JP2021189144A - Method and punch - Google Patents

Abstract

To evaluate easily hole widening property of a pipe material.SOLUTION: A method for evaluating moldability of a pipe material includes steps of: preparing a test piece 2 provided with respective notch parts 23 on symmetrical positions based on a center axis of an annulus material, on one end face (lower end face) 21 of the annulus material using the pipe material as a base metal; and adding a moment for generating tensile strain in the circumferential direction on the peripheral side surface of the test piece 2, at least until a variation of a test load satisfies a prescribed condition, or until the test piece 2 is ruptured.SELECTED DRAWING: Figure 3

Description

The present disclosure relates to methods and punches used to evaluate the formability of pipe materials.

With the increasing complexity and strength of the shapes of automobile structural parts, materials for automobiles are required to have higher formability. As the formability required for the material, there are hole widening property and stretch flange property.

As an evaluation of the hole expanding property, for example, there is a hole expanding test specified in JIS Z 2256 2010. Using an Eriksen tester, a round hole of a predetermined diameter formed in a plate material is expanded, and the hole diameter at the time when a fracture occurs is evaluated. Further, Patent Document 1 discloses a side bend test method for evaluating hole expandability by pulling a plate material having a notch formed from both sides. Further, Patent Document 2 discloses a method for evaluating the fracture toughness of a pipe material by three-point bending.

Japanese Unexamined Patent Publication No. 2009-145138 Japanese Unexamined Patent Publication No. 2011-174808

However, the techniques disclosed in JIS regulations and Patent Document 1 evaluate the hole-expandability of the plate material, and do not evaluate the hole-expandability of the pipe material. Further, the technique disclosed in Patent Document 2 can evaluate the fracture toughness of a pipe material, but evaluates resistance to so-called brittle fracture, and does not evaluate ductile fracture such as perforation property. different. In addition, the test method disclosed in the above document requires a dedicated jig, and skillful skills such as visually confirming the timing of destruction are required.

Therefore, the present disclosure has been made in view of the above problems, and an object thereof is to provide a method and a punch capable of easily evaluating the hole expandability of a pipe material.

According to the present disclosure, it is a method for evaluating the formability of a tube material, and is located at a position symmetrical with respect to the central axis of the ring material on one end face of the ring material having the tube material as a base material. Whether the amount of change in the test load satisfies a predetermined condition for the moment for which the test piece provided with the notch is provided and the moment for causing the tensile strain in the circumferential direction of the peripheral side surface of the test piece is satisfied, or the test piece A method is provided that includes, at least adding, until any of the breaks occur.

According to the present disclosure, it is possible to easily evaluate the hole expandability of the pipe material.

It is a figure which shows the structural example of the hole expansion test method for evaluation of the formability of the pipe material which concerns on one Embodiment of this disclosure. It is a figure which shows the structural example of the punch 1 which concerns on the same embodiment. It is a figure which shows the structural example of the test piece 2 which concerns on the same embodiment. It is a schematic diagram which shows the preparation example of the test piece 2 which concerns on the same embodiment. It is a figure which shows the example of the shape of the cutout portion 23 which concerns on the same embodiment. FIG. 3 is a schematic view of a configuration example of a hole expansion test method for a pipe material according to the same embodiment shown in FIG. 1 as viewed from the side. This is an example of a load-stroke curve obtained by the test method according to the present embodiment for a test piece made of STKM14B as a material. This is an example of a load-stroke curve obtained by the test method according to the present embodiment for a test piece made of STKM13A as a material. It is a figure for showing the example of the deformation amount of the test piece 2 which concerns on the same embodiment. It is a figure for showing the example of the deformation amount of the test piece 2 which concerns on the same embodiment. It is a figure which shows the structural example of the hole expansion test method of the pipe material which concerns on the 1st modification of the same embodiment. 9 is a cross-sectional view of the punch 100 and the test piece 2 shown by the IX-IX'cross-sectional line of FIG. It is sectional drawing of the punch 100A and the test piece 2 used in the hole expansion test method of the pipe material which concerns on the 2nd modification of the same embodiment. It is sectional drawing of the punch 100B and the test piece 2 used in the hole expansion test method of the pipe material which concerns on the 3rd modification of the same Embodiment. It is sectional drawing of the punch 100C and the test piece 2 used in the hole expansion test method of the pipe material which concerns on the 3rd modification of the same embodiment. It is sectional drawing of the punch 100D and the test piece 2 used in the hole expansion test method of the pipe material which concerns on 5th modification of the same embodiment. It is a graph which shows the stress-equivalent plastic strain curve of the pipe material which concerns on 1st Example of this Embodiment. It is a figure which shows the state of deformation of the test piece model in the same modification. It is a graph which shows the relationship between the stroke and the equivalent plastic strain in the same modification. It is a load-stroke diagram obtained by the test by FEM considering the fracture and the extreme deformability which concerns on this deformation example. It is a figure which shows the dimension of the test piece used in the 2nd Example of this Embodiment. It is a figure which shows the dimension of the punch used in the same Example. It is a figure which shows the situation of the experiment in the same Example. It is a graph which shows the relationship between the stroke and the load obtained from the experiment in the same Example. It is a graph which shows the relationship between the stroke and the load obtained from the experiment in the same Example.

