JP2883051B2 - Ultrasonic critical angle flaw detector - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to the field of ultrasonic flaw detection.

[0002]

2. Description of the Related Art As shown in FIG. 4, when an ultrasonic beam 9 is incident on a liquid-solid interface, a part of the energy of the beam 9 propagates into the solid, but most of the energy is incident on the interface. Reflects on the opposite side at an angle equal to the angle. At this time,
Although the intensity of the reflected beam 10 hardly depends on the angle of incidence, the intensity sharply drops at a specific angle of incidence θ, and the intensity is minimized. This is a phenomenon that occurs because much of the energy of the ultrasonic beam 9 incident at this specific angle θ is converted into a solid surface wave 11 at the boundary surface. Θ at this time is referred to as an ultrasonic critical angle. The sound speed of the ultrasonic beam 9 in the liquid is V _L , and the sound speed of the solid surface wave 11 is V _SW
Then, the ultrasonic critical angle θ is expressed by the following equation. θ = Sin ⁻¹ (V _L / V _SW ) (1)

If the sound velocity in a solid is V _t and the Poisson's ratio is ν, the following equation is established. V _SW = ((0.874 + 1.12ν) / (1 + ν)) V _t (2) When the rigidity of the solid is G and the density is ρ, the following equation is established. V _t = √ (G / ρ) (3)

As described above, since the ultrasonic critical angle θ is an amount uniquely determined from the rigidity G and the density ρ of a solid,
By measuring the value, it can be checked whether or not the material of the solid has changed. The change in the material in this case is caused by, for example, accumulation of damage due to fatigue or creep, or progress of embrittlement. The method of inspecting the change of the solid material according to the value of the ultrasonic critical angle θ is called an ultrasonic critical angle flaw detection method.

FIG. 5 shows a conventional technique for performing an ultrasonic critical angle flaw detection method. Referring to FIG.
2 and the receiving-side probe 13 are plane probes for converting ultrasonic waves into parallel beams. The two probes are arranged such that the intersection 6 of the sound axis (the center in the direction in which the ultrasonic wave propagates) is located on the liquid-solid interface, and the probe is positioned with respect to the normal 8 of the interface passing through the intersection 6. Scanning is performed while maintaining the symmetric orientation.

[0006] Ultrasonic flaw detector 14 and XY recorder 15
Calculates the relationship between the orientations of the transmitting probe 12 and the receiving probe 13 and the intensity of the reflected wave measured by the receiving probe 13, and determines the ultrasonic wave when the reflected wave intensity is minimized. This is a device that detects the incident angle of the beam.

As described above, when performing the ultrasonic critical angle flaw detection method, (a) the transmission-side probe 12 and the reception-side probe 1
The intersection 6 of the sound axis with 3 is made to coincide with the liquid-solid interface, and (b) the transmitting probe 12 with respect to the normal 8 of the liquid-solid interface while maintaining the above condition (a). It is necessary to perform scanning so that the direction (incident angle) of the target and the direction (reflection angle) of the receiving probe 13 are equal.

FIG. 6A shows the relationship between the position of the intersection 6 of the sound axes and the reflected wave intensity, and FIG. 6B shows the relationship between the directions of the two probes 12 and 13 and the reflected wave intensity. Angle θ = about 30.7 °
It is a graph shown by taking the case of as an example. In FIG. 9A, when the intersection 6 of the sound axis coincides with the liquid-solid interface, that is, when d = 0, the incident wave intensity sharply decreases at the position of the ultrasonic critical angle θ. The intensity is extremely low as compared with the intensity at other angles of incidence, but the degree decreases as the intersection 6 of the sound axis moves away from the liquid-solid interface.

In FIG. 1B, when the direction of the transmitting probe 12 and the direction of the receiving probe 13 with respect to the normal line 8 of the liquid-solid interface deviate, the ultrasonic critical angle It is shown that the degree of decrease in the incident wave intensity at θ is worse. From these results, for accurate measurement,
It can be seen that the above conditions (a) and (b) are necessary.

In FIG. 5A, when d is positive, that is, when the transmitting probe 12 and the receiving probe 13 approach the liquid-solid interface, the intensity of the reflected wave is reduced. The reason for the increase is that the propagation distance of the ultrasonic wave in the liquid is shortened and the attenuation is reduced.

