is a basic test method for ultrasonic flaw detection tests, is widely applied to detect delamination.
In the vertical flaw detection method, ultrasonic waves are incident on a material through a contact medium (kaplant) such as water or gel coated on the CFRP surface, and the peeling between layers is detected by measuring the reflected wave from the peeling point. In addition, the peeling can be visualized from the C-scan image displaying the intensity distribution of the reflected wave.
However, the vertical flaw detection method has the following problems.
(1) A contact medium to be applied to the CFRP surface is indispensable. (2) Post-treatment (drying, wiping) of the contact medium is required. (3) A large water tank is required when inspecting CFRP by submerging it in water. (4) It is difficult to detect the peeled part near the surface of CFRP. (5) It is difficult to apply thin plates to CFRP.

Therefore, there has been a demand for the application of an inspection means (eddy current flaw detection test method) using an eddy current that does not have these problems. The eddy current flaw detection test method is disclosed in, for example, Patent Document 1.

In the "method for inspecting peeling defects of carbon fiber reinforced plastic" of Patent Document 1, a peeling defect between adjacent CFRP plies having different fiber directions is passed a current in the fiber direction of each ply, and the difference in the degree of contact between the plies is different. It is detected by the impedance change based on.

Japanese Unexamined Patent Publication No. 9-72884

However, in the case of the inspection method of Patent Document 1, there is a problem that the signal of the eddy current sensor varies greatly even in the sound part, and it is difficult to distinguish the delaminated part from the sound part.

In the eddy current flaw detection test for CFRP, the signal change occurs even in the sound part because of the variation in conductivity in CFRP. The conductivity of a CFRP single layer is described by the conductivity in three directions: fiber direction, fiber orthogonal direction, and thickness direction. Although the conductivity in the fiber direction has a relatively small variation, the conductivity in the fiber orthogonal direction and the thickness direction changes depending on the contact state of the fiber, so that the variation is large. Since the eddy current distribution in the CFRP is affected not only by the conductivity in the fiber direction but also by the conductivity in the fiber orthogonal direction and the thickness direction, the signal will vary greatly even in the sound part.

Therefore, in order to detect delamination of CFRP, there has been a strong demand for a test means having excellent sensitivity for detecting delamination.

The present invention has been devised to satisfy the above-mentioned demands. That is, an object of the present invention is to provide an interlayer peeling detection device and a method capable of solving the problems of an ultrasonic flaw detection test method and detecting interlayer peeling of carbon fiber reinforced plastic with high detection sensitivity.

According to the present invention, an exciting coil having a first axis and a detection coil having a second axis.
The second axis is positioned parallel to the first axis to hold the excitation coil and the detection coil, and the first axis and the second axis are relative to the surface of the carbon fiber reinforced plastic plate. An eddy current probe that positions the plane in parallel, including
Provided is an interlayer delamination detecting device including a generated voltage detecting device for applying an exciting AC voltage to the exciting coil to detect the generated AC voltage generated in the detection coil.

Further, according to the present invention, an exciting coil having a first axis and a detection coil having a second axis are prepared.
The second axis is positioned parallel to the first axis to hold the excitation coil and the detection coil, and the first axis and the second axis are relative to the surface of the carbon fiber reinforced plastic plate. Position the planes containing in parallel,
Provided is a method for detecting delamination by applying an exciting AC voltage to the exciting coil to detect the generated AC voltage generated in the detection coil.

According to the present invention, the exciting coil and the detection coil are positioned on the surface of the carbon fiber reinforced plastic plate, and the exciting AC voltage is applied to the exciting coil to detect the generated AC voltage generated in the detection coil.
Further, it was confirmed by the examples described later that the delamination between the carbon fiber reinforced plastic plates can be detected with high detection sensitivity according to the present invention.

