JP7302135B2 - Deformation analysis method for rubber materials - Google Patents

Description

The present invention relates to a deformation analysis method for rubber materials.

A digital image correlation method (DIC) is known as a technique for visualizing the in-plane distortion of a rubber material for deformation analysis of the rubber material. It is useful for the research and development of rubber products to visualize not only the in-plane strain during product use, but also the strain during mechanical testing.

As a deformation analysis method for a rubber material, for example, Non-Patent Document 1 discloses that the distortion of a notch in a test piece made of a rubber material can be visualized by photographing with a camera using visible light and using a digital image correlation method. Are listed. Further, Patent Document 1 describes a method of analyzing the tearing behavior of a rubber material using a method combining an X-ray imaging method and a digital image correlation method.

JP 2019-100814 A

Chang Liu, et al., "Influence of Strain Amplification Near Crack Tip on the Fracture Resistance of Carbon Black-filled SBR," Rubber Chemistry and Technology, Vol.88, No.2, pp276-288 (2015)

In a destructive test, such as a tear test, in which a test piece is destroyed when a force is applied to the test piece to deform it, the contour of the test piece changes as the fracture progresses, such as the growth of a crack. Therefore, it becomes difficult to perform stable calculations in the vicinity of the contour of the test piece, and analytical calculations are performed even in areas where the rubber material no longer exists due to the progression of fracture, and abnormal values are calculated. This may result in a calculation error and abort the analysis.

In view of the above points, an object of the embodiments of the present invention is to provide a deformation analysis method that enables stable analysis in a destructive test of a rubber material.

A deformation analysis method according to an embodiment of the present invention is a deformation analysis method in a fracture test of a rubber material. Obtaining a plurality of images from the initial image to the final image of the deformation to be deformed, setting a plurality of analysis points and subsets in the final image to set the analysis area, at that time, so that the contour of the test piece does not pass setting each subset and calculating the displacement of each analysis point from the final image towards the initial image in the opposite direction of the deformation by means of digital image correlation.

According to the embodiment of the present invention, stable deformation analysis can be performed in a destructive test of a rubber material.

4 is a flowchart showing a deformation analysis method according to one embodiment; Schematic diagram for explaining a destructive test according to one embodiment. An X-ray transmission image in an example. (A) is the initial image, (B) is the final image. A binarized image created from the final image in the example. Explanatory diagram for explaining how to set analysis points and subsets Explanatory diagram for explaining the method of setting analysis points near the contour of the specimen FIG. 10 is a diagram showing analysis results of X-direction displacement and Y-direction displacement of an initial image and a final image in the embodiment; FIG. 4 is a diagram showing analysis results of X-direction distortion, Y-direction distortion, and shear distortion of the initial image and the final image in the example.

Matters related to the implementation of the present invention will be described in detail below.

A deformation analysis method according to one embodiment is a deformation analysis method in a destructive test of a rubber material, and includes the following steps. FIG. 1 is the flow chart.
(a) a step of imparting a random pattern to the test piece (step S1);
(b) a step of capturing an image by photographing the test piece while deforming it (step S2);
(c) setting analysis points and subsets in the final image to set analysis regions (step S3);
(d) calculating the displacement of the analysis point by digital image correlation in the direction opposite to the deformation (step S4);
(e) converting the initial image into a displacement relative to the reference (step S5); and
(f) calculating the distortion in the final image (step S6);

Destructive tests for rubber materials to be subjected to deformation analysis include various mechanical tests involving destruction of rubber materials, and are not particularly limited. More specifically, there are those in which breaking progresses and the profile changes when force is applied to the test piece.

A rubber material is a substance having rubber-like elasticity, and is a concept that includes not only vulcanized rubber but also elastomers such as thermoplastic elastomers. As one embodiment, a vulcanized rubber is preferably used as the rubber material, that is, a vulcanized rubber obtained by vulcanizing a rubber composition in which various compounding agents including a vulcanizing agent such as sulfur are blended with a rubber polymer. is mentioned. Rubber polymers include, for example, various diene-based rubbers such as natural rubber, butadiene rubber, styrene-butadiene rubber, or combinations thereof. In addition, various compounding agents usually used in the rubber industry, such as fillers such as carbon black and silica, softening agents, anti-aging agents, zinc white, stearic acid, waxes, and vulcanization accelerators, can be used as compounding agents. can be done.

