Vibration unit for thin plate bending fatigue test and thin plate bending fatigue test device

Abstract

To provide a vibration unit for thin plate bending fatigue test and a thin plate bending fatigue test device that allow fine adjustment of a frequency and enable high-accuracy testing.SOLUTION: A vibration unit for thin plate bending fatigue test comprises a track-shaped drive coil 2, a magnet 3a, a magnet 3b, a drive arm 4, a specimen holder 5, a drive coil tray 6, a bearing 7, a yoke 8a and a yoke 8b. The track-shaped drive coil 2, the drive coil tray 6 as a holding part, the magnet 3a and the magnet 3b constitute the drive part. The bearing 7 constitutes a rotation part, and the drive arm 4 and the specimen holder 5 constitute the arm part. The bearing 7 comprises a pivot bearing 70 and a boss 71. One end of the bearing 7 is connected to one end of the drive arm 4 using a fastener 9c, and to the other end of the drive arm 4 the specimen holder 5 is attached with a fastener 9d. The other end of the bearing 7 is connected to the drive coil tray 6 using a fastener 9b. The track-shaped drive coil 2 is fixed to the drive coil tray 6.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to a vibration mechanism in an apparatus for performing fatigue testing on thin plate-like test pieces. [Background technology]

[0002] Thin metal plates are essential materials for components used in springs, belts, valves, diaphragms, connectors, switches, etc. In recent years, metal thin plates have also been incorporated into components in battery stacks and electronic devices, and the demand for such plates is expected to increase in the future. The fatigue life of these thin metal plates is an important characteristic value that determines the reliability of products, but there is a problem in that the thinner the sample, the more difficult the fatigue test becomes.

[0003] A known technique for performing fatigue testing on thin plate-shaped test pieces is a fatigue testing method in which one end of the test piece is supported by a cantilever, vibration is applied to the test piece at its natural frequency to resonate, and a change in amplitude of the test piece due to the progression of fatigue is measured (see Patent Document 1). The fatigue testing device in Patent Document 1 has a stress concentration portion provided by forming a notch near one end of the test piece, and is also equipped with a cantilever support means for supporting the test piece by a cantilever, a vibration means for applying vibration to the test piece, a frequency control means for controlling the vibration frequency of the vibration means, a displacement amount measurement means for measuring the amplitude of the test piece, and a calculation processing means for determining stress from measurement data obtained by the displacement amount measurement means. In a fatigue test using the fatigue testing apparatus 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, and the amplitude at a predetermined position near the free end of the test piece is measured.The vibration frequency is then increased in 0.1 Hz increments, and the test piece is vibrated for two seconds each, and the amplitude at these times is measured.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.

[0004] Furthermore, in fatigue testing equipment, there is a need to improve the stability of the support between the vibration mechanism and the test piece. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 08-054331 Summary of the Invention [Problem to be solved by the invention]

[0006] In view of the above circumstances, an object of the present invention is to provide a vibration unit for thin plate bending fatigue testing and a thin plate bending fatigue testing device that can finely adjust the frequency and perform highly accurate testing. [Means for solving the problem]

[0007] 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 by 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 it. 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 to be used as a test piece is provided near the tip of the arm.

[0008] In the vibration unit for thin plate bending fatigue testing of the present invention, the driving section includes two pairs of magnets arranged with a gap between them, and the two pairs of magnets are preferably arranged symmetrically with respect to the center of the driving coil so that the driving forces are directed in the same direction, and the combination of the S and N poles of the pair of magnets is in the opposite direction. With this configuration, a more accurate test can be performed.

[0009] 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. Since the friction torque of the pivot bearing is small, by using the pivot bearing as the bearing of the rotating part that serves as the fulcrum of the arm, the fulcrum position of the arm can be determined with high accuracy, and the double swing origin position of the test piece and the measurement origin position of the laser displacement sensor of the fatigue testing device can be accurately determined.

