JP3782410B2 - Ultrasonic flaw detection method and apparatus using Rayleigh wave - Google Patents

Description

  The present invention relates to an ultrasonic flaw detection method and an apparatus for inspecting internal defects and physical properties without destroying the object by reflected waves, transmitted waves, or diffracted waves from the outside of the object. .

  Recently, safety of various devices and facilities has been demanded, and it has become important to quickly and accurately find flaws that may cause accidents. The nondestructive inspection method is a method for examining flaws and physical properties without destroying the object.The ultrasonic flaw detection method, which is a type of nondestructive inspection method, applies ultrasonic waves from the outside of the object and reflects the reflection. The interior is examined by receiving and analyzing waves, transmitted waves, or diffracted waves.

  Conventional ultrasonic flaw detection methods can detect the presence of flaws with some sensitivity, but it has been difficult to obtain information on the shape and size of flaws. Therefore, a TOFD (Time of Flight Diffraction) method is expected as an ultrasonic flaw detection method capable of measuring the size of a flaw more accurately. In the TOFD method, a pair of an ultrasonic probe for transmission and an ultrasonic probe for reception are arranged opposite to each other with a certain distance from the surface of an object, and the transmission probe is used. Ultrasound is emitted into the object. A wave that travels directly on the surface of the object (lateral wave), and a bottom surface reflected wave that is reflected from the bottom surface of the object, as well as a diffracted wave that is generated by the ultrasonic waves that enter the edge of the flaw when a flaw exists in the object Is received by a receiving probe, and the position and size of the flaw are to be measured based on the propagation time of these waves.

  A decibel drop method, an evaluation level method, a DGS method, and the like have been widely used for measuring the dimensions of flaws in conventional ultrasonic flaw detection tests. Since these methods perform evaluation based on the distance traveled by the probe and the echo height, the measurement accuracy is affected by the probe's beam profile, scan pitch, or tilt angle of the defect. It was inevitable. On the other hand, since the TOFD method uses a propagation time capable of relatively high accuracy measurement, it can be expected to improve the accuracy of flaw dimension measurement.

  FIG. 6 shows an outline of various wave propagation paths in the TOFD method. A pair of transmitting probe 10 and receiving probe 20 are arranged on the surface of the measurement object 30 at a predetermined distance, and a slit-shaped vertical flaw 31 having a height D exists between them. Assume that you want to. At this time, the lateral wave LT transmitted directly through the surface of the object 30 is first received by the wave receiving probe 20, and the upper end 31a (the side closer to the surface on which the ultrasonic probes 10 and 20 are arranged) is not continuously received. The upper end diffracted wave LU from the end of the flaw and the lower end diffracted wave LL from the lower end 31b of the flaw (the end of the flaw far from the surface on which the ultrasonic probes 10 and 20 are arranged) are received. Based on the reception time of each signal, the position Z (distance from the surface) of the upper end 31a of the flaw 31 and the position [Z + D] (distance from the surface) of the lower end 31b are obtained. Here, for the sake of simplicity, for example, assuming that the flaw 31 is in the center between the transmitting probe 10 and the receiving probe 20, the surface between each probe and the flaw is assumed. Since the distances along the line are X and Y, and X = Y (assuming S), the following equations 1 and 2 are obtained.

  However, in the equation, Tlu and Tll are respectively diffracted at the end of the upper end diffracted wave and the lower end diffracted wave as ultrasonic waves from the transmitting probe, and then diffracted as a diffracted wave to the receiving probe. Vl is the propagation speed of the longitudinal wave in the object. From these equations 1 and 2, the height D of the flaw is estimated by the following equation, for example.

  Therefore, when D is sufficiently smaller than Z (D << Z), the height D of the flaw is approximately given by the following equation (4).

  In the equation, θ is an average incident angle when the diffracted wave is incident on the receiving probe. At this time, the difference in propagation time between the upper end diffracted wave and the lower end diffracted wave is radiated as an ultrasonic wave from the transmitting probe and reaches the receiving probe as a diffracted wave is transformed from the above equation (4). Then, the following formula is obtained. Therefore, the detected time difference is caused by the height of the flaw (for example, Non-Patent Document 1).

