JP5945103B2 - Method for measuring plastic strain of metallic materials - Google Patents

Description

  The present invention relates to a pattern used for measurement of the plastic strain of a metal material and a method for measuring the plastic strain of the metal material when evaluating the formability of a metal material such as a steel plate.

For example, thin metal sheets used for automotive parts, or metal materials such as shear, tension, bending, hole expansion, overhang, deep drawing, press, and test pieces used for various tests, plastically deform the metal materials. By measuring the plastic strain, the formability and performance of the metal material are evaluated.
In measuring the plastic deformation of such a metal material, a pattern for measuring plastic strain such as a scribed circle or a lattice is provided on the surface of the target metal material, and the strain of the pattern after the plastic deformation of the metal material is measured. A method for measuring the distribution, size, direction, and the like of plastic strain of a metal material is known.

As the pattern for measuring the plastic strain, for example, as described in Patent Document 1, a pattern in which a plurality of circles are combined, a pattern in a lattice shape, or a pattern in which a plurality of circles and a lattice shape are combined. Is present. In addition, there are various other patterns such as concentric patterns, which are appropriately used depending on the application.
For example, in the case where the pattern includes a circle, when the metal material is deformed into an ellipse by plastic deformation of the metal material, the maximum length of the metal material is measured by measuring the length of the ellipse, the length of the short axis, the deformation direction, etc. Find the direction of strain, minimum strain, and maximum strain. In addition, when the pattern includes a lattice shape, when the lattice shape is deformed due to plastic deformation of the metal material, the vertical and horizontal lengths of the rectangle formed by the lattice shape, the length of the diagonal line, etc. are measured. The direction of the maximum strain, minimum strain, and maximum strain of the metal material is obtained by

However, the pattern for measuring plastic strain is divided into a plurality of areas composed of various unit figures by a line having a certain width (thickness), so that the pattern is deformed after plastic deformation of the metal material. In such a case, when measuring the strain in each area, there is a problem of which part in the width direction of the line dividing each area is used as a reference for measuring the length or the like.
That is, at the time of strain measurement of each area in the pattern, there is a possibility that the handling of the lines dividing each area may be different depending on the measurer, and an error corresponding to the line width may occur. In addition, when the line is deformed, the thickness of the line may also change, and the portion that becomes the reference for measurement by the measurer may be ambiguous.
Therefore, the actual situation is that there is a difference in the measured value depending on which part of the line the measurer measures the length or the like. As a result, there is an error in the measurement value required for the strain in each area, and the strain in each area cannot be measured accurately, which may prevent accurate and stable measurement of the plastic strain of the metal material. there were.

JP-A-6-58704

  The technical problem of the present invention is a means capable of accurately and stably measuring strain related to a pattern provided on a metal material, thereby enabling high-precision measurement of plastic strain of the metal material. It is to provide.

To solve the above SL problems, plastic strain measuring method of the metal material of the present invention, the plastic strain after the metallic material is plastically deformed, strain measurement pattern for the surface strain is disposed in the measurement of the metal material Thus, in the method of measuring the plastic strain of a metal material, as the above pattern, the contours of the respective areas are mutually aligned without having a line that is regularly partitioned into a plurality of areas and that separates these areas. Using a plastic strain measurement pattern that is color-coded with a different color from other adjacent areas that are in line contact with each other, the boundary portion of each color-coded area becomes the start and end points of the length measurement required for strain calculation The distortion of the pattern is measured as a position reference.

In the measurement method of the present invention, the pattern may be color-coded by a color of the surface of the metal material to be measured for plastic strain and another color different from the color of the surface of the metal material. it can.
In the present invention, the pattern may be color-coded by two different colors.

  Furthermore, in the plastic strain measuring method of the present invention, the pattern is preliminarily printed on the surface of the metal material with a paint before plastic deformation of the metal material, and the pattern is transparent on the surface of the metal material after plastic deformation. By pressing the adhesive tape, the pattern after plastic deformation can be transferred to the adhesive tape and the distortion of the pattern can be measured.

According to the present invention, the pattern for plastic strain measurement used for the measurement of plastic strain when plastically deforming a metal material is regularly partitioned into a plurality of areas, and the lines dividing these areas are lined up. without the presence, since the contour of the respective areas are color coded respectively in other areas and mutually different colors adjacent to the line contact with each other, the boundary portion of each area serving as a reference for the calculation of the strain, strain Can be grasped uniquely as the starting and ending positions of the length measurement required for the calculation of the length , and this makes it possible to accurately measure the length required for strain calculation based on the boundary of each area .
Therefore, the problem of handling in the width direction of the lines that divide each area is eliminated, as in the case of a pattern formed only with conventional lines, and errors in measured values due to differences in handling of the lines are prevented. Accordingly, the plastic strain of the metal material can be measured accurately and stably.

