KR102484969B1 - Method of obtaining tensile true stress-strain curves of the material in a large range of strains in tensile testing using digital image correlation technique and mean point technique - Google Patents

Abstract

The present invention, in measuring true stress and true strain in a tensile test, provides a method for obtaining an accurate true stress-true strain curve in the high strain section of a tensile test specimen through a digital image analysis technique and an average point technique. In order to provide this, a method for obtaining a true stress-true strain tensile curve of a tensile specimen in a high strain section using a digital image analysis technique and an average point technique in a tensile test according to an embodiment of the present invention is applied to the surface of the tensile specimen. Forming a pattern for the digital image analysis technique, acquiring continuous surface images of the tensile specimen photographed at preset time intervals while the photographing unit performs the tensile test on the tensile specimen, and measuring the tensile specimen from the acquired image. Determining the necking portion of the specimen, the measuring unit sets a plurality of points horizontal to the necking portion, and obtains the strain of the entire width of the tensile specimen through the average value of the strain at each point, obtained through a tensile test Calculating a true stress-true strain tensile curve based on the true stress obtained from the load may be included.

Description

Method of obtaining tensile true stress-strain curves of the material in a large range of tensile specimens in a high strain range using digital image analysis technique and averaging point technique in tensile test strains in tensile testing using digital image correlation technique and mean point technique}

The present invention relates to a method for obtaining a true stress-true strain tensile curve of a tensile specimen in a high strain section using a digital image analysis technique and an average point technique in a tensile test.

Tensile test is the most common method to obtain the mechanical properties of a tensile specimen in the field of tensile specimen engineering. Elastic modulus, yield strength, tensile strength, and true stress-strain are obtained through load and deformation during the test. Information such as curves can be obtained. Since the tensile test results are different depending on the width, thickness, and gauge length of the specimen, the manufacturing method of the specimen and the specimen width, thickness, gauge length, and test method are international standards for reproducibility of the test. It has been established, and reliable results can be obtained only when the physical properties of the tensile specimen are obtained in accordance with these standards. However, in the case of the method through the international standard, in the section after tensile strength, uneven deformation occurs locally around the necking area of the specimen, but since the strain is calculated over the entire gage length, the true stress-true strain curve cannot be obtained. There are limits.

In order to solve this problem, in measuring the true stress and true strain in the tensile test, the digital image correlation technique is used to reduce the gauge distance and the exact true stress-true strain of the tensile specimen in the highest strain section There was an attempt to obtain a curve (Prior Patent Document 0001). However, since this method calculates the gauge distance in the region where strain is most localized, it tends to be overestimated compared to the actual strain, and thus has a limit in that the true stress is overestimated compared to the actual true stress.

Registered Patent No. 10-1720845 (Announced on March 28, 2017) Registered Patent No. 10-1161775 (Announced on July 09, 2012) Patent Publication 10-2013-0034321 (published on April 05, 2013) Registered Patent No. 10-1262893 (Announced on May 10, 2013)

JI Yoon et al., Korean J. Met. Mater., Vol. 54, pp.231-236 (2016).

According to one embodiment of the present invention, in measuring true stress and true strain in a tensile test, an accurate true stress-true strain curve in the high strain section of a tensile test specimen through a digital image analysis technique and an average point technique A method for obtaining is provided.

In order to solve the above-described problems of the present invention, in a tensile test according to an embodiment of the present invention, using a digital image analysis technique and an average point technique to obtain a true stress-true strain tensile curve of a tensile specimen in a high strain section The method includes forming a pattern for digital image analysis on the surface of the tensile specimen, acquiring continuous surface images of the tensile specimen photographed at predetermined time intervals while the photographing unit performs the tensile test on the tensile specimen, and measuring Determining the necking part of the tensile specimen from the image acquired by the part, the measurement part setting a plurality of points horizontal to the necking part, obtaining the strain of the entire width of the tensile specimen through the average value of the strain at each point, , calculating a true stress-true strain tensile curve based on the true stress obtained from the load obtained through the tensile test.

According to one embodiment of the present invention, there is an effect of accurately obtaining a true stress-true strain curve of a tensile specimen in a high strain range.

