CN115184146B - DIC-based thin-wall structure buckling strength nondestructive probe measurement method - Google Patents
DIC-based thin-wall structure buckling strength nondestructive probe measurement method Download PDFInfo
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- CN115184146B CN115184146B CN202210675720.2A CN202210675720A CN115184146B CN 115184146 B CN115184146 B CN 115184146B CN 202210675720 A CN202210675720 A CN 202210675720A CN 115184146 B CN115184146 B CN 115184146B
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- 239000000523 sample Substances 0.000 title claims abstract description 64
- 238000000691 measurement method Methods 0.000 title claims description 14
- 238000012360 testing method Methods 0.000 claims abstract description 153
- 230000007547 defect Effects 0.000 claims abstract description 40
- 238000000034 method Methods 0.000 claims abstract description 32
- 238000012669 compression test Methods 0.000 claims abstract description 22
- 238000005259 measurement Methods 0.000 claims abstract description 18
- 238000004519 manufacturing process Methods 0.000 claims abstract description 8
- 238000006073 displacement reaction Methods 0.000 claims description 27
- 238000007639 printing Methods 0.000 claims description 13
- 238000004422 calculation algorithm Methods 0.000 claims description 6
- 238000012937 correction Methods 0.000 claims description 6
- 238000005516 engineering process Methods 0.000 claims description 5
- 238000002310 reflectometry Methods 0.000 claims description 3
- 206010027146 Melanoderma Diseases 0.000 claims description 2
- 230000035945 sensitivity Effects 0.000 abstract description 3
- 238000001514 detection method Methods 0.000 abstract description 2
- 238000002474 experimental method Methods 0.000 description 10
- 238000007906 compression Methods 0.000 description 3
- 238000013461 design Methods 0.000 description 3
- 238000006243 chemical reaction Methods 0.000 description 2
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- 230000000881 depressing effect Effects 0.000 description 1
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Classifications
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N3/00—Investigating strength properties of solid materials by application of mechanical stress
- G01N3/08—Investigating strength properties of solid materials by application of mechanical stress by applying steady tensile or compressive forces
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
- G01B11/00—Measuring arrangements characterised by the use of optical techniques
- G01B11/16—Measuring arrangements characterised by the use of optical techniques for measuring the deformation in a solid, e.g. optical strain gauge
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N19/00—Investigating materials by mechanical methods
- G01N19/08—Detecting presence of flaws or irregularities
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- G—PHYSICS
- G06—COMPUTING; CALCULATING OR COUNTING
- G06V—IMAGE OR VIDEO RECOGNITION OR UNDERSTANDING
- G06V10/00—Arrangements for image or video recognition or understanding
- G06V10/20—Image preprocessing
- G06V10/25—Determination of region of interest [ROI] or a volume of interest [VOI]
Abstract
The invention provides a DIC-based nondestructive probe measuring method for buckling strength of a thin-wall structure, which comprises the following steps: manufacturing speckles on the surface of a test piece; performing an axial compression test on the test piece, and acquiring image information by a camera shooting system; analyzing the image information to obtain a deformation rule of the test piece in an axial compression test, and acquiring an initial defect position according to the deformation rule; applying an axial load to the test piece, and applying radial disturbance to the initial defect position of the test piece through the probe; and carrying out secondary fitting according to data consisting of the maximum pressure value and the axial load of the probe, and predicting the ultimate bearing pressure of the test piece. The invention realizes nondestructive detection of the thin-wall cylindrical shell, improves the accuracy of defect sensitivity measurement of the thin-wall cylindrical shell, avoids the loss of the cylindrical shell and saves the cost.
Description
Technical Field
The invention relates to the field of deformation detection technology and structural design, in particular to a DIC-based nondestructive probe measuring method for buckling strength of a thin-wall structure.
