Test specimen, method for manufacturing a test specimen, test apparatus, and test method

Abstract

This invention provides a test specimen that allows for the reproduction of fatigue fracture originating from the inner surface of a tubular body. [Solution] The test specimen 10 is a test specimen for torsional fatigue testing, and has a shape in which a circular hole 10a is formed in the center of a disk, with a reference shape RS, and a parallel surface 11 and an opening 10b formed on the reference shape RS, the parallel surface 11 is formed on the outer circumference of the disk and is a surface perpendicular to a first direction which is one of the radial directions of the disk, the opening 10b is formed on the part opposite to the parallel surface 11 when viewed from the center C of the hole 10a and penetrates from the hole 10a to the outer circumference of the disk, the shortest distance h from the inner surface of the hole 10a to the parallel surface 11 is less than the thickness w of the disk, and the maximum dimension m along the first direction is 4.0 times or more the distance h.

Description

[Technical Field]

[0001] The present invention relates to a test specimen, a method for manufacturing a test specimen, a testing apparatus, and a testing method, and more particularly to a test specimen for torsional fatigue testing, a method for manufacturing the same, and a testing apparatus and a testing method for evaluating the test specimen. [Background technology]

[0002] Many tubular materials (such as metal pipes) are used in mechanical structures. While the quality of the outer surface of metal pipes can be relatively easily assessed visually, the inner surface is difficult to inspect visually, posing a problem for quality control. If there are problems with the properties of the inner surface, such as excessive surface roughness, fatigue failure originating from the inner surface may occur depending on the operating environment. Therefore, it is important to understand the fatigue characteristics of metal pipes originating from the inner surface.

[0003] However, if both ends of a tubular test specimen are simply restrained and repeated torsional or bending loads are applied, fatigue failure will occur on the outer surface or at the restrained (gripping) parts before the inner surface of the specimen. Therefore, it is difficult to conduct tests that reproduce fatigue failure starting from the inner surface.

[0004] Japanese Patent Publication No. 5503608 discloses a method for evaluating fatigue failure of cylindrical metal materials. The publication describes setting the outer diameter of the central part of the cylindrical test material to 90% or less of the outer diameter of the restraining parts at both ends, and setting the ratio of the outer diameter to the inner diameter of the central part to (outer diameter / inner diameter) ≤ 2, applying a compressive residual stress of 25% or more of the material's tensile strength to the outer surface of the central part, and 2.5% or less of the material's tensile strength at a depth of 0.8 mm from the outer surface, and evaluating the fatigue characteristics by inducing fatigue failure on the inner surface of the test material by repeatedly applying bending load or torsional load to the test material.

[0005] Japanese Patent Publication No. 6809213 discloses a test specimen for testing the fatigue characteristics of a steel pipe, and a test method using the same. This test specimen is taken from a steel pipe so as to include the inner surface of the steel pipe, and has a cross-sectional arch-shaped groove with a radius of curvature ρ which is the inner surface of the steel pipe, and the depth d of the groove, the thickness h of the scoring portion, the width w of the scoring portion, and the radius of curvature ρ satisfy predetermined relationships. [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] Patent No. 5503608 [Patent Document 2] Patent No. 6809213 [Non-patent literature]

[0007] [Non-Patent Document 1] Masataka Nishida, “Stress Concentration Expanded Edition”, Morikita Publishing (1973), pp. 174 and 181 [Non-Patent Document 2] "Handbook of Mechanical Engineering α3: Strength of Materials," edited by the Japan Society of Mechanical Engineers, p. 17. [Overview of the project] [Problems that the invention aims to solve]

[0008] The method described in Japanese Patent Publication No. 5503608 uses test specimens that closely resemble the shape of actual metal pipes, which means that depending on the dimensions of the metal pipes, large test specimens and testing equipment may be required. As the test specimens become larger, testing at high frequencies becomes difficult, leading to longer testing times. Furthermore, there are economic problems, such as the large amount of material required to produce the test specimens and the increased processing time.

[0009] Japanese Patent Publication No. 6809213 describes a method for reproducing fatigue fracture originating from the inner surface of a steel pipe using a relatively small test specimen taken from the steel pipe, including the inner surface of the pipe. In this method, gripping portions are provided on both sides of the longitudinal direction of the test specimen, so the test specimen needs to have a certain dimension in the longitudinal direction. Furthermore, since the longitudinal direction of this test specimen is parallel to the longitudinal direction of the steel pipe, it is not possible to evaluate curved pipe-shaped members such as stabilizers and elbows.

