Multi-axial evaluation test structure for metallic materials

Abstract

To provide a multi-axial evaluation test structure for metallic materials.SOLUTION: A multi-axial evaluation test structure 1 for metallic materials includes: a test body 10; a plug-shaped jig 20; and a ring-shaped jig 30. The test body 10 has an opening 11 at one end. The plug-shaped jig 20 is screwed into and fixed within the opening 11. The test body 10 has a test body seal surface 13 provided on its inner peripheral surface. The plug-shaped jig 20 has a plug seal surface 21 provided on its outer peripheral surface correspondingly to the test body seal surface 13. The test body seal surface 13 and the plug seal surface 21 form a seal part due to metal-contact. The test body 10 is fixed to a chuck 201 of a multi-axial evaluation test device 200 via the ring-shaped jig 30 that is fixed to the outer peripheral surface of the test body 10.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present disclosure relates to a multiaxial evaluation test structure for evaluating the deformation behavior (stress-strain response) of metallic materials in a multiaxial stress field. [Background technology]

[0002] Predicting the deformation behavior of metallic materials in a multiaxial stress field is important in various industrial fields. For example, in the field of thin steel sheets, such as automotive steel sheets used in the automobile industry, the secondary workability of thin steel sheets manufactured by cold rolling is important. Specifically, it is important to predict deformation behavior such as work hardening, springback, and working limit in a relatively large strain range of about 10%. In such fields related to thin steel sheets, the deformation behavior due to repeated loads is not emphasized. In other words, the deformation behavior that is emphasized in each industrial field is different.

[0003] In oil wells, natural gas wells, etc. (hereinafter collectively referred to as "oil wells"), oil well pipes such as casings or tubing are used to extract underground resources. Oil well pipes are made of steel pipes connected in sequence, and threaded joints are used for connecting them.

[0004] Steel pipe threaded joints are repeatedly exposed to various combinations of loads in oil wells. The load applied to a steel pipe threaded joint may exceed the yield stress of the metallic material in a local area of ​​the steel pipe threaded joint. In addition, the local area of ​​the steel pipe threaded joint may be in a plastic strain region of about several percent due to the harsh oil well environment, and may be subjected to extremely low cycles of axial and circumferential compression and tension, for example, repeated loads of several hours to several days, during the well development process (drilling process) and production adjustment (opening and closing of production valves). That is, even if the overall strength of a steel pipe threaded joint is not considered a problem, important performance such as sealing performance may be impaired due to local plastic yielding. Therefore, in order to reliably maintain the desired strength and sealing performance of a steel pipe threaded joint in a harsh oil well environment, it is essential to understand the deformation behavior of the metallic material constituting the steel pipe threaded joint in a multiaxial stress field, particularly the deformation behavior when extremely low cycle repeated loads are applied, and to appropriately design the steel pipe threaded joint.

[0005] There are various test methods for evaluating the deformation behavior of metallic materials in a multiaxial stress field. For example, there are methods for applying tensile or compressive loads in two orthogonal in-plane directions to flat or thin-film test pieces, methods for applying out-of-plane loads, and methods for applying internal or external pressure loads together with axial force to cylindrical test pieces. Among these test methods, various test methods are used, such as a method for applying only a monotonically increasing load, a method for applying a cyclic load in a single or double swing, a method for evaluating ultimate fracture properties, and a method for evaluating high-cycle fatigue properties with a relatively short cyclic cycle.

[0006] JP 2012-211823 A (Patent Document 1) discloses a multiaxial load test device capable of performing a highly accurate load test in a multiaxial state. The multiaxial load test device includes a pressure vessel section in which a housing hole for housing a specimen is formed and hydraulic oil is stored around the specimen housed in the housing hole, an internal pressure application section that applies internal pressure to the specimen by hydraulic oil stored in the internal space of the specimen, and an external pressure application section that applies external pressure to the outer periphery of the specimen by hydraulic oil by moving the specimen in the axial direction to change the volume of the working space between the housing hole and the specimen. The specimen is substantially cylindrical and has a shape that is narrowed so that the central part is thin-walled. The lower support part and the upper support part of the specimen are formed to be thick-walled. A groove for mounting an O-ring for sealing is formed on the outer periphery of each of the lower support part and the upper support part. That is, in the multiaxial load test device, the O-ring seals the hydraulic oil for applying external pressure when the specimen is moved in the axial direction.

