JP6657724B2 - Test pieces - Google Patents

Description

  The present invention relates to a test piece used for a three-point bending or four-point bending corrosion test.

  Conventionally, a four-point bending corrosion test or a three-point bending corrosion test has been performed to evaluate the corrosion resistance of steel materials. For example, Japanese Patent Application Laid-Open No. H11-50148 (Patent Document 1) describes that a sulfide corrosion cracking resistance (SSC resistance) is evaluated by a four-point bending test.

The four-point bending corrosion test is performed using a jig as shown in FIG. The jig shown in FIG. 1 includes a support 9b that supports the two rollers 8a that contact the upper surface of the test piece SJ from above, and a weight member 9a that supports the two rollers 8b that contact the lower surface of the test piece SJ from below. A vertical bending load is applied to the test piece SJ. The test piece SJ subjected to the bending load in this manner is exposed to a corrosion solution (H ₂ S solution) for 720 hours, and the presence or absence of a crack is examined.

  In the corrosion test, the load applied to the test piece SJ is controlled. As one of the methods for setting the applied load, as shown in FIG. 2 or FIG. 3, a strain gauge 21 is attached to the test piece SJ. Until the detection value of the strain gauge 21 reaches a predetermined strain (for example, a strain corresponding to 100% yield strength (YS) of the target material), a load is applied to the test piece SJ to bend. In FIG. 2, the strain gauge 21 is attached to the longitudinal center of the test piece SJ. This configuration is applied when the test piece SJ does not include a welded portion, for example, when the test piece is a test piece collected from a base material portion of a steel pipe. In FIG. 3, the strain gauges 21 are attached to both sides of the weld metal SJw at the center of the test piece SJ. This configuration is applied when the test piece SJ includes a weld metal, for example, when the test piece SJ is a test piece collected from a weld joint.

  4 and 5 are diagrams for explaining the shape of the test piece SJ. The test piece SJ1 shown in FIG. 4 is a rectangular parallelepiped and is called a smooth test piece. In the test piece SJ2 shown in FIG. 5, a part of the inner surface SJs of the steel pipe 80 as the target material is directly used as one surface of the test piece, and is referred to as an inner surface As test piece.

  In the above four-point bending corrosion test, the presence or absence of crack generation near the center of the test piece SJ is evaluated. When the strain on the surface of the test piece SJ to which the load is applied is not uniform, a crack may be generated at a position away from the center of the test piece SJ. If a crack occurs at a position distant from the center, it is difficult to properly evaluate. This problem can occur in a three-point bending corrosion test as well.

  Japanese Patent Application Laid-Open No. 2004-279083 (Patent Document 2) discloses a slenderness ratio of a test piece and a jig for supporting the test piece in a bending test in which an axial compressive load is applied to a FRP test piece to bend and deform and break. Have been. According to the test method using these test pieces and jigs, the bending strength and the like of the FRP plate can be measured with high accuracy.

JP-A-11-50148 JP-A-2004-279083

  In the above-mentioned Japanese Patent Application Laid-Open No. 2004-279083, in a test in which an axial compressive load is applied to a test piece of FRP, although there is disclosure about the slenderness ratio of the test piece to obtain high measurement accuracy, in a three-point or four-point bending corrosion test, There is no disclosure about the structure of a test piece for more appropriate evaluation. On the other hand, in the three-point or four-point bending corrosion test, in order to perform proper evaluation at low cost, it is preferable that the strain on the load surface of the test piece be uniform while suppressing the magnitude of the load. It has been recognized by the inventors.

  Therefore, the present application discloses a test piece that can make the strain on the load surface of the test piece closer to uniform while suppressing a required load in a three-point bending or four-point bending corrosion test.