The shape of the test piece can be specified according to the type of destructive test targeted for deformation analysis, and is not particularly limited. For example, when an image is obtained by transmitting radiation in the step (b), the shape of the test piece may be any shape as long as the radiation can be transmitted, and various shapes such as sheet-like, cylindrical, block-like, etc., are preferred. It is in sheet form.

In addition, the test piece may be provided with a site that serves as a starting point of destruction (fracture starting site). Examples of fracture origin sites include cuts and notches provided at the edges of the test piece, slits and holes (that is, openings) provided inside the test piece, and the like. For example, in the test piece 10 in the tear test shown in FIG. 2, a notch 12 as a fracture starting point is provided at the center in the longitudinal direction on one side of the strip-shaped test piece 10 in the width direction. ing. The cut 12 is formed by making a cut in a direction perpendicular to the longitudinal direction of the test piece 10 .

In the deformation analysis method according to the embodiment, first, in step (a), a random pattern is given to a test piece made of a rubber material (step S1).

A random pattern is a random pattern applied to a specimen to perform a digital image correlation method. Therefore, although the random pattern is applied at least to the measurement target site, it may be applied to the entire test piece, for example, as long as it is applied to the measurement target site. The site to be measured is a region where an image is taken in the step (b) in order to perform deformation analysis on the test piece, and is a peripheral site including the above-mentioned fracture origin site.

A random pattern can be applied to the surface or interior of the specimen. For example, if the imaging in step (b) is to obtain a transmission image using radiation, the random pattern may be applied to the surface or interior of the test piece. Also, if the imaging in step (b) uses visible light to obtain an image, the random pattern may be imparted to the surface of the test piece.

When a random pattern is applied to the surface of the test piece, for example, a coating liquid containing marker particles may be applied by spraying onto the surface of the test piece, or a rubber layer containing marker particles may be applied to the surface of the test piece. May be provided on the surface. Further, when an image is acquired using visible light, for example, a colorant may be used to impart a random pattern such as a spotted pattern to the surface of the test piece.

When imparting a random pattern to the interior of the test piece, the random pattern may be imparted to the test piece by blending marker particles into the rubber material and dispersing the marker particles inside the test piece.

Marker particles are fine particles for forming random patterns used in the digital image correlation method. For example, fine particles detectable by radiation such as X-rays, that is, fine particles to be detected in radiographic imaging. As the marker particles, particles containing a metal element (i.e., metal-element-containing particles) are used, which are easily contrasted by radiation. A stable one is mentioned as. Specific examples include metal particles such as tungsten particles, silver particles and lead particles, and alumina particles.

The particle size of the marker particles is not particularly limited, and for example, a particle size equal to or higher than the spatial resolution (the number of effective pixels) of radiographic imaging may be used. Note that the spatial resolution varies depending on the line width and divergence of the radiation used.

In the deformation analysis method according to the embodiment, next, in step (b), the test piece is photographed while being deformed to obtain a plurality of images from the initial image to the final image of the deformation to be analyzed (step S2).

Specifically, the site to be measured is photographed while applying force to the test piece to deform it, that is, imparting strain. The strain to be applied to the test piece can be specified according to the type of destructive test to be subjected to deformation analysis.

While deforming the test piece in this manner, a plurality of two-dimensional still images representing the fracture behavior of the test piece are obtained by continuously photographing the test piece at predetermined time intervals. This includes initial and final images of the deformation to be analyzed. Here, the initial image is an image that serves as a reference for deformation analysis, and may be, for example, an image before deformation (that is, before imparting distortion) (see FIG. 3A). The final image is an image in the target deformation state in deformation analysis, for example, it may be an image at the final stage of fracture in a destructive test, more specifically, an image immediately before the test piece breaks in a tear test (Fig. 3(B)).

An image acquisition method is not particularly limited. For example, it may be photographed by a camera using ordinary visible light, or may be a radiation imaging method in which a test piece is irradiated with radiation such as X-rays. In the radiographic imaging method, a transmission image is obtained by irradiating a test piece with radiation so that the radiation penetrates the test piece. The image acquisition method itself by the radiation imaging method can be performed by a known method, and is not particularly limited. Here, radiation means radiation in a broad sense, and includes particle radiation such as neutron beams, and electromagnetic waves such as X-rays, gamma rays, and ultraviolet rays. X-rays are preferred, and therefore X-ray transmission images are preferably obtained as images.

