CN108195535B - Bolt joint looseness detection method and system based on nonlinear excitation characteristics - Google Patents
Bolt joint looseness detection method and system based on nonlinear excitation characteristics Download PDFInfo
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- CN108195535B CN108195535B CN201711402531.3A CN201711402531A CN108195535B CN 108195535 B CN108195535 B CN 108195535B CN 201711402531 A CN201711402531 A CN 201711402531A CN 108195535 B CN108195535 B CN 108195535B
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Abstract
The invention discloses a bolt joint looseness detection method and system based on nonlinear excitation characteristics, wherein the method comprises the following steps: carrying out simulation modal analysis on the three-dimensional model of the test piece, and determining the local vibration exciter and sensor distribution position of the bolt joint; arranging the vibration exciter and the sensor according to the determined distribution positions of the vibration exciter and the sensor, and determining the vibration exciting parameters of the vibration exciter according to the simulation modal analysis result of the three-dimensional model; keeping the excitation parameters unchanged, performing a pre-experiment on the test pieces of the same type to obtain a corresponding relation between bolt pretightening force and higher harmonic proportionality coefficients, and generating a relation database; and testing the piece to be tested to obtain the higher harmonic proportionality coefficient, inquiring the relational database, determining the bolt pretightening force of the piece to be tested, and judging whether the bolt joint part of the piece to be tested is loosened or not according to the bolt pretightening force of the piece to be tested. The method has the advantages of wide applicability, flexible and convenient use, high sensitivity and the like, can be used for nondestructive testing, and is suitable for actual production.
Description
Technical Field
The invention relates to the technical field of mechanical state detection and maintenance, in particular to a method and a system for detecting looseness of a bolt joint based on nonlinear excitation characteristics.
Background
The bolt connection has the advantages of bearing larger load and being capable of being assembled and disassembled repeatedly, so that the bolt connection is widely applied to various mechanical structures, such as main body stress parts of engineering structures of spacecrafts, machine tools, steel bridges and the like, and all the main body stress parts comprise bolt joint parts. For a screw joint which is subjected to important loads, the pretensioning force is strictly required, since the pretensioning force largely determines the reliability, the load-bearing capacity, the rigidity of the screw connection and has an important influence on the structural dynamics. However, in practical applications, under the action of various loads such as long-term fatigue, impact, vibration and the like, the pretightening force of the connecting bolt can be loosened and is lower than an initial design value, so that the equipment failure performance is reduced if the pretightening force is light, and the pretightening force can be changed into structural damage to cause danger and huge economic loss. Therefore, it is necessary to develop a nondestructive testing method capable of detecting whether the bolt joint portion in the structure is loosened.
In the related art, the bolt looseness detection method mainly comprises a visual image method, a piezoelectric sensor method and a dynamic method: the visual image method is mainly characterized in that a locking mark is added after the bolt is pre-tightened, whether the position of the locking mark is changed or not is determined by observing and processing the image, whether the bolt is loosened or not is judged, and the method cannot detect the condition that the pre-tightening force is reduced because the bolt head does not rotate. The piezoelectric sensor method is mainly characterized in that a pressure sensor is arranged at the position of a bolt head, and whether the bolt is loosened or not is detected according to the change of a piezoelectric signal caused by the change of pretightening force before and after the bolt is loosened. However, the actual structure usually has a large number of bolts, which requires a sensor to be disposed at each bolt, and thus has disadvantages of high cost and poor maintainability. The dynamic method is mainly used for detecting the loosening of the bolt according to the influence of the change of the pretightening force of the bolt on the dynamic characteristics of the structure. The common methods mainly include a sound beating method. The sound beating method is to beat the metal connecting part manually and judge whether the bolt is loosened or not from sound by utilizing the vibration sound production principle. The method of beating sound is the field commonly used method, and detection accuracy is higher for experienced workman, but to workman's experience higher requirement, and the human cost is high requires.