[0010] In the vibration unit for thin plate bending fatigue testing of the present invention, the holding part, the rotating part, and the arm part may be integrally molded. The holding part and the rotating part, or the rotating part and the arm part may be fixed by fasteners such as screws, but by integrally molding them, there is no loosening and more accurate testing is possible.

[0011] 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 breakage occurs due to the stress amplitude. By equipping the thin plate bending fatigue test device with a vibration unit for thin plate bending fatigue testing, it is possible to fine-tune the frequency and perform highly accurate testing. Effect of the Invention

[0012] The vibration unit for thin plate bending fatigue testing and the thin plate bending fatigue testing device of the present invention have the advantage that the frequency can be finely adjusted and highly accurate testing can be realized. [Brief description of the drawings]

[0013] [Figure 1] Front view of the thin plate bending fatigue test device of Example 1 [Diagram 2] Plan view of the vibration unit for thin plate bending fatigue test of Example 1 [Diagram 3] Front view of the vibration unit for thin plate bending fatigue test of Example 1 [Figure 4] Diagram of the vibration mechanism (1) [Diagram 5] Diagram of the vibration mechanism (2) [Figure 6] Image of thin plate bending fatigue test [Figure 7] Pivot bearing diagram DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0014] Hereinafter, an example of an embodiment of the present invention will be described in detail 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. EXAMPLES

[0015] FIG. 1 shows a front view of a thin plate bending fatigue test apparatus of the first embodiment. The thin plate bending fatigue test apparatus 10 shown in FIG. 1 is an apparatus capable of performing a resonance type fatigue test. The resonance type fatigue test is a fatigue test method that utilizes a resonance frequency, which is one of the eigenvalues ​​of a test piece. When the test piece reaches a resonance state, repeated stress can be applied to the test piece with a minimum of energy. Unlike a general mechanical fatigue test, stress can be applied to the test piece with only one side fixed, and highly accurate stress can be applied to a very thin plate material at high speed. The dynamic stress in the resonance state is calculated using FEM (Finite Element Method) analysis.

[0016] In FEM analysis, the target object or structure 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 inside the element is expressed by a mathematical equation or a relational expression. The resonance frequency and the relationship between stress and displacement in the fatigue test using the thin plate bending fatigue test device 10 are obtained by eigenvalue analysis using FEM. The stress amplitude in the fatigue test using the thin plate bending fatigue test device 10 is defined based on FEM analysis. To perform FEM analysis, material property values ​​such as Young's modulus, Poisson's ratio, and density of the material are required, but if these are not available, various experiments are performed and fed back to the FEM analysis. In this embodiment, a commercially available program (e.g., "ABAQUS") is used for the FEM analysis.

[0017] A specific configuration of the thin plate bending fatigue test apparatus 10 will be described. As shown in FIG. The sample unit 20 is placed on a measurement unit body 30a, and the sample unit 20 and the measurement unit body 30a are connected by a cable 14. A vibration-proof mat 15 is provided between the sample unit 20 and the measurement unit 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 a sample made of metal or ceramic material, 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 a test piece 11 attached to a sample holder 5 via a 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.

[0018] The measurement unit 30 includes a laser displacement sensor 12 that measures the 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 a laser light 12a emitted from a sensor head (not shown). Fracture detection is performed by a drop in resonance 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 drop in resonance frequency. The three-axis stage 13 is an XYZ axis stage capable of fine adjustment in three axial directions, and is capable of positioning on the XYZ axes. The measurement unit body 30a outputs an SN curve indicating the relationship between the stress amplitude and the number of repeated fracture / non-fracture cycles based on the stress amplitude obtained from the vibration unit and the vibration frequency obtained from the laser displacement sensor 12.

[0019] 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 a yoke (8a, 8b). The track-shaped drive coil 2, the drive coil tray 6 as a holder, and the magnets (3a to 3d) form a drive section, the bearing 7 forms a rotation section, and the drive arm 4 and sample holder 5 form an arm section. As shown in FIG. 3, a yoke 8b and one end of the rotating shaft 7a of the bearing 7 are fixed onto the sample unit body 21.

