Ultrasonic flaw detection device and ultrasonic flaw detection method

Abstract

To provide an ultrasonic flaw detection device or the like that can enhance defect detection accuracy and detect defect positions with high accuracy in ultrasonic flaw detection using a pulse compression method.SOLUTION: An ultrasonic flaw detection device 100 comprises an ultrasonic probe 1, a power spectrum calculation unit 31, a design waveform generation unit 32, a correlation function calculation unit 33 and a design waveform selection unit 34. The power spectrum calculation unit calculates a power spectrum corresponding to a first design waveform. The design waveform generation unit generates a plurality of second design waveforms having the same power spectrum as the first design waveform. The ultrasonic probe transmits a transmission wave based on the second design waveform to a flaw detection target material S and receives a reception wave reflected inside the flaw detection target material. The correlation function calculation unit calculates a plurality of second correlation functions between a reference wave corresponding to the transmission wave based on the second design waveform and the reception wave corresponding to the second design waveform. The design waveform selection unit selects a design waveform preferable for the ultrasonic probe among the plurality of second design waveforms based on a predetermined criterion.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to an ultrasonic flaw detection device and an ultrasonic flaw detection method for detecting flaws in a material to be detected, such as a steel material, using ultrasonic waves. In particular, the present invention relates to an ultrasonic flaw detection device and an ultrasonic flaw detection method that can know an ultrasonic waveform suitable for an ultrasonic probe in ultrasonic flaw detection using a pulse compression method, and selectively use the suitable ultrasonic waveform to improve defect detection accuracy and detect defect positions with high accuracy. [Background technology]

[0002] 2. Description of the Related Art Conventionally, ultrasonic flaw detection methods have been used to detect defects present inside a material to be flaw-detected, such as a steel material. The ultrasonic testing method uses an ultrasonic probe to transmit ultrasonic waves as transmission waves to the material being tested, and receives the ultrasonic waves (echoes) reflected inside the material as reception waves to detect defects inside the material being tested.

[0003] A more specific ultrasonic flaw detection method is the pulse-echo method, which transmits ultrasonic waves with a short time duration as a transmission wave and detects the presence and location of defects that are reflection sources from the change in the amplitude of the received wave over time. For example, when the material to be detected is a metal material such as steel and defects such as cracks, cavities, and inclusions present inside the material are to be detected, the ultrasonic waves propagating inside the material are reflected at the interface between the defects. Echoes from defects (defect echoes) generated by this reflection appear as changes in amplitude in the time waveform of the received wave, so the presence and location of defects present inside the material can be detected from the presence or absence of changes in this amplitude and the time position at which the changes appear.

[0004] The pulse-echo method uses the time waveform of the received wave to detect defects. Therefore, when noise with a relatively large amplitude is superimposed on the received wave compared to the defect echo, the ratio of the defect echo to noise (S / N) drops significantly, and there is a risk that the defect cannot be detected accurately.

[0005] In order to address the above-mentioned problems with the pulse echo method, a technique called pulse compression has recently been used (see, for example, Patent Document 1). Figure 1 is a diagram illustrating a pulse compression method. In the most basic pulse compression method, a waveform modulated by amplitude modulation, frequency modulation (or a combination of these), or the like, shown by the dashed lines in Figures 1(a) and 1(b), is used as the transmitted wave. Then, the time position of the transmitted wave is shifted relative to the received wave, shown by the solid lines in Figures 1(a) and 1(b), and a correlation function, such as that shown in Figure 1(c), is calculated, which indicates how closely the received wave matches the transmitted wave at each shifted time position. In the correlation function, the horizontal axis represents the time position (the time position of the transmitted wave) and the vertical axis represents the degree of match (the degree of match between the transmitted wave and the received wave). The pulse compression method assumes that ultrasonic waves reflected inside the test material appear in the received wave with a waveform similar to that of the transmitted wave. Therefore, at the time position where the received wave and the time-shifted transmitted wave coincide (the time position shown in Figure 1(b)), the degree of agreement of the correlation function shown in Figure 1(c) is high. At the time position where the received wave and the time-shifted transmitted wave coincide (the time position shown in Figure 1(a)), the degree of agreement of the correlation function shown in Figure 1(c) is low. Furthermore, the degree of agreement between the transmitted wave and random noise with a waveform different from that of the transmitted wave is not high regardless of the time position. Therefore, even if random noise other than the transmitted and received waves is present in the signal obtained from the test material, the pulse compression method focuses only on signals with a high degree of agreement, allowing it to extract only the received wave generated in response to the transmitted wave. This enables high-precision measurements without being affected by noise. Furthermore, if the received wave for which the correlation function shown in Figure 1(c) is obtained is the result of the transmitted wave being reflected by a defect inside the material being inspected, the time position (b) in Figure 1(c) will correspond to the time position corresponding to the round-trip distance of the ultrasonic wave to the defect. Therefore, if the sound speed in the material being inspected is determined in advance, the defect position can be detected based on the time position of the point with the highest degree of match of the correlation function. Furthermore, since the degree of match of the correlation function has a positive correlation with the magnitude of the received wave, it is also possible to estimate the size of the defect from the degree of match.

[0006] The advantage of using pulse compression is that by devising the waveform of the transmitted wave, it is possible to narrow the range of time positions where the degree of coincidence of the correlation function is large (thus improving the accuracy of detecting the defect position), and to increase the S / N ratio of the correlation function (thus improving the accuracy of detecting the defect).This gives the appearance of obtaining a signal waveform compressed in the time axis direction, hence the name pulse compression method.

