Tensile test method

Abstract

To provide a tensile test method capable of surely performing a tensile test even for a honeycomb structure formed of a ceramic material.SOLUTION: A method for tensile testing of a honeycomb structural body 1 formed of a ceramic material includes a test piece preparation step S1 of preparing a test piece 2 of a cylindrical honeycomb structural body so that pores of the honeycomb structural body 1 extend in an axial direction, a tensile step S2 of applying a tensile load to the test piece 2 in a state where both end portions of the test piece 2 in the axial direction are gripped, a cross-sectional area calculation step S2 of calculating a cross-sectional area of the test piece 2 excluding the pores based on an image obtained by imaging a cross section of the test piece fractured in the tensile step S3, and a tensile stress calculation step S3 of calculating a tensile stress based on the cross-sectional area of the test piece 2 calculated in the cross-sectional area calculation step S2 and the tensile load applied in the tensile step S4.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a tensile test method, and more particularly to a tensile test method for a honeycomb structure made of a ceramic material. [Background technology]

[0002] Conventionally, a four-point or three-point bending test has been known as a strength test for a honeycomb structure formed from a ceramic material, as described in Patent Document 1. That is, this is a test method in which a load is applied to the upper surface of a honeycomb fired body formed from a ceramic material, while both ends of the lower surface of the honeycomb fired body are supported by two support members. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent No. 5057802 specification Summary of the Invention [Problem to be solved by the invention]

[0004] In order to properly evaluate the strength of a honeycomb structure formed from a ceramic material, evaluation by a tensile test may be required in addition to evaluation by a bending test. However, honeycomb structures formed from ceramic materials are brittle and therefore easily broken. For example, when a plate-shaped honeycomb structure specimen is prepared and the end of the specimen is clamped by a chuck or the like of a tensile tester, even a small force applied to the specimen can break the end, making it impossible to perform the tensile test.

[0005] The present invention has been made to solve such technical problems, and aims to provide a tensile testing method that can reliably perform tensile testing even on honeycomb structures made of ceramic materials. [Means for solving the problem]

[0006] The tensile testing method according to the present invention is a tensile testing method for a honeycomb structure formed from a ceramic material, and is characterized by comprising a test piece preparation step of preparing a cylindrical test piece of the honeycomb structure so that the pores of the honeycomb structure extend in the axial direction, and a tension step of applying a tensile load to the test piece while gripping both axial ends of the test piece.

[0007] In the tensile testing method according to the present invention, a cylindrical honeycomb structure specimen is prepared so that the pores extend in the axial direction, and a tensile load is applied to the specimen while both axial ends of the prepared specimen are gripped. By gripping the cylindrical specimen in this manner, it is possible to apply a load uniformly to the ends of the specimen, compared to the conventional method of clamping the specimen. This suppresses stress concentration and allows the specimen to be held without damaging the ends. As a result, tensile tests can be reliably performed even on honeycomb structures formed from ceramic materials.

[0008] Furthermore, the tensile testing method according to the present invention preferably further comprises a cross-sectional area calculation step of calculating the cross-sectional area of ​​the test specimen excluding the voids based on an image of the cross-section of the test specimen fractured in the tension step, and a stress calculation step of calculating the tensile stress based on the cross-sectional area of ​​the test specimen calculated in the cross-sectional area calculation step and the tensile load applied in the tension step. Because a honeycomb structure test specimen made of a ceramic material does not constrict like a metal test specimen, it is possible to calculate the tensile stress using the cross-sectional area of ​​the fractured test specimen. Additionally, by calculating the cross-sectional area of ​​the test specimen excluding the voids based on an image of the test specimen's cross-section, it is possible to exclude voids in the honeycomb structure that do not contribute to the distribution of the tensile load, and accurately calculate the tensile stress of the honeycomb structure.

[0009] In the tensile testing method according to the present invention, both ends of the test specimen in the axial direction are provided with a disk-shaped base, gripping pieces formed integrally with the base and erected from the center of the base, a fixed side wall portion having a C-shaped cross section that is erected from the peripheral edge of the base on the side opposite to the gripping pieces and formed integrally with the base, a separation side wall portion having a C-shaped cross section that is provided so as to be mountable on the base and that forms a cylindrical storage space together with the fixed side wall portion, and and a clamping jig having a clamping band that clamps the separated side wall portion and the fixed side wall portion from the outer periphery so as to form the accommodation space, and in the tensile step, the end of the test specimen is gripped by the fixed side wall portion, the separated side wall portion, and the clamping band so as to accommodate the end of the test specimen within the accommodation space, and the end of the test specimen is attached to the chuck of the tensile tester by clamping the gripping pieces with the chuck of the tensile tester. In this way, the test specimen can be attached to the chuck of the tensile tester while both ends are gripped by the clamping jig, so that the test specimen can be held without damaging the end of the test specimen.

