Material testing device and testing method in high-pressure gas

Abstract

To provide a material testing device and testing method in high-pressure gas that is compact and capable of performing highly accurate evaluation tests.SOLUTION: The device is a device for evaluating crack growth using a CT test piece 8 in high-pressure gas, and includes a container part 11 that houses the test piece 8 and into which high-pressure gas is introduced, and has a tension mechanism 2 that supports the upper through-hole of the test piece and applies a load to the lower through-hole, and a loading device 14 that applies a load to the test piece 8 from above the container part 11 via a loading rod 40. The load applied to the test piece 8 acts directly on the through-hole provided on the distal side of the test piece from the load-applying device 14, bypassing the through-hole provided on the proximal side of the test piece.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a fatigue crack growth test device or a fracture toughness test device using a CT (compact tension) test piece in high-pressure gas, and to a method thereof. [Background technology]

[0002] It is known that in high-pressure gas, especially high-pressure hydrogen gas, some metal materials, including steel, show a decrease in strength and elongation due to so-called hydrogen embrittlement.

[0003] In order to evaluate the hydrogen compatibility of metallic materials that are expected to be used, it is essential to conduct material tests in a hydrogen environment.

[0004] Therefore, a high-pressure gas testing device is known in which the internal volume of the container into which the high-pressure gas is introduced is set to 10 to 100 cc (see Patent Document 1). However, the device in Patent Document 1 performs testing using a prismatic test piece, and friction loss occurs between the test piece and the jig, making it difficult to evaluate the net load transmitted to the test piece.

[0005] On the other hand, CT specimens are widely used for fracture toughness and fatigue crack propagation tests. CT specimens are square or nearly circular specimens with a notch at one end, and a load is applied through a through hole (pin hole) near the notch. In conventional fatigue crack propagation tests using CT specimens, U-shaped jigs are attached to the top and bottom of the CT specimen, and tensile stress is applied to at least one of the top and bottom. However, this structure requires a certain height for the container, which makes it difficult to miniaturize the device and results in a high cost. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Laid-Open No. 2013-167512 Summary of the Invention [Problem to be solved by the invention]

[0007] In view of the above circumstances, an object of the present invention is to provide a material testing device and testing method in high-pressure gas that can be made compact and that can perform highly accurate evaluation tests. [Means for solving the problem]

[0008] The material testing device of the present invention is a device for evaluating crack propagation in high-pressure gas using a CT test piece in high-pressure gas, characterized in that the load applied to the test piece acts directly on the through-hole on the distal side of the test piece from the load-applying device, bypassing the through-hole on the proximal side of the test piece. By applying the load to the distal side of the test piece from the load-applying device, a bending moment acts on the through-hole on the distal side, and a tensile stress acts in a direction that widens the notch in the CT test piece. This essentially converts the force applied by the loading device to the test piece into a tensile force.

[0009] The material testing apparatus in high-pressure gas of the present invention is an apparatus for evaluating crack propagation using a CT test piece in high-pressure gas, and may include a container portion for storing the test piece and introducing high-pressure gas, the container portion having a tension mechanism for supporting the upper through-hole of the test piece and applying a load to the lower through-hole, and a loading device for applying a load to the test piece from above the container portion via a loading rod. With this configuration, the apparatus can be made smaller, and fracture toughness and fatigue crack propagation tests can be performed using small CT test pieces. The load may be applied continuously or repeatedly. The high-pressure gas is not limited to hydrogen gas, but other types of high-pressure gas may also be used. The material of the CT test piece may be metal, ceramic, or resin.

[0010] In the case where the high-pressure gas materials testing apparatus of the present invention includes a vessel having a tension mechanism and a loading device, the tension mechanism preferably includes a holder having a pair of through-holes connectable with the upper through-holes of the test piece using first connecting pins and capable of being hung on a pair of supports provided in the longitudinal direction of the vessel, and a loading jig having a pair of through-holes connectable with the lower through-holes of the test piece using second connecting pins and having a recess on its upper surface for receiving the lower end of a loading rod, the through-holes and the recess being arranged so as to straddle the test piece and the holder. This configuration allows for the miniaturization of the apparatus, enabling fracture toughness and fatigue crack propagation tests to be performed using small CT test pieces.

