JP6467811B2 - Ultrasonic flaw detection method - Google Patents

Description

The present invention relates to an ultrasonic flaw detection method , and more particularly to a non-contact ultrasonic flaw detection method that does not use a contact medium such as water or oil.

  In ultrasonic flaw detection in which a defect generated in a subject is detected with ultrasonic waves, an ultrasonic oscillator or ultrasonic wave is used to efficiently cause the ultrasonic wave to enter or exit from the subject. Usually, a contact medium such as water or oil is interposed between the geophone and the subject surface. However, it is difficult to interpose a contact medium in a high-temperature subject or a fast-moving subject, and the so-called non-contact type in which the oscillator and the geophone are separated from the subject and an air layer is interposed therebetween. It is necessary to perform ultrasonic flaw detection.

  Patent Document 1 discloses a device for preventing a decrease in flaw detection accuracy due to attenuation of ultrasonic waves in an air layer in non-contact ultrasonic flaw detection.

JP2008-128965

  However, according to the knowledge of the inventors, in the case of non-contact ultrasonic flaw detection, the use of a focus probe or the like that converges normally used ultrasonic waves to the focal point often reveals the presence or absence of defects. Sometimes it was impossible to judge.

  SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide an ultrasonic flaw detection method and an ultrasonic flaw detection method that can accurately detect defects in non-contact ultrasonic flaw detection.

  As a result of intensive studies on the reason why the presence or absence of defects cannot be accurately determined in non-contact ultrasonic flaw detection, the inventors have found the following reasons. That is, since the sound velocity in the air layer is much slower than the sound velocity in the subject, the ultrasonic wave is refracted greatly in the subject even when the incident angle is small according to Snell's law. At this time, the longitudinal wave has a refraction angle of more than the critical angle and almost reflects off the surface of the subject. However, the transverse wave generated upon incidence on the subject becomes a refraction wave without being reflected. This reflected wave (noise reflected wave) interferes with the transmitted wave transmitted through the subject, thereby causing an erroneous determination when determining the presence or absence of a defect.

The present invention has been made based on the above knowledge, and in the ultrasonic flaw detection method of the present invention, the radius of curvature is such that the oscillation surface converges the oscillating ultrasonic wave via an air layer on one surface of the subject . An ultrasonic oscillator having an arc surface is opposed to the ultrasonic wave receiver, and an ultrasonic wave receiver is opposed to the other surface of the subject via an air layer so that a longitudinal oscillation wave oscillated from the ultrasonic oscillator is generated. The transmitted wave that has passed through the specimen is received by the ultrasonic wave receiver, and the transmitted wave of the longitudinal wave composed of the ultrasonic wave emitted as the longitudinal wave from the center of the oscillation surface of the ultrasonic oscillator at this time, and the ultrasonic wave in a transverse wave refraction wave generated from the ultrasonic wave emitted as a longitudinal wave from the end remote from the center of the oscillation surface of the oscillator, the intensity detection of the transmitted wave of the longitudinal wave from the arrival of the transmitted wave of the longitudinal wave previously when noise reflected wave consisting of transverse wave refraction wave arrives And limited between at determines the presence of a defect in the subject than the intensity of the transmitted wave of the longitudinal wave is received oscillation within the detection time.

In the present invention , the time for detecting the intensity of the transmitted wave is limited between the arrival of the transmitted wave and before the time when the reflected noise wave arrives. Therefore, the transmission is performed before the reflected noise wave interferes with the transmitted wave. Wave intensity detection is performed. Therefore, the influence of the noise reflected wave on the transmitted wave is eliminated, and the presence or absence of a defect in the subject can be determined more accurately than the intensity of the transmitted wave.

  As described above, according to the present invention, it is possible to accurately detect defects that are not affected by noise reflected waves in non-contact ultrasonic flaw detection.

