JP6451410B2 - Test piece holding device and test method - Google Patents

Description

  The present invention relates to a test piece holding device and a test method using the holding device.

  Structures such as bridges are subjected to shear loads according to the conditions of use. When this structure is subjected to a greater shear load than expected, for example, when an earthquake greater than expected occurs, shear cracks occur in structural members such as abutments, and the slope of the bridge surface or falling bridges There is a risk of reaching. In order to prevent the occurrence of such an accident, it is necessary to evaluate the mechanical properties of the structural members.

  However, it is impossible to evaluate the mechanical properties of the structural members of the structure with respect to the actual structure. Therefore, a load form in a structure is simulated by applying a tensile load, a torsion load, or the like to a test piece that simulates an actual component member. The small mechanical test piece is used to evaluate the partial mechanical properties of the structure, and the mechanical properties of the entire structure are estimated based on the evaluation results.

  Examples of the shear property evaluation method include methods described in Patent Documents 1 and 2 and Non-Patent Documents 1 to 3.

  The method described in Patent Document 1 applies a force in a direction parallel to the shear surface of the test piece (so-called misload) by a jig that moves in a direction orthogonal to the axis of the cylindrical test piece. This is a method of applying shear stress. The method described in Patent Document 2 is a method of applying a compressive stress and a shear stress to a test piece by sandwiching a sheet-like test piece with two holding means of a test apparatus and relatively shifting the two holding means. It is.

  The method described in Non-Patent Document 1 is a four-point bending test, and the method described in Non-Patent Document 2 is a three-point bending test. The method described in Non-Patent Document 3 is a method in which a notch is provided in a test piece, and the test piece is compressed to cause shear fracture between these notches.

Japanese Utility Model Publication No. 62-176741 JP 2010-71774 A

Suzuki Tatsuo, Kanno Yoshimasa, Ogawa Masato, “Evaluation of Shear Strength of Si Structures by Asymmetric Four-Point Bending Test Method”, Proc. , P. 719-720 JIS K 7057, “Fiber-Reinforced Plastics – How to Determine Apparent Interlaminar Shear Strength by the Short Beam Method”, established on March 1, 1987 JIS K 7092, “Test method for interlaminar shear strength by notch compression of carbon fiber reinforced plastic”, established on December 20, 2005

  The structural member includes a portion to which not only shear stress but also tensile stress or compressive stress is applied, such as residual stress in a welded portion. Therefore, if a tensile stress or a compressive stress can be applied together with a shear stress, a test simulating a load form in an actual structure can be performed, and more accurate material evaluation can be performed.

  For example, if a tensile stress or a compressive stress can be applied together with a shear stress to a small test piece, there are the following advantages. A test simulating an actual load form can be performed on a small test piece collected from a minute region of the structure so as not to impair the performance of the structure. Thereby, it becomes possible to evaluate the residual strength of the structure itself. In this case, the evaluation can be performed with higher accuracy than a test performed using a simulated test piece simulating a structural member of the structure.

  Conventionally, when applying a shear stress, a tensile stress, or a compressive stress to a test piece, the test piece is held using, for example, a chuck. However, if the test piece is held by the chuck, the test piece may be deformed. Thus, if stress is applied in a state where the test piece is deformed, the accuracy of the material evaluation may be lowered due to the influence of the deformation. In particular, when the test piece is small, the test piece is likely to be deformed, and the accuracy of the material evaluation is likely to be greatly reduced. On the other hand, there is a method using a pin chuck as a method of grasping a small test piece. However, since the small pin chuck is difficult to obtain high dimensional accuracy, the accuracy of material evaluation may be reduced.

  On the other hand, the jig used in the method described in Patent Document 1 cannot move in the axial direction of the test piece. Therefore, neither tensile stress nor compressive stress can be applied to the test piece. Further, in the method described in Patent Document 2, only the entire surface of the sheet-like test piece is sandwiched from both sides by two holding means, and a tensile stress cannot be applied to the test piece.

  Since the method described in Non-Patent Document 1 is a method based on a four-point bending test, and the method described in Non-Patent Document 2 is a method based on a three-point bending test, both tensile stress and compressive stress can be applied. Can not. Also, the method described in Non-Patent Document 3 cannot apply either tensile stress or compressive stress to the portion where shear fracture occurs.

  In the present invention, the test piece can be stably held without being deformed, and a shear stress caused by a so-called misload (hereinafter simply referred to as “shear stress”) is applied to the test piece. It is an object of the present invention to provide a test piece holding device capable of applying a tensile stress or a compressive stress and a test method using this holding device.

  A test piece holding device according to an embodiment of the present invention includes a test part extending in one direction and a step formed in a direction perpendicular to the extending direction of the test part to form a step with respect to the test part. An apparatus for holding a test piece having a pair of holding portions respectively provided at both ends of the test portion in the extending direction, the first fixing portion holding one of the pair of holding portions, A second fixing portion that holds the other of the pair of holding portions, wherein the first fixing portion includes a first extending direction fixing portion that holds the one holding portion from both sides in the extending direction; A first orthogonal direction fixing portion that holds the holding portion from both sides in the orthogonal direction, and the second fixing portion includes a second extending direction fixing portion that holds the other holding portion from both sides in the extending direction. , A second straight for holding the other holding portion from both sides in the orthogonal direction. And a direction fixed part.

  Since the holding device has the above-described configuration, the first fixing portion and the second fixing portion that respectively hold the pair of holding portions of the test piece are relatively displaced in a direction perpendicular to the extending direction of the test portion of the test piece. By making it, a shear stress can be given to a test part. Moreover, a tensile stress or a compressive stress can be applied to the test part by relatively displacing the first fixing part and the second fixing part in the extending direction of the test part.

  A 1st fixing | fixed part and a 2nd fixing | fixed part hold | maintain the holding | maintenance part of a test piece from 4 directions with an orthogonal direction fixing | fixed part and an extending | stretching direction fixing | fixed part. By holding the holding part of the test piece from four directions in this way, at least one of shear stress and tensile stress or shear stress is applied to the test part of the test piece without rotating the holding part of the test piece. can do. Therefore, the test part can be more reliably deformed by a desired stress component, and it becomes possible to perform a highly accurate test for various load forms.

  In addition, by holding the test piece holder from four directions, the test piece can be held without being deformed regardless of the size of the test piece. For example, when a small test piece having a length of several millimeters on one side is used, it is possible to perform highly accurate evaluation even for a minute region on the order of submillimeters.

  The first extending direction fixing portion and the second extending direction fixing portion are respectively an end fixing portion that holds at least a part of an end portion in the extending direction of the test piece, and at least one of the steps of the test piece. And a step fixing portion for holding the portion.

  With this configuration, when the shear stress and the tensile stress or the compressive stress are applied to the test portion of the test piece, the rotation of the holding portion of the test piece can be more reliably prevented.

  In the test piece holding device, the first fixing portion holds a portion other than a connection portion with the test portion in the one holding portion, and the second fixing portion holds the test portion in the other holding portion. Hold the part other than the connection part.

  With this configuration, in the pair of holding portions of the test piece, since the portions other than the connection portion with the test portion are held by the first fixing portion and the second fixing portion, respectively, the holding portion can be held more stably. it can. Therefore, it is possible to perform material evaluation with higher accuracy.

