CN110161118B - Steel plate crack detection method based on ultrasonic guided wave principle - Google Patents
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Abstract
A steel plate crack detection method based on an ultrasonic guided wave principle relates to the technical field of structure nondestructive detection and ultrasonic detection. The invention aims to solve the problems that the existing detection mode can not detect certain types of cracks in the bridge deck under the condition of no damage to the bridge deck and the detection range is limited. The method comprises the following steps that an ultrasonic transducer is used as a transmitting end and a receiving end to perform moving detection in the length direction of a steel plate to be detected, or two ultrasonic transducers are used as the transmitting end and the receiving end respectively to movably detect whether cracks exist on the U-shaped rib and the length of a gap connecting the steel plate to be detected, the receiving end can acquire ultrasonic guided wave signals moving to different positions, and a correlation coefficient between two adjacent time domain characteristics is obtained according to the time domain characteristics of each ultrasonic guided wave signal; and D, obtaining the length of the crack in the U-shaped rib according to the correlation coefficient curve obtained in the step three, and finishing the detection of the crack. The method is used for invisible cracks at the joint of the U-shaped rib and the steel plate to be detected.
Description
Technical Field
The invention relates to a steel plate crack detection method based on an ultrasonic guided wave principle. Belongs to the technical field of structure nondestructive testing and ultrasonic testing.
Background
The orthotropic steel bridge deck is widely applied to various bridge projects at home and abroad due to the outstanding advantages of the orthotropic steel bridge deck in the aspects of mechanical property, service performance, economical efficiency and the like. However, due to the complex structure of the orthotropic steel bridge deck slab and the large number of connecting and welding parts among the components, in recent years, the steel bridge deck slab is easy to have fatigue cracks under the action of increasing traffic flow and overloaded vehicles, as well as the action of factors such as the defects of the structure and welding residual stress. The fatigue crack of the orthotropic steel bridge deck has the characteristics of concealment and dispersion, but develops quickly once appearing, thereby causing serious threat to the service safety of the bridge and greatly reducing the service life of the bridge.
Fatigue cracks in orthotropic steel decking are classified primarily by their location, exemplified by the currently most commonly used closed U-shaped stiffeners. Fig. 2 shows the positions of the main parts, 1 is a U-shaped rib, 2 is a steel plate to be detected, 3 is a diaphragm plate, and 4 is a fatigue crack in a weld between the U-shaped rib and the steel plate to be detected. Fatigue cracks mainly appear at the joint of the U rib and the steel plate, the joint of the U rib and the transverse clapboard, the butt weld joint of the U rib, the U rib crack at the position of the U rib over-weld, the joint of the transverse clapboard and the steel plate and the like. At present, most cracks belong to visible cracks, and the field detection method is an appearance visual inspection method, namely, the positions and characteristics of the cracks are recorded in the steel box girder in a mode of manual checking, marking, numbering, photographing and the like. In addition, some researchers have monitored the dynamic development of a few cracks by using fatigue strain sensors according to the needs of the study, and data are collected only for visually-discovered cracks for research purposes, and cannot be used for detecting visually-undiscovered cracks.
The cracks are special in position, are located at the joint of the U rib and the steel plate and are located inside the closed U rib, and extend along the direction of the U rib, so that the cracks cannot be detected by visual inspection of the appearance and belong to invisible cracks. As shown at 4 in fig. 2. At present, the detection method commonly used in practical engineering is to open a bridge deck pavement layer outside a steel box girder, namely on a bridge deck, expose a flat top surface of a steel plate (namely, a steel plate), and then use ultrasonic diffraction time difference method equipment (namely, a TOFD ultrasonic flaw detector) to scan the steel plate for a long distance along the direction of a weld joint between a U rib and the steel plate. The method needs to block traffic and destroy a pavement layer of the whole lane for detection, strictly speaking, the method does not belong to nondestructive detection, and a large amount of manpower, material resources and financial resources are consumed. In addition, ultrasonic phased array detection can also be adopted, but the ultrasonic phased array has the defects of too small scanning range, scanning blind area and the like. In addition, at present, no effective detection means for invisible cracks at the steel plate part of the orthotropic steel bridge deck plate exists.