Masakazu Takahashi, “Study on Ultrasonic Bevel Inspection”, Tokyo University of Science Doctoral Dissertation (September 2002)

  As described above, in the TOFD method, as shown in, for example, Equation 3 to Equation 4, an attempt is made to measure the position and size of the defect based on the propagation time difference between the upper end diffracted wave and the lower end diffracted wave. . However, when the height D of the flaw is reduced, for example, as shown in Formula 5, the difference between the propagation times of the upper end diffracted wave and the lower end diffracted wave, that is, Tll-Tlu is reduced. As a result, the received signals of the upper end diffracted wave and the lower end diffracted wave overlap with each other in time, and it is difficult to estimate the dimension D that is not based on the difference in propagation time. there were. For this reason, as described in Non-Patent Document 1, for example, in the TOFD method for steel materials using ultrasonic waves of 5 MHz, generally, although it depends on the flaw detection conditions, approximately 3 mm is a lower limit dimension for measuring the height of a flaw. Therefore, it was difficult to measure the size of a flaw smaller than this. Further, in the conventional TOFD method, even if the positions of the upper end and the lower end of the flaw can be estimated, it is difficult to obtain information for evaluating the shape and state of the flaw.

  The present invention has been made against the background of the above circumstances, and by using the Rayleigh wave, it is possible to measure these defects by solving these problems and to evaluate the defects at the same time. It is an object of the present invention to provide an ultrasonic flaw detection method and an apparatus for the same.

As described above, of the ultrasonic flaw detection methods using Rayleigh waves according to the present invention, the invention according to claim 1 is a pair of ultrasonic probe for transmitting wave and ultrasonic probe for receiving wave. When a child is placed on one surface of the target object at a certain distance, an ultrasonic wave is radiated from the transmitting probe into the target object, and a defect exists in the target object, the end of the defect In the ultrasonic flaw detection method of performing ultrasonic flaw detection by receiving a diffracted wave generated by ultrasonic waves incident on the wave receiving probe,
Of the ultrasonic waves received by the receiving ultrasonic probe, a part of the ultrasonic waves incident on one end of the defect is mode-converted and propagated along the inner surface of the defect as a Rayleigh surface wave, A part of this Rayleigh surface wave is mode-converted again at the edge of the defect to detect ultrasonic waves re-radiated into the object, and the defect is evaluated based on the detection signal. .

  The ultrasonic flaw detection method using the Rayleigh wave according to claim 2 is the method according to claim 1, wherein the reradiated ultrasonic wave is detected together with the diffracted wave generated at at least one end of the defect, and reradiated. Further, the size along the inner surface of the defect is estimated based on the propagation time between the ultrasonic wave and the diffracted wave being emitted from the transmitting probe as ultrasonic waves to the receiving probe. It is characterized by that.

  The ultrasonic flaw detection method using the Rayleigh wave according to claim 3 is the invention according to claim 1 or 2, wherein the ultrasonic wave radiated into the object from the transmission probe is mainly a longitudinal wave, In this case, the longitudinal wave component of the diffracted wave generated at the end of the ultrasonic wave and the longitudinal wave component of the ultrasonic wave re-radiated at the end of the defect are respectively detected.

  The invention of the ultrasonic flaw detection method using Rayleigh waves according to claim 4 is characterized in that the length D along the inner surface of the defect is estimated by one or both of the following approximate expressions (a) and (b). An ultrasonic flaw detection method using Rayleigh waves.

