CN115597970A - Strain distribution testing method for copper-containing stainless steel sheet - Google Patents
Strain distribution testing method for copper-containing stainless steel sheet Download PDFInfo
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- 229910001220 stainless steel Inorganic materials 0.000 title claims abstract description 56
- 239000010935 stainless steel Substances 0.000 title claims abstract description 56
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- 230000003247 decreasing effect Effects 0.000 description 3
- 238000006073 displacement reaction Methods 0.000 description 3
- 238000000137 annealing Methods 0.000 description 2
- 229910001566 austenite Inorganic materials 0.000 description 2
- 238000010586 diagram Methods 0.000 description 2
- 238000002360 preparation method Methods 0.000 description 2
- 238000005482 strain hardening Methods 0.000 description 2
- JPVYNHNXODAKFH-UHFFFAOYSA-N Cu2+ Chemical compound [Cu+2] JPVYNHNXODAKFH-UHFFFAOYSA-N 0.000 description 1
- 238000003917 TEM image Methods 0.000 description 1
- 208000027418 Wounds and injury Diseases 0.000 description 1
- 230000009286 beneficial effect Effects 0.000 description 1
- 239000003086 colorant Substances 0.000 description 1
- 229910001431 copper ion Inorganic materials 0.000 description 1
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- 238000004146 energy storage Methods 0.000 description 1
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Abstract
The invention belongs to the technical field of stainless steel mechanical property testing, and particularly relates to a strain distribution testing method of a copper-containing stainless steel sheet. The method comprises three steps: preparing a tensile sample with speckle test points; stretching the stretched sample at different stretching rates, and acquiring and storing images in the stretching process by a three-dimensional motion and deformation measurement system; after stretching is finished, establishing an average strain factor equation of the surface of the copper-containing stainless steel stretching sample at different stretching rates by using strain of speckle points in a deformation area in the acquired three-dimensional deformation image so as to represent the strain distribution condition of the copper-containing stainless steel sheet at different stretching rates. Therefore, the invention can predict the damage evolution of the metal sheet sample through the average strain factor change curve and measure the reliability of the material engineering implementation, thereby further optimizing the process in the aspect of mechanical forming performance.
Description
Technical Field
The invention relates to the technical field of stainless steel mechanical property testing, in particular to a strain distribution testing method of a copper-containing stainless steel sheet.
Background
The copper-containing stainless steel is a novel stainless steel material which is prepared by adding a proper amount of copper element with an antibacterial function into the existing stainless steel and assisting a heat treatment process capable of promoting the uniform precipitation of an antibacterial copper-rich phase, and releases copper ions in a trace manner in the process of contacting with the environment so as to realize the antibacterial function. The material has the advantages of structure and antibacterial function: the stainless steel has the characteristics of high ductility, high toughness and high corrosion resistance, and also has good processability, mechanical property and broad-spectrum antibacterial property. It is widely applied to the fields of kitchen sanitary wares, food processing equipment, medical and sanitary appliances, aerospace and the like.
At present, the research on the copper-containing stainless steel mainly focuses on the aspects of component optimization control, hot brittleness behavior control and precise antibacterial phase control of the copper-containing austenite antibacterial stainless steel. In order to promote the application of the antibacterial stainless steel in the fields of civil use, medical appliances and the like, the mechanical forming performance of the antibacterial stainless steel is still lack of research, and particularly, the research on the relation between the strain distribution and the tensile deformation of the copper-containing stainless steel sheet is not reported.
Disclosure of Invention
In view of the above, the present invention provides a method for testing the strain distribution of a copper-containing stainless steel sheet, and aims to provide a means for studying the mechanical forming performance of the copper-containing stainless steel sheet to understand the relationship between the strain distribution and the tensile deformation of the copper-containing stainless steel sheet, so as to further optimize the process in the mechanical forming performance.
