Electromagnetic drive composite micro-motion fatigue testing device and method based on magnetorheological fluid

Abstract

The present invention discloses a magnetorheologically driven electromagnetically driven composite micro-motion fatigue testing device and method. The device utilizes two composite micro-motion fatigue testing mechanisms, each comprising an electromagnetic excitation device, a fixture, and two ultrasonic magnetically controlled vibration units. The ultrasonic magnetically controlled vibration units comprise a U-shaped cavity, an ultrasonic vibrator, and a gradient coil. The device changes the micro-motion frequency of the U-shaped cavity by varying the vibration frequency of the ultrasonic vibrator, thereby varying the micro-motion frequency of the mating surface. The device also changes the magnetic field of the gradient coil by varying the current, further altering the effect of the magnetic field on the magnetorheological fluid within the U-shaped cavity. This modulates the micro-motion amplitude and direction of the U-shaped cavity, thereby varying the micro-motion amplitude and direction of the metal mating surface. The micro-motion of the U-shaped cavity is combined with the excitation of the electromagnetic excitation device, causing the mating surface to achieve composite directional micro-motion according to a set vibration direction and amplitude, thereby performing fatigue testing on the metal mating surface. The device can simulate composite directional high-frequency vibrations under a variety of complex working conditions.

Description

Technical Field

[0001] The present invention belongs to the field of fretting damage testing of metal materials, and in particular relates to a device and method for testing fretting wear and fatigue performance of metal mating surfaces. Background Art

[0002] Magnetorheological fluids (MRFs) are composed of nanoscale (less than 10 nm) ferromagnetic or superparamagnetic particles stably dispersed in a base fluid (such as oil or water) with the aid of a surfactant. They possess both the magnetic properties of a magnet and the fluidity of a liquid. Since the concept of MRF emerged, researchers both domestically and internationally have actively researched its applications. MRFs are now finding applications in a wide range of fields, including magnetic seals, electroacoustic devices, lubrication, mineral processing, magnetic circuits, healthcare, and biomagnetism. However, the field of electromagnetic micromotion has received relatively little attention.

[0003] Electromagnetic micro-motion drive uses an electromagnetic exciter to output relative displacement. Its greatest advantage is its wide bandwidth, which allows it to simulate high-frequency micro-motion. However, it has disadvantages such as low excitation force and displacement amplitude, poor control accuracy, and a relatively single excitation force direction.

[0004] Fretting damage mainly includes two mechanisms: contact surface wear and fretting fatigue crack formation and expansion. During the use of metal mating, metal materials are often subjected to repeated fretting loads, which leads to alternating tangential and normal loads on the mating surface, causing a composite fretting mode in which tangential and radial fretting act together, ultimately leading to surface wear and fretting fatigue of the mating surface. This fatigue phenomenon will affect the life and performance of the mating surface. Therefore, the study of fretting wear and fatigue behavior of metal mating surfaces is of great significance. However, existing fretting wear test methods have certain limitations in terms of dynamic detection methods of fretting contact interfaces, simulation of composite directional vibrations and low displacement amplitude control, large displacement amplitude span, and large motion frequency span, making it difficult to fully reflect the actual working conditions of metal mating surfaces.

[0005] In view of the above problems, it is necessary to design a method that can vibrate at high frequency in the composite direction. This can effectively improve the test accuracy of the micro-wear test experiment, reduce the test cost, and reduce the steps required to achieve the same degree of wear, which is of great significance. Summary of the Invention

[0006] In response to the shortcomings of the existing technology, the present invention provides an electromagnetic micro-motion fatigue testing device and method based on magnetorheological fluid, which can utilize the characteristics of magnetic fluid to achieve the function of composite directional micro-motion, and has the characteristics of low cost, high output force, low energy consumption, adjustable micro-motion amplitude, and adjustable micro-motion frequency.

[0007] The present invention is an electromagnetically driven composite micro-motion fatigue testing device based on magnetorheological fluid, comprising a frame and two composite micro-motion fatigue testing mechanisms. The composite micro-motion fatigue testing mechanism comprises an electromagnetic excitation device, a clamp, two T-shaped brackets and two ultrasonic magnetically controlled vibration units; the T-shaped bracket is composed of a vertically arranged slide bar and a connecting rod, and two integrally formed slip rings are provided at both ends of the slide bar, wherein the two slip rings of one T-shaped bracket are fixed on two of the slide rails of the frame, and the two slip rings of the other lower T-shaped bracket are fixed on the other two slide rails of the frame; the ultrasonic magnetically controlled vibration unit comprises a U-shaped cavity, an ultrasonic vibrator and a gradient coil; the ultrasonic vibrator and the gradient coil of one ultrasonic magnetically controlled vibration unit are both connected to the U-shaped cavity. The connecting rod of one T-shaped bracket is fixed on the side, and the ultrasonic vibrator and gradient coil of the other ultrasonic magnetic control vibration unit are both fixed to the connecting rod of the other T-shaped bracket. On the same T-shaped bracket, the gradient coil is closer to the slip ring of the T-shaped bracket than the ultrasonic vibrator. The convex parts of the U-shaped cavities of the two ultrasonic magnetic control vibration units are connected to the ends of the connecting rods of the two T-shaped brackets through ball hinges, and magnetorheological fluid is provided in the U-shaped cavities. The concave parts of the U-shaped cavities of the two ultrasonic magnetic control vibration units are arranged opposite each other and are both fixed to the tail of the clamp. The tail end of the clamp is fixed to the electromagnetic excitation device. The clamps of the two composite micro-motion fatigue testing mechanisms are directly opposite each other. The electromagnetic excitation device of the upper composite micro-motion fatigue testing mechanism is fixed to the frame. The electromagnetic excitation device of the lifting platform and the lower composite micro-motion fatigue testing mechanism are both fixed to the cylinder body of the hydraulic cylinder. The piston rod of the hydraulic cylinder is fixed to the frame via a constraint track. The lifting platform, the constraint track fixed to the frame, and the four slide rails of the frame all form a sliding pair. The constraint track is provided with a scale.