FIG. 2 shows an outline of an X-ray imaging test apparatus according to one embodiment. The strip-shaped test piece 10 is attached to a tensile tester with both ends in the longitudinal direction held by grippers (not shown). Granted. The test apparatus is provided with an X-ray tube 22 as irradiation means for irradiating the test piece 10 with X-rays, and a detector 24 for detecting the X-rays transmitted through the test piece 10. An X-ray transmission image is obtained based on the X-rays obtained. The X-ray tube 22 and the detector 24 are arranged in a straight line with the cutout 12 in the test piece 10 and its surroundings as a measurement target site on both sides of the measurement target site.

X-rays to be used are preferably high-intensity X-rays of, for example, 10 ¹⁰ (photons/s/mrad ² /mm ² /0.1% bw) or more. Synchrotrons that emit such X-rays include SPring-8 of Japan Synchrotron Radiation Research Center and Aichi Synchrotron Light Center of ``Knowledge Hub Aichi''.

Also, the energy of X-rays is not particularly limited, and may be, for example, 1 to 100 keV or 10 to 50 keV. The X-ray irradiation time (that is, exposure time) is also not particularly limited, and may be, for example, 0.0001 to 10000 ms or 1 to 1000 ms. The frame rate is also not particularly limited, and may be, for example, 1 to 10000 fps or 1 to 2000 fps.

In the deformation analysis method according to the embodiment, in step (c), a plurality of analysis points and subsets are then set in the final image to set an analysis region (step S3). Thus, in this embodiment, analysis points and subsets are set using the final image rather than the initial image. This is because, in the next step (d), displacement calculation is performed by the digital image correlation method in the direction opposite to the deformation (that is, reverse reproduction).

In step (c), first, in the final image, the contour of the test piece at the measurement site may be obtained. The method of obtaining the contour of the test piece is not particularly limited, but it can be obtained, for example, by binarizing the final image. Specifically, a binarized image is created from the final image by binarizing using the luminance value difference between the rubber polymer, the background (air), and the marker particles, and the test piece is obtained from the binarized image. contours can be extracted. FIG. 4 shows an example of a binarized image created from the final image. Acquisition of a contour by such a binarized image, in combination with an image using radiation such as X-rays, makes it easier to obtain a contour because the difference in contrast between the rubber polymer and the background is greater than in the case of an image using visible light. It has the advantage of being able to extract information.

The contour of the test piece should be obtained at least at the part where the fracture to be analyzed is progressing. good. In the example of the tear test shown in FIG. 4, the notch spreads in the direction of elongation by applying an elongation strain to the test piece, and the outline of the portion along this widened notch can be obtained.

After acquiring the contour, the analysis area is set by setting analysis points and subsets within the specimen in the final image (that is, within the area corresponding to the specimen). Here, the analysis point is an arbitrary point in the test piece used to calculate the displacement in the digital image correlation method, and the deformation of the test piece can be analyzed by calculating the displacement at the analysis point. .

A subset is a minute calculation area for performing pattern matching based on the correlation of the luminance value distribution or the like in order to specify the positions of the analysis points before and after deformation, and consists of a plurality of pixels. A subset is set for each analysis point, so each subset contains one analysis point, and the analysis point is usually set at the center of the subset. In this example, the subset is a rectangular area centered on the analysis point. A rectangle is a concept that includes a square.

An analysis region is a region in which analysis points and subsets are set in the measurement target site, and calculation is performed by the digital image correlation method within this region to calculate the displacement of each analysis point. The analysis region is set to include a portion where fracture is progressing, and in a test piece provided with a fracture initiation site, is set within a range that includes a portion corresponding to the fracture initiation site. For example, in the tear test example, as shown in FIG. 5, the analysis area 28 is set to include the tip of the tear.

In this embodiment, when setting the analysis region, each subset is set so that the outline of the test piece does not pass through. That is, the subset is set so that the outline of the test piece is included in the region so that the air region, which is the background of the test piece, is not included in the region.

