JP5311766B2 - Interface inspection apparatus and interface inspection method - Google Patents

Description

  The present invention relates to an apparatus and method for nondestructively inspecting a specimen with ultrasonic waves, and more particularly to an interface inspection apparatus and an interface inspection method for inspecting a boundary state of a composite material composed of two or more substances. is there.

  For example, the following Non-Patent Document 1 pages 211 to 212 show an apparatus and method for inspecting the state of the boundary surface between an aluminum plate and a honeycomb core, while focusing an ultrasonic beam with an array probe. The state of the boundary surface is inspected by electronic scanning. The method shown as an example in Non-Patent Document 1 uses a frequency of 25 MHz while the thickness of the aluminum plate is 1 mm. Since the sound speed of aluminum is about 6300 m / s, the wavelength is about 0.25 mm. That is, a short wavelength of about 1/4 of the thickness of the aluminum plate is used.

  Further, on page 228 of Non-Patent Document 1 below, a method for inspecting a honeycomb material using ultrasonic waves is shown. Here, an inspection method by a transmission method and an inspection method by a resonance method using a continuous wave are shown.

Japan Nondestructive Inspection Association, "Ultrasonic Flaw Test III" pp. 211-212, pp. 218, Japan Nondestructive Inspection Association, 2001

  If the frequency is increased and the wavelength is shortened as in the conventional device as described above, the echo from the surface of the aluminum plate and the echo from the bottom surface can be separated in time, so the test with a thin plate thickness Although it is possible to inspect the adhesion state of the front surface or the back surface of the body, the probe becomes expensive at a frequency of about 25 MHz. Further, in order to perform digital signal processing, it is necessary to sample the signal. However, if the frequency is high, the sampling frequency needs to be increased, and the transceiver is also expensive. Furthermore, if the wavelength is short, there is a difficulty that the apparatus setting needs to be performed very strictly.

  Further, the inspection by the transmission method can be applied even when the frequency is low, but it is necessary to use two probes facing each other, and there is a problem that the position adjustment is difficult when the specimen is large. It is also necessary to scan two probes simultaneously. Furthermore, it is necessary to assemble a measurement system in which the test body is sandwiched between two probes. When the test body is large, there is a problem that the entire measurement system becomes large.

  Furthermore, in the inspection by the resonance method using a continuous wave, the whole test specimen vibrates, and therefore it is difficult to identify a defective bonding state. In addition, it is considered difficult to apply to inspections that require fine resolution.

  The present invention has been made to solve the above-described problems, and provides a boundary surface inspection apparatus and a boundary surface inspection method using an ultrasonic reflection method that can relatively easily set a measurement system and are inexpensive. It is.

The present invention relates to an ultrasonic probe that transmits ultrasonic waves to a test body and receives ultrasonic waves propagated in the test body, and drives the ultrasonic probe and uses the ultrasonic probe. a transceiver for receiving an electrical signal from the scanning mechanism for scanning within a predetermined range set the ultrasonic probe, the ultrasonic waves from electrical signals and said scanning mechanism from the transceiver A signal processing unit that processes position information of the probe, and the ultrasonic probe receives multiple echoes generated by multiple reflections at two or more boundary surfaces of the specimen, and performs the signal processing. The unit gates the position where the state of the boundary surface of the specimen appears conspicuously with respect to the multiple echo , obtains the amplitude of the signal in the gate, and position information of the ultrasonic probe from the scanning mechanism unit And create Cscan from the amplitude of the signal in the gate, Based on the in-plane period of the Cscan formed by the magnitude of the amplitude of the signal in the gate, an area where there is no adhesive and an unbonded area where the adhesive is present but not adhered are obtained at the boundary surface of the specimen. Mel, the boundary surface inspection apparatus and method wherein the.

  According to the present invention, it is possible to provide a boundary surface inspection apparatus and method using an ultrasonic reflection method that can relatively easily set a measurement system and is inexpensive. Inexpensive probes and transmitters / receivers can be used, and the setting of the equipment is relatively easy.Frequency where the wavelength is the same as the test specimen thickness or longer than the test specimen thickness is used. It is possible to provide a boundary surface inspection apparatus and method that can be specified.