[0007] JP 2016-142730 A (Patent Document 2) discloses a multiaxial fatigue test device capable of performing a load test by rapidly changing the stress state inside a test piece in a multiaxial stress field. The multiaxial fatigue test device includes a load applying unit that applies a load in the axial direction of a cylindrical test piece, a plurality of fluid supply units that each circulate fluids having at least one of different pressures and temperatures inside the test piece, and a switching unit that selectively switches between the plurality of fluid supply units to circulate one of the fluids having at least one of different pressures and temperatures inside the test piece. In addition, Patent Document 2 discloses in an example that when an internal pressure of 20 MPa is applied to a test piece having an outer diameter of 12 mm, circumferential and axial stresses of 200 MPa are generated in the test piece.

[0008] JP 2017-90181 A (Patent Document 3) discloses a biaxial stress loading mechanism for determining the strength characteristics of a tube under a constant biaxial stress ratio. The biaxial stress loading mechanism is composed of a sealed end plug for a tubular test piece fixed to one end of the tubular test piece, and an end plug with a pressure medium introduction hole fixed to the other end of the tubular test piece. The end plug with the pressure medium introduction hole is connected to an internal pressure generating piston via a pressure connecting tube. The tubular test piece and the internal pressure generating piston are combined in series so that when a tensile force is applied to the tubular test piece via a tensile force connecting rod connected to the other end of the internal pressure generating piston, the internal pressure in the tubular test piece increases in proportion to the tensile force due to the inflow of the pressure medium in the internal pressure generating piston. [Prior art documents] [Patent documents]

[0009] [Patent Document 1] JP 2012-211823 A [Patent Document 2] JP 2016-142730 A [Patent Document 3] JP 2017-90181 A Summary of the Invention [Problem to be solved by the invention]

[0010] However, the multiaxial load test device of Patent Document 1 applies external pressure by hydraulic oil by moving the specimen in the axial direction. Accordingly, the O-rings attached to the grooves of the lower support part and the upper support part of the specimen also move in a sliding manner in the axial direction. That is, in the multiaxial load test device, since it is necessary to allow the O-ring to move, the sealing contact pressure of the O-ring cannot be increased. As a result, there is a problem that when excessive external pressure is applied, coupled with the reduction in the diameter of the specimen, the hydraulic oil may leak from the accommodation hole. In addition, Patent Document 1 does not disclose a specific structure for connecting and fixing the operating body or the contact body having a communication passage for storing the hydraulic oil in the internal space of the specimen to the specimen.

[0011] Patent Document 2 does not disclose a specific structure for connecting and fixing the test specimen to the piping including the first inlet passage or the piping including the first outlet passage in order to communicate the internal space of the test specimen with the first inlet passage or the first outlet passage. In addition, the multiaxial fatigue test device of Patent Document 2 tests the fatigue behavior of members used in actual equipment used in power plants, plants, etc. when a stress lower than the yield stress is repeatedly applied. Some materials for steel pipe threaded joints have a high yield stress of more than 1000 MPa, but Patent Document 2 does not target a test for deforming such high-strength materials to the plastic region. If the test specimen of Patent Document 2 and each pipe are connected and fixed by a method other than welding, if an internal pressure is applied to the extent that the test piece assuming a steel pipe threaded joint undergoes plastic deformation, there is a risk of fluid leaking from the communication point between the internal space of the test specimen and the first inlet passage or the first outlet passage. On the other hand, if the test specimen and each pipe are connected and fixed by welding, there is a risk that the metal material of the test piece will be altered by the welding heat, and furthermore, there is a risk that connecting and disconnecting the test specimen and the pipes will require time and money.

[0012] Patent Document 3 does not disclose the application of a compressive load to a tubular test specimen, and it is unclear whether repeated alternating axial loads can be applied appropriately.

[0013] An object of the present disclosure is to provide a multiaxial evaluation test structure for metallic materials in a multiaxial stress field, which is capable of stably and repeatedly applying internal pressure loads as well as tensile and compressive loads to a test specimen in a high-strength steel material without leakage of the internal pressure medium even when a relatively high internal pressure is applied. [Means for solving the problem]

[0014] In order to solve the above problems, the present disclosure is configured as follows. That is, the multiaxial evaluation test structure for metallic materials according to the present disclosure is a multiaxial evaluation test structure for metallic materials for evaluating the deformation behavior of metallic materials in a multiaxial stress field using a multiaxial evaluation test device, and includes a cylindrical test body having an opening at one end, and a plug-shaped jig that is screwed into the opening at one end of the test body and connects a pipe for supplying an internal pressure medium that applies internal pressure to the test body to the test body. The test body includes a tapered test body seal surface on its inner circumferential surface. The plug-shaped jig includes a tapered plug seal surface that is provided on its outer circumferential surface in correspondence with the test body seal surface. When the plug-shaped jig is screwed into the opening of the test body and fixed, the test body seal surface and the plug seal surface come into contact with each other. [Brief description of the drawings]