Preferred embodiments of the present disclosure will be described in detail below with reference to the accompanying drawings. In the present specification and the drawings, components having substantially the same functional configuration are designated by the same reference numerals, so that duplicate description will be omitted.

FIG. 1 is a diagram showing a configuration example of a hole expansion test method for evaluating the formability of a pipe material according to an embodiment of the present disclosure. The "formability" of the pipe material according to the present embodiment may be, for example, the hole-expandability required when the pipe material is drilled. Further, the "formability" may include the hole expandability after punching a hole provided in the pipe material. The hole expandability after punching is an index showing the influence on the hole expandability when a hole is punched under a predetermined punching condition. During punching, large plastic deformation is applied to the hole edge, and in some cases burrs may occur. Therefore, even when the same hole is provided by punching, the hole expandability may differ depending on the punching conditions. In determining such punching conditions, the hole expandability after punching can be evaluated. As shown in the figure, in the method for expanding the hole of the pipe material according to the present embodiment, the test is performed by placing the annular test piece 2 on the support bases 3 and 3 and pushing the punch 1 from the upper part of the test piece 2. A test load is applied to the piece 2. The applied test load is not limited to that of the punch 1, and may be, for example, a test load applied by bending the test piece 2. The test piece 2 mounted on the support base 3 may or may not be restrained by the support base 3. Further, when the test piece 2 is restrained by the support base 3, the restraining direction of the test piece 2 by the support base 3 is not particularly limited. Further, the support base 3 is not limited to the box shape, and can have any support structure.

FIG. 2 is a diagram showing a configuration example of the punch 1 according to the present embodiment. As shown in FIG. 2, for example, the punch 1 can be a plate-shaped member extending in the X direction and the Z direction. A pressing surface 11 is provided at the lower end of the punch 1 (the end in the negative direction in the Z direction). As shown in FIG. 2, for example, the pressing surface 11 may have a shape having a curvature in a part in a cross section orthogonal to the X-axis direction. Such a shape is not particularly limited. A modification of the punch 1 will be described later.

FIG. 3 is a diagram showing a configuration example of the test piece 2 according to the present embodiment. The test piece 2 has a lower end surface 21 and an upper end surface 22. Further, in the test piece 2, notches 23 are provided at positions symmetrical with respect to the central axis of the annular material on one end surface of the annular material having the tube material as the base material. Specifically, the test piece 2 has an outer surface which is an outer surface and an inner surface which is an inner surface when viewed from the center in the radial direction. Two notches 23 are provided on the lower end surface 21 of the test piece 2.

FIG. 4 is a schematic diagram showing a production example of the test piece 2 according to the present embodiment. The test piece 2 is prepared, for example, by the procedure as shown in FIG. First, a hole is punched out and a hole is provided in the pipe material to be evaluated for formability. Such holes are provided at target positions with respect to the central axis of the pipe material. Next, the annular material 20 is obtained by cutting out in a direction orthogonal to the longitudinal direction of the pipe material at a predetermined interval so as to include the hole portion. Then, it is cut along the circumferential direction of the annular material so that the hole portion of the annular material passes through. As a result, the test piece 2 having the notch portion 23 is provided.

