JP7027139B2 - How to analyze the tearing behavior of rubber materials - Google Patents

Description

The present invention relates to a method for analyzing the tearing behavior of a rubber material, and also relates to a test piece suitably used for this analysis method.

Conventionally, in order to analyze the wear mechanism of tread rubber in tire development, for example, it has been required to visualize the deformation behavior of the rubber material at the time of tearing, that is, the tearing behavior.

Non-Patent Document 1 describes photographing with a camera using ordinary visible light and observing the tearing behavior of rubber by using a digital image correlation method. In this camera photography with visible light, silver powder is sprayed on the surface of a black rubber test piece to form a random pattern, which is used as a marker for analysis by a digital image correlation method. However, with this method, the silver powder is peeled off with tearing and cannot be analyzed accurately.

Non-Patent Document 2 describes that the micro-strain amount distribution at the time of cracking can be quantified by performing X-ray imaging measurement using a rubber material containing marker particles. Further, Non-Patent Document 3 describes that the deformation behavior of the crack growth process can be observed by the same X-ray imaging measurement. However, neither document describes a specific analysis method.

Chang Liu and 4 others, "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) Takahiro Mabuchi and 4 others, "Study on Concentration of Strain in Micro-region of Rubber and Its Time Change", [online], (2008), Spring 8 Usage Report, Issue No. 2008A1930, [October 26, 2017] Search], Internet <URL: https://user.spring8.or.jp/apps/experimentreport/detail/4726/en> Takahiro Mabuchi and 4 others, "Concentration of strain in the micro region of rubber and its time change", [online], (2008), Spring 8 usage report, Issue No. 2008B1935, [Search on October 26, 2017] , Internet <URL: https://user.spring8.or.jp/apps/experimentreport/detail/5406/en>

It has been found that the following problems occur when an image is taken by an X-ray imaging method and the tearing behavior is analyzed while performing a tearing test using a rubber material containing marker particles as a test piece.

That is, when the rubber material is provided with a notch that is a starting point of tearing, it is difficult to cut the rubber material vertically because the rubber material is soft. For example, as shown in FIG. 7A showing a cross section along the notch 102 of the test piece 100, the length of the notch 102 differs in the thickness direction of the test piece 100, and the tip 102a of the notch 102 is the surface 104 of the test piece 100. It may be diagonal rather than vertical to. When the tip 102a of the notch 102 is tilted in this way, the X-ray image at the notch at the time of tearing shows the notch together with the marker particles 108 present on the surface 104 of the test piece 100, as shown in FIG. 7B. The marker particles 108 existing in the cross section 106 of 102 are also reflected. Then, in the image analysis, since the marker particles 108 on the surface 104 and the marker particles 108 on the cross section 106 cannot be distinguished, the tearing behavior cannot be accurately analyzed.

In view of the above points, it is an object of the present invention to provide a method capable of analyzing the behavior of a rubber material at the time of tearing.

The analysis method according to the embodiment of the present invention is a method for analyzing the tearing behavior of a rubber material, in which a rubber layer containing the marker particles is provided on the surface of a test piece main body made of a rubber material containing no marker particles and the rubber material is torn. A test piece provided with a notch serving as a starting point of the above is prepared, and while performing a tear test using the test piece, the test piece is irradiated with X-rays so that X-rays pass through the rubber layer, and X-rays are carried out. A plurality of images are acquired by the line imaging method, and the displacement amount of the marker particles is calculated from the obtained plurality of images by the particle image flow velocity measurement method.

The test piece for tearing behavior analysis according to the embodiment of the present invention is a test piece used by irradiating X-rays by an X-ray imaging method to analyze the tearing behavior of a rubber material, and is a rubber containing no marker particles. It is provided with a test piece main body made of a material and a rubber layer containing marker particles provided on the surface of the test piece main body, and is provided with a notch as a starting point of tearing.

