JP7667014B2 - Biaxial Tensile Test Method - Google Patents

Description

The present invention relates to a biaxial tensile test method, and in particular to a biaxial tensile test method that can suppress a decrease in the measurement accuracy of a biaxial tensile test.

A biaxial tensile test is known in which a test piece made of a plate-like elastic body is pulled along two mutually perpendicular four axes to measure the strain-stress data of the test piece. For example, in a conventional biaxial tensile test, the test piece is directly clamped between multiple chucks arranged in four directions, and the multiple chucks are moved in four directions by an actuator to pull the test piece in the four directions (Patent Document 1).

JP 2017-102076 A

However, in biaxial tensile tests in which the test specimen is directly clamped in the chuck, the test specimen that has been tensile deformed in four directions becomes thinner due to the Poisson effect, and the clamping force of the chuck decreases. This can cause the test specimen to slip relative to the chuck, which can cause the measurement accuracy of the biaxial tensile test to decrease.

The present invention has been made to solve the above-mentioned problems, and aims to provide a biaxial tensile testing method that can suppress a decrease in the measurement accuracy of biaxial tensile testing.

To achieve this objective, the biaxial tensile test method of the present invention is a method for performing a biaxial tensile test on a test piece made of a plate-shaped elastic body by pulling the test piece with a biaxial tensile tester along four directions, which are the axial directions of a first axis and a second axis that are perpendicular to each other, and includes a bonding step of bonding one end of the mounting member to at least one surface of the test piece so that multiple mounting members protrude from the test piece along each of the four directions, and a test step of performing the biaxial tensile test by pulling each of the multiple mounting members bonded in the bonding step with the biaxial tensile tester in the direction in which they protrude from the test piece.

According to the biaxial tensile test method described in claim 1, first, in the bonding step, multiple mounting members are bonded to the test piece. In the subsequent test step, the biaxial tensile test of the test piece is performed by pulling the mounting members in each of the directions in which the mounting members protrude from the test piece (the four directions). Since the mounting members are bonded to the test piece, slippage between the test piece and the mounting members in the test step can be suppressed. Therefore, a decrease in the measurement accuracy of the biaxial tensile test caused by this slippage can be suppressed.

In the mounting step, the other ends of the multiple mounting members that are distant from the test piece are respectively mounted to multiple tension members of the biaxial tensile tester. In the test step after the mounting step and the bonding step, the multiple tension members are moved in the four directions by an actuator, thereby pulling the mounting members in the four directions via the multiple tension members.

The mounting member that is adhered to the test specimen is removably attached to the tensile member, so that the test specimen can be replaced together with the mounting member. This eliminates the need to peel the test specimen from the mounting member when replacing the test specimen, or makes it easier to peel the mounting member from the test specimen. In other words, it makes it easier to replace the test specimen.

In the bonding step, the multiple mounting members are bonded to the test piece such that the multiple mounting members protruding along the axial direction of the first axis are aligned at intervals in the axial direction of the second axis, and the multiple mounting members protruding along the axial direction of the second axis are aligned at intervals in the axial direction of the first axis. The biaxial tensile tester includes a pair of first slide sections to which the multiple tensile members are fixed slidably along the axial direction of the first axis and which are moved apart from each other in the axial direction of the second axis by an actuator in the test step, and a pair of second slide sections to which the multiple tensile members are fixed slidably along the axial direction of the second axis and which are moved apart from each other in the axial direction of the first axis by an actuator in the test step.

In this way, the tensile member to which the multiple mounting members are attached can slide in the direction in which the multiple mounting members are arranged, so the spacing between the multiple mounting members can be adjusted to match the tensile deformation of the test piece in the four directions in the test step. As a result, in the test step, constraint of the test piece due to the spacing between the mounting members can be suppressed, and the decrease in measurement accuracy of the biaxial tensile test that accompanies such constraint can be suppressed.

Here, when a discrepancy occurs between the spacing of one end of the mounting member (tensile deformation of the test piece) and the spacing of the tension member, and the mounting member rotates around the other end relative to the tension member, a torsional force is applied to the adhesive portion between the one end and the test piece. However, in the mounting step, the mounting member is attached to the tension member so that rotation of the mounting member around the other end relative to the tension member is restricted, so that the application of a torsional force due to that rotation to the adhesive portion between the one end and the test piece can be suppressed. As a result, the mounting member is less likely to peel off from the test piece.