  In the specimen holding device, at least one of the first fixing portion and the second fixing portion is connected to a stretching direction driving portion that relatively displaces the first fixing portion and the second fixing portion in the stretching direction. In addition, at least one of the first fixing portion and the second fixing portion is connected to an orthogonal direction driving portion that relatively displaces the first fixing portion and the second fixing portion in the orthogonal direction.

  By relatively displacing the first fixed portion and the second fixed portion by the stretching direction drive portion and the orthogonal direction drive portion, a tensile stress or a compressive stress is also applied while applying a shear stress to the test portion of the test piece. The configuration can be realized.

  A test method according to an embodiment of the present invention is a test method using the above-described test piece holding device, and relatively displaces the first fixing portion and the second fixing portion in the orthogonal direction. Thus, a shear stress is applied to the test portion of the test piece.

  In this test method, since the test piece holding device is used, the test piece holding portion can be moved without rotating. Therefore, when the first fixing portion and the second fixing portion are relatively displaced in the orthogonal direction and a shear stress is applied to the test portion of the test piece, the test portion can be subjected to shear deformation, and the shear characteristics are accurate. High evaluation is possible.

  This test method can be applied regardless of the size of the test piece. For example, a test can be performed on a minute test piece having a side length of several millimeters taken from a sample. That is, this test method can be applied to a test piece collected from a minute region of the actual structure so as not to impair the performance of the structure. In this case, the soundness of the structure can be evaluated with higher accuracy than a test using a conventional simulated test piece. Since the soundness of the structure can be evaluated with high accuracy, the repair of the structure can be kept to the minimum necessary, and the repair cost can be reduced. In addition, if this test method is applied when evaluating an expensive sample for the purpose of research and development, material design, etc., it is possible to perform a sufficient evaluation with a small test piece, so that the test cost can be reduced.

  In the test method, the first fixing portion and the second fixing portion are relatively displaced in the stretching direction, thereby applying a tensile stress or a compressive stress to the test portion, and applying a tensile stress or a compressive stress to the test portion. A shear stress is applied to the test portion by relatively displacing the first fixed portion and the second fixed portion in the orthogonal direction in a state where compressive stress is applied.

  By applying shear stress while applying tensile stress or compressive stress to the test part of the test piece, a test simulating the load form in the actual structure can be performed, so a more accurate material evaluation is performed. be able to. In addition, when such stress is applied to a minute test piece, the material evaluation that simulates the multiaxial stress state in the structure using the actual part constituting the structure, and the actual part Evaluation of microscopic areas such as uneven burning, nitrided layers, and spot welds can also be performed. Therefore, many improvement guidelines can be obtained for the material.

  In the above test method, the test piece has the R portion at both ends where the test portion is connected to the pair of holding portions, and the test piece has a central portion in the extending direction of the test portion in plan view. An arc portion having a larger radius of curvature than the R portion is formed so that the width dimension of the portion is the smallest at the central portion.

  When the test portion of the test piece has the R portion, stress concentration at the connection portion between the test portion and the holding portion can be suppressed when stress is applied to the test piece. Thereby, the failure which a test piece fractures | ruptures in a connection part can be decreased. In addition, since the arc part is formed in the test part, there is a very high possibility that deformation due to yielding will occur in the center part of the test part in the extending direction. Can do. Therefore, by using the test piece having the shape as described above, highly accurate evaluation can be performed with a high yield.

  In the test method, the test piece has R portions at both ends where the test portion is connected to the pair of holding portions, and a thickness of the test portion is provided at a central portion in the extending direction of the test portion. A notch having a circular arc shape with a smaller radius of curvature than the R portion is formed so that the thickness dimension is the smallest at the central portion and is ½ or less of the maximum thickness dimension of the test portion.

  Therefore, when the curvature radius of the notch is smaller than the curvature radius of the R portion so that the thickness dimension of the test piece at the bottom portion of the notch is less than or equal to 1/2 of the maximum thickness dimension of the test portion, the notch bottom portion is stressed. It becomes a concentrated part. Since fatigue cracks occur at stress concentration portions, fatigue cracks are generated at the same site in a plurality of test pieces by using a test piece having the above-described shape. Thereby, a fatigue crack can be evaluated efficiently.

  According to the test piece holding apparatus according to the embodiment of the present invention, tensile stress or compressive stress is applied to the test piece together with shear stress in a state where the test piece is stably held regardless of the size of the test piece. be able to.

  According to the test method according to the embodiment of the present invention, a test for applying tensile stress or compressive stress along with shear stress to the test piece can be performed regardless of the size of the test piece, and highly accurate material evaluation is performed. be able to.

FIG. 1 is a schematic view of a test piece holding device according to the present invention. FIG. 1 (a) is a plan view of the whole holding device, and FIG. 1 (b) is a portion around the test piece of FIG. 1 (a). An enlarged view is shown. FIG. 2 is a block diagram showing an example of a specific configuration of the test piece holding device of the present invention. FIG. 2 (a) shows a plan view of the whole holding device, and FIG. 2 (b) shows FIG. The partial enlarged view of the 1st fixing | fixed part and 2nd fixing | fixed part of a) is shown. FIG. 3 is a perspective view of the first fixing portion of the holding device shown in FIG. 2. FIG. 4 is a plan view of the first base member. 5 is a cross-sectional view taken along line VV in FIG. FIG. 6 is a plan view of a test piece suitable for the test method according to the embodiment of the present invention. FIG. 7 is a configuration diagram of a test piece suitable for a fatigue test among the test methods according to the embodiment of the present invention. FIG. 7 (a) shows a plan view and FIG. 7 (b) shows a side view. . FIG. 8 is a diagram showing the result of FEM analysis for the case where stress is applied to the test piece shown in FIG. 7, and FIG. 8A shows the case where shear stress is applied, and FIG. ) Shows the case where tensile stress is applied. FIG. 9 is a nominal shear stress-stroke diagram obtained in the static shear test. FIG. 10 is a plan view of a test piece used in the comparative test. FIG. 11 is a photograph of the appearance of the test piece and the surrounding holding device before and after applying shear stress, FIG. 11 (a) shows the state before applying shear stress, and FIG. 11 (b) shows after applying shear stress. Shows the state. FIG. 12 is a photograph of the arc part of the test part of the test piece before and after applying shear stress, FIG. 12 (a) shows the state before applying shear stress, and FIG. 12 (b) shows the state after applying shear stress. Indicates. FIG. 13 shows the measurement results by EBSD for the specimens. FIG. 14 is an SN diagram obtained by a shear fatigue test. FIG. 15 is an SN diagram obtained by a tensile / compression fatigue test. FIG. 16 is a micrograph of a fracture surface of a test piece fractured by a shear fatigue test, FIG. 16 (a) is an overall view of the fracture surface, and FIG. 16 (b) is a portion surrounded by a square in FIG. 16 (a). FIG. 16C is an enlarged view of a portion surrounded by a square in FIG. 16B.

  Hereinafter, preferred embodiments of a test piece holding apparatus and a test method using the holding apparatus according to the present invention will be described with reference to the drawings. In addition, the dimension of the structural member in each figure does not represent the dimension of an actual structural member, the dimension ratio of each structural member, etc. faithfully.

1. FIG. 1 is a schematic view of a test piece holding device of the present invention, FIG. 1 (a) shows a plan view of the whole holding device, and FIG. 1 (b) shows FIG. The partial enlarged view of the test piece periphery of a) is shown. First, with reference to the schematic diagram of FIG. 1, the structure of the holding | maintenance apparatus of this invention is demonstrated easily.