The cutout portion 23 corresponds to, for example, the edge portion of the hole portion in stretch flange molding, hole expansion molding, burring molding, and the like. The shape of the cutout portion 23 is not particularly limited. FIG. 5 is a diagram showing an example of the shape of the notch portion 23 according to the present embodiment. For example, the notch portion 23a has a semi-arc shape. The cutout portion 23b is in the shape of a part of an arc. The notch portion 23c has an arcuate bottom, and is formed in a straight line parallel to the lower end surface 21 from the arcuate end portion. The cutout portion 23d is formed by two line segments having the bottom as an intersection. The notch portion 23e has an arcuate bottom portion, and is formed in a straight line so as to extend from the arcuate end portion toward the lower end surface 21. Such a shape may correspond to the shape of a hole provided for actually performing stretch flange molding or the like on a pipe material, or may be a shape standardized for a standard test. good.

Returning to FIG. 3, the size of the test piece 2 is not particularly limited. This implementation is performed when the test piece 2 has a size of h <0.7D and 0.005D <t <0.4D when the outer diameter of the test piece 2 is D and the wall thickness is t. It is particularly effective in morphological tests. For example, if h <0.7D, the desired bending mode of the test piece 2 can be obtained. Further, if 0.005D <t <0.4D, a desired bending mode can be obtained. The ligament length h'(distance from the bottom of the notch 23 to the upper end surface 22) may be the same or different in the two notches 23. For example, when it is desired to aim at the notch portion 23 having the larger ligament length h'and break it (the larger the ligament length, the easier it is for strain to enter and the easier it breaks), the two ligament lengths h'can be made different. ..

FIG. 6 is a schematic view of a configuration example of the hole expansion test method for the pipe material according to the present embodiment shown in FIG. 1 as viewed from the side. Here, the support base 3 is described in a simplified manner rather than in a box shape. As shown in FIG. 6, this test method imitates a three-point bending test on a so-called plate material. At the start of the test, the punch 1 is in contact with two portions of the upper end surface 22 corresponding to the positions where the cutout portions 23 of the test piece 2 are provided. Then, the punch 1 is moved in the negative Z direction, and a load is applied to the test piece 2. The load is applied, for example, by a load cell.

When a load is applied to the test piece 2 by the punch 1, a moment that causes tensile strain in the circumferential direction of the peripheral side surface of the test piece 2 is added like a three-point bending. At this time, a larger tensile strain may occur particularly with respect to the hole edge of the notch portion 23. As the stroke of the punch 1 increases, the load amount of the moment also increases, and the strain increases. When the strain reaches the limit (ie, when the extreme deformability is reached), fracture can occur in the notch 23. The timing at which this fracture occurs should be determined by the timing at which the amount of change in the test load satisfies a predetermined condition, more specifically, the change (decrease) in the load (moment), which may occur due to actual fracture or the like. Can be done. That is, it is possible to make a judgment based on a decrease in the test load, instead of making a visual judgment as in the conventional hole expansion test. The predetermined condition here means, for example, when the load double derivative F ″ in the load-stroke curve becomes maximum in the negative direction. That is, it can be said that the timing at which the fracture occurs is the timing at which the load drops sharply. The load may be applied until the load changes or the test piece breaks, or may be continuously applied even after these phenomena occur.

7 and 8 are examples of load-stroke curves obtained by the test method according to the present embodiment for test pieces made of STKM14B and STKM13A. In each graph, the test load F for the stroke and the double derivative F ″ of the test load are plotted. As shown in each figure, it can be seen that the value of the second derivative F ″ is also the maximum in the minus at the point where the test load F changes abruptly. Such a peak can be quantitatively evaluated as the timing of fracture.

Focusing on the peak of the second derivative F ″, the present inventors have found that it is related to the crack propagation stoppage after the crack is generated. That is, the crack propagation stop property of the material of the test piece 2 can be evaluated from the peak value of the second derivative F ″. The crack propagation stop property is a parameter that affects the fracture behavior of a member when a crack starts to occur from a hole edge, for example, at the time of a collision of an automobile. Comparing the examples of FIGS. 7 and 8, STKM13A has a smaller absolute peak value than STKM14B. From this, it can be evaluated that STKM13A is superior to STKM14B in crack propagation stoppage.

The formability is evaluated by measuring the amount of deformation of the test piece 2 when the test piece 2 is broken. There are a plurality of examples of the "deformation amount of the test piece 2". 9 and 10 are views for showing an example of the amount of deformation of the test piece 2 according to the present embodiment. First, referring to FIG. 9, a state in which the test piece 2 is broken by applying a load by a punch 1 (not shown) is shown. The test piece 2'has a shape that is bent inward around the notch 23.

