CN108871638B - Optical fiber measuring device and monitoring method for residual stress of material - Google Patents
Optical fiber measuring device and monitoring method for residual stress of material Download PDFInfo
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01L—MEASURING FORCE, STRESS, TORQUE, WORK, MECHANICAL POWER, MECHANICAL EFFICIENCY, OR FLUID PRESSURE
- G01L5/00—Apparatus for, or methods of, measuring force, work, mechanical power, or torque, specially adapted for specific purposes
- G01L5/0047—Apparatus for, or methods of, measuring force, work, mechanical power, or torque, specially adapted for specific purposes measuring forces due to residual stresses
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01L—MEASURING FORCE, STRESS, TORQUE, WORK, MECHANICAL POWER, MECHANICAL EFFICIENCY, OR FLUID PRESSURE
- G01L1/00—Measuring force or stress, in general
- G01L1/24—Measuring force or stress, in general by measuring variations of optical properties of material when it is stressed, e.g. by photoelastic stress analysis using infrared, visible light, ultraviolet
- G01L1/242—Measuring force or stress, in general by measuring variations of optical properties of material when it is stressed, e.g. by photoelastic stress analysis using infrared, visible light, ultraviolet the material being an optical fibre
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Abstract
The invention discloses an optical fiber measuring device and a monitoring method for material residual stress, wherein the device comprises a rubber base, a rubber base groove, a first layer of fiber grating sensor string, rubber, a second layer of fiber grating sensor string, a quartz protective tube and a fiber grating demodulating device; the invention provides a method for monitoring residual stress of a material, which is characterized in that a method for loading a static load or a dynamic load is adopted for testing the overall stress release of the outer surface of the material; for the internal stress release test research of the material, based on ultrasonic waves and contact type fiber bragg grating sensing arrays, the position of uneven internal stress of the material is positioned according to the response time of different sensors to ultrasonic signals, and the distribution of residual stress in the material is analyzed by combining finite element software.
Description
Technical Field
The invention belongs to the technical field of optical fiber measurement, and particularly relates to an optical fiber measuring device and a monitoring method for residual stress of a material.
Background
With the development of the fiber grating sensing technology, the fiber grating sensor is widely applied in the field of engineering structure longitudinal strain monitoring. Compared with a resistance strain gauge used in traditional strain monitoring, the fiber grating sensor has a wavelength division multiplexing function, can realize simultaneous detection of multiple points of a structure by using one optical fiber, is easy for large-scale networking to realize real-time distributed measurement, is free from electromagnetic interference, does not need insulation protection with a structural material, is resistant to chemical corrosion, and is widely applied to structural health monitoring. At present, the optical fiber optical grid is successfully applied to the fields of spaceflight, ocean platforms, civil bridges, large-span space structures and the like.
For the research on the overall stress release test of the outer surface of the material, at present, the test methods of the residual stress are many, and the test methods can be divided into two categories, namely a destructive test method and a nondestructive test method according to whether a tested member is damaged or not. The common methods of the destructive testing method include a stripping method, a strip taking method, a drilling method, a grooving method and the like, the damage of a member caused by drilling can be reduced by using a blind hole method and a shallow blind hole method in the drilling method, generally speaking, the main principle of the destructive testing method is destructive stress release of a structural member, corresponding displacement and strain are generated at a stress release part, the displacement and the strain are measured by using a tool, and then the original stress of the member is obtained through conversion.
The nondestructive testing method is to measure the residual stress by using the change of physical properties of materials or the change of crystal structure parameters, and currently, fiber grating sensors are usually arranged by methods such as embedded type, adhesive type or contact type.
For the embedded type distribution mode, the common mode is to directly embed the optical fiber into the material structure to monitor the strain and temperature, and meanwhile, the material can also play a good role in packaging and protecting the optical fiber, but the embedding of the optical fiber grating can cause the concentration of the stress/strain around the optical fiber grating, and meanwhile, the thermal residual stress generated in the material curing process can also cause the chirp of the reflection spectrum of the optical fiber grating, thereby affecting the strain measurement precision of the grating. Research in "an intelligent composite material laminate manufacturing method for monitoring longitudinal strain of structure" with patent number CN101570067A shows that when a fiber grating is embedded between zero-degree material layers, the influence on grating reflection spectrum is less, but the material design is difficult to realize, and a bare fiber embedded in the material is very fragile, which cannot guarantee the installation process in large-scale engineering construction.