FIG. 5 is a schematic illustration of this, with the specimen region 32 to the left of the parabolic contour 30 and the background region 34 to the right of the contour 30 . Black circles are analysis points 36. In the test piece region 32, a plurality of equally spaced gratings 38 extending in the Y direction (extension direction) and a plurality of lattice elements extending in the X direction (perpendicular to the extension direction) An analysis point 36 is set at each lattice point which is an intersection with the lattice elements 40 arranged at equal intervals. A subset 42 consisting of a rectangular (square in the example of FIG. 5) area is set around each analysis point 36 . Although only a part of the subsets 42 are shown in FIG. 5, the illustration is omitted, and similar subsets 42 are set for each analysis point 36 .

In the vicinity of the contour 30, not only the grid points existing within the background region 34, but also the grid points existing within the test piece region 32, when a subset is set around the grid points, Analysis points 36 are not set for grid points that pass through the contour 30, and therefore subsets 42 are not set either. Positions in the vicinity of the contour 30 where the subset 42 should not be set are indicated by dotted-line frames 44 in FIG.

In order to set the contour of the test piece so that it does not pass through the subset, it is preferable to set as follows in one embodiment. For example, when the subset is a rectangular area centered on the analysis point, when setting the analysis area, the contour part of the test piece should be separated from the contour by more than half the size of the subset. Set analysis points. More specifically, in the contour portion of the test piece, it is preferable to set the analysis points with a gap of at least half the subset size and less than the subset size from the contour.

Specifically, as shown in FIG. 6A, consider setting a rectangular subset 42 for the contour 30 extending obliquely with respect to the gratings 38,40. In this case, half the subset size is the extent 42A that bisects the subset 42 in the X direction in the X direction and the extent 42B that bisects the subset 42 in the Y direction in the Y direction. Grid points 46 indicated by black circles in FIG. Specifically, the range is equal to or greater than half the subset size 42A, and there is a gap of less than one subset size. In addition, there is a gap (that is, a blank space) in the Y direction between the outline 30 and the range 42B or more, which is half the subset size. Specifically, the range is 42B or more, which is half the subset size, and there is a gap of less than one subset size. Therefore, an analysis point 36 is set for this lattice point 46, and a subset 42 centering on the analysis point 36 is set.

On the other hand, the grid point 48 adjacent to the right side of the grid point 46 and the grid point 50 adjacent to the lower side of the grid point 46 are separated from the outline 30 by ranges 42A and 42B that are half the subset size in the X and Y directions, respectively. There is no Therefore, neither the analysis point 36 nor the subset 42 is set for these lattice points 48 and 50 .

As shown in FIG. 6B, when a rectangular subset 42 is set for the contour 30 extending parallel to the lattice 38 in the Y direction, the grid points 52 indicated by black circles correspond to the contour 30 and There is a gap of 42A, which is half the subset size, not only in the Y direction but also in the X direction. Specifically, in the X direction, there is a gap equal to or greater than half the subset size range 42A and less than one subset size. Therefore, an analysis point 36 is set for this grid point 52, and a subset 42 centering on the analysis point 36 is set. On the other hand, the lattice point 54 adjacent to the right side of the lattice point 52 is not separated from the contour 30 by the range 42A half the subset size in the X direction. Therefore, neither the analysis point 36 nor the subset 42 is set for the grid point 54 . The same applies to the contours 30 extending parallel to the lattice 40 in the X direction, and the same concept may be applied to contours having other shapes or positional relationships.

After setting the analysis area as described above, in the deformation analysis method according to the embodiment, in the step (d), each analysis point is determined by the digital image correlation method from the final image to the initial image in the direction opposite to the deformation. Calculate the displacement (step S4). That is, in general deformation analysis, the displacement is calculated by the digital image correlation method in the direction in which the deformation progresses. Displacement calculation is performed by the image correlation method.

The digital image correlation method is a method of comparing images before and after deformation of a random pattern given to an object to analyze the deformation of the object, and uses movement tracking of luminance value patterns as a measurement principle. Specifically, for the images at the first time t = t ₀ and the second time t = t ₀ + dt, the subset that shows a high correlation with the luminance distribution of the subset in the image at the first time is Any subset is searched by numerical analysis and the corresponding subset is identified. As a result, it is possible to calculate the movement direction and the movement amount of the analysis points in the deformation from the first time to the second time, that is, the displacement, for the subset. The image correlation method itself is described on pages 31 to 46 of "Visualization Information Library 4 PIV and Image Analysis Technology" (published by Asakura Shoten Co., Ltd., edited by Visualization Information Society, published on April 25, 2012). and can also be performed using commercially available software.