For example, the "deformation amount of the test piece 2" may be the stroke St of the punch. The stroke St is the amount of movement of the punch from the start of the test (the state where the punch 1 and the test piece 2 are in contact with each other at the initial position) to the time of breaking or the time of load reduction. By deforming the stroke St, it is possible to directly evaluate at the timing of the decrease in load when the test piece 2 breaks or the like.

The "deformation amount of the test piece 2" is the bending angle θ of the upper end surface 22 of the test piece 2'when the test piece 2'after the test is viewed from the direction in which the cutout portion 23 is in front. May be good. The bending angle θ is the intersection of two straight lines corresponding to the upper end surface 22 that bends left and right around the notch 23 when the test piece 2'after the test is viewed from the direction in which the notch 23 is in front. The angle to do. The bending angle θ is determined by, for example, taking a picture of the test piece 2'from the side where the cutout portion 23 is in front, drawing two straight lines corresponding to the upper end surface 22 from the obtained image, and obtaining the intersection angle thereof. can get. By setting the bending angle θ as the amount of deformation, it is possible to evaluate in a region where the change in the bending angle θ is large with respect to the change in the stroke St.

The "deformation amount of the test piece 2" is the two end points 23-1 and 23-2 of the notch portion 23 when the test piece 2 (2') is viewed from the direction in which the notch portion 23 is in front. It may be a value based on the change in the distance between the test before and after the test. That is, the deformation amount referred to here may be the difference between the distance a0 of the end points before the test and the distance a1 of the end points after the test (at the time of breaking).

Further, as shown in FIG. 10, a grid-like pattern 25 is provided around the cutout portion 23 of the test piece 2, and the “deformation amount of the test piece 2” is the inter-grid distance of the grid-like pattern. The value may be based on the change between before and after the test. For example, the interstitial distance corresponding to the amount of deformation may be the interstitial distance at the portion where the crack 26 generated by the fracture as shown in FIG. 10 is generated. By using such an interstitial distance, more accurate evaluation becomes possible. Further, by acquiring a value based on the change in the interstitial distance, the strain distribution around the notch portion 23 can be obtained. The grid pattern may be attached by a writing tool or the like, or may be attached by a marking or the like.

As shown above, according to the test method according to the present embodiment, a notch is provided in the annular test piece obtained by cutting the pipe material into round slices so that the test piece is bent at three points when viewed from the notch. While supporting the test piece, push the punch into the position corresponding to the notch with the notch as the lower end surface side. By such pushing, the hole expanding process for the pipe material is simulated, and strain is generated near the bottom of the notch. When such strain reaches the limit, fracture occurs at the notch. By measuring the "deformation amount" at the time of breaking by the above means or the like, the breaking characteristics of the test piece can be evaluated. The evaluation of the breaking property of this test piece is the evaluation of the hole widening property of the pipe material. By such a method, the hole expanding property of the pipe material can be easily and highly accurately evaluated without using a special device.

Next, a modification of the present embodiment will be described. The pressing surface 11 of the punch 1 shown in FIGS. 1 and 2 was flat, but the present technique is not limited to this example. FIG. 11 is a diagram showing a configuration example of a hole expanding test method for a pipe material according to a first modification of the present embodiment. Further, FIG. 12 is a cross-sectional view of the punch 100 and the test piece 2 shown by the XI-XI'cross-sectional line of FIG. As shown in FIGS. 11 and 12, in the punch 100 according to this modification, the groove portions 12 are directed to two places on the pressing surface 11 at the lower end of the base material 10'. The groove portions 12 are provided so as to be substantially parallel to each other so as to cross in the Y direction.

As shown in FIG. 12, the width (length in the X direction) of the groove portion 12 is a length corresponding to the wall thickness t of the test piece 2. That is, when the punch 100 and the test piece 2 come into contact with each other, the upper end portion of the test piece 2 fits into the groove portion 12. In this state, the radial movement of the upper end portion of the test piece 2 is restricted. As a result, when a load is applied by the punch 100, deformation (escape) in the XY direction at the upper end portion of the test piece 2 is less likely to occur. Then, tensile stress can be generated more appropriately with respect to the notch portion 23.

