CN110161118A - A kind of steel plate crack detecting method based on supersonic guide-wave principle - Google Patents

Abstract

The invention discloses a steel plate crack detection method based on the principle of ultrasonic guided waves, and relates to the fields of structural nondestructive testing technology and ultrasonic testing technology. The invention aims to solve the problem that the existing detection method cannot detect certain types of cracks in the bridge deck without damaging the bridge deck, and the detection range is limited. Use one ultrasonic transducer as both the transmitting end and the receiving end to perform mobile detection in the length direction of the steel plate to be tested, or use two ultrasonic transducers as the transmitting end and the receiving end to move the U-shaped rib and the steel plate to be detected Whether there is a crack on the length of the gap connecting the gap, the receiving end can collect the ultrasonic guided wave signal when moving to different positions, and obtain the correlation coefficient between two adjacent time domain features according to the time domain characteristics of each ultrasonic guided wave signal ; According to the correlation coefficient curve obtained in step 3, the length of the internal crack of the U-shaped rib is obtained, and the detection of the crack is completed. It is used for invisible cracks at the junction of U-shaped ribs and steel plates to be inspected.

Description

A Steel Plate Crack Detection Method Based on the Principle of Ultrasonic Guided Waves

technical field

The invention relates to a steel plate crack detection method based on the principle of ultrasonic guided waves. The invention belongs to the field of structural non-destructive testing technology and ultrasonic testing technology.

Background technique

Orthotropic steel bridge decks have been widely used in various types of bridge projects at home and abroad because of their outstanding advantages in terms of mechanical properties, performance and economy. However, due to the complex structure of the orthotropic steel bridge deck, there are many connections and welding parts between the components. Bridge decks are prone to fatigue cracks. Fatigue cracks in orthotropic steel bridge decks are concealed and dispersed, but once they appear, they develop rapidly, posing a serious threat to the service safety of bridges and greatly reducing the service life of bridges.

Fatigue cracks in orthotropic steel bridge decks are mainly classified according to their location, taking the most commonly used closed U-shaped stiffener as an example. Figure 2 shows the location of the main parts, 1 is the U-shaped rib, 2 is the steel plate to be tested, 3 is the diaphragm, and 4 is the fatigue crack in the weld between the U-shaped rib and the steel plate to be tested. . Fatigue cracks mainly appear in the joints of U ribs and roof, the joints of U ribs and diaphragms, the butt welds of U ribs, the cracks of U ribs where U ribs pass through welding holes, and the joints of diaphragms and roofs. At present, most of the above-mentioned cracks are visible cracks, and the on-site detection method is the appearance visual inspection method, that is, the location and characteristics of the cracks are recorded inside the steel box girder by manual inspection, marking, numbering, and taking pictures. In addition, some scholars use fatigue strain sensors to monitor the dynamic development of a small number of cracks according to research needs, but only collect data for cracks found visually for research purposes, and cannot be used to detect cracks not found visually.

Among the above-mentioned cracks, there is another type of crack with a special position, which is located at the connection between the U-rib and the top plate and inside the closed U-rib. It expands along the direction of the U-rib. It cannot be detected by visual appearance, and it is an invisible crack. Shown as 4 in Figure 2. At present, the commonly used detection method in actual engineering is to open the bridge deck pavement on the outside of the steel box girder, that is, the bridge deck, to expose the flat top surface of the steel plate (ie, the roof), and then use ultrasonic time-of-flight diffraction equipment (ie, TOFD ultrasonic Flaw detector) scans the steel plate along the weld direction of the U rib and the top plate for a long distance. This method needs to block the traffic and destroy the pavement layer of the entire lane for detection, strictly speaking, it does not belong to non-destructive testing, and consumes a lot of manpower, material resources and financial resources. In addition, ultrasonic phased array detection can also be used, but ultrasonic phased array has shortcomings such as too small scanning range and scanning blind area. In addition, there is currently no effective detection method for invisible cracks in the roof of orthotropic steel bridge decks.

