JPH11108817A - Fatigue tester for micro test piece - Google Patents

Abstract

(57) [Summary] [PROBLEMS] To provide a fatigue tester for a microminiature specimen which can obtain reliable data such as fatigue life. (1) A mechanism for transmitting rotational motion to an eccentric shaft connected to a universal joint at the tip of a motor rotary shaft and converting the rotational motion into linear motion, and a test piece having a linear motion load mounted on a linear guide. Fatigue tester with a mechanism for transmitting to the mounting part. (2) The fatigue tester according to (1), further comprising a bearing fitted to the eccentric shaft and correcting the linear motion in a direction orthogonal to the motor rotation axis. (3) Before or during the fatigue test, the eccentric shaft connected to the universal joint of the free spline shaft in the longitudinal direction of the rotating shaft transmitting the rotating motion of the motor is connected to the spline shaft, the eccentric holding portion of the eccentric shaft, and the bearing. The fatigue tester according to the above (1) or (2), in which the amplitude of the reciprocating linear motion is adjusted by moving the motor in the longitudinal direction of the rotation axis of the motor together with the motor to change the repetitive stress load applied to the test piece.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a micro test piece fatigue tester capable of performing a reliable fatigue test without using a micro test piece without buckling the test piece.

[0002]

2. Description of the Related Art Evaluating fatigue strength, which is one of material properties, is very important in designing mechanical structures.
This is because fatigue strength rather than static strength of a material is often a problem in the strength design of an actual structure. In particular, in the case of automobiles, vehicles, machine tools and the like, in most cases, only the fatigue strength is a problem. Fatigue strength used in design generally refers to fatigue life and fatigue limit. The evaluation of the fatigue life and the fatigue limit is performed as follows. A constant stress amplitude is applied to the test piece, and the number of times of repeated loading until fracture is measured. The number of repetitions
"Fatigue life at that stress amplitude". The stress amplitude was changed at several points, and the fatigue life corresponding to the stress amplitude was measured at several points. The stress amplitude (S) was plotted on the vertical axis, and the repetition rate (N) was plotted on the horizontal axis.
Is plotted to create an SN curve (fatigue life curve). On S-N curves determine the stress amplitude of 10 ⁷ times the fatigue life. This stress amplitude is the fatigue limit. Generally, when a fatigue test is performed on a metal material, it is 10 ⁷ at a certain stress amplitude.
If it does not break more than once, it will not break no matter how many times the stress amplitude is applied thereafter.

In a general fatigue test, a round bar test piece is used, and its standard shaft diameter is 8 to 10 mm, and even a small test piece has a minimum shaft diameter of 4 mm. However, the weld metal and heat-affected zone of the welded joint, parts where the metallographic structure changes only near the surface used in high temperature environments,
It is impossible to evaluate the fatigue strength of a material such as a cold-rolled steel plate at a local portion where the thickness or size of the material is small, using a standard round bar test piece. Therefore, it is necessary to cut out ultra-small test pieces having a diameter of several mm to 1 mm or less from these sites and perform a fatigue test.

[0004] As a method of loading a fatigue test piece in a fatigue tester, there are a hydraulic type, a mechanical type, and the like, of which the hydraulic type is widely used as a general load type. However, the hydraulic type is mainly used for those having a large load, and is not suitable for controlling a minute load. On the other hand, as a mechanical type, for example, a testing machine provided with a rotary vibration mechanism using a rotary eccentric weight has been proposed (Japanese Patent Laid-Open No. 50-890).
No.). This tester has a feature that the amplitude can be changed by changing the position of the eccentric weight by a cylinder during the test. However, the applied load of the micro test piece is about 30 kgf at the maximum,
Very high precision control is required. Such a high-precision control is difficult with the testing machine according to the above proposal. In addition, when using the above-mentioned fatigue testing machine including the conventional fatigue testing machine, when compressive stress is applied to the microminiature fatigue test specimen, buckling easily occurs due to slight deviation from linear load. It was not possible to conduct a fatigue test of the stress waveforms containing it.

[0005] To date, there is no known fatigue tester capable of performing a fatigue test capable of obtaining reliable data such as fatigue life using a micro test piece.

[0006]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a fatigue tester for a micro test piece capable of performing a fatigue test of an arbitrary stress waveform that can provide reliable data such as fatigue life using the micro test piece. Is to provide. Specifically, an object of the present invention is to provide a fatigue tester for a micro test piece having the following functions.

(A) Very high-precision load control or strain control is possible.

(B) It is possible to keep the deviation between the center axis of the test piece and the axis of load or displacement (generation of bending component) within an extremely small range.