For the sticking type arrangement mode, the 'calibration method of a surface-mounted fiber grating strain sensor' with the patent number of CN105066898A shows that the sensitivity of the sticking type fiber grating strain sensor to strain can cause the change of the strain transfer rate due to the difference of the sticking base material and the sticking agent, thereby causing the strain measurement value of the fiber grating to deviate from the true strain value of the to-be-measured piece; meanwhile, in engineering, the fiber grating sensor is usually bonded on the surface of a structure by using polyimide resin or epoxy resin glue, but the fiber is particularly easy to damage in the service process by the bonding mode. At present, the influence of a base material and an adhesive for adhering strain on the strain sensitivity of the fiber bragg grating sensor in actual measurement is not considered in the calibration method of the adhesive fiber bragg grating sensor, so that the actual strain measurement result is deviated.
Disclosure of Invention
Aiming at the defects of the prior art, the invention designs a contact type fiber bragg grating sensing array to measure the residual stress of the material by adopting a contact type arrangement mode. The invention provides an optical fiber measuring device and a monitoring method for material residual stress, wherein the device utilizes rubber to process an optical fiber grating array base, the measuring method comprises the steps of placing a sample to be measured on a rubber bottom paved with an optical fiber grating array, extruding a material model and the rubber base mutually under the action of the self gravity of the sample to be measured or applying certain pressure on the sample to be measured, measuring the stress change on the surface of the material model, measuring the response capacity of the sample to be measured by ultrasonic waves, and further performing the change of the residual stress in the sample to be measured in a reverse mode. The invention aims to provide an optical fiber measuring device for material residual stress with high precision and simple structure and a monitoring method thereof.
In order to achieve the above object, one embodiment of the present invention adopts the following technical solutions:
an optical fiber measuring device for material residual stress comprises a solid cuboid rubber base, wherein a hemispherical rubber base groove is formed in the middle shaft of the upper surface of the rubber base, and an optical fiber grating array is arranged on the upper surface of the rubber base groove through rubber; the fiber grating array comprises a first fiber grating sensor string and a second fiber grating sensor string which are vertically arranged to form a mesh structure; the tail fiber of the fiber grating array is fixed on the rubber base through the quartz sheath, and the rear end of the tail fiber is connected with the fiber grating demodulation device.
In the above optical fiber measuring device for the residual stress of the material, the first fiber grating sensor string and the second fiber grating sensor string are both formed by connecting n fiber grating sensors in series, where n represents a positive integer.
In the optical fiber measuring device for the residual stress of the material, the optical fiber grating sensors in the first optical fiber grating sensor string are arranged in parallel and are spaced at intervals of 3-5 cm, the optical fiber grating sensors in the second optical fiber grating sensor string are arranged in parallel and are spaced at intervals of 3-5 cm, and the number n of the optical fiber grating sensors is determined by the specification of the grooves of the rubber base.
The fiber grating array comprises a first fiber grating sensor string, a second fiber grating sensor string and a third fiber grating sensor string, wherein the first fiber grating sensor string and the second fiber grating sensor string form a two-dimensional mesh structure on the same plane, the third fiber grating sensor string is perpendicular to the two-dimensional mesh structure, and fiber grating sensors in the third fiber grating sensor string are respectively positioned at each grid node of the two-dimensional mesh structure, so that every three fiber grating sensors in the fiber grating array are orthogonal in a three-dimensional space.
The invention provides a method for monitoring the residual stress of a material by using the device, which comprises the following steps:
(1) preparing an optical fiber measuring device;
(2) calibrating the standard model, and measuring the residual stress of the measured material sample by using an optical fiber measuring device;
(3) carrying out simulation test comparison, and respectively carrying out simulation analysis on the conditions of the whole stress change of the tested material sample and the stress change of a certain region by adopting finite element software;
(4) and positioning the internal stress of the tested material sample by utilizing an ultrasonic wave and optical fiber measuring device.
