Wideband fatigue testing machine with adjustable amplitude

Abstract

The utility model provides an amplitude-adjustable broadband fatigue testing machine, which consists of an amplitude-variable cam and a resonance mechanism, the interval and the rotating speed of the amplitude-variable cam can be flexibly adjusted, the amplitude-variable cam has specific parameters and an outer edge curved surface profile, the resonance mechanism is contacted with the amplitude-variable cam, the frequency and the stress amplitude of the device can be independently adjusted, and the application range of a fatigue test is expanded; the fatigue testing machine provided by the utility model can be suitable for high-frequency and high-amplitude fatigue testing of parts and materials, and the application range of the fatigue testing is widened.

Description

Technical Field

[0001] The utility model relates to a machine for testing material fatigue performance, in particular to a broadband fatigue testing machine with adjustable amplitude. Background Art

[0002] Internal damage inflicted by alternating stresses in materials leads to invisible microstructural changes, potentially causing failure at loads below the design level after prolonged service. Fatigue failure occurs when materials are subjected to alternating stresses far below their ultimate strength or even yield strength for a certain number of cycles. Fatigue failure is caused by sudden changes in component dimensions or uneven internal metal structures, which create stress concentration areas and lead to unbalanced stress transfer. This induction of microcracks at these stress concentrations within internal defects. Under alternating stresses, these microcracks continuously initiate and propagate, growing larger and larger. Fatigue can cause lattice dislocations, microplastic deformation, microcracks, and residual stress concentrations in components during use. If appropriate measures are not taken promptly, metal components subjected to cyclic loading will gradually develop permanent cumulative damage. When stress levels do not exceed the material's ultimate strength or even fall below its elastic limit, cracks or sudden fractures may occur, resulting in catastrophic failures.

[0003] In real-world production, many pieces of equipment are susceptible to fatigue failure. Most mechanical products are subjected to alternating loads during operation. Statistics show that 85% of automotive component failures are due to fatigue, while in the aviation and aerospace sectors, 60% to 80% of fractures are due to fatigue. Fatigue issues are not limited to the aviation, aerospace, and transportation sectors; they also occur in nearly all engineering fields, including the nuclear industry, energy, and civil engineering.

[0004] To better select components for equipment that meet specific production environments, it's necessary to predict and calculate the lifespan of components intended for or used in actual production. However, scientific and practical research has proven that there's still a lack of theoretical methods for predicting and calculating the lifespan of component structures in actual production. Therefore, using fatigue testing machines to conduct fatigue tests on components and material structures, measuring their fatigue fracture resistance and calculating their fatigue lifespan is the primary method used to prevent fatigue failure both domestically and internationally.

[0005] Very-High-Cycle Fatigue (VHCF) usually refers to the failure cycle number exceeding 10 7Fatigue, also known as ultra-high-cycle fatigue (VHCF), ultra-long-life fatigue (ULLF), or gigacycle fatigue (Gigacycle Fatigue), is a fatigue test that requires a high frequency of loading. To complete VHCF testing within a reasonable timeframe, high-frequency loading is often employed. VHCF testing techniques can be categorized into two main types: non-resonant and resonant. In non-resonant fatigue testing, both the testing machine and the specimen are subjected to forced vibration. This means high energy consumption at high frequencies. Frequency is inversely proportional to the loading amplitude, and the loading amplitude is very low at high frequencies. Therefore, to achieve the required test stress level, the operating frequency of these testing machines is generally low. This lack of testing efficiency results in a higher time cost for non-resonant fatigue testing machines in VHCF testing. Compared to non-resonant fatigue testing techniques, resonant fatigue testing offers the advantages of low power consumption and high efficiency, making it more suitable for VHCF testing. Resonant fatigue testing techniques can be broadly categorized based on their principles as electromagnetic resonance, electro-hydraulic resonance, and piezoelectrically driven resonance. The operating frequencies of the first two methods are generally less than 1kHz, making them difficult to meet the efficiency requirements of VHCF testing. The latter, on the other hand, typically operates at around 20kHz and is currently the most widely used VHCF testing method. However, piezoelectric-driven resonant fatigue testing machines generally have a fixed operating frequency and cannot adjust the amplitude, making them suitable only for fatigue testing of fixed-shape specimens (not for fatigue testing of components). Furthermore, the operating frequency of piezoelectric-driven resonant testing is often significantly higher than the service loading frequency of the test piece, making frequency effects more pronounced for some materials.

