CN109870354B - Automatic measurement method for elongation after uniaxial tension fracture of metal round bar sample - Google Patents
Automatic measurement method for elongation after uniaxial tension fracture of metal round bar sample Download PDFInfo
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- CN109870354B CN109870354B CN201910052963.9A CN201910052963A CN109870354B CN 109870354 B CN109870354 B CN 109870354B CN 201910052963 A CN201910052963 A CN 201910052963A CN 109870354 B CN109870354 B CN 109870354B
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Abstract
The invention discloses an automatic measurement method for the uniaxial tensile elongation of a round bar sample, belonging to the technical field of metal material mechanical property test. The method accurately deducts the elastic part, and automatically implements a displacement method without identifying the fracture position in a gauge length range, thereby accurately obtaining the elongation after fracture. Compared with the existing manual measurement technology, the method saves complicated measurement links such as marking and fixing the broken sample, improves the measurement precision, and has important significance for testing the mechanical property of the metal material.
Description
Technical Field
The invention relates to a mechanical property test of a metal material, in particular to an automatic elongation measurement method after uniaxial tensile fracture of a metal round bar sample.
Background
Among the mechanical properties of metal materials, the elongation after fracture is an important index reflecting the plasticity of the metal materials, and the larger the value of the elongation after fracture is, the better the plasticity of the metal materials is. The elongation after fracture is mainly measured in two modes, namely manual measurement and automatic measurement. GB/T228.1-2010 specifies a method for measuring elongation after fracture, and the manual measuring method comprises the following steps: carefully matching the fracture parts of the tensile sample together to ensure that the axes are in the same straight line and ensuring that the fracture part of the sample is properly contacted, measuring the post-fracture gauge length l of the sampleuAfter breaking, mark distance luAnd original gauge length l0Substituting the obtained product into the following formula to calculate the elongation A after fracture,
A＝(lu-l0)/l0×100％
for manual measurement, marking of original gauge length and measuring of gauge length after fracture are particularly important. Generally, a method of manually marking a mark is adopted, the method has low working efficiency, and errors of different degrees exist in the operation process of personnel, so that the measurement result of the elongation after fracture is directly influenced. The fracture of the tensile sample needs to be butted when the gauge length after fracture is measured, and the fracture is difficult to be butted accurately because the fracture can have the phenomena of slag falling, block falling and the like. Even if the pressing force requirements at the time of docking are followed by astm e8-16a, the measurement error is difficult to avoid. If the fracture position is not at the middle of the sample gauge length, the measurement is carried out by using a shift method, which is more troublesome.
The automatic measurement adopts an extensometer with the gauge length equal to the original gauge length of the sample, the extensometer automatically measures the total elongation of the sample at the breaking point, and the elastic part is deducted to obtain the elongation delta l after breaking, namely (l)u-l0) And further the elongation after break A is obtained. Automatic measurement methods are simple and feasible, but extensometers cannot automatically identify the fracture location of a sample. In the actual test process, the fracture position of the test sample is mostly not at the extensometer gauge length leThe automatic measurement cannot be corrected like the manual measurement by using a shift method, and the measured elongation Δ l is smaller than the manual measurement. Meanwhile, since the test piece is severely necked at the time of breakage, if the elastic deformation is calculated in accordance with the uniform deformation also at the time of deducting the elastic portion, the deducted elastic portion is inaccurate. For the above two reasons, the automatic measurement of the elongation after fracture has a large error although it is simple and feasible, and the manual measurement is more in practical application.
Disclosure of Invention
Aiming at the two problems of the traditional automatic measuring method for the elongation after uniaxial tension fracture of the round bar sample, the invention aims to establish the automatic measuring method for the elongation after uniaxial tension fracture of the round bar sample, which can accurately deduct an elastic part and automatically implement a displacement method without identifying the fracture position in a gauge length range, thereby obtaining an accurate value of the elongation after fracture. On the premise of the known elastic modulus and Poisson ratio of the material, the invention only needs to measure and record the gauge length elongation and the load value at the tensile breaking moment of the round bar sample, and simultaneously adopts an optical method to collect the outline curve of the broken round bar sample, and obtains the uniaxial tensile breaking elongation of the round bar sample through elastic deformation analysis and calculation.
The technical scheme adopted by the invention comprises the following specific steps:
(1) carrying out uniaxial tensile test on a metal round bar sample, wherein the original gauge length is l0Original gauge length radius of a0Measuring and recording the moment of onset of tensile failure FNAnd gauge length extension dlNCollecting the outline information of the broken longer half of the test bar along the axis direction by an optical method, and obtaining the coordinates G of each point of the outline curve through image processingk(xk,yk) Where k is 0 to M, 0 and M correspond to the fracture point of the specimen in necking and a point near the transition of the circular arc in the parallel length range, respectively, and the fracture point is determined by ykThe smallest value being based on the origin of the coordinate, x, of the axis of the corresponding necking breaking point0＝0；
(2) Elastic correction is carried out on the coordinates of the profile curve of the broken sample, and if the elastic modulus E and Poisson ratio lambda of the metal material are known, the coordinates of each point after correction
Is shown as
Wherein
Reserve all
And (number T +1) and will
Is modified to0+dlN) And/2, corresponding to the seat of the gauge length point at the moment of fractureSign board
Can be expressed as
(3) Based on the formulas (1) and (2), each point including the elastic portion is obtained by solving the equation set
And
the value is obtained.