According to the biaxial tensile test method of claim 2 , in addition to the effects of the biaxial tensile test method of claim 1 , the following effects are achieved. One end of the mounting member bonded to the test piece is rectangular when viewed from a direction perpendicular to the first axis and the second axis. This makes it easier to ensure an adhesive area between the rectangular one end and the test piece compared to when the one end of the mounting member is tapered. As a result, the mounting member is less likely to peel off from the test piece.

According to the biaxial tensile test method of claim 3 , in addition to the effects of the biaxial tensile test method of claim 1 , the following effect is achieved. One end of the mounting member bonded to the test piece has a tapered shape when viewed from a direction perpendicular to the first axis and the second axis. This makes it possible to widen the portion of the test piece that is a predetermined distance away from the bonded portion (a portion that is effective as an evaluation value in the biaxial tensile test) compared to when one end of the mounting member is rectangular, thereby improving the measurement accuracy of the biaxial tensile test.

FIG. 1 is a plan view showing a biaxial tensile testing system in a first embodiment. FIG. 2 is a cross-sectional view of the biaxial tensile testing system taken along line II-II in FIG. 1. 3A is a plan view of a tension member and a mounting member in a second embodiment, and FIG. 3B is a side view of the tension member and the mounting member as viewed from the direction of arrow IIIb in FIG. 13A and 13B are side views of a tension member and a mounting member in a third embodiment;

Preferred embodiments will now be described with reference to the accompanying drawings. FIG. 1 is a plan view showing a biaxial tensile testing system 1 in a first embodiment. FIG. 2 is a partially enlarged cross-sectional view of the biaxial tensile testing system 1 taken along line II-II in FIG. 1. In FIG. 1, the top surfaces (the surfaces on the front side of the paper in FIG. 1) of the first and second slide parts 11, 12, 13, 14, which have a U-shaped cross section, are omitted. For convenience of explanation, the upper side of FIG. 2 will be described as up, and the lower side of FIG. 2 as down, but the up-down direction of FIG. 2 is not necessarily the actual up-down direction.

The biaxial tensile testing system 1 is for performing a biaxial tensile test on a test piece 2 consisting of a rectangular plate made of an elastic material such as rubber with a substantially uniform thickness, using a biaxial tensile testing machine 10 (hereinafter abbreviated as "test machine 10") and multiple mounting members 21. As will be described in detail later, a biaxial tensile test is a test that measures the strain-stress data of the test piece 2 by pulling the test piece 2 substantially uniformly along four directions, which are the axial directions of a first axis X and a second axis Y that are perpendicular to each other.

The axial direction of the first axis X to the left on the paper in FIG. 1 is referred to as the first direction D1, and the axial direction to the right on the paper in FIG. 1 is referred to as the second direction D2. The axial direction of the second axis Y to the top on the paper in FIG. 1 is referred to as the third direction D3, and the axial direction to the bottom on the paper in FIG. 1 is referred to as the fourth direction D4. In order to perform a biaxial tensile test by pulling the test piece 2 approximately uniformly in these four directions D1 to D4, the biaxial tensile test system 1 is configured so that each of the four directions D1 to D4 with respect to the test piece 2 is configured approximately the same.

The testing machine 10 includes a pair of first slide sections 11, 12 extending parallel to the first axis X and spaced apart from each other in the axial directions D3, D4 of the second axis Y, a pair of second slide sections 13, 14 extending parallel to the second axis Y and spaced apart from each other in the axial directions D1, D2 of the first axis X, a plurality of actuators 15 for moving the first slide sections 11, 12 and the second slide sections 13, 14, respectively, and a plurality of tension members 16 slidably fixed to the first slide sections 11, 12 and the second slide sections 13, 14.

The pair of first slide parts 11, 12 and the pair of second slide parts 13, 14 are arranged to surround the test piece 2 from four directions D1 to D4. Hereinafter, the center of the area surrounded by the first slide parts 11, 12 and the second slide parts 13, 14 will be referred to as the center of the testing machine 10.

