CN102944559B - Vision measurement method for anisotropic performance parameters in sheet forming - Google Patents
Vision measurement method for anisotropic performance parameters in sheet forming Download PDFInfo
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Abstract
The invention discloses a vision measurement method for anisotropic performance parameters in sheet forming, belonging to the field of machining methods. The vision measurement method comprises the following steps of: (1) sample preparation; (2) camera calibration; (3) image acquisition; (4) speckle strain calculation; (5) selection of deformation state; (6) regression analysis processing; and (7) calculation of anisotropic performance parameters. The vision measurement method disclosed by the invention has the beneficial effects that the strain data of sheet forming can be measured in a high-efficiency manner so as to calculate the anisotropic performance parameters, and has the characteristics of convenience in measurement operation, high automation degree, accurate and reliable measurement result and non-contact measurement.
Description
Technical field
The invention belongs to machining process field, relate to a kind of measuring method of sheet forming anisotropic properties parameter.
Background technology
Plastic strain ratio
rmean the important indicator because of the leading anisotropic properties of texture, sheet metal sample is stretched to while producing uniform plastic deformation vertically, the ratio of the logarithmic strain of sample marking distance insied width direction and the logarithmic strain of thickness direction, it is defined as follows:
（1）
Wherein:
a 0 ---the thickness of the initial gauge length of sample;
b 0 ---the width of the initial gauge length of sample;
l 0 ---the length of the initial gauge length of sample.
According to become 0 °, 45 ° and 90 ° of three plastic strain ratios that direction records in sheet metal plane with rolling direction
rvalue weighted mean value, can obtain weighted mean plastic strain ratio (
), that is:
（2）
According to become the plastic strain ratio of 0 ° and 90 ° direction in sheet metal plane with main rolling direction
rthe difference of the arithmetic mean value of value and the Lankford r value of 45 ° of directions can obtain degree of planer anisotropy of the plastic strain ratio (
Δ r), that is:
（3）
Conventional plastic strain ratio
rto evaluate plate anisotropic properties, at aspects such as cold-rolled products research and development, quality of production control and industrial selections, be used widely.
The assay method of plate anisotropic properties parameter is mainly determined by experiment at present, under laboratory condition, the experimental facilities of employing standard, under the effect of uniaxial tension power, tensile sample, to the uniform plastic deformation stage, obtains the initial gauge length of different orientation sample by the mode of hand dipping or measurement automatically
l 0 and width
b 0 , the gauge length of regulation under strain level
land width
b, finally measured value substitution formula (1), (2) and (3) are calculated
r,
with
Δ rvalue.Experimental technique can obtain more accurate plastic strain ratio, but due to the repeated measurement sample of needs, this method is obtained plastic strain ratio
rcumbersome, there is following shortcoming: the workload of (1) hand dipping is large, and precision is lower; (2) yield deformation of sample in axial loading procedure, the transient state inertial effect of switching initiation to extensometer system initialization late effect and speed in length and breadth can cause
rthe error of value strain paths feature, affects precision; (3) later experiments data processing complex, efficiency is not high.
Summary of the invention
The object of the invention is to: a kind of vision measuring method of new plate anisotropic properties parameter is provided, can have measured in real time, accurately, efficiently plate plastic strain ratio
r, weighted mean plastic strain ratio
and degree of planer anisotropy of the plastic strain ratio
Δ r, to describe the anisotropic properties of plate.