In order to achieve the purpose of the invention, the technical scheme adopted by the invention is as follows:
a strain distribution testing method of a copper-containing stainless steel sheet comprises the following steps:
s1, preparing a tensile sample with speckle test points; the tensile sample is selected from a copper-containing stainless steel sheet with the thickness of 0.8-1.5 mm;
s2, stretching the stretched sample at different stretching rates, and acquiring and storing images in the stretching process through a three-dimensional motion and deformation measurement system;
s3, after stretching is finished, establishing an average strain factor equation of the surface of the copper-containing stainless steel stretching sample at different stretching rates by using strain of speckle points in a strain field in the collected three-dimensional deformation image
To characterize the strain distribution of the copper-containing stainless steel sheet at different drawing rates;
In the formula (I), the compound is shown in the specification,
in order to obtain an average strain factor,
the strain is the longitudinal point strain of the surface of the tensile sample, namely the main strain, M is the number of speckle points randomly selected in a strain field, N is the number of speckle points randomly selected in a large deformation area or a small deformation area, and M is more than N.
Further, the step S3 specifically includes:
s31, distinguishing a large deformation area and a small deformation area in the deformation area by using the strain rate of speckle sample points in the three-dimensional deformation image and further by using the deformation degree;
s32, randomly selecting the strains of M scattered spots in a strain field, randomly selecting the strains of N scattered spots in a large deformation area and a small deformation area, and performing statistical average calculation, wherein M is larger than N;
s33, finally, utilizing the longitudinal point strain of the surface of the tensile sample
Establishing the average strain of the large deformation zone and the small deformation zone on the surface of the copper-containing stainless steel tensile sample under different tensile ratesEquation of variable factor
。
Further, the strain field is defined as the data of the strain change detected in the whole parallel length of the tensile sample, and the middle third area of the strain field is defined as the deformation area.
Further, the large deformation region among the deformation regions is a region where the gauge width necking is more than 15%.
Further, the small deformation zone in the deformation zone is a zone with the gauge width necking less than 15%.
Preferably, the step S1 specifically includes:
s11, preparing a longitudinal tensile sample, wherein the parallel length of the tensile sample is 80mm, the parallel width of the tensile sample is 20mm, the total length is 170mm, and the total width is 30mm;
s12, spraying paint on the surface of the tensile sample to obtain speckle test points, wherein the paint is sprayed with matt black paint or matt white paint.
Preferably, the speckle test points are obtained by spraying the matte black paint on the surface of the sample, and the speckle test points which are good in contrast, uniform in size and convenient to track by an instrument can be obtained by adopting the matte black paint.
Preferably, the step S2 specifically includes:
s21, fixing the tensile sample on a chuck of a testing machine for stretching, wherein the stretching speed is respectively 0.5mm/min, 1mm/min, 5mm/min, 10mm/min, 20mm/min and 30mm/min;
s22, adjusting the distance between the camera and the tensile sample and the position of an illumination light source, and focusing the camera to enable the picture to be clearly imaged;
and S23, acquiring and storing the image in the stretching process by adopting a three-dimensional motion and deformation measurement system, wherein the image acquisition frequency is 1Hz, and the acquired image is a three-dimensional deformation image.
Further, the average strain factors of the large deformation region and the small deformation region are gradually increased in the uniform deformation stage along with the increase of the strain, and are rapidly increased in the local deformation stage. The uniform deformation stage is described herein as being before the yield point of the tensile specimen and the localized deformation stage is described as being after the yield point of the tensile specimen.
More preferably, the average strain factor of the large deformation region is slightly larger than that of the small deformation region.
In addition, on the basis of the strain distribution test method provided above, the strain distribution test method according to the present invention further includes: s4, observing and analyzing macroscopic and microscopic appearances of the sample after the stretching is finished, and specifically comprising the following steps:
s41, the shape of a macroscopic stretching fracture of the stretched sample is in a cup cone shape, the section of the sample is flat and regular, and the fracture is cracked at an angle of 45 degrees with the stretching direction like a knife edge; along with the increase of the speed, the fracture is changed into a uniform compact and shallow dimple from a larger dimple and a tearing edge, the dimple wall is smooth, and the fracture mode is a ductile fracture mode;
s42, observing and analyzing the stretched sample by adopting a TEM (transmission electron microscope), wherein spherical copper-rich precipitated phases are dispersed and distributed in the stretched sample, and the diameter of the sample is 28.5nm.