Disclosure of Invention
The invention aims to solve the problems that the existing detection mode can not detect certain types of cracks in the bridge deck under the condition of no damage to the bridge deck and the detection range is limited. A steel plate crack detection method based on an ultrasonic guided wave principle is provided.
A steel plate crack detection method based on an ultrasonic guided wave principle comprises the following steps:
firstly, placing a first ultrasonic transducer 6 at the bottom of a steel plate 2 to be detected and on one side of a U-shaped rib 1, applying a voltage signal to the first ultrasonic transducer 6, exciting an ultrasonic guided wave signal in the steel plate 2 to be detected by the voltage signal, collecting the ultrasonic guided wave signal by using the first ultrasonic transducer 6 or a second ultrasonic transducer 7, and placing the second ultrasonic transducer 7 at the bottom of the steel plate 2 to be detected and on the other side of the U-shaped rib 1 or on the side wall of the U-shaped rib 1 or on the same side of the first ultrasonic transducer 6;
secondly, arranging a plurality of collecting 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, sequentially reaching each collecting point by the first ultrasonic transducer 6 along the length direction or simultaneously enabling the first ultrasonic transducer 6 and the second ultrasonic transducer 7 to move at equal intervals along the length direction of the U-shaped rib 1, applying voltage again and collecting ultrasonic guided wave signals according to the mode of the first step, and thus obtaining that the first ultrasonic transducer 6 serves as a collecting end or the second ultrasonic transducer 7 serves as a collecting end and collects the ultrasonic guided wave signals when moving to different positions;
thirdly, obtaining a correlation coefficient between two adjacent time domain characteristics according to the time domain characteristics of each ultrasonic guided wave signal;
and step four, obtaining the invisible fatigue crack length of the root part of the welding seam between the steel plate 2 and the U-shaped rib 1 according to the correlation coefficient curve obtained in the step three, and completing the detection of the crack.
Preferably, a voltage signal is applied to the ultrasonic transducer 9 using a signal generating means.
Preferably, both the ultrasonic transducer 9 and the further ultrasonic transducer 10 are realized as narrow band resonant transducers.
Preferably, the waveform of the voltage signal is:
wherein t is time, V (t) is voltage waveform changing with time, A is maximum amplitude of voltage pulse, H (t) is unit step function, n is period number contained in waveform, f (t) is unit step functioncThe center frequency of the narrow band waveform.
Preferably, the correlation coefficient between the time domain characteristics of two adjacent ultrasonic guided wave signals is obtained as follows:
in the formula (I), the compound is shown in the specification,
and
respectively represents the time domain characteristic curves of the ultrasonic guided wave signals of the ith path and the (i + 1) th path,
representing a signal curve
And
the correlation coefficient between the two components is calculated,
representing characteristic curves of signals
And
middle cooperationThe difference is that the number of the first and second,
and
respectively representing signal characteristic curves
And
the variance of each.
Preferably, in the fourth step, the specific content of obtaining the invisible fatigue crack length of the root of the weld between the steel plate 2 and the U-shaped rib 1 according to the correlation coefficient obtained in the third step is as follows:
according to the sequential movement of the first ultrasonic transducer 6 or the simultaneous movement of the first ultrasonic transducer 6 and the second ultrasonic transducer 7, a plurality of ultrasonic guided wave signals are measured, all correlation coefficients at the continuous movement position are obtained according to the correlation coefficients between the time domain characteristics of two adjacent ultrasonic guided wave signals, and if a certain correlation coefficient suddenly drops, the dropping points respectively correspond to the starting point and the stopping point of the fatigue crack, so that the crack length is measured, and the detection and the positioning of the invisible fatigue crack at the root part of the welding seam between the steel plate 2 and the U-shaped rib 1 are realized.