[0007] However, the pulse compression method has a problem that if the waveform of the actually transmitted transmission wave changes from the designed waveform corresponding to the waveform of the transmission wave to be transmitted due to the characteristics of the ultrasonic probe, the correlation function deteriorates and the detection accuracy deteriorates. Specifically, the range of time positions where the degree of coincidence of the correlation function is large widens, resulting in a correlation function with a poor S / N ratio.

[0008] For this reason, in the pulse compression method, the designed waveform, which is designed as the waveform of the ultrasonic wave to be transmitted from the ultrasonic probe, is determined so that the correlation function between the transmitted wave and the received wave shows a steep peak. However, since the actual transmitted wave based on the designed waveform is transmitted from the ultrasonic probe, the designed waveform is subject to restrictions such as the characteristics of the ultrasonic probe used. For example, it is restricted by the frequency band of the ultrasonic probe (i.e., the frequency band of the transmission wave that can be transmitted from the ultrasonic probe). Generally, if the designed waveform includes a frequency outside the frequency band of the ultrasonic probe, that frequency band will not be included in the transmission wave that is actually transmitted, and the wider the frequency band of the transmission wave, the steeper the peak of the correlation function calculated based on the transmission wave can be. Therefore, the designed waveform is set so that the frequency band of its power spectrum is as wide as possible within the range of the frequency band of the ultrasonic probe. Furthermore, it is limited by the ability of the transmission wave actually transmitted from the ultrasonic probe to track with respect to the design waveform (i.e., the ability to prevent the waveform of the transmission wave actually transmitted from the ultrasonic probe from differing due to differences in the time waveforms, even when the design waveforms are in the same frequency band). If the tracking ability of the transmission wave is high, the transmission wave can be obtained as expected based on the design waveform, and the correlation function can be made to show a steep peak. On the other hand, if the tracking ability of the transmission wave is low, the correlation function will deteriorate. Specifically, the range of time positions where the degree of agreement of the correlation function is high will be wide, resulting in a correlation function with a poor S / N ratio.

[0009] In conventional pulse compression methods, the above-mentioned constraints on tracking are not taken into consideration, which leads to a problem that the correlation function deteriorates, and the accuracy of detecting defects and the accuracy of detecting defect positions may deteriorate. [Prior art documents] [Patent documents]

[0010] [Patent Document 1] Patent No. 7186816 Summary of the Invention [Problem to be solved by the invention]

[0011] The present invention has been made to solve the problems of the above-mentioned conventional technology, and has an object to provide an ultrasonic flaw detection device and an ultrasonic flaw detection method that can improve the defect detection accuracy and detect the defect position with high accuracy in ultrasonic flaw detection using the pulse compression method. [Means for solving the problem]

[0012] In order to solve the above problems, the present invention provides an ultrasonic flaw detection device for detecting defects present inside a material to be detected, the ultrasonic flaw detection device comprising: an ultrasonic probe that transmits ultrasonic waves to the material to be detected as transmission waves and receives ultrasonic waves reflected inside the material to be detected as reception waves; a correlation function calculation unit that calculates a correlation function between the reception waves and a reference wave corresponding to the transmission waves; a power spectrum calculation unit that calculates a power spectrum; a design waveform generation unit that generates a design waveform corresponding to the waveform of ultrasonic waves to be transmitted to the material to be detected; and a design waveform selection unit that selects a design waveform suitable for the ultrasonic probe from among the design waveforms generated by the design waveform generation unit, wherein the power spectrum calculation unit selects a design waveform suitable for the ultrasonic probe from among the design waveforms generated by the design waveform generation unit, the design waveform selection unit selecting ... the design waveform generation unit generates a plurality of second design waveforms as design waveforms having the same power spectrum as the power spectrum corresponding to the first design waveform; the ultrasonic probe transmits a transmission wave based on the second design waveform to the material to be inspected and receives a reception wave corresponding to the second design waveform reflected inside the material to be inspected; the correlation function calculation unit calculates a plurality of second correlation functions which are correlation functions between a reference wave corresponding to the transmission wave based on the second design waveform and a reception wave corresponding to the second design waveform; and the design waveform selection unit selects a design waveform suitable for the ultrasonic probe from the plurality of second design waveforms based on a predetermined criterion. The present invention also includes a defect detection unit that detects defects present inside the test object, The defect detection section may detect defects present inside the material to be detected based on the second correlation function corresponding to a design waveform suitable for the ultrasonic probe.

[0013] In the present invention, the "reference wave" is generated by branching off the "transmission wave" transmitted from the ultrasonic probe, and has substantially the same waveform as the transmission wave. According to the present invention, the correlation function calculation unit calculates a correlation function between a reference wave corresponding to a transmission wave transmitted from the ultrasonic probe and a reception wave received by the ultrasonic probe. Then, as necessary, the defect detection unit detects defects present inside the material to be inspected based on the calculated correlation function. In other words, ultrasonic inspection is performed using the pulse compression method. In this case, the power spectrum calculation unit calculates the power spectrum corresponding to the first design waveform, which is an arbitrary design waveform. The first design waveform may be any waveform and is not limited to a specific waveform (whether or not it is actually transmitted is not an issue), but since it must be capable of being transmitted as a transmission wave from an ultrasonic probe, it must be a waveform whose frequencies at least partially overlap with the frequency band of the transmission wave that can be transmitted from the ultrasonic probe. Furthermore, it is preferable that the first design waveform be a waveform that uses frequency components within the frequency band that can be transmitted by the ultrasonic probe over as wide a band as possible, since this allows the peak of the correlation function to be steep when the correlation function is calculated. Since there are no particular restrictions on the time waveform of the first design waveform, for example, a rectangular wave having frequency components across the entire frequency band of the transmission wave that can be transmitted from the ultrasonic probe can be used. The power spectrum is a spectrum obtained by squaring the coefficients for each frequency obtained by Fourier transforming a time waveform such as a design waveform. The power spectrum calculated by the power spectrum calculation unit is calculated based on the first design waveform, and therefore is calculated as a spectrum that reflects the characteristics of the first design waveform, i.e., the usage status of the frequency band of the first design waveform. Then, the design waveform generating section generates a plurality of second design waveforms as design waveforms having the same power spectrum as the power spectrum calculated by the power spectrum calculating section. The Winer-Khinchin theorem mathematically proves that if two design waveforms have the same power spectrum, their autocorrelation functions will be identical, even if their waveforms on the time axis are different. Therefore, since the multiple second design waveforms generated by the design waveform generator all have the same power spectrum as the first design waveform, the second design waveform can be considered to be essentially the same function as the first design waveform when calculating the correlation function, even though their waveforms on the time axis are different. In other words, the second design waveform can be considered to have the same characteristics as the first design waveform when calculating the correlation function, which is performed using the pulse compression method.

