JP5991278B2 - Tension compression test method and apparatus - Google Patents

Description

  The present invention relates to a tensile and compression test method and apparatus, and more particularly to a tensile and compression test method and apparatus that can be preferably used for a tensile and compression test of a thin steel sheet.

The tensile compression test is a test for evaluating the strength performance of a metal material. Specifically, a tensile load is applied to a metal material processed into a predetermined test piece shape, and after applying a tensile deformation of a specific strain amount, the load is once removed, and a compressive load is applied as it is to cause a compressive deformation. Alternatively, tensile deformation may be applied after compressive deformation is applied.
It is known that when the applied load is reversed from tension to compression, it yields again at a stress lower than the stress value reached at the time of tensile deformation and plastically deforms. This phenomenon is called the Bausinger effect.

In recent years, as the strength of steel sheets for automobiles has increased, the influence of the Bausinger effect has come to be regarded as important.
For example, a dimensional accuracy defect called a spring pack occurs during press forming of a high-strength automotive steel sheet. In this case, when a material having a residual stress generated by press molding is removed from the mold, the shape is recovered by elastic recovery. It is known that the material is subjected to complicated deformation during press molding, and tensile deformation and compression deformation are imparted to the material, so that the above Bauschinger effect affects the magnitude of residual stress.

  In addition, it is known that collision safety performance, which is an important performance of automobiles, is also influenced by the Bauschinger effect. The car body is structured to absorb the collision energy and ensure the safety of the occupant by plastic deformation of the automobile parts at the time of the collision, but during the deformation due to the collision, the material repeatedly undergoes complicated tensile deformation and compression deformation To do. When the direction of the load stress is reversed, the yield stress is reduced by the Bauschinger effect, resulting in an impact on the collision energy.

Therefore, in order to realize press molding with higher accuracy and optimization of collision characteristics, it is necessary to accurately grasp the characteristics of the material including the Bauschinger effect.
When a tensile compression test for evaluating the Bauschinger effect is performed on a thin steel plate (abbreviated as a thin plate), there is a problem that the material undergoes buckling deformation during compression. Further, when the strength of the material to be tested is high and the plate thickness is thin, buckling deformation is more likely to occur, and there is a problem that a highly accurate test is difficult. Conventionally, a tensile compression test method using a thin plate has been studied.

In Patent Document 1, in order to prevent buckling, at least two guide members are installed in parallel to the stress load direction on the test piece so that the stress load direction on the test piece and the test piece longitudinal direction always coincide during the stress test. A proposed test method has been proposed. Thereby, even if a strain of 1.5% or more is applied, a tensile compression test is possible.
Patent Document 2 proposes a test piece holding device that holds a test piece during a tensile and compression test of a thin plate. This prevents bending of the test piece during the compression test, can be performed with high accuracy, and the strain generated on the test piece from the window set in the buckling prevention jig is easily measured. Yes.

  Patent Document 3 proposes a test apparatus and a test method that do not buckle even under biaxial load conditions, and that do not cause defects such as deformation and damage to the load grip even when the test piece breaks. Yes. There, the dimensions of the test piece shape are defined for the purpose of handling a test piece having a relatively large thickness and giving a uniform stress to the test portion.

JP 2008-241530 A JP 2009-257885 A JP 2000-180322 A

In press forming and impact deformation, the strain generated in the steel sheet may be in a region of 5% or more, and there is a need for measurement in such a high strain region in the measurement of the Bausinger effect.
However, as described in the drawings of Patent Document 1 and Patent Document 2, in the conventional method and apparatus, the strain is less than 5% at the maximum, and the plate thickness is about 1.0 mm according to the needs (more specifically, It has been difficult to perform tensile and compressive deformation of a thin steel sheet of 0.7 to 2.0 mm with high accuracy by applying strain of 5% or more.

Since the techniques proposed in Patent Document 1 and Patent Document 3 are test methods for line pipe materials having a thickness of 10 mm or more, structural stainless steels and ceramics, the thickness is several mm or less. When it is implemented with a thin steel sheet for automobiles, there is a problem that buckling deformation easily occurs.
The technique described in Patent Document 2 is a test method for thin steel sheets. However, in strain measurement from a window installed in a buckling prevention jig, a buckling presser is not applied to a specimen portion located in the window. Therefore, it is difficult to make the buckling of the specimen completely zero. Further, since a strain gauge is used as a strain measuring means, it exceeds the maximum limit strain (value less than 5%) of the strain gauge currently on the market. In the strain region of more than 10%, problems such as accuracy reduction and gauge peeling occur. Note that the strain gauge does not support repeated tensile strain and compressive strain, and there is a problem that the accuracy of measurement is not guaranteed in compressive deformation after tensile deformation or tensile deformation after compressive deformation. In addition, the strain gauge is disposable and has a problem with economy.