FIG. 13 is a cross-sectional view of the punch 100A and the test piece 2 used in the hole expanding test method for the pipe material according to the second modification of the present embodiment. The cross-sectional view of the punch 100A and the test piece 2 shown in FIG. 13 is a cross-sectional view shown by the XI-XI'cross-sectional line of FIG. In this modification, the wall portion 14 of the groove portion 12 on the side closer to the center of the base portion 13 is provided longer than the wall portion 15 of the groove portion 12 on the side far from the center of the base portion 13 in the opening direction of the groove portion 12. .. That is, the central portion of the base portion 13 projects downward with the two groove portions 12 as boundaries in the X direction. When the punch 100A and the test piece 2 come into contact with each other when a load is applied, the upper end portion of the test piece 2 fits into the groove portion 12. Then, the wall portion 14 comes into contact with the inner surface of the upper portion of the notch portion 23 of the test piece 2 from above to below the inner surface thereof. In this state, the movement of the upper inner wall of the notch 23 of the test piece 2 toward the center may be restricted. As a result, when the load is applied by the punch 100A, the upper end portion of the test piece 2 is less likely to be deformed (escape) in the radial center direction of the upper portion of the notch portion 23 due to the deformation in the radial outer direction. Then, tensile stress can be generated more appropriately with respect to the notch portion 23. By applying the load while restraining the radial movement of the test piece 2 in this way, it is possible to suppress the escape of the load due to the deformation of the test piece 2 and perform the test with higher accuracy.

FIG. 14 is a cross-sectional view of the punch 100B and the test piece 2 used in the hole expanding test method for the pipe material according to the third modification of the present embodiment. The cross-sectional view of the punch 100B and the test piece 2 shown in FIG. 14 is a cross-sectional view shown by the XI-XI'cross-sectional line of FIG. In this modification, the wall portion 15 extending downward from the base portion 13 of the punch 100B is in contact with the outside of the test piece 2 and is restrained. When the punch 100B and the test piece 2 come into contact with each other when a load is applied, the wall portion 15 comes into contact with the outer surface of the notch portion 23 of the test piece 2. In this state, the movement of the notch 23 of the test piece 2 in the outward radial direction can be restricted. As a result, when the load is applied by the punch 100B, the upper end portion of the test piece 2 is less likely to be deformed (escape) in the radial center direction of the upper portion of the notch portion 23 due to the deformation in the radial outer direction. Then, tensile stress can be generated more appropriately with respect to the notch portion 23. In this way, by applying the load while restraining the movement of the test piece 2 in the radial direction, it is possible to suppress the escape of the load due to the deformation of the test piece 2 and perform the test with higher accuracy. In addition, the groove portion 12 shown in the above-mentioned modification may be provided in the 100B shown in this modification.

FIG. 15 is a cross-sectional view of the punch 100C and the test piece 2 used in the hole expanding test method for the pipe material according to the fourth modification of the present embodiment. The cross-sectional view of the punch 100C and the test piece 2 shown in FIG. 15 is a cross-sectional view shown by the XI-XI'cross-sectional line of FIG. In this modification, similarly to the second modification, the groove portion 12 is provided on the pressing surface 11 of the base portion 17, and the wall portion 14 of the groove portion 12 comes into contact with the inner surface of the test piece 2, but the base portion 17 is separated. It is provided. The two bases 17 are connected by an adjuster 18, and the adjuster 18 moves the base 17 along the direction in which the grooves 12 are arranged side by side (that is, the X direction). Thereby, the position of the groove portion 12 of the punch 100C can be adjusted according to the outer diameter of the test piece 2. That is, the test can be carried out using one punch 100C regardless of the outer diameter of the test piece 2.

FIG. 16 is a cross-sectional view of the punch 100D and the test piece 2 used in the hole expanding test method for the pipe material according to the fifth modification of the present embodiment. The cross-sectional view of the punch 100C and the test piece 2 shown in FIG. 16 is a cross-sectional view shown by the XI-XI'cross-sectional line of FIG. This modification has the same structure as the fourth modification, but further, another base 19 is connected by the adjuster 18A on the radial outer side of the base 17. With the adjuster 18A, the size of the groove portion 12 in the width direction can be adjusted.

Next, an example of the hole expansion test method for the pipe material according to the present embodiment will be described.