[0010] In the tensile testing method according to the present invention, it is preferable that the end of the test specimen is gripped by the fixed side wall portion, the separating side wall portion, and the tightening band with a rubber member interposed between the test specimen and the fixed side wall portion or the separating side wall portion. This prevents the fixed side wall portion and the separating side wall portion from directly contacting the end of the test specimen, thereby suppressing damage to the end of the test specimen. Furthermore, by interposing a rubber member between the test specimen and the fixed side wall portion or the separating side wall portion, slippage between the test specimen and the fixed side wall portion or the separating side wall portion can be suppressed, thereby preventing the test specimen from slipping out of the gripping jig during the tensile test. [Effects of the Invention]

[0011] According to the present invention, a tensile test can be reliably carried out even on a honeycomb structure made of a ceramic material. [Brief explanation of the drawings]

[0012] [Figure 1] FIG. 1 is a flow diagram showing a tensile test method according to an embodiment. [Figure 2] FIG. 1 is a schematic diagram for explaining a test specimen preparation step. [Figure 3] FIG. 1 is a schematic diagram showing how a test specimen is attached to a chuck of a tensile tester. [Figure 4] FIG. 10 is an exploded perspective view showing the end of the test specimen being gripped by the gripping jig. [Figure 5] FIG. 10 is a schematic cross-sectional view showing that a rubber member is interposed between an end of the test specimen and a fixed side wall portion or a separated side wall portion. [Figure 6] 10A and 10B are diagrams showing the results of tensile tests of existing honeycomb structure materials and developed honeycomb structure materials using the tensile test method of the embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0013] Hereinafter, an embodiment of a tensile testing method according to the present invention will be described with reference to the drawings. Prior to the description of the embodiment, however, the background to the invention will be described.

[0014] Honeycomb structures made of ceramic materials are used, for example, in catalytic converters for purifying exhaust gases, and are used as substrates (e.g., GPF (gasoline particulate filter) substrates) that support a catalytic coating layer. Such a honeycomb structure 1 is formed in a cylindrical shape, for example, as shown in FIG. 2, and has a plurality of pores defined therein by lattice-like partition walls. The pores have a cross section that is rectangular or regular hexagonal, and extend in the axial direction of the honeycomb structure 1. The honeycomb structure 1 is mounted in the case of the catalytic converter via an insulating mat, with its axial direction (i.e., the extension direction of the pores) aligned with the flow direction of exhaust gas.

[0015] Examples of ceramic materials used in the honeycomb structure 1 include nitride ceramics such as silicon carbide, aluminum nitride, silicon nitride, boron nitride, and titanium nitride; carbide ceramics such as zirconium carbide, titanium carbide, tantalum carbide, and tungsten carbide; and oxide ceramics such as alumina, zirconia, cordierite, mullite, and aluminum titanate.

[0016] The inventors of the present application conducted an engine reliability evaluation test on a catalytic converter using the above-mentioned honeycomb structure 1, and found that ring cracks (i.e., cracks extending in the circumferential direction) occurred. In order to clarify the mechanism by which ring cracks occur, it is necessary to investigate the tensile stress of the honeycomb structure 1. However, as described above, because the honeycomb structure is brittle, when the end of a test specimen of the honeycomb structure is clamped by the chuck of a tensile tester, even the application of a small force causes breakage at the end, making it impossible to perform a tensile test. It is possible to increase the strength by thickening the end of the test specimen that is clamped by the chuck, but this does not fundamentally prevent end breakage.

[0017] Therefore, the inventors of the present invention have further conducted intensive research as follows.

[0018] First, the inventors of the present invention discovered that the main cause of breakage at the end of a test specimen is that when the end of the specimen is directly clamped by the chuck, stress concentration occurs at the end, leading to breakage. Next, they discovered that stress concentration can be avoided by changing the shape of the test specimen from the conventional plate-like shape to a cylindrical shape and changing the conventional method of holding the specimen by clamping the end to a method of holding the specimen by gripping the end from the periphery (i.e., gripping). Furthermore, as a result of extensive research and prototyping, the inventors of the present invention developed a gripping jig that can grip the end of a test specimen and can be attached to the chuck of a tensile testing machine, thereby completing the present invention.