  As shown in FIG. 1A, the holding device 10 includes a surface plate 11, a first moving body 12, and a second moving body 13. The first moving body 12 and the second moving body 13 are arranged on the surface plate 11. The holding device 10 holds the test piece 60 with the first moving body 12 and the second moving body 13.

  Here, as shown in FIG. 1B, the test piece 60 includes a test portion 61 and a pair of holding portions 62 and 63. The test part 61 is formed so as to extend in one direction at the central part of the test piece 60. The extending direction of the test part 61 coincides with the longitudinal direction of the test piece 60 (the direction of arrow A in the figure). In the longitudinal direction of the test piece 60, the holding part 62 is connected to one end of the test part 61, and the holding part 63 is connected to the other end of the test part 61. The holding portions 62 and 63 protrude in a direction orthogonal to the longitudinal direction of the test piece 60 (in the direction of arrow B in the figure; hereinafter also referred to as “orthogonal direction”), and form a step 65 with respect to the test portion 61. To do.

  The holding unit 62 is held by the first moving body 12. The holding unit 63 is held by the second moving body 13. The first moving body 12 is configured to be movable in the longitudinal direction of the test piece 60. The second moving body 13 is configured to be movable in the orthogonal direction of the test piece 60. FIG. 1A shows a state in which the second moving body 13 is displaced in the orthogonal direction of the test piece 60 so that a shear stress acts on the test piece 60 (more specifically, the test unit 61).

  As shown in FIG. 1A, the first moving body 12 includes a first fixing unit 20, a first connecting member 41, a first load cell 42, and a second load cell 43.

  The first fixing portion 20 has a C shape as viewed from above. As shown in FIG. 1B, the first fixing portion 20 includes a first end fixing portion 21 (end fixing portion), a pair of first step fixing portions 22 (step fixing portions), and a pair of first fixing portions. 1 orthogonal direction fixing | fixed part 23 is provided. In FIG. 1A, the first fixing portion 20 is shown in a simplified manner, and the first end fixing portion 21, the pair of first step fixing portions 22, and the pair of first orthogonal direction fixing portions 23. The boundary line is not shown.

  As shown in FIG. 1B, the first end fixing portion 21 is disposed so as to come into contact with the end portion on the holding portion 62 side among both end portions in the longitudinal direction of the test piece 60. The pair of first step fixing portions 22 are arranged so as to contact the step 65 on the holding portion 62 side with the test portion 61 of the test piece 60 sandwiched from both sides in the orthogonal direction of the test piece 60. A pair of 1st orthogonal direction fixing | fixed part 23 is arrange | positioned so that the one edge part and the other edge part of the holding | maintenance part 62 in the orthogonal direction of the test piece 60 may contact, respectively.

  That is, the first end fixing part 21, the pair of first step fixing parts 22, and the pair of first orthogonal direction fixing parts 23 are arranged so as to surround one holding part 62 of the test piece 60 from four directions. . Therefore, the holding part 62 of the test piece 60 is held from four directions by the first fixing part 20. Specifically, the first end fixing part 21 and the pair of first step fixing parts 22 hold the holding part 62 from both sides in the longitudinal direction of the test piece 60, and the pair of first orthogonal direction fixing parts 23 hold. The part 62 is held from both sides in the orthogonal direction of the test piece 60.

  The first connection member 41 has a shape bent into a substantially L shape when viewed from above. Specifically, the first connecting member 41 has a longitudinal direction extending part 41 a extending in the longitudinal direction of the test piece 60 and an orthogonal direction extending part 41 b extending in the orthogonal direction of the test piece 60. The longitudinal direction extending portion 41 a and the orthogonal direction extending portion 41 b are connected at one end to constitute a first connecting member 41. The first fixing portion 20 is connected to the other end of the orthogonal direction extending portion 41b of the first connecting member 41, and the first driving portion 40 (extending direction driving) is connected to the other end of the longitudinal extending portion 41a. Part) is connected.

  The first load cell 42 has a column part 42a. The first fixed portion 20 and the orthogonally extending portion 41 b of the first connecting member 41 are connected via the column portion 42 a of the first load cell 42. In other words, the first load cell 42 is connected to the first fixing portion 20 and the first connecting member 41, and the load acting on the first fixing portion 20 in the longitudinal direction of the test piece 60, that is, the test portion of the test piece 60. The magnitude of the load acting in the direction of arrow A with respect to 61 is detected.

  The second load cell 43 has a pillar portion 43a. The other end portion of the longitudinally extending portion 41 a of the first connecting member 41 and the first driving portion 40 are connected via a column portion 43 a of the second load cell 43. That is, the second load cell 43 is connected to the first connection member 41 and the first drive unit 40, and the load acting on the first fixing unit 20 and the first connection member 41 in the orthogonal direction of the test piece 60, that is, the test The magnitude of the load acting in the direction of arrow B on the test part 61 of the piece 60 is detected.

  The second moving body 13 includes a second fixing portion 30 and a second connection member 51. The second fixing unit 30 is connected to the second drive unit 50 (orthogonal direction drive unit) via the second connection member 51. One end of the second connection member 51 is connected to the second fixing unit 30, and the other end is connected to the second drive unit 50.

  The 2nd fixing | fixed part 30 has C shape seeing from upper direction. As shown in FIG. 1B, the second fixing portion 30 includes a second end fixing portion 31 (end fixing portion), a pair of second step fixing portions 32 (step fixing portions), and a pair of first fixing portions. 2 orthogonal direction fixing | fixed part 33 is provided. The second end fixing portion 31, the second step fixing portion 32, and the second orthogonal direction fixing portion 33 are, with respect to the holding portion 63, the first end fixing portion 21 and the first step fixing portion 22 with respect to the holding portion 62. , And the first orthogonal direction fixing part 23. Therefore, the holding portion 63 of the test piece 60 is held from four directions by the second fixing portion 30. Specifically, the second end fixing portion 31 and the pair of second step fixing portions 32 hold the holding portion 63 from both sides in the longitudinal direction of the test piece 60, and the pair of second orthogonal direction fixing portions 33 hold. The part 63 is held from both sides in the orthogonal direction of the test piece 60.

  The first drive unit 40 displaces the first moving body 12 in the longitudinal direction of the test piece 60. As a result, the first fixing portion 20 and the second fixing portion 30 are relatively displaced in the longitudinal direction of the test piece 60. The second drive unit 50 displaces the second moving body 13 in the orthogonal direction of the test piece 60. Thereby, the 1st fixing | fixed part 20 and the 2nd fixing | fixed part 30 displace relatively in the orthogonal direction of the test piece 60. FIG.

  Although not particularly shown, the first drive unit 40 and the second drive unit 50 are both configured to be reciprocally movable along a linear guide provided on the surface plate 11 by a motor or the like.

  In the present embodiment, as shown in FIG. 1B, the first fixing portion 20 includes a first end fixing portion 21, a pair of first step fixing portions 22, and a pair of first orthogonal direction fixings. The portion 23 is in contact with the entire portion other than the connection portion C with the test portion 61 of the holding portion 62 as viewed from above. That is, the first end fixing portion 21, the pair of first step fixing portions 22, and the pair of first orthogonal direction fixing portions 23 cover the entire side surfaces of the holding portion 62 as viewed from above. It is in contact with the holding part 62. However, the pair of first end fixing portions 21 may be disposed so as to contact at least a part of the end portion of the test piece 60 in the longitudinal direction. The pair of first step fixing portions 22 may be disposed so as to contact at least a part of the step 65 on the holding portion 62 side. Further, the pair of first orthogonal direction fixing portions 23 may be disposed so as to contact at least part of one end portion and the other end portion of the holding portion 62 in the longitudinal direction of the test piece 60.