[0011] The container of the high-pressure gas material testing device of the present invention is equipped with a clip gauge to measure crack growth in the test piece. Known clip gauges can be used, and the crack length can be measured with high accuracy using the unloading elastic compliance method.

[0012] The container portion of the high-pressure gas material testing device of the present invention has an internal volume of 10 to 100 cc. Furthermore, the container of the high-pressure gas materials testing device of the present invention preferably has a substantially cylindrical shape, which can improve pressure resistance.

[0013] The material testing method of the present invention in high-pressure gas is a method for evaluating crack propagation characteristics using a CT test specimen in high-pressure gas, and is characterized in that the load applied to the test specimen acts directly on the through hole provided on the distal side of the test specimen, bypassing the through hole provided on the proximal side of the test specimen from the load-applying device. [Effects of the Invention]

[0014] The high-pressure gas material testing device and testing method of the present invention have the effect of enabling miniaturization and highly accurate evaluation testing. [Brief explanation of the drawings]

[0015] [Figure 1] Schematic diagram of high-pressure gas material testing equipment [Figure 2] Front and right side views of CT test piece [Figure 3] Explaining the tension mechanism [Figure 4] Schematic diagram of the tension mechanism attached to the CT test piece [Figure 5] Cross-sectional image of the tension mechanism [Figure 6] Clip gauge installation diagram [Figure 7] Explaining how to attach the CT test piece to the holding part after the tension mechanism is attached [Figure 8] Diagram of high-pressure gas material testing equipment [Figure 9] Image of fatigue crack propagation test using rectangular column specimen [Figure 10] Image of conventional fatigue crack growth testing using CT test specimens DETAILED DESCRIPTION OF THE INVENTION

[0016] An example of an embodiment of the present invention will be described in detail below with reference to the drawings. Note that the scope of the present invention is not limited to the following examples and illustrated examples, and many modifications and variations are possible. [Example]

[0017] A high-pressure gas material testing apparatus 1 according to an embodiment of the present invention is an apparatus capable of conducting a fatigue crack growth test or a fracture toughness test. As shown in Figure 1, the high-pressure gas material testing apparatus 1 comprises a frame 10, a measurement mechanism 13, and a loading device 14. The frame section 10 is provided with a container section 11 inside, and the container section 11 has a structure that allows it to be inserted and removed in the longitudinal direction of the frame section 10. The container section 11 has an open top surface, and the surrounding sides and bottom surfaces are closed, and a storage chamber for storing the test specimen 8 is formed inside the container section 11. The internal volume of this container section 11 is designed to be 10 cc or more and 100 cc or less. The test specimen 8 is attached or removed through the open top surface of the container section 11. A loading device 14 is provided above the measurement mechanism 13, which applies a load to the test piece 12 via the measurement mechanism 13. The measurement mechanism 13 is attached to the upper surface of the frame part 10 via the outer cylinder part 41, and measures the magnitude of the load applied to the test piece 8 stored in the container part 11 inserted into the frame part 10. The container part 11 is provided with a tension mechanism 2 and a clip gauge 6. The CT test piece 8 is attached with the tension mechanism 2 and the clip gauge 6 and is fixed in the container part 11.

[0018] Here, we will explain the test specimen used in the high-pressure gas material testing equipment 1. Figure 9 shows an image of a fatigue crack propagation test using a rectangular prism test specimen. As shown in Figure 9, in a fatigue crack propagation test equipment using a rectangular prism test specimen, multiple convex portions 111 are provided on the container portion 110, and a convex portion 401 is also provided on the loading jig 400. A rectangular prism test specimen 12 is placed between these convex portions 111 and a fatigue crack propagation test is performed. Therefore, relative friction occurs between the rectangular prism test specimen 12 and the convex portions (401, 111) shown by the dashed line, and the force is not transmitted accurately. To obtain an accurate value, some kind of correction factor must be applied, but this poses the problem of requiring additional friction and wear experiments. Therefore, the high-pressure gas material testing equipment 1 is configured to use a CT test specimen 8.

