Test fixtures, test equipment, and test methods

Abstract

To provide a test jig capable of conducting a shaft core adjustment of a test piece for a fatigue test with high accuracy.SOLUTION: A test jig is to be used for a fatigue test. The test jig includes a test piece holder 10B to be attached at one side in an axial direction of a test piece, the axial direction being a direction in which a load is applied to the test piece (x direction). The test piece holder 10B includes a test piece installation surface 1211 being a face on which the test piece is to be installed. The test piece holder 10B includes a penetration hole 1211b or a penetration slit 1211a, passing through the test piece installation surface 1211 and extending in a direction perpendicular to the axial direction.SELECTED DRAWING: Figure 10

Description

Technical Field

[0001] The present invention relates to a test jig, a test apparatus, and a test method, and more particularly to a test jig and a test apparatus used for a fatigue test, and a method for a fatigue test.

Background Art

[0002] Conventionally, as a low-cycle fatigue test method for metal materials, a test has been conducted in which the distance between evaluation points of a test piece, and thus the strain, is measured during a load test, and the fracture life and repeated hardening characteristics of the test piece are evaluated.

[0003] Japanese Patent No. 3304551 describes a fatigue test apparatus for a small test piece. The publication describes a test apparatus capable of performing a low-cycle test on a test piece having a total length of 30 mm, a diameter of 2 mm, and a detection length GL of about 2 mm.

[0004] Japanese Patent Application Laid-Open No. 2005-326357 describes a fatigue test jig for an ultra-small test piece including a tensile load member and a compression load member. The publication describes a test jig for a test piece having dimensions such as a cross section of 0.3 mm × 0.3 mm, a parallel portion length of 0.5 mm, and a total length of 2.4 mm.

[0005] Japanese Patent Application Laid-Open No. 2018-69360 describes a shaft connection adjustment mechanism capable of adjusting the misalignment between a tool shaft and a shank.

[0006] Regarding literature on strain measurement techniques, there are Japanese Patent Application Laid-Open Nos. Hei 8-240517, Hei 10-89950, 2003-130610, Sho 64-35203, 2008-224341, etc.

[0007] Non-Patent Document 1 describes that cracks generated during a fatigue test were observed in situ.

Prior Art Documents

Patent Documents

[0008] [Patent Document 1] Patent No. 3304551 [Patent Document 2] Japanese Patent Publication No. 2005-326357 [Patent Document 3] Japanese Patent Publication No. 2018-69360 [Patent Document 4] Japanese Patent Application Publication No. 8-240517 [Patent Document 5] Japanese Patent Application Publication No. 10-89950 [Patent Document 6] Japanese Patent Publication No. 2003-130610 [Patent Document 7] Japanese Patent Application Publication No. 64-35203 [Patent Document 9] Japanese Patent Publication No. 2008-224341 [Non-patent literature]

[0009] [Non-Patent Document 1] Takashi Sumigawa et. al, "In situ observation on formation process of nanoscale cracking during tension-compression fatigue of single crystal copper micron-scale specimen", Acta Materialia, 153 (2018), 270-278 [Overview of the project] [Problems that the invention aims to solve]

[0010] The axial alignment of a fatigue test specimen is usually performed by attaching multiple strain gauges to the parallel section of the specimen and measuring the bending strain. However, when the specimen is very small (for example, with a gauge length of 0.9 mm or less and a cross-sectional area of ​​0.25 mm² in the parallel section), 2 In the following cases, a general-purpose strain gauge cannot be attached, making it impossible to perform proper axis alignment.

[0011] An object of the present invention is to provide a test jig, a test apparatus, and a test method capable of highly accurately adjusting the axis of a test piece in a fatigue test.

Means for Solving the Problems

[0012] A test jig according to an embodiment of the present invention is a test jig used in a fatigue test, having an axial direction as a direction in which a load is applied to a test piece, and including a test piece holder attached to one side in the axial direction of the test piece. The test piece holder includes a test piece installation surface which is a surface on which the test piece is installed, and a through hole or a through slit extending in a direction perpendicular to the axial direction and passing through the test piece installation surface is formed in the test piece holder.

[0013] A test apparatus according to an embodiment of the present invention includes the above-described test jig and a projection image measuring device.

[0014] A test method according to an embodiment of the present invention is a test method using the above-described test apparatus, and includes a step of measuring the position of the through hole or the through slit using the projection image measuring device and adjusting the position of the test piece holder based on the position of the through hole or the through slit.

Effects of the Invention

[0015] According to the present invention, the axis of a test piece in a fatigue test can be adjusted with high accuracy.

