JP2023183636A - Ultrasonic inspection method and ultrasonic inspection device - Google Patents

Abstract

To provide an ultrasonic inspection method and an ultrasonic inspection device that can identify a depth position where a plate material has a defect.SOLUTION: There is provided an ultrasonic inspection method that is implemented in an order of: a measuring process of performing inspection to detect a reflected component by making an ultrasonic wave incident as a burst sine wave in a thickness direction of a plate material S from a surface S1 of the plate material S as an object of inspection while sweeping a frequency of the burst sine wave; a resonance frequency extraction process of extracting, if a plurality of frequencies different from a plate thickness resonance frequency as a resonance frequency corresponding to a plate thickness t of a non-defective plate material S is detected as a resonance frequency at which the reflected component resonates, those frequencies as resonance frequencies of interest; and a defect depth determination process of determining that the plate material has a defect D at a position x of a depth V/2Δf from the surface, where Δf is a difference between two resonance frequencies of interest adjacent along a frequency axis and V is a sound velocity inside the plate material.SELECTED DRAWING: Figure 2

Description

The present invention relates to an ultrasonic inspection method and an ultrasonic inspection apparatus, and more particularly to an ultrasonic inspection method and an ultrasonic inspection apparatus for specifying the depth at which a defect exists inside a plate.

BACKGROUND ART Ultrasonic flaw detection is widely used as a method for detecting defects occurring inside an object to be inspected made of metal or the like. As a method of ultrasonic flaw detection, pulse echo method is generally used. In the pulse echo method, pulsed ultrasonic waves are applied to the object to be inspected, and the reflection of the ultrasonic waves by defects inside the object is detected. After that, the depth position where the defect exists can be specified based on the time taken until the reflected component due to the defect is detected. However, in the pulse echo method, dead zones occur near the surface and bottom of the object to be inspected, where defects cannot be detected even if they occur. When the object to be inspected is a thin plate material, the dead zone occupies a large proportion of the thickness of the plate, and especially when the thickness of the plate is small, the entire area in the thickness direction becomes the dead zone. Therefore, when applying the pulse echo method to a thin plate material, there is a possibility that defects cannot be detected even if they exist.

One of the methods of performing ultrasonic flaw detection on a thin plate material is a method using guided waves (plate waves), such as the method described in Non-Patent Document 1. Guided waves are generated by mode conversion within the plate material, and are components in which a wave packet propagates in a direction along the surface of the plate material. Guided waves are less affected by diffusion loss and can propagate over long distances, and if a defect exists along its propagation path, it can be detected by the occurrence of reflection. Furthermore, another method for performing ultrasonic flaw detection on thin plate materials is the local resonance method. In the local resonance method, a burst wave is applied in the thickness direction of the plate material. If the frequency of the burst wave is adjusted to the resonant frequency determined from the thickness of the board and the speed of sound, resonance will occur between the surface and bottom of the board in a healthy part with no defects, while resonance will occur in an unhealthy part with defects inside. In some areas, resonance does not occur or is weak. By identifying the presence or absence of resonance while changing the incident position of the burst wave along the surface of the plate, and detecting a position where no resonance occurs, it is possible to identify the presence of a defect within that position. Ultrasonic flaw detection using burst waves is disclosed in Patent Documents 1, 2, and the like.

Japanese Patent Application Publication No. 2012-068209 Japanese Patent Application Publication No. 2008-107101

Takuji Kuroishi et al., “Guided wave flaw detection monitoring system that can instantly detect pipe flaws from 5 m to 15 m”, Mitsubishi Heavy Industries Technical Report, Vol. 42, No. 3, pp. 138-141 (2005)

As described above, if ultrasonic flaw detection is performed using guided waves or burst waves, internal defects can be detected even in thin plates. However, when using these methods, although it is possible to identify the position of the defect along the surface of the plate, it is difficult to identify the depth of the defect along the thickness of the plate. It is difficult to pinpoint the location. Identifying the depth at which a defect exists in a plate material is, for example, determining whether the defect exists at a depth where the effect can be ignored, or how deep the plate material should be cut to remove the defect. This information is useful when considering how to handle defects, such as estimating whether or not they are defective.

The problem to be solved by the present invention is to provide an ultrasonic inspection method and an ultrasonic inspection apparatus that can specify the depth position where a defect occurs in a plate material.