The invention has the beneficial effects that:
the invention provides a strain distribution testing method of a copper-containing stainless steel sheet, which comprises the steps of collecting and storing images of samples with different stretching rates in a stretching process, carrying out digital image correlation analysis on the images in the stretching process, distinguishing a large deformation area from a small deformation area through the deformation degree, establishing an average strain factor equation of the large deformation area and the small deformation area on the surface of the copper-containing stainless steel sample at different stretching rates, drawing a corresponding average strain factor change curve, wherein the average strain factors of the large deformation area and the small deformation area are slowly increased along with the increase of strain in an uniform deformation stage, are rapidly increased in a local deformation stage, and are larger than the average strain factor of the small deformation area, so that the process in the aspect of mechanical forming performance is further optimized.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below, and it is obvious that the drawings in the following description are only some embodiments of the present invention, and for those skilled in the art, other drawings can be obtained according to these drawings without creative efforts.
FIG. 1 is a graph of the average strain factor change over a large deformation zone as contemplated by the present invention;
FIG. 2 is a plot of the average strain factor change for small deformation zones as contemplated in the present invention;
FIG. 3 is a schematic representation of a tensile specimen according to the present invention;
FIG. 4 is a graph of macroscopic tensile fracture morphology involved in the present invention;
FIG. 5 is a graph of IPF at a draw rate of 30mm/min as referred to in the present invention;
FIG. 6 is a TEM image of a stretching rate of 30mm/min as referred to in the present invention.
Detailed Description
The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
Due to the current research on the mechanical forming performance of the copper-containing stainless steel, a few documents are reported. To this end, the applicant has attempted to provide a research method to reveal the relationship between the strain distribution and the tensile deformation of copper-containing stainless steel sheets, thereby optimizing the process in terms of mechanical forming properties.
Therefore, the invention provides a strain distribution testing method of a copper-containing stainless steel sheet, which mainly comprises the following three steps:
the first step is as follows: tensile specimens with speckle test points were prepared.
In the first step, the specific preparation process is as follows:
(a) Longitudinal tensile specimens were prepared. The tensile test sample is selected from a copper-containing stainless steel sheet with the thickness of 0.8-1.5 mm. More specifically, the thickness of the copper-containing stainless steel sheet is selected from any one of 0.8mm, 0.9mm, 1.0mm, 1.1mm, 1.2mm, 1.3mm, 1.4mm, 1.5mm or a range between any two thereof. On the basis, the parallel length of the selected tensile sample is 80mm, the parallel width is 20mm, the total length is 170mm, and the total width is 30mm.
(b) And spraying paint on the surface of the selected tensile sample to obtain speckle test points. And spraying paint on the surface of the tensile sample, specifically spraying matte black paint or spraying matte white paint. Preferably, the speckle test points are obtained by spraying the matte black paint on the surface of the sample, and the speckle test points which are good in contrast, uniform in size and convenient to track by an instrument can be obtained by adopting the matte black paint.
The second step is as follows: and stretching the prepared stretching sample at different stretching rates, and acquiring and storing images in the stretching process by a three-dimensional motion and deformation measurement system.
In the second step, the specific stretching process includes:
(c) And (3) fixing the tensile sample prepared in the first step on a chuck of a testing machine for stretching, wherein the stretching speed is respectively 0.5mm/min, 1mm/min, 5mm/min, 10mm/min, 20mm/min and 30mm/min.
(d) The distance between the camera and the tensile sample is adjusted, the lens and the sample surface are kept horizontal, the position of the illumination light source is ensured not to cause the exposure phenomenon on the sample surface, the camera is focused, the resolution ratio is adjusted to enable the picture to be clear to image, and the obvious sawtooth pattern at the edge of the strain field can be seen.
(e) And acquiring and storing images in the stretching process by adopting a three-dimensional motion and deformation measurement system, wherein the image acquisition frequency is 1Hz, and the acquired images are three-dimensional deformation images.