1 is an example of the configuration of equipment used in a method for obtaining a true stress-true strain tensile curve of a tensile specimen in a high strain section using a digital image analysis technique and an average point technique in a tensile test according to an embodiment of the present invention. It is also
2 shows equipment used in a method for obtaining a true stress-true strain tensile curve of a tensile specimen in a high strain section using a digital image analysis technique and an average point technique in a tensile test according to an embodiment of the present invention. It is a diagram illustrating an exemplary computing environment that may be used.
3 is a schematic flowchart of a method for obtaining a true stress-true strain tensile curve of a tensile specimen in a high strain section using a digital image analysis technique and an average point technique in a tensile test according to an embodiment of the present invention.
4 is a true stress-true strain by a method for obtaining a true stress-true strain tensile curve of a tensile specimen in a high strain section using a digital image analysis technique and an average point technique in a tensile test according to an embodiment of the present invention. It is an example of a tensile specimen that produces
5 shows the true stress-true strain by a method for obtaining a true stress-true strain tensile curve of a tensile specimen in a high strain section using a digital image analysis technique and an average point technique in a tensile test according to an embodiment of the present invention. This is an example of arbitrarily selecting a finite number of points horizontal to the center of the necking area where the deformation of the material is the most severe for the tensile specimen to be calculated.
6 is an accurate true stress calculated through a method for obtaining a true stress-true strain tensile curve of a tensile specimen in a high strain section using a digital image analysis technique and an average point technique in a tensile test according to an embodiment of the present invention. -This is a graph comparing the true strain curve, the true stress-true strain curve calculated by reducing the conventional gauge distance, and the analysis model calculated through the finite element method.
7 shows the true stress-true strain in a method for obtaining a true stress-true strain tensile curve of a tensile specimen in a high strain section using a digital image analysis technique and an average point technique in a tensile test according to an embodiment of the present invention. It is a graph showing the true stress-true strain curve calculated through the average of strains from 5 randomly selected points and 20 randomly selected points for the tensile specimen to be calculated.

Hereinafter, preferred embodiments will be described in detail so that those skilled in the art can easily practice the present invention with reference to the accompanying drawings.

1 is an example of the configuration of equipment used in a method for obtaining a true stress-true strain tensile curve of a tensile specimen in a high strain section using a digital image analysis technique and an average point technique in a tensile test according to an embodiment of the present invention. It is also

Referring to FIG. 1, equipment used in a method for obtaining a true stress-true strain tensile curve of a tensile specimen in a high strain section using a digital image analysis technique and an average point technique in a tensile test according to an embodiment of the present invention. The fields 100 may include a photographing unit 120 , a measurement unit 130 and a display 140 .

During the tensile test of the tensile specimen 110, the photographing unit 120 may acquire and store continuous images of the surface of the tensile specimen at predetermined time intervals.

The tensile specimen 110 may be a plate-shaped or bar-shaped tensile specimen for a tensile test.

The measurement unit 130 obtains an average strain based on the stored image data of the tensile specimen surface using a digital image analysis technique and an average point technique, converts the nominal stress into true stress, and obtains a true stress-true strain tensile curve, It can be output through the display 140.

2 shows equipment used in a method for obtaining a true stress-true strain tensile curve of a tensile specimen in a high strain section using a digital image analysis technique and an average point technique in a tensile test according to an embodiment of the present invention. It is a diagram illustrating an exemplary computing environment that may be used.

For example, computing device 1100 may be a personal computer, server computer, handheld or laptop device, mobile device (mobile phone, personal digital assistant, media player, etc.), multiprocessor system, consumer electronics, mini computer, mainframe computer, distributed computing environments that include any of the foregoing systems or devices; and the like.

Computing device 1100 may include at least one processing unit 1110 and memory 1120 . Here, the processing unit 1110 may include, for example, a central processing unit (CPU), a graphics processing unit (GPU), a microprocessor, an Application Specific Integrated Circuit (ASIC), a Field Programmable Gate Arrays (FPGA), and the like. and may have a plurality of cores. The memory 1120 may be volatile memory (eg, RAM, etc.), non-volatile memory (eg, ROM, flash memory, etc.), or a combination thereof.

Additionally, computing device 1100 may include additional storage 1130 . Storage 1130 includes, but is not limited to, magnetic storage, optical storage, and the like. The storage 1130 may store computer readable instructions for implementing one or more embodiments disclosed herein, and may also store other computer readable instructions for implementing an operating system, application programs, and the like. Computer readable instructions stored in storage 1130 may be loaded into memory 1120 for execution by processing unit 1110 .

