CN113588781B - A method for monitoring multi-crack damage in Lamb wave engineering structures - Google Patents
A method for monitoring multi-crack damage in Lamb wave engineering structures Download PDFInfo
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Abstract
The invention discloses a Lamb wave engineering structure multi-crack damage monitoring method, which comprises the following steps: arranging a piezoelectric array on a structural member to be monitored, dividing a monitoring area into a plurality of sector areas, collecting Lamb wave response signals of each monitoring path in the piezoelectric array, and calculating the SDC value of the monitoring path; determining a sector subarea where the damage is located by the SDC value of the radius monitoring path of the sector area; determining the general direction of damage by a three-point positioning method, and then correcting the SDC value of a monitoring path passing through a plurality of sector subareas at the same time; according to a Lamb wave action mechanism of cracks, a cross method is utilized to find out crack directions of single sector subareas, sector subareas imaging is carried out through an elliptical weight model, and finally imaging of all sector subareas is overlapped, so that crack damage images of a structural member to be monitored are obtained. The method can reliably and stably judge the direction of crack damage and realize the accurate monitoring and evaluation of multi-crack damage.
Description
Technical Field
The invention relates to a Lamb wave engineering structure multi-crack damage monitoring method, and belongs to the technical field of structural health monitoring.
Background
With the continuous improvement of the requirements of structural safety and reliability, structural health monitoring technology has been unprecedented. In the use process of the material, under the action of external cyclic stress and strain, the structural member can gradually generate local permanent accumulated damage at one or more positions, and after a period of time, cracks or complete fracture can be generated due to excessive cyclic times. To prevent damage and loss from structural damage, the structure must be effectively assessed.
The generation of Lamb wave is based on the free boundary of the plate, and when the thickness of the plate is in the same order of magnitude as the wavelength of the monitoring signal, the longitudinal wave and the transverse wave are coupled into a special stress wave. Because of the low attenuation characteristic and high sensitivity to micro cracks of the Lamb wave propagating in the plate structure, the Lamb wave is used for structural health monitoring, and the application of the Lamb wave structural health technology is expanded from the aerospace field to the fields of civil engineering, industry, railway and the like, and plays an important role in ensuring structural safety, reducing personnel and property loss and the like. The Lamb wave tomography technology originates from a medical computer tomography technology (Computer Tomography), and compared with a triangulation method and an arc positioning method, the Lamb wave tomography technology can intuitively reconstruct information such as the position, the size and the like of multiple injuries, and has a good research prospect for monitoring and evaluating the multiple crack injuries.
Because Lamb wave has the dispersion characteristic and the mode conversion caused by the end effect during propagation, when the Lamb wave is used for monitoring structural member crack damage, a monitoring signal can be greatly influenced, so that a monitoring result is inaccurate, the difficulty of reconstructing crack damage is improved, and therefore, the existing structural crack damage monitoring technology based on Lamb wave tomography is required to be improved.
Disclosure of Invention
In order to solve the problems in the prior art, the invention provides a Lamb wave engineering structure multi-crack damage monitoring method, which utilizes Lamb wave response signals to obtain SDC values of different paths on a structural member to be detected, corrects a special path through analysis of the SDC values, finally finds out the position of a crack, reconstructs a crack damage image and can effectively improve the accuracy of Lamb wave structure damage monitoring.
In order to solve the technical problems, the invention adopts the following technical means:
the invention provides a Lamb wave engineering structure multi-crack damage monitoring method, which comprises the following steps:
acquiring a piezoelectric array comprising a ring shape and a circle center, and acquiring Lamb wave reference signals of each monitoring path in the piezoelectric array;
collecting Lamb wave actual response signals of each monitoring path in a monitoring area of a structural member to be monitored by utilizing a piezoelectric array;
calculating the SDC value of each monitoring path according to the Lamb wave reference signal and the Lamb wave actual response signal;
obtaining a sector-shaped subarea containing cracks from the monitoring area according to the SDC values of the piezoelectric array and the monitoring path;
analyzing the suspected crack direction in each sector subarea by using a three-point positioning method, selecting a special path from all monitoring paths according to the suspected crack direction, and correcting the SDC value of the special path;
performing SDC value analysis on each sector subarea according to the corrected monitoring area to obtain a crack direction path corresponding to each sector subarea, and performing SDC value correction on the crack direction path;
obtaining a crack damage image of each sector subarea by utilizing an elliptic weight model imaging principle according to the corrected crack direction path;
and superposing the crack damage images of all the fan-shaped subareas to obtain the crack damage image of the structural member to be monitored.