[0019] 2 shows (1) a front view and (2) a right side view of the CT test piece. As shown in FIG. 2(1) or (2), the CT test piece 8 is a known one, having a notch 80 and an upper through-hole 81 and a lower through-hole 82 at opposing positions across the notch 80. In this example, the CT test piece 8 is a small test piece with a height H of approximately 10 mm, a width W of approximately 10 mm, and a thickness T of approximately 4 mm, but is not limited to these sizes. When a load is applied to the CT test piece 8 by the loading device 14, a crack originating from the notch 80 is generated in the CT test piece 8 and propagates within the CT test piece 8. The load applied to the CT test piece 8 may be a continuous load or a so-called fatigue load that is repeatedly applied.

[0020] Conventionally, fatigue crack propagation test devices using such CT test pieces have had the problem of difficulty in miniaturizing the vessel. Figure 10 shows an image of a conventional fatigue crack propagation test using a CT test piece. As shown in Figure 10, in the conventional fatigue crack propagation test, a U-shaped jig 21 is used, and connection pins 70 are inserted and fixed into upper through-holes 81 and lower through-holes 82 of a CT test piece 8, respectively. Tensile stress is then applied to either the upper or lower U-shaped jig 21, thereby performing the fatigue crack propagation test. However, this structure requires a certain height for the vessel, which makes it difficult to miniaturize the device and results in a high cost.

[0021] Therefore, the high-pressure gas material testing device 1 according to an embodiment of the present invention has achieved miniaturization of the device by improving the tensioning mechanism. The structure of the tensioning mechanism will be described in detail. Figure 3 shows an explanatory diagram of the tensioning mechanism. Note that the vessel part 11 is not shown in Figures 3 and 7. As shown in Figure 3, the tensioning mechanism 2 is composed of holders (3a, 3b) and a loading jig 4, each of which is attached to a CT test piece 8.

[0022] Next, the procedure for attaching the tension mechanism 2 to the CT specimen 8 will be described. Figure 4 is an explanatory diagram of the attachment of the tension mechanism to the CT specimen, where (1) shows the holder and (2) shows the attachment of the loading jig. Figure 5 is a cross-sectional image of the tension mechanism, showing the AA cross-section of Figure 4(2). As shown in Figures 4(1) and 5, first, the connection pin 7a is inserted into the through-hole 30a of the holder 3a, the upper through-hole 81 of the CT specimen 8, and the through-hole 30b of the holder 3b, in that order, to connect the holders (3a, 3b) to the CT specimen 8. Next, as shown in Figure 4(2), the loading jig 4 is inserted into the holders (3a, 3b) from the longitudinal direction. As shown in Figure 5, the connection pin 7b is inserted into the through-hole 4a of the loading jig 4, the lower through-hole 82 of the CT specimen 8, and the through-hole 4b of the loading jig 4, in that order, to connect the loading jig 4 to the CT specimen 8.

[0023] Fig. 6 shows an explanatory diagram of the attachment of a clip gauge. As shown in Fig. 6, for the clip gauge 6, the tension mechanism 2 is attached to the CT test piece 8, and then the cantilevers (6a, 6b) are attached to the notch 80 of the CT test piece 8. However, the clip gauge 6 may be attached before the tension mechanism 2 is attached.