Background
In practical application, because the diameter-thickness ratio of the thin-walled cylindrical shell is large, buckling instability is easy to occur under longitudinal load, and the structural performance of the thin-walled cylindrical shell is greatly reduced due to different initial defects generated in the manufacturing and transportation processes. The ultimate bearing capacity of the cylindrical shell is very sensitive to initial imperfections of the structure, which results in a much smaller actual bearing capacity of the thin-walled cylindrical shell than would be expected from theoretical or numerical predictions based on a perfect model. How to reasonably and accurately consider the influence of the initial geometric defect on the buckling load in the design stage of the thin-shell structure, and to realize the buckling load design method which has the characteristics of safety and light weight and is suitable for engineering application is always a difficult point to be solved urgently.
Currently, the research method for the defect sensitivity problem of the cylindrical shell is mainly to combine experiments and numerical simulation. The experiment is mainly to measure the ultimate bearing capacity and defect sensitivity of the thin-walled cylindrical shell by applying different axial pressures to the thin-walled cylindrical shell until buckling instability. However, in each set of experiments, the samples were disposable consumables, and could not be reused, resulting in higher experimental costs, and for cylindrical shells with different initial defects, it was not possible to locate the specific location of the initial defect of the sample without damaging the sample.
Disclosure of Invention
Based on the above, it is necessary to provide a DIC-based nondestructive probe measurement method for buckling strength of a thin-walled structure.
A DIC-based nondestructive probe measurement method for buckling strength of a thin-wall structure comprises the following steps: manufacturing speckles on the surface of a test piece; performing an axial compression test on the test piece, and acquiring image information by a camera shooting system; analyzing the image information to obtain a deformation rule of the test piece in an axial compression test, and acquiring an initial defect position according to the deformation rule; determining a measurement area according to the initial defect position, applying an axial load to a test piece, and applying radial disturbance to the measurement area through a probe; and carrying out secondary fitting according to data consisting of the maximum pressure value and the axial load of the probe, and predicting the ultimate bearing pressure of the test piece.
In one embodiment, the making speckle on the surface of the test piece specifically includes: inputting speckle parameters, wherein the speckle parameters comprise speckle diameter range values, minimum and maximum distance values among speckles and speckle coverage rate specified values; calling a template with a corresponding size according to the size of a test piece, and generating a random DIC speckle pattern on the template according to speckle parameters; and printing the random DIC speckle pattern on the surface of the test piece through a pattern printing process.
In one embodiment, the pattern printing process adopts a matte white background and black spot mode for printing, and the reflectivity of the speckles is 2% -5%.
In one embodiment, the camera shooting system comprises a plurality of cameras and a microcomputer, wherein the microcomputer is connected with the cameras, the cameras are arranged around a test piece, the cameras are miniature cameras, and the pixels of the cameras are more than 500 ten thousand.
In one embodiment, after the camera and microcomputer are used to form a camera shooting system, before the axial compression test is performed on the test piece and the image acquisition is performed on the test piece by the camera shooting system, the method further comprises: acquiring an initial image of a sample checkerboard pattern; adopting a camera shooting system to acquire images of a plurality of sample chessboard patterns to acquire sample images; calculating distortion parameters and inclination parameters of the camera through the sample image and the original image based on the BA algorithm; and carrying out distortion correction on the camera according to the distortion parameters and the inclination parameters.
In one embodiment, the axial compression test is performed on the test piece, and the image acquisition is performed on the test piece through the camera shooting system to obtain image information, which specifically includes: and (3) applying increasing axial load to the test piece, controlling the camera shooting system to acquire images of the state of the test piece, wherein the frequency of image acquisition is the same as or equal to the loading frequency of the axial load, and acquiring image information of the test piece.
In one embodiment, the analyzing the image information to obtain a deformation rule of the test piece in the axial compression test, and obtaining the initial defect position according to the deformation rule specifically includes: acquiring a plurality of image information, calculating a DTL calibration parameter of a camera according to the image information, and combining the image information to form a three-dimensional image set of a test piece; matching corresponding points on the stereo image set of the test piece by adopting a 2D-DIC technology to obtain all image points; converting all the image points into three-dimensional points, and carrying out three-dimensional reconstruction in a three-dimensional coordinate system; deducing the full-field displacement change process of the test piece in a three-dimensional coordinate system according to the triangular mesh vertexes, and obtaining the deformation rule of the test piece in the axial compression process; and determining the position of the test piece, which is subjected to axial load and has displacement change at first, according to the deformation rule, and obtaining the initial defect position of the test piece.