[0011]

As described above, for accurate measurement, the above conditions (a) and (b) must be satisfied, but the intersection 6 of the sound axis is located at the transmitting end. Since it is determined from the geometrical arrangement of the probe 12 and the receiving probe 13, it is very difficult to complete the accuracy. Further, since the probes 12 and 13 need to scan with the liquid-solid interface as the center of rotation,
The mechanism was very complicated. Further, the planar probe used for the transmitting probe 12 and the receiving probe 13 has a large beam diameter (an orthogonal cross-sectional dimension of the transmitted ultrasonic beam, which is substantially equal to the transducer dimension), Since the smallest one is about 10 mm, in the measurement of the area smaller than the incident area of the beam, information of the peripheral area of the target part is also superimposed and measured, so that accurate measurement is difficult.

[0012]

In order to solve the above-mentioned problems, the present invention provides (a) a transmitting-side probe and a receiving-side probe comprising a focused ultrasonic probe; Both probes are installed at a position and a direction where the intersection of the sound axis of the probe and the focus of the two probes coincide with each other, the intersection of the sound axes is determined on the measurement surface of the measurement object, and (C) moving between the pedestal and the object to be measured in the direction normal to the measurement surface, and It is characterized by comprising a part of the ultrasonic beam incident on the measurement target from the probe and an ultrasonic mask for passing only the beam reflected by the measurement target surface.

As described above, a focusing ultrasonic probe is used as the transmitting probe and the receiving probe, and the two probes are set so that the intersection of the respective sound axes and the focal points of the two probes coincide with each other. By placing the stylus on the pedestal and making the angle of incidence and reflection of the ultrasonic beam equal to the normal to the measurement surface, measurement can be performed with the best ultrasonic reception sensitivity Becomes Further, by moving the ultrasonic mask, an ultrasonic beam having a desired incident angle and a desired reflection angle can be extracted without changing the positions and directions of the two probes. In addition, the focusing type ultrasonic probe is composed of an arc-shaped vibrator or an acoustic lens, and has a function of focusing ultrasonic waves at a certain angle with respect to the sound axis, not parallel to the sound axis. is there. Usually, the focal size of a focused ultrasonic probe is smaller than the beam diameter of a plane probe, and there are also those having a diameter of 1 mm or less.

[0014]

FIG. 1 is a block diagram of an embodiment of an ultrasonic critical angle probe according to the present invention. In FIG. 1, the transmission-side probe 1 and the reception-side probe 2 have arc-shaped concave surfaces, and their contours are circular. A line passing through the center of the transmitting probe 1 and perpendicular to the surface of the probe 1 is the transmitting sound axis 4, and similarly passes through the center of the receiving probe 2 and extends on the surface of the probe 2. The vertical line is the receiving-side sound axis 5. The transmitting probe 1 is focused on the transmitting sound axis 4, and the receiving probe 2 is focused on the receiving sound axis 5.

The transmitting probe 1 and the receiving probe 2 are fixed to the pedestal 16, and their positions and orientations satisfy all of the following conditions (A) to (D). Has been adjusted. (A) The transmission-side sound axis 4 and the reception-side sound axis 5 intersect at an intersection 6. (B) The intersection 6 of the sound axes is the focal point of the transmitting probe 1 and the focal point of the receiving probe 2. (C) The intersection 6 of the sound axes is located on a boundary surface (hereinafter referred to as a measurement surface) 7 of the measurement object. (D) The angle θ between the normal line 8 of the measurement surface 7 passing through the intersection 6 of the sound axes and the above two kinds of sound axes 4 and 5 is equal.

As shown in FIG. 2, an ultrasonic mask 3 made of an ultrasonic shielding plate is provided between the pedestal 16 and the measurement surface 7 to be measured. And the ultrasonic mask 3
Is provided with a window 3 ′ that allows only a part of the ultrasonic beam from the transmitting probe 1 and the reflected beam of the beam reflected by the measurement surface 7 to pass. By moving the ultrasonic mask 3 in the direction of the normal line 8 by a moving means (not shown), it becomes possible to extract only the ultrasonic wave incident on the measurement surface at a desired angle. Specifically, when the ultrasonic mask 3 is moved to the measurement surface 7 side, an ultrasonic beam having a large incident angle and a large reflection angle is extracted.
Is moved away from the measurement surface 7, an ultrasonic beam having a small incident angle and a small reflection angle is extracted.