  However, as in the present embodiment, the first end fixing part 21, the pair of first step fixing parts 22, and the pair of first orthogonal direction fixing parts 23 of the first fixing part 20 are viewed from above. It contacts the holding part 62 so as to cover all the side surfaces of the holding part 62, the second end fixing part 31 of the second fixing part 30, the pair of second step fixing parts 32, and the pair of second orthogonal parts. It is preferable that the direction fixing portion 33 contacts the holding portion 63 so as to cover all the side surfaces of the holding portion 63 as viewed from above. Thereby, the holding parts 62 and 63 can be held more stably, and more accurate material evaluation can be performed using the holding device 10.

  In the present embodiment, as shown in FIG. 1A, the first fixing portion 20 is displaced in the longitudinal direction of the test piece 60. On the other hand, the second fixing portion 30 is displaced in the orthogonal direction of the test piece 60. However, the first fixing part 20 may be displaced in the orthogonal direction of the test piece 60, and the second fixing part 30 may be displaced in the longitudinal direction of the test piece 60. Further, both the first fixing part 20 and the second fixing part 30 may be displaced in the longitudinal direction of the test piece 60 and in the orthogonal direction of the test piece 60.

2. Specific Configuration Example of Test Specimen Holding Device In FIG. 1, each component is shown in a simplified manner in order to explain the function of the holding device. Hereinafter, a specific configuration of the holding device will be described with reference to FIGS. 2 to 5.

  FIG. 2 is a block diagram showing an example of a specific configuration of the test piece holding device of the present invention. FIG. 2 (a) shows a plan view of the whole holding device, and FIG. 2 (b) shows FIG. The partial enlarged view of the 1st fixing | fixed part and 2nd fixing | fixed part of a) is shown. 2, the same members as those shown in FIG. 1 are denoted by the same reference numerals as those in FIG. FIG. 2 shows a state in which the holding device 15 holds the test piece 60. In FIG. 2, the longitudinal direction of the test piece 60 is shown as an arrow A direction, and the orthogonal direction of the test piece 60 is shown as an arrow B direction.

  A test piece holding device 15 shown in FIG. 2A includes a surface plate 11, a first moving body 16, and a second moving body 17. The first moving body 16 includes a first fixing portion 80, a first arm 46, a first load cell 47, a second load cell 43, and a case 49. The second moving body 17 includes a second fixing portion 90 and a second arm 56. Is provided.

  The first moving body 16 and the second moving body 17 are specific examples of the configuration of the first moving body 12 or the second moving body 13 in FIG. The first fixing unit 80 and the first load cell 47 are specific examples of the configuration of the first fixing unit 20 or the first load cell 42 in FIG. The second fixing portion 90 is a specific example of the second fixing portion 30 in FIG. The first arm 46 and the second arm 56 are specific examples of the first connection member 41 and the second connection member 51 in FIG. 1, respectively.

  In the holding device 15, a case 49 is attached between the first fixing portion 80 and the first arm 46 in the longitudinal direction of the test piece 60.

  The first arm 46 includes a longitudinal extending portion 46 a extending in the longitudinal direction of the test piece 60 and a case support portion 46 b extending in the orthogonal direction of the test piece 60. The longitudinally extending portion 46a of the first arm 46 and the case support portion 46b are integrally formed.

  The longitudinally extending portion 46 a is connected to the column portion 43 a of the second load cell 43 on one side in the longitudinal direction of the test piece 60. In the longitudinally extending portion 46a, the other side in the longitudinal direction of the test piece 60 is connected to one side in the orthogonal direction of the test piece 60 in the case support portion 46b.

  The case support portion 46 b has a recess 46 c that opens toward the first fixing portion 80 on the other side of the test piece 60 in the orthogonal direction. A load cell storage recess 46d that opens toward the recess 46c is provided in the recess 46c of the case support 46b. Further, a through hole 46e is provided in the case support 46b so as to penetrate the case support 46b and connect to the load cell storage recess 46d.

  The case 49 is formed in a rectangular parallelepiped shape, and has four side surfaces 49a, 49b, 49c, and 49d as viewed from above. The side surfaces 49 a and 49 b of the case 49 are side surfaces extending in parallel with the longitudinal direction of the test piece 60, and the side surfaces 49 c and 49 d are side surfaces extending in parallel with the orthogonal direction of the test piece 60. The case 49 is attached to the case support portion 46b of the first fixing portion 80 such that the side surfaces 49a, 49b, and 49c are in contact with the case support portion 46b and the side surface 49d is opposed to the first fixing portion 80. In the case 49, a through hole 49f is formed in a side surface 49d facing the first fixing portion 80.

  The side surface 49c has a load cell storage recess 49e at a position facing the opening of the load cell storage recess 46d of the case support 46b. The through hole 49f is connected to the load cell accommodating recess 49e. The load cell accommodating recess 49e of the case 49 forms a space in which the first load cell 47 is accommodated together with the load cell accommodating recess 46d of the case support 46b. The first load cell 47 is housed in this space, and the first arm 46 is inserted by a bolt 47a or a bolt 47b inserted into a through hole 46e formed in the case support 46b and a through hole 49f formed in the case 49, respectively. Fixed to.

  Since the case 49 is supported by the case support portion 46 b of the first arm 46 on the three sides 49 a, 49 b, and 49 c, the case 49 is not displaced relative to the first arm 46 in the orthogonal direction of the test piece 60. Therefore, even if stress in the orthogonal direction is applied to the test piece 60, a bending load is generated in the load cell accommodating recess 46d of the case support 46b and the first load cell 47 accommodated in the load cell accommodating recess 49e of the case 49. Without this, the durability of the first load cell 47 can be improved.

  The second arm 56 extends in the longitudinal direction of the test piece 60, and one longitudinal side of the test piece 60 is connected to the second drive unit 50, and the test piece 60 of the longitudinal extension portion 56 a. And a fixing portion support portion 56b extending in the orthogonal direction of the test piece 60. The longitudinal direction extending portion 56a and the fixed portion support portion 56b are integrally formed. A second fixing portion 90 is fixed to the fixing portion support portion 56b on the longitudinal direction side of the test piece 60.

  The first fixed portion 80 of the first moving body 16 and the second fixed portion 90 of the second moving body 17 are relatively displaced in the longitudinal direction of the test piece 60 by the first driving portion 40, and the second driving portion 50. As a result, the test piece 60 is relatively displaced in the orthogonal direction.

  Next, the structure of the 1st fixing | fixed part 80 of the 1st moving body 16 is demonstrated using FIGS. 2-5. FIG. 3 is a perspective view of the first fixing portion of the holding device shown in FIG. 2. FIG. 4 is a plan view of the first base member. 5 is a cross-sectional view taken along line VV in FIG. In the following, the longitudinal direction of the test piece 60 (arrow A direction) and the orthogonal direction of the test piece 60 (arrow B) based on the state in which the test piece 60 is held by the first fixing portion 80 and the second fixing portion 90. Each component of the first fixing unit 80 will be described with reference to (direction). 2 to 4, the longitudinal direction of the test piece 60 is shown as an arrow A direction, and the orthogonal direction of the test piece 60 is shown as an arrow B direction.