Brief Description of the Drawings

[0016] [Figure 1] FIG. 1 is a side view schematically showing the overall configuration of a test apparatus according to an embodiment of the present invention. [Figure 2] FIG. 2 is a plan view showing an example of the configuration of a test piece. [Figure 3] FIG. 3 is a perspective view showing the test piece holder and the coupling extracted from the test jig. [[ID=Figure 4 is an exploded perspective view for explaining the configuration of the test piece holder and the coupling. [Figure 5] Figure 5 is a perspective view showing an enlarged part of the tensile load jig. [Figure 6] Figure 6 is a perspective view showing an enlarged stage of the guide jig. [Figure 7] Figure 7 is a perspective view of the spacer. [Figure 8] Figure 8 is a cross-sectional view of the test piece holder in the plane including the test piece. [Figure 9A] Figure 9A is a schematic diagram for explaining the mechanism of the coupling. [Figure 9B] Figure 9B is a schematic diagram for explaining the mechanism of the coupling. [Figure 10] Figure 10 is a plan view schematically showing the configuration in the vicinity of the test piece holder. [Figure 11A] Figure 11A is a diagram schematically showing the projection image of the dashed line portion in Figure 10. [Figure 11B] Figure 11B is a projection image after adjusting the position of the test piece holder in the y direction and the inclination in the xy plane. [Figure 12] Figure 12 is a side view schematically showing the configuration in the vicinity of the test piece holder. [Figure 13A] Figure 13A is a diagram schematically showing the projection image of the dashed line portion in Figure 12. [Figure 13B] Figure 13B is a projection image after adjusting the position of the test piece holder in the z direction and the inclination in the xz plane. [Figure 14] Figure 14 is an exploded perspective view showing the extraction of the stage, the buckling prevention jig, and the spacer from the configuration of the test piece holder. [Figure 15] Figure 15 is a diagram schematically showing the projection image in the vicinity of the end face of the test piece. [Figure 16A] Figure 16A is a hysteresis loop based on the strain obtained from the crosshead displacement. [Figure 16B]Figure 16B shows a hysteresis loop based on strain determined from the displacement measured by observing the end face of the test specimen using a projection image measuring instrument. [Modes for carrying out the invention]

[0017] Embodiments of the present invention will be described below with reference to the drawings. In the drawings, the same or corresponding parts are denoted by the same reference numerals, and their descriptions will not be repeated. The dimensional ratios between the components shown in each drawing do not necessarily represent the actual dimensional ratios.

[0018] [Test equipment] Figure 1 is a schematic side view showing the overall configuration of a test apparatus 1 according to one embodiment of the present invention. The test apparatus 1 comprises a test fixture 100, a crosshead 31, a load cell 32, a YZ stage 33, and a projection image measuring instrument 40.

[0019] Test apparatus 1 is a device for evaluating the fatigue properties of a target material by repeatedly applying uniaxial tensile and compressive loads to a test specimen 50 taken from the target material. Test apparatus 1 is configured so that the direction in which the load is applied to the test specimen 50 is parallel to the horizontal plane. In the following description, the direction in which the load is applied to the test specimen 50 is called the x-direction, the direction perpendicular to the x-direction in the horizontal plane is called the y-direction, and the direction perpendicular to both the x-direction and the y-direction (i.e., the vertical direction) is called the z-direction. Depending on the shape of the test specimen 50, the x-direction may be called the "axial direction," the y-direction the "width direction," and the z-direction the "thickness direction." In addition, in the x-direction, the direction approaching the center of the test specimen 50 may be called the "inward x-direction," and the opposite direction may be called the "outward x-direction."

[0020] The test fixture 100 comprises specimen holders 10A and 10B, and couplings 20A and 20B. Specimen holder 10A is attached to one axial side of the specimen 50, and specimen holder 10B is attached to the other axial side of the specimen 50. Coupling 20A connects specimen holder 10A to the crosshead 31 (more specifically, the shaft 311 extending from the crosshead 31), and coupling 20B connects specimen holder 10B to the load cell 32 (more specifically, the shaft 321 extending from the load cell 32). The detailed configuration of the test fixture 100 will be described later.

[0021] The crosshead 31 moves along the x-direction by a drive means such as a motor (not shown). As the crosshead 31 moves, the coupling 20A and the specimen holder 10A move in conjunction, and a tensile or compressive load is applied to the specimen 50. The load cell 32 measures the load applied to the specimen 50 at this time.

[0022] The YZ stage 33 is connected to the load cell 32 and is configured to allow the load cell 32 to be moved in parallel along the y and z directions, respectively. Since the load cell 32 is connected to the specimen holder 10B via the coupling 20B, moving the load cell 32 in parallel will cause the specimen holder 10B to move in conjunction with it.

[0023] The projection image measuring instrument 40 comprises a light source 41 and a two-dimensional sensor 42. The projection image measuring instrument 40 is a device that can measure the shape, dimensions, displacement, etc. of an object to be measured with high precision by irradiating the object to be measured with light from the light source 41 and detecting the light that is not blocked by the object to be measured with the two-dimensional sensor 42. For example, the TM-3000 series two-dimensional high-speed measuring instrument and TM-006 sensor head manufactured by Keyence Corporation can be used as the projection image measuring instrument 40. A double-sided telecentric lens manufactured by Mutron Corporation can be used as the lens. Furthermore, it is preferable that the light source 41 is a parallel light source.