In the method for monitoring the residual stress of the material, the step (1) comprises the following steps:
(1.1) preparation of rubber base
Firstly, designing a cuboid mold according to the size of a tested material sample, blending rubber and a curing agent according to a ratio, injecting the blended rubber and curing agent into the cuboid mold, then putting the first hemispherical mold into the cuboid mold from top to bottom, compacting a mixture of the rubber and the curing agent to form a groove in the middle of the first hemispherical mold, and curing to obtain a rubber base; wherein the diameter of the first hemispherical die is smaller than the side length of the rectangular parallelepiped die;
(1.2) laying the fiber grating sensor to form a fiber grating array
Firstly, laying a first layer of fiber bragg grating sensor string on the groove surface of a rubber base, and then injecting a mixture of rubber and a curing agent with the same proportion; then laying a second layer of fiber grating sensor string, wherein the laying direction is vertical to the direction of the first layer of fiber grating sensor string, forming a fiber grating array with a net structure, arranging two orthogonal fiber grating sensors on each measuring point on the surface of the groove of the rubber base to measure the stress distribution in different directions, and continuously injecting a mixture of rubber and curing agent with the same proportion to uniformly lay the mixture on the second layer of fiber grating sensor string; after the mixture of the rubber and the curing agent is solidified, compacting by using a second hemispherical mold to obtain a contact type fiber grating array base; the diameter of the second hemispherical die is smaller than the diameter of the inner surface of the groove of the rubber base;
(1.3) the tail fiber is connected with a fiber grating demodulation device
The reserved part of the tail fiber of the fiber grating array at the outlet of the rubber base is fixed through a quartz sheath, and the rear end of the tail fiber of the fiber grating array is connected with a fiber grating demodulation device.
In the method for monitoring the residual stress of the material, the calibration standard model measures the residual stress of the measured material sample by using an optical fiber measuring device, and the method comprises the following steps:
(2.1) placing the standard model in an optical fiber measuring device, measuring the response of the optical fiber grating array to the standard model, and calibrating the optical fiber measuring device by taking the response parameter as a reference value;
(2.2) placing the tested material sample into an optical fiber measuring device, mutually extruding the tested material sample and the rubber base under the action of gravity of the tested material sample, and measuring the stress change of the surface of the tested material sample;
and (2.3) comparing the stress change of the tested material sample with the response parameter of the standard model, if the fiber grating array of the optical fiber measuring device responds to the stress change of the tested material sample, storing the test result, and ending the test, otherwise, loading a static load or a dynamic load on the tested material sample until the fiber grating array responds to the stress change of the tested material sample.
In the method for monitoring the residual stress of the material, the method for loading the static load on the tested material sample comprises the following steps: the method comprises the steps of placing a tested material sample and an optical fiber measuring device on the same movable platform, arranging a casing with a top cover above the platform, fixing the position of the casing, and slowly moving the movable platform upwards until the top cover of the casing applies a load to the tested material sample, wherein the size of the load applied to the tested material sample is in direct proportion to the displacement of the platform in moving.
In the method for monitoring the residual stress of the material, the method for loading the dynamic load on the tested material sample comprises the following steps: and fixing the optical fiber measuring device on a vibration table, and applying a vibration signal to the measured material sample through the vibration table.
In the method for monitoring the residual stress of the material, the step of positioning the internal stress of the tested material sample by utilizing an ultrasonic wave and optical fiber measuring device comprises the following steps:
(4.1) selecting measurement points at equal intervals in the circumferential direction of the surface of the measured material sample;
(4.2) sending an ultrasonic signal with a specific frequency to any measuring point by using an ultrasonic source, and acquiring the response time of the fiber bragg grating sensors at different positions to the ultrasonic signal;
(4.3) moving the position of the ultrasonic source, repeating the step (4.2), and collecting the response signal of the fiber bragg grating array;
and (4.4) analyzing the distribution of internal stress of the tested sample material by combining finite element software.
Compared with the prior art, the invention has at least the following beneficial effects:
the invention provides an optical fiber measuring device for residual stress of a material, which solves the technical problem that the release process of the residual stress on the surface and the inside of the material is difficult to monitor under the conditions of complex loading and variable environment. The invention researches a high-precision nondestructive testing method for the residual stress of the material by designing the optical fiber measuring device for the residual stress of the material, and has the characteristics of simple structure, high precision and the like.
The invention provides a method for monitoring residual stress of a material, which is characterized in that the overall stress release test is carried out on the outer surface of the material by a method of loading static load or dynamic load; the stress release test in the material is researched based on ultrasonic waves and a contact type fiber bragg grating sensing array, the position of uneven stress in the material is located according to the response time of different sensors to ultrasonic signals, and the distribution of the residual stress in the material is more accurate by combining finite element software.
