JP3459029B2 - Method and apparatus for tensile strength test using cylindrical test piece - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a tensile strength test using a cylindrical test piece suitable for measuring the tensile strength of brittle materials such as ceramics, refractories, concrete, tiles, and ceramics. About. 2. Description of the Related Art Conventionally, in a tensile strength test of a material having a relatively high elasticity such as a metal material, a rod-shaped test piece of a specific size is prepared and subjected to a tensile test performed under a specific load. Destructive tests are widely performed. However, in the case of brittle materials such as ceramics, refractories, concrete, tiles, and porcelains, it is difficult to prepare rod-shaped test specimens of an accurate size. The breaking position is not constant, and the measured values tend to vary, making it difficult to measure the tensile strength accurately. Therefore, the tensile strength of the brittle material is generally estimated indirectly from the measurement of the bending strength and the measurement of the compression strength. [0004] As a method for improving the labor and accuracy of measured values by such indirect measurement, a test piece is formed into a cylindrical shape which is easy to prepare even if it is a brittle material, and a cylindrical shape is used as a load for breaking. There is a method of measuring the tensile strength by applying a uniform pressure to the inner surface of the substrate and generating a tensile stress in the circumferential direction. According to this method, a relatively uniform tensile stress can be generated over the entire measurement test piece as compared with the method of pulling and breaking a rod-shaped test piece, so that it is difficult to generate variation between test pieces. There are advantages. In measuring the tensile strength using this cylindrical test piece, it is necessary to apply uniform pressure to the inner surface of the cylindrical test piece. As a means for achieving this, there is a method of applying gas pressure to the inside of the cylindrical test piece by gas-sealing by press-contacting both end faces of the test piece with a sealing member. However, in this method, it is necessary to apply a large compressive stress in the vertical direction of the cylindrical test piece when gas sealing the upper and lower ends of the cylindrical test piece, so that the measured value is likely to be affected, and the measuring device is large. There is a drawback that tends to be. A rubber balloon filled with a liquid or a gas is placed inside the cylindrical test piece, and the upper and lower ends are covered with the rubber balloon. The balloon is then inflated to apply an internal pressure to the cylindrical test piece. There is also a way to apply. Although this method eliminates the disadvantages of gas sealing both end faces of the cylindrical test piece, the problem is that the rubber balloon is easily swelled and broken by pressure from the gap between the cylindrical test piece and the holding lid. And is not widely used. SUMMARY OF THE INVENTION The present invention relates to a method for measuring tensile strength using a cylindrical test piece, which does not require any special sealing means and does not cause leakage of the pressurized medium. The aim is to find a means by which the inner surface of a cylindrical test piece can be pressed uniformly. SUMMARY OF THE INVENTION The present invention provides a tensile strength test for measuring the tensile strength by applying pressure to the inner peripheral surface of a cylindrical test piece to generate a tensile stress in the circumferential direction of the test piece. The method, wherein the cylindrical test piece is inserted into an inner hole of the cylindrical test piece.