It is a top view which shows 1st Embodiment of the pattern for plastic strain measurement of the metal material which concerns on this invention. It is a principal part enlarged plan view which shows typically the state of the boundary part of the area of the pattern for a plastic strain measurement when a shear force acts on a metal material. However, (a) shows a state before the metal material is plastically deformed, and (b) shows a state after the plastic deformation. It is a top view which shows 2nd Embodiment of the pattern for plastic strain measurement of the metal material which concerns on this invention. It is a top view which shows 3rd Embodiment of the pattern for plastic strain measurement of the metal material which concerns on this invention. It is a top view which shows 4th Embodiment of the pattern for plastic strain measurement of the metal material which concerns on this invention.

FIG. 1 shows a first embodiment of a strain measuring pattern applied to a plastic strain measuring method for a metal material according to the present invention.
The strain measurement pattern is used for measurement of plastic strain when the metal material is plastically deformed. The strain measurement pattern 1A of this embodiment is regularly arranged in a plurality of square areas in plan view. Is formed on the basis of a lattice-shaped pattern, and the surface of the metal material to be plastically deformed, for example, a method of oxidizing the metal material according to the pattern by a silk screen method using an electrolysis solution, It is printed directly by any means such as stamping or printing with a steel plate printer.

In the plastic strain measurement pattern 1A, each area has a square shape of the same shape and the same size in plan view, and each area has another adjacent area where the outlines of the areas are in line contact with each other, in other words, The other adjacent areas where the boundary 4 appears as a line are color-coded by different colors. In the case of the one shown in FIG. 1, each area has a different color from the four areas vertically and horizontally adjacent to each other, while the four areas in the diagonal direction that are in point contact at the corners have the same color. It has become.
Specifically, the plastic strain measurement pattern 1A is composed of the color of the surface of the metal material to be measured for plastic strain (in this embodiment, the background color of the metal material (color without painting)). An area 2 of the first color and an area 3 of the second color that is color-coded from the area 2 of the first color by coloring another color different from the color of the surface of the metal material; It consists of
Therefore, in this plastic strain measurement pattern 1A, a checkered pattern as a whole is formed in which each area is color-coded by two colors, the color of the surface of the metal material and another color different from the surface color. It has become a thing.
In this embodiment, since the first color area 2 of the plastic strain measuring pattern 1A is the ground color of the surface of the metal material, substantially only the second color area 3 is the metal. By printing on the surface of the material, the plastic strain measuring pattern 1A is provided on the surface of the metal material.

The first color area 2 and the second color area 3 in the plastic strain measurement pattern 1A have a visually clear and stable boundary 4 (boundary line) between the other adjacent areas 3 and 2. It is color-coded with colors that can be distinguished. For example, the boundary 4 between adjacent areas is visually determined by increasing the contrast of the colors of both areas so that the area 2 of the first color is white and the area 3 of the second color is black. It is preferable to clarify.
In the example shown in FIG. 1, the area 3 of the second color is painted black with respect to the color of the area 2 of the first color (the ground color of the metal material), and the boundary 4 between both areas is defined. It makes it possible to grasp visually unambiguously.

Here, each of the areas 2 and 3 constituting the plastic strain measurement pattern 1A is color-coded with a different color from other adjacent areas whose contours are in line contact with each other. When measuring strains in areas 2 and 3, it is possible to visually and uniquely determine the measurement start and end points of the length necessary for strain calculation, so that the plastic strain of the metal material is accurate and stable. This is to enable measurement.

As already described, in the case of a plastic strain measurement pattern formed only with conventional lines, when measuring the strain in each area, handling in the width direction of the line that divides the area, that is, each area The position in the width direction of the line is based on the start and end points of the length required to measure the strain (in this embodiment, the vertical / horizontal length of each area, the diagonal length, etc.) However, there was a possibility that it differs depending on the measurer. In addition, when the line is deformed, the thickness of the line may also change, and the portion that becomes the reference for measurement by the measurer may be ambiguous. For this reason, an error corresponding to the width of the line occurs due to the difference in handling of the width of the line that divides each area by the measurer, and as a result, the measured value of the distortion of each area is also caused by the measurer. there were.
The occurrence of an error at the time of measuring the strain in each area of the plastic strain measurement pattern greatly affects the measured value of the plastic strain of the plastically deformed metal material. And it cannot measure stably.