It is an overall block diagram of the interlayer peeling detection apparatus of 1st Embodiment by this invention. It is an overall block diagram of the interlayer peeling detection apparatus of 2nd Embodiment by this invention. It is the whole flow figure of the layer separation detection method by this invention. It is explanatory drawing of the analysis model. It is a figure which shows the eddy current distribution in a CFRP plate. It is a figure which shows the real part of the eddy current distribution when the center of the peeling part is at the position (10,0). It is a figure which shows the relationship between the center coordinate xd of the peeling part B, and the magnetic field deviation ΔHy with respect to various magnetic field detection positions Xp. It is a schematic diagram of an experimental method. It is the eddy current test result in the case of d = 17 mm with respect to the 2nd test body. It is the eddy current test result in the case of d = 17 mm with respect to the 1st test body. It is a figure which shows the detection signal distribution in the case where d = 17 mm, and the peeling part B is between the 6th layer and the 7th layer. It is the eddy current test result in the case of d = 17 mm with respect to the 3rd test body.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. In addition, the same reference numerals are given to the common parts in each figure, and duplicate description is omitted.

FIG. 1 is an overall configuration diagram of the interlayer peeling detection device 10 according to the first embodiment of the present invention.
In this figure, the test piece 1 is a carbon fiber reinforced plastic plate (hereinafter, simply referred to as CFRP plate 1) and has a plurality of plies.

The delamination detection device 10 of the present invention includes an excitation coil 12, a detection coil 14, an eddy current probe 16, and a generated voltage detection device 18.

The exciting coil 12 has a first axis A1 and the detection coil 14 has a second axis A2. The excitation coil 12 and the detection coil 14 are preferably square tangential coils.

The eddy current probe 16 positions the second axis A2 in parallel with the first axis A1 to hold the excitation coil 12 and the detection coil 14. Further, the eddy current probe 16 positions the plane including the first axis A1 and the second axis A2 in parallel with the surface 2 of the CFRP plate 1.
In this case, a certain gap (lift-off e) is formed between the outer surface (lower surface in this figure) of the exciting coil 12 and the detection coil 14 and the surface 2 of the CFRP plate 1. The lift-off e is 0.5 to 1.0 mm in the examples described later.
The eddy current probe 16 is preferably a non-conductive material (eg, plastic or the like).

The generated voltage detecting device 18 applies an exciting AC voltage Vin to the exciting coil 12 to detect the generated AC voltage Vout generated in the detection coil 14.

In FIG. 1, the interlayer peeling detection device 10 further includes an image processing device 20. The image processing device 20 is, for example, a computer (PC) and includes an input device (for example, a keyboard), an output device (for example, a printer, a display device), a storage device, and an arithmetic unit.
The image processing apparatus 20 detects the distribution of the RMS value (root mean square) of the generated AC voltage Vout on the surface 2 of the CFRP plate 1. Further, the image processing apparatus 20 detects delamination from a peculiar portion of strength and weakness of the RMS value.

In FIG. 1, the eddy current probe 16 has a coil spacing adjusting device 22 that changes the distance d between the axes of the exciting coil 12 and the detection coil 14. The coil spacing adjusting device 22 is used to change the inter-axis distance d suitable for the CFRP plate 1 according to the laminated structure (for example, the number of plies) of the CFRP plate 1.
With this configuration, the inter-axis distance d can be appropriately selected by the coil spacing adjusting device 22.

FIG. 2 is an overall configuration diagram of the interlayer peeling detection device 10 according to the second embodiment of the present invention.
In this example, the coil spacing adjusting device 22 of FIG. 1 is omitted, and instead, a plurality of detection coils 14 having different inter-axis distances d from the exciting coil 12 are provided.
The distances d1, d2, and d3 between the axes of the three detection coils 14 from the excitation coil 12 are, for example, 9,17,25 mm.
Other configurations are the same as those of the first embodiment.
With this configuration, the inter-axis distance d can be appropriately selected by selecting one from the plurality of detection coils 14.

FIG. 3 is an overall flow chart of the interlayer peeling detection method according to the present invention.
In this figure, the interlayer peeling detection method of the present invention has each step (step) of S1 to S5.

In the coil preparation step S1, the exciting coil 12 having the first axis A1 and the detection coil 14 having the second axis A2 are prepared.
In the positioning step S2, the second axis A2 is positioned in parallel with the first axis A1 to hold the excitation coil 12 and the detection coil 14, and the first is to the surface 2 of the test piece 1 (CFRP plate 1). The plane including the axis A1 and the second axis A2 is positioned in parallel.
In the voltage detection step S3, an AC voltage Vin is applied to the exciting coil 12 to detect the generated AC voltage Vout generated in the detection coil 14.