[0014] Next, a design waveform suitable for the ultrasonic probe is selected from the plurality of second design waveforms by a design waveform selection unit based on a predetermined criterion. The reason why we say "preferable" here is that, although it is naturally preferable to select the "optimum" design waveform if it is possible to select it, in reality, multiple second design waveforms are generated depending on the power spectrum calculated for an arbitrary first design waveform whose frequency band and degree of tracking ability are unknown, and since an "optimum" (i.e., "preferable") design waveform is selected from among the multiple second design waveforms, the selected second design waveform may not necessarily be "optimum" for the ultrasonic probe. When a design waveform is input to an ultrasonic probe, the ultrasonic probe actually transmits a transmission wave whose waveform is degraded compared to the design waveform due to the characteristics of the ultrasonic probe. In this case, if the waveform of the transmission wave actually transmitted from the ultrasonic probe closely matches the design waveform, the transmission wave is obtained as expected based on the design waveform, and the correlation function exhibits a steep peak. On the other hand, if the waveform of the transmission wave does not closely match the design waveform, the correlation function deteriorates. Specifically, the correlation function widens the range of time positions where the degree of match between the correlation functions is high, resulting in a correlation function with a poor S / N ratio. The design waveform selection unit of the present invention selects a design waveform suitable for the ultrasonic probe from among multiple second design waveforms based on a predetermined criterion. In other words, the design waveform suitable for the ultrasonic probe is selected from among multiple second design waveforms based on a criterion that ensures high tracking of the transmission wave and an appropriate second correlation function (a correlation function with a narrow range of time positions where the degree of match between the correlation functions is high and a high S / N ratio). This allows the above-mentioned constraints to be satisfied. Therefore, the ultrasonic probe transmits a transmission wave corresponding to a design waveform suitable for the selected ultrasonic probe, receives a reception wave corresponding to a design waveform suitable for the ultrasonic probe, the correlation function calculation unit calculates a correlation function between a reference wave based on the design waveform suitable for the ultrasonic probe and a reception wave corresponding to the design waveform suitable for the ultrasonic probe, and the defect detection unit detects defects present inside the material to be detected based on the correlation function corresponding to the design waveform suitable for the ultrasonic probe (i.e., performs ultrasonic testing using a pulse compression method with an optimal design waveform), thereby improving the accuracy of defect detection and enabling the defect location to be detected with high accuracy.

[0015] Specifically, the predetermined criterion is considered to be a criterion for using an evaluation function V(φ(f)) shown in the following formula (1) or formula (2) to select a design waveform obtained by optimizing the evaluation function V(φ(f)) from among the plurality of second design waveforms as a design waveform suitable for the ultrasonic probe.

number

[0016] In the present invention, the second correlation function calculated by the correlation function calculation unit can also be calculated by actually transmitting all of the transmission waves based on the plurality of second design waveforms from the ultrasonic probe. However, when considering using a large number of second design waveforms in order to enable the design waveform selection unit to accurately select a design waveform suitable for the ultrasonic probe, actually transmitting all of the transmission waves based on the second design waveforms is too time-consuming and unrealistic. Therefore, preferably, the correlation function calculation unit has a prediction model that takes the design waveform as an input and outputs a correlation function corresponding to the design waveform, and by inputting the second design waveform into the prediction model, at least some of the multiple second correlation functions to be calculated are replaced with correlation functions output from the prediction model.

[0017] According to the above-described preferred configuration, the correlation function calculation unit replaces at least a part of the calculated second correlation function with the correlation function output from the prediction model by inputting the second design waveform into the prediction model, which has the advantage of saving the effort of actually transmitting the transmission wave.

[0018] Further, in order to solve the above-mentioned problems, the present invention provides an ultrasonic flaw detection method for detecting defects present inside a material to be detected, the ultrasonic flaw detection method including: an ultrasonic probe that transmits ultrasonic waves to the material to be detected as transmission waves and receives ultrasonic waves reflected inside the material to be detected as reception waves; a correlation function calculation unit that calculates a correlation function between the reference wave corresponding to the transmission wave and the reception wave; a power spectrum calculation unit that calculates a power spectrum; a design waveform generation unit that generates a design waveform corresponding to the waveform of ultrasonic waves to be transmitted to the material to be detected; and a design waveform selection unit that selects a design waveform suitable for the ultrasonic probe from among the design waveforms generated by the design waveform generation unit, the ultrasonic flaw detection method including: a power spectrum calculation step that calculates a power spectrum corresponding to a first design waveform that is an arbitrary design waveform using the power spectrum calculation unit; the ultrasonic probe for detecting flaws, the ultrasonic probe for detecting flaws, and the ultrasonic wave transmitting and receiving step for transmitting a transmission wave based on the second design waveform to the material to be detected and receiving a reception wave corresponding to the second design waveform reflected inside the material to be detected; the ultrasonic probe for detecting flaws, the ultrasonic probe for detecting flaws, and the ultrasonic wave transmitting and receiving step for calculating a plurality of second correlation functions, which are correlation functions between a reference wave corresponding to the transmission wave based on the second design waveform and a reception wave corresponding to the second design waveform, and the ultrasonic probe for detecting flaws, the ultrasonic probe for detecting flaws, and the reference wave corresponding to the transmission wave based on the second design waveform and receiving a reception wave corresponding to the second design waveform; and the ultrasonic probe for detecting flaws, the ultrasonic probe for detecting flaws, the ultrasonic probe for detecting flaws, and the ultrasonic wave selecting step for selecting a design waveform suitable for the ultrasonic probe from the plurality of second design waveforms based on a predetermined criterion .... [Effects of the Invention]

