JPH02150765A - Ultrasonic flaw detecting method - Google Patents

Abstract

PURPOSE:To surely detect various flows with high accuracy by using signals obtained by processing two selected signals indicating variation out of each signals from an object inspected by an ultrasonic flaw detector. CONSTITUTION:Two signals indicating variation are selected out of reflected or transmitted each signals obtained as continuous voltage signals during the course of ultrasonic flow detector performed on an object 2 to be inspected and signals f(C) obtained by performing signal processes expressed by prescribed formulae are used for fault detection. The f(S), f(BT), f(R), and f(F) of the formulae respectively represent the reflected/transmitted echo signals from the surface of the object, bottom of the object, a reflecting plate 1, and a fault. The f(Th) and f(C) respectively represent the transmitted echo signals and signals obtained as a result of signal processing. In addition, the A and B respectively represent coefficients for matching the amplitude and level. Namely, two signals, one of which decreases and the other increases, are selected and both signals are processed so that most of them can be superimposed upon another. Since the signal thus obtained is free from the influence of attenuation caused by factors other than a fault, the fault can be recognized clearly.

Description

[Detailed Description of the Invention] <Industrial Application Field> The present invention uses ultrasonic waves to remove defects inherent in metals, non-metal materials, composite materials, etc. used in structural members of mechanical devices, structures, etc., electronic parts, etc. It relates to a method of flaw detection using More specifically, the present invention relates to a method of detecting defects with high accuracy by performing signal processing to reduce the influence of the surface condition of the object, non-uniformity of the material structure, or the edges of the material.

<Prior Art> Ultrasonic flaw detection is the most effective quantitative means for nondestructively inspecting defects inherent in metals, nonmetals, ceramics, composite materials, etc., and is widely used.

Determining the presence or absence of a defect and its size from ultrasound waves affected by a defect within a subject is performed by focusing on the strength of the ultrasound signal, that is, the amplitude value of the ultrasound waves. In the ultrasonic reflection method, the stronger the ultrasonic signal reflected from the defect, the more weakened the signal by the defect in the ultrasonic transmission method, the larger the defect. Ultrasonic waves consume energy and attenuate even in the process of propagating through healthy materials, but the effect of attenuation due to the path distance of this ultrasonic wave is
(Distance A + amplitude Compe
nsation), or AVG (Abst
This can be corrected by a method commonly referred to as "and Verstarkung GroBe" diagram, and this method is widely used. (Non-destructive inspection handbook: 1973
(Published by Nikkan Kogyo Shimbun, April 28, 2017) Problems to be Solved> If the surface of the object to be examined has roughness or undulations, ultrasonic waves will be scattered on the surface of the object and may enter the inside of the object. The amount of ultrasonic waves is reduced compared to a smooth surface. In addition, since all of the ultrasound waves emitted from the probe do not enter the object at the end of the object, the amount of ultrasonic waves that enter the object also decreases here as compared to a smooth surface. Therefore, when determining the presence or absence of a defect by setting a threshold value for the amount of attenuation of the reflected echo signal from an artificial defect of a certain size used for comparison, if the reflected echo signal from an internal defect becomes weaker, a larger defect Even if there is a defect, it may be determined that it is not a defect.

In addition to these phenomena, if there are tissue changes in the plane of the object, the ultrasound that passes through the object will become stronger or weaker, making it difficult to distinguish between attenuation due to defects and fluctuations due to tissue changes. This makes it difficult to determine defects.

In view of these circumstances, the present inventor has developed materials such as metals, non-metals, composite materials, etc., which have roughness or undulations on the surface of the specimen, or materials whose structure changes in the plane direction inside the specimen. As a result of extensive research into an ultrasonic flaw detection method that can accurately determine the position and shape of a defect or a defect at the edge of a test object, the present invention has been completed.

<Means for Solving the Problems> In other words, the present invention selects two echo signals in which fluctuations appear from reflected or transmitted echo signals obtained as continuous voltage signals through ultrasonic flaw detection of a test object, and calculates the following equation by selecting two echo signals showing fluctuations. This is an ultrasonic flaw detection method characterized by detecting defects using a signal f (C) obtained by signal processing expressed as f (C).

