CN111413083B - Electromechanical impedance-based flange bolt looseness detection method - Google Patents
Electromechanical impedance-based flange bolt looseness detection method Download PDFInfo
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- CN111413083B CN111413083B CN202010344135.5A CN202010344135A CN111413083B CN 111413083 B CN111413083 B CN 111413083B CN 202010344135 A CN202010344135 A CN 202010344135A CN 111413083 B CN111413083 B CN 111413083B
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01M—TESTING STATIC OR DYNAMIC BALANCE OF MACHINES OR STRUCTURES; TESTING OF STRUCTURES OR APPARATUS, NOT OTHERWISE PROVIDED FOR
- G01M13/00—Testing of machine parts
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R27/00—Arrangements for measuring resistance, reactance, impedance, or electric characteristics derived therefrom
- G01R27/02—Measuring real or complex resistance, reactance, impedance, or other two-pole characteristics derived therefrom, e.g. time constant
Abstract
The invention discloses a flange bolt looseness detection method based on electromechanical impedance, which comprises the following steps: the method comprises the steps of patch connection, detection frequency band searching, damage state calibration, actual damage curve acquisition and data analysis. According to the invention, the bolt loosening can cause the reduction of the structural connection rigidity, and the electromechanical impedance value is influenced by the structural rigidity of the area, so that the loosening state of the bolt is identified by monitoring the change of the impedance value of the piezoelectric sheet. A novel bolt looseness detection method is provided for the maintenance work of the flange structure.
Description
Technical Field
The invention relates to a nondestructive testing method, in particular to a nondestructive testing method for loosening of a flange fastening bolt based on electromechanical impedance.
Background
The bolt connection has the characteristics of reliable connection, repeated use and the like, so the bolt connection is widely applied to the connection of various mechanical structures, and particularly mainly adopts flange connection. However, in the using process of the bolt, the bolt is affected by environmental factors such as transverse vibration and temperature change, so that the bolt is loosened, the connecting structure fails, and safety accidents may be caused seriously. Therefore, this research area has received attention from many scholars.
At present, the following detection technologies are mainly used for detecting the loosening of the bolt: (1) a measurement method based on the vibration signal; (2) vision-based measurement methods; (3) a measurement method based on electromechanical impedance. The vibration signal is used for exciting a tested piece, extracting a response signal for analysis, and acquiring a system mode to identify the loosening state, so that the method is a common detection method at present. However, for a complex structure or a structure with high connection rigidity, the overall modal characteristics are not sensitive to bolt loosening, so that the bolt loosening cannot be accurately identified. The visual detection method realizes detection by identifying the corner of the head of the bolt, but the early expression form of bolt loosening is microscopic slippage and no obvious head rotation exists, so the method is only suitable for macroscopic detection. The electromechanical impedance method is mainly based on electromechanical coupling effect, the loosening state of the bolt can be identified by detecting the electromechanical impedance of the structure because the structural connection rigidity is reduced due to the loosening of the bolt, and the electromechanical impedance method has very high excitation frequency which can reach over 500kHz and is very sensitive to tiny damage.
Although the bolt looseness detection method based on electromechanical impedance is available at present, the bolt looseness detection method has obvious limitations, for example, piezoelectric ceramic plates are required to be attached to each bolt, the monitoring method is time-consuming and labor-consuming, and therefore a novel flange bolt looseness detection method needs to be developed.
Disclosure of Invention
The invention aims to overcome the limitation of the existing detection method and provides a novel method for detecting the looseness of a flange fastening bolt.