In the second step, stored photographs of the morphology at different stretching rates and the morphology before deformation were subjected to DIC method analysis. The DIC analysis method adopts a sequence similarity image registration method, selects 3 non-collinear speckle subsets in each image, respectively performs correlation analysis on the 3 speckle subsets to obtain the displacement of the 3 speckle subsets, substitutes the displacement into a finite element method, and solves strain through unit node displacement to finally obtain 2 strain components, namely strain in a stretching direction and strain in a vertical stretching direction, wherein the obtained strain field result is a color table diagram, and different colors represent strains with different sizes. DIC method analysis Software adopted in the work is Moire Software.
The third step: after stretching is finished, establishing an average strain factor equation of the surface of the copper-containing stainless steel stretching sample at different stretching rates by using the strain of speckle points in a strain field in the collected three-dimensional deformation image
To characterize the strain distribution of the copper-containing stainless steel sheet at different drawing rates; wherein, the first and the second end of the pipe are connected with each other,
In the formula (I), the compound is shown in the specification,
in order to be the average strain factor,
the method is characterized in that the longitudinal point strain of the surface of a tensile sample is adopted, M is the number of speckle points randomly selected in a strain field, N is the number of speckle points randomly selected in a large deformation area or a small deformation area, and M is larger than N.
In the third step, the specific operation process comprises:
(f) The strain rate of speckle sample points which are formed on the collected image of the tensile sample of the copper-containing stainless steel sheet is utilized, and then a large deformation area and a small deformation area in the deformation area are distinguished through the deformation degree.
Here, the definition of the strain field is first clarified, and in this embodiment, data of the strain change detected throughout the parallel length of the tensile sample is defined as the strain field, and the middle third region of the entire strain field is defined as the deformation region. The deformation area with the gauge length width necking larger than 15% is called a large deformation area, and the deformation area with the gauge length width necking smaller than 15% is called a small deformation area.
(g) And then randomly selecting the strain of M scattered spots in the strain field, and simultaneously randomly selecting the strain of N scattered spots in the large deformation area and the small deformation area respectively, and performing statistical average calculation, wherein M is larger than N.
(h) Finally, longitudinal point strain on the surface of the tensile sample is utilized
Establishing an average strain factor equation of a large deformation zone and a small deformation zone on the surface of a copper-containing stainless steel tensile sample at different tensile rates
And drawing a large deformation area average strain factor change curve and a small deformation area average strain factor change curve.
According to the drawn curve, the average strain factors of the large deformation area and the small deformation area are gradually increased in the uniform deformation stage along with the increase of the strain, and are rapidly increased in the local deformation stage. The uniform deformation stage here is before the yield point of the tensile specimen and the local deformation stage here is after the yield point of the tensile specimen.
Meanwhile, the average strain factor of the large deformation area is slightly larger than that of the small deformation area according to a drawn curve.
In addition, on the basis of the three steps of the strain distribution test method provided above, the strain distribution test method of the present invention further includes:
the fourth step: and (3) observing and analyzing the macroscopic and microscopic appearances of the samples after the stretching is finished, and specifically comprising the following steps:
(i) The appearance of a macroscopic tensile fracture of the stretched sample is in a cup cone shape, the section of the sample is flat and regular, and the fracture cracks at 45 degrees with the stretching direction like a blade; as the rate increases, the fracture changes from a larger dimple and tearing edge to a uniform, dense and shallow dimple with smooth dimple walls and ductile fracture mode.
(j) And (3) observing and analyzing the stretched sample by adopting a TEM (transmission electron microscope), wherein spherical copper-rich precipitated phases are dispersed and distributed in the stretched sample, and the diameter of the spherical copper-rich precipitated phases is 28.5nm.
The following describes a method for testing the strain distribution of a copper-containing stainless steel sheet according to the present invention in detail with reference to specific test procedures, as shown in the examples.
Examples
A strain distribution testing method of a copper-containing stainless steel sheet comprises the following steps:
s1, preparing a tensile sample with speckle test points, wherein the specific preparation process comprises the following steps:
s11, taking a longitudinal tensile sample.
Selecting a copper-containing stainless steel sheet with the thickness of 1mm produced by a certain company, and obtaining a longitudinal tensile sample on the copper-containing stainless steel sheet by wire cutting according to the national standard GB/T228-2010; the parallel length of the tensile sample is 80mm, the parallel width is 20mm, the total length is 170mm, the total width is 30mm, and a dimension model diagram of the tensile sample is shown in FIG. 3.