The object of the invention realizes by following technical proposals:
A vision measuring method for sheet forming anisotropic properties parameter, comprises the following steps successively:
The first step, sample is prepared: plate blank is cut into the sample of standard compliant size and geometric configuration requirement, and in the specimen surface region of required measurement spraying speckle pattern;
Second step, camera calibration: take and obtain image from different azimuth, utilize image to carry out camera calibration calculating, obtain two cameras position relationship accurately by demarcation, described position relationship comprises external parameter, inner parameter and the lens distortion parameter of camera;
The 3rd step, obtains image: according to standard, clamp the sample that has been ready to speckle spray treatment, start Material Testing Machine sample is carried out to stretcher strain loading, and control two camera synchronization and take, to obtain the image sequence of tested sample under deformation state;
The 4th step, speckle strain is calculated: the whole Sample Images that obtain are carried out to the calculating of speckle three dimensional strain, obtain the strain data of different distortion state specimen surface, described strain data comprises average logarithmic strain, length direction logarithmic strain and the Width logarithmic strain of sample;
The 5th step, selects deformation state: according to stress-strain curve, choose sample and take that to meet the average logarithmic strain of calculating in its gauge length region more than 10% be homogeneous deformation steady section, as the range of strain that returns interval calculating;
The 6th step, regretional analysis is processed: the length direction logarithmic strain of the deformation state of picking out in previous step and Width logarithmic strain are processed according to the method for regretional analysis, the length direction logarithmic strain obtaining and Width logarithmic strain are respectively
xaxle with
yaxle, makes intervals linear and returns the slope coefficient obtaining
m;
The 7th step, calculates anisotropic properties parameter: previous step is obtained
mthe following formula of value substitution:
, obtain the plastic strain ratio of this sample
rvalue, at the plastic strain ratio that obtains different orientation sample
rafter value, substitution correlation computations formula, draws weighted mean plastic strain ratio
and degree of planer anisotropy of the plastic strain ratio
Δ r, obtained the anisotropic properties parameter of plate.
As optimal way, in the described first step, the sample of preparation need meet following requirement:
A) the sample edge flawless of preparing, surface is without scratching;
B) specimen surface is smooth: in sample marking distance, the difference of the one-tenth-value thickness 1/10 at any two places should not be greater than 0.01 mm; When thickness is less than 1.0 mm, should be not more than 1% of nominal thickness;
C) the original gauge length insied width of sample both sides are parallel: breadth extreme and minimum widith should be not more than interior 0.1% of the width mean value of measuring of gauge length;
D) prepare the sample of at least 3 kinds of different orientations, and the sample of every type is no less than 3;
E) speckle particle that is sprayed on specimen surface is answered stochastic distribution;
F) speckle contrast is obvious;
G) speckle is prepared scope and should be greater than measured deformed region.
As optimal way, in described second step, comprise the external parameter of camera, the inner parameter of camera and lens distortion parameter, concrete demarcating steps is as follows:
A) start camera from different perspectives and distance gathers target image;
B) calculate the image coordinate at reference mark on target;
C) adopt Method of Direct Liner Transformation to resolve projection matrix;
D) according to the projection matrix of trying to achieve, solve camera inside and outside parameter, thereby obtain demarcating the initial value of each parameter;
E) utilize light beam adjustment Algorithm to camera calibration, obtain accurate camera inside and outside parameter.
As optimal way, in described the 3rd step, obtain image request:
A) the left and right camera image in each deformation state is the image of taking under synchronization;
B) clear picture that gathers, speckle regions contrast is obviously;
C) camera relative position in left and right does not change in shooting process;
D) camera optical axis in left and right is greater than 30 degree with the angle that will measure deformed region plane;
E) institute's employing camera frame frequency is 10 frames/s;
F) testing machine chuck translational speed is no more than 50%
l 0 mm/s.
As optimal way, in described the 4th step, concrete calculation procedure is:
A) choose a deformation state image as base state, the gauge length region that selection will be calculated in the left camera image of base state, and the search forms size in zoning is set;
B), in the selected zoning of the left camera image in base state, choose one or more search forms as the starting point of speckle coupling;
C) use speckle related algorithm and relevant search algorithm to carry out speckle coupling;
D) the corresponding speckle in the camera image of left and right is carried out to three-dimensional reconstruction, obtain the three-dimensional spatial information of deformed region;
E) according to three-dimensional reconstruction result, by the strain at adjacent some calculating three-dimensional point place around of each three-dimensional point.