[0019] According to the present invention, in ultrasonic flaw detection using the pulse compression method, it is possible to improve the accuracy of defect detection and to detect the defect position with high accuracy. [Brief explanation of the drawings]

[0020] [Figure 1] FIG. 1 is a diagram for schematically explaining a pulse compression method. [Figure 2]1 is a diagram illustrating a schematic configuration of an ultrasonic flaw detection device according to an embodiment of the present invention. [Figure 3] FIG. 10 is a diagram schematically illustrating an example of a design waveform. [Figure 4] FIG. 1 is a diagram schematically illustrating a chirp wave used as a design waveform. [Figure 5] 10A and 10B are diagrams for explaining the operation of a correlation function calculation unit; [Figure 6] 1 is a flowchart showing a schematic operation of an ultrasonic flaw detection device according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0021] An ultrasonic flaw detector according to one embodiment of the present invention will be described below with reference to the accompanying drawings as needed. Fig. 2 is a diagram showing a schematic configuration of an ultrasonic flaw detection device according to this embodiment. As shown in Fig. 2, the ultrasonic flaw detection device 100 according to this embodiment is a device that detects defects present inside a material S to be detected, and includes an ultrasonic probe 1, a flaw detector 2, and a calculation processing unit 3. The calculation processing unit 3 has a power spectrum calculation unit 31, a design waveform generation unit 32, a correlation function calculation unit 33, a design waveform selection unit 34, and a defect detection unit 35. Each of the components included in the ultrasonic flaw detection device 100 will be described below.

[0022] <Ultrasonic probe 1> The ultrasonic probe 1 is placed opposite the material to be detected S, transmits ultrasonic waves U to the material to be detected S as transmission waves, and receives ultrasonic waves reflected inside the material to be detected S as received waves. If a defect F exists inside the material to be detected S and is located on the propagation path of the ultrasonic waves U, the received waves will contain ultrasonic waves reflected by the defect (defect echo E), which will appear as a change in amplitude in the time waveform of the received waves. Similarly, the ultrasonic probe 1 can transmit a transmission wave based on a second design waveform described later to the material S to be detected, and receive a reception wave corresponding to the second design waveform reflected inside the material S to be detected. 2 has a single transducer, and performs two-dimensional scanning relative to the material to be detected S as needed. However, the ultrasonic probe 1 is not limited to this, and it is also possible to use a linear array type ultrasonic probe having a plurality of transducers arranged in a line, or a matrix array type ultrasonic probe having a plurality of transducers arranged in a matrix.

[0023] <Flaw detector 2> The flaw detector 2 is electrically connected to the ultrasonic probe 1 and is equipped with well-known components similar to those of flaw detectors equipped in general ultrasonic flaw detection devices, such as a pulser that transmits ultrasonic waves U (transmitted waves) from the transducer possessed by the ultrasonic probe 1, a receiver that causes the transducer possessed by the ultrasonic probe 1 to receive ultrasonic waves (received waves), an amplifier that amplifies the analog flaw detection signal corresponding to the received wave output from the receiver, and an A / D converter that converts the analog signal output from the amplifier into a digital signal.

[0024] <Calculation processing unit 3> The arithmetic processing unit 3 is configured, for example, by a general-purpose computer electrically connected to the flaw detector 2, and stores programs for causing the arithmetic processing unit 3 to function as a power spectrum calculation unit 31, a design waveform generation unit 32, a correlation function calculation unit 33, a design waveform selection unit 34, and a defect detection unit 35. The arithmetic processing unit 3 can then function as the power spectrum calculation unit 31, the design waveform generation unit 32, the correlation function calculation unit 33, the design waveform selection unit 34, and the defect detection unit 35 by executing these programs.

[0025] [Correlation function calculation unit 33] The correlation function calculation unit 33 is a functional unit that calculates the correlation function between a reference wave corresponding to a transmitted wave and a received wave. The ultrasonic flaw detection device 100 according to this embodiment is assumed to use a pulse compression method as an example of ultrasonic flaw detection, and in order to detect defects present inside the material S to be detected, it is necessary to calculate the correlation function (degree of agreement) between a reference wave that has the same waveform as the transmitted wave and is obtained by branching the transmitted wave, and a received wave that is returned by the transmitted wave being reflected inside the material S to be detected. Therefore, when performing ultrasonic flaw detection, the correlation function calculation unit 33 calculates the correlation function between such a reference wave and a received wave. Furthermore, even in the case where transmission waves based on multiple second design waveforms described below are transmitted from the ultrasonic probe 1 to the material S to be inspected and received waves reflected inside the material S to be inspected are received, the correlation function calculation unit 33 similarly calculates the correlation function between the reference wave corresponding to the transmission wave based on the second design waveform and the received wave corresponding to the second design waveform, and the correlation function calculated in this case is specifically referred to as the second correlation function. The correlation functions calculated by the correlation function calculation unit 33 are output to the design waveform selection unit 34 and the defect detection unit 35 as necessary, and the second correlation function in particular is output to the design waveform selection unit 34.