S12, spraying paint on the surface of the selected tensile sample to obtain speckle test points.
The method is characterized in that the surface of the tensile sample is sprayed with the matte black paint to obtain speckle test points, and the speckle test points which are good in contrast, uniform in size and convenient to track by an instrument can be obtained by adopting the matte black paint. It is noted here that: and the paint is sprayed uniformly, so that the matte black paint is ensured to be uniformly attached to the surface of the sample.
S2, stretching the prepared tensile sample at different stretching rates, and collecting and storing images in the stretching process, wherein the specific stretching process is as follows:
and fixing the tensile sample on a chuck of a Shimadzu AGS-100kN universal testing machine to perform a tensile test, adjusting the distance between the camera and the tensile sample and the position of an illumination light source, and focusing the camera to enable the picture to be imaged clearly.
In the tensile test, different tensile rates of 0.5mm/min, 1mm/min, 5mm/min, 10mm/min, 20mm/min and 30mm/min are respectively adopted for testing, and in the tensile test process, images in the tensile process are collected and stored through a three-dimensional motion and deformation measurement system, the image collection frequency is 1Hz, and the collected images are three-dimensional deformation images.
And S3, after the stretching is finished, carrying out digital image correlation analysis on the image acquired in the stretching process.
After the test is finished, in order to quantitatively research the strain process, the strain of 650 scattered spots is randomly selected in a strain field, and simultaneously, 26 scattered spots are randomly selected in a large deformation area and a small deformation area respectively for statistical average calculation, and the strain of longitudinal points on the surface of the sample is utilized
Average strain factor
To characterize the strain distribution of the copper-containing stainless steel samples at different drawing speeds, the strain distribution is specifically shown in formula 1:
here, the strain field specifically refers to a data region of the strain variation detected over the parallel length of the sample, wherein the middle third region of the entire strain field is defined as a deformation region, a large deformation region is defined as a deformation region with a gauge length width necking greater than 15%, and the remaining deformation regions are defined as small deformation regions.
Based on the sample results of equation 1, the large deformation region average strain factor variation curve of fig. 1 and the small deformation region average strain factor variation curve of fig. 2 were plotted, and the test results are shown in tables 1 and 2.
TABLE 1 mechanical Properties at different draw rates
| Stretching rate (mm/min) | Yield strength (MPa) | Tensile strength (MPa) | Elongation (%) |
| 0.5 | 263.4 | 578.4 | 83.7 |
| 1 | 269.3 | 585.3 | 80.6 |
| 5 | 258.5 | 575.8 | 72.4 |
| 10 | 270.9 | 565.3 | 67.9 |
| 20 | 568.6 | 560.2 | 63.2 |
| 30 | 273.2 | 548 | 62.8 |
It can be seen that as the draw rate increases, the principal strain is a gradually decreasing trend: the maximum value of the main strain was 103% at a drawing rate of 0.5mm/min, and 73% at a drawing rate of 30mm/min. As the draw rate increases, the secondary strain is a gradually decreasing trend: the maximum value of the secondary strain was-27.1% at a stretching rate of 0.5mm/min and-22% at a stretching rate of 30mm/min.
The definition of the primary strain and the secondary strain referred to in the above description is: the deformation of a certain line of an object in unit length, such as elongation or shortening, is called main strain; the change in the angle between two intersecting line segments is called secondary strain.
The yield strength of the copper-containing stainless steel at different tensile rates is basically maintained to be about 260 MPa; as the stretching rate increased, the tensile strength showed a tendency to decrease substantially, the tensile strength at 1mm/min was the largest, 585.3MPa, and the tensile strength at 30mm/min was the smallest, 548MPa. The elongation rate showed a steady decrease trend, with the elongation rate of 0.5mm/min being the largest and 83.7%, and the elongation rate of 30mm/min being the smallest and 62.8%.