In one embodiment, the analyzing the image information to obtain a deformation rule of the test piece in the axial compression test, and obtaining the initial defect position according to the deformation rule, further includes: if the number of the cameras is two or more, carrying out plane calibration on the cameras to obtain camera parameters; collecting speckle images of a test piece in an initial stage and a plurality of deformation stages in real time through a camera, and obtaining an initial image and a deformation image; comparing the initial image with the deformed image to obtain a surface deformed point of the test piece and corresponding parallax data; reconstructing three-dimensional coordinates of the surface deformation points according to parallax data and camera parameters of the surface deformation points; and comparing the three-dimensional coordinate changes of the surface deformation points of the test piece at each deformation stage to obtain the full-field displacement change history of the test piece, and acquiring the initial defect position according to the full-field displacement change history.
In one embodiment, the predicting the ultimate bearing pressure of the test piece according to the data composed of the maximum pressure value and the axial load of the probe by performing a second fitting specifically includes: extracting the maximum pressure value of the probe under each axial load; performing secondary fitting on data composed of each axial load and the maximum pressure of the corresponding probe; and predicting the corresponding axial load when the probe pressure is 0 according to the result of the secondary fitting, namely obtaining the ultimate bearing pressure of the test piece.
In one embodiment, after the secondary fitting is performed on the data composed of the maximum pressure value and the axial load according to the probe, the method further comprises: unloading radial disturbance borne by the test piece, applying axial load to the test piece until the test piece collapses, and obtaining an axial load value at the moment of crushing; and comparing the ultimate bearing pressure with the axial load value at the moment of crushing.
Compared with the prior art, the invention has the advantages that: the method comprises the steps of manufacturing speckles on the surface of a test piece, adopting a camera and a microcomputer to form a camera shooting system, carrying out an axial compression test on the test piece, carrying out image acquisition on the test piece through the camera shooting system, obtaining image information, analyzing the image information to obtain a deformation rule of the test piece in the axial compression test, obtaining an initial defect position according to the deformation rule, determining a measuring area according to the initial defect position, applying axial load to the test piece, applying radial disturbance to the measuring area of the test piece through a probe, carrying out secondary fitting according to data consisting of a maximum pressure value and the axial load of the probe, and predicting the ultimate bearing pressure of the test piece, thereby realizing nondestructive measurement of defect positioning and ultimate bearing capacity of a thin-wall structure, reducing experimental cost and improving measurement accuracy.
Drawings
FIG. 1 is a flow diagram of a method for defect localization and non-destructive measurement of thin-wall structures based on full-field DIC in one embodiment;
FIG. 2 is a schematic illustration of a scenario of a hydraulic test in one embodiment;
FIG. 3 is a schematic diagram of experimental equipment for test piece buckling strength probe prediction in one embodiment;
FIG. 4 is a three-dimensional plot of displacement versus pressure for different axial depressing probes in one embodiment;
FIG. 5 is a graph of a quadratic fit of probe maximum pressure versus axial load for one embodiment.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention will be further described in detail by the following detailed description with reference to the accompanying drawings. It should be understood that the specific embodiments described herein are for purposes of illustration only and are not intended to limit the scope of the invention.
In one embodiment, as shown in fig. 1 to 5, a DIC-based thin-wall structure buckling strength nondestructive probe measurement method is provided, comprising the steps of:
and step S101, manufacturing speckles on the surface of the test piece.
Specifically, the test piece is a thin-walled cylindrical shell, speckles are manufactured on the surface of the test piece, and the defect position of the test piece is conveniently determined through the variation of the speckles when the axial compression test is carried out on the test piece. When the speckle is manufactured, the modes of speckle printing, speckle sticker, laser speckle, manual spraying speckle and the like can be adopted.