[0010] The object of the present invention is to provide a test specimen, a method for manufacturing the same, a test apparatus, and a test method that can perform a test that reproduces fatigue fracture originating from the inner surface of a tubular body. [Means for solving the problem]

[0011] A test specimen according to one embodiment of the present invention is a test specimen for torsional fatigue testing, having a standard shape in which a circular hole is formed at the center of a disk, and having a parallel surface and an opening formed on the standard shape, wherein the parallel surface is formed on the outer circumference of the disk and is perpendicular to a first direction which is one of the radial directions of the disk, the opening is formed on the part opposite to the parallel surface when viewed from the center of the hole and penetrates from the hole to the outer circumference of the disk, the shortest distance h from the inner surface of the hole to the parallel surface is smaller than the thickness w of the disk, and the maximum dimension m along the first direction is 4.0 times or more the distance h.

[0012] A method for manufacturing a test specimen according to one embodiment of the present invention is a method for manufacturing the above-mentioned test specimen, comprising the steps of: cutting a metal tube into sections to take a sample of the standard shape; and forming the parallel surface and the opening in the sample.

[0013] A test apparatus according to an embodiment of the present invention is a test apparatus for evaluating the above test piece. A direction in the radial direction of the disc and perpendicular to the first direction is defined as the second direction. A first gripping jig that holds, by sandwiching, a portion of the test piece on one side in the second direction as viewed from the center of the hole in the thickness direction of the test piece, a second gripping jig that holds, by sandwiching, a portion of the test piece on the other side in the second direction as viewed from the center of the hole in the thickness direction of the test piece, and a driving device that rotates at least one of the first gripping jig and the second gripping jig about the second direction as a rotation axis. At least one of the first gripping jig and the second gripping jig has a first guide surface that is a plane perpendicular to the thickness direction of the test piece and a second guide surface that is a plane parallel to the parallel plane.

[0014] A test method according to an embodiment of the present invention is a test method for evaluating the above test piece using the above test apparatus, and includes a step of rotating at least one of the first gripping jig and the second gripping jig by the driving device. The rotation axis passes through a position that approaches the inner peripheral surface of the hole by a distance of 1 / 2 of the distance h from the parallel plane in the first direction and passes through a position at the center in the thickness direction of the test piece in the second direction. When the test piece is projected onto a plane perpendicular to the thickness direction, among the contours of the hole, a point P0 that is the closest to the parallel plane is defined, and among the contours of the hole, a point P1 that intersects with the contours of the first gripping jig and the second gripping jig (when there are two or more intersection points, the point closest to the parallel plane) is defined. A distance d along the first direction between the point P0 and the point P1 is 1 / 4 or less of the distance h.

Advantages of the Invention

[0015] According to the present invention, a test that reproduces fatigue fracture starting from the inner surface of a tubular body can be carried out.

Brief Description of the Drawings

[0016] [Figure 1] FIG. 1 is a front view of a test piece according to an embodiment of the present invention. [Figure 2] FIG. 2 is a side view of the test piece of FIG. 1. [Figure 3] Figure 3 is a front view of a modified specimen of the test piece shown in Figure 1. [Figure 4] Figure 4 is a schematic diagram showing an example of a method for manufacturing the test specimen shown in Figure 1. [Figure 5] Figure 5 is an exploded perspective view schematically showing the configuration of a test apparatus according to one embodiment of the present invention. [Figure 6] Figure 6 is a front view showing an enlarged portion of the test apparatus in Figure 5, near the test specimen. [Figure 7] Figure 7 is a magnified front view showing the gauge mark portion of the test specimen attached to the test apparatus shown in Figure 5. [Figure 8] Figure 8 is a magnified perspective view of the gauge portion of a test specimen attached to the test apparatus shown in Figure 5. [Figure 9] Figure 9 is a cross-sectional view of the surface (hatched in Figure 8) where the maximum shear stress occurs when a torsional load is applied to the test specimen. [Figure 10] Figure 10 schematically shows the relationship between the maximum shear stress and the reference shear stress in a test specimen in which a groove extending parallel to the axis of rotation is formed. [Modes for carrying out the invention]

[0017] The embodiments of the present invention will be described in detail 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 constituent members shown in each drawing do not necessarily represent the actual dimensional ratios.

