CN115184146A - DIC-based nondestructive probe measurement method for buckling strength of thin-wall structure - Google Patents
DIC-based nondestructive probe measurement method for buckling strength of thin-wall structure Download PDFInfo
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Abstract
The invention provides a DIC-based nondestructive probe measurement method for buckling strength of a thin-wall structure, which comprises the following steps: manufacturing speckles on the surface of a test piece; carrying out an axial compression test on the test piece, and carrying out image acquisition on the test piece through a camera shooting system to obtain image information; 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; applying axial load to the test piece, and applying radial disturbance to the initial defect position of the test piece through a probe; and performing secondary fitting according to data formed by the maximum pressure value of the probe and the axial load, and predicting the ultimate bearing pressure of the test piece. The invention realizes the nondestructive detection of the thin-wall cylindrical shell, improves the accuracy of the 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, the buckling instability is easy to occur under longitudinal load due to the large diameter-thickness ratio of the thin-wall cylindrical shell, and the structural performance of the thin-wall cylindrical shell is greatly reduced due to different degrees of initial defects generated in the manufacturing and transporting processes of the thin-wall cylindrical shell. The ultimate bearing capacity of the cylindrical shell is very sensitive to the initial defects of the structure, which results in the actual bearing capacity of the thin-walled cylindrical shell being much smaller than the ultimate bearing capacity based on theoretical or numerical predictions of perfect models. How to reasonably and accurately consider the influence of the initial geometric defects on the buckling load in the design stage of the thin-shell structure and realize a 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 urgently solved.
At present, the problem of defect sensitivity of the cylindrical shell is mainly researched by combining experiments with numerical simulation. The experiment mainly comprises the step of applying different axial pressures to the thin-wall cylindrical shell until buckling instability is achieved so as to measure the ultimate bearing capacity and defect sensitivity of the thin-wall cylindrical shell. However, in each set of experiment, the sample is a disposable consumable, and cannot be reused, which results in higher experiment cost, and for the cylindrical shell with different initial defects, the specific position of the initial defect of the sample cannot be located without damaging the sample.
Disclosure of Invention
In view of the above, it is necessary to provide a nondestructive probe measuring method for buckling strength of thin-wall structure based on DIC.
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; carrying out an axial compression test on the test piece, and carrying out image acquisition on the test piece through a camera shooting system to obtain image information; 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; determining a measuring area according to the initial defect position, applying axial load to the test piece, and applying radial disturbance to the measuring area through a probe; and performing secondary fitting according to data formed by the maximum pressure value of the probe and the axial load, and predicting the ultimate bearing pressure of the test piece.
In one embodiment, the making of the speckles on the surface of the test piece specifically includes: inputting speckle parameters, wherein the speckle parameters comprise a speckle diameter range value, a minimum and maximum spacing value between speckles and a specified value of speckle coverage rate; calling a template with a corresponding size according to the size of the test piece, and generating a random DIC speckle pattern on the template according to the speckle parameters; and printing the random DIC speckle pattern on the surface of the test piece by a pattern printing process.
In one embodiment, the pattern printing process adopts a matte white background black spot mode for printing, and the light reflection rate of the speckles is 2% -5%.
In one embodiment, the camera shooting system comprises a plurality of cameras and a microcomputer, the microcomputer is connected with the cameras, the cameras are arranged around the test piece, the cameras are miniature cameras, and the number of pixels is 500 ten thousand or more.
In one embodiment, after the camera and the microcomputer form the 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, and the image information is acquired, the method further includes: obtaining an initial image of a sample chessboard pattern; adopting a camera shooting system to collect images of a plurality of sample chessboard patterns to obtain sample images; calculating distortion parameters and inclination parameters of the camera through the sample image and the original image based on a BA algorithm; and carrying out distortion correction on the camera according to the distortion parameters and the inclination parameters.