(C) Not only a constant load test or a constant strain test but also a variable load test or a variable strain test is possible.

[0010]

Means for Solving the Problems The present inventors investigated a method for controlling the reciprocating linear motion with high precision and a method for controlling the bending component in the stress applied to the micro test piece within a very small range. The present invention was completed by producing a fatigue tester based on the results. The gist of the present invention resides in the following micro test piece fatigue tester.

(1) By transmitting the rotational motion of the motor to a tapered eccentric shaft connected to a universal joint provided at the end of the rotary shaft of the motor, the rotational motion of the motor is transmitted in a direction orthogonal to the rotational axis of the motor. An ultra-small test piece fatigue tester comprising: a mechanism for converting to a reciprocating linear motion; and a mechanism for applying a repetitive load due to the reciprocating linear motion to a test piece via a test piece mounting portion mounted on a linear guide.

(2) The fatigue tester according to (1), wherein the mechanism for converting the rotational motion of the motor into a reciprocating linear motion in a direction orthogonal to the rotational axis of the motor includes the following bearings.

The above-mentioned bearing portion includes the following bearings, the outside of which is attached to the end of the shaft transmitting the reciprocating linear motion to the test piece mounting portion, and the tapered eccentric shaft connected to the universal joint. And can rotate around the tapered eccentric shaft.

A solid needle roller bearing provided on the inner peripheral side of the bearing portion and capable of moving a fitting position on a tapered eccentric shaft in the axial direction of the tapered eccentric shaft.

A self-aligning ball bearing provided on the outer peripheral side of the bearing for correcting the linear motion axis in a direction perpendicular to the rotation axis of the motor.

(3) Before or during the fatigue test, a tapered eccentric shaft connected to a universal joint provided at the tip of a free spline shaft in the longitudinal direction of the rotating shaft transmitting the rotating motion of the motor is provided. The above spline shaft,
The amplitude of the reciprocating linear motion is adjusted by moving the eccentric holding portion of the shaft that is eccentric in a tapered shape and the bearing that rotates the eccentric holding portion around the shaft in the longitudinal direction of the rotating shaft of the motor, and applying the amplitude to the test piece. The fatigue tester for a micro test piece according to the above (1) or (2), wherein the stress load is changed repeatedly.

The above-mentioned repetitive load includes a repetitive load of a stress waveform including a compressive stress, and may be a constant load control or a load variation control.

The "shaft eccentric in taper" described in the above (1) is hereinafter referred to as "eccentric shaft". Further, the “eccentric holding portion” of the eccentric shaft described in the above (3) is also referred to as “eccentricity adjusting portion”.

[0019]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A fatigue tester according to the present invention comprises:
1. rotation drive mechanism; Linear motion / specimen load mechanism,
3. The load / amplitude adjustment mechanism comprises three mechanisms.

In the rotary drive mechanism, the rotary drive force of the motor is converted to linear motion. The rotational driving force of the motor is used as the power source because the rotational driving force can be obtained relatively accurately with a compact device.

The reason why the linear motion / test piece loading mechanism is changed to the reciprocating linear motion by the tapered eccentric shaft is to reduce the size of the apparatus. The repetitive load based on the reciprocating linear motion is applied to the test piece jig mounted on the linear guide in order to prevent the bending stress from being generated in the test piece. This is to prevent the occurrence of.

In the load / amplitude adjusting mechanism, the amplitude of the reciprocating linear motion is adjusted by two types of mechanisms. One is that the other end of the shaft connected to the universal joint is held by an eccentric holding portion that rotates around the bearing, that is, an eccentric adjusting portion, and the eccentric adjusting portion is moved at an arbitrary distance in a direction perpendicular to the rotating shaft of the motor. It is a mechanism that moves and changes the angle of the shaft to be eccentric in a tapered shape. According to this method, the rough taper angle can be set freely with simple equipment. The other is a motor in which a tapered eccentric shaft connected to a universal joint provided at the end of a free spline shaft in the longitudinal direction of the rotating shaft of the motor is integrated with the spline shaft, the eccentric adjustment unit, the bearing, and the like. Is a mechanism for moving the rotary shaft in the longitudinal direction of the rotary shaft and changing the power transmission position with the shaft connected to the test piece jig. According to this method, the displacement and the load amplitude applied to the micro test piece can be adjusted with extremely high precision.

[0023]

FIG. 1 is a view showing a fatigue tester according to the present invention. Hereinafter, an example of the fatigue tester of the present invention (hereinafter, referred to as “the present embodiment”) will be described with reference to FIG.