Related documents disclose a bolt pretightening force detection method and device, which adopt the steps of obtaining a vibration signal generated by knocking, selecting N wave crest amplitudes and corresponding frequencies of a signal frequency spectrum, and comparing the N wave crest amplitudes and the corresponding frequencies with a signal sample database to detect the bolt pretightening force. The method is also a dynamic detection method, but because the amplitude values of the knocking wave crests of different structures are different from the corresponding frequencies, a complete signal characteristic database needs to be established for the structure to be detected before detection, and the cost is high. In addition, in practical tests, obvious nonlinear phenomena can be caused in the bolt loosening process, so that the knocking force has large influence on the measured vibration signal characteristics, and the knocking force cannot be accurately controlled, so that a large measurement error is introduced, and the detection precision is reduced. In short, the existing bolt looseness detection method has the problems of high cost, poor detection precision and the like, and a new bolt looseness detection method with low cost and high precision needs to be explored.
Disclosure of Invention
The present invention is directed to solving, at least to some extent, one of the technical problems in the related art. Therefore, one aspect of the invention aims to provide a bolt joint part looseness detection method based on the nonlinear excitation characteristics, which is wide in applicability, flexible and convenient to use and high in sensitivity.
The invention also aims to provide a bolt joint looseness detection system based on the nonlinear excitation characteristic.
The realization principle of the invention is that when the bolt joint part loosens, the pretightening force of the joint surface is reduced to cause the joint part to present a stronger nonlinear dynamics phenomenon, and along with the increasing of the looseness, the nonlinear characteristic is enhanced, the energy is dispersed from the fundamental frequency to the higher harmonic wave to cause the higher harmonic wave amplitude proportion to increase. Therefore, the nonlinear excitation characteristic of the amplitude ratio of the high-order harmonic in the vibration signal obtained by excitation can be used for detecting the loosening condition of the bolt joint.
In order to achieve the above object, an embodiment of an aspect of the present invention provides a method for detecting loosening of a bolt joint based on nonlinear excitation characteristics, including the following steps: carrying out simulation modal analysis on the three-dimensional model of the test piece to determine the local vibration exciter and sensor distribution position of the bolt joint; arranging the vibration exciter and the sensor according to the determined distribution positions of the vibration exciter and the sensor, and determining the vibration exciting parameters of the vibration exciter according to the simulation modal analysis result of the three-dimensional model; keeping the excitation parameters unchanged, and performing a pre-experiment on the test pieces of the same type to obtain a corresponding relation between bolt pretightening force and higher harmonic proportionality coefficients, and generating a relational database; the method comprises the steps of testing a piece to be tested, collecting a vibration signal, analyzing the higher harmonic proportionality coefficient of the piece to be tested according to the vibration signal, inquiring the relational database according to the higher harmonic proportionality coefficient of the piece to be tested, determining the bolt pretightening force of the piece to be tested, and judging whether the bolt combination part of the piece to be tested is loosened or not according to the bolt pretightening force of the piece to be tested.
According to the bolt joint part looseness detection method based on the nonlinear excitation characteristics, the test piece simulation model is established, the distribution positions and parameters of the vibration exciter and the sensor are determined, the relation database of bolt pretightening force and higher harmonic proportionality coefficient is generated according to the pre-experiment, the test result of the test piece to be tested is compared with the database data, and whether the bolt is loosened or not is judged. The method has the advantages of wide applicability, flexible and convenient use, high sensitivity and the like, belongs to a nondestructive testing means, and is suitable for actual production.
In some examples, the performing a simulated modal analysis on the three-dimensional model of the test piece to determine the vibration exciter and sensor placement location local to the bolt joint includes: establishing a three-dimensional model of the test piece; carrying out simulation modal analysis on the three-dimensional model through finite element software to determine the low-order modal frequency and the modal shape of the test piece; and selecting a bolt joint part to arrange the sensor and the vibration exciter according to the position of the modal shape and the position of the bolt joint part, and enabling the bolt joint part to transmit dynamic load in the modal shape.
In some examples, the arranging the vibration exciters and the sensors according to the determined arrangement positions of the vibration exciters and the sensors, and determining the excitation parameters of the vibration exciters according to the result of simulation modal analysis performed on the three-dimensional model includes: and (3) according to the modal analysis result of the finite element simulation software, performing trial excitation near the modal frequency of the selected mode, and searching the low-order modal frequency of the actual structure to determine the excitation parameters of the vibration exciter.
