JPH06235689A - Fatigue test method - Google Patents

Abstract

PURPOSE:To make possible accurate test of rotary bending fatigue of a sample having a thin diameter by rotating the sample from both directions thereby eliminating torsional effect due to friction from a supporting part. CONSTITUTION:Since a sample supporting part 13 is coupled through a bearing with a sample 11, the sample 11 is secured only by the supporting part 13 and can rotate thereabout. When a motor 12 is rotated, the sample 11 coupled through a grip chuck with the motor also rotates to transmit the rotation of the motor 12 through gears 14, 14', a transmission shaft 16, and a gear 15' to a gear 15. Since the sample 11, coupled through the grip chuck with the gear 15, also rorates at the other end thereof the sample 11 is prevented from being applied with torsional moment. Since torsional effect due to friction can be eliminated from the supporting part 13, rotary bending fatigue test can be conducted accurately for a sample having thin diameter and rotary fatigue characteristics can be compared directly between samples having thin and thick diameters.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a rotary bending fatigue test method, which is one of the evaluation tests for the mechanical properties of materials.

[0002]

2. Description of the Related Art There are several types of fatigue tests for materials, of which "rotational bending" is a typical test method, such as the Ono type, Nakamura type, Hay Robertson type, and Schenck type. Type has been devised and put to practical use.

FIG. 5 shows a schematic view of an example of a rotary bending fatigue tester. In this figure, 1 is a sample, 2 is a motor for rotating the sample, 3 and 6 are supporting parts for supporting the sample 1, and 4 and 5 are supporting parts for giving bending to the sample 1. In this method, a bending moment is generated in the sample between the supporting parts 4-5 by displacing the supporting parts 4, 5 from the line connecting the supporting parts 3 and 6, and by rotating the sample 1, tensile stress and compressive stress alternate. Cause to.

Now, consider the case of testing a sample having a circular cross section having a diameter d. Assuming that the bending moment that gives the repeated stress ± σ ₀ is M ₁ , the bending moment M ₁ is expressed by the following equation.

M ₁ = σ ₀ × Z ₁ where Z ₁ is the section modulus of the sample,

[Equation 1] Is. In addition, repeated stress ± σ ₀ was applied to the sample with wire diameter d / 2
The bending moment M ₂ give the section modulus of the sample Z ₂
Then, the bending moment M ₂ is expressed by the following equation.

M ₂ = σ ₀ × Z ₂ where

[Equation 2] Since,

[Equation 3] Becomes

Although the above discussion is about the case where the friction of each part of the testing machine is ignored, in reality, friction is generated in the sample support part. Below, we will estimate this effect.

When the sample is rotated, if there is friction in the supporting portion, this tends to hinder the rotation, so that a torsional moment is generated in the sample. In FIG. 5, the support portion 4-5
In the interval, it is affected by the supporting portions of the supporting portions 5 and 6. When a bending moment M ₁ is applied to a sample having a wire diameter d and the test is performed, assuming that the torsion moment generated between the supporting portions 4-5 is T, the stress amplitude σ ₁ is expressed by the following equation.

[0009]

[Equation 4] Here, the size of T is 1/10 of M ₁ (T = 0.1
Assuming that M ₁ ), the stress amplitude σ ₁ is

[Equation 5] Becomes

That is, when a sample with a wire diameter d is tested, even if the stress amplitude is calculated in consideration of the torsional moment, which is assumed to be 1/10 of the bending moment, it is at most 1% larger than when the stress amplitude is ignored. It is a degree.

Here, also when testing a sample having a wire diameter of d / 2 with the same tester, assuming that the relationship of T = 0.1M ₁ holds, the stress amplitude σ ₂ is calculated in the same manner.

[Equation 6] Becomes

That is, when a sample having a wire diameter d / 2 is tested, the effect of the torsional moment is great, and when the stress amplitude is calculated in consideration of this, it is 1.44 times as large as when ignored.

FIG. 6 shows the result of performing the same calculation while changing the wire diameter. FIG. 6 shows a case in which the torsional moment is taken into consideration in the rotating bending fatigue test (the torsional moment at the wire diameter d / the torsional moment /
It is the figure which showed the ratio with respect to the case where the stress calculation value of (when bending moment = 0.1) was disregarded. As is clear from this figure, the effect of the torsional moment based on the friction of the sample support portion appears remarkably in the thin sample and has a great influence on the test result.

[0014]

As described above, when a small-diameter sample is tested by a rotary bending fatigue tester, the results vary widely and accurate data cannot be obtained. With a commercially available tester, a steel wire of about 2 mm in diameter is obtained. Was the limit of the test. For this reason, a thin wire with a diameter of less than 2 mm must be evaluated by, for example, a cantilever type fatigue tester, and the fatigue characteristics of a large diameter sample cannot be directly compared.

The present invention has been made in view of the above,
It is an object of the present invention to provide a fatigue test method that enables accurate measurement even for small diameter samples.

[0016]

In order to achieve the above object, in a fatigue test of a system in which a sample is bent and rotated while a repeated load is applied, the present invention provides a portion of the sample to which a repeated load is applied. However, the main point is to introduce rotational force from both directions.