[0024] In this embodiment, as will be described later, through holes or through slits are provided in each of the test specimen holders 10A and 10B, and the position of these through holes or through slits is measured by the projection image measuring device 40. The axis of the test specimen 50 is adjusted by adjusting the position and inclination of the test specimen holders 10A and 10B based on the measured position of the through holes or through slits.

[0025] Figure 1 illustrates a case where the light source 41 and the two-dimensional sensor 42 are arranged along the z-direction. More specifically, the figure illustrates a case where the light source 41 is placed on the lower side in the z-direction of the test specimen holders 10A and 10B, and the two-dimensional sensor 42 is placed on the upper side in the z-direction of the test specimen holders 10A and 10B. In this arrangement, light passing through through holes or slits penetrating the test specimen holders 10A and 10B in the z-direction can be detected, and the position of the through holes or slits in the xy-plane can be measured.

[0026] In this embodiment, in addition to the arrangement shown in Figure 1, the light source 41 and the two-dimensional sensor 42 may be arranged along the y-direction for measurement. More specifically, the light source 41 may be placed on one side of the test piece holders 10A and 10B in the y-direction, and the two-dimensional sensor 42 may be placed on the other side of the test piece holders 10A and 10B in the y-direction for measurement. In this arrangement, light passing through through holes or slits penetrating the test piece holders 10A and 10B in the y-direction can be detected, and the position of the through hole or slit in the xz plane can be measured.

[0027] [Test piece] Figure 2 is a plan view showing an example of the configuration of the test specimen 50. The test specimen 50 is a plate-shaped test specimen. The test specimen 50 comprises a parallel section 51, gripping sections 52 provided on both sides of the parallel section 51, and a shoulder section 53 provided between the parallel section 51 and the gripping sections 52.

[0028] The test fixture 100, test apparatus 1, and test method using the test apparatus 1 according to this embodiment are particularly suitable when the test specimen 50 is a minute test specimen. Specifically, when the gauge length L2 is 0.9 mm or less, and the cross-sectional area of ​​the parallel portion 51 is 0.25 mm². 2This method is particularly suitable in the following cases: when the test specimen 50 is such a small specimen, it is difficult to adjust the axis by attaching a general-purpose strain gauge. The total length L1 of the test specimen 50 is not particularly limited, but is, for example, 5.0 mm or less.

[0029] [Test fixtures] Figure 3 is a perspective view showing the specimen holder 10A and coupling 20A removed from the test fixture 100 (Figure 1), and Figure 4 is an exploded perspective view illustrating the configuration of the specimen holder 10A and coupling 20A. Since the specimen holder 10A and specimen holder 10B, and the coupling 20A and coupling 20B have the same configuration, the configuration of the specimen holder 10A and coupling 20A will be described below.

[0030] [Test specimen holder] The specimen holder 10A consists of five parts: a tensile load fixture 11, a guide fixture 12, a compression load fixture 13, a buckling prevention fixture 14, and a spacer 15 (Figure 4). These five parts are used in a state where they are integrally fixed together by fasteners such as screws during testing.

[0031] Figure 5 is an enlarged perspective view showing a part of the tensile loading jig 11. The tensile loading jig 11 has a pair of claw portions 111 arranged facing each other in the y direction. A gap 111a is formed between the claw portions 111, and a space 111b is formed behind the claw portions 111 (outward in the x direction). The tensile loading jig 11 is configured so that the gripping portion 52 can be housed in the space 111b with the parallel portion 51 of the test piece 50 (Figure 2) passed through the gap 111a.

[0032] The tensile load jig 11 has a through hole 11a (second through hole) that extends in the y direction and penetrates the tensile load jig 11 in the y direction. When the tensile load jig 11 and the guide jig 12 are assembled, the through hole 11a is formed in the xz plane at a position that coincides with the end face 1212a of the guide wall 1212 (Figure 6), which will be described later. The function of the through hole 11a will be described later.

[0033] The guide fixture 12 (Figure 4) includes a stage 121 and a base 122. The stage 121 is formed to protrude in the z direction from the plate-shaped base 122. The test specimen 50 is placed on the stage 121 of the guide fixture 12.

[0034] Figure 6 is an enlarged perspective view of the stage 121. The stage 121 has a specimen mounting surface 1211 which is a surface perpendicular to the z-direction and on which the specimen 50 is placed. Guide walls 1212 are provided on both sides of the specimen mounting surface 1211 in the y-direction, extending to a position higher than the specimen mounting surface 1211. The width w2 of the specimen mounting surface 1211 (the distance between the two guide walls 1212) is formed to be approximately the same size as the width w1 of the specimen 50 (Figure 2). The guide walls 1212 also have end faces 1212a parallel to the specimen mounting surface 1211.

[0035] When the test specimen 50 is placed on the test specimen mounting surface 1211, the position of the test specimen 50 in the z direction, the inclination around the x-axis, and the inclination around the y-axis are restricted, and the position of the test specimen 50 in the y direction and the inclination around the z-axis are restricted by the guide wall 1212.