In order to solve the above problems, an ultrasonic inspection method and an ultrasonic inspection apparatus according to the present invention have the following configuration.
[1] The ultrasonic inspection method according to the present invention includes an inspection in which ultrasonic waves are incident as a burst sine wave from the surface of a plate material to be inspected in the thickness direction of the plate material, and reflected components are detected. A measurement process is performed while sweeping the frequency of a sine wave, and multiple frequencies are detected as resonance frequencies at which resonance occurs in the reflected component, which are different from the plate thickness resonance frequency, which is a resonance frequency corresponding to the thickness of the plate without defects. , a resonant frequency extraction step in which those frequencies are extracted as a resonant frequency of interest, and the difference between the two adjacent resonant frequencies of interest along the frequency axis is Δf, and the speed of sound inside the plate material is V, In the plate material, a defect depth determination step of determining that a defect exists at a position whose depth from the surface is V/2Δf is carried out in this order.

[2] In the aspect of [1] above, prior to the measurement step, a burst sine wave having the plate thickness resonance frequency is applied from the surface of the plate material in the thickness direction of the plate material, and resonance occurs in the reflected component. An inspection to determine whether or not resonance occurs is performed while changing positions along the surface of the plate material, and if there is a position where resonance does not occur or where resonance is weak, it is determined that a defect exists inside that position. A defect searching step is carried out, and if there is a position where it is determined that a defect is present in the defect searching step, the measuring step, the resonant frequency extraction step, and the defect depth determining step are carried out at that position; It is recommended to evaluate the depth position of the defect.

[3] In the aspect of [1] or [2] above, in the resonance frequency extraction step, an analysis gate is provided in the time domain after forced excitation is reduced for the reflection component, and Then, it is preferable to determine whether resonance is occurring or not, and change the start time of the analysis gate in accordance with the frequency sweep.

[4] The ultrasonic inspection apparatus according to the present invention includes an inspection section capable of generating and detecting ultrasonic waves as burst sine waves, and sweeping the frequency of the burst sine waves generated in the inspection section. It has a sweep section and an analysis section that extracts and analyzes a resonance frequency from the detection results of the inspection section, and carries out any one of the ultrasonic inspection methods according to the above aspects [1] to [3]. It is something to do.

In the ultrasonic inspection method according to the invention [1] above, in the measurement step, the burst sine wave is incident on the plate material and the reflected component is detected while sweeping the frequency, and in the resonant frequency extraction step, the A resonance frequency other than the plate thickness resonance frequency corresponding to the thickness is extracted as a resonance frequency of interest. The resonance of the burst sine wave at this resonant frequency of interest is caused by a defect existing inside the plate material. Therefore, by detecting the resonant frequency, defects inside the plate can be detected. Furthermore, the resonance at the resonant frequency of interest is due to the generation of standing waves between the surface of the plate and the defect, and the resonant frequency of interest is 2x/n, where x is the depth position of the defect and n is a natural number. becomes. From this, as calculated in the defect depth determination step, the difference between two adjacent resonant frequencies of interest (the resonant frequency corresponding to n and the resonant frequency corresponding to n+1) is Δf, and the sound velocity inside the plate is V. In this case, the depth x of the defect can be specified by setting x=V/2Δf. In this way, even in thin plate materials, by sweeping the frequency of the burst sine wave and analyzing the detected resonance frequency, it is possible to not only detect the presence of defects but also identify the depth position of the defects. Can be done.

In the aspect [2] above, in the defect search step, a burst sine wave with a fixed frequency is used to inspect the presence or absence of defects at various positions on the surface of the plate material, and it is determined that a defect exists. The depth position of the defect is determined by the position. In the defect detection process, inspection is performed using the plate thickness resonance frequency, and while resonance occurs in healthy areas with no defects, resonance does not occur or is weak in unhealthy areas with internal defects. It is possible to identify the presence or absence of a defect in a wide area along the surface of the plate, and also to clarify where the defect exists in the in-plane direction of the plate material. In this way, the depth position of the defect is determined by frequency sweeping at the position where the presence of the defect is identified in the in-plane direction. Therefore, it is possible to efficiently acquire information regarding the presence or absence of defects in the plate material, the position of the defects in the in-plane direction, and the position of the defects in the depth direction.