  The test piece in the embodiment of the present invention is a test piece used for a three-point bending or four-point bending corrosion test. The test piece includes a ceiling, a bottom, a pair of side walls, and a partition wall. The ceiling has a first load surface to which a load is applied from above in the three-point bending or four-point bending corrosion test, and extends in a longitudinal direction of the test piece. The bottom has a second load surface on which a load is applied from below in the three-point bending or four-point bending corrosion test, and faces the ceiling. The pair of side walls are formed between both ends in a direction perpendicular to the longitudinal direction of the ceiling and both ends in a direction perpendicular to the longitudinal direction of the bottom, and face each other. The partition wall is formed from the ceiling to the bottom between the pair of side walls. A space surrounded by the ceiling, the bottom, the pair of side walls, and the partition wall forms a plurality of through holes penetrating the test piece in a longitudinal direction. When viewed from the longitudinal direction of the test piece, the shapes of the plurality of through holes are line-symmetric with respect to the vertical axis.

  According to the disclosure of the present application, it is possible to provide a test piece that can make the strain on the load surface of the test piece nearly uniform while suppressing a required load in a three-point bending or four-point bending corrosion test.

FIG. 1 is a diagram showing a jig used for a four-point bending corrosion test. FIG. 2 is a diagram showing a state where a strain gauge is attached to a test piece. FIG. 3 is a diagram showing a state where a strain gauge is attached to a test piece. FIG. 4 is a diagram for explaining the shape of the test piece. FIG. 5 is a diagram for explaining the shape of the test piece. FIG. 6 is a diagram showing an analysis model in the simulation. FIG. 7 is a diagram illustrating the stress-strain characteristics of the target material used in the simulation. FIG. 8A is a diagram showing a mesh (finite element) on the xy plane of the smooth test piece. FIG. 8B is a diagram showing a mesh (finite element) on the xy plane of the inner surface As test piece. FIG. 9A is a graph showing a strain distribution (solid line) and an actually measured value (circle plot) obtained by FEM analysis of a smooth test piece. FIG. 9B is a graph showing a strain distribution (solid line) and an actually measured value (triangular plot) obtained by FEM analysis of the inner surface As test piece. FIG. 10 is a graph showing a strain distribution obtained as a result of performing FEM analysis while changing the thickness of the inner surface As test piece. FIG. 11A is a cross-sectional view of a test piece according to the embodiment of the present invention. FIG. 11B is a plan view of the test piece shown in FIG. 11A. FIG. 11C is a side view of the test piece shown in FIG. 11A. FIG. 12 is a view showing a modification of the test piece shown in FIG. 11A. FIG. 13A is a diagram showing a cross-sectional shape of a test piece subjected to FEM analysis in the example. FIG. 13B is a diagram illustrating a cross-sectional shape of a test piece on which FEM analysis is performed in Example 1. FIG. 13C is a diagram illustrating a cross-sectional shape of a test piece on which FEM analysis is performed in Example 1. FIG. 14 is a graph showing the required load obtained by the FEM analysis of Example 1. FIG. 15 is a graph showing the strain distribution obtained by the FEM analysis of Example 1. FIG. 16A is a contour diagram showing the distribution of the strain longitudinal component of the test piece in Example 1. FIG. 16B is a contour diagram showing the distribution of the stress longitudinal component of the test piece in Example 1. FIG. 17 is a graph showing the relationship between the height of the through hole and the required load obtained by the FEM analysis of Example 2. FIG. 18 is a graph showing the relationship between the height of the through hole and the strain distribution obtained by the FEM analysis of Example 2. FIG. 19 is a graph showing the relationship between the width of the through hole and the required load obtained by the FEM analysis of Example 2. FIG. 20 is a graph showing the relationship between the width of the through-hole obtained by the FEM analysis of Example 2 and the strain distribution. FIG. 21 is a graph showing the relationship between the ratio of the area of the through hole and the required load, obtained by the FEM analysis of Example 2.

  In the three-point bending corrosion test or the four-point bending corrosion test, as described above, the strain gauge is disposed at the center of the load surface of the test piece. The applied load is set so that the strain at the center of the load surface of the test piece has a predetermined value. Therefore, for proper evaluation, it is preferable to evaluate the presence or absence of cracks near the center of the load surface of the test piece. However, the inventors encountered a case where cracks occurred at the strain measurement position of the test piece, that is, at a position distant from the center of the test piece, particularly near the end of the load surface of the test piece. In such a case, the corrosion resistance performance of the target material may not be properly evaluated.