The average strain factor equation of the large deformation zone and the small deformation zone of the surface of the copper-containing stainless steel sample at different stretching rates is established, and a corresponding average strain factor change curve is drawn. From the graph, it can be known that the average strain factors in the large deformation region and the small deformation region both slowly increase in the uniform deformation stage along with the increase of the strain, and rapidly increase in the local deformation stage, and the average strain factor in the large deformation region is larger than the average strain factor in the small deformation region, so that the process in the aspect of mechanical forming performance is further optimized. This is because the large deformation region is damaged sharply due to the occurrence of grain breakage in the large deformation region, an increase in dislocation density, and the occurrence of work hardening.
In this example, the average strain factor curve obtained by equation 1 is fitted to obtain the following fitting equation 2:
Wherein, D-injury factor;
、
-a constant;
-longitudinal point strain. Parameter(s)
The calculation error used to characterize the fitting equation; parameter(s)
For characterizing longitudinal point strain
The degree of influence of the change in (b) on the fitting damage factor D; parameter(s)
Is longitudinal point strain
An allowable error of the value;
is strain with longitudinal point
Closely related parameters.
Table 2 is a table of parameters fitted to equation 2, as follows, from which the parameter y can be seen 0 Decreasing with increasing draw rate, parameter A 1 Increasing with increasing draw rate. The stretching speed is more than 5mm/min, the parameter value is basically stable, y 0 The value is stabilized at about 0.5, A 1 The value fluctuates around 0.02.
TABLE 2 parameter List of fitting equations
When the stretching speed is less than 5mm/min, the damage evolution equation of the deformation region under different stretching speeds can be obtained.
Large deformation zone:
A small deformation area:
The relation between different strain rates V and the damage factor D of the copper-containing stainless steel is established. The damage evolution law of the deformation region of the copper-containing stainless steel at different strain rates can be accurately reflected.
And S4, observing and analyzing the macroscopic and microscopic appearances of the sample after the stretching is finished, and analyzing and researching the strain conditions of the copper-containing stainless steel stretching sample at different stretching rates.
In macroscopic aspect: as shown in FIG. 4, the appearance of the macroscopic tensile fracture of the stretched sample is cup-cone-shaped, the section of the sample is flat and regular, and the fracture is cracked at 45 degrees with the stretching direction like a blade. With the increase of the speed, the fracture is changed into a uniform dense and shallow dimple from a larger dimple and a tearing edge, the dimple wall is smooth, and the fracture mode is a ductile fracture mode. At high stretching speed, the temperature rise speed is accelerated, and the energy in the matrix is rapidly increased. The temperature rise promotes the creation of locally adiabatic shear bands within the microstructure, which in turn leads to increased work hardening at high strain rates.
In the microscopic aspect: the texture of the deformation zone of different tensile test pieces is uniform austenite equiaxial crystal grains, and a large number of straight annealing twin crystals exist. The IPF plot shows random distribution of grain orientation, but there are a number of 110 crystal planes and a purple 111 crystal plane, as shown in FIG. 5. This is because the {110} crystal face and the {111} crystal face of the antibacterial stainless steel have large energy storage and are easy to recrystallize and grow during annealing. By TEM observation and analysis, spherical copper-rich precipitated phases with a diameter of 28.5nm are dispersed in the material, as shown in FIG. 6.
Finally, it should be noted that: although the present invention has been described in detail with reference to the foregoing embodiments, it will be apparent to those skilled in the art that modifications may be made to the embodiments or portions thereof without departing from the spirit and scope of the invention.
Claims (10)
1. The strain distribution testing method of the copper-containing stainless steel sheet is characterized by comprising the following steps of:
s1, preparing a tensile sample with speckle test points; the tensile sample is selected from a copper-containing stainless steel sheet with the thickness of 0.8-1.5 mm;
s2, stretching the tensile sample at different stretching rates, and collecting and storing images in the stretching process through a three-dimensional motion and deformation measurement system;
s3, after stretching is finished, establishing an average strain factor equation of the surface of the copper-containing stainless steel stretching sample at different stretching rates by using strain of speckle points in a strain field in the collected three-dimensional deformation image
To characterize the strain distribution of the copper-containing stainless steel sheet at different drawing rates;
In the formula (I), the compound is shown in the specification,
in order to obtain an average strain factor,
and M is the strain of longitudinal points on the surface of the tensile sample, M is the number of randomly selected speckle points in a strain field, N is the number of randomly selected speckle points in a large deformation area or a small deformation area, and M is more than N.