[0018] [Test piece] Figure 1 is a front view of a test specimen 10 according to one embodiment of the present invention, and Figure 2 is a side view of the test specimen 10. The test specimen 10 is a test specimen for torsional fatigue testing. The test specimen 10 is made of, for example, metal. The test specimen 10 has a shape in which a circular hole 10a is formed in the center of a disc, which is the reference shape (hereinafter referred to as "reference shape RS"), and a parallel surface 11 and an opening 10b are formed on the reference shape RS.

[0019] The standard shape RS is ring-shaped, and more specifically, it is a circular hole 10a with diameter ID formed at the center of a disk with diameter OD (Figure 1) and thickness w (Figure 2), with the hole penetrating the disk in the thickness direction. The disk and the hole 10a are formed so that their centers are in the same position when the test piece 10 is viewed from the front (viewed in the plane of Figure 1) (i.e., the disk and the hole 10a are concentric circles), and both are perfect circles or nearly perfect circles. The standard shape RS can also be described as a cross-section of a tubular body with outer diameter OD and inner diameter ID.

[0020] The parallel surface 11 is formed on the outer circumference of the disk of the reference shape RS. The parallel surface 11 is a surface perpendicular to the radial direction of the disk. Hereafter, the direction normal to the parallel surface 11 will be referred to as the "first direction". That is, the first direction is one of the radial directions of the disk, and the parallel surface 11 is a surface perpendicular to the first direction. Also below, the radial direction of the disk that is perpendicular to the first direction will be referred to as the "second direction" (see Figure 1).

[0021] The opening 10b is formed on the side opposite to the parallel surface 11 when viewed from the center C (Figure 1) of the hole 10a. In other words, if the position of the parallel surface 11 is taken as 0° in the circumferential direction, the opening 10b is formed at the 180° position in the circumferential direction. Alternatively, the opening 10b and the parallel surface 11 can be said to be at the 12 o'clock and 6 o'clock positions when the test piece 10 is viewed from the front. The opening 10b penetrates from the hole 10a to the outer circumference of the disc.

[0022] Let distance h be the shortest distance from the inner surface of hole 10a to the parallel surface 11 (see Figure 1). Distance h is less than the thickness w of the disk (see Figure 2).

[0023] The maximum dimension m is defined as the maximum dimension of the test specimen 10 along the first direction (see Figures 1 and 2). The maximum dimension m is 4.0 times or more the distance h.

[0024] In Figure 1, the end faces 10b1 of the opening 10b are shown to be parallel to each other and parallel to the first direction, but the shape of the opening 10b is not limited to this. As described above, the opening 10b only needs to penetrate from the hole 10a to the outer circumference of the disc, and when a torsional load is applied as described later, the two end faces 10b1 flanking the opening 10b should not come into contact with each other.

[0025] Figure 1 illustrates a case where the test specimen 10, when viewed from the front, has a shape resembling the letter "C". However, as mentioned above, the test specimen only needs to have a maximum dimension m of 4.0 times or more the distance h, and the test specimen may have a shape like the test specimen 10V shown in Figure 3.

[0026] [Method for manufacturing test specimens] Figure 4 is a schematic diagram showing an example of a method for manufacturing the test specimen 10. The test specimen 10 can be manufactured by slicing a metal tube MP with outer diameter OD and inner diameter ID to a thickness w, taking a sample of the standard shape RS, and forming a parallel surface 11 and an opening 10b on this sample.

[0027] [Test equipment] Figure 5 is an exploded perspective view schematically showing the configuration of a test apparatus 20 according to one embodiment of the present invention. The test apparatus 20 is a test apparatus for evaluating a test specimen 10. The test apparatus 20 comprises a first gripping jig 21 and a second gripping jig 22. The first gripping jig 21 holds one side of the test specimen 10 in the second direction, viewed from the center of the hole in the test specimen 10, by gripping it from the thickness direction of the test specimen 10. The second gripping jig 22 holds the other side of the test specimen 10 in the second direction, viewed from the center of the hole in the test specimen 10, by gripping it from the thickness direction of the test specimen 10. The first gripping jig 21 is connected to a drive unit 23, and the second gripping jig 22 is connected to a torque cell 24.