In some examples, the testing a to-be-tested piece, collecting a vibration signal, analyzing a higher harmonic proportionality coefficient of the to-be-tested piece according to the vibration signal, querying the relational database according to the higher harmonic proportionality coefficient of the to-be-tested piece, determining a bolt pretightening force of the to-be-tested piece, and determining whether a bolt joint portion of the to-be-tested piece is loose according to the bolt pretightening force of the to-be-tested piece includes: collecting a vibration time domain signal of a sensor; time domain of the vibrationCarrying out Fourier transform on the signal, and extracting fundamental frequency and peak values of higher harmonics of each order; calculating a proportionality coefficient eta of the square of the higher harmonic amplitude in the sum of the squares of all harmonic amplitudes according to an energy distribution principle; according to η and threshold η0If η<η0Judging that the bolt is not loosened; if eta>η0And judging that the bolt is loosened.
In some examples, the threshold η0Is determined by: performing a preliminary experiment on the bolt joint parts of the same type of test piece, and measuring a proportionality coefficient eta that the higher harmonic amplitude squares corresponding to the bolt joint parts of the test piece account for the sum of the squares of all harmonic amplitudes by quantitatively changing the bolt pretightening force of the bolt joint parts of the test piece to form the relation database; determining a corresponding pretightening force standard of bolt loosening according to a corresponding relation between the pretightening force and the proportional coefficient eta, finding out the corresponding proportional coefficient eta in a relational database through curve fitting and interpolation, and using the proportional coefficient eta as an empirical value eta for judging whether the bolt is loosened0。
In some examples, the excitation parameters include an excitation frequency and an excitation amplitude.
An embodiment of another aspect of the present invention provides a bolt joint looseness detection system based on a nonlinear excitation characteristic, including: the analysis module is used for carrying out simulation modal analysis on the three-dimensional model of the test piece so as to determine the distribution positions of a vibration exciter and a sensor at the local part of the bolt joint part, distributing the vibration exciter and the sensor according to the determined distribution positions of the vibration exciter and the sensor, and determining the vibration exciting parameters of the vibration exciter according to the simulation modal analysis result of the three-dimensional model; the experiment module is used for keeping the excitation parameters unchanged, carrying out a pre-experiment on the test pieces of the same type to obtain the corresponding relation between the bolt pretightening force and the higher harmonic proportionality coefficient and generating a relation database; and the looseness identification module is used for testing the piece to be tested, acquiring a vibration signal, analyzing the higher harmonic proportionality coefficient of the piece to be tested according to the vibration signal, inquiring the relational database according to the higher harmonic proportionality coefficient of the piece to be tested, determining the bolt pretightening force of the piece to be tested, and judging whether the bolt combination part of the piece to be tested is loosened or not according to the bolt pretightening force of the piece to be tested.
According to the bolt joint part looseness detection system based on the nonlinear excitation characteristics, a test piece simulation model is established through an analysis module, the distribution positions and parameters of a vibration exciter and a sensor are determined, a bolt pretightening force and higher harmonic proportional coefficient relation database is generated through a pre-experiment performed according to an experiment module, and a looseness identification module is used for comparing a test result of a test to be performed on a test piece with database data to judge whether the bolt is loosened. The system is simple to operate, convenient to use and suitable for actual production.
Additional aspects and advantages of the invention will be set forth in part in the description which follows and, in part, will be obvious from the description, or may be learned by practice of the invention.
Drawings
The foregoing and/or additional aspects and advantages of the present invention will become apparent and readily appreciated from the following description of the embodiments, taken in conjunction with the accompanying drawings of which:
FIG. 1 is a flow chart of a bolt joint loosening detection method based on nonlinear excitation characteristics according to an embodiment of the invention;
FIG. 2 is a schematic diagram of a conventional fixing bolt joint test piece;
FIG. 3 is an experimental environment schematic diagram of a bolt joint looseness detection method based on a nonlinear excitation characteristic according to an embodiment of the invention;
fig. 4 is a schematic structural diagram of a bolt joint looseness detection device based on a nonlinear excitation characteristic according to an embodiment of the invention.