In the aspect [3] above, in the resonant frequency extraction process, an analysis gate is provided in the time domain after forced excitation is reduced to determine the presence or absence of resonance. It is possible to determine the presence or absence of Forced excitation is accompanied by reflection of ultrasonic waves on the surface and bottom of the plate material, and as the frequency of the incident burst sine wave is swept, the time domain in which forced excitation appears changes. Therefore, by changing the start time of the analysis gate that determines the presence or absence of resonance as the frequency is swept, the presence or absence of resonance can be determined after the forced excitation has been sufficiently reduced at each frequency. .

The ultrasonic inspection apparatus according to the invention [4] above includes an inspection section that generates and detects a burst sine wave, a sweep section that sweeps the frequency of the burst sine wave generated in the inspection section, and an inspection section that generates a burst sine wave. It has an analysis section that extracts and analyzes the resonance frequency from the results, and implements the ultrasonic inspection method of aspects [1] to [3] above to identify the depth position where defects occur in the plate material. It is a suitable device for

1 is a schematic diagram showing an outline of an ultrasonic testing apparatus according to an embodiment of the present invention. It is a figure explaining the behavior of the ultrasonic wave in the board material which has a defect. FIG. 3 is a diagram illustrating the waveform of a reflected wave detected when a burst wave is incident, in which (a) shows a case where resonance occurs, and (b) shows a case where resonance does not occur. FIG. 3 is a schematic diagram showing a resonance frequency detected at a location where a defect occurs. The frequency at which resonance occurs is indicated by a vertical bar. It is a figure showing the structure of the sample used in an example. An example of the waveform of a reflected wave detected in the example is shown. (a) shows a state in which resonance occurs in a healthy part (frequency: 10.7 MHz), (b) shows a state in which resonance does not occur in an artificial defect with a wall thickness of 2.0 mm (frequency: 10.7 MHz), (c) shows a state where resonance occurs (frequency: 11.4 MHz) at the location of the artificial defect. FIG. 3 is a diagram showing the distribution of intensity of reflected components obtained by performing flaw detection on the entire sample surface with the frequency fixed at 10.7 MHz.

EMBODIMENT OF THE INVENTION Below, the ultrasonic inspection method and ultrasonic inspection apparatus concerning embodiment of this invention are demonstrated. An ultrasonic inspection method according to an embodiment of the present invention is for identifying the depth position where a defect exists in a plate material, and can be carried out using an ultrasonic inspection apparatus according to an embodiment of the present invention. Can be done.

[Target of inspection]
Although the material of the plate material to be inspected is not particularly limited, a metal plate material can be suitably inspected. The thickness of the plate material is not particularly limited, but it is preferably thin enough that defects cannot be detected by ultrasonic flaw detection using the pulse echo method. The type of defect is not particularly limited as long as it is formed inside the plate material and reflects at least a portion of the ultrasonic waves incident on the plate material, but if the plate material is made of metal, defects include: Examples include internal damage, impurities such as precipitates, and material deformation.

[Ultrasonic inspection device]
An ultrasonic inspection apparatus according to an embodiment of the present invention will be described. FIG. 1 schematically shows an ultrasonic testing apparatus 1 according to this embodiment. The ultrasonic inspection apparatus 1 includes a probe 2 as an inspection section, a frequency scanner 3 as a sweep section, and a computer 4 as an analysis section.

The probe 2 is a sensor probe that can transmit and receive ultrasonic waves, and in this embodiment, the ultrasonic waves are transmitted as a burst sine wave B (hereinafter sometimes simply referred to as a "burst wave"). Use a form that can be generated and detected. In the following, a case will be described in which a probe 2 is used as the inspection section, which is configured to inject a burst wave B from the surface S1 of the plate material S to be inspected and detect the reflected component reflected from the bottom surface S2, and the device configuration Although this form is preferable from the viewpoint of simplicity of the inspection process, the inspection section may be configured to detect the transmitted component outside the bottom surface S2 of the plate material S.

The frequency scanner 3 sweeps the frequency of the burst sine wave B generated by the probe 2. That is, the frequency of the burst sine wave B is changed within a predetermined range at predetermined increments. By performing inspection with the probe 2 while sweeping the wavelength with the frequency scanner 3, analysis can be performed using the detection results when burst waves B of different frequencies are incident.

