JP7741566B2 - Vibration unit for thin plate bending fatigue testing and thin plate bending fatigue testing device - Google Patents

Description

The present invention relates to a vibration mechanism in an apparatus for conducting fatigue tests on thin plate-shaped test pieces.

Thin metal sheets are an essential material for components used in springs, belts, valves, diaphragms, connectors, switches, and more. In recent years, thin metal sheets have also been incorporated into components in battery stacks and electronic devices, and demand for these materials is expected to increase in the future. The fatigue life of these thin metal sheets is an important characteristic value that determines the reliability of the product, but the thinner the sample, the more difficult the fatigue testing becomes.

A known technique for fatigue testing thin plate-shaped test specimens is a fatigue testing method in which one end of the test specimen is cantilevered, vibrations are applied to the specimen at its natural frequency to cause resonance, and changes in amplitude of the test specimen as fatigue progresses are measured (see Patent Document 1). The fatigue testing apparatus in Patent Document 1 has a stress concentration portion formed by forming a notch near one end of the test specimen, and is also equipped with a cantilever support means for cantilevering the test specimen, a vibration means for applying vibrations to the test specimen, a frequency control means for controlling the vibration frequency of the vibration means, a displacement measurement means for measuring the amplitude of the test specimen, and a calculation processing means for determining stress from measurement data obtained by the displacement measurement means.
In a fatigue test using the fatigue testing device described in this document, one end of the test piece is cantilevered on a chuck member on the front of the speaker and vibrated at a constant frequency for two seconds, measuring the amplitude at a predetermined position near the free end of the test piece at that time.The vibration frequency is then increased in 0.1 Hz increments, and the test piece is vibrated for two seconds each time, measuring the amplitude at that time, and the frequency at which the amplitude is maximum is determined to be the natural frequency of the test piece.
However, the fatigue testing device of Patent Document 1 has a problem in that it is difficult to make finer frequency adjustments, and high-precision testing cannot be performed.

Fatigue testing equipment also needs to improve the stability of the support between the vibration mechanism and the test specimen.

Japanese Patent Application Publication No. 08-054331

In light of this situation, the present invention aims to provide a vibration unit for thin plate bending fatigue testing and a thin plate bending fatigue testing device that allows fine frequency adjustment and high-precision testing.

In order to solve the above problems, the vibration unit for thin plate bending fatigue testing of the present invention has a drive coil and at least a pair of magnets arranged with a gap between them to sandwich the drive coil, and a holding part to which the drive coil is fixed, and is equipped with a drive part that generates a drive force whose direction periodically reverses by passing an alternating current through the drive coil, a rotating part connected to the drive part and rotates the thin plate around a bearing using the drive force, and an arm part connected to the rotating part and holds one end of the thin plate near its tip and vibrates the other end of the thin plate by rotating.
By providing a driving section using a pair of magnets and a driving coil as a vibration unit for thin plate bending fatigue testing, it is possible to fine-tune the frequency and perform high-precision testing.
The drive coil is preferably a track-shaped drive coil made of self-bonding copper wire with a fusion coating formed on the outer layer, and is fixed to a tray-shaped holder using an adhesive or the like. A pair of magnets are arranged so that one is the north pole and the other is the south pole, or one is the south pole and the other is the north pole, and each is fixed to a yoke. A holder for holding one end of a thin plate that will serve as a test specimen is provided near the tip of the arm.

In the vibration unit for thin plate bending fatigue testing of the present invention, the drive section includes two pairs of magnets arranged with a gap between them and the drive coil, and the two pairs of magnets are preferably arranged symmetrically about the center of the drive coil so that the driving force is directed in the same direction, with the S and N poles of each pair of magnets facing in opposite directions. This configuration enables more accurate testing.

In the vibration unit for thin plate bending fatigue testing of the present invention, the bearing of the rotating part is preferably a pivot bearing. Because pivot bearings have low friction torque, they are used as the bearing of the rotating part that serves as the fulcrum for the arm part. This allows the fulcrum position of the arm part to be determined with high precision, and the origin position of the test piece's swing and the measurement origin position of the fatigue testing device's laser displacement sensor to be accurately determined.