Contents of the invention

The invention aims to solve the problem that the existing detection method cannot detect certain types of cracks in the bridge deck without damaging the bridge deck, and the detection range is limited. A steel plate crack detection method based on the principle of ultrasonic guided waves is now provided.

A steel plate crack detection method based on the principle of ultrasonic guided waves, said method comprising the following steps:

Step 1. Place the No. 1 ultrasonic transducer 6 on the bottom of the steel plate 2 to be detected and on the side of the U-shaped rib 1, and apply a voltage signal to the No. 1 ultrasonic transducer 6, and the voltage signal excites ultrasound in the steel plate 2 to be detected. For the guided wave signal, the No. 1 ultrasonic transducer 6 or the No. 2 ultrasonic transducer 7 is used to collect the ultrasonic guided wave signal, and the No. 2 ultrasonic transducer 7 is placed on the bottom of the steel plate 2 to be detected and located on the other side of the U-shaped rib 6. One side is either placed on the side wall of the U-shaped rib 6 or on the same side as the No. 1 ultrasonic transducer 6;

Step 2: Set a plurality of collection points at the bottom of the steel plate 2 to be detected and along the length direction of the steel plate 2 to be detected, and the No. 1 ultrasonic transducer 6 arrives at each collection point sequentially along the length direction or simultaneously makes the No. 1 ultrasonic transducer 6 The No. 1 ultrasonic transducer 6 and the No. 2 ultrasonic transducer 7 are moved at equal intervals along the length direction of the U-shaped rib 1, and the voltage is applied again and the ultrasonic guided wave signal is collected according to the method of step 1, so that the No. 1 ultrasonic transducer 6 is obtained as the collection terminal. Or when the No. 2 ultrasonic transducer 7 moves to a different position as the collecting end, the ultrasonic guided wave signal is collected;

Step 3, according to the time-domain characteristics of each ultrasonic guided wave signal, the correlation coefficient between two adjacent time-domain characteristics is obtained;

Step 4: According to the correlation coefficient curve obtained in Step 3, the length of the crack inside the U-shaped rib 6 is obtained, and the detection of the crack is completed.

Preferably, a signal generating device is used to apply a voltage signal to the ultrasonic transducer 9 .

Preferably, both the ultrasonic transducer 9 and the other ultrasonic transducer 10 are realized by narrow-band resonant transducers.

Preferably, the waveform of the voltage signal is:

In the formula, t is time, V(t) is the voltage waveform changing with time, A is the maximum amplitude of the voltage pulse, H(t) is the unit step function, n is the number of cycles contained in the waveform, f _c is the narrowband waveform center frequency.

Preferably, the correlation coefficient between the time domain features of two adjacent ultrasonic guided wave signals is obtained as:

In the formula, and represent the time-domain characteristic curves of the ultrasonic guided wave signals of the i-th path and the i+1-th path, respectively, Indicates the signal curve and The correlation coefficient between Represents the signal characteristic curve and The covariance between and respectively represent the signal characteristic curve and respective variances.

Preferably, in step four, according to the correlation coefficient obtained in step three, the specific content of obtaining the length of the crack inside the U-shaped rib 6 is:

According to the sequential movement of No. 1 ultrasonic transducer 6 or the simultaneous movement of No. 1 ultrasonic transducer 6 and No. 2 ultrasonic transducer 7, multiple ultrasonic guided wave signals are measured. The correlation coefficient between the domain features obtains all the correlation coefficients at the continuous moving position. If there is a sudden drop point in a certain correlation coefficient, these drop points correspond to the start and end points of the fatigue crack, so that the crack length can be measured, and the top plate 2 and U Detection and location of invisible fatigue cracks at the root of the weld between rib 1.