In this embodiment, as shown in FIG. 3, the displacement of each analysis point is calculated by the digital image correlation method (DIC) in reverse reproduction from the final image to the initial image. That is, the calculation is performed while sequentially updating the reference image from the final image to the initial image. More specifically, the image at the first time is set as the final image, the image at the time of deformation one before is set as the image at the second time, and calculation is performed by the digital image correlation method. Calculation is performed by the digital image correlation method using the image at the time of deformation as the image at the first time, and the image at the time of deformation two before the final image as the image at the second time, and the initial image is reached in the same way. Calculation by the digital image correlation method is performed using the images sequentially traced back to .

This gives the displacement from the final image to the initial image for each analysis point in the analysis region.

In the deformation analysis method according to the embodiment, then, in step (e), the displacement of each analysis point obtained by the above calculation is converted into a displacement in the final image based on the initial image (step S5).

In that case, the displacement of each analysis point calculated while sequentially updating in the direction opposite to the deformation as described above is converted to the displacement based on the image before deformation at each update, so that the displacement based on the initial image is can be converted to Alternatively, the displacement may be converted to the displacement based on the initial image by converting the image before deformation to the displacement based on each update. Alternatively, the displacement in the initial image relative to the final image may be calculated and then directly converted to the displacement in the final image relative to the initial image.

As a result, the displacement in the final image based on the initial image is obtained for each analysis point in the analysis area. For example, the X-direction displacement in the final image for each analysis point (displacement in ) and the Y-direction displacement (displacement in the stretch direction) are obtained.

After the initial image is converted into a displacement based on the reference in this way, in step (f), the distortion at each analysis point in the final image is calculated from the converted displacement (step S6).

Strain can be obtained by differentiating the distribution of displacement, for example, in two orthogonal directions, such as X-direction strain (strain in the direction perpendicular to the direction of elongation) and Y-direction strain (strain in the direction of elongation). Strain may be determined, and shear strain may be determined. The shear strain is obtained by adding a value obtained by differentiating the X-direction displacement with respect to the Y-direction coordinate and a value obtained by differentiating the Y-direction displacement with respect to the X-direction coordinate.

As described above, according to the present embodiment, it is possible to perform deformation analysis by applying the digital image correlation method to a mechanical test involving destruction of a rubber material. Specifically, by performing image analysis in reverse playback from the final image of the deformation to be analyzed toward the initial image, the analysis area is set in the final image, so the destruction progresses It is possible to define an analysis region that can be stably calculated in the vicinity of the contour, even though it is an analysis of a destructive test in which the contour of the specimen changes.

In addition, when setting the analysis area, each subset is set so that the contour does not pass through the contour part of the test piece, so the background air region is not included in the subset, improving the stability of the analysis. can be enhanced.

Therefore, according to this embodiment, even though it is an analysis of a destructive test in which the contour of the test piece changes as the fracture progresses, calculation errors are less likely to occur, and calculations can be performed stably. can be obtained. Therefore, it can be used for material development of rubber products.

Examples of the present invention are shown below, but the present invention is not limited to these examples.

Using a Banbury mixer, 100 parts by mass of styrene-butadiene rubber ("JSR1502" manufactured by JSR Corporation), 50 parts by mass of carbon black ("Seist 3" manufactured by Tokai Carbon Co., Ltd.) and zinc oxide (Mitsui Kinzoku Mining ( Co., Ltd. “zinc white 1”) 2 parts by mass, stearic acid (Kao Co., Ltd. “Lunac S-20”) 1 part by mass, sulfur (Hosoi Chemical Industry Co., Ltd. “rubber powder sulfur 150 mesh") and 1 part by mass of a vulcanization accelerator (Ouchi Shinko Kagaku Kogyo Co., Ltd. "Noccellar CZ") were added and kneaded. Then, 4 parts by mass of marker particles (product number 327077 Silver flakes 10 μm manufactured by Sigma-Aldrich) were roll-mixed at a roll surface temperature of 60° C. to prepare an unvulcanized rubber composition.

The obtained unvulcanized rubber composition is formed into an unvulcanized rubber sheet having a thickness of 1 mm using a roll, and is pressed with a metal mold (160° C., 30 minutes) to form a rubber sheet having a thickness of 1 mm. was made. The obtained rubber sheet was punched into a strip of 9 mm width×30 mm length, and a test piece was prepared by making a slit of 5 mm length in the center of the strip.