Wherein, the step of making speckle on the surface of the test piece comprises: inputting speckle parameters, wherein the speckle parameters comprise speckle diameter range values, minimum and maximum distance values among speckles and speckle coverage rate specified values; calling a template with a corresponding size according to the size of a test piece, and generating a random DIC speckle pattern on the template according to speckle parameters; and printing a random DIC speckle pattern on the surface of the test piece through a pattern printing process.
Specifically, when each individual random speckle is generated, the individual random speckle satisfies the speckle diameter range value. In order to reduce labor cost and error, a pattern printing process is preferably adopted, and speckles are printed on the surface of a test piece according to the generated random DIC speckle pattern.
In order to ensure the definition of speckle images in the camera acquisition process, the pattern printing adopts matte white background black speckles, and the reflectivity of the speckle is 2% -5%.
In one embodiment, after step S101, before step S102, the method further includes: acquiring an initial image of a sample chessboard pattern, and acquiring a sample image by adopting a camera shooting system to acquire the image of the sample chessboard pattern; based on BA (Bundle Adjustment, beam adjustment method) algorithm, calculating distortion parameters and inclination parameters of the camera according to the sample image and the original image; and carrying out distortion correction on the camera according to the distortion parameters and the inclination parameters.
Specifically, BA (Bundle Adjustment, beam adjustment method) algorithm is a display calibration method that estimates the internal and external parameters of a camera by repeatedly observing sparse scene points in different directions of observation, the beam adjustment method allowing lens distortion correction based on a nonlinear distortion model. Calibrating the plurality of chessboard patterns through a BA algorithm, calculating to obtain distortion parameters and inclination parameters of each camera, and correcting the influence of point distortion of acquired test piece image information.
The camera shooting system comprises a plurality of cameras and a microcomputer, wherein the microcomputer is connected with the cameras, the cameras are arranged around a test piece, the cameras are miniature cameras, and the pixels are more than 500 ten thousand.
Specifically, the system required by the experiment is burned into a microcomputer, such as a DIC script, a BA algorithm and the like; and determining cameras required by experiments, connecting all cameras, and accessing the cameras into a microcomputer to form a camera shooting system, so that all cameras can work simultaneously, and the acquired image information is stored. Wherein, a plurality of cameras need encircle the test piece setting, are convenient for carry out image acquisition to the test piece is whole.
Specifically, the number of cameras and the included angle between each pair of cameras are determined by the size of the test piece and the shooting range of the cameras. The camera can be fixed around the test piece by adopting the bracket, and the equipment uses two illumination lamps to illuminate around, so that the quality of the photo is improved.
The camera is a miniature camera with adjustable focal length, the pixels are more than 500 ten thousand, and the focal length of the camera needs to be adjusted before the axial compression test is carried out on a test piece.
And S102, performing an axial compression test on the test piece, and acquiring image information by performing image acquisition on the test piece through a camera shooting system.
Specifically, when an axial compression test is performed on a test piece, an increasing axial load is applied to the test piece, for example, from 0 to within the ultimate bearing capacity of the test piece, and meanwhile, a camera shooting system is used for controlling a camera to perform image acquisition on the test piece, so that image information is obtained.
The method comprises the steps of applying increasing axial load to a test piece, controlling a camera shooting system to collect images of the state of the test piece, and acquiring image information of the test piece, wherein the frequency of image collection is the same as or equal to the loading frequency of the axial load.
Specifically, when the load is applied to the test piece, the camera shooting system is controlled to collect images of the state of the test piece, and the loading frequency of the axial load is ensured to be the same as the frequency of the image collection or equal proportion multiple, so that the obtained image information is in one-to-one correspondence with the deformation stage of the test piece, and the deformation rule of the test piece in the axial compression process is analyzed later.
And step S103, analyzing the image information to obtain a deformation rule of the test piece in the axial compression test, and acquiring an initial defect position according to the deformation rule.
