JP6412479B2 - Tensile testing machine - Google Patents

Description

  The present invention relates to a tensile tester.

Conventionally, tensile tests have been performed for the purpose of measuring general strength properties of materials. This tensile test is usually performed under the conditions of strain rate of 0.001 / s or more and 0.01 / s or less using a test piece having a parallel part length of about 50 mm. On the other hand, when examining the deformation behavior of steel plates, resin members, etc. at the time of a car collision, the material strength has strain rate dependence, so a high-speed tensile test up to about 1000 / s is performed. There is a need to do.
In a static tensile test with a strain rate of about 0.001 / s or more and 0.01 / s or less, when a load is applied to a test piece, a driving unit of the tensile tester, a test piece, a load cell as a load measuring unit, and In a system composed of devices for fixing and holding them, the load is increased or decreased in a steady state according to the material characteristics of the test piece, and the load is measured by the load cell.

On the other hand, when the crosshead speed of the tensile tester can be increased, a tensile test in which the crosshead speed exceeds 1000 mm / s, that is, when the distance between grades is 50 mm, the strain rate is 20 / s. When a tensile test is performed at such a high speed, the load increases rapidly. For this reason, propagation of stress waves occurs in the tensile testing machine system, and load vibrations make it difficult to measure an accurate load.
As a method to solve this problem, a long load cell of several meters called a Hopkinson bar is used, and the test piece is broken before the load acting on the test piece is reflected in the tensile tester system and reaches the load cell. A split-type Hopkinson pressure bar method has been proposed.
In this method, a high-speed tensile test with a strain rate of about 500 / s or more and 2000 / s or less is possible, and more accurate load measurement can be performed.
However, this method limits the shape of the test piece that can be measured with a small degree of freedom of the fixed portion of the test piece. In addition, since the strain rate is limited to about 500 / s or more and 2000 / s or less, it is difficult to test at a strain rate smaller than this, and it is difficult to grasp the strain rate dependency of the material properties of the test piece. is there.

On the other hand, a method capable of performing a tensile test in a wide range where the strain rate is 0.01 / s or more and 1000 / s or less has been proposed (for example, see Patent Document 1). The basic principle of the method described in Patent Document 1 is that a test piece is connected to a small protrusion provided on a load measurement block, and a load is applied to the test piece by a load application block. The stress wave propagated through the test piece from the load application block with application of the load is dissipated on the surface of the load measurement block.
This makes it possible to perform a high-speed tensile test that was difficult except for the Hopkinson pressure bar method, and to perform a tensile test in a wider strain rate range.

Japanese Patent No. 3769175

However, in the method described in Patent Document 1, there are restrictions on the shape of the test piece that can be measured and the test temperature. Basically, the test piece must have a predetermined shape, and the test temperature can be changed. A tensile test cannot be performed. In practice, when the strain rate exceeds 100 / s, the dissipation of the stress wave becomes insufficient, load vibration occurs, and the measurement accuracy of the load measurement cannot be maintained.
The present invention has been made in view of such problems, and avoids a decrease in measurement accuracy of load measurement due to load vibration, and provides high selectivity of test piece shape and test temperature. An object of the present invention is to provide a tensile testing machine.

According to one aspect of the present invention, the first chucking member and the second chucking member that grip the test piece face to face are connected to the opposite side of the first test piece to the test piece side. A fixed portion that is connected to the second chucking member on the opposite side of the test piece side, a movable portion that pulls the test piece to the opposite side of the fixed portion, and a tensile load that acts on the test piece A tensile tester comprising a load measuring unit for measuring at least one of the fixed unit and the first chucking member and the movable unit and the second chucking member. On the other hand, there is provided a tensile tester including a block that absorbs a stress wave propagated from the test piece and prevents the stress wave from being reflected and input to the load measuring unit .

  According to one aspect of the present invention, it is possible to avoid a decrease in measurement accuracy of load measurement due to load vibration, to perform a high-speed tensile test without being restricted by the shape of the test piece, and to change the test temperature. All the tensile tests can be performed, and the versatility of the tensile tester can be further improved.