  As described above, in the prior art, in a tensile compression test of a thin steel plate test piece having a thickness of about several millimeters, if the compressive strain is 5% or more, the measurement accuracy is likely to be reduced in both buckling deformation and tensile and compression. There was a problem that the economy was not good.

The present invention has been made to solve the above problems, and the gist of the present invention is as follows.
[1] A tensile and compression test method for performing a load repetition test from tension to compression and from compression to tension on the test portion of the test piece 1,
The relationship of the test portion of the test piece 1 and the length L test section width W and L / W ≧ 4.0, the test section shoulder R and R ≦ 2.0 mm,
The joining extensometer holding fixture 11 by resistance welding to the side surface of the test piece 1, firmly fixed more elongation meter 2 to extensometers holding metal fitting 11 which is the junction,
The adhesive is applied with the elongation meter 2 of the measuring part to the contact part of the side surface of the test piece 1,
The measuring part of the extensometer 2 is pressed against and held by the elastic body 10 on the side surface of the test piece,
Under the condition that the test piece 1 is sandwiched between the buckling prevention jig 7 and the buckling prevention base jigs 3 and 4 from both sides in the thickness direction, and a force resisting buckling is generated by the spring 9A.
The actuator is driven so as stroke speed is constant, the output of the extensometer as a target value, and to the compression from tension to the test unit, tension and characterized by applying the load cycle test with the tension from the compression Compression test method.
[2] A tensile and compression test apparatus for performing a load repetition test from tension to compression and from compression to tension on the test portion of the test piece 1,
The relationship of the test portion of the test piece 1 and the length L test section width W and L / W ≧ 4.0, the test section shoulder R and R ≦ 2.0 mm,
The extensometer holding metal fitting 11 is joined to the side surface of the test piece 1 by resistance welding, and the extensometer 2 is firmly fixed to the joined extensometer holding metal fitting 11,
The adhesive is applied with the elongation meter 2 of the measuring part to the contact part of the side surface of the test piece 1,
The measuring part of the extensometer 2 is pressed against and held by the elastic body 10 on the side surface of the test piece,
A test jig in which the test piece 1 is sandwiched between the buckling prevention jig 7 and the buckling prevention base jigs 3 and 4 from both sides in the thickness direction, and a force that resists buckling is generated by a spring 9A. 100 is incorporated in a high-rigidity slide mechanism that is a slide mechanism using a slide shaft 400 with a ball bearing 300 of the test jig base 200. The entire high-rigidity slide mechanism is assembled in a grounding jig 500, and the slide shaft is set in the horizontal direction. None , A tensile / compression test apparatus , wherein the test portion is subjected to a load repetition test from tension to compression and from compression to tension .

  According to the present invention, a jig for preventing buckling during compression by measuring strain at the time of the repeated load test using an extensometer fixed to the side surface of the test piece whose shape has been specified, and further preventing buckling during compression. Since the jig and the buckling prevention base jig) are used, it is possible to measure the strain during the repeated load test with high accuracy. In addition, since the extensometer is fixed by an elastic body instead of the conventional strain gauge sticking, workability and economy are improved. Furthermore, since the test apparatus can be placed horizontally, it can be applied to many types of actuators, and the entire apparatus can be downsized. In addition, it is possible to perform stable measurement by using a method of driving the actuator with a constant stroke speed and a value of the extensometer as a target value.

In the control system used for an example of embodiment of this invention, (a) is a block diagram which shows the transmission path | route of a signal, (b) is a flowchart which shows the flow of control. It is a three-dimensional view showing an example of a horizontally placed state of the tensile compression test apparatus according to the present invention. In one example of an embodiment of the present invention, (a) is a shape of a test piece, (b) is an overall outline of a tensile / compression test apparatus, (c) is a setting state of the test piece, (d) is a detail of an extensometer measuring unit. FIG. It is an exploded view of the test jig 100 in FIG. 1B (b). It is a diagram which shows an example of the relationship between the center part distortion | strain (lambda) C of the test piece which carried out the tension test by changing a dimension variously, and error (DELTA) (lambda) (= (lambda) E- (lambda) C) of the side part distortion | strain (lambda) with respect to this (lambda) C. 2 is a diagram showing a stress-strain history curve obtained in the test of Example 1. FIG. 6 is a diagram showing a stress-strain history curve obtained in the test of Example 2. FIG. 4 is a diagram showing a stress-strain history curve obtained in the test of Example 3. FIG.