[0015] [Figure 1] FIG. 1 is a vertical cross-sectional view showing a multi-axis evaluation test structure according to the first embodiment. [Diagram 2] FIG. 2 is an enlarged vertical cross-sectional view showing the evaluation portion of FIG. [Diagram 3] FIG. 3 is a vertical cross-sectional view showing a multi-axis evaluation test structure according to the second embodiment. [Figure 4] FIG. 4 is a graph showing an example of a combination of internal pressure load and tensile and compressive load. [Diagram 5] FIG. 5 is a graph showing the axial stress-strain response. [Figure 6] FIG. 6 is a graph showing the circumferential stress-strain response. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0016] The inventors considered that it would be difficult to appropriately predict the deformation behavior of the high-strength metallic materials that make up threaded joints for steel pipes using the test devices or test methods described in the three patent documents mentioned above, and therefore conducted extensive research into a new multi-axial evaluation test structure.

[0017] In this multiaxial evaluation test, the loading conditions desired by the inventors are, as described above, extremely low cycle repeated loads of tension, compression and internal pressure applied to localized parts of a threaded joint for steel pipes that are in a plastic strain region of about several percent due to the harsh oil well environment. In other words, the multiaxial evaluation test structure disclosed herein is required to not leak the internal pressure medium (high-pressure water) even when repeatedly loaded with a load equal to or greater than the yield stress of the high-strength metallic material.

[0018] In addition, the cylindrical specimen must be accurately and precisely formed in the evaluation section for evaluating the deformation behavior, while minimizing the deterioration of the metal material, in terms of the dimensions and surface roughness of the inner and outer surfaces. If the inner diameter of the opening of the specimen is too small, it is difficult to properly form the inner surface of the evaluation section. Therefore, it is preferable that the inner diameter of the opening at one end of the specimen is equal to or larger than the inner diameter of the internal space of the specimen. When the opening of the specimen has a relatively large inner diameter, it is usually difficult to connect the specimen and the test jig by a method other than welding to prevent leakage of the internal pressure medium from the opening. However, as described above, when the specimen and the test jig are connected by welding, there is a risk that the metal material of the specimen may be deteriorated by the welding heat, and further, there is a risk that the connection and dismantling of the specimen and the test jig may require time and cost.

[0019] Based on this viewpoint, the inventors have investigated a connection structure between a test specimen and a test jig that can suppress leakage of the internal pressure medium even if the connection structure is other than welding, and have completed the multi-axial evaluation test structure for metallic materials according to the present disclosure.

[0020] (Configuration 1) The multiaxial evaluation test structure for metallic materials according to this embodiment is a multiaxial evaluation test structure for metallic materials for evaluating the deformation behavior of metallic materials in a multiaxial stress field using a multiaxial evaluation test device, and includes a cylindrical test body having an opening at one end, and a plug-shaped jig that is screwed into the opening at one end of the test body and connects a pipe for supplying an internal pressure medium that applies internal pressure to the test body to the test body. The test body includes a tapered test body seal surface on its inner circumferential surface. The plug-shaped jig includes a tapered plug seal surface provided on its outer circumferential surface in correspondence with the test body seal surface. When the plug-shaped jig is screwed into the opening of the test body and fixed, the test body seal surface and the plug seal surface come into contact with each other.

[0021] The test specimen seal surface and the plug seal surface come into contact with each other to form a seal by metal contact. This makes it possible to prevent leakage of the internal pressure medium from the test specimen even when axial tensile and compressive loads are applied while the internal pressure load is applied. As a result, the internal pressure load and axial tensile and compressive loads can be applied repeatedly to the test specimen in a stable manner.

[0022] (Configuration 2) In the multiaxial evaluation test structure for metallic materials of configuration 1, the test specimen may include a test specimen female thread portion on an inner circumferential surface between one end of the test specimen and the test specimen seal surface. The plug-shaped jig may include a plug male thread portion provided on an outer circumferential surface in correspondence with the test specimen female thread portion. The plug-shaped jig may be fixed to the test specimen by fastening the test specimen female thread portion and the plug male thread portion. This fastens the test specimen and the plug-shaped jig, making it possible to more reliably fix the test specimen and the plug-shaped jig.

[0023] (Configuration 3) The multiaxial evaluation test structure for metallic materials of configuration 1 or 2 may include a ring-shaped jig that connects the multiaxial evaluation test device and the test specimen. The test specimen may include a test specimen fixing portion on its outer peripheral surface that fixes the test specimen to the inner peripheral surface of the ring-shaped jig. By connecting the test specimen to the multiaxial evaluation test device via the ring-shaped jig, the tensile and compressive loads transmitted from the multiaxial evaluation test device can be appropriately applied to the test specimen.