Drawings
FIG. 1 is a schematic view of the whole apparatus for measuring the morphology of a material to be measured and an optical fiber according to the present invention;
FIG. 2 is a schematic cross-sectional view of a fiber grating array according to the present invention;
FIG. 3 is a schematic diagram of the operation of one of the sensor strings of the present invention;
FIG. 4 is a schematic view of the process for manufacturing the rubber base and the fiber grating array of the optical fiber measuring device of the present invention;
FIG. 5 is a schematic diagram of the process of measuring the residual stress of the material by the contact fiber grating sensor array according to the present invention;
FIG. 6 is a schematic view of a static load loading method of the present invention;
FIG. 7 is a schematic diagram of the dynamic load loading method of the present invention;
FIG. 8 is a schematic view of the contact between the spherical shell of the material to be measured and the base structure of the fiber grating sensor array according to the present invention;
FIG. 9 is a diagram illustrating a simulation result of residual stress of a contact fiber grating array measurement material according to the present invention;
FIG. 10 is a schematic view of the propagation of ultrasound within a material according to the present invention;
FIG. 11 is a schematic view of the process flow of the present invention for locating internal stress non-uniformities in materials for ultrasonic and fiber grating arrays;
FIG. 12 is a flow chart of a finite element analysis of the residual stress evolution process of the material according to the present invention;
fig. 13 is a schematic cross-sectional structure view in the three-dimensional direction of a fiber grating array laid in embodiment 2 of the present invention.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is described in further detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.
Example 1
The invention discloses an optical fiber measuring device for residual stress of a material, which is combined with a graph 1-3 and comprises a rubber base 1, a rubber base groove 2, a first fiber grating sensor string 3, rubber 4, a second fiber grating sensor string 5, a quartz sheath 6 and a fiber grating demodulating device 7, wherein the rubber base 1 is a cuboid rubber solid structure with the side length of 700-1000 mm, and the middle part of the rubber base is provided with a hemispherical rubber base groove 2 with the radius of 200-300 mm; the two fiber grating sensor strings form a fiber grating array, the fiber grating array is in a net structure by arranging a first fiber grating sensor string 3 and a second fiber grating sensor string 5, the first fiber grating sensor string 3 and the second fiber grating sensor string 5 are formed by connecting n identical fiber grating sensors in series, the number n of the fiber grating sensors is determined by the specification of the rubber base groove 2, and n represents a positive integer. The fiber grating sensors are optical fibers with standard diameters of 125 mu m, gratings with different central wavelengths are simultaneously engraved on the optical fibers, the interval between every two adjacent fiber grating sensors is 30-50 mm, the length of each fiber grating is the same, and the central wavelength of each grating can be controlled to be 1510-1590 nm. The fiber grating array is of a net structure, fiber grating sensors are distributed on each measuring point and are perpendicular to each other, stress distribution in different directions is measured, and the fact that the sensor strings are parallel in the horizontal direction and the vertical direction and are the same in quantity is guaranteed in the laying process in the groove 2 of the rubber base.
The reserved part of the tail fiber of the fiber grating array at the outlet of the rubber base 1 is fixed by a quartz sheath 6, and finally the tail fiber of the fiber grating array is connected with a fiber grating demodulation device 7.
The method for monitoring the residual stress of the material utilizes the device and comprises the following four steps:
(1) preparing an optical fiber measuring device;
(2) calibrating the standard model, and measuring the residual stress of the measured material sample by using an optical fiber measuring device;
(3) carrying out simulation test comparison, and respectively carrying out simulation analysis on the conditions of the whole stress change of the tested material sample and the stress change of a certain region by adopting finite element software;
(4) and positioning the internal stress of the tested material sample by utilizing an ultrasonic wave and optical fiber measuring device.