The beneficial effects of the present invention are:

Compared with the existing ultrasonic detection methods, the steel plate fatigue crack detection method based on the principle of ultrasonic guided wave proposed by this application makes full use of the characteristic that ultrasonic guided wave can propagate in a large range in the steel plate. The ultrasonic guided wave transducer is arranged at a certain distance between the seams, which can achieve a larger detection range compared with the traditional ultrasonic method, and avoid detection blind spots (such as the position where the weld along the U rib intersects with the diaphragm in Figure 2). The ultrasonic guided wave transducer is used for mobile detection, and the correlation coefficient between the time domain features of two adjacent ultrasonic guided wave signals is obtained according to the time domain characteristics of two ultrasonic guided wave signals extracted from every two adjacent positions. Multiple correlation coefficients obtained from continuous positions can obtain the internal crack length of U-shaped ribs, and complete long-distance and large-scale roof fatigue crack detection.

Description of drawings

Fig. 1 is a flow chart of a steel plate crack detection method based on the principle of ultrasonic guided waves described in Embodiment 1;

Fig. 2 is the structural diagram of the existing closed U-shaped stiffener orthotropic steel bridge deck;

Fig. 3 is a structural schematic diagram of two ultrasonic transducers arranged at the bottom of the steel bridge deck;

Fig. 4 is a structural schematic diagram in which an ultrasonic transducer is arranged on the bottom of the steel bridge deck, and the other is arranged on the U rib;

Fig. 5 is the structural representation of embodiment 1;

Fig. 6 is the correlation coefficient analysis curve figure of embodiment 1;

Fig. 7 is the structural representation of embodiment 2;

FIG. 8 is a schematic structural view of Embodiment 3.

Detailed ways

The present invention will be further described below in conjunction with accompanying drawing.

Figure 3 is a typical steel plate with U-shaped ribs, 7 is the asphalt concrete pavement layer on the steel plate, that is, the road surface, this position cannot be detected by ultrasonic method, and 4 is the possible cracks on the steel plate. Inside the ribs, it cannot be detected by visual means. Therefore, the existing detection methods cannot detect cracks without damaging the bridge deck, and the detection range is limited. In view of the above-mentioned technical defects, the present invention proposes a method for identifying fatigue cracks in steel plates with U ribs based on the principle of ultrasonic guided waves, which is especially suitable for the detection of invisible cracks on the top plate connected with U ribs in orthotropic steel bridge decks .

Example 1:

FIG. 4 and FIG. 5 show a schematic diagram of a steel plate crack detection method based on the principle of ultrasonic guided waves in Embodiment 1. The steel plate crack detection method based on the ultrasonic guided wave principle is used to accurately detect internal cracks and crack lengths of the steel plate without damaging the steel plate pavement layer.

Referring to Fig. 4 and Fig. 5, a steel plate crack detection method based on the principle of ultrasonic guided wave in this embodiment includes the following steps:

Step 1. Place No. 1 ultrasonic transducer 6 and No. 2 ultrasonic transducer 7 under the steel plate 2 to be tested and respectively on both sides of the U-shaped rib or place No. 1 ultrasonic transducer 6 on the U-shaped rib. Place the No. 2 ultrasonic transducer 7 on the U-shaped rib under the steel plate to be detected on the side, when the No. 1 ultrasonic transducer 6 and the No. On both sides of the U-shaped rib, the distance between the No. 2 ultrasonic transducer 7 and the U-shaped rib is determined according to the actual U-shaped rib spacing. The No. 1 ultrasonic transducer 6 is a mobile ultrasonic transducer, which is directly connected to the steel plate through the coupling agent. Contact and excite the ultrasonic guided wave in the steel plate, and use the two-core shielded signal line to connect the No. 1 ultrasonic transducer 6 with the signal generating device 8; the signal generating device can be a signal generator, or a data generator with analog output function. board or module;

Step 2: The signal generating device applies the narrow-band voltage signal represented by Formula 1 to the No. 1 ultrasonic transducer 6. At the same time, the No. 1 ultrasonic transducer 6 excites the ultrasonic guided wave to propagate in the entire cross-section of the steel plate, carrying the propagating The ultrasonic guided wave of the damage information in the path propagates to the No. 2 ultrasonic transducer 7 through the steel plate, and the data acquisition device 9 connected to it stores and analyzes the received ultrasonic guided wave signal in real time or for subsequent offline analysis;