Specifically, distortion correction is carried out on the acquired image information, the DIC script is adopted to carry out image analysis and three-dimensional reconstruction on the corrected image information, the full-field displacement change process of the test piece is obtained, the initial defect position of the test piece is positioned according to the full-field displacement change of the test piece,
acquiring a plurality of image information, calculating a DTL calibration parameter of a camera according to the plurality of image information, and combining the plurality of image information to form a three-dimensional image set of a test piece; matching corresponding points on the stereo image set of the test piece by adopting a 2D-DIC technology to obtain all image points; converting all the image points into three-dimensional points, and carrying out three-dimensional reconstruction in a three-dimensional coordinate system; deducing the full-field displacement change process of the test piece in a three-dimensional coordinate system according to the triangular mesh fixed points, and obtaining the deformation rule of the test piece in the axial compression process; and determining the position of the test piece, which is subjected to axial load and has displacement change at first, according to the deformation rule, and obtaining the initial defect position of the test piece.
Specifically, calculating DTL calibration parameters of a camera, namely imaging quality parameters of the camera, according to the image information after distortion correction, and combining a plurality of image information to form a three-dimensional image set of a test piece; performing corresponding image point matching on test piece images acquired from two angles by adopting a 2D-DIC technology to acquire all image points; converting all the image points into three-dimensional points, and carrying out three-dimensional reconstruction in a three-dimensional coordinate system; using three-dimensional coordinates in the triangular mesh vertexes and the current configuration to deduce deformation rules such as full-field displacement, deformation, strain and the like of the test piece; and according to the deformation rule, the position of the test piece, which is the initial defect position, at which the displacement change occurs first when the test piece receives the axial load is determined, so that the measurement accuracy is improved, the initial defect position can be obtained on the premise of not damaging the test piece, and the cost is saved.
The DIC (Digital Image Correlation, digital image correlation method) is a non-contact optical measurement method for measuring deformation displacement and other data by spraying random speckle on the surface of an object and precisely matching corresponding points in speckle images before and after deformation of the object, and the 2D-DIC can measure the displacement of the deformed object in a planar two-dimensional space, further calculate information such as strain through displacement data, can be used for analyzing mechanical properties of the object in the deformation process, and is mainly applied to measurement of full-field displacement, deformation, amplitude, modal and other information.
When there are two or more cameras, the method further comprises: performing plane calibration on a camera to obtain camera parameters; collecting speckle images of a test piece in an initial stage and a plurality of deformation stages in real time through a camera, and obtaining an initial image and a deformation image; comparing the initial image with the deformed image to obtain a surface deformed point of the test piece and corresponding parallax data; reconstructing three-dimensional coordinates of the surface deformation points according to parallax data and camera parameters of the surface deformation points; and comparing the three-dimensional coordinate changes of the surface deformation points of the test piece at each deformation stage to obtain the full-field displacement change history of the test piece, and acquiring the initial defect position according to the full-field displacement change history.
When a plurality of cameras exist, the image information acquired by the plurality of cameras is required to be matched, and the point corresponding to the test piece is determined, so that the full-field deformation information of the test piece can be obtained by comparing the three-dimensional coordinate change of each point in the measurement area of each deformation stage, the coordinate point of the initial defect position is obtained, and the initial defect position of the test piece is determined. Wherein the axial load at the initial stage is 0, and the final axial load is smaller than the ultimate bearing capacity of the test piece. The samples with different initial defects have different displacement changes under the same axial pressure, namely, the ultimate bearing capacity is different.
Step S104, determining a measuring area according to the initial defect position, applying an axial load to the test piece, and applying radial disturbance to the measuring area through the probe.
Specifically, a measurement area is determined according to the initial defect position, for example, a circle with the initial defect position as the center and 2mm is used as the measurement area, radial disturbance is applied to the measurement area through the probe, axial load is uniformly applied to a test piece, and displacement and pressure data of the probe under different axial loads are derived; and the probe applies disturbance to the test piece in a mode of radial movement and fixed displacement at a fixed speed, and is slowly unloaded when the displacement standard value is reached. And when the final value of the pressure curve shown by the probe reaches about 80% of the maximum value, stopping increasing the axial load, and preventing the test piece from being crushed.
