CN116929236A - Connecting rod deformation detection method based on fiber grating sensor - Google Patents
Connecting rod deformation detection method based on fiber grating sensor Download PDFInfo
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- G—PHYSICS
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- G01B11/00—Measuring arrangements characterised by the use of optical techniques
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- G01B11/165—Measuring arrangements characterised by the use of optical techniques for measuring the deformation in a solid, e.g. optical strain gauge by means of a grating deformed by the object
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Abstract
The invention discloses a connecting rod deformation detection method based on a fiber grating sensor, which comprises the steps of establishing a connecting rod finite element model, carrying out finite element analysis, designing an arrangement scheme of the fiber grating sensor, calibrating two types of fiber grating sensors, preparing a connecting rod experiment to be detected, carrying out a connecting rod loading experiment to be detected, calculating deformation parameters, reconstructing each structural unit of the connecting rod, reconstructing the whole structure of the connecting rod, comparing deformation detection results and the like. The beneficial effects are that: the invention can utilize the fiber grating sensor to carry out integral deformation detection on the connecting rod related to the thin-wall annular structure and the long rod member structure at the same time; the method can output the detection result more intuitively and accurately, and provides a new feasible method for the accurate detection of the performance of the connecting rod and the deformation detection of other weight-related parts of the ship power equipment.
Description
Technical Field
The invention relates to a method for detecting deformation of an engine connecting rod, in particular to a method for detecting the deformation of the connecting rod based on a fiber grating sensor, and belongs to the technical field of structural member deformation detection.
Background
The connecting rod is used as an important component in engines of automobiles, ships and the like, the performance of the connecting rod can directly influence the overall performance, and the connecting rod can deform after being stressed, including bending, twisting and the like, and the deformation can cause the blockage or clamping stagnation of a crankshaft and can damage an engine cylinder body when serious.
The connecting rod is a transmission device which connects the piston and the crankshaft, transmits the acting force applied by the piston to the crankshaft, and converts the reciprocating motion of the piston into the rotary motion of the crankshaft.
The connecting rod consists of three parts, and the part connected with the piston pin is called a connecting rod small head; the part connected with the crankshaft is called a connecting rod big end, and the rod part connecting the small end and the big end is called a connecting rod body. The small connecting rod end and the large connecting rod end are of thin-wall annular structures, and the connecting rod body is a long rod piece. The deformation of the connecting rod is mainly concentrated on the deformation of the three parts, so that it is important to obtain an accurate and reliable deformation detection method which can be used for actual deformation.
Along with the development of high-end equipment and the increasing precision, the accurate detection of the deformation of the connecting rod is particularly urgent, and the deformation rule is mastered, so that the high-precision measurement of the deformation is realized. However, since the connecting rod is in high-speed operation in the process of installation, the prior art cannot directly measure the deformation of the connecting rod with high precision. At present, the detection of the deformation of the connecting rod mainly uses an experimental analysis method to infer the deformation of the connecting rod of the same batch or the connecting rod of the same structure.
The most common deformation detection methods in the experimental process include a strain gauge detection method, a visual detection method, a laser scanning detection method, a method for detecting by using a fiber bragg grating sensor and the like. Although the strain gauge detection method has small volume and light weight, and is easy to be conformal with an object to be detected, various interference factors exist in practical application to make measurement unstable, so that deviation of measurement precision is generated; although the visual detection method has high detection efficiency, does not need to be in contact with an object to be detected, and has lower cost, the internal deformation cannot be detected in practical application, and the detection cannot be performed when the vision is limited; the laser scanning detection method does not need to be in contact with a detected object, does not need complex post-processing and calculation, has higher precision, is easily interfered by environment in practical application, and is difficult to realize dynamic measurement.
The method for detecting by using the fiber bragg grating sensor is widely used for detecting the local deformation of various important parts, and because the connecting rod assembly simultaneously relates to a thin-wall annular structure and a long rod piece, the single fiber bragg grating sensor cannot complete the deformation detection of the whole connecting rod.
Disclosure of Invention
The invention aims to: the invention aims to solve the problem that the deformation of an engine connecting rod cannot be accurately detected in the prior art, and provides a connecting rod deformation detection method based on a fiber grating sensor.