Therefore, in the present invention, each area of the pattern for measuring plastic strain is color-coded with a different color from other adjacent areas whose contours are in line contact with each other, thereby making each area like a conventional pattern. By eliminating the presence of the dividing lines, the handling of the lines at the time of measurement is eliminated, and the boundary (boundary line) between both areas is clarified visually.
Thereby, when measuring the strain of each area in the pattern for measuring plastic strain, there is no line that divides each area, so FIG. 2 (however, FIG. 2 shows an example of shearing a metal material. As shown in the white arrow, the direction in which the shearing force acts is shown), and before and after the plastic deformation of the metal material, the boundary portion between adjacent areas can be visually grasped and specified uniquely. As a result, since the starting point and the ending point of the measurement of the length required for the calculation of the strain can be determined visually with reference to the boundary part of both areas, the measurement of the plastic strain of the metal material is compared with the conventional method. It becomes possible to carry out accurately and stably.

In addition, the length of the boundary line between each area of the pattern for measuring plastic strain and the adjacent area is suitably about 1.0 mm to 100 mm, more preferably 1.0 to 50 mm, and further The thickness is preferably 1.0 to 10 mm.
The reason why the lower limit of the length of the boundary line between each area and the adjacent area is set to 1.0 mm is due to practical restrictions in plastic strain measurement.
On the other hand, the appropriate upper limit is set to 100 mm, and if it exceeds 100 mm, even if a conventional plastic strain measurement pattern with a relatively large line width of about 0.2 mm is used, the measurement error This is because there is a possibility that the advantage of the present invention over the conventional one is not so much exhibited.
Furthermore, the more preferable upper limit is set to 50 mm. If the upper limit exceeds 50 mm, even if a conventional plastic strain measurement pattern having a general line width of about 0.1 mm is used, the measurement error This is because the superiority of the present invention may not be exerted so much.
Further, the more preferable upper limit is set to 10 mm. In this case, in the case of the conventional plastic strain measurement pattern, the measurement error becomes remarkable regardless of the line width, and therefore the present invention compared with the conventional one. This is because the measurement accuracy of the plastic strain is extremely high. In this regard, according to experiments by the present inventors, it is known that a measurement error of about 1.2% occurs in the conventional case.

Hereinafter, the case where the plastic strain of a metal material is measured using the plastic strain measuring pattern 1A having the above configuration will be described.
First, before plastically deforming a metal material, a plastic strain measurement pattern 1A is printed in advance on the surface of the metal material.
Thereafter, the metal material provided with the pattern 1A for measuring plastic strain, for example, a metal plate such as a thin steel plate used for various moldings, a metal test piece used for various performance tests, shearing, Plastic deformation is performed by tension, bending, hole expansion, overhang, deep drawing, pressing, or the like, and the strain of the strain measurement pattern is measured.

When measuring the strain related to the plastic strain measuring pattern 1A, the plastic strain measuring pattern 1A disposed on the plastically deformed metal material is constantly monitored by a camera.
Then, the images from the camera are sequentially taken into an electronic computer, the images are output to a monitor or the like, and the images are converted into image data having two-dimensional coordinates. Further, based on the two-dimensional coordinates of the image data, the vertical and horizontal lengths, diagonal lengths, etc. of each of the areas 2 and 3 having a substantially square shape in plan view of the plastic strain measurement pattern 1A are measured. Finally, based on these measured values, the maximum strain, the minimum strain, the direction of the maximum strain, etc. of the plastically deformed metal material are obtained.
Such a strain measuring method has an advantage that the strain of the metal material can be measured in real time.