Further, the method for acquiring Lamb wave reference signals of each monitoring path in the piezoelectric array comprises the following steps:
determining the position of a circle center and the size of an annular ring surrounding the circle center according to the size of a structural member to be monitored, and arranging piezoelectric sensors on the circle center and the annular ring to obtain a piezoelectric array comprising the annular ring and the circle center;
each piezoelectric sensor in the piezoelectric array is sequentially selected as an excitation element, other piezoelectric sensors are used as sensing elements, and one excitation element and one sensing element form a monitoring path;
in each monitoring path, lamb wave ultrasonic signals are loaded on an excitation element through a function generator and a power amplifier, the excitation element is utilized to send Lamb wave ultrasonic signals to a sensing element, and Lamb wave response signals under excitation are obtained at the sensing element and used as Lamb wave reference signals of the monitoring path.
Further, the calculation formula of the SDC value is as follows:
wherein, SDC ij SDC value, t, representing a monitoring path consisting of an ith excitation element and a jth sensing element 0 Indicating the direct time of the excitation signal in the monitoring path, deltaT indicating a time window, x ij (t) Lamb wave reference signal representing the monitoring path formed by the ith excitation element and the jth sensing element at the moment t, y ij (t) represents Lamb wave actual response signal of monitoring path formed by ith excitation element and jth sensing element at t moment x Sum mu y Average values of Lamb wave reference signals and Lamb wave actual response signals are respectively represented, i, j=1, 2, …, L, and i noteq j, L is the total number of piezoelectric sensors in the piezoelectric array.
Further, the method for obtaining the fan-shaped subarea containing the cracks comprises the following steps:
piezoelectric sensors at the circle center in the piezoelectric array are used as excitation elements, piezoelectric sensors on the ring shape are used as sensing elements, and a plurality of radius monitoring paths are obtained;
comparing the SDC value of each radius monitoring path with a preset damage threshold value, and when the radius monitoring path P ab When the SDC value of (2) is greater than the damage threshold, the path P is monitored by radius ab Taking a sector from the monitoring area as a sector-shaped subarea containing cracks for the central line, wherein P ab The radius monitoring path from the piezoelectric sensor at the center of the circle in the piezoelectric array to the b-th piezoelectric sensor on the ring is represented, b=1, 2, …, L-1, L is the total number of the piezoelectric sensors in the piezoelectric array, the center of the fan-shaped subarea is the center of the circle of the piezoelectric array, and 2 endpoints of the circular arc of the fan-shaped subarea are 2 piezoelectric sensors adjacent to the b-th piezoelectric sensor on the ring of the piezoelectric array.
Further, for each sector-shaped subarea, the method for analyzing the suspected crack direction and selecting a special path comprises the following steps:
obtaining 3 positioning monitoring paths according to the circle center of the sector subarea D and 2 arc endpoints, wherein d=1, 2, …, D and D are the number of the sector subareas;
for each positioning monitoring path, extracting an SDC value after an A0 wave band of a Lamb wave actual response signal of the positioning monitoring path, and judging that the direction of the positioning monitoring path is the suspected crack direction of a sector subarea d when the SDC value fluctuates;
comparing each monitoring path in the piezoelectric array with the suspected crack direction, and considering the monitoring path as a special path when the included angle between one monitoring path and the suspected crack direction is within +/-25 degrees and the monitoring path passes through the sector-shaped subarea d and other sector-shaped subareas simultaneously.
Further, the method for obtaining the crack direction path corresponding to each sector-shaped subarea comprises the following steps:
screening all cross path groups of the sector subareas D from all monitoring paths on the ring of the piezoelectric array by using a crisscross method, wherein each cross path group comprises 2 monitoring paths passing through the sector subareas D, the included angle between the 2 monitoring paths is 80-100 degrees, and d=1, 2, …, D and D are the number of the sector subareas;
calculating the absolute difference value of the SDC values of 2 monitoring paths in each cross path group according to the corrected monitoring area;
comparing the absolute values of the differences of all the cross path groups to obtain the cross path group with the largest absolute value of the differences
From a group of intersecting pathsAnd selecting a monitoring path with a small SDC value as a crack direction path corresponding to the sector-shaped subarea d.