The technical scheme is as follows: a connecting rod deformation detection method based on a fiber grating sensor comprises the following steps:
step one, establishing a finite element model of a connecting rod, and establishing the finite element model of the connecting rod according to the structural size of the connecting rod to be tested, the elastic modulus of the material and the poisson ratio;
step two, finite element analysis, namely analyzing the deformation of the connecting rod by applying a simulated load to the finite element model of the connecting rod to be tested, which is established in the step one, and respectively obtaining the simulated deformation types and the simulated deformation amounts of the small end of the connecting rod, the big end of the connecting rod and the rod body of the connecting rod;
step three, designing an arrangement scheme of the fiber bragg grating sensors, and respectively designing distribution of the fiber bragg grating sensors on the small connecting rod end, the large connecting rod end and the connecting rod body according to the simulated deformation type and the simulated deformation amount in the step two;
step four, calibrating two types of fiber bragg grating sensors, namely designing a spiral fiber bragg grating sensor for a small end of a connecting rod and a large end of the connecting rod and a calibrating experiment for an inclined fiber bragg grating sensor of a connecting rod body, determining the corresponding relation between the wavelength offset of the fiber bragg grating sensor and displacement and curvature according to the wavelength offset of the fiber bragg grating sensor, and completing the calibration of the two types of fiber bragg grating sensors;
step five, preparing a connecting rod experiment to be tested, arranging a fiber grating sensor according to the design scheme of the step three, connecting data acquisition equipment, connecting the fiber grating sensor to a fiber grating sensor demodulator, connecting the fiber grating sensor demodulator with a host computer through a data connector, and demodulating and transmitting the central wavelength of the fiber grating sensor to an upper computer of the host computer through the fiber grating sensor demodulator;
step six, a connecting rod loading experiment to be tested is carried out, wherein a connecting rod small end, a connecting rod large end and a connecting rod body are respectively subjected to a simulated load experiment, the central wavelength of each fiber grating sensor is changed when the connecting rod is deformed, and the offset of the central wavelength is used for obtaining corresponding change according to the calibration result of the step four;
step seven, calculating deformation parameters, wherein the host calculates deformation curvature k of each measuring point and arc length l after deformation according to the change amount obtained in the step six;
step eight, reconstructing each structural unit of the connecting rod, and respectively reconstructing the structures of the small end of the connecting rod, the big end of the connecting rod and the rod body of the connecting rod according to the deformation information of each structural unit by using a deformation reconstruction method;
step nine, reconstructing the whole structure of the connecting rod, and combining all the structural units in the step eight into a whole according to a reconstruction algorithm to complete the reconstruction of the whole structure of the connecting rod;
and step ten, comparing the deformation detection result, and comparing the simulation analysis result of the finite element model with the experimental result to obtain the real deformation type and deformation amount of the connecting rod to be detected.
The invention obtains the deformation types of the small end and the large end of the connecting rod of the batch or the type to be planar drum shape, inclined drum shape and bending shape through finite element analysis on the connecting rod to be detected, and the deformation of the rod body of the connecting rod is bending deformation; respectively designing an arrangement scheme of the fiber bragg grating sensor according to the simulated deformation type and the simulated deformation quantity of the finite element analysis; the corresponding relation between the wavelength offset and the displacement and curvature of the fiber bragg grating sensor is determined by respectively adopting spiral type and inclined type fiber bragg grating sensors for the two deformation modes and respectively carrying out calibration experiments; and after the calibrated corresponding relation is obtained, carrying out experimental detection on the connecting rod to be detected, carrying out reconstruction of each structural unit of the connecting rod and reconstruction of the whole structure of the connecting rod through data acquired in the experiment, and comparing the result of finite element model simulation analysis with the experimental result to obtain the real deformation type and deformation amount of the connecting rod to be detected. The invention can output the detection result more intuitively and accurately, and provides a new feasible method for the accurate detection of the performance of the connecting rod and the deformation detection of other weight-related parts of the ship power equipment.
In order to realize accurate detection of the thin-wall annular structure, the arrangement forms of the small end of the connecting rod and the fiber grating sensor on the large end of the connecting rod in the third step are the same and are uniformly distributed on the inner walls of the small end of the connecting rod and the large end of the connecting rod in a spiral mode, the spiral angle of the fiber grating sensor on the large end of the connecting rod is alpha, and the spiral angle of the fiber grating sensor on the small end of the connecting rod is beta.
The optical fiber grating sensor is convenient to arrange on the premise of ensuring the detection effect, the number of the optical fiber grating sensors on the small end of the connecting rod and the large end of the connecting rod is at least two, and the number of grating points on each optical fiber grating sensor is at least two. According to the invention, under the condition of arranging the spiral fiber grating sensor, the integral deformation condition of the small end and the large end of the connecting rod can be calculated according to the data measured by the limited grating points by the algorithm reconstruction method, so that the arrangement of the fiber grating sensor can be facilitated, the number of grating points in the fiber grating sensor can be reduced, and the cost can be saved.
In order to further improve the rationality and accuracy of the arrangement of the fiber grating sensors on the thin-wall annular structure, the spiral angle of the fiber grating sensor on the big end of the connecting rod is respectively determined to be alpha, and the spiral angle of the fiber grating sensor on the small end of the connecting rod is determined to be beta;
the method for determining the helix angle of the fiber grating sensor is the same and comprises the following specific steps:
step 4.1, obtaining the relation between the axial strain and the helix angle according to the principle that the fiber grating sensor is stretched, wherein the relation is as follows:
wherein: epsilon is the strain of the spiral fiber grating sensor, alpha is the helix angle, epsilon b Poisson's ratio for μmaterial for axial strain;
step 4.2, determining the strain range of the fiber bragg grating sensor through a finite element simulation stretching experiment, setting a helix angle interval, and determining corresponding axial strain through a relational expression;
step 4.3 the following relationship exists due to axial strain and lateral strain:
ε a ＝-με b
wherein: epsilon a For transverse strain, ε b Poisson's ratio for μmaterial for axial strain;
the poisson ratio of the material in step 4.4 is known, the corresponding axial strain can be determined according to the helix angle interval set by the tensile test, and the relation between the axial strain and the transverse strain shows that when the axial strain is maximum, the absolute value of the transverse strain is maximum, so that the angle with the maximum axial strain is selected as the helix angle.