[0026] [Power spectrum calculation unit 31] The power spectrum calculation unit 31 is a functional unit that calculates a power spectrum. More specifically, the power spectrum calculation unit 31 calculates a power spectrum corresponding to a first design waveform, which is an arbitrary design waveform. The first design waveform may be any waveform and is not limited to a specific waveform (whether it is actually transmitted or not is irrelevant), but since it must be capable of being transmitted as a transmission wave from the ultrasonic probe, it is necessary for the waveform to have at least a portion of its frequency overlapping with the frequency band of the transmission wave transmittable from the ultrasonic probe 1. The first design waveform is preferably a waveform using frequency components within the frequency band transmittable by the ultrasonic probe 1 over as wide a band as possible, since this allows the peak of the correlation function to be steep when the correlation function is calculated. There are no particular restrictions on the time waveform of the first design waveform, so for example, a rectangular wave having frequency components across the entire frequency band of the transmission wave transmittable from the ultrasonic probe 1 can be used. One of the objectives of the ultrasonic flaw detection device 100 of this embodiment is to improve the accuracy of defect detection and enable highly accurate detection of defect positions by enabling transmission waves with high tracking capability to be transmitted from the ultrasonic probe 1. To achieve this, it is necessary to find a transmission wave having a waveform with high tracking capability for the ultrasonic probe 1. Since it is easier to find a transmission wave with high tracking ability if there is a reference waveform, in this embodiment, a first design waveform is first generated as an arbitrary design waveform. As described above, the first design waveform can be, for example, a square wave having frequency components that span the entire frequency band of the transmission wave that can be transmitted from the ultrasonic probe 1 (even if they extend beyond the band). This is because such a square wave can make it possible to use a wide range of the frequency band of the transmission wave that can be transmitted from the ultrasonic probe 1, and it is thought that the range of time positions where the degree of match is high when the correlation function is calculated can be narrowed. Then, the power spectrum calculation unit 31 calculates a power spectrum for the first design waveform thus obtained. As is generally known, the power spectrum corresponds to a spectrum obtained by squaring each coefficient for each frequency obtained by Fourier transforming the waveform along the time axis. The power spectrum calculated by the power spectrum calculation unit 31 is output to the design waveform generation unit 32.

[0027] [Design waveform generation unit 32] The design waveform generating unit 32 is a functional unit that generates a design waveform corresponding to the waveform of the ultrasonic waves to be transmitted to the material S to be flaw-detected. More specifically, the design waveform generation unit 32 generates a plurality of second design waveforms as design waveforms having the same power spectrum as the power spectrum corresponding to the first design waveform calculated by the power spectrum calculation unit 31. The design waveform generation unit 32 can also actually generate the above-mentioned first design waveform. The Winer-Khinchin theorem mathematically proves that if two design waveforms have the same power spectrum, their autocorrelation functions will be identical, even if their waveforms on the time axis are different. Therefore, since multiple second design waveforms all have the same power spectrum as the first design waveform, the second design waveform will calculate the exact same correlation function, even though its waveform on the time axis is different from the first design waveform. In other words, multiple second design waveforms are equivalent to mass-produced waveforms with different time waveforms that, based on the first design waveform, produce the same results when calculating the correlation function. The second design waveform generated by the design waveform generating unit 32 is output to the ultrasonic probe 1 via the design waveform selecting unit 34 and the flaw detector 2.

[0028] [Design Waveform Selection Section 34] The design waveform selection unit 34 is a functional unit that selects a design waveform suitable for the ultrasonic probe 1 from among the design waveforms generated by the design waveform generation unit 32. More specifically, the design waveform selection unit 34 selects a design waveform suitable for the ultrasonic probe 1 from among the plurality of second design waveforms generated by the design waveform generation unit 32 based on a predetermined criterion. That is, the design waveform selection unit 34 selects a suitable design waveform based on a criterion (predetermined criterion) that provides high tracking of the transmission wave and an appropriate second correlation function (a correlation function with a narrow time position range where the degree of coincidence of the correlation functions is high and a high S / N ratio). Details of the predetermined criterion will be described later. The following will more specifically explain the thinking that led to the configuration of the design waveform selection section 34 and the operation of the design waveform selection section 34 with reference to the drawings.

[0029] FIG. 3 is a diagram showing a schematic example of a design waveform. The design waveforms shown in FIG. 3(a) and FIG. 3(b) both appear to have smooth amplitude changes at first glance, but the tracking ability of the transmitted wave may differ. Specifically, the design waveforms shown in FIG. 3(a) and FIG. 3(b) are examples in which they have the exact same power spectrum and common frequency characteristics, but the waveforms on the time axis are different. In this case, the tracking ability of the transmitted wave may differ. As such, even design waveforms having the same power spectrum may have different tracking capabilities of the transmitted wave. Therefore, in this embodiment, the design waveform generation unit 32 generates multiple second design waveforms having the same power spectrum (the same power spectrum as the power spectrum corresponding to the first design waveform), the correlation function calculation unit 33 calculates a second correlation function, which is the correlation function between each of the reference waves corresponding to the transmitted wave based on the multiple generated second design waveforms and the received wave reflected by the material to be detected S and returned, corresponding to the second design waveform, and the design waveform selection unit 34 uses this second correlation function to select a design waveform suitable for the ultrasonic probe 1 from the multiple second design waveforms based on a predetermined criterion.