In addition, when measuring the plastic strain of a metal material after plastic deformation, including when the metal material is ruptured by plastic deformation, press a transparent adhesive tape on the surface of the metal material after plastic deformation. Thus, it is also possible to transfer the plastic strain measuring pattern 1A after plastic deformation to the adhesive tape and measure the strain of the pattern.
For example, when the metal material is ruptured by plastic deformation, the plastic strain measurement pattern located on one half of the ruptured portion is transferred to the adhesive tape. Thereafter, for the plastic strain measurement pattern located on the other half side, the same adhesion is obtained with the rupture portion and the rupture portion of the already transferred half-side plastic strain measurement pattern mutually matched. Transfer to tape.
Thereby, the pattern for plastic strain measurement at the time of the fracture | rupture of a metal material can be obtained.
Then, the transferred image of the plastic strain measurement pattern is taken into an electronic computer, and the image is converted into image data having two-dimensional coordinates. Further, based on the two-dimensional coordinates of the image data, the vertical and horizontal lengths, diagonal lengths, etc. of each of the square-shaped areas 2 and 3 in the plan view of the plastic strain measurement pattern are measured. Based on the above, the maximum strain, the minimum strain, the direction of the maximum strain, etc. of the plastically deformed metal material are obtained.

Here, when the image of the camera related to the plastic strain measurement pattern 1A is converted into image data having two-dimensional coordinates, the boundary 4 of each area 2 and 3 having a square shape in plan view in the plastic strain measurement pattern 1A. Get coordinates based on.
The areas 2 and 3 are color-coded into different colors from other adjacent areas whose outlines are in line contact with each other, that is, the first color area 2 and the second color area 3. Therefore, the boundary 4 of each area can be uniquely identified visually with the boundary line of the color.
As a result, the positions that are the starting and ending points of the measurement of the lengths and widths of the areas 3 and 4 and the lengths of the diagonal lines necessary for calculating the strains of the areas 3 and 4 are also visually unique. Can be specified. Accordingly, the measurement error due to the difference in the width direction of the measurer that has occurred in the past is eliminated, and the two-dimensional coordinates related to the boundary 4 of each area 2 and 3 can be accurately and stably identified and acquired. Is possible.
As a result, since it is possible to stably measure the strains of the areas 2 and 3 of the plastic strain measurement pattern 1A with high accuracy, it is possible to accurately and stably measure the plastic strain of the metal material. It will be possible.

  When the image acquired by the camera is converted into image data having two-dimensional coordinates, it is preferable to binarize the image into, for example, white and black. The boundary 4 can be identified more reliably visually, and the two-dimensional coordinates can be identified more easily.

As described above, the plastic strain measuring pattern 1A used for measuring the plastic strain when the metal material is plastically deformed is regularly divided into a plurality of areas 2 and 3, and each of these areas 2 and 3 is divided. However, by adopting a configuration in which the contours are color-coded by different colors from other adjacent areas that are in line contact with each other, it becomes a reference for calculation of strain in each of the areas 2 and 3 in the plastic strain measurement pattern 1A. The part of the boundary 4 of each area 2 and 3 can be visually grasped uniquely and can be specified. As a result, it is possible to accurately measure the length necessary for calculating the strain with reference to the boundary 4 between the areas 2 and 3.
Therefore, since the handling of the lines that divide each area, such as the conventional plastic strain measurement pattern formed by only the lines, is eliminated, it is possible to reliably prevent reading errors in the measurement values caused by the difference in the handling of the lines. Therefore, highly accurate and stable measurement of the plastic strain of the metal material can be performed.

In the first embodiment, the plastic strain measurement pattern 1A is formed in a lattice shape as a whole, divided into a plurality of substantially square areas in plan view, and color-coded so as to form a checkered pattern. I was trying.
However, the plastic strain measurement pattern shown in FIG. 3 is a pattern having a plurality of concentric circles.

3 shows a plastic strain measurement pattern 1B according to the second embodiment of the present invention. The plastic strain measurement pattern 1B according to the second embodiment includes a plurality of concentric circles, and A plurality of areas 2 and 3 are regularly partitioned by a plurality of straight lines extending in the radial direction of the concentric circles, and each of these areas 2 and 3 is different from other adjacent areas that are in line contact with each other. It is formed by scribed circles that are color-coded by color.
The plurality of concentric circles have different diameters at a constant rate, and are set such that the distance between the inner peripheral concentric circle and the outer peripheral concentric circle is constant.
Further, the radial straight line extends radially from the centers of the plurality of concentric circles (16 directions in FIG. 2).
The areas 2 and 3 defined by the concentric circles and the radial straight lines are different in color from other adjacent areas whose outlines are in line contact with each other. The areas 4 of the two colors are respectively color-coded, and the boundary 4 between the areas 2 and 3 where the contours are in line contact can be visually and uniquely identified and identified by the color classification.
In this embodiment, as in the first embodiment described above, the color of area 1 of the first color is the background color of the metal material, and area 3 of the second color is filled with black. Both areas are color-coded in two colors. Further, the area of the central circular portion is not subjected to color coding as a portion not subjected to plastic strain measurement.