Computing device 1100 can also include input device(s) 1140 and output device(s) 1150 . Here, the input device(s) 1140 may include, for example, a keyboard, mouse, pen, voice input device, touch input device, infrared camera, video input device, or any other input device. Output device(s) 1150 may also include, for example, one or more displays, speakers, printers, or any other output device, or the like. Additionally, computing device 1100 may use an input device or output device included in another computing device as input device(s) 1140 or output device(s) 1150 .

Computing device 1100 may also include communication connection(s) 1160 that allow it to communicate with other devices (eg, computing device 1300 ) over network 1200 . Here, communication connection(s) 1160 may be a modem, network interface card (NIC), integrated network interface, radio frequency transmitter/receiver, infrared port, USB connection, or other device for connecting computing device 1100 to other computing devices. May contain interfaces. Further, communication connection(s) 1160 may include a wired connection or a wireless connection.

Each component of the aforementioned computing device 1100 may be connected by various interconnections such as a bus (eg, peripheral component interconnection (PCI), USB, firmware (IEEE 1394), optical bus structure, etc.) and may be interconnected by networks.

As used herein, terms such as "measurement unit" and the like generally refer to a computer-related entity that is hardware, a combination of hardware and software, software, or software in execution. For example, a component may be, but is not limited to, a process running on a processor, a processor, an object, an executable, a thread of execution, a program, and/or a computer. For example, both the application running on the controller and the controller may be components. One or more components can reside within a process and/or thread of execution and a component can be localized on one computer or distributed between two or more computers.

3 is a schematic flowchart of a method for obtaining a true stress-true strain tensile curve of a tensile specimen in a high strain section using a digital image analysis technique and an average point technique in a tensile test according to an embodiment of the present invention.

Referring to FIG. 3 together with FIG. 1, obtaining a true stress-true strain tensile curve of a tensile specimen in a high strain section using a digital image analysis technique and an average point technique in a tensile test according to an embodiment of the present invention The method is largely divided into a step of implementing a random pattern on the surface of the tensile specimen 110 (first step) (S10), and a step of obtaining a digital image of the surface of the specimen by the photographing unit 120 while performing a tensile test (first step). Step 2) (S20), in the image obtained in this way, the measurement unit 130) determines a horizontal area in the width direction at the necking part where the deformation of the tensile specimen is the most severe (third step) (S30), measurement The unit 130 calculates the strain at each point at a finite number of points randomly selected horizontally on the necking part where the deformation of the material is the most severe, measures the true strain through the average value, and applies the nominal stress using the measured true strain. It can be divided into the step of converting into stress (fourth step) (S40).

(Step 1) (S10)

First, a step of forming a pattern for a digital image analysis technique is performed on the surface of the prepared tensile specimen 110.

In this first step, an arbitrary pattern is implemented on the surface of the metal tensile specimen 110. A method of implementing such a pattern may be formed by spraying according to the size of the tensile specimen 110, the image measurement method, and the image magnification. For example, a method using white and black spray or etching the surface Patterns can be formed on the tensile specimen 110 by various methods, such as a method of depositing a micro-grid, a method of scratching through mechanical polishing, and the like. In non-magnification image magnification, a method using white and black spray is most widely used, but is not limited thereto.

(Step 2) (S20)

In the second step, a tensile test is performed on the tensile specimen 110, and at the same time, the arbitrary pattern implemented in the first step is measured through a digital image and stored in a data storage unit (not shown) of the measuring unit 120. Save. Digital image analysis is possible by obtaining a series of consecutive images of the same magnification at regular time intervals with digital image measurement techniques. A method for obtaining an image may use a photographing unit 120 such as a digital camera, a high-speed camera, a camcorder, an optical microscope, a scanning electron microscope, or an atomic force microscope according to a desired image magnification.

(Step 3) (S30)

Next, by analyzing the continuous images taken in the second step by the measuring unit 130, a step of determining a horizontal region in the width direction of the necking region where the deformation of the material is the most severe is performed.

(4th step) (S40)

Next, through the display 140, the measurement unit 130 randomly selects a finite number of points in the width direction of the necking region where the deformation is the most severe, and analyzes continuous images at each point of the finite number of points. The step of obtaining the true stress-true strain is performed.