It is a schematic sectional drawing explaining one Embodiment of this invention. It is a figure which shows the simulation model which shows the advancing path | route of a transmitted wave. It is a figure which shows the simulation model which shows the advancing path | route of a noise reflected wave. It is a figure which shows an example of the received waveform which set the intensity | strength detection time of this invention. It is a schematic plan view of a subject showing a scanning path of ultrasonic flaw detection. It is a figure which shows intensity distribution of the transmitted wave obtained by the intensity detection time of this invention. It is a figure which shows an example of the receiving waveform which set the conventional intensity | strength detection time. It is a figure which shows intensity distribution of the transmitted wave obtained by the conventional intensity detection time.

  The embodiment described below is merely an example, and various design improvements made by those skilled in the art without departing from the gist of the present invention are also included in the scope of the present invention.

  FIG. 1 shows an example in which a defect in a subject is detected by non-contact ultrasonic flaw detection. In FIG. 1, an ultrasonic oscillator 2 is opposed to a plate-like subject 1 having a constant thickness with an interval on one plate surface 1 a and an interval is provided on the other plate surface 1 b of the subject 1. The ultrasonic geophone 3 is opposed. Therefore, the ultrasonic wave (thick arrow in the figure) oscillated from the ultrasonic oscillator 2 enters the subject 1 from the plate surface 1a of the subject 1 through the air layer, passes through the subject 1, and passes through the plate surface. The light is emitted from 1b and is received by the ultrasonic receiver 3 through the air layer. If there is a defect in the subject 1, the intensity of the transmitted wave received by the ultrasonic receiver 3 is reduced, so that the presence or absence of the defect can be determined by detecting this.

  A simulation model of such a non-contact type ultrasonic flaw detection is considered with reference to FIGS. 2 and 3, the ultrasonic oscillator 2 has an arc surface having a radius of curvature R so that the oscillation surface 2a converges the oscillation ultrasonic wave. The ultrasonic receiver 3 also has a vibration receiving surface 3a having a circular arc surface similar to the oscillation surface 2a.

  The ultrasonic wave emitted as a longitudinal wave from the central portion of the oscillation surface 2a of the ultrasonic oscillator 2 passes through an air layer of a distance A as shown by a thick arrow in FIG. The light enters the center substantially perpendicularly (incident angle is zero) and passes through the subject 1 having a thickness Y as a longitudinal wave. The longitudinal transmitted wave is incident on the ultrasonic receiver 3 through the air layer at a distance A from the center of the other surface 1b of the subject 1 again.

  The ultrasonic wave emitted as a longitudinal wave from the end portion away from the center portion of the oscillation surface 2a of the ultrasonic oscillator 2 passes through an air layer at a distance L1 as shown by a thick arrow in FIG. The incident light enters the surface 1a at an incident angle θ1, and generates a transverse refracted wave having a refraction angle θ2. The transverse refracted wave is transmitted through the distance L2 within the subject 1 and reaches the side surface of the subject 1 and is reflected there, and is transmitted as a noise reflected wave through the distance L3 within the subject 1 and transmitted as shown in FIG. , And enters the ultrasonic geophone 3 through the air layer of the distance A.

The distances L1, L2, and L3 are calculated as follows.
L1 = (R− (RA) / cos θ1
L2 = (X + (R−A) * tan θ1) / sin θ2
L3 = ((Y− (X + (RA) * tan θ1)) / tan θ2) / cos θ2
Here, when C = 340 m / s and the specimen is an acrylic resin, Ct = 2730 m / s and Cs = 1430 m / s. 2 and 3 are set to R = 40 mm, 2X = 30 mm, Y = 30 mm, A = 25 mm, θ1 = 10.2 °, and θ2 = 47.59 °. Furthermore, six burst waves at 330 KHz are used as ultrasonic waves, and the duration is 18.2 μs.

  Therefore, while the longitudinal wave of the burst ultrasonic wave is emitted from the ultrasonic oscillator 2 and is incident on the ultrasonic wave receiver 3 as a transmitted wave through the path of FIG. 2, a noise reflected wave is transmitted through the path of FIG. Whether to enter the ultrasonic geophone 3 is calculated below.