Embodiment 1 FIG.
This invention demonstrates the interface inspection apparatus and method by Embodiment 1 referring FIG. 1 ~ FIG. In the first embodiment, a case where the bonding state between the skin of the honeycomb material and the core is inspected using the amplitude of multiple echoes will be described. In addition, what is described as “probe” in the text means an ultrasonic probe.

  1 is a diagram showing a configuration of a boundary surface inspection apparatus according to Embodiment 1 of the present invention. FIG. 2 is a diagram for explaining multiple echoes when the probe is in the air portion of the core. FIG. 3 is a diagram illustrating an example of multiple echoes received when a probe is in the air portion of the core. FIG. 4 is a diagram for explaining multiple echoes in the case where a probe is provided on the pillar portion of the core. FIG. 5 is a diagram illustrating an example of multiple echoes received when a probe is in the pillar portion of the core. FIG. 6 is a diagram for explaining multiple echoes when the probe is in a region where there is no adhesive. FIG. 7 is a diagram illustrating an example of multiple echoes received when the probe is in a region where there is no adhesive. FIG. 8 is a diagram comparing multiple echoes. FIG. 9 is a Cscan created based on multiple echoes obtained in an experiment targeting an area where there is no adhesive and an in-gate signal.

  The interface inspection apparatus according to the present invention shown in FIG. 1 includes a probe 1 that is an ultrasonic probe, a honeycomb material skin 2, a honeycomb material core 3, an adhesive agent 4, a contact medium 5, a transceiver 6, and signal processing. Unit 7 and scanning mechanism unit 8. The probe 1 is connected to a transmitter / receiver 6 and is fixed to a scanning mechanism unit 8. The adhesive 4 adheres the skin 2 and the core 3. The transceiver 6 is connected to the signal processing unit 7. The contact medium 5 is filled between the probe 1 and the skin 2.

  Next, the operation will be described. An electrical signal for exciting the probe 1 is emitted from the transceiver 6 to excite the probe 1. In the probe 1, the electric signal is converted into an ultrasonic wave, and the ultrasonic wave propagates into the contact medium 5. As the contact medium 5, water, glycerin, oil, or the like is used. However, the contact medium 5 is not limited thereto, and any material may be used as long as it can efficiently transmit ultrasonic waves.

  The ultrasonic wave that has propagated through the contact medium 5 is reflected by the skin 2. The reflected wave propagates in the direction of the probe 1, is converted into an electric signal by the probe 1, and is received as an echo by the transmitter / receiver 6. The received echo is stored in the signal processing unit 7 together with the position information of the probe 1. The position information of the probe 1 may be information from the scanning mechanism unit 8 or information obtained by another method. It is only necessary to know the relative positional relationship between the probe 1 and the test body (2 to 4) when the echo is transmitted and received.

  After the echo and the position information of the probe 1 are stored in the signal processing unit 7, the scanning mechanism unit 8 moves the probe 1. The probe 1 is excited at the probe position after the movement, and echoes are similarly received. The received echo and the position information of the probe 1 are stored in the signal processing unit 7. This operation is repeated over the scanning range. When the scanning of the probe 1 is completed, the received echo and the position information of the probe 1 are stored in the signal processing unit 7.

  The signal processing unit 7 obtains the state of the boundary surface between the skin 2 and the core 3 based on the received echo and the position information of the probe 1. This operation and the inspection method of the boundary surface will be described below.

  The echo reflected and received by the skin 2 is a multiple echo at a frequency that satisfies a certain condition. This will be described with reference to FIG. FIG. 2 is a diagram when the probe 1 is in the air portion of the core 3. In the figure, reference numeral 10 denotes a pillar portion of the core 3. The ultrasonic wave that has propagated through the contact medium 5 is reflected by the surface of the skin 2, but part of the energy propagates into the skin 2 as shown in FIG. 2. Then, the light is reflected from the bottom surface of the skin 2 and received. This echo is shown as “B1” in FIG. 2 in the sense that it is reflected once at the bottom and received.

  Further, there is an echo that is reflected from the bottom surface of the skin 2, reflected from the surface of the skin 2, and reflected again from the bottom surface of the skin 2 and received. This echo is shown as “B2” in FIG. 2 in the sense that it is reflected twice at the bottom and received. Furthermore, there is also an echo that is reflected and received three times on the bottom surface, and is shown as “B3”. Of course, there are echoes received by three or more reflections, but they are omitted in FIG. In this way, the echo reflected and received by the bottom surface and the surface of the skin 2 is referred to as “multiple echo” in the sense of an echo accompanying multiple reflection.