In one embodiment, the performing an axial compression test on the test piece, and acquiring an image of the test piece by using the camera shooting system to obtain image information specifically includes: and applying an increasing axial load to the test piece, controlling the camera shooting system to acquire an image of the state of the test piece, wherein the image acquisition frequency is the same as or equal to a proportional multiple of the loading frequency of the axial load, and acquiring the 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 an initial defect position according to the deformation rule specifically includes: acquiring a plurality of pieces of image information, and calculating DTL calibration parameters of a camera according to the image information, wherein the plurality of pieces of image information are combined to form a three-dimensional image set of the test piece; matching corresponding points on a stereo image set of the test piece by adopting a 2D-DIC technology to obtain all image points; converting all image points into three-dimensional points, and performing three-dimensional reconstruction in a three-dimensional coordinate system; deducing the full-field displacement change history of the test piece according to the vertex of the triangular mesh in the three-dimensional coordinate system, and acquiring the deformation rule of the test piece in the axial compression process; and determining the position of the test piece which is firstly subjected to displacement change when the test piece is subjected to the axial load according to the deformation rule, and acquiring 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 an initial defect position according to the deformation rule further includes: if two or more cameras exist, performing plane calibration on the cameras to obtain camera parameters; acquiring speckle images of a test piece at an initial stage and a plurality of deformation stages in real time through a camera to obtain an initial image and a deformation image; comparing the initial image with the deformation image to obtain surface deformation points of the test piece and corresponding parallax data; reconstructing three-dimensional coordinates of the surface deformation points according to the parallax data of the surface deformation points and the camera parameters; and comparing the three-dimensional coordinate change of the surface deformation point of the test piece in each deformation stage to obtain the full-field displacement change process of the test piece, and acquiring the initial defect position according to the full-field displacement change process.
In one embodiment, the performing second-order fitting according to data composed of the maximum pressure value of the probe and the axial load to predict the ultimate bearing pressure of the test piece specifically includes: extracting the maximum pressure value of the probe under each axial load; performing quadratic fitting on data consisting of each axial load and the maximum pressure of the corresponding probe; and when the probe pressure is predicted to be 0 according to the result of the quadratic fitting, acquiring the limit bearing pressure of the test piece according to the corresponding axial load.
In one embodiment, after performing quadratic fitting according to data composed of the maximum pressure value and the axial load of the probe and predicting the ultimate bearing pressure of the test piece, the method further includes: unloading the radial disturbance on the test piece, applying an axial load to the test piece until the test piece collapses, and obtaining the axial load value at the moment of crushing; and comparing the limit bearing pressure with the axial load value at the crushing moment.
Compared with the prior art, the invention has the advantages and beneficial effects that: the speckle is manufactured on the surface of the test piece, a camera shooting system is formed by a camera and a microcomputer, an axial compression test is carried out on the test piece, image acquisition is carried out on the test piece through the camera shooting system, image information is obtained, the image information is analyzed, the deformation rule of the test piece in the axial compression test is obtained, the initial defect position is obtained according to the deformation rule, the measuring area is determined according to the initial defect position, the axial load is applied to the test piece, radial disturbance is applied to the measuring area of the test piece through a probe, secondary fitting is carried out according to the maximum pressure value of the probe and the data formed by the axial load, and the limit bearing pressure of the test piece is pre-measured, so that the nondestructive measurement of the defect positioning and the limit bearing capacity of the thin-wall structure is realized, the experiment cost is reduced, and the measurement accuracy is improved.
Drawings
FIG. 1 is a schematic flow chart of a full field DIC-based thin-walled structure defect localization and non-destructive measurement method in one embodiment;
FIG. 2 is a schematic view of an embodiment of an axial compression test;
FIG. 3 is a schematic diagram of an experimental setup for specimen buckling strength probe prediction in one embodiment;
FIG. 4 is a three-dimensional graph of probe displacement versus pressure for different axial pressures in one embodiment;
FIG. 5 is a graph of a quadratic fit of the maximum pressure of the probe to the axial load in one embodiment.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is further described in detail by the following detailed description in conjunction with the accompanying drawings. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.