Embodiments of the present invention will be described below with reference to the drawings and the background to the present invention.
When measuring the strain on the side surface of the test piece 1, if an arbitrary test piece shape is used, the strain becomes non-uniform in the width direction of the test piece, and there is a concern about an error in the strain value with the center portion of the test piece. As a result of the development examination experiment with each test piece shape, in the test piece shape shown in FIG. 1B (a), the relationship between the test portion (parallel portion) length L and the test portion width W is L / W ≧ 4.0. In addition, by using a test piece having a test piece shoulder R of R ≦ 2.0 mm, the knowledge that the center strain and the side strain are substantially equal (with an error of 0.15% or less) is obtained. It was.
(Example of development study experiment)
The test piece size (test part length L, width W, shoulder R) was changed to a maximum of 14% by applying a marking line to the test piece with each level shown in Table 1 to change the marking line spacing. The relationship between the strain λC at the center of the test piece and the difference Δλ (= λE−λC) of the side surface strain λE was obtained. Then, for example, as shown by a diagram in FIG. 2, Δλ is λC in S4 and S5 that are within a size range satisfying L / W ≧ 4.0 and R ≦ 2.0 mm (referred to as a specific size range for convenience). Exhibiting a valley-shaped curve having a minimum point (Δλ = −0.15% at the minimum point) (maximum value is 0.15% at | Δλ |) that changes from increasing to decreasing with increasing It was found that S1 to S3, S6, and S7 outside the size range exhibited a monotonically decreasing curve with respect to an increase in λC. Table 1 shows the maximum error Δλmax (value of Δλ where | Δλ | is the maximum) at 14% tension at each level.

Based on the above findings, the test pieces used in the present invention were limited to those having L / W ≧ 4.0 and R ≦ 2.0 mm.
By limiting the size of the test piece as described above, it is possible to eliminate a measurement error during the load repetition test, which has been apt to occur in the past, which has been measured with a strain gauge.
At the same time, as shown in FIGS. 1B (a), (b), and (c), the work efficiency is improved by fixing the extensometer 2 to the extensometer holding metal fitting 11 joined to the side surface of the test piece 1 by the elastic body 10. Significantly improved. Since the extensometer 2 can be used repeatedly, it becomes possible to eliminate the uneconomical effect as in the conventional test form in which a strain gauge discarded every test is used.

  In order to fix the extensometer 2, an extensometer holding metal fitting 11 is required on the side of the test piece 1, but the extensometer holding metal fitting 11 can be fixed to the test piece 1 simply and firmly by using resistance welding. It becomes. The measuring part of the extensometer 2 is pressed and held on the side surface of the test piece by the elastic force of the elastic body 10 fixed by the extensometer holding metal fitting 11. Since the measurement part of the extensometer 2 is fixed to the side part of the test piece 1 without slipping by the elastic force during the test, highly accurate strain measurement can be performed.

  Further, when the tension / compression test apparatus is used in a horizontal position, it is used by being assembled in an installation jig 500 as shown in FIG. 1A. As shown in the figure, the front side of the testing machine (the side on which the buckling presser 8 and the spring-loaded bolt 9 are assembled) needs to be on the upper side due to workability problems, but the weight of the extensometer 2 in FIG. As a result, the contact area between the measuring part of the extensometer 2 and the test piece 1 becomes small, and both tend to be slippery. In that case, this problem can be solved by applying an adhesive such as an instantaneous adhesive to the measuring part of the extensometer 2 and improving the followability to the side part of the test piece 1. As described above, if the tensile / compression test apparatus can be used in a horizontal position, it can be applied to many types of actuators. As the adhesive, an adhesive such as Aron Alpha (registered trademark) can be preferably used.

  In order to prevent buckling, as shown in FIG. 1C, one surface of the test piece 1 is brought into contact with the concave vertical plane of the buckling prevention base jigs 3 and 4 divided into upper and lower parts. The buckling prevention jig 7 is brought into contact with the other surface, and the test piece 1 is sandwiched between the buckling prevention jig 7 and the buckling prevention base jigs 3 and 4. It is pressed by a buckling retainer 8 and a bolt 9 with a buckling restraining force adjusting spring 9A (see FIG. 1C). By using the test jig having such a configuration, it becomes possible to perform a test while suppressing as much as possible buckling deformation at the time of compression with a strain of 5% or more in a tensile compression test of a thin steel plate having a thickness of about several millimeters or less. .