[0020] Here, the structure of the bearing 7 will be described. As shown in FIG. 2, the bearing 7 is composed of a pivot bearing 70 and a boss 71. FIG. 7 is an explanatory diagram of a pivot bearing, showing a cross-sectional image. As shown in FIG. 7, the 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, six rolling elements 7b are provided. The apex angle θ of the conical portion 7d of the rotating shaft 7a is 60°, and the conical portion 7d is machined into a conical shape to form the conical portion 7d. The outer ring 7c is fixed to the boss 71 shown in FIG. 2 using a fastener (not shown). The small pitch diameter of the rolling elements 7b and the shape of the conical portion 7d have the advantage of small friction torque.

[0021] As shown in Fig. 2, one end of the driving arm 4 is connected to one end of the bearing 7 using a fastener 9c, and the sample holder 5 is attached to the other end of the driving arm 4 using a fastener 9d. The other end of the bearing 7 is connected to the driving coil tray 6 using a fastener 9b. The driving coil tray 6 has walls on all four sides, but the connection surface with the bearing 7 is set higher than the other surfaces as shown in Fig. 3 in order to stably fix the bearing 7 to the fastener 9b (see Figs. 4 and 5). Note that the driving arm 4, the sample holder 5, the driving coil tray 6, and the bearing 7 may be partly or entirely formed as a single unit. The track-shaped drive coil 2 is fixed to the drive coil tray 6 with an adhesive or the like. The track-shaped drive coil 2 is made of a 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.

[0022] 3, yoke 8a is fixed to yoke 8b using fastener 9a with a gap provided therebetween by means of support 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).

[0023] Next, the excitation mechanism of the excitation unit 1 will be described. Figures 4 and 5 are explanatory diagrams of the excitation mechanism. As shown in Figure 4(1) or Figure 5(1), between magnet 3a and magnet 3c, magnet 3a is arranged so that it is the N pole, and magnet 3c is arranged so that it is the S pole. Also, between magnet 3b and magnet 3d, magnet 3b is arranged so that it is the S pole, and magnet 3d is arranged so that it is the N pole. That is, magnet 3a and magnet 3c, or magnet 3b and magnet 3d, are each a pair of magnets, and strong magnets are arranged in the opposite directions, NS and SN, on both ends of track-shaped drive coil 2 with the coil sandwiched between them, and a static magnetic field B in the opposite directions is applied to each pair.

[0024] Therefore, when an AC current I is applied to 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 FIG. 4(2), a driving force F is generated in the right direction as shown by FIG. 4(1), and when the current is negative as shown by the thick line in FIG. 5(2), a driving force F is generated in the left direction as shown by FIG. 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 range when an AC current I is applied to the track-shaped drive coil 2 is 100 to 1000 Hz, and can be finely adjusted in units 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. The sample holder 5 vibrates (sways) minutely due to minute rotation.

[0025] Next, the fixing structure of the sample holder and the test image are explained. Figure 6 is an image diagram of a thin plate bending fatigue test, showing an enlarged perspective view of the part C shown in Figure 1. Conventionally, a sample was attached to a fixture by bonding, which made attachment difficult. In contrast, in this embodiment, as shown in Fig. 6, a sample holder 5 is attached to a drive arm 4 using a fastener 9d. A female screw portion 4a shown in Fig. 3 is formed on the drive arm 4, and a female screw portion is also formed on the sample holder 5 (not shown), so that the drive arm 4 and the sample holder 5 can be fixed by screwing 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 into which a fastener 9e can be screwed (not shown). When mounting 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. In this manner, according to the configuration of this embodiment, the test piece 11 can be attached to the sample holder 5 using a dedicated jig, and can be easily fixed in place.