In one embodiment, as shown in fig. 1-5, there is provided a DIC-based thin-walled structure buckling strength nondestructive probe measurement method comprising the steps of:
and S101, manufacturing speckles on the surface of the test piece.
Specifically, the test piece is a thin-wall cylindrical shell, speckles are manufactured on the surface of the test piece, and the defect position of the test piece is convenient to determine through the change of the speckles when the axial compression test is carried out on the test piece. When the speckles are manufactured, modes such as speckle printing, speckle paster, laser speckle, manual spraying speckle and the like can be adopted.
The method for manufacturing the speckles on the surface of the test piece comprises the following steps: inputting speckle parameters, wherein the speckle parameters comprise a speckle diameter range value, a minimum and maximum space value among speckles and a specified value of speckle coverage rate; calling a template with a corresponding size according to the size of the test piece, and generating a random DIC speckle pattern on the template according to the speckle parameters; the random DIC speckle pattern was printed on the surface of the test piece by a pattern printing process.
Specifically, when each random speckle individual is generated, the random speckle individual satisfies the speckle diameter range value. In order to reduce labor cost and errors, a pattern printing process is preferably adopted, and speckles are printed on the surface of the test piece according to the generated random DIC speckle pattern.
In order to ensure that the speckle images are clear in the camera acquisition process, the pattern printing adopts matte white background black spots, and the light reflection rate of the speckles is 2-5%.
In one embodiment, after step S101 and before step S102, the method further includes: acquiring an initial image of the sample chessboard pattern, and acquiring the sample image by adopting a camera shooting system to acquire the image of the sample chessboard pattern; calculating distortion parameters and inclination parameters of the camera according to the sample image and the original image based on a BA (Bundle Adjustment) algorithm; and carrying out distortion correction on the camera according to the distortion parameter and the inclination parameter.
Specifically, the BA (Bundle Adjustment) algorithm is a display calibration method that estimates internal and external parameters of a camera by repeatedly observing sparse scene points in different observation directions, and allows lens distortion correction based on a nonlinear distortion model. And calibrating the chessboard patterns through a BA algorithm, calculating distortion parameters and inclination parameters of each camera, and correcting the influence of point distortion of the acquired test piece image information.
The camera shooting system comprises a plurality of cameras and a microcomputer, the microcomputer is connected with the cameras, the cameras are arranged around the test piece, the cameras are miniature cameras, and the number of pixels is 500 ten thousand or more.
Specifically, a system required by the experiment is burnt into a microcomputer, such as DIC scripts, BA algorithm and the like; determining cameras required by the experiment, connecting all the cameras, connecting the cameras into a microcomputer to form a camera shooting system, ensuring that all the cameras can work simultaneously, and storing the acquired image information. 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 specimen and the shooting range of the cameras. The camera can be fixed around the test piece by adopting a support, and two irradiation lamps are used for illuminating around the equipment, so that the photo quality is improved.
The camera is a miniature camera with an adjustable focal length, the pixel is 500 ten thousand or more, and the focal length of the camera needs to be adjusted before the test piece is subjected to an axial compression test.
And S102, carrying out an axial compression test on the test piece, and carrying out image acquisition on the test piece through a camera shooting system to obtain image information.
Specifically, when the axial compression test is performed on the test piece, image information is acquired by applying an increasing axial load to the test piece, for example, from 0 to within the limit bearing capacity of the test piece, and simultaneously controlling the camera to perform image acquisition on the test piece through the camera shooting system.
The method comprises the steps of applying an increasing axial load to a test piece, controlling a camera shooting system to carry out image acquisition on the state of the test piece, and acquiring image information of the test piece, wherein the image acquisition frequency is the same as or in equal proportional multiple with the loading frequency of the axial load.
Specifically, when a load is applied to the test piece, the camera shooting system is controlled to acquire an image of the state of the test piece, and the loading frequency of the axial load is ensured to be the same as or equal to a proportional multiple of the image acquisition frequency, so that the acquired image information and the deformation stage of the test piece are conveniently in one-to-one correspondence, and the deformation rule of the test piece in the axial compression process is conveniently analyzed in the subsequent process.