The technical scheme of the invention is as follows:
a flange bolt looseness detection method based on electromechanical impedance comprises the following steps:
step 1, uniformly installing piezoelectric ceramic pieces on the front side of a test piece to be detected, wherein the piezoelectric ceramic pieces are connected and installed on the surface of a flange at the middle position of every two bolts in an adhering mode; and the test piece to be tested is stably placed on the flat surface; selecting a piezoelectric ceramic piece on a test piece to be tested as a calibration piezoelectric ceramic piece, and connecting an impedance analyzer to the piezoelectric ceramic piece;
(1) Defining two bolts beside the calibration piezoelectric ceramic wafer as near-field bolts, screwing the two near-field bolts to an expected pretightening force, and keeping the other bolts in a loosened state;
(2) defining bolts distributed on the left side and the right side of the two near-field bolts as far-field bolts corresponding to the calibration piezoelectric ceramic plate, screwing the two far-field bolts in different working conditions, wherein the working conditions are 5 working conditions in total, and the working condition 1 is that the far-field bolts are completely loosened; working condition 2 is that the far-field bolt is screwed to one fourth of the expected pre-tightening force; working condition 3 is that the far-field bolt is screwed to one half of the expected pre-tightening force; working condition 4 is that the far-field bolt is screwed to three quarters of the expected pre-tightening force; working condition 5 is that the far-field bolt is screwed to the expected pretightening force; after each tightening, frequency sweeping is carried out on the frequency band selected from low to high of the calibration piezoelectric ceramic piece, the selected frequency band is uniformly distributed and at least comprises one obvious impedance peak value, the frequency is up to 5MHz, and finally, the scanning result is stored;
(3) processing the scanning result to realize comparison of impedance curves of different working conditions under each frequency band from low to high until finding that the loosening state of a far-field bolt under a certain frequency band has no influence on the impedance curve of the calibrated piezoelectric ceramic piece, and considering that the monitoring range of the piezoelectric ceramic piece to be detected under the frequency band only comprises a near-field bolt, so that the flange bolt loosening detection is carried out under the frequency band, and the impedance curve is stored and marked as a healthy state;
(1) Loosening two near-field bolts around the calibrated piezoelectric ceramic plate to an appointed pre-tightening force according to working conditions, wherein the working conditions are divided into 4 working conditions in total, and the working condition 1 is that the bolts are loosened to seven eighths of the expected pre-tightening force; working condition 2 is that the loosening is six eighths of the expected pre-tightening force; working condition 3 is that the loosening is five eighths of the expected pre-tightening force; working condition 4 is one half of the expected pre-tightening force; for each working condition, respectively acquiring an impedance curve under a detection frequency band, and marking the working condition; the calibration process is adjusted according to needs, and the finer the working condition classification is, the more accurate the final detection result is;
(2) extracting characteristics from the obtained impedance curve: establishing linear fitting equations between different pretightening forces and the peak frequency position deviation and the RMSD respectively as classification bases during detection;
step 4, simulation experiment
Randomly loosening part of bolts, simulating the actual working condition, and acquiring an impedance curve of the piezoelectric ceramic piece near the loosened bolts under a detection frequency band as detection data, wherein the impedance curve is marked as a damage curve;
Firstly, extracting characteristics of a damage curve, including peak frequency position offset and an RMSD value; and (4) substituting the characteristics of the damage curve into a linear fitting equation, namely acquiring whether bolts are loosened near the piezoelectric ceramic piece or not, and giving the size of the loosening degree.
The piezoelectric ceramic piece is connected to the input end of the impedance analyzer through the ultrasonic probe, and the output end of the impedance analyzer is connected to the computer through the data line.
The flat surface is a ground surface or a soft foam surface.
According to the method, the structural rigidity is reduced due to the fact that the bolt is loosened, and the electromechanical impedance value is influenced by the structural rigidity of the area, so that the loosening state of the bolt is identified by monitoring the change of the impedance value of the piezoelectric ceramic piece. The method comprises the steps of generating high-frequency excitation by utilizing piezoelectric ceramic pieces distributed according to a certain rule, obtaining impedance information of structures near the piezoelectric ceramic pieces, and comparing the impedance information with curve characteristics calibrated in advance to determine whether bolts are loosened and the loosening degree near the piezoelectric ceramic pieces.
