CN111766301A - Crack detection method, device and system - Google Patents

Crack detection method, device and system Download PDF

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CN111766301A
CN111766301A CN202010724850.1A CN202010724850A CN111766301A CN 111766301 A CN111766301 A CN 111766301A CN 202010724850 A CN202010724850 A CN 202010724850A CN 111766301 A CN111766301 A CN 111766301A
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CN111766301B (en
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李富才
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Wuxi Meisde Intelligent Measurement And Control Technology Co ltd
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Abstract

The invention relates to the technical field of detection, and particularly discloses a crack detection method, which comprises the following steps: generating a trigger excitation signal of the tested piece, and sending out the trigger excitation signal at equal intervals; respectively acquiring reflection signals and transmission signals under N triggering periods, wherein the reflection signals and the transmission signals under one triggering period can be generated by a tested piece every time the tested piece receives a triggering excitation signal, and N is an integer greater than 1; performing signal analysis according to the reflection signals and the transmission signals under the N triggering periods to obtain a crack identification result of the tested piece; the measured part is in a vibration state, and the reflection signals and the transmission signals in the N triggering periods comprise nonlinear lamb wave reflection signals and nonlinear lamb wave transmission signals in the N triggering periods. The invention also discloses a crack detection device and a crack detection system. The crack detection method provided by the invention effectively overcomes the influence of structural vibration on the crack detection process.

Description

Crack detection method, device and system
Technical Field
The invention relates to the technical field of detection, in particular to a crack detection method, a crack detection device and a crack detection system.
Background
In the fields of ships, electric power, heavy-duty machinery and the like, the health state monitoring and maintenance of large-scale equipment are of great importance. The early damage detection can timely discover potential safety hazards, prolong the service life of equipment and reduce economic loss. In the long-term operation process of large equipment, fatigue cracks are one of the most common damage forms and mainly go through three stages of crack generation, crack expansion and crack breakage, wherein the crack generation and crack expansion stages are generally slow and hidden, and the crack is completed instantly when the crack expands to a certain stage, so that catastrophic accidents are often caused, and great property and life loss is caused to national defense and civil lives. Therefore, it is necessary to perform early crack detection on large equipment operating for a long time. The traditional nondestructive testing technology mainly comprises the following steps: radioscopy, laser interferometry, thermography, ultrasonic scanning, eddy current testing, electromagnetic flaw detection, and the like. However, most of these techniques are too large and complicated, the detection cost is high, the efficiency is low, and the equipment is required to stop running in the detection process. For most large facilities, shutdown and restart often represent economic losses and investment in time, labor and materials.
Aiming at the defects of the traditional detection technology such as huge and complicated equipment, high detection cost and low efficiency, the nondestructive detection technology based on the ultrasonic guided waves can be well overcome. According to the method, a millimeter-level sensor is arranged on the surface of a measured piece to excite and receive guided wave signals, when crack damage exists in a structure, guided waves can interact with the crack damage and generate phenomena of reflection, scattering and the like, the damage information can be carried in the received guided wave signals, signal characteristics reflecting the damage information are extracted by a signal processing method, crack damage identification is carried out, and the health state of the structure is judged. The method has the characteristics of small attenuation along the propagation path, long propagation distance and capability of causing particle vibration energy to spread inside and on the surface of the member, and can greatly improve the detection efficiency of large-scale equipment. However, in order to avoid the influence of structural vibration generated when large-scale equipment operates on the ultrasonic guided wave detection process, the application of the existing technology generally needs the equipment to be in a shutdown state, and the technology needs to rely on reference signals to a great extent to acquire ultrasonic guided wave signals under the undamaged state of the equipment, so that the complexity of field detection is increased, and the detection time is prolonged.
Disclosure of Invention
The invention provides a crack detection method, a crack detection device and a crack detection system, which solve the problem that the detection in a vibration state cannot be realized in the related technology.