{f(R)X^1B) /f(S)=f(C), {f
(BT) ×A + B) /f(S)=f(C),
f (R) / f (S) = f (C), f (BT
) /f(S)=f(C), f(F)x^/f(BT)
=f(C), f(F)X^/f(R) =f((:)
, {f(Th) x^1B ) /f(S>=f(C
), f(Th) /f(S)=f(C) or f(F)
×A /f(Th>=f(C) In the present invention, the ultrasonic flaw detection method is selected from the following three commonly used methods.

(1) A method in which ultrasonic waves are incident from the surface of the object using one probe, and the ultrasonic echoes reflected from defects are detected using the same probe (ultrasonic reflection method) (2) One probe Ultrasonic waves are incident into the subject using a probe, and a reflector is placed on the symmetrical side of the subject, so that the ultrasonic waves that have once passed through the subject are reflected by the reflector and pass through the subject again. (3) Two probes are placed symmetrically across the subject,
A method in which one probe emits ultrasonic waves and the other probe detects the ultrasonic echoes that pass through the subject (ultrasonic transmission method). A method of direct contact or a method of keeping a distance and using an ultrasonic transmission medium such as water is used. In these ultrasound propagation processes, the echoes to be analyzed include the reflected echo from the surface of the object, the reflected echo from defects inside the object, the reflected echo from the bottom of the object, the reflected echo from the ultrasonic reflector, and the reflected echo from the object. There is a transmitted echo that has passed through the specimen.

The surface echo signal from the surface of the object is not affected by the structure or defects in the material at all, but only by the surface condition, and is attenuated if the surface has roughness or waviness. If the surface has roughness or undulations, the amount of incident ultrasonic waves will be reduced, and therefore reflected echo signals from the bottom surface of the object or defects will be attenuated.

Furthermore, if there is a defect, the reflected echo signal from the bottom surface of the object or the ultrasonic reflector is attenuated due to the influence of the defect, while the reflected echo signal from the defect appears. If there is a tissue change within the subject, its influence will appear superimposed on the reflected echo from the defect.

In other words, the probe is continuously moved in contact with or close to the test object to perform flaw detection, and the continuous voltage signals obtained from the test object surface, defects inside the test object, the bottom surface of the test object, and the ultrasonic reflector are obtained as voltage signals. An attenuated echo signal is found from the reflected echo signal and the transmitted echo signal transmitted through the object, and the amount of attenuation is determined. scattering by the surface of the object,
Variations due to tissue changes at the edge of the object or defects within the object will affect the echo signal in the same way, resulting in similar attenuation in the absence of a defect or one attenuation in the presence of a defect. However, contradictory fluctuations in which one increases and the other increases appear as a continuous echo signal. These fluctuations are appearing2
A stone that selects one signal, processes the two signals so that they almost overlap, reduces the effects of fluctuations, and clarifies the reflected echo signal from the defect.

Hereinafter, the present invention will be explained in detail based on the drawings.

FIG. 1 is a block diagram showing an example of a subject, a probe, a signal processing device, and an output device of the present invention. The flaw detection method is shown using the ultrasonic reflector method.

In FIG. 1, the probe (3) is controlled by a motor controller Q[il to control each axis xlY according to the position control data of the C scan control program (c). The pulser/receiver (4) sends a transmission pulse signal to the probe (3) and transmits it to the object (
Receiving signals of ultrasonic echoes such as surface echoes from 2), reflected echoes from defects, and reflected echoes from the reflector plate (1) are received. Gate circuit I (5), (6) sets two gates for the echo signal amplified or attenuated by this pulser/receiver (4), and selects an analog signal that matches the strength of the received echo signal within the gate. , an oscilloscope (7) for monitoring these received echo signals,
(8), an analog signal processing device (9) that processes the echo signal (analog output signal) selected by the gate circuits (5) and (6), and converts the output signal from this gate circuit into a digital signal. The A/D converter α1 sends out to the waveform storage device αD, the digital signal processing device ■ performs signal processing on the digitized echo signals sequentially sent out from this waveform storage device αD, and the image input/output device 0 performs signal processing. At 9), the device stores the data transmitted from the screen as image data, and transfers the data to the CRT display αO as a C-scope image.

FIG. 2 is a schematic diagram and part of a block diagram of the ultrasound reflection method, and FIG. 3 is a diagram showing a part of the block diagram of the ultrasound transmission method.