[0024] Figure 7 is an explanatory diagram of the attachment of the CT test piece to the holder after the tension mechanism has been attached, with (1) showing the state before attachment and (2) showing the state after attachment. Note that the clip gauge 6 is not shown. As shown in Figure 7(1), the support parts (5a, 5b) are convex parts provided on the container part 11. The contact parts between the support parts (5a, 5b) and the holders (3a, 3b) have a concave-convex shape (not shown), which fits together when attached and provides an anti-slip function. After the tension mechanism 2 is attached to the CT test piece 8, the holders (3a, 3b) are attached to the support parts (5a, 5b). Although not shown here, the support part 5b is divided into two parts, which individually support the holders 3a and 3b. This leaves a gap between the two support parts 5b, preventing interference with the cantilevers (6a, 6b) of the clip gauge 6.

[0025] After the CT test piece is attached to the holder after the tension mechanism is attached, the holders (3a, 3b) shown in Fig. 5 are supported by the support parts (5a, 5b), and the loading jig 4 is connected to the lower through-hole 82 across the upper through-hole 81 of the CT test piece 8, so that by applying a load to the recess 4c of the loading jig 4, the load from the loading jig 4 can be converted into a tensile stress on the lower through-hole 82. Furthermore, the tension mechanism 2 can be designed to be lower in height than tension mechanisms of the prior art, which allows the container part 11 to be made smaller.

[0026] Fig. 8 shows a configuration diagram of a material testing device in high-pressure gas. As shown in Fig. 8, a recess 4c is provided on the upper surface of the loading jig 4 to receive the lower end 40a of the loading rod 40 provided in the measurement mechanism 13. This recess 4c is located directly above the upper through-hole 81 and lower through-hole 82 of the CT test piece 8 inserted into the storage chamber.

[0027] As shown in Fig. 8, a casing 35 for holding the container 11 is formed inside the frame 10. A side surface 36 of the frame 10 is detachable, and by removing the side surface 36, the container 11 can be inserted into or removed from the casing 35.

[0028] The frame section 10 is provided with an air supply passage 37 for supplying high-pressure hydrogen gas or inert gas into the container section 11 inserted into the casing section 35, and an exhaust passage 38 for discharging high-pressure hydrogen gas or inert gas from the container section 11. When the container section 11 is housed in the frame section 10 and the side section 36 is closed as shown in Figure 8, the internal pressure acting on the container section 11 is supported by the frame section 10. A passage 39 is provided on the top surface of the frame section 10 for inserting the measuring mechanism 13 from above.

[0029] When conducting the test, the tensile mechanism 2 and clip gauge 6 are attached to the CT test piece 8 and placed inside the container part 11, and the container part 11 is then inserted into the casing part 35 with the side part 36 removed, and then the side part 36 of the frame part 10 is closed to seal the inside of the container part 11.

[0030] The structures, functions, and mounting methods of the round bar-shaped load rod 40, the cylindrical outer cylinder 41 that houses the load rod 40, the welded portion 42, the cover body 43, the space 44, and the sealing members (50, 51) that make up the measurement mechanism 13 are the same as those of the invention described in Patent Document 1. The sensor member 45 is mounted near the lower end of the load rod 40.

[0031] Then, with the container 11 sealed, high-pressure hydrogen gas is supplied into the container 11 from the air supply path 37, creating a high-pressure hydrogen gas atmosphere, and the CT test piece 8 is exposed to the high-pressure hydrogen gas atmosphere.

[0032] With the CT specimen 8 placed in the high-pressure hydrogen gas atmosphere, a load is applied from above the measurement mechanism 13 by the loading device 14, and the load is transmitted to the CT specimen 8 via the loading rod 40 of the measurement mechanism 13 and the loading jig 4. The holders (3a, 3b) are connected to the upper through-hole 81 of the CT specimen 8 via the connection pin 7a and are attached to the supports (5a, 5b), while the loading jig 4 is connected to the lower through-hole 82 of the CT specimen 8 via the connection pin 7b, so that a downward load is applied to the lower through-hole 82. As a result, a bending moment acts on the CT specimen 8 in a direction that bends the notch 80 of the CT specimen 8 convexly to the right, and a tensile stress acts on the CT specimen 8 in a direction that widens the notch 80 of the CT specimen 8.