As a first aspect of the present invention, there is provided a crack detection method, comprising:
generating a trigger excitation signal of a tested piece, and sending out the trigger excitation signal at equal intervals;
respectively acquiring reflection signals and transmission signals under N triggering periods, wherein the reflection signals and the transmission signals under one triggering period can be generated by the tested piece every time the tested piece receives the triggering excitation signal, and N is an integer greater than 1;
performing signal analysis according to the reflection signals and the transmission signals in the N triggering periods to obtain a crack identification result of the tested piece;
the measured part is in a vibration state, and the reflection signals and the transmission signals in the N triggering periods comprise nonlinear lamb wave reflection signals and nonlinear lamb wave transmission signals in the N triggering periods.
Further, the performing signal analysis according to the reflection signal and the transmission signal under the N trigger periods to obtain a crack identification result of the tested piece includes:
calculating damage factors according to the reflection signals and the transmission signals in the N triggering periods to respectively obtain the damage factors of the N-1 reflection signals and the damage factors of the N-1 transmission signals;
drawing a damage factor sequence curve chart of the reflection signals according to the damage factors of the N-1 reflection signals, and drawing a damage factor sequence curve chart of the transmission signals according to the damage factors of the N-1 transmission signals;
and analyzing according to the damage factor sequence graph of the reflection signal and the damage factor sequence graph of the transmission signal to obtain a crack identification result of the detected piece.
Further, the performing damage factor calculation according to the reflection signals and the transmission signals in the N trigger periods to obtain damage factors of the N-1 reflection signals and damage factors of the N-1 transmission signals respectively includes:
intercepting a preset threshold duration of the initial stage of the reflection signal in each trigger period as a reflection signal analysis signal of each trigger period, and intercepting a preset threshold duration of the initial stage of the transmission signal in each trigger period as a transmission signal analysis signal of each trigger period to obtain N groups of analysis signals, wherein each group of analysis signals comprises a reflection signal analysis signal of one trigger period and a transmission signal analysis signal of one trigger period;
and taking a first group of analysis signals in the N groups of analysis signals as reference signals, carrying out correlation analysis on the reference signals and the other N-1 groups of analysis signals, and respectively obtaining damage factors of the N-1 reflection signals and the N-1 transmission signals according to a damage factor formula.
Further, the plotting a graph of a sequence of impairment factors of the reflected signals according to the impairment factors of the N-1 reflected signals and a graph of a sequence of impairment factors of the transmitted signals according to the impairment factors of the N-1 transmitted signals includes:
respectively intercepting each group of analysis signals from an initial position according to a rectangular window function to obtain intercepted signals;
calculating an interception damage factor according to the interception signal;
time shifting the rectangular window function to obtain a plurality of intercepted signals and corresponding intercepted damage factors;
and drawing a damage factor sequence curve chart of the analysis signals according to the intercepted signals and the corresponding intercepted damage factors.
Further, the analyzing the damage factor sequence graph of the reflected signal and the damage factor sequence graph of the transmitted signal to obtain a crack identification result of the tested piece includes:
comparing the sequence graphs of the damage factors of the reflection signal and the transmission signal of the tested piece with 0 respectively;
if the damage factor sequence graphs of the reflection signal and the transmission signal of the tested piece are both close to 0, judging that the tested piece has no crack, otherwise, judging that the tested piece has the crack, wherein the condition that the damage factor sequence graphs are close to 0 comprises that the magnitude of the difference between the damage factor value in the damage factor sequence graphs of the reflection signal and the transmission signal of the tested piece and 0 is at least 10-2Magnitude.
Further, the equal interval time length is based on the principle that the response caused by the trigger excitation signal of the previous time does not influence the response caused by the trigger excitation signal of the next time, and the trigger excitation signal can be sent out for multiple times when the tested piece is in one period.
Further, the trigger excitation signal satisfies a phase velocity matching principle.