It is a block diagram which shows an example of the tensile testing machine to which this invention is applied. It is an example of the load measurement result in the tension test at the time of using the tensile testing machine to which this invention is applied. It is a characteristic view which shows an example of the stress strain characteristic at the time of performing a low temperature tensile test. It is a characteristic view which shows an example of the stress strain characteristic at the time of performing a low temperature tensile test.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
In the following detailed description, numerous specific specific configurations are set forth in order to provide a thorough understanding of embodiments of the present invention. However, it will be apparent that other embodiments may be practiced without limitation to such specific specific configurations. The following embodiments do not limit the invention according to the claims. In addition, not all the combinations of features described in the embodiments are essential for the solving means of the invention.

As shown in FIG. 1, a tensile tester 1 to which the present invention is applied includes a frame part 2, a drive part 3, and a measurement part 4.
The frame unit 2 has a structure in which the upper base 13 is supported on the lower base 11 via a plurality of support columns 12, and the driving unit 3 is disposed on the upper base 13.
The drive unit 3 includes a drive device 21 as a hydraulic actuator, a hydraulic unit 22 that supplies hydraulic oil for operating the drive device 21, and an accumulator 23 that accumulates the hydraulic oil supplied to the hydraulic unit 22. .
The drive device 21 includes, for example, a hydraulic cylinder, and moves the piston up and down with hydraulic oil from the hydraulic unit 22.

  The measuring unit 4 includes a movable rod guide unit 31, a movable rod (movable unit) 32, a movable block 33 connected to one end of the movable rod 32, and a test piece TP fixed to the movable block 33 by a connecting member 34. A movable side chucking member (second chucking member) 35 that grips one end of the test piece TP, a fixed side chucking member (first chucking member) 36 that grips the other end of the test piece TP, and a fixed side block 38. A load cell 37 serving as a load measuring portion provided between the fixed side chucking member 36 and the fixed side block 38, and a fixing rod (fixed portion) 39 for fixing the fixed side block 38 to the lower base 11. And the central axes of these parts are arranged so as to coincide with the common central axis. The movable rod guide 31 holds the movable rod 32 so as to be slidable.

The movable rod 32 is composed of a piston rod connected to the piston of the drive device 21.
The movable side chucking member 35 and the fixed side chucking member 36 include a grip part for gripping the test piece TP. For example, the test piece TP is gripped by passing a pin through a hole formed in the grip part. ing.
For example, both ends of the connecting member 34 and the load cell 37 are threaded, and thereby, the movable block 33 and the movable chucking member 35 are connected via the connecting member 34, and the load cell 37 is also connected. Thus, the fixed side chucking member 36 and the fixed side block 38 are connected.

  The movable side block 33 and the fixed side block 38 are vibration absorbing blocks for leveling stress waves generated by sudden changes in stress and suppressing stress vibration. In order to suppress the stress vibration, it is advantageous to use a larger block because the stress is attenuated and it takes time until the stress is reflected from the block surface and reaches the load cell 37 again. However, since the block is connected to both the movable side chucking member 35 and the fixed side chucking member 36, the movable side block 33 connected to the movable side chucking member 35 has a large mass due to the inertia of the block. Stroke control becomes unstable. Therefore, it is preferable to adjust the mass of the movable block 33 according to the magnitude of the tensile load applied to the test piece TP.

Further, in order to cancel the stress wave generated in the test piece TP by being reflected by the movable side block 33 and the fixed side block 38, the distance from the test piece TP to the movable side block 33, the test piece TP and the fixed side block It is preferable that the distance to 38 is equal, and the movable block 33 and the fixed block 38 have the same mass and the same shape. At this time, the cross-sectional shape of the block having the smallest mass and the most effective damping of stress vibration is circular.
The cross-sectional shape here refers to the shape of the cross section when the block is cut along a plane perpendicular to the central axis of the measuring unit 4.

When a tensile test was performed using blocks having various shapes such as a circle, a square, and a star as the movable block 33 and the fixed block 38, the block having a circular cross section had the most stress vibration. It was confirmed that there is an effect on deterrence. If the cross-sectional shape is circular, the shape of the movable block 33 and the fixed block 38 may be a cylinder or a sphere, but a cylinder is simple to create.
As the movable side block 33 and the fixed side block 38, for example, a cylindrical block made of carbon steel and having a diameter of 100 mm and a height (height in the central axis direction of the measuring unit 4) of 50 mm can be applied. In addition, it is preferable to change the shape and size of the movable block 33 and the fixed block 38 according to the strength level of the test piece TP, the tensile test speed, the natural frequency of the tension support machine, and the like.