The computer 4 is inputted with the detection result in the inspection section, that is, a detection signal indicating the waveform of the detected ultrasonic wave, and extracts and analyzes the resonance frequency from the detection result, as will be explained in detail later regarding the ultrasonic inspection method. . Then, based on the analysis results, it is determined whether or not there is a defect in the plate material S to be inspected, and the position of the defect is specified. Further, the computer 4 can control various devices constituting the ultrasonic inspection apparatus 1, such as the frequency scanner 3 and the moving unit 5 described below.

In addition to the probe 2, the frequency scanner 3, and the computer 4, the ultrasonic inspection apparatus 1 may include other members such as a moving section 5 and a water tank (not shown). The moving unit 5 relatively moves the probe 2 along the surface S1 of the plate material S to be inspected. The moving unit 5 allows ultrasonic inspection using the probe 2 to be performed at various locations on the surface S1 of the plate material S. In the illustrated embodiment, the probe 2 is moved by the moving unit 5 with respect to the fixed plate S, but the probe 2 may be fixed and the plate S moved. The water tank can be used to perform an ultrasonic test using a water immersion method by immersing the plate material S and the probe 2 in stored water.

[Ultrasonic testing method]
Next, an ultrasonic inspection method according to an embodiment of the present invention, which is carried out using the above-mentioned ultrasonic inspection apparatus 1, will be described. In the ultrasonic inspection method according to the present embodiment, (1) a defect search step is optionally performed, and then (2) a measurement step, (3) a resonance frequency extraction step, and (4) a defect depth determination step. Execute in this order. Each step will be explained below.

(1) Defect search process In the defect search process, the presence or absence of a defect is determined for the plate material S whose presence or absence and location of the defect are unknown, and if a defect exists, the defect is detected in the in-plane direction of the plate material S. Identify the location.

In the defect search step, ultrasonic inspection using a burst wave B with a fixed frequency is performed at a plurality of positions on the surface S1 of the plate material S. Specifically, a burst wave B is incident in the thickness direction of the plate material S from the surface S1 of the plate material S, and a reflected component is detected. This is carried out at each position in a wide area of the surface S1 of the plate material S while moving along the same direction.

The frequency of the burst wave B is set to a resonant frequency corresponding to the thickness of the plate material S without defects. In other words, the frequency is set such that resonance occurs between the surface S1 and the bottom surface S2 of the plate S in a region where the plate S has no defects, such as a sound part P1 shown in FIG. 2, and a standing wave W is generated. This resonant frequency will be hereinafter referred to as plate thickness resonant frequency F (F ₁ , F ₂ , F ₃ , . . . ). Since the standing wave W is generated under the condition that an integer multiple of the half wavelength of the incident burst wave B is equal to the plate thickness, the plate thickness resonance frequency F is calculated as follows: t is the plate thickness, V is the sound velocity inside the plate S, and n is expressed by the following equation (1), where is a natural number.
F=nV/2t (1)
The plate thickness resonance frequency F may be determined by calculation using the above formula (1) or by actual measurement. In the case of actual measurement, the sound part P1 may be inspected with the probe 2 while sweeping the frequency using the frequency scanner 3 to identify the frequency at which resonance occurs.

When a burst wave B having a plate thickness resonance frequency F is incident on the plate S, resonance occurs in the healthy portion P1, as shown in FIG. However, in the unhealthy part P2 where the defect D exists inside, resonance does not occur or resonance becomes weak (hereinafter collectively referred to as "no resonance"). Strictly speaking, resonance does not occur for at least some n values.

Therefore, when an inspection is performed at the plate thickness resonance frequency F while moving the probe 2 along the surface S1 of the plate S, resonance occurs in the healthy part P1, and the analysis shown in FIG. 3(a) As seen in the gate G, a high-intensity reflected component appears, whereas in the unhealthy part P2, as seen in the analysis gate G in FIG. 3(b), resonance does not occur and the reflected component is low. It only appears with intensity. 3(a) and (b) show the waveform of the time change of the sound pressure of the reflected component, and the high-intensity forced excitation (region R1) originating from the reflection at the surface S1 and bottom surface S2 of the plate material S is shown in FIG. After the reduction, an analysis gate G is provided to detect a signal at a time when free vibration (region R2) occurs. The intensity of the reflected component in this free vibration region R2 reflects the presence or absence of resonance.