[0036] The specimen mounting surface 1211 has two through-slits 1211a and one through-hole 1211b. Each of these through-slits 1211a and through-hole 1211b extends in the z-direction and is formed to penetrate the entire guide fixture 12, including the base 122 (Figure 4), not just the stage 121, in the z-direction. The two through-slits 1211a are formed at the inner end in the x-direction of the specimen mounting surface 1211, and at both ends in the y-direction. Each of the two through-slits 1211a has a U-shaped planar shape (shape of the xy plane). The through-hole 1211b is formed near the center of the specimen mounting surface 1211. The through-hole 1211b has a rectangular planar shape (shape of the xy plane) with rounded corners that extends in the x-direction. The through-hole 1211b is also formed in the xy plane at a position that coincides with the end face 52a of the specimen 50 (Figure 2). The functions of the through-slit 1211a and the through-hole 1211b will be described later.

[0037] The compression load jig 13 (Figure 4) has a compression load projection 131 that protrudes in the x direction. When the compression load jig 13 is assembled to the tensile load jig 11, the compression load projection 131 is positioned so that it faces the end face 52a (Figure 2) of the test piece 50 with a spacer 15 in between.

[0038] The buckling prevention jig 14 (Figure 4) has a projection 141 that protrudes in the z direction. The projection 141 has a specimen support surface 1411. When the buckling prevention jig 14 is assembled to the tensile loading jig 11, the specimen support surface 1411 is configured to be parallel to the specimen mounting surface 1211 (Figure 6) of the guide jig 12 and to be in contact with the surface of the specimen 50 (the surface perpendicular to the z direction). The specimen 50 is sandwiched from both sides in the z direction by the specimen support surface 1411 and the specimen mounting surface 1211. This makes it possible to suppress buckling of the specimen 50 when a load is applied to the specimen 50 in the x direction.

[0039] The buckling prevention jig 14 has a through hole 14a that extends in the z direction and penetrates the buckling prevention jig 14 in the z direction. The through hole 14a is formed in the xy plane at a position that coincides with the end face 52a of the test piece 50 (Figure 2). The function of the through hole 14a will be described later.

[0040] The spacer 15 (Figure 4) is positioned between the compression loading projection 131 of the compression loading jig 13 and the test piece 50. Figure 7 is a perspective view of the spacer 15. The spacer 15 has a through slit 15a formed at the end that contacts the end face 52a of the test piece 50, which penetrates the spacer 15 in the z direction. The through slit 15a has a semicircular planar shape (shape in the x and y planes). In the x and y planes, the through slit 15a is formed at a position that overlaps with the through hole 1211b of the stage 121 (Figure 6) and the through hole 14a of the buckling prevention jig 14. The function of the through slit 15a will be described later.

[0041] Figure 8 shows cross-sectional views (xy cross-sections) of the specimen holders 10A and 10B in a plane including the specimen 50. When the specimen holder 10A moves outward in the x-direction, the claw portion 111 of the tensile loading fixture 11 catches on the shoulder portion 53 (Figure 2) of the specimen 50, and a tensile load is applied to the specimen 50. When the specimen holder 10A moves inward in the x-direction, the compression loading projection 131 of the compression loading fixture 13 presses against the end face 52a (Figure 2) of the specimen 50 via the spacer 15, and a compressive load is applied to the specimen 50.

[0042] [Coupling] The coupling 20A (Figure 4) and the test piece holder 10A are used in a state where they are integrally fixed together by fastening components such as screws. The coupling 20A has a hole 20a formed therein for inserting the shaft 311 (Figure 1), which extends in the x-direction and opens at the end face on the outer side in the x-direction. The coupling 20A also has eight screw holes 20b formed on its outer circumferential surface, extending in a direction perpendicular to the x-direction. The screw holes 20b are formed at 90° intervals at four circumferential positions at each of the two positions in the x-direction. Each of the screw holes 20b is continuous with the hole 20a. A screw 21 is fastened to each of the screw holes 20b. The screw 21 supports the shaft 311 (Figure 1) by contacting the outer circumferential surface of the shaft 311 from four directions in the circumferential direction of the shaft 311 at each of the two positions in the axial direction of the shaft 311.

[0043] Figures 9A and 9B are schematic diagrams illustrating the mechanisms of couplings 20A and 20B. Figure 9A shows the case where the direction in which the shaft 321 extends is inclined from the x-direction in the xy-plane.

[0044] As previously described, couplings 20A and 20B are components that connect the specimen holders 10A and 10B to shafts extending from external equipment (shaft 311 extending from the crosshead 31 or shaft 321 extending from the load cell 32). Couplings 20A and 20B are configured to adjust the inclination of the specimen holders 10A and 10B with respect to the direction in which shafts 311 and 321 extend.