[0026] When the vibration unit 1 is operated 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, which generates a driving force F whose direction is periodically reversed by the magnetic field. The drive unit is connected to the rotating unit, so the rotating unit rotates around the bearing 7 by 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 by rotating. In this way, by generating vibration using the vibration unit 1, the test piece 11 swings left and right via the pivot bearing 7 as shown by the dashed line in FIG. 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.

[0027] The accuracy verification results of the thin plate bending fatigue test device 10 of Example 1 will be described. Although a strain gauge cannot be used for a thin plate bending fatigue test piece, since the maximum stress on the thin plate surface is determined by the radius of curvature of the test piece 11, it is possible to obtain the strain distribution by differentiating the displacement distribution. If a correction coefficient is obtained in the measurement with a high-speed camera, an accurate stress amplitude can be obtained. Markers were placed on the test specimen and the trajectory was automatically detected with a high-speed camera to measure and analyze the displacement amplitude. It was found that the maximum left deflection and maximum right deflection precisely repeated ideal sine wave waveforms.

[0028] In addition, when the displacement amplitude of the test piece was verified, the results of measurements using a high-speed camera in both air and vacuum were almost equivalent to the results of FEM analysis.

[0029] From the above, it has been found that the vibration unit 1 of Example 1 and the thin plate bending fatigue test apparatus 10 equipped with the vibration unit 1 can realize a highly accurate test not available in the past in a fatigue test apparatus. The reason for this is that, firstly, by adopting the 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 is possible to accurately determine the origin position of the double swing of the test piece 11 and the measurement origin position of the laser displacement sensor 12. This is a revolutionary structure that can ignore the instability of the fulcrum, which is a drawback of the drive structure using speakers, etc. of the conventional technology.

[0030] Pivot bearings are sometimes used as rotary bearings that guide the movement of the head of a hard disk drive (HDD: Hard Disk Drive), 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 HDDs, which use an arm control method for positioning purposes. In addition, the AC control is based on an accurate sine wave, and has frequency adjustment precision and amplitude adjustment precision, providing feedback control that accurately maintains torque in both directions. Furthermore, since the vibration unit 1 and the sample holder 5 can be made smaller and lighter, the moment of inertia of the drive system is reduced, and a high-speed double-swing vibration structure that has not been achieved in the past is realized. [Industrial Applicability]

[0031] The present invention is useful as a technique for conducting fatigue tests on thin plates. [Explanation of symbols]

[0032] 1. Vibration unit 2 Track-shaped drive coil 3a~3d Magnets 4 Drive Arm 4a Female thread 5 Sample holder 5a Holder body 5b Mounting material 6 Drive coil tray 7. Bearings 7a Rotation axis 7b Rolling element 7c outer ring 7d Cone section 8a,8b York 9a~9e Fasteners 10. Thin plate bending fatigue testing equipment 11 Test specimen 12 Laser displacement sensor 12a Laser light 13 3-axis stage 14 Cable 15 Anti-vibration 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 Driving Force I alternating current θ vertical angle

Claims

1. a drive unit including 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, the drive unit generating a drive force whose direction is periodically reversed by passing an alternating current through the drive coil; a rotation unit connected to the drive unit and configured to rotate the drive unit 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:

2. 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 symmetrical positions relative to the center of the drive coil so that the direction of the drive force is the same, and the combination of the S and N poles of the pair of magnets are opposite.

3. 3. The vibration unit for thin plate bending fatigue testing according to claim 2, wherein the bearing of the rotating part is a pivot bearing.

4. 2. The vibration unit for thin plate bending fatigue testing according to claim 1, wherein the holding portion, the rotating portion and the arm portion are integrally formed.

5. A sample unit including a vibration unit for thin plate bending fatigue testing 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 according to the present invention is characterized in that the measurement unit outputs a correlation between a stress amplitude applied to the thin plate in the sample unit and a number of repetitions until fracture occurs due to the stress amplitude.

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