Corresponding to x minus elastic partTThe value can be calculated by
In view of the symmetric distribution of the elongation of the sample based on the fracture position as the center by the displacement method, the gauge length l of the sample round rod sample after uniaxial tension fractureu＝2·xTAnd finally, calculating and obtaining the elongation after fracture of the metal round bar sample according to the following formula.
A＝(lu-l0)/l0×100％ (4)
The invention has the beneficial effects that:
1) by adopting the scheme of the invention, the elongation after fracture can be automatically calculated only by measuring and recording the gauge length elongation and the load value of the round bar sample at the fracture moment and extracting the outer contour curve of the test bar after fracture, the elastic part of the sample with uneven deformation is deducted, and the same effect of a displacement method can be achieved without judging the fracture position. Compared with the existing manual measurement technology, the complicated measurement links such as marking and fixing the broken sample are omitted, and the measurement time and the measurement cost are saved;
2) the invention avoids excessive manual measurement error due to adopting the data of the extensometer and the optical measurement, has high calculation precision, is easy to realize programming in the calculation process and has operability.
Drawings
FIG. 1 shows a photograph after uniaxial tension fracture and coordinate information of an outer contour curve.
FIG. 2 is a model of elongation calculation after fracture of a round bar sample.
Detailed Description
The invention will be further explained with reference to the following specific examples and the accompanying drawings.
(1) Carrying out uniaxial tensile test on a low-carbon steel round bar sample, wherein the original gauge length is l050mm, original gauge length radius is a0Measuring and recording the load F at the moment of onset of tensile failure, 5mmN25320N and gauge length extension dlNCollecting the outer contour information of the half test bar in the axial direction by optical method, and obtaining the coordinates G of each point of the outer contour curve by image processing as shown in FIG. 1k(xk,yk) Where k is 0 to M, 0 and M correspond to the fracture point of the specimen in necking and a point near the transition of the circular arc in the parallel length range, respectively, and the fracture point is determined by ykThe smallest value being based on the origin of the coordinate, x, of the axis of the corresponding necking breaking point0＝0；
(2) As shown in FIG. 2, the coordinates of the outer contour curve of the sample subjected to elastic unloading after fracture are elastically corrected, and if the elastic modulus E and the Poisson ratio lambda of the metal material are known, the coordinates of each point after correction
Is shown as
Wherein
Reserve all
And (number T +1) and will
Is modified to0+dlN) 2, coordinates of the gauge length point corresponding to the fracture moment
Can be expressed as
(3) Based on the formulas (1) and (2), each point including the elastic portion is obtained by solving the equation set
And
the value is obtained.
Corresponding to x minus elastic partTThe value can be calculated by
Calculated, xT29.253 mm. In view of the symmetric distribution of the elongation of the sample and the breaking position as the center based on the displacement method, the gauge length l of the round bar sample after uniaxial stretching breakingu＝2·xT58.506mm ≈ 58.5mm, finally according to the following formula
A＝(lu-l0)/l0×100％ (4)
And calculating to obtain the elongation A of the round metal rod sample after fracture to be 17.0 percent.
Claims (1)
1. The automatic measurement method for the elongation after fracture of the uniaxial tensile test of the metal round bar sample is characterized by comprising the following specific steps of:
(1) carrying out uniaxial tensile test on a metal round bar sample, wherein the original gauge length is l0Original gauge length radius of a0Measuring and recording the moment of onset of tensile failure FNAnd gauge length extension dlNCollecting the outline information of the broken longer half of the test bar along the axis direction by an optical method, and obtaining the coordinates G of each point of the outline curve through image processingk(xk,yk) Where k is 0 to M, 0 and M correspond to the fracture point of the specimen in necking and a point near the transition of the circular arc in the parallel length range, respectively, and the fracture point is determined by ykThe smallest value being based on the origin of the coordinate, x, of the axis of the corresponding necking breaking point0＝0；
(2) Elastic correction is carried out on the coordinates of the profile curve of the broken sample, and if the elastic modulus E and Poisson ratio lambda of the metal material are known, the coordinates of each point after correction
Is shown as
Wherein
Reserve all
Is T +1, and will
Is modified to0+dlN) 2, coordinates of the gauge length point corresponding to the fracture moment
Can be expressed as
Based on the formulas (1) and (2), each point including the elastic portion is obtained by solving the equation set
And
a value;
In view of the symmetric distribution of the elongation of the sample based on the fracture position as the center by the displacement method, the gauge length l of the sample round rod sample after uniaxial tension fractureu＝2·xT；
And finally, calculating and obtaining the elongation of the round metal rod sample after fracture according to the following formula:
A＝(lu-l0)/l0×100％。
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| CN113310437B (en) * | 2021-05-28 | 2023-05-16 | 广东韶钢松山股份有限公司 | Method and device for automatically measuring wire rod area shrinkage |
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