Height higher than the cylindrical specimen by an amount equivalent to the volume of the gap
A high-elastic body having a high elasticity is arranged, and pressurizing plates are arranged on both end faces of the high-elastic body, and pressure is applied from both end faces of the high-elastic body. The high elastic body used in the present invention is a solid high elastic body having rubber-like elasticity. The outer peripheral surface expands when pressure is applied from one or both of the both end surfaces, and when the pressure is released. It has elasticity such that the bulge returns to its original state. For example, natural rubber,
Synthetic rubber or other synthetic resins can be used. The high elastic body has a function of applying pressure to the inner surface by deforming the cylindrical test piece by applying pressure, and therefore, the original shape is not particularly limited. However,
If the gap with the inner surface of the cylindrical test piece is too large, the high elastic body will be greatly deformed by pressurization, and the high elastic body will break beyond the elastic limit of the high elastic body. It must be large enough to give pressure to the inner surface. Further, in order to perform a test with higher accuracy, it is necessary to uniformly apply pressure to the inner surface of the cylindrical test piece. In this case, it is preferable to use a disc-shaped high elastic body. If the height of the disc-shaped high elastic body is too high, accurate measurement cannot be performed because a part of the high elastic body protrudes outside the test piece due to pressurization. The contact area of the highly elastic body with the inner hole of the test piece is reduced, and pressure is not applied to a part, so that accurate measurement cannot be performed. Therefore, it is ideal that the height of the high elastic body is high by an amount corresponding to the volume of the gap between the cylindrical test piece and the high elastic body. However, in reality, bubbles and the like are contained in the high elastic body. Usually, the height of the cylindrical test piece is preferably in the range of +5 mm to 0 mm. [0015] The cylindrical test piece is made of ceramics, refractories,
It is suitable for brittle materials such as concrete, tiles and ceramics. The thickness of the cylindrical test piece can be appropriately determined according to the strength of the material. For example, if the material is a high-strength material such as fine ceramics, the maximum pressing force can be suppressed by making it a thin cylindrical test piece, and a thick cylindrical test piece is used for relatively low-strength refractories. By doing so, it is possible to obtain a measurement value with a small error. If the hardness of the high elasticity material is too hard, the pressure in the vertical direction cannot be transmitted uniformly to the inner wall surface of the cylindrical shape. If the hardness is too soft, high elasticity will be generated from the gap between the cylindrical test piece and the upper and lower pressing plates. Since the body protrudes, the upper and lower pressing forces do not show linear characteristics on the inner wall surface of the cylindrical test piece. The hardness of this highly elastic body is JIS K
6301 20-90 hardness by spring hardness test
It was found that the above problem could not occur when the hardness was 30 to 40 and that the pressure could be uniformly applied to the inner wall surface of the cylindrical test piece. At this time, the high elastic body preferably has a tear strength of 5 KN / m or more from the viewpoint of repeated use. The outer diameter of the disc-shaped pressure plate is smaller than the inner diameter of the cylindrical test piece, and the difference is preferably within 6 mm. If it exceeds 6 mm, the highly elastic body may bite between the pressure plate and the test piece during pressurization, and accurate measurement may not be performed. The pressure plate is used to press the high elastic body in between. When the high elastic body is compressed from the upper and lower surfaces, the high elastic body tends to protrude in the radial direction of the cylindrical test piece. Blocked by the cylindrical test piece and the upper and lower pressing plates, a tensile stress in the circumferential direction inside the cylindrical test piece is generated according to the pressing force from the upper and lower surfaces. Then, the tensile strength can be known by calculation from the pressure at the time of breaking of the cylindrical test piece. The stress generated on the outer surface of the cylindrical test piece can be obtained by calculation, and the tensile modulus of the material can be calculated from the measurement result of the amount of strain on the outer surface. By arranging a plurality of strain gauges in the circumferential direction, it is possible to know the stress-strain characteristics at each part of the material, so that the uniformity of the structure in the circumferential direction can be evaluated. Therefore, it is possible to find a defect in the structure of a large-sized article or the like, and feed it back to the manufacturing process to manufacture a product with a more uniform structure. In addition, large-sized articles such as refractories and ceramics may have some defects due to, for example, insufficient filling of the compound in the molding step and uneven pressure. This partial defect is a problem that may cause breakage during use. The physical properties of the cylindrical test piece can be known directly and accurately by knowing the load and strain amount when the test piece breaks such a defect. Further, the relationship between the stress of the cylindrical test piece obtained by the tensile strength test of the present invention and the strain obtained by the strain gauge attached to the outer surface of the cylindrical test piece is quantified to obtain a numerical value. It can be used for evaluation of characteristics. Embodiments of the present invention will be described below by way of examples. Embodiment 1 In FIG. 1 showing a first embodiment of the present invention, an inner diameter 50 is placed on a pedestal 1 of an Amsler testing machine via a spacer 2.
A cylindrical test piece 3 having an outer diameter of 90 mm, an outer diameter of 90 mm, and a height of 50 mm is placed, and an inner hole pressing jig is arranged in the inner hole. The inner hole pressing jig is placed on a disc-shaped lower pressing plate 4 having an outer diameter of 48 mm, and has an outer diameter of 48 mm, a height of 52 mm, and JIS K63.
