CN101520318A - Method for measuring sheet metal deformation based on images - Google Patents

Abstract

The invention discloses a method for measuring sheet metal deformation based on images, which adopts a multi-axis rotation and lifting structure, a CCD camera, an optical lens, and an image and data processing computer. The images of a sheet metal before and after deformation are shot and stored in the image and data processing computer to form data files; and a forming limit diagram and parameter information are acquired through a bulging test and a tension test respective to form standard data files. The method can store and analyze material performance in various aspects so as to screen spare sheet metals from various aspects.

Description

Method for measuring sheet metal deformation based on image

Technical field

The present invention relates to the measuring technique of engineering structure and material deformation in a kind of photodynamics art of image analysis.

Background technology

The grid strain measurement of plate is the important method of research sheet forming performance, and the scientist who studies sheet forming as far back as states such as eighties of last century U.S.'s sixties just begins to apply it in the practice.Can use the distortion and the strain of displacement sensor, calculating plate for common one directional tensile test.But for the strain of part, and the strain measurement of various piece after the large-scale plate generation plastic yield, common method is then powerless.

Measure for these class methods and can only use coordinate grid method, promptly on the plate that plastic yield does not take place, print the known grid of length in advance, behind sheet metal deformation, analyze plate strain size everywhere by the distortion of measuring grid.Initial research mainly is to adopt tape or common ruler to measure, because the size of mesh opening of distortion rear surface has only the 2-5 millimeter, measuring accuracy is had relatively high expectations, and the error that these methods measure is bigger, developed again afterwards and tool microscope, used till today always.Tool microscope amplifies measured zone, can relatively accurately measure, but for curved surface ground measurement, is difficult to very accurately, and can only measure a grid at every turn, and efficiency of measurement is low, and labour intensity is big.

Recent years, the full-automatic grid measuring system based on computer vision technique successively was developed in some developed countries, such as the ASAME software of the U.S..These measuring systems are measured accurately, and efficient is higher.But price is very expensive, and is not optimized at China's national standard, still lacks purchasing power for common school and general R﹠D institution, so can't be widely used.Domestic some engineering structures and the material deformation measuring technique (Chinese patent also developed, application number 03128736.0, publication number CN1458528A), and this class image measuring device and be not suitable for the strain measurement of the sheet forming performance test under the laboratory condition, can not satisfy the time series Testing requirement, post-processed can not be applied mechanically domestic accordingly, international standard.

Summary of the invention

The present invention seeks to utilize lower cost that the method for the integrated collection of sheet forming experimental data, processing, demonstration, preservation and output of one cover is provided, make the experimenter carry out to standardization the experimental work of sheet forming aspect continuously, draw experimental result with cogency, carry out the comparative analysis of a series of experiments easily, and generation can be by the file of finite element analysis or other software transfer.

The present invention adopts following technical scheme for achieving the above object:

The present invention is based on the method for measuring sheet metal deformation of image, adopt multiaxis rotation and lifting structure, CCD shooting and optical lens and image and data handling machine, wherein CCD shooting and optical lens are arranged on multiaxis rotation and the lifting structure, CCD shooting and the data output end map interlinking picture of optical lens and the data input pin of data handling machine is characterized in that described measurement disposal route may further comprise the steps:

The first step: print in panel surface and to meet GB GB/T 15825.8---1995 or the grid of ISO12004 standard;

Second step: take plate by CCD shooting and optical lens and be out of shape forward and backward image and depositing image in and data handling machine;

The 3rd step: adopt image and data handling machine (3) comparison plate the forward and backward surface mesh pattern of distortion promptly described data file of second step go forward side by side rower fixed after, the full-size(d) information of panel surface of reducing also forms data file:

A) bulging test

With described data file of the 3rd step according to GB GB/T 15825.8---1995 or the ISO12004 standard carry out process of fitting treatment and obtain standard compliant forming limit diagram being out of shape back panel surface full-size(d) information;

B) stretching experiment

Adopt image and data handling machine (3) that described data file of the 3rd step is handled the parameter information that obtains view data through regression Calculation;

The 4th step: with the 3rd step a), b) parameter information of described forming limit diagram and view data deposits in the database, saves as the normal data file.

Beneficial effect of the present invention:

1, with respect to engineering structure and material deformation measuring technique, this patent can carry out more fully data processing, and strain measurement is science more.