Further, a structure to be monitored is providedThe minimum SDC value of the judging damage in the piece is W min Judging the maximum SDC value of the damage to be W max Correcting the SDC value of the special path to W min Correcting the SDC value of the crack direction path to W max 。
Further, for each sector-shaped subarea, the method for acquiring the crack damage image by using the imaging principle of the elliptical weight model comprises the following steps:
taking two endpoints of a crack direction path of the sector-shaped subarea d as two focuses of an ellipse to obtain an ellipse area corresponding to the sector-shaped subarea d;
and (3) assigning values to points in the elliptical region by using an elliptical weight model, and judging the position, the size and the direction of the crack in the sector-shaped subarea d according to an assignment result and a preset crack threshold value to obtain a crack damage image of the sector-shaped subarea d.
The following advantages can be obtained by adopting the technical means:
the invention provides a Lamb wave engineering structure multi-crack damage monitoring method, which comprises the steps of constructing a piezoelectric array on a structural member to be detected, acquiring an SDC value of each monitoring path by utilizing Lamb wave response signals, searching a special path meeting requirements on the structural member by utilizing a three-point positioning method, correcting the special path, analyzing the SDC value by utilizing a cross method, finding a crack direction, finally acquiring the position and the size of a crack by utilizing an elliptic weight model, and reconstructing a crack damage image. According to the invention, the monitoring area of the structural member is divided into a plurality of sector areas by utilizing the piezoelectric array consisting of the ring shape and the circle center, the sector subareas suspected to be damaged are searched according to the size of the SDC value, and then the path correction, crack searching and damage imaging operations are carried out by taking the sector subareas as a unit, so that the monitoring area can be thinned, the mutual influence among cracks is weakened, the monitoring difficulty is reduced, the accuracy of Lamb wave structural damage monitoring can be improved, and the accurate monitoring and evaluation of multi-crack damage are realized.
Drawings
FIG. 1 is a flow chart showing the steps of a method for monitoring multi-crack damage of a Lamb wave engineering structure;
FIG. 2 is a schematic diagram of a piezoelectric array and fan-shaped sub-regions in an embodiment of the present invention;
FIG. 3 is a schematic view of a structure to be monitored, a piezoelectric array, and crack damage in an embodiment of the present invention;
FIG. 4 is a waveform time domain diagram of a narrowband monitoring signal according to an embodiment of the invention;
FIG. 5 is a schematic diagram of three-point positioning of suspected crack directions in an embodiment of the present invention;
FIG. 6 is an image of a conventional elliptical weight model in accordance with an embodiment of the present invention;
FIG. 7 is a crack damage image of a sector-shaped sub-region in an embodiment of the present invention;
FIG. 8 is a crack damage image of another fan-shaped sub-region in an embodiment of the present invention;
fig. 9 is an image of crack damage to a structure to be monitored in an embodiment of the present invention.
Detailed Description
The technical scheme of the invention is further described below with reference to the accompanying drawings:
the invention provides a Lamb wave engineering structure multi-crack damage monitoring method, which is based on the following basic principle: thinning the monitoring area to weaken the mutual influence among cracks; any sector subarea responds to the SDC value of the signal part through three-point positioning extraction structure, the crack direction of each subarea is roughly estimated, if the phase shift of the reflected segment signal occurs, the crack is more similar to the monitoring path, so that the monitoring paths of the cracks which are mutually interfered are distinguished; for a single sector subarea suspected to be damaged, according to the action mechanism of a crack on a monitoring signal, the incidence angle of the monitoring signal entering the crack is different, and the influence of the crack is also different, namely the difference (SDC value) between a reference signal and an actual response signal is related to the incidence angle of the monitoring signal entering the crack.
As shown in fig. 1, the method specifically comprises the following steps:
and step A, acquiring a piezoelectric array comprising a ring shape and a circle center, and acquiring Lamb wave reference signals of each monitoring path in the piezoelectric array.