[0024] (Configuration 4) In the multiaxial evaluation test structure for metallic materials of configuration 3, the test specimen seal surface may be provided so as to overlap the test specimen fixing portion in the radial direction when the test specimen and the plug-shaped jig are fixed. When a high internal pressure load is applied to the test specimen, the test specimen may expand and deform in the radial direction. The test specimen seal surface and the test specimen fixing portion overlap in the radial direction, that is, the ring-shaped jig is fixed so as to overlap in the radial direction on the radial outside of the seal portion constituted by the test specimen seal surface and the plug seal surface, thereby suppressing the expansion and deformation of the test specimen in the seal portion. This makes it possible to suppress a decrease in contact pressure in the seal portion, and to suppress leakage of the internal pressure medium from the test specimen. As a result, the internal pressure load and the tensile and compressive loads can be repeatedly applied more stably. In this disclosure, "the test specimen seal surface and the test specimen fixing portion overlap in the radial direction" means that "when viewed in a radial cross section, there is a region in which the test specimen seal surface and the test specimen fixing portion are in the same cross section."

[0025] (Configuration 5) In the multiaxial evaluation test structure for metallic materials of configuration 3 or 4, the plug-shaped jig may have a pedestal portion exposed from an opening at one end of the test body and extending in the radial direction. The pedestal portion may be fixed to a ring-shaped jig fixed to the outer circumferential surface of the test body. A gap may be formed between the test body and the pedestal portion. This makes it difficult for a relative axial misalignment to occur between the test body seal surface and the plug-shaped jig seal surface even when an axial tensile and compressive load is applied while an internal pressure load is applied, and it is possible to suppress leakage of the internal pressure medium from the test body. As a result, it is possible to stably and repeatedly apply an internal pressure load and an axial tensile and compressive load to the test body.

[0026] (Configuration 6) A multiaxial evaluation test structure for a metal material according to any one of configurations 1 to 5, wherein the test piece includes an evaluation portion provided between one end and the other end of the test piece, which is thinner than the one end and the other end of the test piece and has a constant thickness, and may satisfy the following formulas (1) and (2). D / t<0.062×E / σY (1) D / L<1.5···(2) In formulas (1) and (2), D is the outer diameter of the evaluation part, t is the wall thickness of the evaluation part, L is the axial length of the evaluation part, E is the elastic modulus of the metal material, and σY is the yield stress of the metal material. This makes it possible to suppress buckling deformation of the evaluation part even when tensile and compressive loads that cause plastic deformation are repeatedly applied.

[0027] (Configuration 7) In the multiaxial evaluation test structure for metallic materials according to any one of configurations 1 to 6, a lubricant may be applied between the test specimen seal surface and the plug seal surface. This makes it easier to screw the plug-shaped jig into the opening of the test specimen, and improves the sealing performance between the test specimen seal surface and the plug seal surface. This makes it possible to more effectively suppress leakage of the internal pressure medium.

[0028] (Configuration 8) In the multiaxial evaluation test structure for metallic materials according to any one of configurations 1 to 7, either the test specimen seal surface or the plug seal surface may be plated with a metal having a lower hardness than the metallic material constituting either the test specimen or the plug-shaped jig, thereby improving the sealing performance of the test specimen seal surface and the plug seal surface, and more effectively suppressing leakage of the internal pressure medium.

[0029] Hereinafter, the present embodiment will be described in detail with reference to the drawings. In the drawings, the same or corresponding parts are designated by the same reference numerals, and the description thereof will not be repeated. Furthermore, the dimensional ratios between the components shown in each drawing do not necessarily represent the actual dimensional ratios.

[0030] [First embodiment] 1, the multiaxial evaluation test structure 1 according to the first embodiment includes a test specimen 10, a plug-shaped jig 20, a ring-shaped jig 30, and a ring-shaped jig 40. The test specimen 10 is connected to a pipe 100 for supplying an internal pressure medium to the internal space of the test specimen 10 via the plug-shaped jig 20. The test specimen 10 is fixed to a multiaxial evaluation test device 200 (specifically, a chuck 201 of the multiaxial evaluation test device 200) via the ring-shaped jig 30.

[0031] The test specimen 10 has a cylindrical shape and includes an opening 11 at one end (the end on the lower side of the test specimen 10 in the drawing), an opening 12 at the other end (the end on the upper side of the test specimen 10 in the drawing), a test specimen sealing surface 13, a test specimen female thread portion 14, a test specimen fixing portion 15, and an evaluation portion 16.

