CN111766301B - Crack detection method, device and system - Google Patents
Crack detection method, device and system Download PDFInfo
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- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N29/00—Investigating or analysing materials by the use of ultrasonic, sonic or infrasonic waves; Visualisation of the interior of objects by transmitting ultrasonic or sonic waves through the object
- G01N29/04—Analysing solids
- G01N29/041—Analysing solids on the surface of the material, e.g. using Lamb, Rayleigh or shear waves
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- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N29/00—Investigating or analysing materials by the use of ultrasonic, sonic or infrasonic waves; Visualisation of the interior of objects by transmitting ultrasonic or sonic waves through the object
- G01N29/22—Details, e.g. general constructional or apparatus details
- G01N29/24—Probes
- G01N29/2437—Piezoelectric probes
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- G01N29/34—Generating the ultrasonic, sonic or infrasonic waves, e.g. electronic circuits specially adapted therefor
- G01N29/341—Generating the ultrasonic, sonic or infrasonic waves, e.g. electronic circuits specially adapted therefor with time characteristics
- G01N29/343—Generating the ultrasonic, sonic or infrasonic waves, e.g. electronic circuits specially adapted therefor with time characteristics pulse waves, e.g. particular sequence of pulses, bursts
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- G01N29/00—Investigating or analysing materials by the use of ultrasonic, sonic or infrasonic waves; Visualisation of the interior of objects by transmitting ultrasonic or sonic waves through the object
- G01N29/34—Generating the ultrasonic, sonic or infrasonic waves, e.g. electronic circuits specially adapted therefor
- G01N29/348—Generating the ultrasonic, sonic or infrasonic waves, e.g. electronic circuits specially adapted therefor with frequency characteristics, e.g. single frequency signals, chirp signals
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- G—PHYSICS
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- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N29/00—Investigating or analysing materials by the use of ultrasonic, sonic or infrasonic waves; Visualisation of the interior of objects by transmitting ultrasonic or sonic waves through the object
- G01N29/44—Processing the detected response signal, e.g. electronic circuits specially adapted therefor
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- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
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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 a tested piece, and sending the trigger excitation signal in an equidistant mode; respectively obtaining a reflected signal and a transmitted signal under N trigger periods, wherein each time the tested piece receives a trigger excitation signal, the reflected signal and the transmitted signal under one trigger period can be generated, and N is an integer greater than 1; performing signal analysis according to the reflected signals and the transmitted signals under N trigger periods to obtain a crack identification result of the measured piece; the reflected signals and the transmitted signals of the measured piece in the vibration state under the N trigger periods comprise nonlinear lamb wave reflected signals and nonlinear lamb wave transmitted signals under the N trigger 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
Technical Field
The present invention relates to the field of detection technologies, and 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 engineering machinery and the like, the health status monitoring and maintenance of large-scale equipment are very important. The early damage detection can discover potential safety hazards in time, prolong the service life of equipment and reduce economic loss. In the long-term running process of large equipment, fatigue cracks are one of the most common damage forms, and mainly undergo three stages of crack generation, crack expansion and fracture, wherein the crack generation and expansion stages are usually slow and hidden, the fracture is completed instantaneously when the crack is expanded to a certain stage, so that disastrous accidents are often caused, and important property and life losses are caused for national defense and civil engineering. Early crack detection is therefore necessary for large equipment that is operated for long periods of time. Conventional nondestructive testing techniques mainly include: radioscopy, laser interferometry, infrared thermography, ultrasonic scanning, eddy current testing, electromagnetic flaw detection, and the like. However, most of these techniques are too large and complex, have high detection costs, are inefficient, and require equipment to be shut down during the detection process. For most large-scale equipment, shutdown and restarting often means economic loss and investment of time, manpower and material resources.