As another aspect of the present invention, there is provided a crack detecting apparatus, comprising:
the generating module is used for generating a trigger excitation signal of the tested piece and sending out the trigger excitation signal in an equal interval mode;
the acquisition module is used for respectively acquiring a reflection signal and a transmission signal under N trigger periods, wherein the reflection signal and the transmission signal under one trigger period can be generated by the tested piece every time the tested piece receives the trigger excitation signal, and N is an integer greater than 1;
the analysis module is used for carrying out signal analysis according to the reflection signals and the transmission signals under the N triggering periods to obtain a crack identification result of the tested piece;
the measured part is in a vibration state, and the reflection signals and the transmission signals in the N triggering periods comprise nonlinear lamb wave reflection signals and nonlinear lamb wave transmission signals in the N triggering periods.
As another aspect of the present invention, there is provided a crack detection system, comprising: the crack detection device comprises a signal generating device, a signal collecting device and the crack detection device, wherein the signal generating device and the signal collecting device are both in communication connection with the crack detection device,
the crack detection device is used for generating a trigger excitation signal and carrying out signal analysis according to the received reflection signal and the transmission signal to obtain a crack identification result;
the signal generating device is used for carrying out signal processing on the trigger excitation signal and applying the processed signal to a tested piece;
the signal acquisition device is used for acquiring a reflection signal and a transmission signal which are generated after the tested piece responds to the trigger excitation signal, and sending the reflection signal and the transmission signal to the crack detection device.
Further, the signal generating device comprises an exciter, and the signal collecting device comprises a reflection signal sensor and a transmission signal sensor.
According to the crack detection method provided by the invention, the trigger excitation signals are sent to the detected piece at equal intervals, the response of the detected piece to the trigger excitation signals is obtained, and whether the detected piece has cracks or not is analyzed according to the response.
Drawings
The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and together with the description serve to explain the principles of the invention and not to limit the invention.
Fig. 1 is a flowchart of a crack detection method provided by the present invention.
Fig. 2 is a schematic view of the installation of the exciter and the sensor provided by the invention.
Fig. 3 is a flowchart of a specific implementation process of the crack detection method provided by the present invention.
Fig. 4 is a schematic structural diagram of a crack detection system provided by the present invention.
Detailed Description
It should be noted that the embodiments and features of the embodiments may be combined with each other without conflict. The present invention will be described in detail below with reference to the embodiments with reference to the attached drawings.
In order to make those skilled in the art better understand the technical solution of the present invention, the technical solution in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
It should be noted that the terms "first," "second," and the like in the description and claims of the present invention and in the drawings described above are used for distinguishing between similar elements and not necessarily for describing a particular sequential or chronological order. It is to be understood that the data so used may be interchanged under appropriate circumstances in order to facilitate the description of the embodiments of the invention herein. Furthermore, the terms "comprises," "comprising," and "having," and any variations thereof, are intended to cover a non-exclusive inclusion, such that a process, method, system, article, or apparatus that comprises a list of steps or elements is not necessarily limited to those steps or elements expressly listed, but may include other steps or elements not expressly listed or inherent to such process, method, article, or apparatus.
In the present embodiment, a crack detection method is provided, and fig. 1 is a flowchart of a crack detection method provided according to an embodiment of the present invention, as shown in fig. 1, including:
s110, generating a trigger excitation signal of a tested piece, and sending out the trigger excitation signal at equal intervals;
s120, respectively acquiring reflection signals and transmission signals under N trigger periods, wherein the reflection signals and the transmission signals under one trigger period can be generated by the tested piece every time the tested piece receives the trigger excitation signal, and N is an integer greater than 1;
s130, performing signal analysis according to the reflection signals and the transmission signals in the N triggering periods to obtain a crack identification result of the tested piece;
the measured part is in a vibration state, and the reflection signals and the transmission signals in the N triggering periods comprise nonlinear lamb wave reflection signals and nonlinear lamb wave transmission signals in the N triggering periods.
According to the crack detection method provided by the embodiment of the invention, the trigger excitation signals are sent to the detected piece at equal intervals, the response of the detected piece to the trigger excitation signals is obtained, and whether the detected piece has cracks or not is analyzed according to the response.
It should be understood that the crack detection method provided by the invention is mainly directed at the low-frequency vibration of large equipment, the length of an analysis signal is ensured to be micro-duration relative to the low-frequency vibration period, and a crack opening is in a quasi-static state in the process of collecting the analysis signal.