  The first fixing portion 80 includes a first base member 25, a first insertion member 27, and a pair of first slide members 28.

  As shown in FIGS. 3 to 5, the first base member 25 has a shape in which a concave portion having a V-shaped cross section is formed on the upper surface of a rectangular parallelepiped member as a whole. Specifically, the first base member 25 includes a substantially rectangular base portion 25a as viewed from above, a pair of plate-like front walls 25c positioned on one end side of the base portion 25a in the longitudinal direction of the test piece 60, and a test. And a plate-like rear wall 25e located on the other end side of the base portion 25a in the longitudinal direction of the piece 60. The base 25a, the front wall 25c, and the rear wall 25e are integrally formed.

  As shown in FIG. 5, the base 25 a has an upper surface 25 b that is recessed in a V shape when viewed from the longitudinal direction of the test piece 60. That is, the base portion 25a has the largest height dimension at both end portions in the orthogonal direction of the test piece 60 and the smallest height at the center portion. As a result, a concave portion having a V-shaped cross section is formed on the upper surface 25b of the first base member 25 as described above. A pair of first slide members 28 is placed on the upper surface 25b of the base portion 25a. The inclination angle of the upper surface 25b of the base portion 25a with respect to the horizontal plane can be 45 °, for example. In order to allow the pair of first slide members 28 to move in the orthogonal direction of the test piece 60 on the upper surface 25b, the inclination angle is less than 90 °. The inclination angle is preferably as small as possible.

  A gap 25d extending in the vertical direction is provided between the pair of front walls 25c. In the pair of front walls 25c, a pair of first step fixing portions 22 are formed at end portions located on the gap 25d side. A pair of 1st level | step difference fixing | fixed part 22 is formed by notching the base 25a side of the said edge part in a pair of front wall 25c. The pair of first step fixing portions 22 sandwich the test piece 60 positioned in the gap 25d in the orthogonal direction in a state where the test piece 60 is disposed in the first fixing portion 80 as shown in FIG. Positioned on. Specifically, the pair of first step fixing portions 22 includes a first orthogonal direction fixing portion 23 (to be described later) and a test piece 60 arranged in the first fixing portion 80 as shown in FIG. The test piece 60 is positioned so as to be in contact with the step 65 on the holding portion 62 side. A stage 29 is disposed in a gap 25d located between the pair of front walls 25c. The stage 29 will be described later.

  On the rear wall 25e, a gap 25f is formed at the center of the test piece 60 in the orthogonal direction. Specifically, the gap 25f is formed to extend from the upper end of the rear wall 25e to a substantially central portion in the vertical direction of the rear wall 25e. A first end fixing portion 21 described below is inserted into the gap 25f.

  The first insertion member 27 is a member having a T shape as viewed from above. The first insertion member 27 includes a plate-like stable portion 27a extending in the orthogonal direction of the test piece 60, and a first end fixing portion 21 extending in the longitudinal direction of the test piece 60 from the longitudinal central portion of the stable portion 27a. . The first end fixing portion 21 is inserted into a gap 25f provided in the rear wall 25e. Thereby, the first end fixing portion 21 comes into contact with the end portion in the longitudinal direction of the test piece 60 in a state where the test piece 60 is disposed in the first fixing portion 80 as shown in FIG. Positioned on. The stable portion 27a is fixed to the rear wall 25e by a bolt (not shown). Accordingly, the first end fixing portion 21 is also fixed at a position in contact with the end portion in the longitudinal direction of the test piece 60.

  Therefore, in the first fixing portion 80 of the present embodiment, the first end fixing portion 21 can be fixed at a position in contact with the end portion in the longitudinal direction of the test piece 60 according to the size of the test piece 60. it can. As described above, since the pair of first step fixing portions 22 are in contact with the step 65 on the holding portion 62 side of the test piece 60, the first end fixing portion 21 and the pair of first step fixing portions 22 Thus, the holding portion 62 of the test piece 60 can be held from both sides in the longitudinal direction of the test piece 60 without being deformed. In addition, as described above, the first end fixing portion 21 is inserted into the gap 25f provided in the rear wall 25e, so that the first end fixing portion 21 and the pair of paired portions are independent of the size of the test piece 60. The holding part 62 of the test piece 60 can be held by the first step fixing part 22.

  The pair of first slide members 28 is a prismatic member having a trapezoidal cross section perpendicular to the axis and extending along the axis. Each of the pair of first slide members 28 has a first orthogonal direction fixing portion 23 protruding in the axial direction on one of the end faces in the axial direction. The pair of first slide members 28 are placed on the upper surface 25 b of the base portion 25 a so that the axial direction is the longitudinal direction of the test piece 60. Thereby, as for a pair of 1st slide member 28, the movement in the longitudinal direction of the test piece 60 is controlled by the front wall 25c and the rear wall 25e. In the pair of first slide members 28, the first orthogonal direction fixing portion 23 is positioned within the first step fixing portion 22 of the front wall 25 c, thereby restricting movement of the test piece 60 in the orthogonal direction. As shown in FIG. 2B, the pair of first slide members 28 has the test piece 60 disposed in the first fixing portion 80, and the first orthogonal direction fixing portion 23 holds the holding portion 62 of the test piece 60. The test piece 60 is sandwiched from both sides in the orthogonal direction, and is arranged so that the first orthogonal direction fixing portion 23 is in contact with the first step fixing portion 22. The pair of first slide members 28 are respectively fixed to the base portion 25 a of the first base member 25 by bolts 24.

  Therefore, in the first fixing portion 80 of the present embodiment, the first orthogonal direction fixing portion 23 is arranged on both sides in the orthogonal direction of the test piece 60 with respect to the holding portion 62 of the test piece 60 according to the size of the test piece 60. It can fix to the position which touches from. That is, the pair of first step fixing portions 22 can be held from both sides in the orthogonal direction of the test piece 60 without deforming the holding portion 62 of the test piece 60.

  The second fixing unit 90 also has the same configuration as the first fixing unit 80. Specifically, the second fixing portion 90 includes the second end fixing portion 31, the second step fixing portion 32, the second orthogonal direction fixing portion 33, the bolt 34, the second base member 35, the base portion 35a, and the base upper surface 35b. A front wall 35c, a front wall gap 35d, a rear wall 35e, a rear wall gap 35f, a second insertion member 37, a stabilizing portion 37a, and a second slide member 38. These members of the second fixing portion 90 include the first end fixing portion 21, the first step fixing portion 22, the first orthogonal direction fixing portion 23, the bolt 24, and the first base member 25 of the first fixing portion 80, respectively. , The base 25a, the base upper surface 25b, the front wall 25c, the front wall gap 25d, the rear wall 25e, the rear wall gap 25f, the first insertion member 27, the stabilizing portion 27a, and the first slide member 28. . Note that the second base member 35 may be formed integrally with the second arm 56.

  As described above, the stage 29 is disposed in the gap 25d between the pair of front walls 25c. The stage 29 is disposed so as to be positioned also in the gap 35d between the pair of front walls 35c. That is, the stage 29 is positioned in the gap 25d and the gap 35d. A test piece 60 is placed on the stage 29.