[0019] 1 is a flow diagram showing a tensile test method according to an embodiment. The tensile test method according to this embodiment is a tensile test method for a honeycomb structure 1 formed from a ceramic material, and includes a test piece preparation step S1, a tension step S2, a cross-sectional area calculation step S3, and a stress calculation step S4.

[0020] In the specimen preparation step S1, a specimen 2 of a cylindrical honeycomb structure 1 is prepared so that the pores of the honeycomb structure 1 extend in the axial direction. Specifically, as shown in Fig. 2, a honeycomb structure 1 of the size of a substrate is used to prepare a cylindrical specimen 2 by cutting or hollowing out the honeycomb structure 1. The specimen 2 has a size of, for example, an outer diameter of 30 mm and a length of 100 mm.

[0021] In the tension step S2, a tensile load is applied to the test specimen 2 prepared in the test specimen preparation step S1 while both axial ends of the test specimen 2 are gripped. Here, the both axial ends of the test specimen 2 are not directly clamped by the chucks (upper chuck 4, lower chuck 5) of the tensile testing machine 3, but the ends of the test specimen 2 are attached to the chucks via a gripping jig 6.

[0022] As shown in Figure 4, the gripping jig 6 has a disk-shaped base 61, a gripping piece 62 formed integrally with the base 61 and erected from the center of the base 61, a fixed side wall portion 63 with a C-shaped cross section that stands up from the peripheral portion of the base 61 on the side opposite the gripping piece 62 of the base 61 and is formed integrally with the base 61, a separation side wall portion 64 with a C-shaped cross section that is mountable on the base 61 and forms a cylindrical storage space 60 together with the fixed side wall portion 63, and a tightening band 65 that tightens the separation side wall portion 64 and the fixed side wall portion 63 from the outer periphery to form the storage space 60 when the separation side wall portion 64 is placed on the base 61.

[0023] That is, the base 61, gripping piece 62, and fixed side wall portion 63 are integrated. The separate side wall portion 64 and tightening band 65 are separate bodies from the integrated base 61, gripping piece 62, and fixed side wall portion 63. The base 61, gripping piece 62, fixed side wall portion 63, and separate side wall portion 64 are formed of, for example, a hard resin material or a metal material such as iron. On the other hand, the tightening band 65 is, for example, a stainless steel hose band, and includes a band and tightening fittings.

[0024] Therefore, in the tensile step S2, first, the end of the test specimen 2 is gripped by the fixed side wall portion 63, the separating side wall portion 64, and the tightening band 65 so as to accommodate the end of the test specimen 2 within the accommodation space 60, and the gripping piece 62 is clamped by the chuck of the tensile tester 3, thereby attaching the end of the test specimen 2 to the chuck of the tensile tester 3. The tensile tester 3 has a load cell and can output a stress-strain diagram for the test specimen.

[0025] As shown in FIG. 3, one end of the test piece 2 is attached to an upper chuck 4 via a gripping jig 6, and the other end is attached to a lower chuck 5 via a gripping jig 6.

[0026] 5, with a rubber member 7 interposed between the test specimen 2 and the fixed side wall portion 63 or the separated side wall portion 64, the end of the test specimen is gripped by the fixed side wall portion 63, the separated side wall portion 64, and the tightening band 65. Specifically, there are two rubber members 7, each provided in a one-to-one correspondence with the fixed side wall portion 63 and the separated side wall portion 64. The rubber members 7 are formed in a C-shape so as to suitably fit the curved shapes of the fixed side wall portion 63 and the separated side wall portion 64, respectively, and are fixed to the inner wall surfaces of the fixed side wall portion 63 and the separated side wall portion 64 with an adhesive or the like. Silicone rubber, butyl rubber, ethylene-propylene rubber, or the like is used for the rubber members 7.

[0027] Next, the drive motor attached to the tensile tester 3 is operated, and as shown in Figure 3, the upper chuck 4 is raised in the direction of the arrow (i.e., upward) at a constant speed, applying a tensile load in the axial direction of the test specimen 2. At this time, the load-elongation characteristics can be obtained using the tensile tester 3 (see Figure 6(b) described below). The tensile load is applied until the test specimen 2 breaks.