[0045] The shaft 321 is supported by being sandwiched between screws 21(1) and 22(2), and screws 21(3) and 21(4), which are positioned opposite each other in the y-direction. Screws 21(1) and 21(2), and screws 21(3) and 21(4) support the shaft 321 at two positions in the direction in which the shaft 321 extends. Therefore, by adjusting the degree of tightening of screws 21(1) to 21(4), the direction of the coupling 20B can be tilted with respect to the direction in which the shaft 321 extends.

[0046] Specifically, for example, as shown by the white arrows in Figure 9A, the coupling 20B can be rotated around the z-axis by loosening screws 21(1) and 22(4) and tightening screws 21(2) and 22(3). This allows the longitudinal direction of the specimen holder 10B to be aligned with the x-direction, as shown in Figure 9B. To rotate the coupling 20B in the opposite direction, screws 21(1) and 22(4) should be tightened and screws 21(2) and 22(3) should be loosened.

[0047] Although not shown in the diagram, the coupling 20B can also be rotated around the y-axis by adjusting the degree of fastening of screws positioned at a location rotated 90° around the x-axis from the positions of screws 21(1) to 21(4).

[0048] Thus, the configuration of couplings 20A and 20B allows the specimen holders 10A and 10B to be rotated around the z-axis and y-axis.

[0049] Each of the couplings 20A and 20B may have more than eight screws. That is, each of the couplings 20A and 20B may have screws at two or more axial positions on the shaft 311 or 321 that support the shaft from four or more circumferential directions.

[0050] [Test Method] Next, we will explain the test method using test apparatus 1 (Figure 1).

[0051] [Adjusting the axis] The test method according to this embodiment is a test method using the test apparatus 1 (Figure 1), and may include the step of measuring the position of the through hole 1211b or through slit 1211a of the test piece mounting surface 1211 (Figure 6) using the projection image measuring instrument 40, and adjusting the position of the test piece holder 10A or test piece holder 10B based on the position of the through hole 1211b or through slit 1211a.

[0052] Figure 10 is a schematic plan view (xy-plane view) showing the configuration of the vicinity of the specimen holders 10A and 10B. Figure 10 illustrates a case where the y-direction position of specimen holder 10A and the y-direction position of specimen holder 10B do not coincide, and the inclination of specimen holder 10A and the inclination of specimen holder 10B do not coincide. An example of a method for adjusting the y-direction position and the inclination in the xy-plane of specimen holder 10B from this state will be explained.

[0053] This adjustment is performed with the buckling prevention fixture 14 (Figure 4) removed from the specimen holders 10A and 10B. Furthermore, this adjustment is performed without the specimen 50 and spacer 15 in place. In this state, the light source 41 and two-dimensional sensor 42 of the projection image measuring device 40 (Figure 1) are positioned along the z-direction to acquire projection images of the specimen holders 10A and 10B. More specifically, the light source 41 is positioned on one side of the specimen holders 10A and 10B in the z-direction, and the two-dimensional sensor 42 is positioned on the other side of the specimen holders 10A and 10B in the z-direction to acquire projection images.

[0054] Figure 11A schematically shows the projection image of the dashed-dotted line portion of Figure 10. In Figure 11A, the hatched areas represent the parts where light was blocked by the test specimen holders 10A and 10B, while the white areas represent the parts where light was not blocked (hereinafter referred to as "transmitted areas") (the same applies to Figures 13A, 13B, and 15 described later).

[0055] As shown in Figure 11A, in this projection image, the portion corresponding to the through-slit 1211a, the portion corresponding to the through-hole 1211b, and the gap between the tensile load fixture 11 are transparent areas. Although Figure 10 appears to show a gap between the stage 121 and the tensile load fixture 11, this portion is not a transparent area because the base 122 (Figure 4) is located on the far side in the z direction.

[0056] While viewing this projected image, the position of the specimen holder 10B in the y-direction and its inclination in the xy-plane are adjusted. Specifically, for example, the YZ stage 33 (Figure 1) is operated to move the specimen holder 10B in the y-direction so that the position of the through-slit 1211a of the specimen holder 10B coincides with the position of the through-slit 1211a of the specimen holder 10A. In addition, the coupling 20B (Figure 1) is operated to rotate the specimen holder 10B around the z-axis so that the through-slit 1211a of the specimen holder 10B is parallel to the through-slit 1211a of the specimen holder 10A. Figure 11B shows the projected image after adjusting the position of the specimen holder 10B in the y-direction and its inclination in the xy-plane.

[0057] The above describes the case where the position of the specimen holder 10B in the y-direction and the inclination in the xy-plane are adjusted based on the position of the through-slit 1211a, but the adjustment may also be made based on the position of the through-hole 1211b.

[0058] The test method according to this embodiment may include a step of measuring the position of the end face 1212a of the guide wall 1212 (Figure 6) using a projection image measuring instrument 40, and adjusting the position of the test piece holder 10A or the test piece holder 10B based on the position of the end face 1212a. The test piece holders 10A and 10B are configured so that the end face 1212a of the guide wall 1212 can be observed by the projection image measuring instrument 40, as described below.