The reaction force and displacement curves of the probe at different axial pressures are shown in fig. 4, and when the axial load increases, the maximum value of the reaction force of the probe gradually decreases, and an inflection point appears.
And step S105, performing secondary fitting according to data consisting of the maximum pressure value and the axial load of the probe, and predicting the ultimate bearing pressure of the test piece.
Specifically, the maximum pressure value of the probe under each axial load is extracted, data composed of the maximum pressure values corresponding to each axial load in an experiment are subjected to secondary fitting, and when the probe pressure is predicted to be 0 according to the result of the secondary fitting, the corresponding axial load value is the ultimate bearing pressure of the test piece.
In the test, a curve obtained by twice fitting the maximum pressure value and the axial load value of the probe is shown in fig. 5, and the ultimate bearing pressure of the thin-shell structure under the condition of no disturbance is predicted according to the curve, wherein the axial load value in each group of data is increased at a certain frequency, but the radial displacement of the probe is unchanged.
After step S105, further including: unloading radial disturbance borne by the test piece, applying axial load to the test piece until the test piece collapses, and obtaining an axial load value at the moment of crushing; the ultimate load bearing pressure is compared with the axial load value at the moment of crushing.
Specifically, the test piece is enabled to bear axial pressure under the condition of no disturbance, the axial load value of the test piece in the moment of crushing is obtained, the ultimate bearing pressure and the axial load value in the moment of crushing are compared, the error condition of the experiment is obtained, the experiment can be completed when the experimental error is smaller, the damage to the test piece can be avoided when the subsequent defect positioning and ultimate bearing capacity measurement are carried out, the nondestructive measurement is realized, the cost is saved, the error condition between the prediction and the experiment can be judged, the adjustment to the experiment is facilitated, and the measurement precision is improved.
In the embodiment, the axial compression test is carried out on the test piece by manufacturing the speckles on the surface of the test piece, adopting a camera and a microcomputer to form a camera shooting system, carrying out image acquisition on the test piece by the camera shooting system, acquiring image information, analyzing the image information to obtain the deformation rule of the test piece in the axial compression test, acquiring the initial defect position according to the deformation rule, determining the measuring area according to the initial defect position, applying axial load to the test piece, applying radial disturbance on the measuring area of the test piece by a probe, carrying out secondary fitting according to the data consisting of the maximum pressure value and the axial load of the probe, and predicting the ultimate bearing pressure of the test piece, thereby realizing the nondestructive measurement of the defect positioning and ultimate bearing capacity of the thin-wall structure, reducing the experimental cost and improving the measuring accuracy.
The foregoing is a further detailed description of the invention in connection with specific embodiments, and is not intended to limit the practice of the invention to such descriptions. It will be apparent to those skilled in the art that several simple deductions or substitutions may be made without departing from the spirit of the invention, and these should be considered to be within the scope of the invention.
Claims (8)
1. The DIC-based nondestructive probe measurement method for the buckling strength of the thin-wall structure is characterized by comprising the following steps of:
manufacturing speckles on the surface of a test piece;
performing an axial compression test on the test piece, and acquiring image information by a camera shooting system;
analyzing the image information to obtain a deformation rule of the test piece in the axial compression test, and acquiring an initial defect position according to the deformation rule, wherein the method comprises the following steps: acquiring a plurality of image information, calculating a DTL calibration parameter of a camera according to the image information, and combining the image information to form a three-dimensional image set of a test piece; matching corresponding points on the stereo image set of the test piece by adopting a 2D-DIC technology to obtain all image points; converting all the image points into three-dimensional points, and carrying out three-dimensional reconstruction in a three-dimensional coordinate system; deducing the full-field displacement change process of the test piece in a three-dimensional coordinate system according to the triangular mesh vertexes, and obtaining the deformation rule of the test piece in an axial compression test; determining the position of the test piece, which is subjected to axial load and has displacement change at first, according to the deformation rule, and obtaining the initial defect position of the test piece; if the cameras are two or more, carrying out plane calibration on the cameras to obtain camera parameters; collecting speckle images of a test piece in an initial stage and a plurality of deformation stages in real time through a camera, and obtaining an initial image and a deformation image; comparing the initial image with the deformed image to obtain a surface deformed point of the test piece and corresponding parallax data; reconstructing three-dimensional coordinates of the surface deformation points according to parallax data and camera parameters of the surface deformation points; comparing the three-dimensional coordinate changes of the surface deformation points of the test piece at each deformation stage to obtain the full-field displacement change history of the test piece, and acquiring an initial defect position according to the full-field displacement change history;
determining a measurement area according to the initial defect position, applying an axial load to a test piece, and applying radial disturbance to the measurement area through a probe;
and carrying out secondary fitting according to data consisting of the maximum pressure value and the axial load of the probe, and predicting the ultimate bearing pressure of the test piece.