If the thickness of the skin 2 is d, the propagation distance difference between B1 and B2 is 2d. In addition, the phase of the ultrasonic wave is reversed in both the bottom surface and the surface reflection of the skin 2. Therefore, when the wavelength of the ultrasonic wave in the skin 2 is λ, when the propagation distance difference is an integral multiple of the wavelength λ,
2d = λ × n (n = 1, 2, 3,...) (1)
B1 and B2 are intensifying relationships. Since the propagation distance difference between B2 and B3 is also 2d, B2 and B3 are in a mutually reinforcing relationship when equation (1) holds. Thus, the expression (1) is a condition for strengthening multiple echoes.

  When Expression (1) is satisfied, multiple echoes that are continuous in time are received as shown in FIG. In FIG. 3, the amplitude of the multiple echo is shown to decrease with time, but the main reason for the decrease in amplitude is that the spread of the ultrasonic beam and the reflectivity due to the bottom and surface of the skin 2 are not 100%. is there.

  FIG. 4 is a diagram for explaining multiple echoes when the probe 1 is located at the position of the core pillar 10. The mechanism for generating multiple echoes is the same as in FIG. 2, but the reflection on the bottom surface of the skin 2 is disturbed because the pillar 10 of the core 3 is on the bottom surface of the skin 2. Due to this disturbance, the amplitude of B1 becomes small. Similarly, the amplitudes of B2 and B3 are reduced. As a result, a multiple echo having a large amplitude decrease with time is received. FIG. 5 shows multiple echoes in this case.

  In this way, if there is an object that disturbs reflection on the bottom surface of the epidermis 2, the amplitude of the multiple echo with respect to time will be greatly reduced. If this characteristic is used and the magnitude of the amplitude of the multiple echoes is relatively evaluated, the air portion of the core 3 of the honeycomb material and the column 10 portion of the core 3 can be distinguished.

  Further, by using the amplitude of the multiple echoes, not only the air portion and the column 10 portion of the core 3 can be identified, but also the state of the boundary surface between the skin 2 and the core 3 can be obtained. This is shown in FIG. FIG. 6 is a diagram for explaining multiple echoes in the case where an area without the adhesive 4 is created by simulating peeling on the boundary surface between the skin 2 and the core 3. As shown in FIG. 6, when there is no adhesive 4, there is no factor that disturbs reflection on the bottom surface of the skin 2 even if the probe 1 is on the pillar portion of the core 3. Therefore, the multiple echo is received with a large amplitude as shown in FIG.

  A comparison of these multiple echoes is shown in FIG. FIGS. 8A to 8C show multiple echoes arranged side by side when the probe 1 is in the air portion of the core 3, the column 10 portion of the core 3, and the region without the adhesive. And gated at the same time. As shown in FIG. 8, the amplitude in the gate changes depending on the position of the probe 1. In the air portion of the core 3 and in the region where there is no adhesive, the amplitude of the multiple echo in the gate is large, and in the portion of the column 10 of the core 3, the multiple echo amplitude is small. Thus, the bottom surface state of the epidermis 2 can be investigated by using the amplitude of multiple echoes.

  When the probe 1 is located at the column 10 of the core 3, the reason why the amplitude of the multiple echoes decreases with time is the number of reflections. In one reflection, even if the bottom surface state of the skin 2 is hardly known, a slight difference in the bottom surface state of the skin 2 appears as the number of reflections is repeated two times, three times,. That is, even a slight difference is accumulated and appears as a detectable difference. In FIG. 8, the gate position is not in the rising portion of the multiple echo but in a portion that is slightly delayed in time, but the multiple reflection integration effect does not sufficiently appear in the rising portion of the multiple echo. In order to obtain a multi-echo integration effect, it is desirable to gate a portion that is delayed in time. However, if the delay is excessive, effects such as attenuation of the ultrasonic wave and spread of the ultrasonic beam appear. Considering these, a gate is hung at a position where a difference in the bottom surface state of the skin 2 appears remarkably.