A disc-shaped high elastic body 5 having a hardness of 30 according to a 01 spring type hardness test is mounted thereon, and an outer diameter of 48
The upper pressure plate 6 in the form of a disk having a diameter of 1 mm is placed thereon. The high elastic body 5 has an outer diameter smaller by 2 mm than the inner diameter of the cylindrical test piece 3 and a height higher than the height of the cylindrical test piece by 2 mm.
mm higher. The outer diameter of both pressure plates 4 and 6 is smaller by 2 mm than the inner diameter of cylindrical test piece 3 and is made of steel and both sides are polished. The measurement is performed by lowering the Amsler head 7 to press the highly elastic body through the pressure plate, and measuring the tensile strength on the inner surface of the cylindrical test piece from the load when the cylindrical test piece breaks. Can be calculated. The spacer 2 is used to hold the cylindrical test piece at first, and when the pressurization is started, the test piece is held by expanding the high elastic body. Therefore, the spacer can be removed immediately after the start of pressurization, or can be used as it is in the case of an elastic spacer. As described above, in this measurement test, the pressurizing means can be applied to the Amsler testing machine used for measuring the bending strength and the compressive strength, and the tensile strength can be measured with a very simple device. Can be measured. In this apparatus, the optimum value of the hardness of the high elastic body 5 used for the inner hole pressing jig was examined. The high elastic body 5 has a hardness of 100, a hardness of 90,
Select a synthetic rubber with a hardness of 40, a hardness of 30, a hardness of 20, and a hardness of 10, and a uniform inner diameter of 80 m with a clear elastic modulus on the outer peripheral surface
An acrylic cylinder having a length of m, an outer diameter of φ120 and a height of 50 mm was arranged, and pressure was applied from above and below to apply a tensile stress to the acrylic cylinder. In order to examine the variation in the distortion of the outer peripheral surface of the acrylic cylinder at this time, strain gauges were attached to the upper, middle, and lower portions of the outer peripheral surface, and the amount of distortion when a load of 2 t was applied at full pressure was indexed. It is shown in Table 1. In the same table, the measured value 6 of the strain amount in the central part of the sample when using a synthetic rubber having a hardness of 30
The exponent is shown with 80 με as 100. Further, the variation in the amount of distortion was represented by the maximum value-minimum value of the exponent of the amount of distortion. A large change in strain for each part means that the pressing force changes for each part, and that there is a problem in using such a high elastic body as a pressurizing medium. I do. At a hardness of 30, 40, there is no variation in the upper, middle, and lower portions, so that a load is uniformly applied to the inner surface of the acrylic cylinder, which indicates that the acrylic cylinder is suitable as a pressure medium. In the case of a high elastic body having a hardness of 10, the elastic body protrudes from the gap between the test piece and the holding jig, and the pressure does not propagate stably to the inner wall surface of the cylindrical test piece. Damaged. Further, when a high elastic body having a hardness of 100 is used, the difference in strain is as large as 15, and pressure is not propagated at the center, and uneven load on the inner wall surface is confirmed. Further, when a rubber having a hardness of 30 is used,
The percentage of the vertical pressure that propagates to the inner wall surface of the cylindrical test piece was calculated using the elastic modulus of acrylic, and it was confirmed that 95% of the total pressure was applied to the side surface. Since 95% of the load applied to the highly elastic body is uniformly transmitted to the inner surface of the cylindrical test piece, the transfer coefficient is not as high as that of the liquid, but the pressure is uniformly applied by a simple method. It is an excellent medium for transmitting to walls, and the results obtained are reliable values. Table 1 Embodiment 2 FIG. 2 shows a second embodiment of the present invention. A core rod 8 having a diameter of 15 mm provided at the center of the lower pressing plate 4 is inserted into a through-hole 9 having a diameter of 15 mm provided at the center of the high elastic body 5. The inner pressure jig inserted into the 3 mm hole 10 is arranged in the inner hole of the cylindrical test piece 3. Other upper and lower pressure plates 4,
6, dimensions of the high elastic body 5, and the cylindrical test piece 3 are the same as those of the first embodiment. As in the case of FIG. 1, the tensile strength can be determined simply by placing the device on an Amsler and applying pressure. In the case of this embodiment, the center axis of the cylindrical test piece 3 and the center axis of the pressing jig composed of the upper and lower pressing plates 4 and 6 are aligned with each other. Eliminates measurement errors such as contact and breakage due to unbalanced load. The gap between the diameter of the core rod 8 and the through hole of the high elastic body 5 and the inner diameter of the hole 10 of the upper pressing plate 6 should be as small as possible without causing the center to be displaced. It is preferable that it is as small as possible. The pressure plate may be of a disk-shaped type as shown in FIG. 2 and detachably mounted on the Amsler tester, or may be fixed to the pedestal itself of the Amsler tester for exclusive use. As shown in FIG. 2, the use of the inner hole pressing jig has an advantage of being used in combination with an existing compression measuring device or the like. Example 3 FIG. 3 is a diagram showing a state in which a strain amount during pressurization is continuously detected by a dynamic strain meter, and the stress-strain characteristics of the cylindrical test piece are determined by calculation. The state where the strain gauge 11 was stuck on the surface is shown. Thus, the tensile modulus of the cylindrical test piece 3 is calculated from the relationship between the amount of strain on the outer surface and the generated stress, and this elastic modulus is used to calculate the tensile modulus of the cylindrical test piece 3.