[0028] The first gripping jig 21 comprises a base 211 and a lid 212. The base 211 includes a first guide surface 211a, which is perpendicular to the thickness direction of the test piece 10, and a second guide surface, which is parallel to the parallel surface 11 of the test piece 10 (i.e., perpendicular to the first direction). The lid 212 has a generally plate-like shape.

[0029] The test specimen 10 is positioned on the base 211 such that one side in the thickness direction is in contact with the first guide surface 211a and the parallel surface 11 is in contact with the second guide surface 211b. The lid 212 is positioned so as to be in contact with the other side of the test specimen 10 in the thickness direction. From this position, the test specimen 10 can be held by clamping it from the thickness direction by tightening the bolts 213 that fasten the first guide surface 211a and the lid 212.

[0030] The first gripping jig 21 is equipped with a pin 214 in addition to the bolt 213, which connects the first guide surface 211a and the lid 212 at a different position from the bolt 213 (a position further from the test piece 10). The fitting tolerance of the pin 214 is preferably an intermediate fit. The pin 214 can ensure the parallelism of the lid 212.

[0031] The second gripping jig 22, like the first gripping jig 21, includes a base 221, a cover 222, a bolt 223, and a pin 224. The base 221 also includes a first guide surface 221a and a second guide surface 221b, similar to the base 211 of the first gripping jig 21. The configuration of each of these components is the same as that of the first gripping jig 21.

[0032] The first gripping jig 21 and the second gripping jig 22 are positioned such that the first guide surface 211a of the first gripping jig 21 and the first guide surface 221a of the second gripping jig 22 are parallel and on the same plane. The first gripping jig 21 and the second gripping jig are also positioned such that the second guide surface 221b of the first gripping jig 21 and the second guide surface 221b of the second gripping jig 22 are parallel and on the same plane.

[0033] The drive device 23 is configured to rotate the first gripping jig 21 with the second direction of the test piece 10 as the axis of rotation. More specifically, the drive device 23 is configured so that the axis of rotation is perpendicular to both the normal direction of the first guide surface 211a (the direction parallel to the thickness direction of the test piece 10) and the normal direction of the second guide surface 211b (the direction parallel to the first direction of the test piece 10).

[0034] The torque cell 24 is configured to measure the magnitude of the torque applied to the second gripping fixture 22 around the test piece 10 in a second direction. More specifically, the torque cell 24 is configured to measure the magnitude of the torque around both the direction normal to the first guide surface 221a (parallel to the thickness direction of the test piece 10) and the direction normal to the second guide surface 221b (parallel to the first direction of the test piece 10).

[0035] Figure 6 is a magnified front view of the test apparatus 20, showing the area near the test piece 10. The base 211 and lid 212 of the first gripping jig 21 each have end faces 211c and 212c, respectively. Each of the end faces 211c and 212c is a surface facing the second gripping jig 22. The base 211 and lid 212 are positioned such that each of their end faces 211c and 212c is perpendicular to the second direction and is on the same plane as each other.

[0036] Similarly, the base 221 and lid 222 of the second gripping jig 22 also have end faces 221c and 222c, respectively. Each of the end faces 221c and 222c is a surface facing the first gripping jig 21. The base 221 and lid 222 are positioned such that each of the end faces 221c and 222c is perpendicular to the second direction and lies on the same plane as the other.

[0037] As a result, end faces 211c, 212c, 221c, and 222c all become parallel surfaces. The first gripping jig 21 and the second gripping jig 22 are positioned with a predetermined distance s between them in the second direction. More specifically, the distance s is the distance between end face 211c and end face 221c (or the distance between end face 212c and end face 222c).

[0038] [Test Method] The method for evaluating the test piece 10 using the test apparatus 20 will be described in detail below. First, as shown in Figure 5, the test piece 10 is held by the first gripping jig 21 and the second gripping jig 22. More specifically, one side of the test piece 10 is held by the first guide surface 211a and the lid 212 of the first gripping jig 21, and the other side of the test piece 10 is held by the first guide surface 221a and the lid 222 of the second gripping jig 22. At this time, the test piece 10 is positioned so that its parallel surface 11 (Figure 1) is in contact with the second guide surface 211b of the first gripping jig 21 and the second guide surface 221b of the second gripping jig 22. This makes it possible to align the second direction of the test piece 10 with the rotation axis of the drive device 23.