However,
Tlr: The ultrasonic longitudinal wave component radiated from the transmission probe is incident on one end of the defect from the transmission probe, and a part of the ultrasonic longitudinal wave is subjected to mode conversion, and the Rayleigh surface wave. And propagates along the inner surface of the defect, and at the other end of the defect, a part of this Rayleigh surface wave is mode-converted again into an ultrasonic wave and re-radiated into the object to receive the wave as a ultrasonic longitudinal wave component. Propagation time to the tentacle.
Tlu: The longitudinal component of the ultrasonic wave radiated from the transmission probe is transferred from the transmission probe at the upper end of the defect (the end of the defect near the surface on which the ultrasonic probe is disposed). Propagation time to the receiving probe as diffracted wave longitudinal wave component.
Tll: The longitudinal component of the ultrasonic wave radiated from the transmission probe is at the lower end of the defect (end of the defect far from the surface where the ultrasonic probe is arranged) from the transmission probe. Propagation time to the receiving probe as diffracted wave longitudinal wave component.
Vr: Propagation speed of Rayleigh surface wave in the object.
Vl: Longitudinal wave propagation speed in the object.
θ: An average incident angle when each longitudinal wave component is incident on the receiving probe.

  The ultrasonic flaw detection method using the Rayleigh wave according to claim 5 is the invention according to any one of claims 1 to 4, wherein any one of the transmitting probe and the receiving probe is used. The transmitter probe is scanned in the front-rear direction along a line substantially parallel to the line connecting the transmitter probe and receiver probe, either alone or at the same time. An ultrasonic wave is radiated from the probe and received by the receiving probe. At this time, the detection signal has a detection signal whose amplitude periodically varies with the position of the probe. It is determined that the received signal is an ultrasonic wave re-radiated by the Rayleigh surface wave propagated along the line.

  An ultrasonic flaw detector using a Rayleigh wave according to claim 6 comprises a pair of a transmitting ultrasonic probe and a receiving ultrasonic probe, and further comprising the transmitting ultrasonic probe. A part of the ultrasonic wave radiated from the contact and incident on one end of the defect of the object is mode-converted and propagated along the inner surface of the defect as a Rayleigh surface wave. It is characterized by comprising means capable of detecting the ultrasonic wave re-radiated into the object by the mode conversion of the part again.

  The ultrasonic flaw detector using the Rayleigh wave according to claim 7 is the invention according to claim 6, wherein the detecting means detects a diffracted wave diffracted at the edge of the defect together with the re-radiated ultrasonic wave. Is possible.

As described above, according to the ultrasonic flaw detection method of the present invention, a part of the ultrasonic wave incident on one end of a defect such as a flaw among ultrasonic waves received by the ultrasonic probe for receiving waves is obtained. Mode-converted and propagated along the inner surface of the defect as a Rayleigh surface wave, and a part of this Rayleigh surface wave is mode-converted again at the other end of the defect to detect ultrasonic waves re-radiated into the object. Since the defect is evaluated based on the detection signal, it becomes possible to measure the size of the defect even smaller than that of the conventional TOFD method, and the defect can be evaluated together.
Further, according to the ultrasonic flaw detection apparatus of the present invention, the re-radiated ultrasonic wave can be detected, and the above-described effect can be obtained with certainty.

  In the TOFD method, a part of ultrasonic waves incident on one end of a defect such as a flaw in the TOFD method is mode-converted and propagated along the inner surface of the defect as a Rayleigh surface wave, and this Rayleigh surface wave is transmitted at the other end of the defect. We found that a part of the image was re-radiated into the object as an ultrasonic wave after mode conversion again. FIG. 1 is an example in which this phenomenon is reproduced by computer simulation, and shows a vector diagram of ultrasonic vibration displacement over time (FIGS. A to d). A part of the longitudinal ultrasonic wave incident on the upper end of the flaw, which is a defect, is mode-converted to generate a Rayleigh surface wave, which propagates toward the lower end not along the inner surface of the flaw. Part of the Rayleigh surface wave that has reached the lower end is mode-converted again and re-radiated as an ultrasonic wave from the lower end into the object, and part of the wave is reflected at the lower end of the scratch toward the upper end along the inner surface of the scratch. Propagate. When the Rayleigh surface wave reaches the upper end, re-emission and reflection are performed again, and similar re-emission and reflection are repeated until the Rayleigh surface wave is attenuated. Similarly, the ultrasonic longitudinal wave incident on the lower end of the flaw repeats the propagation along the inner surface, the reflection and the re-radiation when the Rayleigh surface wave is generated by the mode conversion. As a result, a lot of information about the flaw can be obtained from the received wave signal of the ultrasonic wave re-radiated by the Rayleigh surface wave propagated along the inner surface of the flaw.