[0008] Preferably, the frame includes a top plate, a bottom plate, a slide rail and a bottom frame, and the top plate and the bottom plate are fixed by four slide rails; the electromagnetic excitation device of the upper composite micro-motion fatigue testing mechanism is fixed to the top plate, the constraint rail is fixed to the bottom plate, and the bottom plate is fixed to the bottom frame.

[0009] Preferably, the end of the connecting rod of the T-shaped bracket is fixed to the spherical support of the ball hinge, and the convex part of the U-shaped cavity is fixed to the ball head of the ball hinge.

[0010] Preferably, the slip ring of the T-shaped bracket is supported on the slide rail via a rolling bearing.

[0011] Preferably, the gradient coil is cylindrical with uniform wall thickness and is fixed on a cylindrical connecting rod in the T-shaped bracket, and the connecting rod is in contact with the inner wall of the gradient coil.

[0012] Preferably, the ultrasonic vibrator, electromagnetic excitation device, gradient coil, frequency sensor, displacement sensor and gyroscope are all connected to the PID controller, which adjusts the vibration frequency of the ultrasonic vibrator, the excitation parameters of the electromagnetic excitation device and the magnetic field generated by the gradient coil, and receives the vibration frequency detected by the frequency sensor, the amplitude detected by the displacement sensor and the vibration direction detected by the gyroscope.

[0013] More preferably, the PID controller is connected to a display module.

[0014] The electromagnetic driven composite fretting fatigue testing method based on magnetorheological fluid of the present invention comprises the following steps:

[0015] Step 1: The metal mating surfaces are clamped by two fixtures; the direction, frequency, amplitude, and duration of the vibration of the metal mating surfaces, the frequency and amplitude of the electromagnetic excitation device, the amplitude of the ultrasonic vibrator, and the fatigue boundary conditions are set.

[0016] Step 2: The PID controller changes the micro-motion frequency of the U-shaped cavity by changing the vibration frequency of the ultrasonic vibrators of the two ultrasonic magnetically controlled vibration units, thereby changing the micro-motion frequency of the metal mating surface, and changes the gradient coil magnetic field by changing the gradient coil current of the two ultrasonic magnetically controlled vibration units, further changing the effect of the magnetic field on the magnetorheological fluid in the U-shaped cavity, to adjust the micro-motion amplitude and direction of the U-shaped cavity, thereby changing the micro-motion amplitude and direction of the metal mating surface, and the micro-motion of the U-shaped cavity is combined with the excitation generated by the electromagnetic excitation device, so that the metal mating surface can achieve composite directional micro-motion according to the set vibration direction and amplitude, thereby performing fatigue testing on the metal mating surface.

[0017] Preferably, the relationship between the magnetic field strength H(x,y,z) of the gradient coil at any point (x,y,z) in space and the current is as follows:

[0018]

[0019] Among them, G x , G y , G z are the gradients of the gradient coil in the X, Y, and Z directions, I x , I y , I z are the currents of the gradient coil in the X, Y, and Z directions respectively, are the unit vectors in the X, Y, and Z directions respectively.

[0020] More preferably, the relationship between the magnetic field intensity that can be generated by the gradient coil at the centroid of the contact surface between the U-shaped cavity and the fixture and the bulk modulus and shear modulus of the magnetorheological fluid in the U-shaped cavity is constructed as follows:

[0021] The comprehensive mechanical response G of the magnetorheological fluid at the centroid of the contact surface between the U-shaped cavity and the fixture under the action of the magnetic field intensity H * (H) is:

[0022] G * (H) = 10G′(H) + iG″(H)

[0023] G′(H) is the storage modulus, G″(H) is the loss modulus, and i is the imaginary unit.

[0024] The empirical formulas for G′(H) and G″(H) are:

[0025] G′(H)=3.11×10 -8 H 2 +3.56×10 -5 H+0.578×10 2

[0026] G″(H)=3.47×10 -9 H 2 +3.85×10 -6 H+6.31×10 -3

[0027] The equivalent Lame constant of the magnetorheological fluid in the U-shaped cavity of the ultrasonic magnetically controlled vibration unit is:

[0028]

[0029] Wherein, λ(d) is the first Lame parameter, which represents the bulk modulus of the magnetorheological fluid material; μ(d) is the second Lame parameter, which represents the shear modulus of the magnetorheological fluid material; C is the correction factor, E is the Young's modulus of the magnetorheological fluid material, and the Poisson's ratio v of the magnetorheological fluid material is calculated as follows:

[0030]

[0031] The relationship between the vibration frequency ω of the ultrasonic vibrator and the displacement of any point in the U-shaped cavity is as follows:

[0032] The wave equation of the elastic wave of the ultrasonic magnetically controlled vibration unit incident vertically on the U-shaped cavity and transmitted in the magnetorheological fluid is:

[0033]

[0034] Where ξ(d,t) is the displacement function of the elastic wave; t is the time variable, σ is the damping coefficient, d represents the distance along a certain dimension (X, Y, Z), and d = 0 corresponds to the point where the magnetorheological fluid is closest to the ultrasonic vibrator, and d = L corresponds to the point where the magnetorheological fluid is farthest from the ultrasonic vibrator. The value of d ranges from 0 to L; c L is the wave speed, and ρ is the density of the magnetorheological fluid, and K(d) is the comprehensive elastic coefficient of the magnetorheological fluid affected by elastic waves, which is calculated as follows:

[0035] K(d)=K0(d)×F f (ω) (2)

[0036] Among them, the static elastic coefficient K0(d)=λ(d)+2μ(d); the frequency compensation coefficient F f (ω) is calculated as follows:

[0037]

[0038] F T is the temperature compensation coefficient, which is calculated by the following formula:

[0039] F t =1+β(T-T0)

[0040] Where T0 is the reference temperature, β is the temperature influence coefficient, and T is the room temperature of the magnetorheological fluid.

[0041] Substituting into equation (1), the wave equation of the one-dimensional elastic wave generated by the ultrasonic vibrator in the magnetorheological material with a gradient structure under the influence of the magnetic field is:

[0042]

[0043] When the elastic wave is a simple harmonic wave, the displacement function of the elastic wave in the magnetorheological fluid contained in the U-shaped cavity in the magnetically controlled vibration unit is expressed as follows:

[0044] ξ(d,t)=ξ(d)e iωt (4)

[0045] Where ξ(d) represents the displacement of the elastic wave at different positions d in the magnetorheological fluid when time t is fixed. Substituting equation (4) into equation (3), we get:

[0046]

[0047] Let k(d) be:

[0048]

[0049] Substituting formula (6) into formula (5), we get:

[0050]

[0051] The boundary conditions are: When d=0, ξ(d)=A, ξ(d) = 0 at position A, where A is the amplitude of the ultrasonic vibrator. Solving equation (7) yields ξ(d), so that when the magnetorheological fluid in the U-shaped cavity of the magnetically controlled vibration unit is subjected to the magnetic field generated by the gradient coil, the displacement of the point at position d in the magnetorheological fluid is expressed as:

[0052]

[0053] The displacements of a particle in the solid-state magnetorheological fluid at a distance d in the X, Y, and Z dimensions are solved by equation (8).

[0054] The micro-motion effect of each position of the U-shaped cavity and the fixture contact surface on the fixture and the metal matching surface is considered to be the same as the micro-motion effect of the centroid of the U-shaped cavity and the fixture contact surface on the fixture and the metal matching surface. To achieve the set metal matching surface amplitude and vibration direction, the current I required by the gradient coil in the X, Y, and Z directions is x , I y , I z The calculation is as follows: the amplitude obtained by removing the amplitude component of the electromagnetic excitation device from the set metal mating surface amplitude is decomposed into the components along the X, Y, and Z dimensions, which are respectively used as the amplitudes of the corresponding dimensions at the centroid of the contact surface between the U-shaped cavity and the fixture, and are substituted into u in formula (8) respectively. d , derive the corresponding comprehensive mechanical response G * (H), then through G * The magnetic field intensity H of the corresponding dimension is inferred from the relationship between (H) and the magnetic field intensity H received by the magnetorheological fluid at that location. Finally, the H(x,y,z) on the left side of the H(x,y,z) expression is substituted with the magnetic field intensity H of the corresponding dimension. The right side of the H(x,y,z) expression only retains the coefficient before the unit vector of the corresponding dimension. In this way, an equation is established, and the X, Y, and Z coordinates of the contact surface centroid of the U-shaped cavity and the fixture are substituted into the equation to obtain the current I of the gradient coil in the X, Y, and Z dimensions. x , I y , I z Finally, the current I required by the gradient coil in the X, Y, and Z directions is obtained x , I y , I z , so that the metal mating surfaces can vibrate at a specific frequency according to the set amplitude and vibration direction.

[0055] The present invention has the beneficial effects:

[0056] 1. The present invention changes the micro-motion frequency of the U-shaped cavity by changing the vibration frequency of the ultrasonic vibrator, thereby changing the micro-motion frequency of the metal mating surface, and changes its magnetic field by changing the current of the gradient coil, further changing the effect of the magnetic field on the magnetorheological fluid in the U-shaped cavity, to adjust the micro-motion amplitude and direction of the U-shaped cavity, thereby changing the micro-motion amplitude and direction of the metal mating surface. The micro-motion of the U-shaped cavity is combined with the excitation generated by the electromagnetic excitation device, so that the metal mating surface can achieve composite directional micro-motion according to the set vibration direction and amplitude, thereby performing fatigue testing on the metal mating surface, and can simulate composite directional high-frequency vibration modes under various complex working conditions, thereby improving the authenticity and practicality of the test.

[0057] 2. The present invention uses magnetorheological electromagnetic micro-motion control to conduct micro-motion wear test experiments on metal mating surfaces under various complex working conditions. It is simple to operate, low in cost, and can improve the experimental effect. BRIEF DESCRIPTION OF THE DRAWINGS

[0058] Figure 1 It is a structural schematic diagram of the device of the present invention;

[0059] Figure 2 The figure is a flow chart of the steps for adjusting the amplitude of the metal fitting surface in the method of the present invention. DETAILED DESCRIPTION

[0060] The present invention will be further described below with reference to specific embodiments, but the present invention is not limited to these specific embodiments. Those skilled in the art should recognize that the present invention encompasses all possible alternatives, improvements, and equivalents within the scope of the claims.