[0006] Therefore, providing a fatigue testing machine that can independently adjust the amplitude and frequency and can achieve more efficient and effective fatigue testing of more materials and components is of great significance for better predicting and calculating the life of component structures to be used or used in actual production in actual life and production, making the equipment safer. Utility Model Content

[0007] In response to the shortcomings and defects of the existing technology, the present invention provides a wide-band fatigue testing machine with adjustable amplitude. The fatigue testing machine mainly consists of a variable amplitude cam with specific parameters and outer edge curved surface profile, which can flexibly adjust the spacing and speed, and is composed of a resonant mechanism in contact with the variable amplitude cam. Due to the adjustable speed, the device frequency is adjustable, and the resonance mechanism is kept within the resonance bandwidth during the test. When the resonance occurs, the longitudinal movement of the end in contact with the variable amplitude cam is approximately sinusoidal. The outer edge curved surface profile of the variable amplitude cam can cause the resonant mechanism to generate sinusoidal acceleration. The movement of the variable amplitude cam will not hinder the self-vibration of the resonant mechanism, thereby significantly reducing unnecessary power. Moreover, due to the adjustable spacing of the variable amplitude cam, the amplitude and stress amplitude of the resonant mechanism can be adjusted independently of the loading frequency and are independently adjustable. This expands the scope of application of fatigue testing. Furthermore, the fatigue testing machine provided by the present invention can be applied to fatigue testing of components and some flexible materials, thus broadening the scope of application of fatigue testing.

[0008] In order to achieve the above invention objectives, the present invention adopts the following technical methods:

[0009] A wide-band fatigue testing machine with adjustable amplitude comprises a variable amplitude cam composed of two opposing cams, the outer edge of the variable amplitude cam having a curved profile, the rotational speed of the variable amplitude cam being adjustable, and the spacing between the two opposing cams being adjustable; and an optical axis on which a test piece can be mounted, wherein one end of the optical axis contacts the curved profile of the outer edge of the variable amplitude cam via a second universal wheel, and the other end is connected to the optical axis via the second universal wheel, the optical axis and the test piece having the same longitudinal wave resonance frequency, and the optical axis and the test piece form a resonant mechanism.

[0010] Furthermore, the luffing cam parameters satisfy the following equation:

[0011]

[0012]

[0013] in:

[0014]

[0015] x, y, z represent the coordinates of the contact point between the sphere of the second universal wheel and the curved surface contour of the outer edge of the variable amplitude cam, A m is the maximum value of the optical axis amplitude, is the minimum value of the axial inclination angle between the contact surface of the luffing cam and the sphere of the second universal wheel and the luffing cam, r is the radius of the sphere of the second universal wheel, R0 is the base circle radius of the luffing cam, k is the number of teeth of the luffing cam, and:

[0016] .

[0017] Furthermore, it also includes a first universal wheel, a clamp, a self-aligning bench vise, a linkage shaft, a first ball bearing sleeve, a second ball bearing sleeve, a spring, a motor, and a coupling; the clamp is installed on the self-aligning bench vise to clamp the variable amplitude cam from both sides, the first universal wheel is installed at the contact point between the clamp and the variable amplitude cam, and the linkage shaft passes through the variable amplitude cam; the optical axis passes through the first ball bearing sleeve, and a spring is installed at the other end opposite to the end where the second universal wheel is installed, and the spring is in contact with the second ball bearing sleeve; the coupling is installed on the motor and connected to the linkage shaft.

[0018] Furthermore, the fatigue testing machine is suitable for resonant mechanisms composed of optical axes and test specimens with different resonant frequencies. If different test specimens have different resonant frequencies, the optical axis parameters (such as length) can be adjusted to align with the test specimen's resonant frequency. During fatigue testing, the speed of the variable amplitude cam can be adjusted to ensure the device's frequency falls within the resonant bandwidth of the resonant mechanism.