In this way, by fixing the frequency of the burst wave B incident on the plate material S to the plate thickness resonance frequency F and performing an inspection to detect the reflected component, the position where resonance is occurring on the surface S1 of the plate material S can be determined. , it can be determined that the position where the defect D does not exist is a healthy part P1, while the position where resonance does not occur is an unhealthy part P2 where the defect D exists inside. Therefore, by inspecting each position on the surface S1 of the plate material S, it is possible to determine the presence or absence of the defect D and to specify the position of the defect D within the plane of the plate material S. The position can be identified with a spatial resolution comparable to the spot diameter of the burst wave B emitted from the probe 2.

In this defect search step, when the position where the defect D exists in the plate material S is specified within the plane of the surface S1, the subsequent steps (2) to (4) are carried out at the specified position, and the defect Evaluate the position of D in the depth direction. As a result, on the surface S1 of the plate material S, it is only necessary to perform the subsequent process on the position where the defect D is known to exist. The position of the defect D can be efficiently identified in both the direction and the depth direction. In addition, if the position where the defect D occurs in the plate material S is known based on the manufacturing characteristics of the plate material S or the results of other inspections, the defect search step is omitted and the defect is detected at the known position. What is necessary is to specify the depth position of D. In addition, in cases where the area of the plate material S is small, etc., the defect detection step is omitted, and the following inspections (2) to (4) are performed at each of a plurality of positions on the surface S1 of the plate material S to detect defects. The presence or absence of D and the depth position may also be specified.

(2) Measurement process Next, in the position where the defect D is revealed to be the unhealthy part P2 in which the defect D exists in the above defect search process, measurement is carried out in order to specify the depth position of the defect D. Implement the process.

In the measurement process, a burst wave B is applied in the thickness direction of the plate material S, and an inspection is performed to detect a reflected component while sweeping the frequency of the burst wave B. In other words, the probe 2 is placed on the surface S1 of the unhealthy part P2, and the frequency scanner 3 sweeps the frequency of the sine wave that constitutes the burst wave B, while the probe 2 generates and detects the burst wave B. conduct. The measurement results obtained in the measurement step are obtained as detection signals indicating the waveform of the detected ultrasonic waves for each frequency of the incident wave, and are input to the computer 4.

(3) Resonant frequency extraction step Next, based on the measurement results obtained in the measurement step, the computer 4 extracts the frequency at which resonance occurs.

When resonance occurs at a certain frequency in a measurement process in which inspection is performed while sweeping the frequency, the intensity of the reflected component increases, as shown in FIG. 3(a) in the defect search process in which the frequency is fixed. On the other hand, when resonance is not occurring, the intensity of the reflected component remains small, as shown in FIG. 3(b). Therefore, in the resonance frequency extraction step as well, the presence or absence of resonance is determined based on the intensity of the reflected component, similarly to the defect search step. The presence or absence of this resonance is determined for each frequency, and the frequency at which resonance occurs is extracted.

The position at which the measurement process was performed on the surface S1 of the plate material S was found to be an unhealthy part P2 in which a defect D has occurred inside due to the previous defect search process, and the defect D reflects ultrasonic waves. do. Therefore, when a burst wave B is incident on such an unhealthy part P2, a standing wave W' is generated between the surface S1 of the plate material S and the defect D, as shown in FIG. 2, and resonance may occur. There is sex. Since the standing wave W' is selectively generated under the condition that an integral multiple of the half wavelength is equal to the distance x between the surface S1 of the plate material S and the defect D, the standing wave W' is generated while sweeping the frequency of the burst wave B in the measurement process. In the measurement results of the reflected components, resonance occurs only at specific frequencies. This resonant frequency will be referred to as a resonant frequency of interest f (f ₁ , f ₂ , f ₃ , . . . ). The resonant frequency f of interest is expressed by the following equation (2), where n is a natural number.
f=nV/2x (2)

The resonant frequency f of interest and the plate thickness resonant frequency F are different from each other. This is also reflected in the difference between equations (1) and (2) depending on whether the denominator includes t or x, and since x<t, the natural number n (constant If the number of antinodes of existing waves is the same, the resonant frequency f of interest is higher than the plate thickness resonant frequency F (f _n >F _n ). That is, in the location where the defect D exists, when the frequency is swept, the resonant frequency f of interest occurs at a frequency different from the plate thickness resonant frequency F as a resonant frequency. Strictly speaking, at least a portion of the resonant frequency f of interest occurs at a frequency different from the plate thickness resonant frequency F. FIG. 4 shows the resonance frequency observed in the unhealthy portion P2 where the defect D has occurred. Here, the horizontal axis represents frequency, and vertical bars are displayed at positions where resonance appears. As shown in the figure, due to reflection at the defect D, resonance occurs discretely at the resonant frequencies of interest f ₁ , f _{2 , . . . corresponding to n=1, 2} , . The resonant frequencies f of interest appear at regular intervals. On the other hand, in the unhealthy portion P2, no resonance occurs at the plate thickness resonance frequency F (F ₁ , F ₂ , . . . ).