Aiming at the defects of the traditional detection technology with huge and complex equipment, high detection cost and low efficiency, the nondestructive detection technology based on ultrasonic guided waves can be well overcome. According to the method, millimeter-level sensors are arranged on the surface of a measured piece to excite and receive guided wave signals, when crack damage exists in a structure, the guided wave interacts with the crack damage and generates phenomena such as reflection and scattering, damage information is carried in the received guided wave signals, signal characteristics of the reaction damage information are extracted by a signal processing method, crack damage identification is performed, and then the health state of the structure is judged. The method has the characteristics of reduced attenuation along the propagation path, long propagation distance and capability of leading particle vibration energy to spread inside and on the surface of the component, and can greatly improve the detection efficiency of large-scale equipment. However, in order to avoid the influence of structural vibration generated during the operation of large-scale equipment on the ultrasonic guided wave detection process, the application of the technology at present generally needs that the equipment is in a stop state, and the technology needs to rely on a reference signal to a great extent to acquire the ultrasonic guided wave signal in the undamaged state of the equipment, so that the complexity of on-site 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 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 the trigger excitation signal in an equidistant mode;
respectively obtaining a reflected signal and a transmitted signal under N trigger periods, wherein each time the tested piece receives the trigger excitation signal, the tested piece can generate the reflected signal and the transmitted signal under one trigger period, and N is an integer larger than 1;
performing signal analysis according to the reflected signals and the transmitted signals in the N trigger periods to obtain a crack identification result of the measured piece;
the measured piece is in a vibration state, and the reflection signals and the transmission signals under the N trigger periods comprise nonlinear lamb wave reflection signals and nonlinear lamb wave transmission signals under the N trigger periods.
Further, the signal analysis is performed according to the reflected signals and the transmitted signals under the N trigger periods to obtain a crack identification result of the measured piece, including:
performing damage factor calculation according to the reflected signals and the transmitted signals under N trigger periods to respectively obtain damage factors of N-1 reflected signals and damage factors of N-1 transmitted signals;
drawing a damage factor sequence graph of the reflected signals according to the damage factors of the N-1 reflected signals, and drawing a damage factor sequence graph of the transmitted signals according to the damage factors of the N-1 transmitted signals;
and analyzing the damage factor sequence curve graph of the reflected signal and the damage factor sequence curve graph of the transmitted signal to obtain a crack identification result of the measured piece.
Further, the calculating the damage factor according to the reflected signals and the transmitted signals under the N trigger periods to obtain the damage factors of N-1 reflected signals and the damage factors of N-1 transmitted signals respectively includes:
intercepting a preset threshold time length of a reflection signal initial stage under each trigger period as a reflection signal analysis signal of each trigger period, and intercepting a preset threshold time length of a transmission signal initial stage under 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 performing correlation analysis on a first group of analysis signals in the N groups of analysis signals serving as reference signals and the other N-1 groups of analysis signals, and respectively obtaining damage factors of N-1 reflection signals and damage factors of N-1 transmission signals according to a damage factor formula.
Further, the drawing the damage factor sequence graph of the reflected signals according to the damage factors of the N-1 reflected signals, and drawing the damage factor sequence graph of the transmitted signals according to the damage factors of the N-1 transmitted signals includes:
according to the rectangular window function, signal interception is carried out on each group of analysis signals from an initial position 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 graph of the analysis signals according to the intercepted signals and the corresponding intercepted damage factors.
Further, the analyzing the damage factor sequence graph according to the reflected signal and the damage factor sequence graph according to the transmitted signal to obtain a crack identification result of the measured piece includes:
comparing the damage factor sequence graphs of the reflected signal and the transmitted signal of the measured piece with 0 respectively;
if the damage factor sequence curve graphs of the reflected signal and the transmitted signal of the tested piece are close to 0, judging that the tested piece is not cracked, otherwise, judging that the tested piece is cracked, wherein the close to 0 comprises that the magnitude order of the difference between the damage factor value and 0 in the damage factor sequence curve graphs of the reflected signal and the transmitted signal of the tested piece is at least 10 -2 Magnitude.