The pair of first slide parts 11, 12 are members whose cross section perpendicular to the first axis X is formed in a U-shape so as to open toward the center of the testing machine 10, and rod-shaped fixing parts 11a, 12a parallel to the first axis X are provided in the center of the U-shape cross section. The pair of second slide parts 13, 14 are members whose cross section perpendicular to the second axis Y is formed in a U-shape so as to open toward the center of the testing machine 10, and rod-shaped fixing parts 13a, 14a parallel to the second axis Y are provided in the center of the U-shape cross section.

The first slide parts 11, 12 and the second slide parts 13, 14 are formed from a material (e.g., metal, resin, or ceramics) that has a degree of rigidity such that deformation in a biaxial tensile test on the test piece 2 can be ignored, i.e., a rigidity that is sufficiently large relative to the test piece 2. Hereinafter, a material with such rigidity will be referred to as a rigid material.

The actuators 15 are air cylinders that are individually provided on the first slide sections 11, 12 and the second slide sections 13, 14. Each actuator 15 includes a cylinder 15a that is fixed to a base (not shown) and a rod 15b that protrudes from the cylinder 15a and is fixed to either the first slide sections 11, 12 or the second slide sections 13, 14.

The actuator 15 extends and retracts the rod 15b relative to the cylinder 15a, thereby moving the first slide parts 11 and 12 in the axial directions D3 and D4 of the second axis Y. Similarly, the actuator 15 extends and retracts to move the second slide parts 13 and 14 in the axial directions D1 and D2 of the first axis X.

The tension members 16 are rigid members, four of which are provided on each of the first slide sections 11, 12 and the second slide sections 13, 14. The tension members 16 protrude vertically from the first slide sections 11, 12 or the second slide sections 13, 14 toward the center of the testing machine 10.

The tension members 16 are slidably fixed to the fixing parts 11a, 12a, 13a, and 14a. That is, the tension members 16 provided on the first slide parts 11 and 12 are slidable in the axial directions D1 and D2 of the first axis X, and the tension members 16 provided on the second slide parts 13 and 14 are slidable in the axial directions D3 and D4 of the second axis Y.

The multiple mounting members 21 are rigid members that connect one test piece 2 to the multiple tension members 16. In this embodiment, one mounting member 21 is provided on each of the upper and lower sides of one tension member 16.

The mounting member 21 has one end 21a that is adhered to the test piece 2 with adhesive 22, and the other end 21b that is the end opposite to the one end 21a and is detachably attached to the tension member 16 with a single bolt 24. The one end 21a has a rounded tapered shape in a plan view (when viewed from a direction perpendicular to the first axis X and the second axis Y). The tapered shape is a shape that becomes narrower as it approaches the tip away from the other end 21b.

Next, a biaxial tensile test method using the biaxial tensile test system 1 will be described. First, one end 21a of the mounting member 21 is adhered to both the top and bottom surfaces of the test piece 2 with adhesive 22 so that the multiple mounting members 21 protrude from the test piece 2 along the four directions D1 to D4 (adhesion step). In this adhesion step, the multiple mounting members 21 protruding along the axial directions D1 and D2 of the first axis X are aligned at intervals along the axial directions D3 and D4 of the second axis Y, and the multiple mounting members 21 protruding along the axial directions D3 and D4 of the second axis Y are aligned at intervals along the axial directions D1 and D2 of the first axis X.

The adhesive 22 used should be appropriately selected so that the mounting member 21 will not peel off from the test piece 2 during the biaxial tensile test. Since a technique for firmly bonding metal and rubber by vulcanization adhesion is known, it is preferable to use a metal mounting member 21 and an adhesive 22 of a type suitable for vulcanization adhesion to the metal. This makes it easy to achieve strong adhesion between the rubber test piece 2 and the mounting member 21 by vulcanization adhesion.

After the adhesion step, the other end 21b of the multiple mounting members 21 is attached to the tip of the tension member 16 (the end on the central side of the testing machine 10) with a bolt 24 (mounting step). In this mounting step, the mounting members 21 are attached to the tension member 16 so that the protruding direction of the mounting members 21 from the test piece 2 is opposite to the protruding direction of the tension member 16 from the first slide parts 11, 12 or the second slide parts 13, 14.