In order to accurately detect the deformation of the rod body of the connecting rod, the fiber grating sensors on the rod body of the connecting rod in the third step are respectively arranged on two adjacent side surfaces, wherein the fiber grating sensors are identical in inclination angle and distributed on the surface of the rod body of the connecting rod in a central symmetry mode, and the inclination angle is gamma.
Preferably, in order to improve the accuracy of detecting the deformation of the rod body of the connecting rod, the inclination directions of the fiber grating sensors on two adjacent side surfaces of the rod body of the connecting rod are opposite, and at least two grating points are arranged on each fiber grating sensor. The two adjacent side surfaces on the connecting rod body are arranged in opposite inclined directions of the fiber bragg grating sensors, so that the fiber bragg grating sensors can be conveniently arranged on the premise of ensuring the detection precision, and the cost is reduced.
In order to further improve the accuracy of detecting the deformation of the rod body of the connecting rod, the inclination angle of the fiber grating sensor on the rod body of the connecting rod is gamma, and the specific steps of determining the inclination angle are as follows:
step 7.1, according to the principle that the fiber bragg grating sensor is stretched, the relation between longitudinal strain and inclination angle is as follows:
wherein: epsilon is the strain of the fiber bragg grating sensor, gamma is the inclination angle, epsilon d Poisson's ratio for μmaterial for longitudinal strain;
step 7.2, determining the strain range of the fiber bragg grating sensor through a finite element simulation stretching experiment, setting an inclination angle interval, and determining corresponding longitudinal strain through a relational expression;
step 7.3 the following relationship exists due to longitudinal strain and transverse strain:
ε c ＝-με d
wherein: epsilon c For transverse strain, ε d Poisson's ratio for μmaterial for longitudinal strain;
in step 7.4, the poisson ratio of the material is known, the corresponding longitudinal strain can be determined according to the inclination angle interval set by the tensile test, and the relation between the longitudinal strain and the transverse strain shows that when the longitudinal strain is maximum, the absolute value of the transverse strain is maximum, so that the angle with the maximum longitudinal strain is selected as the helix angle.
Preferably, in order to realize the reconstruction shape of the deformation of the small end and the large end of the connecting rod, in the seventh step, the deformation curvature k of the small end and the large end of the connecting rod and the arc length l after deformation,
the deformation of the corresponding measuring point is calculated as follows:
according to the relation between the wavelength and the strain of the fiber bragg grating sensor and the sensing principle that the spiral fiber bragg grating sensor is stretched, the strain is calculated as follows:
wherein: lambda (lambda) B Is Bragg wavelength, unit is nm, deltalambda B The wavelength offset is given in nm, epsilon is the strain of the spiral FBG, and p e Is the elasto-optical coefficient, the unit is nm/mu epsilon, alpha T The grating has a thermal expansion coefficient, zeta is the photothermal coefficient of the grating, alpha is the helix angle and epsilon b Poisson's ratio for μmaterial for axial strain;
the change of the axial length of the deformation is calculated according to the relation between the strain and the length, and is as follows:
Δb＝ε b *b
wherein: Δb is the axial length change, ε b Is axial strain, b is pitch;
calculating the length l of a generatrix where the j-th grating point of the i-th fiber bragg grating sensor is located according to the change of the axial length ij (i=1, 2,3,6,7,8; j=1, 2, … …) is:
l ij ＝l-Δb ij
r of the inner wall of the connecting rod is known, the deflection angle phi of the bending direction and the base coordinate j And curvature k j The method comprises the following steps:
and fusing the data information of each fiber bragg grating sensor to obtain the reconstruction shape of the deformation of the big end and the small end of the connecting rod.
In order to accurately detect the deformation of the rod body of the connecting rod, the calibration experimental method for the inclined fiber grating sensor of the rod body of the connecting rod in the fourth step adopts a standard curvature die, and the corresponding relation between the wavelength offset of the fiber grating sensor and the curvature is determined according to the change of the wavelength offset of the fiber grating sensor under different curvatures, so that the calibration of the fiber grating sensor is completed.
In order to realize the reconstruction shape of the deformation of the rod body of the connecting rod, the method for reconstructing the structure of the rod body of the connecting rod by using the deformation information in the step eight comprises the following steps:
obtaining the curvature K of the corresponding measuring point of the rod body part of the connecting rod according to the calibration method in the fourth step;
the radius R corresponding to the jth grating point of the fiber bragg grating sensor can be obtained according to the calibration relation ij (i=4, 5; j=1, 2, … …) is:
from radius R ij The length d of the rod body of the connecting rod can obtain the arc length l of the rod body after deformation ij The method comprises the following steps:
and (5) fusing the data information of each fiber bragg grating sensor to obtain the reconstruction shape of the deformation of the rod body of the connecting rod.