  In order to investigate the cause of the occurrence of cracks near the end of the test piece, the inventors measured the difference in strain between the vicinity of the center of the load surface of the test piece subjected to the load and the vicinity of the end. The measurement was performed by actual measurement and simulation. In the simulation, FEM analysis for a four-point bending corrosion test was performed using the analysis model shown in FIG.

  In FIG. 6, the longitudinal direction of the test piece SJv is the z direction, the vertical direction of the test piece SJv, that is, the load direction is the y direction, and the direction perpendicular to the z direction and the y direction is the x direction. In the example illustrated in FIG. 6, the center point in the z direction and the x direction of the load surface (evaluation surface) on which a load is applied from above is set as the center point C0 in the test piece SJv. A plane that passes through the symmetric boundary line TKx in the x direction and is parallel to the xy plane is a symmetric boundary surface in the longitudinal direction (z direction) of the test piece SJv. A plane that passes through the z-direction symmetric boundary line TKz and is parallel to the yz plane is a symmetric boundary surface of the test piece SJv in the x direction.

  The rollers 8av and 8bv were rigid models. The size of the test piece SJv was width SW = 10 mm, height SH = 2 mm, and length SL = 75 mm. The shape of the test piece SJv was analyzed in two cases, that is, a smooth test piece and an inner As test piece. The target material of the test piece SJv was a martensitic stainless steel tube (outer diameter 300 mm × wall thickness 15 mm). The stress-strain curve shown in FIG. 7 was used as the data of the stress-strain characteristics of the target material.

  FIG. 8A shows a mesh (finite element) in the xy plane of the smooth test piece. FIG. 8B shows a mesh (finite element) in the xy plane of the inner surface As test piece. 8A and 8B show only the right half of the symmetric boundary surface TSz including the symmetric boundary line TKz.

  FIG. 9A is a graph showing a strain distribution (solid line) and an actually measured value (circle plot) obtained by FEM analysis of a smooth test piece. FIG. 9B is a graph showing a strain distribution (solid line) and an actually measured value (triangular plot) obtained by FEM analysis of the inner surface As test piece. 9A and 9B show positions on a line extending in the x direction through the center point C0 on the load surface of the test piece SJv. As shown in FIG. 9A and FIG. 9B, the analysis result and the measured value are almost the same. Thus, it is considered that the strain distribution can be accurately estimated by the FEM analysis.

  From the results shown in FIGS. 9A and 9B, it was found that the strain was larger near the end of the test piece than at the center of the load surface. It is considered that the cause of the occurrence of cracks near the load surface end of the test piece is that uniform strain is not applied to the load surface of the test piece. That is, since the strain near the end portion is larger than that near the center of the load surface of the test piece, it is considered that a crack is generated near the end portion of the test piece far from the center of the load surface.

  The inventors further studied by a FEM analysis how to reduce the difference in strain between the vicinity of the center and the end of the load surface of the test piece when the load is applied to the test piece in the four-point bending corrosion test. As a result, it was found that the strain difference can be reduced by increasing the thickness of the test piece. FIG. 10 is a graph showing the strain distribution when the thickness (height SH) of the inner surface As test piece was 2 mm, 4 mm, 8 mm, and 10 mm. In this FEM analysis, the target material is a martensitic stainless steel pipe (outer diameter 220 mm × wall thickness 11 mm). The analysis results shown in FIG. 10 show that by setting the height SH of the inner surface As test piece from 2 mm to 8 mm, the strain ratio near the edge to the strain at the center of the load surface of the test piece was 1.19 to 1. 0.01 can be reduced. On the other hand, when the height SH of the test piece is changed from 2 mm to 10 mm, the required load increases from 436N to 11180N. Thus, the inventors predict the strain difference between the center and the end of the load surface according to the steel pipe size (inner diameter), and can perform a four-point bending corrosion test in a state where the strain difference is not a problem. A method for determining the thickness (height SH) has been found.

  When the height SH of the test piece is increased, the four-point bending load for obtaining a predetermined strain also increases. Then, the inventors repeated further analysis and studied a test piece shape that can reduce the required load. As a result, a plurality of through holes penetrating in the longitudinal direction of the test piece are formed, and the shape of the through hole as viewed from the longitudinal direction of the test piece is made symmetric about the vertical direction, while suppressing the required load, It has been found that the strain on the load surface of the test piece can be made uniform. An embodiment of the invention based on this finding will be described below.