It should be noted that the nonlinear lamb wave can detect the fatigue crack of a smaller scale, and the crack opening and closing process caused by the structural vibration can be roughly decomposed into a plurality of quasi-static states, in different quasi-static states of crack openings, the nonlinear components of the induced lamb waves are different, this feature will help identify crack damage, and therefore in terms of nonlinear second harmonic accumulation principles, that is, when lamb waves propagate in a nonlinear material or to a local nonlinear damage source, a second harmonic accumulation phenomenon occurs, when the frequency of the excitation signal meets the phase velocity matching principle, a more obvious second harmonic signal can be obtained, when the group velocity matching principle is satisfied, the energy of the fundamental frequency signal and the energy of the frequency doubling signal (i.e. the second harmonic) can be more effectively converted, and the second harmonic signal with higher amplitude can be obtained.
It should be noted that the equal interval time length is based on the principle that the response caused by the previous trigger excitation signal does not affect the response caused by the next trigger excitation signal, and the trigger excitation signal can be sent out multiple times when the tested piece is in one period.
In addition, the trigger excitation signal satisfies the phase velocity matching principle.
Specifically, the phase velocity matching principle needs to draw a corresponding phase velocity dispersion curve according to the material characteristics, density, elastic modulus and poisson ratio of a measured piece; according to the phase velocity dispersion curve, selecting the frequency which satisfies the condition that the phase velocity value corresponding to the fundamental frequency is the same as the double frequency phase velocity value.
In addition, the group velocity matching principle specifically comprises the steps of drawing a corresponding group velocity dispersion curve according to the material characteristics, density, elastic modulus and Poisson ratio of the detected piece; according to the group velocity dispersion curve, selecting the frequency which satisfies that the group velocity value corresponding to the fundamental frequency is the same as the frequency doubling group velocity value.
As shown in fig. 2, an actuator 2, a reflection signal sensor 31, and a transmission signal sensor 32 are provided on the surface of a test object 1, respectively, the actuator 2 and the reflection signal sensor 31 being provided at one end, and the transmission signal sensor 32 being provided at the other end.
The actuator 2, the reflection signal sensor 31, and the transmission signal sensor 32 are made of a sheet-like piezoelectric ceramic material.
Under the vibration state of the measured piece, the measured piece is continuously triggered and excited in an equal-interval triggering mode, and the reflection signal sensor 31 and the transmission signal sensor 32 are synchronously utilized to respectively acquire nonlinear lamb wave reflection signals and transmission signals under multiple triggering periods.
Specifically, the performing signal analysis according to the reflection signal and the transmission signal in the N trigger periods to obtain a crack identification result of the detected piece includes:
calculating damage factors according to the reflection signals and the transmission signals in the N triggering periods to respectively obtain the damage factors of the N-1 reflection signals and the damage factors of the N-1 transmission signals;
drawing a damage factor sequence curve chart of the reflection signals according to the damage factors of the N-1 reflection signals, and drawing a damage factor sequence curve chart of the transmission signals according to the damage factors of the N-1 transmission signals;
and analyzing according to the damage factor sequence graph of the reflection signal and the damage factor sequence graph of the transmission signal to obtain a crack identification result of the detected piece.
Further specifically, the performing damage factor calculation according to the reflection signals and the transmission signals in the N trigger periods to obtain damage factors of the N-1 reflection signals and damage factors of the N-1 transmission signals respectively includes:
intercepting a preset threshold duration of the initial stage of the reflection signal in each trigger period as a reflection signal analysis signal of each trigger period, and intercepting a preset threshold duration of the initial stage of the transmission signal in each trigger period as a transmission signal analysis signal of each trigger period to obtain N groups of analysis signals, wherein each group of analysis signals comprises a reflection signal analysis signal of one trigger period and a transmission signal analysis signal of one trigger period;
and taking a first group of analysis signals in the N groups of analysis signals as reference signals, carrying out correlation analysis on the reference signals and the other N-1 groups of analysis signals, and respectively obtaining damage factors of the N-1 reflection signals and the N-1 transmission signals according to a damage factor formula.