And 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, DIC scripts are adopted to carry out image analysis and three-dimensional reconstruction on the corrected image information to obtain the whole-field displacement change process of the test piece, the initial defect position of the test piece is positioned according to the whole-field displacement change of the test piece,
the method comprises the steps of obtaining a plurality of pieces of image information, calculating a DTL (digital to analog) calibration parameter of a camera according to the plurality of pieces of image information, and combining the plurality of pieces of image information to form a three-dimensional image set of a test piece; matching corresponding points on a stereo image set of the test piece by adopting a 2D-DIC technology to obtain all image points; converting all image points into three-dimensional points, and performing three-dimensional reconstruction in a three-dimensional coordinate system; deducing the full-field displacement change history of the test piece in a three-dimensional coordinate system according to the triangular grid fixed points, and acquiring the deformation rule of the test piece in the axial compression process; and determining the position of the test piece which is the first to appear displacement change when the test piece is subjected to the axial load according to the deformation rule, and acquiring the initial defect position of the test piece.
Specifically, calculating a DTL calibration parameter of the camera, namely an imaging quality parameter 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 the test piece; carrying out corresponding image point matching on the test piece images obtained from two angles by adopting a 2D-DIC technology to obtain all image points; converting all image points into three-dimensional points, and performing three-dimensional reconstruction in a three-dimensional coordinate system; deducing deformation rules of the test piece, such as full-field displacement, deformation, strain and the like, by using the triangular grid vertex and the three-dimensional coordinates in the current configuration; and according to the deformation rule, the position where the displacement change occurs first when the test piece is subjected to the axial load is determined, namely the initial defect position, 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 2D-DIC can measure the displacement of the deformed object in a planar two-dimensional space, further calculate information such as strain and the like through displacement data, can be used for analyzing the mechanical property of the object in the deformation process, and is mainly applied to measurement of information such as full-field displacement, deformation, amplitude, modal and the like.
When there are two or more cameras, the method further comprises the following steps: carrying out plane calibration on a camera to obtain camera parameters; acquiring speckle images of a test piece at an initial stage and a plurality of deformation stages in real time through a camera to obtain an initial image and a deformation image; comparing the initial image with the deformation image to obtain surface deformation points of the test piece and corresponding parallax data; reconstructing three-dimensional coordinates of the surface deformation points according to the parallax data of the surface deformation points and the camera parameters; and comparing the three-dimensional coordinate change of the surface deformation point of the test piece in each deformation stage to obtain the full-field displacement change process of the test piece, and acquiring the initial defect position according to the full-field displacement change process.
When a plurality of cameras exist, image information acquired by the cameras needs to be matched, and points corresponding to the test piece are determined, so that full-field deformation information of the test piece can be obtained by comparing three-dimensional coordinate changes of all points in a measurement area in each deformation stage, coordinate points of an initial defect position are obtained, and the initial defect position of the test piece is determined. The axial load at the initial stage is 0, and the final axial load is smaller than the limit bearing capacity of the test piece. The displacement change of the samples with different initial defects under the same axial pressure is different, namely the ultimate bearing capacity is different.
And step S104, determining a measuring area according to the initial defect position, applying axial load to the test piece, and applying radial disturbance to the measuring area through the probe.
Specifically, a measuring area is determined according to the initial defect position, for example, a circle of 2mm with the initial defect position as the center is used as the measuring area, radial disturbance is applied to the measuring area through a probe, axial load is uniformly applied to the test piece at the same time, and displacement and pressure data of the probe under the action of different axial loads are derived; and the probe radially moves at a fixed speed and applies disturbance to the test piece in a fixed displacement mode, and when the displacement standard value is reached, the probe is slowly unloaded. 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 versus displacement curve of the probe at different axial pressures is 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 formed by the maximum pressure value of the probe and the axial load, and predicting the ultimate bearing pressure of the test piece.