[0061] See also Figure 1 , an electromagnetically driven composite micro-motion fatigue testing device based on magnetorheological fluid, including a frame and two composite micro-motion fatigue testing mechanisms. The composite micro-motion fatigue testing mechanism includes an electromagnetic excitation device 1 (or electromagnetic exciter), a fixture 5, two T-shaped brackets 6 and two ultrasonic magnetically controlled vibration units; the T-shaped bracket 6 is composed of a vertically arranged slide bar and a connecting rod, and two integrally formed slip rings are provided at both ends of the slide bar, the two slip rings of one T-shaped bracket 6 are fixed on two of the slide rails of the frame, and the two slip rings of the other lower T-shaped bracket 6 are fixed on the other two slide rails of the frame; the ultrasonic magnetically controlled vibration unit includes a U-shaped cavity 2, an ultrasonic vibrator 3 (composed of an ultrasonic transducer and an amplitude rod) and a gradient coil 4 (including three coils perpendicular to the x, y and z axes, respectively, to generate a three-directional magnetic field). The gradient coil 4 can use the gradient coil in the Ingenia system of Philips Healthcare, and its X-direction gradient (G x ): 45mT / m, Y direction gradient (G y ): 45mT / m, Z-direction gradient (G z): 45mT / m, maximum gradient strength: 45mT / m, maximum gradient rise rate: 200T / m / s; the ultrasonic vibrator 3 and gradient coil 4 of one ultrasonic magnetic control vibration unit are fixed to the side of the connecting rod of a T-shaped bracket 6, and can be connected by screws, and the ultrasonic vibrator 3 and gradient coil 4 of the other ultrasonic magnetic control vibration unit are fixed to the side of the connecting rod of another T-shaped bracket 6, and on the same T-shaped bracket 6, the gradient coil 4 is closer to the slip ring of the T-shaped bracket 6 than the ultrasonic vibrator 3; The convex parts of the U-shaped cavities 2 of the two ultrasonic magnetically controlled vibration units are connected to the ends of the connecting rods of the two T-shaped brackets 6 through ball hinges respectively, and magnetorheological fluid is provided in the U-shaped cavity 2; the concave parts of the U-shaped cavities 2 of the two ultrasonic magnetically controlled vibration units are arranged opposite to each other and are both fixed at the tail end of the clamp 5, and the inner walls of the U-shaped cavities 2 of the two ultrasonic magnetically controlled vibration units can be magnetically adsorbed on the tail end of the clamp 5; the tail end of the clamp 5 is fixed to the electromagnetic excitation device 1, and the tail end of the clamp 5 and the electromagnetic excitation device 1 can be plug-in connected. The clamps 5 of the two composite micro-motion fatigue testing mechanisms are facing each other up and down, the electromagnetic excitation device 1 of the upper composite micro-motion fatigue testing mechanism is fixed to the frame, the lifting platform 7 and the electromagnetic excitation device 1 of the lower composite micro-motion fatigue testing mechanism are both fixed to the cylinder body of the hydraulic cylinder 10, and the piston rod of the hydraulic cylinder 10 is fixed to the frame through the constraint rail 11; the lifting platform 7 and the constraint rail 11 fixed on the frame and the four slide rails of the frame all constitute a sliding pair; the constraint rail 11 is provided with a scale, and the cooperation between the lifting platform 7, the constraint rail 11 and the four slide rails ensures that the electromagnetic excitation device 1 maintains smooth and precise vertical movement during operation, thereby improving the reliability and operation accuracy of the micro-motion fatigue test, and the position of the clamp 5 of the lower composite micro-motion fatigue testing mechanism can be accurately adjusted through the scale of the lifting platform 7 on the constraint rail 11.

[0062] As a preferred embodiment, the frame includes a top plate, a bottom plate, slide rails and a bottom frame, and the top plate and the bottom plate are fixed by four slide rails; the electromagnetic excitation device 1 of the upper composite micro-motion fatigue testing mechanism is fixed to the top plate, the constraint rail 11 is fixed to the bottom plate, and the bottom plate is fixed to the bottom frame.

[0063] As a preferred embodiment, the connecting rod end of the T-shaped bracket 6 is fixed to the spherical support of the ball hinge, and the convex part of the U-shaped cavity 2 is fixed to the ball head of the ball hinge, ensuring that the T-shaped bracket 6 fixes the U-shaped cavity, helping to improve the flexibility and controllability of the system, while ensuring the stability and reliability of the structure.

[0064] As a preferred embodiment, the slip ring of the T-shaped bracket 6 is supported on the slide rail through a rolling bearing, providing smooth rolling motion, reducing friction, and improving the stability and accuracy of motion.

[0065] As a preferred embodiment, the gradient coil is designed as a cylinder with uniform wall thickness and is fixed on a cylindrical connecting rod in the T-shaped bracket 6. The connecting rod fits the inner wall of the gradient coil to ensure good stability and reliability during operation.