  As the movable side block 33 and the fixed side block 38, a layered block in which a plurality of blocks are stacked may be mounted. By using the layer-shaped blocks in this way, the masses of the movable block 33 and the fixed block 38 can be easily adjusted by adjusting the number of blocks to be stacked. In addition, as the movable block 33 and the fixed block 38, a plurality of blocks having different masses are prepared, and suitable for this depending on the strength level of the test piece TP, the tensile test speed, the natural frequency of the tension support machine, and the like. Alternatively, a block having a large mass may be selected, and the selected block may be mounted as the movable block 33 and the fixed block 38.

The hydraulic unit 22 is controlled by a control device (not shown). Further, the detection signal of the load cell 37 is input to the control device, and the control device displays the measured load by the load cell 37 on a display device (not shown) or the like.
Thus, in the tensile testing machine 1 in the present embodiment, the movable side block 33 and the fixed side block 38 are provided as vibration absorption blocks.
Therefore, even when a stress change occurs suddenly in the test piece TP during the tensile test and a stress wave is thereby generated, the stress wave is absorbed by the movable side block 33 and the fixed side block 38. Therefore, it is possible to avoid the stress wave reflected from the movable block 33 and the fixed block 38 from being input to the load cell 37. Therefore, the load cell 37 can perform load measurement without being affected by the stress wave, and as a result, the accuracy of the tensile test can be improved.

Since load measurement can be performed without being affected by stress waves in this way, load measurement that is not affected by stress waves can be performed even when the strain rate is large or small. Can do.
Although the load measurement can be performed without being affected by the stress wave by providing the movable block 33 and the fixed block 38 as described above, the stress can be measured from the relationship between the strain rate and the natural frequency. There are cases where waves cannot be sufficiently suppressed. In this case, the natural frequency may be shifted by changing the masses of the movable block 33 and the fixed block 38. As described above, when the movable side block 33 and the fixed side block 38 are formed of layer-shaped blocks, the mass may be adjusted by adjusting the number of blocks to be stacked. In the case of the method of mounting a block selected from a plurality of blocks having different masses as the movable side block 33 and the fixed side block 38, another block having a different mass is newly selected, and this is moved to the movable side block 33 and the fixed side block 38. What is necessary is just to mount | wear as the block 33 and the fixed side block 38.

Further, as shown in FIG. 1, the tensile testing machine 1 in the present embodiment is configured to fix the test piece TP between the movable side chucking member 35 and the fixed side chucking member 36. The chucking member 35 moves in the vertical direction in FIG.
Therefore, the test piece TP can be held by the movable side chucking member 35 and the fixed side chucking member 36, and the position of the movable side chucking member 35 in the state where the test piece TP is held is set as the initial position. If the movable side chucking member 35 can move further upward by a sufficient distance to give the required tensile load, a tensile test can be performed. That is, the longer the movable distance in the vertical direction in FIG. 1 of the movable side chucking member 35, the longer the tensile test can be performed on the test piece TP that is longer in the vertical direction. Therefore, the degree of freedom of the size and shape of the test piece TP can be expanded as compared with the conventional tensile testing machine.

For example, the user holds one end of the test piece TP with the fixed-side chucking member 36 while moving the movable-side chucking member 35 upward, and then lowers the movable-side chucking member 35. What is necessary is just to hold | grip the other end of the test piece TP with the movable side chucking member 35. FIG. By performing such an operation, it is possible to perform a tensile test on a test piece TP having a larger size. In addition, by adjusting the height position of the upper base 13, it is possible to perform tests on test pieces TP of various sizes.
At this time, for example, the distance between the fixed side chucking member 36 and the movable side chucking member 35 is formed by variably forming the length of the fixed rod 39 and further adjusting the length of the fixed rod 39. Is secured and a larger test piece TP can be gripped, so that a tensile test can be performed on the test pieces TP having more shapes.

The fixing rod 39 is adjusted by, for example, forming the fixing rod 39 to be replaceable, and selecting a rod having a length suitable for the size and shape of the test piece TP from a plurality of rods having different lengths. The selected rod may be fixed to the lower base 11 as the fixed rod 39.
In addition, the tensile testing machine 1 in the present embodiment can be realized by providing at least one of the movable side block 33 and the fixed side block 38 as vibration absorbing blocks in the existing tensile testing machine 1. That is, it can be easily realized without significant changes to the existing tensile testing machine 1.