The beneficial effects are that: the invention can utilize the fiber grating sensor to carry out integral deformation detection on the connecting rod related to the thin-wall annular structure and the long rod member structure at the same time; the method can output the detection result more intuitively and accurately, and provides a new feasible method for the accurate detection of the performance of the connecting rod and the deformation detection of other weight-related parts of the ship power equipment.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings that are required to be used in the embodiments or the description of the prior art will be briefly described below, and it is obvious that the drawings in the following description are only embodiments of the present invention, and that other drawings can be obtained according to the provided drawings without inventive effort for a person skilled in the art.
FIG. 1 is a flow chart of the detection method of the present invention;
FIG. 2 is a schematic diagram of a fiber grating sensor according to the present invention;
FIG. 3 is a schematic view of a standard curvature mold of the present invention;
FIG. 4 is a schematic diagram of the arrangement of the fiber grating sensor on the connecting rod according to the present invention;
FIG. 5 is a schematic diagram of the detection system of the present invention;
FIG. 6 is a schematic diagram of a finite element model and path selection of a connecting rod according to the present invention;
FIG. 7 is a schematic diagram of a deformation of the thin-walled annular structures of the small and large connecting rod ends of the present invention.
Detailed Description
The following description of the embodiments of the present invention will be made clearly and completely with reference to the accompanying drawings, in which it is apparent that the embodiments described are only some embodiments of the present invention, but not all embodiments. All other embodiments, which can be made by those skilled in the art based on the embodiments of the invention without making any inventive effort, are intended to be within the scope of the invention.
In the description of the present invention, it should be understood that the terms "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc. indicate orientations or positional relationships based on the drawings, are merely for convenience in describing the present invention and simplifying the description, and do not indicate or imply that the devices or elements referred to must have a specific orientation, be configured and operated in a specific orientation, and thus should not be construed as limiting the present invention.
In the present invention, unless expressly stated or limited otherwise, a first feature "above" or "below" a second feature may include both the first and second features being in direct contact, as well as the first and second features not being in direct contact but being in contact with each other through additional features therebetween. Moreover, a first feature being "above," "over" and "on" a second feature includes the first feature being directly above and obliquely above the second feature, or simply indicating that the first feature is higher in level than the second feature. The first feature being "under", "below" and "beneath" the second feature includes the first feature being directly under and obliquely below the second feature, or simply means that the first feature is less level than the second feature.
As shown in fig. 1, a method for detecting the deformation of a connecting rod based on a fiber grating sensor comprises the following steps:
step one, establishing a finite element model of a connecting rod, and establishing the finite element model of the connecting rod according to the structural size of the connecting rod to be tested, the elastic modulus of the material and the poisson ratio;
step two, finite element analysis, namely analyzing the deformation of the connecting rod by applying a simulated load to the finite element model of the connecting rod to be tested, which is established in the step one, and respectively obtaining the simulated deformation types and the simulated deformation amounts of the small end of the connecting rod, the big end of the connecting rod and the rod body of the connecting rod;
step three, designing an arrangement scheme of the fiber bragg grating sensors, and respectively designing distribution of the fiber bragg grating sensors on the small connecting rod end, the large connecting rod end and the connecting rod body according to the simulated deformation type and the simulated deformation amount in the step two;
step four, calibrating two types of fiber bragg grating sensors, namely designing a spiral fiber bragg grating sensor for a small end of a connecting rod and a large end of the connecting rod and a calibrating experiment for an inclined fiber bragg grating sensor of a connecting rod body, determining the corresponding relation between the wavelength offset of the fiber bragg grating sensor and displacement and curvature according to the wavelength offset of the fiber bragg grating sensor, and completing the calibration of the two types of fiber bragg grating sensors;
step five, preparing a connecting rod experiment to be tested, arranging a fiber grating sensor according to the design scheme of the step three, connecting data acquisition equipment, connecting the fiber grating sensor to a fiber grating sensor demodulator, connecting the fiber grating sensor demodulator with a host computer through a data connector, and demodulating and transmitting the central wavelength of the fiber grating sensor to an upper computer of the host computer through the fiber grating sensor demodulator;
step six, a connecting rod loading experiment to be tested is carried out, wherein a connecting rod small end, a connecting rod large end and a connecting rod body are respectively subjected to a simulated load experiment, the central wavelength of each fiber grating sensor is changed when the connecting rod is deformed, and the offset of the central wavelength is used for obtaining corresponding change according to the calibration result of the step four;
step seven, calculating deformation parameters, wherein the host calculates deformation curvature k of each measuring point and arc length l after deformation according to the change amount obtained in the step six;
step eight, reconstructing each structural unit of the connecting rod, and respectively reconstructing the structures of the small end of the connecting rod, the big end of the connecting rod and the rod body of the connecting rod according to the deformation information of each structural unit by using a deformation reconstruction method;
step nine, reconstructing the whole structure of the connecting rod, and combining all the structural units in the step eight into a whole according to a reconstruction algorithm to complete the reconstruction of the whole structure of the connecting rod;
and step ten, comparing the deformation detection result, and comparing the simulation analysis result of the finite element model with the experimental result to obtain the real deformation type and deformation amount of the connecting rod to be detected.