In the embodiment of the present invention, a test piece provided with a rubber layer containing marker particles on the surface of the test piece main body is used as a test piece in order to acquire an image by an X-ray imaging method while performing a tear test. Since the test piece does not have marker particles as a whole in the thickness direction, the image is formed by the marker particles existing in the rubber layer on the surface of the test piece and is not affected by the cross section of the notch. Therefore, even if the notch is formed with an inclination, problems such as erroneous recognition due to the presence of marker particles in the cross section of the inclined incision in the image analysis by the particle image velocimetry method are solved, and the test piece is used. It is possible to analyze the tearing behavior of.

A flowchart showing a tearing behavior analysis method according to an embodiment. A diagram for explaining the manufacturing process of the test piece according to the embodiment, (A) a perspective view of the test piece main body, (B) a perspective view of the rubber sheet, and (C) a perspective view of the test piece after the rubber sheet is attached. , (D) Perspective view of the test piece with a notch Schematic diagram of the X-ray imaging test apparatus according to one embodiment The figure which shows the analysis result in Example 1. Image by X-ray imaging showing particles to be tracked in Example 2 Graph showing the analysis result in Example 2 (A) Enlarged cross-sectional view of the main part of the test piece according to the comparative example, (B) Schematic diagram of the X-ray imaging image using the test piece.

Hereinafter, matters related to the practice of the present invention will be described in detail.

The analysis method according to the present embodiment is a method for analyzing the tearing behavior of a rubber material, and is obtained by a step of preparing a test piece and a step of acquiring an image by an X-ray imaging method using the test piece. Includes a step of analyzing the image.

Here, the rubber material is a substance having rubber-like elasticity, and is a concept including not only vulcanized rubber but also an elastomer such as a thermoplastic elastomer.

In the step of preparing the test piece, a rubber layer containing the marker particles is provided on the surface of the test piece main body made of a rubber material containing no marker particles, and a test piece having a notch as a starting point of tearing is prepared.

As the test piece main body, for example, a thin plate-shaped rubber material is used. As the rubber material, vulcanized rubber is preferably used, that is, vulcanized rubber obtained by vulcanizing a rubber composition obtained by blending a rubber polymer with various compounding agents containing a vulcanizing agent such as sulfur. Examples of the rubber polymer include natural rubber, butadiene rubber, styrene-butadiene rubber, and various diene-based rubbers such as a combination thereof. In addition, as the compounding agent, various compounding agents usually used in the rubber industry such as fillers such as carbon black and silica, softeners, antiaging agents, zinc oxide, stearic acid, wax, and vulcanization accelerators should be used. Can be done. However, marker particles are not mixed with the rubber material of the test piece body.

The thickness of the test piece body is not particularly limited, but one having a thickness of 2.0 mm or less in the direction along the axis of the incident X-ray is preferably used, and more preferably 1.0 to 2.0 mm.

As the rubber layer, a layer made of vulcanized rubber may be mentioned as in the case of the test piece main body, but it may be used without vulcanization as long as it is adhered to the surface of the test piece main body. The rubber composition forming the rubber layer is not particularly limited, but the same rubber composition as the rubber composition forming the test piece main body can be used. However, marker particles are blended in the rubber layer.

Here, the marker particles are fine particles that can be detected by X-rays, that is, fine particles to be detected in the X-ray imaging method, and examples thereof include silver particles and alumina particles that can absorb X-rays.

The blending amount of the marker particles is not particularly limited, and may be, for example, 0.01 to 100 parts by mass or 1 to 10 parts by mass with respect to 100 parts by mass of the rubber polymer.

The thickness of the rubber layer is not particularly limited, but the thickness in the direction along the axis of the incident X-ray is preferably less than 1.0 mm, more preferably 0.1 mm or more and less than 1.0 mm, and further preferably. Is 0.1 to 0.5 mm. By reducing the thickness of the rubber layer, problems such as erroneous recognition due to marker particles existing in the thickness direction can be more reliably eliminated.