Next, a procedure for performing the ultrasonic critical angle flaw detection by the above-described apparatus will be described. As described above, the ultrasonic critical angle flaw detection method is based on the difference in ultrasonic critical angle between a reference material having a known material (for example, a material having the same composition as the material to be measured and having no change in material) and the material to be measured. Since it is intended to evaluate the change in the material of the material to be measured, it is usual that the ultrasonic critical angle of the material to be measured cannot be grasped at the time of measurement. Therefore,
When performing the ultrasonic critical angle flaw detection with this apparatus, the measurement is performed on the assumption that the ultrasonic critical angle θ _C of the measurement target material is equal to the ultrasonic critical angle θ _{C0 of the} reference material. Specifically, as shown in FIG. 3, the transmission side search is performed such that the angle between the measurement side sound axis 4 and the reception side sound axis 5 and the normal line 8 of the measurement surface becomes the ultrasonic critical angle θ _{C0 of the} reference material. The probe 1, the receiving probe 2, and the pedestal 16 are set.

As described above, even if the positions and the like of the transmission-side probe 1 and the reception-side probe 2 are set based on the ultrasonic critical angle θ _C0 of the reference material, the ultrasonic mask 3 can be used in this apparatus. Since the beam can be moved along the normal line 8 to change the angle of the incident beam from the transmitting probe 1 from θ _C0 −α to θ _C0 + α,
If θ _C0 −α ≦ θ _C ≦ θ _C0 + α, it becomes possible to detect the ultrasonic critical angle θ _C of the material to be measured.

The ultrasonic critical angle θ _{C of the} material to be measured is θ
If the angle is not in the range of _C0 -α to θ _C0 + α, the angle cannot be detected. Therefore, α is set to a relatively large value by using the transmitting probe 1 and the receiving probe 2 having large dimensions in advance. It is good to keep. α can be obtained from the diameter D and the focal length L of the transmission-side probe 1 and the reception-side probe 2 by the following formula. α (degree) = Tan ^-1 (D / 2L) (4)

[0020]

According to the present invention, since the probe is previously set at an appropriate position and direction, it is possible to easily create the best condition of the ultrasonic reception sensitivity, and to complete the measurement accuracy. It becomes possible to be. Further, in addition to the above configuration, by employing an ultrasonic mask, it becomes possible to extract an ultrasonic beam having a desired incident angle and a desired reflection angle without changing the position and the direction of the probe. No mechanism is required. Further, by employing the focusing type ultrasonic probe, it becomes possible to input an ultrasonic beam having a small beam diameter, so that highly accurate measurement can be performed even in a minute area.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of a transmitting probe, a receiving probe, and a pedestal according to an embodiment of the present invention.

FIG. 2 is a diagram showing a moving state of an ultrasonic mask according to one embodiment of the present invention.

FIG. 3 is an explanatory diagram relating to detection of an ultrasonic critical angle according to an embodiment of the present invention.

FIG. 4 is a diagram illustrating the concept of ultrasonic critical angle flaw detection.

FIG. 5 is a configuration diagram of a conventional apparatus for performing ultrasonic critical angle flaw detection.

FIG. 6 is a graph showing a relationship between a measurement state and a reflected wave intensity in the ultrasonic critical angle flaw detection method.

[Explanation of symbols]

 Reference Signs List 1, 12 Transmitter probe 2, 13 Receiver probe 3 Ultrasonic mask 3 'Window of ultrasonic mask 4 Transmitting sound axis 5 Receiving sound axis 6 Intersection of sound axis 7 Measurement surface to be measured 8 Measurement surface normal 9 Incident beam 10 Reflected beam 11 Solid surface wave 14 Ultrasonic flaw detector 15 XY recorder 16 Pedestal

Continuation of the front page (72) Inventor Yasuo Kida 1-1-1, Wadazaki-cho, Hyogo-ku, Kobe-shi, Hyogo Pref. 58) Field surveyed (Int.Cl. ⁶ , DB name) G01N 29/00-29/28

Claims (1)

(57) [Claims] 1. A transmitting probe and a receiving probe comprising a focused ultrasonic probe, and (b) an intersection of a sound axis of both probes and a focal point of both probes. The two probes are installed at the position and direction to be matched, the intersection of the sound axes is determined on the measurement surface of the measurement target, and the sound axes of both probes are equiangular with respect to the normal to the measurement surface. (C) a part of the ultrasonic wave which is moved between the pedestal and the object to be measured in a direction normal to the measurement surface and is incident on the object to be measured from the transmitting probe. An ultrasonic critical angle flaw detector comprising: a beam; and an ultrasonic mask that allows only the beam reflected by the surface to be measured to pass.