The invention has the beneficial effects that:
compared with the existing ultrasonic detection method, the steel plate fatigue crack detection method based on the ultrasonic guided wave principle makes full use of the characteristic that the ultrasonic guided wave can be propagated in a steel plate in a large range, and the ultrasonic guided wave transducer is arranged in the steel box girder at a certain distance from a welding line, so that the steel plate fatigue crack detection method has a larger detection range compared with the traditional ultrasonic method, and a detection blind area (such as the position where the welding line along the U rib is intersected with the diaphragm plate in figure 2) is avoided. The method comprises the steps of carrying out movable detection through an ultrasonic guided wave transducer, obtaining correlation coefficients between the time domain characteristics of two adjacent ultrasonic guided wave signals according to the time domain characteristics of two ultrasonic guided wave signals extracted from every two adjacent positions, obtaining the length of a crack inside a U-shaped rib according to a plurality of correlation coefficients obtained from continuous positions, and completing long-distance and large-range steel plate fatigue crack detection.
Drawings
Fig. 1 is a flowchart of a steel plate crack detection method based on an ultrasonic guided wave principle according to a first embodiment;
FIG. 2 is a structural diagram of a conventional orthotropic steel bridge deck with closed U-shaped stiffening ribs;
FIG. 3 is a schematic structural diagram of two ultrasonic transducers arranged at the bottom of a steel bridge deck;
FIG. 4 is a schematic structural diagram of an ultrasonic transducer arranged at the bottom of a steel bridge deck and another ultrasonic transducer arranged on a U-shaped rib;
FIG. 5 is a schematic structural view of embodiment 1;
FIG. 6 is a graph showing a correlation coefficient analysis in example 1;
FIG. 7 is a schematic structural view of embodiment 2;
fig. 8 is a schematic structural view of embodiment 3.
Detailed Description
The invention will be further explained with reference to the drawings.
Fig. 3 shows a typical steel plate with U-shaped ribs, 7 is an asphalt concrete pavement layer on the steel plate, i.e., a pavement, where cracks cannot be detected by using an ultrasonic method, and 4 is a possible crack on the steel plate, which cannot be detected by a visual method if inside the U-shaped ribs. Therefore, the existing detection mode can not detect cracks under the condition of no damage to the bridge deck, and the detection range is limited. Aiming at the technical defects, the invention provides a method for identifying fatigue cracks in a U-ribbed steel plate based on an ultrasonic guided wave principle, which is particularly suitable for detecting invisible cracks on the steel plate connected with U ribs in an orthotropic steel bridge deck.
Example 1:
fig. 4 and 5 show a principle schematic diagram of a steel plate crack detection method based on the ultrasonic guided wave principle in embodiment 1. The steel plate crack detection method based on the ultrasonic guided wave principle is used for accurately detecting the internal cracks and the crack lengths of the steel plates under the condition that the steel plate pavement layer is not damaged.
Referring to fig. 4 and 5, the method for detecting cracks in a steel plate based on the ultrasonic guided wave principle of the present embodiment includes the following steps:
step one, respectively placing a first ultrasonic transducer 6 and a second ultrasonic transducer 7 below a steel plate 2 to be detected and respectively positioned at two sides of a U-shaped rib or placing the first ultrasonic transducer 6 below the steel plate to be detected at one side of the U-shaped rib, placing the second ultrasonic transducer 7 on the U-shaped rib, when the first ultrasonic transducer 6 and the second ultrasonic transducer 7 are respectively placed below the steel plate 2 to be detected and respectively positioned at two sides of the U-shaped rib, determining the distance between the second ultrasonic transducer 7 and the U-shaped rib according to the actual distance between the U-shaped rib, wherein the first ultrasonic transducer 6 is a movable ultrasonic transducer, directly contacts the steel plate through a coupling agent and excites ultrasonic guided waves in the steel plate, and connecting the first ultrasonic transducer 6 with a signal generating device 8 by using two-core shielding signal wires; the signal generating device can be a signal generator and also can be a data board card or a module with an analog output function;
step two, the signal generating device applies the narrow-band voltage signal represented by the formula 1 to the first ultrasonic transducer 6, meanwhile, the first ultrasonic transducer 6 excites the ultrasonic guided wave to propagate in the whole section of the steel plate, the ultrasonic guided wave carrying the damage information in the propagation path is transmitted to the second ultrasonic transducer 7 through the steel plate, and the data acquisition device 9 connected with the second ultrasonic transducer stores and analyzes the received ultrasonic guided wave signal in real time or is used for subsequent off-line analysis;