As optimal way, in described the 5th step, described average true range of strain is 10%-20%.
As optimal way, described orientation, comprises and becomes 0 °, 45 ° and 90 ° with rolling direction.
Beneficial effect of the present invention:
(1), because this method is simple to operate, be convenient to use under experiment condition.
(2) because digital speckle pattern spraying work in this method is simple, strain is calculated can full automation, so measuring period is shorter, efficiency is higher.
(3) because this method is calculated specimen surface strain by speckle image, and by Interval Regression method, calculate the anisotropic properties parameter of plate, carry out formula again calculate and compare with traditional measurement gauge length and width dimensions, precision is higher.
(4) because adopting extensometer, this method do not measure, so can not cause because of the transient state inertial effect of extensometer system initialization late effect and speed switching initiation in measuring process
rthe error of value strain paths feature, affects precision.
(5) what use due to this method is the mode of optical measurement, so be a kind of non-contact measurement method.
Accompanying drawing explanation
Fig. 1 is the process flow diagram of concrete operation step of the present invention;
Fig. 2 is the inventive method experimental provision sketch;
Fig. 3 is the sample that speckle spray treatment is prepared and passed through to the inventive method;
Fig. 4 is camera calibration process flow diagram;
Fig. 5 is speckle strain calculation flow chart;
Fig. 6 is the true stress and strain curve of embodiment 1;
Fig. 7 is length direction logarithmic strain and the Width logarithmic strain straight line that the Interval Regression matching of embodiment 1 obtains;
Fig. 8 is the true stress and strain curve of embodiment 2;
Fig. 9 is length direction logarithmic strain and the Width logarithmic strain straight line that the Interval Regression matching of embodiment 2 obtains;
Figure 10 is the true stress and strain curve of embodiment 3;
Figure 11 is length direction logarithmic strain and the Width logarithmic strain straight line that the Interval Regression matching of embodiment 3 obtains;
Figure 12 is the steel test specimen speckle image that adopts vision measuring method to obtain in demonstration test;
Figure 13 is the steel test specimen surface strain field that adopts vision measuring method to obtain in demonstration test;
Figure 14 is the measurement result contrast of vision measuring method and extensometer measuring method.
Embodiment
Following non-limiting examples is used for illustrating the present invention.
embodiment 1:
The present invention proposes a kind of plate anisotropic properties parametric measurement method, and concrete operation step as shown in Figure 1.The hardware configuration of the experimental provision adopting as shown in Figure 2, is mainly comprised of 1 material stretch test machine 1,2,2 CCD cameras of plate sample, 4,1 controller 5 of 3,2 LED illumination lamps and 1 computing machine 6 etc.
The first step, sample is prepared, and plate blank is cut into the sample (GB/T5027-1999) that meets standard size and geometric configuration requirement, and one group of experimental sample being formed by certain complex laminate material cutting is as shown in Figure 3.In the specimen surface region of required measurement, use the mode of manually spraying paint to make speckle pattern.Plate sample prepare to require: a) should guarantee the sample edge flawless of preparation, the surface defects such as scuffing that do not have; B) require specimen surface smooth, unless otherwise prescribed, thickness should be product through thickness, but in sample marking distance, the difference of the one-tenth-value thickness 1/10 at any two places should not be greater than 0.01 mm; When thickness is less than 1.0 mm, should be not more than 1% of nominal thickness; C) the original gauge length insied width of sample both sides nonparallelism should be as far as possible little, and breadth extreme and minimum widith should be not more than interior 0.1% of the width mean value of measuring of gauge length; D) prepare the sample of 3 kinds of different orientations (becoming 0 °, 45 ° and 90 ° with rolling direction), and the sample of every type is no less than 3; E) speckle particle that is sprayed on specimen surface is answered stochastic distribution; F) speckle contrast should be obvious; G) speckle is prepared scope and should be greater than measured deformed region.