After the mounting step, the actuator 15 is retracted to move the first slide parts 11, 12 and the second slide parts 13, 14 in each of the four directions D1 to D4 away from the test piece 2, and a preliminary tensile load is applied to the test piece 2 (pre-tension step). More specifically, in the pre-tension step, the mounting member 21 is pulled in the protruding direction from the test piece 2 (four directions D1 to D4) via the first slide parts 11, 12 and the second slide parts 13, 14 moved by the actuator 15 and the tension members 16 fixed thereto. As a result, the test piece 2 bonded to the mounting member 21 is tensilely deformed in the four directions D1 to D4. The magnitude of the preliminary tensile load is set to be the same in the four directions D1 to D4.

In the pre-tensioning step, a pre-tensioning load is applied to the test piece 2 for a predetermined period of time, and then the actuator 15 is extended to return the test piece 2 to the state it was in before the pre-tensioning step. If the rubber test piece 2 has entangled molecular chains, the pre-tensioning step can untangle the molecular chains. This can reduce the effect of entangled molecular chains on the measurement results (strain-stress data) of the biaxial tensile test.

When the molecular chains become untangled, some of the tensile deformation of the test piece 2 remains even after the application of the preliminary tensile load is terminated, and the test piece 2 may become wavy. In a conventional biaxial tensile test in which the test piece 2 is clamped from above and below by a chuck, the clamping force of the chuck must be adjusted to match the waviness of the test piece 2. If the clamping force adjustment is inconsistent, the measurement results of the biaxial tensile test will also vary.

In contrast, in this embodiment, the mounting member 21 is adhered to the test piece 2, so that waviness of the test piece 2 at the adhesion portion can be suppressed and adjustment of the clamping force is unnecessary. As a result, the variation in the measurement results of the biaxial tensile test due to adjustment of the clamping force can be suppressed.

After the preliminary tension step, the actuator 15 is retracted again, and the test piece 2 is tensile-deformed in each of the four directions D1 to D4, thereby performing a biaxial tensile test on the test piece 2 (test step). The tensile deformation of the test piece 2 in this test step is the same as the tensile deformation of the test piece 2 in the preliminary tension step, except that the magnitude of the tensile load is different.

A known method is used to evaluate the biaxial tensile test (strain-stress data). One known method is to mark multiple measurement points on the test piece 2 in advance, and use image processing to measure the change in the spacing between the measurement points due to the tensile deformation of the test piece 2. In this method, the change in the spacing between the measurement points is regarded as strain, and the tensile load is regarded as stress, and the strain-stress data is calculated. Of course, other known methods may be used to calculate the strain-stress data of the biaxial tensile test. Furthermore, if the test piece 2 is wavy, the test piece 2 is tensile-deformed until the waviness is removed, and the strain-stress data is calculated in this state, which is regarded as the no-load state.

The portion of the test piece 2 that is effective as an evaluation value for the strain in the biaxial tensile test is a portion that is at least as far away from the bonded portion (constrained portion) with the mounting member 21 as the width of the bonded portion. Since one end 21a of the mounting member 21 that is bonded to the test piece 2 has a tapered shape in a plan view, the portion that is effective as an evaluation value for the biaxial tensile test can be made wider than when one end 21a is rectangular in a plan view. As a result, the measurement accuracy of the biaxial tensile test can be improved.

Here, in a conventional biaxial tensile test in which the test piece 2 is clamped above and below with a chuck, the test piece 2 and the chuck may slip, which may reduce the measurement accuracy of the biaxial tensile test. In contrast, in this embodiment, the mounting member 21 is bonded to the test piece 2, so that slippage between the test piece 2 and the mounting member 21 during the test step can be suppressed. Therefore, it is possible to suppress the decrease in measurement accuracy of the biaxial tensile test caused by this slippage.

Since the mounting members 21 are attached to both sides of the test piece 2, it is easy to apply uniform tensile deformation to the test piece 2 in the thickness direction in the testing step. This makes it possible to suppress the effect of non-uniform tensile deformation of the test piece 2 in the thickness direction on the measurement results of the biaxial tensile test.

In addition, since the tensile member 16 to which the mounting members 21 are attached can slide in the direction in which the mounting members 21 are arranged, the spacing between the mounting members 21 can be adjusted to match the tensile deformation of the test piece 2 in the test step. As a result, in the test step, the constraint of the test piece 2 due to the spacing between the mounting members 21 can be suppressed, and the decrease in measurement accuracy of the biaxial tensile test that accompanies this constraint can be suppressed.