[0066] The ultrasonic vibrator 3, electromagnetic excitation device 1, gradient coil, frequency sensor, displacement sensor, and gyroscope are all connected to a PID controller 9. The PID controller 9 adjusts the vibration frequency of the ultrasonic vibrator 3, the excitation parameters of the electromagnetic excitation device 1, and the magnetic field generated by the gradient coil. It also receives the vibration frequency of the metal mating surface detected by the frequency sensor, the amplitude of the metal mating surface detected by the displacement sensor, and the vibration direction of the metal mating surface detected by the gyroscope. The PID controller 9 is connected to a display module 8.

[0067] The electromagnetic driven composite fretting fatigue testing method based on magnetorheological fluid includes the following steps:

[0068] Step 1: The metal mating surfaces are clamped by two fixtures; the direction, frequency, amplitude, and duration of the vibration of the metal mating surfaces, the frequency and amplitude of the electromagnetic excitation device 1, and the amplitude of the ultrasonic vibrator 3 are set, and the fatigue boundary conditions are set.

[0069] Step 2: The PID controller 9 changes the micro-motion frequency of the U-shaped cavity by changing the vibration frequency of the ultrasonic vibrator 3 of the two ultrasonic magnetically controlled vibration units, thereby changing the micro-motion frequency of the metal mating surface, and changes the magnetic field by changing the gradient coil current of the two ultrasonic magnetically controlled vibration units, further changing the effect of the magnetic field on the magnetorheological fluid in the U-shaped cavity 2, to adjust the micro-motion amplitude and direction of the U-shaped cavity, thereby changing the micro-motion amplitude and direction of the metal mating surface (the effect of the magnetic field on the magnetorheological fluid makes the micro-motion frequency of the U-shaped cavity change very little, which is negligible. It is only based on the frequency of the electromagnetic excitation device 1 and the ultrasonic vibrator 3, and the vibration frequency of the ultrasonic vibrator 3 is adjusted through the feedback of the frequency sensor detection result to make the vibration frequency of the metal mating surface reach the set value), and the U-shaped cavity is placed at the front end of the ultrasonic vibrator to minimize the excitation influencing factors. At the same time, the micro-motion of the U-shaped cavity is combined with the excitation generated by the electromagnetic excitation device 1, so that the metal mating surface achieves composite directional micro-motion according to the set vibration direction and amplitude, see Figure 2 , thereby performing fatigue testing on metal mating surfaces, avoiding the singleness of conventional electromagnetic excitation methods and improving practicality.

[0070] Furthermore, the relationship between the magnetic field strength and current of the gradient coil at any point in space is as follows:

[0071] Assuming the center of the gradient coil's end face close to the ultrasonic transducer is the origin of the coordinate system, the magnetic field intensity H(x,y,z) at any point in space with coordinates (x,y,z) affected by the gradient coil is expressed as:

[0072]

[0073] Among them, G x , G y , G z are the gradients of the gradient coil in the X, Y, and Z directions, I x , I y , I z are the currents of the gradient coil in the X, Y, and Z directions respectively, are the unit vectors in the X, Y, and Z directions respectively.

[0074] Furthermore, the relationship between the magnetic field intensity that the gradient coil can generate at the centroid of the contact surface between the U-shaped cavity and the fixture and the bulk modulus and shear modulus of the magnetorheological fluid in the U-shaped cavity is constructed as follows:

[0075] The comprehensive mechanical response G of the magnetorheological fluid at the centroid of the contact surface between the U-shaped cavity and the fixture under the action of the magnetic field intensity H * (H) is:

[0076] G * (H) = 10G′(H) + iG″(H)

[0077] G′(H) is the storage modulus, in MPa, representing the energy storage characteristics of the magnetorheological fluid in the U-shaped cavity, and its value is affected by the elasticity of the magnetorheological fluid; G″(H) is the dissipation modulus, in MPa, representing the energy dissipation characteristics of the magnetorheological fluid in the U-shaped cavity, and its value is affected by the viscosity of the magnetorheological fluid; i is an imaginary unit.

[0078] The empirical formulas for G′(H) and G″(H) are:

[0079] G′(H)=3.11×10 -8 H 2 +3.56×10 -5 H+0.578×10 2

[0080] G″(H)=3.47×10 -9 H 2 +3.85×10 -6 H+6.31×10 -3

[0081] Magnetorheological fluid will become solid-like under the action of a magnetic field, mainly showing solid-state properties. Therefore, based on elastic mechanics, the equivalent Lame constant of the magnetorheological fluid in the U-shaped cavity of the ultrasonic magnetically controlled vibration unit is calculated as:

[0082]

[0083] Wherein, λ(d) is the first Lame parameter, which represents the bulk modulus of the magnetorheological fluid material; μ(d) is the second Lame parameter, which represents the shear modulus of the magnetorheological fluid material; C is the correction factor, which is 9.84×10 -3 ; E is the Young's modulus of the magnetorheological fluid material, which is 71.6 GPa in this embodiment; the Poisson's ratio v of the magnetorheological fluid material is calculated as follows:

[0084]

[0085] The relationship between the vibration frequency ω of the ultrasonic vibrator and the displacement and stress at any point in the U-shaped cavity is as follows:

[0086] Using the wave equation of one-dimensional elastic wave transmission in vibration theory, the wave equation of elastic wave transmitted by ultrasonic magnetic control vibration unit vertically incident on U-shaped cavity in solid-state magnetorheological fluid is established as follows:

[0087]