[0039] From this state, the drive device 23 rotates the first gripping jig 21 with the second direction as the axis of rotation. This allows a torsional load to be applied to the test piece 10. In addition, the torque cell 24 can be used to measure the magnitude of the torque applied to the test piece 10.

[0040] As shown in Figure 6, the test piece 10 can be divided into three parts: a gripping portion 10A, a gripping portion 10B, and a gauge mark portion 10C. Of the test piece 10, the portion restrained by the first gripping jig 21 is the gripping portion 10A, the portion restrained by the second gripping jig 22 is the gripping portion 10B, and the portion connecting the gripping portion 10A and the gripping portion 10B, which is not restrained by either the first gripping jig 21 or the second gripping jig 22, is the gauge mark portion 10C.

[0041] The test specimen 10 is positioned such that its center in the second direction is exactly midway between the first gripping fixture 21 and the second gripping fixture 22. This results in the gauge mark portion 10C having a symmetrical shape in the second direction. Furthermore, the distance s along the second direction between the first gripping fixture 21 and the second gripping fixture 22 becomes the dimension of the gauge mark portion 10C along the second direction.

[0042] Although Figure 6 illustrates the case where the width b of the opening 10b is greater than the distance s, the width b may also be smaller than the distance s. If the width b is smaller than the distance s, there will be parts near the opening 10b that are not constrained by either the first gripping jig 21 or the second gripping jig 22, but these parts will not be included in the reference point.

[0043] Figures 7 and 8 show enlarged views of the gauge portion 10C of the test specimen 10. Figure 7 is a front view (viewed from the thickness direction of the test specimen 10), and Figure 8 is a perspective view. As shown in Figures 7 and 8, the gauge portion 10C has the shape of a rectangular parallelepiped with length s, width w, and height (h+d), with a cylindrical groove (annular notch) of radius of curvature ρ formed within it.

[0044] Here, s is the distance along the second direction between the first gripping fixture 21 and the second gripping fixture 22, as described above. w is the thickness of the test piece 10. h is the shortest distance from the inner circumferential surface of the hole 10a to the parallel surface 11. d is the depth of the groove.

[0045] The groove depth d is more specifically defined as follows: As shown in Figure 7, when the test piece 10 is projected onto a plane perpendicular to the thickness direction, the point in the contour of the hole 10a closest to the parallel plane 11 is defined as P0, and the point in the contour of the hole 10a that intersects with the contours of the first gripping fixture 21 and the second gripping fixture 22 (if there are two or more intersections, the point closest to the parallel plane 11) is defined as point P1. The distance between point P0 and point P1 along the first direction is the groove depth d.

[0046] The groove depth d is determined by the distance s and the diameter ID of the hole 10a. Geometrically, d = {ID - (ID 2 -s 2 ) 1 / 2} / 2, s = 2 × {d(ID-d)} 1 / 2 The relationship is as follows: Also, ρ = ID / 2.

[0047] The rotation axis RA of the drive device 23 (Fig. 5) passes through a position that approaches the inner peripheral surface of the hole 10a by 1 / 2 of the distance h in the first direction from the parallel plane 11, and is adjusted so as to pass through the central position in the thickness direction of the test piece in the second direction.

[0048] Fig. 9 is a cross-sectional view of the surface (the hatched surface in Fig. 8) where the maximum shear stress occurs when a torsional load is applied to the test piece 10. More specifically, Fig. 9 is a cross-sectional view of a plane perpendicular to the second direction of the test piece 10 and passing through the center in the second direction of the test piece 10. The test piece 10 is configured such that w > h as described in Figs. 1 and 2. Therefore, in the cross-section of Fig. 9, the shear stress increases at the positions (points PA and PB in Fig. 9) at the center in the thickness direction on the plane perpendicular to the first direction. Comparing point PA and point PB, as shown in Fig. 8, since point PA is at the deepest part of the cylindrical groove (annular notch), a larger shear stress occurs at point PA than at point PB. Therefore, when a torsional load is applied to the test piece 10, the maximum shear stress occurs at point PA.

[0049] [Effects of this Embodiment, etc.] According to this embodiment, it is possible to generate the maximum shear stress on the inner peripheral surface of the hole 10a of the test piece 10. Thereby, for example, it becomes possible to conduct a test that reproduces fatigue failure starting from the inner surface of the metal pipe MP (Fig. 4).