And A01, determining the position of the circle center and the size of the ring around the circle center according to the size of the structural member to be monitored, and arranging piezoelectric sensors on the circle center and the ring to obtain a piezoelectric array comprising the ring and the circle center, as shown in fig. 2.
A02, placing the piezoelectric array on a healthy structural member, sequentially selecting each piezoelectric sensor in the piezoelectric array as an excitation element, and other piezoelectric sensors as sensing elements, constructing a monitoring channel, acquiring a monitoring path, and forming a monitoring path by one excitation element and one sensing element, for example, setting the excitation element as S i The sensing element is S j S is then i And S is j The monitoring path of the composition is P ij I, j=1, 2, …, L and i+.j, L is the total number of piezoelectric sensors in the piezoelectric array.
A03, loading Lamb wave ultrasonic signals to an excitation element through a function generator and a power amplifier in each monitoring path, and exciting the monitoring signals in the structure; the Lamb wave ultrasonic signal is sent to the sensing element by the exciting element, the Lamb wave response signal under excitation is obtained by the sensing element, and the Lamb wave response signal is sensed, amplified and transmitted into the computer through the data acquisition card by the charge amplifier Lamb wave structure response signal to be used as the Lamb wave reference signal of the monitoring path.
Traversing all monitoring paths in the piezoelectric array to obtain Lamb wave reference signals of all the monitoring paths.
The method can excite Lamb wave signals with single mode or special mode as main mode under preset center frequency, and then excite narrowband signals based on the Lamb wave signals to be used as monitoring signals.
And B, acquiring Lamb wave actual response signals of each monitoring path in a monitoring area of the structural member to be monitored by utilizing a piezoelectric array, wherein the method for acquiring the Lamb wave actual response signals is identical to the method in the step A, and the difference is that the Lamb wave actual response signals are acquired on the structural member to be monitored.
And C, calculating a signal difference coefficient, namely an SDC value, of each monitoring path according to the Lamb wave reference signal and the Lamb wave actual response signal.
The calculation formula of the SDC value is as follows:
wherein, SDC ij SDC value, t, representing a monitoring path consisting of an ith excitation element and a jth sensing element 0 Indicating the direct time of the excitation signal in the monitoring path, deltaT indicating a time window, x ij (t) Lamb wave reference signal representing the monitoring path formed by the ith excitation element and the jth sensing element at the moment t, y ij (t) represents Lamb wave actual response signal of monitoring path formed by ith excitation element and jth sensing element at t moment x Sum mu y Average values of the Lamb wave reference signal and the Lamb wave actual response signal are shown, respectively.
And D, obtaining a sector subarea containing cracks from the monitoring area according to the SDC values of the piezoelectric array and the monitoring path.
In the step D01, in order to refine the monitoring area, the piezoelectric sensor at the center of a circle in the piezoelectric array is used as an excitation element, the piezoelectric sensor on the ring shape is used as a sensing element, and a plurality of radius monitoring paths are obtained, and the radius monitoring paths can divide the whole monitoring area into a plurality of sector areas.
Step D02, comparing the SDC value of each radius monitoring path with a preset damage threshold, and when the radius monitoring path P ab When the SDC value of (2) is greater than the damage threshold, the path P is monitored by radius ab Taking a sector from the monitoring area as a sector-shaped subarea containing cracks for the central line, wherein P ab Representing the radius monitoring path of the piezoelectric sensor at the center of the circle in the piezoelectric array to the b-th piezoelectric sensor on the ring, b=1, 2, …, L-1.
The circle center of the sector subarea is the circle center of the piezoelectric array, 2 endpoints of the circular arc of the sector subarea are 2 piezoelectric sensors adjacent to the b-th piezoelectric sensor on the ring shape of the piezoelectric array, as shown in figure 2, if the radius monitors the path P a1 If the SDC value of (2) is greater than the damage thresholdThe sector-shaped subarea containing the cracks is a sector formed by the points 2, 16 and a.
Step E, analyzing the suspected crack direction in each sector subarea by using a three-point positioning method, selecting a special path from all monitoring paths according to the suspected crack direction, and correcting the SDC value of the special path, wherein the specific operation of the step E is as follows:
and E01, obtaining 3 positioning monitoring paths according to the circle center of the sector subarea D and 2 arc endpoints, wherein d=1, 2, …, D is the number of the sector subareas.