The vibration unit for thin plate bending fatigue testing of the present invention may have a holding section, a rotating section, and an arm section molded as a single unit. The holding section and the rotating section, or the rotating section and the arm section, may each be fixed with fasteners such as screws, but by molding them as a single unit, there is no loosening, enabling more accurate testing.

The thin plate bending fatigue testing apparatus of the present invention comprises a sample unit equipped with any of the above-mentioned vibration units for thin plate bending fatigue testing, and a measurement unit connected to the sample unit and equipped with a laser displacement sensor and a multi-axis stage, and is characterized in that the measurement unit outputs the correlation between the stress amplitude applied to the thin plate in the sample unit and the number of repetitions until fracture occurs due to the stress amplitude.
By providing the thin plate bending fatigue testing device with a vibration unit for thin plate bending fatigue testing, it is possible to finely adjust the frequency and perform highly accurate testing.

The vibration unit for thin plate bending fatigue testing and thin plate bending fatigue testing device of the present invention have the advantage of allowing fine adjustment of frequency and enabling high-precision testing.

Front view of the thin plate bending fatigue test device of Example 1 Plan view of a vibration unit for a thin plate bending fatigue test according to Example 1 Front view of the vibration unit for thin plate bending fatigue test of Example 1 Explanation of the vibration mechanism (1) Explanation of the vibration mechanism (2) Image of thin plate bending fatigue test Pivot bearing diagram

An example of an embodiment of the present invention will be described in detail below, with reference to the drawings. Note that the scope of the present invention is not limited to the following examples and illustrated examples, and many modifications and variations are possible.

Figure 1 shows a front view of the thin plate bending fatigue testing device of Example 1. The thin plate bending fatigue testing device 10 shown in Figure 1 is capable of performing resonance fatigue testing. Resonance fatigue testing is a fatigue testing method that utilizes the resonance frequency, which is one of the eigenvalues of the test piece. Once the test piece reaches a resonance state, repeated stress can be applied to the test piece with minimal energy. Unlike typical mechanical fatigue testing, stress can be applied while only one side of the test piece is fixed, making it possible to apply highly accurate stress at high speed to very thin plate materials. The dynamic stress in the resonance state is calculated using FEM (Finite Element Method) analysis.

In FEM analysis, the object or structure being analyzed is divided into small elements, and the behavior of each element is mathematically modeled. Each element has a geometric shape such as a triangle or a rectangle, and the behavior within the element is expressed by mathematical equations and relationships. The resonance frequency and the relationship between stress and displacement in fatigue testing using the thin plate bending fatigue testing device 10 are determined by eigenvalue analysis using FEM. The stress amplitude in fatigue testing using the thin plate bending fatigue testing device 10 is defined based on FEM analysis. To perform FEM analysis, the material's Young's modulus, Poisson's ratio, and density are required; if these values are not available, various experiments are conducted and the results are fed back into the FEM analysis. In this example, a commercially available program (e.g., "ABAQUS") is used for the FEM analysis.

A specific configuration of the thin plate bending fatigue testing device 10 will be described below. As shown in FIG. 1, the thin plate bending fatigue testing device 10 is composed of a sample unit 20 and a measurement unit 30.
The sample unit 20 is placed on the measurement unit main body 30a, and the sample unit 20 and the measurement unit main body 30a are connected by a cable 14. A vibration-proof mat 15 is provided between the sample unit 20 and the measurement unit main body 30a.
The sample unit 20 includes a drive arm 4 and a sample holder 5, and a test piece 11 is attached to the sample holder 5. The test piece 11 can be made of metal or ceramic material, and can be tested on samples with a thickness of 0.05 to 0.8 mm, a width of 3 to 5 mm, and a length of 15 to 35 mm.
A fatigue test is performed by vibrating the test piece 11 attached to the sample holder 5 via the drive arm 4 using vibrations generated by a vibration unit (described later). The amplitude range of the vibration of the test piece 11 is within ±5 mm. The test temperature conditions are room temperature to 200°C.