The invention obtains the deformation types of the small end and the large end of the connecting rod of the batch or the type to be planar drum shape, inclined drum shape and bending shape through finite element analysis on the connecting rod to be detected, and the deformation of the rod body of the connecting rod is bending deformation; respectively designing an arrangement scheme of the fiber bragg grating sensor according to the simulated deformation type and the simulated deformation quantity of the finite element analysis; the corresponding relation between the wavelength offset and the displacement and curvature of the fiber bragg grating sensor is determined by respectively adopting spiral type and inclined type fiber bragg grating sensors for the two deformation modes and respectively carrying out calibration experiments; and after the calibrated corresponding relation is obtained, carrying out experimental detection on the connecting rod to be detected, carrying out reconstruction of each structural unit of the connecting rod and reconstruction of the whole structure of the connecting rod through data acquired in the experiment, and comparing the result of finite element model simulation analysis with the experimental result to obtain the real deformation type and deformation amount of the connecting rod to be detected. The invention can output the detection result more intuitively and accurately, and provides a new feasible method for the accurate detection of the performance of the connecting rod and the deformation detection of other weight-related parts of the ship power equipment.
The connecting rod deformation detection system based on the fiber grating sensor comprises a connecting rod 1 to be detected, a plurality of fiber grating sensors 2 which are arranged in a spiral mode, a demodulator 3, a host 4 and a display 5, wherein the structure schematic diagram is shown in fig. 4 and 5, the fiber grating sensors 2 are connected in parallel, a group of 3 fiber grating sensors 2 with the spiral angle alpha are distributed on the inner wall of the big end of the connecting rod, and a group of 3 fiber grating sensors 2 with the spiral angle beta are distributed on the inner wall of the small end of the connecting rod; the same group of fiber grating sensors 2 are distributed at intervals of 120 degrees, and wavelength data of the fiber grating sensors 2 arranged on the rod body of the connecting rod 1 to be detected are demodulated by the demodulator 3 and then output. The demodulator 3 is connected with the host computer 4 through a communication interface, and the central wavelength of the fiber bragg grating sensor is demodulated and transmitted to an upper computer of the host computer 4 by the demodulator 3; data information of all fiber bragg grating sensors are fused and displayed on a display 5, and the structures of a small connecting rod end, a large connecting rod end and a connecting rod body are respectively reconstructed; and then each structural unit is combined into a whole to complete the reconstruction of the whole structure of the connecting rod; and comparing the simulation analysis result of the finite element model with the experimental result to obtain the real deformation type and deformation amount of the connecting rod to be detected, and intuitively and accurately obtaining the detection result.
As shown in fig. 6 and 7, a finite element model of the connecting rod is built according to the structural size of the connecting rod to be tested, the elastic modulus of the material and the poisson ratio; finite element analysis of its deformation was performed using Ansys. The model material is structural steel, the Poisson ratio is 0.3, and the density is 7850kg/m3. The mesh division is performed in the form of triangular units, the size of the division units is set to be 1mm, and 836385 units and 1176939 nodes are generated in total. By applying loads of different magnitudes and directions to the connecting rod large head portion, the deformation of the large head portion can be generalized to three different situations (as shown in fig. 7): planar drums, beveled drums, and curved shapes.
As shown in fig. 1 and 4, the arrangement forms of the fiber grating sensors on the small end of the connecting rod and the large end of the connecting rod are the same and are spirally distributed on the inner walls of the small end of the connecting rod and the large end of the connecting rod, the helix angle of the fiber grating sensor on the large end of the connecting rod is alpha, and the helix angle of the fiber grating sensor on the small end of the connecting rod is beta.
The number of the fiber bragg grating sensors on the small end of the connecting rod and the large end of the connecting rod is three, and as shown in fig. 2, the number of grating points on each fiber bragg grating sensor is multiple.
Respectively determining the helix angle alpha of the fiber grating sensor on the big end of the connecting rod and the helix angle beta of the fiber grating sensor on the small end of the connecting rod;
the method for determining the helix angle of the fiber grating sensor is the same and comprises the following specific steps:
step 4.1, obtaining the relation between the axial strain and the helix angle according to the principle that the fiber grating sensor is stretched, wherein the relation is as follows:
wherein: epsilon is the strain of the spiral fiber grating sensor, alpha is the helix angle, epsilon b Poisson's ratio for μmaterial for axial strain;
step 4.2, determining the strain range of the fiber bragg grating sensor through a finite element simulation stretching experiment, setting a helix angle interval, and determining corresponding axial strain through a relational expression;
step 4.3 the following relationship exists due to axial strain and lateral strain:
ε a ＝-με b
wherein: epsilon a For transverse strain, ε b Poisson's ratio for μmaterial for axial strain;
the poisson ratio of the material in step 4.4 is known, the corresponding axial strain can be determined according to the helix angle interval set by the tensile test, and the relation between the axial strain and the transverse strain shows that when the axial strain is maximum, the absolute value of the transverse strain is maximum, so that the angle with the maximum axial strain is selected as the helix angle.