[0030] Here, if we assume that the transmitted wave does not change (perfectly tracks) the designed waveform, the calculated correlation function will be the autocorrelation function of the transmitted wave. As is clear from the Winer-Khinchin theorem, the autocorrelation functions of transmitted waves with the same power spectrum will match perfectly even if the waveforms on the time axis are different. Therefore, the autocorrelation functions of the designed waveforms shown in Figures 3(a) and 3(b) will match perfectly. Therefore, if a design waveform with the same power spectrum is used in the pulse compression method, it is sufficient to consider only that the frequency band of the power spectrum of the designed waveform is set to use a wide range of the frequency band of the ultrasonic probe 1. On the other hand, if constraints on the tracking of the transmitted wave to the designed waveform are not taken into consideration (perfect tracking is assumed), as in the case of conventional pulse compression methods, a chirp wave such as that shown in Figure 4, which has the smallest peak value / effective value (smallest amplitude fluctuation) among countless designed waveforms with the same power spectrum, is often used as the designed waveform. However, there is a possibility that this chirp wave is not excellent in terms of tracking of the transmitted wave.

[0031] Therefore, as shown in Figure 5, the correlation function calculation unit 33 transmits from the ultrasonic probe 1 multiple (preferably a large number of) transmission waves based on the second design waveforms having the same power spectrum, which are determined by the constraint that they must be included in the frequency band of the ultrasonic probe 1, and calculates the second correlation function based on the received waves obtained by receiving the ultrasonic waves reflected inside the material S to be detected.

[0032] The second correlation function calculated by the correlation function calculation unit 33 can also be calculated by actually transmitting all of the transmission waves based on the plurality of second design waveforms from the ultrasonic probe 1. However, when considering using a large number of second design waveforms in order to enable the design waveform selection unit 34 to accurately select a design waveform suitable for the ultrasonic probe 1, actually transmitting all of the transmission waves based on the second design waveforms is too time-consuming and unrealistic. Therefore, in a preferred embodiment, the correlation function calculation unit 33 has a prediction model that receives a design waveform as input and outputs a correlation function corresponding to the design waveform. By inputting the second design waveform into the prediction model, at least some of the calculated second correlation functions are replaced with the correlation functions output from the prediction model. This prediction model may be generated by training a machine learning model using a combination of the design waveform and a correlation function corresponding to an actually obtained design waveform as training data. The machine learning model is not limited to this, but may be, for example, a regression model. Furthermore, by regarding the design waveform as an image, a deep learning model may also be used. The prediction model may be generated by the correlation function calculation unit 33 of the ultrasonic flaw detection device 100 of this embodiment itself learning a machine learning model, or a prediction model generated by another similar ultrasonic flaw detection device may be stored in the correlation function calculation unit 33 of the ultrasonic flaw detection device 100 of this embodiment.

[0033] As described above, the design waveform selection unit 34 selects a design waveform suitable for the ultrasonic probe 1 from among the multiple second design waveforms based on a predetermined criterion using the second correlation function calculated by the correlation function calculation unit 33. Specifically, the predetermined criterion is a criterion for using the evaluation function V(φ(f)) shown in the following equation (1) or equation (2) to select, from among a plurality of second design waveforms, a design waveform obtained by optimizing the evaluation function V(φ(f)), as a design waveform suitable for the ultrasonic probe 1.

number

[0034] Furthermore, the evaluation function V(φ(f)) shown in the above formula (2) is a function that directly evaluates the amount of change in the transmitted wave relative to the designed waveform. Specifically, the evaluation function V(φ(f)) shown in formula (2) is obtained by integrating, over a certain time width (t1≦t≦t2), the square of the difference between the case where the transmitted wave does not change at all from the designed waveform (= the autocorrelation function of the designed waveform) and the second correlation function. This time width may be a time width corresponding to the entire second correlation function, or a partial time width, as long as it includes at least the vicinity of the time position where the second correlation function shows a peak. The evaluation function V(φ(f)) shown in the above equation (1) is obtained by multiplying the square of the “half-width of the second correlation function,” which corresponds to whether or not the second correlation function shows a steep peak, and the square of the “maximum amplitude of the second correlation function,” which corresponds to the S / N ratio of the second correlation function, by coefficients α and β, respectively, and then adding them together. For either of the evaluation functions V(φ(f)) shown in formula (1) and formula (2), the absolute value (i.e., power spectrum) of each frequency f of the design waveform suitable for the ultrasonic probe 1 is determined, so the phase φ(f) of each frequency f can be determined to determine (select) the design waveform suitable for the ultrasonic probe 1. Therefore, optimizing the evaluation function V(φ(f)) shown in formula (1) or formula (2) corresponds to solving the optimization problem of the phase φ(f).

[0035] In this manner, the design waveform suitable for the ultrasonic probe 1 selected by the design waveform selection unit 34 is output to the flaw detector 2. The flaw detector 2 (a pulser provided in the flaw detector 2) outputs the design waveform suitable for the ultrasonic probe 1 to the ultrasonic probe 1, so that the ultrasonic probe 1 can transmit a transmission wave based on the design waveform suitable for the ultrasonic probe 1 and receive a reception wave corresponding to the design waveform suitable for the ultrasonic probe 1.