Specifically, the maximum pressure value of the probe under each axial load is extracted, quadratic fitting is performed on data composed of the maximum pressure values corresponding to each axial load in the experiment, and when the probe pressure is predicted to be 0 according to the quadratic fitting result, the corresponding axial load value is the ultimate bearing pressure of the test piece.
In the test, a curve obtained by quadratic fitting of 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, the method further includes: unloading the radial disturbance on the test piece, applying an axial load to the test piece until the test piece collapses, and acquiring an axial load value at the moment of crushing; and comparing the limit bearing pressure with the axial load value at the crushing moment.
Specifically, the test piece bears the axial pressure under the condition of no disturbance, the axial load value of the test piece at the moment of crushing is obtained, the limit bearing pressure and the axial load value at the moment of crushing are compared, the error condition of the experiment is obtained, when the experiment error is small, the experiment can be completed, when the follow-up defect positioning and the limit bearing capacity measurement are carried out, the damage to the test piece can be avoided, the nondestructive measurement is realized, the cost is saved, the error condition between the prediction and the experiment can be judged, the experiment can be conveniently adjusted, and the measurement precision is improved.
In the embodiment, speckles are manufactured on the surface of a test piece, a camera shooting system is composed of a camera and a microcomputer, an axial compression test is performed on the test piece, image acquisition is performed on the test piece through the camera shooting system, image information is acquired, the image information is analyzed, the deformation rule of the test piece in the axial compression test is obtained, an initial defect position is acquired according to the deformation rule, a measuring area is determined according to the initial defect position, an axial load is applied to the test piece, radial disturbance is applied to the measuring area of the test piece through a probe, secondary fitting is performed according to data formed by the maximum pressure value of the probe and the axial load, and the limit bearing pressure of the test piece is pre-measured, so that nondestructive measurement of thin-wall structure defect positioning and the limit bearing capacity is achieved, the experiment cost is reduced, and the measurement accuracy is improved.
The foregoing is a more detailed description of the present invention that is presented in conjunction with specific embodiments, and the practice of the invention is not to be considered limited to those descriptions. For those skilled in the art to which the invention pertains, numerous simple deductions or substitutions may be made without departing from the spirit of the invention, which shall be deemed to belong to the scope of the invention.
Claims (10)
1. A DIC-based nondestructive probe measurement method for buckling strength of a thin-wall structure is characterized by comprising the following steps:
manufacturing speckles on the surface of a test piece;
carrying out an axial compression test on the test piece, and carrying out image acquisition on the test piece through a camera shooting system to obtain image information;
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;
determining a measuring area according to the initial defect position, applying axial load to the test piece, and applying radial disturbance to the measuring area through a probe;
and performing secondary fitting according to data formed by the maximum pressure value of the probe and the axial load, and predicting the ultimate bearing pressure of the test piece.
2. The DIC-based nondestructive probe for measuring buckling strength of a thin-walled structure according to claim 1, wherein the speckle is fabricated on the surface of the test piece, and the method specifically comprises the following steps:
inputting speckle parameters, wherein the speckle parameters comprise a speckle diameter range value, a minimum and maximum space value among speckles and a specified value of speckle coverage rate;
calling a template with a corresponding size according to the size of the test piece, and generating a random DIC speckle pattern on the template according to the speckle parameters;
and printing the random DIC speckle pattern on the surface of the test piece by a pattern printing process.
3. The DIC-based nondestructive testing method for the buckling strength of the thin-walled structure as defined in claim 2 wherein the pattern printing process is performed by means of black spots on a matte white background, and the reflectance of the spots is 2-5%.
4. The DIC-based nondestructive probe for measuring buckling strength of thin-walled structures as defined in claim 1 wherein the camera imaging system comprises a plurality of cameras and a microcomputer, the microcomputer is connected to the plurality of cameras, the plurality of cameras are disposed around the test piece, the cameras are miniature cameras, and the number of pixels is 500 ten thousand or more.