[0032] The opening 11 at one end is formed at one end of the test piece 10. The inner diameter of the opening 11 is the same as or larger than the inner diameter of the evaluation part 16. This allows the dimensions of the evaluation part 16 or the surface roughness of the inner surface of the evaluation part 16 to be appropriately formed.

[0033] The opening 12 at the other end has an inner diameter smaller than the inner diameter of the evaluation section 16. That is, the opening 12 is formed by a relatively thin hole. For example, the inner diameter of the opening 12 is equivalent to the inner diameter of a flow path 151 of a pipe 150 described later.

[0034] The test specimen seal surface 13 is provided on the inner circumferential surface of the test specimen 10. It is a tapered conical surface whose diameter decreases from the opening 11 toward the evaluation portion 16 in the axial direction CL.

[0035] The test specimen female thread portion 14 is provided on the inner peripheral surface of the test specimen 10 between the opening 11 and the test specimen seal surface 13 .

[0036] The test specimen fixing portion 15 is provided on the outer peripheral surface of the test specimen 10, and fixes the test specimen 10 to the inner peripheral surface of a ring-shaped jig 30 described later. In this embodiment, the test specimen fixing portion 15 is a test specimen male thread portion provided on the outer peripheral surface of the test specimen 10. The test specimen fixing portion 15 is provided so as to overlap the test specimen seal surface 13 in the radial direction DL when the test specimen 10 and a plug-shaped jig 20 described later are fixed. In other words, the test specimen seal surface 13 is positioned on the inner peripheral surface of the test specimen 10 so as to correspond to the test specimen fixing portion 15 provided on the outer peripheral surface of the test specimen 10 in the radial direction DL.

[0037] The evaluation portion 16 is provided between one end and the other end of the test piece 10 in the axial direction CL. As shown in FIG. 2, the evaluation portion 16 is a part of a thin-walled portion 17 formed by cutting out the outer peripheral surface of the test piece 10 in an annular shape to have a thinner wall than the one end and the other end of the test piece 10. As shown in FIG. 2, the thin-walled portion 17 has, in a vertical cross-sectional view, a curved portion 17a on one end side of the test piece 10, a curved portion 17b on the other end side, and a straight portion 17c located between the curved portion 17a and the curved portion 17b. The evaluation portion 16 is a cylindrical thin-walled portion having a constant wall thickness, including the straight portion 17c.

[0038] 2, the evaluation part 16 has an outer diameter D, a wall thickness t, and an axial length L. When the elastic modulus of the metal material of the test piece 10 is E and the yield stress of the metal material is σY, the following formulas (1) and (2) are satisfied. D / t<0.062×E / σY (1) D / L<1.5···(2) This makes it possible to suppress buckling deformation and the like of the evaluation portion 16 even when tensile and compressive loads that would cause plastic deformation are repeatedly applied.

[0039] The plug-shaped jig 20 is screwed into and fixed to the opening 11 at one end of the test piece 10. The plug-shaped jig 20 includes a plug seal surface 21, a plug male thread portion 22, a flow path 23, and a piping connection hole 24.

[0040] The plug seal surface 21 is provided on the outer circumferential surface of the plug-shaped jig 20 so as to correspond to the test specimen seal surface 13. The plug seal surface 21 comes into contact with the test specimen seal surface 13 when the plug-shaped jig 20 is screwed and fixed into the opening 11 of the test specimen 10. That is, the plug seal surface 21 and the test specimen seal surface 13 form a seal portion by metal contact. This makes it possible to suppress leakage of the internal pressure medium from the internal space of the test specimen 10 even when axial tensile and compressive loads are applied while the internal pressure load is applied. At this time, it is preferable that the diameter of the plug seal surface 21 is larger than the diameter of the test specimen seal surface 13 before screwing. As a result, when the plug-shaped jig 20 is screwed and fixed into the opening 11 of the test specimen 10, the plug seal surface 21 and the test specimen seal surface 13 fit together and are in close contact with each other to form an interference fit. This makes it possible to more effectively suppress leakage of the internal pressure medium from the internal space of the test specimen 10. The greater the difference between the diameter of the plug seal surface 21 and the diameter of the test specimen seal surface 13 (also called the amount of seal interference), the greater the metal seal contact force, making it possible to more effectively suppress leakage of the internal pressure medium.

[0041] A lubricant may be applied between the test specimen seal surface 13 and the plug seal surface 21. The lubricant may be, for example, lubricating grease or sealing grease. This makes it easier to screw the plug-shaped jig 20 into the opening 11 of the test specimen 10, and improves the sealing performance between the test specimen seal surface 13 and the plug seal surface 21. This makes it possible to more effectively suppress leakage of the internal pressure medium.