The measurement unit 30 includes a laser displacement sensor 12 for measuring displacement amplitude, a three-axis stage 13, and a measurement unit main body 30a. The laser displacement sensor 12 detects the deflection of the test piece 11 in a non-contact manner based on laser light 12a emitted from a sensor head (not shown). Fracture detection is performed by detecting a decrease in resonant frequency. This utilizes the fact that when a fatigue crack occurs and propagates in the test piece, the stiffness of the test piece decreases, resulting in a decrease in resonant frequency.
The three-axis stage 13 is an XYZ axis stage that can be finely adjusted in three axial directions, and can be positioned on the XYZ axes.
The measuring unit main body 30a outputs an SN curve showing the relationship between the stress amplitude and the number of breakage/non-breakage repetitions based on the stress amplitude obtained from the vibration unit and the vibration frequency obtained from the laser displacement sensor 12.

Here, the vibration unit provided in the thin plate bending fatigue test apparatus 10 of Example 1 will be described. Fig. 2 shows a plan view of the vibration unit for the thin plate bending fatigue test of Example 1. Fig. 3 shows a front view of the vibration unit for the thin plate bending fatigue test of Example 1. For convenience of explanation, Fig. 3 shows a state in which the sample holder 5 is not attached.
2 or 3, the vibration unit 1 includes a track-shaped drive coil 2, magnets (3a to 3d), a drive arm 4, a sample holder 5, a drive coil tray 6, bearings 7, and yokes (8a, 8b). The track-shaped drive coil 2, the drive coil tray 6 as a holding unit, and the magnets (3a to 3d) constitute the drive unit, the bearing 7 constitutes the rotating unit, and the drive arm 4 and sample holder 5 constitute the arm unit.
As shown in FIG. 3, the yoke 8 b and one end of the rotation shaft 7 a of the bearing 7 are fixed onto the sample unit body 21 .

The structure of bearing 7 will now be explained. As shown in Figure 2, bearing 7 consists of pivot bearing 70 and boss 71. Figure 7 is an explanatory diagram of a pivot bearing, showing a cross-sectional image. As shown in Figure 7, pivot bearing 70 has the same structure as a known pivot ball bearing, and is composed of a rotating shaft 7a, rolling elements 7b, and an outer ring 7c. Although not shown, there are six rolling elements 7b. The apex angle θ of the conical portion 7d of rotating shaft 7a is 60°, and is machined into a conical shape to form conical portion 7d. The outer ring 7c is fixed to boss 71 shown in Figure 2 using a fastener (not shown). The small pitch diameter of rolling elements 7b and the shape of conical portion 7d have the advantage of low friction torque.

As shown in Fig. 2, one end of the bearing 7 is connected to one end of the drive arm 4 using a fastener 9c, and the sample holder 5 is attached to the other end of the drive arm 4 using a fastener 9d. The other end of the bearing 7 is connected to the drive coil tray 6 using a fastener 9b. The drive coil tray 6 has walls on all four sides, but the connection surface with the bearing 7 is higher than the other surfaces as shown in Fig. 3 (see Figs. 4 and 5) in order to stably fix the bearing 7 to the drive arm 4 using the fastener 9b. Note that the drive arm 4, sample holder 5, drive coil tray 6, and bearing 7 may be partly or entirely molded as a single unit.
The track-shaped drive coil 2 is fixed to the drive coil tray 6 with adhesive or the like. The track-shaped drive coil 2 is made of self-bonding copper wire with a fusion coating formed on the outer layer, and has a diameter of 0.18 mm, approximately 240 turns, and a thickness of 1.7 mm or more.

3, yoke 8a is fixed to yoke 8b using fasteners 9a, with a gap provided between them via supports 17. Magnets (3a, 3b) are fixed to yoke 8a, and magnets (3c, 3d) are fixed to yoke 8b.
A gap is provided between the drive coil tray 6 and the track-shaped drive coil 2 and the magnets (3a to 3d), so that they do not come into contact with each other (see FIGS. 4 and 5).