By using collected nonlinear lamb wave signals (such as N trigger periods) with multiple trigger periods, intercepting unattenuated parts at the initial stage of each trigger period as analysis signals of each period to form N groups of analysis signals, and analyzing the signals (S) by using a first group0) As a reference signal, in combination with another N-1 group analysis signal (S)n-1) Correlation analysis was performed to obtain N-1 groups of injury factors as:
Figure BDA0002601307450000061
wherein: RMS is root mean square, N is the number of analysis signal groups, and N is the total number of analysis signal groups.
Specifically, the plotting of the sequence of the impairment factors of the reflected signals according to the impairment factors of the N-1 reflected signals and the plotting of the sequence of the impairment factors of the transmitted signals according to the impairment factors of the N-1 transmitted signals includes:
respectively intercepting each group of analysis signals from an initial position according to a rectangular window function to obtain intercepted signals;
calculating an interception damage factor according to the interception signal;
time shifting the rectangular window function to obtain a plurality of intercepted signals and corresponding intercepted damage factors;
and drawing a damage factor sequence curve chart of the analysis signals according to the intercepted signals and the corresponding intercepted damage factors.
Selecting a rectangular window function, intercepting a pair of analysis signals for calculating the damage factor from an initial position, and utilizing the intercepted signal S0(u)＝g(u-t)S0(u)，Sn-1(u)＝g(u-t)Sn-1(u) calculation of injury factor
Figure BDA0002601307450000062
And then, a window function is shifted to the right at certain intervals in a time shifting mode to obtain a series of intercepted signals and corresponding damage factor sequences, so that a damage factor sequence curve is drawn, wherein g (u-t) represents a rectangular window function.
Specifically, the analyzing the damage factor sequence graph of the reflected signal and the damage factor sequence graph of the transmitted signal to obtain the crack identification result of the tested piece includes:
comparing the sequence graphs of the damage factors of the reflection signal and the transmission signal of the tested piece with 0 respectively;
if the damage factor sequence graphs of the reflection signal and the transmission signal of the tested piece are both close to 0, judging that the tested piece has no crack, otherwise, judging that the tested piece has the crack, wherein the condition that the damage factor sequence graphs are close to 0 comprises that the magnitude of the difference between the damage factor value in the damage factor sequence graphs of the reflection signal and the transmission signal of the tested piece and 0 is at least 10-2Magnitude.
It should be understood that, the crack is in the continuous opening and closing process in the vibration state, and the time length of the analysis signal is much shorter than the low-frequency vibration period of the structure, then when each group of analysis signals is acquired, the crack opening can be regarded as being in a quasi-static state, the crack states of the groups of analysis signals are different when the groups of analysis signals are acquired, and the signals acquired by the damage-free structure in the vibration state should be approximately the same, then the closer the damage factor and sequence curve graph calculated by the groups of analysis signals is to zero, the lower the probability of the crack is, and vice versa.
The following describes in detail a specific implementation of the crack detection method according to the embodiment of the present invention with reference to fig. 3.
Firstly, a phase velocity dispersion curve and a group velocity dispersion curve of a material are drawn according to the material attribute of a tested piece 1 (the tested piece can be a 304 steel beam), and then, based on a phase velocity matching principle and a group velocity matching principle in a nonlinear second harmonic accumulation effect, a detection signal excitation frequency which meets the condition that a fundamental frequency phase velocity is equal to a frequency doubling phase velocity and a fundamental frequency group velocity is equal to a frequency doubling group velocity is selected from the dispersion curves and is 720 kHz. The detection signal is thus a five-cycle sinusoidal amplitude modulated pulse signal with a center frequency of 720kHz modulated by a hanning window.
An exciter and sensor arrangement step: the exciter and the sensor are arranged at two ends of the surface of the measured piece, the exciter and the reflected signal sensor are arranged at one end, the transmitted signal sensor is arranged at the other end, and the exciter and the sensor are arranged in a manner of transmitting and receiving.