Step 3, measure the length of the steel plate 2 to be detected to be 80 cm, so move No. 1 ultrasonic transducer 6 and No. 2 ultrasonic transducer 7 every 2 cm, and No. 1 ultrasonic transducer 6 moves along the length of the steel plate to be detected. The steel plate 2 moves, and the No. 2 ultrasonic transducer 7 moves along the length direction of the U-shaped rib or moves in the length direction of the other side of the steel plate 2 to be detected. After moving, apply voltage and collect guided wave signals according to step 2. Transducer 6 and No. 2 ultrasonic transducer 7 have moved 40 position points respectively, so No. 2 ultrasonic transducer 7 measures the guided wave signals of 40 position points in total and collects 40 measuring points,

Step 4, after the ultrasonic guided wave signal is collected by the No. 2 ultrasonic transducer 7, the envelope of the guided wave signal is calculated, and then used for correlation coefficient analysis;

Step five, Fig. 6 are the correlation coefficient analysis results of embodiment 1, as can be seen from the figure, at the position of measuring point 13, the correlation coefficient becomes smaller, after this, the correlation coefficient becomes larger; at the position of measuring point 32, the correlation coefficient It becomes smaller again; this result indicates that there is a fatigue crack between measuring point 13 and measuring point 32, and the length is about 38 cm. This result is consistent with the actual fatigue crack location, which verifies the effectiveness of this method.

The working principle of a steel plate crack detection method based on the principle of ultrasonic guided waves in this embodiment will be described below.

In order to accurately measure whether there is a crack and the length of the crack, this embodiment first measures the length of the steel plate to be detected to be 80 cm, and sets a collection point every 2 cm on the length, so that the No. Each time the length of the detection plate reaches a collection point, an ultrasonic signal is excited, and when the No. 1 ultrasonic transducer moves to a collection point, the No. 2 ultrasonic transducer also moves to another position. The No. 1 ultrasonic transducer and the No. 2 ultrasonic transducer The ultrasonic transducers keep equal distances and move at the same time. Therefore, the No. 1 ultrasonic transducer excites an ultrasonic signal, the No. 2 ultrasonic transducer collects an ultrasonic guided wave signal, and the No. 2 ultrasonic transducer The time domain characteristics of the two collected ultrasonic guided wave signals are obtained to obtain the correlation coefficient between the time domain characteristics of two adjacent ultrasonic guided wave signals; multiple continuous correlation coefficients are obtained according to the continuous moving position, and the internal crack length of the U-shaped rib is obtained. Complete the detection of cracks. Compared with the traditional ultrasonic method, this embodiment has a larger detection range and avoids detection blind spots.

In a preferred embodiment of the present invention, the signal generating device can be a narrowband resonant transducer, a non-narrowband resonant transducer or other devices capable of outputting narrowband waveforms, and its resonant frequency matches the center frequency of the narrowband waveform mentioned above. The narrow-band voltage signal sent out is a narrow-band pulse signal, which helps to reduce the waveform distortion of the guided-wave signal caused by the dispersion effect of the guided-wave.

In a preferred embodiment of the present invention, the waveform of the voltage signal is:

In the formula, t is time, V(t) is the voltage waveform changing with time, A is the maximum amplitude of the voltage pulse, H(t) is the unit step function, n is the number of cycles contained in the waveform, f _c is the narrowband waveform center frequency. The frequency is mainly selected based on the principle that the corresponding guided wave wavelength matches the crack size. For steel plates in actual engineering, this frequency is approximately between 30kHz and 200kHz.

In this preferred embodiment, the voltage waveform represented by Formula 1 is one of the narrowband waveforms in the frequency domain, and other formulas can also be used to represent the narrowband waveforms in other frequency domains. In a preferred embodiment of the present invention, a certain time-domain feature of the ultrasonic guided wave signals collected at different positions, such as the envelope, is extracted, and then the correlation between the time-domain features of two adjacent ultrasonic guided wave signals is obtained in turn. The calculation method of the correlation coefficient is:

In the formula, and represent the time-domain characteristic curves of the ultrasonic guided wave signals of the i-th path and the i+1-th path, respectively, Indicates the signal curve and The correlation coefficient between Represents the signal characteristic curve and The covariance between and respectively represent the signal characteristic curve and respective variances.