  In the present invention, a part of the ultrasonic wave incident on one end of a defect such as a flaw is mode-converted and propagated along the inner surface of the defect as a Rayleigh surface wave, and a part of the Rayleigh surface wave is transmitted at the other end of the defect. Using the phenomenon of mode conversion again and re-radiation into the object as an ultrasonic wave, the ultrasonic wave re-radiated by the Rayleigh surface wave propagated along the inner surface of the defect is detected, and based on the detection signal Measure and evaluate the dimensions of defects.

  FIG. 2 shows that the ultrasonic longitudinal wave L radiated from the transmission probe 10 is incident on the upper end 31a of a vertical slit 31 in the object 30, and a part of the ultrasonic longitudinal wave is a mode. The Rayleigh surface wave R is converted and propagated along the inner surface of the flaw 31, and a part of the Rayleigh surface wave is mode-converted again at the lower end 31 b of the flaw 31, and is regenerated into the object 30 as the ultrasonic longitudinal wave L. The propagation path which is radiated and reaches the wave receiving probe 20 is shown. In order to simplify the description, for example, a case is assumed in which a flaw is in the center between a pair of a transmitting probe and a receiving probe. Similarly to the object shown in FIG. 5, the position of the upper end 31a of the flaw 31 is Z (distance from the surface) and the position of the lower end 31b is [Z + D] (distance from the surface). Further, if the distance between the probe and the scratch on the surface of the object is X and Y, respectively, X = Y (assuming S). The propagation time Tlr from 10 to the receiving probe 20 is given by the following equation. In the equation, Vr is the propagation speed of the Rayleigh surface wave in the object.

  In this case, it is assumed that the flaw is in the center between the pair of probes. The ultrasonic wave propagation time Tlr is incident on the lower end of the flaw and propagates through the flaw surface as a Rayleigh surface wave. The ultrasonic waves that have passed through the propagation path are simultaneously superimposed and received. Then, either one of the transmitting probe and the receiving probe is used alone, or both of the probes are simultaneously moved in the front-rear direction (transmitting probe and receiving probe). When moving in a direction substantially parallel to the line connecting the transducers, the amplitude of the ultrasonic wave reception signal mode-converted again from the Rayleigh surface wave exhibits periodic fluctuations depending on the position of the probe. This is because the propagation path length of the ultrasonic wave incident on the upper end of the flaw and re-radiated from the lower end of the flaw, and the propagation path length of the ultrasonic wave incident on the lower end of the flaw and re-radiated from the upper end of the flaw first, This is because the ultrasonic waves that have passed through both paths interfere with each other and are added and received because they change differently with the movement of the probe. On the other hand, the amplitudes of the upper end diffracted wave and the lower end diffracted wave show a gentle change corresponding to the change in the propagation distance due to the movement of the position of the probe.

In the present invention, an ultrasonic wave reception signal is scanned while either one of the probe for transmission and the probe for reception is scanned alone, or both probes are simultaneously scanned in the front-rear direction. Provides the function to record and measure the position of the probe along with the change in the position of the probe. The received signal of the ultrasonic wave re-radiated by the Rayleigh surface wave propagated in this manner can be discriminated.
Regarding the ultrasonic wave re-radiated by the Rayleigh surface wave propagated along the inner surface of the defect, regarding the propagation time Tlr from the transmitting probe to the receiving probe and the upper end diffracted wave of the defect, The time difference between the propagation time Tlu from the transmitting probe to the receiving probe is given by the following equation.