It is possible to know the maximum tensile stress generated on the inner surface. In addition, by arranging a plurality of strain gauges 11 in the circumferential direction, it is possible to know the stress-strain characteristics at each part of the material and to evaluate the uniformity of the structure in the circumferential direction. . Using this apparatus, a cylindrical test piece having an inner diameter of 220 mm, an outer diameter of 270, and a height of 50 mm was continuously cut from the lower end of a long nozzle made of alumina-graphite as a refractory for continuous casting from the lower end at four positions. Was measured for tensile strength. As a comparative example, eight 20 × 20 × 80 mm test pieces were cut out at the same site from the same production history and subjected to a three-point bending test. Table 2 shows the results. Table 2 Although the maximum tensile strength decreases as going to the lower end,
This tendency is not seen in bending strength. Intrinsic defects that are difficult to detect with conventional bending strength measurement methods can be broken at the weakest part in the circumferential direction by applying tensile stress over the entire circumference of the cylindrical sample using this method. Defects could be easily found. (1) By using a simpler method than in the past, a tensile stress can be generated over the entire circumference of the test piece and the test piece can be broken at the weakest part, so that the tensile strength of the material can be accurately measured. Can be measured. (2) A more uniform pressure can be applied to the test piece than before, and an accurate measurement result can be obtained. (3) By detecting the characteristics of each part of the test piece, a defect in the tissue can be found, and by feeding it back to the manufacturing process, a product with a more uniform tissue can be manufactured. .

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a sectional view showing a first embodiment of the present invention. FIG. 2 is a sectional view showing a second embodiment of the present invention. FIG. 3 shows an example in which a strain gauge is attached as a third embodiment of the present invention. [Explanation of symbols] 1. Pedestal of Amsler testing machine 2. Spacer 3
Cylindrical test piece 4 Lower pressure plate 5 High elastic body 6
Upper pressure plate 7 Amsler head 8 Core rod 9
Through hole 10 Upper pressure plate hole 11 Strain gauge

────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Yoshitaka Hiraiwa 1-1-1, Higashihama-cho, Yawatanishi-ku, Kitakyushu-city, Fukuoka Prefecture (56) References JP-A-58-167937 (JP, A) 8-170939 (JP, A) JP-A-5-232001 (JP, A) JP-A-2-120641 (JP, A) JP-A-1-307588 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) G01N 3/00-3/62

Claims (1)

(57) [Claim 1] In a tensile strength test method for measuring tensile strength by applying pressure to the inner peripheral surface of a cylindrical test piece to generate tensile stress in the circumferential direction of the test piece. body of the gap between the cylindrical test piece in the bore of the cylindrical test piece
A high elastic body that is higher than the cylindrical test piece by an amount corresponding to the product is arranged, pressing plates are arranged on both end faces of the high elastic body, and a pressing force is applied from both end faces of the high elastic body. A tensile strength test method using a cylindrical test piece.