In some two tests, due to the short distance between two adjacent paths, the difference between the two paths is small in the case of no fatigue cracks or when both paths pass through fatigue cracks. Therefore, at this time and Correlation coefficient between larger. And when one of the paths passes through the fatigue crack and the other path does not pass through the fatigue crack, at this time and Correlation coefficient between will be significantly reduced compared to the previous case. According to the above principles, the calculated correlation coefficients are arranged in order. If the correlation coefficients are all high, it means that there is no fatigue crack in the weld between the top plate and the U-shaped intercostal of the detection section. If there is a sudden drop point in the correlation coefficient, these abrupt points correspond to The starting and ending points of the fatigue cracks, so as to realize the detection and positioning of the invisible fatigue cracks at the root of the weld between the top plate and the U-shaped ribs of the detection section.

Example 2:

FIG. 7 shows a schematic diagram of a steel plate crack detection method based on the principle of ultrasonic guided waves in Example 2. The steel plate crack detection method based on the ultrasonic guided wave principle is used to accurately detect internal cracks and crack lengths of the steel plate without damaging the steel plate pavement layer.

Referring to Fig. 7, a steel plate crack detection method based on the principle of ultrasonic guided waves in this embodiment includes the following contents:

Place the No. 1 ultrasonic transducer 6 on one side of the U-shaped rib under the steel plate to be tested. The distance between the No. 1 ultrasonic transducer 6 and the U-shaped rib is determined according to the actual U-shaped rib spacing. The No. 1 ultrasonic transducer 6 It is a mobile ultrasonic transducer, which is in direct contact with the steel plate through a couplant, and connected to the No. 1 ultrasonic transducer 6 is an ultrasonic signal excitation-receiving module 10, which can realize Pulse-Echo, that is, pulse-echo Ultrasonic testing mode. The module firstly applies a voltage signal to the No. 1 ultrasonic transducer 6, and at this time, the No. 1 ultrasonic transducer 6 works as a driver. Then switch to data acquisition mode for a short time. At this time, No. 1 ultrasonic transducer 6 works as a sensor, receiving ultrasonic guided wave reflections from fatigue cracks, welds, etc. in the steel plate; the received ultrasonic guided wave signals are stored and analyzed in real time or used for subsequent offline analysis. In this embodiment, the scanner can also be used to carry the No. 1 ultrasonic transducer 6 and the excitation-receiving module 10 for continuous multi-point detection (moving vertically to the screen in FIG. 7 ) to improve work efficiency.

The working principle of a steel plate crack detection method based on the principle of ultrasonic guided waves in this embodiment will be described below.

This application adopts No. 1 ultrasonic transducer 6 as the device for sending and receiving signals, uses the scanner to carry No. 1 ultrasonic transducer 6 for continuous multi-point detection, processes the signals detected at each point, and finally detects cracks and crack length. Compared with the traditional ultrasonic method, this embodiment has a larger detection range and avoids detection blind spots.

In a preferred embodiment of the present invention, the signal generating device can be a narrowband resonant transducer, a non-narrowband resonant transducer or other devices capable of outputting narrowband waveforms, and its resonant frequency matches the center frequency of the narrowband waveform mentioned above. The narrow-band voltage signal sent out is a narrow-band pulse signal, which helps to reduce the waveform distortion of the guided-wave signal caused by the dispersion effect of the guided-wave.

In a preferred embodiment of the present invention, the waveform of the voltage signal is:

In the formula, t is time, V(t) is the voltage waveform changing with time, A is the maximum amplitude of the voltage pulse, H(t) is the unit step function, n is the number of cycles contained in the waveform, f _c is the narrowband waveform center frequency. The frequency is mainly selected based on the principle that the corresponding guided wave wavelength matches the crack size. For steel plates in actual engineering, this frequency is approximately between 30kHz and 200kHz.