[0042] Either the specimen seal surface 13 or the plug seal surface 21 may be plated with copper. Copper is a metal with a relatively low hardness. In this way, by plating either the specimen seal surface 13 or the plug seal surface 21 with a metal with a lower hardness than the metal material constituting the specimen 10 and the plug-shaped jig 20, the plated metal is deformed in the process of screwing the plug-shaped jig 20 into the opening 11 of the specimen 10, and the real contact area between the specimen seal surface 13 and the plug seal surface 21 increases. Furthermore, compared to the case where no plating is performed, the microscopic gap between the specimen seal surface 13 and the plug seal surface 21 becomes narrower and is divided, making it difficult for a leak path to be formed. This improves the sealing performance of the specimen seal surface 13 and the plug seal surface 21, and more effectively suppresses leakage of the internal pressure medium.

[0043] The plug male thread portion 22 is provided on the outer circumferential surface of the plug-shaped jig 20 in correspondence with the test specimen female thread portion 14. The plug male thread portion 22 is screwed into the test specimen female thread portion 14 when the plug-shaped jig 20 is screwed into the opening portion 11 of the test specimen 10. This fastens the test specimen 10 and the plug-shaped jig 20 together, enabling the plug-shaped jig 20 to be more reliably fixed to the test specimen 10.

[0044] The flow path 23 and the pipe connection hole 24 are through holes that penetrate the plug-shaped jig 20 in the axial direction CL. The end of the pipe 100 described later is screwed into the pipe connection hole 24 to be fixed. Although not shown in the figure, the plug-shaped jig 20 and the pipe 100 are fixed by screwing the female thread of the high-pressure pipe joint of the conventional technology formed on the inner circumferential surface of the pipe connection hole 24 with the male thread of the high-pressure pipe joint of the conventional technology formed on the end of the pipe 100. At this time, the flow path 101 of the pipe 100 is sealed by a seal structure provided in the high-pressure pipe joint of the conventional technology and communicates with the flow path 23 of the plug-shaped jig 20. As a result, the flow path 101 of the pipe 100 is communicated with the internal space of the test body 10, and the internal pressure medium is supplied from the pipe 100 to the internal space of the test body 10. Although not shown in the figure, a pump is connected to the other end of the pipe 100.

[0045] The pipe 150 is connected to the opening 12 at the other end by a conventional high-pressure pipe joint. The flow path 151 of the pipe 150 communicates with the opening 12 while being connected to the opening 12. The pipe 150 discharges the internal pressure medium from the internal space of the test specimen 10.

[0046] The ring-shaped jig 30 is fixed to one end of the test specimen 10 (the end on the lower side in the drawing of the test specimen 10). The ring-shaped jig 30 has, on its inner peripheral surface, a ring female thread portion 31 that corresponds to the above-mentioned test specimen fixing portion (test specimen male thread portion) 15 provided on the outer peripheral surface of one end of the test specimen 10. The test specimen 10 is fixed to the ring-shaped jig 30 by screwing the test specimen fixing portion (test specimen male thread portion) 15 and the ring female thread portion 31 together. This allows the tensile and compressive loads transmitted from the multiaxial evaluation test device 200 to be appropriately applied to the test specimen 10.

[0047] As described above, the test specimen fixing portion 15 is provided so as to overlap the test specimen seal surface 13 in the radial direction. That is, the ring-shaped jig 30 is fixed to the outer peripheral surface of the test specimen 10 so as to overlap the test specimen seal surface 13 in the radial direction. This makes it possible to suppress excessive radial expansion deformation of the test specimen 10 in the seal portion due to the high internal pressure of the internal pressure medium, and to suppress a decrease in the contact pressure in the metal contact between the test specimen seal surface 13 and the plug seal surface 21. As a result, the internal pressure medium does not leak even when a high internal pressure load is applied, and a multiaxial evaluation test can be stably performed even when tensile and compressive loads are applied while the internal pressure load is applied.

[0048] The ring-shaped jig 40 is fixed to the other end (the upper end of the test piece 10 as shown in the figure) of the test piece 10. The structure for fixing the ring-shaped jig 40 to the other end of the test piece 10 is similar to that of the ring-shaped jig 30, and therefore a detailed description thereof will be omitted.

[0049] The ring-shaped jig 30 is fixed to a chuck 201 of a multi-axis evaluation test device 200 by having the chuck 201 grip the upper and lower surfaces, as shown in the figure, of the outer edge portion of the ring-shaped jig 30 .

[0050] The ring-shaped jig 40 is fixed to a chuck 202 of a multiaxial evaluation test device 200 by gripping the upper and lower surfaces, as shown in the figure, of the outer edge of the ring-shaped jig 40. The chucks 201 and 202 are spaced apart, and tensile and compressive loads are repeatedly applied to the test piece 10 by moving either or both of the chucks 201 and 202 in the axial direction.