The rubber layer is a layer provided on the surface of the test piece main body. Specifically, the rubber layer is provided on one of the front and back surfaces of the plate-shaped test piece main body. In the present embodiment, in order to analyze the tearing behavior starting from the notch, the rubber layer may be provided at least in the vicinity thereof including the notch. The rubber layer is usually provided perpendicular to the axis of the incident X-rays, and the X-rays are irradiated so as to pass through the test piece main body together with the rubber layer in the thickness direction.

In one embodiment, the test piece preparation steps include a step S1 for preparing the test piece main body, a step S2 for preparing the rubber sheet forming the rubber layer, and rubber on the side surface of the test piece main body, as shown in FIG. The step S3 of attaching the sheet and the step S4 of providing a notch in the attached test piece may be included. As described above, the rubber layer may be formed by attaching a rubber sheet containing the marker particles to the surface of the test piece main body.

For example, in step S1, an unvulcanized test piece main body made of a rubber material containing no marker particles is produced. In step S2, an unvulcanized rubber sheet containing marker particles is produced. Then, in step S3, a rubber sheet is attached to the surface of the test piece main body and both are integrally vulcanized to obtain a test piece having marker particles only on the rubber layer on the surface. Then, in step S4, a notch is provided in the obtained test piece by using a notch device having a blade such as a razor blade.

FIG. 2 is a diagram showing a manufacturing process of the test piece 10 according to the embodiment. As shown in FIG. 2A, a strip-shaped test piece main body 12 made of unvulcanized rubber is produced. Further, as shown in FIG. 2B, a rubber sheet 14 made of unvulcanized rubber containing marker particles is produced in the same shape as the test piece main body 12. Then, the rubber sheet 14 is superposed on one surface of the test piece main body 12 and vulcanized, so that the rubber sheet 14 is attached to the test piece main body 12 as shown in FIG. 2C. Next, as shown in FIG. 2D, a notch 16 is provided in the central portion in the longitudinal direction of the obtained vulcanized molded product. As a result, a test piece main body 12 made of a rubber material containing no marker particles and a rubber layer 15 made of a rubber sheet 14 containing the marker particles provided on the surface thereof are provided, and a notch 16 serving as a starting point of tearing is provided. The test piece 10 is obtained.

The notch 16 is formed by making a cut perpendicular to the longitudinal direction at the center of the strip-shaped test piece 10 on one side in the width direction. The notch 16 is provided perpendicular to the surface of the test piece 10, and is provided as a whole in the thickness direction of the test piece 10 composed of the test piece main body 12 and the rubber layer 15. In the figure, the thickness of the test piece main body 12 is indicated by T1, and the thickness of the rubber layer 15 is indicated by T2.

Next, as shown in FIG. 1, a step S5 (that is, an image acquisition step) of acquiring an image by an X-ray imaging method using the test piece obtained above is performed.

In the image acquisition step, while performing a tear test on the test piece, the test piece is irradiated with X-rays so that X-rays pass through the rubber layer, and a plurality of two-dimensional images are acquired by an X-ray imaging method. Specifically, the test piece is pulled in the longitudinal direction to perform tearing starting from the notch, and at least the crevice portion (that is, the tip portion of the notch) is irradiated with X-rays. Then, by continuously photographing the test pieces to be torn and deformed at predetermined time intervals by using the synchrotron radiation X-ray imaging method, a plurality of still images showing the tearing behavior can be obtained.

The present embodiment is characterized by the configuration of the test piece, and the image acquisition method itself by the X-ray imaging method can be performed by a known method and is not particularly limited.

FIG. 3 shows an outline of the X-ray imaging test apparatus according to the embodiment. The strip-shaped test piece 10 is attached to a tensile tester with both ends in the longitudinal direction held by a grip (not shown), and the grips on both sides are moved in a direction to separate from each other in the longitudinal direction. Be pulled. The tearing behavior of the test piece 10 at the notch 16 at this time, that is, the process of crack growth is visualized.