step three, measuring the length of the steel plate 2 to be detected to be 80 cm, moving the first ultrasonic transducer 6 and the second ultrasonic transducer 7 once every 2 cm, moving the first ultrasonic transducer 6 along the steel plate 2 to be detected, moving the second ultrasonic transducer 7 along the length direction of the U-shaped rib or moving the second ultrasonic transducer 7 along the length direction of the other side of the steel plate 2 to be detected, applying voltage and collecting guided wave signals according to the step two after moving, moving the first ultrasonic transducer 6 and the second ultrasonic transducer 7 by 40 position points respectively, measuring the guided wave signals of 40 position points by the second ultrasonic transducer 7 and collecting 40 measuring points,
step four, calculating an envelope of the guided wave signal after acquiring the ultrasonic guided wave signal through the second ultrasonic transducer 7, and then analyzing the correlation coefficient;
step five, fig. 6 is the result of the correlation coefficient analysis of the embodiment 1, and it can be seen from the figure that the correlation coefficient becomes smaller at the position of the measuring point 13, and thereafter, the correlation coefficient becomes larger; at the position of the measuring point 32, the correlation coefficient becomes smaller again; the results indicate that a fatigue crack exists between point 13 and point 32, which is approximately 38 cm in length. The result is consistent with the actual fatigue crack position, and the effectiveness of the method is verified.
The working principle of the steel plate crack detection method based on the ultrasonic guided wave principle according to the present embodiment will be described below.
In order to accurately measure whether cracks exist or not and the length of the cracks, in the embodiment, the length of a steel plate to be detected is measured to be 80 cm, an acquisition point is arranged at intervals of 2 cm on the length, so that an ultrasonic transducer excites an ultrasonic signal every time when reaching one acquisition point along the length of the steel plate to be detected, an ultrasonic transducer moves to one acquisition point every time the ultrasonic transducer moves to the other position, and the ultrasonic transducer and an ultrasonic transducer move simultaneously at equal intervals, so that the ultrasonic transducer excites the ultrasonic signal once, the ultrasonic transducer collects the ultrasonic guided wave signal once, and the ultrasonic transducer obtains a correlation coefficient between time domain characteristics of two adjacent ultrasonic guided wave signals according to the time domain characteristics of the two ultrasonic guided wave signals collected at every two adjacent positions; and obtaining a plurality of continuous correlation coefficients according to the continuous moving positions, obtaining the length of the crack in the U-shaped rib, and finishing the detection of the crack. Compared with the traditional ultrasonic method, the ultrasonic detection method has a larger detection range and avoids a detection blind area.
In a preferred embodiment of the present invention, the signal generating device may be a narrow-band resonant transducer, a non-narrow-band resonant transducer, or other devices capable of outputting a narrow-band waveform, a resonant frequency of the narrow-band resonant transducer matches with a center frequency of the narrow-band waveform, and the emitted narrow-band voltage signal is a narrow-band pulse signal, which helps to reduce waveform distortion of the guided wave signal caused by the guided wave dispersion effect.
In a preferred embodiment of the present invention, the waveform of the voltage signal is:
wherein t is time, V (t) is voltage waveform changing with time, A is maximum amplitude of voltage pulse, H (t) is unit step function, n is period number contained in waveform, f (t) is unit step functioncThe center frequency of the narrow band waveform. The frequency is selected mainly on the principle that the corresponding guided wave wavelength is matched with the crack size. For steel sheets in practical engineering, the frequency is approximately between 30kHz and 200 kHz.
In the preferred embodiment, the voltage waveform represented by equation 1 is a narrow-band waveform in one of the frequency domains, and other equations may be used to represent narrow-band waveforms in other frequency domains. In a preferred embodiment of the present invention, a certain time domain feature, such as an envelope, of the ultrasonic guided wave signals collected at different positions is extracted, and then correlation coefficients between two adjacent time domain features of the ultrasonic guided wave signals are sequentially obtained, where the calculation method of the correlation coefficients is as follows:
in the formula (I), the compound is shown in the specification,
and
respectively represents the time domain characteristic curves of the ultrasonic guided wave signals of the ith path and the (i + 1) th path,
representing a signal curve
And
the correlation coefficient between the two components is calculated,
representing characteristic curves of signals
And
the covariance of the two or more different signals,
and
respectively representing signal characteristic curves
And
the variance of each.