[0019] Furthermore, it also includes a base, the motor is fixed on the base through the motor seat, the self-centering bench vise is fixed on the base through the first fixed block, the linkage shaft passes through the bearing seat, and the bearing seat is fixed to the base through the second fixed block; the first ball sleeve and the second ball sleeve are fixed to the base through the third fixed block and the fourth fixed block respectively.

[0020] The utility model provides a wide-band fatigue testing machine with adjustable amplitude, which has the following beneficial technical effects:

[0021] 1. The broadband fatigue testing machine provided by the utility model can adjust the rotation speed of the variable amplitude cam. When the variable amplitude cam contacts the optical axis and the test piece through the universal wheel, the resonant mechanism composed of the optical axis and the test piece vibrates back and forth under the rotation drive of the variable amplitude cam. The inertial force generates an alternating load at the center of the test piece, thereby performing a fatigue test on the test piece. Moreover, since the rotation speed of the variable amplitude cam is adjustable, the frequency of the reciprocating vibration of the resonant mechanism can be made consistent with its own resonant frequency, and the resonant mechanism will resonate. At this time, the power consumption of the device during continuous operation will be significantly lower than that during non-resonant operation, which significantly reduces the equipment power consumption of the testing machine and improves the test efficiency.

[0022] 2. The adjustable-amplitude, broadband fatigue testing machine provided by this utility model derives the parameters of the variable amplitude cam from an analytical formula for the curved surface profile of the variable amplitude cam's outer edge. The variable amplitude cam designed according to this analytical formula ensures that the longitudinal motion of the end in contact with the variable amplitude cam during resonance of the resonant mechanism is approximately sinusoidal. When the curved surface profile of the cam's outer edge precisely enables the resonant mechanism to generate sinusoidal acceleration, the movement of the variable amplitude cam will not hinder its self-oscillation, thereby significantly reducing unnecessary power. The amplitude of the resonant mechanism's vibration is independent of the variable amplitude cam's rotational speed, i.e., the test frequency. The frequency and amplitude are not inversely proportional, and high amplitudes can still be achieved under high-frequency loading.

[0023] 3. The testing machine of the present invention can control the spacing between the two variable amplitude cams, which is linearly related to the amplitude of the resonant mechanism, thereby controlling the amplitude of the resonant mechanism and affecting the size of the alternating load at the center of the specimen. The adjustable amplitude is achieved while having a simple structure and significant effect. It is also applicable to resonant mechanisms composed of optical axes and specimens with different resonant frequencies, and can also test complex specimens, broadening the scope of application of the fatigue testing machine. The loading frequency can be changed by adjusting the cam speed. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 : Schematic diagram of a wide-band fatigue testing machine with adjustable amplitude

[0025] Figure 2 :Schematic diagram of the variable amplitude cam structure

[0026] Figure 3 : Schematic diagram of fixture structure

[0027] Figure 4 : Schematic diagram of the contact between the second universal wheel and the variable amplitude cam (part 1)

[0028] Figure 5 : Schematic diagram of the second universal wheel and the variable amplitude cam contact (part 2)

[0029] Figure 6 : Schematic diagram

[0030] In the figure: 1-first universal wheel; 2-luffing cam; 3-clamp; 4-self-aligning bench vise; 5-first fixed block; 6-bearing seat; 7-second fixed block; 8-linking shaft; 9-second universal wheel; 10a-first ball bearing sleeve; 10b-second ball bearing sleeve; 11-optical axis; -third fixed block; 12b-fourth fixed block; 13-test piece; 14-spring; 15-motor seat; 16-coupling; 17-table; 18-motor. DETAILED DESCRIPTION

[0031] This section further illustrates the device provided by the present utility model with reference to specific embodiments. It should be noted that the embodiments are intended only to illustrate the present utility model and are not intended to limit the scope of the present utility model. Persons skilled in the art may make various modifications or alterations to the present utility model that do not substantially alter the present utility model, and these modifications and alterations are still within the scope of the appended claims.

[0032] Example 1

[0033] A wide-band fatigue testing machine with adjustable amplitude includes a variable amplitude cam 2 composed of two opposing cams, the outer edge of the variable amplitude cam 2 having a curved profile, the rotational speed of the variable amplitude cam 2 being adjustable, and the spacing between the two opposing cams being adjustable; and an optical axis 11 on which a test piece can be mounted, the optical axis 11 being in contact with the curved profile of the outer edge of the variable amplitude cam 2 via a second universal wheel 9 at one end and connected to the test piece via the second universal wheel 9 at the other end, the optical axis 11 and the test piece having the same longitudinal wave resonance frequency, and forming a resonant mechanism with the test piece.