  Therefore, the length D along the inner surface of the defect is obtained from the time difference between Tlr and Tlu as shown in the following equation (10).

  On the other hand, the time difference between the above-described propagation time Tlr and the propagation time Tll from the probe for transmitting the bottom edge diffracted wave of the defect to the probe for receiving is given by the following equation.

  Therefore, the length D along the inner surface of the defect is also obtained from the time difference between Tlr and Tll as follows.

  For the same defect, the defect height D (hereinafter referred to as D1) obtained by the formula (3) or the formula (4) focusing on the upper end diffraction wave and the lower end diffraction wave, for example, by the conventional TOFD method, The situation of the defect can also be evaluated by comparing the length D (hereinafter referred to as D2) along the inner surface of the defect obtained by the equation (10) or (12). In the case of D1≈D2, it is estimated that the defect is substantially linear, in the case of D1 <D2, it is estimated that the defect is not linear but is curved, for example, and in the case of D1> D2 It is estimated that the defect is interrupted between the upper end and the lower end. In addition, when the top and bottom diffracted waves are received, the ultrasonic wave re-radiated by the Rayleigh surface wave propagated along the inner surface of the defect is weak or not received regardless of the position of the probe. It is estimated that the defect is in a closed state or a state close thereto.

  The ratio of the propagation velocity Vl of the longitudinal wave and the propagation velocity Vr of the Rayleigh surface wave differs depending on the material. For example, in the case of a steel material, it is about 2.1 (Vl≈2.1 Vr). Therefore, for example, assuming that the incident angle θ of the ultrasonic wave is 60 °, cos θ = 0.5, so that the propagation time Tlr of the ultrasonic longitudinal wave obtained by mode conversion again from the Rayleigh surface wave with respect to a minute defect and the lower end, for example, The time difference from the propagation time Tll of the diffracted wave is expressed by the following equation from the equation (11).

  On the other hand, for example, the time difference between the propagation time Tll of the lower-end diffracted wave and the propagation time Tlu of the upper-end diffracted wave used in the conventional TOFD method is expressed by the following equation from Equation 5 under the same conditions.

  Therefore, in the present invention, a time difference of about 1.6 times can be secured for the same defect under the above conditions, compared with the conventional TOFD method. Therefore, when the time resolution for measuring the propagation time of each ultrasonic signal is the same, In the present invention, the size can be measured up to a smaller defect which is approximately 0.6 (≈1 / 1.6) times that of the conventional TOFD method.

Hereinafter, an embodiment of the present invention will be described.
FIG. 3 is a schematic diagram of the ultrasonic flaw detector according to the present invention, which includes a transmitting probe 10 and a receiving probe 20. The transmission probe 10 is connected to the transmission control unit 1, and the reception probe 20 is connected to the reception control unit 2. The transmission control unit 1 and the reception control unit 2 are integrally configured, and each control the transmission probe 10 and the reception probe 20, and receive the received wave. Wave signal processing is performed.
The transmission control unit 1 and the reception control unit 2 include a common timer (not shown), and the ultrasonic wave radiated from the transmission probe 10 is received by the reception probe 20. It is possible to measure the time to wave. The receiving control unit 2 is connected to a display unit 3 for displaying a waveform based on the received signal. As the display unit 3, an appropriate display device such as a CRT or an LCD can be used. Moreover, the display part 3 may be comprised with a touch panel, and the input by a user may be enabled.