[0050] When the depth d (Fig. 7) of the groove is small, the ratio (stress concentration factor) α of the shear stress generated at point PA to the shear stress generated at point PB f is α f = 1 + (d / ρ) 1 / 2 (Neuber's formula. See page 174 of Non-Patent Document 1). That is, the shear stress τ max generated at point PA is α f times the shear stress τ0 generated at point PB. The shear stress τ max generated at point PA is τ max = αf × τ0, τ0 = 1 / k1 × (T / wh 2) k1 is the coefficient of torsional stress in a rectangular cross-section, and is published in literature, etc. (see, for example, Non-Patent Document 2).

[0051] Note that this stress concentration factor α f This is the same formula as the stress concentration factor when a groove extending parallel to the axis of rotation is formed (see Figure 10 and page 181 of Non-Patent Document 1).

[0052] Here, in order to more reliably cause fatigue failure on the inner surface of hole 10a, α f It is preferable to set the groove depth d so that α is 1.05 or greater. f It is more preferably 1.10 or higher, and even more preferably 1.20 or higher.

[0053] Furthermore, from the viewpoint of adjustment accuracy, it is preferable that the groove depth d be 0.10 mm or more.

[0054] On the other hand, if the groove depth d is too large, α f The above formula can no longer be used to approximate this. Preferably, the groove depth d is 1 / 4 or less of the shortest distance h from the inner circumferential surface of the hole 10a to the parallel surface 11. More preferably, the groove depth d is 1 / 8 or less of the distance h.

[0055] As mentioned above, the groove depth d is the distance s along the second direction between the first gripping jig 21 and the second gripping jig 22, and s = 2 × {d(ID-d)} 1 / 2 This relationship exists. For example, to make the groove depth d less than or equal to 1 / 4 of the distance h, the distance s must be {h(ID-h / 4)}. 1 / 2 Here's what you should do:

[0056] The test specimen 10 (Figure 1) according to this embodiment has a parallel surface 11. The test apparatus 20 (Figure 5) has first guide surfaces 211a and 221a perpendicular to the thickness direction of the test specimen 10, and second guide surfaces 211b and 221b parallel to the parallel surface 11. With this configuration, the rotation axis of the drive device 23 can be precisely aligned with the second direction of the test specimen.

[0057] In this embodiment, the test piece 10 (Figure 1) has a maximum dimension m along the first direction of the test piece 10 that is 4.0 times or more the distance h. With this configuration, as shown in Figure 6, the area of ​​the gripping portions 10A and 10B (area projected onto a plane perpendicular to the thickness direction; the same applies hereinafter) can be made sufficiently large compared to the area of ​​the gauge portion 10C. This allows for the application of a large torque and suppresses fracture due to fretting fatigue. The maximum dimension m is more preferably 8.0 times or more the distance h, and even more preferably 16.0 times or more the distance h.

[0058] As shown in Figure 4, the test specimen 10 according to this embodiment has a shape close to the standard shape RS obtained by cutting a metal pipe MP into sections. Therefore, it is possible to make efficient use of material (it can be made from less material) and reduce the processing time. In addition, since the thickness w can be small (for example, about 3.5 mm), it can also be taken from curved pipes.

[0059] As previously described, the opening 10b of the test piece 10 may have any shape as long as it penetrates from the hole 10a to the outer circumference of the disc. Also, the width b of the opening 10b may be greater than or less than the distance s (Figure 6). On the other hand, from the viewpoint of increasing the area of ​​the gripping parts 10A and 10B, and from the viewpoint of reducing the amount of machining from the reference shape RS (Figure 4), a smaller width b is preferable. The width b is preferably less than or equal to the diameter ID of the hole 10a, more preferably less than or equal to 1 / 2 of the diameter ID, even more preferably less than or equal to 1 / 4 of the diameter ID, and even more preferably less than or equal to 1 / 8 of the diameter ID. On the other hand, if the width b is too small, the two end faces 10b1 sandwiching the opening 10b may come into contact with each other when a torsional load is applied. The lower limit of the width b is preferably 0.10 mm.

[0060] The above describes a test specimen, a method for manufacturing the test specimen, a test apparatus, and a test method according to one embodiment of the present invention. According to this embodiment, it is possible to perform a test that reproduces fatigue fracture originating from the inner surface of a tubular body. [Examples]

[0061] The present invention will be described more specifically below with reference to examples. The present invention is not limited to these examples.