  Further, as shown in FIG. 1, each part included in the measurement unit 4 is arranged so that the central axes of the respective parts coincide with each other and moves along the central axis, so that the movable side chucking member 35 and the fixed side chucking member The periphery of the test piece TP held between the two is relatively open. Therefore, for example, it is possible to store the movable side chucking member 35 and the fixed side chucking member 36 in the cooling chamber while holding the test piece TP. Therefore, for example, the inside of the cooling chamber can be a nitrogen atmosphere in which liquid nitrogen is heated and the tensile test can be performed in a state where the test piece TP is maintained in the nitrogen atmosphere. That is, the tensile test can be performed by changing the environmental temperature to a desired temperature. Similarly, the temperature can be raised.

As described above, because the restrictions on the shape of the test piece are expanded, for example, a joint test piece, a product member, etc. itself can be subjected to a high-speed tensile test as it is, and a test etc. by changing the test temperature can be performed. Can also contribute greatly to product design in manufacturing.
A load cell 37 is provided on the fixed rod 39 side. Here, when the load cell 37 is provided on the movable rod 32 side, the load cell 37 moves up and down as the movable rod 32 moves up and down during the tensile test. When the load cell 37 moves up and down, wirings (not shown) connected to the load cell 37 also move together, which may interfere with the wiring. However, since the load cell 37 is provided on the fixed rod 39 side in the tensile testing machine 1 in the present embodiment, the wiring of the load cell 37 does not move during the tensile test.

In the above-described embodiment, the case where the movable side block 33 and the fixed side block 38 are provided on the movable rod 32 side and the fixed rod 39 side, respectively, has been described. However, the present invention is not limited to this. You may provide only in either one of the rods 39 side. That is, theoretically, it is preferable to provide a block on both the movable rod 32 side and the fixed rod 39 side. However, when a block is provided on both the movable rod 32 side and the fixed rod 39 side, only on the fixed rod side. When the obtained load measurement results are compared with the case where the block is provided, the difference between these load measurement results is slight, and even if the block is provided only on the fixed rod 39 side, the influence of stress vibration is suppressed. It was confirmed that a sufficient load measurement result could be obtained. Similarly, when the block is provided only on the movable rod 32 side, a load measurement result that can be used substantially sufficiently was obtained.
As described above, when a block is provided on the movable rod 32 side, the stroke control of the movable rod 32 may be difficult due to the inertia of the block. In consideration of stability, by providing a block only on the fixed rod 39 side, it is possible to obtain a load measurement result having desired accuracy while ensuring stability of stroke control.

In the above embodiment, the case where the movable rod 32 is driven using the hydraulic unit 22 has been described. However, the present invention is not limited to this, and the movable rod 32 may be mechanically driven. The movable rod 32 may be driven using any device as long as it can move up and down to apply a desired load to the test piece TP. Similarly, the chucking members 35 and 36 are not limited to a method in which the test piece TP is fixed using a pin, and any type of chucking member may be used as long as the test piece TP can be fixed removably. It can be applied even if it exists.
Moreover, in the said embodiment, although the case where the movable rod 32 was moved up and down and the test piece TP was pulled up and down was demonstrated, it is not restricted to this, Even when the test piece TP is driven to the left and right direction Can be applied.

A tensile test was performed using the tensile tester 1 shown in FIG. As a test piece, a 590 MPa class high-tensile steel plate was used. The distance between the scores of the test pieces was 10 mm, the thickness was 1.6 mm, and a tensile test was performed at a speed of 10,000 mm / s.
As a comparative example, a test piece having the same shape was used, and a tensile test was performed in the same tensile tester 1 without mounting a block. These load measurement results are shown in FIG.
In FIG. 2, a characteristic line L1 indicated by a solid line represents a load measurement result when the tensile tester 1 is used, and a characteristic line L2 indicated by a broken line indicates a test using the tensile tester 1 without mounting a block. The load measurement result when performed is shown. Moreover, the horizontal axis of FIG. 2 represents the movable rod displacement [mm], and the vertical axis represents the load [N].
From FIG. 2, the characteristic line L2 vibrates, whereas the characteristic line L1 does not vibrate, and the load measurement value which is not affected by the stress wave when the tensile testing machine 1 in the present embodiment is used. It can be seen that