[Embodiment]
11A is a cross-sectional view of the test piece according to the embodiment of the present invention, FIG. 11B is a plan view of the test piece shown in FIG. 11A, and FIG. 11C is a side view of the test piece shown in FIG. 11A.

  The test piece 10 shown in FIGS. 11A to 11C is a test piece used for a three-point bending or four-point bending corrosion test. As shown in FIG. 11A, the test piece 10 includes a ceiling 1, a bottom 2, a pair of side walls 3, and a partition wall 4. The ceiling portion 1 has a first load surface 1a (hereinafter, referred to as a load surface 1a) to which a load is applied from above in a three-point bending or four-point bending corrosion test, and extends in the longitudinal direction (z direction) of the test piece 10. Extend. The bottom 2 has a second load surface 2a (hereinafter, referred to as a load surface 2a) to which a load is applied from below in a three-point bending or four-point bending corrosion test. The bottom 2 faces the ceiling 1. The pair of side walls 3 are formed between both ends in the direction (x direction) perpendicular to the longitudinal direction of the ceiling 1 and both ends in the direction (x direction) perpendicular to the longitudinal direction of the bottom 2. opposite. The partition wall 4 is formed from the ceiling 1 to the bottom 2 between the pair of side walls 3. A space surrounded by the ceiling 1, the bottom 2, the pair of side walls 3, and the partition wall 4 forms a plurality of through holes 5 penetrating the test piece 10 in the longitudinal direction (z direction). When viewed from the longitudinal direction of the test piece 10, the shape of the plurality of through holes 5 is line-symmetric with respect to the axis A in the vertical direction (y direction).

  Since the test piece 10 has the through hole 5 penetrating in the longitudinal direction, the magnitude of the load applied to the test piece 10 in the three-point bending or the four-point bending corrosion test can be smaller than that in the case of the solid state. . For this reason, it is possible to increase the thickness (height) of the test piece in the load direction while suppressing the increase in the load, and to make the distortion of the load surfaces 1a and 2a when the load is applied close to uniform. Further, the test piece 10 has a partition wall 4 that divides an internal space surrounded by the ceiling 1, the bottom 2, and the side wall 3 to form a plurality of through holes 5. The through hole 5 is formed so as to be line-symmetric with respect to the axis A in the vertical direction when viewed from the longitudinal direction. Thereby, the difference between the vicinity of the center and the vicinity of the end in the x direction of the strain on the load surfaces 1a and 2a when a load is applied becomes smaller. As a result, it is possible to make the distribution of strain in the x-direction of the load surfaces 1a and 2a evenly close to each other while suppressing an increase in the load required during the test.

  In the example shown in FIG. 11A, the partition wall 4 is arranged at the center of the pair of side wall portions 3. Two through holes 5 are formed between the partition wall 4 and a pair of side wall portions 3 on both sides of the partition wall 4. The shapes of the two through holes 5 in the cross section are the same. As described above, by forming the test piece 10 having the two through holes 5 partitioned by the center partition wall 4 of the pair of side wall portions 3, a line symmetric through hole with a simple structure is realized. Can be. That is, complication of the structure of the test piece 10 can be suppressed. As a result, the processing at the time of collecting the test piece from the target material can be simplified.

  It is preferable that the area of the cross section of the through hole 5 is 50% or more of the area of the cross section of the test piece 10 without the through hole 5. The cross section of the test piece 10 is a cross section of a plane perpendicular to the longitudinal direction (z direction). In the example shown in FIG. 11A, the area of the cross section of the test piece in the case where there is no through hole 5 corresponds to the line of the outer peripheral surface of the test piece 10 in the cross section, that is, the outer surfaces of the load surfaces 1a, 2a and the side wall portion 3. It is the area of the region surrounded by the line. As described above, by increasing the area of the through hole 5, the internal space of the test piece 10 can be widened. As a result, it is possible to reduce the load required to obtain a predetermined strain on the load surface 1a, as compared with a solid case. The area of the cross section of the through hole 5 is more preferably 60% or more of the area of the cross section of the test piece 10 having no through hole 5. If the cross-sectional area of the through hole 5 is too large, the thickness of the ceiling portion 1 and the bottom portion 2 becomes small, and the stress distribution on the load surfaces 1a, 2a tends to be uneven. Therefore, the area of the cross section of the through hole 5 can be 90% or less of the area of the cross section of the test piece 10 without the through hole 5.