[0088] Wherein, ξ(d,t) is the displacement function of the elastic wave; t is the time variable, indicating the change of the wave with time; σ is the damping coefficient, which in this embodiment is set to σ = 2.2 N·s / m; d represents the distance along a certain dimension (X, Y, Z), and is defined as d = 0 corresponding to the point where the magnetorheological fluid is closest to the ultrasonic vibrator, and d = L corresponding to the point where the magnetorheological fluid is farthest from the ultrasonic vibrator, and the value of d ranges from 0 to L; c L is the wave speed, and ρ is the density of the magnetorheological fluid, and K(d) is the comprehensive elastic coefficient of the magnetorheological fluid affected by elastic waves, which is calculated as follows:

[0089] K(d)=K0(d)×F f (ω) (2)

[0090] Among them, the static elastic coefficient K0(d)=λ(d)+2μ(d); the frequency compensation coefficient F f (ω) is calculated as follows:

[0091]

[0092] F T is the temperature compensation coefficient, which is calculated by the following formula:

[0093] F t =1+β(T-T0)

[0094] Wherein, T0 is the reference temperature, which is 28.7°C in this embodiment, and β is the temperature influence coefficient, which is β=1.1123×10 -2 , T is the room temperature of the magnetorheological fluid.

[0095] The material properties of magnetorheological fluid are mainly affected by the magnetic field in which it is located. The intensity of the magnetic field affecting the U-shaped cavity in the ultrasonic magnetic control vibration unit of the present invention shows a gradient change in the X, Y, and Z directions. Since the vibration frequency of the ultrasonic vibrator is predetermined, Substituting into equation (1), the wave equation of the one-dimensional elastic wave generated by the ultrasonic vibrator under the working condition of fixed vibration frequency in the magnetorheological material with gradient structure under the influence of magnetic field is:

[0096]

[0097] When the incident elastic wave of the magnetorheological fluid contained in the U-shaped cavity in the magnetically controlled vibration unit is a simple harmonic wave, the displacement function of the magnetorheological fluid contained in the U-shaped cavity in the magnetically controlled vibration unit is as follows:

[0098] ξ(d,t)=ξ(d)e iωt (4)

[0099] Where i is an imaginary unit, ξ(d) represents the displacement of the elastic wave at different positions d in the magnetorheological fluid when time t is fixed. Substituting equation (4) into equation (3), we can obtain:

[0100]

[0101] Let k(d) be:

[0102]

[0103] Substituting formula (6) into formula (5), we get:

[0104]

[0105] The boundary conditions are: When d=0, ξ(d)=A, ξ(d) = 0 at position d, where A is the amplitude of the ultrasonic vibrator 3. Solving equation (7) yields ξ(d), so that when the magnetorheological fluid in the U-shaped cavity of the magnetically controlled vibration unit is subjected to the magnetic field generated by the gradient coil, the displacement and stress at position d in the magnetorheological fluid are expressed as:

[0106]

[0107] Right now:

[0108]

[0109] The displacement and stress in the X, Y, and Z dimensions of a particle at a distance d in the solid-state magnetorheological fluid are solved by equations (8) and (9).

[0110] The micro-motion effect of each position of the U-shaped cavity and the fixture on the fixture and the metal fitting surface can be approximately considered to be the same as the micro-motion effect of the centroid of the U-shaped cavity and the fixture on the fixture and the metal fitting surface. To achieve the set metal fitting surface amplitude and vibration direction, the current I required by the gradient coil in the X, Y, and Z directions is x , I y , I z The calculation is as follows: the amplitude obtained by removing the amplitude component of the electromagnetic excitation device 1 from the set metal mating surface amplitude is decomposed into the components along the X, Y, and Z dimensions, which are respectively used as the amplitudes of the corresponding dimensions at the centroid of the contact surface between the U-shaped cavity and the fixture, and are combined with the known A, ω, and F T , the d value of the contact surface between the U-shaped cavity and the fixture at the X, Y, and Z dimensions is substituted into the displacement equation (8), and then combined with c L , K(d), K0(d), F f The corresponding comprehensive mechanical response G is obtained by solving the expressions of (ω), μ(d), λ(d), v, and k(d). * (H), then through G * The magnetic field intensity H of the corresponding dimension is inferred from the relationship between (H) and the magnetic field intensity H received by the magnetorheological fluid at that location. Finally, the H(x,y,z) on the left side of the H(x,y,z) expression is substituted with the magnetic field intensity H of the corresponding dimension. The right side of the H(x,y,z) expression only retains the coefficient before the unit vector of the corresponding dimension. In this way, an equation is established, and the X, Y, and Z coordinates of the contact surface centroid of the U-shaped cavity and the fixture are substituted into the equation to obtain the current I of the gradient coil in the X, Y, and Z dimensions. x , I y , I z Finally, the current I required by the gradient coil in the X, Y, and Z directions is obtained x , I y , I z , so that the metal mating surface vibrates according to the set amplitude and vibration direction at a specific frequency (the set metal mating surface vibration frequency).