Next, the vibration mechanism of the vibration unit 1 will be described. Figures 4 and 5 are explanatory diagrams of the vibration mechanism. As shown in Figure 4 (1) or Figure 5 (1), magnet 3a is positioned between magnet 3a and magnet 3c so that magnet 3a is the north pole and magnet 3c is the south pole. Furthermore, magnet 3b is positioned between magnet 3d so that magnet 3b is the south pole and magnet 3d is the north pole. In other words, magnet 3a and magnet 3c, or magnet 3b and magnet 3d, are each a pair of magnets, and powerful magnets are positioned in opposite north-south and north-south directions on both ends of the track-shaped drive coil 2, sandwiching the coil, creating a structure that applies opposite static magnetic fields B to each.

Therefore, when an AC current I is passed through the track-shaped drive coil 2, a driving force is generated that periodically reverses direction (Fleming's left-hand rule). Specifically, when the current is positive, as shown by the thick line in Figure 4(2), a driving force F is generated in the right direction, as shown in Figure 4(1). When the current is negative, as shown by the thick line in Figure 5(2), a driving force F is generated in the left direction, as shown in Figure 5(1). By modulating the vibration frequency, the number of vibrations per unit time of the track-shaped drive coil 2 can be controlled. The vibration frequency when an AC current I is passed through the track-shaped drive coil 2 ranges from 100 to 1000 Hz, and can be finely adjusted in increments of 0.001 Hz.
In this way, the vibration unit 1 has a moving coil (MC) type voice coil motor (VCM) structure that utilizes Fleming's left-hand rule in the magnetic circuit. A slight rotation causes the sample holder 5 to vibrate (swing).

Next, the fixing structure of the sample holder and the test image will be described. Figure 6 is an image diagram of a thin plate bending fatigue test, showing an enlarged perspective view of the portion C shown in Figure 1.
In the past, samples were attached to fixtures with adhesive, making attachment difficult. In contrast, in this embodiment, as shown in Figure 6, the sample holder 5 is attached to the drive arm 4 using a fastener 9d. The drive arm 4 has a female screw 4a (shown in Figure 3) and the sample holder 5 also has a female screw (not shown). Therefore, the drive arm 4 and the sample holder 5 can be fixed together by screwing in the fastener 9d.
The sample holder 5 includes a holder body 5a and a mounting member 5b. The holder body 5a has a through-hole with a female screw portion, not shown, into which a fastener 9e can be screwed. To mount the test piece 11, the mounting member 5b is removed from the holder body 5a, the test piece 11 is placed in the recess of the holder body 5a, the mounting member 5b is fitted into the recess, and the fastener 9e is screwed into the female screw portion. The tip of the fastener 9e presses against the mounting member 5b, thereby fixing the test piece 11.
As described above, according to the configuration of this embodiment, the test piece 11 can be easily attached to the sample holder 5 using a special jig and fixed thereto.

When the vibration unit 1 is activated with the test piece 11 fixed to the sample holder 5, an AC current I flows through the track-shaped drive coil 2, generating a periodically changing magnetic field. This generates a driving force F whose direction periodically reverses due to the magnetic field. The drive unit is connected to the rotating unit, which rotates around the bearing 7 due to the driving force F. The rotating unit is connected to the drive arm 4, so the sample holder 5 attached to the tip of the drive arm 4 holds the test piece 11 and vibrates the other end of the test piece 11 as it rotates. In this way, by generating vibrations using the vibration unit 1, the test piece 11 sways from side to side via the pivot bearing 7, as shown by the dashed line in Figure 6, and a fatigue test is performed. The laser displacement sensor 12 measures the displacement amplitude of the test piece 11 based on the laser light 12a emitted from the sensor head.

The accuracy verification results of the thin plate bending fatigue testing device 10 of Example 1 will be described. Although strain gauges cannot be used for thin plate bending fatigue test pieces, the maximum stress on the thin plate surface is determined by the radius of curvature of the test piece 11, so it is possible to obtain the strain distribution by differentiating the displacement distribution. By calculating a correction factor in measurements using a high-speed camera, it is possible to obtain an accurate stress amplitude.
Markers were placed on the test specimen, and the trajectory was automatically detected using a high-speed camera to measure and analyze the displacement amplitude. As a result, it was found that the ideal sinusoidal waveform was precisely repeated at the time of maximum left deflection and maximum right deflection.