As a pulling operation of both ends of the test piece 10 by the tensile tester, for example, the test piece is gradually torn while fixing one grip and moving the other grip in a direction to separate them at a constant speed. The test piece 10 may be fixed, or the test piece 10 may be fixed by widening the distance between the grips on both sides to a certain size at a time so that the elongation rate of the test piece becomes a constant value. May be gradually torn.

The test apparatus is provided with an X-ray tube 22 as an irradiation means for irradiating the test piece 10 with X-rays as an imaging means by X-ray imaging, and a detector 24 for detecting the X-rays transmitted through the test piece 10. A two-dimensional image is acquired based on the X-rays detected by the detector 24. The X-ray tube 22 and the detector 24 are arranged in a straight line with the crevice portion of the tear starting from the notch 16 in the test piece 10 interposed therebetween, and at least the crevice portion is irradiated with X-rays. The heights of the wire tube 22 and the detector 24 are set.

The X-rays emitted from the X-ray tube 22 irradiate the surface 10A of the test piece 10 so as to pass through the rubber layer 15. In this example, the surface 10A is perpendicular to the axis of the incident X-rays, and the X-rays pass through the test piece main body 12 together with the rubber layer 15 in the thickness direction of the test piece 10. In FIG. 3, the test piece 10 is irradiated with X-rays from the surface on the rubber layer 15 side, but the test piece 10 is installed so as to irradiate the X-rays from the surface on the opposite side. You may.

As the X-ray to be used, for example, it is preferable to use high-luminance X-ray of 10 ¹⁰ (photons / s / mrad ² / mm ² / 0.1% bw) or more. Examples of such a synchrotron that emits X-rays include SPring-8 of the High-Brightness Photon Science Research Center and Aichi Synchrotron Optical Center of "Knowledge Hub Aichi".

The X-ray energy 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, the 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.

Next, an image analysis step of calculating the displacement amount of the marker particles from the plurality of two-dimensional images obtained above by the particle image velocimetry method (PIV) is performed.

The particle image velocimetry method is a method of estimating a velocity vector by obtaining a displacement vector of particles in a minute time from a visualization image obtained by continuously photographing a flow field containing particles. Therefore, the displacement amount of each marker particle existing in the image can be calculated from the plurality of two-dimensional images obtained above, and thus the deformation amount in the torn portion of the test piece can be visualized. That is, the direction and magnitude of deformation at each site in the teared portion of the test piece can be obtained, and in-plane distribution and quantitative deformation amount analysis with respect to the tearing behavior becomes possible. Further, the strain can be calculated by differentiating the amount of deformation. For example, if the deformation amount distribution in the x direction is differentiated in the x direction, the strain in the x direction can be calculated.

The particle image velocimetry method includes a digital image correlation method (DIC) and a particle tracking method (PTV). The digital image correlation method is a suitable method when the density of marker particles is high, and the particle tracking method is a suitable method when the density of marker particles is low. Therefore, either method may be selected according to the density of the marker particles in the image obtained above.

The digital image correlation method is an analysis method based on the measurement principle of movement tracking of a brightness value pattern, and more specifically, for a particle image at the first time t = t ₀ and the second time t = t ₀ + dt, one hour. The cross-correlation function between the brightness value distribution in the minute area (inspection area) in the image of the eye and the brightness value distribution in the area (exploration area) in the image at the second time is obtained, and the position where the maximum value is obtained is determined in the inspection area. This is a method of estimating the average relative position of the particles in the particle group and obtaining the displacement vector.

On the other hand, the particle tracking method is an analysis method whose measurement principle is the movement tracking of individual particle images. More specifically, the particles are automatically tracked using the position information of the individual particles, and the tracked particles are used. This is a method of calculating the velocity vector by converting the image coordinates of the above into real space.

The digital image correlation method 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, April 25, 2012). It can be done by using the method of. Further, the particle tracing method can be performed by using the method described on pages 16 to 30 of the same document.