Next, the operation of the ultrasonic flaw detector will be described.
A desired ultrasonic wave is emitted from the transmission probe 10 to the object 30 by the control of the transmission control unit 1. When the flaw 31 exists in the object 30, as described above, a Rayleigh wave propagating on the surface of the diffracted wave or the flaw is generated by the flaw 31, and the Rayleigh wave is re-radiated as an ultrasonic wave. These diffracted waves and re-radiated ultrasonic waves are received by the receiving probe 20, and a received signal is sent to the receiving control unit 2. The reception control unit 2 controls the display unit 3 on the basis of the received signal so that the reception pattern can be displayed on the display unit 3. The display unit 3 can recognize ultrasonic waves and diffracted waves re-radiated based on the received pattern. Therefore, the reception control unit 2 and the display unit 3 also function as means capable of detecting the re-radiated ultrasonic wave and the diffracted wave diffracted at the end of the flaw. The reception control unit 2 detects the re-radiated ultrasonic wave and the diffracted wave by the timer based on the detection of the re-radiated ultrasonic wave and the diffracted wave diffracted at the edge of the flaw. It is also possible to obtain a propagation time from the transmitting probe to the receiving probe, which is radiated as an ultrasonic wave, and to function as a calculation unit that calculates the dimension along the inner surface of the flaw. Note that the receiving control unit 2 may have a function of detecting the re-radiated ultrasonic wave and the diffracted wave diffracted at the end of the flaw based on the received signal.

  FIG. 4 shows a test object including a vertical slit-shaped flaw having a height of 3 mm in the first embodiment of the present invention, and a 5 MHz ultrasonic longitudinal wave is radiated and diffracted by a receiving probe. It is an example of the signal waveform of the longitudinal wave ultrasonic wave which received etc. The longitudinal wave (LR) re-radiated by the Rayleigh surface wave that propagates along the inner surface that does not follow the lateral wave (LT), upper-end diffracted wave (LU), and lower-end diffracted wave (LL) is recorded. Yes. In this embodiment, since the height of the flaw is small, the received signals of the upper end diffracted wave and the lower end diffracted wave are superimposed, which makes it difficult to estimate the height that cannot be achieved by the conventional TOFD method. However, in the present invention, the time of reception of the longitudinal wave component of the upper-end diffracted wave and the time difference from the reception time of the ultrasonic longitudinal wave re-radiated by the Rayleigh surface wave that propagated along the inner surface immediately before the reception time By applying the formula, the length along the inner surface of the flaw could be estimated accurately.

  FIG. 5 shows a signal waveform of a longitudinal ultrasonic wave radiated by a 5 MHz ultrasonic longitudinal wave and received by a receiving probe for a specimen containing an unknown flaw in the second embodiment of the present invention. It is an example. The longitudinal wave (LR) re-radiated by the Rayleigh surface wave that propagates along the inner surface that does not follow the lateral wave (LT), upper-end diffracted wave (LU), and lower-end diffracted wave (LL) is recorded. Yes. Here, since the upper end diffracted wave and the lower end diffracted wave are recorded separately, the height of the flaw is estimated to be about 5 mm by applying the formula (3) or (4), for example, by the conventional TOFD. . On the other hand, the length along the inner surface of the flaw was estimated to be about 7 mm by applying the formula (10) or the formula (12) according to the present invention. Therefore, it is estimated here that the shape of the flaw is curved, for example, not linear.

(A)-(d) figure is a figure which shows the simulation result of the Rayleigh surface wave which propagates the inner surface of a defect according to elapsed time. It is a schematic diagram of the propagation path of the ultrasonic wave including the Rayleigh surface wave propagating along the inner surface of the defect in the present invention. It is a figure which shows the Example of the ultrasonic flaw detector of this invention. It is a figure which similarly shows the received signal waveform in 1st Example. It is a figure which similarly shows the received signal waveform in 2nd Example. It is a figure which shows the outline | summary of the propagation path of the ultrasonic wave utilized by the conventional TOFD method.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Control part for transmission 2 Control part for reception 3 Display part 10 Probe for transmission 20 Probe for reception 30 Target object 31 Scratch 31a Scratch upper end 31b Scratch bottom

Claims (7)