(1) Finite element method analysis First, using the finite element method (FEM) analysis, the validity of the hole expansion test method for the pipe material according to the present embodiment is evaluated, and the molding breakage prediction by FEM analysis is performed. The feasibility was examined.

In this example, using Simufact Forming, FEM analysis was performed on a model of a test piece generated by simulating a pipe material whose material is STKM13A. The Young's modulus of the tube material was 200 GPa, the Poisson's ratio was 0.29, and the yield stress was 260 MPa. The stress-equivalent plastic strain curve of the pipe material is as shown in FIG. The outer diameter of the test piece model was 50.8 mm, the height was 12.5 mm, and the wall thickness was 3.2 mm. The notch had a semicircular arc shape, the notch radius was 5 mm, and the ligament length was 7.5 mm. Such FEM analysis is performed, for example, in a computer equipped with a processor such as a CPU or GPU. That is, the FEM analysis application read from the storage is expanded in the memory, and the processor accesses the memory, so that the function of the FEM analysis can be exhibited in the computer.

FIG. 18 is a diagram showing a state of deformation of the test piece model in this modified example. In the analysis in this modified example, a method of contacting and pressing the punch at the punch contact portion of 1 was simulated. The vicinity of the punch contact portion and the notch portion is fixed so as not to be deformed. Here, the amount of deformation (that is, the stroke) of the punch contact portion, the load applied to the punch contact portion, and the equivalent plastic strain at the bottom of the notch portion (strain measurement point) were measured.

As shown in FIG. 18, it is clear from the contour diagram that the equivalent plastic strain at the bottom of the notch increases as the amount of deformation increases. FIG. 19 is a graph showing the correlation between the stroke and the equivalent plastic strain. As shown in FIG. 19, it is shown that the equivalent plastic strain increases linearly with respect to the stroke. From this, it is possible to specify the relationship between the equivalent plastic strain and the stroke, etc., and it is possible to estimate the equivalent plastic strain at the time of fracture. That is, it is possible to estimate the superiority or inferiority of the hole expandability (ductility) of the pipe material from the amount of deformation such as the stroke. Further, since the ultimate deformability (threshold value which is the upper limit of the equivalent plastic strain) can be estimated from the result of the stroke at the time of fracture, it is possible to predict the fracture of the molding in the molding simulation. Therefore, it is possible to reduce the actual number of prototypes of the component.

FIG. 20 is a load-stroke diagram obtained by a test by FEM in consideration of fracture and extreme deformability according to this deformation example. The FEM test considering fracture and extreme deformability is a test in which an algorithm is introduced to delete (that is, fracture) the mesh in which the equivalent plastic strain reaches the ultimate deformability. The various conditions of the test in FEM are as described above. As shown in FIG. 20, it can be seen that the FEM test considering the fracture when the equivalent plastic strain reaches the limit deformability FP reflects the sharp decrease in the load due to the fracture. In addition, it is possible to reproduce how the crack propagates after the first fracture occurs. As described above, by considering the above-mentioned extreme deformability, it is possible to predict the forming breakage.

(2) Verification by experiment Next, an example by an actual experiment will be described. FIG. 21 is a diagram showing the dimensions of the test piece used in this example. As a test piece, a test piece made of STKM14B having an outer diameter of 50.8 mm, a plate thickness of 3.2 mm, a height of 10 mm, and a notch diameter of 5 mm was prepared. The tensile strength of STKM14B is 500 MPa (or more), the yield stress is 355 MPa (or more), and the total elongation (EL) is 15% (or more). Further, FIG. 22 is a diagram showing the dimensions of the punch used in this embodiment. The radius of curvature on the pressing surface of the punch is 3 mm.

FIG. 23 is a diagram showing the state of the experiment in this embodiment. As shown in FIG. 23, the punch 1 applies a load downward to the test piece 2 by the load cell 30. The test piece 2 is supported by two support bases 3. The distance between the two supports 3 is 40 mm.

FIG. 24 is a graph showing the relationship between the stroke and the load obtained from the experiment in this example. As shown in FIG. 24, the load drops sharply when a fracture occurs. From this, the timing of occurrence of fracture can be specified by the decrease in load.