Further, in the distribution detection step S4, the excitation coil 12 and the detection coil 14 are moved while maintaining the distance d between the axes, and the distribution of the RMS value of the generated AC voltage Vout on the surface 2 of the test body 1 (CFRP plate 1) is detected. do.
Alternatively, in the peeling detection step S5, stripping between layers is detected from a peculiar portion of the RMS value.

Hereinafter, embodiments of the present invention will be described in detail.

(Finite element method analysis)
The potential, eddy current distribution, and magnetic field distribution in the CFRP plate were investigated by FEM analysis, and their changes due to the presence of peeling were investigated.
4A and 4B are explanatory views of an analysis model, FIG. 4A is an overall perspective view, FIG. 4B is a front view of the exciting coil 12, and FIG. 4C is a side view of the exciting coil 12.

This figure is a model in which the exciting coil 12 (in this example, a square tangential coil: e-type coil) is arranged on the CFRP plate 1. The size of the CFRP plate 1 is 100 mm in length, 80 mm in width, and 1.25 mm in thickness, and the laminated structure is [0/90] s. The exciting coil 12 has an internal region having a length, width, and height of 5 mm, and is arranged in a lift-off e (= 1 mm) at the center of the surface of the CFRP plate 1.
In the figure, the x direction represents the 0 ° direction of the CFRP plate 1, the y direction represents the 90 ° direction, and the z direction represents the thickness direction, and z = 0 is the surface 2 of the CFRP plate 1. The origin O of this coordinate system is directly below the exciting coil 12 on the surface 2.
In this analysis, the thickness of one layer of CFRP plate 1 was assumed to be 0.3 mm. Further, in the case of simulating the inter-story separation, it is assumed that there is an inter-story separation between the first layer (0 ° layer) and the second layer (90 ° layer).
Further, a point separated from the center of the exciting coil 12 in the x direction by a detection distance p is referred to as a magnetic field detection position Xp. The coordinates of the magnetic field detection position Xp are (p, 0, 0).

(Electromagnetic field when there is no peeling)
FIG. 5 is a diagram showing an eddy current distribution in the CFRP plate 1. In this figure, (A) is the first layer, (B) is the layer between the first layer and the second layer, and (C) is the second layer. Represents the real part of.

In FIGS. 5A and 5C, the dotted arrow in the figure indicates the direction of the electric current. Eddy currents flow along the fiber direction in the first and second layers due to high conductivity in the fiber direction, and flow in the thickness direction between the first and second layers to form a "butterfly loop" as a whole. You can see that. Therefore, it can be seen that the conduction in the thickness direction between the layers plays an important role in the eddy current drawing a loop.

In FIG. 5B, a region surrounded by a solid line indicates a positive current, a region surrounded by a broken line indicates a negative current, and the thickness of each line indicates the magnitude of the amount of current.
In this figure, the portion where the amount of current flowing in the thickness direction between the layers of the first layer and the second layer is large (thick line region) corresponds well to the portion where the potential measured separately is large, and the location in the thickness direction is determined by the potential gradient. It can be seen that the current to is generated. Therefore, if there is delamination between layers in the vicinity of a portion where the potential gradient is large, the flow of current in the thickness direction is obstructed.

(Electromagnetic field when there is peeling)
When simulating peeling, it was assumed that the conductivity between the first layer and the second layer in the x-direction and the y-direction was zero. Further, in the peeling portion B, the z-direction conductivity is also set to 0, and the flow of the eddy current in the thickness direction is set to 0.
As a result, it was found that the current flows so as to avoid the peeling portion B, and the amount of the current increases at the peeling end portion.

FIG. 6 is a diagram showing a real part of the eddy current distribution when the center of the peeling portion B of 20 mm × 20 mm is at the position (10, 0). In this figure, (A) shows the distribution of the current density in the x direction of the first layer, and (B) shows the distribution of the current density in the y direction of the second layer.
The shaded portion in the figure is the peeling portion B. The area surrounded by the solid line indicates the positive current density, the area surrounded by the broken line indicates the negative current density, and the thickness of the line indicates the magnitude of the current density.
From this figure, it can be seen that in the second layer, the current density in the y direction is large outside the peeling portion B because the current flows from the second layer to the first layer while avoiding the peeling portion B. Since the eddy current avoiding the peeling portion B flows in the first layer, it can be seen that the eddy current distribution in FIG. 6A extends in a certain direction.