The ultrasonic waves transmitted from the probe (3) are reflected on the surface of the object (2) to produce a surface echo (B wave), a defect echo (F wave) reflected from a defect, and a bottom surface reflected from the bottom surface. Echo (B wave), reflector echo reflected by reflector (1) (
R waves) and transmitted echoes (Th waves) transmitted through the object (2) and received by the probe at 0 seconds are obtained. These are the fourth
Oscilloscope (7) as the A scope waveform shown in the figure,
(8) is displayed. Symbols 51FSB, R, and Th represent echo signals corresponding to B waves, F waves, B waves, R waves, and Th waves, respectively. Further, the symbol T represents a transmission pulse signal. Note that the symbol t in FIGS. 2 and 3 represents the thickness of the subject, and the symbol t in FIG. 4 represents the propagation time of the ultrasound in the subject.

In Figure 3, on the receiver side, the ultrasonic wave transmitted from the probe (3) passes through the object (2) and is received by the probe α. Circuits (5), (6) and subsequent circuits are arranged in the same manner as in the block diagram of FIG.

In the ultrasonic reflection method shown in FIG. 2, when the thickness of the subject is thin, the propagation time of the ultrasonic waves becomes short as shown in FIG. 6, and the received echo signals overlap and cannot be separated.

In such a case, the ultrasonic reflector method shown in FIG. 1 is used. Also, if the shape of the object to be examined becomes complex, such as a curved surface structure, it becomes difficult to arrange the reflector, and in that case, the third
The ultrasound transmission method shown in the figure is used.

When using the ultrasonic reflection method, as shown in Figure 5, B
Set a gate on the wave and B wave echo signals.

When the thickness of the object to be examined is thin or the shape of the object is complicated, such as a curved structure, set a gate for each echo signal including S wave, F wave, and B wave as shown in Figure 6, and use a reflector and a gate. A gate is set on the R wave of the echo signal from (1) or the Th wave received by probe 0, and gate circuits (5) and (6
) is sent to an analog signal processing device (9) and/or an A/D converter aQ.

These sent signals are processed by an analog signal processing device (9)
And/or signal processing is performed on the digital signal processing device side.

FIG. 7 is a diagram showing an example of signal processing according to the present invention. A schematic diagram illustrating the state of flaw detection when there is waviness in ', zj of an object by the ultrasonic reflector method and an example of the processing procedure of the obtained signal are shown.

Ultrasonic waves are scattered by the surface undulations, and the reflected echo signal r (s) from the surface is attenuated. The magnitude of attenuation (amplitude) varies depending on the degree of scattering. The reflected echo from the reflector is a reflection from the surface! , the signal f (R) becomes lower than the level of the reflected echo signal f (S). f (R) is attenuated due to the influence of reflection from the surface and the influence of the subject tissue itself, and exhibits a variation similar to f (S) in areas without defects, although the amplitude is different.

If there is a defect, f(R) becomes further attenuated, while a reflected echo (F wave) from the defect appears (not shown in FIG. 7), and contradictory fluctuations appear.

Focusing on f (R) and f (S), signal processing is performed to bring the amplitude and level of f (R) closer to the amplitude and level of f (S). Gate circuits are set for f (R) and f (S), and f (R) and f (S) are displayed on the CRT display.

First, a multiplication process is performed to bring the amplitude of f (R) closer to the amplitude of f (S). Multiply f (R) by a coefficient A so that the amplitude values of both signals are the same.

f(R) ] Displayed signal f
Adjust coefficient A while checking the amplitude of (^). The coefficient A represents a positive real number, and although it depends on the amplitude values of both signals, it is usually a value less than lO. By this process, f
The amplitudes of (R) and f (S) are almost the same.

Next, an addition process is performed to bring the level of f (A) closer to f (S>. A coefficient B corresponding to the level difference between f (A) and f (S) is added to f (A). f ( A)+B
=f(B) {f(B) represents a signal obtained by multiplying the coefficient A. ] Increase or decrease the coefficient A while watching the level of the displayed signal f (B). Coefficient B represents a positive or negative real number (unit: v). Normally, the maximum signal strength obtained from an ultrasonic flaw detector is about 10V, so the coefficient B is 1Ov.
The value is as follows.