Second step, camera calibration, takes and obtains image from different azimuth, utilizes image to carry out camera calibration calculating, by demarcation, obtains two cameras position relationship accurately, comprises the external parameter of camera, the inner parameter of camera and lens distortion parameter.Concrete demarcating steps is (as shown in Figure 4) as follows: a) start camera from different perspectives and distance collection target image; B) calculate the image coordinate at reference mark on target; C) adopt Method of Direct Liner Transformation to resolve projection matrix; D) according to the projection matrix of trying to achieve, solve camera inside and outside parameter, thereby obtain demarcating the initial value of each parameter; E) utilize light beam adjustment Algorithm to camera calibration, obtain accurate camera inside and outside parameter.
The 3rd step, obtain image, for all sizes of preparing and the plate sample of geometric configuration, starting characteristics test machine (material stretch test machine), sample is out of shape to loading, and utilizes computer control two camera synchronization to take to obtain plate sample at the image sequence of deformation state.Obtain image request: a) the left and right camera image in each deformation state should be the image of taking under synchronization; B) the image that gathers should be clear, speckle regions contrast is obviously; C) camera relative position in left and right can not change in shooting process; D) camera optical axis in left and right should be greater than 30 degree with the angle that will measure deformed region plane; E) institute's employing camera frame frequency is 10 frames/s; F) testing machine chuck translational speed should not surpass 50%
l 0 mm/s.
The 4th step, speckle strain is calculated, and the whole Sample Images that obtain are carried out to the calculating of speckle three dimensional strain, obtains average logarithmic strain, length direction logarithmic strain and the Width logarithmic strain of different distortion state specimen surface.Concrete calculation procedure (as shown in Figure 5) is: a) choose a deformation state image as base state, and the gauge length region that selection will be calculated in the left camera image of base state, and the search forms size in zoning is set; B), in the selected zoning of the left camera image in base state, choose one or more search forms as the starting point of speckle coupling; C) use speckle related algorithm and relevant search algorithm to carry out speckle coupling; D) the corresponding speckle in the camera image of left and right is carried out to three-dimensional reconstruction, obtain the three-dimensional spatial information of deformed region; E) according to three-dimensional reconstruction result, by the strain at adjacent some calculating three-dimensional point place around of each three-dimensional point.
The 5th step, according to true stress and strain curve (as shown in Figure 6), chooses sample homogeneous deformation steady section (getting deformation extent at 10%-20%), as returning the range of strain calculating.Check speckle strain result of calculation, select suitable deformation state, meet the average logarithmic strain that calculates in its gauge length region in above-mentioned range of strain.
The 6th step, the length direction logarithmic strain of the deformation state of picking out in previous step and Width logarithmic strain are processed according to the method for regretional analysis, wherein length direction logarithmic strain is as x axle, Width logarithmic strain is as y axle, and the regression curve of setting up by observation, further reject undesirable deformation state, matching is to revise regression curve (as shown in Figure 7) again.According to finally fitting Interval Regression straight line, obtain slope coefficient
m=-0.42753.
the 7th step, in the definition of plastic strain ratio, establish respectively:
Can obtain:
, will
mthe above-mentioned formula of value substitution, obtains moulding of this sample
property strain ratio
r=0.74682.Different orientation (comprising 0 °, 45 ° and 90 °) sample is calculated to its plastic strain ratio
rafter value, according to GB/T 5027-1999, require to bring correlation computations formula into, draw weighted mean plastic strain ratio
and degree of planer anisotropy of the plastic strain ratio
Δ r, obtained the anisotropic properties parameter of plate.
embodiment 2:
In the same manner as in Example 1, the sample material that the present embodiment is used is AA6061(aluminium to the implementation step of the present embodiment), specimen size is as shown in Figure 3.Utilize the true stress―strain curve of the AA6061 sample that the inventive method obtains as shown in Figure 8, the length direction logarithmic strain and the Width logarithmic strain straight line that according to Interval Regression matching as shown in Figure 9, obtain, obtain slope
m=-0.39755, and then calculate
r=0.65989.
embodiment 3:
In the same manner as in Example 1, the sample material that the present embodiment is used is SPCC(cold-rolled low carbon steel to the implementation step of the present embodiment), specimen size is as shown in Figure 3.Utilize the true stress―strain curve of the SPCC sample that the inventive method obtains as shown in figure 10, the length direction logarithmic strain and the Width logarithmic strain straight line that according to Interval Regression matching as shown in figure 11, obtain, obtain slope
m=-0.60718, and then calculate
r=1.54570.