  The plastic strain measurement pattern 1B according to the second embodiment basically has the same operations and effects as those of the first embodiment described above, but the metal material is deep-drawn due to the characteristics of the pattern. It is extremely useful in doing so.

  In addition, the measurement of the plastic strain of the metal material using the plastic strain measurement pattern 1B according to the second embodiment having the above-described configuration is basically the same as the measurement method in the first embodiment described above. The procedure is performed, and the actions and effects are the same as those in the first embodiment, and thus detailed description thereof is omitted.

FIG. 3 shows a third embodiment of the plastic strain measurement pattern according to the present invention. The plastic strain measurement pattern 1C according to the third embodiment includes a plurality of circles and a lattice shape. It is a combined pattern.
That is, as shown in FIG. 3, a plurality of circles having the same diameter are arranged regularly while overlapping, and a lattice shape having a substantially square space in one side having the same length as the radius of the circle. Furthermore, by arranging in an overlapping manner, it is regularly partitioned into a plurality of areas. Furthermore, each of these areas is color-separated into a first color area 2 and a second color area 3 in different colors from other adjacent areas whose outlines are in line contact with each other. ing.
Accordingly, for each of the areas 2 and 3, the color coding allows the portion of the boundary 4 with the areas 3 and 2 where the contours are in line contact to be visually and uniquely identified and specified.
In this embodiment, as in the first and second embodiments described above, the color of the first color area 2 is the ground color of the metal material, and the second color area 3 is black. Both areas are color-coded in two colors.

The plastic strain measurement pattern 1C according to the third embodiment basically has the same functions and effects as those of the first embodiment described above, but the metal material is stretched and formed due to the characteristics of the pattern. This is particularly useful when the direction of plastic strain of the metal material is diverse, such as when processing or forming the processed metal material into a relatively complicated shape by pressing or the like.
The measurement of the plastic strain of the metal material using the plastic strain measurement pattern 1C according to the third embodiment having the above configuration is basically the same as the measurement method in the first embodiment described above. The procedure is performed, and the actions and effects are the same as those in the first embodiment, and thus detailed description thereof is omitted.

FIG. 5 shows a fourth embodiment of the plastic strain measurement pattern of the present invention. The plastic strain measurement pattern 1D of the fourth embodiment is the same as that of the third embodiment described above. Similarly, it is a combination of a plurality of circles and a lattice shape, but is formed in a pattern different from that of the third embodiment.
That is, as shown in FIG. 5, the plastic strain measurement pattern 1D according to this embodiment arranges a plurality of circles of the same diameter regularly and linearly in the vertical and horizontal directions, and the center of each circle. It is based on a scribed circle that is regularly partitioned into a plurality of areas by further overlapping and arranging a grid shape having a substantially square space in plan view, which consists of straight lines passing through. Each of these areas is color-coded into a first color area 2 and a second color area 3 with different colors from other adjacent areas whose outlines are in line contact with each other. 2 and 3 can visually identify and specify the boundary 4 with the adjacent area by color coding.
Also in this embodiment, as in the first to third embodiments described above, the color of the first color area 2 is the ground color of the metal material, and the second color area 3 is black. Both areas are color-coded in two colors.

The plastic strain measurement pattern 1D according to the fourth embodiment basically has the same functions and effects as the first embodiment described above, but the plastic strain according to the third embodiment. Similar to the measurement pattern 1C, it is useful when the direction of plastic strain of the metal material is complicated, such as when the metal material is stretch-molded, or when it is processed and molded into a relatively complicated shape by a press or the like. .
In addition, the measurement of the plastic strain of the metal material using the plastic strain measurement pattern 1D according to the fourth embodiment having the above-described configuration is basically the same as the measurement method in the first embodiment described above. The procedure is performed, and the actions and effects are the same as those in the first embodiment, and thus detailed description thereof is omitted.

Incidentally, in each area constituting the plastic strain measurement pattern 1B~1D in the second to fourth embodiments, the length of the boundary line between the adjacent area A is to about 1.0mm~100mm Is the same as the first embodiment, more preferably 1.0 to 50 mm, and further preferably 1.0 to 10 mm.