In one embodiment, the image analysis step includes a step S6 for calculating the concentration or density of the marker particles, a step S7 for determining whether or not the calculated concentration is equal to or higher than the discrimination value, and a step S7 for calculating the discrimination value or higher, as shown in FIG. In this case, the step S8 for calculating the displacement amount using the digital image correlation method and the step S9 for calculating the displacement amount using the particle tracking method when the value is less than the discrimination value may be included. By selecting the digital image correlation method and the particle tracking method based on the density of the marker particles in the two-dimensional image in this way, it is possible to calculate the displacement amount with higher accuracy.

As the concentration used for such discrimination, the relative distance ρ _γ represented by the following formula (1) described on page 18 of the above-mentioned document “Visualization Information Library 4 PIV and Image Analysis Technology” may be used.

In the equation, γ _max is the maximum moving distance of particles in the image, N ₀ is the number of particles in the whole image, A ₀ is the area of the image, and N ₀ / A ₀ is the size of the area to which one particle is assigned. show. When ρ _γ ≧ 1, the digital image correlation method can be used as the high density, and when ρ _γ <1, the particle tracking method can be used as the low density.

According to the present embodiment described above, a test piece provided with a rubber layer containing marker particles on the surface of the test piece main body is used as a test piece in order to acquire an image by an X-ray imaging method while performing a tear test. Therefore, the marker particles can be analyzed without peeling at the time of tearing.

Further, since the test piece does not have marker particles as a whole in the thickness direction, the image is formed by the marker particles existing in the rubber layer on the surface of the test piece and is not affected by the cross section of the cut. Therefore, even if the cut is formed with an inclination, it is possible to solve a problem such as erroneous recognition due to the presence of marker particles in the cross section of the inclined cut in the image analysis by the particle image velocimetry method. Therefore, the tearing behavior of the test piece can be analyzed accurately.

In addition, since image analysis is performed using the particle image velocimetry method, it is possible to analyze the in-plane distribution and quantitative deformation amount of the behavior during tearing.

[Example 1]
Using a Banbury mixer, 100 parts by mass of styrene butadiene rubber (“JSR1502” manufactured by JSR Co., Ltd.), 50 parts by mass of carbon black (“Cist 3” manufactured by Tokai Carbon Co., Ltd.), and Zinchua (Mitsui Metal Mining Co., Ltd. (Mitsui Metal Mining Co., Ltd.) 2 parts by mass of "Zinchua 1 type" manufactured by Hosoi Chemical Industry Co., Ltd., 1 part by mass of stearic acid ("Lunac S-20" manufactured by Kao Co., Ltd.), and sulfur (150 parts of powdered sulfur for rubber manufactured by Hosoi Chemical Industry Co., Ltd.) Mesh ") 2 parts by mass and 1 part by mass of vulcanization accelerator (" Noxeller CZ "manufactured by Ouchi Shinko Kagaku Kogyo Co., Ltd.) are added and kneaded to prepare an unvulcanized rubber composition for the main body of the test piece. did.

Further, the unvulcanized rubber composition is mixed with marker particles (“Product No. 327007 Silverflakes 10 μ product” manufactured by Sigma-Aldrich) at a roll surface temperature of 60 ° C., and the marker particles are not used for the marker rubber layer. A vulcanized rubber composition was prepared. 4 parts by mass of the marker particles were added to 100 parts by mass of the styrene-butadiene rubber.

The unvulcanized rubber composition for the main body of the test piece obtained above was molded into an unvulcanized rubber sheet having a thickness of 1.5 mm using a roll. Further, the unvulcanized rubber composition for the marker rubber layer obtained above was molded into an unvulcanized rubber sheet having a thickness of 0.5 mm using a roll. The rubber sheet for the marker rubber layer was attached to the surface of the obtained rubber sheet for the test piece body without any gaps, and the thickness T2 of the marker rubber layer was 0.5 mm and the thickness T1 of the test piece body was 1.5 mm, for the total. An unvulcanized rubber sheet having a thickness of 2.0 mm was obtained. Then, the unvulcanized rubber sheet is pressed by a die mold (160 ° C., 30 minutes) to prepare a rubber sheet having a thickness of 2.0 mm, and the obtained rubber sheet is punched into a strip shape having a width of 10 mm. rice field. Further, a notch having a length of 5 mm was made in the width direction from the marker rubber layer side to obtain a test piece for tearing.