2, the present invention can realize the Dynamic and Non-contact measurement in the stretching experiment process, thereby obtains the time series data of sheet metal deformation, draws the deformation path of plate each point, understands the influence of each experiment parameter to experimental result.

3, the present invention has realized standardization to a great extent, and automated job has reduced influence artificial, subjective factor, has improved the comparability of experimental result.

4, the present invention can store the many-sided performance of material, analyzes, and is convenient to from every side alternative plate be screened, thereby selection is had very high directive significance.

Description of drawings

Fig. 1 is a calculation procedure process flow diagram of the present invention;

Fig. 2 is a structural representation of the present invention;

Fig. 3 triangle distortion synoptic diagram.(triangle (a), distortion Vee formation shape (b) before the distortion);

Fig. 4 strain Mohr Circle of Plastic algorithm synoptic diagram (E _MinBe minimum principal strain, E _MaxBe maximum principal strain, E _AverageBe principal strain mean value, E ₁₁X is to strain, E ₂₂Y is to strain, E ₁₂Xy is to strain);

Fig. 5 weighted mean and local average algorithm synoptic diagram ((a) weighted mean, (b) local average.Numeral is each sub-region right value among the figure).

Embodiment

Be elaborated below in conjunction with the technical scheme of accompanying drawing to invention:

As shown in Figure 1 and Figure 2, method for measuring sheet metal deformation based on image, adopt multiaxis rotation and lifting structure 1, CCD shooting and optical lens 2 and image and data handling machine 3, wherein CCD shooting and optical lens 2 are arranged on multiaxis rotation and the lifting structure 1, CCD shooting and the data output end map interlinking picture of optical lens 2 and the data input pin of data handling machine 3 is characterized in that described measurement disposal route may further comprise the steps:

The first step: print in panel surface and to meet GB GB/T 15825.8---1995 or the grid of ISO12004 standard;

Second step: take plate by CCD shooting and optical lens and be out of shape forward and backward image and depositing image in and data handling machine 3;

The 3rd step: adopt image and data handling machine (3) comparison plate the forward and backward surface mesh pattern of distortion promptly described data file of second step go forward side by side rower fixed after, the full-size(d) information of panel surface of reducing also forms data file:

A) bulging test

With described data file of the 3rd step according to GB GB/T 15825.8---1995 or the ISO12004 standard carry out process of fitting treatment and obtain standard compliant forming limit diagram being out of shape back panel surface full-size(d) information;

B) stretching experiment

Adopt image and data handling machine (3) that described data file of the 3rd step is handled the parameter information that obtains view data through regression Calculation: the strain hardening COEFFICIENT K, strain hardening index n,, yield tensile ratio is yield strength ratio yield limit: σ ₀/ σ, contents such as thick anisotropy index r value;

The 4th step: with the 3rd step a), b) parameter information of described forming limit diagram and view data deposits in the database, saves as the normal data file.

Above-mentioned image acquisition and processing computing machine 3 possesses:

Data acquisition function: read in the normal data file that the stretching experiment machine generates, or the grid image of panel surface before and after the stretching, bulging;

Data processing function: by GB the normal data file that cupping machine generates is analyzed, handled, obtain material strain coefficient of intensification K, strain hardening index n.By the algorithm that among GB GB/T 15825.8-1995 or the ISO12004 match is carried out at the dependent variable strong point to stretch, the plate image is handled before and after the bulging, analyzes the thick anisotropy index of plate r value, data such as the forming property limit;

Data presentation, hold function: the resulting result of video data processing unit, and it is saved in the database;

Data output function: result is generated the normal data file call or printout in order to other analysis software.

If pass through the deformation information of image measurement plate, before experiment, just need print standard compliant grid in panel surface.For stretching experiment, need to take a series of images in the whole deformation process of record plate.And the bulging experiment, only need after experiment, to utilize the designed multiaxis of this invention to rotate and lifting structure 1 (Fig. 2), wherein multiaxis rotation and two hinges of lifting structure are realized the rotation around two axles of CCD shooting and optical lens 2 respectively, pinion and rack realizes that CCD shooting and optical lens move up and down vertically, like this behind sheet forming, through overregulating CCD shooting and optical lens, just can try one's best and take along distortion surface of the work normal direction, guarantee to take precision.Image can be handled after demarcating.Concrete strain solution procedure is as follows:

According to GB GB/T 15825.8---1995 described methods are printed grid, thereby the ultimate strain circle that can directly measure plate is afterwards drawn the ultimate strain curve.