3 and 4 show the stress when the low-temperature tensile test of the resin material is performed using the tensile tester provided with the fixed side block 38 only on the fixed rod 39 side in the tensile tester 1 shown in FIG. It is a characteristic view which shows a distortion characteristic.
ABS resin and PP (polypropylene) were used as resin materials, and a high-speed tensile test was performed by changing the strain rate in the range of 1 / s to 300 / s in the temperature range of room temperature to −40 ° C. and higher. In the tensile testing machine 1 shown in FIG. 1, the movable side chucking member 35 and the fixed side chucking member 36 and the test piece TP gripped by these chucking members are accommodated in the cooling chamber, and in the cooling chamber. Tensile tests were performed in a nitrogen atmosphere in which liquid nitrogen was heated at a controlled temperature.

  3 shows a case where ABS resin is used as the resin material, FIG. 4 shows a case where PP is used as the resin material, and the temperature environment is room temperature (RT) (FIGS. 3A and 4A), −10 The results in the case of ° C. (FIG. 3B, FIG. 4B) and −40 ° C. (FIG. 3C, FIG. 4C) are shown. 3A, the characteristic line a1 has a strain rate of 1.1 / s, the characteristic line a2 has a strain rate of 12.2 / s, and the characteristic line a3 has a strain rate of 359 / s. Indicates. In FIG. 3B, the characteristic line b1 indicates the case where the strain rate is 1.83 / s, the characteristic line b2 indicates the case where the strain rate is 20 / s, and the characteristic line b3 indicates the case where the strain rate is 179 / s. . In FIG. 3C, the characteristic line c1 has a strain rate of 1.56 / s, the characteristic line c2 has a strain rate of 14.6 / s, and the characteristic line c3 has a strain rate of 216 / s. Indicates. In FIG. 4A, the characteristic line a11 has a strain rate of 1.45 / s, the characteristic line a12 has a strain rate of 11.2 / s, and the characteristic line a13 has a strain rate of 347 / s. Indicates. In FIG. 4B, the characteristic line b11 has a strain rate of 1.06 / s, the characteristic line b12 has a strain rate of 9.07 / s, and the characteristic line b13 has a strain rate of 311 / s. Indicates. In FIG. 4C, the characteristic line c11 has a strain rate of 1.1 / s, the characteristic line c12 has a strain rate of 16.5 / s, and the characteristic line c13 has a strain rate of 197 / s. Indicates.

3 and 4 that the load vibration is suppressed in both cases. That is, it was confirmed that it is possible to perform a high-speed tensile test in which the strain rate is changed in an environment where the test temperature is changed.
It should be noted that the scope of the present invention is not limited to the illustrated and described exemplary embodiments, but includes all embodiments that provide the same effects as those intended by the present invention. Further, the scope of the invention can be defined by any desired combination of specific features among all the disclosed features.

DESCRIPTION OF SYMBOLS 1 Tensile tester 2 Frame part 3 Drive part 4 Measuring part 11 Lower base 12 Support | pillar 13 Upper base 21 Drive apparatus 22 Hydraulic unit 23 Accumulator 31 Movable rod guide part 32 Movable rod (movable part)
33 movable side block 34 connecting member 35 movable side chucking member (second chucking member)
36 Fixed side chucking member (first chucking member)
37 Load cell (load measuring section)
38 Fixed block 39 Fixed rod (fixed part)
TP specimen

Claims (5)

A first chucking member and a second chucking member for gripping the test piece facing each other;
A fixing portion connected to the opposite side of the test piece side of the first chucking member;
A movable part connected to the opposite side of the test piece side of the second chucking member and pulling the test piece to the opposite side of the fixed part;
A load measuring unit for measuring a tensile load acting on the test piece;
In a tensile testing machine equipped with
Between the first chucking member with the fixed portion and, on at least one of between the second chucking member and the movable portion, to absorb the stress wave propagating from the specimen A tensile testing machine comprising: a block that prevents the stress wave from being reflected and input to the load measuring unit .   The tensile testing machine according to claim 1, wherein the block is provided only between the fixed portion and the first chucking member.   The tensile tester according to claim 1, wherein the load measuring unit is provided on the fixed part side of the first chucking member. Having the block between the fixed part and the first chucking member;
The tensile tester according to claim 3, wherein the load measuring unit is provided between the first chucking member and the block.   The tensile testing machine according to any one of claims 1 to 4, wherein a shape of a cross section of the block perpendicular to a tensile direction of the test piece is circular.

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