[0034] In order to achieve adjustable speed of the variable amplitude cam 2, any technical solution in the existing technology that can achieve this effect can be selected, such as using a motor with adjustable power frequency as a driving mechanism to drive the rotation of the variable amplitude cam 2; in order to achieve adjustable spacing between the two facing wheels of the variable amplitude cam 2, any technical solution in the existing technology that can achieve this effect can be selected, such as manual adjustment, or the use of computer technology to control the spacing adjustment.

[0035] The fatigue testing machine provided in this embodiment operates as follows: when performing a fatigue test on a specimen, the specimen 13 is mounted at the rear end of the optical axis 11. The specimen 13 and the optical axis 11 form a test resonance mechanism, and a strain gauge is attached to the central surface of the specimen 13. The spacing between the two opposing wheels of the variable amplitude cam 2 is adjusted to zero, at which point the amplitude output by the device is a minimum. The rotation speed of the variable amplitude cam 2 is slowly increased until the speed stabilizes within the resonance bandwidth of the optical axis 11. The resonance mechanism formed by the specimen 13 and the optical axis 11 contacts the curved surface profile of the variable amplitude cam 2 via the second universal wheel 9. The spacing between the two opposing wheels of the variable amplitude cam 2 is slowly adjusted. When the second universal wheel 9 contacts, the displacement amplitude increases, and the resonant vibration increases. The stress amplitude is observed through the strain gauge until the stress amplitude reaches the stress amplitude required for the test. During this period, the resonant mechanism reciprocates and remains within the resonance bandwidth, with a low operating power. The fatigue limit of the specimen is calculated and read until the specimen reaches its fatigue limit and breaks, or the set number of fatigue loading cycles is reached.

[0036] Example 2

[0037] Compared with Example 1, the difference of this embodiment is that the parameters of the variable amplitude cam 2 satisfy the following equations:

[0038]

[0039]

[0040] in:

[0041]

[0042] x, y, z represent the coordinates of the contact points between the sphere of the second universal wheel 9 and the curved surface contour of the outer edge of the variable amplitude cam 2, respectively.m is the maximum value of the amplitude of the optical axis 11, is the minimum value of the axial inclination angle between the contact surface of the luffing cam 2 and the sphere of the second universal wheel 9 and the luffing cam 2, r is the radius of the sphere of the second universal wheel 9, R0 is the base circle radius of the luffing cam 2, k is the number of teeth of the luffing cam 2, and:

[0043] .

[0044] The adjustable amplitude wide-band fatigue testing machine provided in this embodiment derives the parameters of the variable amplitude cam through an analytical expression for the curved surface profile of the outer edge of the variable amplitude cam. The variable amplitude cam designed according to the analytical expression makes the longitudinal movement of the contact end with the variable amplitude cam approximately sinusoidal motion when the resonant mechanism resonates. When the curved surface profile of the outer edge of the cam just causes the resonant mechanism to generate a sinusoidal acceleration, the movement of the variable amplitude cam will not hinder its self-vibration, thereby significantly reducing unnecessary power.

[0045] Example 3

[0046] Compared with Example 2, this embodiment is different in that: it also includes a first universal wheel 1, a variable amplitude cam 2, a clamp 3, a self-centering bench vise 4, a linkage shaft 8, a first ball sliding sleeve 10a, a second ball sliding sleeve 10b, a spring 14, a motor 18, and a coupling 16; the variable amplitude cam 2 is composed of two opposite wheels, and the outer edge of the variable amplitude cam 2 is a curved surface profile; the clamp 3 is installed on the self-centering bench vise 4, clamping the variable amplitude cam 2 from both sides, and the first universal wheel 1 is installed at the contact point between the clamp 3 and the variable amplitude cam 2, and the linkage shaft 8 passes through the variable amplitude cam Wheel 2; the optical axis 11 passes through the first ball sleeve 10a, one end of which is equipped with a second universal wheel 9, which can contact the curved surface contour of the outer edge of the variable amplitude cam 2, and the other end is equipped with a spring 14, which is connected to the outer shell of the second ball sleeve 10b; when installing the test piece, the test piece 13 is fixed to the tail of the optical axis 11 by threaded fitting, and the spring 14 is sleeved on the outside of the optical axis 11, with one end fixedly connected to the surface of the optical axis 11 and the other end in contact with the outer shell of the ball sleeve 10b; the coupling 16 is installed on the motor 18 and connected to the linkage shaft 8.