In the said 1st-4th embodiment, although the example using the pattern 1A-1D for plastic strain measurement which has the specific shape of FIG. 1, FIG. 3-FIG. 5 is demonstrated, it is for plastic strain measurement. If the pattern is regularly divided into a plurality of areas, and each of these areas is color-coded with a different color from other adjacent areas whose outlines are in line contact with each other, the first to first patterns An appropriate pattern other than the plastic strain measurement patterns 1A to 1D described in the fourth embodiment can be used.
Further, the color coding of each area of the pattern for measuring plastic strain is not limited to two colors as long as the boundary portion between adjacent areas can be uniquely identified visually, and three or more colors are used. May be color-coded.

In the first to fourth embodiments, the plastic strain measurement of the metal material using the plastic strain measurement patterns 1A to 1D is monitored by monitoring the plastic strain measurement pattern with a camera. , converts the image into image data having a two-dimensional coordinate, based on the 2-dimensional coordinates to measure the length necessary for the measurement of strain in each area, plastic strain measurements metal material on the basis of the measured values Is used.
Alternatively, the plastic strain may be measured based on a measurement value obtained by measurement by the measurer.

In order to confirm the effect of the present invention, it was formed only with a metal material (hereinafter referred to as “example of the present invention”) printed with the plastic strain measurement pattern 1A described in the first embodiment and a conventional line. An experiment was performed to compare the measurement accuracy of plastic strain measurement using a metal material (hereinafter referred to as “comparative example”) on which a plastic strain measurement pattern composed of a lattice-shaped pattern was printed.
In the above experiment, the plastic strain measurement pattern according to the present invention example and the plastic strain measurement pattern according to the comparative example are printed on the surfaces of separate thin steel plates, respectively, and the overhang test is performed on each thin steel plate. Went. Then, the pattern for measuring plastic strain after fracture is transferred with an adhesive tape, the image is taken into an electronic computer, and the vertical and horizontal lengths of each area in the pattern are read on the monitor image. It was examined how much reading error occurred in the inventive example and the comparative example.
The overhang test is performed 62 times for each of the present invention example and the comparative example, and the length and width of each area are read twice by the same measurer on different days. It was.
Each of the plastic strain measurement patterns of the present invention example and the comparative example has a lattice shape composed of a square area in a plan view having a side of 2 mm, and for the comparative example, the width (thickness) of a line dividing the area Was about 0.1 mm. Further, when measuring the length of the area according to the comparative example, the inner side of the line dividing each area is set as the starting point or the ending point of the measurement.

As a result of this experiment, it was found that a reading error of 0.121 mm occurred on the average in the comparative example. This means that an error of about 6% occurs with respect to 2 mm which is the vertical and horizontal length of each area in the plastic strain measurement pattern.
On the other hand, in the case of the present invention, almost no reading error occurred. For this reason, the reading accuracy of the example of the present invention is improved by about 6% compared to the comparative example. This is because, since each adjacent area is color-coded, the handling itself in the width direction of the line that divides each area as in the comparative example is eliminated, and the occurrence of reading errors corresponding to the width of this line is prevented. It is thought that.
From the above, it was found that the present invention can accurately and stably measure the strain related to the plastic strain measuring pattern provided on the metal material. Therefore, it was proved that the plastic strain of the metal material can be measured with high accuracy.

1A to 1D Plastic Strain Measurement Pattern 2 First Color Area 3 Second Color Area 4 Boundary

Claims (4)

In the method of measuring the plastic strain of the metal material by measuring the strain of the pattern for strain measurement disposed on the surface of the metal material, the plastic strain after the metal material is plastically deformed,
As the above pattern, the colors of the areas are different from those of other adjacent areas that are in line contact with each other without regularly dividing into a plurality of areas and having lines separating the areas. Using the plastic strain measurement patterns color-coded in the above, the boundary of each color-coded area is used to measure the strain of the pattern using the length measurement start and end points necessary for strain calculation as a reference. A method for measuring plastic strain of a metal material. 2. The metal material according to claim 1 , wherein the pattern is color-coded by a color of the surface of the metal material to be measured for plastic strain and another color different from the color of the surface of the metal material. Plastic strain measurement method. 3. The method for measuring plastic strain of a metal material according to claim 1, wherein each area of the pattern is color-coded by two different colors. Before the plastic deformation of the metal material, the pattern is preliminarily printed on the surface of the metal material with a paint, and a transparent adhesive tape is pressed against the surface of the metal material after the plastic deformation, so that the adhesive tape is plasticized. 4. The method for measuring a plastic strain of a metal material according to claim 1, wherein the pattern after deformation is transferred and the strain of the pattern is measured.

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