FIG. 5 is a schematic diagram of a fitting curve of the higher harmonic ratio with variation in pretension according to an embodiment of the present invention;
fig. 6 is an experimental field schematic diagram of a bolt joint looseness detection method based on a nonlinear excitation characteristic according to an embodiment of the invention.
Detailed Description
Reference will now be made in detail to embodiments of the present invention, examples of which are illustrated in the accompanying drawings, wherein like or similar reference numerals refer to the same or similar elements or elements having the same or similar function throughout. The embodiments described below with reference to the drawings are illustrative and intended to be illustrative of the invention and are not to be construed as limiting the invention.
The realization principle of the invention is that when the bolt joint part loosens, the pretightening force of the joint surface is reduced to cause the joint part to present a stronger nonlinear dynamics phenomenon, and along with the increasing of the looseness, the nonlinear characteristic is enhanced, the energy is dispersed from the fundamental frequency to the higher harmonic wave to cause the higher harmonic wave amplitude proportion to increase. Therefore, the nonlinear excitation characteristic of the amplitude ratio of the high-order harmonic in the vibration signal obtained by excitation can be used for detecting the loosening condition of the bolt joint.
Fig. 1 is a flowchart of a method for detecting loosening of a bolt joint based on nonlinear excitation characteristics according to an embodiment of the present invention, and the method for detecting loosening of a bolt joint based on nonlinear excitation characteristics includes the following steps:
s1: and carrying out simulation modal analysis on the three-dimensional model of the test piece to determine the local vibration exciter and sensor distribution position of the bolt joint.
Specifically, the vibration exciter and sensor placement positions of the bolt joint part are determined. Modeling a test piece of the type to be tested, introducing finite element software (such as ANSYS) for modal analysis, knowing the modal vibration types of the first orders and corresponding natural frequencies, roughly determining the positions of a vibration exciter and a sensor distribution point at the local part of a bolt joint part according to the simulated mode, and selecting the position with larger vibration amplitude in the modal vibration types for the vibration exciter and the sensor distribution point so as to conveniently excite and acquire the modal vibration information of the orders.
Fig. 2 is a schematic structural diagram of a conventional fixing bolt joint test piece, which includes two bolt joints, and may represent a type of mechanical test piece including a linear fixing bolt joint. Taking this test piece as an example, a more specific example is: and establishing a three-dimensional CAD model (such as Solidworks software) for the test piece, and importing the three-dimensional CAD model into finite element software (such as ANSYS software) for modal simulation analysis. And during modal simulation analysis, setting the contact surface and the fixed surface according to an actual test environment to obtain the modal frequencies and modal vibration modes of a plurality of orders in front of the test piece. For example: the first-order modal frequency of the test piece is 295Hz, the modal shape is torsion, therefore, the vibration excitation point of the vibration exciter is considered to be arranged at the upper right corner of the test piece, and the acceleration sensor is arranged at the upper left corner of the test piece so as to obtain a better vibration excitation effect and a better signal-to-noise ratio.
S2: arranging the vibration exciter and the sensor according to the determined distribution positions of the vibration exciter and the sensor, and determining the vibration exciting parameters of the vibration exciter according to the simulation modal analysis result of the three-dimensional model.
In a specific example, vibration exciter parameters are determined, specifically including the excitation frequency and the excitation amplitude. And performing frequency sweep or random vibration test according to the simulation result of the S1, verifying the correctness of the simulation mode according to the frequency response function curve of the sensor, and obtaining the actual natural frequency of the mode. And selecting proper frequency near the natural frequency of the actual mode as test excitation frequency, wherein the excitation amplitude is better so that the acceleration signal noise collected by the sensor is better. Recording the excitation frequency and the excitation amplitude, and ensuring that the excitation frequency and the excitation force amplitude are unchanged in the subsequent experiment.