Further, the principle that the response caused by the trigger excitation signal of more than one time with equal interval does not affect the response caused by the next trigger excitation signal is taken as a principle, and the trigger excitation signal can be sent out for a plurality of 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 detection device, including:
the generating module is used for generating a trigger excitation signal of the tested piece and sending the trigger excitation signal in an equidistant mode;
the acquisition module is used for respectively acquiring the reflected signals and the transmitted signals under N trigger periods, wherein each time the tested piece receives the trigger excitation signal, the reflected signals and the transmitted signals under one trigger period can be generated, and N is an integer larger than 1;
the analysis module is used for carrying out signal analysis according to the reflected signals and the transmitted signals under the N trigger periods to obtain a crack identification result of the measured piece;
the measured piece is in a vibration state, and the reflection signals and the transmission signals under the N trigger periods comprise nonlinear lamb wave reflection signals and nonlinear lamb wave transmission signals under the N trigger periods.
As another aspect of the present invention, there is provided a crack detection system, including: the signal generating device, the signal collecting device and the crack detecting device are in communication connection with each other,
the crack detection device is used for generating a trigger excitation signal, and carrying out signal analysis according to the received reflected signal and the received 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 acting the processed signal on the tested piece;
the signal acquisition device is used for acquiring a reflected signal and a transmitted signal generated after the tested piece responds to the trigger excitation signal, and sending the reflected signal and the transmitted signal to the crack detection device.
Further, the signal generating device comprises an exciter, and the signal acquisition device comprises a reflected signal sensor and a transmitted 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 are included to provide a further understanding of the invention, and are incorporated in and constitute a part of this specification, illustrate the invention and together with the description serve to explain, without limitation, the invention.
Fig. 1 is a flowchart of a crack detection method provided by the present invention.
Fig. 2 is a schematic diagram of the installation of the actuator and the sensor provided by the invention.
FIG. 3 is a flowchart illustrating a specific implementation process of the crack detection method according to 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, without conflict, the embodiments of the present invention and features of the embodiments may be combined with each other. The invention will be described in detail below with reference to the drawings in connection with embodiments.
In order that those skilled in the art will better understand the present invention, a technical solution in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in which it is apparent that the described embodiments are only some embodiments of the present invention, not all embodiments. All other embodiments, which can be made by those skilled in the art based on the embodiments of the present invention without making any inventive effort, shall fall within the scope of the present invention.
It should be noted that the terms "first," "second," and the like in the description and the claims of the present invention and the above figures are used for distinguishing between similar objects and not necessarily for describing a particular sequential or chronological order. It is to be understood that the data so used may be interchanged where appropriate in order to describe 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 this embodiment, a crack detection method is provided, and fig. 1 is a flowchart of the 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 the trigger excitation signal in an equidistant mode;
s120, respectively acquiring a reflected signal and a transmitted signal under N trigger periods, wherein each time the tested piece receives the trigger excitation signal, the tested piece can generate the reflected signal and the transmitted signal under one trigger period, and N is an integer larger than 1;
s130, carrying out signal analysis according to the reflected signals and the transmitted signals under the N trigger periods to obtain a crack identification result of the measured piece;
the measured piece is in a vibration state, and the reflection signals and the transmission signals under the N trigger periods comprise nonlinear lamb wave reflection signals and nonlinear lamb wave transmission signals under the N trigger 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 of the invention is mainly aimed at low-frequency vibration of large-scale equipment, ensures that the length of an analysis signal is micro-long relative to the period of the low-frequency vibration, and the 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 fatigue cracks with more micro scale, the crack opening and closing process caused by structural vibration can be roughly decomposed into a plurality of quasi-static states, and in different crack opening quasi-static states, the nonlinear components of the induced lamb wave will be different, the characteristic will help to identify crack damage, so that when the excitation signal frequency is selected, according to the nonlinear second harmonic accumulation principle, that is, when the lamb wave propagates in nonlinear material or propagates to a local nonlinear damage source, the second harmonic accumulation phenomenon will occur, when the excitation signal frequency meets the phase velocity matching principle, a more remarkable second harmonic signal can be obtained, and when the group velocity matching principle is simultaneously met, the fundamental frequency signal energy and the frequency multiplication signal (that is, the second harmonic) energy can be converted more effectively, and a higher amplitude second harmonic signal will be obtained.