Using the obtained test piece, as shown in FIG. 3, an image was acquired by an X-ray imaging method while performing a tear test. The tear test was carried out at a tensile speed of 50 mm / min with the test piece set in a tensile tester. The X-ray conditions and shooting conditions were a frame rate of 150 fsp, an X-ray exposure time of 2 ms, an X-ray energy of 20 keV, and a resolution of the shot image: 0.7 μm / px.

Next, the obtained plurality of images were subjected to image analysis by the digital image correlation method (DIC). FIG. 4 is a diagram showing the analysis results. In FIG. 4, the absolute value (μm) of the y component (component in the pulling direction) of the displacement vector when the test piece was pulled up and down to perform a tear test was plotted. In the gray scale of FIG. 4, the larger the absolute value of the y component, the closer to white it is represented by the contour line.

As shown in FIG. 4, it can be seen that the amount of deformation of the test piece changes hierarchically around the notch. In addition, it can be seen that the amount of deformation is large in the portion near the notch.

[Example 2]
The amount of the marker particles to be blended in the unvulcanized rubber composition for the marker rubber layer was 1.5 parts by mass with respect to 100 parts by mass of the styrene-butadiene rubber, and the other test pieces were prepared in the same manner as in Example 1. Further, using the obtained test piece, an image was acquired by an X-ray imaging method in the same manner as in Example 1.

The obtained plurality of images were subjected to image analysis by the particle tracking method (PTV). In the analysis, as shown in FIG. 5, when the test piece was pulled up and down to perform the tear test, the particles were tracked by focusing on a plurality of marker particles (Nos. 1 to 5) in the order closer to the notch. .. FIG. 5 shows the locus of each marker particle of interest together with the moving direction. The displacement vector of each marker particle was obtained from the coordinates of the marker particles, and in FIG. 6, the absolute value of the y component (component in the pulling direction) of the displacement vector was plotted on the vertical axis and the time was plotted on the horizontal axis.

As a result, as shown in FIG. 6, it was found that the marker particles having different locations had different deformation amounts and complicated deformation behaviors.

10 ... test piece, 12 ... test piece body, 14 ... rubber sheet, 15 ... rubber layer, 16 ... notch

Claims (5)

It is a method to analyze the tearing behavior of rubber materials.
A test piece made of a rubber material that does not contain marker particles is provided with a rubber layer containing marker particles on one of the front and back surfaces of the main body, and a test piece having a notch that is a starting point of tearing is prepared.
While performing a tear test using the test piece, the test piece is irradiated with X-rays so that X-rays pass through the rubber layer, and a plurality of images are acquired by an X-ray imaging method.
A method for analyzing the tearing behavior of a rubber material, which calculates the displacement of marker particles from a plurality of obtained images by the particle image velocimetry method. The method for analyzing the tearing behavior of a rubber material according to claim 1, wherein the particle image velocimetry method is a digital image correlation method. The method for analyzing the tearing behavior of a rubber material according to claim 1, wherein the particle image velocimetry method is a particle tracking method. The tearing behavior of the rubber material according to any one of claims 1 to 3, wherein the rubber sheet containing the marker particles is attached to either one of the front and back surfaces of the test piece main body to form the rubber layer. analysis method. A test piece used by irradiating X-rays by the X-ray imaging method to analyze the tearing behavior of rubber materials.
A test piece main body made of a rubber material containing no marker particles and a rubber layer containing marker particles provided on either one of the front and back surfaces of the test piece main body are provided.
There is a notch that is the starting point of tearing,
Test piece for tear behavior analysis.

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