[0059] Figure 12 is a schematic side view (xz side view) showing the configuration near the specimen holders 10A and 10B. Figure 12 illustrates a case where the position of specimen holder 10A in the z direction does not coincide with the position of specimen holder 10B in the z direction, and the inclination of specimen holder 10A does not coincide with the inclination of specimen holder 10B. An example of a method for adjusting the position of specimen holder 10B in the z direction and its inclination in the xz plane from this state will be explained.

[0060] This adjustment is performed with the buckling prevention fixture 14 (Figure 4) removed from the specimen holders 10A and 10B. Furthermore, this adjustment is performed without the specimen 50 and spacer 15 in place. In this state, the light source 41 and two-dimensional sensor 42 of the projection image measuring device 40 (Figure 1) are positioned along the y-direction to acquire projection images of the specimen holders 10A and 10B. More specifically, the light source 41 is positioned on one side of the specimen holders 10A and 10B in the y-direction, and the two-dimensional sensor 42 is positioned on the other side of the specimen holders 10A and 10B in the y-direction to acquire projection images.

[0061] Figure 13A schematically shows the projection image of the dashed-dotted line portion of Figure 12. As shown in Figure 13A, in this projection image, the portion corresponding to the through hole 11a that does not overlap with the guide wall 1212, and the gap between the tensile load fixtures 11 become the transparent portion.

[0062] While viewing this projected image, the position of the specimen holder 10B in the z direction and its inclination in the xz plane are adjusted. Specifically, for example, the YZ stage 33 (Figure 1) is operated to move the specimen holder 10B in the z direction so that the position of the end face 1212a of the specimen holder 10B coincides with the position of the end face 1212a of the specimen holder 10A. In addition, the coupling 20B (Figure 1) is operated to rotate the specimen holder 10B around the y axis so that the end face 1212a of the specimen holder 10B is parallel to the end face 1212a of the specimen holder 10A. Figure 13B shows the projected image after adjusting the position of the specimen holder 10B in the z direction and its inclination in the xz plane.

[0063] [Measurement of specimen displacement] The test method according to this embodiment may include a step of measuring the position of the end face 52a (Figure 2) of the test piece 50 using a projection image measuring device 40 (Figure 1) during the fatigue test. The test piece holder 10A and the test piece holder 10B are configured so that the end face 52a of the test piece 50 can be observed by the projection image measuring device 40, as described below.

[0064] Figure 14 is an exploded perspective view showing the stage 121, buckling prevention fixture 14, and spacer 15 extracted from the configuration of the specimen holder 10A. The through-hole 1211b of the stage 121 and the through-hole 14a of the buckling prevention fixture 14 are formed in a position that coincides with the end face 52a of the specimen 50 in the xy plane. In addition, the through-hole 1211b of the stage 121, the through-hole 14a of the buckling prevention fixture 14, and the through-slit 15a of the spacer 15 are formed in a position that coincides with each other in the xy plane.

[0065] The light source 41 of the projection image measuring device 40 (Figure 1) is placed on one side in the z-direction of the test specimen holders 10A and 10B, and the two-dimensional sensor 42 is placed on the other side in the z-direction of the test specimen holders 10A and 10B, and the fatigue test is performed while acquiring a projection image. More specifically, a tensile load or a compressive load is applied to the test specimen 50 while acquiring a projection image.

[0066] Figure 15 schematically shows a projection image of the vicinity of the end face 52a of the test specimen 50. As shown in Figure 15, in this projection image, the area where the through hole 1211b of the stage 121, the through hole 14a of the buckling prevention fixture 14, and the through slit 15a of the spacer 15 overlap becomes a transparent area. Since the through hole 1211b of the stage 121 and the through hole 14a of the buckling prevention fixture 14 are formed in positions that overlap with the end face 52a of the test specimen 50, the x-direction position of the end face 52a of the test specimen 50 can be measured from this projection image. This makes it possible to directly measure the displacement of the test specimen 50 during fatigue testing.

[0067] [Effects of this embodiment] The above describes a test fixture 100, a test apparatus 1, and a test method using the test apparatus 1 according to one embodiment of the present invention.

[0068] The test fixture 100 according to this embodiment includes test piece holders 10A and 10B, which are attached to one and the other axial side of the test piece 50, respectively. Each of the test piece holders 10A and 10B includes a test piece mounting surface 1211 (Figure 6) on which the test piece 50 is placed, and each of the test piece holders 10A and 10B has a through slit 1211a and a through hole 1211b that pass through the test piece mounting surface 1211 and extend in a direction perpendicular to the axial direction.

[0069] With this configuration, the position and inclination of the test specimen mounting surface 1211 in the xy plane can be measured with high precision by measuring the position of the through-slit 1211a or through-hole 1211b using the projection image measuring device 40 (Figure 1).