And E02, extracting SDC values after the Lamb wave actual response signal A0 wave band of each positioning monitoring path. In general, the SDC value after the A0 band will quickly tend to be stable, but when one monitoring path is approximately parallel to the crack, the SDC value after the A0 band of the one monitoring path will fluctuate, so when the SDC value fluctuates, it is indicated that the positioning monitoring path may be parallel to the crack in the sector-shaped subarea, and the direction of the positioning monitoring path is determined to be the suspected crack direction of the sector-shaped subarea d.
And E03, comparing each monitoring path in the piezoelectric array with the suspected crack direction, and considering the monitoring path as a special path when the included angle between one monitoring path and the suspected crack direction is within +/-25 degrees (approximately parallel) and the monitoring path passes through the sector-shaped subarea d and other sector-shaped subareas simultaneously.
In step E04, the special path passes through multiple suspected damage areas at the same time, and multiple cracks are mutually affected, so that the subsequent cross method is easy to fail, and therefore, the special path is subjected to SDC value correction. The damage judging range [ W ] of the structural member to be detected can be obtained according to the material, the size, the service life and the like of the structural member to be detected min ,W max ]When the SDC value is within the damage determination range, it is considered that there is a possibility of crack damage, W min To determine the minimum SDC value of the lesion, W max To determine the maximum SDC value of the lesion. After finding out the special path, correcting the SDC value of the special path to W min 。
And F, performing SDC value analysis on each sector-shaped subarea according to the corrected monitoring area to obtain a crack direction path corresponding to each sector-shaped subarea, and performing SDC value correction on the crack direction path.
On the basis of the corrected monitoring area, the method sequentially judges the crack direction path corresponding to each sector subarea by using a crisscross method, and specifically comprises the following steps:
and F01, acquiring all monitoring paths on the ring of the piezoelectric array, combining all the monitoring paths in any pair, and screening all cross path groups of the sector-shaped subarea d meeting the requirements by using a crisscross method, wherein each cross path group comprises 2 monitoring paths passing through the sector-shaped subarea d, and the included angle between the 2 monitoring paths is 80-100 degrees, namely the 2 monitoring paths are approximately vertical.
And F02, calculating the absolute difference value of the SDC values of 2 monitoring paths in each crossing path group according to the corrected monitoring area.
Set cross path groupThe 2 monitoring paths in the network are respectively P ij And P mn Then->Difference absolute value +.>The method comprises the following steps:
where m, n=1, 2, …, L.
F03, comparing the absolute values of the differences of all the cross path groups to obtain the cross path group with the largest absolute value of the differences
Step F04,Comparing sets of intersecting pathsAnd selecting the monitoring path with small SDC value as a crack direction path corresponding to the sector-shaped subarea d, wherein the direction of the crack direction path is the direction of the crack in the sector-shaped subarea d.
In order to compensate the missing characteristic data in the crack direction, the invention corrects the SDC value of the crack direction path to W max 。
And G, obtaining crack damage images of each sector subarea by utilizing an elliptic weight model imaging principle according to the corrected crack direction path.
In order to avoid the mutual influence among cracks, the invention respectively carries out image reconstruction on each sector subarea, and specifically:
and G01, taking two endpoints of a crack direction path of the sector-shaped subarea d as two focuses of an ellipse to obtain an ellipse area corresponding to the sector-shaped subarea d.
And G02, assigning values to points in the elliptical area by using an elliptical weight model, wherein theoretically, the points closer to the crack direction path are assigned larger.
And judging the position, the size and the direction of the crack in the sector-shaped subarea d according to the assignment result and a preset crack threshold value, and obtaining a crack damage image of the sector-shaped subarea d. And comparing the value of each point in the elliptical area with a crack threshold value, if the value of the point is larger than the crack threshold value, reserving the point, otherwise deleting the point, and finally, forming a crack damage image by the reserved point.
The structural component is considered to establish a Cartesian coordinate system, and the space distribution function of SDC values in the elliptical area is as follows:
wherein s is ij (u, v) represents a crack direction path of P ij Coordinate points (u) in a time Cartesian coordinate systemSDC value at v), β is the ellipse eccentricity, for controlling the size of the ellipse.