FIG. 25 is a diagram showing a state of a test piece broken by the experiment in this example. As shown in FIG. 25, it can be seen that a fracture accompanied by a constriction occurs at the bottom of the notch 23'of the test piece 2'at the time of fracture. That is, it can be seen that ductile fracture occurs at the bottom of the notch 23'. By such a test method, it is possible to reproduce the state of ductile fracture at the edge of the hole where the hole expanding process or the like provided in the pipe material is performed. It was shown that the hole expandability of the pipe material can be evaluated by such a method.

Although the preferred embodiments of the present disclosure have been described in detail with reference to the accompanying drawings, the technical scope of the present disclosure is not limited to such examples. It is clear that anyone with ordinary knowledge in the art of the present disclosure may come up with various modifications or amendments within the scope of the technical ideas set forth in the claims. Is, of course, understood to belong to the technical scope of the present disclosure.

In addition, the effects described herein are merely explanatory or exemplary and are not limited. That is, the technique according to the present disclosure may exert other effects apparent to those skilled in the art from the description of the present specification, in addition to or in place of the above effects.

The following configurations also belong to the technical scope of the present disclosure.
(Item 1)
It is a method for evaluating the formability of pipe materials.
On one end face of the annulus material obtained by cutting at a predetermined interval in the direction orthogonal to the longitudinal direction of the pipe material, the annulus material is cut at a position symmetrical with respect to the central axis of the annulus material. Providing a test piece with a notch and
A moment that causes tensile strain in the circumferential direction of the peripheral side surface of the test piece is added at least until the amount of change in the test load satisfies a predetermined condition or the test piece breaks. To do and
Including, how.
(Item 2)
The end face on the side where the notch is provided and the end face of the portion where the notch is not provided is supported in the circumferential direction of the test piece.
A load is applied by punching to a portion of the end face of the test piece in the circumferential direction in which each of the notches of the test piece is provided and opposite to the side on which the notch is provided. By doing so, the moment is added.
The method according to item 1.
(Item 3)
When the change amount of the test load satisfies a predetermined condition, the deformation amount of the test piece at the time when the change amount of the test load satisfies the predetermined condition is measured.
The method according to item 1 or 2.
(Item 4)
When the test piece is broken, the amount of deformation of the test piece at the time of breaking of the test piece is measured.
The method according to item 1 or 2.
(Item 5)
The test load is a portion where each of the notch portions of the test piece is provided in the circumferential direction of the test piece, and is punched at a portion of an end surface opposite to the side where the notch portion is provided. Applied by
The method according to item 3 or 4, wherein the amount of deformation of the test piece is the stroke of the punch.
(Item 6)
The amount of deformation of the test piece is the end face of the test piece on the side opposite to the side where the notch portion is provided when the test piece after the test is viewed from the direction in which the notch portion faces the front. The method according to any one of items 3 to 5, which is a bending angle.
(Item 7)
The amount of deformation of the test piece is based on the change in the distance between the two endpoints of the notch when the test piece is viewed from the direction in which the notch is in front, before and after the test. The method according to any one of items 3 to 6, which is a value.
(Item 8)
A grid pattern is provided around the notch on the peripheral side surface of the test piece.
The method according to any one of items 3 to 7, wherein the amount of deformation of the test piece is a value based on the change in the interstitial distance of the grid pattern between before and after the test.
(Item 9)
The method according to any one of items 2 to 8, wherein the test load is applied while restraining the radial movement of the test piece.
(Item 10)
Item 9. The method according to item 9, wherein the test load is applied while restraining the radial movement of at least the upper end surface of the test piece.
(Item 11)
Item 9. The method according to item 9 or 10, wherein the test load is applied while restraining the movement of the inner surface of the test piece toward the center.
(Item 12)
The method according to any one of items 1 to 11, wherein the shape of the cutout portion includes at least an arc shape.
(Item 13)
Item 2. The method according to any one of items 1 to 12, wherein the distance between the bottom of the notch and the end face of the notch and the end surface on the side opposite to the provided side is different for each of the notches. ..
(Item 14)
The method includes a method by analysis by the finite element method.
The test piece is a model generated in the analysis of the finite element method.
When the amount of change in the test load satisfies a predetermined condition or the test piece breaks, the equivalent plastic strain generated in the notch has a predetermined threshold value. Including timing beyond
The method according to any one of items 1 to 13.
(Item 15)
The method according to any one of items 1 to 14, wherein the predetermined condition relating to the change amount of the test load includes the case where the value of the double derivative of the test load with respect to the stroke becomes the maximum in the minus.
(Item 16)
The method according to item 15, wherein the crack propagation stop property of the material of the test piece is evaluated based on the value when the double derivative of the test load becomes maximum at minus.
(Item 17)
A punch used in a method for evaluating the formability of pipe materials.
It has a base with a pressing surface at the lower end,
A punch in which two grooves are provided substantially in parallel on the pressing surface.
(Item 18)
Item 17. The punch according to item 17, wherein the wall portion of the groove portion on the side near the center of the base portion is provided longer in the opening direction of the groove portion than the wall portion of the groove portion on the side far from the center of the base portion.
(Item 19)
Item 17. The punch according to item 17 or 18, wherein the base is movable along a direction in which the two grooves are arranged side by side.