In order to verify the precision of digital speckle image calculation strain, adopt the image collecting device shown in Figure 12 to design and Implement the standard tensile experiment of steel test specimen, and utilize extensometer to carry out precision test and contrast, as shown in figure 13, wherein figure is left is successively decreased by the index value outside interior, as scheme the right side from top to bottom as shown in.Material for test is Q235 steel, and thickness 2mm is cut according to standard processing and obtained by line; Extensometer gage length is 50mm, and strain measurement precision reaches 0.5%, and measurable maximum strain is 50%.
First, to the test specimen processing of spraying paint, form surperficial speckle characteristics.Then, utilize the clamp device of standard material testing machine that the square plate test specimen of customization is fixed, and arrange that on test specimen surface extensometer is used for testing contrast.When test specimen starts to stretch, open camera and carry out image acquisition.Finally, the image gathering is processed and resolved.
Fig. 9 is in steel sheet test specimen stretching experiment process, the mean strain correlation curve of the same deformed region in test specimen surface that utilization this paper method and extensometer record respectively.As seen from Figure 14, the measurement result of two kinds of methods is basically identical.In addition, the strain that the inventive method calculates if take as
coordinate, the strain that the extensometer of take records as
coordinate, can obtain some coordinate points, and these coordinate points of matching can obtain straight line, and equation is:
, from equation, can find out, the relative error of two kinds of methods is approximately less than 0.1 strain percentage value.
Above confirmatory experiment has proved precision and the reliability of measuring method of the present invention on length direction logarithmic strain is calculated, it is consistent due to this measuring method, in length direction logarithmic strain calculating, calculating with Width logarithmic strain the Computing Principle using, therefore can illustrate that the present invention passes through the method that speckle strain calculates and obtains length direction logarithmic strain and Width logarithmic strain, and matching strain result is set up regression curve, and to measure the method for anisotropic properties parameter be reliable and effective.
The foregoing is only preferred embodiment of the present invention, not in order to limit the present invention, all any modifications of doing within the spirit and principles in the present invention, be equal to and replace and improvement etc., within all should being included in protection scope of the present invention.
Claims (6)
1. a vision measuring method for sheet forming anisotropic properties parameter, is characterized in that comprising the following steps successively:
The first step, sample is prepared: plate blank is cut into the sample of standard compliant size and geometric configuration requirement, and in the specimen surface region of required measurement spraying speckle pattern;
Second step, camera calibration: take and obtain image from different azimuth, utilize image to carry out camera calibration calculating, obtain two cameras position relationship accurately by demarcation, described position relationship comprises external parameter, inner parameter and the lens distortion parameter of camera;
The 3rd step, obtains image: according to standard, clamp the sample that has been ready to speckle spray treatment, start Material Testing Machine sample is carried out to stretcher strain loading, and control two camera synchronization and take, to obtain the image sequence of tested sample under deformation state;
The 4th step, speckle strain is calculated: the whole Sample Images that obtain are carried out to the calculating of speckle three dimensional strain, obtain the strain data of different distortion state specimen surface, described strain data comprises average logarithmic strain, length direction logarithmic strain and the Width logarithmic strain of sample;
The 5th step, selects deformation state: according to stress-strain curve, choose sample and take that to meet the average logarithmic strain of calculating in its gauge length region more than 10% be homogeneous deformation steady section, as the range of strain that returns interval calculating;
The 6th step, regretional analysis is processed: the length direction logarithmic strain of the deformation state of picking out in previous step and Width logarithmic strain are processed according to the method for regretional analysis, to obtain length direction logarithmic strain and Width logarithmic strain is respectively