It was investigated how the amount of change in the magnetic field due to the peeling portion B changes depending on the magnetic field detection position Xp. It is assumed that the position where the magnetic field is detected is the magnetic field detection position Xp shown in the analysis model of FIG. The center coordinate xd of the peeling portion B was changed, and the magnetic field distribution Hy in the y direction of the magnetic field at the magnetic field detection position Xp was calculated. The difference between the calculated y-direction magnetic field distribution Hy and the y-direction magnetic field distribution Hy when there is no separation is defined as the magnetic field deviation ΔHy.

FIG. 7 is a diagram showing the relationship between the center coordinate xd of the peeling portion B and the magnetic field deviation ΔHy with respect to various magnetic field detection positions Xp.
From this figure, the relationship between the magnetic field deviation ΔH and the center coordinate xd of the peeling portion B differs greatly depending on the magnetic field detection position Xp. In FIG. 7, the magnetic field deviation ΔHy becomes the largest when the magnetic field detection position Xp = 20 mm and the center coordinate xd = 10 mm of the separated portion B. That is, when an eddy current sensor in which the detection coil 14 is arranged so as to measure the magnetic field at a position 20 mm away from the center of the exciting coil 12 is used, it is large when there is a peeling portion B between the exciting coil 12 and the detection coil 14. A signal change will be obtained.

When a sensor in which the excitation coil 12 and the detection coil 14 are arranged close to each other is used as the result of the detection distance p = 0,10 mm, the magnitude of the magnetic field deviation ΔHy is smaller and the detection sensitivity to the peeling portion B is higher. It will be low.
When the distance d between the axes of the exciting coil 12 and the detection coil 14 is made too large (for example, the detection distance p = 35 mm), the magnitude of the magnetic field deviation ΔHy becomes small, and the sensitivity to the peeled portion B decreases. From the above results, it was shown that the detection sensitivity to delamination can be improved by selecting an appropriate magnetic field detection position Xp.

(experiment)
An experiment was conducted to verify whether the detection sensitivity of delamination changes by changing the distance d between the axes of the exciting coil 12 and the detection coil 14.

FIG. 8 is a schematic diagram of the experimental method. In this figure, (A) is a perspective view of the exciting coil 12 and the detection coil 14, and (B) is a side view of the exciting coil 12 and the detection coil 14 as viewed from the y-axis direction.
The test body 1 is an 8-layer CFRP orthogonal laminated board, and the laminated structure is [ _02/902 ] _s . As shown in FIG. 8B, the x-axis is defined in the 0 ° direction, the y-axis is defined in the 90 ° direction, and the z-axis is defined in the thickness direction. The size of the test piece 1 is 200 mm in length and 200 mm in width. This test body 1 was prepared by laminating a prepreg (T700SC / 2592) and pressing.

Three types of test bodies 1 having different sizes of the peeling portion B were prepared.
The first test body 1A and the second test body 1B have peeling portions B of 10 mm × 10 mm and 20 mm × 20 mm, respectively. The peeling portion B was simulated by inserting a polyimide film having a thickness of 50 μm between the 0 ° -90 ° layers of the second layer and the third layer of the laminated plate at the time of laminating. This peeling portion B was inserted in the center of the laminated plate in the xy plane.
The third test body 1C is a test piece having a peeling portion B at the end portion of the laminated plate. The peeling portion B at this end was simulated by inserting a film in the center of the side parallel to the y-axis of the laminated plate. The size of the peeling portion B was 40 mm × 40 mm, and the film was inserted between the second layer and the third layer.

For both the exciting coil 12 and the detection coil 14, a 30-turn square tangential coil having an internal region of 5 mm × 5 mm × 5 mm was prepared. The lift-off e of the eddy current probe 16 including the exciting coil 12 and the detection coil 14 was set to 0.5 mm. Let d be the distance between the axes of the center of the exciting coil 12 (first axis A1) and the center of the detection coil 14 (second axis A2), and conduct experiments for three ways of distance d = 9,17,25 mm. rice field.