  The dimension H (height H) in the vertical direction of the through hole 5 can be 60% or more of the dimension SH (height SH) in the vertical direction of the test piece 10. Thereby, the required load can be reduced and the stress distribution on the load surfaces 1a, 2a in the x direction can be made more uniform. In this respect, the height H of the through-hole 5 is more preferably equal to or greater than 65% of the height SH of the test piece 10, and more preferably equal to or greater than 75%. From the viewpoint of securing the thickness of the ceiling 1 and the bottom 2, the height H of the through hole 5 can be set to 90% or less of the height SH of the test piece 10.

  The thickness ts of the ceiling 1 can be greater than the thickness t of the bottom 2. As a result, the thickness of the ceiling portion 1 can be ensured, so that the strain distribution on the load surface 1a can be made more uniform. In the example shown in FIG. 11A, the load surface 1a of the ceiling 1 is a curved surface, and the load surface 2a of the bottom 2 is a flat surface. The difference in strain tends to be larger in the curved load surface 1a than in the flat load surface 2a. Therefore, by making the thickness ts of the ceiling portion 1 having the curved load surface 1a larger than the thickness t of the bottom portion 2, the difference in strain can be effectively reduced in the load surface 1a. In addition, the load surface 1a of the ceiling portion 1 is an evaluation surface on which the presence or absence of a crack is evaluated. Therefore, it is preferable to make the strain distribution on the load surface 1a, which is the evaluation surface, close to uniform.

  The thickness PW of the partition wall 4 can be set to 5% or more of the dimension SW (that is, the width SW) of the test piece 10 in the thickness direction (x direction) of the partition wall 4. Thereby, the part which supports the ceiling part 1 and the bottom part 2 of the partition wall 4 can be enlarged, and the strain distribution on the load surfaces 1a, 2a can be made more uniform. It is preferable that the thickness PW of the partition wall 4 is substantially the same as the thickness of the side wall portion 3. Thus, the balance between the support of the ceiling 1 by the side wall 3 and the support of the ceiling 1 by the partition wall 4 can be maintained, and the strain distribution on the load surface 1a can be made more uniform.

  In the configuration illustrated in FIG. 11A, the connection area between the partition wall 4 and the ceiling 1 and the connection area between the partition wall 4 and the bottom 2 are arranged at positions overlapping when viewed from above (in the y direction). That is, the partition wall 4 is formed to extend in the up-down direction. As a result, the partition wall 4 is configured to easily support the load in the vertical direction, and the variation in the stress on the load surfaces 1a and 2b can be reduced.

  The area of the cross section of the through hole 5 of the test piece 10 is constant in the longitudinal direction. That is, the size of the through hole 5 is constant in the longitudinal direction. Thereby, the stress distribution in the longitudinal direction of the test piece 10 tends to be uniform.

  The test piece 10 shown in FIG. 11A is bent such that the load surface 1a of the ceiling 1 becomes convex during a four-point bending or three-point bending corrosion test. That is, the evaluation surface is bent so as to be convex.

  In the example shown in FIGS. 11A to 11C, there is one partition wall 4 and two through holes 5, but the number of partition walls 4 and through holes 5 is not limited thereto. For example, three through holes 5 may be provided by providing two partition walls 4. Alternatively, three or more partition walls 4 may be provided. Four or more through holes 5 may be provided.

  Further, a horizontal partition wall extending in the x direction between the pair of side wall portions 3 and intersecting with the partition wall 4 may be further provided. For example, if one horizontal partition wall is added to the configuration shown in FIG. 11A, the number of through holes 5 becomes four.