A pair of ultrasonic transducers for transmitting and receiving waves and a ultrasonic probe for receiving waves are arranged at a certain distance on one surface of the object, and the transmitting probe is placed in the object. Ultrasonic flaw detection is performed by receiving a diffracted wave generated by the ultrasonic wave incident on the edge of the defect when the defect is present in the object and receiving the diffracted wave with the receiving probe. In the method
Of the ultrasonic waves received by the receiving ultrasonic probe, a part of the ultrasonic waves incident on one end of the defect is mode-converted and propagated along the inner surface of the defect as a Rayleigh surface wave, A feature is that ultrasonic waves re-radiated into the object are detected by mode-converting a part of the Rayleigh surface wave again at the edge of the defect, and the defect is evaluated based on the detection signal. An ultrasonic flaw detection method using Rayleigh waves. The re-radiated ultrasonic wave is detected together with a diffracted wave generated at at least one end of the defect, and the re-radiated ultrasonic wave and the diffracted wave are radiated as an ultrasonic wave from a transmission probe. 2. The ultrasonic flaw detection method according to claim 1, wherein a Rayleigh wave is used to estimate a dimension along the inner surface of the defect based on a propagation time to the wave receiving probe. The ultrasonic waves radiated into the object from the probe for transmission are mainly longitudinal waves, and mainly the longitudinal wave component of the diffracted wave generated at the edge of the defect and the ultrasonic waves re-radiated at the edge of the defect. The ultrasonic flaw detection method using Rayleigh waves according to claim 1 or 2, wherein the longitudinal wave component is mainly detected. An ultrasonic flaw detection method using Rayleigh waves, wherein the length D along the inner surface of the defect is estimated by one or both of the following approximate expressions (a) and (b):

However,
Tlr: The ultrasonic longitudinal wave component radiated from the transmission probe is incident on one end of the defect from the transmission probe, and a part of the ultrasonic longitudinal wave is subjected to mode conversion, and the Rayleigh surface wave. And propagates along the inner surface of the defect, and at the other end of the defect, a part of this Rayleigh surface wave is mode-converted again into an ultrasonic wave and re-radiated into the object to receive the wave as a ultrasonic longitudinal wave component. Propagation time to the tentacle.
Tlu: The longitudinal component of the ultrasonic wave radiated from the transmission probe is transferred from the transmission probe at the upper end of the defect (the end of the defect near the surface on which the ultrasonic probe is disposed). Propagation time to the receiving probe as diffracted wave longitudinal wave component.
Tll: The longitudinal component of the ultrasonic wave radiated from the transmission probe is at the lower end of the defect (end of the defect far from the surface where the ultrasonic probe is arranged) from the transmission probe. Propagation time to the receiving probe as diffracted wave longitudinal wave component.
Vr: Propagation speed of Rayleigh surface wave in the object.
Vl: Longitudinal wave propagation speed in the object.
θ: An average incident angle when each longitudinal wave component is incident on the receiving probe. Either one of the transmitting probe and the receiving probe is used alone or both probes are connected simultaneously, and the transmitting probe and the receiving probe are connected. Ultrasound is emitted from the transmitting probe while scanning in the front-rear direction along a direction substantially parallel to the line, and received by the receiving probe, at which time the position of the probe And a detection signal whose amplitude periodically fluctuates and discriminates that the detection signal is a received signal of an ultrasonic wave re-radiated by a Rayleigh surface wave propagated along the inner surface of the defect. Item 5. An ultrasonic flaw detection method using Rayleigh waves according to any one of Items 1 to 4. An ultrasonic probe for transmitting and a receiving ultrasonic probe to be paired; and an ultrasonic wave radiated from the transmitting ultrasonic probe and incident on one end of the defect of the object A part of the sound wave is mode-converted and propagated along the inner surface of the defect as a Rayleigh surface wave, and a part of this Rayleigh surface wave is re-radiated into the object by being mode-converted again at the other end of the defect. An ultrasonic flaw detector using Rayleigh waves, characterized in that it comprises means capable of detecting ultrasonic waves. The ultrasonic flaw detection apparatus using Rayleigh waves according to claim 6, wherein the detecting means is capable of detecting a diffracted wave diffracted at an edge of the defect together with the re-radiated ultrasonic wave.

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