[0033] In this way, a strength test of the CT test piece 8 is carried out in the high-pressure hydrogen gas atmosphere in the container 11. During the test, the magnitude of the load applied to the CT test piece 8 in the container 11 is measured by the sensor member 45. Furthermore, the progression of a crack that occurs in the CT test piece 8 from the notch 80 as a base point is detected by an increase in the resistance value of a metal thin film (not shown) attached to the clip gauge 6.

[0034] After the test is completed, the exhaust path 38 is opened and the high-pressure hydrogen gas in the vessel 11 is discharged from the exhaust path 38. Also, an inert gas is supplied into the vessel 11 through the air supply path 37 to purge it.

[0035] Thereafter, the side portion 36 of the frame portion 10 is opened, and the CT test piece 8 is taken out of the container portion 11 after the test is completed.

[0036] As described above, the high-pressure gas materials testing device 1 according to the embodiment of the present invention reduces disassembly work and facilitates maintenance. Furthermore, by separately installing a heater or cooling device to adjust the temperature inside the container 11, the mechanical properties of the test piece can be evaluated at various temperatures. [Industrial Applicability]

[0037] The present invention is useful for crack propagation evaluation tests of CT test pieces in high-pressure gas. [Explanation of symbols]

[0038] 1. High-pressure gas material testing equipment 2. Tension mechanism 3a,3b Holder 4,400 Loading jig 4a,4b,30a,30b through hole 4c Recess 5a,5b Support part 6 Clip Gauges 6a,6b Cantilever 7a, 7b, 70 connection pins 8 CT specimens 10 Frame section 11,110 Container section 12 Prismatic specimens 13 Measurement mechanism 14 Loading device (device for applying load) 21 U-shaped jig 35 Casing 36 Side part 37 Air supply path 38 Exhaust duct 39 Passage 40 Loading rod 40a bottom end 41 Outer cylinder 42 Welded section 43 Cover body 44 Space 45 Sensor components 50,51 Sealing member 80 Notch 81 Upper through hole 82 Lower through hole 111,401 Convex

Claims

1. An apparatus for evaluating crack growth using a CT (compact tension) test piece in high-pressure gas, A material testing device in high pressure gas, characterized in that the load applied to the test piece acts from the device that applies the load directly on the through hole provided on the distal side of the test piece, bypassing the through hole provided on the proximal side of the test piece.

2. An apparatus for evaluating crack growth using a CT test piece in high-pressure gas, comprising: a container portion that houses the test piece and has a tension mechanism into which high-pressure gas is introduced, and which supports the upper through-hole of the test piece and applies a load to the lower through-hole; a loading device that applies a load to the test piece via a loading rod from above the container portion; A material testing device in high pressure gas, comprising:

3. The tensioning mechanism includes: a holder provided with a pair of through holes that can be connected to the upper through holes of the test piece using a first connecting pin, and that can be attached by hanging it over a pair of support parts that are provided in the longitudinal direction of the container part; a loading jig provided with a pair of through holes that can be connected to the lower through holes of the test piece using a second connecting pin, and a recess on the upper surface that receives the lower end of the loading rod, the through holes and the recess being arranged so as to straddle the test piece and the holder; 3. The high-pressure gas material testing device according to claim 2, further comprising:

4. 4. The material testing device for high-pressure gas according to claim 2, wherein a clip gauge is provided in the container portion to measure crack growth in the test piece.

5. 4. The high-pressure gas material testing device according to claim 2, wherein the container portion has an internal volume of 10 to 100 cc.

6. 4. The high-pressure gas material testing device according to claim 2, wherein the container portion has a substantially cylindrical shape.

7. A method for evaluating crack growth characteristics using a CT test piece in high-pressure gas, comprising: A material testing method in high-pressure gas, characterized in that the load applied to the test piece acts from a device that applies the load directly to a through hole provided on the distal side of the test piece, bypassing a through hole provided on the proximal side of the test piece.

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