Fig. 4 shows a process of manufacturing the fiber measurement device, which includes preparing a rubber base, laying a fiber grating sensor to form a fiber grating array, and connecting a pigtail to a fiber grating demodulation device. Firstly, designing a cuboid mold 8 according to the size of a tested material sample, estimating the using amount of a mixture of rubber and a curing agent according to the volume of the cuboid mold 8, weighing the required rubber by an electronic scale, weighing the curing agent according to a certain proportion, wherein the adding amount of the general curing agent is 2-3%, and uniformly stirring the rubber and the curing agent to form the mixture. The rubber and the curing agent must be uniformly stirred, if the rubber and the curing agent are not uniformly stirred, one rubber in the mold is cured and the other rubber is not cured, the rubber is not uniformly dried and cured, the service life of the rubber and the mold turnover frequency are influenced, and even the condition of scrapping the mold is caused; pouring the stirred rubber into a mold, then putting the first hemispherical mold 9 into a cuboid mold from top to bottom, compacting the mixture of the rubber and the curing agent to form a groove in the middle, and curing to obtain the rubber base; wherein the diameter of the first hemispherical die is smaller than the side length of the rectangular parallelepiped die; secondly, firstly, laying a first layer of fiber bragg grating sensor string on the groove surface of the rubber base, and then injecting a mixture of rubber and a curing agent with the same proportion; then laying a second layer of fiber grating sensor string, wherein the laying direction is vertical to the direction of the first layer of fiber grating sensor string, forming a fiber grating array with a net structure, arranging two orthogonal fiber grating sensors on each measuring point on the surface of the groove of the rubber base to measure the stress distribution in different directions, and continuously injecting a mixture of rubber and curing agent with the same proportion to uniformly lay the mixture on the second layer of fiber grating sensor string; after the mixture of the rubber and the curing agent is solidified, compacting by using a second hemispherical die 10 to obtain a contact type fiber grating array base; the diameter of the second hemispherical die is smaller than the diameter of the inner surface of the groove of the rubber base; and thirdly, fixing the reserved part of the tail fiber of the fiber grating array at the outlet of the rubber base through a quartz sheath, and connecting the rear end of the tail fiber of the fiber grating array with a fiber grating demodulation device.
FIG. 5 is a process of a method for monitoring residual stress of a material, calibrating a standard model, and measuring the residual stress of a measured material sample by using an optical fiber measuring device, comprising the following steps: placing the standard model in an optical fiber measuring device, measuring the response of the optical fiber grating array to the standard model, and calibrating the optical fiber measuring device by taking the response parameter as a reference value; placing the tested material sample into an optical fiber measuring device, mutually extruding the tested material sample and a rubber base under the action of gravity of the tested material sample, and measuring the stress change of the surface of the tested material sample; and comparing the stress change of the tested material sample with the response parameter of the standard model, if the fiber grating array of the fiber measuring device responds to the stress change of the tested material sample, storing the test result, and ending the test, otherwise, loading a static load or a dynamic load on the tested material sample until the fiber grating array responds to the stress change of the tested material sample.
The method of loading static and dynamic loads is shown in fig. 6 and 7. The method for loading the static load on the tested material sample comprises the following steps: the method comprises the steps of placing a tested material sample and an optical fiber measuring device on the same movable platform, arranging a casing with a top cover above the platform, fixing the position of the casing, and slowly moving the movable platform upwards until the top cover of the casing applies a load to the tested material sample, wherein the size of the load applied to the tested material sample is in direct proportion to the displacement of the platform in moving. The method for loading the dynamic load on the tested material sample comprises the following steps: and fixing the optical fiber measuring device on a vibration table, applying a periodic signal vertical to the vibration table surface to the vibration table, and measuring the dynamic response of the optical fiber grating array.
The method for monitoring the residual stress of the material comprises the following steps of (3) carrying out simulation test comparison, and respectively carrying out simulation analysis on the conditions of the whole stress change and the stress change of a certain area of the material to be tested by adopting finite element software. The adopted method is that Comsol software is adopted to carry out simulation analysis on the conditions of the whole stress change and the stress change of a certain area of the material spherical shell respectively. In the simulation process, the Young modulus of the material is set to be 10GPa, the Poisson ratio is set to be 0.33, and the density is set to be 7850kg/m 3; the Young's modulus of the rubber base is 7.8MPa, the Poisson ratio is 0.48, and the density is 1030kg/m 3. FIG. 8 is a schematic view of the structure of the spherical shell and the fiber grating array base of the material to be measured according to the present invention; in the simulation process, when the integral residual stress of the material spherical shell is 2Mpa and the residual stress of a certain area is 2Mpa, the stress distribution of the rubber film layer where the optical fiber grating array is located is realized. When the residual stress is changed from 0.2Mpa to 2Mpa, the strain of a certain point of the rubber film layer where the fiber grating array is located is changed, i.e. the strain response of a certain fiber grating sensor is shown in fig. 9. As can be seen, the response of the fiber grating sensor to residual stress is about 28 μ ε/MPa. When the wavelength demodulation scheme is adopted, the testing precision of the grating sensor is 1 mu epsilon, and the precision of the sensing system for measuring the residual stress of the material is higher than 0.04Mpa and far higher than the requirement of the prior art.