Let the crack direction path of the sector-shaped subarea d be P ij The excitation element of (2) has a coordinate point (u) in a Cartesian coordinate system id ,v id ) The coordinate point of the sensing element in the Cartesian coordinate system is (u) jd ,v jd )，R ij The calculation formula of (u, v) is as follows:
and step H, overlapping the crack damage images of all the fan-shaped subareas to obtain a crack damage image of the structural member to be monitored.
Because the probability of a single sector-shaped subarea can only express the damage distribution of a single area, the probability distribution map of all sector-shaped subareas is overlapped, and the damage distribution probability of any point on a structural member to be monitored is as follows:
to verify the effect of the method of the invention, the following examples are given:
examples an aluminum plate with dimensions 600mm x 3mm was used as the structural member to be tested, young's modulus e=70gpa, poisson's ratio 0.33, density ρ=2711 kg/m 3 The coordinate system is established by taking the circle center as the origin, piezoelectric sensors are uniformly arranged on a circular ring with the radius of 210mm and the origin to form a piezoelectric array with the circular ring and the circle center, the piezoelectric constant is 160 multiplied by 10 < -12 > C/N, the structural member and the piezoelectric array are shown in figure 3, and W is calculated according to the material of the structural member to be monitored and the like min ＝0.15，W max =1, sdc is defined as follows:
(1) Sequentially selecting origin and ring-up pressure in the piezoelectric array of fig. 3The electric sensor is used as an excitation element, a five-peak narrow-band monitoring signal is loaded on the excitation element, so that the excitation element generates a force consistent with the signal amplitude in the vertical direction of the plate structure, and the excitation signal A is excited in the structure 0 Single mode Lamb wave signals with mode as the main. The adopted monitoring signal is a sinusoidal modulation signal with the center frequency of 200kHz, the waveform time domain of the narrow-band monitoring signal is shown in figure 4, and Lamb wave actual response signals of all monitoring paths in the current state of the structure are collected at the sensing element.
(2) And calculating the SDC value of each monitoring path according to the Lamb wave reference signal and the Lamb wave actual response signal by using a formula (7).
(3) When the piezoelectric sensor at the center of the circle is used as an excitation element, a radius monitoring path is formed with the piezoelectric sensor on the ring; as shown in FIG. 5, the crack passing P is judged by SDC value 03 、P 05 Two paths can be known that the first crack damage (marked as damage 1) exists in a sector-shaped subarea (marked as sector-shaped subarea 1) formed by the piezoelectric sensor No. 0# -2# -4, and the second crack damage (marked as damage 2) also can be known to exist in a sector-shaped subarea (marked as sector-shaped subarea 2) formed by the piezoelectric sensor No. 0# -4# -6.
(4) In the three-point positioning, the crack direction of each sector subarea is roughly estimated by extracting the SDC value of the structural response signal part, so that the direction of the damage 1 and the monitoring path P can be known 24 Approximately, the direction of the lesion 2 and the monitoring path P 06 And (5) approximating. And further, the possibility that two crack injuries are intersected can be judged, so that the SDC value of a monitoring path passing through the two sector-shaped subareas simultaneously is corrected to be 0.15, and the defect that the SDC value is larger due to the mutual influence of cracks is eliminated.
(5) As can be seen from fig. 3, the path P is monitored 15 、P 26 、P 311 、P 312 、P 313 、P 415 、P 416 All pass through sector-shaped subareas 1, P 26 、P 37 、P 48 、P 49 、P 513 、P 514 All passing through the sector-shaped sub-area 2. Calculating the included angles of the monitoring paths, finding out 2 monitoring paths which are approximately perpendicularly crossed in each sector subarea to form a crossingA set of fork paths.
The group of intersecting paths in sector-shaped sub-region 1 is P 15 ⊥P 311 、P 26 ⊥P 312 、P 26 ⊥P 313 The method comprises the steps of carrying out a first treatment on the surface of the The group of intersecting paths in sector-shaped sub-region 2 is P 16 ⊥P 49 、P 37 ⊥P 513 、P 46 ⊥P 514 . And calculating the absolute value of the difference value of the SDC values of the cross path groups, and finding out crack direction paths corresponding to each sector-shaped subarea.