In this way, in the resonance frequency extraction process, by detecting resonance at the focused resonance frequency f, which is different from the plate thickness resonance frequency F, it can be confirmed that the defect D has occurred inside the location where the measurement process was performed. can. Furthermore, by extracting a plurality of resonant frequencies f of interest having different values of n, the depth x of the defect D can be specified in the next defect depth determination step.

Here, it is preferable to provide an analysis gate G to determine the presence or absence of resonance in the resonance frequency extraction step. Regarding the defect search process, as described with reference to FIG. 3, an analysis gate G is provided in the free vibration region R2 after the high-intensity forced excitation has sufficiently decreased, and measurements that fall within the analysis gate G are performed. By using only the results for analysis, the effects of forced excitation can be avoided and subsequent analyzes can be performed with high accuracy. Here, it is preferable to change the start time of the analysis gate G as the frequency of the burst wave B incident on the plate material S is swept. As mentioned above, forced excitation is due to the reflection of the burst wave B on the surface S1 and bottom surface S2 of the plate material S, and as the time required for reflection changes depending on the frequency, the reflected component originating from forced excitation is This is because the time required for the intensity to sufficiently decrease varies depending on the frequency. The higher the frequency, the earlier the intensity of forced excitation decreases, and even if the start time of the analysis gate G is set early, the influence of forced excitation can be sufficiently avoided. For example, the gate start time s can be set using equation (3) below.
s=m・a/f+b (3)
Here, m indicates the wave number of the burst wave B. a and b are constants. The constant b includes contributions such as the time required for reflection at the surface S1 and the response time of the probe 2.

(4) Defect Depth Determination Step In the plate material S, if a defect D occurs inside the location where the measurement step was performed, resonances at a plurality of focused resonance frequencies f are detected in the previous resonance frequency extraction step. Here, regarding the plurality of resonant frequencies f of interest, the n-th resonant frequency from the low frequency side is f _n , the n+1-th resonant frequency is f _n+1 , and the difference between these resonant frequencies is Δf. In this case, using equation (2), the difference Δf can be expressed as shown in equation (4) below.
Δf=f _n+1 - f _n
=(n+1)V/2x-nV/2x
=V/2x (4)

Furthermore, from equation (4), the depth x of defect D is expressed as shown in equation (5) below.
x=V/2Δf (5)
In other words, when two adjacent resonance frequencies f _n and f _{n+1 are} extracted along the frequency axis, such as frequencies f ₁ and f 2 and frequencies f ₂ and f ₃ shown in FIG. , the depth x of the defect D can be specified by Equation (5). Specifically, in the plate material S, it can be determined that the defect D exists at a position where the depth from the surface S1 is V/2Δf.

As described above, in the ultrasonic inspection method according to the present embodiment, the presence or absence of the defect D in the plate material S is evaluated and the position in the in-plane direction where the defect D exists is specified by the defect search process as appropriate. Then, by performing an inspection using burst wave B while sweeping the frequency and extracting the focused resonance frequency f where resonance occurs at a frequency different from the plate thickness resonance frequency F, the depth position where the defect D exists can be determined. can be specified. Thereby, the defect D can be detected even on the thin plate material S, which could not be sufficiently detected by the conventional pulse echo method due to the presence of a dead zone. Furthermore, unlike flaw detection using a burst wave with a fixed frequency or a guided wave, the depth position of the defect D can be specified. By specifying the depth position of the defect D, it is possible to consider how to handle the defect D according to the depth position. For example, if a defect D is formed in a metal plate S, if the position of the defect D is sufficiently shallow, the defect D is ignored as it does not seriously affect the material properties, while the position of the defect D is ignored. If the defect D is deep, a decision can be made to take measures to remove the defect D, such as cutting off part of the thickness of the plate material S. Furthermore, when removing the defect D, it is possible to obtain an index of the thickness to which the material should be removed.