For example: after step S1 is completed, a standard test piece arrangement experimental environment (shown in fig. 3) in which the bolts are not loosened as shown in fig. 2 is selected, and a preliminary experiment is performed on the test piece to determine excitation parameters. The preliminary experiment comprises a sine frequency sweep experiment, the actual natural frequency of the test piece is determined to be 290Hz, and the mode shape is verified to be torsion according to the response of the acceleration sensor. And selecting a proper frequency such as 280Hz as a test excitation frequency near the actual natural frequency, and selecting a proper excitation force amplitude such as 3N according to the amplitude of the acceleration sensor so as to ensure a better signal-to-noise ratio.
S3: and keeping the excitation parameters unchanged, and performing a pre-experiment on the test pieces of the same type to obtain a corresponding relation between the bolt pretightening force and the higher harmonic proportionality coefficient to generate a relational database.
In a specific example, the excitation parameters determined in the step S2 are kept unchanged, and a pre-experiment is performed on the same type of test piece to obtain a database corresponding to the bolt pre-tightening force and the higher harmonic ratio. I.e. on the same type of test piece, holding the cloth in S2The point and the excitation parameters are unchanged, the bolt pretightening force of the test piece is changed by a torque wrench or other tools capable of quantitatively changing the bolt pretightening force, the vibration signal of the acceleration sensor is collected by data collection equipment, the vibration signal is subjected to Fourier transform by a data analyzer, and the fundamental frequency vibration amplitude and each order of high-order harmonic vibration amplitude are obtained. And obtaining a higher harmonic proportional coefficient eta (the proportion of the sum of squares of the higher harmonic amplitude to the sum of squares of the total vibration amplitude), eta and a corresponding relation database of different bolt pretightening forces. Selecting a pretightening force value which considers that the bolt is loosened as required, obtaining a variation curve of eta along with the pretightening force of the bolt through curve fitting, obtaining a eta value corresponding to the pretightening force value which considers that the bolt is loosened by utilizing interpolation, and taking the eta value as a judgment empirical value eta of the bolt looseness0。η0The judgment result is a judgment empirical value of bolt looseness, namely an eta value corresponding to a pretightening force threshold value of the bolt looseness.
For example, for the test piece shown in fig. 2, the bolt pretension of the test piece is gradually changed at equal intervals by using a tool such as a torque wrench for quantitatively changing the bolt pretension, while keeping the obtained excitation parameters unchanged, for example: at a pretension torque of 20Nm, no loosening occurred, and then pretensioning was performed with 15Nm, 10Nm, 5Nm torque and almost all loosening. The test piece is excited and the vibration signal of the acceleration sensor is acquired by the data acquisition equipment, and the signal in one direction of the sensor, such as the x direction, can be adopted for analysis. Fourier transform is carried out on the collected vibration signals on a signal analyzer or a computer, the excitation frequency and the response amplitude of the frequency doubling position are observed, the proportion value eta of the square sum of the higher harmonic amplitude of the frequency doubling position to the square sum of all harmonic amplitudes is calculated, and a database is formed corresponding to the bolt pre-tightening force of the test piece. The relationship between the bolt pretightening force and eta of the test piece is obtained through curve fitting and interpolation, generally speaking, as the bolt loosening pretightening force is reduced, the nonlinear vibration characteristic of the test piece is enhanced, so that the proportion of higher harmonics of the vibration response signal under the same vibration condition is increased, namely the corresponding eta value is increased. FIG. 5 is a graph of a higher harmonic ratio versus pretension fit curve according to an embodiment of the present invention, where the results are shown in FIG. 5. According to the boltDetermining the pretightening force threshold value of the bolt which is considered to be loose, and calculating the corresponding eta value as an inspection parameter eta0For example, if 15Nm is used as the loosening criterion, the η value calculated according to the fitting curve is 7.06%, i.e. η0And 7.06 percent of the total weight is taken.
S4: and testing the piece to be tested, acquiring a vibration signal, analyzing the higher harmonic proportionality coefficient of the piece to be tested according to the vibration signal, inquiring a relational database according to the higher harmonic proportionality coefficient of the piece to be tested, determining the bolt pretightening force of the piece to be tested, and judging whether the bolt joint part of the piece to be tested is loosened or not according to the bolt pretightening force of the piece to be tested.