The method comprises the steps that loads in the vertical and horizontal directions are applied to the small end part and the large end part of the connecting rod, when the small end part and the large end part of the connecting rod deform, the central wavelength of each fiber bragg grating sensor also changes, and corresponding offset amounts are generated by the fiber bragg grating sensors 2-1, 2-2, 2-3, 2-6, 2-7 and 2-8;
the host 4 calculates the deformation curvature k of each measuring point according to the offset of the central wavelengths of the spiral F fiber grating sensors 2-1, 2-2, 2-3, 2-6, 2-7 and 2-8;
the deformation of the corresponding measuring point is calculated as follows:
according to the relation between the wavelength and the strain of the fiber bragg grating sensor and the sensing principle that the spiral fiber bragg grating sensor is stretched, the strain is calculated as follows:
wherein: lambda (lambda) B Is Bragg wavelength, unit is nm, deltalambda B The wavelength offset is given in nm, epsilon is the strain of the spiral FBG, and p e Is the elasto-optical coefficient, the unit is nm/mu epsilon, alpha T The grating has a thermal expansion coefficient, zeta is the photothermal coefficient of the grating, alpha is the helix angle and epsilon b Poisson's ratio for μmaterial for axial strain;
the change of the axial length of the deformation is calculated according to the relation between the strain and the length, and is as follows:
Δb＝ε b *b
wherein: Δb is the axial length change, ε b Is axial strain, b is pitch;
calculating the length l of a generatrix where the j-th grating point of the i-th fiber bragg grating sensor is located according to the change of the axial length ij (i=1, 2,3,6,7,8; j=1, 2, … …) is:
l ij ＝l-Δb ij
r of the inner wall of the connecting rod is known, the deflection angle phi of the bending direction and the base coordinate j And curvature k j The method comprises the following steps:
and fusing the data information of each fiber bragg grating sensor to obtain the reconstruction shape of the deformation of the big end and the small end of the connecting rod.
As shown in fig. 4, the fiber grating sensors on the connecting rod body in the third step are respectively arranged on two adjacent side surfaces, wherein the fiber grating sensors are respectively provided with the fiber grating sensors which have the same inclination angle and are distributed on the surface of the connecting rod body in a central symmetry manner, and the inclination angle is gamma.
The inclination directions of the fiber grating sensors on two adjacent side surfaces of the connecting rod body are opposite, and a plurality of grating points are arranged on each fiber grating sensor.
The inclination angle of the fiber grating sensor on the rod body of the connecting rod is gamma, and the specific steps for determining the inclination angle are as follows:
step 7.1, according to the principle that the fiber bragg grating sensor is stretched, the relation between longitudinal strain and inclination angle is as follows:
wherein: epsilon is the strain of the fiber bragg grating sensor, gamma is the inclination angle, epsilon d Poisson's ratio for μmaterial for longitudinal strain;
step 7.2, determining the strain range of the fiber bragg grating sensor through a finite element simulation stretching experiment, setting an inclination angle interval, and determining corresponding longitudinal strain through a relational expression;
step 7.3 the following relationship exists due to longitudinal strain and transverse strain:
ε c ＝-με d
wherein: epsilon c For transverse strain, ε d Poisson's ratio for μmaterial for longitudinal strain;
in step 7.4, the poisson ratio of the material is known, the corresponding longitudinal strain can be determined according to the inclination angle interval set by the tensile test, and the relation between the longitudinal strain and the transverse strain shows that when the longitudinal strain is maximum, the absolute value of the transverse strain is maximum, so that the angle with the maximum longitudinal strain is selected as the helix angle.
As shown in fig. 3, the calibration experimental method for the inclined fiber grating sensor of the connecting rod body in the fourth step adopts a standard curvature mold, and determines the corresponding relationship between the wavelength offset of the fiber grating sensor and the curvature according to the change of the wavelength offset of the fiber grating sensor under different curvatures, thereby completing the calibration of the fiber grating sensor.
The method for reconstructing the rod body of the connecting rod in the step eight and respectively reconstructing the structure of the rod body of the connecting rod by using deformation information comprises the following steps:
obtaining the curvature K of the corresponding measuring point of the rod body part of the connecting rod according to the calibration method in the fourth step;
the vertical and horizontal loads are applied to the rod body of the connecting rod, the central wavelength of the fiber bragg grating sensor is changed along with the deformation of the rod body, and the fiber bragg grating sensors 2-4 and 2-5 generate corresponding offset;
the host 4 calculates the arc length l of each measuring point after deformation according to the offset of the central wavelength of the fiber grating sensors 2-4 and 2-5;
the radius R corresponding to the jth grating point of the fiber bragg grating sensor can be obtained according to the calibration relation ij (i=4, 5; j=1, 2, … …) is:
from radius R ij The length d of the rod body of the connecting rod can obtain the arc length l of the rod body after deformation ij The method comprises the following steps:
and (5) fusing the data information of each fiber bragg grating sensor to obtain the reconstruction shape of the deformation of the rod body of the connecting rod.