In two tests, because the distance between two adjacent paths is short, the difference between the two paths is small under the condition of no fatigue crack or when the two paths pass through the fatigue crack, so that the two paths have small difference at the moment
And
coefficient of correlation between
Is relatively large. When one of the paths passes through the fatigue crack and the other path does not pass through the fatigue crack, the method is used
And
coefficient of correlation between
There is a significant reduction from the former case. And according to the principle, the calculated correlation coefficients are arranged in sequence, if the correlation coefficients are higher, the fact that the welding seam between the steel plate and the U-shaped rib at the detection section has no fatigue crack is shown, and if the correlation coefficients have sudden descending points, the sudden descending points respectively correspond to the starting point and the stopping point of the fatigue crack, so that the detection and the positioning of the invisible fatigue crack at the root part of the welding seam between the steel plate and the U-shaped rib at the detection section are realized.
Example 2:
fig. 7 shows a schematic diagram of a steel plate crack detection method based on the ultrasonic guided wave principle in example 2. The steel plate crack detection method based on the ultrasonic guided wave principle is used for accurately detecting the internal cracks and the crack lengths of the steel plates under the condition that the steel plate pavement layer is not damaged.
Referring to fig. 7, the method for detecting cracks in a steel plate based on the ultrasonic guided wave principle includes the following steps:
the first ultrasonic transducer 6 is arranged on one side of a U-shaped rib below a steel plate to be detected, the distance between the first ultrasonic transducer 6 and the U-shaped rib is determined according to the actual distance between the U-shaped ribs, the first ultrasonic transducer 6 is a movable ultrasonic transducer and is directly contacted with the steel plate through a coupling agent, an ultrasonic signal excitation-receiving module 10 is connected with the first ultrasonic transducer 6, and the module can realize Pulse-Echo, namely a Pulse-Echo ultrasonic detection mode. The module first applies a voltage signal to the first ultrasonic transducer 6, while the first ultrasonic transducer 6 operates as a driver. Then switch to data acquisition mode for a short period of time. At the moment, the first ultrasonic transducer 6 works as a sensor and receives ultrasonic guided wave reflected waves from fatigue cracks, welding seams and the like in the steel plate; and the received ultrasonic guided wave signals are stored and analyzed in real time or used for subsequent off-line analysis. In this embodiment, the scanner may also be used to carry the first ultrasonic transducer 6 and the excitation-reception module 10 for continuous multi-point detection (moving perpendicular to the screen in fig. 7), thereby improving the working efficiency.
The working principle of the steel plate crack detection method based on the ultrasonic guided wave principle according to the present embodiment will be described below.
The ultrasonic transducer 6 is used as a device for sending and receiving signals, the scanner is used for carrying the ultrasonic transducer 6 for continuous multi-point detection, signals detected at all points are processed, and finally cracks and crack lengths are detected. Compared with the traditional ultrasonic method, the ultrasonic detection method has a larger detection range and avoids a detection blind area.
In a preferred embodiment of the present invention, the signal generating device may be a narrow-band resonant transducer, a non-narrow-band resonant transducer, or other devices capable of outputting a narrow-band waveform, a resonant frequency of the narrow-band resonant transducer matches with a center frequency of the narrow-band waveform, and the emitted narrow-band voltage signal is a narrow-band pulse signal, which helps to reduce waveform distortion of the guided wave signal caused by the guided wave dispersion effect.
In a preferred embodiment of the present invention, the waveform of the voltage signal is:
wherein t is time, V (t) is voltage waveform changing with time, A is maximum amplitude of voltage pulse, H (t) is unit step function, n is period number contained in waveform, f (t) is unit step functioncThe center frequency of the narrow band waveform. The frequency is selected mainly on the principle that the corresponding guided wave wavelength is matched with the crack size. For steel sheets in practical engineering, the frequency is approximately between 30kHz and 200 kHz.