The absolute values of the differences of the cross path groups in the embodiment of the invention are shown in the following table:
TABLE 1
| Cross path group | Absolute value of difference |
| P 15 ⊥P 311 | 0.1200 |
| P 26 ⊥P 312 | 0.1731 |
| P 26 ⊥P 313 | 0.0991 |
| P 16 ⊥P 49 | 0.0039 |
| P 37 ⊥P 513 | 0.0023 |
| P 46 ⊥P 514 | 0.0501 |
After comparative calculation according to Table 1, the crack direction path of sector-shaped subregion 1 was P 26 The crack direction path of the sector-shaped subarea 2 is P 514 Will P 26 And P 514 The SDC value of (c) is corrected to 1.
(6) And respectively reconstructing crack damage images of each sector subarea by using an elliptic weight model imaging principle, wherein as shown in fig. 6, the brighter the color is, the greater the probability of crack occurrence is.
Let the crack threshold be 1.2, thresholding the crack damage image according to the crack threshold, fig. 7 and 8 are respectively the crack damage images of the damage 1 and the damage 2, the crack damage image of the structural member to be monitored is shown in fig. 9, wherein the bright color part is the position where the crack is located, and the reconstructed crack image can accurately reflect the distribution of the crack damage in the plate.
The method of the invention divides the monitoring area of the structural member into a plurality of sector areas by utilizing the piezoelectric array formed by the ring and the circle center, thereby realizing the refinement of the monitoring area; the special paths meeting the requirements on the structural member are searched by using a three-point positioning method, and corrected, so that the mutual influence of multiple cracks can be reduced, and the effect of the crisscross method is ensured; and analyzing the SDC value by using a crisscross method to find out the crack direction, so that an accurate and reliable crack damage image can be obtained. The method can improve the accuracy of Lamb wave structural damage monitoring while reducing the monitoring difficulty, and realize the accurate monitoring and evaluation of multi-crack damage.
The foregoing is merely a preferred embodiment of the present invention, and it should be noted that modifications and variations could be made by those skilled in the art without departing from the technical principles of the present invention, and such modifications and variations should also be regarded as being within the scope of the invention.
Claims (6)
1. A Lamb wave engineering structure multi-crack damage monitoring method is characterized by comprising the following steps:
acquiring a piezoelectric array comprising a ring shape and a circle center, and acquiring Lamb wave reference signals of each monitoring path in the piezoelectric array;
collecting Lamb wave actual response signals of each monitoring path in a monitoring area of a structural member to be monitored by utilizing a piezoelectric array;
calculating the SDC value of each monitoring path according to the Lamb wave reference signal and the Lamb wave actual response signal;
obtaining a sector-shaped subarea containing cracks from the monitoring area according to the SDC values of the piezoelectric array and the monitoring path;
analyzing the suspected crack direction in each sector subarea by using a three-point positioning method, selecting a special path from all monitoring paths according to the suspected crack direction, and correcting the SDC value of the special path;
performing SDC value analysis on each sector subarea according to the corrected monitoring area to obtain a crack direction path corresponding to each sector subarea, and performing SDC value correction on the crack direction path;
obtaining a crack damage image of each sector subarea by utilizing an elliptic weight model imaging principle according to the corrected crack direction path;
overlapping crack damage images of all the fan-shaped subareas to obtain a crack damage image of the structural member to be monitored;
the method for analyzing the suspected crack direction and selecting the special path aiming at each sector subarea comprises the following steps:
obtaining 3 positioning monitoring paths according to the circle center of the sector subarea D and 2 arc endpoints, wherein d=1, 2, …, D and D are the number of the sector subareas;
for each positioning monitoring path, extracting an SDC value after the Lamb wave actual response signal A0 wave band, and judging that the direction of the positioning monitoring path is the suspected crack direction of the sector subarea d when the SDC value fluctuates;
comparing each monitoring path in the piezoelectric array with the suspected crack direction, and considering the monitoring path as a special path when the included angle between one monitoring path and the suspected crack direction is within +/-25 degrees and the monitoring path passes through the sector-shaped subarea d and other sector-shaped subareas simultaneously;
the method for obtaining the corresponding crack direction path of each sector-shaped subarea comprises the following steps:
screening all cross path groups of the sector subareas D from all monitoring paths on the ring of the piezoelectric array by using a crisscross method, wherein each cross path group comprises 2 monitoring paths passing through the sector subareas D, the included angle between the 2 monitoring paths is 80-100 degrees, and d=1, 2, …, D and D are the number of the sector subareas;
calculating the absolute difference value of the SDC values of 2 monitoring paths in each cross path group according to the corrected monitoring area;
comparing the absolute values of the differences of all the cross path groups to obtain the cross path group with the largest absolute value of the differences
From a group of intersecting pathsAnd selecting a monitoring path with a small SDC value as a crack direction path corresponding to the sector-shaped subarea d.