The invention has the beneficial effects that: the method reduces the number of the required piezoelectric ceramic pieces, namely, each piezoelectric ceramic piece can simultaneously monitor two bolts; the piezoelectric ceramic piece is directly arranged on the surface of the flange to be detected, the structure or the bolt does not need to be processed in advance, and the completely lossless bolt looseness detection is realized; after the pre-calibration is completed, whether the bolt is loosened or not can be detected, and the loosening degree of the bolt can be determined, so that a novel bolt loosening detection method is provided for the maintenance work of the flange structure.
Drawings
FIG. 1 is a flange bolt looseness detection apparatus of the present invention;
FIG. 2 is a diagram showing the arrangement positions of the piezoelectric ceramic plates according to the present invention;
fig. 3 is a flow chart of the bolt looseness detection of the present invention.
In the figure: 1, a flange to be tested; 2, connecting a bolt; 3 piezoelectric ceramic plates; 4, an impedance analyzer; 5 a computer system.
Detailed Description
The following takes a certain type of four-bolt transmission shaft connecting flange as an example to further explain the specific implementation mode of the invention.
Step 1, preparation:
11. the piezoelectric ceramic plates are uniformly arranged on the front surface of the connecting flange, the mounting rule is that the piezoelectric ceramic plates are arranged on the surface of the flange at the middle position of every two bolts, and the mounting mode is glue joint.
12. The flange is placed flat on a flat surface.
13. And selecting one of the piezoelectric ceramic pieces as a calibration piezoelectric ceramic piece in the next step, and connecting an impedance analyzer to the piezoelectric ceramic piece.
21. two bolts beside the calibration piezoelectric ceramic plate are defined as near-field bolts, the two near-field bolts are screwed to 60 N.m, and the other bolts are still in a loosened state.
22. And defining bolts distributed on the left side and the right side of the two near-field bolts as far-field bolts corresponding to the calibration piezoelectric ceramic piece, screwing the two far-field bolts to 30 N.m and 50 N.m respectively in different working conditions, selecting a frequency band from low to high for the calibration piezoelectric ceramic piece after each screwing, and finally storing a scanning result.
23. And comparing impedance curves of different working conditions under various frequency bands by using a computer until the loosening state of the far-field bolt under a certain frequency band is found, wherein the impedance curve of the piezoelectric ceramic piece to be calibrated has no influence, and finally, the frequency band is selected to be 958kHz to 960 kHz.
31. and respectively loosening two near-field bolts around the calibrated piezoelectric ceramic chip to 50 N.m and 30 N.m, and respectively obtaining four groups of impedance curves under the frequency band of 958kHz-960 kHz.
32. And (3) importing the obtained calibration curve into processing software, and extracting the characteristics of each curve as follows:
and establishing a linear fitting equation between different pretightening forces, peak frequency position deviation and RMSD as a classification basis during detection, wherein the final prediction result is determined by the RMSD and the peak deviation together.
If the actual measured curve RMSD is 0.00030 and the peak frequency position deviation is 100Hz, the equation is substituted to obtain T1＝41.397N·m，T2Since the bolt loosening occurred in the vicinity of the piezoelectric sheet, it was found that the loosening degree was about 40.729N · m.