  FIG. 9 shows experimental results using the boundary surface detection apparatus according to this embodiment. The experiment was performed using a probe 1 having a frequency of 5 MHz and a diameter of 3 and water as the contact medium 5 with a thickness of 0.3 mm. A digital ultrasonic flaw detector was used for the transceiver 6, and a personal computer was used for the signal processor 7. The test body is a honeycomb material in which the skin 2 and the core 3 are aluminum. The thickness of the skin 2 is 1.27 mm, and the interval between the pillars 10 of the core 3 is about 6 mm. In addition, a specimen was prepared by cutting out the adhesive 4 only at a certain part, simulating peeling. The probe 1 was scanned at a pitch of 0.2 mm in a 35 mm × 25 mm region using the scanning mechanism unit 8.

  Since the thickness of the skin 2 is 1.27 mm, if n = 2 in the equation (1), the multiple echoes strengthen each other when the wavelength λ is 1.27 mm. Since the sound speed of aluminum (longitudinal wave sound speed) is about 6300 m / s, the frequency spectrum of the multiple echoes received by the probe 1 has a characteristic showing a peak at 4.96 MHz. Therefore, if the probe 1 having a frequency of 5 MHz has a certain bandwidth, this multiple echo can be sufficiently received. If n = 1 in Equation (1), the wavelength λ is 2.54 mm, and the frequency spectrum corresponding to this wavelength is 2.48 MHz. Therefore, it is possible to use the probe 1 having a frequency of 2.5 MHz. However, since it was difficult to obtain the probe 1 having a small φ at this frequency, the probe 1 of 5 MHz was used in the experiment. When φ is large, the spatial resolution is degraded. Thus, the method using multiple echoes also has the advantage that the value of n in equation (1) can be selected according to various conditions.

  9D is a top view (Cscan) created by exciting the probe 1 and applying a gate at a position of 4 μs to 5 μs and expressing the maximum amplitude value in the gate in shades. is there. Further, (a) to (c) on the left side of FIG. 9 exemplify three multiple echoes that create Cscan. Cscan shows that the larger the in-gate amplitude of multiple echoes, the closer it is to black. In the peripheral portion of this Cscan, a portion with a large amplitude and a portion with a small amplitude appear periodically. This period coincides with the interval between the pillars 10 of the core 3 of the honeycomb material. That is, as described above, the amplitude of the multiple echo increases when the probe 1 is in the air portion of the core 3, and the multiple echo amplitude increases when the probe 1 is in the column 10 portion of the core 3. The Cscan has become smaller and has such a cycle. If the spatial resolution is good, the large-amplitude portion becomes a hexagon, which is a Cscan that more reflects the shape of the honeycomb material, but in this experiment it was not a hexagon but a shape close to a circle.

  There is a large amplitude area at the center of Cscan. This region is a region where the adhesive 4 is cut out. That is, as described above, the probe 1 is located in a region where the adhesive 4 is not present, and the amplitude of the multiple echo is increased, resulting in such a Cscan.

  As described above, by using the boundary surface inspection apparatus according to this embodiment and performing the inspection based on the amplitude of the multiple echoes, the bottom surface of the skin 2 can be obtained even at a frequency where the wavelength is the same as the thickness of the skin 2. There is an effect that the state can be obtained. If the bottom surface state of the skin 2 can be obtained using only the amplitude of the signal in the gate, the boundary surface can be inspected without creating Cscan. For example, a certain threshold value may be provided, and an inspection apparatus that determines that there is an abnormality on the bottom surface of the skin 2 when the amplitude of the in-gate signal exceeds the threshold value may be used.

  As described above, the experimental results for the region without the adhesive 4 of the honeycomb material are shown, and it is shown that the bottom surface state of the skin 2 can be obtained by using the boundary surface inspection apparatus and method in this embodiment. However, the present invention is not limited to the region where the adhesive 4 is not present. Other states can be detected as long as the bottom surface state of the skin 2 is reflected in the amplitude of the multiple echo.

  Further, the case of obtaining the bottom surface state of the skin 2 has been described. However, since multiple echoes are generated by reflection of the bottom surface and the surface of the skin 2, it is natural that the surface state of the skin 2 can be obtained. .

  Furthermore, although the case where the honeycomb material is used as a test body has been described here, the present invention is not limited to the honeycomb material. As long as the state of the surface and the bottom surface of the test specimen is reflected in the amplitude of the multiple echo, it can be applied to other test specimens.