It should be noted that, the principle that the response caused by the trigger excitation signal at more than one time of the equal interval does not affect the response caused by the next trigger excitation signal is taken as a principle, 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 of the measured piece, the density, the elastic modulus and the poisson ratio; according to the phase velocity dispersion curve, selecting the frequency which meets the condition that the phase velocity value corresponding to the fundamental frequency is the same as the frequency doubling phase velocity value.
In addition, the group velocity matching principle specifically comprises that a corresponding group velocity dispersion curve is drawn according to the material characteristics of the measured piece, and the density, the elastic modulus and the poisson ratio; according to the group velocity dispersion curve, selecting the frequency which meets the condition that the group velocity value corresponding to the fundamental frequency is the same as the doubling group velocity value.
As shown in fig. 2, the actuator 2, the reflected signal sensor 31, and the transmitted signal sensor 32 are provided on the surface of the object 1, respectively, and the actuator 2 and the reflected signal sensor 31 are provided at one end, and the transmitted signal sensor 32 is provided at the other end.
The actuator 2, the reflection signal sensor 31, and the transmission signal sensor 32 are made of a piezoelectric ceramic material in a sheet form.
In the vibration state of the measured piece, the measured piece is continuously triggered and excited in an equidistant triggering mode, and the reflected signal sensor 31 and the transmitted signal sensor 32 are synchronously utilized to respectively acquire nonlinear lamb wave reflected signals and transmitted signals in a plurality of triggering periods.
Specifically, the signal analysis is performed according to the reflected signals and the transmitted signals under the N trigger periods to obtain a crack identification result of the measured piece, including:
performing damage factor calculation according to the reflected signals and the transmitted signals under N trigger periods to respectively obtain damage factors of N-1 reflected signals and damage factors of N-1 transmitted signals;
drawing a damage factor sequence graph of the reflected signals according to the damage factors of the N-1 reflected signals, and drawing a damage factor sequence graph of the transmitted signals according to the damage factors of the N-1 transmitted signals;
and analyzing the damage factor sequence curve graph of the reflected signal and the damage factor sequence curve graph of the transmitted signal to obtain a crack identification result of the measured piece.
Further specifically, the calculating the damage factor according to the reflected signals and the transmitted signals under the N trigger periods, to obtain the damage factor of N-1 reflected signals and the damage factor of N-1 transmitted signals respectively, includes:
intercepting a preset threshold time length of a reflection signal initial stage under each trigger period as a reflection signal analysis signal of each trigger period, and intercepting a preset threshold time length of a transmission signal initial stage under 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 performing correlation analysis on a first group of analysis signals in the N groups of analysis signals serving as reference signals and the other N-1 groups of analysis signals, and respectively obtaining damage factors of N-1 reflection signals and damage factors of N-1 transmission signals according to a damage factor formula.
The acquired nonlinear lamb wave signals with multiple trigger periods (such as N trigger periods) are utilized to intercept unattenuated parts of the initial stages of the trigger periods as analysis signals of each period to form N groups of analysis signals, and a first group of analysis signals (S 0 ) As a reference signal, the same as the other N-1 group analysis signal (S n-1 ) Performing correlation analysis to obtain N-1 groups of damage factors as follows:
wherein: RMS is root mean square, N is the serial number of the analysis signal set, and N is the total number of the analysis signal set.
Specifically, the drawing the damage factor sequence graph of the reflected signals according to the damage factors of the N-1 reflected signals, and drawing the damage factor sequence graph of the transmitted signals according to the damage factors of the N-1 transmitted signals includes:
according to the rectangular window function, signal interception is carried out on each group of analysis signals from an initial position 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 graph of the analysis signals according to the intercepted signals and the corresponding intercepted damage factors.