Since the mounting member 21 that is adhered to the test piece 2 is detachably attached to the tensile member 16 by the bolts 24, when replacing the test piece 2 for the biaxial tensile test, the test piece 2 is first removed together with the mounting member 21. Next, a mounting member 21 different from the one that has been used for the biaxial tensile test is adhered to the new test piece 2 in advance, and the mounting member 21 is attached to the tensile member 16 by the bolts 24. After the tensile test, the mounting member 21 may be peeled off from the test piece 2 and reused, or may be discarded if it is difficult to peel off.

In this way, when replacing the test specimen 2, the task of peeling the test specimen 2 from the mounting member 21 is not required. In addition, the mounting member 21 can be peeled off from the test specimen 2 in a state in which the mounting member 21 is not restrained by the testing machine 10 and is easy to handle, making the peeling task easier. As a result, the task of replacing the test specimen 2 can be made easier.

Next, a second embodiment will be described with reference to Figures 3(a) and 3(b). In contrast to the first embodiment, the second embodiment describes a case in which a configuration is provided to restrict the rotation of the mounting members 35, 36 relative to the tension member 30. Note that the same parts as those in the first embodiment are given the same reference numerals and the following description will be omitted.

Figure 3(a) is a plan view of the tension member 30 and the mounting member 35 in the second embodiment. Figure 3(b) is a side view of the tension member 30 and the mounting members 35, 36 as viewed from the direction of the arrow IIIb in Figure 3(a).

The tension member 30 in the second embodiment is a rigid material that protrudes vertically from the first slide portion 11, 12 or the second slide portion 13, 14 (see FIG. 1) toward the center of the testing machine 10 (the side of the test piece 2), as in the first embodiment. In FIG. 3(a) and FIG. 3(b), the tension member 30 and the mounting members 35, 36 located in the second direction D2 of the test piece 2 are shown, but the tension members 30 and the mounting members 35, 36 located in the first direction D1, the third direction D3, and the fourth direction D4 of the test piece 2 are also configured in the same manner. Below, the tension member 30 and the mounting members 35, 36 on the second direction D2 side of the test piece 2 are described as examples, and some of the descriptions of the other tension members 30 and the mounting members 35, 36 are omitted.

The tip 31 of the tensile member 30 on the test piece 2 side is formed in a rectangular parallelepiped shape extending in a direction (third direction D3 and fourth direction D4) perpendicular to the protruding direction (first direction D1) of the tensile member 30 in a plan view. The lower surface of the tip 31 (the surface on the lower side of the paper in FIG. 3(b)) is a flat surface parallel to the first axis X and the second axis Y. The upper surface of the tip 31 (the surface on the upper side of the paper in FIG. 3(b)) is provided with a stopper 32 that protrudes upward over the entire length from the edge in the second direction D2, and a pair of stoppers 33 that protrude upward from the edge in the first direction D1 except for the center.

The mounting members 35, 36 are rigid members that connect the test piece 2 and the tip 31 of the tensile member 30. The mounting member 35 has one end 35a that is bonded to the upper surface of the test piece 2 with adhesive 22, and the other end 35b that is the end opposite the one end 35a and is detachably attached to the upper surface of the tip 31 with a single bolt 24. The mounting member 36 has one end 36a that is bonded to the lower surface of the test piece 2 with adhesive 22, and the other end 36b that is the end opposite the one end 36a and is detachably attached to the lower surface of the tip 31 with a single bolt 24.

The one end 35a, 36a is formed in a rectangular shape in a plan view. That is, the width of the one end 35a, 36a of the mounting member 35, 36 extending along the axial directions D1, D2 of the first axis X (the dimension in the axial directions D3, D4 of the second axis Y) is approximately constant. This makes it easier to ensure the adhesion area between the one end 35a, 36a and the test piece 2 compared to the first embodiment in which the one end 21a has a tapered shape in a plan view. As a result, the mounting member 35, 36 is less likely to peel off from the test piece 2.

The mounting member 35 passes between a pair of stoppers 33, and the other end 35b extends between and along the stoppers 32, 33, forming a T-shape overall. The center of the other end 35b is attached to the tip 31 with a single bolt 24. In this attached state, the rotation of the mounting member 35 around the bolt 24 (other end 35b) relative to the tension member 30 is restricted by the stoppers 32, 33.