[0028] In the cross-sectional area calculation step S3, the cross-sectional area of ​​the test specimen 2 excluding pores is calculated based on an image of the cross-section of the test specimen 2 fractured in the tensile step S2. Here, the reasons for excluding pores and for calculating the cross-sectional area using the cross-section of the fractured test specimen 2 will be explained.

[0029] In other words, unlike solid specimens, the pores of the honeycomb-structured specimen 2 do not contribute to the distribution of tensile load, and these pores must be removed in order to accurately calculate the tensile stress.

[0030] Furthermore, a portion of the end of the test specimen 2 is deformed by the gripping load from the gripping jig 6 (more specifically, the clamping force of the clamping band 65). For this reason, the cross-sectional area of ​​the test specimen 2 can be calculated more accurately by using the cross-section of the end held by the gripping jig 6 rather than the cross-section of a portion other than the end held by the gripping jig 6. In addition, taking into consideration that the test specimen 2, which is a honeycomb structure formed from a ceramic material, does not constrict like a metal test specimen, and that fracture occurs near the end held by the gripping jig 6, the cross-section of the fractured test specimen 2 is used.

[0031] In the cross-sectional area calculation step S3, an image analysis device equipped with an imaging unit is used. Specifically, the image analysis device first uses the imaging unit to capture an image of the cross section of the test piece 2 that broke in the tensile step S2. Next, the image analysis device imports the captured image data, removes noise and distortion, and then detects the outline of the cross section of the test piece 2 (i.e., identifies the boundary with the rubber member 7).

[0032] Next, the image analysis device identifies pore areas in the cross section and colors the pore areas so as to distinguish between the identified pore areas and the areas excluding the pores (i.e., the pore areas in the cross section).The image analysis device then calculates the cross-sectional area based on the colored pore areas.

[0033] In the stress calculation step S4, the tensile stress is calculated based on the cross-sectional area of ​​the test specimen 2 calculated in the cross-sectional area calculation step S3 and the tensile load applied in the tension step S2. At this time, the tensile stress is calculated as tensile stress = tensile load / area based on the analysis results of the image analysis device and the tensile load at the time of fracture of the test specimen 2 measured by the tensile tester 3.

[0034] In this embodiment, the reason for calculating tensile stress instead of tensile load is that the tensile load is affected by the size of the area and therefore the superiority or inferiority of the test specimen cannot be determined, whereas the tensile stress (i.e., tensile load per unit area) eliminates the influence of the size of the area and therefore allows for a more accurate evaluation of the test specimen.

[0035] In the tensile testing method according to this embodiment, in the test specimen preparation step S1, a cylindrical honeycomb structure test specimen 2 is prepared so that the pores extend in the axial direction, and in the tension step S2, a tensile load is applied to the test specimen 2 while both axial ends of the prepared test specimen 2 are gripped. By gripping the cylindrical test specimen 2 in this manner, it is possible to apply a load uniformly to the ends of the test specimen 2 compared to the conventional method of holding the test specimen by clamping it, thereby suppressing the occurrence of stress concentration and enabling the test specimen 2 to be held without damaging the ends of the test specimen 2. As a result, a tensile test can be reliably performed even on a honeycomb structure formed from a ceramic material.

[0036] Further, in a cross-sectional area calculation step S3, the cross-sectional area of ​​the test specimen 2 excluding voids is calculated based on an image of the cross-section of the broken test specimen 2, and in a stress calculation step S4, the tensile stress is calculated based on the calculated cross-sectional area and the tensile load at the time of breakage. Because the test specimen 2 of a honeycomb structure formed from a ceramic material does not constrict like a metal test specimen, it is possible to calculate the tensile stress using the cross-sectional area of ​​the broken test specimen 2. In addition, by calculating the cross-sectional area of ​​the test specimen 2 excluding voids based on an image of the cross-section of the test specimen 2, it is possible to exclude voids in the honeycomb structure that do not contribute to the distribution of the tensile load, and accurately calculate the tensile stress of the honeycomb structure 1.