If select another kind of mode, no matter print cylinder lattice or square grid in advance, all side's of being based on grids are calculated in strain.For Dan Yuan and staggered cylinder lattice, square node forms by connecting each round heart, and each center of circle becomes a node.The initial mesh size is printed according to the ISO12004 standard.

Calculate for the strain of node, near each node square is divided into two triangles.Each triangle is calculated Lagrange strain, thereby obtain each leg-of-mutton logarithmic strain and should change direction.The node strain is exactly that these strains obtain by weighted mean or local average method (being selected by the user).

Fig. 3 has shown the triangle (b) after undeformed triangle (a) and the distortion.Undeformed triangle aligns with cartesian coordinate system, and the triangle after the distortion is arbitrarily located in three dimensions.If 1 ₀Equal initial mesh length, a is the new length after the not deforming triangle right-angle side distortion, and b is the new length of another right-angle side, and c is the new length of hypotenuse.Then being out of shape each limit of Vee formation shape can be tried to achieve by following formula:

${\stackrel{\&RightArrow;}{v}}_1=(x_2-x_1,y_2-{\mathrm{<figure-callout\; id="1"\; label="y"\; filenames="A200910030254E00111.png,A200910030254E00122.png"\; state="\{\{state\}\}">y</figure-callout>}}_1,z_2-z_1)$ $a=\left|{\stackrel{\&RightArrow;}{v}}_1\right|$

${\stackrel{\&RightArrow;}{v}}_2=(x_3-x_1,y_3-{\mathrm{<figure-callout\; id="1"\; label="y"\; filenames="A200910030254E00111.png,A200910030254E00122.png"\; state="\{\{state\}\}">y</figure-callout>}}_1,z_3-z_1)$ $b=\left|{\stackrel{\&RightArrow;}{v}}_2\right|$

${\stackrel{\&RightArrow;}{v}}_3={\stackrel{\&RightArrow;}{v}}_2-{\stackrel{\&RightArrow;}{v}}_1=(x_2-x_1,y_2-{\mathrm{<figure-callout\; id="1"\; label="y"\; filenames="A200910030254E00111.png,A200910030254E00122.png"\; state="\{\{state\}\}">y</figure-callout>}}_1,z_2-z_1)$ ? $c=\left|{\stackrel{\&RightArrow;}{v}}_3\right|$

By v ₁, v ₂And v ₃Can calculate each component that Cauchy-Green is out of shape tensor C:

$C_{11}=\frac{{\left|{\stackrel{\&RightArrow;}{v}}_1\right|}^2}{{\mathrm{<figure-callout\; id="0"\; label="l"\; filenames="A200910030254E00122.png"\; state="\{\{state\}\}">l</figure-callout>}}_0^2}=\frac{{(x_2-x_1)}^2+{(y_2-y_1)}^2+{(z_2-z_1)}^2}{{\mathrm{<figure-callout\; id="0"\; label="l"\; filenames="A200910030254E00122.png"\; state="\{\{state\}\}">l</figure-callout>}}_0^2}=\frac{a^2}{{\mathrm{<figure-callout\; id="0"\; label="l"\; filenames="A200910030254E00122.png"\; state="\{\{state\}\}">l</figure-callout>}}_0^2}$

$C_{22}=\frac{{\left|{\stackrel{\&RightArrow;}{v}}_2\right|}^2}{{\mathrm{<figure-callout\; id="0"\; label="l"\; filenames="A200910030254E00122.png"\; state="\{\{state\}\}">l</figure-callout>}}_0^2}=\frac{{(x_3-x_1)}^2+{(y_3-y_1)}^2+{(z_3-z_1)}^2}{{\mathrm{<figure-callout\; id="0"\; label="l"\; filenames="A200910030254E00122.png"\; state="\{\{state\}\}">l</figure-callout>}}_0^2}=\frac{b^2}{{\mathrm{<figure-callout\; id="0"\; label="l"\; filenames="A200910030254E00122.png"\; state="\{\{state\}\}">l</figure-callout>}}_0^2}$