  In FIG. 11A, the partition wall 4 is perpendicular to the load surfaces 1a, 2a. As a variant, a partition wall 4 that is not perpendicular to the load surfaces 1a, 2a can be provided. For example, in the configuration of FIG. 11A, partition walls inclined with respect to the partition wall 4 may be further added to both sides of the central partition wall 4.

  The shape of the cross section of the through hole 5 is not limited to a rectangle as shown in FIG. 11A. The shape of the cross section of the through hole 5 may be a circle or an ellipse. By making the cross section of the through hole 5 circular, the processing for forming the through hole 5 is simplified. In the example shown in FIG. 11A, R (roundness) is formed at the corner of the rectangular through hole 5 in the cross section.

  The size of the through hole 5 is not limited to the above example. For example, as shown in FIG. 12, the cross-sectional shape of the through-hole 5 may be circular, and the height H, that is, the diameter of the through-hole 5 may be about 30% of the height H of the test piece. However, when the cross-sectional shape of the through hole 5 is circular, the ratio of the area in the cross section of the through hole 5 to the area in the solid cross section cannot be larger than that in the rectangular shape. Therefore, from the viewpoint of securing the area of the through-hole 5, it is preferable that the cross-sectional shape of the through-hole 5 is rectangular (including those having R).

  The test piece 10 shown in FIG. 11A is an inner surface As test piece, and the load surface 1a of the ceiling 1 is a curved surface of the inner diameter surface of the steel pipe as the target material. On the other hand, the load surface 1a of the ceiling 1 may be a flat surface, and the test piece 10 may be a rectangular parallelepiped smooth test piece.

  The four-point bending corrosion test can be performed with the ceiling 1 and the bottom 2 upside down. Further, the test piece 10 is not limited to the four-point bending corrosion test, and can be used for a three-point bending corrosion test.

[Example 1]
In order to study the cross-sectional shape of the test piece that can reduce the load, the inventors performed FEM analysis using the analysis model shown in FIG. 6 and the data of the stress-strain characteristics shown in FIG. 13A, 13B, and 13C show the cross-sectional shapes of the test pieces 101, 102, and 103 on which the FEM analysis was performed in this example. Although not shown, FEM analysis was also performed on a test piece having the same width SW, height SH, and length SL as in FIGS. 13A to 13B and having no through hole.

  The test piece 101 shown in FIG. 13A has no partition wall and has one through hole 5. The test piece 102 shown in FIG. 13B has the same configuration as that of FIG. 11A, has one partition wall 4 at the center of the pair of side wall portions 3, and has two through holes 5 on both sides thereof.

  The test piece 103 shown in FIG. 13C has two partition walls 4 at the center of the pair of side wall portions 3, and has three through holes 5. In the test piece 103, the two partition walls 4 are arranged line-symmetrically with respect to the longitudinal direction (z direction), with the vertical direction (y direction) at the center of the test piece 103 as the axis of symmetry A. Thereby, the through hole 5 between the two partition walls 4 and the through hole 5 between each of the two partition walls 4 and the side wall 3 also become line-symmetric.

  FEM analysis was performed by setting the sizes of the test piece 101 and the test piece 102 as shown in Table 1 below, and setting the size of the test piece 103 in three ways as shown in Table 2 below. In Tables 1 and 2, the unit of the numerical value is mm. Case 1 in Table 1 is the size of the test piece 101 shown in FIG. 13A, and case 2 is the size of the test piece 102 shown in FIG. 13B. Cases 3-1 to 3-3 in Table 2 are the sizes of the test pieces 103 shown in FIG. 13C.

  FIG. 14 is a graph showing necessary loads obtained by FEM analysis of case 1, 2, 3-1 to 3-3 shown in Tables 1 and 2. In FIG. 14, the vertical axis indicates the ratio of the required load of each case to the required load of the solid test piece. The required load was a load required to generate a strain equivalent to a yield strength of 100% at the center of the load surface of the test piece.

  FIG. 15 is a graph showing a strain distribution obtained by FEM analysis of case 1, 2, 3-1 to 3-3 shown in Tables 1 and 2. In FIG. 15, the horizontal axis indicates a position on a line extending in the X direction through the center point C0 of the load surface 1a of the ceiling 1.