Multi-trigger period signal excitation and acquisition steps: and under the vibration state of the measured piece, continuously triggering and exciting the measured piece in an equal-interval triggering mode, and synchronously acquiring nonlinear lamb wave transmission signals and reflection signals under a plurality of triggering periods by using a sensor. The vibration state of the tested piece is realized by placing the tested piece on a vibration table, and the parameters of the vibration table are set to be 10Hz/0.05mm so as to simulate the characteristics of low frequency and high amplitude of large-scale equipment; the triggering interval is selected for 10ms according to the principle that the response caused by the previous triggering excitation does not influence the response caused by the next triggering excitation and the fact that multiple triggering is contained in one vibration period is guaranteed; and (4) comprehensively considering the precision and the time consumption of the collected signals, and collecting the nonlinear lamb wave signals in 4 trigger periods.
And (3) calculating a damage factor: intercepting 400 mu s duration of each trigger period initial stage as an analysis signal of each period by using four trigger period nonlinear lamb wave signals obtained by collection to form four groups of analysis signals, taking the first group of analysis signals as reference signals, performing correlation analysis on the first group of analysis signals and the other three groups of analysis signals, and utilizing a damage factor formula
Figure BDA0002601307450000071
The damage factors for separately obtaining the transmission signal and the reflection signal are shown in table 1.
TABLE 1 Damage factor for transmitted and reflected signals
Figure BDA0002601307450000072
And (3) a step of drawing a damage factor sequence curve: selecting a rectangular window function with the length of 12 mu S, carrying out signal interception on a pair of analysis signals for calculating the damage factor from an initial position, and utilizing the intercepted signal S0(u)＝g(u-t)S0(u)，Sn-1(u)＝g(u-t)Sn-1(u) calculation of injury factor DI < S0(u),
Figure BDA0002601307450000073
Then, a time-shifting mode is adopted, and a window function is shifted to the right at intervals of 0.4 mu s, so that a series of intercepted signals and corresponding damage factor sequences are obtained.
And (3) crack identification: as can be seen from the results of the damage factors of the transmission signals and the reflection signals of the crack beam and the lossless beam shown in Table 1, the damage factor value of the crack beam is much higher than that of the lossless beam, the difference is in one order of magnitude, and the damage factor value of the lossless beam is 10-2Magnitude, close to zero, and a crack beam with a damage factor value of 10-1Magnitude; interference caused by electric signal noise during collection can be eliminated by the damage factor sequence comparison graph, and the difference between the damage factors of the nondestructive beam and the crack beam can be observed more visually, so that the process of identifying the crack of the detected piece is realized.
As another embodiment of the present invention, there is provided a crack detection apparatus including:
the generating module is used for generating a trigger excitation signal of the tested piece and sending out the trigger excitation signal in an equal interval mode;
the acquisition module is used for respectively acquiring a reflection signal and a transmission signal under N trigger periods, wherein the reflection signal and the transmission signal under one trigger period can be generated by the tested piece every time the tested piece receives the trigger excitation signal, and N is an integer greater than 1;
the analysis module is used for carrying out signal analysis according to the reflection signals and the transmission signals under the N triggering periods to obtain a crack identification result of the tested piece;
the measured part is in a vibration state, and the reflection signals and the transmission signals in the N triggering periods comprise nonlinear lamb wave reflection signals and nonlinear lamb wave transmission signals in the N triggering periods.
According to the crack detection device provided by the embodiment of the invention, the trigger excitation signals are sent to the detected piece at equal intervals, the response of the detected piece to the trigger excitation signals is obtained, and whether the detected piece has cracks or not is analyzed according to the response.
For a specific working principle of the crack detection device provided in the embodiment of the present invention, reference may be made to the foregoing description of the crack detection method, and details are not described herein again.
As another embodiment of the present invention, there is provided a crack detection system, as shown in fig. 4, including: a signal generating device 200, a signal collecting device 300 and the crack detecting device 100 described above, wherein the signal generating device 200 and the signal collecting device 300 are both connected with the crack detecting device 100 in a communication way,
the crack detection device 100 is configured to generate a trigger excitation signal, and perform signal analysis according to the received reflection signal and transmission signal to obtain a crack identification result;
the signal generating device 200 is configured to perform signal processing on the trigger excitation signal, and apply the processed signal to a measured object;
the signal acquisition device 300 is configured to acquire a reflection signal and a transmission signal generated after the detected object responds to the trigger excitation signal, and send the reflection signal and the transmission signal to the crack detection device.