In a specific example, the higher harmonic proportionality coefficient of the vibration signal data collected from the piece to be tested is analyzed to judge whether the bolt joint is loosened. Obtaining a higher harmonic proportionality coefficient eta according to the steps, and comparing eta and eta0If η is a magnitude relation of<η0The bolt is not loosened; if eta>η0And judging whether the bolt is loosened, and further detecting whether the bolt of the test piece to be detected is loosened.
For example: a to-be-tested part with unknown bolt looseness is placed in the experimental environment shown in the figure 3, and the error influence caused by experimental arrangement is reduced as much as possible. For the sake of verification, the two bolts of the test piece were pre-tightened with (20Nm, 5Nm) and (5Nm, 20Nm), respectively. And carrying out excitation test on the test piece according to the flow, and calculating to obtain a higher harmonic proportionality coefficient eta. The eta values of the test piece obtained by the test were 31.97% and 40.05%, respectively. The eta value and eta measured by the tested piece0The values are compared and are clearly all greater than the previously determined η0The value is 7.06%, and therefore, it is judged that the bolt of the test piece is loosened.
Fig. 6 is an experimental site schematic diagram of a bolt joint loosening detection method based on a nonlinear excitation characteristic according to an embodiment of the present invention.
According to the method for detecting the looseness of the bolt joint based on the nonlinear excitation characteristics, by establishing a test piece simulation model, the distribution positions and parameters of a vibration exciter and a sensor are determined, a database of relation between bolt pretightening force and higher harmonic proportional coefficient is generated according to a pre-experiment, the test result of the test piece to be detected is compared with database data, and whether the bolt is loosened or not is judged. The method has the advantages of wide applicability, flexible and convenient use, high sensitivity and the like, belongs to a nondestructive testing means, and is suitable for actual production.
In another aspect of the present invention, a system for detecting loosening of a bolt joint based on nonlinear excitation characteristics is further provided, as shown in fig. 4, which is a schematic structural diagram of a system for detecting loosening of a bolt joint based on nonlinear excitation characteristics according to an embodiment of the present invention, and the system structure 10 for detecting loosening of a bolt joint based on nonlinear excitation characteristics includes: an analysis module 101, an experiment module 102 and a loosening identification module 103.
Specifically, the analysis module 101 is configured to perform simulation modal analysis on a three-dimensional model of the test piece to determine the location of the vibration exciter and the sensor at the local part of the bolt joint, arrange the vibration exciter and the sensor according to the determined location of the vibration exciter and the sensor, and determine the excitation parameters of the vibration exciter according to the result of the simulation modal analysis performed on the three-dimensional model.
The experiment module 102 is configured to keep the excitation parameters unchanged, perform a pre-experiment on the same type of test pieces to obtain a corresponding relationship between the bolt pre-tightening force and the higher harmonic proportionality coefficient, and generate a relational database.
The looseness identification module 103 is used for testing the piece to be tested, collecting vibration signals, analyzing the higher harmonic proportionality coefficient of the piece to be tested according to the vibration signals, inquiring the relational database according to the higher harmonic proportionality coefficient of the piece to be tested, determining the bolt pretightening force of the piece to be tested, and judging whether the bolt combination part of the piece to be tested is loosened or not according to the bolt pretightening force of the piece to be tested.
It should be noted that the above explanation of the embodiment of the method for detecting the looseness of the bolt coupling portion based on the nonlinear excitation characteristic is also applicable to the system for detecting the looseness of the bolt coupling portion based on the nonlinear excitation characteristic, and the details are not repeated here.
According to the bolt joint looseness detection system based on the nonlinear excitation characteristics, a test piece simulation model is established through an analysis module and an experiment module, the distribution positions and parameters of a vibration exciter and a sensor are determined, a bolt pretightening force and higher harmonic proportional coefficient relation database is generated according to a pre-experiment, a test result of a test to be tested is compared with database data through a looseness identification module, and whether a bolt is loosened or not is judged. The system has the advantages of wide applicability, flexible and convenient use, high sensitivity and the like, belongs to a nondestructive testing means, and is suitable for actual production.