  As described above, the first insertion member 27 and the pair of first slide members 28 are movable with respect to the first base member 25. The first insertion member 27 is fixed to the first base member 25 by bolts (not shown), and the pair of first slide members 28 are fixed to the first base member 25 by bolts 24. The second insertion member 37 and the pair of second slide members 38 are movable with respect to the second base member 35. The second insertion member 37 is fixed to the second base member 35 by bolts (not shown), and the pair of second slide members 38 are fixed to the second base member 35 by bolts 34. Therefore, the first end fixing portion 21, the pair of first step fixing portions 22, and the pair of first orthogonal direction fixing portions 23 are fixed at positions where they contact the holding portion 62 of the test piece 60, and the second end fixing. The part 31, the pair of second step fixing parts 32, and the pair of second orthogonal direction fixing parts 33 can be fixed at positions where they contact the holding part 63 of the test piece 60. Therefore, it is possible to hold a small test piece having a side length of several millimeters without deforming the holding portion. As an example of a test piece having a size applicable to the holding device shown in FIG. 2, the length of the test piece having the shape shown in FIG. 6 to be described later is 3 mm in length, the width in the orthogonal direction of the test piece is 2 mm, and thick. The thing which set the thickness to 0.3 mm is mentioned.

3. Test Method Using Test Specimen Holding Device As shown in FIG. 2, the first fixing unit 80 is configured such that one of the pair of holding units 62 and 63 of the test piece 60 is moved in the longitudinal direction of the test piece 60. It is held from both sides and both sides of the test piece 60 in the orthogonal direction, that is, from four directions. Similarly, the second fixing portion 90 holds the other holding portion 63 from four directions. As described above, the holding device 15 holds the holding parts 62 and 63 from the four directions by the first fixing part 80 and the second fixing part 90. Therefore, in a state where the test piece 60 is held using the holding device 15, the first driving unit 40 tests the first fixing unit 80 of the first moving body 16 and the second fixing unit 90 of the second moving body 17. By relatively displacing in the longitudinal direction of the piece 60, tensile stress or compressive stress can be applied to the test portion 61 of the test piece 60. In the test piece holding device 15 according to the present embodiment, since the shearing stress and the tensile stress or the compressive stress can be applied in a state where the test portion 61 of the test piece 60 is exposed, the test portion 61 after the stress is applied is provided. It can be easily observed.

  The first fixing portion 80 and the second fixing portion 90 are displaced relatively and periodically in the longitudinal direction of the test piece 60, and tensile stress or compressive stress is repeatedly applied to the test portion 61 as a repeated stress. A fatigue test by compressive stress can be performed. An example of the cyclic stress applied in the fatigue test is a double-swing stress. The swing stress is a stress that alternately changes between a positive maximum value and a negative minimum value, which have the same absolute value, when the tensile stress is positive and the compressive stress is negative. A value obtained by dividing the minimum value of the stress by the maximum value of the stress is referred to as a minimum / maximum stress ratio R, and R = −1 in the double swing stress. The repeated stress applied in the fatigue test is not limited to the double swing stress, but may be a partial swing stress, a single swing stress, a partial single swing stress, or the like.

  In addition, the second driving unit 50 relatively displaces the second fixing unit 90 of the second moving body 17 and the first fixing unit 80 of the first moving body 16 in the orthogonal direction of the test piece 60, whereby the test unit A shear stress can be applied to 61. The holding device 15 holds the holding portions 62 and 63 from four directions by the first moving body 16 and the second moving body 17, and therefore rotates the holding portions 62 and 63 when applying shear stress to the test portion 61. It can be moved without Therefore, the deformation of the test unit 61 does not include a bending component, a tensile component, or the like, and it is possible to evaluate the shear characteristics with high accuracy.

  A fatigue test using a shear stress can be performed by periodically displacing the first fixing portion 80 and the second fixing portion 90 in the orthogonal direction of the test piece 60 and applying a shear stress to the test portion 61 as a repeated stress. it can. The repeated stress of the shear stress is also classified into a double swing stress, a partial swing stress, a single swing stress, and a partial single swing stress according to the change in the stress. The definition of the cyclic stress when the one direction of the shear stress is positive and the opposite direction of the one direction is negative is the same as the case of the tensile / compressive stress.

  Further, the first fixing unit 80 and the second fixing unit 90 are relatively displaced in the longitudinal direction of the test piece 60 and tensile stress or compressive stress is applied to the test unit 61. By relatively displacing the fixing portion 90 in the orthogonal direction of the test piece 60, a shear stress can be applied to the test portion 61. Thus, the test which simulated the load form in an actual structure can be performed by giving a shear stress, giving a tensile stress or a compressive stress.

  In addition, the first fixing part 80 and the second fixing part 90 are relatively displaced in the longitudinal direction of the test piece 60 and tensile stress or compressive stress is applied to the test part 61. By cyclically displacing the second fixed part 90 in the orthogonal direction of the test piece 60, shear stress can be applied to the test part 61 as repeated stress. Further, the first fixing unit 80 and the second fixing unit 90 are relatively and periodically displaced in the longitudinal direction of the test piece 60, and are also periodically displaced in the orthogonal direction of the test piece 60, whereby the test unit It is also possible to apply tensile / compressive stress and shear stress to 61 as repetitive stresses. Therefore, by using the holding device 15 described above, a fatigue test simulating a load form to which various repeated stresses are applied can be performed.

4). FIG. 6 is a plan view of a test piece suitable for the test method according to the embodiment of the present invention. As described with reference to FIG. 1B, the test piece 60 shown in FIG. 6 is arranged between a pair of holding parts 62 and 63 arranged at both ends in the longitudinal direction and the holding parts 62 and 63. And a test unit 61. The holding parts 62, 63 protrude in the orthogonal direction of the test piece 60 and form a step 65 with respect to the test part 61.

  Furthermore, as shown in FIG. 6, the test unit 61 has R portions 61 a at both ends connected to the holding units 62 and 63. In the test part 61, an arc part 61 b is formed at the center part in the longitudinal direction of the test piece 60. The arc portion 61 b is formed such that the width dimension of the test portion 61 is smallest at the center portion in the longitudinal direction of the test piece 60. The radius of curvature of the arc portion 61b is larger than the radius of curvature of the R portion 61a.

  In the test method according to the embodiment of the present invention, as described above, it is preferable to use a test piece having a shape in which the test portion 61 includes the R portion 61a and the arc portion 61b. The reason is as follows. When stress is applied to the test piece 60 by the R portion 61a, stress concentration at the connection portion between the test portion 61 and the holding portions 62 and 63 can be suppressed, and the failure of the test piece to break at this connection portion can be prevented. Can be reduced. When stress is applied to the test piece 60 by the arc portion 61b, the possibility of deformation due to yielding occurring in the central portion in the longitudinal direction of the test piece 60 of the test portion 61 becomes very high, and the same position for a plurality of test pieces Can be used to evaluate deformation. Therefore, it is possible to perform highly accurate evaluation with a high yield.

  FIG. 7 is a configuration diagram of a test piece suitable for a fatigue test among the test methods according to the embodiment of the present invention. FIG. 7 (a) shows a plan view and FIG. 7 (b) shows a side view. . A test piece 70 shown in FIG. 7 has a pair of holding portions 72 and 73 located at both ends in the longitudinal direction, and a test portion 71 provided between the holding portions 72 and 73. The holding parts 72 and 73 protrude in the orthogonal direction of the test piece 70 and form a step 75 with respect to the test part 71.