xaxle with
yaxle, makes intervals linear and returns the slope coefficient obtaining
m;
The 7th step, calculates anisotropic properties parameter: previous step is obtained
mthe following formula of value substitution:
, obtain the plastic strain ratio of this sample
rvalue, at the plastic strain ratio that obtains different orientation sample
rafter value, substitution correlation computations formula, draws weighted mean plastic strain ratio
and degree of planer anisotropy of the plastic strain ratio
Δ r, obtained the anisotropic properties parameter of plate;
In described second step, comprise the external parameter of camera, the inner parameter of camera and lens distortion parameter, concrete demarcating steps is as follows:
A) start camera from different perspectives and distance gathers target image;
B) calculate the image coordinate at reference mark on target;
C) adopt Method of Direct Liner Transformation to resolve projection matrix;
D) according to the projection matrix of trying to achieve, solve camera inside and outside parameter, thereby obtain demarcating the initial value of each parameter;
E) utilize light beam adjustment Algorithm to camera calibration, obtain accurate camera inside and outside parameter.
2. the vision measuring method of sheet forming anisotropic properties parameter as claimed in claim 1, is characterized in that: in the described first step, the sample of preparation need meet following requirement:
A) the sample edge flawless of preparing, surface is without scratching;
B) specimen surface is smooth: in sample marking distance, the difference of the one-tenth-value thickness 1/10 at any two places should not be greater than 0.01 mm; When thickness is less than 1.0 mm, should be not more than 1% of nominal thickness;
C) the original gauge length insied width of sample both sides are parallel: breadth extreme and minimum widith should be not more than interior 0.1% of the width mean value of measuring of gauge length;
D) prepare the sample of at least 3 kinds of different orientations, and the sample of every type is no less than 3;
E) speckle particle that is sprayed on specimen surface is answered stochastic distribution;
F) speckle contrast is obvious;
G) speckle is prepared scope and should be greater than measured deformed region.
3. the vision measuring method of sheet forming anisotropic properties parameter as claimed in claim 1, is characterized in that: in described the 3rd step, obtain image request:
A) the left and right camera image in each deformation state is the image of taking under synchronization;
B) clear picture that gathers, speckle regions contrast is obviously;
C) camera relative position in left and right does not change in shooting process;
D) camera optical axis in left and right is greater than 30 degree with the angle that will measure deformed region plane;
E) institute's employing camera frame frequency is 10 frames/s;
F) testing machine chuck translational speed is no more than 50%
l 0 mm/s.
4. the vision measuring method of sheet forming anisotropic properties parameter as claimed in claim 1, is characterized in that: in described the 4th step, concrete calculation procedure is:
A) choose a deformation state image as base state, the gauge length region that selection will be calculated in the left camera image of base state, and the search forms size in zoning is set;
B), in the selected zoning of the left camera image in base state, choose one or more search forms as the starting point of speckle coupling;
C) use speckle related algorithm and relevant search algorithm to carry out speckle coupling;
D) the corresponding speckle in the camera image of left and right is carried out to three-dimensional reconstruction, obtain the three-dimensional spatial information of deformed region;
E) according to three-dimensional reconstruction result, by the strain at adjacent some calculating three-dimensional point place around of each three-dimensional point.
5. the vision measuring method of sheet forming anisotropic properties parameter as claimed in claim 1, is characterized in that: in described the 5th step, described average true range of strain is 10%-20%.
6. the vision measuring method of sheet forming anisotropic properties parameter as claimed in claim 1 or 2, is characterized in that: described orientation, comprises and become 0 °, 45 ° and 90 ° with rolling direction.
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| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN110849727A (en) * | 2019-11-28 | 2020-02-28 | 大连理工大学 | Method for determining anisotropy parameters of pipe |
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