An AC voltage of 4 MHz (excited AC voltage Vin) was applied to the exciting coil 12 from a waveform generator (AFG 3021C, Tektronix Inc.). The voltage generated in the detection coil 14 (generated AC voltage Vout) was measured with an oscilloscope (Picocospe5442B, Pico Technology). The 63 mm × 63 mm region around the peeled portion B of the CFRP plate 1 was scanned at 1 mm intervals to obtain the distribution of the RMS value of the generated AC voltage Vout.

FIG. 9 is an eddy current test result when d = 17 mm for the second test piece 1B.
This figure shows the distribution of the RMS value of the generated AC voltage Vout in the region of 63 mm × 63 mm. The shaded area in the figure is the peeling portion B in the sample. Further, each coordinate in the figure corresponds to the center position of the detection coil 14.
The area surrounded by the solid line indicates a portion having a large RMS value, and the region surrounded by a broken line indicates a portion having a small RMS value, and the size is indicated by the thickness of each line.

In this figure, a portion having a high RMS value of the generated AC voltage Vout is generated around the peeling portion B. This indicates that a clear increase in the detection magnetic field is observed when the center of the peeling portion B is located between the excitation coil 12 and the detection coil 14.

At d = 9 mm with respect to the second test piece 1B, variations in the RMS value of the generated AC voltage Vout are confirmed even in the sound part, and it is difficult to specify the peeling point. In the case of d = 25 mm, as in the case of d = 17 mm, an increase in the RMS value of the generated AC voltage Vout was observed around the detached portion, and it was possible to clearly distinguish it from the voltage change in the sound portion. From the above, it was shown that the detection sensitivity of the detached portion B can be improved by appropriately selecting the distance d between the axes of the exciting coil 12 and the detection coil 14.

FIG. 10 is an eddy current test result when d = 17 mm for the first test piece 1A.
The description content of this figure is the same as that of FIG.

This figure shows the distribution of the RMS value of the generated AC voltage Vout when the peeling portion B is between the second layer and the third layer. From this figure, it is possible to confirm the region where the RMS value of the generated AC voltage Vout is high in the vicinity of the peeling portion B. Therefore, as in the test result of the second test body 1B, the signal change of the peeling portion B is clear as compared with the fluctuation of the detected signal in the sound portion, and it can be seen that the inter-story peeling can be detected.

The first test piece 1A was inspected from the back surface, and the case where the interlayer peeling was between the sixth layer and the seventh layer was also tested. FIG. 11 is a diagram showing the distribution of the RMS value of the generated AC voltage Vout when d = 17 mm and the peeling portion B is between the 6th layer and the 7th layer.
From this figure, the detection signal has a higher value than the surroundings only in the peeling portion B, and it is possible to specify the presence or absence of peeling. Therefore, it was shown that peeling at the depths of the 6th and 7th layers from the CFRP surface can also be detected.

FIG. 12 is an eddy current test result when d = 17 mm for the third test piece 1C. The description content of this figure is the same as that of FIG.
From this figure, a region where the RMS value of the generated AC voltage Vout is lowered can be seen at the peeling position, and the peeling region can be specified more clearly. From FIG. 12, it was shown that not only the buried peeling but also the peeling portion B at the end can be detected by the eddy current flaw detection test.

In the present invention, an eddy current test method suitable for detecting delamination in CFRP was investigated by FEM analysis, and its effectiveness was verified by experiments.

(1) First, the potential distribution and the eddy current distribution when an eddy current was generated in the CFRP plate 1 by the exciting coil 12 (tangential coil) were investigated. It was shown that the magnitude of the potential distribution changed in the thickness direction, and the driving source of the thickness direction current required for the delamination detection of the CFRP plate 1 was clarified. It was also clarified that the eddy current draws a loop by the current flowing in the thickness direction between the layers whose fiber directions are orthogonal to each other.