In the present specification, each embodiment is described in a progressive manner, and each embodiment is mainly described in a different point from other embodiments, and identical and similar parts between the embodiments are all enough to refer to each other. For the device disclosed in the embodiment, since it corresponds to the method disclosed in the embodiment, the description is relatively simple, and the relevant points refer to the description of the method section.
The previous description of the disclosed embodiments is provided to enable any person skilled in the art to make or use the present invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other embodiments without departing from the spirit or scope of the invention. Thus, the present invention is not intended to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.
Claims (10)
1. The connecting rod deformation detection method based on the fiber grating sensor is characterized by comprising the following steps of:
step one, establishing a finite element model of a connecting rod, and establishing the finite element model of the connecting rod according to the structural size of the connecting rod to be tested, the elastic modulus of the material and the poisson ratio;
step two, finite element analysis, namely analyzing the deformation of the connecting rod by applying a simulated load to the finite element model of the connecting rod to be tested, which is established in the step one, and respectively obtaining the simulated deformation types and the simulated deformation amounts of the small end of the connecting rod, the big end of the connecting rod and the rod body of the connecting rod;
step three, designing an arrangement scheme of the fiber bragg grating sensors, and respectively designing distribution of the fiber bragg grating sensors on the small connecting rod end, the large connecting rod end and the connecting rod body according to the simulated deformation type and the simulated deformation amount in the step two;
step four, calibrating two types of fiber bragg grating sensors, namely designing a spiral fiber bragg grating sensor for a small end of a connecting rod and a large end of the connecting rod and a calibrating experiment for an inclined fiber bragg grating sensor of a connecting rod body, determining the corresponding relation between the wavelength offset of the fiber bragg grating sensor and displacement and curvature according to the wavelength offset of the fiber bragg grating sensor, and completing the calibration of the two types of fiber bragg grating sensors;
step five, preparing a connecting rod experiment to be tested, arranging a fiber grating sensor according to the design scheme of the step three, connecting data acquisition equipment, connecting the fiber grating sensor to a fiber grating sensor demodulator, connecting the fiber grating sensor demodulator with a host computer through a data connector, and demodulating and transmitting the central wavelength of the fiber grating sensor to an upper computer of the host computer through the fiber grating sensor demodulator;
step six, a connecting rod loading experiment to be tested is carried out, wherein a connecting rod small end, a connecting rod large end and a connecting rod body are respectively subjected to a simulated load experiment, the central wavelength of each fiber grating sensor is changed when the connecting rod is deformed, and the offset of the central wavelength is used for obtaining corresponding change according to the calibration result of the step four;
step seven, calculating deformation parameters, wherein the host calculates deformation curvature k of each measuring point and arc length l after deformation according to the change amount obtained in the step six;
step eight, reconstructing each structural unit of the connecting rod, and respectively reconstructing the structures of the small end of the connecting rod, the big end of the connecting rod and the rod body of the connecting rod according to the deformation information of each structural unit by using a deformation reconstruction method;
step nine, reconstructing the whole structure of the connecting rod, and combining all the structural units in the step eight into a whole according to a reconstruction algorithm to complete the reconstruction of the whole structure of the connecting rod;
and step ten, comparing the deformation detection result, and comparing the simulation analysis result of the finite element model with the experimental result to obtain the real deformation type and deformation amount of the connecting rod to be detected.
2. The method for detecting the deformation of the connecting rod based on the fiber bragg grating sensor according to claim 1, wherein the method comprises the following steps: and in the third step, the arrangement forms of the fiber bragg grating sensors on the small end of the connecting rod and the large end of the connecting rod are the same and are spirally distributed on the inner walls of the small end of the connecting rod and the large end of the connecting rod, the helix angle of the fiber bragg grating sensor on the large end of the connecting rod is alpha, and the helix angle of the fiber bragg grating sensor on the small end of the connecting rod is beta.
3. The method for detecting the deformation of the connecting rod based on the fiber bragg grating sensor according to claim 2, wherein the method comprises the following steps: the number of the fiber bragg grating sensors on the small end of the connecting rod and the large end of the connecting rod is at least two, and the number of grating points on each fiber bragg grating sensor is at least two.
4. The method for detecting the deformation of the connecting rod based on the fiber bragg grating sensor according to claim 2, wherein the method comprises the following steps: respectively determining the helix angle alpha of the fiber grating sensor on the big end of the connecting rod and the helix angle beta of the fiber grating sensor on the small end of the connecting rod;
the method for determining the helix angle of the fiber grating sensor is the same and comprises the following specific steps:
step 4.1, obtaining the relation between the axial strain and the helix angle according to the principle that the fiber grating sensor is stretched, wherein the relation is as follows:
wherein: epsilon is the strain of the spiral fiber grating sensor, alpha is the helix angle, epsilon b Poisson's ratio for μmaterial for axial strain;
step 4.2, determining the strain range of the fiber bragg grating sensor through a finite element simulation stretching experiment, setting a helix angle interval, and determining corresponding axial strain through a relational expression;
step 4.3 the following relationship exists due to axial strain and lateral strain:
ε a ＝-με b
wherein: epsilon a For transverse strain, ε b Poisson's ratio for μmaterial for axial strain;
the poisson ratio of the material in step 4.4 is known, the corresponding axial strain can be determined according to the helix angle interval set by the tensile test, and the relation between the axial strain and the transverse strain shows that when the axial strain is maximum, the absolute value of the transverse strain is maximum, so that the angle with the maximum axial strain is selected as the helix angle.