Selecting a rectangular window function, performing signal interception on a pair of analysis signals for calculating the damage factors from an initial position, and utilizing intercepted signals S 0 (u)＝g(u-t)S 0 (u)，S n-1 (u)＝g(u-t)S n-1 (u) calculating the injury factor
Then a time shift mode is adopted to shift the window function to the right at a certain interval to obtain a series of intercepted signals and corresponding signalsThereby plotting the sequence of injury factors, wherein g (u-t) represents a rectangular window function.
Specifically, the analysis of the damage factor sequence graph according to the reflected signal and the damage factor sequence graph according to the transmitted signal to obtain a crack identification result of the measured piece includes:
comparing the damage factor sequence graphs of the reflected signal and the transmitted signal of the measured piece with 0 respectively;
if the damage factor sequence curve graphs of the reflected signal and the transmitted signal of the tested piece are close to 0, judging that the tested piece is not cracked, otherwise, judging that the tested piece is cracked, wherein the close to 0 comprises that the magnitude order of the difference between the damage factor value and 0 in the damage factor sequence curve graphs of the reflected signal and the transmitted signal of the tested piece is at least 10 -2 Magnitude.
It should be understood that when the crack is in a non-breaking process in the vibration state and the time length of the analysis signal is far less than the low-frequency vibration period of the structure, the crack opening can be regarded as being quasi-static when each group of analysis signals are collected, the crack states of each group of analysis signals are different when the analysis signals are collected, the signals collected by the non-damaged structure in the vibration state are about the same, the damage factor and the sequence graph calculated by each group of analysis signals are closer to zero, which indicates that the probability of occurrence of the crack is lower, and the probability of occurrence of the crack is larger.
The following describes in detail the implementation of the crack detection method according to the embodiment of the present invention with reference to fig. 3.
Firstly, drawing a phase velocity dispersion curve and a group velocity dispersion curve of a material according to the material property of a measured piece 1 (the measured piece can be a 304 steel beam), and then selecting a detection signal excitation frequency meeting the fundamental frequency phase velocity equal to the frequency multiplication phase velocity and the fundamental frequency group velocity equal to the frequency multiplication group velocity from the dispersion curve based on a phase velocity matching principle and a group velocity matching principle in a nonlinear second harmonic accumulation effect, wherein the excitation frequency is 720kHz. The detection signal is thus a five-period sinusoidal amplitude modulated pulse signal with a center frequency of 720kHz modulated by the 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 one-to-one manner.
Multiple trigger period signal excitation and acquisition: and under the vibration state of the measured piece, continuously triggering and exciting the measured piece in an equidistant triggering mode, and synchronously acquiring nonlinear lamb wave transmission signals and reflection signals under a plurality of triggering periods by using the sensor. The vibration state of the measured piece is realized by placing the measured piece on a vibration table, and 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 equipment; the triggering interval is 10ms according to the principle that the response caused by the last triggering excitation does not influence the response caused by the next triggering excitation and the principle that multiple triggering is contained in one vibration period is ensured; the precision and the time consumption of the acquired signals are comprehensively considered, and nonlinear lamb wave signals in 4 trigger periods are acquired.
And a damage factor calculating step: the acquired nonlinear lamb wave signals with four trigger periods are utilized to intercept 400 mu s duration of the initial stage of each trigger period as analysis signals of each period to form four groups of analysis signals, the first group of analysis signals are used as reference signals, correlation analysis is carried out with the other three groups of analysis signals, and a damage factor formula is utilized
The impairment factors for the transmitted and reflected signals, respectively, are shown in table 1.
TABLE 1 Damage factors for transmitted and reflected signals
And (3) drawing a damage factor sequence curve: selecting a rectangular window function with the length of 12 mu S, performing signal interception on a pair of analysis signals for calculating the damage factors from an initial position, and utilizing intercepted signals S 0 (u)＝g(u-t)S 0 (u)，S n-1 (u)＝g(u-t)S n-1 (u) calculating the damage factor DI < S 0 (u),
And then a window function is shifted right at intervals of 0.4 mu s in a time shifting mode to obtain a series of intercepted signals and corresponding injury factor sequences.