By this process, f(B)' and f(S) other than the defective area overlap. Next, f(B) and f(S
) is performed. f(B}/f(S)=f(C)
{f(C) represents a signal obtained by division processing. ] If there is no defect in the object as a result of this process, then f (C
) approaches a signal of a certain value with no amplitude. If there is a defect in the object, the defect attenuates the ultrasonic waves, so f (S) and (R) will not have similar fluctuations in that part, and f (C) will have an amplitude only due to the defect. This makes it possible to perform ultrasonic flaw detection by setting a threshold value.

The ultrasonic reflector method described above is a method used when the thickness of the subject is so thin that the echo signals from the surface of the subject and the echo signals from the bottom of the subject overlap and cannot be separated. The ultrasonic reflection method is used when the two can be separated. In that case, the reflected echo signal from the bottom surface of the object is defined as f (BT>), {f(BT) ×A
+B}/f (S) = f (C) signal processing is performed, and the defect can be accurately identified using the signal f (C) that reduces the effect of ultrasonic attenuation due to roughness or undulations on the surface of the object to be inspected. can.

Although the attenuation of the ultrasound is small and the amplitude and level of the echo signal from the surface of the object and the echo signal from the bottom of the object or the ultrasound reflector are different, if they are close, f(
BT) /f(S)=f(C) or f(R)/f
Only by signal processing of (S) = f (C), it is possible to reduce the effect of attenuation of ultrasonic waves due to roughness or undulations on the surface of the object to be inspected, and it is possible to accurately grasp defects using the signal f (C).

It is also possible to reduce the effect of ultrasound attenuation at the end of the object using the above method.

In addition, as a method to reduce the effect of attenuation of ultrasound waves due to tissue changes inside the object, where the reflected echo signal from a defect inside the object is f (P), f (F) × A / f (BT)
=f(C) or f(F) x A/f(R) =f(
C) signal processing is performed.

If the transmitted echo signal received by the probe placed on the opposite side of the subject in the ultrasonic transmission method is f (Th), then f (R
) can also be replaced with f(Th). Note that in the signal processing described above, it is also possible to replace the denominator and numerator of the division processing.

Which of the above signal processes is to be performed is appropriately selected in consideration of the shape of the subject, the degree of separation of echo signals, and the degree of reduction of the influence of attenuation.

The signal processing of the present invention may be performed even when one of the two signals does not exhibit any fluctuations such as attenuation.

<Examples> Hereinafter, the present invention will be explained in detail based on Examples, but the present invention is not limited to these Examples.

FIG. 8 shows a specimen with an irregular surface condition.

The object (2) is an acrylic plate, and its surface has a width of 2~
A rectangular groove of 3mm x depth 2-3III11 is machined at a 3M pitch. In addition, since ultrasonic waves are reflected at interfaces of materials with different densities and sound velocities, that is, interfaces with different acoustic impedances, five pieces of 3mm wide A1 tape were pasted on the bottom of the specimen as reflectors to simulate defects, and ultrasonic waves were Flaws were detected using the reflector method. Here, the symbols ■ to ■ are A1 tapes attached to the bottom surface of the object as artificial defects, and the symbols ■ to ■ in the voltage output chart and the C-scan display indicate the positions of these A1 tapes.

First, a part of the echo signal f (R) from the ultrasonic reflector when the probe (3) is C-scanned without signal processing is shown as a voltage output chart in the lower column of FIG. There are parts where the attenuation of the ultrasonic waves due to the irregular surface condition of the object (2) is greater than the artificial defects marked with symbols (■) to (■). The results obtained by C-scanning with the threshold values set are shown in the right column of FIG. A region where no artificial defect is detected occurs at the position marked with symbol ■ in the C-scan display.

As you can see from the output voltage chart of f(R) only, if you set the threshold so that all five AI tapes with artificial defects are displayed as C-scope images, the difference is due to the rectangular groove shape on the surface of the object. Attenuation and attenuation due to the influence of the end of the object are also displayed as a C scope image.

Therefore, assuming that the echo signal from the surface of the subject is f (S), the division signal processing of f (R) /f (S) = f (C) is performed, and the results are shown in the middle column of FIG. All of the artificial defects with 5 pieces of A1 tape pasted on the bottom of the specimen are C.
Displayed as a scope image. However, a portion of the rectangular groove shape on the surface of the object and the edge of the object was also detected and displayed as a C-scope image.