Examples of the present invention are shown below. Note that the present invention is not limited to these Examples. Here, we verified whether it was possible to identify the depth of defects by performing ultrasonic inspection using frequency-variable burst waves on samples with artificial defects.

[Test method]
As a sample, as shown in FIG. 5, an aluminum plate with a thickness of 5 mm in which artificial defects were formed was prepared. As the artificial defect, a groove with a square cross section was formed from the bottom side (lower side) of the plate material. Three types of artificial defects were created in which the wall thickness from the surface of the plate material to the bottom (upper end) of the groove (hereinafter simply referred to as "thickness") was 2.5 mm, 2.0 mm, and 1.5 mm, respectively. .

A flaw detection test based on the ultrasonic inspection method according to the embodiment of the present invention described above was performed on the prepared sample. In the flaw detection test, a burst sine wave was applied from the surface side of the plate material at the position of each artificial defect, and the reflected component was detected while sweeping the frequency of the burst sine wave. A flat type probe with a transducer diameter of 6.4 mm was used as the probe. The frequency sweep was performed in the range of 7 to 15 MHz in 0.1 MHz increments. Furthermore, a 2 to 20 MHz bandpass filter was used to detect reflected waves. The inspection was conducted using the water immersion method, and the water distance was 30 mm.

When extracting the resonance frequency, an analysis gate was set according to the frequency using the above equation (3). Then, the intensity of the reflected component was determined by averaging the sum of squares of the detection signal within the analysis gate, and the maximum value of the intensity was determined as the resonance frequency. In addition, for reference, the frequency of the burst wave was fixed at 10.7 MHz, which corresponds to the plate thickness resonance frequency, and a flaw detection test was performed in which the burst wave was applied at each position on the entire sample surface and the reflected components were detected. went.

[Test results]
First, the results of a flaw detection test performed on the entire sample surface with the frequency fixed at 10.7 MHz are shown. Figures 6(a) and (b) show the waveforms of the reflected components detected in a healthy part where no artificial defect is formed and an unhealthy part where an artificial defect (thickness 2.0 mm) is formed, respectively. However, in the unhealthy part, the amplitude in the free vibration region is clearly smaller than in the healthy part, confirming that the resonance occurring in the healthy part does not occur in the unhealthy part.

Furthermore, FIG. 7 shows the intensity distribution of the reflected component at each position on the sample surface. Here, the position where the detection intensity is higher is displayed brighter. In FIG. 7, streak-like dark regions are observed at positions corresponding to the three artificial defects. This is because, as shown in FIGS. 6(a) and 6(b), at the plate thickness resonance frequency, resonance occurs in a healthy part, but no resonance occurs in an unhealthy part where an artificial defect exists. In FIG. 7, all three artificial defects give similar intensity distributions, and the thickness of the artificial defects cannot be distinguished from the results of this inspection. In this manner, in the flaw detection inspection in which the frequency is fixed to the plate thickness resonance frequency, the position of the artificial defect in the in-plane direction can be specified, but information regarding the depth position of the defect cannot be obtained.

Next, we will show the results of an inspection conducted while sweeping the frequency of the burst wave at the position where the artificial defect was provided. As mentioned above, Fig. 6(b) shows the waveform of the reflected component obtained by injecting a burst wave of 10.7 MHz, which is the plate thickness resonance frequency, at the position of the artificial defect (wall thickness 2.0 mm). However, the strength of the free vibration region is small, and no resonance occurs. On the other hand, Fig. 6(c) shows the waveform of the reflected component obtained by injecting a burst wave with a frequency of 11.4 MHz at the same artificial defect position, but the resonance shown in Fig. 6(b) has not occurred. The strength of the free vibration region is clearly greater than the case where there is no vibration, and a behavior similar to the case where resonance occurs in the healthy part of FIG. 6(a) is observed. This confirms that resonance occurs at a frequency different from the plate thickness resonance frequency at the position of the artificial defect.

Furthermore, Table 1 summarizes the reflected wave intensities at representative frequencies obtained at the positions of three types of artificial defects.