According to the crack detection system provided by the embodiment of the invention, the crack detection device is adopted, the trigger excitation signals are sent to the detected piece at equal intervals, the response of the detected piece to the trigger excitation signals is obtained, and whether the detected piece has cracks or not is analyzed according to the response.
Specifically, the signal generating device comprises an exciter, and the signal collecting device comprises a reflection signal sensor and a transmission signal sensor.
As shown in FIG. 4, in which the test pieces were 304 steel beams (650mm, 25mm, 5mm), two test pieces were fabricated in total, one of which had fatigue cracks of 8mm and the other was a non-destructive test piece, in order to demonstrate the principle and effect of the test. An actuator and two sensors are arranged for each specimen, receiving the reflected signal and the transmitted signal, respectively. The exciter and the sensor adopt piezoelectric ceramic strain gauges. The excitation signal is a five-period sine amplitude modulation pulse signal modulated by a Hanning window.
Specifically, the crack detection device 100 is configured to generate an excitation signal and process an acquired nonlinear lamb wave signal to identify crack damage; the signal generating device 200 is composed of a waveform generator, a power amplifier and an exciter, wherein the waveform generator converts an excitation signal generated by the control unit into an electric signal, transmits the electric signal to the power amplifier to amplify the energy of the electric signal, and converts the electric signal into stress through the exciter composed of a piezoelectric ceramic strain gauge to act on a tested piece; the signal acquisition device 300 is composed of a sensor and an oscilloscope, wherein the sensor composed of a piezoelectric ceramic strain gauge converts a force signal into an electric signal, transmits the electric signal to the oscilloscope, converts the electric signal into a digital signal, and transmits the digital signal to the signal control and analysis unit for crack damage identification.
It will be understood that the above embodiments are merely exemplary embodiments taken to illustrate the principles of the present invention, which is not limited thereto. It will be apparent to those skilled in the art that various modifications and improvements can be made without departing from the spirit and substance of the invention, and these modifications and improvements are also considered to be within the scope of the invention.

Claims (10)

1. A crack detection method, comprising:
generating a trigger excitation signal of a tested piece, and sending out the trigger excitation signal at equal intervals;
respectively acquiring reflection signals and transmission signals under N triggering periods, wherein the reflection signals and the transmission signals under one triggering period can be generated by the tested piece every time the tested piece receives the triggering excitation signal, and N is an integer greater than 1;
performing signal analysis according to the reflection signals and the transmission signals in the N triggering periods to obtain a crack identification result of the tested piece;
the measured part is in a vibration state, and the reflection signals and the transmission signals in the N triggering periods comprise nonlinear lamb wave reflection signals and nonlinear lamb wave transmission signals in the N triggering periods.
2. The crack detection method according to claim 1, wherein the performing signal analysis according to the reflection signal and the transmission signal in the N trigger periods to obtain a crack identification result of the tested object comprises:
calculating damage factors according to the reflection signals and the transmission signals in the N triggering periods to respectively obtain the damage factors of the N-1 reflection signals and the damage factors of the N-1 transmission signals;
drawing a damage factor sequence curve chart of the reflection signals according to the damage factors of the N-1 reflection signals, and drawing a damage factor sequence curve chart of the transmission signals according to the damage factors of the N-1 transmission signals;
and analyzing according to the damage factor sequence graph of the reflection signal and the damage factor sequence graph of the transmission signal to obtain a crack identification result of the detected piece.