The rotation drive mechanism comprises a motor 1, a spline shaft 2, a universal joint 3, an eccentric shaft 4, and an eccentric holding unit, that is, an eccentric adjusting unit 5. The motor 1 is an AC servomotor having a maximum rotation speed of 3000 rpm and a maximum output of 120 W. The spline shaft 2 is attached to the motor 1 and directly transmits the rotation drive from the motor. The spline shaft 2 is free in the axial direction. Further ahead is an eccentric shaft 4, and the spline shaft 2 and the eccentric shaft 4 are connected by a universal joint 3. The universal joint is a mechanism that can rotate even if there is eccentricity. The eccentric shaft 4 is fixed to the eccentric adjustment section 5. The eccentricity of the eccentric shaft is roughly adjusted by the eccentricity adjusting unit.

The linear motion / specimen load mechanism section includes an eccentric shaft 4
It comprises a bearing part 6, a shaft 7, a universal joint 8, a linear motion shaft 9, a test piece jig 10, and a linear guide 11 fitted to each other.

FIG. 2 shows a case where the direction of the reciprocating linear motion is corrected by the bearing 6 so as to be orthogonal to the rotation axis of the motor, and a case where it is not corrected. FIG. 2A shows a case where a bearing having a function of correcting the direction of reciprocating linear motion so as to be orthogonal to the rotation axis of the motor, and FIG. 2B shows a case of a bearing without the above correction. Show. The bearing 6 fitted to the eccentric shaft 4 has a solid needle roller bearing mounted on the inner peripheral side and a self-aligning ball bearing mounted on the outer peripheral side, and rotates around the eccentric shaft 4. Solid needle roller bearings are necessary to allow the position of engagement on the eccentric shaft 4 to be movable in the axial direction, while self-aligning bearings require that the linear motion axis 9 is slightly Tilt is needed to compensate for it. Further, a shaft 7 is attached to an outer peripheral portion of a bearing portion 6 fitted to the eccentric shaft 4, and the rotational drive is converted into a linear motion by this mechanism. The linear motion is applied to the test piece via the universal joint 8 and the linear motion axis 9. As described above, when the rotational drive of the motor is converted into a linear motion, the displacement becomes constant. When an ultra-small test piece is used, the test piece easily buckles when an excessive load occurs,
Or, there is a risk of abnormal breakage. However, according to the mechanism adopted by the present invention, an excessive load does not occur. The linear motion is loaded on the test piece jig and finally on the test piece. This test piece jig is mounted on the linear guide 11. For this reason, the test piece is in a state where movement other than linear movement in the axial direction is restricted. With this mechanism, the center axis of the test piece and the load axis do not deviate, so that loads other than tension and compression, ie, bending loads, are not applied to the test piece, and buckling or abnormal fracture of the test piece is suppressed. be able to. Therefore, even with an ultra-small test piece that tends to buckle or break abnormally in a conventional testing machine, the testing machine of the present invention has enabled a fatigue test capable of applying a stress wave including a compressive stress. In the tester of the present embodiment, a load cell 12 is attached to measure a load applied to a test piece. Although not attached in this embodiment, a leaf spring or the like may be attached for the purpose of adjusting the load and displacement as needed.

The load adjusting mechanism includes a bearing housing 13,
The slide table 14 includes a slide table position adjusting screw (hereinafter referred to as “position adjusting screw”) 15. The slide table 14, the eccentricity adjusting portion 5, the eccentric shaft 4, the universal joint 3, and the spline shaft 2 of the rotation drive mechanism can be moved in the axial direction of the spline shaft 2, that is, in the longitudinal direction of the motor rotation shaft by the position adjusting screw 15. It has become. At this time, since the bearing 6 fitted to the eccentric shaft moves along the eccentric shaft 4, the linear motion / test piece loading mechanism does not move. The slide table 14 and the like are moved by the position adjusting screw, and as a result, the displacement applied to the test piece can be adjusted very finely.

FIG. 3 is a schematic view for explaining the eccentricity adjusting mechanism. FIG. 3A shows a case where the amount of eccentricity is large, and FIG.
(B) shows a case where the amount of eccentricity is reduced. As described above, the amount of eccentricity is roughly adjusted by the eccentricity adjusting unit 5.
After this rough adjustment, as shown in FIG. 3, the eccentricity of the bearing 6 fitted to the eccentric shaft 4 changes as the eccentricity adjusting unit moves in the axial direction. Using this mechanism, the displacement applied to the test piece is adjusted with high accuracy. Such adjustments can be made during the test. In the test machine of this embodiment, the displacement can be adjusted with an accuracy of 0.025 mm per rotation of the position adjusting screw. When a micro test piece is subjected to a fatigue test, the load and the displacement become very small. For this reason, highly accurate load or displacement control is required. Further, it is necessary to fine-tune the load or displacement immediately after the start of the test or during the test. This mechanism has made it possible to control the load or displacement with sufficient accuracy even in a fatigue test using an ultra-small test piece. Although not mounted on the fatigue tester of the present embodiment, it is also possible to mount a stepping motor on the position adjusting screw part and adjust or periodically change the displacement by the motor to perform a variable load test. .