  Further, as shown in FIG. 7, the test unit 71 has R parts 71 a at both ends connected to the holding parts 72 and 73, and a parallel part 71 c having a uniform width W between the R parts 71 a. The parallel portion 71 c is formed with a notch 71 b in the center portion in the longitudinal direction of the test piece 70. The notch 71b is provided so as to extend in the orthogonal direction of the test piece 70, and its cross section has an arc shape. Therefore, the thickness dimension of the test part 71 is the smallest at the center part in the longitudinal direction of the test piece 70, that is, the bottom part of the notch 71b. The other surface in the thickness direction of the test piece 70 is flat. Further, the thickness t of the test piece 70 at the bottom of the notch 71b is ½ or less of the maximum thickness dimension h of the test portion 71, and the radius of curvature of the arc constituting the cross section of the notch 71b is the radius of curvature of the R portion 71a. Therefore, when tensile stress, compressive stress, or shear stress is applied to the test piece 70, the bottom of the notch 71b becomes a stress concentration portion. As described above, when a shear fatigue test is performed using the test piece 70, a fatigue crack is generated at the bottom of the notch 71b. Therefore, the fatigue crack can be evaluated at the same position for a plurality of test pieces. Therefore, evaluation can be performed with a high yield.

The cross-sectional area (W × t) at the bottom of the notch 71b of the test piece 70 is preferably 0.05 mm ² or more. By setting the cross-sectional area at the bottom of the notch 71b to 0.05 mm ² or more, a sufficiently large stress can be applied during the fatigue test, and highly accurate measurement can be performed. The cross-sectional area at the bottom of the notch 71b is more preferably 0.075 mm ² or more.

  In the parallel part 71c, it is preferable that the relationship between the width W and the length L in the longitudinal direction of the test piece 70 satisfies W> L. In this case, since the shear stress acts larger than the bending stress during the shear fatigue test, the central portion in the width direction of the bottom of the notch 71b becomes the stress concentration portion. Since the fatigue crack is generated at this stress concentration portion, it is possible to perform evaluation with higher yield. The reason why W> L is preferable will be described below.

When the shearing force P in the orthogonal direction of the test piece 70 is applied to the holding portion 73 of the test piece 70, the maximum shear stress τ _max generated in the cross section including the bottom of the notch 71b is expressed by the following equation (i).
τ _max = (3/2) × (P / tW) (i)
Further, in this case, the maximum value σ _{max of the} stress generated on the boundary surface between the R portion 71a and the parallel portion 71c on the holding portion 73 side is set to L in the longitudinal direction of the test piece 70 of the parallel portion 71c. Assuming the bending stress of the surface, it is expressed by the following equation (ii).
^{_{σ max ≒ (PL × W /}} 2) / (hW 3/12) = 6PL / hW 2 ... (ii)

Here, assuming that the fracture law of the test piece 70 follows the misses stress, when the following equation (iii) holds, the misses stress in the cross section including the bottom of the notch 71b is the R portion 71a on the holding portion 73 side and the parallel portion 71c. It becomes more than the misses stress at the boundary surface. That is, the shear stress acts more than the bending stress. In this case, the test piece 70 is broken at the bottom of the notch 71b.
τ _max ≧ σ _max / 3 ^1/2 (iii)

Here, as described above, the thickness t of the test piece 70 at the bottom of the notch 71b is equal to or less than ½ of the maximum thickness dimension h of the test piece 70, that is, h / 2 ≧ t. The following formula (iv) is obtained from h / 2 ≧ t and the formulas (i) to (iii), and the formula (v) is further obtained from the formula (iv). From the equation (v), it is understood that W> L is preferable.
h / 2 ≧ (3 ^1/2 / 2) × (hW / L) ≧ t (iv)
W / L ≧ 2/3 ^1/2 ≈1 (v)

  FIG. 8 is a diagram showing the result of analyzing the test piece 70 by a finite element method (FEM) in terms of stress distribution. As a result of the analysis by FEM, in the test piece 70, the stress is concentrated at the bottom of the notch 71b in both cases where shear stress is applied and tensile / compressive stress is applied as shown in FIG. Was confirmed to occur. When shear stress is applied, maximum stress is generated particularly at the center in the width direction of the bottom of the notch 71b. The notch 71b may be provided on only one of the surfaces in the thickness direction of the test piece 70, or may be provided on both.

  It is preferable that both the test piece 60 and the test piece 70 are pickled and then used for the test. This is for removing a surface layer such as an electric discharge machining layer or a residual stress layer formed on the surface when a test piece is produced by electric discharge machining, for example.

  In order to verify the effect of the configuration of the embodiment as described above, a static shear test was performed to evaluate the accuracy.

  The static shear test was performed using a test piece holding device shown in FIG. The test material was collected from the HAZ part in the spot welded part of a 590 MPa class high-tensile steel plate. The chemical composition of the test material was as shown in Table 1.

  The test piece was cut out from this specimen into the shape shown in FIG. The test piece had a length in the longitudinal direction (arrow A direction) of 3 mm, a width in the orthogonal direction (arrow B direction) of 2 mm, and a thickness of 0.3 mm. Moreover, the width of the test part of the test piece was 0.3 mm at the narrowest part. The test speed was 1 μm / min.

  FIG. 9 is a nominal shear stress-stroke diagram obtained in the static shear test. As shown in FIG. 9, the nominal shear stress-stroke diagram was a shape having two shelves, and the stress at the bending point of each shelf was 50 MPa and 400 MPa in order from the smallest. The bending point of 50 MPa is considered to be generated due to the play generated in the first fixing portion and the second fixing portion of the holding device, and the bending point of 400 MPa is considered to be generated due to the yield of the test piece. That is, it can be said that the shear yield stress of the specimen measured by a static shear test using the test piece holding device of the present invention was 400 MPa.

  As a comparative test, a tensile test using the same specimen was performed. The tensile test was also performed using the specimen holding device shown in FIG. As shown in FIG. 10, the test piece had the same shape as the test piece shown in FIG. FIG. 10 also shows the dimensions of the test piece. The test speed was 1 μm / min.

  The tensile strength and tensile yield stress measured by the comparative test were as shown in Table 2. Table 2 also shows the shear strength and shear yield stress estimated from the Tresca stress.

  As shown in Table 2, the shear yield stress estimated from the results of the tensile test was 426 MPa. This value was equivalent to the yield stress (400 MPa) measured by the static shear test using the specimen holding device of the present invention. Therefore, it became clear that the yield stress can be evaluated from the nominal shear stress measured for a minute test piece using the holding device of the present invention.

  FIG. 11 is a photograph of the appearance of the test piece and the surrounding holding device before and after applying shear stress, FIG. 11 (a) shows the state before applying shear stress, and FIG. 11 (b) shows after applying shear stress. Shows the state. From FIG. 11, it can be seen that the shape of the holding part of the test piece is hardly changed, and that the deformation is concentrated on the arc part of the test part of the test piece. That is, according to the holding device of the present invention, it can be seen that the evaluation of the material properties on the submillimeter order can be performed stably.

  FIG. 12 is a photograph of the arc part of the test part of the test piece before and after applying shear stress, FIG. 12 (a) shows the state before applying shear stress, and FIG. 12 (b) shows the state after applying shear stress. Indicates. The test piece in the photograph is in a state where the surface is electropolished. Comparing FIG. 12A and FIG. 12B, it can be confirmed that a large number of slip bands are generated in parallel to the direction in which shear stress is applied (horizontal direction in the figure). From FIG. 12, it can be seen that by using the holding device of the present invention and using the test piece having the shape shown in FIG. 6, stress can be reliably applied to the arc portion of the test portion of the test piece.