4 is a true stress-true strain by a method for obtaining a true stress-true strain tensile curve of a tensile specimen in a high strain section using a digital image analysis technique and an average point technique in a tensile test according to an embodiment of the present invention. It is an example of a tensile specimen that produces

Referring to FIG. 4 together with FIGS. 1 and 3, the randomly selected finite number of points must exist within a horizontal area in the width direction of the necking region, and at least five or more points are selected (S41).

If the randomly selected finite number of points is less than five, there is a risk of poor image analysis, and a more reliable true stress-true strain curve can be obtained as the number of finite points increases.

The finite number of arbitrarily selected points must exist at equal intervals, and must be evenly distributed throughout the width direction of the tensile specimen 110.

In the step of obtaining true stress-true strain (S40), the local strain (ε _{y (i)} ) at a finite number of randomly designated points, including the horizontal region in the width direction of the necking portion where the deformation is the most severe, is targeted As shown in Equation 1 below, a process of obtaining an average strain over the entire width of the tensile specimen is included (S42). That is, the true stress-true strain curve is obtained in the high strain section by calculating the true strain based on the average value of tensile axial strain (ε _y(AVERAGE) ) at a finite number of points.

(Equation 1)

(n: the number of points in the average point method)

The step of obtaining the true stress-true strain includes converting the load obtained through the tensile test into a nominal stress as shown in Equation 2 below (S43).

(Equation 2)

(Where σ _eng is the nominal stress, P is the load, w is the width of the tensile specimen, and t is the thickness of the tensile specimen)

The step of obtaining the true stress-true strain includes a process of converting the nominal stress into the true stress according to the tensile test and the calculated nominal stress as shown in Equation 3 below. That is, by calculating the true stress from the nominal stress to obtain the true stress-true strain curve, an accurate true stress-true strain curve is obtained in the high strain section (S44).

(Equation 3)

(Where σ _true is the true stress).

As described above, in the fourth step (S40), the random patterns implemented in the first step (S10) measure the positional change during the tensile test and extract continuous images using the images obtained in the second step (S20). This step calculates the true stress-true strain using

5 shows the true stress-true strain by a method for obtaining a true stress-true strain tensile curve of a tensile specimen in a high strain section using a digital image analysis technique and an average point technique in a tensile test according to an embodiment of the present invention. This is an example of arbitrarily selecting a finite number of points horizontal to the center of the necking area where the deformation of the material is the most severe for the tensile specimen to be calculated.

Referring to FIG. 5, in order to know the local strain in the horizontal area in the width direction in the necking area where the deformation is the most severe, a finite number of randomly selected points are designated and the strain at each point is obtained, and the correct true stress-true strain is obtained through the average. can be calculated.

As described above, when the true stress-true strain curve is extracted using the digital image analysis technique and the average point technique according to the present invention, an accurate true stress-true strain curve as shown in FIG. 6 can be obtained.

6 is an accurate true stress calculated through a method for obtaining a true stress-true strain tensile curve of a tensile specimen in a high strain section using a digital image analysis technique and an average point technique in a tensile test according to an embodiment of the present invention. -This is a graph comparing the true strain curve, the true stress-true strain curve calculated by reducing the conventional gauge length, and the analysis model calculated through the finite element method.

As described above, when the true stress-true strain curve is extracted using the digital image analysis technique and the average point technique according to the present invention, as shown in FIG. In comparison, a very accurate true stress-true strain curve can be obtained. An accurate true stress-true strain curve derives the optimal parameters through the parameter backtracking method, and then extracts the finite element analysis results and analytical model based on these parameters to determine the optimal parameters. It can be known by derivation.

That is, when the true stress-true strain curve is extracted using the digital image analysis technique and the average point technique according to the present invention, it can be seen that it matches the analysis model as shown in FIG. 6. On the other hand, the conventional method of obtaining an accurate true stress-true strain curve while reducing the gauge length is the true stress-true strain curve of the analytical model because the experimentally obtained hardening is overestimated as the necking intensifies in the high strain range. It can be seen that it does not match.

(Example 1)

An embodiment of a method for calculating accurate true stress-true strain of a tensile specimen through a tensile test according to the present invention through such a method is as follows.

First, prepare a tensile specimen for the tensile test.

On the surface of the prepared specimen, white spray is applied to the entire surface of the specimen, and then black spray is applied to form spots.