Although it is feared that the buckling pressing force affects the deformation of the test piece in the tensile direction, in the present invention, the buckling pressing force is applied by the bolt 9 with the buckling pressing force adjusting spring 9A, and the buckling pressing force is applied. It is possible to adjust the level, and it is possible to test with the effect of buckling holding force as small as possible.
Further, buckling is likely to occur when the test piece 1 is compressed, but one surface of the test piece 1 is always in contact with the end plane of the buckling prevention jig 7 and the other surface of the test piece 1 is The majority of the measurement unit including the measurement part comes into contact with the concave vertical plane of the buckling prevention base jigs 3 and 4, and the buckling prevention base jigs 3 and 4 come close to each other at the time of compression. Can be sufficiently prevented.

  As for actuator control, the actuator is driven so that the displacement increment per unit time is constant with respect to the elapsed time, and the load is reversed when the extensometer value reaches the target value. Therefore, the tension / compression load can be reversed with the desired strain, and the displacement between the measurement part of the extensometer 2 and the side part of the test piece 1 due to the impact caused by the sudden increase in displacement that occurs when the backlash is eliminated. Therefore, stable measurement is possible. A signal transmission path in the control system is shown in FIG. 1A, and a control flowchart is shown in FIG.

  Further, the tensile and compression test apparatus according to the present invention is a slide mechanism in which the test jig 100 (see FIG. 1C) is a slide mechanism 400 using a slide shaft 400 with a ball bearing 300 of the test jig base 200 as shown in FIG. 1B (b). The device was built into a high-rigidity slide mechanism. Thereby, it is possible to prevent the shaft in the tension / compression load direction from being decentered during the test, and it is possible to perform a stable tension / compression test without buckling deformation.

Example 1
As Example 1, a test piece sampled from a thin steel plate of 1.6 mm in thickness and TS (abbreviation of tensile strength; the same applies hereinafter) = 590 MPa class to the level S5 in Table 1 was used, as shown in FIG. In accordance with the embodiment shown in FIGS. 1A, 1B, and 1C, a tensile compression test was performed under the conditions 2, 3, and 4 shown in Table 2 (provided that the condition 4 is tensile only), and the treatment shown in FIG. A stress-strain history curve representing the relationship between true stress and true strain was obtained. In addition, the contact part of the measurement part of the extensometer 2 and the side part of the test piece 1 was fixed with an adhesive (Aron Alpha).
(Example 2)
As Example 2, a test piece collected from a thin steel plate having a thickness of 1.6 mm and a TS = 980 MPa class in accordance with the dimension of level S5 in Table 1 is shown in FIGS. 1, 1A, 1B, and 1C. According to the embodiment as described, a tensile compression test is performed under the conditions 2, 3 and 4 shown in Table 2 (provided that the condition 4 is tensile only), and the relationship between the true stress and the true strain shown in FIG. A stress-strain history curve was obtained. In addition, the contact part of the measurement part of the extensometer 2 and the side part of the test piece 1 was fixed with an adhesive (Aron Alpha).