With reference to fig. 10, the method for monitoring residual stress of a material according to the present invention is based on ultrasonic and contact fiber grating sensor arrays to perform a residual stress test inside the material. The basic principle of ultrasonic measurement of residual stress in a material is that when ultrasound passes through a certain stress non-uniformity in the material, the ultrasound is scattered in all directions, thereby causing a difference in the time of response of a sensor to an ultrasonic signal. The difficulty in testing the residual stress in the material by using the ultrasonic and contact fiber grating sensing arrays is how to quickly respond to the response time change caused by the internal residual stress in the fiber grating sensing arrays.
Referring to fig. 11, the method for monitoring residual stress of a material according to the present invention, the step (4) of locating internal stress of the material using a contact fiber grating array of an ultrasonic and fiber optic measuring device includes the following steps: selecting a plurality of measuring points at equal intervals in the circumferential direction of the surface of the measured material sample; loading an ultrasonic signal to a certain test point, sending an ultrasonic signal with a specific frequency to the certain test point by using the ultrasonic source, acquiring the response time of the fiber grating sensors at different positions to the ultrasonic signal, wherein the response time of the grating sensors at different positions to the ultrasonic signal has a certain difference; moving the position of the ultrasonic source, measuring the signal response of the sensor to other test points, and collecting the response signal of the fiber bragg grating array; and analyzing the distribution of internal stress of the tested sample material by combining finite element software.
Due to the high ultrasonic frequency, the passive fiber grating can be realized by using a phase demodulation method. However, since rubber absorbs high-frequency vibration to a greater extent, in order to improve the sensitivity of the sensor, an active fiber grating DFB may be used instead of a passive fiber grating, and a phase demodulation scheme may be used.
When the internal residual stress of the material is measured by ultrasonic, a 980nm pump source is selected to pass through WDM and then enter an active grating DFB array, laser excited by the DFB enters an unequal-arm Michelson interferometer, light beams are divided into two at the input end and enter two arms of the interferometer to be independently propagated to generate phase difference, a high-frequency signal is loaded on one path of the laser, an interference signal is formed at the output end, interference signals with different wavelengths in the grating array are separated by using a Dense Wavelength Division Multiplexing (DWDM) technology, and the optical power change of the interference signal is detected by using a detection circuit to obtain sensing information. The scheme can improve the sensitivity of the sensor by 2-3 orders of magnitude.
When the contact type fiber bragg grating sensing array base is manufactured, a source fiber bragg grating sensor is arranged at a specific position to measure ultrasonic signals, and the distance between the mth sensor and the nth sensor is Smn. The method is characterized in that an appropriate ultrasonic source is selected to send an ultrasonic signal with a specific frequency to a tested material, when the ultrasonic wave passes through a certain stress distribution nonuniform position in the tested material, the ultrasonic wave is scattered to other directions, the propagation path of the ultrasonic wave in the tested material is changed, so that the response signal time of the fiber grating sensor at different positions is changed, and the response time of the sensor at different positions has certain difference which is respectively marked as t1, t2 and … … tn. According to the response time of different sensors to ultrasonic signals, the position of the detected material with uneven internal stress can be positioned, if the sampling rate of a demodulation system is 10MHz, the time signal which can be effectively resolved by the system is 1 mu s, the propagation speed of ultrasonic waves in the detected material is several km/s, and the positioning precision of the fiber grating sensing array can reach cm magnitude.
The invention adopts finite element software based on general software ABAQUS and secondary development technology thereof, and aims at the finite analysis of the stress evolution process of the structural member. And respectively establishing a finite element simulation analysis model for the links of the measured material, such as processing, heating, curing and the like, and reasonably setting the grid size according to the external load loading mode and the space scale of the evolution of the internal stress field of each link. And associating each manufacturing link through the internal stress field mapping of the workpiece to obtain a complete internal stress field evolution and machining deformation analysis model of the workpiece. The method utilizes Python language to carry out the secondary development of ABAQUS, realizes the automatic application of residual stress in corresponding parts, then carries out the calculation of finite elements, and the flow is combined with the flow shown in figure 12.