Crack identification: as can be seen from the transmission signal and reflection signal damage factor results of the crack beam and the nondestructive beam in Table 1, the damage factor value of the crack beam is far higher than that of the nondestructive beam, the difference is in an order of magnitude, and the damage factor value of the nondestructive beam is 10 -2 Magnitude is near zero, and the damage factor value of the crack beam is 10 -1 Magnitude of magnitude; the damage factor sequence comparison graph can eliminate the interference caused by the electrical signal noise during the acquisition and more intuitively observe the difference between the nondestructive beam and the crack beam on the damage factor, thereby realizing the crack identification process of the measured piece.
As another embodiment of the present invention, there is provided a crack detection device including:
the generating module is used for generating a trigger excitation signal of the tested piece and sending the trigger excitation signal in an equidistant mode;
the acquisition module is used for respectively acquiring the reflected signals and the transmitted signals under N trigger periods, wherein each time the tested piece receives the trigger excitation signal, the reflected signals and the transmitted signals under one trigger period can be generated, and N is an integer larger than 1;
the analysis module is used for carrying out signal analysis according to the reflected signals and the transmitted signals under the N trigger periods to obtain a crack identification result of the measured piece;
the measured piece is in a vibration state, and the reflection signals and the transmission signals under the N trigger periods comprise nonlinear lamb wave reflection signals and nonlinear lamb wave transmission signals under the N trigger 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.
The specific working principle of the crack detection device provided by the embodiment of the present invention may refer to the description of the crack detection method, and will not be repeated here.
As another embodiment of the present invention, there is provided a crack detection system, including, as shown in fig. 4: the signal generating device 200, the signal acquisition device 300 and the crack detection device 100 are connected with the signal generating device 200 and the signal acquisition device 300 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 reflected signal and the received transmitted 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 the measured piece;
the signal acquisition device 300 is configured to acquire a reflected signal and a transmitted signal generated after the measured object responds to the trigger excitation signal, and send the reflected signal and the transmitted 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 acquisition device comprises a reflected signal sensor and a transmitted signal sensor.
As shown in FIG. 4, wherein the test pieces were 304 steel beams (650 mm 25mm 5 mm), two test pieces were fabricated in total, one with 8mm fatigue cracks and the other with no damage, in order to demonstrate the principle and effect of the test. Each test piece is provided with an exciter, and two sensors respectively receive a reflected signal and a transmitted signal. The exciter and the sensor are 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 a nonlinear lamb wave signal obtained by acquisition to identify crack damage; the signal generating device 200 consists 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, the electric signal is transmitted to the power amplifier to amplify the energy of the electric signal, and then the electric signal is converted into stress through the exciter consisting of piezoelectric ceramic strain gauges and acts on a measured piece; the signal acquisition device 300 is composed of a sensor and an oscilloscope, wherein the sensor composed of piezoelectric ceramic strain gages converts force signals into electric signals, the electric signals are transmitted to the oscilloscope, and then the electric signals are converted into digital signals and transmitted to a signal control and analysis unit for crack damage identification.
It is to be understood that the above embodiments are merely illustrative of the application of the principles of the present invention, but not in limitation thereof. Various modifications and improvements may be made by those skilled in the art without departing from the spirit and substance of the invention, and are also considered to be within the scope of the invention.