5. The method for detecting the deformation of the connecting rod based on the fiber bragg grating sensor according to claim 1, wherein the method comprises the following steps: and in the third step, the arrangement form of the fiber bragg grating sensors on the connecting rod body is that two adjacent side surfaces are respectively provided with one fiber bragg grating sensor which has the same inclination angle and is distributed on the surface of the connecting rod body in a central symmetry manner, and the inclination angle is gamma.
6. The method for detecting the deformation of the connecting rod based on the fiber bragg grating sensor according to claim 5, wherein the method comprises the following steps: the inclination directions of the fiber grating sensors on two adjacent side surfaces of the connecting rod body are opposite, and at least two grating points are arranged on each fiber grating sensor.
7. The method for detecting the deformation of the connecting rod based on the fiber bragg grating sensor according to claim 6, wherein the inclination angle of the fiber bragg grating sensor on the rod body of the connecting rod is gamma, and the specific steps of determining the inclination angle are as follows:
step 7.1, according to the principle that the fiber bragg grating sensor is stretched, the relation between longitudinal strain and inclination angle is as follows:
wherein: epsilon is the strain of the fiber bragg grating sensor, gamma is the inclination angle, epsilon d Poisson's ratio for μmaterial for longitudinal strain;
step 7.2, determining the strain range of the fiber bragg grating sensor through a finite element simulation stretching experiment, setting an inclination angle interval, and determining corresponding longitudinal strain through a relational expression;
step 7.3 the following relationship exists due to longitudinal strain and transverse strain:
ε c ＝-με d
wherein: epsilon c For transverse strain, ε d Poisson's ratio for μmaterial for longitudinal strain;
in step 7.4, the poisson ratio of the material is known, the corresponding longitudinal strain can be determined according to the inclination angle interval set by the tensile test, and the relation between the longitudinal strain and the transverse strain shows that when the longitudinal strain is maximum, the absolute value of the transverse strain is maximum, so that the angle with the maximum longitudinal strain is selected as the helix angle.
8. The method for detecting deformation of a connecting rod based on a fiber grating sensor according to claim 4, wherein in the seventh step, the deformation curvature k of the small end and the large end of the connecting rod and the arc length l after deformation are determined,
the deformation of the corresponding measuring point is calculated as follows:
according to the relation between the wavelength and the strain of the fiber bragg grating sensor and the sensing principle that the spiral fiber bragg grating sensor is stretched, the strain is calculated as follows:
wherein: lambda (lambda) B Is Bragg wavelength, unit is nm, deltalambda B The wavelength offset is given in nm, epsilon is the strain of the spiral FBG, and p e Is the elasto-optical coefficient, the unit is nm/mu epsilon, alpha T The grating has a thermal expansion coefficient, zeta is the photothermal coefficient of the grating, alpha is the helix angle and epsilon b Poisson's ratio for μmaterial for axial strain;
the change of the axial length of the deformation is calculated according to the relation between the strain and the length, and is as follows:
Δb＝ε b *b
wherein: Δb is the axial length change, ε b Is axial strain, b is pitch;
calculating the length l of a generatrix where the j-th grating point of the i-th fiber bragg grating sensor is located according to the change of the axial length ij (i=1, 2,3,6,7,8; j=1, 2, … …) is:
l ij ＝l-Δb ij
r of the inner wall of the connecting rod is known, the deflection angle phi of the bending direction and the base coordinate j And curvature k j The method comprises the following steps:
and fusing the data information of each fiber bragg grating sensor to obtain the reconstruction shape of the deformation of the big end and the small end of the connecting rod.
9. The method for detecting the deformation of the connecting rod based on the fiber bragg grating sensor according to claim 7, wherein the method comprises the following steps: the calibration experimental method for the inclined fiber grating sensor of the connecting rod body in the fourth step adopts a standard curvature die, and the corresponding relation between the wavelength offset of the fiber grating sensor and the curvature is determined according to the change of the wavelength offset of the fiber grating sensor under different curvatures, so that the calibration of the fiber grating sensor is completed.
10. The method for detecting the deformation of the connecting rod based on the fiber bragg grating sensor according to claim 9, wherein the method for reconstructing the structure of the connecting rod body by using the deformation information in the step eight comprises the following steps:
obtaining the curvature K of the corresponding measuring point of the rod body part of the connecting rod according to the calibration method in the fourth step;
the radius R corresponding to the jth grating point of the fiber bragg grating sensor can be obtained according to the calibration relation ij (i=4, 5; j=1, 2, … …) is:
from radius R ij The length d of the rod body of the connecting rod can obtain the arc length l of the rod body after deformation ij The method comprises the following steps:
and (5) fusing the data information of each fiber bragg grating sensor to obtain the reconstruction shape of the deformation of the rod body of the connecting rod.
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