5. The DIC-based nondestructive probe for measuring buckling strength of thin-walled structures as defined in claim 1, wherein after the camera shooting system is composed of the camera and the microcomputer, the method further comprises, 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 to obtain the image information:
obtaining an initial image of a sample chessboard pattern;
adopting a camera shooting system to collect images of a plurality of sample chessboard patterns to obtain sample images;
calculating to obtain distortion parameters and inclination parameters of the camera through the sample image and the original image based on a BA algorithm;
and carrying out distortion correction on the camera according to the distortion parameter and the inclination parameter.
6. The DIC-based nondestructive probe for measuring buckling strength of a thin-walled structure as defined in claim 1, wherein the axial compression test is performed on a test piece, and the image acquisition is performed on the test piece by the camera shooting system to obtain image information, specifically comprising:
and applying an increasing axial load to the test piece, controlling the camera shooting system to acquire an image of the state of the test piece, wherein the image acquisition frequency is the same as or equal to a proportional multiple of the loading frequency of the axial load, and acquiring the image information of the test piece.
7. The DIC-based nondestructive probe for measuring buckling strength of a thin-wall structure of claim 1, wherein the analyzing the image information to obtain a deformation rule of the test piece in an axial compression test and obtaining an initial defect position according to the deformation rule comprises:
acquiring a plurality of pieces of image information, and calculating DTL calibration parameters of a camera according to the image information, wherein the plurality of pieces of image information are combined to form a three-dimensional image set of the test piece;
matching corresponding points on a stereo image set of the test piece by adopting a 2D-DIC technology to obtain all image points;
converting all image points into three-dimensional points, and performing three-dimensional reconstruction in a three-dimensional coordinate system;
deducing the full-field displacement change history of the test piece according to the vertex of the triangular mesh in the three-dimensional coordinate system, and acquiring the deformation rule of the test piece in the axial compression test;
and determining the position of the test piece which is firstly subjected to displacement change when the test piece is subjected to the axial load according to the deformation rule, and acquiring the initial defect position of the test piece.
8. The DIC-based nondestructive probe for measuring buckling strength of a thin-walled structure as recited in claim 7, wherein the analyzing the image information to obtain a deformation rule of the test piece in an axial compression test and obtaining an initial defect position according to the deformation rule further comprises:
if two or more cameras exist, performing plane calibration on the cameras to obtain camera parameters;
acquiring speckle images of a test piece at an initial stage and a plurality of deformation stages in real time through a camera to obtain an initial image and a deformation image;
comparing the initial image with the deformation image to obtain surface deformation points of the test piece and corresponding parallax data;
reconstructing three-dimensional coordinates of the surface deformation points according to the parallax data of the surface deformation points and the camera parameters;
and comparing the three-dimensional coordinate change of the surface deformation point of the test piece in each deformation stage to obtain the full-field displacement change process of the test piece, and acquiring the initial defect position according to the full-field displacement change process.
9. The DIC-based nondestructive probe for measuring buckling strength of thin-walled structures according to claim 1, wherein the step of performing quadratic fitting according to data consisting of the maximum pressure value and the axial load of the probe to predict the ultimate bearing pressure of the test piece comprises:
extracting the maximum pressure value of the probe under each axial load;
performing quadratic fitting on data consisting of each axial load and the maximum pressure of the corresponding probe;
and when the probe pressure is predicted to be 0 according to the result of the quadratic fitting, acquiring the limit bearing pressure of the test piece according to the corresponding axial load.
10. The DIC-based nondestructive probe for measuring buckling strength of thin-walled structures of claim 1, wherein after performing quadratic 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, the method further comprises:
unloading the radial disturbance on the test piece, applying an axial load to the test piece until the test piece collapses, and obtaining the axial load value at the moment of crushing;
and comparing the limit bearing pressure with the axial load value at the crushing moment.
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| CN117367652A (en) * | 2023-10-16 | 2024-01-09 | 江苏信息职业技术学院 | Bolt axial force detection method and device based on end face speckle image |
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