  Furthermore, in order to demonstrate the effect of the configuration of the embodiment as described above, a shear fatigue test was performed to evaluate the influence of the axial force load on the shear fatigue characteristics.

  The shear fatigue test was performed using a test piece holding device shown in FIG. The specimen was taken from a hot rolled material of ultra low carbon steel. The chemical composition of the test material was as shown in Table 3, and the average crystal grain size was 31 μm. Moreover, the measurement result by the electron beam backscattering diffraction method (Electron Back-Scatter Diffraction, EBSD) about a test material was as showing in FIG. In FIG. 13, the crystal orientation in the normal direction of the rolled surface is shown in different colors according to the lower left reverse pole figure color key. In addition, although the measurement result by EBSD is originally displayed in color, it was displayed in black and white due to restrictions on the drawing.

  The test piece was cut out from this specimen into the shape shown in FIG. The test piece had a length in the longitudinal direction (arrow A direction) of 2.4 mm, a width in the orthogonal direction (arrow B direction) of 1.8 mm, and a thickness of 0.3 mm. Moreover, the test part of the test piece made thickness at the notch bottom part smaller than the width | variety of an orthogonal direction. The radius of curvature of the arc constituting the notch cross section was made smaller than the radius of curvature of the R portion between the holding portion and the test portion.

  The shear fatigue test was performed in a state where an axial force (tensile stress or compressive stress) was applied and a state where no axial force was applied. The magnitude of the axial force was 150 MPa for both tensile stress and compressive stress. The shear stress was a swing stress.

  FIG. 14 is a diagram (SN diagram) showing the relationship between the number of repetitions of fracture and the stress amplitude obtained by the shear fatigue test. The shear fatigue limit was 144 MPa when no axial force was applied, and ± 20 MPa when no axial force was applied when the axial force was applied. When tensile stress was applied, a tendency to decrease the life was observed, and when compressive stress was applied, a tendency to improve the life was observed.

  As a comparative test, a tensile test and a tensile / compression fatigue test using the same specimen were performed. These comparative tests were also performed using the test piece holding device shown in FIG. The test speed of the tensile test was 1 μm / s. In the tensile / compression fatigue test, a swing stress was applied to the test piece.

Table 4 shows the tensile strength, tensile yield stress, yield ratio, and fatigue limit (σ _W0 ) measured by the comparative test. FIG. 15 is an SN diagram obtained by a tensile / compression fatigue test.

As described above, the influence of the axial force on the shear fatigue test was ± about 20 MPa. Further, the shear fatigue limit (τ _W0 ) calculated from the fatigue limit (σ _W0 ) obtained by the comparative test is τ _W0 = σ _W0 × 3 ^−0.5 = 92 MPa. That is, the influence of the axial force on the shear fatigue was ± about 20% with respect to τ _W0 .

FIG. 16 is a photomicrograph of the fracture surface of a test piece that was subjected to a shear fatigue test at a stress amplitude of 120 MPa while applying a tensile stress, and fractured at a fracture repetition number of 2.31 × 10 ⁵ . From FIG. 16, it can be estimated that the starting point of fatigue failure is a crack generated at the center in the width direction of the bottom of the notch, and this crack has progressed to a semi-elliptical shape. From FIG. 16, it can be seen that by holding the test piece having the shape shown in FIG. 7 by the holding device of the present invention, stress can be reliably concentrated on the notch bottom of the test part of the test piece in the shear fatigue test.

  The test piece holding apparatus according to the present invention can be applied to a test apparatus capable of applying tensile stress or compressive stress while applying shear stress without causing deformation of a small test piece.

10, 15 Holding device 20 First fixing portion 21 First end fixing portion (end fixing portion)
22 First step fixing part (step fixing part)
23 First orthogonal direction fixing part 30 Second fixing part 31 Second end fixing part (end fixing part)
32 Second step fixing part (step fixing part)
33 2nd orthogonal direction fixing | fixed part 40 1st drive part (stretching direction drive part)
50 Second drive unit (orthogonal direction drive unit)
60, 70 Test piece 61, 71 Test part 61a, 71a R part 61b Arc part 71b Notch 71c Parallel part 62, 72 One holding part 63, 73 Other holding part 65, 75 Step 80 First fixing part 90 Second fixing Part A Stretch direction of test part (longitudinal direction of test piece)
B Direction perpendicular to the stretching direction of the test part (orthogonal direction of the test piece)
C Connection part of holding part with test part

Claims (7)

A pair of test portions extending in one direction and provided at both ends of the test portion in the extending direction so as to protrude in a direction perpendicular to the extending direction of the test portion and to form a step with respect to the test portion. An apparatus for holding a test piece having a holding part,
A first fixing portion that holds one of the pair of holding portions;
A second fixing portion that holds the other of the pair of holding portions;
The first fixing part is
A first stretching direction fixing portion that holds the one holding portion from both sides in the stretching direction;
A first orthogonal direction fixing part that holds the one holding part from both sides in the orthogonal direction;
The second fixing part is
A second stretching direction fixing portion that holds the other holding portion from both sides in the stretching direction;
Have a second orthogonal direction fixing portion for holding the other holding portion from both sides of the perpendicular direction,
The first fixing part holds a part other than a connection part with the test part in the one holding part,
The second fixing portion holds a portion other than a connection portion with the test portion in the other holding portion.
Test piece holding device. The specimen holding device according to claim 1,
The first extending direction fixing portion and the second extending direction fixing portion are respectively an end fixing portion that holds at least a part of an end portion in the extending direction of the test piece, and at least one of the steps of the test piece. A test piece holding device having a step fixing part for holding the part. The specimen holding device according to claim 1 or 2 ,
At least one of the first fixing part and the second fixing part is connected to an extension direction driving part that relatively displaces the first fixing part and the second fixing part in the extension direction;
At least one of the first fixing part and the second fixing part is connected to an orthogonal direction driving part that relatively displaces the first fixing part and the second fixing part in the orthogonal direction. Holding device. A test method using the specimen holding device according to any one of claims 1 to 3 ,
A test method in which a shear stress is applied to the test portion of the test piece by relatively displacing the first fixing portion and the second fixing portion in the orthogonal direction. The test method according to claim 4 , wherein
Applying tensile stress or compressive stress to the test portion by relatively displacing the first fixing portion and the second fixing portion in the stretching direction,
In a state where tensile stress or compressive stress is applied to the test portion, shear stress is applied to the test portion by relatively displacing the first fixed portion and the second fixed portion in the orthogonal direction. Test method. The test method according to claim 4 or 5 ,
The test piece is
The test part has R parts at both ends connected to the pair of holding parts,
In a plan view, an arc portion having a larger radius of curvature than the R portion is formed in the central portion of the test portion in the extending direction so that the width dimension of the test portion is the smallest in the central portion. Test method. The test method according to claim 4 or 5 ,
The test piece is
The test part has R parts at both ends connected to the pair of holding parts,
In the central part of the test part in the extending direction, from the R part, the thickness dimension of the test part is the smallest in the central part and is ½ or less of the maximum thickness dimension of the test part. A test method in which an arc-shaped notch with a small curvature radius is formed.