In this preferred embodiment, the voltage waveform represented by Formula 1 is one of the narrowband waveforms in the frequency domain, and other formulas can also be used to represent the narrowband waveforms in other frequency domains. In a preferred embodiment of the present invention, a certain time-domain feature of the ultrasonic guided wave signals collected at different positions, such as the envelope, is extracted, and then the correlation between the time-domain features of two adjacent ultrasonic guided wave signals is obtained in turn. The calculation method of the correlation coefficient is:

In the formula, and represent the time-domain characteristic curves of the ultrasonic guided wave signals of the i-th path and the i+1-th path, respectively, Indicates the signal curve and The correlation coefficient between Represents the signal characteristic curve and The covariance between and respectively represent the signal characteristic curve and respective variances.

In some two tests, due to the short distance between two adjacent paths, the difference between the two paths is small in the case of no fatigue cracks or when both paths pass through fatigue cracks. Therefore, at this time and Correlation coefficient between larger. And when one of the paths passes through the fatigue crack and the other path does not pass through the fatigue crack, at this time and Correlation coefficient between will be significantly reduced compared to the previous case. According to the above principles, the calculated correlation coefficients are arranged in order. If the correlation coefficients are all high, it means that there is no fatigue crack in the weld between the top plate and the U-shaped intercostal of the detection section. If there is a sudden drop point in the correlation coefficient, these abrupt points correspond to The starting and ending points of the fatigue cracks, so as to realize the detection and positioning of the invisible fatigue cracks at the root of the weld between the top plate and the U-shaped ribs of the detection section.

Example 3:

FIG. 8 shows a schematic diagram of a steel plate crack detection method based on the principle of ultrasonic guided waves in Embodiment 3. The steel plate crack detection method based on the ultrasonic guided wave principle is used to accurately detect internal cracks and crack lengths of the steel plate without damaging the steel plate pavement layer.

Referring to Fig. 8, a steel plate crack detection method based on the principle of ultrasonic guided waves in this embodiment includes the following contents:

Place the No. 1 ultrasonic transducer 6 and the ultrasonic transducer 7 on the bottom of the steel plate 2 to be detected and the No. 1 ultrasonic transducer 6 and the ultrasonic transducer 7 are all located on the same side of the U-shaped rib, and the No. 1 ultrasonic transducer Both the ultrasonic transducer 6 and the ultrasonic transducer 7 are mobile ultrasonic transducers. The No. 1 ultrasonic transducer 6 and the ultrasonic transducer 7 always keep the same distance and move together along the length direction of the steel plate 2 to be detected. The No. 1 ultrasonic transducer Whenever the transducer 6 and the ultrasonic transducer 7 move to a position, the No. 1 ultrasonic transducer 6 excites the ultrasonic guided wave signal, and the No. 2 ultrasonic transducer 7 receives the ultrasonic guided wave signal. If there is a crack in the connection gap between the U-shaped rib between the transducer 6 and the ultrasonic transducer 7 and the steel plate to be tested, the ultrasonic guided wave sent by the No. 1 ultrasonic transducer 6 will propagate to the crack, and will be reflected by the crack No. 2 ultrasonic transducer 7, at this time, the signal received by No. 2 ultrasonic transducer 7 is different from the signal without cracks; use No. 1 ultrasonic transducer 6 and ultrasonic transducer 7 to move and collect the entire steel plate to be detected (2) according to the collected signal to analyze whether there is a crack and the length of the crack at the connection gap between the U-shaped rib and the steel plate to be detected.

The working principle of a steel plate crack detection method based on the principle of ultrasonic guided waves in this embodiment will be described below.

This application adopts No. 1 ultrasonic transducer 6 and No. 2 ultrasonic transducer 7 to move from one end of the steel plate 2 to be detected to the other end of the steel plate 2 to be detected along the length direction of the U-shaped rib. The length of the connecting seam of the steel plate is detected, and the detected signal is used to judge whether there is a crack in the seam and obtain the length of the crack. Compared with the traditional ultrasonic method, this embodiment has a larger detection range and avoids detection blind spots.