As shown in FIG. 4, strain and stress were measured with high accuracy under both conditions 2 and 3 (both are examples of the present invention) and condition 4 (a reference example).
In Examples 1 and 2, the example of the present invention is the case of the tensile / compressive load repetition test. However, the present invention is applied to the case of other compression / tensile load repeated tests. It has been confirmed that the same highly accurate strain measurement can be performed.
(Conventional example)
As a conventional example, instead of using the extensometer, a conventional tension / compression tester in which a strain gauge is attached to a test piece and the base jigs 3 and 4 and the buckling prevention jig 7 of FIG. Then, a test under the same conditions as in Example 1 and Example 2 was attempted. As a result, in the condition 2 during the second tensile (strain + 10%) loading, in the condition 3 during the first tensile (strain + 10%) loading, and in the condition 4 during the first tensile (strain + 15%) loading, In either case, the strain gauge was broken and strain measurement was not possible. In condition 2, the test piece was bent at the time of compression (strain-5%) load, and the compressive strain was not accurately applied in the longitudinal direction (L) of the test piece.
(Example 3)
As Example 3, the case where the tension / compression test apparatus is used horizontally is shown. Using an actuator that generates a displacement in the horizontal direction, a tensile / compression test was performed with the tensile / compression test apparatus placed horizontally as shown in FIG. 1A. As shown in FIG. 1B (c), in order to make it difficult for the measuring part of the extensometer 2 and the side part of the test piece 1 to slip, it was fixed using an adhesive (Aron Alpha). Embodiment as shown in FIG. 1, FIG. 1A, FIG. 1B, and FIG. 1C using the test piece extract | collected from the thin steel plate of thickness 1.4mm and TS = 980MPa class according to the dimension of the level S5 of Table 1. Thus, a tensile compression test was performed under the conditions 1 and 4 shown in Table 2 to obtain a stress-strain history curve representing the relationship between the true stress and the true strain shown in FIG. In Example 3, the tension / compression test apparatus was used in a horizontal position, but a tensile / compression repeated test with the same strain amount as that used in a vertical position is possible.
(Comparative example)
As a comparative example, as shown in FIG. 1A, a tensile / compression test apparatus is used in a horizontal position, and an adhesive is applied to the contact portion between the measuring portion of the extensometer 2 and the side portion of the test piece 1 in FIG. Tensile and compression tests were conducted without taking measures against slipping. Embodiment as shown in FIG. 1, FIG. 1A, FIG. 1B, and FIG. 1C using the test piece extract | collected from the thin steel plate of thickness 1.4mm and TS = 980MPa class according to the dimension of the level S5 of Table 1. Thus, a tensile test was performed under the condition 1 shown in Table 2. In the comparative example, since a slip occurred between the measurement part of the extensometer 2 and the side part of the test piece 1, a correct test result could not be obtained.

DESCRIPTION OF SYMBOLS 1 Test piece 2 Extensometer 3, 4 Buckling prevention base jig | tool 7 Buckling prevention jig | tool 8 Buckling presser 9A Spring 9 Bolt with spring 10 Elastic body 11 Extensometer holding metal fitting 100 Test jig 200 Test jig base 300 Ball Bearing 400 Slide shaft 500 Grounding jig 600 Actuator connection shaft

Claims (2)

A tensile compression test method for performing a load repetition test from tension to compression and from compression to tension on the test portion of the test piece 1,
The relationship of the test portion of the test piece 1 and the length L test section width W and L / W ≧ 4.0, the test section shoulder R and R ≦ 2.0 mm,
The joining extensometer holding fixture 11 by resistance welding to the side surface of the test piece 1, firmly fixed more elongation meter 2 to extensometers holding metal fitting 11 which is the junction,
The adhesive is applied with the elongation meter 2 of the measuring part to the contact part of the side surface of the test piece 1,
The measuring part of the extensometer 2 is pressed against and held by the elastic body 10 on the side surface of the test piece,
Under the condition that the test piece 1 is sandwiched between the buckling prevention jig 7 and the buckling prevention base jigs 3 and 4 from both sides in the thickness direction, and a force resisting buckling is generated by the spring 9A.
The actuator is driven so as stroke speed is constant, the output of the extensometer as a target value, and to the compression from tension to the test unit, tension and characterized by applying the load cycle test with the tension from the compression Compression test method. A tensile and compression test apparatus for performing a load repetition test from tension to compression and from compression to tension on the test portion of the test piece 1,
The relationship of the test portion of the test piece 1 and the length L test section width W and L / W ≧ 4.0, the test section shoulder R and R ≦ 2.0 mm,
The extensometer holding metal fitting 11 is joined to the side surface of the test piece 1 by resistance welding, and the extensometer 2 is firmly fixed to the joined extensometer holding metal fitting 11,
The adhesive is applied with the elongation meter 2 of the measuring part to the contact part of the side surface of the test piece 1,
The measuring part of the extensometer 2 is pressed against and held by the elastic body 10 on the side surface of the test piece,
A test jig in which the test piece 1 is sandwiched between the buckling prevention jig 7 and the buckling prevention base jigs 3 and 4 from both sides in the thickness direction, and a force that resists buckling is generated by a spring 9A. 100 is incorporated in a high-rigidity slide mechanism that is a slide mechanism using a slide shaft 400 with a ball bearing 300 of the test jig base 200. The entire high-rigidity slide mechanism is assembled in a grounding jig 500, and the slide shaft is set in the horizontal direction. None , A tensile / compression test apparatus , wherein the test portion is subjected to a load repetition test from tension to compression and from compression to tension .

Images