  Finally, the probe 1 will be described. In this embodiment, the probe 1 has been described assuming a probe used in a normal nondestructive inspection. However, a so-called electromagnetic ultrasonic probe that excites ultrasonic waves with electromagnetic force may be used. In this case, the contact medium 5 is not necessary. Moreover, you may use what is called an air ultrasonic probe which can excite the intense ultrasonic wave in the air. Even in this case, the contact medium 5 is unnecessary.

Embodiment 2. FIG.
A boundary surface inspection apparatus and method according to Embodiment 2 of the present invention will be described with reference to FIGS. In the second embodiment, as in the first embodiment, a case where the bonding state between the skin of the honeycomb material and the core is inspected will be described. In addition, what is described as “probe” in the text means an ultrasonic probe.

  FIG. 10 is a diagram for explaining multiple echoes when there is a probe in an unbonded region. FIG. 11 shows an example of multiple echoes received when the probe 1 is in an unbonded area. FIG. 12 is a diagram showing Cscans created based on multiple echoes obtained in experiments targeting unbonded regions and in-gate signals. In each figure, the same or corresponding parts as those in the first embodiment are denoted by the same reference numerals.

  Since the configuration of the boundary surface inspection apparatus according to the second embodiment is the same as that of the first embodiment, the description thereof is omitted. In the second embodiment, as the bottom surface state of the skin 2 in the first embodiment, an unbonded region where the adhesive 4 is present but not bonded is assumed. FIG. 10 is a diagram for explaining multiple echoes when the probe 1 is in an unbonded region. Reference numeral 9 in FIG. 10 denotes an inclusion that is between the adhesive 4 and the core 3 and prevents the adhesion between the two.

  The operation of this embodiment will be described. As in the first embodiment, the ultrasonic wave propagated through the contact medium 5 is reflected by the surface of the skin 2, but part of the energy propagates into the skin 2. Then, the light is reflected from the bottom surface of the skin 2 and received. However, due to the inclusion 9, the reflection from the bottom surface of the epidermis 2 changes, and the change is reflected in the multiple echoes. If the bottom surface reflection of the epidermis 2 is weakened by the inclusions 9, the amplitude of the multiple echoes becomes small. Conversely, if the bottom surface reflection of the epidermis 2 becomes strong due to the inclusions 9, the amplitude of the multiple echoes increases. This is shown in FIGS. 11A and 11B. The principle that multiple echoes are received is the same as in the first embodiment.

  In any case, if the probe 1 is in an unbonded area, multiple echoes are affected. Therefore, when the probe 1 is scanned and a Cscan is generated by multiplying multiple echoes in the same manner as in the first embodiment, the spatial periodicity appearing in the peripheral portion of the Cscan in FIG. By observing the collapse of the spatial periodicity, the bottom surface state of the skin 2 can be obtained.

  A test body provided with an unbonded region with inclusions 9 was prepared and tested. The experimental results are shown in FIG. The display of the experimental conditions and the results is the same as in FIG. 9, and the diagram (d) on the right side of FIG. 12 is a top view (Cscan) created by expressing the maximum amplitude value in the gate in shades, and (a) on the left side. (C) shows three examples of multiple echoes that created Cscan. In the peripheral portion of Cscan in FIG. 12, a portion with a large amplitude and a portion with a small amplitude appear periodically in the gate. This is the period of the core 3 as in the case of FIG.

  On the other hand, in the Cscan of FIG. 12, there is no region with a large amplitude at the center, and the periodicity is clearly broken. This area is an unbonded area. In this experiment, the result in the case where the bottom surface reflection of the epidermis 2 is weakened by the inclusion 9 is obtained. That is, as described above, the probe 1 is on the non-bonded region, and the amplitude of the multiple echo is reduced, resulting in such a Cscan. Therefore, even if the wavelength is the same as the thickness of the skin 2 by performing the inspection based on the collapse of the spatial periodicity of the multiple echoes using the boundary surface inspection apparatus and method in this embodiment, The bottom surface state of the skin 2 can be obtained.

  As described above, the experimental results for the unbonded region are shown, and it is shown that the bottom surface state of the skin 2 can be obtained by using the boundary surface inspection apparatus and method according to this embodiment. However, the present invention is not limited to the unbonded area. If the bottom surface state of the epidermis 2 is reflected in the spatial periodicity of multiple echoes, other states can be detected.