This signal processing does not clearly identify only artificial defects, so {f(R) x A+ B) /f(S) = f(C
) signal processing was performed. The results are shown in the upper column of FIG.

Here, code A is the multiplication coefficient of f(R), and code B is f(R).
)×A is an addition coefficient for adding a signal of a specific constant value. By performing this signal processing, attenuation due to the influence of the edge of the object was partially displayed as a C scope image, but only the simulated defect could be clearly identified.

FIG. 9 shows an example in which a test object (2) having undulations on its surface and impact damage was detected. This test object (2) is a 2.3M thick FRP fabric laminate made of plain weave carbon fiber and glass fiber. This subject (
The surface of 2) has undulations with a pitch of about 4M and a height of about 100 μm. Radius 8 IIlffi
As a result of an iron ball weighing 6 kg falling onto the test object (2) of this FRP fabric material laminate, defects were generated in the test object due to impact damage. For comparison, 6m IIX6am, 4m
A 2 mm x 2 mm A1 tape was attached to the bottom of the subject (2).

This specimen (2) was tested for flaws using the ultrasonic reflector method. A threshold is set for the f (R) signal, which corresponds to the attenuation of ultrasonic waves by a 2 tm x 2 mm Al tape, and attenuation exceeding this value is displayed as a defect. displayed as an image.

However, f (R) / f (S) = f (C)
(7) By performing signal processing and displaying f (C), defects caused by impact damage and artificial defects caused by the Al tape could be clearly identified.

<Effects of the Invention> The method of the present invention eliminates the effects of attenuation of ultrasound due to factors other than defects, such as roughness or undulations on the surface of the object that impede the incidence of ultrasound waves, or tissue changes at the edges of the object or inside the object. It is possible to clearly understand defects existing within the object by reducing
Efficient inspection becomes possible.

[Brief explanation of the drawing]

Figure 1 is a block diagram of the ultrasonic flaw detection method using the ultrasonic reflector method, Figure 2 is a schematic diagram of the ultrasonic reflection method, and Figure 3 is a schematic diagram and block diagram of the ultrasonic transmission method and ultrasonic flaw detection method. Part 1, Fig. 4 is a schematic diagram of the A scope image, Fig. 5 is a schematic diagram of the gate setting method for signal processing in accordance with the flaw detection arrangement shown in Fig. 2, and Fig. 6 is a schematic diagram of the A scope image. Schematic diagram of gate setting method for signal processing in the flaw detection arrangement shown in Figure 7.
This figure is an explanatory diagram of the signal processing procedure, and FIGS. 8 and 9 are diagrams in which only defects of a subject with an irregular surface state are displayed as C-scope images. (1) Reflector plate (2) Object (3) Probe (4) Vacuum/Shiba (5) Gate circuit (6) Gate circuit (7)
Oscilloscope (8) Oscilloscope (9) Analog signal processing device α (I A/D
Converter Corporation Waveform storage device side Digital signal processing device ■ Screen input/output device Q4 CRT display α51C scan control program αe Motor controller α Ultrasonic transmission medium 0 seconds Probe α inside Receiver Figure Figure Figure Figure Figure

Claims (1)

[Claims] 1. Select two echo signals showing fluctuations from among the reflected or transmitted echo signals that are continuously obtained as voltage signals through ultrasonic flaw detection of the test object, and select them as expressed by the following equation. An ultrasonic flaw detection method characterized by detecting defects using a signal f(C) obtained by signal processing. {f(R)×A+B)/f(S)=f(C), {f(BT)×A+B)/f(S)=f(C), f(R)/f(S)=f( C), f(BT)/f(S)
=f(C), f(F)×A/f(BT)=f(C), f(F)×A/f(R)=f(C), {f(Th)×A+B}/f (S)=f(C), f(Th)/f(S)=f(C) or f(F)×A/f(Th)=f(C) [where f(S), f (BT), f(R), f(F) and f(Th) are the object surface, bottom surface, reflector plate,
Represents the reflected and transmitted echo signals from the defect. f(C) represents a signal obtained by signal processing. A
is a positive real number that is a coefficient for adjusting the signal amplitude, and B is a positive or negative real number that is a coefficient for adjusting the signal level (
Unit: V). ]