In the description of the present invention, it is to be understood that the terms "central," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "clockwise," "counterclockwise," "axial," "radial," "circumferential," and the like are used in the orientations and positional relationships indicated in the drawings for convenience in describing the invention and to simplify the description, and are not intended to indicate or imply that the referenced devices or elements must have a particular orientation, be constructed and operated in a particular orientation, and are therefore not to be considered limiting of the invention.
Furthermore, the terms "first", "second" and "first" are used for descriptive purposes only and are not to be construed as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one such feature. In the description of the present invention, "a plurality" means at least two, e.g., two, three, etc., unless specifically limited otherwise.
In the present invention, unless otherwise expressly stated or limited, the terms "mounted," "connected," "secured," and the like are to be construed broadly and can, for example, be fixedly connected, detachably connected, or integrally formed; can be mechanically or electrically connected; they may be directly connected or indirectly connected through intervening media, or they may be connected internally or in any other suitable relationship, unless expressly stated otherwise. The specific meanings of the above terms in the present invention can be understood by those skilled in the art according to specific situations.
In the present invention, unless otherwise expressly stated or limited, the first feature "on" or "under" the second feature may be directly contacting the first and second features or indirectly contacting the first and second features through an intermediate. Also, a first feature "on," "over," and "above" a second feature may be directly or diagonally above the second feature, or may simply indicate that the first feature is at a higher level than the second feature. A first feature being "under," "below," and "beneath" a second feature may be directly under or obliquely under the first feature, or may simply mean that the first feature is at a lesser elevation than the second feature.
In the description herein, references to the description of the term "one embodiment," "some embodiments," "an example," "a specific example," or "some examples," etc., mean that a particular feature, structure, material, or characteristic described in connection with the embodiment or example is included in at least one embodiment or example of the invention. In this specification, the schematic representations of the terms used above are not necessarily intended to refer to the same embodiment or example. Furthermore, the particular features, structures, materials, or characteristics described may be combined in any suitable manner in any one or more embodiments or examples. Furthermore, various embodiments or examples and features of different embodiments or examples described in this specification can be combined and combined by one skilled in the art without contradiction.
Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention, and that variations, modifications, substitutions and alterations can be made to the above embodiments by those of ordinary skill in the art within the scope of the present invention.
Claims (2)
1. A bolt joint part looseness detection method based on nonlinear excitation characteristics is characterized by comprising the following steps:
carrying out simulation modal analysis on the three-dimensional model of the test piece to determine the local vibration exciter and sensor distribution position of the bolt joint part, and the method comprises the following steps: establishing a three-dimensional model of the test piece; carrying out simulation modal analysis on the three-dimensional model through finite element software to determine the low-order modal frequency and the modal shape of the test piece; selecting a position with larger vibration amplitude in the modal shape to arrange the sensor and the vibration exciter according to the position of the modal shape and the bolt joint part, and enabling the bolt joint part to transmit dynamic load in the modal shape;
arranging the vibration exciter and the sensor according to the determined distribution positions of the vibration exciter and the sensor, and determining the vibration exciting parameters of the vibration exciter according to the simulation modal analysis result of the three-dimensional model, wherein the method comprises the following steps: according to the mode analysis result of finite element simulation software, trial excitation is carried out near the mode frequency of a selected mode, and the low-order mode frequency of the actual structure is searched to determine the excitation parameters of the vibration exciter, wherein the excitation parameters comprise the excitation frequency and the excitation amplitude;
keeping the excitation parameters unchanged, and performing a pre-experiment on the test pieces of the same type to obtain a corresponding relation between bolt pretightening force and higher harmonic proportionality coefficients, and generating a relational database;