  Further, the case of obtaining the bottom surface state of the skin 2 has been described. However, since multiple echoes are generated by reflection of the bottom surface and the surface of the skin 2, it is natural that the surface state of the skin 2 can be obtained. .

  Furthermore, although the case where the honeycomb material is used as a test body has been described here, the present invention is not limited to the honeycomb material. As long as the state of the surface and bottom surface of the specimen is reflected in the spatial periodicity of multiple echoes, it can be applied to other specimens.

  Finally, the probe 1 will be described. Similarly to the first embodiment, in the second embodiment, a so-called electromagnetic ultrasonic probe of a type that excites an ultrasonic wave with an electromagnetic force may be used. Moreover, you may use what is called an air ultrasonic probe which can excite the intense ultrasonic wave in the air. In these cases, the contact medium 5 is not necessary.

It is a figure which shows the structure of the interface inspection apparatus by Embodiment 1 of this invention. It is a figure for demonstrating the multiple echo in case a probe exists in the air part of the core in Embodiment 1 of this invention. It is a figure which shows an example of the multiple echo received when a probe exists in the air part of the core in Embodiment 1 of this invention. It is a figure for demonstrating the multiple echo in case a probe exists in the pillar part of the core in Embodiment 1 of this invention. It is a figure which shows an example of the multiple echo received when a probe exists in the pillar part of the core in Embodiment 1 of this invention. It is a figure for demonstrating the multiple echo in case the probe exists in the area | region where there is no adhesive agent in Embodiment 1 of this invention. It is a figure which shows an example of the multiple echo received when a probe exists in the area | region where there is no adhesive agent in Embodiment 1 of this invention. It is the figure which compared the multiple echo in Embodiment 1 of this invention. It is a figure which shows Cscan produced based on the multiple echo obtained by experiment for the area | region which does not have the adhesive agent in Embodiment 1 of this invention, and the signal in a gate. It is a figure for demonstrating the multiple echo in case the probe exists in the non-bonding area | region in Embodiment 2 of this invention. It is a figure which shows an example of the multiple echo received when there exists a probe in the unbonded area | region in Embodiment 2 of this invention. It is a figure which shows Cscan produced based on the multiple echo obtained by the experiment for the non-adhesion area | region in Embodiment 2 of this invention, and the signal in a gate.

Explanation of symbols

  1 (ultrasonic) probe, 2 epidermis, 3 core, 4 adhesive, 5 contact medium, 6 transceiver, 7 signal processing unit, 8 scanning mechanism unit, 9 inclusion, 10 pillars.

Claims (2)

An ultrasonic probe that transmits ultrasonic waves to the test body and receives ultrasonic waves propagated through the test body;
A transceiver that drives the ultrasound probe and receives electrical signals from the ultrasound probe;
A scanning mechanism that scans the ultrasonic probe within a predetermined range; and
A signal processing unit that processes electrical signals from the transceiver and positional information of the ultrasonic probe from the scanning mechanism unit;
With
The ultrasonic probe receives multiple echoes caused by multiple reflections at two or more interfaces of the specimen;
The signal processing unit gates the multiple echoes at a position where the state of the boundary surface of the specimen appears prominently , obtains the amplitude of the signal in the gate, and the ultrasonic probe from the scanning mechanism unit Cscan is created from the position information of the signal in the gate and the amplitude of the signal in the gate, and there is no adhesive on the boundary surface of the specimen based on the in-plane period of the Cscan formed by the amplitude of the signal in the gate Mel and the region, there is an adhesive but the unbonded areas not adhered determined,
A boundary surface inspection device characterized by that. Ultrasonic waves are transmitted into the specimen by an ultrasonic probe that is scanned within a set range, and multiple echoes generated by multiple reflections at two or more boundary surfaces of the specimen are detected by the ultrasonic probe. Receiving with a probe, and applying a gate to the position where the state of the boundary surface of the specimen appears prominently for the multiple echo, obtaining the amplitude of the signal in the gate, and the position information of the ultrasonic probe, A Cscan is created from the amplitude of the in- gate signal , and based on the in-plane period of the Cscan formed by the magnitude of the amplitude of the in- gate signal , an adhesive-free region on the boundary surface of the specimen and an adhesive boundary surface inspection method is is characterized in that the unbonded area that is not bonded Mel determined.

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