[0036] [Defect detection section 35] The defect detection unit 35 is a functional unit that detects defects present inside the material to be detected S. More specifically, the defect detection unit 35 detects defects present inside the material to be detected S based on a second correlation function that corresponds to a design waveform that is suitable for the ultrasonic probe 1. For example, if the degree of coincidence of the second correlation function corresponding to the design waveform suitable for the ultrasonic probe 1 is equal to or greater than a predetermined threshold value, it is possible to determine that a defect exists inside the material S to be inspected, and to detect the defect position based on the time position at which the second correlation function shows a peak. In addition, the ultrasonic flaw detection device 100 of this embodiment may be configured to include a defect detection unit 35, since various ultrasonic flaw detections are possible using a design waveform suitable for the ultrasonic probe 1 if the design waveform suitable for the ultrasonic probe 1 can be identified.However, on the other hand, if it is not necessary to detect defects or if a separate defect detection method is used, the device may be configured not to include the defect detection unit 35.

[0037] Next, the operation of the ultrasonic flaw detection device 100 according to this embodiment will be described with reference to Fig. 6. Fig. 6 is a flow chart showing the general operation of the ultrasonic flaw detection device 100 according to this embodiment. As shown in FIG. 6, when the processing in the ultrasonic flaw detector 100 starts, the process proceeds to step S101.

[0038] (Step S101) In step S101, an arbitrary first design waveform is created, preferably as a design waveform whose frequencies at least partially overlap with the frequency band of a transmission wave that can be transmitted from the ultrasonic probe 1. Then, using the power spectrum calculation unit 31, a power spectrum corresponding to the first design waveform, which is an arbitrary design waveform, is calculated (power spectrum calculation step). The power spectrum calculated in step S101 is output to the design waveform generation unit 32. When the processing in step S101 is completed, the process proceeds to step S103.

[0039] (Step S103) In step S103, the design waveform generator 32 generates a plurality of second design waveforms as design waveforms having the same power spectrum as the power spectrum corresponding to the first design waveform (second design waveform generation step). Since the plurality of second design waveforms all have a common power spectrum (common to the first design waveform as well), they are the same waveform in terms of correlation function calculation, but are generated as waveforms with different spectra on the time axis. The generated plurality of second design waveforms are output to the ultrasonic probe 1 via the flaw detector 2. When the processing in step S103 is completed, the process proceeds to step S105.

[0040] (Step S105) In step S105, the ultrasonic probe 1 is used to transmit a transmission wave based on the second design waveform to the material S to be detected, and a reception wave corresponding to the second design waveform reflected inside the material S to be detected is received (ultrasonic transmission / reception step). When the processing in step S105 is completed, the process proceeds to step S107.

[0041] (Step S107) In step S107, a plurality of second correlation functions, which are correlation functions between a reference wave corresponding to a transmission wave based on the second design waveform and a received wave corresponding to the second design waveform, are calculated using correlation function calculation unit 33 (second correlation function calculation step). Since this process is performed for each of the plurality of second design waveforms, a plurality of second correlation functions are also calculated. The calculated plurality of second correlation functions are output to design waveform selection unit 34 and, as appropriate, defect detection unit 35. When the processing in step S107 is completed, the process proceeds to step S109.

[0042] (Step S109) In step S109, the design waveform selection unit 34 is used to select a design waveform suitable for the ultrasonic probe 1 from among the multiple second design waveforms based on the above-mentioned predetermined criteria (criteria using equation (1) or equation (2)) (design waveform selection step). By making such a selection, it is possible to select a design waveform that is more suitable for the ultrasonic probe 1 from among a plurality of second design waveforms that have the same frequency characteristics (through the fact that the power spectrum is the same). If the design waveform that is suitable for the ultrasonic probe 1 is known, then by utilizing the design waveform that is suitable for the ultrasonic probe 1 during ultrasonic flaw detection in the ultrasonic flaw detection device 100, flaw detection with less degradation becomes possible. When the process in step S109 is completed, the process proceeds to step S111.

[0043] (Step S111) In step S111, the defect detection unit 35 is used to detect defects present inside the material S to be detected based on the second correlation function corresponding to the design waveform suitable for the ultrasonic probe 1. In step S111, defects may be detected by transmitting and receiving ultrasonic waves again using the design waveform suitable for the ultrasonic probe 1 selected in step S109 and calculating the correlation function, but since the correlation function corresponding to the design waveform suitable for the ultrasonic probe 1 has already been calculated when the design waveform suitable for the ultrasonic probe 1 is selected in step S109, defects inside the material S to be detected can also be detected using the correlation function. When the processing in step S111 is completed, the processing is terminated in the ultrasonic flaw detection device 100. Note that the processing in step S111 may be omitted, and the processing in the ultrasonic flaw detection device 100 may be terminated when the processing in step S109 is completed (i.e., when the design waveform suitable for the ultrasonic probe 1 is determined).

[0044] As described above, according to the ultrasonic flaw detection device 100 of this embodiment, ultrasonic flaw detection is performed by the pulse compression method using a waveform designed for the ultrasonic probe 1. In this case, the power spectrum calculation unit 31 calculates a power spectrum corresponding to an arbitrary first design waveform, preferably using a wide frequency band of the ultrasonic probe 1, and the design waveform generation unit 32 generates a plurality of second design waveforms under the condition that the second design waveforms have the same power spectrum as the power spectrum of the first design waveform. As a result, the second design waveforms have the characteristic of widely overlapping the frequency band of the ultrasonic probe 1, similar to the first design waveform. Therefore, by having the design waveform selection unit 34 select a design waveform suitable for the ultrasonic probe 1 from among the multiple second design waveforms, the selected design waveform suitable for the ultrasonic probe 1 can satisfy the constraints on the frequency band of the ultrasonic probe 1, thereby improving the accuracy of defect detection and enabling the defect position to be detected with high accuracy. Furthermore, the design waveform selection unit 34 selects a design waveform suitable for the ultrasonic probe 1 from among the multiple second design waveforms based on a predetermined criterion (a criterion using Equation (1) or Equation (2)). If the trackability is high enough that the actually transmitted transmission wave matches the design waveform, the transmission wave is obtained as expected based on the design waveform, and the second correlation function exhibits a steep peak. On the other hand, if the trackability of the transmission wave is low (the waveform of the transmission wave actually transmitted from the ultrasonic probe differs due to a difference in the time waveform), the second correlation function deteriorates. Specifically, the second correlation function has a wide range of time positions where the degree of match of the correlation function is high, resulting in a correlation function with a poor S / N ratio. The design waveform selection unit 34 selects a design waveform suitable for the ultrasonic probe 1 from among the multiple second design waveforms based on a predetermined criterion. In other words, a suitable design waveform is selected based on criteria that ensure high tracking of the transmitted wave and that make the second correlation function an appropriate correlation function (a correlation function with a narrow range of time positions where the degree of coincidence of the correlation functions is high and a high S / N ratio), thereby improving the tracking of the transmitted wave in the ultrasonic probe 1 to the design waveform. Defects present inside the material S to be inspected can be detected using a design waveform suitable for the ultrasonic probe 1 selected by the design waveform selection unit 34, thereby improving the accuracy of defect detection and enabling the defect position to be detected with high precision. [Explanation of symbols]