In the preferred embodiment, the voltage waveform represented by equation 1 is a narrow-band waveform in one of the frequency domains, and other equations may be used to represent narrow-band waveforms in other frequency domains. In a preferred embodiment of the present invention, a certain time domain feature, such as an envelope, of the ultrasonic guided wave signals collected at different positions is extracted, and then correlation coefficients between two adjacent time domain features of the ultrasonic guided wave signals are sequentially obtained, where the calculation method of the correlation coefficients is as follows:
in the formula (I), the compound is shown in the specification,
and
respectively represents the time domain characteristic curves of the ultrasonic guided wave signals of the ith path and the (i + 1) th path,
representing a signal curve
And
the correlation coefficient between the two components is calculated,
representing characteristic curves of signals
And
the covariance of the two or more different signals,
and
respectively representing signal characteristic curves
And
the variance of each.
In two tests, because the distance between two adjacent paths is short, the difference between the two paths is small under the condition of no fatigue crack or when the two paths pass through the fatigue crack, so that the two paths have small difference at the moment
And
coefficient of correlation between
Is relatively large. When one of the paths passes through the fatigue crack and the other path does not pass through the fatigue crack, the method is used
And
coefficient of correlation between
There is a significant reduction from the former case. And according to the principle, the calculated correlation coefficients are arranged in sequence, if the correlation coefficients are higher, the fact that the welding seam between the steel plate and the U-shaped rib at the detection section has no fatigue crack is shown, and if the correlation coefficients have sudden descending points, the sudden descending points respectively correspond to the starting point and the stopping point of the fatigue crack, so that the detection and the positioning of the invisible fatigue crack at the root part of the welding seam between the steel plate and the U-shaped rib at the detection section are realized.
Example 3:
fig. 8 shows a schematic diagram of a steel plate crack detection method based on the ultrasonic guided wave principle in example 3. The steel plate crack detection method based on the ultrasonic guided wave principle is used for accurately detecting the internal cracks and the crack lengths of the steel plates under the condition that the steel plate pavement layer is not damaged.
Referring to fig. 8, the method for detecting cracks in a steel plate based on the ultrasonic guided wave principle includes the following steps:
placing a first ultrasonic transducer 6 and an ultrasonic transducer 7 at the bottom of a steel plate 2 to be detected, wherein the first ultrasonic transducer 6 and the ultrasonic transducer 7 are both positioned at the same side of a U-shaped rib, the first ultrasonic transducer 6 and the ultrasonic transducer 7 are both movable ultrasonic transducers, the first ultrasonic transducer 6 and the ultrasonic transducer 7 always move along the length direction of the steel plate 2 to be detected at the same distance, and when the first ultrasonic transducer 6 and the ultrasonic transducer 7 move to one position, the first ultrasonic transducer 6 excites an ultrasonic guided wave signal, the second ultrasonic transducer 7 receives the ultrasonic guided wave signal, if a crack exists in a connecting gap between the U-shaped rib between the first ultrasonic transducer 6 and the ultrasonic transducer 7 and the steel plate to be detected, the ultrasonic guided wave emitted by the first ultrasonic transducer 6 can propagate to the crack and is reflected to the second ultrasonic transducer 7 by the crack, at this time, the signal received by the second ultrasonic transducer 7 is different from the signal without the crack; the length of the whole steel plate (2) to be detected is movably collected by the first ultrasonic transducer 6 and the first ultrasonic transducer 7, and whether cracks exist at the connecting gaps of the U-shaped ribs and the steel plate to be detected and the length of the cracks are analyzed according to collected signals.
The working principle of the steel plate crack detection method based on the ultrasonic guided wave principle according to the present embodiment will be described below.
This application adopts ultrasonic transducer 6 and No. two ultrasonic transducer 7 from waiting to detect the one end of steel sheet 2, moves to the other end of waiting to detect steel sheet 2 along U type rib length direction, detects whole U type rib and the length of waiting to detect the steel sheet joint seam, judges whether this gap department has the crackle and derives the crackle length according to the signal that detects. Compared with the traditional ultrasonic method, the ultrasonic detection method has a larger detection range and avoids a detection blind area.