A tensile test is conducted while pulling the prepared tensile specimen at a strain rate of 10 ^-3 s ^-1 , and at the same time, using two non-magnifying cameras, a continuous three-dimensional image of the same magnification is taken once every 2 seconds. got

Images obtained during the tensile test were analyzed using ARAMIS software. ARAMIS software was used to determine the necking area with the most deformation. Five random points were selected at regular intervals along the entire width while being horizontal to the necking area, and the strain at each point could be determined.

Through the average value of the strain at each point, a uniform true strain across the entire width was found. By calculating the true stress using the load during the tensile test, an accurate true stress-true strain curve was obtained.

In this example, it was performed on DP980 plate, which is a type of advanced high strength steel.

(Example 2)

In order to compare the reliability of the true stress-true strain calculated from 5 randomly selected points and 20 randomly selected points for the tensile specimen for which the true stress-true strain is calculated according to the present invention, the tensile test method and preparation of the tensile specimen are Example 2 was performed in the same manner as Example 1 above.

Unlike Example 1, using the ARAMIS software to select 20 random points horizontally and at equal intervals across the entire width of the necking area, and using the average of the strain at each point calculated and the load during the tensile test, the accurate true stress-true strain curves could be obtained.

7 shows the true stress-true strain in a method for obtaining a true stress-true strain tensile curve of a tensile specimen in a high strain section using a digital image analysis technique and an average point technique in a tensile test according to an embodiment of the present invention. It is a graph showing the true stress-true strain curve calculated through the average of strains from 5 randomly selected points and 20 randomly selected points for the tensile specimen to be calculated.

Referring to FIG. 7, looking at the true stress-true strain curves of the tensile specimen at 5 randomly selected points and 20 randomly selected points according to the present invention, the shapes of the curves match regardless of the number of randomly selected points, but are arbitrarily selected. It was confirmed that the true stress-true strain curves for the 20 selected points were smoother than the true stress-true strain curves for the randomly selected 5 points.

As in Example 1, in this example, the DP980 plate, which is a kind of advanced high strength steel, was performed, and as shown in FIG. 6, the analysis model was extracted and compared through the parameter back tracking method. It can be seen that a very accurate true stress-true strain curve was obtained compared to the method of reducing the gauge length.

As described above, according to the method of obtaining a true stress-true strain curve of a material in a high strain range according to the present invention, a conventional tensile test is performed to obtain a true stress-true strain curve of a material in a high strain range. There is an effect that can be obtained accurately.

Another effect of the present invention is that the accurate deformation behavior of the material can be obtained by obtaining an accurate true stress-true strain curve from the tensile test to fracture through the present invention, and the deformation of the material, not the deformation behavior limited to tension, can be obtained. It has the effect of contributing greatly to the development and research of future materials by helping to accurately predict the deformation behavior of materials in various process processes.

In addition, another effect of the present invention is that according to the method for obtaining the true stress-true strain curve of a material in the high strain range, the test method is not complicated or difficult because it is performed based on a tensile test widely used in the field of material engineering. -In addition to true strain, mechanical properties such as modulus of elasticity, yield strength, and tensile strength can be provided.

In addition, the effect of the present invention is that, unlike conventional tensile tests that require the use of KS or ASTM tensile specimens, accurate strain measurement is possible by means of the average point technique, so that even if the tensile specimen shape deviates from the standard specification, accurate true stress- That is, the true strain curve can be derived.

The present invention described above is not limited by the above-described embodiments and the accompanying drawings, but is limited by the claims to be described later, and the configuration of the present invention can be varied within a range that does not deviate from the technical spirit of the present invention. Those skilled in the art can easily know that the present invention can be changed and modified accordingly.

100: Equipment used in the method of the present invention
110: tensile specimen
120: shooting unit
130: measurement unit
140: display

Claims (10)