[0047] The motor 18 is a three-phase AC variable frequency motor with an inverter assembly that can adjust the speed. The motor 18 drives the variable amplitude cam 2 to rotate via the linkage shaft 8. The motor shaft 18 is connected to the linkage shaft 8 via the coupling 16, which reduces vibration and compensates for the position error between the two shafts. The variable amplitude cam 2 contacts the second universal wheel 9 connected to the optical axis 11, causing the resonant mechanism composed of the optical axis 11 and the test piece 13 to vibrate back and forth. The spring 14 ensures that the resonant mechanism is always in contact with the variable amplitude cam 2. When the frequency of the resonant mechanism's reciprocating vibration is consistent with its own resonant frequency and within the resonant bandwidth, the resonant mechanism will resonate. At this time, the power of the device during continuous operation will be significantly lower than when it is not resonant. The test piece vibrates back and forth, and the inertial force generates an alternating load at the center of the test piece, thereby performing fatigue testing on the test piece.

[0048] A self-centering bench vise 4 controls the centering motion of the fixture 3, thereby controlling the spacing between the two variable amplitude cams 2. The spacing of the variable amplitude cams 3 is linearly correlated with the amplitude of the resonant mechanism, thereby controlling the amplitude of the resonant mechanism and influencing the magnitude of the alternating load at the center of the specimen 13. A second universal wheel 9 is installed at the end of the optical axis 11 that contacts the outer curved contour of the variable amplitude cam 2. This direct contact between the second universal wheel 9 and the variable amplitude cam 2 prevents wear on the components due to friction.

[0049] The working process of the fatigue testing machine provided in this embodiment is as follows: for example, when used to measure the fatigue limit of a Tc4 titanium alloy under tension and compression at room temperature with a stress amplitude of 600 MPa, the fatigue testing machine includes the following steps:

[0050] Step 1: Install the specimen 13 at the end of the rod, for example, by fixing it to the end of the optical axis through threaded engagement, and attach a strain gauge to the middle surface of the specimen 13;

[0051] Step 2: Adjust the self-centering bench vise 4 to control the centering movement of the fixture 3 so that the distance between the two opposite wheels of the variable amplitude cam 2 is 0. At this time, the amplitude that the device can output is 0;

[0052] Step 3: Since the first-order resonant frequency of the optical axis used in this embodiment is 2.5 kHz, start the motor and slowly adjust the motor speed until it stabilizes at 3000 rpm, so that the operating frequency of the device and the optical axis are within the resonant bandwidth. During this time, the resonant mechanism formed by the optical axis 11 and the test piece 13 contacts the curved surface contour of the outer edge of the variable amplitude cam 2 through the second universal wheel 9.

[0053] Step 4: Slowly adjust the self-centering bench vise to increase the distance between the two variable amplitude cams, and observe the stress amplitude through the strain gauge until the stress amplitude reaches the test requirement of 600 MPa. During this period, the resonant mechanism composed of the optical axis 11 and the specimen 13 maintains reciprocating vibration. The operating frequency of the device is 2.5 kHz. The optical axis 11 and the specimen 13 are both within their resonance bandwidth, and the operating power is low.

[0054] Step 6: Fatigue test data is read and calculated until the specimen reaches its fatigue limit and fractures or reaches the set number of fatigue loading cycles. Reading and calculating the fatigue limit can be achieved using existing technologies such as encoders. For example, an encoder connected to the linkage shaft 8 can be used to read and calculate fatigue test data such as the fatigue limit.

[0055] When the tested specimens are different, their resonant frequencies are different. In this case, the length of the optical axis can be adjusted to make it the same as the resonant frequency of the specimen, and when performing fatigue testing, the speed of the variable amplitude cam can be adjusted to make the frequency of the device within the resonant bandwidth of the resonant mechanism.