Claims

1. A magnetorheological electromagnetically driven composite micro-motion fatigue testing device, comprising a frame and two composite micro-motion fatigue testing mechanisms, characterized by: The composite micro-motion fatigue testing mechanism includes an electromagnetic excitation device, a fixture, two T-shaped brackets and two ultrasonic magnetic control vibration units; the T-shaped bracket is composed of a vertically arranged sliding rod and a connecting rod, and two integrally formed slip rings are provided at both ends of the sliding rod, the two slip rings of one T-shaped bracket are fixed on two of the slide rails of the frame, and the two slip rings of the other lower T-shaped bracket are fixed on the other two slide rails of the frame; the ultrasonic magnetic control vibration unit includes a U-shaped cavity, an ultrasonic vibrator and a gradient coil; the ultrasonic vibrator and gradient coil of one ultrasonic magnetic control vibration unit are fixed to the side of the connecting rod of one T-shaped bracket, and the ultrasonic vibrator and gradient coil of the other ultrasonic magnetic control vibration unit are fixed to the side of the connecting rod of the other T-shaped bracket, and on the same T-shaped bracket, the gradient coil is larger than the ultrasonic The vibrator is close to the slip ring of the T-shaped bracket; the convex parts of the U-shaped cavity of the two ultrasonic magnetically controlled vibration units are connected to the ends of the connecting rods of the two T-shaped brackets through ball hinges respectively, and magnetorheological fluid is provided in the U-shaped cavity; the concave parts of the U-shaped cavities of the two ultrasonic magnetically controlled vibration units are arranged opposite to each other and are both fixed at the tail end of the fixture; the tail end of the fixture is fixed to the electromagnetic excitation device; the fixtures of the two composite micro-motion fatigue testing mechanisms are facing each other up and down, the electromagnetic excitation device of the upper composite micro-motion fatigue testing mechanism is fixed to the frame, the electromagnetic excitation device of the lifting platform and the lower composite micro-motion fatigue testing mechanism are both fixed to the cylinder body of the hydraulic cylinder, and the piston rod of the hydraulic cylinder is fixed to the frame through a constraint track; the lifting platform and the constraint track fixed on the frame and the four slide rails of the frame all constitute a sliding pair; the constraint track is provided with a scale.

2. The magnetorheological electromagnetic driven composite micro-fatigue testing device according to claim 1 is characterized in that: The frame includes a top plate, a bottom plate, a slide rail and a bottom frame. The top plate and the bottom plate are fixed by four slide rails; the electromagnetic excitation device of the upper composite micro-motion fatigue testing mechanism is fixed to the top plate, the constraint rail is fixed to the bottom plate, and the bottom plate is fixed to the bottom frame.

3. The magnetorheological electromagnetic driven composite micro-fatigue testing device according to claim 1 is characterized in that: The end of the connecting rod of the T-shaped bracket is fixed to the spherical support of the ball hinge, and the convex part of the U-shaped cavity is fixed to the ball head of the ball hinge.

4. The magnetorheological electromagnetic driven composite micro-fatigue testing device according to claim 1 is characterized in that: The slip ring of the T-shaped bracket is supported on the slide rail through a rolling bearing.

5. The magnetorheological electromagnetic driven composite micro-fatigue testing device according to claim 1 is characterized in that: The gradient coil is cylindrical with uniform wall thickness and is fixed on a cylindrical connecting rod in a T-shaped bracket. The connecting rod fits the inner wall of the gradient coil.

6. The magnetorheological electromagnetic driven composite micro-fatigue testing device according to claim 1 is characterized in that: The ultrasonic vibrator, electromagnetic excitation device, gradient coil, frequency sensor, displacement sensor and gyroscope are all connected to the PID controller. The PID controller adjusts the vibration frequency of the ultrasonic vibrator, the excitation parameters of the electromagnetic excitation device and the magnetic field generated by the gradient coil, and receives the vibration frequency detected by the frequency sensor, the amplitude detected by the displacement sensor and the vibration direction detected by the gyroscope.

7. The magnetorheological electromagnetic driven composite micro-fatigue testing device according to claim 6, characterized in that: The PID controller is connected to the display module.

8. The fatigue testing method of the magnetorheological electromagnetic driven composite micro-motion fatigue testing device according to claim 6 or 7, characterized in that: The following steps are involved: Step 1: Clamp the metal mating surfaces with two fixtures; set the direction, frequency, amplitude, and duration of the metal mating surface vibration, the frequency and amplitude of the electromagnetic excitation device, the amplitude of the ultrasonic vibrator, and set the fatigue boundary conditions; Step 2: The PID controller changes the micro-motion frequency of the U-shaped cavity by changing the vibration frequency of the ultrasonic vibrators of the two ultrasonic magnetically controlled vibration units, thereby changing the micro-motion frequency of the metal mating surface, and changes the gradient coil magnetic field by changing the gradient coil current of the two ultrasonic magnetically controlled vibration units, further changing the effect of the magnetic field on the magnetorheological fluid in the U-shaped cavity, to adjust the micro-motion amplitude and direction of the U-shaped cavity, thereby changing the micro-motion amplitude and direction of the metal mating surface, and the micro-motion of the U-shaped cavity is combined with the excitation generated by the electromagnetic excitation device, so that the metal mating surface can achieve composite directional micro-motion according to the set vibration direction and amplitude, thereby performing fatigue testing on the metal mating surface.

9. The fatigue testing method of the magnetorheological electromagnetic driven composite micro-motion fatigue testing device according to claim 8, characterized in that: The relationship between the magnetic field strength H(x,y,z) of the gradient coil at any point in space (x,y,z) and the current is as follows: Among them, G x , G y , G z are the gradients of the gradient coil in the X, Y, and Z directions, I x , I y , I z are the currents of the gradient coil in the X, Y, and Z directions respectively, are the unit vectors in the X, Y, and Z directions respectively.