[0017]

[Function] Among the fatigue tests, the rotary bending fatigue test is widely used because of its advantages such as high speed. When the fatigue resistance of the steel wire is evaluated by this test, it is φ1. We paid attention to the fact that there is a large variation in the data for the 8 mm steel wire. As a result of investigating this difference, it is estimated that the influence of friction of each part of the testing machine may appear strongly when the sample becomes thin, and a trial calculation was performed.Thus, in the thin wire sample, the torsion moment due to the friction of the sample support part was found. It became clear that it was hard to ignore.

In the rotary bending test, the sample is subjected to bending and rotation, but in the conventional tester, the rotation is usually introduced from one end of the sample. In this case, since the sample must be supported on the side opposite to the rotation introducing side, it is unavoidable that a torsional moment is generated due to the friction of this portion. Of course, efforts have been made to reduce the friction in this portion, but it is impossible to set it to 0 in principle, and it is currently difficult to test a line thinner than φ2 mm.

Therefore, in the present invention, the influence of the torsion due to the friction of the supporting portion is eliminated by rotating the sample from both directions.

[0020]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 shows a first embodiment of the present invention.
Reference numeral 1 is a sample, 12 is a motor provided with a chuck for gripping a sample, 13 is a sample support portion, and 14 and 14 'and 15, 15'.
Are gears that mesh with each other to transmit rotation, and a chuck for holding a sample is attached to the gear 15.
Reference numeral 16 is a transmission shaft that transmits the rotation of the gear 14 'to the gear 15'. Here, the sample support 13 is coupled to the sample 11 via a bearing, and as a result,
Only the position of the sample 11 is fixed by the sample support portion 13, and the sample 11 is rotatable with respect to the sample support portion 13.

In this embodiment, when the motor 12 rotates, the gear 15 also rotates in the same way via the gears 14, 14 ', 15', so that it is possible to prevent a torsion moment from being generated in the sample 11. . If there is no transmission mechanism such as gears 14, 14 ', 15', 15 as in the conventional tester, the sample 11 is given a rotational force only from the motor 12 side, and the friction at the support portion 13 is Since it works so as to prevent rotation, a torsion moment is generated between the motor 12 and the sample support portion 13.

The structure of the above-mentioned transmission mechanism is as follows.
The present invention is not limited to the above-mentioned embodiment, but for example, as shown in the second embodiment of FIG. 2, both ends of the sample 11 are supported by the sample support portions 13, and the rotation of the motor 12 is controlled by the transmission shaft 2.
5 and gears 26 'and 27' may be transmitted to the gears 26 and 27 to rotate the gears 26 and 27 in the same direction.

FIG. 3 shows a third embodiment of the present invention.
Reference numeral 1 is a sample, 32 and 32 'are motors that rotate in synchronization with each other, and 33 and 34 are sample supports. Here, the sample support portions 33 and 34 are coupled to the sample 31 via bearings, and as a result, the sample 31 is
Only the position is fixed by the sample support portions 33 and 34,
It is rotatable with respect to the sample support portions 33 and 34.

In the present embodiment, the sample support portions 33, 3
It is possible to prevent the influence of the twisting moment by effectively aligning the two frictions, paying attention that the twisting moment does not occur unless there is a difference in friction between the four.

FIG. 4 shows a fourth embodiment of the present invention,
The rotation of the sample 31 is detected by the sensors 47 and 47 ', and the motor rotation controller 44 is controlled in the personal computer 48 so that the rotations of the two coincide with each other.

Therefore, according to this embodiment, the sensor 4
Since the sample 31 at the positions 7 and 47 ′ rotate in the same manner, it is possible to prevent the sample 31 from generating a torsion moment.

In FIG. 4, the same elements in FIG. 3 are designated by the same reference numerals.

[0029]

As described above, according to the present invention,
By rotating the sample from both directions, the effect of torsion due to the friction of the supporting part is eliminated, so the torsional moment generated in the sample can be removed, and the rotating bending fatigue test of the small diameter sample can be performed accurately. . In addition, as is well known, since the fatigue properties depend on the test method, the rotary bending fatigue properties of the large diameter sample and the fatigue properties of the small diameter sample by other test methods could not be directly compared, but the present invention According to, it becomes possible to make a direct comparison.

[Brief description of drawings]

FIG. 1 is a diagram showing a configuration of a first exemplary embodiment of the present invention.

FIG. 2 is a diagram showing a configuration of a second exemplary embodiment of the present invention.

FIG. 3 is a diagram showing a configuration of a third exemplary embodiment of the present invention.

FIG. 4 is a diagram showing a configuration of a fourth exemplary embodiment of the present invention.

FIG. 5 is a diagram showing a conventional example.

FIG. 6 is a diagram for explaining a problem of a conventional example.

[Explanation of symbols]

1, 11, 31 Sample 2, 12, 32, 32 'Motor 3, 4, 5, 6 Support 13, 33, 34 Sample Support 14, 14', 15, 15 ', 26, 26', 27, 2
7'gear 16,25 transmission shaft 44 motor rotation controller 47,47 'sensor 48 personal computer

Claims (1)

[Claims] 1. A fatigue test in which a load is applied repeatedly by bending the sample while bending it, and fatigue is characterized by introducing a rotational force from both directions to a portion of the sample to which the load is applied repeatedly. Test method.