According to the optical fiber measuring device and the monitoring method for the residual stress of the material, the actual test result of the residual stress of the material by the contact type optical fiber grating sensing array and the simulation analysis of finite element software are adopted, the force, heat, vibration and coupling in-situ loading and experimental data analysis technology for the material is developed, the evolution law of the residual stress field of the material under the conditions of force, heat, vibration and coupling is researched, and the characterization method for the residual stress distribution in the material is explored. Simulating the residual stress of the actual test result of the fiber grating sensor array by points, surfaces and bodies, and developing data processing software to visualize the distribution result of the residual stress of the material.
Example 2
This example is the same as example 1, and differs mainly in that:
with reference to fig. 13, this embodiment shows a device for measuring material morphology based on optical fibers, which lays a three-dimensional fiber grating array, lays every three fiber sensor strings with multiple gratings perpendicular to each other, ensures that each grating is distributed perpendicular to each other, and lays in a rubber base groove 2 with an inner diameter of 200-300 mm through rubber 4. And each sensor string is ensured to be parallel and the same in quantity in the horizontal and vertical directions in the laying process in the rubber base groove 2. Finally, uniformly paving rubber 4 with the same thickness and the same proportion on the fiber bragg grating sensor string which forms a net-shaped structure in the horizontal direction, so that a layer of rubber 4 film is formed on the surface of the groove 2 of the rubber base; the grating on the fiber grating sensor string is vertical to the grating in the horizontal direction, and 3-5 layers are laid in the vertical direction; the other steps are the same.
Although the invention has been described herein with reference to illustrative embodiments thereof, it should be understood that numerous other modifications and embodiments can be devised by those skilled in the art that will fall within the spirit and scope of the principles of this disclosure. More specifically, various variations and modifications may be made to the component parts and/or arrangements of the subject combination arrangement within the scope of the disclosure herein. In addition to variations and modifications in the component parts and/or arrangements, other uses will also be apparent to those skilled in the art.
Claims (8)
1. A method for monitoring residual stress of a material utilizes an optical fiber measuring device, and is characterized by comprising the following steps:
(1) preparing an optical fiber measuring device; the optical fiber measuring device comprises a solid cuboid rubber base, a hemispherical rubber base groove is formed in the middle shaft of the upper surface of the rubber base, and the upper surface of the rubber base groove is provided with an optical fiber grating array through rubber rows; the fiber grating array at least comprises a first fiber grating sensor string and a second fiber grating sensor string which are vertically arranged to form a mesh structure; the tail fiber of the fiber bragg grating array is fixed on the rubber base through the quartz sheath, and the rear end of the tail fiber is connected with the fiber bragg grating demodulating device;
(2) calibrating the standard model, and measuring the residual stress of the measured material sample by using an optical fiber measuring device;
(3) carrying out simulation test comparison, and respectively carrying out simulation analysis on the conditions of the whole stress change of the tested material sample and the stress change of a certain region by adopting finite element software;
(4) the method for positioning the internal stress of the tested material sample by utilizing the ultrasonic and optical fiber measuring device comprises the following steps:
(4.1) putting the sample to be measured into an optical fiber measuring device, and selecting measuring points at equal intervals in the circumferential direction of the surface of the sample of the material to be measured;
(4.2) sending an ultrasonic signal with a specific frequency to any measuring point by using an ultrasonic source, and acquiring the response time of the fiber bragg grating sensors at different positions to the ultrasonic signal;
(4.3) moving the position of the ultrasonic source, repeating the step (4.2), and collecting the response signal of the fiber bragg grating array;
and (4.4) analyzing the distribution of internal stress of the tested sample material by combining finite element software.
2. The method for monitoring the residual stress of the material according to claim 1, wherein the step (1) comprises the steps of:
(1.1) preparation of rubber base
Firstly, designing a cuboid mold (8) according to the size of a tested material sample, blending rubber and a curing agent according to a ratio, injecting the blended rubber and curing agent into the cuboid mold, then putting a first hemispherical mold (9) into the cuboid mold from top to bottom, compacting a mixture of the rubber and the curing agent to form a groove in the middle of the mixture, and curing to obtain a rubber base; wherein the diameter of the first hemispherical die is smaller than the side length of the rectangular parallelepiped die;
(1.2) laying the fiber grating sensor to form a fiber grating array
Firstly, laying a first layer of fiber bragg grating sensor string on the groove surface of a rubber base, and then injecting a mixture of rubber and a curing agent with the same proportion; then laying a second layer of fiber grating sensor string, wherein the laying direction is vertical to the direction of the first layer of fiber grating sensor string, forming a fiber grating array with a net structure, arranging two orthogonal fiber grating sensors on each measuring point on the surface of the groove of the rubber base to measure the stress distribution in different directions, and continuously injecting a mixture of rubber and curing agent with the same proportion to uniformly lay the mixture on the second layer of fiber grating sensor string; after the mixture of the rubber and the curing agent is solidified, compacting by using a second hemispherical mold (10) to obtain a contact type fiber grating array base; the diameter of the second hemispherical die is smaller than the diameter of the inner surface of the groove of the rubber base;
(1.3) the tail fiber is connected with a fiber grating demodulation device
The reserved part of the tail fiber of the fiber grating array at the outlet of the rubber base is fixed through a quartz sheath, and the rear end of the tail fiber of the fiber grating array is connected with a fiber grating demodulation device.