2. The method for testing the strain distribution of the copper-containing stainless steel sheet according to claim 1, wherein the step S3 specifically comprises:
s31, distinguishing a large deformation area and a small deformation area in the deformation area by using the strain rate of speckle sample points in the three-dimensional deformation image and further through the deformation degree;
s32, randomly selecting the strains of M scattered spots in a strain field, randomly selecting the strains of N scattered spots in a large deformation area and a small deformation area, and performing statistical average calculation, wherein M is larger than N;
s33, finally, utilizing the longitudinal point strain of the surface of the tensile sample
Establishing an average strain factor equation of a large deformation zone and a small deformation zone on the surface of a copper-containing stainless steel tensile sample at different tensile rates
。
3. The method as claimed in claim 2, wherein the strain distribution of the copper-containing stainless steel sheet is measured by defining the strain field as the data of the strain variation detected over the parallel length of the tensile sample, and defining the middle third region of the strain field as the deformation zone.
4. The method of claim 3, wherein the large deformation zone is a zone having a gauge width necking greater than 15%.
5. The method of claim 3, wherein the small deformation zone is a zone with a gauge width necking of less than 15%.
6. The method for testing the strain distribution of the copper-containing stainless steel sheet according to claim 2, wherein the step S1 specifically comprises:
s11, preparing a longitudinal tensile sample, wherein the parallel length of the tensile sample is 80mm, the parallel width of the tensile sample is 20mm, the total length of the tensile sample is 170mm, and the total width of the tensile sample is 30mm;
s12, spraying paint on the surface of the tensile sample to obtain speckle test points, wherein the paint is sprayed with matte black paint or matte white paint.
7. The method for testing the strain distribution of the copper-containing stainless steel sheet according to claim 6, wherein the step S2 specifically comprises:
s21, fixing the tensile sample on a chuck of a testing machine for stretching, wherein the stretching speed is respectively 0.5mm/min, 1mm/min, 5mm/min, 10mm/min, 20mm/min and 30mm/min;
s22, adjusting the distance between the camera and the tensile sample and the position of an illumination light source, and focusing the camera to enable the picture to be clearly imaged;
and S23, acquiring and storing the image in the stretching process by adopting a three-dimensional motion and deformation measurement system, wherein the image acquisition frequency is 1Hz, and the acquired image is a three-dimensional deformation image.
8. The method of claim 7, wherein the average strain factors of the large deformation zone and the small deformation zone are gradually increased in a uniform deformation stage and rapidly increased in a local deformation stage with the increase of strain; the uniform deformation stage is before the yield point of the tensile specimen and the local deformation stage is after the yield point of the tensile specimen.
9. The method of claim 8, wherein the average strain factor of the large deformation zone is slightly greater than the average strain factor of the small deformation zone.
10. The method of claim 9, further comprising the steps of:
s4, observing and analyzing macroscopic and microscopic appearances of the sample after the stretching is finished, and specifically comprising the following steps:
s41, the shape of a macroscopic stretching fracture of the stretched sample is in a cup cone shape, the fracture surface of the sample is flat and regular like a blade, and the fracture cracks at an angle of 45 degrees with the stretching direction; along with the increase of the speed, the fracture is changed into a uniform compact and shallow dimple from a larger dimple and a tearing edge, the dimple wall is smooth, and the fracture mode is a ductile fracture mode;
s42, observing and analyzing the stretched sample by adopting a TEM (transmission electron microscope), wherein spherical copper-rich precipitated phases are dispersed and distributed in the stretched sample, and the diameter of the sample is 28.5nm.
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Inventor after: Zhao Guanghui Inventor after: Li Jiacai Inventor after: Li Yugui Inventor after: Li Huaying Inventor after: Li Juan Inventor after: Song Yaohui Inventor before: Li Yugui Inventor before: Zhao Guanghui Inventor before: Li Jiacai Inventor before: Li Huaying Inventor before: Li Juan Inventor before: Song Yaohui |