[0070] Figures 10 and 12 illustrate that the entire specimen holder 10B is tilted in conjunction with the specimen mounting surface 1211. However, in reality, the specimen mounting surface 1211 may be tilted relative to the outer shape of the specimen holder 10B, or the center of the specimen mounting surface 1211 may not coincide with the center of the specimen holder 10B. Therefore, even if the position and tilt are adjusted based on the outer shape of the specimen holder 10B or the gap 111a of the claw portion 111 (Figure 5), the specimen mounting surface 1211 may be shifted from its original position or tilted from its original direction.

[0071] In this embodiment, the position of the test specimen mounting surface 1211 can be directly measured by measuring the positions of the through-slit 1211a and through-hole 1211b passing through the test specimen mounting surface 1211. By measuring the position of the test specimen mounting surface 1211 that regulates the position and inclination of the test specimen 50, the axis of the test specimen 50 can be adjusted with higher precision.

[0072] Furthermore, by positioning the projection image measuring device 40 along the y-direction and measuring the position of the end face 1212a of the guide wall 1212 (Figure 6), the position and inclination of the specimen mounting surface 1211 in the xz plane can be measured with high accuracy. In this measurement, the position of the specimen mounting surface 1211 is not measured directly, but the position of the end face 1212a of the guide wall 1212 adjacent to the specimen mounting surface 1211 is measured. Therefore, compared to adjusting based on the outer shape of the specimen holder 10B, the position and inclination of the specimen mounting surface 1211 in the xz plane can be measured with higher accuracy.

[0073] In this embodiment, the through-hole 1211b is further formed in a position that overlaps with the end face 52a of the test piece 50. With this configuration, the position of the end face 52a of the test piece 50 can be measured using the projection image measuring instrument 40 (Figure 1) during the fatigue test. Conventionally, the displacement of the test piece 50 could only be estimated from the displacement of the crosshead 31 (Figure 1), but according to this embodiment, the displacement of the test piece 50 can be measured directly. The displacement of the crosshead 31 includes components due to deformation of the test fixture 100, in addition to the displacement of the test piece 50. Since the test fixture 100 according to this embodiment can directly measure the displacement of the test piece 50, the displacement of the test piece 50 can be measured with higher accuracy. For this reason, the test fixture 100 is particularly suitable as a test fixture for low-cycle fatigue testing.

[0074] The above describes a case where the specimen holder 10A is composed of five parts: a tensile load fixture 11, a guide fixture 12, a compressive load fixture 13, a buckling prevention fixture 14, and a spacer 15. This configuration is illustrative, and the specimen holder 10A may have any configuration that performs a similar function, and may be composed of four or fewer parts, or six or more parts.

[0075] More specifically, the specimen holder 10A should include a portion corresponding to the specimen mounting surface 1211 (Figure 6), which is the surface on which the specimen 50 is placed (a portion that performs a similar function; the same applies hereinafter), a portion corresponding to the claw portion 111 (Figure 5) that applies a tensile load to the specimen 50, a portion corresponding to the compression load projection 131 (Figure 4) that applies a compressive load to the specimen 50, a portion corresponding to the specimen support surface 1411 (Figure 4) that supports the specimen 50 from the opposite side of the specimen mounting surface 1211, and a portion corresponding to the spacer 15 (Figure 7) that fills the gap between the specimen 50 and the compression load projection 131.

[0076] The specimen holder 10A does not need to have all of these parts, and depending on the conditions of the fatigue test being performed, it may not have some of these parts. For example, if no compressive load is applied, the specimen holder 10A does not need to have the part corresponding to the compressive load projection 131 (Figure 4). The specimen holder 10A only needs to have at least the part corresponding to the specimen mounting surface 1211 (Figure 6).

[0077] Furthermore, the portion described above as a through hole may be changed to a through slit, or the portion described above as a through slit may be changed to a through hole. For example, the through hole 11a (second through hole) may be changed to a through slit (second through slit).

[0078] The above describes the case where repeated tensile and compressive loads are applied to the test specimen 50. Buckling is more likely to occur in fatigue tests that include compression, and the axis needs to be adjusted with higher precision. For this reason, the test fixture 100, test apparatus 1, and test method using the test apparatus 1 according to this embodiment can be more suitably used in fatigue tests that include compression. However, the test fixture 100, test apparatus 1, and test method using the test apparatus 1 according to this embodiment can also be used in fatigue tests that do not include compression.

[0079] Furthermore, although the above description described the case where the test specimen 50 is a plate-shaped test specimen, the test fixture 100, test apparatus 1, and test method using the test apparatus 1 according to this embodiment can also be applied to, for example, a rod-shaped test specimen. [Examples]

[0080] The present invention will be described more specifically below with reference to examples. The present invention is not limited to these examples.

[0081] A tensile-compression fatigue test was performed using a plate-shaped test specimen with the shape shown in Figure 2. The dimensions of the test specimen were: total length L1 of 2.4 mm, gauge length L2 of 0.5 mm, and cross-sectional area of ​​the parallel section of 0.09 mm². 2 The width w1 was 1.6 mm and the thickness was 0.3 mm.