A fatigue test was performed using the above-mentioned fatigue tester. The material to be tested was S45C, which was an ultra-small one with a parallel part diameter of 0.8 mm and a parallel part length of 15 mm of the fatigue test piece.

FIG. 4 is a diagram showing the results of a fatigue test performed on the above-described test pieces by the fatigue tester of the present embodiment.
The repetitive load was such that the amplitudes of the compressive stress and the tensile stress were one-to-one, that is, R = −1. The result shown in FIG. 4 was a result that can be regarded as the same as the result of a fatigue test performed by a normal fatigue tester using a normal size fatigue test piece.

[0031]

According to the fatigue tester of the present invention, a high-precision fatigue test such as a stress amplitude and a fatigue test of a stress wave including a compressive stress can be performed using a micro test piece. As a result, it is possible to accurately know the fatigue strength of a local portion such as the vicinity of the surface of the material, and to provide powerful information for material development, structural material design, and the like.

[Brief description of the drawings]

FIG. 1 is a view showing a fatigue tester of the present invention.

FIG. 2 shows a case where the direction of the reciprocating linear motion is corrected so as to be orthogonal to the rotation axis of the motor, and a case where it is not corrected.
(A) has a bearing part having a function of correcting the direction of reciprocating linear motion so as to be orthogonal to the rotation axis of the motor,
(B) shows the case of a bearing part without the above correction.

FIG. 3 is a schematic diagram illustrating an eccentricity adjusting mechanism. (A)
Shows a case where the amount of eccentricity is increased, and (b) shows a case where the amount of eccentricity is decreased.

FIG. 4 is a view showing the results of a fatigue test performed on a micro test piece by the fatigue tester of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Motor 2 ... Spline shaft 3 ... Universal joint 4 ... Eccentric shaft 5 ... Eccentric adjustment part (eccentric holding part) 6 ... Bearing fitted to the eccentric shaft 7 ... Shaft 8 ... Universal joint 9 ... Linear motion axis 10 ... Test piece Jig 11 Linear guide 12 Load cell 13 Bearing housing 14 Slide table 15 Slide table position adjusting screw 16 Fatigue test piece 17 Eccentric amount

Claims (3)

[Claims] The present invention relates to a reciprocating motion in a direction perpendicular to a rotation axis of a motor by transmitting the rotation movement of the motor to a tapered eccentric shaft connected to a universal joint provided at a tip of a rotation axis of the motor. A micro test piece fatigue tester comprising: a mechanism for converting to a linear motion; and a mechanism for applying a repetitive load due to the reciprocating linear motion to a test piece via a test piece mounting portion mounted on a linear guide. . 2. A mechanism for converting a rotary motion of a motor into a reciprocating linear motion in a direction orthogonal to a rotation axis of the motor.
The fatigue tester for a micro test piece according to claim 1, further comprising a bearing portion described below. Bearing part: equipped with the following bearings, the outside of which is attached to the end of the shaft that transmits reciprocating linear motion to the test piece mounting part, and is fitted to the tapered eccentric shaft connected to the universal joint and the tapered shape A bearing that can rotate around a shaft that is eccentric to the shaft. : A solid needle roller bearing provided on the inner peripheral side of the bearing portion and capable of moving a fitting position on a tapered eccentric shaft in the axial direction of the tapered eccentric shaft. : A self-aligning ball bearing provided on the outer peripheral side of the bearing for correcting a linear motion axis in a direction perpendicular to the rotation axis of the motor. 3. A tapered eccentric shaft connected to a universal joint provided at the tip of a free spline shaft in the longitudinal direction of a rotating shaft transmitting a rotating motion of a motor before or during a fatigue test, The amplitude of the reciprocating linear motion is adjusted by moving the spline shaft, the eccentric holding portion of the tapered eccentric shaft, and the bearing that rotates the eccentric holding portion around the spline shaft in the longitudinal direction of the rotating shaft of the motor, and testing. The fatigue tester for a micro test piece according to claim 1 or 2, wherein a repetitive stress load applied to the test piece is changed.