The time t1 until the transmitted wave enters the ultrasonic wave receiver through the path of FIG. 2 is calculated by the following equation (1).
t1 = A / C + Y / Ct + A / C = 156.76 (μs) (1)
Considering the duration of six burst ultrasonic waves, the time during which the transmitted wave is incident on the ultrasonic wave receiver through the path shown in FIG. 2 is 156.76 (μs) after emission from the ultrasonic oscillator. To 174.94 (μs).

On the other hand, the time t2 until the noise reflected wave reaches the ultrasonic wave receiver through the path of FIG. 3 is calculated by the following equation (2).
t2 = L1 / C + L2 / Cs + L3 / Cs + A / C = 170.21 (μs) (2)
According to this, the noise reflected wave that follows the path of FIG. 3 reaches and enters around the 4.4th wave while the transmitted wave is incident on the ultrasonic wave receiver 3, and the transmitted wave and the noise reflected wave are incident. May interfere with each other and strengthen or weaken each other, and the intensity of the transmitted wave may fluctuate, and the determination of the presence or absence of a defect may be erroneous.

  Therefore, in the present embodiment, the time for detecting the intensity of the transmitted wave is limited to the time from when the transmitted wave arrives until before the noise reflected wave arrives. That is, as shown in FIG. 4, the transmitted wave intensity detection time td1 is limited to only the head part of the transmitted wave that is not affected by the noise reflected wave (for example, four transmitted waves). Note that the vibration receiving sensitivity is increased in order to obtain a sufficient transmitted wave intensity at the head of the transmitted wave. With such a setting, as shown in the plan view of FIG. 5, the ultrasonic oscillator 2 and the ultrasonic receiver 3 are opposed to the plate surface of the rectangular acrylic plate 1 as the subject as described above. When the entire plate surface is scanned as shown by the arrows in the figure, the intensity distribution of the transmitted wave is uniform as shown in FIG. In addition, the shading in FIG. 6 has shown the strength of the transmitted wave. However, the dark part of the peripheral part of the acrylic plate is a part with low transmitted wave intensity.

  On the other hand, when the transmission wave intensity detection time td2 is set long (FIG. 7) as in the prior art, the entire surface of the acrylic board having no defect is the same as described above due to interference of noise reflected waves. Even when scanning is performed, the intensity distribution of the transmitted wave greatly fluctuates locally as shown in FIG. 8, and the presence / absence of a defect cannot be determined accurately. In addition, the shading in FIG. 8 has shown the strength of the transmitted wave. However, the dark part of the peripheral part of the acrylic plate is a part with low transmitted wave intensity.

 1 ... Subject, 2 ... Ultrasonic oscillator, 3 ... Ultrasonic geophone.

Claims (1)

An ultrasonic oscillator having an arc surface with a radius of curvature that causes the oscillation surface to converge the oscillating ultrasonic wave is opposed to one surface of the subject via an air layer, and air is opposed to the other surface of the subject. The ultrasonic oscillator is opposed to each other through the layer, and the transmitted wave in which the longitudinal oscillation wave oscillated from the ultrasonic oscillator passes through the subject is received by the ultrasonic receiver, and the ultrasonic oscillator at this time Generated from a longitudinal transmitted wave composed of an ultrasonic wave emitted as a longitudinal wave from the central portion of the oscillation surface and an ultrasonic wave emitted as a longitudinal wave from an end portion away from the central portion of the oscillation surface of the ultrasonic oscillator. The longitudinal wave transmitted wave intensity detection is limited to the time between the arrival of the longitudinal wave transmitted wave and the time before the arrival of the reflected noise wave composed of the transverse wave refracted wave. from the foregoing intensity of the transmitted wave of the longitudinal wave is received oscillation within Ultrasonic flaw detection method characterized by determining the presence or absence of a defect in the specimen.