The mounting member 36 has a step 36c that is recessed at one end 36a side relative to the other end 36b attached to the underside of the tip 31. This step 36c contacts the surface of the tip 31 on the side of the test piece 2. As a result, the step 36c restricts the rotation of the mounting member 36 around the bolt 24 (other end 36b) relative to the tension member 30.

In the second embodiment, as in the first embodiment, the tension member 30 slides relative to the first slide portion 11, 12 or the second slide portion 13, 14 (see FIG. 1), so that the distance between the one ends 35a, 36a of the mounting members 35, 36 can be adjusted in accordance with the tensile deformation of the test specimen 2. Here, when a discrepancy occurs between the distance between the one ends 35a, 36a and the distance between the tension members 30, and the mounting members 35, 36 rotate around the bolt 24 (other end 36b) relative to the tension member 30, a torsional force is applied to the adhesive portion between the one ends 35a, 36a and the test specimen 2.

However, in this embodiment, as described above, the mounting members 35, 36 are attached to the tension member 30 so that the rotation of the mounting members 35, 36 around the bolt 24 relative to the tension member 30 is restricted by the stoppers 32, 33 and the step 36c. This makes it possible to prevent a torsional force from being applied to the adhesive portion between the one end 35a, 36a and the test specimen 2 due to the rotation of the mounting members 35, 36 around the bolt 24. As a result, the mounting members 35, 36 are less likely to peel off from the test specimen 2.

In addition, by preparing mounting members 36 with different recesses on the one end 36a side due to step 36c, the distance between one end 35a and one end 36a where test piece 2 is clamped can be easily adjusted. This improves the degree of freedom in the thickness of test piece 2 that can be used for biaxial tensile testing.

Next, a third embodiment will be described with reference to Figures 4(a) and 4(b). In the second embodiment, a case where the distance from one end 35a to one end 36a, where the test piece 2 is clamped by the step 36c of the mounting member 36, is adjusted is described. In contrast, in the third embodiment, a case where the distance between a pair of upper and lower ends 21a, where the test piece 2 is clamped by the step 42 provided in the tension member 40, is adjusted is described. Note that the same parts as in the first embodiment are given the same reference numerals and the following description is omitted.

Figure 4(a) is a side view of the tension member 40 and the pair of upper and lower mounting members 21 in the third embodiment. Figure 4(b) is a side view of the tension member 40 and the mounting members 21 and 46. The mounting member 46 is configured in the same way as the mounting member 21, except that the length from one end 21a to the other end 21b is shorter than that of the mounting member 21.

The tension member 40 in the third embodiment is a rigid material that protrudes vertically from the first slide portion 11, 12 or the second slide portion 13, 14 (see FIG. 1) toward the center of the testing machine 10 (the side of the test piece 2), as in the first embodiment. In FIG. 4(a) and FIG. 4(b), the tension member 40 and the mounting members 21, 46 located in the second direction D2 of the test piece 2 are shown, but the tension members 40 and the mounting members 21, 46 located in the first direction D1, the third direction D3, and the fourth direction D4 of the test piece 2 are similarly configured. Below, the tension member 40 and the mounting members 21, 46 on the second direction D2 side of the test piece 2 are described as examples, and some of the descriptions of the other tension members 40 and mounting members 21, 46 are omitted.

The tip end (end on the side of the test piece 2) of the tensile member 40 comprises a thick portion 41 and a thin portion 43 connected to the tip end side (on the side of the test piece 2) of the thick portion 41. The tensile member 40 has a step 42 so that the lower surface of the thin portion 43 is recessed relative to the lower surface of the thick portion 41. The upper surfaces of the thick portion 41 and the thin portion 43 are formed flush with each other, and no step is provided. Therefore, in the tensile member 40, the thickness of the thin portion 43 is smaller than the thickness (vertical dimension) of the thick portion 41.

The thin-walled portion 43 has a bolt hole 45 that penetrates vertically. A bolt hole 44 is also provided on the underside of the thick-walled portion 41. A bolt hole (not shown) is also provided on the upper surface of the thick-walled portion 41 on the opposite side to the bolt hole 44. The mounting member 21 is removably attached to the upper surface of the thick-walled portion 41 by fitting a bolt 24 that penetrates the other end 21b of the mounting member 21 into the bolt hole on the upper surface.