[0062] A test specimen with the shape described above was taken from a steel pipe, and a fatigue test was performed by repeatedly applying a torsional load using the test apparatus described above, confirming that fatigue failure occurred at the location corresponding to the inner surface of the steel pipe. In addition, a test specimen with the shape described in Japanese Patent Publication No. 6809213 was taken from a steel pipe of the same material, and a fatigue test was performed similarly. The dimensions of each test specimen were adjusted so that the magnitude of the maximum shear stress generated at the location corresponding to the inner surface of the steel pipe was the same. As a result, almost identical test results (fatigue life) were obtained for the two test specimens.

[0063] 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 within the scope of the invention. [Explanation of Symbols]

[0064] 10, 10V test piece RS standard shape 10a hole 10b opening 11 Parallel planes 10A, 10B gripping section 10C Gauge section 20 Test equipment 21. First gripping jig 22. Second gripping jig 211, 221 base 211a, 221a First guide surface 211b, 221b Second guide surface 211c, 221c end face 212, 222 lid 213, 223 volts 214, 224 pins 23 Drive unit 24 Torque Cell

Claims

1. A test specimen for torsional fatigue testing, A disc with a circular hole formed in its center is used as the base shape, and the base shape has parallel surfaces and an opening formed on it. The parallel surface is formed on the outer circumference of the disk and is perpendicular to a first direction, which is one of the radial directions of the disk. The opening is formed on the side opposite to the parallel surface when viewed from the center of the hole, and penetrates from the hole to the outer circumference of the disc. The shortest distance h from the inner circumferential surface of the hole to the parallel surface is smaller than the thickness w of the disk. A test specimen in which the maximum dimension m along the first direction is 4.0 times or more the distance h.

2. A method for producing a test specimen as described in claim 1, A step of taking a sample of the aforementioned standard shape by cutting a metal tube into rings, A method for manufacturing a test specimen, comprising the step of forming the parallel surface and the opening in the sample.

3. A test apparatus for evaluating a test specimen as described in claim 1, The second direction is defined as the radial direction of the disk that is perpendicular to the first direction. A first gripping jig that holds one side of the test piece in the second direction, viewed from the center of the hole, by clamping it from the thickness direction of the test piece, A second gripping jig that holds the other side of the test piece in the second direction, viewed from the center of the hole, by clamping it from the thickness direction of the test piece, The device comprises a drive device that rotates at least one of the first gripping jig and the second gripping jig with the second direction as the axis of rotation, A testing apparatus wherein at least one of the first gripping fixture and the second gripping fixture has a first guide surface which is perpendicular to the thickness direction of the test piece, and a second guide surface which is parallel to the parallel surface.

4. The test apparatus according to claim 3, A testing apparatus wherein the rotation axis passes through a position in the first direction that is closer to the inner circumferential surface of the hole by a distance of half the distance h from the parallel surface, and passes through the center of the thickness direction of the test piece in the second direction.

5. A test apparatus according to claim 3 or 4, When the aforementioned test specimen is projected onto a plane perpendicular to the thickness direction, Let P0 be the point in the contour of the hole that is closest to the parallel surface. Point P1 is defined as the point in the contour of the hole that intersects with the contours of the first gripping jig and the second gripping jig (if there are two or more points of intersection, the point closest to the parallel plane). A test apparatus in which the distance d along the first direction between point P0 and point P1 is 1 / 4 or less of the distance h.

6. A test apparatus according to claim 3 or 4, When the diameter of the aforementioned hole is denoted as ID, The distance s between the first gripping jig and the second gripping jig along the second direction is {h (ID - h / 4)} １／２ The test apparatus is as follows:

7. A test method for evaluating a test specimen according to claim 1 using the test apparatus according to claim 3, The drive device includes a step of rotating at least one of the first gripping jig and the second gripping jig, The rotation axis passes through a position in the first direction that is closer to the inner circumferential surface of the hole by a distance of half the distance h from the parallel plane, and passes through the center of the thickness direction of the test piece in the second direction. When the aforementioned test specimen is projected onto a plane perpendicular to the thickness direction, Let P0 be the point in the contour of the hole that is closest to the parallel surface. Point P1 is defined as the point in the contour of the hole that intersects with the contours of the first gripping jig and the second gripping jig (if there are two or more points of intersection, the point closest to the parallel plane). A test method in which the distance d along the first direction between point P0 and point P1 is 1 / 4 or less of the distance h.

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