(2) Next, the eddy current distribution and the magnetic field distribution in the CFRP when the detached portion B was present were investigated by FEM analysis. It was shown that if there is a detachment B, the eddy current flows in a path that avoids the detachment B. As a result, it was clarified that the expansion of the eddy current distribution occurred around the detached portion B, and as a result, the expansion of the magnetic field distribution also occurred. Further, it was shown that the amount of change in the magnetic field due to delamination differs depending on the distance d between the axes of the exciting coil 12 and the detection coil 14. When the distance d between the axes of the exciting coil 12 and the detection coil 14 is small, the sensitivity to delamination is low from the analysis and the result of d = 9 mm, but the detection sensitivity can be improved by selecting an appropriate distance d between the axes. It turned out to be.

(3) Finally, an eddy current flaw detection test using a tangier coil was performed on a CFRP orthogonal laminated plate sample having delamination. By changing the distance d between the axes of the exciting coil 12 and the detection coil 14 in various ways and selecting an appropriate distance d between the axes, the detection sensitivity to delamination is improved, and the signal change due to the variation in the conductivity of the CFRP plate 1. It was clarified that it is distinguishable from. The minimum peeling size detected in the present invention is 10 mm × 10 mm. When the peeling of this size is between the 2nd and 3rd layers of the 8-layer orthogonal laminated board and between the 6th and 7th layers, a clear change in the detection signal due to the peeling is obtained. I was able to.

By the eddy current flaw detection test method shown in the present invention, delamination of the CFRP plate 1 can be detected.

According to the present invention described above, the exciting coil 12 and the detection coil 14 are positioned on the surface 2 of the carbon fiber reinforced plastic plate 1, and the exciting AC voltage Vin is applied to the exciting coil 12 to generate the generated AC voltage in the detection coil 14. Detect Vout.
Further, it was confirmed by Examples that the delamination between the carbon fiber reinforced plastic plates 1 can be detected with high detection sensitivity according to the present invention.

It should be noted that the present invention is not limited to the above-described embodiment, and it goes without saying that various modifications can be made without departing from the gist of the present invention.

A1 1st axis, A2 2nd axis, B peeling part,
d, d1, d2, d3 Distance between axes, e lift-off (gap),
Hy y direction magnetic field distribution, ΔHy magnetic field deviation, p detection distance,
Vin excitation AC voltage, Vout generated AC voltage,
xd center coordinates, Xp magnetic field detection position,
1 Specimen (CFRP plate) 2 Surface,
10 Interlayer peeling detector, 12 Excitation coil, 14 Detection coil,
16 eddy current probe, 18 generated voltage detector,
20 Image processing device (computer), 22 Coil spacing adjustment device

Claims (7)

An exciting coil having a first axis, a detection coil having a second axis, and
The second axis is positioned parallel to the first axis to hold the excitation coil and the detection coil, and the first axis and the second axis are relative to the surface of the carbon fiber reinforced plastic plate. An eddy current probe that positions the plane in parallel, including
A delamination detection device comprising: a generated voltage detecting device for applying an exciting AC voltage to the exciting coil to detect the generated AC voltage generated in the detection coil. The interlayer separation detecting device according to claim 1, wherein the eddy current probe has a coil spacing adjusting device for changing the distance between the excitation coil and the axis of the detection coil. The interlayer separation detection device according to claim 1, further comprising the plurality of detection coils having different distances between axes from the exciting coil. The interlayer peeling detection device according to claim 1, wherein the exciting coil or the detection coil is a square tangential coil. An excitation coil having a first axis and a detection coil having a second axis are prepared.
The second axis is positioned parallel to the first axis to hold the excitation coil and the detection coil, and the first axis and the second axis are relative to the surface of the carbon fiber reinforced plastic plate. Position the planes containing in parallel,
A delamination detection method in which an exciting AC voltage is applied to the exciting coil to detect the generated AC voltage generated in the detection coil. The excitation coil and the detection coil are moved while maintaining the distance between the axes to detect the distribution of the RMS value of the generated AC voltage on the surface.
The method for detecting delamination according to claim 5, wherein delamination is detected from a peculiar portion of the RMS value. The interlayer peeling detection method according to claim 5, wherein the distance between the axes of the excitation coil and the detection coil is changed according to the laminated structure of the carbon fiber reinforced plastic plate.

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