Claims (5)
1. A steel plate crack detection method based on an ultrasonic guided wave principle is characterized by comprising the following steps:
the method comprises the following steps that firstly, an ultrasonic transducer (6) is placed at the bottom of a steel plate (2) to be detected and located on one side of a U-shaped rib (1), a voltage signal is applied to the ultrasonic transducer (6), the voltage signal excites an ultrasonic guided wave signal in the steel plate (2) to be detected, the ultrasonic guided wave signal is collected by the ultrasonic transducer (6) or a second ultrasonic transducer (7), and the second ultrasonic transducer (7) is placed at the bottom of the steel plate (2) to be detected and located on the other side of the U-shaped rib (1) or placed on the side wall of the U-shaped rib (1) or on the same side of the ultrasonic transducer (6);
secondly, arranging a plurality of collecting points at the bottom of the steel plate (2) to be detected and along the length direction of the U-shaped rib (1), sequentially reaching each collecting point along the length direction by the first ultrasonic transducer (6) or simultaneously enabling the first ultrasonic transducer (6) and the second ultrasonic transducer (7) to move at equal intervals along the length direction of the U-shaped rib (1), applying voltage again and collecting ultrasonic guided wave signals according to the mode of the first step, and thus obtaining the ultrasonic guided wave signals collected when the first ultrasonic transducer (6) serves as a collecting end or the second ultrasonic transducer (7) serves as a collecting end and moves to different positions;
thirdly, obtaining a correlation coefficient between two adjacent time domain characteristics according to the time domain characteristics of each ultrasonic guided wave signal;
step four, obtaining the invisible fatigue crack length of the root part of the welding seam between the steel plate (2) and the U-shaped rib (1) according to the correlation coefficient curve obtained in the step three, and completing the detection of the crack;
obtaining the correlation coefficient between the time domain characteristics of two adjacent ultrasonic guided wave signals as follows:
in the formula (I), the compound is shown in the specification,
and
respectively represents the time domain characteristic curves of the ultrasonic guided wave signals of the ith path and the (i + 1) th path,
representing a signal curve
And
the correlation coefficient between the two components is calculated,
representing characteristic curves of signals
And
the covariance of the two or more different signals,
and
respectively representing signal characteristic curves
And
the respective variance;
in the fourth step, the specific content of the invisible fatigue crack length of the root part of the welding seam between the steel plate (2) and the U-shaped rib (1) is obtained according to the correlation coefficient obtained in the third step as follows:
the method comprises the steps that a plurality of ultrasonic guided wave signals are measured according to sequential movement of a first ultrasonic transducer (6) or simultaneous movement of the first ultrasonic transducer (6) and a second ultrasonic transducer (7), all correlation coefficients at continuous movement positions are obtained according to correlation coefficients between time domain characteristics of two adjacent ultrasonic guided wave signals, and if a certain correlation coefficient suddenly drops, the dropping points respectively correspond to starting and stopping points of fatigue cracks, so that the crack length is measured, and the detection and positioning of invisible fatigue cracks at the root parts of welding seams between a steel plate (2) and a U-shaped rib (1) are realized.
2. The method for detecting the cracks of the steel plate based on the ultrasonic guided wave principle according to claim 1, wherein a signal generating device is adopted to apply voltage signals to the ultrasonic transducer (6).
3. The method for detecting the cracks of the steel plate based on the ultrasonic guided wave principle according to claim 2, wherein the first ultrasonic transducer (6) and the second ultrasonic transducer (7) are both realized by using narrow-band resonant transducers.
4. The method for detecting the crack of the steel plate based on the ultrasonic guided wave principle according to claim 3, wherein the waveform of the voltage signal is as follows:
wherein t is time, V (t) is voltage waveform changing with time, A is maximum amplitude of voltage pulse, H (t) is unit step function, n is period number contained in waveform, f (t) is unit step functioncThe center frequency of the narrow band waveform.
5. The method for detecting the crack of the steel plate based on the ultrasonic guided wave principle according to claim 1, wherein the spacing distances of the plurality of collecting points are equal.
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| CN110596243B (en) * | 2019-09-27 | 2020-05-22 | 哈尔滨工业大学 | Orthotropic steel bridge deck plate top plate fatigue crack detection system based on ultrasonic guided wave method |
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