Furthermore, as shown in FIG. 4(a), the mounting member 21 is also detachably attached to the underside of the thick-walled portion 41 by fitting a bolt 24 that passes through the other end 21b of the mounting member 21 into a bolt hole 44 on the underside of the thick-walled portion 41. This determines the distance between the one end 21a of the pair of mounting members 21 according to the thickness of the thick-walled portion 41, and a test piece 2 of a thickness that matches this distance can be sandwiched between the one end 21a.

4(b), the mounting member 46 is detachably attached to the underside of the thin-walled portion 43 by fitting a bolt 47 passing through the other end 21b of the mounting member 46 into a bolt hole 45 on the underside of the thin-walled portion 43 instead of the bolt hole 44 of the thick-walled portion 41. At this time, the length of the mounting member 46 is adjusted so that one end 21a of the mounting member 21 attached to the upper surface of the thick-walled portion 41 and one end 21a of the mounting member 46 attached to the underside of the thin-walled portion 43 face each other vertically.
As a result, the distance between one end 21a of mounting member 21 and one end 21a of mounting member 46 is determined according to the thickness of thin-walled portion 43, and a test piece 2 of a thickness that matches this distance can be sandwiched between the one ends 21a.

In this way, by changing the attachment position of the attachment members 21, 46 on the underside of the tensile member 40 and using attachment members 21, 46 with a length that matches that position, the distance between the pair of ends 21a between which the test piece 2 is clamped can be easily adjusted. This improves the degree of freedom in the thickness of the test piece 2 that allows biaxial tensile testing.

The shaft of the bolt 47 fitted into the bolt hole 45 on the lower surface of the thin-walled portion 43 protrudes from the upper surface of the thin-walled portion 43. The protruding bolt 47 is inserted into the through hole 21c provided in the mounting member 21 on the upper surface side of the tension member 40. This allows the bolt 47 inserted into the through hole 21c to restrict the rotation of the mounting member 21 attached to the upper surface of the thick-walled portion 41 of the tension member 40 by the bolt 24 around the bolt 24 (the other end 21b). Therefore, as in the second embodiment, the application of a torsional force to the adhesive portion between the one end 21a and the test piece 2 due to the rotation of the mounting member 21 around the bolt 24 can be suppressed, making it difficult for the mounting member 21 to peel off from the test piece 2.

The present invention has been described above based on the embodiments, but the present invention is in no way limited to the above embodiments, and it can be easily imagined that various improvements and modifications are possible within the scope of the invention without departing from its spirit.

In the above embodiment, the mechanism (testing machine 10) for pulling the test piece 2 in each of the four directions D1 to D4 by separate actuators 15 has been described, but the test piece 2 may be pulled in each of the four directions D1 to D4 by using another known mechanism. For example, in a plan view, a total of four shafts are provided that extend from each of the pair of first slide parts 11, 12 toward each other at a 45° angle. Both ends of the pair of second slide parts 13, 14 are slidably fixed to each of these shafts. In this way, simply by widening the gap between the pair of first slide parts 11, 12 with one actuator 15, the gap between the pair of second slide parts 13, 14 sliding on the shaft also widens, and the test piece 2 can be pulled in the four directions D1 to D4. The actuator 15 is not limited to an air cylinder, and may be hydraulic or electric.

In the above embodiment, four tension members 16, 30, 40 are slidably fixed to the first slide portions 11, 12 and the second slide portions 13, 14, respectively, but the number of tension members 16, 30, 40 may be changed as appropriate. Also, the first slide portions 11, 12 and the second slide portions 13, 14 may be omitted, and the test specimen 2 may be pulled in the four directions D1 to D4 via the mounting members 21, 35, 36, 46 by the tension members 16, 30, 40 arranged one each in the four directions D1 to D4 of the test specimen 2.

In the above embodiment, the case where one end 21a, 35a, 36a of the mounting member 21, 35, 36, 46 is adhered to both sides of the test piece 2 has been described, but one end 21a, 35a, 36a may be adhered to only one side of the test piece 2. In this case, the thickness of the test piece 2 can be freely set compared to the case where the test piece 2 is sandwiched between the upper and lower one ends 21a, 35a, 36a.