[0051] By fixing the multiaxial evaluation test device 200 and the ring-shaped jig 30 in this manner, the tensile and compressive loads applied to the test piece 10 are less likely to act on the plug-shaped jig 20 or on the seal portion formed by the test piece seal surface 13 and the plug seal surface 21. As a result, even if tensile and compressive loads are repeatedly applied to the test piece 10, loosening of the seal portion can be suppressed, and leakage of the internal pressure medium can be continuously suppressed, making it possible to carry out the multiaxial evaluation test more stably.

[0052] Although not specifically shown, gripping portions may be provided on the outer surface of the plug-shaped jig 20 and the outer surface of the test piece 10 so that the plug-shaped jig 20 can be easily screwed into the opening 11 of the test piece 10 .

[0053] [Second embodiment] Next, the multi-axis evaluation test structure 1 according to the second embodiment will be specifically described with reference to Fig. 3. Descriptions of the same configurations as those in the first embodiment will be omitted, and basically, configurations different from those in the first embodiment will be described in detail.

[0054] 3, the multiaxial evaluation test structure 1 according to the second embodiment is different from the first embodiment in that it does not have a specimen female thread portion 14 and a plug male thread portion 22. That is, the inner peripheral surface of the specimen 10 and the outer peripheral surface of the plug-shaped jig 20 are in contact with each other at the specimen seal surface 13 and the plug seal surface 21.

[0055] The plug-shaped jig 20 has a pedestal portion 25. The pedestal portion 25 is exposed from the opening 11 at one end of the test piece 10 and is formed by extending in the radial direction. As in the first embodiment, the ring-shaped jig 30 is fixed to the outer circumferential surface of the test piece 10. Therefore, in the figure, the lower surface of the ring-shaped jig 30 and the upper surface of the pedestal portion 25 face each other. The pedestal portion 25 is fixed to the ring-shaped jig 30 via a connector 26. The connector 26 is, for example, a bolt. However, the structure is not limited as long as the connector 26 can fix the pedestal portion 25 and the ring-shaped jig 30. The piping connection hole 24 is provided in the pedestal portion 25 as shown in the figure. The ring-shaped jig 30 and the pedestal portion 25 fixed to each other are held in the chuck 201 of the multiaxial evaluation test device 200 in the vertical direction as shown in the figure. That is, the ring-shaped jig 30 and the base portion 25, which are fixed to each other, are fixed to the chuck 201 by the chuck 201 gripping the upper surface of the outer edge portion of the ring-shaped jig 30 as shown in the figure and the lower surface of the outer edge portion of the base portion 25 as shown in the figure.

[0056] A gap G is formed between the test specimen 10 and the pedestal portion 25. As a result, tensile and compressive loads are not transmitted from the pedestal portion 25 to the test specimen 10, and the tensile and compressive loads transmitted from the multiaxial evaluation test device 200 can be appropriately transmitted to the test specimen 10 via the ring-shaped jig 30.

[0057] Furthermore, in the multiaxial evaluation test structure of the second embodiment, as in the multiaxial evaluation test structure of embodiment 1, the contact between the test specimen seal surface 13 and the plug seal surface 21 makes it possible to prevent leakage of the internal pressure medium from the internal space of the test specimen 10, even when axial tensile and compressive loads are applied while an internal pressure load is applied.

[0058] Although the embodiments have been described above, the present disclosure is not limited to the above-described embodiments, and various modifications are possible without departing from the spirit of the present disclosure. EXAMPLES

[0059] In order to demonstrate the effects of the multiaxial evaluation test structure according to the present disclosure, a multiaxial cyclic test was conducted on each of the multiaxial evaluation test structure of the above-mentioned first embodiment (Example 1) and the multiaxial evaluation test structure of the second embodiment (Example 2), in which axial tensile and compressive loads were repeatedly applied while a constant internal pressure was applied.

[0060] In both the test specimens of Examples 1 and 2, the test specimens were made of quenched and tempered martensitic steel having a yield stress of 930 MPa and an elastic modulus of 204 GPa, and the test portion had an outer diameter of φ24 mm, a wall thickness of 3 mm, and a length of 25 mm. In both the plug-shaped jig and the ring-shaped jig of Example 1 and Example 2, the test specimens were made of general-purpose SCM steel, and had a yield stress of about 900 MPa due to heat treatment. The taper of the test specimen seal surface and the plug seal surface was 1:4.