3. The crack detection method according to claim 2, wherein the performing damage factor calculation according to the reflection signal and the transmission signal in the N trigger periods to obtain damage factors of N-1 reflection signals and N-1 transmission signals respectively comprises:
intercepting a preset threshold duration of the initial stage of the reflection signal in each trigger period as a reflection signal analysis signal of each trigger period, and intercepting a preset threshold duration of the initial stage of the transmission signal in each trigger period as a transmission signal analysis signal of each trigger period to obtain N groups of analysis signals, wherein each group of analysis signals comprises a reflection signal analysis signal of one trigger period and a transmission signal analysis signal of one trigger period;
and taking a first group of analysis signals in the N groups of analysis signals as reference signals, carrying out correlation analysis on the reference signals and the other N-1 groups of analysis signals, and respectively obtaining damage factors of the N-1 reflection signals and the N-1 transmission signals according to a damage factor formula.
4. The crack detection method of claim 3, wherein the plotting the sequence of damage factors for the reflected signals as a function of the damage factors for the N-1 reflected signals and the sequence of damage factors for the transmitted signals as a function of the damage factors for the N-1 transmitted signals comprises:
respectively intercepting each group of analysis signals from an initial position according to a rectangular window function to obtain intercepted signals;
calculating an interception damage factor according to the interception signal;
time shifting the rectangular window function to obtain a plurality of intercepted signals and corresponding intercepted damage factors;
and drawing a damage factor sequence curve chart of the analysis signals according to the intercepted signals and the corresponding intercepted damage factors.
5. The crack detection method according to claim 2, wherein analyzing the crack identification result of the tested object according to the damage factor sequence graph of the reflection signal and the damage factor sequence graph of the transmission signal comprises:
comparing the sequence graphs of the damage factors of the reflection signal and the transmission signal of the tested piece with 0 respectively;
if the damage factor sequence graphs of the reflection signal and the transmission signal of the tested piece are both close to 0, judging that the tested piece has no crack, otherwise, judging that the tested piece has the crack, wherein the condition that the damage factor sequence graphs are close to 0 comprises that the magnitude of the difference between the damage factor value in the damage factor sequence graphs of the reflection signal and the transmission signal of the tested piece and 0 is at least 10-2Magnitude.
6. The crack detection method according to claim 1, wherein the equal interval time length is based on the principle that the response caused by the previous trigger excitation signal does not affect the response caused by the next trigger excitation signal, and the trigger excitation signal can be emitted multiple times when the tested piece is in one cycle.
7. The crack detection method of claim 1, wherein the trigger excitation signal satisfies a phase velocity matching principle.
8. A crack detection device, comprising:
the generating module is used for generating a trigger excitation signal of the tested piece and sending out the trigger excitation signal in an equal interval mode;
the acquisition module is used for respectively acquiring a reflection signal and a transmission signal under N trigger periods, wherein the reflection signal and the transmission signal under one trigger period can be generated by the tested piece every time the tested piece receives the trigger excitation signal, and N is an integer greater than 1;
the analysis module is used for carrying out signal analysis according to the reflection signals and the transmission signals under the N triggering periods to obtain a crack identification result of the tested piece;
the measured part is in a vibration state, and the reflection signals and the transmission signals in the N triggering periods comprise nonlinear lamb wave reflection signals and nonlinear lamb wave transmission signals in the N triggering periods.
9. A crack detection system, comprising: a signal generating device, a signal collecting device and the crack detecting device of claim 8, wherein the signal generating device and the signal collecting device are both in communication connection with the crack detecting device,
the crack detection device is used for generating a trigger excitation signal and carrying out signal analysis according to the received reflection signal and the transmission signal to obtain a crack identification result;
the signal generating device is used for carrying out signal processing on the trigger excitation signal and applying the processed signal to a tested piece;
the signal acquisition device is used for acquiring a reflection signal and a transmission signal which are generated after the tested piece responds to the trigger excitation signal, and sending the reflection signal and the transmission signal to the crack detection device.
10. The crack detection system of claim 9, wherein the signal generating device comprises an actuator and the signal acquisition device comprises a reflection signal sensor and a transmission signal sensor.
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Publication number Priority date Publication date Assignee Title
CN1978977A (en) * 2006-12-01 2007-06-13 北京工业大学 Supersonic guide-wave time reversion detection apparatus and method for defect of pipeline
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