In Table 1, the columns corresponding to the resonance frequencies extracted as the frequencies that take the maximum value are shown in black. In the case of a wall thickness of 2.0 mm and a frequency of 11.4 MHz, where resonance is confirmed to occur in FIG. 6(c), it is also extracted as a resonant frequency. According to Table 1, for any of the three types of artificial defects, while resonance does not occur at the plate thickness resonance frequency of 10.7 MHz, resonance occurs at a frequency different from the plate thickness resonance frequency. Furthermore, the resonance frequencies of the three types of artificial defects are different from each other. For each artificial defect, multiple resonance frequencies are extracted. In particular, for an artificial defect with a wall thickness of 2.5 mm, three resonant frequencies are extracted within the displayed frequency range, and these resonant frequencies appear at equal intervals. Furthermore, the interval Δf between the resonant frequencies becomes smaller as the thickness of the artificial defect becomes larger. These behaviors suggest that the observed resonance frequency appears due to resonance between the sample surface and the artificial defect.

Furthermore, for each of the three types of artificial defects, the depth position (x) of the defect is calculated from the resonance frequency interval Δf based on the above formula (5) (sound speed: 6320 m/s), and the depth position (x) of the defect is calculated at the bottom right of the table. As shown in , the artificial defects with wall thicknesses of 1.5 mm, 2.0 mm, and 2.5 mm are 1.58 mm, 2.11 mm, and 2.43 mm, respectively. In both cases, the calculated results almost match the thickness of the artificial defect formed. These results show that the observed resonance occurs in the region between the sample surface and the artificial defect, and that the resonance frequency reflects the wall thickness, that is, the distance between the sample surface and the artificial defect. I understand that. It has been confirmed that the depth position of a defect can be identified by performing ultrasonic inspection while sweeping the frequency of the burst wave and analyzing the interval between resonance frequencies.

The embodiments of the present invention have been described above. The present invention is not particularly limited to these embodiments, and various modifications can be made.

1 Ultrasonic inspection device 2 Probe (inspection section)
3 Frequency scanner (sweep section)
4 Computer (analysis department)
5 Moving part B Burst (sine) wave D Defect G Analysis gate P1 Healthy part P2 Unhealthy part R1 Forced excitation region R2 Free vibration region S Plate material S1 Surface S2 Bottom surface W Standing wave W' in healthy part Standing wave in unhealthy part Wave t Plate thickness x Depth position of defect

Claims (4)

A measurement step in which an ultrasonic wave is incident as a burst sine wave in the thickness direction of the plate material to be inspected from the surface of the plate material to be inspected, and an inspection is performed to detect a reflected component while sweeping the frequency of the burst sine wave;
If a plurality of frequencies different from the plate thickness resonance frequency, which is a resonance frequency corresponding to the thickness of the plate without defects, are detected as resonance frequencies at which resonance occurs in the reflected component, those frequencies are set as the focused resonance frequencies. a resonant frequency extraction step,
It is determined that a defect exists in the plate at a position where the depth from the surface is V/2Δf, where Δf is the difference between the two adjacent resonant frequencies of interest along the frequency axis, and V is the sound velocity inside the plate. a defect depth determination step;
An ultrasonic examination method in which the following steps are performed in this order. Prior to the measurement step, a burst sine wave having the plate thickness resonance frequency is applied from the surface of the plate material in the thickness direction of the plate material, and an inspection is performed to determine whether resonance occurs in the reflected component. A defect searching process is performed while changing the position along the surface of the plate material, and if there is a position where resonance does not occur or resonance is weak, it is determined that a defect exists inside that position,
In the defect searching step, if there is a position where it is determined that a defect exists inside, the measuring step, the resonant frequency extraction step, and the defect depth determination step are performed at that position to evaluate the depth position of the defect. The ultrasonic testing method according to claim 1. In the resonant frequency extraction step,
An analysis gate is provided in the time domain after the forced excitation is reduced for the reflected component, and it is determined whether resonance is occurring in the analysis gate,
The ultrasonic inspection method according to claim 1, wherein the start time of the analysis gate is changed in accordance with the frequency sweep. an inspection section capable of generating and detecting ultrasonic waves as burst sine waves;
a sweep section that sweeps the frequency of the burst sine wave generated in the inspection section;
an analysis section that extracts and analyzes a resonance frequency from the detection results of the inspection section;
An ultrasonic inspection device that implements the ultrasonic inspection method according to any one of claims 1 to 3.

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