Using the obtained test piece, an image was acquired by an X-ray imaging method while performing a tear test as shown in FIG. A tear test was performed by setting a test piece in a tensile tester and stretching it at a tensile speed of 50 mm/min until it was stretched from 0 to 100% (the distance between the grips on both sides was doubled). The X-ray conditions and imaging conditions were as follows: frame rate: 100 fsp, X-ray exposure time: 10 ms, X-ray energy: 15 keV, resolution of photographed image: 7 μm/px.

Then, for the final image among the obtained multiple images, binarize using the difference in luminance values to create a binarized image, determine the contour of the test piece, and set analysis points and subsets. to set the analysis area. The subset was a square area of 21×21 pixels, and the analysis point was set at its center. At that time, as described above, by setting each analysis point with a gap of more than half of the subset size between the contour part of the test piece and the contour, the contour of the test piece does not pass through each subset. made it

Next, when the displacement of each analysis point was calculated by applying the digital image correlation method in reverse playback from the final image to the initial image, the displacement could be calculated stably without calculating outliers. did it. The obtained displacement was converted into a displacement based on the initial image, and the distortion in the final image at each analysis point was calculated from the converted displacement.

FIG. 7 is a diagram showing the distribution of X-direction displacement and Y-direction displacement with respect to the initial image (0% elongation) and the final image (100% elongation). In each image, the unit of numerical values for the X-axis and Y-axis is μm, and the unit of numerical values for the right scale bar is also μm. The analysis area is shown in grayscale, and the analysis area set in the final image has a shape that is greatly shrunk in the Y direction, especially around the notch in the initial image. Since the displacement distribution is based on the initial image, the displacement in the initial image is 0 μm over the entire range of the analysis area. In the final image, the displacement in the X direction increased with increasing distance from the notch in the X direction, and the absolute value of the displacement in the Y direction increased with increasing distance from the tip of the crack in the Y direction.

FIG. 8 shows distributions of X-direction strain, Y-direction strain, and shear strain with respect to the initial image (0% elongation) and the final image (100% elongation). In each image, the unit of numerical values for the X and Y axes is μm, and the unit of numerical values for the right scale bar is %. As in FIG. 7, the analysis area is shown in grayscale. Since the strain distribution is based on the initial image, the strain in the initial image is 0% over the entire analysis area. The grayscale in the final image shows the distribution of X-, Y- and shear strains in the tear test of the specimen.

As a comparative example, forward reproduction is performed instead of reverse reproduction. In other words, after setting the analysis area in the initial image, calculation is performed by the digital image correlation method from the initial image toward the final image, and the rest is the same as the above embodiment. When the analysis was performed, it was found that an abnormal value was calculated by performing the analytical calculation even though the rubber material did not exist in the vicinity of the contour, and a stable calculation could not be performed.

10... test piece, 12... notch, 28... analysis area, 30... contour, 36... analysis point, 42... subset, 42A, 42B... half range of subset size

Claims (5)

A deformation analysis method in a destructive test of a rubber material,
imparting a random pattern to a test piece made of a rubber material;
Obtaining a plurality of images from the initial image to the final image of the deformation to be analyzed by photographing the test piece while deforming;
setting a plurality of analysis points and subsets in the final image to set an analysis region, and setting each subset so that the contour of the test piece does not pass through;
calculating the displacement of each analysis point from the final image towards the initial image by digital image correlation in the opposite direction of the deformation;
Deformation analysis method for rubber materials including 2. The method of claim 1, further comprising transforming the calculated displacement of each analysis point into a displacement relative to the initial image, and calculating a distortion in the final image from the transformed displacement. Deformation analysis method described. The subset is a rectangular area centered on the analysis point, and when setting the analysis area, each analysis point is set with a gap of at least half the size of the subset from the contour of the test piece. The deformation analysis method according to claim 1 or 2. 4. The deformation analysis method according to any one of claims 1 to 3, wherein said imaging is to obtain an X-ray transmission image using X-rays, and said random pattern is formed by metal element-containing particles. The deformation analysis method according to any one of claims 1 to 4, wherein the destructive test is a tear test, and the analysis region includes a tip of the tear in the tear test.

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