[0082] The specimen's axis was adjusted using the method described above. A fatigue test was conducted under a strain gradual increase condition, increasing the maximum elongation from ±1 μm to ±15 μm in 1.5 μm increments every 5 cycles, and a hysteresis loop (cyclic stress-strain curve) was obtained. The strain rate was 0.003 / s (displacement rate: 1.5 μm / s). In this test, a strain equivalent to 1.0% was applied to the specimen, but no significant buckling or out-of-plane deformation was observed in the specimen after the test.

[0083] Figure 16A shows the hysteresis loop based on strain determined from crosshead displacement, while Figure 16B shows the hysteresis loop based on strain determined from displacement measured by observing the end face of the specimen using a projection image measuring instrument. An abnormal bending point is observed in Figure 16A, but a stable hysteresis loop is obtained in Figure 16B.

[0084] The embodiments of the present invention have been described above. The embodiments described above are merely illustrative examples for carrying out the present invention. Therefore, the present invention is not limited to the embodiments described above, and it is possible to carry out the present invention by appropriately modifying the embodiments described above without departing from the spirit of the invention. [Explanation of symbols]

[0085] 1. Test apparatus 100 Test fixtures 10A, 10B Test specimen holder 11. Tensile Loading Fixture 111 Nail area 11a Through hole (second through hole) 12 Guide fixtures 121 stages 1211 Test specimen mounting surface 1211a Through-slit 1211b Through hole 1212 Guide Wall 1212a End face 13 Compression Loading Fixture 131 Compression Load Protrusion 14. Buckling prevention jig 14a Through hole 141 Protrusion 1411 Specimen support surface 15 Spacers 15a Through slit 20A, 20B coupling 20a hole 20b Screw hole 21 screws 31 Crosshead 311 Shaft 32 load cells 321 Shaft 33 YZ Stage 40 Projection Image Measuring Instrument 41 Light source 42 Two-dimensional sensors 50 test specimens 51 Parallel section 52. Grip section 52a End face 53 Shoulder

Claims

1. A test fixture used for fatigue testing, The direction in which a load is applied to the test specimen is axial, and the test specimen holder is attached to one side of the test specimen in the axial direction. The specimen holder includes a specimen mounting surface, which is the surface on which the specimen is placed. The specimen holder has a through hole or through slit formed therein that passes through the specimen mounting surface and extends in a direction perpendicular to the axial direction. The aforementioned test specimen has a gauge length of 0.9 mm or less and a cross-sectional area of ​​the parallel portion of 0.25 mm. ２ The following is the test fixture.

2. A test fixture used for fatigue testing, The direction in which a load is applied to the test specimen is axial, and the test specimen holder is attached to one side of the test specimen in the axial direction. The specimen holder includes a specimen mounting surface, which is the surface on which the specimen is placed. The specimen holder has a through hole or through slit formed therein that passes through the specimen mounting surface and extends in a direction perpendicular to the axial direction. A test fixture in which the through-hole or through-slit is formed at a position that overlaps with the end face of the test piece.

3. A test fixture according to claim 2, The aforementioned test specimen has a gauge length of 0.9 mm or less and a cross-sectional area of ​​the parallel portion of 0.25 mm. ２ The following is the test fixture.

4. A test fixture according to any one of claims 1 to 3, The aforementioned test specimen is a plate-shaped test specimen, The through-hole or through-slit is formed extending in the thickness direction of the test piece. A test fixture wherein the width direction is defined as the direction perpendicular to both the axial and thickness directions of the test specimen, and the test specimen holder has guide walls that restrict the position of the test specimen in the width direction.

5. A test fixture according to claim 4, The guide wall has an end face parallel to the test specimen mounting surface, A test fixture comprising a test specimen holder having a second through-hole or second through-slit formed at a position overlapping with the end face of the guide wall and extending in the width direction.

6. A test fixture according to any one of claims 1 to 3, The device further comprises a coupling that connects the specimen holder to a shaft extending from an external device. The coupling has a hole for inserting the shaft. The coupling is a test fixture comprising screws that support the shaft from four or more directions in the circumferential direction of the shaft at two or more positions in the axial direction of the shaft.

7. A test fixture according to any one of claims 1 to 3, A test apparatus comprising a projection image measuring instrument.

8. A test method using the test apparatus described in claim 7, A test method comprising the steps of measuring the position of the through-hole or through-slit using the projection image measuring device, and adjusting the position of the test piece holder based on the position of the through-hole or through-slit.

9. A test method using a test apparatus comprising the test fixture described in Claim 5 and a projection image measuring instrument, A test method comprising the steps of measuring the position of the end face of the guide wall using the projection image measuring device and adjusting the position of the test piece holder based on the position of the end face of the guide wall.

10. A test method using a test apparatus comprising the test fixture described in claim 2 or 3 and a projection image measuring instrument, A test method comprising the step of measuring the position of the end face of the test piece using the projection image measuring device during a fatigue test.

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