2. The method for monitoring the multi-crack damage of the Lamb wave engineering structure according to claim 1, wherein the method for collecting Lamb wave reference signals of each monitoring path in the piezoelectric array is as follows:
determining the position of a circle center and the size of an annular ring surrounding the circle center according to the size of a structural member to be monitored, and arranging piezoelectric sensors on the circle center and the annular ring to obtain a piezoelectric array comprising the annular ring and the circle center;
each piezoelectric sensor in the piezoelectric array is sequentially selected as an excitation element, other piezoelectric sensors are used as sensing elements, and one excitation element and one sensing element form a monitoring path;
in each monitoring path, lamb wave ultrasonic signals are loaded on an excitation element through a function generator and a power amplifier, the excitation element is utilized to send Lamb wave ultrasonic signals to a sensing element, and Lamb wave response signals under excitation are obtained at the sensing element and used as Lamb wave reference signals of the monitoring path.
3. The method for monitoring multi-crack damage of Lamb wave engineering structure according to claim 1 or 2, wherein the calculation formula of the SDC value is as follows:
wherein, SDC ij SDC value, t, representing a monitoring path consisting of an ith excitation element and a jth sensing element 0 Indicating the direct time of the excitation signal in the monitoring path, deltaT indicating a time window, x ij (t) Lamb wave reference signal representing the monitoring path formed by the ith excitation element and the jth sensing element at the moment t, y ij (t) represents Lamb wave actual response signal of monitoring path formed by ith excitation element and jth sensing element at t moment x Sum mu y Average values of Lamb wave reference signals and Lamb wave actual response signals are respectively represented, i, j=1, 2, …, L, and i noteq j, L is the total number of piezoelectric sensors in the piezoelectric array.
4. The method for monitoring the multi-crack damage of the Lamb wave engineering structure according to claim 1 or 2, wherein the method for obtaining the sector-shaped subarea containing the crack is as follows:
piezoelectric sensors at the circle center in the piezoelectric array are used as excitation elements, piezoelectric sensors on the ring shape are used as sensing elements, and a plurality of radius monitoring paths are obtained;
comparing the SDC value of each radius monitoring path with a preset damage threshold value, and when the radius monitoring path P ab When the SDC value of (2) is greater than the damage threshold, the path P is monitored by radius ab Taking a sector from the monitoring area as a sector-shaped subarea containing cracks for the central line, wherein P ab The radius monitoring path from the piezoelectric sensor at the center of the circle in the piezoelectric array to the b-th piezoelectric sensor on the ring is represented, b=1, 2, …, L-1, L is the total number of the piezoelectric sensors in the piezoelectric array, the center of the fan-shaped subarea is the center of the circle of the piezoelectric array, and 2 endpoints of the circular arc of the fan-shaped subarea are 2 piezoelectric sensors adjacent to the b-th piezoelectric sensor on the ring of the piezoelectric array.
5. The method for monitoring multiple crack damage of Lamb wave engineering structure according to claim 1, wherein the minimum SDC value of damage judgment in the structural member to be monitored is W min Judging the maximum SDC value of the damage to be W max Correcting the SDC value of the special path to W min Correcting the SDC value of the crack direction path to W max 。
6. The method for monitoring the multi-crack damage of the Lamb wave engineering structure according to claim 1, wherein the method for acquiring the crack damage image by utilizing the elliptic weight model imaging principle is as follows:
taking two endpoints of a crack direction path of the sector-shaped subarea d as two focuses of an ellipse to obtain an ellipse area corresponding to the sector-shaped subarea d;
and (3) assigning values to points in the elliptical region by using an elliptical weight model, and judging the position, the size and the direction of the crack in the sector-shaped subarea d according to an assignment result and a preset crack threshold value to obtain a crack damage image of the sector-shaped subarea d.
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