In the above second embodiment, the mounting member 35 is adhered to one side of the test piece 2 and the mounting member 36 is adhered to the other side of the test piece 2. However, the mounting member 35 may be adhered to both sides of the test piece 2, or the mounting member 36 may be adhered to both sides of the test piece 2. In this case, the shape of the tensile member 30 is adjusted to match the shape of the mounting members 35, 36.

In the above embodiment, the mounting members 21, 35, 36, 46 are detachably attached to the tensile members 16, 30, 40 by the bolts 24, 47, but the method of attachment may be changed as appropriate. For example, the tensile members 16, 30, 40 may be configured with chucks that clamp the mounting members 21, 35, 36, 46 from above and below. In this case, a conventional biaxial tensile tester that clamps the test piece 2 from above and below with chucks can be used for the biaxial tensile test of the present invention.

In the above embodiment, the test piece 2 is a rectangular plate, but the shape of the test piece 2 may be changed as appropriate. For example, the test piece 2 may be made of a cross-shaped plate material. Furthermore, the test piece 2 is not limited to rubber, and other elastic materials such as thermoplastic elastomers and relatively soft resins may be used for the test piece 2.

In the above embodiment, the case where the attachment step of attaching the attachment members 21, 35, 36, 46 to the tension members 16, 30, 40 is performed after the adhesion step of adhering the attachment members 21, 35, 36, 46 to the test piece 2 has been described, but for example, the adhesion step may be performed after the attachment step. Also, the attachment members 21, 35, 36, 46 may be adhered to one side of the test piece 2 and the attachment members 21, 35, 36, 46 may be attached to the tension members 16, 30, 40, and then the attachment members 21, 35, 36, 46 may be adhered to the other side of the test piece 2 and the attachment members 21, 35, 36, 46 may be attached to the tension members 16, 30, 40.

2 Test piece 10 Biaxial tensile tester 11, 12 First slide portion 13, 14 Second slide portion 15 Actuator 16, 30, 40 Tensile member 21, 35, 36, 46 Mounting member 21a, 35a, 36a One end portion 21b, 35b, 36b Other end portion X First axis Y Second axis D1 First direction (axial direction of first axis)
D2: Second direction (axial direction of the first shaft)
D3: Third direction (axial direction of the second shaft)
D4 Fourth direction (axial direction of the second shaft)

Claims (3)

A biaxial tensile testing method for performing a biaxial tensile test on a test piece made of a plate-like elastic body by pulling the test piece along four directions, which are axial directions of a first axis and a second axis perpendicular to each other, using a biaxial tensile testing machine,
a bonding step of bonding one end of the mounting member to at least one surface of the test piece such that a plurality of mounting members protrude from the test piece along each of the four directions;
a mounting step of mounting the mounting member to the biaxial tensile testing machine;
A test step of performing the biaxial tensile test by pulling each of the mounting members bonded in the bonding step in a direction protruding from the test piece by the biaxial tensile tester ,
The biaxial tensile tester includes a plurality of tensile members to which the other ends of the plurality of mounting members remote from the test piece are detachably attached,
an actuator that moves the plurality of tension members in each of the four directions;
a pair of first slide portions to which a plurality of the tension members are fixed so as to be slidable along the axial direction of the first axis, and which are moved away from each other in the axial direction of the second axis by the actuator in the testing step;
A pair of second slide portions to which the tension members are fixed so as to be slidable along the axial direction of the second axis and which are moved away from each other in the axial direction of the first axis by the actuator in the testing step,
In the test step after the bonding step and the mounting step, the actuator pulls the mounting member in each of the four directions via the plurality of tension members,
In the bonding step, the plurality of mounting members are bonded to the test piece such that the plurality of mounting members protruding along the axial direction of the first axis are arranged at intervals in the axial direction of the second axis, and the plurality of mounting members protruding along the axial direction of the second axis are arranged at intervals in the axial direction of the first axis,
A biaxial tensile testing method, characterized in that in the mounting step, the mounting member is attached to the tensile member so that rotation of the mounting member around the other end portion with respect to the tensile member is restricted . 2. The biaxial tensile test method according to claim 1 , wherein the one end of the mounting member adhered to the test piece is rectangular when viewed in a direction perpendicular to the first axis and the second axis. 2. The biaxial tensile test method according to claim 1 , wherein the one end of the mounting member adhered to the test piece has a tapered shape when viewed in a direction perpendicular to the first axis and the second axis.

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