Forming a pattern for digital image analysis on the surface of the tensile specimen;
Acquiring continuous surface images of the tensile specimen photographed at predetermined time intervals while the photographing unit performs the tensile test on the tensile specimen;
Setting a necking part of the tensile specimen from the image acquired by the measuring unit; and
The measurement unit sets a plurality of points horizontal to the necking portion, and the true strain of the entire width of the tensile specimen is obtained through the average value of the tensile axial strain at each point, based on the true stress obtained from the load obtained through the tensile test. Calculating a true stress-true strain tensile curve by doing;
A method for obtaining a true stress-true strain tensile curve of a tensile specimen in a high strain section using a digital image analysis technique and an average point technique in a tensile test, including a.
According to claim 1,
The step of forming a pattern for the digital image analysis technique on the surface of the tensile specimen,
On the surface of the tensile specimen,
a method of forming a pattern by applying with a spray;
how to etch a surface;
a method of depositing a micro-grid; and
A method of forming scratches through mechanical polishing;
A method of obtaining a true stress-true strain tensile curve of a tensile specimen in a high strain section using a digital image analysis technique and an average point technique in a tensile test in which a pattern is formed by any one of the methods.
According to claim 1,
The step of obtaining continuous surface images of the tensile specimen,
High strain using digital image analysis technique and average point technique in tensile test, in which the photographing unit stores image data photographed by any one of digital camera, high-speed camera, camcorder, optical microscope, scanning electron microscope, and atomic force microscope for tensile specimen. A method for obtaining the true stress-true strain tensile curve of a tensile specimen in the interval.
Forming a pattern for digital image analysis on the surface of the tensile specimen;
Acquiring continuous surface images of the tensile specimen photographed at predetermined time intervals while the photographing unit performs the tensile test on the tensile specimen;
Setting a necking part of the tensile specimen from the image acquired by the measuring unit; and
The measurement unit sets a plurality of points horizontal to the necking portion, obtains the strain of the entire width of the tensile specimen through the average value of the strain at each point, and based on the true stress obtained from the load obtained through the tensile test, the true stress- Calculating a true strain tensile curve;
including,
In the step of calculating the true stress-true strain tensile curve,
setting a plurality of horizontal points on the necking part by the measurement unit;
obtaining an average value of the strain of each of the plurality of points by the measuring unit;
obtaining the true stress of the tensile specimen with the load obtained by the measuring unit through the tensile test; and
Calculating a true stress-true strain curve of the tensile specimen based on the average value of the true stress and the strain by the measuring unit
A method for obtaining a true stress-true strain tensile curve of a tensile specimen in a high strain section using a digital image analysis technique and an average point technique in a tensile test, including a.
According to claim 4,
The step of setting a plurality of horizontal points on the necking part
In the tensile test, which sets a plurality of points horizontally and equally spaced in the width direction at the center of the necking region, the true stress-true strain tensile curve of the tensile specimen is obtained in the high strain section by using a digital image analysis technique and an average point technique. How to.
According to claim 5,
The step of setting a plurality of horizontal points on the necking part
A method of obtaining a true stress-true strain tensile curve of a tensile specimen in a high strain section using a digital image analysis technique and an average point technique in a tensile test, which sets at least five points.
According to claim 4,
The step of obtaining the average value of the strain of each of the plurality of points
A method for obtaining the true stress-true strain tensile curve of a tensile specimen in a high strain section using a digital image analysis technique and an average point technique in a tensile test, in which the average value of strain at each point is obtained according to Equation 1 below
(Equation 1)

(Where n is the number of points in the average point method).
According to claim 4,
The step of obtaining the true stress-true strain,
In the tensile test, the nominal stress is obtained from the load calculated during the tensile test according to Equation 2 below, and the true stress is obtained according to Equation 3 below. How to obtain the true stress-true strain tensile curve of a specimen
(Equation 2)

(Where σ _eng is the nominal stress, P is the load, w is the width of the tensile specimen, and t is the thickness of the tensile specimen)

(Equation 3)

(Where σ _true is the true stress).
According to claim 4,
The step of forming a pattern for the digital image analysis technique on the surface of the tensile specimen,
On the surface of the tensile specimen,
a method of forming a pattern by applying with a spray;
how to etch a surface;
a method of depositing a micro-grid; and
A method of forming scratches through mechanical polishing;
A method of obtaining a true stress-true strain tensile curve of a tensile specimen in a high strain section using a digital image analysis technique and an average point technique in a tensile test in which a pattern is formed by any one of the methods.
According to claim 4,
The step of obtaining continuous surface images of the tensile specimen,
High strain using digital image analysis technique and average point technique in tensile test, in which the photographing unit stores image data photographed by any one of digital camera, high-speed camera, camcorder, optical microscope, scanning electron microscope, and atomic force microscope for tensile specimen. A method for obtaining the true stress-true strain tensile curve of a tensile specimen in the interval.

Images