3. The method for monitoring the residual stress of the material according to claim 1, wherein the calibration standard model measures the residual stress of the tested material sample by using an optical fiber measuring device, and comprises the following steps:
(2.1) placing the standard model in an optical fiber measuring device, measuring the response of the optical fiber grating array to the standard model, and calibrating the optical fiber measuring device by taking the response parameter as a reference value;
(2.2) placing the tested material sample into an optical fiber measuring device, mutually extruding the tested material sample and the rubber base under the action of gravity of the tested material sample, and measuring the stress change of the surface of the tested material sample;
and (2.3) comparing the stress change of the tested material sample with the response parameter of the standard model, if the fiber grating array of the optical fiber measuring device responds to the stress change of the tested material sample, storing the test result, and ending the test, otherwise, loading a static load or a dynamic load on the tested material sample until the fiber grating array responds to the stress change of the tested material sample.
4. The method for monitoring the residual stress of the material according to claim 3, wherein the method for loading the static load on the tested material sample comprises the following steps: the method comprises the steps of placing a tested material sample and an optical fiber measuring device on the same movable platform, arranging a casing with a top cover above the platform, fixing the position of the casing, and slowly moving the movable platform upwards until the top cover of the casing applies a load to the tested material sample, wherein the size of the load applied to the tested material sample is in direct proportion to the displacement of the platform in moving.
5. The method for monitoring the residual stress of the material according to claim 3, wherein the method for loading the dynamic load on the tested material sample comprises the following steps: and fixing the optical fiber measuring device on a vibration table, and applying a vibration signal to the measured material sample through the vibration table.
6. The method for monitoring the residual stress of the material according to claim 1, wherein the first fiber grating sensor string and the second fiber grating sensor string are both composed of n fiber grating sensors connected in series, wherein n represents a positive integer.
7. The method for monitoring the residual stress of the material according to claim 6, wherein the fiber grating sensors in the first fiber grating sensor string are arranged in parallel and are spaced from each other by 3-5 cm, the fiber grating sensors in the second fiber grating sensor string are arranged in parallel and are spaced from each other by 3-5 cm, and the number n of the fiber grating sensors is determined by the specification of the rubber base groove (2).
8. The method for monitoring the residual stress of the material according to claim 1, wherein the fiber grating array comprises a first fiber grating sensor string, a second fiber grating sensor string and a third fiber grating sensor string, the first fiber grating sensor string and the second fiber grating sensor string form a two-dimensional mesh structure on the same plane, the third fiber grating sensor string is arranged perpendicular to the two-dimensional mesh structure, and the fiber grating sensors in the third fiber grating sensor string are respectively located at each mesh node of the two-dimensional mesh structure, so that every three fiber grating sensors in the fiber grating array are orthogonal in a three-dimensional space.
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| CN109916952B (en) * | 2019-04-12 | 2024-01-19 | 中国工程物理研究院化工材料研究所 | System and method for measuring surface convection heat transfer coefficient of hollow sphere configuration |
| CN110940445B (en) * | 2019-12-16 | 2021-03-16 | 中国工程物理研究院化工材料研究所 | Optical fiber ring type residual stress test system and residual stress test method |
| CN111521312A (en) * | 2020-05-08 | 2020-08-11 | 中国工程物理研究院化工材料研究所 | Method for calibrating residual stress of optical fiber measurement material based on blind hole method |
| CN117725806B (en) * | 2024-02-08 | 2024-05-07 | 北京理工大学 | Layering step difference forecasting method and device for composite material grid structure |
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