In addition, when the displacement amplitude of the test specimen was verified, the results of measurements taken using a high-speed camera were roughly equivalent to the FEM analysis results for both atmospheric and vacuum data.

From the above, it has been found that the vibration unit 1 of Example 1 and the thin plate bending fatigue test device 10 equipped with the vibration unit 1 can realize high precision testing that has not been possible with conventional fatigue test devices.
The reason for this is that, firstly, by employing an ultra-precise pivot bearing 70 at the fulcrum of the drive arm 4, the fulcrum position of the drive arm 4 can be determined with high precision, and it has become possible to accurately determine the origin position of the test piece 11's swing and the origin position of the measurement of the laser displacement sensor 12. This can be said to be an innovative structure that can ignore the instability of the fulcrum, which is a drawback of drive structures using speakers, etc. in the prior art.

Pivot bearings are sometimes used as rotary bearings that guide the movement of the head of a hard disk drive (HDD), which is an external memory for a computer. However, the vibration unit 1 of Example 1 is characterized in that it is a bi-directional vibration exciter that maintains an accurate, constant, high torque, unlike an HDD, which uses a positioning method for controlling the arm.
Furthermore, AC control using an accurate sine wave has frequency adjustment accuracy and amplitude adjustment accuracy, and is feedback control that accurately maintains torque in both directions.
Furthermore, the vibration unit 1 and the sample holder 5 can be made smaller and lighter, which reduces the moment of inertia of the drive system and realizes a high-speed bi-directional vibration structure that has not been available before.

This invention is useful as a technology for conducting fatigue tests on thin plates.

DESCRIPTION OF SYMBOLS 1 Excitation unit 2 Track-shaped drive coil 3a to 3d Magnet 4 Drive arm 4a Female screw portion 5 Sample holder 5a Holder body 5b Mounting member 6 Drive coil tray 7 Bearing 7a Rotating shaft 7b Rolling element 7c Outer ring 7d Conical portion 8a, 8b Yoke 9a to 9e Fastener 10 Thin plate bending fatigue test device 11 Test piece 12 Laser displacement sensor 12a Laser light 13 Three-axis stage 14 Cable 15 Vibration-proof mat 17 Support 20 Sample unit 21 Sample unit body 30 Measurement unit 30a Measurement unit body 70 Pivot bearing 71 Boss B Static magnetic field F Drive force I AC current θ Apex angle

Claims (5)

a drive unit that includes a drive coil, at least one pair of magnets arranged with a gap between them so as to sandwich the drive coil, and a holder to which the drive coil is fixed, and that generates a drive force whose direction periodically reverses by passing an alternating current through the drive coil;
a rotation unit connected to the drive unit and rotated around a bearing by the drive force;
an arm portion connected to the rotating portion, holding one end of the thin plate near its tip, and vibrating the other end of the thin plate by the rotation;
A vibration unit for thin plate bending fatigue testing, comprising: the driving unit includes two pairs of magnets arranged with a gap between them and the driving coil;
The vibration unit for thin plate bending fatigue testing as described in claim 1, characterized in that the two pairs of magnets are arranged in positions symmetrical with respect to the center of the drive coil so that the direction of the drive force is the same, and the combinations of the S and N poles of the paired magnets are opposite. A vibration unit for thin plate bending fatigue testing as described in claim 2, characterized in that the bearing of the rotating part is a pivot bearing. A vibration unit for thin plate bending fatigue testing as described in claim 1, characterized in that the holding portion, the rotating portion, and the arm portion are integrally molded. a sample unit including a vibration unit for a thin plate bending fatigue test according to any one of claims 1 to 4;
a measurement unit connected to the sample unit and including a laser displacement sensor and a multi-axis stage;
The thin plate bending fatigue testing device is characterized in that the measurement unit outputs a correlation between the stress amplitude applied to the thin plate in the sample unit and the number of repetitions until fracture occurs due to the stress amplitude.