  When the FEM analysis results (case 1) shown in FIGS. 14 and 15 for the test piece 101 (FIG. 13A) having one through hole 5, the required load is reduced by about 30% as compared with the solid test piece. However, the difference in strain between the vicinity of the center and the vicinity of the end in the x direction of the load surface 1a of the test piece 101 was larger than that of the solid test piece. This is considered to be due to the fact that the ceiling 1 near the center in the x direction of the test piece 101 is thinner and therefore more easily deformed than the end.

  When the FEM analysis results (case 2) shown in FIGS. 14 and 15 for the test piece 102 (FIG. 13B) having two through holes 5, the required load is reduced by about 30% as compared with the solid test piece. Was. The difference in strain between the vicinity of the center and the vicinity of the end of the load surface 1a of the test piece 102 in the x direction was smaller than that of the solid test piece.

  The FEM analysis results (cases 3-1, 3-2, 3-3) of the test piece 103 (FIG. 13C) having three through holes 5 shown in FIG. 14 and FIG. The required load was reduced by about 23-30%. The difference in strain between the vicinity of the center and the end of the load surface 1a in the x direction of the test piece 103 was equal to or less than that of the solid test piece.

  FIG. 16A is a contour diagram showing the distribution of strain longitudinal components near the intersection of two symmetrical boundary surfaces of the test piece 102. FIG. 16B is a contour diagram showing the distribution of stress longitudinal components near the intersection of two symmetrical boundary surfaces of the test piece 102. 16A and 16B are a cross section near an intersection of a symmetric boundary surface passing through the symmetric boundary line TKz in the z-axis direction and a symmetric boundary surface passing through the symmetric boundary line TKx in the x-axis direction, and the load surface of the ceiling 1. 1a is shown. From FIG. 16A and FIG. 16B, it was confirmed that the strain and stress near the through-hole 5 were smaller than the strain and stress of the load surface 1a. Therefore, it is considered that a crack is unlikely to occur near the through hole 5 in the four-point bending corrosion test. That is, it is considered that there is a low possibility that proper evaluation cannot be performed due to the formation of a crack near the through hole 5 and the occurrence of a crack.

  According to the analysis results shown in FIGS. 14 and 15, a plurality of through holes penetrating in the longitudinal direction is provided by providing the partition wall 4 extending from the ceiling 1 to the bottom 2 between the pair of side walls 3 of the test piece 10. 5 were formed, and it was found that it is preferable that the plurality of through holes 5 be symmetrical when viewed from the longitudinal direction. With such a configuration, it is possible to suppress an increase in the difference in strain between the central portion and the end portion on the evaluation surface (load surface 1a) while suppressing the required load. Further, it was confirmed that the four-point bending corrosion test can be performed in a state where the strain and stress around the through hole 5 do not exceed those on the evaluation surface.

[Example 2]
In order to study the preferred cross-sectional shape of the through hole in the test piece, the size of the test piece 102 shown in FIG. 13B was set as shown in Table 3 below, and FEM analysis was performed. In Table 3, the unit of the numerical value is mm.

  FIG. 17 is a graph showing the relationship between the height H of the through hole 5 and the required load obtained by the FEM analysis. The vertical axis of FIG. 17 shows the ratio of the required load of the test piece 102 to the required load of the solid test piece. From the analysis results in FIG. 17, it was found that the required load became smaller as the height H of the through hole 5 became larger. When the height H is 6 mm or more, the required load can be reduced by 15% or more, and when the height H is 7 mm or more, the required load can be reduced by 30% or more.

  FIG. 18 is a graph showing the relationship between the height H of the through hole 5 and the strain distribution obtained by the FEM analysis. The horizontal axis indicates the distance from the center of the load surface 1a in the x direction. From the analysis results shown in FIG. 18, the difference in strain between the center and the end is solid in all cases where the height H of the through hole 5 is 3.5 mm, 5.5 mm, 7.5 mm, and 8.5 mm. It was smaller than the test piece. In particular, in the case of H = 7.5 mm and 8.5 mm, it was confirmed that the difference in strain at the end portion became smaller as the distance from the center increased. 17 and 18, the height H of the through-hole 5 is preferably 60% or more of the height SH of the test piece 102, more preferably 65% or more, and 70% or more. It was found that it was more preferable, and that the content was more preferably 75% or more.