$C_{12}=\frac{{\stackrel{\&RightArrow;}{v}}_1\&CenterDot;{\stackrel{\&RightArrow;}{v}}_2}{{\mathrm{<figure-callout\; id="0"\; label="l"\; filenames="A200910030254E00122.png"\; state="\{\{state\}\}">l</figure-callout>}}_0^2}=\frac{(x_2-x_1)(x_3-x_1)+(y_2-y_1)(y_3-y_1)+(z_2-z_1)(z_3-z_1)}{{\mathrm{<figure-callout\; id="0"\; label="l"\; filenames="A200910030254E00122.png"\; state="\{\{state\}\}">l</figure-callout>}}_0^2}=\frac{a^2+b^2-{\mathrm{<figure-callout\; id="2"\; label="c"\; filenames="A200910030254E00112.png,A200910030254E00121.png"\; state="\{\{state\}\}">c</figure-callout>}}^2}{2{\mathrm{<figure-callout\; id="0"\; label="l"\; filenames="A200910030254E00122.png"\; state="\{\{state\}\}">l</figure-callout>}}_0^2}$

Can calculate Lagrange strain E thus

C＝I+2E

Wherein I is a unit matrix

$E_{11}=\frac{C_{11}-1}{2}=\frac{a^2}{2{\mathrm{<figure-callout\; id="0"\; label="l"\; filenames="A200910030254E00122.png"\; state="\{\{state\}\}">l</figure-callout>}}_0^2}-\frac{1}{2}$ X is to strain

$E_{22}=\frac{C_{22}-1}{2}=\frac{b^2}{2{\mathrm{<figure-callout\; id="0"\; label="l"\; filenames="A200910030254E00122.png"\; state="\{\{state\}\}">l</figure-callout>}}_0^2}-\frac{1}{2}$ Y is to strain

$E_{12}=\frac{C_{12}}{2}=\frac{a^2+b^2-{\mathrm{<figure-callout\; id="2"\; label="c"\; filenames="A200910030254E00112.png,A200910030254E00121.png"\; state="\{\{state\}\}">c</figure-callout>}}^2}{4{\mathrm{<figure-callout\; id="0"\; label="l"\; filenames="A200910030254E00122.png"\; state="\{\{state\}\}">l</figure-callout>}}_0^2}$ Xy is to strain

At this moment, can try to achieve by Mohr Circle of Plastic as the true principal strain of Fig. 4.Wherein A point and B point are respectively maximum principal strain, minimum principal strain.

The principal strain directions angle is:

$\mathrm{\&theta;}=\frac{1}{2}{\tan }^{-1}\left(\frac{{2E}_{12}}{E_{11}-E_{22}}\right)$

Fig. 5 has shown one 2 * 2 square node.Each grid is divided into two triangles, and numeral has shown for Centroid, each peripheral leg-of-mutton weight.The strain of Centroid is to obtain by these leg-of-mutton Lagrange strain are weighted on average.And the substantive difference of weighting or local average method just is to choose leg-of-mutton weight difference.

After trying to achieve the node strain, can carry out match to the strain of material surface according to the described method of ISO12004 standard, thereby try to achieve the ultimate strain of material.

Claims (1)

1, a kind of method for measuring sheet metal deformation based on image, adopt multiaxis rotation and lifting structure (1), CCD shooting and optical lens (2) and image and data handling machine (3), wherein CCD shooting and optical lens (2) are arranged on multiaxis rotation and the lifting structure (1), the data output end map interlinking of CCD shooting and optical lens (2) looks like to connect the data input pin of data handling machine (3), it is characterized in that described measurement disposal route may further comprise the steps:

The first step: print in panel surface and to meet GB GB/T 15825.8---1995 or the grid of IS012004 standard;

Second step: take plate by CCD shooting and optical lens and be out of shape forward and backward image and depositing image in and data handling machine (3);

The 3rd step: adopt image and data handling machine (3) comparison plate the forward and backward surface mesh pattern of distortion promptly described data file of second step go forward side by side rower fixed after, the full-size(d) information of panel surface of reducing also forms data file:

A) bulging test

With described data file of the 3rd step according to GB GB/T15825.8---1995 or the ISO12004 standard carry out process of fitting treatment and obtain standard compliant forming limit diagram being out of shape back panel surface full-size(d) information;

B) stretching experiment

Adopt image and data handling machine (3) that described data file of the 3rd step is handled the parameter information that obtains view data through regression Calculation;

The 4th step: with the 3rd step a), b) parameter information of described forming limit diagram and view data deposits in the database, saves as the normal data file.

Images