[0056] Example 4

[0057] Based on Example 2, this embodiment also includes a base 17, a motor 18 is fixed to the base 17 through a motor base 15, a self-centering bench vise 4 is fixed to the base 17 through a first fixing block 5, a linkage shaft 8 passes through a bearing seat 6, and the bearing seat 6 is fixed to the base 17 through a second fixing block 7; the first ball sleeve 10a and the second ball sleeve 10b are fixed to the base 7 through a third fixing block 12a and a fourth fixing block 12b respectively.

[0058] The utility model provides a wide-band fatigue testing machine with adjustable amplitude. The adjustable speed realizes the adjustable frequency of the device. During the test, the test piece is kept within the resonance bandwidth, and the movement of the variable amplitude cam does not hinder the self-vibration of the test piece, thereby greatly reducing unnecessary power. Moreover, since the adjustable spacing of the variable amplitude cam realizes the adjustment of the amplitude and stress amplitude of the resonant mechanism independently of the loading frequency, the independent adjustability expands the scope of application of the fatigue test, and can be applied to fatigue testing of components and some flexible materials.

Claims

1. A broadband fatigue testing machine with adjustable amplitude, characterized by: The invention comprises a variable amplitude cam (2) composed of two cams facing each other, the outer edge of the variable amplitude cam (2) is a curved surface profile, the rotation speed of the variable amplitude cam (2) is adjustable and the spacing between the two cams facing each other is adjustable; and further comprises an optical axis (11) on which a test piece can be mounted, one end of the optical axis (11) contacts the curved surface profile of the outer edge of the variable amplitude cam (2) through a second universal wheel (9), and the other end is connected to the test piece, the optical axis (11) and the test piece have the same longitudinal wave resonance frequency, and the optical axis (11) and the test piece form a resonant mechanism.

2. The wide-band fatigue testing machine with adjustable amplitude according to claim 1, characterized in that: The parameters of the variable amplitude cam (2) satisfy the following equations: in: ； x, y, z represent the coordinates of the contact point between the sphere of the second universal wheel (9) and the curved surface contour of the outer edge of the variable amplitude cam (2), respectively. m is the maximum value of the amplitude of the optical axis (11), is the minimum value of the axial inclination angle between the contact surface of the amplitude-changing cam (2) and the sphere of the second universal wheel (9) and the amplitude-changing cam (2), r is the radius of the sphere of the second universal wheel (9), R0 is the base circle radius of the amplitude-changing cam (2), k is the number of teeth of the amplitude-changing cam (2), and: 。 3. The wide-band fatigue testing machine with adjustable amplitude according to claim 2, characterized in that: It also includes a first universal wheel (1), a clamp (3), a self-centering bench vise (4), a linkage shaft (8), a first ball bearing sleeve (10a), a second ball bearing sleeve (10b), a spring (14), a motor (18), and a coupling (16); the clamp (3) is mounted on the self-centering bench vise (4) to clamp the amplitude-changing cam (2) from both sides; the first universal wheel (1) is mounted at the contact point between the clamp (3) and the amplitude-changing cam (2); the linkage shaft (8) passes through the amplitude-changing cam (2); the optical axis (11) passes through the first ball bearing sleeve (10a), and a spring (14) is mounted at the other end opposite to the end where the second universal wheel (9) is mounted, and the spring (14) contacts the second ball bearing sleeve (10b); the coupling (16) is mounted on the motor (18) and connected to the linkage shaft (8).

4. The wide-band fatigue testing machine with adjustable amplitude according to claim 3, characterized in that: The fatigue testing machine can be applied to a resonant mechanism composed of an optical axis and a test piece with different resonant frequencies.

5. The wide-band fatigue testing machine with adjustable amplitude according to claim 3, characterized in that: The invention also includes a base (17), a motor (18) is fixed on the base (17) through a motor base (15), a self-centering bench vise (4) is fixed on the base (17) through a first fixing block (5), a linkage shaft (8) passes through a bearing seat (6), and the bearing seat (6) is fixed on the base (17) through a second fixing block (7); and a first ball bearing sleeve (10a) and a second ball bearing sleeve (10b) are fixed on the base (17) through a third fixing block (12a) and a fourth fixing block (12b), respectively.

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