  FIG. 19 is a graph showing the relationship between the width W of the through hole 5 obtained by the FEM analysis and the required load. The vertical axis in FIG. 19 shows the ratio of the required load of the test piece 102 to the required load of the solid test piece. From the analysis results of FIG. 17, it was found that the required load became smaller as the width W of the through hole 5 became larger. If the width W is 2.5 mm or more (25% of the width SW of the test piece), the required load can be reduced by 20% or more, and if the width W is 3.5 mm or more (35% of the width SW of the test piece). The required load could be reduced by 30% or more.

  FIG. 20 is a graph showing the relationship between the width W of the through hole 5 obtained by the FEM analysis and the strain distribution. From the analysis results shown in FIG. 20, the difference in strain distribution was smaller in each case where the width W of the through hole 5 was 2.5 mm and 3.5 mm, as compared with the solid test piece. In particular, when W = 3.5 mm, the difference in strain became smaller. 17 and 18 that the width W of the through hole 5 is preferably 25% or more of the width SW of the test piece 102, and more preferably 35% or more.

  FIG. 21 is a graph showing the relationship between the ratio of the area occupied by the area of the through hole 5 in the cross section of the test piece 102 and the required load, obtained by FEM analysis. The vertical axis in FIG. 20 indicates the ratio of the required load of the test piece 102 to the required load of the solid test piece. The horizontal axis indicates the ratio (SK / SA) of the area SK of the through hole 5 in the cross section to the area SA of the cross section of the test piece 102 when there is no through hole 5. As the proportion of the area of the through hole 5 increased, the required load decreased. When the ratio of the area of the through hole 5 was 0.5 (that is, 50%), the required load was reduced by 30%.

  As mentioned above, although one Embodiment of this invention was described, the above-mentioned embodiment is only an illustration for implementing this invention. Therefore, the present invention is not limited to the above-described embodiment, and can be implemented by appropriately modifying the above-described embodiment without departing from the spirit thereof.

1: ceiling part 2: bottom part 3: side wall part 4: partition wall 5: through hole 10: test piece

Claims (6)

A test piece used for a three-point bending or four-point bending corrosion test,
A ceiling portion that has a first load surface to which a load is applied from above in the vertical direction in the three-point bending or four-point bending corrosion test, and extends in a longitudinal direction of the test piece;
In the three-point bending or four-point bending corrosion test has a second load surface on which a load is applied from below in the vertical direction, and a bottom portion facing the ceiling portion,
Both end portions in a direction perpendicular to the longitudinal direction of the ceiling portion, and a pair of side wall portions formed between both end portions in a direction perpendicular to the longitudinal direction of the bottom portion, facing each other,
A partition wall formed between the ceiling portion and the bottom portion, between the pair of side wall portions,
The ceiling, the bottom, a space surrounded by the pair of side walls and the partition wall form a plurality of through holes that penetrate the test piece in a longitudinal direction,
A test piece, wherein the shape of the plurality of through holes is line-symmetric with respect to the vertical axis when viewed from the longitudinal direction of the test piece. The test piece according to claim 1,
The partition wall is disposed at the center of the pair of side wall portions,
A test piece, wherein the two through holes are formed between the partition wall and the pair of side wall portions on both sides of the partition wall. The test piece according to claim 1 or 2,
The test piece, wherein the area of the cross section of the through hole is 50% or more of the area of the cross section of the test piece in the absence of the through hole. It is a test piece according to any one of claims 1 to 3,
The test piece, wherein a size of the through hole in the vertical direction is 60% or more of a size of the test piece in the vertical direction. It is a test piece according to any one of claims 1 to 4,
A test piece wherein the thickness of the ceiling is larger than the thickness of the bottom. It is a test piece according to any one of claims 1 to 5,
The test piece, wherein a thickness of the partition wall is 5% or more of a size of the test piece in a thickness direction of the partition wall.

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