Claims (7)

1. a kind of steel plate crack detecting method based on supersonic guide-wave principle, which is characterized in that the described method comprises the following steps:

Step 1: No.1 ultrasonic transducer (6) is placed on steel plate to be detected (2) bottom and is located at U-shaped rib (1) side, to one Number ultrasonic transducer (6) applies voltage signal, and voltage signal excitation ultrasound guided wave signals in steel plate to be detected (2) use The No.1 ultrasonic transducer (6) acquires ultrasonic guided wave signals, and No. two ultrasonic transducers using No. two ultrasonic transducers (7) (7) be placed on steel plate to be detected (2) bottom and be located at U-shaped rib (6) other side or be placed on U-shaped rib (6) side wall or with No.1 ultrasonic transducer (6) is ipsilateral；

Step 2: multiple collection points, No.1 ultrasonic transduction is arranged in steel plate to be detected (2) bottom and along U-shaped rib (1) length direction Device (6) along the length direction successively reach each collection point or make simultaneously No.1 ultrasonic transducer (6) and No. two it is super Sonic transducer (7) keeps equidistant mobile along U-shaped rib (1) length direction, applies voltage again simultaneously in the way of step 1 Ultrasonic guided wave signals are acquired, to obtain No.1 ultrasonic transducer (6) as collection terminal or No. two ultrasonic transducer (7) conducts Collection terminal collects ultrasonic guided wave signals when being moved to different location；

Step 3: obtaining the related coefficient between two neighboring temporal signatures according to the temporal signatures of each ultrasonic guided wave signals；

Step 4: obtaining U-shaped rib (6) underbead crack length according to the related coefficient curve that step 3 obtains, complete to crackle Detection.

2. a kind of steel plate crack detecting method based on supersonic guide-wave principle according to claim 1, which is characterized in that adopt Voltage signal is applied to ultrasonic transducer (6) with signal generation apparatus.

3. a kind of steel plate crack detecting method based on supersonic guide-wave principle according to claim 2, which is characterized in that one Number ultrasonic transducer (6) and No. two ultrasonic transducers (7) are all made of the realization of narrow band resonances formula energy converter.

4. a kind of steel plate crack detecting method based on supersonic guide-wave principle according to claim 3, which is characterized in that electricity Press the waveform of signal are as follows:

In formula, t is the time, and V (t) is the voltage waveform changed over time, and A is voltage pulse maximum amplitude, and H (t) is unit rank Jump function, and n includes periodicity, f by waveform_cFor the centre frequency of narrow band waveform.

5. a kind of steel plate crack detecting method based on supersonic guide-wave principle according to claim 1, which is characterized in that obtain Obtain the related coefficient between adjacent two ultrasonic guided wave signals temporal signatures are as follows:

In formula,WithThe time-domain characteristic curve of the ultrasonic guided wave signals of the i-th paths and i+1 paths is respectively indicated,Indicate signal curveWithBetween related coefficient,Indicate signal characteristic curveWithBetween association Variance,WithRespectively indicate signal characteristic curveWithRespective variance.

6. a kind of steel plate crack detecting method based on supersonic guide-wave principle according to claim 1, which is characterized in that step In rapid four, according to the related coefficient that step 3 obtains, the particular content of U-shaped rib (1) underbead crack length is obtained are as follows:

According to No.1 ultrasonic transducer (6) successively move or No.1 ultrasonic transducer (6) and No. two ultrasonic transducers (7) It is mobile simultaneously, multiple ultrasonic guided wave signals are measured, according to the phase relation between adjacent two ultrasonic guided wave signals temporal signatures Number obtains related coefficient all in continuous moving position, if there is unexpected drop point in some related coefficient, these declines Point respectively corresponds the start-stop point of fatigue crack, to measure crack length, realizes to weld seam root between top plate (2) and U-shaped rib (1) The detection and positioning of the invisible fatigue crack in portion.

7. a kind of steel plate crack detecting method based on supersonic guide-wave principle according to claim 1, which is characterized in that more The spacing distance of a collection point is equal.