[0037] Furthermore, in the tensile step S2, the test specimen 2 can be attached to the chuck of the tensile tester 3 while both ends of the test specimen 2 are gripped via the gripping jig 6 having the above-described structure, so that the test specimen 2 can be held without damaging the ends of the test specimen 2. In addition, by interposing a rubber member 7 between the end of the test specimen 2 and the fixed side wall portion 63 or the separation side wall portion 64 of the gripping jig 6, the fixed side wall portion 63 and the separation side wall portion 64 can be prevented from directly hitting the end of the test specimen 2, thereby suppressing damage to the end of the test specimen 2. Furthermore, this can suppress slippage between the end of the test specimen 2 and the fixed side wall portion 63 or the separation side wall portion 64, so that the test specimen 2 can be prevented from coming off the gripping jig 6 during the tensile test.

[0038] As described above, according to the tensile testing method of the present embodiment, it is possible to reliably perform a tensile test even on a honeycomb structure formed of a ceramic material. This makes it possible to properly evaluate the strength of a honeycomb structure formed of a ceramic material, which can contribute to the development of ceramic honeycomb structures.

[0039] Figure 6 shows the results of tensile tests of existing and developed honeycomb structure materials using the tensile test method of the embodiment. In Figure 6, (a) shows a photograph of the cross section taken by an image analyzer in the cross-sectional area calculation step S3 and the calculated cross-sectional area, and (b) shows the load (N)-elongation (mm) results measured by a tensile tester in the tensile step S2. The test specimens for both the existing and developed materials were cylindrical with an outer diameter of 30 mm and a length of 100 mm.

[0040] As shown in Figure 6(b), it was found that the developed material had a higher tensile load than the conventional material. Also, as shown in Figure 6(a), it was found that the calculated cross-sectional area of ​​the cross section that broke in the tensile test was smaller for the developed material than for the conventional material. When the tensile stress was calculated using the measured tensile load and the calculated cross-sectional area, it was found that the tensile stress of the developed material was higher than that of the conventional material. From these results, it was found that the developed material can obtain a higher tensile load even with a smaller cross-sectional area compared to the conventional material.

[0041] This shows that the tensile test method of this embodiment can properly evaluate the strength of a honeycomb structure formed from a ceramic material, and can contribute to the development of honeycomb structures.

[0042] Although the embodiments of the present invention have been described in detail above, the present invention is not limited to the above-described embodiments, and various design modifications can be made without departing from the spirit of the present invention as set forth in the claims. [Explanation of symbols]

[0043] 1: honeycomb structure, 2: test piece, 3: tensile tester, 4: upper chuck, 5: lower chuck, 6: gripping jig, 7: rubber member, 60: accommodation space, 61: base, 62: gripping piece, 63: fixed side wall portion, 64: separation side wall portion, 65: fastening band

Claims

1. A tensile test method for a honeycomb structure formed from a ceramic material, comprising: a test specimen preparation step of preparing a cylindrical test specimen of the honeycomb structure so that pores of the honeycomb structure extend in an axial direction; a tension step of applying a tensile load to the test specimen while gripping both axial end portions of the test specimen; A tensile testing method comprising:

2. a cross-sectional area calculation step of calculating a cross-sectional area of ​​the test specimen excluding the pores based on an image of a cross section of the test specimen fractured in the tensile step; a stress calculation step of calculating a tensile stress based on the cross-sectional area of ​​the test specimen calculated in the cross-sectional area calculation step and the tensile load applied in the tensile step; The tensile testing method of claim 1 further comprising:

3. both axial end portions of the test specimen are attached to chucks of a tensile tester via a gripping jig having a disk-shaped base, gripping pieces formed integrally with the base and erected from a central position of the base, a fixed side wall portion having a C-shaped cross section that is erected from a peripheral portion of the base on the side opposite to the gripping pieces and formed integrally with the base, a separated side wall portion also having a C-shaped cross section that is mountable on the base and forms a cylindrical storage space together with the fixed side wall portion, and a fastening band that fastens the separated side wall portion and the fixed side wall portion from their outer peripheries so as to form the storage space when the separated side wall portion is mounted on the base, 3. The tensile testing method according to claim 1, wherein in the tensile step, the end of the test specimen is gripped by the fixed side wall portion, the separated side wall portion, and the tightening band so as to accommodate the end of the test specimen within the accommodation space, and the end of the test specimen is attached to a chuck of the tensile testing machine by clamping the gripping piece with the chuck of the tensile testing machine.

4. 4. A tensile testing method according to claim 3, wherein an end of the test specimen is gripped by the fixed side wall portion, the separating side wall portion, and the tightening band with a rubber member interposed between the test specimen and the fixed side wall portion or the separating side wall portion.

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