Claims (3)
1. A flange bolt looseness detection method based on electromechanical impedance is characterized by comprising the following steps:
step 1, uniformly installing piezoelectric ceramic pieces on the front side of a test piece to be detected, wherein the piezoelectric ceramic pieces are connected and installed on the surface of a flange at the middle position of every two bolts in an adhering mode; and the test piece to be tested is stably placed on the flat surface; selecting a piezoelectric ceramic piece on a test piece to be tested as a calibration piezoelectric ceramic piece, and connecting an impedance analyzer to the piezoelectric ceramic piece;
step 2, searching a suitable detection frequency band of the test piece to be detected
(1) Defining two bolts beside the calibration piezoelectric ceramic wafer as near-field bolts, screwing the two near-field bolts to an expected pretightening force, and keeping the other bolts in a loosened state;
(2) defining bolts distributed on the left side and the right side of the two near-field bolts as far-field bolts corresponding to the calibration piezoelectric ceramic plate, screwing the two far-field bolts in different working conditions, wherein the working conditions are 5 working conditions in total, and the working condition 1 is that the far-field bolts are completely loosened; working condition 2 is that the far-field bolt is screwed to one fourth of the expected pre-tightening force; working condition 3 is that the far-field bolt is screwed to one half of the expected pre-tightening force; working condition 4 is that the far-field bolt is screwed to three quarters of the expected pre-tightening force; working condition 5 is that the far-field bolt is screwed to the expected pretightening force; after each tightening, frequency sweeping is carried out on the frequency band selected from low to high of the calibration piezoelectric ceramic piece, the selected frequency band is uniformly distributed and at least comprises one obvious impedance peak value, the frequency is up to 5MHz, and finally, the scanning result is stored;
(3) processing the scanning result to realize comparison of impedance curves of different working conditions under each frequency band from low to high until the loosening state of a far-field bolt under a certain frequency band is found to have no influence on the impedance curve of the calibrated piezoelectric ceramic piece, and considering that the monitoring range of the calibrated piezoelectric ceramic piece to be detected under the frequency band only comprises a near-field bolt, so that the loosening detection of the flange bolt is carried out under the frequency band, and the impedance curve is stored and marked as a healthy state;
step 3, calibrating
(1) Loosening two near-field bolts around the calibrated piezoelectric ceramic plate to an appointed pre-tightening force according to working conditions, wherein the working conditions are divided into 4 working conditions in total, and the working condition 1 is that the bolts are loosened to seven eighths of the expected pre-tightening force; working condition 2 is that the loosening is six eighths of the expected pre-tightening force; working condition 3 is that the loosening is five eighths of the expected pre-tightening force; working condition 4 is one half of the expected pre-tightening force; for each working condition, respectively acquiring an impedance curve under a detection frequency band, and marking the working condition; the calibration process is adjusted according to needs, and the finer the working condition classification is, the more accurate the final detection result is;
(2) extracting characteristics from the obtained impedance curve: establishing linear fitting equations between different pretightening forces and the peak frequency position deviation and the RMSD respectively as classification bases during detection;
step 4, simulation experiment
Randomly loosening part of bolts, simulating the actual working condition, and acquiring an impedance curve of the piezoelectric ceramic piece near the loosened bolts under a detection frequency band as detection data, wherein the impedance curve is marked as a damage curve;
step 5, data analysis
Firstly, extracting characteristics of a damage curve, including peak frequency position offset and an RMSD value; and (4) substituting the characteristics of the damage curve into a linear fitting equation, namely acquiring whether bolts are loosened near the piezoelectric ceramic piece or not, and giving the size of the loosening degree.
2. A flange bolt looseness detecting method based on electromechanical impedance as claimed in claim 1, wherein said piezoceramic wafer is connected to an input terminal of an impedance analyzer through an ultrasonic probe, and an output terminal of the impedance analyzer is connected to a computer through a data line.
3. A flange bolt looseness detection method based on electromechanical impedance according to claim 1 or 2, wherein the flat surface is a ground surface or a soft foam surface.
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| CN112985818A (en) * | 2021-04-23 | 2021-06-18 | 大连理工大学 | Method capable of quantitatively applying uniform circumferential radial force |
| CN113267536B (en) * | 2021-05-14 | 2022-09-20 | 大连理工大学 | Multi-frequency band impedance fusion loose bolt positioning method |
| CN113758996A (en) * | 2021-08-30 | 2021-12-07 | 浙江工业大学 | Flange bolt looseness detection method and detection device based on frequency mixing nonlinear ultrasound |
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