[0061] The test consisted of repeating tensile and compressive loads five times at a strain rate of 0.6% / min with an axial strain range of 1.2% while maintaining an internal pressure (water pressure) of 50 MPa on each specimen. If there was no leakage of the internal pressure medium (high-pressure water) after that, each specimen was replaced with a new one, the internal pressure was increased by 50 MPa (100 MPa for the second time), and the same test was repeated. This test was continued until the strain range was 2.0% and the internal pressure was 200 MPa. Figure 4 shows the combination of axial load and internal pressure load.

[0062] The stress-strain response in the axial direction obtained in the above test is shown in Fig. 5, and the stress-strain response in the circumferential direction is shown in Fig. 6. As a result of the above test, even when a maximum internal pressure of 200 MPa was applied, no leakage of the internal pressure medium (high-pressure water) occurred in both the test specimens of Examples 1 and 2. In this way, by using the multiaxial evaluation test structure disclosed herein, it was possible to stably perform an extremely low cycle stress-strain response in which a plastic strain of several percent occurs in a multiaxial stress field on a test specimen made of a high-strength metallic material without leakage of the internal pressure medium. [Explanation of symbols]

[0063] 1: Multi-axis evaluation test structure 10: Test specimen 11: Opening (one end of the test specimen) 12: Opening (other end of test specimen) 13: Test specimen sealing surface 14: Female thread part of test specimen 15: Test specimen fixing part 16: Evaluation section 17: Thin section 20: Plug-shaped jig 21:Plug seal surface 22: Male thread of plug 23: Flow path 24: Pipe connection hole 25: Base 26: Connector D:Outer diameter t: Thickness L: Axial length

Claims

1. A multiaxial evaluation test structure for evaluating the deformation behavior of a metallic material in a multiaxial stress field using a multiaxial evaluation test device, A cylindrical test specimen having an opening at one end; a plug-shaped jig that is screwed into an opening at one end of the test body and connects a pipe to the test body for supplying an internal pressure medium that applies an internal pressure to the test body; the test specimen includes a tapered test specimen seal surface on an inner circumferential surface; the plug-shaped jig includes a tapered plug seal surface provided on an outer circumferential surface thereof in correspondence with the test specimen seal surface, A multiaxial evaluation test structure for metallic materials in which the test specimen seal surface and the plug seal surface are in contact with each other when the plug-shaped jig is screwed into and fixed in the opening of the test specimen.

2. A multi-axis evaluation test structure for metallic materials according to claim 1, The test specimen includes a test specimen female thread portion on an inner circumferential surface between one end of the test specimen and the test specimen seal surface, the plug-shaped jig includes a plug male thread portion provided on an outer circumferential surface thereof in correspondence with the test specimen female thread portion, A multiaxial evaluation test structure for metallic materials, wherein the plug-shaped jig is fixed to the test specimen by fastening the test specimen female thread portion and the plug male thread portion together.

3. A multi-axis evaluation test structure for metallic materials according to claim 1, a ring-shaped jig for connecting the multiaxial evaluation test device and the test specimen; The test specimen has a multi-axial evaluation test structure including a test specimen fixing portion on its outer peripheral surface that fixes the test specimen to the inner peripheral surface of the ring-shaped jig.

4. A multi-axis evaluation test structure for metallic materials according to claim 3, A multi-axial evaluation test structure, in which the test specimen sealing surface is arranged to radially overlap the test specimen fixing portion when the test specimen and the plug-shaped jig are fixed.

5. A multi-axis evaluation test structure for metallic materials according to claim 3, the plug-shaped jig has a base portion exposed from an opening at one end of the test piece and extending in a radial direction; The base portion is fixed to the ring-shaped jig fixed to the outer peripheral surface of the test piece, A multi-axial evaluation test structure, wherein a gap is formed between the test body and the base portion.

6. A multi-axis evaluation test structure for metallic materials according to claim 1, The test piece includes an evaluation portion that is provided between one end and the other end of the test piece, is thinner than the one end and the other end of the test piece, and has a constant thickness; A multi-axis evaluation test structure that satisfies the following formulas (1) and (2). D / t<0.062×E / σY...(1) D / L<1.5...(2) In the formulas (1) and (2), D is the outer diameter of the evaluation portion, t is the thickness of the evaluation portion, L is the axial length of the evaluation portion, E is the elastic modulus of the metal material, and σY is the yield stress of the metal material.

7. A multi-axis evaluation test structure for metallic materials according to claim 1, A multi-axis evaluation test structure, wherein a lubricant is applied between the test specimen seal surface and the plug seal surface.

8. A multi-axis evaluation test structure for metallic materials according to claim 1, A multi-axis evaluation test structure, wherein either the test specimen seal surface or the plug seal surface is plated with a metal having a hardness lower than that of the metal material constituting either the test specimen or the plug-shaped jig.

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