Claims (7)
1. A crack detection method, comprising:
generating a trigger excitation signal of a tested piece, and sending the trigger excitation signal in an equidistant mode;
respectively obtaining a reflected signal and a transmitted signal under N trigger periods, wherein each time the tested piece receives the trigger excitation signal, the tested piece can generate the reflected signal and the transmitted signal under one trigger period, and N is an integer larger than 1;
performing signal analysis according to the reflected signals and the transmitted signals in the N trigger periods to obtain a crack identification result of the measured piece;
the measured piece is in a vibration state, and the reflected signals and the transmitted signals under the N trigger periods comprise nonlinear lamb wave reflected signals and nonlinear lamb wave transmitted signals under the N trigger periods;
the method for analyzing the signals according to the reflected signals and the transmitted signals under the N trigger periods to obtain crack identification results of the measured piece comprises the following steps:
performing damage factor calculation according to the reflected signals and the transmitted signals under N trigger periods to respectively obtain damage factors of N-1 reflected signals and damage factors of N-1 transmitted signals;
drawing a damage factor sequence graph of the reflected signals according to the damage factors of the N-1 reflected signals, and drawing a damage factor sequence graph of the transmitted signals according to the damage factors of the N-1 transmitted signals;
analyzing the damage factor sequence curve graph of the reflected signal and the damage factor sequence curve graph of the transmitted signal to obtain a crack identification result of the measured piece;
the method for calculating the damage factors according to the reflected signals and the transmitted signals under N trigger periods respectively obtains the damage factors of N-1 reflected signals and the damage factors of N-1 transmitted signals, and comprises the following steps:
intercepting a preset threshold time length of a reflection signal initial stage under each trigger period as a reflection signal analysis signal of each trigger period, and intercepting a preset threshold time length of a transmission signal initial stage under 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;
taking a first group of analysis signals in the N groups of analysis signals as reference signals, performing correlation analysis with other N-1 groups of analysis signals, and respectively obtaining damage factors of N-1 reflection signals and damage factors of N-1 transmission signals according to a damage factor formula;
wherein the drawing of the damage factor sequence graph of the reflected signals according to the damage factors of the N-1 reflected signals and the drawing of the damage factor sequence graph of the transmitted signals according to the damage factors of the N-1 transmitted signals includes:
according to the rectangular window function, signal interception is carried out on each group of analysis signals from an initial position 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 graph of the analysis signals according to the intercepted signals and the corresponding intercepted damage factors.
2. The crack detection method according to claim 1, wherein 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 test piece includes:
comparing the damage factor sequence graphs of the reflected signal and the transmitted signal of the measured piece with 0 respectively;
if the damage factor sequence curve graphs of the reflected signal and the transmitted signal of the tested piece are close to 0, judging that the tested piece is not cracked, otherwise, judging that the tested piece is cracked, wherein the close to 0 comprises that the magnitude order of the difference between the damage factor value and 0 in the damage factor sequence curve graphs of the reflected signal and the transmitted signal of the tested piece is at least 10 -2 Magnitude.
3. The crack detection method according to claim 1, wherein the time length of the equal interval is based on the principle that the response caused by the last trigger excitation signal does not affect the response caused by the next trigger excitation signal, and the trigger excitation signal can be emitted a plurality of times when the test piece is in one period.
4. The crack detection method according to claim 1, wherein the trigger excitation signal satisfies a phase velocity matching principle.
5. A crack detection device for implementing the crack detection method as claimed in any one of claims 1 to 4, comprising:
the generating module is used for generating a trigger excitation signal of the tested piece and sending the trigger excitation signal in an equidistant mode;
the acquisition module is used for respectively acquiring the reflected signals and the transmitted signals under N trigger periods, wherein each time the tested piece receives the trigger excitation signal, the reflected signals and the transmitted signals under one trigger period can be generated, and N is an integer larger than 1;
the analysis module is used for carrying out signal analysis according to the reflected signals and the transmitted signals under the N trigger periods to obtain a crack identification result of the measured piece;
the measured piece is in a vibration state, and the reflection signals and the transmission signals under the N trigger periods comprise nonlinear lamb wave reflection signals and nonlinear lamb wave transmission signals under the N trigger periods.
6. A crack detection system, comprising: a signal generating device, a signal collecting device and a crack detecting device according to claim 5, 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 reflected signal and the received 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 acting the processed signal on the tested piece;
the signal acquisition device is used for acquiring a reflected signal and a transmitted signal generated after the tested piece responds to the trigger excitation signal, and sending the reflected signal and the transmitted signal to the crack detection device.
7. The crack detection system of claim 6, wherein the signal generating device comprises an exciter and the signal acquisition device comprises a reflected signal sensor and a transmitted signal sensor.
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