2. The DIC-based thin-wall structure buckling strength nondestructive probe measurement method of claim 1, wherein the manufacturing of the speckles on the surface of the test piece comprises the following steps:
inputting speckle parameters, wherein the speckle parameters comprise speckle diameter range values, minimum and maximum distance values among speckles and speckle coverage rate specified values;
calling a template with a corresponding size according to the size of a test piece, and generating a random DIC speckle pattern on the template according to speckle parameters;
and printing the random DIC speckle pattern on the surface of the test piece through a pattern printing process.
3. The DIC-based thin-wall structure buckling strength nondestructive probe measurement method is characterized in that the pattern printing process adopts a matte white background and black spot mode for printing, and the reflectivity of speckles is 2% -5%.
4. The DIC-based thin-wall structure buckling strength nondestructive probe measurement method according to claim 1, wherein the camera shooting system comprises a plurality of cameras and a microcomputer, the plurality of cameras are connected with the microcomputer, the plurality of cameras are arranged around a test piece, the cameras are miniature cameras, and the pixels are more than 500 ten thousand.
5. The DIC-based thin-wall structure buckling strength nondestructive probe measurement method according to claim 1, wherein after the speckle is formed on the surface of the test piece, the axial compression test is performed on the test piece, and the image acquisition is performed on the test piece through the camera shooting system, and before the image information is obtained, the method further comprises:
acquiring an initial image of a sample checkerboard pattern;
adopting a camera shooting system to acquire images of a plurality of sample chessboard patterns to acquire sample images;
calculating distortion parameters and inclination parameters of the camera through the sample image and the original image based on the BA algorithm;
and carrying out distortion correction on the camera according to the distortion parameters and the inclination parameters.
6. The DIC-based thin-wall structure buckling strength nondestructive probe measurement method according to claim 1, wherein the performing an axial compression test on the test piece and performing image acquisition on the test piece through the camera shooting system to obtain image information comprises the following steps:
and (3) applying increasing axial load to the test piece, controlling the camera shooting system to acquire images of the state of the test piece, wherein the frequency of image acquisition is the same as or equal to the loading frequency of the axial load, and acquiring image information of the test piece.
7. The DIC-based thin-wall structure buckling strength nondestructive probe measurement method according to claim 1, wherein the predicting the ultimate bearing pressure of the test piece according to the quadratic fit of the data consisting of the maximum pressure value and the axial load of the probe comprises the following steps:
extracting the maximum pressure value of the probe under each axial load;
performing secondary fitting on data composed of each axial load and the maximum pressure of the corresponding probe;
and predicting the corresponding axial load when the probe pressure is 0 according to the result of the secondary fitting, namely obtaining the ultimate bearing pressure of the test piece.
8. The DIC-based thin-wall structure buckling strength nondestructive probe measurement method according to claim 1, wherein after the secondary fitting is performed according to the data composed of the maximum pressure value and the axial load of the probe, the method further comprises:
unloading radial disturbance borne by the test piece, applying axial load to the test piece until the test piece collapses, and obtaining an axial load value at the moment of crushing;
and comparing the ultimate bearing pressure with the axial load value at the moment of crushing.
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Citations (10)
| Publication number | Priority date | Publication date | Assignee | Title |
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