the method comprises the following steps of testing a piece to be tested, collecting a vibration signal, analyzing the higher harmonic proportionality coefficient of the piece to be tested according to the vibration signal, inquiring the relational database according to the higher harmonic proportionality coefficient of the piece to be tested, determining the bolt pretightening force of the piece to be tested, and judging whether the bolt combination part of the piece to be tested is loosened or not according to the bolt pretightening force of the piece to be tested, and comprises the following steps: collecting a vibration time domain signal of a sensor; carrying out Fourier transform on the vibration time domain signal, and extracting fundamental frequency and peak values of higher harmonics of each order; calculating a proportionality coefficient eta of the square of the higher harmonic amplitude in the sum of the squares of all harmonic amplitudes according to an energy distribution principle; according to η and threshold η0If η<η0Judging that the bolt is not loosened; if eta>η0Judging that the bolt is loosened; wherein the threshold η0Is determined by:
performing a preliminary experiment on the bolt joint parts of the same type of test piece, and measuring a proportionality coefficient eta that the higher harmonic amplitude squares corresponding to the bolt joint parts of the test piece account for the sum of the squares of all harmonic amplitudes by quantitatively changing the bolt pretightening force of the bolt joint parts of the test piece to form the relation database; determining a corresponding pretightening force standard of bolt loosening according to a corresponding relation between the pretightening force and the proportional coefficient eta, finding out the corresponding proportional coefficient eta in a relational database through curve fitting and interpolation, and using the proportional coefficient eta as an empirical value eta for judging whether the bolt is loosened0。
2. A bolt joint part looseness detection system based on nonlinear excitation characteristics is characterized by comprising:
the analysis module is used for carrying out simulation modal analysis on the three-dimensional model of the test piece so as to determine the distribution positions of a vibration exciter and a sensor at the local part of the bolt joint part, distributing the vibration exciter and the sensor according to the determined distribution positions of the vibration exciter and the sensor, and determining the excitation parameters of the vibration exciter according to the simulation modal analysis result of the three-dimensional model, wherein the analysis module is further used for establishing the three-dimensional model of the test piece; carrying out simulation modal analysis on the three-dimensional model through finite element software to determine the low-order modal frequency and the modal shape of the test piece; selecting a position with larger vibration amplitude in the modal shape to arrange the sensor and the vibration exciter according to the position of the modal shape and the bolt joint part, and enabling the bolt joint part to transmit dynamic load in the modal shape;
the experiment module is used for keeping the excitation parameters unchanged, pre-experiment is carried out on the test pieces of the same type by utilizing the vibration exciter, the vibration sensor, the data acquisition equipment and the analyzer to obtain the corresponding relation between the bolt pretightening force and the higher harmonic proportional coefficient, and a relation database is generated;
the looseness identification module is used for testing a piece to be tested, acquiring a vibration signal, analyzing a higher harmonic proportionality coefficient of the piece to be tested according to the vibration signal, inquiring the relational database according to the higher harmonic proportionality coefficient of the piece to be tested, determining bolt pretightening force of the piece to be tested, and judging whether a bolt combining part of the piece to be tested is loosened or not according to the bolt pretightening force of the piece to be tested, wherein the looseness identification module is further used for acquiring a vibration time domain signal of a sensor; carrying out Fourier transform on the vibration time domain signal, and extracting fundamental frequency and peak values of higher harmonics of each order; calculating a proportionality coefficient eta of the square of the higher harmonic amplitude in the sum of the squares of all harmonic amplitudes according to an energy distribution principle; according to η and threshold η0If η<η0Judging that the bolt is not loosened; if eta>η0Judging that the bolt is loosened; wherein the threshold η0Is determined by:
performing a preliminary experiment on the bolt joint parts of the same type of test piece, and measuring a proportionality coefficient eta that the higher harmonic amplitude squares corresponding to the bolt joint parts of the test piece account for the sum of the squares of all harmonic amplitudes by quantitatively changing the bolt pretightening force of the bolt joint parts of the test piece to form the relation database; determining a corresponding pretightening force standard of bolt loosening according to a corresponding relation between the pretightening force and the proportional coefficient eta, finding out the corresponding proportional coefficient eta in a relational database through curve fitting and interpolation, and using the proportional coefficient eta as an empirical value eta for judging whether the bolt is loosened0。
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