10. The fatigue testing method of the magnetorheological electromagnetic driven composite micro-motion fatigue testing device according to claim 9, characterized in that: The relationship between the magnetic field intensity generated by the gradient coil at the centroid of the contact surface between the U-shaped cavity and the fixture and the bulk modulus and shear modulus of the magnetorheological fluid in the U-shaped cavity is constructed as follows: The comprehensive mechanical response G of the magnetorheological fluid at the centroid of the contact surface between the U-shaped cavity and the fixture under the action of the magnetic field intensity H * (H) is: G * (H)=10G′(H)+iG″(H) G′(H) is the storage modulus, G″(H) is the loss modulus, and i is the imaginary unit; The empirical formulas for G′(H) and G″(H) are: G′(H)=3.11×10 -8 H 2 +3.56×10 -5 H+0.578×10 2 G″(H)=3.47×10 -9 H 2 +3.85×10 -6 H+6.31×10 -3 The equivalent Lame constant of the magnetorheological fluid in the U-shaped cavity of the ultrasonic magnetically controlled vibration unit is: Wherein, λ(d) is the first Lame parameter, which represents the bulk modulus of the magnetorheological fluid material; μ(d) is the second Lame parameter, which represents the shear modulus of the magnetorheological fluid material; C is the correction factor, E is the Young's modulus of the magnetorheological fluid material, and the Poisson's ratio v of the magnetorheological fluid material is calculated as follows: The relationship between the vibration frequency ω of the ultrasonic vibrator and the displacement of any point in the U-shaped cavity is as follows: The wave equation of the elastic wave of the ultrasonic magnetically controlled vibration unit incident vertically on the U-shaped cavity and transmitted in the magnetorheological fluid is: Where ξ(d,t) is the displacement function of the elastic wave; t is the time variable, σ is the damping coefficient, d represents the distance along a certain dimension (X, Y, Z), and d = 0 corresponds to the point where the magnetorheological fluid is closest to the ultrasonic vibrator, and d = L corresponds to the point where the magnetorheological fluid is farthest from the ultrasonic vibrator. The value of d ranges from 0 to L; c L is the wave speed, and ρ is the density of the magnetorheological fluid, and K(d) is the comprehensive elastic coefficient of the magnetorheological fluid affected by elastic waves, which is calculated as follows: K(d)=K0(d)×F f (ω) (2) Among them, the static elastic coefficient K0(d)=λ(d)+2μ(d); the frequency compensation coefficient F f (ω) is calculated as follows: F T is the temperature compensation coefficient, which is calculated by the following formula: F T =1+β(T-T0) Where T0 is the reference temperature, β is the temperature influence coefficient, and T is the room temperature of the magnetorheological fluid; Substituting into equation (1), the wave equation of the one-dimensional elastic wave generated by the ultrasonic vibrator in the magnetorheological material with a gradient structure under the influence of the magnetic field is: When the elastic wave is a simple harmonic wave, the displacement function of the elastic wave in the magnetorheological fluid contained in the U-shaped cavity in the magnetically controlled vibration unit is expressed as follows: ξ(d,t)=ξ(d)e iωt (4) Where ξ(d) represents the displacement of the elastic wave at different positions d in the magnetorheological fluid when time t is fixed. Substituting equation (4) into equation (3), we get: Let k(d) be: Substituting formula (6) into formula (5), we get: The boundary conditions are: When d=0, ξ(d)=A, ξ(d) = 0 at position A, where A is the amplitude of the ultrasonic vibrator. Solving equation (7) yields ξ(d). Thus, when the magnetorheological fluid in the U-shaped cavity of the magnetically controlled vibration unit is subjected to the magnetic field generated by the gradient coil, the displacement of the point at position d in the magnetorheological fluid is expressed as: The displacements of a particle in the solid-state magnetorheological fluid at a distance d in the X, Y, and Z dimensions are solved by equation (8); The micro-motion effect of each position of the U-shaped cavity and the fixture contact surface on the fixture and the metal matching surface is considered to be the same as the micro-motion effect of the centroid of the U-shaped cavity and the fixture contact surface on the fixture and the metal matching surface; To achieve the set metal matching surface amplitude and vibration direction, the current I required by the gradient coil in the X, Y, and Z directions is x , I y , I z The calculation is as follows: the amplitude obtained by removing the amplitude component of the electromagnetic excitation device from the set metal mating surface amplitude is decomposed into the components along the X, Y, and Z dimensions, which are respectively used as the amplitudes of the corresponding dimensions at the centroid of the contact surface between the U-shaped cavity and the fixture, and are substituted into u in formula (8) respectively. d , derive the corresponding comprehensive mechanical response G * (H), then through G * The magnetic field intensity H of the corresponding dimension is inferred from the relationship between (H) and the magnetic field intensity H received by the magnetorheological fluid in the U-shaped cavity at that location. Finally, the H(x,y,z) on the left side of the H(x,y,z) expression is substituted with the magnetic field intensity H of the corresponding dimension. The right side of the H(x,y,z) expression only retains the coefficient before the unit vector of the corresponding dimension. In this way, an equation is established, and the X, Y, and Z coordinates of the contact surface centroid of the U-shaped cavity and the fixture are substituted into the equation to obtain the current I of the gradient coil in the X, Y, and Z dimensions. x , I y , I z Finally, the current I required by the gradient coil in the X, Y, and Z directions is obtained x , I y , I z , so that the metal mating surfaces can vibrate at a specific frequency according to the set amplitude and vibration direction.

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