1,100 Punch 2 Test piece 3 Support stand 11 Base 12 Groove 21 Lower end surface 22 Upper end surface 23 Notch

Claims (19)

It is a method for evaluating the formability of pipe materials.
A test piece having a notch at a position symmetrical with respect to the central axis of the annular material is provided on one end surface of the annular material using the tube material as a base material.
A moment that causes tensile strain in the circumferential direction of the peripheral side surface of the test piece is added at least until the amount of change in the test load satisfies a predetermined condition or the test piece breaks. To do and
Including, how. The end face on the side where the notch is provided and the end face of the portion where the notch is not provided is supported in the circumferential direction of the test piece.
A load is applied by punching to a portion of the end face of the test piece in the circumferential direction in which each of the notches of the test piece is provided and opposite to the side on which the notch is provided. By doing so, the moment is added.
The method according to claim 1. When the change amount of the test load satisfies a predetermined condition, the deformation amount of the test piece at the time when the change amount of the test load satisfies the predetermined condition is measured.
The method according to claim 1 or 2. When the test piece is broken, the amount of deformation of the test piece at the time of breaking of the test piece is measured.
The method according to claim 1 or 2. The test load is a portion where each of the notch portions of the test piece is provided in the circumferential direction of the test piece, and is punched at a portion of an end surface opposite to the side where the notch portion is provided. Applied by
The method according to claim 3 or 4, wherein the amount of deformation of the test piece is the stroke of the punch. The amount of deformation of the test piece is the end face of the test piece on the side opposite to the side where the notch is provided when the test piece after the test is viewed from the direction in which the notch is in front. The method according to any one of claims 3 to 5, which is a bending angle. The amount of deformation of the test piece is based on the change in the distance between the two endpoints of the notch when the test piece is viewed from the direction in which the notch is in front, before and after the test. The method according to any one of claims 3 to 6, which is a value. A grid pattern is provided around the notch on the peripheral side surface of the test piece.
The method according to any one of claims 3 to 7, wherein the amount of deformation of the test piece is a value based on a change in the interstitial distance of the grid pattern between before and after the test. The method according to any one of claims 2 to 8, wherein the test load is applied while restraining the radial movement of the test piece. The method according to claim 9, wherein the test load is applied while restraining the radial movement of at least the upper end surface of the test piece. The method according to claim 9 or 10, wherein the test load is applied while restraining the movement of the inner surface of the test piece toward the center. The method according to any one of claims 1 to 11, wherein the shape of the cutout portion includes at least an arc shape. 13. Method. The method includes a method by analysis by the finite element method.
The test piece is a model generated in the analysis of the finite element method.
When the amount of change in the test load satisfies a predetermined condition or the test piece breaks, the equivalent plastic strain generated in the notch has a predetermined threshold value. Including timing beyond
The method according to any one of claims 1 to 13. The method according to any one of claims 1 to 14, wherein the predetermined condition relating to the change amount of the test load includes the case where the value of the double derivative of the test load with respect to the stroke becomes the maximum in the minus. The method according to claim 15, wherein the crack propagation stop property of the material of the test piece is evaluated based on the value when the double derivative of the test load becomes maximum at minus. A punch used in a method for evaluating the formability of pipe materials.
It has a base with a pressing surface at the lower end,
A punch in which two grooves are provided substantially in parallel on the pressing surface. 17. The punch according to claim 17, wherein the wall portion of the groove portion on the side closer to the center of the base portion is provided longer than the wall portion of the groove portion on the side far from the center of the base portion in the opening direction of the groove portion. The punch according to claim 17 or 18, wherein the base is movable along a direction in which the two grooves are arranged side by side.

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