[0045] 1...Ultrasonic probe 2...Flaw detector 3. Processing unit 31 Power spectrum calculation section 32...Design waveform generation section 33 Correlation function calculation section 34. Design waveform selection section 35 Defect detection section 100...Ultrasonic flaw detection equipment S...Material to be tested

Claims

1. An ultrasonic flaw detection device for detecting defects present inside a material to be inspected, an ultrasonic probe that transmits ultrasonic waves to the test object as transmission waves and receives ultrasonic waves reflected inside the test object as reception waves; a correlation function calculation unit that calculates a correlation function between a reference wave corresponding to the transmission wave and the reception wave; a power spectrum calculation unit that calculates a power spectrum; a design waveform generating unit that generates a design waveform corresponding to the waveform of an ultrasonic wave to be transmitted to the test object; a design waveform selection unit that selects a design waveform suitable for the ultrasonic probe from among the design waveforms generated by the design waveform generation unit; Equipped with the power spectrum calculation unit calculates a power spectrum corresponding to a first design waveform, which is an arbitrary design waveform; the design waveform generating unit generates a plurality of second design waveforms as design waveforms having the same power spectrum as the power spectrum corresponding to the first design waveform; the ultrasonic probe transmits a transmission wave based on the second design waveform to the material to be detected, and receives a reception wave corresponding to the second design waveform reflected inside the material to be detected; the correlation function calculation unit calculates a plurality of second correlation functions which are correlation functions between a reference wave corresponding to a transmission wave based on the second design waveform and a reception wave corresponding to the second design waveform; the design waveform selection unit selects a design waveform suitable for the ultrasonic probe from among the plurality of second design waveforms based on a predetermined criterion. Ultrasonic flaw detection equipment.

2. a defect detection unit that detects defects present inside the test object, The ultrasonic flaw detection device according to claim 1 , wherein the defect detection unit detects defects present inside the material to be detected based on the second correlation function corresponding to a design waveform suitable for the ultrasonic probe.

3. 2. The ultrasonic flaw detection device of claim 1, wherein the predetermined criterion is a criterion for using an evaluation function V(φ(f)) shown in the following equation (1) or (2) to select, from among the plurality of second design waveforms, a design waveform obtained by optimizing the evaluation function V(φ(f)), as a design waveform suitable for the ultrasonic probe. [Equation 3] In the above formula (1), α and β are predetermined coefficients. In the above formula (2), t is the time position, and (t) indicates a function of the time position t. t1 and t2 are predetermined constants. f is the frequency, and (f) indicates a function of the frequency f. φ(f) is the phase of the design waveform for each frequency f.

4. The correlation function calculation unit a prediction model that receives the design waveform as an input and outputs a correlation function corresponding to the design waveform; 3. The ultrasonic flaw detection device according to claim 1, wherein at least some of the calculated second correlation functions are replaced with correlation functions output from the prediction model by inputting the second design waveform into the prediction model.

5. An ultrasonic flaw detection method for detecting defects present inside a material to be inspected, comprising: an ultrasonic probe that transmits ultrasonic waves to the test object as transmission waves and receives ultrasonic waves reflected inside the test object as reception waves; a correlation function calculation unit that calculates a correlation function between a reference wave corresponding to the transmission wave and the reception wave; a power spectrum calculation unit that calculates a power spectrum; a design waveform generating unit that generates a design waveform corresponding to the waveform of an ultrasonic wave to be transmitted to the test object; a design waveform selection unit that selects a design waveform suitable for the ultrasonic probe from among the design waveforms generated by the design waveform generation unit; Using an ultrasonic flaw detector equipped with a power spectrum calculation step of calculating a power spectrum corresponding to a first design waveform, which is an arbitrary design waveform, using the power spectrum calculation unit; a second design waveform generating step of generating, using the design waveform generating unit, a plurality of second design waveforms as design waveforms having the same power spectrum as the power spectrum corresponding to the first design waveform; an ultrasonic transmitting / receiving step of transmitting a transmission wave based on the second design waveform to the material to be detected using the ultrasonic probe and receiving a reception wave corresponding to the second design waveform reflected inside the material to be detected; a second correlation function calculation step of calculating, using the correlation function calculation unit, a plurality of second correlation functions which are correlation functions between a reference wave corresponding to a transmission wave based on the second design waveform and a received wave corresponding to the second design waveform; a design waveform selection step of selecting a design waveform suitable for the ultrasonic probe from among the plurality of second design waveforms based on a predetermined criterion using the design waveform selection unit; The ultrasonic flaw detection method has the following features.

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